Spin differences in the Zr90 compound nucleus induced by (p,p′) , (p,d) , and (p,t) surrogate reactions

Abstract

The effect of the production mechanism on the decay of a compound nucleus is investigated. The nucleus $^{90}\mathrm{Zr}$ was produced by three different reactions, namely $^{90}\mathrm{Zr}(p,{p}^{\ensuremath{'}})^{90}\mathrm{Zr}$, $^{91}\mathrm{Zr}(p,d)^{90}\mathrm{Zr}$, and $^{92}\mathrm{Zr}(p,t)^{90}\mathrm{Zr}$, which served as surrogate reactions for $^{89}\mathrm{Zr}(n,\ensuremath{\gamma})$. The spin-parity $({J}^{\ensuremath{\pi}})$ distributions of the states populated by these reactions were studied to investigate the surrogate reaction approach, which aims at indirectly determining cross sections for compound-nuclear reactions involving unstable targets such as $^{89}\mathrm{Zr}$. Discrete $\ensuremath{\gamma}$ rays, associated with transitions in $^{90}\mathrm{Zr}$ and $^{89}\mathrm{Zr}$, were measured in coincidence with light ions for scattering angles of ${25}^{\ensuremath{\circ}}--{60}^{\ensuremath{\circ}}$ and $^{90}\mathrm{Zr}$ excitation energies extending above the neutron separation energy. The measured transition systematics were used to gain insights into the ${J}^{\ensuremath{\pi}}$ distributions of $^{90}\mathrm{Zr}$. The $^{90}\mathrm{Zr}(p,{p}^{\ensuremath{'}})$ reaction was found to produce fewer $\ensuremath{\gamma}$ rays associated with transitions involving high spin states $(J=6--8\phantom{\rule{4.pt}{0ex}}\ensuremath{\hbar})$ than the other two reactions, suggesting that inelastic scattering preferentially populates states in $^{90}\mathrm{Zr}$ that have lower spins than those populated in the transfer reactions investigated. The $\ensuremath{\gamma}$-ray production was also observed to vary by factors of 2--3 with the angle at which the outgoing particle was detected. These findings are relevant to the application of the surrogate reaction approach.