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None Question about BRBias 

Forum: Run Management
Date: 22 Oct, 2007
From: Kareem Kazkaz <>

Hello everyone.

I have a question about using BRBias from the G4 Radioactive Decay Manager (the /grdm/brbias
command). From the G4RDM documentation, here is the description of the command:

     If true probability of sampling each branching ratios will be equal.  If false, the probability
     will be made proportional to the branching ratio.

If I want to obtain accurate gamma ratios out of the G4RDM, I figured I needed to set brbias to
false. I then ran a quick simulation to determine the average gamma multiplicity from both
Co-60 and Tl-208. Co-60 should have a gamma multiplicity very close to 2 (by analyzing the
branching ratio of an entire gamma chain, we get 2*0.9988 + 1*0.0012 = 1.9988), whereas
Tl-208 should have a gamma multiplicity of about 2.35 ( = 2*0.64 + 3*0.34).

With brbias set to false, the gamma multiplicities I obtained were 1.50 and 2.95 for Co-60 and
Tl-208, respectively. With brbias set to true, the ratios were 1.9989 and 2.37...much, much
closer to what I was expecting.

So the brbias flag seems to work opposite from what the documentation says...By the
measure of gamma multiplicities, if I want correct gamma ratios I actually need to set the
brbias to true.

Here's my question: Is this a bug? Is the documentation incorrect? Or am I using brbias

Thank you for any help you might be able to give.

Kareem Kazkaz

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1 None: Re: Question about BRBias   (Kareem Kazkaz - 22 Oct, 2007)
(_ None: Re: Question about BRBias   (Fan Lei - 06 Nov, 2007)
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