A NaI(Tl) scintillation spectrometer, limited to 1.5-Mev gamma rays, detected 430±20 kev radiation when separated ${\mathrm{Li}}^6$ was bombarded with monochromatic protons from 180 kev to 415 kev. Spectrometer efficiency was measured using an ${\mathrm{Au}}^{198}$ source of beta-gamma coincidences. The thick target yield was (7±4)×${10}^{-13\mathrm{}}$ gamma per proton at 180 kev and (170±35)×${10}^{-13\mathrm{}}$ at 415 kev. The 430-kev gamma ray was interpreted as part of the cascade decay of the broad 6.35-Mev state of ${\mathrm{Be}}^7$. Assuming $s$-wave capture, the experimental yield has been fitted with a Breit-Wigner resonance curve. At 415 kev, a cross section of 0.7±0.2 μb is obtained for the decay of the capture state through the 430-kev state. This gives $\mathrm{}(2J+1)\mathrm{}{\Gamma }_{\gamma }$ a value of 1.0±0.3 ev for this cascade process. The spectrometer, when unlimited, detected gamma rays corresponding to transitions from the capture level to the ground and 430-kev states. The number of transitions from the capture state to the 430-kev state of ${\mathrm{Be}}^7$ is 35±5 percent of the total radiative decays. Transitions through the 4.65-Mev state of ${\mathrm{Be}}^7$ occur in less than 4 percent of the total radiative decays.

• Received 8 November 1954

DOI:https://doi.org/10.1103/PhysRev.97.1245