Re: Secondary protons in shielding

From: Alfredo Ferrari <>
Date: Tue, 24 Mar 2009 00:07:09 +0100

Dear Joel

very likely you got the beam dimensions wrong. Apparently you set the
simulated beam as large as your detectors, while I bet the real one was
much larger. That's the explaination of your results, it is a typical
mistake. Secondary protons are emitted at wide angles, if you have small
detectors after a large shield with a large beam you conpensate what you
lose from the axis with what you get from the surrounding, while if
you look at the axis only on a narrow beam you never see the buildup
(and you MUST never see it in those conditions!).

BTW the FLUKA reproduction of the curve in Radiat Environ Biophys 46, 107
(2007) is perfect (of course using the right beam size), as well
as it is for many other dose-profile data at lower and higher energies.


| Alfredo Ferrari || Tel.: + |
| CERN-EN/STI || Fax.: + |
| 1211 Geneva 23 || e-mail: |
| Switzerland || |

On Mon, 23 Mar 2009, Joel DeWitt wrote:

> fluka-discuss:
> As part of a shielding baseline I have run 1 GeV protons on Al, Cu,
> and polyethylene targets of various depths. The attached plot shows
> the results of such simulations. As you can see, FLUKA and experiment
> disagree both quantitatively and qualitatively. Background: We used
> Al2O3 OSLDs to measure dose in these experiments since the LET of the
> protons is too low to see with plastic detectors.
> Consider also that in Radiat Environ Biophys 46, 107 (2007) a similar
> experiment was performed and compared to results of the PHITS code.
> Here they agree very well. The increase in dose--both in our
> experimental results and theirs--is attributed to secondary protons
> emitted from the target material.
> Why FLUKA is not showing this phenomenon is puzzling.
> Any feedback will be appreciated.
> Joel DeWitt
> Oklahoma State University
Received on Tue Mar 24 2009 - 09:05:11 CET

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