Re: Operational Technical Question

["David W. Lee" <lee_david_w@lanl.gov>]

Tad:  

See the Appendix in ANSI N43.3 (NBS Handbook 111), Revised 1977, "Radiation Safety for X-Ray Diffraction and Fluorescence Analysis Equipment."  Suffice it to say that the accuracy of any correction factor you generate critically hinges upon your knowing the precise diameter of the x-ray beam that traverses the ion chamber sensitive volume, and assumes that the x-ray beam does not diverge as it traverses the sensitive volume.  Measuring the x-ray beam diameter, by film, fluorescent screen, etc., is sometimes more difficult than finding yourself another appropriate radiation detector (TLD??) whose sensitive volume is fully irradiated by the incoming x-ray beam.  Rather than generate a correction factor geometrically, you could fully irradiate a TLD and then place your ion chamber in the beam in the same geometry and compare the two different readings.  Then the ion chamber reading correction factor would be the response corrected/temp/pressure corrected of the TLD divided by the energy and temp/pressure corrected reading of the ion chamber.  REGARDS  David



At 10:48 AM 11-03-98 -0600, you wrote:
>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
>        http://panza.gsfc.nasa.gov/205/205-2/Health/RADPROT.HTM
>
>************************************************************************
>
>


David W. Lee
Los Alamos National Laboratory
Radiation Protection Services Group (ESH-12)
PO Box 1663, MS K483
Los Alamos, NM  87545
PH:   (505) 667-8085
FAX:  (505) 667-9726
lee_david_w@lanl.gov