Re: Low energy pocket dosimeters

[jgbarnes@ix.netcom.com (JAMES BARNES)]

Dear Richard,


You wrote: 
>
> Does anyone know of a source for low energy pocket ion chambers
> (self-reading)?
>
> The dosimeters are to be used by nontechnical personnel (security 
guards) and are not intended to be record dosimetry. Our primary 
concerns are expense and ease of use.

    We used Dosimeter Corp low energy equipment and were satisfied with 
its performance.  Unfortunately, Dosim Corp decided to discontinue 
production of the dosimeters as they found they over-responded at 
high-energy (We knew this from our in-house testing, but were willing 
to live with it).

    As far as alternatives, you might check out the Sieman's electronic 
dosimeters.  They are claimed to be Beta sensitive, thus they may work 
well for low energy photons.  Downside is that they are somewhat pricey 
compared to a standard P(ocket) O(ptical) D(osimeter).

    The next thing you might try is using a "standard" POD, but 
calibrate it low energies and apply a correction factor.  It's messy, 
but it should give you what you want; instantaneous readout for a 
non-technical person.  The trick is that you then have to have an 
administrative system that teaches the user to multiply his readout by 
"such and such."  Generally a major pain.

    Now a "personal" question.  Are you badging because you have 
uncomfortable workers, or for your own information.  If the former 
case, we have had good results in the "comfort zone" issue by 
installing direct readout Area Radiation Monitors in areas where the 
guards or non-radiological workers might encounter the fields.  That 
way they can look at the meter themselves and satisfy themselves that 
nothing amiss is going on.

> Alternatively, we need a method for getting real time measurements of 
the total dose from exposure to a pulsed x-ray system with the 
following characteristics: 50 nanosecond pulse, 25 pulses per second, 
150 kVp and 1 microseivert per pulse at 1 meter (according to the 
manufacturer).
>
>
> In a related issue, virtually the only instruments we have found that 
could detect the radiation emitted by this unit are integrating ion 
chambers. None of the event detecting instruments we have are useful. 
We tried organic and NaI scintillators, compensated and uncompensated 
G-Ms and semiconductor detectors coupled to analog and digital 
counters. Low end (cheap) integrating ion chambers are getting hard to 
find.

    We had similar problems with our F.E.L.  After struggling with the 
electronics of the problem, we fell back to using TLDs and integrating 
dose over a period of time.  Given a second chance (the F.E.L. project 
is now completed), I think I would have used our Victoreen Ion Chamber 
and integrated the dose.  I know of nothing cheap and available that 
responds fast enough for instantaneous response.  However, you might 
try to raise Mike Grissom at Lawrence Berkeley Lab as I suspect he has 
some solutions to this, being an accelerator kind of guy.

    Also have been told that Stanford Linear Accelerator Center (SLAC) 
has some interesting approaches to the problem.

Hope it helps.

Jim Barnes, CHP
RSO
Rocketdyne Division, Rockwell International
Canoga Park, CA