Many people see this type of arrangement as very cold. However, you see from the picture that this is actually a misconception.
Somewhere between the warm rustics and somewhat cool Scandinavian design of interior decoration, an Industrial style has emerged, as a kind of combination of these two styles. This style is inspired by industrialization that happened at the end of the nineteenth century and at the beginning of the twentieth century. Industrial style may not necessarily be cold, on the contrary, like all other styles can serve as a guideline in creating very warm home. This style can be found in some modest attics as well as in a richly decorated large luxury houses.
This is an increasingly popular type of arrangement for which younger people decide. People who make decision for this extravagant type of arrangement are those people who don't want modern minimalism in their space, and who want something new and who are brave to turn their desire into real life. Except in the interior design, this style can also be applied in the exterior arrangement. For example, large cables and bulbs can be used to get the desired effect. The world has recently become obsessed with renovating old warehouses, stables, old industrial buildings and creating a very pleasant ambience of these ruins.
The industrial style is perfectly imperfect. Walls of brick, steel beams and rods, concrete, bare installations, untreated wood are the basic characteristics of this style. This probably sounds very cold, but if you add vases and flower pans to it, leather furniture or furniture from a fabric material, shelves for books and decorations, curtains and similar details, you will get a very warm corner for you and your loved ones. And very modern, of course.
Metals such as nickel, copper, iron are unavoidable in the arrangement of this style. Namely, at the time of steel and iron production in all parts of the world, iron has been widely used, both for the production of locks, as well as for water and sewage networks, stairs, roof and supporting elements. Today, in homes around the world is used wrought iron.
If you are arranging your home in this style, you must inevitably have some kind of artwork on the wall, or totally the opposite some plain poster, and even a wall you can print or draw some symbol on it. Take advantage of the mural but do not forget the fireplace in the living room. All this will bring you and your guests back into history.
Make your bedroom minimalist decorated with only a few details. The bed can be large and comfortable regardless of whether it is made of formal or informal iron. The cupboard can be metal like those used in the dressing room. Thanks to the modern kitchen elements of stainless steel, the kitchen will be easiest to arrange. Choose tiles in your bathroom or kitchen in one color and the fug mass in the opposite color. Do not exaggerate with metallic details, but cleverly use a few that will give your space a glamour note.
Enjoy the gallery, you may find some old, but very modern detail that you will love for your home.
Converting abandoned old buildings with high walls, converting stables and warehouses, old factories into residential areas has become a very popular trend around the world.
One of trademarks of industrialism is iron and steel. Iron is widely used and here you can see how to give your home with the help of iron pipes a note of extravagance.
This style is easiest to apply in the kitchen thanks to modern stainless steel used for production of kitchen appliances.
Large bulbs and metal pieces of furniture can be found in this very brave way of arranging apartments and houses.
This style reminds a lot on the Scandinavian style of interior design. In both styles is used wood, iron, leather and other natural materials.
Bald installations, bare walls and untreated wood that look very useful and old are essential in this design.
In this design, it is not necessary to hide the age of the building, but with the right details and furnitureto emphasize the age and the ruin of the building.
These is very bold arrangement of the wall in the hallway or living room. The gears are actually a mirror frame. A wall arranged in this way definitely returns to history.
This shelf will surely not leave any of your guests indifferent.
Legs of the table and chairs made of iron, as well as the iron chandelier, are very discreetly embedded in this modern space and give it the necessary charm.
If you want your kitchen to be arranged according to this extravagant style, bare at least one wall to the brick and choose furniture with solid iron parts as this table and chairs.
Although this room seems incomplete at first sight, it is actually very smartly arranged and it is even warm.
Posters and inscriptions or symbols on the walls may look very interesting.
Because of brick, iron and a lot of light in the room, we can say that there are combined Scandinavian and industrial style.
Tall bare walls, lots of iron and little details. Modern industrial style with minimal details.
Because more and more time people spend at work or out of the home, a bit of time is left to fix the house. That is why everything (furniture and ornaments) in modern homes is primarily functional. Instead of wiping dust off thousands of decorations, you better go on massage and relax yourself.
Untreated beams that look very old do not have to be hidden anymore. On the contrary, they are wonderful as they are, and smartly used will be great decoration in your home. Emphasize that beams and its faults!
Very nice old lamps that for sure return in the past.
Everything in this room is in the spirit of old industrialism starting from these old windows. Old but urban. The bare walls are unavoidable in this interior.
If you decide for a leather sofa, do not hide places where it is cracked because of using. This is very desirable in this arrangement.
If your room looks a little bit too cold, make it more warmly by adding flowerpots and vases with flowers and green plants.
A very creative bookcase in the spirit of the past on which every fan of this design would envy to you.
Industrialism also in the toilet. The toilet paper holder is very interestingly done.
This design allows your walls to be only overshadowed without color. One or two walls in your apartment will give to it a completely different look. Be careful and smart.
The gray color and black details are one more characteristic of the industrial style.
Green plants and knitted baskets are responsible for the warmth of this space. Without them this would be a very cold space full of iron and glass.
Here's an example of how bare installations can fit nicely into space. A total contrast to them is this large gorgeous chandelier and furniture made of textile.
Only the bravest will choose this kind of lighting above the dining table. What is this – pots or chandeliers ???
A modern, minimalist apartment, with a very cleverly chosen wire fence and inscriptions on the wall. Everything is in the spirit of industrialism.


Drainage systems that fail or broken pool pump can cause water damage to properties. Life will not exist without water, but it could be a big problem if it causes serious damage to properties. Water can seep into the most vulnerable areas of our home, causing too much problem. And when water damage reach a neighbor's property, serious disputes may arise.
In real estate investment, beware and check for the possibility of the presence of water damage, especially in very old properties or properties that long never been lived. So it is important to consult your realtor to know the extent and details of damage, and to guide you hire the best water damage restoration company for any of your existing and future real estate investment. If emergency response is delayed more than 48 hours ,seeping water can be pervasive, progressive and it also mean important objects may become permanently damaged. You can call for water mitigation for immediate steps to reduce the amount of long-term damage commonly caused by plumbing failure caused by water damage.
You can detect flood damage by closing the water main and shut off all water source, to stop the flooding and shut down electrical breaker before removing or unplugging electrical devices from wet submerged areas. To prevent permanent staining, you can put aluminum foil under your furniture's feet which are in contact with water or wet carpet to prevent permanent stains. Raise draperies or curtains away from water or wet carpet, and tack up and lift any skirts of your upholstered furniture. It is important to also remove shoes, fabrics, potted plants, books, papers or other items that can stain wet carpet. Never vacuum because it can result to electrical shock, damaging your equipment as well. It is a common practice placing newspaper in traffic areas can transfer ink easily to wet carpet fibers, so avoid using it to prevent permanent staining. Do not walk on carpet otherwise necessary to prevent damage from spreading to unaffected areas. Act promptly and call the services of a water damage restoration company, because shopping vacuums or carpet drying equipment can't prevent water from climbing on the walls, beneath baseboard, and molding into still plates.
In water damage, if internal humidity is not controlled, those objects that are undamaged from flood can also be damaged by absorbing moisture from the air. We are a water damage restoration company with highly knowledgeable, highly skilled and highly trained restoration technicians, utilizing the latest state-of-the-art equipment and technology to dry an entire structure as fast as possible. If you and your realtor are looking for a trusted and reliable water damage restoration company, you may check our website for more details regarding our restoration services.


text:
Surface Engineering Forum / General Discussion / Testing and Trashing / Spring for hydrogen fuel cell commercial vehicles?
Spring for hydrogen fuel cell commercial vehicles?
Hydrogen industry is a solution to the problems of energy shortage and environmental degradation faced by human beings. It is called future energy and ultimate energy. With the gradual approaching of hydrogen-fueled vehicles, the development of hydrogen industry is a path for human energy restructuring and industrial restructuring. At present, many countries in the world have started to study and try hydrogen energy.
In the automotive industry, hydrogen fuel cell vehicles have attracted the attention of governments, professional institutions and related enterprises because of their near-zero pollution advantages.
Recently, whether in the field of van logistics vehicles, Park junction vehicles or urban buses, a hydrogen-fueled vehicle powered by hydrogen fuel cells is breaking through the three barriers of technology, cost and business mode, and entering the stage of large-scale demonstration operation. Commercial vehicle representatives mainly based on hydrogen fuel cells are witnessing their strength to make hydrogen-fueled commercial vehicles commercialized. Camps become reality.
On March 5, 2018, two Dongfeng brand hydrogen fuel cell logistics vehicles were delivered to Jingdong Logistics Center, which is located in the largest logistics center of Shanghai, "Jingdong Asia No. 1 Base". It is reported that 500 hydrogen fuel cell logistics vehicles have been licensed and qualified in Shanghai. After that, 45 new hydrogen fuel cell logistics vehicles were put into operation.
On June 28, 2018, a batch of "Sichuan-made" hydrogen fuel cell buses were put into operation on the P09 bus line in Pidu District of Chengdu, marking the first demonstration line of hydrogen fuel cell buses in Sichuan Province to enter commercial demonstration operation.
On September 18, 2018, five Beijing 384 bus lines from Xiyuhe Bus Station to Zhongguancun 1st Street ushered in the first show of Futian Ouhui BJ6123FCEVCH-1 hydrogen fuel cell bus. This is the third phase of China's Fuel Cell Bus Commercialization demonstration project to carry out the demonstration operation of hydrogen fuel cell bus, which means that Beijing Bus has begun the demonstration operation of hydrogen fuel cell bus.
Breakthrough in Hydrogen Fuel Production Technology and Innovation in Automobile Indu Virgo 0 160 12-12-2018
Last Post: Virgo

