The twice forbidden beta spectrum of ${\mathrm{Cl}}^{36}$ has been measured with a $4\pi$ scintillation spectrometer which is particularly well suited for measuring beta spectrum shapes from sources with low specific activity. The distribution was measured to as low as 89 kev with three sources of average thicknesses of 9, 19, and 20 μg/${\mathrm{cm}}^2$. The data were analyzed by using the exact twice forbidden shape factor for the linear combination of the $S$ and $T$ couplings for $\Delta J=2\mathrm{}$. The ratios of nuclear beta moments appearing in the shape factor were treated as variable parameters. The best fit to the data was for $\frac{R_{\mathrm{ij}}}{T_{\mathrm{ij}}}=0\mathrm{}$ and $\frac{A_{\mathrm{ij}}}{T_{\mathrm{ij}}}=14.2\mathrm{}$.

• Received 13 February 1956

DOI:https://doi.org/10.1103/PhysRev.102.1142