[ RadSafe ] RE: Ion Chamber Effective Center

alstonchris at netscape.net alstonchris at netscape.net
Thu Feb 24 01:17:08 CET 2005


Robert

I'd think that you'd want to orient the chamber by setting its axis perpendicular to the beam axis (this may be what you mean).  The center of the chamber is usually marked in some way, maybe dots on the exterior of the "can", or an indented ring on some cutie pies.  However, if the chamber is a simple right cylinder, or maybe a rectangular "solid", it shouldn't be hard to measure to the center.  A meter like the Victoreen Panoramic does present a problem; there I would either consult the manual, and mark the build-up cap *very* carefully, in accordance with the dimensions given in the diagrams, or call the manufacturer.  I await the slings and arrows.

Cheers
cja

P.S.  Remember that if you're too close to the source, it becomes difficult to uniformly irradiate the chamber, regardless of the accuracy of your measurements.  I suggest that you consider replacing the source(s).  J.L.Shepard is a good vendor for such a service.




"Robert D Holcomb" <dholcomb at austin.utexas.edu> wrote:
>Hi, does anyone have a quick reference on the calculation for detector effective center, relating to proper distances for calibration.  Our cal source is getting weaker, and it is becoming a potential accuracy issue. My specific application is the typical 3" diam. cylindrical ion chamber, oriented vertically.
>Thanks for your help.
>R. DeWayne Holcomb
>The Univ. of Texas at Austin
>EH&S - Radiation Safety
>(512) 471-2038  Office

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