redpajama_set_name: RedPajamaCommonCrawl


text:
Home Chevron icon It indicates an expandable section or menu, or sometimes previous / next navigation options. Military & Defense Contributors
NATO is considering opening a new North Atlantic command — and it's stirring echoes of the Cold War
Gen. Petr Pavel during a NATO defense-ministers meeting in Brussels.
BRUSSELS (Reuters) - NATO needs to establish a new regional base for protecting the North Atlantic against increased Russian naval strength, a senior alliance general said on Monday, as allies consider the next step in a military build-up reminiscent of the Cold War.
General Petr Pavel, head of NATO's military committee, will help put the case to allied defense ministers this week for a new planning and strategy base to be located in a chosen NATO ally and focused on keeping Atlantic shipping lanes safe from enemy submarines.
It would be the first such expansion in two decades after NATO sharply cut back its commands in 2011...
"If we look at the growing capabilities of countries like Russia and China, with a global reach, it is quite obvious that maritime lines of communication have to be protected," Pavel, a Czech army general, told Reuters in an interview.
"We observe increased Russian naval activity in the Arctic in the northern Atlantic ... We also assess that for any future crisis, the reinforcement of Europe and free lines of communication will be vital for European security," Pavel said.
If approved, the new North Atlantic Command would survey a vast area and, in the event of any potential conflict with Russia, have the task of making sea lanes safe for U.S reinforcements to Europe.
A German submarine participates in NATO's Dynamic Mongoose anti-submarine exercise in the North Sea off the coast of Norway, May 4, 2015.
REUTERS/Balazs Koranyi
Strong in symbolism, the decision is unlikely to revive a much larger Cold War-era Atlantic Command that was disbanded in 2002, but it would broaden NATO's new deterrent against Russia.
Despite NATO's cooperation with Moscow in the Balkans after a 1997 pact formalized friendly ties, the alliance sees the Kremlin's incursions in Georgia and eastern Ukraine and its seizure of Crimea as unacceptable breaches of international law.
Pavel described Russia as a "potential threat", while the West was alarmed by Moscow's war games in September that massed tens of thousands of troops and may have tested electronic warfare tools on Latvia, NATO officials say.
Since Russia's 2014 Crimea annexation, NATO has sought to reassure its Baltic allies by sending troops to the Baltics, Poland and the Black Sea, setting up a network of NATO outposts, holding more exercises and preparing a rapid response force, including air, maritime and special operations components.
The United States have also returned tanks and troops to Europe after a long drawdown at the end of the Cold War.
Russia condemns the moves as an aggressive strategy on its frontiers that threatens to destabilize eastern Europe.
Logistics, costs
U.S. Defense Secretary Jim Mattis will join other allied defense ministers on Wednesday and Thursday to decide whether to approve the North Atlantic Command, as well as a logistics command to focus on moving troops more quickly across Europe.
Micael Byden, the supreme commander of the Swedish armed forces, with US soldiers during the joint NATO exercise Aurora 17 at Save airfield in Goteborg, Sweden, September 13, 2017.
With renewed purpose since Russia's annexation of Crimea, NATO allies are broadly in favor of the two commands. Many are keen to lock in U.S. support given President Donald Trump's early doubts about the alliance he now says he strongly backs.
Pavel cautioned that cost is likely to be an issue for NATO governments and said there were no short cuts in deterrence.
"I believe we are now out of the realm of doing more with less. We simply have to understand that wherever we want to do more, there will be resource implications," Pavel said.
The alliance is being asked by Trump to do more in Afghanistan, in fighting Islamist militants and to stop migrants from the Middle East and North Africa reaching Europe.
Many European NATO nations are still struggling to meet an alliance goal by 2024 to spend two percent of economic output on defense every year.
"We can call it modernization, we can call it adaptation. We simply have to adapt to a new reality," Pavel said.
(Reporting by Robin Emmott; editing by Richard Balmforth)
Read the original article on Reuters. Copyright 2017. Follow Reuters on Twitter.
SEE ALSO: NATO may make major changes to its command structure amid ongoing tensions with Russia
NOW WATCH: How Russia's most advanced military equipment stacks up against NATO hardware
More: Reuters NATO Russia Germany
Defense Spending


text:
\section{Introduction}
\label{sec:introduction}

Nuclear $\beta$-decay studies have contributed significantly to our
understanding of the charged-current weak interaction and, more
generally, the fundamental symmetries underlying the Standard Model of
electroweak interactions.  Today, a rich program of $\beta$-decay
studies of nuclei, free neutrons, and pions continues in earnest, with
recent high-precision results providing important information on
Standard Model parameters and constraints on proposed
beyond-the-Standard-Model new physics scenarios
\cite{nico05,severijns06,abele08}.

In neutron $\beta$-decay, measurements of angular correlation
parameters and the lifetime continue to probe the limits of the
vector--axial-vector ($V-A$) description of the weak interaction.
Assuming the validity of the $V-A$ theory, the differential decay rate
distribution of the electron and neutrino momenta and the electron
energy in spin-polarized neutron $\beta$-decay (averaged over the
final-state electron spin) can be written in terms of angular
correlation parameters as \cite{jackson57}
\begin{equation}
\frac{dW}{dE_{e}d\Omega_{e}d\Omega_{\nu}}
\propto N(E_{e}) \left[1 + a \frac{\vec{p}_{e} \cdot \vec{p}_{\nu}}
{E_{e}E_{\nu}} + \langle\vec{\sigma}_{n}\rangle \cdot
\left( A\frac{\vec{p}_{e}}{E_{e}} + B\frac{\vec{p}_{\nu}}{E_{\nu}}
\right) \right],
\label{eq:distribution-correlations}
\end{equation}
where $E_{e}$ ($E_{\nu}$) and $\vec{p}_{e}$ ($\vec{p}_{\nu}$) denote,
respectively, the electron (neutrino) energy and momentum; $E_{0}$
($=782$ keV) denotes the electron endpoint energy; $N(E_{e}) =
p_{e}E_{e}(E_{0} - E_{e})^{2}$ is the electron energy spectrum;
$m_{e}$ is the electron mass; and $\langle \vec{\sigma}_{n} \rangle$
denotes the neutron polarization.  Neglecting recoil-order
corrections, the correlation parameters $a$ (the
$e$-$\overline{\nu}_{e}$-asymmetry), $A$ (the $\beta$-asymmetry), and
$B$ (the $\overline{\nu}_{e}$-asymmetry) are functions only of
$\lambda \equiv g_{A}/g_{V}$, defined as the ratio of the weak
axial-vector, $g_{A}$, and vector, $g_{V}$, couplings of the nucleon
to the $W$-boson \cite{wilkinson82,gardner01}.  Therefore,
measurements of $a$, $A$, and $B$ determine $\lambda$, by itself, a
fundamental parameter of the weak interaction.  In addition, a value
for $\lambda$, combined with a value for the lifetime, $\tau_{n}$,
where \cite{czarnecki04}
\begin{equation}
\frac{1}{\tau_{n}} = \frac{G_{\mu}^{2}|V_{ud}|^{2}}{2\pi^{3}}
m_{e}^{5}\left(1 + 3\lambda^{2}\right)\left(1 + \mathrm{RC}\right)f,
\label{eq:tau-lambda}
\end{equation}
permits an extraction of the CKM quark-mixing matrix element $V_{ud}$,
given a value for the Fermi constant $G_{\mu}$ as determined in muon
decay.  Here, $f$ is a phase-space factor, and RC represents the total
effect of all electroweak radiative corrections relative to muon decay
\cite{czarnecki04}.  A value for $V_{ud}$ derived solely from neutron
$\beta$-decay observables is particularly compelling for a first-row
CKM unitarity test \cite{abele04}, because the result is insensitive
to corrections for nuclear structure that must be applied to
extractions of $V_{ud}$ from measurements of $ft$ values in
superallowed $0^{+} \rightarrow 0^{+}$ nuclear $\beta$-decay
transitions \cite{hardy05}.

In the remainder of this paper, we describe a solenoidal electron
spectrometer designed to extract the neutron $\beta$-asymmetry
parameter $A$ from measurements of the angular correlation between the
neutron spin and the decay electron's momentum in the $\beta$-decay of
spin-polarized ultracold neutrons.  This experiment, the UCNA
experiment \cite{ucna} at the Los Alamos National Laboratory, will
yield the first-ever measurement of $A$ with ultracold neutrons (UCN),
offering different systematics than previous and ongoing measurements
employing beams of polarized cold neutrons \cite{abele02}.  The
ultimate goal of the UCNA experiment is a 0.2\% measurement of $A$.
We begin, in Section \ref{sec:requirements}, by detailing the
requirements on the spectrometer imposed by the consideration of
systematic uncertainties inherent to a measurement of $A$.  We follow
this in Section \ref{sec:design-construction} with a discussion of the
spectrometer design and construction.  Results from performance
studies of the spectrometer with conversion-electron sources are
presented in Section \ref{sec:calibration}.  We then conclude with a
brief summary in Section \ref{sec:summary}.

\section{Spectrometer requirements}
\label{sec:requirements}

\subsection{Overview of experiment}
\label{sec:requirements-overview}

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.45,clip=]{ucna_schematic.ps}
\end{center}
\caption{Schematic diagram of the UCNA $\beta$-asymmetry experiment.}
\label{fig:ucna_schematic}
\end{figure}

To provide some context for a discussion of the spectrometer
requirements, a schematic diagram of the UCNA experiment is shown in
Fig.\ \ref{fig:ucna_schematic}.  UCN are produced in a superthermal
solid deuterium source \cite{morris02,saunders04}, spin-polarized via
transport through a 7-Tesla field, and then directed to the center of
a decay trap, where a fraction of them decay.  The decay trap consists
of a 3-m long, 10-cm diameter, diamond-coated quartz tube situated
within the warm bore of the solenoidal spectrometer.  Note that as an
option to increase the UCN density in the spectrometer (and, hence,
the $\beta$-decay rate), the ends of the decay trap can be closed off
with thin ($< 1$ $\mu$m) foils.  The spectrometer field strength of
1.0-Tesla is oriented along the axis of the decay trap (defining the
spin direction) and generated by a superconducting solenoidal magnet.
Two identical multiwire proportional chambers \cite{ito07} and plastic
scintillator detector packages are mounted on both ends of the
spectrometer and situated within 0.6-Tesla field-expansion regions.

Depending on their direction of emission, the decay electrons spiral
along the solenoidal field lines towards one of the two electron
detector packages, distributed over energy and angle according to
\begin{equation}
dW(\beta,\theta) \propto 1 + P_{n}A\beta\cos\theta,
\end{equation}
with $P_{n}$ the neutron polarization, $\beta$ the electron velocity
relative to $c$, and $\theta$ the angle of emission relative to the
neutron spin (or magnetic field).  The $\beta$-asymmetry $A$ is then,
in principle, extracted from the (energy-dependent)
experimental-asymmetry, $A_{\mathrm{exp}}(E_{e})$, measured in the two
detectors' count rates,
\begin{equation}
A_{\mathrm{exp}}(E_{e}) = \frac{N_{1}(E_{e})-N_{2}(E_{e})}
{N_{1}(E_{e})+N_{2}(E_{e})} = P_{n} A \beta \langle \cos \theta \rangle.
\label{eq:Aexp}
\end{equation}
The expected magnitude of the asymmetry is $A_{\mathrm{exp}} \sim
4.5$\% for $P_{n} = 1$, $\langle\cos\theta\rangle = 1/2$, and $\beta
\sim 0.75$ (for $E_{e} \sim 300$ keV, near the peak of the
$\beta$-decay spectrum).  In practice, ratios of the two detectors'
count rates for neutrons polarized parallel and anti-parallel to the
field [via transport through an adiabatic-fast-passage (AFP)
spin-flipper field region] are formed to extract the asymmetry via a
``super-ratio'' technique.  Here, the experimental asymmetry,
$A_{\mathrm{exp}}(E_{e})$, is extracted from the super ratio, $R$,
according to
\begin{eqnarray}
R &=& \frac{N_{1}^{\downarrow}(E_{e}) \cdot N_{2}^{\uparrow}(E_{e})}
{N_{1}^{\uparrow}(E_{e}) \cdot N_{2}^{\downarrow}(E_{e})}, \nonumber \\
A_{\mathrm{exp}}(E_{e}) &=& \frac{1 - \sqrt{R}}{1 + \sqrt{R}} =
P_{n} A \beta \langle \cos \theta \rangle,
\label{eq:super-ratio}
\end{eqnarray}
where $\uparrow$ and $\downarrow$ denote the two neutron spin states.
The advantage of the super-ratio technique is that differences between
the two detectors' efficiencies and variations in the UCN density for
the two spin states cancel in the ratio.

\subsection{Field uniformity requirement}
\label{sec:requirements-field-uniformity}

For a charged particle in a magnetic field $B$, the magnetic flux
enclosed by the particle's orbit (i.e., $Br_{L}^{2}$, with $r_{L}$ the
Larmor radius) is an adiabatic invariant~\cite{jackson}.  From this,
it can be shown that $p_{\perp}^{2}/B$, with $p_{\perp}$ the
transverse momentum, is also an adiabatic invariant.  The angle of
emission relative to the magnetic field (or spin) direction is, of
course, simply $\theta = \cos^{-1}(p_{\parallel}/p)$, with
$p_{\parallel}$ the longitudinal momentum, and $p =
\sqrt{p_{\perp}^{2} + p_{\parallel}^2}$ the total momentum.
Hereafter, we will frequently refer to $\theta$ as the pitch angle for
the trajectory.

