Isomeric yield ratios and fractional chain yields for 117In and 117Cd produced by proton-induced fission of Bi, Th and U

Abstract

The relative independent yields of the isomeric pair 117 g In- 117 m In produced by proton-induced nuclear fission have been measured as a function of energy from 15–157 MeV and target element. The high spin to low spin yield ratio is generally increasing with increasing proton energy, and below 115 MeV proton energy the three targets produce the same curve. Above this energy the ratio from uranium fission seems to level off while the other reactions do not show this effect. The ratios obtained at the lowest bombarding energies are as low or lower than known isomeric yield ratios from thermal neutron-induced fission. Comparison of the results with calculations based on statistical level density theory also show that at low proton energy the primary fission fragments are formed with a very low intrinsic angular momentum. The fractional chain yields of 117In is shown to be increasing with increasing bombarding energy for all targets, and to be much larger for reactions with bismuth target than for uranium and thorium. Lastly, the cumulative high spin to low spin isomeric yield ratio for the pair 117 m Cd- 117 g Cd has been obtained and is increasing with increasing proton energy.