# Re: MGDRAW Directional Cosines

From: John Clem <clem_at_bartol.udel.edu>
Date: Thu, 12 Jan 2012 09:57:11 -0500

Hi Vasilis,

Thanks for the suggestion. Not familiar with this structure of FLUKA,
but will experiment with a few test cases. Initially I thought enough
information in TRACKR is available to reconstruct original incoming
direction, but perhaps my knowledge of the track parameters is not
accurate. Please review the summary below.

It is my understanding, the quantities
"DPTRCK(1, j) , DPTRCK(2, j) , DPTRCK(3, j)"
are the components of the momentum loss vector of the jth deposition
track. These components are available in the TRACKR common. Now if I
were to assume "ETRACK" represents the total energy at the end of the
track segment (please verify), the magnitude of the associated momentum
can then determined as
"PTRACK = SQRT (ETRACK^2 - AM(JTRACK)^2)"

The magnitude can be decomposed into individual momentum vector
components using the directional cosines at the track segment end point.
"PTRACKxf = PTRACK* CXTRCK"
"PTRACKyf = PTRACK* CYTRCK"
"PTRACKzf = PTRACK* CZTRCK"

Can I then calculate the momentum components at the start point using
the momentum loss components in the following ??
"PTRACKxi = PTRACK* CXTRCK + DPTRCK(1, j)"
"PTRACKyi = PTRACK* CYTRCK + DPTRCK(2, j)"
"PTRACKzi = PTRACK* CZTRCK + DPTRCK(3, j)"

therefore the directional cosines of the original incoming direction..
"CXTRCKi = PTRACKxi / SQRT ( PTRACKxi^2 + PTRACKyi^2 + PTRACKzi^2)"
"CYTRCKi = PTRACKyi / SQRT ( PTRACKxi^2 + PTRACKyi^2 + PTRACKzi^2)"
"CZTRCKi = PTRACKzi / SQRT ( PTRACKxi^2 + PTRACKyi^2 + PTRACKzi^2)"

Is this correct??

Thanks, John

On 1/12/2012 4:05 AM, Vasilis Vlachoudis wrote:
> Hi John,
> indeed multiple scattering will change the original incoming direction,
> however the original direction is not kept it FLUKA but rather the C[XYZ]TRCK
> contain the direction at the end of the step or for beginning of the next step.
> Therefore I would suggest to store this information for each particle, maybe
> the best place would be the user variables that are carried along each particle
> (SPAREK, ISPARK). You initialize them on the creation of the particle inside
> the routines like STUPRF STUPRE and update them after each step in MGDRAW
>
> Cheers=
> Vasilis Vlachoudis
> Dep EN, CERN=
> CH-1211 GENEVA 23
> SWITZERLAND
>
> Phone: +41-22 767 9851
> GSM: +41-76 487 4378
> Fax: +41-22 766 9644
>

```--
>>  John Clem
>>  Research Associate Professor
>>  Bartol Research Institute
>>  Department of Physics and Astronomy
>>  217 Sharp Lab
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>>  Newark, DE 19716
>>  off 302-831-4354
>>  cell 302-388-1218
```
Received on Thu Jan 12 2012 - 17:22:53 CET

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