A counter ratio study has been made of the ($p, n$) reactions on ${\mathrm{T}}^3$, ${\mathrm{Li}}^7$, ${\mathrm{Be}}^9$, and ${\mathrm{F}}^{19}$. The ground state threshold energy for the reaction ${\mathrm{F}}^{19}(p, n){\mathrm{Ne}}^{19}$ was found to be 4.235±0.005 Mev. Other neutron thresholds were observed which indicated excited states in ${\mathrm{Be}}^7$ at 0.434±0.004 Mev, in ${\mathrm{B}}^9$ at 2.326±0.006 Mev and in ${\mathrm{Ne}}^{19}$ at 0.241±0.004 and 0.280±0.004 Mev. A broad maximum in the yield of slow neutrons from the bombardment of ${\mathrm{Be}}^9$ was observed which could be due to the three-body breakup, ${\mathrm{Be}}^9(p, pn){\mathrm{Be}}^8$, or to a broad, even parity state in ${\mathrm{B}}^9$ at 1.4 Mev. The cross sections for the reactions ${\mathrm{Be}}^9(p, n)B^9$, ${\mathrm{B}}^{11}(p, n){\mathrm{C}}^{11}$, ${\mathrm{C}}^{13}(p, n){\mathrm{N}}^{13}$, and ${\mathrm{F}}^{19}(p, n){\mathrm{Ne}}^{19}$ were measured.

• Received 22 June 1955

DOI:https://doi.org/10.1103/PhysRev.100.91