Neutron Thresholds in theV51(p, n)Cr51,Mn55(p, n)Fe55,Zn70(p, n)Ga70, andAs75(p, n)Se75Reactions

Abstract

The two-counter slow-to-fast ratio technique has been used with proton energies up to about 2 Mev in a study of neutron thresholds from the following four reactions. In the ${\mathrm{V}}^{51}(p, n){\mathrm{Cr}}^{51}$ reaction, the ground-state threshold was measured to be 1.564±0.002 Mev. No excited states were observed in the region of excitation from zero to 0.41 Mev. In the ${\mathrm{Mn}}^{55}(p, n){\mathrm{Fe}}^{55}$ reaction, the ground-state threshold was measured to be 1.034±0.002 Mev. Excited-state thresholds were found at 1.455±0.003 and 1.982±0.002 Mev, corresponding to energy levels in ${\mathrm{Fe}}^{55}$ at 0.414±0.003 and 0.931±0.002 Mev, respectively. In the ${\mathrm{Zn}}^{70}(p, n){\mathrm{Ga}}^{70}$ reaction, the ground-state threshold was measured to be 1.457±0.002 Mev. No excited states were observed in the region of excitation from zero to 0.53 Mev. In the ${\mathrm{As}}^{75}(p, n){\mathrm{Se}}^{75}$ reaction, the ground-state threshold was measured to be 1.669±0.002 Mev. An excited state threshold was found at 1.960±0.002 Mev, corresponding to an energy level in ${\mathrm{Se}}^{75}$ at 0.287±0.002 Mev. A two-counter detector of high sensitivity and a low-background experimental arrangement are described.