Coincidence Experiments in Antimony 124

Jurney, E. T.; Mitchell, Allan C. G.

doi:10.1103/physrev.73.1153

Phys. Rev.

1948

DOI: 10.1103/physrev.73.1153

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Coincidence Experiments in Antimony 124

E. T. Jurney

Allan C. G. Mitchell

Abstract: The radiations from Sb m (60 d.) have been measured with the help of coincidence counting methods. The beta-ray absorption curve was measured and analyzed by the method of Bleuler and Zunti. Two groups of electrons were found with end points at 2.24 and 0.51 Mev. Gamma-gamma and beta-gamma coincidences were measured. A plot of the number of betagamma coincidences per recorded beta-particle indicates that the spectrum is complex. Two low energy groups were found with end points at 0.75 and 0.47 Mev.

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Cited by 12 publications

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“…Such a resonance was observed in carbon at 30 Mev, 1 in copper at 22 Mev, 1 in tantalum at 16 Mev, 2 and for photofission in thorium and in uranium at 16-18 Mev. 1 The suggestion was made that this phenomenon may be due to the interplay of increasing level density and increasing competition from other processes such as, for instance, the (y y 2n) process.…”

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On Nuclear Dipole Vibrations

1948

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The high frequency resonances recently observed for (y,n) reactions as well as photo-fission are interpreted in analogy with the "reststrahl frequencies" of polar crystals. The estimated frequencies are in good agreement with the experimental results. An interesting consequence of this interpretation is the conclusion that strong resonance scattering of 7-rays should take place at a frequency characteristic of the scattering nucleus. I T has been observed recently 1 that some nuclear photo-disintegrations, (y.n) reactions as well as photo-fission, exhibit a behavior which has the appearance of a high frequency resonance. Such a resonance was observed in carbon at 30 Mev, 1 in copper at 22 Mev, 1 in tantalum at 16 Mev, 2 and for photofission in thorium and in uranium at 16-18 Mev. 1 The suggestion was made that this phenomenon may be due to the interplay of increasing level density and increasing competition from other processes such as, for instance, the (y y 2n) process. Recent experiments 3 show, however, that in the case of Cu 63 as well as other nuclei the decrease in the (y,n) cross section in the high energy region is not compensated to any considerable extent by an increase in the (T,2W) cross section. It is, furthermore, desirable to explain why such different processes as (y,n) reactions and photo-fission should have maximum cross sections at so similar 7-energies.We propose to interpret these frequencies as resonances, somewhat different from those caused by definite nuclear levels, and analogous to the "reststrahl frequencies'' of polar crystals. We assume that the 7-rays excite a motion in the nucleus in which the bulk of the protons move in one direction while the neutrons move in the opposite direction. We shall call this motion the 1 G. C. Baldwin and G. S. Klaiber, Phys. Rev. 71, 3 (1947) and Phys. Rev. 73, 1156(1948). 2 J. McElhinney and A. O. Hanson, private communication. 3 M. L. Perlman and G. Friedlander, Phys. Rev. 74, 442 (1948). We are indebted to Dr. Friedlander for informing us of these results before publication. "dipole vibration." Such a vibration will have a high frequency as a result of the partial separation of the protons from the neutrons to which they are strongly bound. The maximum in the 7-absorption cross section will give rise to similar maxima for several nuclear processes in which 7-absorption is the first step. We shall see below that the magnitude of the integrated cross sections deduced from experiments is too great to be explained by the motion of a single proton or of a small fraction of the protons contained in the nucleus.The breadth of the resonance-so far only crudely known-is probably due to the transfer of energy from the orderly vibration described above into other modes of nuclear motion. Thus, the breadth is due to a process analogous to damping by friction. One may use a nuclear model in which the ordered dipole vibration of protons and neutrons in opposite directions correspond to well defined quantum states. Coupling with other degrees of freedom will b...

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