RaDEF Standard Sources for Beta-Disintegration Rate Determinations

The preparation and use of calibrated RaDEF equilibrium sources for absolute beta-counting is described. The sources are essentially weightless and are mounted on a thin backing to reduce self-absorption and back-scattering correction problems. Calibration was done by determination of the alpha-disintegration rate of RaF in a parallel plate alpha-ionization chamber. No secondary standards are required and the sources can be recalibrated at any time. As an example of the application of such standards, details of the calibration of a P32 solution distributed by the Bureau of Standards for intercalibration in February 1949 are given. The final result is 88.8 mrd/ml at 8 A.M. C.D.T. March 1, 1949. The precision of the measurement is 0.3 percent. The accuracy is estimated to be 1–2 percent.