In G4MuonMinusBoundDecay::GetMuonDecayRate(G4int Z) there is a factor (1-2.5*x*x) applied to the free mu- decay rate (x = Z_eff/137). The 2.5 accounts for the change in phase space but there are a couple of other corrections that nearly cancel this. A more accurate correction is (1-0.5*x*x). References: H. Uberall, Phys. Rev. 119, 365 (1960). H. C. Von Baeyer and D. Leiter, Phys. Rev. A 19, 1371 (1979).
Hello Duncan, Thank you for the report. The current implementation is based on N.C.Mukhopadhyay Phys. Rep. 30 (1977) and T. Suzuki, D. F. Measday, J.P. Roalsvig Phys. Rev. C35 (1987) 2212. using Zeff. Although the formula you suggest seems to be better for light nuclei it is much worse for the very heavy ones. We shall try to somehow improve the current one to achieve a better agreement for all Z. Krzysztof
I modified G4MuonMinusBoundDecay::GetMuonDecayRate to use the Von Baeyer/Leiter, Phys. Rev. A 19, 1371 (1979) formula up to Al(Z=13), assuming the mass of the nucleus of the most abundant isotope for a given Z, and then a formula based on a polynomial fit to the data quoted in Phys.Rev. C35 (1987) 2212. It should improve the overall agreement with the available data for all the nuclei. It is available starting with Geant4 10.5.
