"Breaks" in the Activation Curve of theP31(γ, n)P30Reaction

Discontinuities in the slope of the activation curve of the ${\mathrm{P}}^{31}(\gamma , n){\mathrm{P}}^{30}$ reaction were found while using two large NaI(Tl) crystals to detect the annihilation gammas from ${\mathrm{P}}^{30}$. These breaks correspond well with resonances found recently in the ${\mathrm{Si}}^{30}(p, n){\mathrm{P}}^{30}$ reaction. The correspondence between breaks and known resonances in some light nuclei is discussed. Such a correspondence was found to exist in the case of ${\mathrm{N}}^{14}$, ${\mathrm{F}}^{19}$, and ${\mathrm{P}}^{31}$ and is in doubt in the case of ${\mathrm{C}}^{12}$. The detection system used allowed accurate measurements of the thresholds of the ${\mathrm{P}}^{31}(\gamma , n){\mathrm{P}}^{30}$ reaction (12.23±0.04 Mev) and the ${\mathrm{Cl}}^{35}(\gamma , n){\mathrm{Cl}}^{34}$ reaction (12.66±0.04 Mev).