Thimble Ion Chambers

Strict manufacturing tolerances and waterproof construction makes these detectors ideal for dosimetry calibrations in water, air and other phantom materials.

The Exradin Advantage

  • Waterproof construction backed by five-year warranty.
  • Rugged Shonka plastic provides years of reliable use and excellent conductivity.
  • Lack of stem-effect and low leakage provides precise, consistent measurements.
  • Proven guard design stabilizes measurements and reduces settling time.
  • Homogeneous material throughout the chamber minimizes perturbation of the beam.
  • **NEW** We now offer MR-Compatible Thimble Ion Chambers.


Exradin A19 Ion Chamber

The A19 fits existing plastic phantom cavities and build-up caps, limiting perturbation and minimizing settling time in absolute dosimetry calibration. This chamber is characterized for TG-51 procedures.

Also available in MR compatible version.

Exradin A12 Ion Chamber

Characterized in TG-51 and TRS-398, the A12 has fast settling time and a removable stem for superior absolute dosimetry calibrations in water, air or phantoms.

Also available in MR compatible version.

Exradin A12S Ion Chamber

The A12S is designed for absolute dosimetry calibrations in water, air or phantoms. The collector of the A12S is approximately one-third the size of the A12, confining collecting volume to the tip of the chamber.

Also available in MR compatible version.

Exradin A1SL Ion Chamber

The A1SL, available in air or tissue equivalent plastic, provides a perfect balance between fast scanning and point-dose measurements within 1cm in water, air or phantom materials. This chamber is characterized for TG-51 and TRS-398 procedures.

  • 6x7mm field size

Also available in MR compatible version.

Exradin A1 Ion Chamber

The Exradin A1 has the same internal dimensions and collecting volume as the A1SL, yet the larger diameter is ideal for use in solid phantoms. This chamber is characterized in TG-51 and TRS-398.

Exradin A2 Ion Chamber

Ideal for precise measurement of exposure and air kerma in photon beams and absorbed dose in photon, electron, proton and other beams.

Available in air, polystyrene, tissue and magnesium equivalent plastic.

Exradin A28 Ion Chamber

The Model A28 Chamber features exceptional omni-directional spatial resolution for relative dosimetry scanning in water phantoms and use in minute field measurements.

Also available in MR compatible version.


Exradin A1 Exradin A1SL Exradin A2 Exradin A19 Exradin A12 Exradin A12S Exradin A28
Collecting Volume 0.053 cm3 0.053 cm3 0.53 cm3 0.62 cm3 0.64 cm3 0.24 cm3 0.125 cm3
Centroid of Collecting Volume* 3.86 mm 4.06 mm 6.96 mm 13.0 mm 12.9 mm 5.79 mm 4.47 mm
Outside Diameter of Shell 6.0 mm 6.35 mm 11.4 mm 7.1 mm 7.1 mm 7.1 mm 8.0 mm
Inside Diameter of Shell 4.0 mm 4.0 mm 9.5 mm 6.1 mm 6.1 mm 6.1 mm 5.8 mm
Shell Wall Thickness 1.0 mm 1.1 mm 1.0 mm 0.5 mm 0.5 mm 0.5 mm 1.1 mm
Collector Diameter 1.0 mm 1.0 mm 4.6 mm 1.0 mm 1.0 mm 1.0 mm 1.0 mm
Collector Length 4.4 mm 4.4 mm 8.4 mm 21.6 mm 21.6 mm 7.5 mm 6.4 mm
Shell, Collector, and Guard Material A, T A A, P, T A A A A
Nominal Air Kerma Calibration Factor 5.4E+8 Gy/C 5.4E+8 Gy/C 5.4E+7 Gy/C 4.5E+7 Gy/C 4.4E+7 Gy/C 1.2E+8 Gy/C 2.3E+8 Gy/C
Nominal Leakage +/- 10 fA +/- 10 fA +/- 10 fA +/- 10 fA +/- 10 fA +/- 10 fA +/- 10 fA
Maximum Polarizing Voltage 1000 VDC 1000 VDC 1000 VDC 1000 VDC 1000 VDC 1000 VDC 1000 VDC
Waterproof Yes Yes Yes Yes Yes Yes Yes
Included Build-up Cap None None None 60Co 60Co 60Co 60Co

*From exterior tip of shell


Product Resources

Publications, tech notes, testimonials, and other resources to support Thimble Ion Chambers.

