From: Chris Theis (Christian.Theis@cern.ch)
Date: Wed May 16 2007 - 16:11:14 CEST
Hello Adolf,
you're on the right track, but there are a couple of trick issues that you should be aware of. USRDUMP will produce what the FLUKA manual calls a collision tape and chapter 11 of the manual describes in more detail which information is contained. However, from your description I assume that the default implementation will not fulfill your needs and you will need to modify the existing code in MGDRAW.f. This is the routine which is called when a USRDUMP card is present in the input. Chapter 11 gives a detailed description of the available variables and examples on how to dump the information (I think there should also be a description on the web-course that can be found on the FLUKA web-page). Thus, you can implement to dump only those particles that are interesting for you, but you must be extremely careful not to forget something!! Whatever you miss here will not be present in the second step of your calculation and thus, you basically interfere with the physical reality. T!
herefore, I strongly recommend to carefully test your routines and cross-check the agreement by performing calculations in one step and in two steps for the same problem set.
In the second step you will have to implement a source routine (look for source.f in the manual) that loads the information from the file and starts the respective particles. And here is another pitfall that you have to consider and this is the normalization. In the second step you have to make sure that the total weight that is used for normalization is the total primary weight from the first step because otherwise your results will be normalized incorrectly. For example in the first step you have 10 primary particles with a total weight of 10, which produce an output of 100 secondary particles that you write into your file. In the second step you will have to use the total primary weight of 10 for the correct normalization because if you had done the calculation in one step your results would have been normalized per primary unit weight!
As you can see there are a couple of quite subtle issues connected to what you want to do. Thus, I really recommend to carefully test your routines by comparing the results of simple calculations that were performed in one step to those that were performed in two steps.
Best regards
Chris
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Chris Theis
CERN/SC-RP - European Organization for Nuclear Research
1211 Geneva 23, Switzerland
Phone: +41 22 767 8069 Office: 892-2A-015
e-mail: Christian.Theis@cern.ch www: http://www.cern.ch/theis
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> -----Original Message-----
> From: owner-fluka-discuss@mi.infn.it [mailto:owner-fluka-
> discuss@mi.infn.it] On Behalf Of Adolf Nordin
> Sent: Wednesday, May 16, 2007 11:17 AM
> To: fluka-discuss@fluka.org
> Subject: USERDUMP Help
>
> Hallo everyone
>
> I've been using Fluka for two years now simulating an accelerator for
> various things, from generating percentage depth dose curves to bunker
> shielding. My results compare well with measured data, however, there
> is still one thing that I can't do and will appreciate help on this
> topic.
>
> I would like to create a “phase space file” under the flattening filter
> of my accelerator. That way I don't have to simulate the production of
> x-rays in the target every time I change the field size but use the
> “phase space file” as a source input. As far as I understand USERDUMP
> is used for this. So my questions are:
>
> 1. Can USERDUMP be used to create a “phase space file”?
> 2. If so, how is the position where the USERDUMP file must be
> created defined because I can't find anything about it in the manual (I
> might have missed it)? Using USERDUMP, as far as I understand, all
> particles in all directions will be dumped into the file and I would
> like only particles going into a certain direction to be dumped into
> the file.
> 3. If this USERDUMP file has been generated, how does one use it in
> other simulations as the source input?
>
> As mentioned I want to create a “phase space file” under the flattening
> filter which is a known distance under the target (target at z = 0).
>
> Any help regarding this will be appreciated.
>
> Adolf
>
>
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