Exclusive studies of the GDR in excited nuclei

Abstract

Current designs of fision-reactor systems seek to use radiation-resistan$ low-activation materials that support long service lifetimes and minimize radioactive-waste problems atler decommissioning. Reliable assessment of. fusion materials perfonrmnce requires accurate neutronreaction cross sections and radioactive-decay constants. The problem areas usually involve cross sections since decay parameters tend to be better known. The present L stud was motivated by two specific questions: i) Why are the V(n,np)sOTi cross section values in the ENDFLB-VI library so large (a gas production issue)? ii) How well known are the cross sections associated with producing 7.4X105 y 'Al in silicon carbide by the process 28Si(n,np+d)27Al(n,2n)2sAI (a long-lived radioactivity issue)? The energy range 14-15 MeV of the D-T fhsion neutrons is emphasized. Cross-section error bars are needed so that uncertainties in the gas and radioactivity generated over the lifetime of a reactor can be estimated. We address this issue by comparing values obtained from prominent evaluated cross-section libraries. Small differencesbetween independent evaluations indicate that a physical quantity is well known while the opposite signals a problem. Hydrogen from 51 V(n,p)5% and helium from 5*V(n,a)4*Scare also important sources of gas in vanadium, so they too were examined. We conclude that 'lV(n p)5*TIis adequately known but 51 V(n,np+d)50Tiis not. he status for helium generation data is quite good. Due to recent experimental work, 2'Al(n,2n)2GAl seems to be fairly well known. However, the situation for %i(n,np+d)27Alremains unsatisfactory.