The cross section for the reaction ${\mathrm{Be}}^9(n, \alpha ){\mathrm{He}}^6$ has been measured for neutron energies of 0.7 Mev (threshold) to 4.4 Mev. The cross section exhibits a smooth rise from less than 0.1 mb at the expected threshold to a broad maximum of 104±7 mb at 3.0 Mev, followed by a gradual decrease to 70 mb at 4.4 Mev.

• Received 1 March 1957

DOI:https://doi.org/10.1103/PhysRev.106.1252