RE: X-ray dose

["Feldman, Gerald" <gfeldman@msx.ndc.mc.uci.edu>]

In addition to the confounding factors already mentioned in other postings,
if the tube is old or has been abused, material from the anode may have been
sputtered off onto the tube window.  This added filtration will reduce the
proportion of low energy x-rays, and the resulting "hardened" beam will give
a lower output.

Hope this helps.

Gerald Feldman, M.S.
Radiation Safety Officer
University of California, Irvine Medical Center
Orange, California
gfeldman@uci.edu  

-----Original Message-----
From: D J Hornsey [mailto:bssdjh@bath.ac.uk]
Sent: Thursday, September 23, 1999 4:31 AM
To: Multiple recipients of list
Subject: X-ray dose



  Dear Radsafers,
              I wonder if some of you could suggest an explanation for the
following problem I have. It concerns the considerable differences I am
finding between the  expected and measured dose in the main beam of an
X-ray source.
              The tube is running at 60 kV with a tube current of 3 mA.
The filtration is 1 mm Be. According to my calculations, at 17cm from
the window, the dose should be 170 cGy (170 rads) for a 10 sec exposure.
A TLD in the main beam consistently records a factor of about 10x less
i.e. 140 mGy (14 rads). A series of measurements under different
conditions reproduces this factor of a 10x inconsistency. Would this be
expected? Should I not be using a TLD for this type of measurement and if
not, what should I be using?
     Any suggestions will be most welcome.

                 David Hornsey


        

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