Spectroscopy of ⁴¹K by thermal neutron capture in ⁴⁰K

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.