Looking for a user manual?

Available on request. Contact your Account Manager


View publications related to this product from experts in the fields of medical physics and oncology.

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Tech Notes

Find detailed instructions on how to setup and execute common processes from our experienced technicians.

Go to Tech Notes »

Frequently Asked Questions

I have a non-floating electrometer. Can I use it with an Exradin chamber?

While the vast majority of electrometers are of the floating design, there are some older electrometers with a non-floating design. While effective use of Exradin chambers can be achieved in plastic phantoms or in a water tank with the assistance of a thin, sealed sleeve around the chamber body, usage of a non-floating electrometer is discouraged due to a resulting shock hazard.

What is the typical Exradin Ion Chamber leakage?
All Exradin chambers should exhibit leakages on the order of 10 x 10-15 amps or less.
How often should I send my ion chamber in for calibration?
  • The IEC (International Electrotechnical Commission) recommends ion chamber calibration every two years to assure optimal performance.
    • IEC 60731 – Medical electrical equipment – Dosimeters with ion chambers such as used in radiotherapy.
    • IEC 61674 – Medical electrical equipment – Dosimeters with ion chambers and/or semi-conductor detectors as used in X-ray diagnostic imaging.
  • Standard Imaging works with the University of Wisconsin ADCL to perform calibrations, but also provides free inspection and testing services, as well as expedited repair service, if necessary. Click here to initiate a calibration and service appointment.
    • Standard Imaging’s goal is a two week turn around upon receipt of equipment, although actual time may vary depending on the UW ADCL’s schedule.
I am seeing drift or leakage with my electrometer + ion chamber system. Is there something wrong with my chamber, electrometer, or both?
  • You may need to zero your electrometer. Refer to your electrometer’s user manual for more details.
    Check all cables for crimping or damage, and allow settling time after setup or movement.
  • Crimping, damage, and significant movement such as unwinding from a spool can cause or contribute to system leakage.
  • It is recommended to use as short of an extension cable as possible. In general, the longer the cable, the longer the signal settling time and the longer for bias voltage to dissipate.
  • A common cause is dust that has collected on the inside of the connector on the chamber cable, extension cable, and/or electrometer. Standard Imaging has created a tech note containing a triax connector cleaning procedure. This procedure should be periodically performed or whenever there are concerns of drift or leakage. Heavier product use may require more frequent cleanings. In addition, utilize dust caps on chamber and electrometer triax connectors whenever possible.

Determine which part of the electrometer + extension cable + chamber system is exhibiting the leakage or causing drift, in this order of troubleshooting:

  1. Electrometer: With nothing attached and the dust cap in place, warm up the electrometer and check for stability. Perform a 60 second charge collection and determine if the signal shown is within the manufacturer’s stated acceptable limits.
  2. Extension cable: If it has been determined that the electrometer is not exhibiting leakage or drift, connect the desired extension cable (with no bias applied at time of connection, no chamber attached, but dust cap on), and determine if the signal level settles in the cable manufacturer’s stated settling time estimate.
  3. Exradin Ion Chamber: If it has been determined the electrometer is not exhibiting leakage or drift, connect the desired chamber directly to electrometer (with no extension cables attached), and determine if the signal level settles within 5-10 minutes and the leakage of the chamber is less than 10 x 10-15 amps.
  • If these techniques do not resolve the drift or leakage problems, contact Standard Imaging representative or your electrometer’s manufacturer for assistance. Click here for contact information.
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