Unexpected results in USRBIN Dose-Eq plotting

Scoring
1

Hello,

I’m scoring Dose-Equivalent around a target 2 hours after the end of the irradiation, both with and without a concrete shield between the target and the measurement point. I have attached two USRBIN plots showing the data in each case. You can clearly see the concrete shield between 60 cm and 80 cm on the horizontal (z) axis, and the target at z = 0 cm. Given that both plots are from the same input file (I used Mat(Decay) to place the concrete in the decay of one of the runs), I expect the plots to be identical everywhere to the left of z = 60 cm. Instead I see that the plots are clearly different in all areas, notably in the shape and size of the “rings”. I’m hoping you can help me understand how the presence of the shielding which starts at z = 60 cm could affect the field values in areas where z < 60 cm.

Note the target itself is not symmetric, so the general asymmetry around z=0 is expected.

Thanks,
Rory

Without Concrete.pdf (1.7 MB)
With Concrete.pdf (1.7 MB)
GaNi Stuck Target.flair (5.1 KB)
GaNi Stuck Target.inp (4.2 KB)

2

Dear @RStokes,
I would say that the difference is caused by the backscattering of the induced radiation on the concrete shielding. Does it make sense to you?

3

Hi @amario ,

Thanks for your reply, it makes sense.

Rory

4