Decay Constants ofK40

Abstract

gested several of the chemical separations. Thanks are also due Mr. Bernie Rossi and the 60-inch cyclotron crew for carrying out the bombardments. APPENDIX. CHEMICAL PROCEDURETo the solution of Mn in HC1 10 mg amounts of Co, Cu, Fe, Ni, Zn carriers were added. The IN solution was saturated with (NHJsSCN and shaken with a 50 percent mixture of diethyl ether and amyl alcohol. After several washings the alcohol-ether extract was found to be free of Mn. The remaining metals were removed I. INTRODUCTIONOOTASSIUM 40 is known to decay by beta-and * gamma-ray emission and by electron capture, but recent measurements of the decay constants have been in rather poor agreement. The most reliable recent measurements 1-6 of the beta-half-life have given values ranging from 12.0 to 17.8X10 8 yr., with an average value of about 14.4X10 8 yr. The most ingenious method was that of Stout, 4 who mixed into his potassium sources an accurately known activity of Na 24 , which has nearly the same beta-energy as K 40 , and measured the ratio of K 40 to Na 24 counting rates. Knowing the specific activity of the Na 24 , he was then able to determine the K 40 activity directly, without corrections, and obtained 13.1X10 8 yr.There is even more disparity between the recent estimates of electron-capture intensity, the values ranging from 5 to 190 electron captures per 100 betarays. The discrepancies here can be attributed to the uncertainties inherent in the methods used in making the measurements. The measurement of Bleuler and 1

DISINTEGRATION-RATE DETERMINATION BY 4π-COUNTING: PART IV. SELF-ABSORPTION CORRECTION: GENERAL METHOD AND APPLICATION TO Ni63 β-RADIATION

“…Its use in this laboratory to coat VYNS source-mounting films with gold has already been described (15). Further it has already been used to mount radioactive materials both for beta-spectrometry (10,19) and in 4n-counters (6,21). However no regular use of it nor any attempt to employ it in the present way for selfabsorption studies has been reported.…”

Disintegrations ofNd147andPm149

“…The results indicate a half-life of 65=fc3 days, in good agreement with the value reported by DuBridge and Marshall. 1 The secondary electrons ejected from a 50-mg/cm 2 uranium radiator shows K and L shell photo-electron peaks for the 65-day activity, corresponding to a gamma-ray of energy 513=1=3 kev. This was at first thought to be annihilation radiation.…”

“…1 Pm 149 further decays with a half-life of about 2 days. 1 "Specpure" Nd 2 0 3 was irradiated by slow neutrons in the Harwell pile for 4 weeks, and the resulting activities were studied at this Institute using a 0-ray spectrometer. 2 Finely powdered Nd2C>3 was spread with an average thickness of about 2 mg/cm 2 over an aluminum backing of 2 mg/cm 2 .…”

Beta-Ray Spectrum ofK40

“…Swiss Federal Institute of Technology, Zurich, Switzerland (Received July 9,1951) A N electron bound to an impurity is usually treated like a hydrogen atom in which the electrostatic force is reduced by the dielectric constant c of the crystal. 1 We shall use a more detailed treatment for a phosphorus impurity in silicon.…”