Hi There,
I have built a simulation for the radioactive decay of U, Th & K in natural materials and the transport/deposition of energy by secondary particles such as alpha, beta and gamma. So far I have been using the shielding physics list as it appeared to have the necessary components (radioactive decay, high precision at low energies, covers alpha, beta & gamma).
Out of curiosity, is there a physics list that would be better suited to my purpose or am I good with shielding?
Thanks
Shielding sounds like exactly what you’re wanting to use. We use it in CDMS for the same kind of background studies.
You should note that Geant4 is not going to model “natural materials” out of the box. If you set your source, for example, to U-238, then on each event you’re going to get one decay from each step in the full decay chain, all the way down to Pb-208, with time stamps of millions to billions of years.
What you’ll want to do is (a) solve the Bateman equations to determine the secular equilibrium mix of decay-chain isotopes, given a specified age for your rock; and (b) write a custom generator (GPS can do this via macro commands, I think!) where you pick an isotope randomly from that secular mix. For a nice long run, you’ll get integrated results that reflect the natural rock.
If you’re only interested in gammas, there are packages like SOURCES4C (if you only care about gammas) or RadSrc from LLNL which can do this for you and give you a spectrum you can feed to Geant4 (GPS).
Hello, Could I ask you about the objective of your simulation ?
N.B: I am also working on natural radioactivity and Geant4
Thank you very much
The SuperCDMS experiment is a deep-underground dark matter detection experiment. With an expected signal of a few events per year, we focus almost all of our simulation effort on sources of background. That is primarily radiogenic, either from part-per-million or less radioactivity in the materials of the apparatus, or from the cavern walls, or from some idiot bringing a banana into the lab 
Radiogenic contaminants in refined materials (think copper extracted from ore) will not include just one isotope, but it also won’t contain the full natural mix of decay chain daughters. You need to be careful about the mix of isotopes that you simulate (or at least, check the timestamps on the generated Geant4 tracks), so that you are reproducing what you would expect to be in your material.
Thanks for this. Do you use the standard EM? I’m trying to decide which EM physics list is best for handling the interactions typical of U235, U235, Th232 and K40 decay energies.
We use standard EM for our overall background simulations (which involve radiogenics in metals and the cavern wall, including the U-Th chains and K40 from shotcrete). Our silicon detectors have to be calibrated using K-edge X-rays, so for such detailed studies we use Shielding_EMZ (EM option4).
Cheers this is helpful. Have you had any success with Shielding + Livermore? I get significantly different energy depositions with that list compared to Shielding + standardEM. Not sure which to trust more…
Unfortunately, I’m not the EM expert in our collaboration. I know we had a graduate student several years ago to an evaluation of several of the EM options, which is how we settled on option4 (EMZ).
Understood. I appreciate your time.
All the best.
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