Re: Operational Technical Question

[tdc@ehssun.lbl.gov]

>RADSAFERs,

>What type of correction factor should be applied (if any) when using
>an ionization chamber who's volume is greater than the incident beam?

>(Drawing shown below)


>Ionization Chamber Detector dimensions (3 1/2" dia X 4" long)
               VVVVV
              -------
              |     |
 _____________|_____|________
 _____________|_____|________ <---Xray Beam (1/2" diameter)
              |     |
            --       --
            |         |
            |         |
            |         |
            |         |
            -----------


End on is better - but to a first order approximation the ratio is simply
the ratio of the exposed to total chamber volumes.  This assumes little
divergence  - but that could be calculated as well - and a small field
gradient - either through inverse square or any other sort of beam
non-uniformity.

If very intense beam - worry about maintaining saturation.

If possibly non uniform - photo image.

Ted de Castro
tdc@ehssun.lbl.gov
University of California Lawrence Berkeley Laboratory
Bldg 75B Rm 112A
Berkeley, CA 94720
(510) 486-5256
(510) 486-5506 - FAX