We obtained spectra for the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$($\alpha$,${\alpha }_1$)${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ for $E_{\chi }\left({}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}\right)\le 6.25$ MeV at ${\theta }_{\mathrm{lab}}=176.3\mathrm{}°$ and intermediate angles and for incident $\alpha$ energies of $12\le E_{\alpha }\le 15$ MeV in steps of 0.25 MeV. The appearance or nonappearance of peaks at this back angle allows one to discriminate between natural and unnatural parity for about 30 levels in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$. Combining the present results with published spectroscopic information leads to new unambiguous $J^{\pi }$ assignments for some levels and the confirmation of previously determined values for others.

NUCLEAR REACTIONS ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$($\alpha$, ${\alpha }_i$), $12<~E_{\alpha } \left(\mathrm{MeV}\right)\le 15$; $\Delta E_{\alpha }=0.25\mathrm{}$ MeV; measured yield ($E$,$E_{\alpha }$, $\theta$). ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ deduced levels, natural target.

• Received 28 February 1979

DOI:https://doi.org/10.1103/PhysRevC.20.38