THE PHOTONEUTRON CROSS SECTIONS FOR THE REACTIONS Br81 (γ,n) Br80 AND Br81 (γ,n) Br80* AND AN ANALYSIS OF THE RATIO BETWEEN THESE CROSS SECTIONS

Abstract

Cross-section curves have been measured as a function of energy for the reactions Br81(γ,n)Br80 and Br81(γ,n)Br80* and the ratio between these cross sections has been examined critically. The curves exhibit the peaked shape characteristic of photonuclear reactions with maximum cross sections of 88 and 42 millibarns respectively. It is shown that the ratio of the cross sections depends on the spins of the excited levels in which the Br80 nucleus is left prior to γ cascading and thus on the reaction leading to it. An elementary analysis based on this point of view gives results consistent with the ratio measured for six different types of reactions.