The low energy alpha-groups from the reaction ${\mathrm{F}}^{19}(p,\alpha ){\mathrm{O}}^{16*}$ have been studied at various resonances between proton energies of 340 kev and 1381 kev. Four groups have been identified. For the reaction energy of the ${\alpha }_{\pi }$ group, preceding the pair emission, we find $Q_{\pi }=2.061\mathrm{}\pm 0.010$ Mev and for the three other groups preceding gamma-ray emission we find $Q_1=1.977\mathrm{}\pm 0.008$, $Q_2=1.204\mathrm{}\pm 0.008$ and $Q_3=1.002\mathrm{}\pm 0.008$ Mev. Each of the $Q$-values when added to the corresponding pair-energy or gamma-ray energy found by Rasmussen, Hornyak, Lauritsen, and Lauritsen gives a value for the total reaction energy of ${\mathrm{F}}^{19}(p,\alpha ){\mathrm{O}}^{16}$ which is the same for all the groups, namely 8.113±0.030 Mev. The relative intensities of the ${\alpha }_1$, ${\alpha }_2$, and ${\alpha }_3$ groups are found to vary from one resonance to another and the sum of their absolute yields per proton per $4\pi$-steradians at 138° is found to be very close to the absolute yield of the gamma-rays per proton per $4\pi$-steradians at 90° at all the resonances investigated, the gamma-ray yield being measured simultaneously with the alpha-particle yields. The absolute yield of the ${\alpha }_{\pi }$-group agrees in order of magnitude with the pair yield determined in this laboratory and elsewhere. The small discrepancies can probably be attributed to angular distribution factors. The excitation functions of the ${\alpha }_1$- and ${\alpha }_2$-groups have been compared carefully with that of the gamma-rays over certain regions of the proton energy. Over each resonance, the excitation functions of the alpha-groups and the gamma-rays can be represented by the same curve by suitable normalizations. Our excitation curve of the ${\alpha }_{\pi }$-group is found to run parallel with the excitation curve of the pairs found by Bennett et al.

• Received 6 March 1950

DOI:https://doi.org/10.1103/PhysRev.79.108