Looking at the contribution from the backscattered neutrons to activation and residual dose rates.

Hello everyone,

I am seeing another behaviour that does not make sense to me. In order to see the effect of backscattered neutrons
from a steel shielding outside the target material, I setup three runs: 1) no steel shielding, 2) steel shielding, 3)
steel shielding geometry but with the region filled with air instead of steel. I then look at the time evolutions of
residual dose rates in a detector.

Now, the only difference between case 1 and case 3 is the size of the detector in which I score DOSE-EQ. The detector
has a cylindrical shape, extended along Z, with center aligned with the center of the target.

Case 1: R_in = 100 cm, R_out = 110 cm, L = 100 cm
Case 3: R_in = 150 cm, R_out = 160 cm, L = 200 cm

Now, simple logic tells me I should get same results for cases 1 and 3. But I don't! What I see are similar results
fro cases 2 and 3:

              Time(s) DR (mSv/h)
                        Ta26_no_Shielding Ta26_steel_Shielding Ta26_Air
   1 1h_SOB 3.6000E+03 2.13484E+05 9.38366E+04 9.39949E+04
   2 1d_SOB 8.6400E+04 1.23124E+06 5.39347E+05 5.38636E+05
   3 3d_SOB 2.5920E+05 1.42768E+06 6.25480E+05 6.24645E+05
   4 10d_SOB 8.6400E+05 1.46799E+06 6.43360E+05 6.42518E+05
   5 0s_EOB 2.0808E+06 1.48433E+06 6.50573E+05 6.49682E+05
   6 1h_EOB 2.0844E+06 1.27088E+06 5.56750E+05 5.55701E+05
   7 1d_EOB 2.1672E+06 2.53825E+05 1.11551E+05 1.11369E+05
   8 10d_EOB 2.9448E+06 2.27816E+04 1.00479E+04 9.98383E+03
   9 40d_EOB 5.5368E+06 9.56453E+03 4.21563E+03 4.20325E+03
10 1y_EOB 3.3617E+07 2.35498E+03 1.04729E+03 1.04521E+03
11 2y_EOB 6.5153E+07 1.52702E+03 6.79373E+02 6.78128E+02
12 3y_EOB 9.6689E+07 1.05230E+03 4.68141E+02 4.67327E+02
13 5y_EOB 1.5976E+08 5.05950E+02 2.25016E+02 2.24657E+02

I have a feeling I am not comparing apples with apples because of the difference in the size of the detectors between
case 1 and cases 2 and 3. and that the detector in cases 2 and 3 is farther away (radially) from the target.

I appreciate any suggestions.
Best wishes,
Mina
Received on Wed Aug 22 2012 - 11:17:22 CEST