Re: x-ray calibrations

[mcnaught@lanl.gov (Mike McNaughton)]

>On the subject of calibrating survey equipment for analytical x-ray
>machines:
>
>>  could you specify what type of analytical equipment, such an electron
>> microscope?
>
>Unfortunately, both electron microscopes and x-ray diffraction units.
>Double-unfortunately, as we are a research university, current/voltage/target
>material in the XRDs is quite varied.  Triple-unfortunately, I also have
>amusing things such as accelerators, experimental fusion devices and the
>like to survey around. :-)  However, for the purposes of the question of
>calibration appropriateness, let's say the equipment consists of EMs and
>XRDs.  The XRDs are for the most part in interlocked, shielded enclosures.

A committee of x-ray "experts" met at Livermore last month and concluded:

A thin walled GM detector should be used to detect leakage.

An ion chamber should be used to measure dose rates.

At Los Alamos, we use ion chambers calibrated with Cs-137 to measure
leakage dose rates, and integrating ion chambers calibrated according to
NIST x-ray protocol to measure the main beam.  But I wonder if we are
making this more complicated than we need to.

As I understand it, a concern is that ion chambers show a decreased
response to lower energy photons (below 10 keV) and so calibration with low
energy photons might be appropriate.

I think the key questions are:
a. What causes this decreased response at low energies?
b. Is there a similar decreased response in the skin of the body?
If the skin response is similar to the ion chamber response then there is
no problem, and the ion chamber will give an accurate result.

I don't know the answers to questions a and b, and (as usual) I am eager to
learn.

"Shlala gashle" (Zulu greeting, meaning "Stay safe")
mike (mcnaught@LANL.GOV)