Search

In this paper we present the first systematic analysis of the impact of the populated vs. intrinsic spin distribution on the nuclear level density and γ-ray strength function retrieved through the Oslo Method. We illustrate the effect of the spin distribution on the recently performed 239Pu(d,pγ)240Pu experiment using a 12 MeV deuteron beam performed at the Oslo Cyclotron Lab. In the analysis we couple state-of-the-art calculations for the populated spin-distributions with the Monte-Carlo nuclear decay code RAINIER to compare Oslo Method results to the known input. We find that good knowledge of the populated spin distribution is crucial and show that the populated distribution has a significant impact on the extracted nuclear level density and γ-ray strength function for the 239Pu(d,pγ)240Pu case.

We have done a systematic study of the low-energy behavior of the γ-ray strength function with full-configuration shell-model calculations. We have performed calculations in several isotonic and isotopic chains, spanning several mass regions. There are systematic trends: The strength function shows a low-energy enhancement that is more pronounced near shell closures and less so in the mid-shell regions. We predict that the low-energy enhancement is omnipresent, but that for high-mass nuclei it has so far been out of experimental reach due to detector thresholds, except for the case of 151, 153Sm.

In this work, we have studied the low-energy behaviour of the \(\gamma \)-ray strength function within the framework of the shell model. We have done calculations on isotopic and isotonic chains, spanning several mass regions. We find systematic trends, where the strength function exhibits a low-energy enhancement that is steeper near shell closures and flatter in the mid-shell regions. Further, we compile strength functions from discrete experimental data and find evidence for a low-energy enhancement.