The Aztec Research Guide to Radiation
Many of us know that a mobile phone emits radiation, and a nuclear power station contains lots of it and naturally assume it's the same thing in both cases, but from a scientific point of view, the two are very different.
There are two main catagories of radiation, Ionizing and non-ionizing. Ionizing radiation is what gets emitted from radioactive substances like nuclear ower station fuels and atomic bombs. In large doses, it damages and destroys living things. Non-ionizing radiation is what gets emitted from mobile phones and microwave ovens, and is mostly considered to be safe for living things.
This is a simple guide explaining what Ionizing Radiation (the stuff that is emitted from things that are radioactive) is. The heavy duty physics behind this phenomenon has been left out for simplicity.
Before I explain what ionizing radiation is, I will define some terms that will be used in the description to make things clearer.
Electromagnetic Radiation : It is easiest to say that Electromagnetic radiation consists of waves that move along at a speed of 300 000 000 meters per second (The speed of light) and are made up of both electric and magnetic fields. A more detailed description would not make this a simple guide. These waves include things like radio waves, microwaves (used to transmit information as well as overcook food), waves that our eyes can see and interpret (light) and X-Rays.
Radioactive Substance : A radioactive substance is something that is undergoing radioactive decay. Radioactive decay occurs when the nuclei of the atoms in the substance are unstable. In order for the atoms to stabilize themselves they emit radiation in the form of particles or electromagnetic waves. When a radioactive element decays, it turns into a different element. The new element may or may not be radioactive. An example is Radium 226 which decays into Radon 222.
Neutrons, Protons and Electrons : These are the component parts of an atom. The centre of the atom (the nucleus) is made of Neutrons and Protons, in a cloud around the nucleus are the electrons. Neutrons have no electrical charge, protons have a positive charge and electrons have a negative charge. The solids, liquids and gasses that surround us are made of atoms. To give you an idea of size, it would take 20 million atoms of hydrogen gas to make a line one millimeter long. The full scientific explanation of how atoms are constructed would take a lot more explaining and would delve into the depths of quantum theory, so again, this definition will have to do for now.
Half-life : The half-life of a radioactive substance is the time it takes for half of the substance to undergo decay. Generally speaking, the longer half-life a radioactive substance has, the less radiation it emits in a given time period. Some examples of the half-lives of radioactive elements are Bismuth 214 - 19.7 minutes, Lead 210 - 22 years and Uranium 238 - 4,500,000,000 years.
Ionizing Radiation : Ionizing radiation is either normal electromagnetic radiation or energetic particles (see below) that are powerful enough to knock electrons off of the atoms it bumps into while it is flying around.
Non-Ionizing Radiation : Non Ionizing radiation is electromagnetic radiation (such as waves emitted by cell phones & television transmitting stations) that is not energetic enough to cause ionization (see below).
'Ionizing Radiation' is used as a general term for two types of radiation emitted by radioactive objects.
The first is particle ionizing radiation and consists of 'bits' of the atom that are thrown out in order to gain stability. These 'bits' are listed below.
Alpha particle : Consists of 2 neutrons and 2 protons stuck together. As an alpha particle is quite large and heavy by atomic standards they are also quite feeble and consequently cannot even penetrate a piece of paper or the skin of a human being.
It is for this reason that radioactive substances which emit only alpha radiation are only considered dangerous if you eat them. Some examples of alpha emitting substances include americium (used in smoke alarms) and plutonium (used in atomic bombs). So next time you are assembling a plutonium based nuclear device, remember not to lick you fingers.
Beta Particle : Consists of a high energy electron. These particles fly out of a decaying atom with considerable energy but can be stopped by a sheet of aluminum or perspex. Examples of a beta emitting substances are Iodine 131 which is used in medicine and Tritium which is used H-Bombs and glow in the dark watches. Beta particle emitting substances are a lot more hazardous that Alpha emitting ones.
The second type is electromagnetic ionizing radiation :
Gamma Radiation : Consists of waves similar to light but with much greater energy (200,000 times more approx). Gamma radiation is emitted from decaying radioactive substances in order to stabilize the atom.
X-Radiation : Is very similar to gamma radiation in composition, but is not as energetic. Received in small amounts from space and generated in X-Ray medical equipment and TV sets (in small quantities).
Here is a comparison of the ralitive energy levels.
|Alpha Particle||Bowling Ball||Slow, Large, Heavy, Easily stopped by crashing into things|
|Beta Particle||Fast golf ball||Quite fast, high matter penetrating energy.|
|Gamma Radiation||Zero mass bullet||Travels at the speed of light, penetrates almost anything, can only be fully stopped by 1 metre of concrete or 10 cm of lead.|
Ionization : Ionizing radiation causes ionization of atoms that it comes into contact with. The energy of either particle or wave ionizing radiation is sufficient to knock electrons off of the atoms it encounters. This leads to a situation where some atoms have an electron missing (and have a positive charge) and there are free electrons. The movement of these electrons causes an effect which can be picked up with a Geiger counter.
Well, that's about it. The example below brings together some of the stuff discussed above.
Dave has a chunk of rock on his kitchen table which contains the radioactive element Radium 226. The radium in the rock is in a constant state of radioactive decay. When Radium 226 decays, each atom throws out an alpha particle and a quantity of gamma radiation. So the chunk of rock is emitting many rays of gamma radiation and many alpha particles into the air and table around it.
As explained earlier, alpha particles are feeble so the alpha radiation from the rock will get probably less than an inch into the air before it looses energy and absolutely noware into the table. However, the gamma radiation being emitted from the rock will easily penetrate the table and the air around it for a few feet.
Dave could use a geiger counter to detect the alpha and gamma radiation from the rock. The reading on the counter would increase the closer the probe is moved to the rock.
Contrary to popular myth, generally speaking radioactive substances do not glow. The reason that some clock and watch dials glow in the dark is that the painted numbers contain a mixture of Radium and zinc sulphide. The radiation emitted by the Radium energises the zinc sulphide which in turn glows a greenish color.
Also, this means that Dave's rock would no glow in the dark or emit any kind of buzzing or humming sound as in all of those old poor quality sci-fi films.