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

[Joel Baumbaugh <baumbaug@nosc.mil>]

Mr. Jo,

	I agree with Ron (who has had more experience that I EVER will in Health
Physics) with "almost" everything he said below - except about using a low
energy ionization chamber (unless that's all you have).  I have surveyed
more than my share of diffraction units from the old XRD-5's up to the
newest now available on the market, and over the years I have found that a
low energy scintillation works better for finding those unwanted "leaks".
Not that the cutie pie is not an excellent instrument for surveying for low
energy x-rays, but a low-energy scintillation probe is smaller (excellent
for getting into those small places that FINGERS need to get into on an
XRD, has a very fast response to changes in field strengths - and - if
connected to a meter that makes noise lets you pay more attention to where
you (your hand) and your probe are at any given minute.  The low energy
scintillation probe will also give you the varying kVp/keV range needed for
the bremsstrahlung and characteristic x-rays (no matter your cathode
composition) mentioned by Ron below.  Now, having said all of that, the
scintillation probe will NOT give you an exposure rate - for that, we're
back to the ionization chamber again... Of course, if you have no leaks,
than you don't HAVE to worry about exposure - as there isn't any.....

	Just my 2 cents...



	Joel Baumbaugh
	baumbaug@nosc.mil

At 07:16 PM 6/5/98 -0500, you wrote:
>Dear Mr. Jo --
>
>The problem might be a little more complex than you might think.  There will
>also be bremsstrahlung as well as characteristic x-rays, and the effective
>energy of any leakage radiation may well be somewhat higher than the 8 keV
>characteristic from Cu, particularly if there is any filtration by the tube
>housing.  In any case, the same instrument should serve -- a good low energy
>ionization chamber (ie cutie pie) should do the job; several companies,
>including Victoreen and Eberline to name 2, make CP's that can do the job.
>Remember, diffraction units put out a very small (ie 'pencil') beam with
>extremely high intensity, and the beam does not come out parallel to the
>floor but is angled slightly downward.  Because of the high intensity, be
>extra cautious around the beam port; I've seen several cases of skin burns
>from 8 keV diffraction units in my career, and the older units are not
>equipped with the same level of safety interlocks as are common on modern
units.
>
>Good luck with your measurements.
>
>Ron Kathren, CHP
>
>  
>
> .  At 05:24 PM 6/5/98 -0500, Mr Jo wrote:
>>We have an old but recently assembled  (parts from a number of
non-operational
>>units) x-ray defraction unit which produce 8 kev x-rays from copper anode.
>The x-ray
>>unit looks pretty good and tight as far as leakage and beam enclosure is
>concerned.
>>I used a pan-cake GM to survey for leakage because I did not have
>anythingelse.  I
>>would like to know what is commercially available to measure
>>8 kev x-ray. Thank you and have a good weekend. M. Jo
>>========================================================
>>Myung Chul Jo, RSO
>>EH&S, Mail Stop 328
>>University of Nevada, Reno
>>Reno, Nevada 89557
>>(702)784-4540
>>(702)784-4553 fax
>>
>>
>>
>
>
>