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 Exradin Ion Chambers
Prostate Implant Equipment
IMRT Equipment
External Beam Equipment
IVB Equipment
Exradin Ion Chambers









Exradin Ion Chambers

Ion Chambers Equilibrium Caps Conducting PlasticsVirtual Water (pdf)



SeeDOS provides the world-famous Exradin ion chambers. For over 25 years, Exradin chambers have provided uncompromising quality, scientific integrity and dependability. Exradin ion chambers are waterproof, fully guarded, and the chamber electrodes are made entirely of homogenous conducting plastic, providing excellent conductivity. For more information on Exradin products click here.

New (March 2004) EXRADIN Ionization Chambers pdf brochure

New (March 2004) ACE (Axial, Coronal, Edge ) PHANTOM pdf brochure

New (March 2004) IMRT Dose Verification PHANTOM pdf brochure

New (March 2004) QUASAR Body and Beam Geometry PHANTOM pdf brochure : QUASAR ( Quality Assurance System for Advanced Radiotherapy )

NEW  : The A16 Micropoint Chamber at only 0.007cc is designed primarily for applications like IMRT and stereotactic surgery, which use cobalt and higher energy beams. It is used for assessing pinpoint radiation fields for orthovoltage, x-rays and stereotactic and superficial skin therapy. A typical calibration factor for air kerma in a cobalt beam is 3.5 x 109 Gy/C.

For the latest pdf brochure on the range of Exradin ion chambers including the new A16 Micropoint, please click here

For a pictorial listing of available Cable Connectors, please click here

For an Acrobat Reader to read the pdf file please click on the adjacent Acrobat logo 

For an Electrometer for use with your Exradin Ion Chamber please click here

Exradin ionization chambers are available from SeeDOS for a wide range of dosimetric measurements in diverse radiation beams. The chambers find applications in the fields of radiation therapy, diagnostic radiology, and radiation protection and research. Applications for which Exradin chambers are suited include beam calibration, quality assurance, dose assessment, depth-dose studies, mixed field dosimetry, monitoring, background measurements, and a variety of research studies.

Model 1 - Miniature Shonka Thimble Chamber

Model 1SL - Slim Line Miniature Shonka Thimble Chamber

Model 2 - Spokas Thimble Chamber

Models A3-A6 - Shonka-Wyckoff Chambers

Model A10 - Planar Electron Chamber, Markus®-Type

Model 11 - Spokas Planar Chamber

Model 11TW - Spokas Thin-Window Planar Chamber

Model 12 - Farmer-Type Chamber, 0.6 cc

Model 12S - Modified Farmer-Type Chamber, 0.25 cc

Model 14 - Exradin Microchamber

Model 14SL - Slim Line Exradin Microchamber

Model 14P - Exradin Parallel Plate Microchamber

Model 15 - Low Energy Parallel Plate Diagnostic Chamber

Model A16 - Micropoint Chamber

Model A18 - Scanning Ion Chamber , 0.125cc

Connector Types (PDF)

All Exradin chambers are the three-terminal type (guarded design) and employ homogeneous construction. The chamber electrodes are made entirely of one of three conducting Shonka plastics except for the magnesium chambers which utilize pure magnesium. Except for the Models 6 chamber, all chambers are attached to a 1.5 m length of a low-noise flexible triaxial cable. A variety of stem configurations are available for these chambers.  Model A6 is fitted with a triaxial BNC plug connector directly to the end of its stem. 

[ Exradin Home ] Model 1SL ] Model 11 ] Model 14 ]
[ Products Home ] Model 2 ] Model 11TW ] Model 14SL ]
  Models 3-6 ] Model 12 ] Model 14P ]
Model 1 ] Model 10 ] Model 12S ] Model 15 ]

Models 1,  A1SL2,  A10 ,11 , 11TW,  A12,  A12S , 14 , 14P,  A14SL are inherently waterproof and may be operated while fully submerged without any kind of protective sheath. The chamber will vent through a flexible, rugged tube that surrounds the triaxial cable. This vent tube is sealed to the chamber body and is open to the ambient near the connector, ensuring the collecting volume is in pressure equilibrium with the surroundings. Furthermore, thin-window planar models (A10 and 11TW) require a protective cover over the window, which is included with the chamber and conform to the AAPM TG-51 protocol. Although Models M1 and M2, which are constructed of magnesium, have waterproof construction, the reactivity of magnesium argues against their unprotected immersion in water.

