[Gate-users] [SUSPECTED SPAM] Radioactive Decay in Vacuum

[Andreas Bolke]

Dear Gate Community,

during my recent investigations of radioactive decay in Gate I noticed 
something peculiar when simulating Zirconium-89 in vacuum. In order to 
understand how Gate mimics radioactive decay I created two simple setups:
- I have built hollow sphere, attached a Phasespace Actor to it and 
placed a point source at the center. Volume and World are vacuum. I call 
this simulation sim1.
- I have built hollow sphere, built inside that sphere a smaller normal 
sphere made of water, attached a Phasespace Actor to the hollow sphere 
and placed a point source at the center of both spheres (they share the 
same center). I call this simulation sim2.

Looking at the decay scheme and data of Zr-89 [1], one notices that 
99.03 % of all decays end up in emitting a 908.(97) keV gamma. 
Therefore, when simulating e.g. 1800 seconds @ 1 kBec I would expect 
approximately 1.8E+06 gamma particles with the energy 908.(97) keV. 
Given the two setups, I looked at the gamma spectra of both simulations 
and noticed that the setup with the water volume (sim2) would live up to 
my expectations while the setup with only vacuum (sim1) would not. In 
particular the 908.(97) keV counts of sim1 are too little to be 
accounted to statistical fluctuations. They are approximately 60% of the 
amount I get from sim2.

Is this a known bug or is my setup flawed? I have added the .mac-files 
as well as a histogram to the attachment.

Sincerely yours,
Andreas


[1] http://www.nucleide.org/DDEP_WG/Nuclides/Zr-89_tables.pdf

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