Two considerations which follow from the adiabatic invariant influence
the requirement on the field uniformity.  First, electrons emitted
with momentum $p_{0} = \sqrt{p_{\perp,0}^2 + p_{\parallel,0}^2}$ in
some local field $B_{0}$ will be reflected from field regions $B$ if
$B > B_{\mathrm{crit}} \equiv (p_{0}^{2}/p_{\perp,0}^{2})B_{0}$, thus
contributing to a false asymmetry.  Second, by this same process,
electrons emitted at large pitch angles in the vicinity of a local
field minimum will be trapped.  These trapped electrons will scatter
from residual gas isotropically and dilute the extracted value of $A$.
A detailed analysis of both of these considerations showed that the
effect on the asymmetry is negligible for a field uniformity of $\pm 5
\times 10^{-4}$~\cite{ucna}.

\subsection{Fiducial volume definition}
\label{sec:requirements-fiducial}

Unlike previous measurements of $A$ utilizing flight paths of cold
neutron beams from research reactors, the UCNA experiment employs a
novel technique where the polarized UCN are transported to the center
of a material-walled decay trap situated within the warm bore of the
electron spectrometer.  Consequently, $\beta$-decay electrons
originating near the walls of the decay trap can scatter from the
walls prior to impacting the electron detector packages, leading to a
distortion in the measured energy spectrum.  Thus, one of the
requirements for the electron spectrometer is the ability to
reconstruct the transverse $(x,y)$ position of the $\beta$-decay event
with resolution sufficient to define a fiducial volume with a minimal
loss of counting statistics.

Reconstruction of the $(x,y)$ position is achieved via readout of the
induced charge on the two cathode planes of the multiwire proportional
chamber (MWPC), oriented at right angles relative to each other.
Complete details concerning the MWPC's design, construction, and
initial offline performance tests may be found in \cite{ito07}.  With
the maximum Larmor diameter for an endpoint-energy electron (with
$90^{\circ}$ pitch angle) of 7.76~mm in the 1-Tesla field, allowing
for a (conservative) 10\% safety factor yields a fiducial volume
radius of $(50 - 7.76 \times 1.10)$~mm $= 41.5$~mm (or, a 69\%
fiducial volume).  As discussed in detail later in this paper,
position resolutions of $\sim 2$~mm have been achieved.  This
resolution permits identification of the 8.5~mm radial cut annulus
with high confidence.

\subsection{Suppression of backscattering events}
\label{sec:requirements-backscattering-suppression}

Identification of electron events that undergo Coulomb backscattering
from any of the MWPC components or the plastic scintillator is
important for an extraction of the $\beta$-asymmetry $A$
\cite{martin06,schumann08}.  Particularly problematic are those events
termed ``missed backscattering events'', in which the electron
backscatters from one detector package with energy deposition
\textit{below} that detector's threshold.  Such unidentifiable
backscattering events contribute to a systematic shift in the
extracted value of the asymmetry, and can only be corrected for in
simulation.  Thus, the spectrometer includes the following features
designed to suppress the total and missed backscattering fractions.
First, the backscattering probability increases rapidly with the angle
away from normal incidence.  Large pitch-angles are eliminated with
the field-expansion ratio of 0.6, which maps pitch angles of
$90^{\circ}$ in the 1.0-Tesla region to $51^{\circ}$ in the 0.6-Tesla
region.\footnote{For the same reason, the transverse $(x,y)$ position
of the trajectory in the 1.0-Tesla region maps to that in the
0.6-Tesla region via a $1/\sqrt{0.6}$ factor.}  Second, the placement
of a low-energy-threshold MWPC in front of the plastic scintillator
detector facilitates the identification of low-energy-deposition
backscattering events which would otherwise not trigger the plastic
scintillator (e.g., due to dead-layer\footnote{The scintillator's
dead-layer was measured offline with a variable energy 0--130~keV
electron gun and found to be $3.0 \pm 0.3$ $\mu$m
\cite{junhua-thesis}.} and/or threshold effects).  Finally, for fixed
energy, the backscattering probability increases with atomic number
$Z$ \cite{tabata71}.  Thus, the MWPCs were constructed with low-$Z$
materials \cite{ito07}.

Note that results from backscattering studies carried out with
conversion-electron sources are not reported in this paper.  Instead,
a detailed companion paper comparing these data with Monte Carlo
studies is in preparation \cite{backscattering-paper}.

\subsection{Energy reconstruction}
\label{sec:requirements-energy}

A measurement of the total electron energy is required, as the
experimental asymmetry, $A_{\mathrm{exp}}(E_{e})$ in Eq.\
(\ref{eq:Aexp}), is proportional to $\beta = v/c$.  The chosen
detector, plastic scintillator, offers a low average atomic number
$Z$, important for the suppression of backscattering events, and fast
timing, defining the event trigger.  The primary requirements for the
scintillator detector are as follows.  First, the scintillator must be
sufficiently thick to provide a total energy measurement of the entire
neutron $\beta$-decay spectrum up to the endpoint $E_{0}$.  Second,
high energy resolution is required, demanding a high photoelectron
collection efficiency in the spectrometer's magnetic field
environment.  Third, a low energy threshold is required, again
demanding a high photoelectron yield, and also a low dark rate.
Fourth, the scintillator's fast timing response, coupled to fast
photomultiplier tubes, permits the identification and separation of
backscattering events triggering both scintillators.  Fifth, the size
of the scintillator is mechanically constrained by the size of the
solenoidal spectrometer's warm bore.  Finally, the scintillator
resides in the 0.6-Tesla field expansion region, requiring that the
light be transported along light guides to a lower field region ($\sim
300$ Gauss) for readout with the photomultiplier tubes.

\subsection{Suppression of backgrounds}
\label{sec:requirements-backgrounds}

One primary advantage of a neutron $\beta$-asymmetry measurement with
ultracold neutrons produced via a low-frequency (typically, 1/10 to
1/20 Hz) pulsed spallation-driven superthermal solid deuterium source
is the supression of (or, near absence of) beam-related backgrounds.
Signal-to-noise ratios in previous $A$ experiments with cold neutron
beams from research reactors were typically 7:1~\cite{abele02}, with
gamma-ray induced events constituting the primary background.  The
desire for a high signal-to-noise experiment was one motivation for
the introduction of the MWPC, as the requirement of a coincidence
between the MWPC and the scintillator leads to a significant reduction
in gamma-ray backgrounds.  Further, as discussed below, the
scintillator is coupled adiabatically to a series of light guides
which transport the light to four photomultiplier tubes.  Requiring at
least a two-fold photomultiplier tube coincidence further suppresses
noise from dark currents and low-energy gamma backgrounds.

\section{Spectrometer design, construction, and operation}
\label{sec:design-construction}

\subsection{1-Tesla superconducting solenoidal magnet}
\label{sec:design-construction-magnet}

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.50,clip=]{scs_photo.ps}
\end{center}
\caption{(Color online) Photograph of the 1-Tesla superconducting
solenoidal magnet.  Provided courtesy of American Magnetics, Inc.}
\label{fig:scs_photo}
\end{figure}

A photograph of the as-built 1-Tesla superconducting solenoidal magnet
is shown in Fig.\ \ref{fig:scs_photo}.  In general terms, the magnet
is a warm-bore (35-cm diameter) 4.5-m long superconducting solenoid
with three 7-cm (vertical) $\times$ 4-cm (horizontal) rectangular
radial penetrations through the center of the coil.  One such
penetration is required for the transport of UCN to the decay trap (as
indicated schematically in Fig.\ \ref{fig:ucna_schematic}).  The
capacity of the magnet's liquid helium cryostat is $\sim 1600$ liters,
with a heat load during operation in persistence mode equivalent to a
boil-off rate of $\sim 10$ liters/hour.

The required radial penetration complicated the design of the
solenoid.  Analytic studies indicated that a single split-coil
solenoid would not satisfy the $\pm 5 \times 10^{-4}$ field
homogeneity requirement, but a multi-coil design with varied
currents/windings could be tuned to satisfy this requirement
\cite{junhua-thesis}.  The design proposed to the chosen vendor,
American Magnetics, Inc.\ (AMI) \cite{ami}, consisted of a
configuration of 32 50-cm diameter, 7-cm wide coils (each modeled as
70 current filaments spaced 1~mm apart) all separated by 7-cm, with
six different currents ranging from 1600--1800 A-turns
\cite{junhua-thesis}.  Ultimately, the designs of the coil
configurations for both the 1-Tesla region and the 0.6-Tesla
field-expansion region were proprietary.  The vendor's end-product
consisted of a main coil winding with a single persistence heater
switch, 28 shim coil windings (each with individual persistence heater
switches), and three rectangular 7-cm $\times$ 4-cm radial
penetrations (two providing horizontal access, one providing vertical
access, to the warm bore).

The cryostat for the magnet was fabricated by Meyer Tool and
Manufacturing, Inc.\ \cite{meyer}.  Although the cryostat was equipped
with a liquid nitrogen jacket buffer volume, in practice we have
forced the (colder) liquid helium boil-off through the liquid nitrogen
volume, as we have found this reduces the rate of liquid helium
boil-off.  Liquid helium is supplied by a helium liquefaction plant
operated solely for the UCNA experiment in a closed-loop mode.  This
plant consists of a Koch Model 1630 liquefier coupled to a 4000-liter
supply dewar, low-pressure ($\sim$ few psi) magnet boil-off return
lines coupled to 240-psi (supply-side) compressors, and a 240-psi
``medium pressure storage'' ambient temperature ballast tank with a
$\sim 2300$ liquid liters equivalent volume.

The power supply for the main coil, an AMI Model 12200PS-420
(200~A/12~V), functions as a slave to an AMI Model 420 Power Supply
Programmer unit.  The full energized field strength of 1.0 Tesla
requires a current of 124.0 A.  The power supply for the shim coils, a
bipolar Kepco Model BOP 20-10M ($\pm 20$ V/$\pm 10$ A), also functions
as a slave to a second AMI Model 420 Power Supply Programmer unit.
During magnet operations, the shim coils are energized one-by-one to
their optimized current values.  A LabView-based program installed on
a PC functions as the interface between the user and the Model 420
Power Supply Programmer units.

The MWPC/plastic scintillator electron detector packages, described in
detail below, are mounted to the two ends of the solenoidal magnet via
41.9-cm conflat flanges.  The central axis of the spectrometer is
located 2.74~m above the experimental floor.

\subsection{Multiwire proportional chambers}
\label{sec:design-construction-mwpc}

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.51,clip=]
{detector_package_schematic.ps}
\end{center}
\caption{Schematic diagram of the MWPC and plastic scintillator detector
package.}
\label{fig:detector_package_schematic}
\end{figure}

A schematic diagram illustrating the main components of the
MWPC/plastic scintillator detector package is shown in Fig.\
\ref{fig:detector_package_schematic}.  As noted already, the MWPCs are
relatively insensitive to gamma ray backgrounds, offer a low threshold
for the detection of backscattering events, and permit reconstruction
of the transverse $(x,y)$ coordinates of the $\beta$-decay events.
Although described in detail in \cite{ito07}, for completeness we
briefly review some of the MWPCs' most important features here.

