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Forum: Event and Track Management
Re: Question Redirecting the Electrons from a Beta Decay
Re: None Re: Redirecting the Electrons from a Beta Decay (Vladimir IVANTCHENKO )
Date: 09 Aug, 2006
From: Giovanni Santin <Giovanni Santin>

User Vladimir IVANTCHENKO wrote:

>> On Mon, 7 Aug 2006 wrote:
>> > *** Discussion title: Event and Track Management
>> > Email replies to must include:
>> >   In-Reply-To: <"/eventtrackmanage/527">
>> >   Subject: ...change this to be about your reply.
>> > 
>> >  Dear geant4 experts,
>> > 
>> > I need to change the momentum direction of e- particles which are being
>> > emmited randomly from radioactive decay of a stationary source. The
>> > reason to do this is to investigate the energy deposit of e- particles
>> > in a specific detector which is placed along the z-axis. As I read in
>> > some of the previous threads, this is possible by defining a new
>> > process. I was just wondering what that means exactly, and if someone
>> > can show me an example of how to do this.
>> > 
>> >  Thanks in advance,
>> >  Best regards,
>> >  Maryam
>> > 
>> > 
>> Hello,
>> It may be optimal to create your own primary generator or to use GPS 
>> generator with predefine spectrum and angular distribution.
>> VI


This is true for simple beta dacays, but in cases such as Sr90 there is the extra issue of the decay chain, with Y90 decays following the first Sr90 beta emission. This adds some complication in a specific description of the Sr90 source in GPS or in a C++ class.

If the source is in equilibrium, one can model separately the 2 beta sources with GPS (GPS can model multiple parallel sources with different intensities). The disadvantage is that you are not able to reproduce the correct timing and correlation of the electrons (and corresponding Bremsstrahlung emissions) but maybe this is not relevant to your application.

Also, I would be careful in general in limiting the emission angle or redirecting the e-, because of the electron scattering: Sr isotopes are not held in vacuum, so not all e- leaving the source in the "right" direction will reach your sensitive volume, and not all the e- leaving in the "wrong" direction will miss it.

Because of all these issues, I personally tend to accept a (reasonable) CPU inefficiency to avoid introducing unexpected / unwanted / unknown biasing in the results.

Best regards,


 Giovanni Santin
 Space Environments and Effects Analysis
 Keplerlaan 1, 2200 AG Noordwijk, Netherlands
 Tel: +31 71 565 6267
 Fax: +31 71 565 4999

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