Modification of Hwang's criteria for determining the number of resonances contributing to overlap effects

The concept of a fictitious half-width for each resonance leading to Hwang's criterion for determining the number of resonances contributing to the overlap effect in the resolved region has been examined. The fictitious half-width was calculated for several sample resonances of Pu 239 at three different temperatures. The overlap contribution was evaluated for many sample resonances at three different temperatures with ten neighbouring resonances on either side of the reference resonance. The results show the very possibility of missing certain strongly overlapping but distant resonances in energy space while evaluating the overlap correction. The present investigations confirm that Hwang's criterion needs modification especially when the distant resonances have a very large decay width. We also report our modified criterion for efficiently calculating the overlap contribution. (orig.)