Re: Operational Technical Question

["Gerald Falo"<gerald_falo_at_chppm7__apgea@chppm-ccmail.apgea.army.mil>]

     Tad,
     
     It seems to me that you would have to estimate the fraction of the 
     effective detector volume that is irradiated.  Then divide the 
     detector's output by that fraction.
     
     The volume used in the calibration of the detector is the effective volume 
of the chamber.  Assuming that the physical volume is about the effective volume
seems reasonable as a first estimate.  So the ionization measured by the 
detector is divided by the volume of the detector to give roentgens.  However, 
in your case, only part of the detector volume is irradiate; thus, only that 
volume that contributes to the ionization should be used.

     I that this helps.


Jerry Falo
jer3ry@aol.com

This is my humble opinion dashed off quickly and I disavow any knowledge of it. 
;-)

______________________________ Reply Separator _________________________________
Subject: Operational Technical Question 
Author:  <radsafe@romulus.ehs.uiuc.edu > at internet-mail
Date:    3/11/98 10:46 AM


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)
              |     |
            --       --
            |         |
            |         |
            |         |
            |         |
            -----------
     
     
************************** /^\   /^\ *********************************** 
Tad  Blanchard            /__ \ /___\   NASA-Goddard Space Flight Center 
Nat'l Health Svc, Inc          O         Code 205.9, Greenbelt, MD 20771 
Sr Health Physics Tech        / \                    Phone: 301-286-9157 
Assistant RSO                /___\                   Fax:   301-286-1618
                 mailto:Tad.M.Blanchard.1@GSFC.NASA.gov
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