Evaporated targets of natural boron and enriched ${\mathrm{B}}^{10}$ deposited on thin Formvar films were bombarded with deuterons produced by the MIT-ONR Van de Graaff accelerator. Incident energies from 4.0 to 8.5 Mev were used, and charged particles leaving the target at 90 degrees to the deuteron beam direction were analyzed by a 180-degree magnetic spectrograph. The studies covered a region of excitation from 7.50 to 11.46 Mev in ${\mathrm{B}}^{11}$, and from zero to 3.40 Mev in ${\mathrm{B}}^{12}$.

In the case of ${\mathrm{B}}^{11}$, two new groups have been found in addition to those previously reported. These have excitation energies of 7.987±0.014 Mev and 10.32±0.02 Mev; the former level is paired with the 7.39-Mev level in ${\mathrm{C}}^{11}$. The width of the 10.32-Mev level is noticeably broad, 54±17 kev, whereas all the other boron levels detected in this work had widths less than 10 kev. The new levels in ${\mathrm{B}}^{12}$ found by ($d, p$) reaction have excitation energies of 1.674±0.011, 2.618±0.011, 2.723±0.011, and 3.383±0.009 Mev. An analysis of the presently known properties of ${\mathrm{C}}^{12}$ levels lying in the excitation region corresponding to the first five levels in ${\mathrm{B}}^{12}$ suggests the possibility that most of these ${\mathrm{C}}^{12}$ levels have a total isotopic spin of 1.

• Received 23 June 1953

DOI:https://doi.org/10.1103/PhysRev.92.127