Pressurized Argon Ionization Chamber - 10CC Volume

What is the purpose for this device?

http://www.tyne-engineering.com/10%20cc%20Ion%20Chamber.html

http://www.vacutec-gmbh.de/en/products/industry/industrial-ionization-chambers.html

Hi SolarEagle:

Thanks for response. Good links indeed.

It is to measure environmental gamma radiation background from very low exposure rate of 1mR/hour to reasonably high (not extremely high) accidental radiation exposure estimation and emergency planning.

Detection limit shown in first reference is 0.2mR/hour or 1fA for 0.1 mCi/m³ of Tritium which is good detection capability. Only measurement of 1fA going to be serious problem.

Ionised materials have the capability of passing an electrical current, so the leakage current parameter is unlikely to be realisable.

http://www.bing.com/search?q=Pressurized+Argon+Ionization+Chamber&src=IE-SearchBox&FORM=IENTTR&conversationid=

Hi PWSlack:

Yes, I do know that point. There is leakage resistance of the electrode insulator which is supposed to be 10^+17 ohms order to achieve 1fA leakage current from 100V bias voltage.

Good luck with that.

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The company I work for actually makes argon chambers for radiation detection. I am working on mechanical design so I can't answer your questions but I can direct you to someone who might.

Drew K

hi Drew K:

which company is this one? any link to products they make?

Best take it to IM.

I suggest you contact people who make flash lamps for lasers. These people have the types of technologies you require.

You can't get the performance you need with a scintillation crystal and a photon counter? Really?

Have you considered pure silicon instead? I suspect that low level gamma could produce charge carriers that would allow the material to conduct momentarily.

I think they call these silicon drift detectors.

It appears you want an extremely high dynamic range radiation detector, but I do not think you will find it in a polarized gas being ionized by gamma.

Hi James Stewart:

Ionization chambers are primary standard devices for ionizing radiation detection and calibration as they collect almost all charge produced within the chamber. Other detectors are calibrated against ion chambers.

I have used spherical ion chamber before of about 300 mm diameter with 25 atmospheric pressure of Argon gas filled in it.

Unfortunately in India no one manufactures these and I need to import these from some good reliable source. Biggest problem is the leakage of the filled gas at pressure.

At 25 bar internal pressure, what are these made from? Steel? Aluminum?

Why do you want cylindrical? Sphere not good for present measurement need?

Do these ionization chambers have a central conductor wire? How are you polarizing? How are you reading the current?

Do you have some links to share with us about this topic?

Here are some.

Drew K

Hi James Stewart:

I am only user of the chamber so can't say exactly how they were manufactured.

NIST uses reactor grade graphite to construct outer wall of the chamber and perhaps ceramic insulator and protective hard wall. Spherical chambers are made in two hemispheres and then they are joined together. Inner electrode design also differs from rod to sphere. High electrical field gradient is to be avoided in ion chambers as there is no charge multiplication. Charge drift time is in milli seconds at high pressure and also due to larger size of the chamber and lower electric field.

Triaxial cable is used to avoid leakage current flow into measurement electrode from bias voltage ranging from -100V to -500V depending on size of the ion chamber. Measured current is often 1fA to few hundred pA level. Charge is integrated from 1s to 10s duration and rarely for shorter time. Pulsed current measurement may also be used for chopped beam.

Spherical chambers has symmetry and measurement does not get affected by placement direction.

Cubic atmospheric pressure ion chambers are easiest to construct with just flushed dry Nitrogen or Argon gas flowing through chamber at very low flow rate. These are good for x-ray machine beam exposure measurement and calibration.

Charge measurement method is better than temperature rise method.

Sounds like I need to read up on this.

I have been reading "Atoms in the Field" by Don Cooper, it has good explanations and information on radiation and detectors. I am reading about how ion chambers work in an effort to understand what the original poster is looking for.

Drew K

Hi Drew K:

Ion chambers of small size in volume 1CC is generally used for calibrating radiation field geometry in cancer therapy. There ion chambers are known as thimble ion chambers. See below reference

https://www.medphysics.wisc.edu/courses/mp501/501_lecture25.pdf

When you bias the chamber electrodes, you generate small electric field which attracts electrons and ions generated by ionization within its cavity in filled gas which is often Argon or Nitrogen or CH4. Not all ions are collected by the electrodes and many recombine while in transit. As we start increasing the bias voltage, more and more ions start getting collected and obviously the ion current increases proportionately till it saturate at some maximum operating voltage point. Thereafter if you further increase voltage then ions will get accelerated and cause secondary ionization and enter into proportional reason and leave behind primary ionization zone. We avoid entering proportional reason and operate in ionization reason.

Generally chopper amplifiers of low drift and ultra low current measurement are used. These were also called electrometer amplifiers. See following reference for transimpedance amplifier of ultra low current type

http://www.analog.com/media/en/technical-documentation/user-guides/ADA4530-1R-EBZ_UG-865.pdf

I was surprised at how much voltage affects the readings. The book I am reading has a simple graph with Ion pairs produced per ionizing event vs operating voltage applied to gas-filled tube.

I think the chambers we normally produce here are only 10 bar. You would have to speak with our sales people who would then get the EE and ME team to look into a 25 bar design.

Drew K

Hello Drew K: Are you using ceramic seal for electrode fixing and are these supplied by some other manufacturer as they may not be produced inhouse. That is a crucial part of the chamber design. Any idea about electrode shape and its manufacturer part number of PDF catalog? Thanks. Shyam

I am not sure, I have not worked on any of those yet. My main projects have been with the mechanical hardware associated with the cases and some of the scintilators.

Drew K

It is alright. Thanks for sending me contact details.