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).
I. Dostrovsky, R. Davis Jr., A. M. Poskanzer, and P. L. Reeder, "Cross Sections for the Production of Li9, C16, and N17 in Irradiations with GeV-Energy Protons," Phys. Rev. 139, B1513 (1965).
G. T. Emery and M. L. Perlman, "Dynamic Penetration Effects in the Internal Conversion of Electric Dipole Transitions in Lu175," Phys. Rev. 151, 984 (1966).
A. M. Poskanzer, R. McPherson, R. A. Esterlund, and P. L. Reeder, "Beta-Delayed Protons from Ar33, Ca37 and Ti41," Phys. Rev. 152, 995 (1966).
J. P. Bocquet, Y. Y. Chu, O. C. Kistner, M. L. Perlman, and G. T. Emery, "Chemical Effect on Outer-Shell Internal Conversion in Sn119; Interpretation of the Mössbauer Isomer Shift in Tin," Phys. Rev. Letters 17, 809 (1966).

Nuclear transitions, atomic effects

Experiments at Brookhaven gave the first proof that electrons are ejected from the deep shells of an atom when the nucleus undergoes alpha decay. The ejection probabilities for the different electron shells are one or two orders of magnitude greater than predicted by a theory similar to one that is apparently adequate for ordinary collision processes. This indicates a previously unsuspected, and as yet unresolved, flaw in this kind of theory.

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.
J. A. Miskel and M. L. Perlman, "Double Vacancies in the K-Shell Associated with K-Electron Capture in Ar37," Phys. Rev. 94, 1683 (1954).
M. Wolfsberg and M. L. Perlman, "Multiple Electron Excitation in Auger Processes," Phys. Rev. 99, 1833 (1955).


Radioactivity applied to archaeology and to the study of works of art

The first application of neutron activation analysis to the study of archaeological materials was made at BNL. In some Greek terra cotta figurines it was found that the trace impurity compositions fall into patterns which are correlated to locations of origin and manufacture. Ancient commerce in Roman Aretine pottery, in South Arabian pottery, and in Mayan pottery has been traced. An extensive study of ancient glass has revealed many facts concerning the technology of its manufacture. A number of institutions have now adopted neutron activation techniques for work in these areas. It was at BNL that activation autoradiography was for the first time applied to investigations of works of art such as paintings and to recovery of images from badly faded historic photographs. In paintings, the different pigments give rise to radiations decaying with different half-lives, and a sequence of radioautographs may provide information about layers of pigments used by the artist and about his techniques of application.

E. V. Sayre, "Some Ancient Glass Specimens with Compositions of Particular Archaeological Significance," BNL 879 (T-354), July 1964.
E. V. Sayre and H. N. Lechtman, "Neutron Activation Autoradiography of Oil Paintings," Studies in Conservation 13, 161 (1968).

Lepton conservation

The neutrino capture reaction, n + Cl37 ® Ar37 + e-, was shown not to proceed with the antineutrinos emitted by a nuclear reactor, thus experimentally demonstrating that neutrinos and antineutrinos differ in their interactions with nuclei. This result is one of the prime experimental facts supporting the principle of lepton conservation. [An early step leading to the 2002 Nobel Prize for Raymond Davis, Jr., ed.]

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

Measurements have been made of the stable and radioactive products produced in meteorites by cosmic radiation. From these measurements and from the high energy production cross sections for these products it is possible to obtain information about the cosmic ray intensity. Two important conclusions have been made: 1) the intensity of cosmic radiation has been constant in time, that is, the average intensity over the last 400 years is the same as the average intensity over the last 400,000 years; 2) the intensity of the cosmic. Radiation near the earth is about 20 percent lower than the intensity at several earth-sun distances from the sun.

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).
O. A. Schaeffer, R. Davis Jr., R. W. Stoenner, and D. Heymann, "The Temporal and Spatial Variation in Cosmic Rays," Proc. Intl. Conf. on Cosmic Rays, Jaipur, India, 3, 480 (1963).
R. Davis Jr. and D. S. Harmer, "Solar Neutrino Detection by the Cl37-Ar37 Method," Proc. Informal Conf. on Experimental Neutrino Physics, CERN 65-32 (Geneva) 1965.
R. Davis Jr. and D. S. Harmer, "Solar Neutrinos," Die Umschau 2, 56 (1966).

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Last Modified: June 28, 2012