Nonexistence of a 9.0-Mev Level inC12

Abstract

An energy level in ${\mathrm{C}}^{12}$ at 9.0 Mev has been reported as a result of ($p, \gamma , \gamma$) triple 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 reaction has been reinvestigated in a similar experimental arrangement by using alternately Pilot-$B$, CsI and NaI scintillators for detection of the protons. Only the Pilot-$B$, which had been used in the previous work, exhibits the proton group corresponding to a "9.0-Mev level" in ${\mathrm{C}}^{12}$. The triple coincidence effect in this case is actually due to the intense ∼17-Mev protons in the ${\mathrm{B}}^{10}({\mathrm{He}}^3, p){\mathrm{C}}^{12}$ reaction leading to the 4.43-Mev first excited state of ${\mathrm{C}}^{12}$ which upon entering the scintillator can inelastically scatter from carbon and produce secondary gamma radiation of 4.43 Mev. The net energy deposited in the scintillator has the appearance of a proton group to a 9.0-Mev level in ${\mathrm{C}}^{12}$ in triple coincidence with two 4.43-Mev gamma rays. The magnitude of the effect is calculated from published cross sections for inelastic scattering and it agrees with the apparent population intensity of the nonexistent "9.0-Mev level."