|Message: Radioactive decay and photon evaporation - Data files||Not Logged In (login)|
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I simulate the energy deposited in a germanium detector by gamma radiation emitted by radioactive samples. This I do to determine the full energy peak efficiencies for different energies so that I am able to calculate the activities of the samples. (The detector geometry is 'tuned' to reproduce measured efficiencies, see many publications like Helmer et al., NIM A, 2003, 511, 360-381 etc.)
I'm using Geant4 9.5.p01 with a software package developed by my collaboration which handles the data output, read-in of GDML defined geometries etc.
Since during the decay of many nuclides gamma cascades are emitted, I use GRDM to simulate the decay within my samples. This does work perfectly but for many gamma lines the emission probabilities are not reproduced correctly, showing deviations of 10% or more. Since I rely on the PhotonEvaporation data (true coincidence summing is likely for close geometries, so single simulated gammas are often no alternative), the calculated results deviate the same.
I know this is a general problem, see for example
http://hypernews.slac.stanford.edu/HyperNews/geant4/get/hadronprocess/786.html http://hypernews.slac.stanford.edu/HyperNews/geant4/get/hadronprocess/1270.html http://bugzilla-geant4.kek.jp/show_bug.cgi?id=1340 http://bugzilla-geant4.kek.jp/show_bug.cgi?id=1431
I also know that the import of the nudat2 data base is currently developed but unfortunately not released yet.
Also i could not find any difference between the evaporation data for for example Bi-210 (z83.a210, Pb-210 decay) in 9.5 and 9.6, so I expect no big improvement by upgrading to 9.6.
I simulated the decay of Pb-210 (500k events), the 46.539keV photon is emitted with probability p = 0.03932 +- 0.00028. The literature gives a value of p = .04252 +- 0.0004, which is a difference of nearly 10% resulting in an (in this case) overestimation of the sample activity by 10% as well.
Since I usually trust the data by the Decay Data Evaluation Project (DDEP)
I did compare the total conversion coefficient for the relevant transition found in the Geant4 data file (... share/Geant4-9.5.1/data/PhotonEvaporation2.2/z83.a210 , first row, 7th column) with the data given by
(second last row, second last value is Total conversion coefficient, see format manual http://ie.lbl.gov/databases/ensdf-manual.pdf ). The Geant4 data value is too large, resulting in a too low emission of the gamma. After fixing this to the value in the mentioned document, the emission probability is much better, beeing aproximately p = 0.04260 +- 0.00029
Since I want to hand in my thesis soon, I can not wait for the release of the new PhotonEvaporation data. How were the current data created in the first place? How are the partial conversion coefficients calculated from which data (ENSDF?) and how where they extracted? Do exist some tools for it? The same holds for the RadioactiveDecay data files, since for example the branching ratios do sometimes not agree with the DDEP data influencing the gamma emission probabilities as well.
I experiencing problems with Ba-133, Eu-152, Pb-210 and need all other nuclides of the natural decay chains as well, so I am currently willing to somehow 'transplant' the data available at http://www.nucleide.org/DDEP_WG/DDEPdata.htm into my Geant4 data, since I usually only need a small set of the data (the data of the DDEP have been always sufficient up to now).
Any help is appreciated! Thank you very much for your support.
Best regards, Till