Energy Levels ofBe9,C12, andC13

Abstract

The reactions ${\mathrm{Li}}^7({\mathrm{He}}^3, p){\mathrm{Be}}^9$, ${\mathrm{B}}^{10}({\mathrm{He}}^3, p){\mathrm{C}}^{12}$, and ${\mathrm{B}}^{11}({\mathrm{He}}^3, p){\mathrm{C}}^{13}$ have been used to study the level structures of ${\mathrm{Be}}^9$, ${\mathrm{C}}^{12}$, and ${\mathrm{C}}^{13}$, respectively. Levels of ${\mathrm{Be}}^9$ were observed at 1.83, 2.43, 3.1, and 4.8 Mev. Observations of the group corresponding to 1.83 Mev at different angles are consistent with the assumption of a level in ${\mathrm{Be}}^9$ although a 3-body spectrum from ${\mathrm{He}}^3+{\mathrm{Li}}^7\to {\mathrm{Be}}^8+n+p$ could also fit the data. With the groups corresponding to the well-known ${\mathrm{C}}^{12}$ levels at 4.43, 7.65, 9.61, and 16.10 Mev used as calibrations, other levels were observed at 10.90, 11.84, 12.69, 13.30, 14.05, 14.97, 15.62, and 16.57 Mev. For the 7.65-Mev level $\frac{{\Gamma }_{\gamma }}{{\Gamma }_{\alpha }}<1.4\%$ if the level emits a single $\gamma$ ray of 7.65 Mev, and $\frac{{\Gamma }_{\gamma }}{{\Gamma }_{\alpha }}<0.9\%$ if there is a cascade through the 4.43-Mev state as it would if it were a ${\mathrm{O}}^{+}$ leve. A proton group due to an $\alpha$-particle level, predicted to lie at 5.53 Mev in ${\mathrm{C}}^{12}$, was not found and must be more than 4000 times weaker than the proton group leading to the 4.43-Mev level. Rough estimates of $\frac{{\Gamma }_{\gamma }}{{\Gamma }_{\alpha }}$ for the 14.97- and 12.69-Mev levels are 50±25% and 3±1%, respectively. With the well-known ${\mathrm{C}}^{13}$ levels up to 6.87 Mev being used as calibrations, other levels were observed at 5.51, 6.10, 7.55, 8.87, 9.52, and 9.91 Mev. The levels at 5.51 and 6.10 Mev have not previously been detected.