Shift in the maximum dose rate point

Dear Experts,

This is a shielding case. The Dose Eq is scored in XYZ bins, on the surface of the geometry, at 5 cm and at 1 m from the surface on the geometry.

I noticed that the maximum value at 1 m on the Top has shifted to the left ( x = -9.0 to -7.0 bin) while the maximum on the surface is near-above (x = 1.0 to 3.0 bin) the source(at 0,0,0) - results in binning no. 1 & 3 - 0212_3E07…lis (1input). I couldn’t follow this.

Secondly, the scores in binning nos. 10, 11 & 12 ( 2results.lis & 2input), the values are increasing as I am moving away from the geometry - i don’t understand why.

Kindly suggest any corrections or errors, if any.

Raksha Rajput.
1input.inp (9.9 KB)
2input.inp (10.2 KB) 0212_3E07,15spawns,6cycles,EMFCUT.lis (10.2 KB)
2results.lis (10.7 KB)

Dear Raksha,

I don’t fully understand the problem you observe in your output. Perhaps you could attach plots or line number in the lis files so I can identify the problematic detector or bins. Also please let me know the output from which detector is relevant.

I suggest you assign different unit numbers to the different detectors in your scoring. You results would be divided in different files which you might find more convenient.

Dear Benoit L,

Am really sorry to reply late.

Please refer the 0212_22.bnn.lis, why is there shift of the maximum dose rate on LHS at 1 m (“DETop1m”), while the maximum is at almost the centre for surface dose rates (“DETop”) and at 5 cm from the surface (“DETop5cm”) ?

Secondly, please refer 0212-26.bnn.lis, I can’t find the order of decrease or increase in the Dose Eq values for the binnings n. 1 , 2 , 3…which are at 1 m in different directions (only n. 4 - “DEFront1m” shows a proper decrease). If I move away, the values should decrease ( I have scored along X - direction, 3 bins in x-direction) and vice versa. But why is it not so here ? Has is to do something with the bin size I have used, as I am at more than 1 m for the source ?
The input and the .lis files are attached for reference.

Kindly suggest.

Raksha Rajput.0212.flair (9.8 KB) 0212.inp (10.3 KB) 0212_22.bnn.lis (2.9 KB) 0212_26.bnn.lis (2.7 KB)

Dear Raksha,

The issue could be with the statistical error of your simulation results. I noticed the relative error is of the order of 10% for most bin values. Such large error would make it difficult to see variations of the dose equivalent over just a few centimeters. I advise that you first estimate the expected change in dose equivalent from one point to another, then estimate what error is necessary to achieve observe these expected variations in the simulation.

Taking for example your scorer DELHS1m. From z=-132cm to z=-135cm you would except a decrease in dose equivalent of very roughly 5% as the fluence decreases as 1/r^2 assuming you are in vacuum and very far from the source. Given that the error is 12% in your lis file, you are not sensitive to this variation.

Increasing the number of primaries as a way to decrease the statistical error would likely help you make a sense of the results.

Dear Benoit L,

Thank you for the explanation. I would try that and check the results.