Re: Flash X-rays

[rkathren@tricity.wsu.edu (ron kathren)]

NOTE:  Integrating ionization chamber devices are likely to be rate
dependent because of recombination effects at the high ionization densities
present during the pulse.  JW Boag has discussed the theory of this effect,
which has been described in many dosimetry textbooks, including Hine and
Brownell, and its successor by Attix Roesch and Tochilin.  TLD and Film seem
to be ok at exposure rates to 10E10 R/s (2.58E6 C/kg-s) or even higher, but
pocket ionization chambers and r-meters may respond an order of magnitude
less at high exposure rates.

Ron Kathren

>>I received a request for information about radiation protection requirements
>>for use with 'flash' x-rays. The gentleman who called said this would use
>>x-ray plses in the MeV range with a duration of less than a microsec per
>>pulse but with enough intensity to produce an exposure of normal density. My
>>reaction was that the requirements would depend on the total radiation
>>exposure (or workload) similar to a normal x-ray device. He said he
>>remembered vaguely from some previous work that such short pulses somehow
>>reduced the need for shielding, perhaps by producing less damage in the cell.
>>
>>Does anyone have any experience with flash x-rays or know of any special
>>protection requirements?
>
>I agree with your reaction.  The relevant quantity is the integrated dose.
>
>The integrated dose may be difficult to measure.  A LANL expert on this is
>David W Lee, internet address lee_david_w@lanl.gov, who says: "Integrating
>instruments are better under these short x-ray pulse duration
>circumstances, such an a Radcal (MDH) Model 9015 with 0.6 cc Baldwin-Farmer
>chamber with appropriate build-up cap. TLD's can also be used in this way
>as integrating instruments."
>
>Mike McNaughton, mcnaught@lanl.gov
>
>Stay safe, mike (mcnaught@LANL.GOV)
>
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