A Photographic Study of the Neutron Spectra fromAl(αn)andSi(dn)

The two neutron spectra named have been studied by the photographic method, using the new Eastman NTB nuclear particle emulsion. Details of the experimental method are discussed, with reference also to some features of the histogram representation employed here. The following mass differences are obtained: ${\mathrm{P}}^{30}$-${\mathrm{Al}}^{27}$=2.998 06±0.24×${10}^{-3\mathrm{}}$ mass units, ${\mathrm{P}}^{29}$-${\mathrm{Si}}^{28}$=1.006 64±0.14×${10}^{-3\mathrm{}}$, ${\mathrm{P}}^{30}$-${\mathrm{Si}}^{29}$=1.002 15±0.21×${10}^{-3\mathrm{}}$, ${\mathrm{P}}^{31}$-${\mathrm{Si}}^{30}$=1.000 88±0.18×${10}^{-3\mathrm{}}$. A level in ${\mathrm{P}}^{30}$ at 1.02±0.12 Mev above ground is found and confirmed, and three levels in ${\mathrm{P}}^{31}$ established. Group widths and intensities are listed.