First, to suppress missed backscattering events (again, those events
depositing no energy above threshold in the MWPC), the entrance window
separating the MWPC fill gas from the spectrometer vacuum was designed
to be as thin as possible.  Second, because of this thin entrance
window requirement, the fill gas pressure was required to be as low as
possible.  The chosen fill gas, C$_{5}$H$_{12}$ (2,2-Dimethylpropane,
or ``neopentane''), a low-$Z$ heavy hydrocarbon, was shown to yield
sufficient gain at a pressure of 100 Torr.  The minimum window
thickness for a 15-cm diameter window (equal to the diameter of the
plastic scintillator, discussed below) shown to support a 100 Torr
difference with a minimal leak rate (from pinholes) was 6 $\mu$m of
aluminized Mylar,\footnote{Note that when the spectrometer is
configured such that the ends of the decay trap are not closed off
with thin foils, the nominal 6 $\mu$m aluminized Mylar entrance window
is replaced with a UCN-reflective $^{58}$Ni-coated aluminized Mylar
window (to suppress contamination from neutron capture on $^{27}$Al).}
reinforced by Kevlar fiber.  Third, the MWPC mechanical size was
constrained by the requirement that the MWPC housing fit within the
solenoid's 35-cm warm bore diameter while also providing sensitivity
to the entire 10-cm diameter decay trap (projecting to a
$10/\sqrt{0.6} = 12.9$~cm diameter in the 0.6 Tesla field expansion
region where the MWPC/scintillator is mounted).  Finally, the anode
plane was strung with 64 10-$\mu$m diameter gold-plated tungsten
wires, and the cathode planes, separated from the anode plane by 10
mm, were strung with 64 50-$\mu$m diameter gold-plated aluminum wires.
The wire spacing on both the anode and the two cathode planes is 2.54
mm, yielding an active area of $16.3 \times 16.3$ cm$^{2}$.  This
active area maps to a $12.6 \times 12.6$ cm$^{2}$ square in the
1.0-Tesla region, providing full coverage of the 10-cm diameter decay
trap.

All of the anode wires are connected via conductor tracks on the anode
wireplane support frame; thus, the anode signal that is read-out is
the summation of the signals on the 64 individual wires.  With the
wires on one cathode plane oriented ``vertically'', providing
information on the ``horizontal'' coordinate (defined to be the
$x$-coordinate), and the wires on the other cathode plane oriented
``horizontally'', providing information on the ``vertical'' coordinate
($y$-coordinate), the $(x,y)$ position for each event is reconstructed
from the center-of-gravity of the two cathode planes' signals.

Note that the 64 wires on each of the two cathode planes are read-out
in groups of four.  This four-wire-grouping reduced the number of
electronics channels (thereby reducing the cost), but did not, as
shown later, degrade the resulting position resolution, as the typical
four-wire-group multiplicity is $\sim 3$--4 for the 368.1~keV
electrons from a $^{113}$Sn conversion-electron source.\footnote{The
368.1~keV energy we reference hereafter is the weighted mean (by
intensity) of the $^{113}$Sn K-, L-, and M-shell conversion-electron
energies of 363.8 keV (28.4\%), 387.5 keV (5.6\%), and 390.9 keV
(1.1\%).  The resolution of the scintillator is not sufficient to
distinguish the individual lines.}

\subsection{Plastic scintillator detectors}
\label{sec:design-construction-scintillator}

\subsubsection{Scintillator}
\label{sec:design-construction-scintillator-scintillator}

The plastic scintillator detector (or, hereafter, the
``$\beta$-scintillator'') is a 15-cm diameter, 3.5-mm thick disk of
Eljen Technology EJ-204 scintillator \cite{eljen}.  The EJ-204
wavelength of maximum emission is 408~nm.  This wavelength couples
well to a typical bialkili photocathode's wavelength sensitivity, and
is also sufficiently long for efficient optical transmission through a
UVT light guide.  Other desirable features of the EJ-204 scintillator
which motivated its choice include a high light output (68\% of
anthracene), long attenuation length (1.6~m), fast rise time (0.7~ns),
narrow pulse width (2.2~ns FWHM), and an index of refraction (1.58)
well-matched to that of UVT light guide (1.49).

The 15-cm diameter in the 0.6-Tesla field-expansion detector region
maps to a $15\sqrt{0.6} = 11.6$~cm diameter disc in the 1.0-Tesla
region of the spectrometer, providing full coverage of the 10-cm
diameter decay trap.  As discussed in~\cite{junhua-thesis}, the 3.5-mm
thickness was determined by two factors.  First, the range of an
$E_{0} = 782$~keV endpoint energy electron in plastic scintillator is
3.1~mm.  Thus, a total energy measurement requires a thickness of at
least 3.1~mm.  Second, the probability of a gamma ray interaction in
thin plastic scintillator is expected to scale with the scintillator
volume.  Thus, suppression of this background demands the thinnest
possible scintillator.\footnote{For the 3.5-mm thickness, the typical
energy deposition from cosmic-ray muons in the $\beta$-scintillator is
$\sim 700$--1500~keV (i.e., the peak is very broad).  Increasing the
scintillator thickness would have shifted the muon ``peak'' past the
neutron $\beta$-decay endpoint, but would have increased the total
background rate from gamma rays.  Note that muons are vetoed with a
scintillator located immediately behind the $\beta$-scintillator (see
Fig.\ \ref{fig:detector_package_schematic}).}  The chosen 3.5~mm
thickness included an additional thickness ``safety factor'' for the
energy measurement.

\subsubsection{Light guide system}
\label{sec:design-construction-scintillator-lightguide}

As indicated in Fig.\ \ref{fig:detector_package_schematic}, the light
from the scintillator disc is transported out of the 0.6-Tesla
field-expansion region over a distance of $\sim 1$~m along a series of
UVT light guides to photomultiplier tubes, situated in a region where
the magnetic field is $\sim 300$~Gauss.  Two options were considered
for light collection from the scintillator: (a) coupling light guides
directly to the scintillator back face, or (b) coupling light guides
to the scintillator edge.  Ultimately, edge collection was chosen for
the following reasons.  First, the surface area of the back face is a
factor $\sim 10$ greater than the surface area of the edge, requiring
an order-of-magnitude more photocathode coverage (leading to higher
cost, and also higher dark noise), while only yielding $\sim 18$\%
more light collection~\cite{junhua-thesis}.  Second, cosmic-ray muons
traversing the light guides generate \v{C}erenkov light.  Suppression
of this background favored the smaller light guide volume associated
with edge collection.

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.42,clip=]{light_guide_schematic.ps}
\end{center}
\caption{Schematic diagram (front view) of the light guide system at
the scintillator edge interface.}
\label{fig:light_guide_schematic}
\end{figure}

The design for the edge collection light guide system was constrained
by the requirement that the detector system (shown in Fig.\
\ref{fig:detector_package_schematic}) fit within the spectrometer's
35-cm diameter warm bore, with an additional radial space allowance
for cabling and efficient vacuum pumping.  The design that was
implemented, shown schematically in Fig.\
\ref{fig:light_guide_schematic}, consisted of twelve rectangular
strips of 39-mm wide $\times$ 10-mm thick UVT light guide coupled to
the edge of the scintillator concentrically around its circumference
(via optical grease).  Each of these twelve strips includes a 5-mm
straight section, which couples the 3.5-mm thick scintillator edge to
the 10-mm thick light guide.  Following the 5-mm straight sections,
the light guides are then bent through $90^{\circ}$ over a 35-mm bend
radius and directed towards the photomultiplier tubes.  A novel
feature of the light guide transport system is that the twelve
rectangular strips adiabatically transform into four $39 \times
30$~mm$^{2}$ rectangular clusters, which are then coupled to the
(four) photomultiplier tubes.  The entire light guide system is
supported by an aluminum ring-like support frame.  A photograph of the
as-built light guide system, manufactured by Suzuno Giken
\cite{suzuno}, appears in Fig.\ \ref{fig:light_guide_photo}.

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.50,clip=]{light_guide_photo.ps}
\end{center}
\caption{(Color online) Photograph of the $\beta$-scintillator and
light guide assembly.}
\label{fig:light_guide_photo}
\end{figure}

\subsubsection{Photomultiplier tubes}
\label{sec:design-construction-scintillator-pmts}

The choice of readout by four photomultiplier tubes (PMTs) was
motivated by the following considerations.  The effective light
collection surface area of the twelve rectangular light guides at the
scintillator edge interface is $12 \times (39 \times 10$~mm$^{2})$ =
4680~mm$^{2}$.  This surface area maps onto thirteen 1-inch PMTs,
three 2-inch PMTs, or one 3-inch PMT.  Readout by more than one PMT
was desired, as the requirement of a multi-PMT coincidence suppresses
dark noise and backgrounds from gamma-ray interactions in the
scintillator and \v{C}erenkov light from cosmic-ray muons traversing a
set of light guides coupled to the same PMT.  Ultimately, readout with
four 2-inch PMTs\footnote{Note that four (as opposed to three) 2-inch
PMTs are actually required in order to couple the rectangular geometry
of the light guides to the circular geometry of the photocathodes.}
was chosen as it provides for a multi-PMT coincidence, but requires
fewer electronics channels than readout with 1-inch PMTs.

The Burle 8850, a 12-stage photomultiplier with a bialkili
photocathode and a high-gain gallium-phosphide first dynode
\cite{burle-8850}, was chosen for the experiment.  This PMT was
favored as it is optimized for single-photon counting and features a
low dark noise rate, a fast rise time of 2.1~ns, a high gain of $1.6
\times 10^{7}$ at a nominal operating voltage of 2000~V (well below its
maximum operating voltage of 3000~V), and a peak quantum efficiency at
420~nm (well matched to the EJ-204 scintillator's 408~nm wavelength of
maximum emission).  The PMTs are glued to the ends of the rectangular
light guides.  High voltage for the PMTs is supplied with a LeCroy
HV4032 power supply unit.

\subsubsection{Photomultiplier tube magnetic shielding}
\label{sec:design-construction-scintillator-shielding}

The magnetic field in the region of the PMTs is oriented primarily in
the axial direction, with a magnitude of $\sim 300$ Gauss.  This field
is shielded with an array of active and passive magnetic shielding
components, shown schematically in Fig.\
\ref{fig:magnetic_shielding_schematic}.  Moving from the exterior to
the interior, the first element is a 0.64-cm-thick 520 DOM steel
shield, with a nominal outer diameter of 11.4-cm.  The next element
is a close-fitting 0.64-cm-thick 1026 medium-carbon steel shield with
a nominal outer diameter of 10.2-cm.  The lengths of both of these
steel shields are 55.9-cm.  The third and fourth layers consist of a
$\sim 37.6$-cm-long 3-layer $\sim 325$-turn solenoid wound (with 18
AWG copper magnet wire) on the surface of a 7.6-cm outer diameter,
0.10-cm-thick cylinder of Advance Magnetics AD-MU-80 $\mu$-metal.
Note that because the $\mu$-metal shield is only 30.5-cm in length,
a 38.1-cm-long, 0.010-cm-thick sheet of AD-MU-80 $\mu$-metal foil was
wrapped on the surface of the 30.5-cm-long $\mu$-metal cylinder, with
the solenoids then actually wound on the surface of the thin
$\mu$-metal foil.

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.50,clip=]
{magnetic_shielding_schematic.ps}
\end{center}
\caption{Schematic diagram of the magnetic shielding for the
photomultiplier tubes.  See text for explanation of layers.}
\label{fig:magnetic_shielding_schematic}
\end{figure}

Bench tests of this magnetic shielding configuration with fields
comparable to the spectrometer fields in the region of the PMTs (i.e.,
up to $\sim 200$--400 Gauss) showed that residual shielded fields of
$\sim 0.1$ Gauss could be achieved with solenoid currents no greater
than 1.0~A.  Magnetic end caps were not required.

