Re: Problem in the understanding of the activation results

Dear Julie

the explaination by Mario is very likely the good one for your question.
I guess you have plenty of 181-Re produced as well (for example by
182-W(p,2n) or 184-W(p,4n)) which decays via EC into 181-W therefore
"feeding" that isotope more than what you computed from the direct
production of 181-W alone. Since T_1/2 for 181-Re is << T_1/2 181-W, you
can with little error sum up the yield of both when computing the 181-W
activity after 1 year if you want to roughly cross check the FLUKA result.
This of course assuming 181-Re is the only feeding isotope.

Same applies to 173-W, where 173-Re can feed (and maybe others).

In general FLUKA solves the coupled growth and Bateman equations for all
siotopes in the problem at the same time. Once the yield per proton of all
isotopes is given, the claculation is fully analytical and only decay
constants, and branching ratios enter into it.

                  Best regards
                 Alfredo Ferrari

+----------------------------------------------------------------------+
| Alfredo Ferrari || Tel.: +41.22.76.76119 |
| CERN-EN/STI || Fax.: +41.22.76.69474 |
| 1211 Geneva 23 || e-mail: Alfredo.Ferrari_at_cern.ch |
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+----------------------------------------------------------------------+

On Sat, 27 Oct 2012, Santana, Mario wrote:

> Hi Julie,
>
> Your consistency test is missing something:
> You are isolating 181-W isotope when in reality your target is also producing
> other neighboring isotopes that will also decay. Some of them may decay into 181-W and thus will contribute to its production.
> In other words, you should check the isotope chart and the decay chains, write down the production of all isotopes that decay into
> 181-W and the run
> the bateman equations to obtain the real time evolution of 181-W. This may be a long equation or a system of (long) equations.
>
> Mario
>
>
> On Oct 25, 2012, at 1:21 AM, Julie Barbier wrote:
>
>> Dear fluka experts,
>> =20
>> 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:
>> * RADDECAY : active
>> * 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/cm^3/pr) of all the radionuclides in presence and RESNUCLEi+DCYTIMES give me the activity
>> (Bq/cm^3) from these isotopes.
>> If I focus on one nuclide : tungsten 181, for example :
>> The yield done by Fluka is 2.72E5 nuclei/cm=3DB3/pr. If I use this yieldwith the radioactive growth equation, the saturation activity
>> (time tends to infinite) equals to 1.70E5 Bq/cm^3 and the activity after 1year of irradiation equals to 1.49E5 Bq/cm^3.
>> After1 year of irradiation the activity provided by Fluka is 1.91E5 Bq/cm^3.
>> I tought that normaly A(1year fluka) =3D 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 1year to 10 minutes. The results for tungsten 173 are :
>> Calculations via the yield done by fluka : A(saturation) =3D 2.06E4 Bq/cm^3 and A(10 minutes) =3D 1.23E4 Bq/cm^3
>> Fluka result for the activity at 10 minutes : 8.47E6 Bq/cm^3
>> 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
>>
>
>
Received on Sun Oct 28 2012 - 19:18:26 CET