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

Sometimes the answers come on the bike ride home on a nice, brisk, fall-like weather.

The answer is size and position matter. In this case, I am looking at the dose rate farther away from the source of
residual radiation (by 50 cm in radial direction) and the detector extends farther along z.

When I repeated the run setting the detector size and position the same in case 1 as in cases 2 and 3, I see similar
results for case 1 and 3 (considering the errors). Also, the small difference in case 2 indicates very small to no
contribution to the dose rate due to the activation from backscattered neutrons off steel.

              Time(s) DR (mSv/h)
                            Ta26_no_Shielding Ta26_steel_Shielding Ta26_Air
   1 1h_SOB 3.6000E+03 9.486E+01 +/- 0.30 % 9.384E+01 +/- 0.12 % 9.399E+01 +/- 0.29 %
   2 1d_SOB 8.6400E+04 5.401E+02 +/- 0.19 % 5.393E+02 +/- 0.11 % 5.386E+02 +/- 0.11 %
   3 3d_SOB 2.5920E+05 6.261E+02 +/- 0.18 % 6.255E+02 +/- 0.10 % 6.246E+02 +/- 0.12 %
   4 10d_SOB 8.6400E+05 6.437E+02 +/- 0.18 % 6.434E+02 +/- 0.09 % 6.425E+02 +/- 0.14 %
   5 0s_EOB 2.0808E+06 6.509E+02 +/- 0.18 % 6.506E+02 +/- 0.09 % 6.497E+02 +/- 0.14 %
   6 1h_EOB 2.0844E+06 5.561E+02 +/- 0.20 % 5.567E+02 +/- 0.10 % 5.557E+02 +/- 0.16 %
   7 1d_EOB 2.1672E+06 1.111E+02 +/- 0.35 % 1.116E+02 +/- 0.35 % 1.114E+02 +/- 0.39 %
   8 10d_EOB 2.9448E+06 1.002E+01 +/- 0.35 % 1.005E+01 +/- 0.31 % 9.984E+00 +/- 0.27 %
   9 40d_EOB 5.5368E+06 4.217E+00 +/- 0.29 % 4.216E+00 +/- 0.26 % 4.203E+00 +/- 0.24 %
10 1y_EOB 3.3617E+07 1.045E+00 +/- 0.40 % 1.047E+00 +/- 0.41 % 1.045E+00 +/- 0.30 %
11 2y_EOB 6.5153E+07 6.781E-01 +/- 0.42 % 6.794E-01 +/- 0.44 % 6.781E-01 +/- 0.31 %
12 3y_EOB 9.6689E+07 4.674E-01 +/- 0.43 % 4.681E-01 +/- 0.44 % 4.673E-01 +/- 0.31 %
13 5y_EOB 1.5976E+08 2.247E-01 +/- 0.43 % 2.250E-01 +/- 0.43 % 2.247E-01 +/- 0.30 %

Cheers,
Mina

On 12-08-21 11:33 AM, Mina Nozar wrote:
> 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 Thu Aug 23 2012 - 11:05:12 CEST