Isomeric Cross Section Ratios for 14 Mev Neutron Reactions

Abstract

The cross sections for the production of isomeric pairs in the following reactions with 14 Mev neutrons have been measured by the activation method using the sample sandwiched plastic scintillator: As 75 ( n , p )Ge 75 (25±5 mb), As 75 ( n , p )Ge 75 m (10±2 mb); Br 81 ( n , 2 n )Br 80 (470±50 mb), Br 81 ( n , 2 n )Br 80 m (510±50 mb); Ba 138 ( n , α)Xe 135 (13±2 mb), Ba 138 ( n , α)Xe 135 m (13±2 mb); Ho 165 ( n , p )Dy 165 (40±10 mb), Ho 165 ( n , p )Dy 165 m (<1 mb). Their isomeric cross section ratios are compared with the statistical model calculations based on the method of angular momentum sampling. For Br 81 ( n , 2 n ) and Ba 138 ( n , α) reactions, these ratios can be reproduced by these calculations with the value of the level density parameter σ=4±1, but not for the other two. The disagreement in As 75 ( n , p ) reaction can be explained by the predominance of the direct interaction process.