Ramsauer-Townsend effect in the total cross section ofHe4+He4andHe3+He3

Total scattering cross-section measurements for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ + ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ + ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ are presented for velocities between 60 and 900 m/sec and 105 to 1000 m/sec, respectively. For ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ + ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, a Ramsauer-Townsend effect is resolved and $s$ and $d$ phase shifts are obtained. The behavior of the $s$ phase shift suggests that this system is not bound. For ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ + ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ a virtual state at 135 m/sec is resolved and some $p$ phase shifts are obtained. A fit to the data for both pairs indicates that mass-polarization effects are negligible.