Natural radioactivity of K-40, Rb-87 and Lu-176

Activity standardization of two enriched 40K solutions for the determination of decay scheme parameters and the half-life

In this paper we describe experiments on two enriched ⁴⁰K solutions to accurately determine decay data. The first solution was measured in 2004/2005 by means of a gamma-ray spectrometer with low background and a liquid scintillation (LS) counter to apply the CIEMAT/NIST efficiency tracing method. A combination of results yields an emission probability of the 1461 keV gamma-rays of P_γ = 0.1030(11) which is lower than current results of data evaluations. The activity concentration of the second solution was also determined by means of LS counting, but here, the CIEMAT/NIST efficiency tracing method as well as the TDCR method were applied. Again, the result was combined with that of independent gamma-ray spectrometry and the gamma-ray emission probability was found to be P_γ = 0.1029(9) in good agreement with the result obtained from the first solution. A combination of both experiments yields P_γ = 0.1029(9). The spectra of a TriCarb LS counter were carefully analyzed and a beta minus emission probability [Formula: see text]  = 0.8954(14) was determined. The new results for P_γ and [Formula: see text] indicate that the overall probability of the decay via EC in recent data evaluations is overestimated. The LS counting efficiencies were computed with a stochastic model and up-to-date calculations of the beta spectrum and fractional EC probabilities were used. The final activity result of the second solution is combined with the outcome of a comprehensive isotopic analysis to determine the half-life of ⁴⁰K which is found to be 1.2536(27) ·10⁹ years. All above-stated uncertainties are standard uncertainties (k = 1).

Half-life of 176Lu

The half-life of 176Lu, measured using gamma-ray spectrometry, has been found to be (3.56+/-0.07)x10(10)yr. Comparison has been made between present results and literature data.

Half-life measurements of by liquid scintillation counting

The specific activity of natural 87Rb was measured by means of 4pibeta liquid scintillation counting in a two-photomultiplier-tube spectrometer. 3H-efficiency tracing was used together with the CIEMAT/NIST method to obtain the detection efficiency. For this purpose a new parameterization of the shape factor for the third forbidden non-unique beta-transition was performed. The hygroscopic behaviour of the salts used for sample preparation was studied. The half-life of 87Rb was found to be T1/2 = 4.967(32) x 10(10)y.

Geochronology: Recent Development in the Lutetium-176/Hafnium-176 Dating Method

The application of the lutetium-176/ hafnium-176 method to gram quantities of minerals containing rare earths is made possible by the development of analytical and isotope dilution techniques for microgram amounts of lutetium and hafnium. The geological redetermination of the half-life of lutetium-176 (3.3 +/- 0.5 x 10(10) years) is in agreement with recent physical measurements.