Isomeric ratio measurements for the radiative neutron capture ¹⁷⁶Lu(n,γ) at DANCE

In this paper we describe a new method using the high efficiency and granularity of the Detector for Advanced Neutron Capture Experiments (DANCE) array (Los Alamos National Laboratory) working with a digital data acquisition system. The isomeric ratio for the neutron capture reaction ¹⁷⁶Lu(n,γ) on the J^π=5/2^-, 761.7 keV, T_1/2=32.8 ns level of ^177mLu, has been determined in the neutron energy range 8.5 eV-100 keV. Our method to determine isomeric cross section ratios (R) consists in a careful study of γ-cascades using the time information of each γ-ray of the cascade. In a large coincidence window of 250 ns, all the γ rays following the neutron capture are recorded. All the γ-rays of this window located in the first 20 ns define the prompt γ-cascade. The others γ-rays are assigned as delayed γ-rays. Experimentally we have obtained: R(761.7 keV) = 11.3 ± 0.8 % and comparisons with Hauser-Feshbach predictions show large discrepancies