Distribution of Partial Radiation Widths

Abstract

The gamma-ray spectra that result from the capture of neutrons in resonances of Hg 199 , Pt 196 , W 183 , and Se 77 are measured. A least-squares fitting of the spectra gives relative values of partial widths for various sets of high-energy radiative transitions. These widths are treated as statistical samples drawn from populations governed by a x 2 distribution with v degrees of freedom. A technique of hypothesis testing that makes use of Monte Carlo calculations is used to derive unbiased values of v from the small samples of experimental widths. The over-all result of the analysis is ^=1.34db0.33±0.21. The previously reported partial radiation widths for resonances of Gd 155 , Yb 173 , Hf 177 , and Hg 201 are also analyzed. The result is v = 1.14±0.44=b0.21. Thus, both sets of data are in good agreement with the value v = l that is expected from the Porter-Thomas description of the distribution of the widths associated with a single exit channel.

Nuclear Spectroscopy with Average Spectra from Neutron Resonance Capture

“…1 Previously we reported 2 on a new class of measurements in which the random fluctuations are averaged out by measuring directly the y-ray spectra that result from the capture of neutrons in an energy band containing many resonances. In the experiment reported in Ref.…”

Spectrum of High-Energy Gamma Rays Following Thermal-Neutron Capture byEr166

“…The detailed nature of the distribution function has been calculated in the random-matrix approximation, 18 and this result has been confirmed experimentally. 19 Because of the manner in which the radiative widths are distributed, the capture 7-ray spectrum will be featured by a majority of transitions that have smaller than average widths and very few transitions with larger than average widths, just as is observed for the Er 166 (?z,y)Er 167 reaction. According to the statistical model, however, the probability of a particular width being sixteen times the average is only ~ 10~7.…”

Gamma Rays from theHg199(n, γ)Hg200Reaction an

“…Additional data have been obtained through resonance-capture experiments. [26][27][28][29][30] As a result of these measurements, many levels with excitation energies up to 1500 keV have been well established and their spins and parities determined. Above 1570 keV numerous states have been found and spins and parities of several of these levels have been determined through very recent polarization correlation 31 and coincidence experiments.…”