The Model 1 chambers are small size thimble type with collection volume of 0.05 cm3. These are known as Miniature Shonka Thimble Chambers. Their small size allows good spatial resolution in depth dose measurements. The chambers may also be used for beam calibration. Three versions are available: Model A1 is made of the air-equivalent plastic C552, Model M1 is made of magnesium, and Model T1 is made of the tissue-equivalent plastic A150. Using an M1 and T1 in combination would allow one to separate the neutron and photon contributions to the dose in mixed fields. In this application, the use of argon in the M1 will minimize its neutron response.


The Model 2  Spokas chambers also have thimble geometry but a collecting volume of 0.5 cm3. Four versions are produced: Model A2 is constructed of air-equivalent plastic C552, Model M2 is constructed of magnesium, Model P2 is made of polystyrene-equivalent plastic, and Model T2 employs the tissue-equivalent plastic A150. The chambers are ideal for routine beam calibration. A2 is intended for exposure and air kerma measurement while the others facilitate the determination of absorbed dose. The M2 and T2 chambers are frequently used together to separate the neutron and photon dose components in neutron beams.


The Model A12 chamber is a Farmer-type thimble chamber and is made of air-equivalent plastic C552. The chamber is particularly suited for calibration of therapy beams in terms of absorbed dose in water in accordance with established protocols such as that published by the American Association of Physicists in Medicine.


The Model A12S thimble chamber is a modified A12 Farmer-Type chamber. The collector length of the A12S is approximately one-third the size of the A12, which confines it's collecting volume to more of the tip of the chamber than the A12.


The Model 14 Microchambers were developed specifically for assessment of the radiation fields encountered in stereotactic radiosurgery. Two versions of the Model 14 are available: A14, which is constructed of air-equivalent plastic C552, and T14, which is constructed of tissue-equivalent plastic A150. Outwardly, the Microchamber is identical to the Miniature Shonka Thimble Chamber for both use the same base and shell. The Microchamber, however, has a special collector-guard assembly, with a collector of zero length, which confines the sensitive volume to the very tip of the chamber.


Model 14P chambers represent planar versions of the Thimble Microchamber. In these, the collecting volume has parallel plate geometry with an air gap of 1.0 mm. Two versions are available: Model A14P is constructed of air-equivalent plastic C552 while Model T14P uses the tissue-equivalent Shonka plastic A150. The 14P's provide better spatial resolution than the Model 14's.


Model A1SL and  A14SL thimble chambers are the Slim-Line verisons of their parent model number. The Model A1SL has the exact same internal dimensions and collecting volume as the Model A1, yet the entire chamber has the uniform diameter of 0.250" (6.4 mm). This small uniform diameter is enjoyed when this chamber is needed to fit into a small phantom, since the machining of any holes for the chamber is a simple single drilling operation. The relationship of the A14SL to its parent A14 chamber follows the same pattern as the A1SL to the A1.

Model 1, 2, A12, A12S, 14, and 14P chambers may be adapted for use in the RSVP Phantom which is available from The Phantom Laboratory, Salem, New York. The RSVP Phantom is a hollow plastic shell which is normally filled with water and which allows various detectors to be inserted through the base. The adaptation includes a special lexan stem, O-ring seal between stem and chamber, and a substitute phenolic ball for the phantom for use with the chamber.


Model A10  is a parallel plate, vented, waterproof and fully guarded ion chamber ideally suited to the calibration of electron beams. The circular collector of 5.4 mm diameter allows accurate measurements in small fields. Since the A10 has the same external dimensions as the Markus® chamber, solid phantoms machined to accept the Markus® would also accept the A10 chamber. The collecting volume of the A10 is 0.051 cc. These units employ a stretched conductive Kapton film of thickness 0.001 inch (3.85 mg/cm2). The collector, guard, and window supports are made of air-equivalent plastic C552.


