[mcstas-users] Question please

Peter Kjær Willendrup pkwi at fysik.dtu.dk
Wed Mar 14 10:18:17 CET 2018

Hello Mahmoud,

Find my comments and answers below.

On 14 Mar 2018, at 06:16 , Mahmoud Yaseen Suaifan <mahma7 at gmail.com<mailto:mahma7 at gmail.com>> wrote:

Sorry i'm just forwarding the below email as a gentle reminder and since my first email (to mcstas-support) was not sent due to (delivery failure issues).

Thanks for reminding me, I have silently removed the mcstas-support at mcstas.org<mailto:mcstas-support at mcstas.org> address, I much prefer to have users ask their questions here in the open forum. :-)

Actually, i'm a Jordanian graduate student in South Korea trying to make a conceptual design for a neutron imaging facility using McStas simulations. So i got some questions please like the one attached in the photo regarding the source component. Please your help & explanations are highly appreciated.
The numbers in the photo are exact. Neck dimensions ( assume 10 cm × 10 cm). How can i decide where is target & focus & dist. I understand ray trace. I understand solid angle & divergance. I understand Flux, intensities units. I got lost because i couldn't find explanation for results.

The logic is that you specify the illuminated solid angle (~divergence out of the source) either by

1) dist in combination with focus_xw, focus_yh (A small rectangle of size focus_xw x focus_yh will be placed at (0, 0, dist) wrt the source)

2) target_index=N in combination with focus_xw, focus_yh (A small rectangle of size focus_xw x focus_yh will be placed at (tx, ty, tz) wrt the source, where tx,ty,tz is coordinates of a component N positions "further down the instrument"

( Attached also part of simple McStas script (source & detector only) please check it.

I found no .instr example attached to your email, but there are many too look at within the examples/ folder of your McStas installation.

Now, to get properly started on McStas, I propose you to e.g.

0) Try the simple SANS oriented tutorial available here:

1) Read chapter 3 of the McStas user manual, available here:
http://mcstas.org/documentation/manual/mcstas-2.4.1-manual.pdf and by running mcdoc.pl -m on your own system

2) There are a couple of older sets of “school” material available on the web, e.g.
http://nobugs2016.mcstas.org and http://april2017.mcstas.org that you can try following

Also, there was an email from Georg Ehlers (SNS) <ehlersg at ornl.gov<mailto:ehlersg at ornl.gov>> requesting people to indicate if they would be interested in a McStas school later this year in Oak Ridge - see  https://mailman2.mcstas.org//pipermail/mcstas-users/2018q1/001234.html

Best regards,


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