\subsection{Detector housing and spectrometer mount}
\label{sec:design-construction-mount}

The combined MWPC/plastic scintillator detector package is mounted
within a detector housing and inserted into the warm bore of the
1-Tesla solenoidal spectrometer.  After insertion, the
$\beta$-scintillator is located 2.2~m from the center of the UCN decay
trap.  As shown on the detector schematic in Fig.\
\ref{fig:detector_package_schematic}, the $\beta$-scintillator and the
light guide assembly are enclosed within a $\sim 64$-cm-long,
26.7-cm outer diameter stainless steel nipple with a 30.5-cm conflat
flange welded to one end, and a 41.9-cm flange (with an O-ring
groove) welded to the other end.  The MWPC is mounted to the nipple
via 30.5-cm conflat flanges.  The 41.9-cm flange on the other end of
the nipple is mounted to the 41.9-cm conflat flange on the
spectrometer warm bore.

Also shown on the schematic in Fig.\
\ref{fig:detector_package_schematic} are the magnetic shields for the
PMTs, which extend beyond the 41.9-cm flange on the end of the nipple.
The next-to-outermost shield layers, the 0.64-cm-thick 1026
medium-carbon steel shields, also serve as the vacuum seal (via O-ring
grooves) for the region beyond the 41.9-cm flange on the nipple.

\subsection{Gas flow and vacuum system}
\label{sec:design-construction-vacuum}

A schematic of the gas flow and vacuum system for the MWPC and
$\beta$-scintillator detector assembly is shown in Fig.\
\ref{fig:vacuum_system_schematic}.  The MWPC volume (nominally, 100
Torr of neopentane) is separated from the spectrometer vacuum by the
MWPC entrance window.  The detector housing for the
$\beta$-scintillator, light guide, and PMT assembly (nominally, $\sim
95$ Torr of nitrogen\footnote{As noted in \cite{ito07}, the pressure
of the nitrogen in the scintillator detector housing is maintained at
a somewhat lower pressure than the MWPC pressure.  This is to ensure
that the MWPC exit window bows out, or away, from the MWPC interior,
avoiding contact with the MWPC wire planes.})  is separated from the
MWPC volume by the MWPC exit window.  During normal operation, the
spectrometer, MWPC, and scintillator detector housing are first
evacuated at a rate of $< 1$~Torr/s, to minimize pressure gradients
across the MWPC windows.  Pressures in the spectrometer volume of
$\sim 10^{-6}$ Torr are typical.  The MWPC and scintillator detector
housing are then filled (at a rate significantly less than 1 Torr/s)
with neopentane and nitrogen, respectively, to their nominal operating
presures with the gas handling system described in \cite{ito07}.  Also
shown in \cite{ito07} is a photograph of the entire
MWPC/$\beta$-scintillator assembly on a rolling cart.

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.48,clip=]
{vacuum_system_schematic.ps}
\end{center}
\caption{Schematic diagram of the gas flow and vacuum system for the
MWPC and $\beta$-scintillator detector package coupled to the
spectrometer vacuum.}
\label{fig:vacuum_system_schematic}
\end{figure}

\subsection{Gain monitoring system}
\label{sec:design-construction-gms}

Possible temporal shifts in the $\beta$-scintillator's photomultiplier
tubes' gains are monitored, and subsequently corrected for, with a
gain monitoring system (GMS).  Separate (but identical) GMS systems
were constructed for the two $\beta$-scintillators.  Note that these
two separate systems are not redundant, as the gains of the PMTs in
the two detector packages can vary independently.  An overview of the
GMS system is as follows.

A Nichia Corporation UV LED (Model NSHU590) is enclosed within a
light-tight aluminum box.  The LED is driven in pulsed mode by a
voltage pulse from a CAEN Model C 529 (6-channel) LED driver installed
in a CAMAC crate, and controlled by a PC laptop.  The LED light is
transported along two fiber optic cables to the $\beta$-scintillator
(as indicated in Fig.\ \ref{fig:detector_package_schematic}) and to a
``monitor'' setup consisting of a NaI crystal viewed by a PMT.  A
gamma ray source ($^{60}$Co, 1.173 MeV and 1.333 MeV lines) is located
nearby.  The $^{60}$Co spectrum measured by the monitor PMT provides a
reference point for the stability of the amplitude of the LED output
pulse.  Variations in the LED spectra recorded in the
$\beta$-scintillator PMTs are then referenced to variations in the LED
spectrum relative to the $^{60}$Co spectrum observed in the monitor
PMT.

It can then be shown that the gain correction for some
$\beta$-scintillator PMT, $G_{\beta}(t)$, at some particular time $t$
relative to some starting time $t=0$ is
\begin{equation}
G_{\beta}(t) = \left(\frac{\mathrm{LED}_{m}(t)}{\mathrm{LED}_{m}(0)}\right)
\left(\frac{^{60}\mathrm{Co}_{m}(0)}{^{60}\mathrm{Co}_{m}(t)}\right)
\left(\frac{\mathrm{LED}_{\beta}(0)}{\mathrm{LED}_{\beta}(t)}\right).
\end{equation}
Here, $\mathrm{LED}_{m}(\ldots)$ denotes the response of the monitor
PMT to the LED pulse, $^{60}\mathrm{Co}_{m}(\ldots)$ the response of
the monitor PMT to the $^{60}$Co gamma ray spectrum, and
$\mathrm{LED}_{\beta}(\ldots)$ the response of the
$\beta$-scintillator PMT to the LED pulse.  The referencing of the LED
response to the $^{60}$Co response compensates for fluctuations in the
LED output.  Note that drifts in the gain of the monitor PMT are also
compensated, as the $^{60}$Co and LED spectra shift proportionally.

\subsection{Electronics and data acquisition}
\label{sec:design-construction-daq}

\subsubsection{Event trigger logic}
\label{sec:design-construction-daq-triggers}

The electronics for the experiment consists of a VME system for the
event trigger logic (via discriminators and programmable logic units)
and the readout of scalers, analog-to-digital convertors (ADCs), and
time-to-digital convertors (TDCs).  A NIM system coupled to the VME
system is employed for the implementation of a ``busy logic''.  This
busy logic vetos event triggers arriving during ADC and TDC conversion
times (i.e., while the ADC and TDC states are ``busy''), and was
implemented to prevent re-triggering (and subsequent readout of the
ADCs and TDCs) by scintillator afterpulses (single photoelectron
pulses from the slow-time component of the scintillator light
emission).  Bench studies showed that a veto time of $\sim 1$ $\mu$s
was sufficient to completely suppress contamination from re-triggering
by afterpulses \cite{junhua-thesis}.

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.52,clip=]
{trigger_logic_schematic.ps}
\end{center}
\caption{Simplified schematic diagram of the trigger logic.  A
significant number of modules and circuit paths have been omitted.  As
noted in the text, the ``main trigger'' is an \texttt{OR} of all
possible event triggers.}
\label{fig:trigger_logic_schematic}
\end{figure}

A schematic diagram of the trigger logic is shown in Fig.\
\ref{fig:trigger_logic_schematic}, and an overview is as follows.  For
each detector package (detector 1 or detector 2), a trigger is defined
by a two-fold PMT coincidence requiring at least two PMTs with analog
signals above the discriminator threshold.  Note that the
discriminator threshold for each PMT is set at $\sim 1/2$ of the
amplitude of its single photoelectron peak.  An \texttt{OR} of a
detector 1 two-fold coincidence trigger, detector 2 two-fold
coincidence trigger, global GMS LED trigger, detector 1 GMS monitor
trigger (from $^{60}$Co events), detector 2 GMS monitor trigger
($^{60}$Co), and other experiment triggers then generates the main
event trigger.  The trigger logic for the two detectors' two-fold
coincidences and the main event trigger are performed with CAEN V495
Dual Programmable Logic Units (PLUs).  Those event triggers that are
not vetoed by the busy logic then trigger gate/delay generators for
the readout of the ADCs, TDCs, and scaler modules.

Among other variables, the TDCs (CAEN V775 modules with a 32-event
buffer memory, operated in \texttt{COMMON STOP} mode) provide a
relative measurement of the two detectors' two-fold coincidence
trigger arrival times.  Such relative timing information permits
identification of the earlier trigger (if two such triggers arrive),
important for the correct assignment of the initial direction of
incidence for backscattering events triggering both
$\beta$-scintillators.  Two types of ADC modules are used.  A
charge-integrating ADC (CAEN V792 QADC module with a 32-event buffer
memory), triggered for readout by a $\sim 140$~ns gate from a CAEN
V486 gate/delay generator, provides a measurement of the total charge
measured in each PMT.  The sum of the QADC spectra from the four PMTs
on each side is proportional to the energy deposition in the
scintillator.  Peak-sensing ADCs (CAEN V785 PADC modules with a
32-event buffer memory), triggered for readout by a $\sim 6$~$\mu$s
gate from a CAEN V462 gate generator, digitize the MWPC anode and
cathode-plane signals.  Scalers (CAEN V820 and V830 modules; the V830
module features a 32-event buffer memory) are used for deadtime
monitoring.

System deadtimes were measured offline as a function of the trigger
rate with a random pulser and found to be smaller than 10\% for event
rates up to $\sim 5$~kHz.\footnote{Beyond $\sim 5$~kHz, the data
acquisition system deadtime dominates the event loss.}  At lower rates
of $\sim 0.5$--1.0~kHz, the deadtime is proportional to the event
rate, of order $\sim 1$\%, and dominated by the ADC and TDC
digitization times.

\subsubsection{Data acquisition}
\label{sec:design-construction-daq-daq}

The data acquisition system is based on the MIDAS package
\cite{midas}.  Among many components, MIDAS features a buffer manager
for data flow management, a frontend acquisition code, a data logger
for the storage of data on disk, online analysis capabilities, a
web-browser-based run control, and an alarm system.  The UCNA
experiment utilizes a dedicated Linux-based workstation for
implementation of the frontend acquisition code, and another separate
Linux-based workstation for run control and online analysis.  The
frontend acquisition code accesses the VME system via a Struck PCI/VME
interface.\footnote{A Struck SIS1100 PCI card hosted by the Linux
workstation running the frontend acquisition code is connected via a
fiber optic link to a Struck SIS3100 VME board hosted by the VME
crate.}  The frontend continually polls the data-ready status of the
ADCs and TDCs.  Whenever any of the ADCs and/or TDCs have data ready
for readout in memory, the raw data from all ADC, TDC, and scaler
modules are transferred to the data buffer manager.  The MIDAS event
format structure consists of ``banks'' of raw data, which are
subsequently decoded by the MIDAS analyzer into formats readable by
the CERNLIB analysis packages ROOT and PAW (i.e., ``Ntuples'').

\section{Results from spectrometer performance studies}
\label{sec:calibration}

In this section we show select results from performance studies of the
electron spectrometer carried out with a source of $^{113}$Sn
368.1~keV conversion electrons with an event rate (above background)
as measured in the spectrometer of $\sim 85$~Hz.  The principal
analysis results shown below include energy spectra, position spectra,
an assessment of the spectrometer's position resolution, and an
assessment of the spectrometer's instrumental asymmetry.

