# Problem in the understanding of the activation results

From: Julie Barbier <Julie.Barbier_at_iba-group.com>
Date: Thu, 25 Oct 2012 09:50:44 +0200

Dear fluka experts,

I'm actually working on the activation of a tungsten target.
My model consists in a cylindrical target of tungsten (182-W; 183-W; 184-W; 186-W) bombard with a beam of 230MeV protons.
Here are the CARDS used in my input files:

· IRRPROFI 6.24E+9 protons/sec during 1 year

· DCYTIMES from -1year to 1year

· RESNUCLEi to score residual nuclei produced

· RESNUCLEi card coupled with the times of DCYTIMES to perform radioactive decay of the residual nuclei

My results don't seem consistent to me. Indeed, in the output files, RESNUCLEi card give me the yield (nuclei/cm³/pr) of all the radionuclides in presence and RESNUCLEi+DCYTIMES give me the activity (Bq/cm³) from these isotopes.
If I focus on one nuclide : tungsten 181, for example :
The yield done by Fluka is 2.72E5 nuclei/cm³/pr. If I use this yield with the radioactive growth equation, the saturation activity (time tends to infinite) equals to 1.70E5 Bq/cm³ and the activity after 1year of irradiation equals to 1.49E5 Bq/cm³.
After1 year of irradiation the activity provided by Fluka is 1.91E5 Bq/cm³.
I tought that normaly A(1year fluka) = A(1year calculated) and A(saturation calculated) > A(1year)
I cannot figure out why does my calculations differ from the Fluka results.

In a second time I changed the irradiation interval of IRRPROFILe from 1 year to 10 minutes. The results for tungsten 173 are :
Calculations via the yield done by fluka : A(saturation) = 2.06E4 Bq/cm³ and A(10 minutes) = 1.23E4 Bq/cm³
Fluka result for the activity at 10 minutes : 8.47E6 Bq/cm³
In this case, A(saturation calculated) > A(1year) but A(1year fluka) still not equals to A(1year calculated)!

That would be great to have you help on this issue !

Julie

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Received on Thu Oct 25 2012 - 10:39:05 CEST

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