__ANY_URI 0, __BOUNCE_CHALLENGE_SUBJ 0, __BOUNCE_NDR_SUBJ_EXEMPT 0, __CP_URI_IN_BODY 0, __CT 0, __CTE 0, __CT_TEXT_PLAIN 0,
__HAS_FROM 0, __HAS_MSGID 0, __MIME_TEXT_ONLY 0, __MIME_VERSION 0, __MOZILLA_MSGID 0, __MOZILLA_USER_AGENT 0, __SANE_MSGID 0,
__SUBJ_ALPHA_END 0, __TO_MALFORMED_2 0, __URI_NO_MAILTO 0, __URI_NS , __USER_AGENT 0'
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (smtp1.mi.infn.it [192.84.138.69]); Sat, 17 Nov 2012
17:54:34 +0100 (CET)
X-Virus-Scanned: clamav-milter 0.97.6 at smtp1.mi.infn.it
X-Virus-Status: Clean
Sender: owner-fluka-discuss_at_mi.infn.it
Dear Alberto,
it's not my intention to contradict you, however the F5 tally in MCNP/X
is called "point detector". Every MCNP/X manual describes it as a next
event estimator, with the following meaning (the quote is from the
MCNP4B manual):
> A point detector is a deterministic estimate (from the current event
> point) of the flux at a point in space. Contributions to the point detec-
> tor tally are made at source and collision events throughout the random
> walk.
The same technique is also available in Geant4 through the GAMOS
interface. The situation is best described in the GAMOS User's Guide:
> The point detector scorer covers the problems where the quantity to be
> calculated is the flux or the dose of neutral particles (neutrons or
> gammas) in a very small detector (small with respect to the setup
> dimensions) situated far from the primary particles source. In this
> kind of problems the fraction of particles that reach the detector is
> very reduced, and therefore if one wants to calculate the flux or dose
> by conventional methods the statistics needed would be prohibitive.
>
> The technique implemented in GAMOS is similar to the F5 tally
> implemented in MCNP. It is based on the following idea: normal tracks
> are propagated and for each neutron or gamma interaction is calculated
> the probability that it would be deviated in the direction of the point
> detector (instead of the real direction towards which it is deviated)
> and the probability that it reaches the point detector without any
> further interaction. The first probability is based on a precalculated
> table of angle probabilities [...]
As far as MCNP/X is concerned, validation of the above technique can be
found e.g. in the paper by J.J. DeMarco et al. (Med. Phys. 22, 11–16,
1995) and in the LANL Report LA-UR-98-363, 1999 by D.P. Gierga and K.J.
Adams
(http://www.osti.gov/bridge/servlets/purl/663200-owvwwk/webviewable/663200.pdf).
So, even though undesirable aspects are present, sometimes it's the only
way of estimating gamma fluxes using feasible computing times.
Anyway, I take note that the technique is not implemented in Fluka and
likely never will be.
Cheers,
Michele
On 17/11/2012 12:24, Alberto Fasso' wrote:
>
> A point detector (or next event estimator) is not what you describe,
> which is
> what is commonly called "range rejection". Neither of them is available in
> FLUKA, as a deliberate choice of the developers. Both techniques in fact
> present a number of undesirable aspects, which are discussed at length in
> Monte Carlo textbooks.
Received on Sun Nov 18 2012 - 20:40:27 CET
This archive was generated by hypermail 2.2.0 : Sun Nov 18 2012 - 20:40:28 CET