Dear Yang,
the problem is in the source routine of method 3. Because the weight
summing is happening inside the loop, the weight of each gamma is added to
the sum. That is, each gamma emission is treated as an independent decay
event.
In the end, fluka gives you the results divided by the total weight
accumulated and the weight is counted twice. In other words, it appears as
though only one photon is emitted per primary.
The simplest solution is to edit the source routine and move this line
"WEIPRI = WEIPRI + WTFLK (NPFLKA)" outside of the loop.
Cheers,
Nikhil
On Thu, Dec 1, 2016 at 5:38 PM, YANG Tao <yangt_at_ihep.ac.cn> wrote:
> Dear Nikhil,
>
> Thanks for your reply. Attachments are the relevant input files and
> the source routines. I think there may be some problems in the source
> routine of method 2, so please point out them.
>
> Best regards,
>
> Yang
>
>
> -----原始邮件-----
> *发件人:* "nikhil shetty" <nikhil.nitk_at_gmail.com>
> *发送时间:* 2016年12月1日 星期四
> *收件人:* "YANG Tao" <yangt_at_ihep.ac.cn>
> *抄送:* fluka-discuss <fluka-discuss_at_fluka.org>
> *主题:* [fluka-discuss]: Re: [fluka-discuss]: Comparisons of different
> methods to obtain γ-rays of Cobalt-60 in FLUKA !
>
>
> Hello,
>
> Irrespective of method 1 and 2, it seems that there is a physical problem
> in method 3. In reality, the two gamma rays are emitted simultaneously and
> both with almost 100 % probability. The way it is implemented in method 3,
> the gammas are sampled independently, however it is not true.
>
> Well, regarding your actual question, it helps if you post the source
> routines so that someone can debug them.
>
> Cheers,
> Nikhil
>
>
>
>
> On Thu, Dec 1, 2016 at 11:59 AM, YANG Tao <yangt_at_ihep.ac.cn> wrote:
>
>> Dear FLUKA users,
>>
>> Recently I have simulated the dose given by cobalt-60 source and I
>> have some confusions. As is known, two γ-rays with energy of 1.17 MeV and
>> 1.33 MeV are emitted in the decay process. To obtain the beam of two
>> energies, I try to finish it in three different ways.
>>
>> 1. Set the BEAM card to ISOTOPE, and then define Co-60 with the HI-PROPE and
>> RADDECAYcards.
>>
>> 2. Write a user routine to define the source, which is mainly relied on
>> method by Giuseppe( *http://www.fluka.org/web_archive/earchive/new-fluka-discuss/2860.htm
>> <http://www.fluka.org/web_archive/earchive/new-fluka-discuss/2860.htm>*l).
>> I also declare a array titled Egamma(N) and inject
>> two photons in a DO loop.
>>
>> 3. A similar user routine with method 2, but I don't define an array of
>> photon energy, but a sampling method as follows:
>>
>> IF (FLRNDM(XDUMMY) .LE. 0.5) THEN
>>
>> TKEFLK (NPFLKA) = 0.001333
>>
>> ELSE
>>
>> TKEFLK (NPFLKA) = 0.001173
>>
>> END IF
>> Then I compare the different results. Method 1 seems to give the
>> correct results compared to the experiments. Results of method 2 and 3 are
>> almost the same with each other and only about one half of the one given by
>> method 1. I guess only one PHOTON/primary is emitted in method 2 and 3, so
>> I define a region to wrap the Co-60 source region and score the photons
>> from source using the USRBDX card, and the results confirm the guess,
>> method 1 gives 2 particles/primar, while method 2 and 3 both gives 1
>> particles/primary.
>>
>> Result of method 1 is correct since it simulates the real isotope
>> decay process and emits two photons for each event by the internal
>> setting of FLUKA. Method 3 emits one PHOTON each event also doesn't puzzle
>> me since I use a sampling method and it selects one photon energy by
>> the random number each time. However, method 2 as the explanation
>> of Giuseppe will inject two PHOTONS for each event, why does it give the
>> results like one PHOTON each time? I guess method 2 and 3 may indeed only
>> emit one PHOTON/primary each time and I should multiply the result by 2 to
>> obtain the real value, if that is the case, what is the difference of
>> method 2 and 3?
>>
>> Any help is appreciated.
>>
>> T. Yang
>>
>> CAS
>>
>
>
>
>
>
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Received on Fri Dec 02 2016 - 13:35:04 CET