Radiation Widths of Bound Nuclear Levels in the Vicinity of the Neutron Threshold

Abstract

The radiation widths of bound nuclear levels excited by (y, y') reactions in nuclei '39La, '3 Te, Sn, 6Sr, Se, and 6Zn have been measured. The present results together with results published by other authors using (y, y') reactions are summarized and compared with similar results obtained in capture reactions of thermal and resonance neutrons. The expected properties of the nuclear levels obtained by extrapolation of the giant-dipole resonance to lower energies are compared with the present experimental data. The fluctuation in partial radiative widths from these bound levels is shown to be compatible with the Porter-Thomas distribution.The 536-keV (2+) first excited state of Xe~h as been investigated by means of nuclearresonance-Quorescence scattering experiments. The use of a Ge{Li) detector allowed a good determination of the Rayleigh scattering contribution which amounted to about 30% of the resonant peak. The level width was found to be (5.2 + 0.9) X10 eV, corresponding to a mean life of (1.3+0.3) x10~sec and aBN2)) of (0.69+0.15)e2&&10 cm4. From this result and the relative transition probabilities determined previously in a Coulomb-excitation experiment by Pieper, Anderson, and Heydenburg, the absolute B(E2) values for the first excited states of eu8 and Xe(32 were obtained.

Dipole strength inSe80forsprocess and nuclear transmutation ofSe79

“…In earlier NRF studies of 80 Se, the deexcitation of a level at 7820 keV was investigated [40,41]. In the present work, we could not confirm transitions depopulating a 7820 keV level, but we newly identified 180 γ rays up to 9.6 MeV in 80 Se.…”

“…First, a spectrum of the ambient background adjusted to the intensities of the transitions from 40 K and 208 Tl decay in the in-beam spectrum was subtracted from the measured spectrum. To correct the spectrum for the detector response, spectra of monoenergetic γ rays were calculated in steps of 10 keV by using the simulation code GEANT4.…”

Studies on the level schemes of66Zn,144Sm and120Sn using the (γ, γ′) reaction

“…The resonance level at 8.995 MeV in Sm was first attributed to 15~ [9,10] but later studies showed that it in fact belonged to 144Sm [11]. The studies on these nuclei reported in Ref.…”

“…These nuclei have also been studied by the (7, Y') reaction, using nickel and lead capture 7 ray sources to excite corresponding resonant levels [8][9][10]. The resonance level at 8.995 MeV in Sm was first attributed to 15~ [9,10] but later studies showed that it in fact belonged to 144Sm [11].…”

“…The studies on these nuclei reported in Ref. [9] were concerned mainly with the statistical behaviour of highly energetic states in the neighborhood of the nuclear threshold, and little attention was paid to the precise determination of the nuclear parameters for the different low lying levels thus populated. Furthermore, in the same work is shown that the de-excitation of the high levels to low-lying levels is governed mainly by Porter-Thomas fluctuations and multipolarity rules which may vary considerably from level to level; thus the decay scheme obtained for a given nucleus may vary according to the excited state reached in the photoexcitation process, and consequently, use of an additional source to study the level structure of a certain nucleus, such as 66Zn, will offer in any case more information on the low lying levels of the nucleus investigated.…”