Average angular momentum in compound nucleus reactions deduced from isomer ratio measurements

Abstract

We have measured the ratio of the yields for the metastable and ground states of ${}^{119}$Te produced in the fusion-evaporation reactions ${}^{110}$Pd${(}^{12}$C,3$n)$ and ${}^{115}$In${(}^{7}$Li,3$n)$ by off-line observation of delayed $\ensuremath{\gamma}$-ray emission. The absolute cross sections for the formation of the metastable ${(J}^{\ensuremath{\pi}}$ = 11/2${}^{\ensuremath{-}}$, ${T}_{1/2}$ = 4.68 d) and ground ${(J}^{\ensuremath{\pi}}$ = 1/2${}^{+}$, ${T}_{1/2}$ = 16.05 h) states were determined at energies close to the Coulomb barrier for both systems. We have deduced the average angular momentum from these isomer ratio measurements through statistical model calculations. The deduced mean angular momentum agrees quite well with those calculated by a simple fusion model. The expected constant value of the average total angular momentum at subbarrier energies was confirmed for the ${}^{12}$C+${}^{110}$Pd system. The predicted variation of the mean orbital angular momentum with the reduced mass of the entrance channel was also verified.