Re: Positron fluence

Dear Prasanta,
Your consideration is not exact:
if you have a gamma of energy E0 which then undergoes a pair-production
process, the distribution of kinetic energy of the positron (or of
the electron) ranges from 0 to (E0 - 2*me), while (E0 - 2*me)/2 is the
average kin. energy of the positron (or of the electron). In other words,
the sum of kinetic energy of e+ and e- is E0 - 2*me and each member
of the pair access the whole range (and the other is of course balancing
the first).
Now, if you have an electron beam of 2.5 GeV, you can really produce
a photon of energy close to the electron one which then can produce a
positron (of course the probability is small) up to the maximum value.

We have not your input file, but we made the exercise of sending
electrons of 2.5 GeV onto a lead target (of course the thickness is
surely different from yours) and the correct resulting
spectrum of gamma, e- and e+ resulting after the target
is attached to this mail. You should get a similar result.

Best regards

        Anna Ferrari & Giuseppe Battistoni

On Wed, 18 Jun 2008 pksahani@cat.ernet.in wrote:

> Dear Fluka Users,
> I am a new FLUKA user.I used very simple geometry to calculate the
> electron ,photon and positron fluence after a lead target.I incident
> 2.5GeV electron pencil beam on lead target and by using the USRBDX
> card i score the fluence after the target. I got very nice spectra
> for e- and photon from 0 to Maximum (2.5GeV) as expected . But the
> e+ spectrum also shows a distribution from 0 to 2.5GeV. But i think
> the positron production is only through pair production , if so then
> it must go from 0 to 1.25GeV[(2.5GeV-1.02MeV)/2 ]. Then how in FLUKA
> simulation I got the spectrum upto 2.5GeV.
> So please help me in this regard.
>
> Thank You
>
> With Regards
> Prasanta Kumar Sahani
> Scientific Officer-C
> Raja Ramanna Centre for Advanced Technology
> Indore-452013
> INDIA
>