Re: [fluka-discuss]: RE: EXPRESSIONN OF AREA USED IN USRBDX CARD

From: Francesc Salvat-Pujol <francesc.salvat.pujol_at_cern.ch>
Date: Mon, 5 Mar 2018 12:08:59 +0100

Dear Riya,

I have not seen your input file, so I shall assume you have a beam of
whichever particles impinging on a sphere in vacuum with no additional
regions other than a surrounding blackhole and that you are indeed
scoring fluence. I naively suspect your problem is the following.

If you score fluence using USRBDX with one-way scoring vacuum->sphere,
you are only scoring surface-crossing events on the first half of the
spherical surface, as the other half corresponds to sphere->vacuum.
Thus, you are a factor ~2 short if you want the fluence through the
whole spherical surface.

If you use USRTRACK, the fluence scoring is done by accumulating track
lengths within the sphere (and dividing by the sphere volume in the end
etc). Thus, here you pick up the whole passage through the sphere, not
just the entrance as above, hence (probably) the observed discrepancy.

Feel free to take a look e.g. at
https://indico.cern.ch/event/604018/contributions/2435691/attachments/1395454/2242757/08_Scoring_2017.pdf

Cheers,

Cesc


On Mon, Mar 05 2018, at 14:22 +0530, riya dey wrote:
>
>Dear Experts,
>
>If I put 4*pi*r^2 as area in USRBDX ( with one way scoring) and 4/3*pi*r^3
>as volume of the spherical detector in USRTRACK , then the result in
>USRTRACK is appearing to be 2 times the value from USRBDX.
>
>Both the values should be the same theoretically. Why is this discrepancy
>happening ?
>
>
>
>With regards,
>
>Riya Dey
>
>
>
>From: riya dey [mailto:riyadey_at_barc.gov.in]
>Sent: 05 March 2018 13:47
>To: 'fluka-discuss_at_fluka.org' <fluka-discuss_at_fluka.org>
>Subject: EXPRESSIONN OF AREA USED IN USRBDX CARD
>
>
>
>Dear FLUKA Experts,
>
>
>
>Suppose I want to calculate the fluence from vacuum to a spherical target .
>What should be the expression for area that has to be given in USRBDX card
>?? Is it 4*pi*r^2 or pi*r^2 ??
>
>
>
>Note : Fluence is defined as dN/dA where dN the number of particles incident
>on a sphere of cross-sectional area dA. And the cross sectional area of a
>sphere is pi*r^2 .
>
>
>
>With regards,
>
>Riya Dey
>

--
Francesc Salvat Pujol
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
Tel: +41 22 76 64011
Fax: +41 22 76 69474
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Received on Mon Mar 05 2018 - 13:30:05 CET

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