The ${5/2}^{-}$ level expected in the mass-13 nuclei according to shell-model calculations has been searched for by magnetic analysis of the ${\mathrm{B}}^{11}({\mathrm{He}}^3,p){\mathrm{C}}^{13}$ and ${\mathrm{N}}^{14}({\mathrm{He}}^3,\alpha ){\mathrm{N}}^{13}$ reactions using a broad-range magnetic spectrograph. Up to an excitation energy of 7.9 MeV in ${\mathrm{C}}^{13}$ and 7.0 MeV in ${\mathrm{N}}^{13}$, no new levels have been found. ${\mathrm{C}}^{13}$ states reported previously at 5.51 and 6.10 MeV in the ${\mathrm{B}}^{11}({\mathrm{He}}^3,p){\mathrm{C}}^{13}$ reaction have not been confirmed. The apparent absence of a ${5/2}^{-}$ state up to ≅7 MeV excitation suggests that the intermediate coupling parameter $\frac{a}{K}$ may be smaller than presupposed. In an investigation of the ${\mathrm{B}}^{11}({\mathrm{He}}^3,\alpha ){\mathrm{B}}^{10}$ reaction we have resolved the 5.11-5.16-MeV doublet. ${\mathrm{B}}^{10}$ levels reported previously at 2.86, 5.58, and 6.40 MeV have not been confirmed by studies of this reaction.

• Received 26 September 1962

DOI:https://doi.org/10.1103/PhysRev.129.1765