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

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

>>  Does Keithley make a CT pencil type detector with a long cable?  I 
>>remember
>>  using a RADCAL 1015 with a CT probe taped vertically in front of the
>>  film cassette plate, with enough play in the cable to prevent the
>>  probe from being torn loose during rotation.  

I wouldn't tape that probe to the film plate for 3 reasons:

1:  I THINK it is 1 cm in dia - thus too large.

2:  It is a Bragg Gray chamber meant to be in equilibrium within the 
    appropriate phantom.  NOT free in air or against metal.

3:  Against the film plate is NOT the appropriate position for ENTRANCE 
    exposure.

Besides - what would be the point of measureing the full integrated R for 
the full orbit??  That would really be the DOSE!  It WOULD be the entrance 
exposure - BUT the insult is not all to the same tissue - thus one would 
have to carefully consider the meaning - if any - of the measurement!

The "dwell time" on a given element of tissue is very important - and that 
would be evaluated at point of entrance exposure.

In real world - it would be an info only measurement since Panoramic units 
seem to have little latitude in exposure parameters - so the exposure really 
shoudln't change too much over the life of the unit........ I would expect.

Anyone have experience to the contrary on this last point??