Re: Keithley chambers for equip. performance evaluations of Panorex units

[tdc@ehssun.lbl.gov (Ted M. de Castro)]

>>Can anyone on RADSAFE recommend a suitable Keithley chamber for equipment
>>performance evaluations of Panorex dental units?  Specifically, the 
>>Panorex  units of interest have a vertical fan beam 1/4 inch wide that 
>>rotate about a central axis.  Certainly, the requirement for meeting 
>>detector charged particle  equilibrium would be a major criterion for such 
>>a beam.  Any suggestions?

Well you COULD use the 0.6 cc Farmer probe - but that is both expensive and 
insensitive.

But let's just be practical - here is what I usually do:

FIRST remove the slit collimator!  After all R is R!  Then I use the 15 cc 
probe.

ALSO - if possible - I render the unit unable to rotate.  When this is 
possible the unit will STILL go through its cycle and you won't have to have 
you probe orbit about with the film holder.

This method works pretty well.

ANOTHER METHOD:

Time the exposure in panoramic mode and note the current.

remove the slit and measure the output in cephlometric mode at the same 
current OR establish mR/mAs linearity and calculate.

Either method will give an acceptably accurate answer and are a practical 
means of making the measurement with good sensitivity and convenience.

In all cases but one I was able to easily accomplish this - in ONE case I 
had to use whatever at hand to raise the tube carrier just a bit so its 
drive wheel would spin free and thus not orbit.

I really don't think using a very small probe (low sensitivity) and trying 
to locate - and remain - within the slit is very practical - that beam has 
quite a penumbra! - making hard to locate the TRUE beam area.

Regardless of officialdom or agencies may say - I beleive these methods to 
be completely technically defensible.