|Message: problems with G4RadioactiveDecay in geant4.9.4||Not Logged In (login)|
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We are interested in the simulation of radioactive decays of isotopes inside a detector, that is, all the emissions generated are relevant for us. We encountered problems in the past using the Radioactive Decay Model mainly due to the missing energy in beta- and EC emitters, as reported in problem report #1001( http://bugzilla-geant4.kek.jp/show_bug.cgi?id=1001). When using the last available version 4.9.4.p01, many of these problems have been solved, although some remain and also some new issue has appeared.
Our particular doubts, using the last version, are the following:
1) From the sequence of isotopes in the natural radioactive chains, there are still problems for 228Ra (from 232Th chain) and 227Ac (from 235U chain), both beta- emitters with Q around 45 keV. In an ideal detector registering all the emissions, we expect a superposition of several beta spectra starting at the energies of the excited levels of daughters, but this expectation is not acomplished. Beta shapes start in some cases below the level energies, so it seems that there is still some missing energy (I attach the spectrum obtained for 227Ac).
2) Concerning the electron energy spectrum for a beta- decay, I would like to know if as stated in the forum post (http://hypernews.slac.stanford.edu/HyperNews/geant4/get/hadronprocess/766.html) and as it seems having a glance at the code in G4RadioactiveDecay.cc, LoadDecayTable(), case BetaMinus:, the considered shape is still always that of allowed transitions, and if the correction implemented in version 4.9.4 at G4RadioactiveDecay.cc suggested in the problem report #1068 (http://bugzilla-geant4.kek.jp/show_bug.cgi?id=1068) is exclusively for 40K isotope. Our problem here is the following. The beta spectrum shape obtained for 40K with previous version (9.3.p02) agreed very well with the spectral information obtained from the book "Table of Isotopes" (Wiley, 1999) coming apparently from calculation having into account the order of forbiddenness, while after the specific correction for 40K implemented in the new version (9.4.p01) the agreement is much worse. The following table shows the comparisons:
energy range (keV) % Simulation (geant4.9.3.p02) % Tables % Simulation (geant4.9.4.p01) 0 a 10 0.49 0.495 0.403 10 a 20 0.51 0.51 0.41 20 a 40 1.1 1.1 0.87 40 a 100 3.9 3.9 3.02 100 a 300 18.0 17.9 13.8 300 a 600 32.0 32 27.4 600 a 1300 33.3 33.4 43.4 >1300 0.001 0.000326 0.0016 <E> 453.9 455 525.8
Mean energy <E> is calculated over 40K decays (not over electrons emitted in beta decays). We have checked that for other isotope (210Bi, first-forbidden transition) the agreement of the simulated beta spectrum with the information on Tables is also very good with the previous version. Are we misunderstanding anythig?
3) It seems that the decay of 234Th (from 238U chain) is not properly reproduced in version 4.9.4.p01. * According to tables of isotopes, the beta decay ends almost always to the metastable state of 234Pa at 73.92 keV, either directly (70.3%, according to /RadioactiveDecay3.3/z90.a234 file) or through excited states with higher energy. The 234mPa decays beta- (mainly to the ground state of 234U, 98.2% from /RadioactiveDecay3.3/z91.a234 file) having a negligible probability of IT to the ground state of 234Pa (0.16%). * From the simulation, however, I encounter that in many cases (roughly, 70%) 234Pa[0.0], that is the ground state, is produced. Its beta- decay is very different from that of the metastable state, giving rise to the emission of a lot of gamma lines from 234U deexcitation. This problem was not present in previous version (I checked 9.3.p02) where 234Pa[73.9] state was correctly produced. Are you aware of this problem? Can be avoided in some way?
Many thanks for your help in any of these questions, Susana Cebrian
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