Capture-Gamma Determination ofV51Levels

Abstract

A fast-coincidence scintillation spectrometer has been developed for thermal-neutron capture-gamma studies at the Livermore 1-Mw pool-type reactor. The added-neutron binding energy in ${\mathrm{V}}^{51}$ was measured as 11.1\ifmmode\pm\else\textpm\fi{}0.1 Mev. Cascade radiations for ${\mathrm{V}}^{51*}$ were observed and a decay scheme is established which verifies a previously proposed ($p, {p}^{\ensuremath{'}}$) level scheme. Spin assignments for most of the ${\mathrm{V}}^{51}(p, {p}^{\ensuremath{'}})$ reported levels below 4.0 Mev are proposed and the level order for the ${(1{f}_{\frac{7}{2}})}^{3}$ proton configuration levels is established as $\frac{7}{{2}^{\ensuremath{-}}}$ (ground state), $\frac{5}{{2}^{\ensuremath{-}}}$, $\frac{3}{{2}^{\ensuremath{-}}}$, $\frac{11}{{2}^{\ensuremath{-}}}$, $\frac{9}{{2}^{\ensuremath{-}}}$, and $\frac{15}{{2}^{\ensuremath{-}}}$ spin with excitation energies of 0.32, 0.93, 1.61, 1.81, and 2.70 Mev, respectively. Of the various nuclear force assumptions that can be made, the short-range force approximation ($\ensuremath{\delta}$-type interaction) and weak surface-coupling effects for ${\mathrm{V}}^{51*}$ configuration states appear to give the best match between theory and experiment. A previous calculation using experimentally measured splittings of the ${j}^{2}$ configuration together with tabulated coefficients of fractional parentage gives excellent agreement with experiment. Evidence is also found for ${(1{{f}_{\frac{7}{2}}}^{2})}_{0}2{p}_{\frac{3}{2}}$- and ${(1{{f}_{\frac{7}{2}}}^{2})}_{0}1{f}_{\frac{5}{2}}$-proton single-particle levels at 2.41 and 2.55 Mev, respectively, as well as for additional low-spin states between 2.70 and 3.38 Mev which possibly represent even states resulting from excitation of a lower shell proton to give a ${(1{{f}_{\frac{7}{2}}}^{4})}_{0}$ configuration plus a proton hole in the vacated shell. Experimental results suggest that the ${\mathrm{V}}^{51*}$ 20-28 core is a more rigid structure than the ${\mathrm{Ca}}^{43*}$ 20-20 core.