The effects of Coulomb impurities on the inhibition rule of Morpurgo for $\Delta T=0\mathrm{}$, $M1\mathrm{}$ transitions in light ($A<~20$), self-conjugate nuclei are discussed and a comparison is made between Morpurgo's rule and the experimentally known $M1\mathrm{}$ transition strengths. An upper limit to the average inhibition of ∼10 is indicated by the experimental evidence. There are no known $\Delta T=0\mathrm{}$, $M1\mathrm{}$ transitions in light, self-conjugate nuclei with strengths greater than 0.1 Weisskopf unit. The work of Morpurgo is shown to lead to $J$-dependent lower limits of the order of $0.5\times {10}^{-2\mathrm{}}A(A+2\mathrm{})\mathrm{}$ Weisskopf units for the matrix elements of $\Delta T=0\mathrm{}$, $M1\mathrm{}$ transitions in self-conjugate nuclei. These limits are invoked to assign isotopic spin to several levels in ${\mathrm{B}}^{10}$, ${\mathrm{N}}^{14}$, and ${\mathrm{F}}^{18}$.

• Received 22 September 1958

DOI:https://doi.org/10.1103/PhysRev.113.595