Inconsistency in residual dose while using MAT decay

Dear @horvathd ,

I am referring to the previous post, as I feel I missed some points.

I used DOSE in USRBIN and DOSEEQ in USRBIN. I applied necessary conversion terms so that I can obtain dose in pGy/s and doseEq in pSv/s. [the fluka output for DOSE card is GeV-cc/g per s; where as for DOSEEQ card is pSv-cc per s in the present case].

I expected these two quantities should be similar (at least order wise). When I did not use mat decay card for the irradiation target, these values were of same order. However, when I used matdecay, they are not equal and also the values are changing depending on the material chosen in the card. As I understood from the previous post is that any material other than whatever is used for other regions can be set as matdecay.

I am attaching my observations for a cooling time of 0s:

using dose in usrbin (pGy/s) using doseEq in usrbin (pSv/s)
without mat decay 9.78E+09 3.56E+09
with mat decay = VACUUM 1.96E+09 4.77E+06
with mat decay = water 1.45E+09 9.23E+06
with mat decay = air 1.85E+09 4.85E+06

Water_decay.inp (13.0 KB)
Without_MAT.inp (12.9 KB)

Dear Riya,

The dose and dose equivalent scoring do not necessarily give the same numerical results. For example, there can’t be dose deposition in a vacuum, but the dose equivalent (converted from particle fluence) is still meaningful.

When you use different materials in the decay phase instead of the activated tungsten, your results are in the same order of magnitude compared to each other. You need to check the statistical errors to see if it is a meaningful difference or not.

Cheers,
David

Dear @horvathd ,

The scoring region for all these examples is a region called DET and AIR is chosen as material for all these cases. Only difference is the selection of material in the MAT decay. Thus it arises two doubts:

  1. if we compare only DOSE output, why is it changing with material selection in MAT decay card? (it is understood, without mat decay, the result includes decay of target as well. However, why the values are different for different mat decay material? In other words, how the MAT decay material is effecting the results?

  2. Since the region is air in the DET region for all these cases, it is not expected to have this much variations of dose and doseEq value, I guess.

Can you please clarify these?

Regards,

Riya

Dear Riya,

As mentioned, you cannot compare these results without their statistical error. Since they are in the same order of magnitude and if they have high statistical errors (which is usually the case with deposited dose in air, compared to dose equivalent scorings), they can be the measurements of the same value.

So, could you post the same table of results including the statistical errors?

Also, the decay material can influence the backscattering of the radiation into the detector, thus slightly altering the radiation field.

Cheers,
David

Dear @horvathd ,

Please find the tables with statistical error. The errors are less than 10% for all these cases.

using dose in usrbin (pGy/s) rel error (%) using doseEq in usrbin (pSv/s) rel error (%)
without mat decay 9.78E+09 4.03E-01 3.56E+09 3.46E-02
with mat decay = VACUUM 1.96E+09 6.14E+00 4.77E+06 9.66E+00
with mat decay = water 1.45E+09 5.71E+00 9.23E+06 6.29E+00
with mat decay = air 1.85E+09 5.53E+00 4.85E+06 8.22E+00

Regards,

Riya

Dear @horvathd ,

Can you please provide any insight on the above observation?

Regards,

Riya