[Gate-users] Cannot get characteristic photons, gamma-rays from Gadolinium/Boron neutron cross section.

[Andreas Resch]

Am 2017-12-21 02:26, schrieb Kurt V:
> Kurt V has shared a OneDrive file with you. To view it, click the
> link below.
> 
>  [1]
>  ExProtonGateForum.mac [1] 		
> 
> Yes, the process requires a significant neutron fluence but, suppose I
> change the proton beam to a neutron beam that is heavily weighted to
> lower energies.
> 
> I aim the neutron beam on a Gadolinium based phantom. I still do not
> receive the prompt gamma rays and characteristic x-rays that should be
> represented from the interactions.
> 
> Gadolinium has an enormous cross section for thermal neutrons
> approximately 48890 barns. Soft tissue is approximately 0.1 b.
> 
> The main spectral signature for Gd neutron capture reactions for
> X-rays at 43 keV (Gd Ka) and 49 keV (Gd Kb), and gamma-rays at 79.5
> keV and 181.9 keV.
> 
> Either a proton beam or especially a neutron beam on Gadolinium should
> produce photons with these spectral energies.
> 
> I am using around 1 million particles incident on a Gd Phantom with a
> NaI detector.
> 
> I have tried these physics builders: QGSP_BIC_HP, QGSP_BERT_HP,
> FTFP_BERT_HP. I have seen no capture reactions as a result.
> 
> _I AM STARTING TO WONDER IF I DO NEED AN ENTIRE MODIFIED PHYSICS
> LIST._
> 
> _ALSO, THE MODIFIED PHYSICS LIST MIGHT REQUIRE VERY SPECIFIC PHYSICS
> MODELS FOR THIS TO WORK._
> 
> _I.E. PROTONS -> NEUTRON FLUENCE -> THERMAL N + GD CAPTURE REACTION ->
> GAMMA-RAYS + CHARACTERISTIC PHOTONS._
> 
> I am using the EnergySpectrumActor and can measure counts as a
> function of energy seen at the NaI detector. The only problem is that
> I am not seeing a representation of those neutron capture reaction
> energies measured at the detector. They should be clearly defined.
> 
> _THE PRIMARY PROBLEM IS NOT SEEING THESE CAPTURE REACTIONS. _
> 
> I’ll post an example of my macro, to provide greater insight.
> 
> As always, thank you for all the help, and all suggestions are greatly
> appreciated.
> 
> Thank you,
> 
> Kurt Van Delinder
> 
> 
> Links:
> ------
> [1] https://1drv.ms/u/s!Ao5xa2lc-7bTiRM7kQ3UAWWDKUU_
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Hi Kurt,

I guess to solve your problem you have to find out whether your photons 
are not produced because of physics settings or some mistake or if you 
do not detect them
a) use a phase space actor (maybe there is a problem in the energy 
spectr actor? can you add two particle filters like in lines 112 and 
114? )
b) use 360 degrees for detection to increase statistics
c) you could try a high energetic monoenergetic proton beam rather than 
a SOBP with low energies. Or even use a neutron beam (if possible)
d) do you need to track e- and e+ ? if not you can significantly speed 
up your simulations by using a high one (e.g. 10 cm)



cheers,
andreas

MEDICAL UNIVERSITY OF VIENNA
Department of Radiotherapy
Christian Doppler Laboratory for Medical Radiation Physics for Radiation
Oncology