It's hard to understand the results of induced radionuclide yields

Dear FLUKA and Flair experts,
I tried to calculate the activities of the induced radionuclides produced in carbon and copper by 150 MeV electrons hitting the carbon target coated with copper. By using the usrsuwev command, some results file like “*res.lis” can be worked out under certain parameters such as beam intensity, irradiation time, and different decay time.

  1. The nuclides that did not appear at the time of shutdown ( decay time = 0 s ) were produced after a period of decay time ( such as decay time = 1day ). For example, H, Mn, etc. induced radionuclides in copper that appeared at decaying by one day while without appearing at beam shutdown.
  2. There are more nuclides in the result file “*sum.lis” than in “*res.lis” under the “Residual nuclei distribution” column. Why is that?
    Could you please help me to figure out these puzzling problem?
    Thanks!activation_exercise_test.flair (5.8 KB) activation_exercise_test_resnucle_80_ir30y_coolling_1min_5min_30min_1h_1d_1w_1mon_1y_sum.lis (127.4 KB) activation_exercise_test_resnucle_80_ir30y_coolling_1min_5min_30min_1h_1d_1w_1mon_1y_tot.lis (3.0 KB) activation_exercise_test_resnucle_isomer_sum.lis (32.8 KB) activation_exercise_test_resnucle_80_ir30y_coolling_1min_5min_30min_1h_1d_1w_1mon_1y_res.lis (37.0 KB)

Hello @liuqy,

Let me start by addressing point 2. In the files you attached you find 2 .sum files. If you look at the header you will see that they contain somewhat different information.
In " activation_exercise_test_resnucle_isomer_sum.lis" you see that the quantities are given in (n/cmc/pr) which means “nuclides per cm3 per primary particle”. Thus, the numbers denote a production yield of a certain nuclide (stable as well as unstable ones!) originating from one primary beam particle. In case you have defined a volume of your scoring region, which I would highly suggest to do by default, it will be normalized per cm3. Otherwise the numbers are to be understood as total nuclide yield in your whole scoring region even though the unit is still reported as “n/cmc/pr”!

If you then look at activation_exercise_test_resnucle_80_ir30y_coolling_1min_5min_30min_1h_1d_1w_1mon_1y_sum.lis you will see that now you can find irradiation + decay time + beam intensity and the quantities are given in units of “Bq/cmc”. Here you will naturally find only unstable nuclides as the data reflects activity in Bq and not a yield!

For example we find 7.36195183E+11 Bq/cmc for detector 1, 946080000s of irradiation and 0s of cooling. When you then go to activation_exercise_test_resnucle_80_ir30y_coolling_1min_5min_30min_1h_1d_1w_1mon_1y_res.lis you will find the same value reported. The info in this file is identical to the one in the .sum file which includes the activities but in a form that is somewhat simpler to read for humans.

Personally I would suggest to look at this file unless you have a specific reason, like your own post-processing program, for using the rather difficult to read matrix format given in the .sum file.

Regarding point 1 referring to the composition of the nuclide inventory you have to keep in mind two things: the yield data contains also stable nuclides which are naturally excluded when one looks at activity values that can only be reported for unstable nuclides. In addition, the actual content is a function of irradiation as well as cooling time. There might be cases where some nuclides are not produced directly but only via decay. Thus, they will only show up after a decay period which allows them to be produced.

Hope that helps

1 Like

Hello @ctheis,
Thank you very much for your answer! It’s a great help! Thanks again! :grinning:

Hello @ctheis
It suddenly occurred to me that the decay and production of nuclides occur at the same time. As long as the irradiation time is long enough, they should be in dynamic equilibrium. So it seems that it should show up at the time of shutdown, especially the long-lived nuclide like tritium.
Could you please tell me is that right?


yes that’s right. If you have a look at decay = 0s you would find H-3 with 9.640E+10 for example.

Based on the calculated yield FLUKA’s usrsuwev tool determines the nuclide activities for a defined irradiation and cooldown period(s) using an analytic solution of the Bateman equation which accounts for buildup via direct production, decay during irradiation, decay during cooldown and cross-feeding from different decay chains.


hello, @ctheis
ok, I got it! Thank you for your help and patience!