The differential cross sections for the six highest energy proton groups from the ${\mathrm{Be}}^9({\mathrm{He}}^3, p){\mathrm{B}}^{11}$ reaction have been measured as a function of angle at a bombarding energy of 4.5 Mev. For the five highest energy groups, the cross sections are largest in the forward direction and are not symmetric about 90°. For all six proton groups, yields observed at large angles to the incident beam direction are comparable to the forward yields. A strong maximum in the backward direction is observed for the third excited state proton group. At 4.5 Mev, the total cross sections are 11.5 millibarns for the ground-state proton group and 7.4 millibarns for the first excited state proton group. For the proton groups leaving ${\mathrm{B}}^{11}$ in the ground and first excited states, differential cross sections have been measured at six angles as a function of bombarding energy in the range from 1.8 to 5.0 Mev. In each case, the total cross section for the reaction shows no resonances. The change in the angular distributions which may be inferred from these yield curves is seen to proceed in a gradual manner with increasing bombarding energy. Differential cross sections for the second and third excited state proton groups were measured at 7° and 90° in the bombarding energy interval from 3.0 to 5.0 Mev. The observed characteristics for this reaction taken together indicate that direct interactions are important.

• Received 17 July 1959

DOI:https://doi.org/10.1103/PhysRev.116.1585