[Halld-tagger] Photon flux calibration

[Eugene Chudakov]

Hi,

The yesterday's discussion on the photon flux calibration did not
convince me that one desperately needs a 1nA current.

One needs to measure the ratio of the pair spectrometer rate to the
total absorption counter rate (for a given energy bin in the tagger).
This ratio should not be very sensitive to the type of the
radiator. Both detectors see the same photon beam. So, instead of
using a 1nA beam current run one may use a thin radiator or a scanning
wire with a 50nA run. I suppose it is easy to simulate the acceptance
of the pair spectrometer to find out what would be the dependence on
reasonable shifts in the beam spot profile (say, a 20% variation of
the radiator thickness across the beam).  One should also keep in mind
that a low current beam might have a different profile with respect to
the full current beam, so this kind of uncertainty always exists.

Eugene


On Mon, 9 Jul 2012, Richard Jones wrote:

> Hello,
>
> Please remember our biweekly working group meeting this morning at 11:30EST. 
> The draft agenda is posted in the usual place.  Please install links in the 
> agenda page to any materials that you will be presenting.
>
> -Richard J.
>
>