A system suitable for detection of high-energy gamma rays produced with low cross sections in the presence of high background counting rate is described. It is applied to a study of radiative capture of ${\mathrm{He}}^3$ by ${\mathrm{Li}}^7$ for bombarding energies up to 3.0 MeV. Gamma transitions to the first six states in ${\mathrm{B}}^{10}$ are observed and their energy dependence is measured. The excitation functions at 90° show peaks at 1.1 and 2.2 MeV for the transitions to the ground state and the one at 4.77 MeV, with c.m. widths of less than 500 and 420 keV, respectively. Transitions to the first and fourth excited states show a broad maximum around 1.4 MeV with a c.m. width of less than 600 keV. The cross section for the decay to 4.77 MeV is largest, with $\frac{d\sigma }{d\Omega }$ reaching 5 μb/sr at the 2.2-MeV peak. At some excitation energies asymmetries $\frac{Y\left(0\mathrm{}°\right)}{Y\left(90\mathrm{}°\right)}$ are obtained which indicate strong interferences. The peaks are interpreted as resonances and lower limits on $\mathrm{}(2J+1)\mathrm{}{\Gamma }_{\gamma }$ are presented.

• Received 11 September 1964

DOI:https://doi.org/10.1103/PhysRev.137.B493