The cross section for the ${\mathrm{C}}^{12}(n, p){\mathrm{B}}^{12}$ reaction has been measured for 14.9- to 17.5-Mev neutrons. The neutrons were obtained from the $\mathrm{T}(d, n){\mathrm{He}}^4$ reaction and their flux density was determined by counting the recoil alpha particles or by counting the neutrons directly with a ${\mathrm{Li}}^6$I(Eu) scintillation counter. A cylindrical plastic scintillator 5 inches in diameter and 3 inches in length served as the carbon-containing target and permitted the counting of the ${\mathrm{B}}^{12}$ decay beta rays in nine consecutive 7-msec intervals during the "beam off" period of a pulsed neutron beam cycle. The cross section rises from slightly above the reaction threshold of 13.6-Mev to a value of 29.09±4.36 millibarns at 17.5-Mev. The ${\mathrm{B}}^{12}$ beta-decay half-life has been redetermined as 18.87±0.50 milliseconds.

• Received 2 September 1958

DOI:https://doi.org/10.1103/PhysRev.113.890