Time window for coincidence detection

Particles, Track, Event, Run and Biasing
1

Hello everyone
I am constructing a PET scanner made from NaI(Tl) scintillation detectors. This detector has a time resolution or time constant factor with it which I think I need to implement by defining time window for the detection (Kindly let me know if there is other method to do the same). I am using global time to store the time information but the values of global time are absurd in e+13 terms. What is the default unit of global time? How can I use it to compare between two hits?

Any answer will be highly appreciated.
Thank you so much

2

I also have simular question.

may be you can store the difference time about global time. I think you want to know the e+ time and e- time, so the value of( e+ time - global time) and vlalueo of(e- time -global time ) may be more important than global time.

3

Thank you for the reply @Ziyang_He .
I need the global time for the photons that hit the detectors. So for that I don’t know the units of time it gives. Could you explain in this regard?

Thank you so much

4

my teacher tells me the unit is ns for time

5

Hi,

When using Geant4 the user is expected to always use units. You must divide your G4float by the unit you want the quantity to be displayed.

auto global_time = step->GetPostStepPoint()->GetGlobalTime();
G4cout << " Time in seconds " << global_time / s << G4endl;
G4cout << " Time in nanoseconds " << global_time / ns << G4endl;

/Pico
P.S: If you look in the file /usr/include/Geant4/CLHEP/Units/SystemOfUnits.h you will see the following

  static constexpr double nanosecond  = 1.;
  static constexpr double second      = 1.e+9 *nanosecond;

so technically the teacher is right. However the teacher should have pointed out that the users are expected to use the units they want/need.

6

Thank you very much.

I have a similar problem about it.

Is there any way to achieve Flow intensity about beam, such as I need 20 na proton , lasting for 2 minutes in Geant4. Thanks

7

Geant4 events are primary-by-primary so you have to the homework yourself.

  • Just do the math and use that number as the amout of primaries to be used.

  • It is possible to have more than one primary but they are tracked one at a time, so there is no interference or anything like that. If you want to set up a (prompt) coincidences in your detectors is possible but you have to code it yourself.

Also, in case you would like to do some offline time (delay) pile-up analysis of sorts you may want to modify their initial time such that if you have, say 1 particle per second (1 Hz), the first particle starts with time 0s the second one with time 1s, etc… something like

  G4double rate = 1*Hz;
  G4double time= (G4double)(evn_ctr / rate);   // evn_ctr is the number of the event
  fParticleGun->SetParticleTime(time);
  ...

This should work for both, G4GeneralParticleSource and G4GeneralParticleSource

/Pico

8

Thank you very much
As you mentioned，I want to do some offline time analysis, but I don’t know how to do it (because the reaction will generate some long-lived nuclides)
To use this api , I think I can do it quickly.
:grinning: