Scattering of Protons from Helium and Level Parameters inLi5

Abstract

The scattering of protons from helium has been investigated experimentally from 2.0 to 5.5 Mev with the Rice Institute Van de Graaff accelerator and a differentially pumped, large-volume scattering chamber. Excitation curves reveal no new states in ${\mathrm{Li}}^5$ up to an excitation energy of 6.5 Mev. A phase-shift analysis has been made of the angular distributions at laboratory bombarding energies of 3.03, 3.51, 4.02, 4.50, and 5.00 Mev. The phase shifts derived from this experiment and from experiments at other laboratories, in the energy range 1 to 18 Mev, have been interpreted in terms of the dispersion theory, and level parameters have been extracted. The nuclear radius which best fits the $P$-wave phase shifts is 2.6×${10}^{-13\mathrm{}}$ cm. For the ground state, ${\left(E_{\mathrm{res}}\right)}_{\mathrm{lab}}=2.6\mathrm{}$ Mev, $J={\frac{3}{2}}^{-}$, ${{\gamma }_p}^2=12\mathrm{}\times {10}^{-13\mathrm{}}$ Mev-cm, and ${{\theta }_p}^2=0.40\mathrm{}$. For the first excited state, ${\left(E_{\mathrm{res}}\right)}_{\mathrm{lab}}=10.8\mathrm{}$ Mev, $J={\frac{1}{2}}^{-}$, ${{\gamma }_p}^2=30\mathrm{}\times {10}^{-13\mathrm{}}$ Mev-cm, and ${{\theta }_p}^2=1.0\mathrm{}$. The $S$-wave phase shift is moderately well fit by a hard-sphere interaction with a radius of 2.0×${10}^{-13\mathrm{}}$ cm. At the present time, the $D$-wave phase shifts are so inaccurately known, that very little interpretation is possible.