MEASUREMENT OF THE HALF-PERIOD OF POLONIUM 213

In the recently discovered (4n + 1) radioactive series, bismuth 213 transforms to polonium 213 by β-emission. The latter rapidly transforms by α-emission to lead 209. The present paper describes a measurement of the half-period of polonium 213. A preparation of radium 225 was placed between two Geiger–Müller counters. One detected β-particles while the other detected α and β-particles. Coincidences were counted with a modified Rossi circuit. The pulse-width on the grid of one of the tubes of the coincidence unit was made variable, while the pulse-width on the other remained fixed. The pulse-width associated with the counter that responded only to β-particles was chosen to be variable. Coincidences were counted as a function of the pulse-width. Corrections were made for accidental coincidences and exact coincidences arising from other causes. The final value for the half-period T of polonium 213 is T = 4.2 ± 0.8 μsec. A subsidiary experiment to determine the half-period of thorium C′ gave the value T = 0.34 ± 0.06 μsec. in reasonable agreement with measurements by other workers.