RESNUCLEI Scoring timed out error and subsequent DETECT scoring

Scoring
1

Dear Experts,

I have two queries regarding a simulation involving a proton beam incident on a Nickel target.

(a) While running this input, some of the runs stop midway with a TIMED-OUT error. However, this issue does not occur for smaller numbers of histories.

(b) In this simulation, the irradiated target contains residual activity. Is there a way to obtain the photon spectrum from this irradiated target (after a certain decay period) using the DETECT card, with the target placed in front of a NaI detector?

For this purpose, do I need to perform separate simulations for each radionuclide, assuming a uniform distribution throughout the target geometry, then normalize the spectra with respect to their activities and finally merge them?

Or, is there a way to perform this within the same input file?

12MeV_Activation.inp (17.1 KB)

Regards,

Riya

3

a) the TIMED-OUT message from Flair does not necessarily imply an error: the run might still be ongoing. You shall look at the log and err files in the fluka_ temporary directory to learn more about the problem.

b) if you want the photon spectrum (number of photons as a function of photon energy), you should rather use USRTRACK, which can be associated to a cooling time.
This is not the case for DETECT, which gives an energy deposition spectrum (aka pulse height spectrum). To obtain the latter within the same input file, one can use RADDECAY in Semi-Analogue mode (forgetting about IRRPROFI, DCYTIMES and DCYSCORE), increase significantly the number of Replicas, and activate by USERWEIGHT a comscw.f of this kind (4.2 KB), where a cooling time interval filter is applied after taking into account the irradiation time. Results will be given per primary beam particle (but an acceptable statistical quality may be hard to achieve, in view of the time filter).

4

Hello @riya,

After a fruitful discussion with @ceruttif , I would like to point out a few considerations.

Using directly RADDECAY in semi-analogue mode together with a time filter in comscw.f is possible, but it has some important limitations. DETECT scores the total energy deposited in the detector for one primary history. Therefore, if several radionuclides produced by the same beam primary decay within the selected time interval, their energy-deposition contributions are summed in the same DETECT event. The same problem appears, and becomes worse, when replicas are used: decays from different replicas, possibly through different decay channels, may be summed together.

This is not what happens in a measurement with your hypothetical NaI. The detector records the energy deposited by radiation within a very short charge-collection window, essentially seeing one decay at a time. Summation of gammas from the same decay may occur, but summing unrelated decays over the full detector acquisition period does not reproduce the detector response. For this reason, the use of replicas should be avoided. More generally, biasing is not compatible with the DETECT scoring, and the use of replicas is a form of biasing.

To avoid both summation issues, namely replicas and multiple decays occurring within the same time interval, a suitable approach would be a two-step calculation. In the first step, activation mode can be used to obtain the activities of the radionuclides in the target at the desired cooling time. In the second step, semi-analogue mode can be used with a source routine that samples radionuclides according to the activity information obtained in the first step.

To avoid double counting, a filter should be put in place so that only products from the decay of the sampled radionuclide are scored, and not products from the decay of its daughters. This is needed because the first step already provides the complete inventory of radionuclides, including daughters. Therefore, daughters of the radionuclide sampled in the second step should either be prevented from decaying or their products should be ignored.

For the spatial distribution of the radionuclides, different approximations are possible: sampling uniformly in the activated volume, using a residual nuclei USRBIN obtained in the first step and sampling from it in the second, or generating a more detailed phase-space file to sample from.

Hope this helps.

Kind regards,
Fran