just a comment on low efficiency at high photon energy
On Wed, 17 Sep 1997, Elton Smith wrote:
>
> Also, the "low" efficiency measured at high photon energy (low T-counter
> numbers) is indeed probably due to Moller electrons. See J. Arends et. al. NIM 201
> (1982) p. 361 (especially Figure 4.)
>
> Elton.
the Moller contribution can be evaluated by MC and experimentally
verified by comparing the efficiency behavior at different primary
beam energy or with different radiator being the total cross section
ratio for the Moller and the Bremsstrahlung processes :
Moll/Brem \sim Z/A Xo/Eo
i.e. for a 4 GeV beam and an Al radiator the effect is about
4 time less than for a 2 GeV beam and a C radiator.
For a 2 GeV beam and a carbon radiator I would roughly expect
a 20% effect on counter which tag photons of 0.95Eo and
only a 5% effect on counter which tag photons of 0.9Eo,
due to the strong energy dependence of the Moller cross section.
Regards
Nicola Bianchi