Radiation Output Measurement of the Primary Beam of X-Ray Diffraction Units

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

Dear Radsafers:

I wish to solicit the expert advice of any Radsafer knowledgable in the following regard.  Does any Radsafer know of any professional journal articles wherein the authors have actually performed radiation measurements of the primary beam on x-ray diffraction (XRD) units?  I am searching for articles that quote numerical values of radiation intensity of such units, and preferably professional articles that describe the radiation measurement technique, what they used, how they did it, etc.  Perhaps Melissa Woo, who has compiled internet radiation safety guidance for such units, might know of such articles.

My search so far indicates that few such articles exist.  This is not surprising when one considers that measuring the primary beam of XRDs is confounded by at least four complicating factors:

a.  Small  primary beam cross-sectional area, which prevents the full sensitive volume of many detectors from being fully exposed to the primary beam photons;

b.  Low photon energy, which on an XRD operated at even a 'high' x-ray tube kilovoltage of say 45 kVp, yields photons the majority of which are 10 keV or less--a photon energy region where the energy response of TLDs and ion chambers begins to dramatically fall off.

c.  High beam intensity on the order of many thousand R/min, in which case care must be taken to avoid detector saturation problems.

d.  The likely inaccuracy of the inverse square law at such low photon energies due to absorption via the photoelectric effect of the photons in air which implies that it may not be at all accurate to measure the intensity at a long distance and inverse square your way back inward to the point at which you really desire to know the beam intensity.

The American National Standards Institute (ANSI) standard regarding XRDs, ANSI N43.2, Radiation Safety for X-Ray Diffraction and Fluorescence Analysis Equipment, on page 9 quotes an exposure rate figure of 400,000 R/minute at the x-ray tube exit port; however, the literature citation from which this figure allegedly came is in "Radiological Health Data and Reports," Vol. 8, May 1967, pp. 245-249, by Howley and Robbins which is out of print and which I have not been able to locate a of the pertinent pages copy.

Another paper quotes a figure of 36,000 R/sec, but the authors due not specify a reference where this figure came from.  This paper is from the International Tables for X-Ray Crystallography, Vol III, Physical and Chemical Tables, 1968, Chapter 6, Kynoch Press, Birmingham, England.  This 36 kR/sec figure is the largest figure I have ever seen regarding the radiation intensity of XRDs.  Weigensberg et al., in Health Physics (HPJ) 39:237-241 (1980) estimated an XRD primary beam intensity in the range of 16,000 to 27,000 R/min using a 250R Victoreen ionization chamber and the inverse square law.

Two papers by R. Jenkins and D.J. Haas published in X-Ray Spectrometry in 1973, Vol 2 and in 1975, Vol 4 talk about XRDs but with no mention of output measurement values or techniques.  The same can be said for a long article by R. Rudman, "Journal of Chemical Education," Vol 44, Jan 1967, and an article by on "Radiation Hazards Associated with X-Ray Diffraction Techniques," published in Acta Crystallographica, Vol 16, 1963, pp. 324--328, as well as an article by Lubenau, J.O., et al., in the HPJ Vol 16; 739-746, 1969.

The Howley article cited above seems to be frequently referenced as an authoritative source of XRD primary beam output measurement data.  If any Radsafer has a copy of it, could you please FAX it to me.

Presumably, the 'best' way to measure the radiation output of XRDs is via TLDs, but as mentioned above, care would have to be exercised to calibrate the TLDs to the low photon energies involved, given that the TLD energy response curve, for LiF, drops of below about 10 keV.

If any Radsafer can refer me to any professional journal articles that describe the measurement of XRD primary beam intensity, what detectors were used, how they did it, what values they measured, I would sincerely appreciate it.  I suspect that this topic may be of interest to many Radsafers; however, please feel free to reply to me individually at  lee_david_w@lanl.gov

Thank-you.  Best regards,

David W. Lee, PO Box 1663, MS K483, Los Alamos, NM  87545; Ph (505) 667-8085; FAX: (505) 667-9726



David W. Lee
Radiation Protection Policy
& Programs Analysis Group (ESH-12)
Los Alamos National Laboratory
PO Box 1663, MS K483
Los Alamos, NM  87545
Ph:  (505) 667-8085
FAX: (505) 667-9726