Re: Low energy x-ray (8 kev) survey meter

[Joel Baumbaugh <baumbaug@nosc.mil>]

	Ted,

	At 8 kev, you have "LESS" than 0.01% efficiency with a G.M. (pancake, even less with a end-window), but are exceeding 10% efficiency with a low energy scintillation probe!  With an end-window G.M., you may as well be using florescent paper in a darkened room!  You are missing a LOT of photons there my friend!  I wonder if you have ever done a survey and compared the two - I think not... Sure I use a pancake G.M. too initially, to look for the big leaks, but when I am through, I always go back and do another survey and look more carefully with a scintillation probe - that extra 5 - 10 minutes is WELL worth it as far as detecting scattering angles (leaks) no-one would have imagined before hand...  As you, Ron and I all mentioned in our posts, the idea is not to measure the "dose" (rate), but to find and eliminate unwanted leaks (ALARA).  Why limit yourself to a G.M. or a ion chamber whose response and efficiency are orders of magnitude less than a scintillation probe????  

	Another 2 cents,

	Joel Baumbaugh
	baumbaug@nosc.mil


At 07:11 PM 6/9/98 -0500, you wrote:
>Let me chime in on this one.
>
>I read the two previous responses and agree with Ron that an ION chamber
>would be the best to MEASURE with BUT there are serious geometry
>considerations that make accurate measurements non-trivial - to say the
>least.
>
>I disagree with the use of a low energy scintilattor to MEASURE these beams
>since their energy is on the steep shoulder of the instruments' response.
>Since such and instrument is so energy dependant - in order to MEASURE the
>x-ray dose - your would need to know the x-ray spectrum - which is a
>daunting task - at least.
>
>I would also restate Ron's caution that the characteristic radiation is NOT
>the energy of MOST concern to the HP - but the bemstraulung continum.
>
>But - I would suggest that there is not need to MEASURE these radiations -
>but merely to DETECT them.  I feel the best policy is to detect them and
>then eliminate tham when found - since this is so easy to do.  This leaves
>nothing left to MEASURE.
>
>For detection - I find a pancake GM plenty sensitive enough and allows a
>quick survey.  IF we allowed open beam x-ray units (which we DO NOT) then I
>might use an end window GM for closer work - but areas harder than that to
>get into are not likely to accessible to personel either.
>
>I seldom find any good reason to attempt to measure the primary beam - ONLY
>in accident reconstruction.  This is another process that requires great
>care and consideration.
>
>Ted de Castro
>X-Ray Safety Officer
>tdc@ehssun.lbl.gov University of California Lawrence
>Berkeley Laboratory Bldg 75B Rm 112A Berkeley, CA 94720 (510) 486-5256
>(510) 486-5506 - FAX
>
>
>

Joel T. Baumbaugh, MPH, MHP
baumbaug@nosc.mil
Radiation Safety Officer
SSC San Diego, CA


	NOTE:	The contents of this message have not been reviewed, nor approved by the Federal Government, the U.S. Navy, my bosses or my wife... My wife keeps complaining I never listen to her...or something like that.



	If we are what we eat; I guess I'm cheap, fast, and easy.