The ${\mathrm{He}}^3(\alpha , \gamma ){\mathrm{Be}}^7$ reaction has been investigated using gaseous helium targets behind thin nickel foils and using monoenergetic alpha-particle beams with energies from 0.42 to 5.80 MeV. The prompt gamma rays were detected using NaI(Tl) scintillation spectrometers, and the resulting pulse-height spectra were analyzed to determine both the total capture cross section and the branching ratio between the cascade and the crossover transitions as functions of energy. These cross-section measurements have been used to obtain a new value for the zero-energy intercept of the cross-section factor $S\left(E\right)\mathrm{}$ for this reaction: $S_0=0.47\mathrm{}\pm 0.05$ keV-b, and ${\left(\frac{\mathrm{dS}}{\mathrm{dE}}\right)}_0=-2.8\mathrm{}\times {10}^{-4\mathrm{}}$ b.

• Received 8 May 1963

DOI:https://doi.org/10.1103/PhysRev.131.2578