Is there any way I can define pH of soil in GEANT4

Hello, my detector is made up of soil with some chemical composition. I want to specify the pH for my soil layers. How can I do it?

pH is nothing but the potential of hydrogen. It denotes the concentration of hydrogen ions in the soil concentration. I guess we can specify hydrogen concentration in geant4.

Hi. I am not sure of the relevance of pH to nuclear reactions. You can specify a concentration of hydrogen ions [H] (in practice a concentration of hydrogen nuclei). To maintain chemical equilibrium in an aqueous solution, you will need to also specify a concentration of hydronium ions [OH] (again really just nuclei pairs), such that [H][OH] is a constant. However, as pH increases or decreases, [H] and [OH] increase/decrease in direct opposition such that the total number of hydrogen nuclei remains a constant. If you are considering nuclear reactions on the hydrogen nuclei, the nuclear physics processes only care about the number of hydrogen nuclei, not what kind of ions they are in (perhaps with the exception of very low energy neutrons).

If I am missing something, I apologize. Maybe you could elaborate a bit on what you are trying to do.

Geant4 is a particle physics simulation framework. It models how radiation (gamma rays, X-rays, beta particles, and high-energy beams of nucleons or nuclei) interacts with materials. Geant4 does not do diffusion of gases or liquids. Geant4 does not do chemistry.

If you have a model where there is radon that collects at some depth in soil, then you can definitely use Geant4 to answer a question like “how much dose would a person receive at the surface of X feet of soil?” But Geant4 can’t answer the question of “how much radon from depth X will diffuse out into the atmosphere?”

The decay of radon and uranium does not depend on the materials in the soil, rather only on the radon and uranium concentrations. Radon is an inert gas, so its movement through the soil will be governed by diffusion and will depend on physical properties of the soil materials, such as porosity, density, etc. Radon’s daughters are solids and will adhere to materials electrostatically. The sticking will be governed by electrochemical processes. As noted, Geant4 does not model physical processes like diffusion or electrochemical processes. So you really need physical/chemical transport modelling software. The choice of materials really depends on those latter processes.

Are you wanting to actually collect the radon? That is a problem of gaseous diffision through a porous medium, which Geant4 cannot solve. You will need to use an appropriate soil diffusion model, which is presumably available in your field (I’m not an environmental engineering specialist).

If you already have a distribution of radon as a function of soil depth (from a soil diffusion model), then what Geant4 can tell you about is the radiation dose (the flux of alpha particles, or betas, or gamma rays) from decays of the radon. You can set up either a scoring surface, or a stepping action, or a sensitive detector, at some appropriate position or volume above the soil surface. Geant4 will tell you (via N-tuples or histograms) the number of events with radiation incident on your target.

Combining that with the number of radon particles you simulated (effectively, your /run/beamOn) you can compute the dose by converting your number of events into a radon density (parts per million or whatever).

Okay, that Geant4 can do. You can use the examples to see how to define materials, create your geometry, and so on. What you want to do is relatively simple: You’ll define a set of G4Material instances (probably mixtures of other materials) to represent each particular soil compositon you want (the way G4 works each different “varying moisture” must be implemented as a different material). You’ll make your nested or layered volumes each with the appropriate material.

Define a scoring surface at the top of your stack of soil layers. Or create a volume that you place just above the soil, and attach a sensitive detector to it.

Then you set up your source as a radon atom placed randomly somewhere in the geometry. For each event, pick a random position somewhere in the overall soil and put a radon atom there to decay. Then you can score the radiation you see in your sensitive detector, along with the primary position for that event.

If you throw enough events (probably at least 10^7), you should be able to make a nice plot of dose vs. primary depth.

Just to be clear- The radon in your model will no move. With Geant4 you can set up your soil composition/geometry based on known studies, then follow the decay of Uranium/Radon to see how the decay products (beta, electrons, alpha, etc) travel through your geometry and deposit energy.

You mention multiple times

I want to calculate the number of radon particles I get at the surface of each sphere and am also interested in radon count in the outer sphere.


radon particles (radon flux) will I get on the surface

These are not things you can do with Geant4. The flux of radon particles is not determined by particle physics, but by chemical and physical properties of a gas

how radon particle count and energy deposited vary.

You can use Geant4 to look at energy deposited from decaying radon that you place in your geometry. For radon count (decaying from uranium in the soil) I don’t think Geant4 is even the software you want for that, though you may be able to solve it by tracking the number of uranium decays, which starts a complicated chain that involves radon