[Gate-users] Help on simulating x-ray tube[Paul Betteridge]

[Emmanuel Marfo]

________________________________
From: Paul Betteridge <paul.betteridge at adaptiximaging.com>
Sent: Saturday, 10 June 2017 3:40 a.m.
To: Emmanuel Marfo
Subject: Re: [Gate-users] Help on simulating x-ray tube

Dear Emmanuel,

> Please, it appears the problem is coming from my tungsten(anode). I
> change the anode to copper and I had photons coming out of it. I think
> my problem has been the tungsten. Please is there any possible solution
> to these or Is there a way I can get photons from the tungsten.

Yes, I think your problem is, to some degree, because of the tungsten;
because tungsten is such a good absorber of x rays.

I ran your script with 1e5 primaries, and it produced a small number of
photons - as in the attached image.

I think the problem is this: Gate uses "cuts" as a way to speed up
simulations (by removing low energy particles that are not actually
going to be 'useful'.) See:
http://wiki.opengatecollaboration.org/index.php/Users_Guide_V8.0:Cut_and_Variance_Reduction_Technics
Users Guide V8.0:Cut and Variance Reduction Technics ...<http://wiki.opengatecollaboration.org/index.php/Users_Guide_V8.0:Cut_and_Variance_Reduction_Technics>
wiki.opengatecollaboration.org
Production threshold, step limiter and special cuts Production threshold. To avoid infrared divergence, charged particles processes (ionization and bremsstrahlung ...




Partly because of the way they are specified, and partly because of the
rather effective absorption of photons by tungsten, your simulation was
set up to only produce photons with an energy greater than about 106
keV. There are not many of these.

You can check the cuts applied by adding

/gate/physics/displayCuts

I recommend this for every simulation, just so you can check what is
happening.

If you add a line like this:

/gate/physics/Gamma/SetCutInRegion anode 10 um

after the physics setup, you should find that the energy limit is much
reduced. I've attached my modified script for you to compare.

Specifying the cut energy using a length isn't that convenient for the
type of simulation you are trying to do. It can make a significant
difference to the time a simulation takes to run though, so it is
worthwhile trying to establish a sensible value.

I am still a bit concerned about you electron source, which seems to
spread electrons over a wide volume. I don't suppose the real device is
like that.

Don't forget that it is better to keep all messages on the mailing list,
because (a) other people may be able to help (b) other people may find
the correspondence useful.

Best wishes

Paul

--
Paul Betteridge
Adaptix Imaging
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.opengatecollaboration.org/mailman/private/gate-users/attachments/20170609/8a192ff5/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: tungsten_target_1e5_e-.png
Type: image/png
Size: 43311 bytes
Desc: tungsten_target_1e5_e-.png
URL: <http://lists.opengatecollaboration.org/mailman/private/gate-users/attachments/20170609/8a192ff5/attachment-0001.png>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: test2_modified.mac
URL: <http://lists.opengatecollaboration.org/mailman/private/gate-users/attachments/20170609/8a192ff5/attachment-0001.ksh>