Angular Distributions and Total Cross Sections of Reactions of Li6, Li7 on B10, B11

Abstract

Charged particles from four sets of reactions induced by ${\mathrm{Li}}^6$, ${\mathrm{Li}}^7$ on ${\mathrm{B}}^{10}$, ${\mathrm{B}}^{11}$ targets have been observed. The incident beam energy in each case corresponds to 3.05 MeV in the center-of-mass system. A $\frac{\mathrm{dE}}{\mathrm{dx}}$, $E$ counter coupled to an on-line computer is used to obtain 115 angular distributions and absolute cross sections of $p$, $d$, $t$, ${\mathrm{He}}^3$, and ${\mathrm{He}}^4$ particles. ${\mathrm{N}}^{14}$, ${\mathrm{N}}^{15}$, ${\mathrm{N}}^{16}$, and ${\mathrm{C}}^{13}$ are formed in several different reactions. The observed relative cross sections are often independent of the mode of formation. Cross sections for low-lying states of these nuclei, and ${\mathrm{C}}^{12}$, ${\mathrm{C}}^{14}$ are closely proportional to ($2J+1$) where $J$ is the spin of the residual state. On this basis it is suggested that the statistical compound nucleus mechanism dominates the cross sections to many low-lying states. At high-level excitations, yields typically deviate upwards from ($2J+1$) dependence. The ${\mathrm{N}}^{15}$ 9.16-MeV and ${\mathrm{N}}^{14}$ 9.13-, 10.09-, and 11.06-MeV states have very large yields in the (${\mathrm{Li}}^6$, $d$), (${\mathrm{Li}}^7$, $t$) reactions. At these higher excitations direct reactions evidently supplement the statistical yields. Unambiguous evidence for the following unreported levels is found: 7.17±0.04, 7.37, 8.14, 8.55, 8.93, 9.26, and 9.74 MeV in ${\mathrm{N}}^{17}$; 7.66±0.05, 8.10, 8.36, 8.83, and 9.47 MeV in ${\mathrm{N}}^{16}$; and 10.79±0.03 MeV in ${\mathrm{N}}^{14}$ (previously reported as 10.71±0.09 MeV).