Issue of Activation in the Gamma spectra of NaI detector

Respected All,

Greetings! The attached figure is a comparison of the experimental and Geant 4 spectrum. The experimental spectrum is not calibrated for energy and Ignoring the non-linearity at the x-axis. For a rough idea, the big peak right after channel 200 is a 2.2 MeV Hydrogen capture peak. The comparison mostly looks okay, but at the low energy i.e. at channel <100 there is a significant dip in the Geant4 spectrum, I do not understand this phenomenon. I believe this is due to lack of Activation but I am open to suggestions. Any ideas on how to rectify this issue?

My geometry is mostly of Concrete and Water.

My physics implementation is:

G4VModularPhysicsList* phys = new QGSP_BIC_HP();

Many thanks in advance!

Sanchit Sharma

in real spectrum you have also electronic noise, which is absent in Monte Carlo. It is not easy to say, why this drop is seen in simulation, you may try to change Geant4 cuts significantly (increase or decrease in 10 times).


1 Like

Thanks for your reply,

I just seek a confirmation, currently the cut in the QGSP_BIC_HP is set as:

defaultCutValue = 0.7*CLHEP::mm;  
SetCutValue(0, "proton");  

Should I just recompile Geant4 with 0.07mm and 7mm and rerun? or is there an easier way?


Also the noise part is in the Geant4 spectrum and not experimental.


Respected Dr. Ivantchenko,

I redid my simulations with a cutoff of 0.07mm and 0.7 mm (default) with QGSP_BIC_HP I am still getting the same results. I am really confused as to why this low energy dip is occurring in my spectrum.

I would appreciate any help in this regard.