The Half-Life of Iodine (128)

The half-life of iodine (128) has been measured with high accuracy by means of a G-M counter and amplifying circuit of tested reliability. An absolute calibration of the counter was carried out by a simple method. The half-life was determined from the data by an arithmetical, rather than a graphical method. The results of four closely concordant experiments give for the best value of the half-life, $T=24.99\mathrm{}\pm 0.02$ minutes. It is suggested that this radio-element can now be used in a quick and convenient calibration of counters or other instruments for measurement of radioactivity.