Half-life determination of 40K by LSC

On Variations of Pre-Supernova Model Properties

“…This isotope is also a special case as it is radioactive, but the half-life is long enough (1.248×10 9 yr, Malonda & Carles 2002;Kossert & Günther 2004) that it is included in compilations of the solar composition. The overproduction factor may reflect an uncertain solar abundance.…”

Measurement of the shape-factor functions of the long-lived radionuclides 87Rb, 40K and 10Be

“…For 87 Rb, the spectrum is shifted by the shape-factor function into the opposite direction, i.e., to the low-energy part. For the activity standardization of the long-lived nuclides the shape-factor functions must therefore be exactly known [11][12][13]. In particular for 87 Rb with its comparatively low endpoint energy, the dependence on the beta spectrum computation is considerable.…”

Comment on the “Joint determination of 40K decay constants and 40Ar∗/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology” by Paul R. Renne et al. (2010)

“…Since the call by Begemann et al (2001), several authors (see e.g., Min et al, 2000;Nägler and Villa, 2000;Grau Malonda and Grau Carles, 2002;Kwon et al, 2002;Trieloff et al, 2003;Kossert and Gü nther, 2004;Krumrei et al, 2006;Mundil et al, 2006;Schwarz and Trieloff, 2007a,b;Renne et al, 2010) have contributed to the discussion of whether -and if so, in which way -the convention of constants used for K-Ar and Ar-Ar dating by Steiger and Jäger (1977) needs to be reevaluated.…”

“…Their results are partially based on values for the 40 K decay constant from two liquid scintillation counting (LSC) experiments of Grau Malonda and Grau Carles (2002) and Kossert and Gü nther (2004). An important -though easily overseen -point in these two studies is that the calculated total decay constant in LSC measurements depends on a specifically adopted branching ratio P b /P ec of the probabilities for b À decay to 40 Ca and electron capture (ec, including both possible decays, electron capture to the ground state and electron capture followed by c emission) to 40 Ar (89.14/10.86%, Kossert and Gü nther, 2004;89.3/10.7%, Grau Malonda and Grau Carles, 2002) and a certain 40 K/ K ratio of 0.01167(2)% (Garner et al, 1975).…”

“…1: for example, a relative decrease in the probability for the ec branch of about 1% leads to a total decay constant that is lower by about 0.1%, when using the same 40 K/K ratio of 0.01167. Therefore, the statements in Section 2.4 about the activity data from Grau Malonda and Grau Carles (2002) and Kossert and Gü nther (2004) and the resulting combined decay constant in Renne et al (2010) as well as the sentence on page 5356: "Rather, miscalibration of k b in the opposite sense is suggested, consistent with the previously discussed LSC data which indicate a $0.22% larger value (5.555 Â 10 À10 a À1 ) of k tot than that (5.543 Â 10 À10 a À1 ) recommended by Steiger and Jäger (1977)" are not correct. The decay constant calculated by Kossert and Gü nther (2004) of 5.554 Â 10 À10 a À1 (t ½ = 1.248(3) Ga) would decrease to approx.…”