Re: Problem with the stopping power of polyethylene

From: Alberto Fasso' <fasso_at_slac.stanford.edu>
Date: Sat, 9 Jan 2010 06:57:11 -0800 (PST)

Oooops, that was really a stupid mistake of mine.
But why did it work before? (I just checked my old inputs and outputs).
Thanks for the correction

Alberto

On Sat, 9 Jan 2010, Alfredo Ferrari wrote:

> 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)
>>
>>
>

-- 
Alberto Fasso`
SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
Phone: (1 650) 926 4762   Fax: (1 650) 926 3569
fasso_at_slac.stanford.edu
Received on Sun Jan 10 2010 - 22:42:55 CET

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