Transmission resonance spectroscopy in the third minimum of 232Pa

TL;DR

This study measured the fission probability of 232Pa to identify hyperdeformed transmission resonances, revealing structures indicative of hyperdeformed shapes and estimating the energy of the third minimum in the fission barrier.

Contribution

First observation of hyperdeformed transmission resonances in 232Pa using the (d,pf) reaction and detailed analysis of the fission barrier parameters.

Findings

Identification of transmission resonances at 5.7 and 5.9 MeV

Interpretation of resonance structure as hyperdeformed rotational bands

Estimated energy of the third minimum at 5.05 MeV

Abstract

The fission probability of 232Pa was measured as a function of the excitation energy in order to search for hyperdeformed (HD) transmission resonances using the (d,pf) transfer reaction on a radioactive 231Pa target. The experiment was performed at the Tandem accelerator of the Maier-Leibnitz Laboratory (MLL) at Garching using the 231Pa(d,pf) reaction at a bombarding energy of E=12 MeV and with an energy resolution of dE=5.5 keV. Two groups of transmission resonances have been observed at excitation energies of E=5.7 and 5.9 MeV. The fine structure of the resonance group at E=5.7 MeV could be interpreted as overlapping rotational bands with a rotational parameter characteristic to a HD nuclear shape. The fission barrier parameters of 232Pa have been determined by fitting TALYS 1.2 nuclear reaction code calculations to the overall structure of the fission probability. From the average level spacing of the J=4 states, the excitation energy of the ground state of the 3rd minimum has been deduced to be E(III)=5.05 MeV.