Nuclear Spectroscopy and Structure 1947-67
In experiments carried out at the Cosmotron, several of the small number of delayed proton-emitting nuclei were discovered. These include Ti41, Ca37, Ar33, and Ne17. A new delayed neutron emitter, Be12, was found also. Detailed nuclear spectroscopic studies were made on these and other very unstable nuclei.
Studies of internal conversion electrons emitted in the decay of Sn119m showed that 5s electron density at the nucleus is less in SnO2 than in metallic Sn. From this result and the Mössbauer isomer shift it was possible to conclude that the charge radius of the 24-keV state is ~3 x 10-4 larger than that of the ground state. This conclusion has removed a troubling uncertainty from the interpretation of a large number of Mössbauer investigations of the structures of tin compounds, and work of this kind has been taken up elsewhere.
Measurements of electron capture decay rates and especially of probabilities of electron capture decay to excited states were done here. Results were applied in early efforts to understand transitions between low-lying excited states in even-even nuclei.
When nuclear gamma transitions are greatly hindered, the ordinarily negligibly small nuclear penetration matrix elements may contribute measurably to internal conversion. A study made of a triplet of hindered E1 transitions occurring in the decay of Yb175 provided the first case in which the relative magnitudes of these matrix elements could be compared. Their ratios were found to agree with the ratios expected from theory.
The earliest precise studies of radioactive nuclide masses were made at Brookhaven; values of the H3-He3 and C14-N14 mass differences were determined by chemical mass spectrometry with a precision that has remained unchallenged. The success of this work depended in part on the use of isotopic species that required special chemical preparation and in part on the development of the mass synchrometer in the BNL Physics Department. The doublets used were HD+―3He+, C2H4+―C2D2+ and HT+―D2+.
L. Friedman and L. G. Smith, "The Mass Difference T-He3 and
the Mass of the Neutrino," Phys. Rev. 109, 2214 (1958).
Nuclear transitions, atomic
Ejection of electrons from an atom may occur when the nucleus undergoes
an electron-capture transition. This process was for the first time detected
and measured at BNL. In the case of Ar37 decay, the total
probability for K ejection was found to be in approximate accord with
theoretical estimates made elsewhere, but the probability of ejection to
bound states relative to ejection to the continuum is less than predicted.
Experimental and theoretical studies were made also of atomic charge accumulation in transitions associated with deep vacancy production in electron capture and internal conversion processes. The effect of the sudden perturbation of field in causing additional loss of electrons in the Auger process was discovered in the course of this work with Ar37 and Xe131m
W. Rubinson and W. Bernstein, "The Emission of L X-Rays of Lead in Po210
Decay, " Phys. Rev. 86, 545 (1952.
RADIOACTIVITY AND NUCLEAR REACTIONS APPLIED TO ASTROPHYSICS, PARTICLE PHYSICS, ARCHAEOLOGY, AND THE STUDY OF ART WORKS
Radioactivity applied to archaeology and to the study of works of art
E. V. Sayre, "Some Ancient Glass Specimens with Compositions of Particular
Archaeological Significance," BNL 879 (T-354), July 1964.
R. Davis, "An Attempt to Observe the Capture of Reactor Neutrinos in Chlorine-37," Proc. 1st UNESCO Conf., I, 728 (1958).
Application of radioactivity and nuclear reactions to astrophysics
The Cl36-Ar36 method used extensively for determining accurate cosmic ray exposure ages of meteorites originated at BNL.
The time interval which elapsed between formation of the elements and formation of an earth capable of retaining atmosphere was deduced to be 2.7 x 108 years. This number is based on a BNL measurement of the half-life of I129, 1.72 x 107 years, and on the justifiable assumption that most of the Xe129 now present on earth originated from that part of the original I129 still remaining to decay after the earth was formed.
An experiment is underway to test the present theory of the solar energy generation process by observation of the neutrino radiation emitted from the sun. The method used depends upon measurement of the neutrino-capture reaction n + Cl37 ® Ar37 + e- in a detection system containing 610 tons of the chlorine-containing compound C2Cl4. Observations show that the neutrino capture rate in the detector is at least a factor of seven below that expected from current theory. [Another step leading to the 2002 Nobel Prize for Raymond Davis, Jr., ed.]
S. Katcoff, O. A. Schaeffer, and J. M. Hastings, "Half-Life of I129 and
the Age of the Elements," Phys. Rev. 82, 688 (1951).
Last Modified: June 28, 2012