The Beta-Decay ofB12andLi8

The electron spectra of ${\mathrm{B}}^{12}$ and ${\mathrm{Li}}^8$ have been studied, using a magnetic lens spectrometer. The end point of the ${\mathrm{B}}^{12}$ distribution is 13.43±0.06 Mev, while the ${\mathrm{L}}^8$ spectrum tails off gradually with a shape which is consistent with the known broadness of the excited state of ${\mathrm{Be}}^8$ to which the decay occurs. Neither distribution corresponds to the shape indicated for simple "allowed" transitions, but it seems probable that more than one state of the residual nuclei may be involved in the decay schemes. The discrepancy between the observed end point of the ${\mathrm{B}}^{12}$ spectrum and the mass differences suggests the existence of an excited state at 0.9 Mev either in ${\mathrm{B}}^{12}$ or ${\mathrm{C}}^{12}$.