Re: Problem with the stopping power of polyethylene

From: Alfredo Ferrari <alfredo.ferrari_at_cern.ch>
Date: Sat, 9 Jan 2010 14:49:06 +0100

Dear Alberto

the bug is the input, I don't believe it ever worked!!

the Polyethylene definition you use, has the density of H and C swapped,
indeed you use:

* C H
MATERIAL 0.0 0.0 0.94 36.0 0.0POLY
COMPOUND -0.143711 CARBON -0.856289 HYDROGEN 0.0 POLY

while it should be

* C H
MATERIAL 0.0 0.0 0.94 36.0 0.0POLY
COMPOUND -0.143711 HYDROGEN -0.856289 CARBON 0.0 POLY

of course since it is a (CH2)n polymer.....

Why the general Sternheimer-Peierls formula gets crazy for a compound
which is almost fully H with "impossible" density (liquid hydrogen is
well below 1) I don't know, but clearly it is related to the "impossible"
compound. Swapping H with C it works nicely and it gives:

    ***** Sternheimer density effect parameters:
*****
    ***** X0 = 0.2000, X1 = 2.0000, C = -2.9707, A = 0.3514 m =
3.0000 D0 = 0.0000 *****

which are ok

                     Ciao
                    Alfredo

+----------------------------------------------------------------------+
| Alfredo Ferrari || Tel.: +41.22.76.76119 |
| CERN-EN/STI || Fax.: +41.22.76.69474 |
| 1211 Geneva 23 || e-mail: Alfredo.Ferrari_at_cern.ch |
| Switzerland || |
+----------------------------------------------------------------------+

On Fri, 8 Jan 2010, Alberto Fasso' wrote:

> It seems that a bug has been introduced in FLUKA. The input attached
> was working until a short time ago (with a few trivial changes that
> do not concern materials).
> The log file says: Floating exception.
> The .out and the .err file report a number of error messages such as:
> *** dp/dx:d,imat,ztar,ij,po,eo -0.00108121724 36 1.06943913 1 1.51030313
> 1.77802432 ***
> *** x,xoster,ccster,d0ster 0.206735223 0.2 -0.556058849 0. ***
>
> The material to which the messages refer (imat=36) is POLY, defined as
> follows:
> MATERIAL 0.0 0.0 0.94 36.0 0.0POLY
> COMPOUND -0.143711 CARBON -0.856289 HYDROGEN 0.0 POLY
> This definition was working in the past. Trying to run again the old
> input gives now the same error message.
>
> Looking into the source code, it appears that the message is sent when the
> "d" variable is negative (-0.00108121724 in the example shown above).
>
> In the .out file, it can be seen that the Sternheimer parameters of POLY have
> problems:
> ***** dp/dx : material number 36 "POLY " *****
>
> ***** Average excitation energy : 2.1479E+01 eV, weighted Z/A : 9.2137E-01
> ****
> *
> ***** Sternheimer density effect parameters: ****
> *
> ***** X0 = 0.2000, X1 = 2.0000, C = -0.5561, A = ******** m =
> -22.4849 D0 = 0.0000 ****
>
> The value of A ( -0.0626 in a past run without error) has been replaced
> by a string of asterisks, and that of m (3.0000 in the past) is now
> -22.4849.
>
> Can somebody please find out what has been changed in the code and fix it?
>
> Alberto
> and Kelly (Qiu Rui, SLAC RP)
>
>
Received on Sat Jan 09 2010 - 15:28:11 CET

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