Capture-Gamma Determination of Chromium-54 Structure

Abstract

Gamma emission following thermal-neutron capture in separated chromium-53 has been studied at the Livermore 2-MW pool-type reactor using a fast coincidence scintillation spectrometer. A quartz-crystal thermal-neutron filter is described which produces a flux of ${10}^6$ neutrons/${\mathrm{cm}}^2$ sec at the target with a cadmium ratio better than ${10}^4$. Capture gammas are observed at 9.72, 8.88, 7.10, 6.88, 6.64, 6.28, 6.00, 4.86, 3.72, 2.60, 2.24, 2.00, 1.77, and 0.84 MeV. Cascade transitions were studied using coincidence, sum coincidence, and angular correlation methods. A "double-window" coincidence technique used in these measurements is described. This technique systematically subtracts coincident background and is particularly applicable to angular correlation measurements. Energy levels are established at 0.84, 2.61, 2.84, 3.08, 3.44, 3.72, and 4.86. MeV. The spins of the first four excited states are 2, 2, 0, and 2, respectively, as determined by angular correlation and cascade systematics. The results are discussed in terms of recent nuclear models.