Recent work on the radioactivity of potassium and some related geophysical problems

The half-life now of K40 appears fixed at 1.3×109 years, with an uncertainty of about 10 per cent. About 12 per cent of the disintegration forms A40 by K-capture, while 88 per cent results in Ca40 by β-emission. The mean energy released per disintegration is 0.71 Mev, yielding 27×10−6 cal/gm.year of ordinary potassium at the present time. With these constants, the production of the A40 of the atmosphere, heat production by potassium in the earth, and measurement of age are discussed. Ample quantities of A40 have been produced, but release to the atmosphere involves uncertainties. A large part of the heat conducted to the surface of the earth may be generated by potassium decay. The existence of reasonably reliable decay constants should encourage additional efforts to obtain ages of potassium minerals.