Total radiation widths of levels in antimony, mercury, ruthenium and iridium

Abstract

An extension and elaboration of the “thin-thick” area method for the determination of the total widths of neutron resonances using transmission studies is described. Such determinations were made for a variety of levels in various isotopes of antimony, mercury, ruthenium and iridium, using the Brookhaven fast chopper and 1024-channel time-of-flight analyser. Using a broad range of sample thicknesses, these data, in conjunction with the neutron widths obtained for these levels, resulted in a determination of the total radiation widths of a total of 18 resonances in these nucleides. Of particular importance were the total radiation widths obtained for the 6.23, 15.4 and 29.7 eV levels in Sb 121 and the 43.3 and 71.8 eV levels in Hg 201. Previously reported experiments found these widths to differ by approximately a factor of 2 for levels in the same nucleide, contrary to what has been found in almost all medium and heavy nuclei investigated. The results presented here find these widths to be the same, within experimental error, for the levels in Sb 121, in disagreement with previous work, and confirm the wide fluctuations found for the resonances in Hg 201. A total of five radiation widths were obtained for levels in Ru, and in conjunction with data obtained using enriched isotopes, these results served to isotopically identify a level in Ru 99 and one in Ru 102, which were not uniquely assigned on the basis of data from separated isotopes only. Total radiation widths were also obtained for three levels in Ir 191 and one level in Ir 193. A discussion of these results is presented.