The neutron cross-section standards evaluations for ENDF/B-VI (Evaluated Nuclear Data File)

The measurement of neutron cross sections can often be significantly simplified by using a cross-section standard that eliminates the need for a direct measurement of the fluence. The accuracy of such a cross-section measurement is limited by the uncertainty in the standard cross section relative to which it is measured. Improvements in the standard cause all cross sections measured relative to that standard to be improved. This is the reason for the emphasis on the neutron cross-section standards, which include H(n,n), {sup 3}He(n,p), {sup 6}Li(n,t), {sup 10}B(n,{alpha}), {sup 10}B(n,{alpha}{sub 1}{gamma}), C(n,n), {sup 197}Au(n,{gamma}), and {sup 235}U(n,f). Measurement programs have continuously improved the data base of the standards. Evaluations have also improved with time; however, there have been significant weaknesses in earlier evaluations. The evaluation process for the ENDF/B-VI (Evaluated Nuclear Data File) standards has removed many of these weaknesses by being more thorough and logically consistent than earlier evaluations. New evaluations for ENDF/B-VI have been produced for each of the cross-section standards by the standards subcommittee of the Cross Section Evaluation Working Group.