[Gate-users] Bremsstrahlung not working properly

thibaultmauxion thibault.mauxion at gmail.com
Mon Jan 20 18:54:56 CET 2014

Hi Chris, 

I know there are (or used to be) discrepancies in beta (plus or minus) spectra for the built-in radionuclides sources (due to the fact that these sources were created for imaging purpose) but not sure it would impact your results. 

However, have a look at this paper, especially section II.A.1. 

The paper mentions an underestimation of photon abundance with energies higher than 500 keV by MC code, as compared to measurements. 
Since we're talking about normalized data, you can also see it as an overestimation of photon abundance for energies lower than 500 keV. I actually happen to have the data in my lab and I noticed a difference of a factor up to 2 for photons around 100-200 keV. 

As far I as know, it is currently recommended to use the measured spectrum. 

Hope this helps. 


Post-doctoral fellow
Division of Medical Imaging Physics 
Johns Hopkins Medical Institutions
JHOC 4260, 601 N. Caroline street, Baltimore, MD, 21287
Tel: +1 410 502 3772
Fax: +1 410 614 1060

On Jan 20, 2014, at 11:50 AM, Christopher Oldfield <christopher.oldfield at manchester.ac.uk> wrote:

> Dear Gate users,
> I have been trying to simulate bremsstrahlung imaging of an electron source but have found that the photon energy spectrum coming out of GATE is noticeably different to the spectrum measured experimentally, primarily at energies below 150 keV.
> This disagreement is found in GATE 6.1 with Geant4.9.3, GATE 6.2 with Geant4.9.5 and the latest version of GATE 7.0 with Geant4.9.6.
> The simulation geometry and physics has been verified with gamma sources and matches experimental measurements well.
> Has anyone else experienced this problem?
> Thanks
> Chris
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> Gate-users at lists.opengatecollaboration.org
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