\subsection{Solenoidal field map}
\label{sec:calibration-fieldmap}

First, however, we show results from field maps of the 1.0-Tesla
region (measured with an NMR probe) in Fig.\
\ref{fig:scs_field_map_sept05}.  As can be seen there, the field
profile satisfies the $\pm 5 \times 10^{-4}$ field uniformity
requirement over the 3-m extent of the UCN decay trap region.  Figure
\ref{fig:field_expansion_map_sept05} displays a field map of the
1.0-Tesla to 0.6-Tesla field-exansion region (measured with a Hall
probe).

\begin{figure}[t!]
\begin{center}
\includegraphics[scale=0.70]
{scs_field_map_sept05.ps}
\end{center}
\caption{Field maps from three different scans along the UCN decay
trap's 3-m length, showing uniformities at the level of $\pm 3 \times
10^{-4}$.}
\label{fig:scs_field_map_sept05}
\end{figure}

\begin{figure} [t!]
\begin{center}
\includegraphics[scale=0.70]
{field_expansion_map_sept05.ps}
\end{center}
\caption{Field map of the 1.0-Tesla to 0.6-Tesla field-expansion
region.}
\label{fig:field_expansion_map_sept05}
\end{figure}

\subsection{Energy spectra}
\label{sec:calibration-energyspectra}

A typical MWPC anode spectrum extracted from a run taken with the
$^{113}$Sn source positioned with the spectrometer's fiducial volume
is shown in Fig.\ \ref{fig:west_anode_spectrum}.  The
$\beta$-scintillator spectrum (summed over the response of the four
photomultiplier tubes) for this same run, shown before and after
application of the cut on the MWPC anode response, is shown in Fig.\
\ref{fig:west_scintillator_spectrum}.  As can be seen there, the
requirement of a coincidence between the MWPC and the
$\beta$-scintillator greatly reduces the background from gamma-ray
interactions.  The low-energy tail on the $^{113}$Sn spectrum is
primarily the result of energy loss in the MWPC entrance and exit
windows.\footnote{Note that for the data shown here, the MWPC entrance
and exit window thicknesses were 25 $\mu$m Mylar (non-aluminized), not
the optimized 6 $\mu$m thickness.}  Backscattering from the
MWPC/$\beta$-scintillator also contributes to the tail, but the
contribution of this process to the structure of the tail is small (as
the total detected backscattering event fraction is small, $\sim
4.6$\% for the 368.1~keV $^{113}$Sn conversion electron energies)
compared to the energy loss in the MWPC windows.

The impact of energy loss in the MWPC windows is illustrated in Fig.\
\ref{fig:sn_energy_tail}.  There, results from a \texttt{GEANT4}
simulation of the energy loss in the MWPC windows are plotted versus
the simulated visible energy\footnote{The visible energy is defined to
be the total energy loss in the $\beta$-scintillator active region
(beyond the dead layer) for those events generating a two-fold PMT
coincidence trigger.} deposition in the $\beta$-scintillator, and
overlaid with a histogram of the visible energy deposition.  Although
not shown there, the energy loss in the MWPC windows is correlated
with the initial pitch angle in the 1.0-Tesla region.

\begin{figure}[t!]
\begin{center}
\includegraphics[scale=0.70]{west_anode_spectrum.ps}
\end{center}
\caption{Typical MWPC anode spectrum (PADC channel number) from a run
with the $^{113}$Sn source positioned within the fiducial volume.  The
dashed line indicates the typical position of the cut.}
\label{fig:west_anode_spectrum}
\end{figure}

\begin{figure}[h!]
\begin{center}
\includegraphics[scale=0.70]{west_scintillator_spectrum.ps}
\end{center}
\caption{Typical $\beta$-scintillator spectra from a run with the
$^{113}$Sn source positioned within the fiducial volume.  The
light-shaded (dark-shaded) histogram shows the spectrum before (after)
the cut on the MWPC anode response.}
\label{fig:west_scintillator_spectrum}
\end{figure}

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.46,clip=]{sn_energy_tail.ps}
\end{center}
\caption{\texttt{GEANT4} simulated results for energy loss from
$^{113}$Sn conversion electrons in the MWPC windows plotted versus the
visible energy deposition in the $\beta$-scintillator, overlaid with
a histogram of the visible energy distribution.}
\label{fig:sn_energy_tail}
\end{figure}

\subsection{Event types}
\label{sec:calibration-eventtypes}

\subsubsection{Definitions}
\label{sec:calibration-eventtypes-definitions}

The $\beta$-asymmetry measurement requires an accurate determination
of the electron's initial direction of incidence.  Complicating the
extraction of the asymmetry are the five different event types, shown
schematically in Fig.\ \ref{fig:event_types}.

\begin{itemize}

\item
\textit{Correct events}: Events in which an electron, incident
initially on one of the $\beta$-detector packages, does not
backscatter from any element of that side's $\beta$-detector package,
and is then detected in that side's $\beta$-scintillator.

\item
\textit{Type I backscattering events}: Events in which an electron,
incident initially on one of the $\beta$-detector packages, deposits
sufficient energy to generate a two-fold trigger in that side's
$\beta$-scintillator, backscatters from that side's
$\beta$-scintillator, and is then detected in the opposite side's
$\beta$-scintillator.

\item
\textit{Type II backscattering events}: Events in which an electron,
incident intially on one of the $\beta$-detector packages, deposits
energy above the cut in that side's MWPC, backscatters either from
that side's MWPC (i.e., gas, wire planes, or back window) or
$\beta$-scintillator without depositing sufficient energy to generate
a two-fold trigger (e.g., backscatters from the scintillator's dead
layer), and is then detected in the opposite side's
$\beta$-scintillator.

\item
\textit{Type III backscattering events}: Events in which an electron,
incident initially on one of the $\beta$-detector packages, deposits
sufficient energy to generate a two-fold trigger in that side's
$\beta$-scintillator, backscatters from that side's
$\beta$-scintillator, deposits energy above the cut in the opposite
side's MWPC, and is then stopped in either the opposite-side MWPC's
gas, wire planes, or back window or the opposite-side's
$\beta$-scintillator's dead layer.

\item
\textit{Type IV backscattering events}: Events in which an electron,
incident initially on one of the $\beta$-detector packages,
backscatters from that side's MWPC without depositing energy above
the cut (e.g., backscatters from the MWPC entrance window), and is
then detected in the opposite side's $\beta$-scintillator.

\end{itemize}

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.58,clip=]{event_types.ps}
\end{center}
\caption{Schematic diagram of the five event types.  See text for
descriptions.}
\label{fig:event_types}
\end{figure}

Note that Type I backscattering events can be identified via
examination of the two detectors' two-fold coincidence trigger arrival
times, thus determining the initial direction of incidence
unambiguously (as discussed earlier in Section
\ref{sec:design-construction-daq-triggers}).  In contrast, simulation
input (regarding the energy deposition in the MWPCs) is needed to
distinguish Type II from Type III backscattering events.  For example,
without using any such simulation input (i.e., using only the
$\beta$-scintillator trigger to determine the direction of incidence),
the Type II and Type III events shown in Fig.\ \ref{fig:event_types}
would appear identical, with the direction of incidence for the Type
II event misidentified.  Type IV events cannot, of course, be
distinguished from Correct events; these are the ``missed
backscattering events'' discussed earlier in Section
\ref{sec:requirements-backscattering-suppression} which can only be
corrected for in simulation.

The analysis results presented hereafter are only for those events
identified by the event reconstruction as Correct events.  Because
this event sample also includes (unidentifiable) Type IV
backscattering events, we label these events ``Type 0 events''.  As
noted earlier, a detailed companion paper discussing the
identification of, and energy spectra of, the various backscattering
event types is in preparation \cite{backscattering-paper}.

\subsubsection{Selection of Type 0 events}
\label{sec:calibration-eventtypes-type 0}

The trigger logic (shown in Fig.\ \ref{fig:trigger_logic_schematic})
is such that each two-fold trigger generates the \texttt{START} for
its respective TDC channel.  The main event trigger (as noted earlier,
an \texttt{OR} of the two-fold triggers and any other event triggers)
is delayed by $\sim 92$~ns and generates the \texttt{COMMON STOP} for
the TDC.  A typical two-fold coincidence arrival time spectrum (shown
here for detector 1 two-fold triggers) at the main trigger logic unit
is shown in Fig.\ \ref{fig:east_two_fold_timing}.  Main event triggers
generated by the arrival of a detector 1 two-fold trigger appear at
the delay time of $\sim 92$~ns (i.e., an ``on time'' trigger) ,
whereas main event triggers generated by the arrival of a detector 2
two-fold trigger, with no later arrival of a detector 1 two-fold
trigger, appear at the peak at 0~ns (i.e., a ``time-out'' for that TDC
channel).  Those events located between these two extremes (i.e., the
broad secondary peak located at $\sim 68$~ns) correspond to main event
triggers generated by the arrival of a detector 2 two-fold trigger at
the logic unit, with the later arrival of a detector 1 two-fold
trigger.  In other words, these are events which backscattered from
the detector 2 package into the detector 1 backage (i.e., Type I
backscattering events incident initially on the detector 2 package).
Note that a 150 keV electron will traverse the 4.4~m separation
between the two $\beta$-scintillators in 23.2~ns; thus, the $\sim
24$~ns separation between these two peaks is as expected.  Note that
the spectrum is cut off below $\sim 15$~ns because the dynamic range
of the TDC was set at its minimum value of 140~ns for this run.

\begin{figure}[t!]
\begin{center}
\includegraphics[scale=0.70]{east_two_fold_timing.ps}
\end{center}
\caption{Typical two-fold coincidence trigger arrival timing
spectrum.  See text for interpretation of the peaks.}
\label{fig:east_two_fold_timing}
\end{figure}

Type 0 events were identified according to the following selection rules:

\begin{itemize}

\item
The initial incidence detector package's two-fold coincidence trigger
arrival time must reconstruct to the $\sim 92$~ns delay time.  The
other detector package's two-fold coincidence trigger arrival time
must reconstruct to a TDC ``time-out''.

\item
The MWPC on the $\beta$-scintillator hit side must display an anode
signal above the cut (as indicated in Fig.\
\ref{fig:west_anode_spectrum}).  The MWPC on the other side must
display an anode signal below the cut.

\item
The muon-veto scintillator (as shown in Fig.\
\ref{fig:detector_package_schematic}) on the $\beta$-scintillator hit
side must not record a hit.

\end{itemize}

\subsection{Position spectra}
\label{sec:calibration-positionspectra}

\subsubsection{Cathode-plane multiplicities}
\label{sec:calibration-positionspectra-multiplicities}

As noted earlier, the 64 wires (with 2.54-mm spacing) on each of the
two MWPC cathode planes are read-out in groups of four.  Henceforth,
we will refer to each of these four-wire configurations simply as a
``wire''.  Despite this four-wire grouping, most of the events exhibit
a multiplicity (on each cathode plane) of $\geq 3$, where we define
the event-by-event cathode multiplicity to be the number of wires with
a signal above a prescribed threshold.  A typical distribution of
multiplicities from a run with the $^{113}$Sn source is shown in Fig.\
\ref{fig:cathode_plane_multiplicity}.  Here, the threshold was defined
by a two-sigma limit ($\sim 50$ channels) of the cathode pedestal
peaks, as determined by Gaussian peak fitting.

\begin{figure}[t!]
\begin{center}
\includegraphics[scale=0.70]{cathode_plane_multiplicity.ps}
\end{center}
\caption{Typical cathode-plane multiplicity (shown here for the
detector 1 $x$-plane) from a run with the $^{113}$Sn source.}
\label{fig:cathode_plane_multiplicity}
\end{figure}

\subsubsection{Position reconstruction results}
\label{sec:calibration-positionspectra-algorithm}

The transverse $(x,y)$ positions are computed from the cathode-plane
wire spectra according to weighted sums,
\begin{equation}
x_{\mathrm{MWPC}} = \frac{\sum_{i} Q_{i} x_{i}}{\sum_{i} Q_{i}},~~~~~
y_{\mathrm{MWPC}} = \frac{\sum_{j} Q_{j} y_{j}}{\sum_{j} Q_{j}},
\end{equation}
where $Q_{i}$ denotes the signal above pedestal for the
$i^{\mathrm{th}}$ channel, $x_{i}$ and $y_{i}$ denote the $x$- and
$y$-coordinate of the $i^{\mathrm{th}}$ channel, and the sums $i$ and
$j$ run over all of the $x$- and $y$-plane cathode channels,
respectively, satisfying the two-sigma pedestal threshold.

