Interaction of Two Beams Products with Each Other

Hello Geant4 experts,

I am recently using Geant4 and the “Chem2” example. I ran this example, but it seems that the products of two particles of beam do not interact with each other (I defined two point sources).
Could you please help me? I want to know whether the products of two beams interact with each other in Geant4 or not? Is it considered in this example?

_Geant4 Version: 11.1.2
_Operating System: Ubuntu 22.04.3 LTS
_CMake Version: 3.22.1

In Geant4 each event is entirely independent of one another. When you run, let’s say, /run/beamOn 100, each one of those 100 events starts from the same initial state you set up in your DetectorConstruction class.

Within an event, the tracks run individually as well, so in general each track sees the same initial environment. There’s a good reason for this. Tracks are not processed in temporal order: they’re processed in the (reverse) order in which they are put onto the tracking stack.

That means that you can’t rely on a track “later” in the simulation to actually represent a particle later in time. So you don’t want to try to “accumulate effects” from track to track, because they aren’t in time order.

Thank you for your response.

I mean, for example I define two point sources as a gps in the macro file, when I run, they enter the water phantom and react with its molecules and generate products and other reactions.

According to your definition, both of these particles start from the same initial state that we set in the DetectorConstruction class. Does this mean that these two events, even though they are running at the same time, do not see each other’s effect in the phantom? And Does this make the products of these two particles not react with each other?

Is this due to the Geant4 base definition? I mean, is it possible to solve this by adding an algorithm to Geant4 or we should add it to this example?

[quote=“SFR1993, post:3, topic:11299”]
Does this mean that these two events, even though they are running at the same time,[/quote]

What do you mean by “the same time”? Do you mean in the same event, or do you just mean different events in the same run?

If these “products” are in different events, then they certainly don’t “react” with each other.

If you’re running one of the DNA or chem examples, then I think “products” from the same track do react, but I don’t know enough to say whether products from different tracks react, and if so, whether they handle the timestamping properly (a secondary from the future shouldn’t react with one from the past, obviously).

As far as I know, this is not possible as you are describing it. I do not think the world materials are updated based on interactions with particles. For instance, if you had a volume of 6Li, and hit it with enough thermal neutrons that there was an appreciable amount of alpha/3H particles instead of 6Li, the efficiency of the 6Li volume would not drop. So each particle “sees” the same detector material.

So in your case, the second beam (or different particles from the same beam) would not behave differently due to interactions from the first particle (damage in the source, new molecules created, etc)

Thank you for taking the time to answer my question.

I mean when they enter the phantom at the same time. I try to create this condition by defining two sources. Therefore, I defined the beam macro file in this way:

/tracking/verbose 0


/gps/source/intensity 1
/gps/particle proton
/gps/direction 0 0 1
/gps/position 0 0 -1 micrometer
/gps/energy 10 keV

/gps/source/add 1
/gps/particle proton
/gps/direction 0 0 1
/gps/position 0 0.1 -1 micrometer
/gps/energy 10 keV

#/gps/source/multiplevertex 1
/run/beamOn 2

Considering that they go through the same events, I want to know if some of the primary particles from each particle react with each other? (based on the definition of reactions in the “Chem2” example),

And also for secondary particles, do the defined reactions only happen between the species resulting from a particle? or the secondary products from particle1 can react with secondary products from particle2?

Thanks for your response, but I asked this question according to the chemistry modules that defined in this example. I want to know whether the products of two particles (sources) interact with each other or not?

Are the new “chemistry” processes described in the Physics Reference Manual, or in the README for the specific examples? Those would be the places to look. If your question is not answered in either place, I’d encourage you to create a Bugzilla request in the “Documentation” category, so the docs can be improved.

Thank you for the recommendation, I will definitely check them out.