Angular and energy distributions ofNa24fragments formed by the reaction of 11.5-GeV protons withAu197

Abstract

The angular distribution and the range distributions at three angles have been measured for the light nuclear fragment $^{24}\mathrm{Na}$ formed by the interaction of 11.5-GeV protons with $^{197}\mathrm{Au}$. The angular distribution has a peak at a laboratory angle ${\ensuremath{\theta}}_{L}=70\ifmmode^\circ\else\textdegree\fi{}$ and is thus quite different from the forward-peaked angular distribution previously observed for $^{24}\mathrm{Na}$ at a bombarding energy of 2.9 GeV. The velocity distributions derived from the range distributions are relatively narrow, and the mean velocity decreases from 2.11 (${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{A})}^{\mathrm{\textonehalf{}}}$ at ${\ensuremath{\theta}}_{L}=30\ifmmode^\circ\else\textdegree\fi{} \mathrm{to} 1.86$ (${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{A})}^{\mathrm{\textonehalf{}}}$ at 156.5\ifmmode^\circ\else\textdegree\fi{}. The data are analyzed in terms of the two-step model of nuclear reactions and are found to be consistent with that model. The model parameters derived from this analysis are $〈{v}_{\ensuremath{\parallel}}〉=0.14$ (${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{A})}^{\mathrm{\textonehalf{}}}$ and $〈V〉=2.00$ (${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{A})}^{\mathrm{\textonehalf{}}}$.The angular distribution in the frame moving with the velocity ${v}_{\ensuremath{\parallel}}$ is found to be symmetric about 90\ifmmode^\circ\else\textdegree\fi{}, with an intensity ratio $\frac{I(90\ifmmode^\circ\else\textdegree\fi{})}{I(0\ifmmode^\circ\else\textdegree\fi{})}=1.43$. The implications of this analysis for the reaction mechanism are discussed.NUCLEAR REACTIONS $^{197}\mathrm{Au}$($p$,$x$)$^{24}\mathrm{Na}$, ${E}_{p}=11.5$ GeV; measured angular distribution and range distributions at 30\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, and 156.5\ifmmode^\circ\else\textdegree\fi{}; inferred parameters of two-step model.