Sample MWPC reconstructed position spectra (shown here for detector 1
$x$-reconstruction and detector 2 $y$-reconstruction) for Type 0
events, extracted from a run with the $^{113}$Sn source located within
the fiducial volume, are shown in Fig.\
\ref{fig:mwpc_position_spectra}.  Note that the position spectra shown
here, and all spectra shown hereafter, have been projected back to the
spectrometer's 1.0-Tesla region.  Gaussian fits to the peaks are
plotted, showing fitted widths slightly better than $\sim 2$~mm.  The
widths of these distributions agree well with those extracted from a
\texttt{GEANT4} Monte Carlo simulation of the MWPC response to the
368.1~keV $^{113}$Sn conversion electrons (shown in the insets).

A two-dimensional plot of detector 1 $(x,y)$ positions are shown in
Fig.\ \ref{fig:muon_position_spectra} for those events identified by
the muon-veto scintillator as muons.  As expected, these background
events are distributed uniformly over the MWPC's sensitive area.

\begin{figure}[t!]
\begin{center}
\includegraphics[angle=270,scale=0.52,clip=]
{mwpc_position_spectra_data_simulation.ps}
\end{center}
\caption{Typical MWPC reconstructed position spectra for Type 0 events
from a run with the $^{113}$Sn source located within the fiducial
volume.  The solid curves are the results of Gaussian fits to the
peaks, with the fitted widths indicated.  Distributions obtained from
a \texttt{GEANT4} simulation of the MWPC response are shown in the
insets.}
\label{fig:mwpc_position_spectra}
\end{figure}

\begin{figure}[t!]
\begin{center}
\includegraphics[scale=0.43]{muon_position_spectra.ps}
\end{center}
\caption{(Color online) Two-dimensional plot of detector 1 $(x,y)$
positions for events tagged as muons by the muon-veto scintillator.
The circle denotes the extent of the 41.5-mm radius fiducial volume.}
\label{fig:muon_position_spectra}
\end{figure}

\subsection{Spectrometer position resolution}
\label{sec:calibration-resolution}

To assess the position response of the spectrometer, we analyzed data
from runs taken with the $^{113}$Sn source located at 96 different
positions within the fiducial volume.  We extracted the position
resolution of the spectrometer from distributions of differences
between the nominal (known) positions, and the positions reconstructed
by the MWPC [i.e., histograms of
$(x_{\mathrm{MWPC}}-x_{\mathrm{nom}})$ and
$(y_{\mathrm{MWPC}}-y_{\mathrm{nom}})$].  These difference
distributions are shown for the detector 1 reconstruction in Fig.\
\ref{fig:spectrometer_position_resolution}.

The dashed curves are the results of Gaussian fits to the
distributions, with the means fitted as free parameters.  Note that a
slight mispositioning ($\sim$ few mm) of the detectors relative to the
magnetic field lines may contribute to the non-zero fitted means.
Because we were interested in assessing the resolution relative to the
nominal positions, we also performed constrained-Gaussian fits to
these distributions, in which the means were fixed to be 0; the
results of these fits are shown as the solid curves.  Because the
differences between the fitted widths from the free- and
constrained-Gaussian fits were not great, we defined the average of
the two fitted widths to be the spectrometer position resolution.  The
resulting values are listed in Table
\ref{tab:spectrometer_position_resolution}.  These data have
demonstrated that the position resolution of the spectrometer is $\sim
2.0$~mm over the fiducial volume.

\begin{figure}
\begin{center}
\includegraphics[angle=270,scale=0.60]
{spectrometer_position_resolution.ps}
\end{center}
\caption{Histograms of $(x_{\mathrm{MWPC}}-x_{\mathrm{nom}})$ and
$(y_{\mathrm{MWPC}}-y_{\mathrm{nom}})$ difference distributions for
reconstruction by the dectector 1 MWPC.  The dashed (solid) curves are
the results of Gaussian fits in which the means were fitted as a free
parameter (constrained to be 0).}
\label{fig:spectrometer_position_resolution}
\end{figure}

\begin{table}[t!]
\begin{center}
\caption{Extracted values of the spectrometer position resolution from
MWPC position reconstruction.  Listed are the fitted widths for the
free- and constrained-Gaussian fits to the reconstructed--nominal
position difference distributions.  The position resolution for each
coordinate is defined to be the average of the free and constrained
fitted widths.}
\begin{tabular}{lccc} \hline\hline
& \multicolumn{2}{c}{Fitted Widths $\sigma$ [mm]}& Position \\
Reconstruction& Free-Fit $\mu$& Constrained $\mu = 0$&
  Resolution [mm] \\ \hline\hline
Detector 1 MWPC $x$& 2.11& 2.50& 2.31 \\
Detector 1 MWPC $y$& 2.08& 2.21& 2.15 \\ \hline
Detector 2 MWPC $x$& 1.57& 2.14& 1.86 \\
Detector 2 MWPC $y$& 1.55& 1.45& 1.50 \\ \hline\hline
\multicolumn{4}{c}{Average Position Resolution = 1.96 mm} \\ \hline\hline
\end{tabular}
\label{tab:spectrometer_position_resolution}
\end{center}
\end{table}

\subsection{Spectrometer instrumental asymmetry}
\label{sec:calibration-asymmetry}

We analyzed the data from all of our $^{113}$Sn calibration runs and
calculated an instrumental asymmetry, denoted $\xi$, for Type 0 events
according to
\begin{equation}
\xi = \frac{N_{1}-N_{2}}
{N_{1}+N_{2}}.
\end{equation}
We found that the mean instrumental asymmetry for those runs
satisfying the fiducial volume radius cut of 41.5~mm is $\xi = (-0.400
\pm 0.083)$\%.

The instrumental asymmetry is itself $\sim 10$\% of the expected
physics asymmetry, $A_{\mathrm{exp}} =
P_{n}A\langle\beta\cos\theta\rangle \sim 4.5$\%.  The origin of a
non-zero instrumental asymmetry (from an isotropic source) is likely
the choice of cuts (e.g., cuts on the MWPC anode spectra, or cuts for
muon identification) for the event selection.  Although non-zero, the
instrumental asymmetry cancels to all orders in the extraction of the
$\beta$-asymmetry $A$ from the experimental super-ratio,
Eq.~(\ref{eq:super-ratio}), as the super-ratio asymmetry is insensitive to
differences between the two detectors' efficiencies.

\section{Summary}
\label{sec:summary}

In this paper we described a solenoidal electron spectrometer designed
for a precision measurement of the neutron $\beta$-asymmetry with
ultracold neutrons.  This spectrometer consists of a 1.0-Tesla
superconducting solenoid, with a combined MWPC and plastic
scintillator detector package for detection of the $\beta$-decay
electrons.  The UCNA experiment is currently operating at the
Los Alamos National
Laboratory, and collection of $\beta$-asymmetry data is ongoing.
Further experiments to perform a precise measurement of the neutron
$\beta$-decay energy spectrum, and to extract small energy-dependent
terms in the $\beta$-asymmetry due to recoil-order corrections, are
possible if the spectrometer's energy resolution can be improved.
This will be achieved by implementing large-area silicon detectors as
an alternate technology to the plastic scintillator detectors.  Other
experiments aimed at the determination of other angular correlation
parameters, such as $a$ and $B$ in Eq.\
(\ref{eq:distribution-correlations}), can be conducted if proton
detection can be incorporated into the apparatus.  We intend to
achieve proton detection by introducing thin
secondary-electron-emitting foils into the apparatus, into which the
decay protons would be accelerated by an electrostatic potential.
Both initiatives in detector technology development are ongoing at
this time.

We conclude this paper by emphasizing that our techniques and results
for the rejection of gamma-ray induced events and an assessment of the
spectrometer's position resolution are generally applicable to a
variety of precision $\beta$-decay experiments utilizing neutrons and
nuclei. \\

\textbf{Acknowledgments} \\ \\
We thank R.\ Cortez and J.\ Pendlay for their skillful technical
contributions to the design, fabrication, and deployment of the
detector systems.  We thank S.~Currie for his devoted efforts to the
operation and maintenance of the helium liquefaction plant.  We thank
the entire UCNA collaboration for many valuable suggestions.  This
work was supported in part by the National Science Foundation under
grant numbers PHY-0079767 (a Major Research Instrumentation Program
grant), PHY-0244899, PHY-0555674, and also by the Natural Sciences and
Engineering Research Council of Canada.

redpajama_set_name: RedPajamaArXiv


Viswanathan, a famous director, is haunted by the death of his wife and a young man whom he accidentally hit while driving. Later he meets Shyama, the daughter of his friend, still struggling with the death of her boyfriend, the man whom Viswanathan had killed. They fall in love but Viswanatan tries to avoid her. In the climax, he reveals the truth to shyama. He tries to leave the town but is stopped by her brother chandran. They have a fight and Viswanathan is hurt. The film ends where shyama and viswanathan consoles each other and is united.


