The ${\mathrm{Li}}^7(p, n){\mathrm{Be}}^7$ and ${\mathrm{Li}}^6(p, n){\mathrm{Be}}^6$ reactions were studied at $E_p=10.5\mathrm{}$ Mev, by the method of proton recoils in nuclear emulsions. The ${\mathrm{Li}}^7(p, n){\mathrm{Be}}^7$ spectra at 30° and 90° show the known states of ${\mathrm{Be}}^7$ at 0, 0.43, and 4.53 Mev. The cross section for formation of the ground state at 90° (lab) is 3.2 mb/sterad (±30%). The ${\mathrm{Li}}^6(p, n){\mathrm{Be}}^6$ spectra at 30°, 60°, 90°, and 135° show ground-state groups with $Q=-5.05\mathrm{}\pm 0.2$ Mev. This leads to ($M-A$) for ${\mathrm{Be}}^6$=20.13±0.2 Mev. ${\mathrm{Be}}^6$(0) is thus unbound with respect to (${\mathrm{He}}^4$+$2p$) by 1.35 Mev. The cross section for formation of ${\mathrm{Be}}^6$(0) at 90° (lab) is 0.5 mb/sterad (±30%). At 90°, there is also indication of a sharp excited state at $E_x=1.5\mathrm{}\pm 0.2$ Mev. The lifetimes of ${\mathrm{Be}}^6$(0) and ${\mathrm{Be}}^6$(1.5 Mev) are ≳4×${10}^{-21\mathrm{}}$ sec and >7×${10}^{-21\mathrm{}}$ sec, respectively. These results are discussed in terms of the other available information on the $A=6\mathrm{}$ isobars.

• Received 31 July 1959

DOI:https://doi.org/10.1103/PhysRev.116.1521