Model 11 chambers have a parallel plate geometry. The collector is circular of radius 10 mm. A collector of smaller size can be supplied on special order. An electrode gap of 2 mm gives a collecting gas volume of 0.6 cm3. Three versions of the Model 11 chamber are available: A11 is made of air-equivalent plastic C552, P11 is made of conducting polystyrene-equivalent plastic, and T11 is constructed of the tissue-equivalent plastic A150. While planar chambers are usually recommended for electron beams, they offer a number of advantages for photon beams as well. The thin collecting volume enables excellent resolution in depth dose studies.


Model 11TW  chambers are thin-window versions of Model 11 chambers. These units employ a stretched conductive Kapton film of thickness 0.001 inche (3.85 mg/cm2). Since the external dimensions of Model 11 and 11TW chambers are the same and both models use the same collector-guard arrangement, the air gap is 3 mm giving a sensitive gas volume of nearly 1 cm3 for standard-sized collector. A protective cover is available to set over the window for underwater operation. 


Model A15 , not suited for underwater use, is similar to A11TW's thin window and collector guard arrangement, but with an increased air gap for use in mammography.


Models A3,A4,A5 and A6 have the Shonka-Wyckoff design with spherical outer electrodes and are constructed entirely of the air-equivalent formulation C552. Model A3 is the original thin-walled chamber (Radiation Dosimetry, Vol. II, 2nd ed., pp. 54-55, edited by Attix and Roesch, Academic Press, 1966). A4, A5, and A6 represent scaled-up versions of the original design. These chambers are ideally suited to the measurement of exposure and air kerma. The original Shonka-Wyckoff chamber was intended as a transfer standard. Models A3, A4, and A5 are well suited to this application and may also be used for beam calibration. The larger volumes of A5 and A6 provide adequate sensitivity for leakage measurement and low-level monitoring.


Equilibrium Caps in a variety of wall thicknesses are available for chamber Models 1 through 6, A10, 11, 11TW, A12, A12S, 14, 14P, and both SL's.


Conducting Plastics


Standard formulations of conducting plastics are available which simulate air, polystyrene, tissue and bone. These are highly homogeneous blends consisting of one or two thermoplastic polymers as a matrix in which finely divided inert powders are uniformly dispersed. Carbon black is a common powder in all blends and is the main source of electrical conductivity of the blends. An important application of these materials is as the electrodes in ion chambers and proportional counters. In this case, the bulk electrical conductivity is quite adequate so troublesome coatings are not needed.


EXRADIN Ion Chambers for IMRT

Please click here to go to IMRT Phantoms



Model 14 or 14SL Microchamber

 Model 1 or 1SL Thimble Chamber




Collecting Volume

0.009 cc

0.05 cc



Outside Diameter of Collecting Shell

6 mm

6 mm



Projected Collecting Area

6 mm by 4 mm

6 mm by 8 mm



Centroid of Collecting Volume, mm from Tip of Chamber

2.0 mm

4.0 mm



Nominal Calibration

365 R/nC

60 R/NC



nC per 100 MU





Materials Available

Model 14 A or T

Model 14SL A only

Model 1 A, T, or M

Model 1SL A only



A = Air Equivalent C552


T = Tissue Equivalent A150



M = Pure Magnesium





1. 10 x 10 field; 2.5 depth solid water phantom; 100 cm SSD; 6 Mv photons



If you are interested in any of the products mentioned here, please fill out an Enquiry Form or Go To the Ion Chamber Product List / Quotation Request Form, so that we may promptly respond to your request.



Please contact Colin Walters at cwalters@seedos.com if you would like further  information or you have questions

or comments about this web site.
SeeDOS Ltd, 26, The Maltings, Leighton Buzzard, Bedfordshire LU7 4BS, United Kingdom
Tel: +44 1525 850 670  • Fax: +44 1525 850 685