For the new Power Functions. 36 studs long. Very detailed model. Roof can be taken off to place minifigs in the modelled interior. Prepared for front lighting with the new Lego Leds on the second channel of the remote control (Leds not included). Standard combination exists of 1 motorized end carriage (LB15), 1 middle carriage (LB17) and 1 non-motorized end carriage (LB16). Power Function set is optional/not included.
Only 1 bogie included. For the other bogie you need a PF Motor.


text:
Previous article 12 Magical Reasons To Visit Morocco & 3 Reasons Not To
Next article 55+ Romantic Couple Travel Quotes & Fun Travel Puns
Why Do People Travel? We Asked The Experts.
June 19, 2020Justine Jenkins12 min read2 comments
It's commonly said that the reason why people travel is to "find themselves". Think about it: how many blog posts, articles and Instagram stories have you seen to this effect?
But really… how accurate is that?
For this article, we'll be delving into the history of why do people travel, the science behind why some choose to travel and others don't, plus some exclusive interviews with travel writers and other travellers to find out more about why they travel and their thoughts on why travel is good for you.
Some of the answers may even surprise you!
Jump to your destination:
Why Do People Travel? Part 1: History
Why Do People Travel? Part 2: Science
Why Do People Travel? Part 3: Real-Life Answers
Why Do People Travel? Conclusion.
The History of Travel
"Those who do not learn from history are doomed to repeat it," George Santayana, a Spanish Philosopher once said.
But what does history teach us?
It's quite simple really: we are travellers. Whether it be to find new lands, cultures, food, experiences, you name it. As a species, we are intent on travelling in order to find something. History tells us so.
Wherever you head in the world, you will somehow be affected by what has happened before you visited.
Maybe you travelled to Berlin and spotted the bullet holes throughout the city?
Or maybe you flew to Hawaii and found a Buddhist temple there, reminding you of Japan's connection to this beautiful US state?
Back in the day, travel was a necessity in order to build up the thriving empires we see today. And war, religion, finance, agriculture and tourism have all had an impact on what a country is like now versus before.
The world is built on travel.
Let's think about this for a moment.
If British explorers hadn't visited India, we Brits probably wouldn't love tea quite so much.
If the Vikings hadn't travelled in order to establish settlements in Iceland and Greenland, these countries wouldn't have much going for them today other than impressive landscapes.
What all this means is that whether you love travel or prefer to be a homebody, there's no denying that our ancestors were devout travellers – whether we've subsequently chosen to follow in their path or not.
The Wanderlust Gene
"Wanderlust (n): a strong desire or impulse to wander, travel or explore the world."
The term wanderlust comes from the German words: wandern (to hike) and Lust (desire). Wandern has often been mistranslated to mean "to wander", giving birth to one of the most overused words within the travel circle today: wanderlust.
What we want to know is: are some people genetically predisposed to travel and a feeling of wanderlust? Science says maybe.
According to a variety of sources, including The Telegraph, researchers have repeatedly tried to link behaviour traits of exploring and risk-taking to a gene variant, with the less than glamourous name of DRD4-7R.
Thankfully, marketers have since dubbed this "the wanderlust gene", sparking a whole range of debates over whether some people are more prone to travel simply because of their genes.
Okay, are you ready for the sciency bit? DRD4 is a dopamine receptor that helps control the levels of dopamine in our brains. Dopamine is an organic chemical, which encourages us to seek novelty (or new experiences), resulting in "happy feelings".
It's thought that those with the "wanderlust gene" (approximately 20% of us) have a lower sensitivity to dopamine. In other words, we are more likely to seek new experiences that in turn release more dopamine, thus happy feelings.
Fun Time:
The Telegraph has recently published a couple of quizzes so that you can find out:
a) whether you have the wanderlust gene
b) … and how extensively you've travelled
What we will say is to take these quizzes with a pinch of salt.
My results were:
"One of your relatives may have the gene, but you don't." (As if! I'm the most widely travelled of all of my family, aside from maybe my ex-Army Dad!)
"You're an average traveller – you've been to plenty of countries but there's many more to explore." (This in fairness is most definitely true… but surely we can all say that unless we've visited every single country in the world?!)
Anyway, back to the debate at hand.
Other than trying to baffle you with science and genetics, the point of telling you all of this about the "wanderlust gene" is that scientists are trying to claim that those of us with this gene travel in order to seek new experiences.
Surely then this is proof of one of the many reasons why people travel?
Placing history and science aside for a moment, we decided to put this question to the test.
We asked a small sample of travellers and travel bloggers why they travel and what they're looking for when they do.
Here's what we found out:
Over 80% of travellers confirmed they are searching for something when travelling.
But what exactly are they searching for?
In Search Of… Beautiful Landscapes
Many travellers leave their hometowns in order to seek out beautiful and dramatic landscapes.
This is especially the case if their homes are built-up cities, barren wastelands or a whole host of other uninspiring viewpoints.
This is the case with Victoria from Follow Me Away, who says:
"When I travel, I search for beautiful landscapes in other lands! Growing up in flat Florida, it is fantastic to see the diversity in nature that the world has to offer! It is also interesting to see that although the world has differences, after you have been to a lot of mountain ranges, you can see the similarities as well as the differences! The same goes for people, culture, anything!"
Whilst Claire from Zigzag on Earth told us:
"I am looking for the most magical places. I am blown away by the work of Nature: deserts, forests, lakes, mountains, geological wonders… Admiring the unique details in shades and shapes makes me feel grateful to be alive."
In Search Of… Adventure
This really should be expected, shouldn't it?
If the wanderlust gene exists in risk-takers, surely this means a lot of travellers are looking for a sense of adventure? We would have to agree with this… to a certain extent.
I'm not about to throw myself out of an aeroplane in search of adventure, but scuba-diving and paragliding are quite high on my list of things to try. Scott would say different though as he has actually already jumped out of a plane!
Cacinda from Points and Travel and Catalina from Miss Adventures Abroad are both in agreement with us, citing:
"I am searching for adventure, cultural, or smart luxury experiences. I love a day at the beach, scuba diving, or rappelling down a waterfall… but that is just the fun part of travel. I am also searching for cultural experiences so that I can get to know the people better and understand why they do what they do, what type of foods they eat or special drinks that they make. There is always a story or reason why they do the things they do."
"The number 1 thing I am searching for when travelling is adventure. For me, this doesn't always have to be something extremely daring like skydiving. Adventure can simply be trying something new. Tasting a unique food for the first time, learning a new language, seeing a landmark in person that I've only read about in books – each of these experiences is an adventure of its own. I love being able to experience the world, and being able to collect tales of these adventures from everywhere I go."
In Search Of… New Experiences
Travelling always presents us with new experiences whether it be activities or just new things to see!
For instance, when exploring Finland last year, husky sledding was first on our list as something we didn't think we'd be able to do anywhere else.
Melanie from The Wandering Darlings agrees with the concept of searching for new experiences, saying:
"I'm always searching for new experiences and places to explore. I love feeling enriched when I'm away from my normal daily life. Seeing the different landscapes, buildings, people, cultures and history of a place is what I'm searching for. I want to see beyond the list of must see places in a destination."
Whilst Jean from Traveling Honeybird says:
"I am always searching for new experiences. I'm unmarried, no children and have no mortgage so tend to spend my money on looking for new experiences that add value to my life. Whether that be a culinary adventure or hiking in the wilderness."
I also spoke with a non-blogger, Scott from Bristol who told me: "I travel to experience new cultures and try new things, although I wouldn't say I'm searching for anything in particular when travelling. That said, I do like to find some decent weather, either sunshine for beach holidays or plenty of snow for skiing."
In Search Of… Balance
We've often heard travellers saying they're able to find a sense of balance during their travels.
This could be balance in work versus personal life or even instilling some sense of health into our lifestyles.
Personally, we'd agree with this concept – not only does travel give us all an escape from work, but it also gives us a break from the mundane "normal day" as well!
Nanouk from Digital Nomad With Kids explains that they are always searching for balance in their lives and when travelling:
"We're on a continuous quest for finding balance in our lives. On a daily basis, we want to decide what to do. Have time with the kids, do some work, do cultural activities, meet new people or anything else we want to do on that day. By travelling – and working location independent – we are trying to reach that balance."
In Search Of… Peace and Zen
There have been so many places we've travelled to that have allowed us to invoke a sense of peace and zen into our day.
From wandering through the Californian redwoods, to discovering a Buddhist temple in Hawaii, finding zen differs from person to person; traveller to traveller.
But if there's one thing to learn from travelling, it's definitely the art of a peaceful and zen lifestyle. Maybe that's why we're so desperate to visit Japan: the very essence of zen!
In Search Of… People and Cultures
Searching for different types of people and cultures to learn from is a pretty common answer we hear as to why do people travel.
And it's easy to see why!
By venturing outside of our comfort zones and into other cultures, we can learn so much from others and how their society works.
Nathan from Foodie Flash Packer is always on the hunt to learn from other cultures, saying:
"I wouldn't say that I'm searching for any one thing in particular, but having been on the road for quite a while now, I travel because of the things I know I'll continue to find. Things like interesting new people, places I've read about but never imagined I would actually see, and tasty new local dishes. I've met some people on the road doing amazing things and I've gone on to stay friends with so many of them. These are the things that keep me travelling."
Whilst Kristen from Travels and Treats likes to establish good connections with those she meets when travelling:
"I'm always looking to have conversations with locals when I travel. The food and sights are definitely a huge part of my travel experience, but it has always been my interactions with real people who live in the places I travel to that send me home feeling the most satisfied, enriched and educated. That said, I guess I'm constantly in search of a destination's truth, whatever that may be. It's easy to look at pretty, colourful, scenic photos of a place and develop a desire to go there. And don't get me wrong, I love coming home with beautiful photos. But what's the story behind these places? That, I've found, is something that best comes from the people who have a lifetime full of history in a place; they are the ones who can share stories and information that we may have no other way of obtaining. This is what I search for while travelling, because it expands my mind and heart in ways that not many other things are able to."
In Search Of… Stories to Tell
This is definitely an interesting concept.
When we travel, we come back with so many stories to tell. Why do you think there are so many travel writers out there? Or photographers?
However you decide to share your travel story, there are always going to be a good number of ears willing to listen.
Take Suman from Nomadic Shoes as an example. When coming home from travelling, her students are always on the lookout for her stories:
"I search for experiences, which includes people, food and culture. I look forward to learning something new each time I travel. And, I bring home a bag full of stories to tell my students and share how the world is beautiful outside our comfort zones."
In Search Of… Learning
This answer goes hand in hand with the people and cultures side of things as there can be so much to learn from them. But not only that, there is also much we can learn from nature and the environment too.
Olga from Latinas Who Travel says:
"I travel to expand my horizons, to learn about other cultures and to interact with the locals. Travelling feeds my hunger and curiosity for life like nothing else. It's the best university in life and has made me growh not only personally but also professionally."
Whilst Priyadarshini from Glorious Sunrise enjoys a spot of people-watching during her travels:
"I search for the local hotspots as I love people-watching. I can learn so much about the locals and their culture that way. Also the food is guaranteed to be great in the places that the locals frequent. I ask for locals' suggestions for things to do :)"
And finally, Alejandra from Euless in Texas is on the hunt for something when travelling. He told us he goes travelling to: "Learn the local culture, history and gastronomy." Alejandra prefers to "go to places less travelled by tourists, like the local dives and hangouts." He told us that this allows him to "meet new people and exchange thoughts and experiences."
In Search Of… Living A Life Less Ordinary
When travelling, planning travels, and when coming home from travels; these are the times when we feel like we're in our element. These are our own moments to shine as individuals and put our own kind of stamp on the world.
Without travel, I hate to think that I could be a mere shell of a woman… and what kind of life would that be like to live? Thus, for both myself and Scott, we travel in search of living a life less ordinary.
To sum all of this up, here are the top reasons why do people travel and also why travel is good for you:
History dictates that we are born travellers
Some people have a love of travel within their DNA thanks to the "wanderlust gene"
You can find beautiful landscapes across the world
You can experience adventure and gain new experiences
You can find balance and a sense of zen within everyday life
You can learn a lot from other people and their cultures
And all of this means that you can tell stories and live a life less ordinary
With all this said though, should we even be asking the question: why do people travel? Rishabh and Nirali from Gypsy Couple suggest not:
"This is a difficult question to answer. We are both searching and not searching for a particular thing while travelling and the complexity of the balance between the two is what makes travel so interesting. We research our destination but still search for something new. While revisiting a favourite destination, we are searching for the same experience that made it so dear to us while not searching for anything else at all. At best, it's a difficult question and one we shouldn't attempt to search for an answer, because that's what makes travel so interesting."
But what do you think? Why do you travel? And why do you think travel is good for you? Let us know in the comments…
Did you like these unique insights? Don't forget to share them!
Shop Things We Love
Travel Hack Tote Review: Affordable Luxury For A Weekend Getaway
35 Best National Trust Places You'll Love!
Nowadays people travel to post pictures on Instagram and make their life seem fabulous.
Justine Jenkins says:
Hi B, thanks for commenting!
Sadly I think you're probably right about some people but I wouldn't say this is why we all travel ?