Thermal neutron capture cross sections and neutron separation energies for 23Na(n,γ)

Prompt thermal neutron capture gamma-ray cross sections sigma(gamma) were measured for the Na-23(n,gamma) reaction with guided cold neutron beams at the Budapest Reactor. The Na-24 gamma-ray cross sections were internally standardized with a stoichiometric NaCl target by using standard Cl-35(n,gamma)Cl-36 gamma-ray cross sections. Transitions were assigned to levels in Na-24 based primarily upon the known nuclear structure information from the literature, producing a nearly complete neutron capture decay scheme. The total radiative thermal neutron cross section sigma(0) was determined from the sum of prompt gamma-ray cross section populating the ground state as 0.540 (3) b, and from the activation gamma-ray cross sections for the decay of Na-24 as 0.542 (3) b. The isomer cross section sigma(0) (Na-23(m), t(1/2) = 20.20 ms) = 0.501 (3) b and the Na-24 neutron separation energy S-n = 6959.352 (18) keV were also determined in these experiments. New level spins and parities were proposed on the basis of new transition assignments and the systematics of reduced transition probabilities for the primary gamma rays.