Re: [fluka-discuss]: DELTARAY Card

From: Paola Sala <>
Date: Wed, 27 Mar 2019 15:50:02 +0100

Dear Julien,
first of all a small clarification for all readers: you are using the
PRECISION defaults, which sets the delta ray threshold to 100 keV (see
manual). The DELTARAY card that you activate (or not) sets instead the
threshold at 1 MeV. Thus, the "with_DELTARAY" plot has an higher delta
threshold than the "without_DELTARAY".

The "stairs" that you see correspond to steps in the transport. Step
length (far from boundaries) is calculated so to obtain an energy loss
that is a given percentage of the particle energy (5% when using
PRECISION).If the delta-ray threshold is so high that all losses ar
treated as continuous, all particles will experience more or less the same
step length and energy loss, with relatively small fluctuations (much
smaller than the average energy loss). Being the step larger than the bin
size, one will equally split the energy loss over many bins up to the next
step. Instead, when delta-rays can be produced, they are treated as
interactions and the step is truncated at the delta production point.
Different primaries will have different delta production points,
segmenting the steps differently and distributing the energy loss over
smaller number of bins.

A similar example varying the step size is in the additional material of
the fluka course slides about ionization:
slide 58

Hope this helps

> Dear Fluka users,
> I am always simulating protons in water.
> When I enable Deltaray card (with or without EMFCUT-Prodcut), simulation
is very shorter in time (1h to few minutes) and the dose profile produce
"stairs" before the Bragg peak. (see attached graphics).
> I understand the difference between discrete losses above the EMFCUT
energy but it seems to be very discretised in terms of energy... If
somebody could help me.
> Thanks
> PhD student at CELIA (FRANCE)

Paola Sala
INFN Milano
tel. Milano +39-0250317374
tel. CERN +41-227679148

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Received on Wed Mar 27 2019 - 17:10:06 CET

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