Spectroscopy of 41K by thermal neutron capture in 40K

Abstract

The γ-ray spectrum emitted after thermal neutron capture in 40K has been studied at the ILL high flux reactor with curved crystal Bragg, pair and Ge(Li) spectometers. 585 transitions were assigned to the reaction 40K(n, γ) 41K and 490 of them were placed into a 41K level scheme; 68 new states are proposed. On the basis of γ-ray branches to states with established spin and parity, many new spin-parity assignments were made. The level energies up to 4 MeV were measured with a precision of 8–50 eV relative to the 411.8 keV 198Au standard, those above 4 MeV with a precision of 50–100 eV. The spin of the capture state was found to be I = 7 2 ; the neutron binding energy was determined to E B = 10095.25(10) keV. The level density of I π = 5 2 ±, 7 2 ±, 9 2 ± states was analyzed in terms of the constant-temperature Fermi gas model. It was shown that in this spin window the level scheme is almost complete up to an excitation energy of 5 MeV.