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

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 ${\theta }_L=70\mathrm{}°$ 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 (${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{A})}^{\mathrm{½}}$ at ${\theta }_L=30\mathrm{}° \mathrm{to} 1.86$ (${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{A})}^{\mathrm{½}}$ at 156.5°. 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 $〈v_{\parallel }〉=0.14\mathrm{}$ (${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{A})}^{\mathrm{½}}$ and $〈V〉=2.00\mathrm{}$ (${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{A})}^{\mathrm{½}}$.The angular distribution in the frame moving with the velocity $v_{\parallel }$ is found to be symmetric about 90°, with an intensity ratio $\frac{I\left(90\mathrm{}°\right)}{I\left(0\mathrm{}°\right)}=1.43\mathrm{}$. The implications of this analysis for the reaction mechanism are discussed.