Efficiency inversion when simulating both Co-60 gamma energies in Marinelli geometry with HPGe detector

Scoring
1

Dear Fluka Experts,

I am currently simulating the two gamma energies of Co-60 (1173.2 keV and 1332.5 keV) placed in a Marinelli geometry using an HPGe detector.

In my Fortran source file, I used the following lines:

  *momentum_energy = 0.00117302*

  *call sample_isotropic_direction( direction_cosx, direction_cosy, direction_cosz )*

  *CALL REGIONSOURCE ( coordinate_x, coordinate_y, coordinate_z,*

 *&   NREGION, XMIN, XMAX, YMIN, YMAX, ZMIN, ZMAX )*

  *radioactive_isotope = .false.*

  *energy_logical_flag = .false.*

  *gaussian_divergence_logical_flag = .false.*

  *direction_flag = 0* 

  *call set_primary()*



  *momentum_energy = 0.00133229*

  *call sample_isotropic_direction( direction_cosx, direction_cosy, direction_cosz )*

  *CALL REGIONSOURCE ( coordinate_x, coordinate_y, coordinate_z,*

 *&   NREGION, XMIN, XMAX, YMIN, YMAX, ZMIN, ZMAX )*

  *radioactive_isotope = .false.*

  *energy_logical_flag = .false.*

  *gaussian_divergence_logical_flag = .false.*

  *direction_flag = 0*     

  *call set_primary()*

As shown in the figure below, when I simulate both energies together using this code, the efficiency at 1332.5 keV becomes higher than at 1173.2 keV.
However, when I simulate each energy separately, the 1173.2 keV efficiency is higher, which is the expected result.

Could someone please explain why this inversion occurs when both energies are simulated together, or suggest how to correct it?

Thank you in advance for your help!

CO-60
CO-601344×650 39.2 KB

source_newgen_with_regionsource-1.f (21.2 KB)

Best regards,

3

Dear @fatimazahra.er ,

The issue you face might not have to do with your source routine but rather the way in which you score the results and/or the geometry you use. Could you provide in addition your input file from which I can see your scoring approach and in addition how you compute the detector efficiency?

Cheers and thanks,

Andreas