[ RadSafe ] Recommendations for ion chamber survey instrument

[Geo>K0FF]

Ludlum ion chambers, Model 9 and Model 17 ( 10 keV to 2 MeV plus beta 
window) are unique in that they have audio circuits. The sound they make 
reminds me of a metal detector.
Both models are nearly identical except for the size of the chamber, 
therefore the sensitivity.
Like many ambient-pressure chambers ("air-ion chamber"), they are vented to 
atmosphere, making the readings altitude and humidity reliant. Desiccators 
are provided, but to me it is a tedious chore to keep them dry.

For this reason alone, I prefer pressurized ion-chambers. As an added bonus, 
chambers with very high pressure (20 atm) are made, and have remarkable 
sensitivity, as well as flat response.  A typical model number would be 
Inovision (Victoreen, Fluke et al.) 451P. Look for the "P" in the model 
number. 6 atm pressure, only specified 25 keV. Unfortunately the law of 
physics is that a chamber wall strong enough to hold high pressure, is dense 
enough to block extraordinarily low energy gamma/ X- rays. It does have 
integration. If the use is critical, get 3. One AT the shop, one IN TRANSIT 
and one to use.


Vibrating-reed type electrometer based ion-chamber detectors are also very 
sensitive and can have thin windows, allowing for low energy detection.
I'm not sure of they would be as suitable for pulsed systems.
http://hps.org/publicinformation/ate/q6213.html

While we are on the subject, even though they are NOT for pulsed systems, 
the Bicron micro rem ( actual spelling on the device, although the 
advertisements capitalize both words)  is a flat-response scintillometer of 
remarkable sensitivity. To my personal knowledge it is the only 
scintillometer that has a flat response. Normal versions go down to 40 keV, 
while the  "low energy" version will go down to 17 keV.

Also depending upon the R.F. environment in your lab, the instrumentation 
may be limited to, or at least include so called "RF" versions such as the 
venerable 440RF/X series.

I'm thinking that most if not all of the thin-window ion chambers will 
actually detect much lower energy that their ratings indicate, however they 
may be out of tolerance indication-wise. For example the RO-20 specification 
shows +/- 15% above 33 keV and +/- 3-% above 8 keV.

Don't overlook the two piece design, using an electrometer and ion-chamber 
probe. These can pretty well be custom tailored to the application.


George Dowell
NLNL
New London Nucleonics Lab


----- Original Message ----- 
From: "ROY HERREN" <royherren2005 at yahoo.com>
To: "Carl Willis" <willis.219 at osu.edu>; <radsafe at radlab.nl>
Sent: Thursday, December 06, 2007 12:48 AM
Subject: Re: [ RadSafe ] Recommendations for ion chamber survey instrument


> Carl,
>
>     Check out http://www.ludlums.com/, http://www.ludlums.com/product.htm, 
> and http://www.ludlums.com/product.htm#Ion%20Chambers.  Ludlums has great 
> prices and really good quality.  You might be able to pick up a used Model 
> 9, see http://www.chpconsultants.com/Instrumentation1.htm.  Keep in mind 
> though that you will still need to have the used instrument calibrated 
> (Ludlums also provides this service).
>
> Carl Willis <willis.219 at osu.edu> wrote:
>  Hello RadSafers,
>
> The small accelerator company I work with is looking to buy an ion chamber 
> survey instrument that has fairly flat exposure response down to ~10 keV, 
> to be used for area surveys around pulsed, low-energy x-ray-producing 
> accelerator components. I have some personal experience with a few of the 
> older instruments (Victoreen 470, 471; Eberline RO-3) but am probably 
> underinformed about the contemporary selection. Thus, I'm interested in 
> users' recommendations, and also am interested if there are any dealers 
> with used but functional equipment they want to mention to me off-list 
> (email is willis.219 at osu.edu).
>
> Some features of interest:
> -Flat exposure response down to ~10 keV
> -Integrating mode available
> -Easy (inexpensive) to calibrate
> -Preferably no hard-to-find bias batteries that we cannot just run out and 
> buy at K-mart.
>
> Thanks!
> Carl Willis, Linac Systems LLC, Albuquerque, NM USA
>
> ___________________
>
> Carl Willis
> USDOE NE Graduate Fellow
> The Ohio State University
> (505) 412-3277
> willis.219 at osu.edu
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> Roy Herren
>
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