An energy level in ${\mathrm{C}}^{12}$ at 9.0±0.1 Mev has been detected by means of ($p, \gamma , \gamma$) coincidence measurements on the ${\mathrm{B}}^{10}({\mathrm{He}}^3, p){\mathrm{C}}^{12}$ reaction at $E_{{\mathrm{He}}^3}=2.2\mathrm{}$ Mev. This state decays by a gamma-gamma cascade through the 4.43-Mev first excited state. An upper limit of 5% is placed on the ground-state gamma-ray transition. The intensity of the proton group leading to the 9.0-Mev state (followed by gamma-ray emission) is (0.21±0.07)% relative to the proton branch to the 4.43-Mev level. Gamma-ray branches from the 15.10- and 12.78-Mev states in ${\mathrm{C}}^{12}$ to the 4.43-Mev level have been determined as (4±1)% and (20±7)%, respectively, relative to the corresponding ground-state transitions. The radiations from the 9.0-Mev level have prevented a sensitive search from being made for the 3.2-Mev gamma radiation from the 7.66-Mev level in ${\mathrm{C}}^{12}$ by means of this reaction.

• Received 5 May 1960

DOI:https://doi.org/10.1103/PhysRev.119.1970