[fluka-discuss]: RE: 4GeV protons in Iron

From: Anton Lechner <Anton.Lechner_at_cern.ch>
Date: Tue, 9 Oct 2018 13:30:32 +0000

Hello,

Since protons are hadrons, they are subject to nuclear collisions. At GeV energies, protons will not just slow down due to ionisation processes until they come to rest, but they will rather disappear in inelastic nuclear encounters. That's why you don't see many beam protons beyond 2 meters. The inelastic scattering length of a 4 GeV proton in iron is about 15.7 cm, so after 2 m only a small fraction of the initial beam protons will have survived (2.6E-6). After 4 m the survival fraction is only 8E-12.

In other words, the results are not surprising (and beware that PSTAR can only give you the range based on ionisation losses, but does not take into account nuclear interactions).

Best regards,
Anton

________________________________________
From: owner-fluka-discuss_at_mi.infn.it [owner-fluka-discuss_at_mi.infn.it] on behalf of Udrea, Serban Dr. [S.Udrea_at_gsi.de]
Sent: 09 October 2018 11:59
To: fluka-discuss_at_fluka.org
Subject: [fluka-discuss]: 4GeV protons in Iron

Hello,

I'm very new to FLUKA and trying to learn by using very simple set-ups. One of these consists of an iron cylinder surrounded by vacuum and a 4GeV pencil proton beam irradiating it from one side (protons initially propagate along the cylinder's axis). I used USRBIN to also take a look at the fluence of the original protons inside the target and have the feeling that something is not OK. According to NIST/PSTAR (https://physics.nist.gov/PhysRefData/Star/Text/PSTAR.html) the projected range of 4GeV protons in iron should be about 3m (2.495E+03g/cm² / 7.874g/cm³) but the fluence in the simulation shows practically no (beam) protons beyond approx. 2m (see attached image). I cannot find the reason for this(*). Any hints?

Thank you very much in advance for your support!

Best regards,
Serban Udrea

(*) Initially I thought that I wrote the wrong number in the input file, but this was not the case (the *.out file contains a line confirming the 4GeV kinetic energy).
--
Dr. Serban Udrea
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p-Linac/p-Bar-Target
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Received on Tue Oct 09 2018 - 17:00:51 CEST

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