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:
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.
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:
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?
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.
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.
sorry for the late reply, it took some time to investigate and run simulations.
To address the two main points:
The “effect” of different decay materials is questionable since the statistical errors are still too high to see if they converge to the same numerical value or if there is a real difference (that is not expected). Remember that the resulting statistical error is just in turn a Monte Carlo estimate of the error, increasingly less accurate as the error gets large. (On a region basis, one should aim at a 1-2% error, which you comfortably achieved only in the first case).
The change in the dose/dose equivalent ratio resulting from the removal of the activated tungsten target would require further investigation.
The energy spectra of the different (EM) particles need to be checked with regard to their fluence-to-dose equivalent conversion factors (https://flukafiles.web.cern.ch/flukafiles/documents/deq2.pdf).
Figure 12 shows the conversion factors for photons, and there you can see there is a 2 orders of magnitude difference in the factors for MeV and 10 keV photons.
Thank you @horvathd for the insight. The removal of Tungsten target will definitely reduce the dose at the detector, since in this case, only contribution from activated Cu dump is present, and induced activity in Cu dump is much lesser than the activated target.
However, it surprised me seeing the difference between dose and dose Eq by almost 2 orders of magnitude for the case when the target is removed during post irradiation period. As you suggested, i will have a look at the photon spectra from Cu dump.
In this context, can you please confirm the following:
When using doeEq, first it estimates fluence and then it gets multiplied with DCF internally. What is the default bin size (no of bins) over which the fluence values are scored/distributed in the default doseEq card?
Is it then a better approach to use Dose card, instead of DoseEq to estimate residual dose at post irradiation ?
just a reminder, besides the copper, you have activated air as well (even inside the detector itself).
The conversion from fluence to dose equivalent is done before scoring and binning of the results, using interpolated values for the conversion factors between the data points.