Half-life measurements at the National Institute of Standards and Technology.

For nearly half a century the half-lives of many radionuclides have been measured with increasing precision. The results of these measurements for many long-lived radionuclides, such as 60Co, 137Cs, 85Kr, 133Ba, 207Bi, 152Eu, 154Eu, and 155Eu, have been updated recently by the Radioactivity Group of NIST. These long-lived radionuclides are used extensively to calibrate various nuclear counting and monitoring systems. The long-term precision of these calibrations can be greatly affected by the uncertainties in the calibrant half-lives. Results for the half-lives of many radionuclides measured over the last four decades are tabulated. In addition, values of the half-lives of several short-lived radionuclides used in nuclear medicine are addressed, which are critical in determining the correct dosage given in patient treatment, are addressed. Comparisons with the recommended values from the International Atomic Energy Agency Coordinated Research Program and the Evaluated Nuclear Structure Data File from Brookhaven National Laboratory are presented and any apparent disagreements noted.