Alpha-Gamma Angular Correlation in Ionium (Th230)

The angular correlation between the alpha particle leading to the first excited state of ${\mathrm{Ra}}^{226}$ at 67.8 kev and the subsequent gamma ray to the ground state leads to a definite assignment of $I=2^{+}$ for this state. The correlation is weakened by what is believed to be an interaction of the nuclear electric quadrupole moment with crystalline electric field gradients in the source. The lifetime of the excited state is about 1×${10}^{-8\mathrm{}}$ second.