X-ray dose

[D J Hornsey <bssdjh@bath.ac.uk>]

  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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