RE: [fluka-discuss]: determining cross-section- sanity check

From: Anton Lechner <Anton.Lechner_at_cern.ch>
Date: Tue, 26 Nov 2013 10:48:05 +0000

Dear Andrew,

There are two key points to be considered when scoring the yield of pi-zeros:

1) Pi-zeros have a very short mean lifetime (around 8E-17 seconds) and will decay before crossing your boundary to vacuum. For example, considering a 10 GeV pi-zero, time dilation will give you a mean lifetime of 6E-15 seconds in the lab frame which means an average range of ~2E-4 cm. This is much less than your target thickness of 0.01 cm. Instead of scoring the yield of particles crossing from your target to vacuum, you should consider to score directly the yield of particles emerging from inelastic interactions. This is also possible with USRYIELD, by setting on the first card WHAT(4)=-1.0 and WHAT(5)=-2.0 (other fields can remain the same).

2) You define your hydrogen target with a density of 0.8988E-02 g/cm3, which results in an inelastic scattering length for protons (at 50 GeV) of 6034 cm (you can find this number in the output file). Considering that your target is 0.01 cm thick, you would need to run many more primary events: on average, less than two protons out of 1 million will have an inelastic nuclear interaction. Running 10000 primaries, as specified in your input, is hence not sufficient to generate a spectrum with reasonable statistics.

Just a final remark: when defining a material, it is not recommended to set the atomic weight manually (WHAT(2) on the MATERIAL card) but to leave it blank (FLUKA internally derives the correct value).

Cheers, Anton



________________________________
From: owner-fluka-discuss_at_mi.infn.it [owner-fluka-discuss_at_mi.infn.it] on behalf of Andrew Taylor [taylora_at_cp.dias.ie]
Sent: 25 November 2013 13:20
To: fluka-discuss_at_fluka.org
Subject: [fluka-discuss]: determining cross-section- sanity check

Dear Fluka People,

I'm trying to do a sanity check at the moment by determining the
p-p cross-section for a fixed target set-up. However, using the
attached input file, I don't seem to get any flux recorded in my
output file (though the simulation seems to run ok).

Since I'm a newbie, I suspect my mistake is a trivial one. Could
someone more experienced take a look + highlight what's wrong?

Many thanks,
Andrew


--
------------------------------------------------------------
Dr. Andrew Taylor-Castillo
School of Cosmic Physics
Dublin Institute for Advanced Study
Ireland
office: +353 16621333x337
mob.: +353 877116296
Received on Tue Nov 26 2013 - 12:59:07 CET

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