Böhm Extrapolation Chamber Type 23392

Low energy extrapolation chamber with adjustable volume depth for measurements of absorbed dose in soft tissue

  • Measures absolute dose of beta radiation and X-rays in soft tissue equivalent material very precisely
  • Includes a micrometer screw for the depth } Very Suitable for beta calibration at PSDLs and SSDLs

The Böhm extrapolation chamber is a high quality device for absorbed dose measurements of beta and low energy X radiation in certain depths below the surface of the entrance window. Primary standard dosimetry laboratories (PSDL) use it for low energy radiation calibration.

The dose is determined from the ionization density in a small air gap, the extrapolation chamber volume, embedded in tissue equivalent material (PMMA). The chamber is supplied with a very thin entrance window of 0.75 mg//cm2 and a collecting electrode of 30 mm in diameter. By means of the built-in micrometer screw, the collecting electrode surrounded by a guard ring of 15 mm can be moved to adjust the depth of the sensitive volume between 10.5 mm and 0.5 mm. The zero point of the chamber depth setting can be obtained by measuring the chamber capaciting charge C versus the chamber depth x and extrapolating C-1 towards x = 0.

The chamber is equipped with two BNC sockets for signal and polarizing voltage. A connection cable from both BNC sockets to an electrometer with M type connector is available. An electrometer with the input circuits on ground potential is required. The extrapolation chamber comes in a protective storage case.

Type of product extrapolation chamber according to Böhm
Application absolute dosimetry of beta radiation and X-rays
Measuring quantities absorbed dose in soft tissue
Design not waterproof, vented, guarded
Nominal sensitive volume (0.353 ... 7.422) cm³
Reference point inner surface of the entrance window, at the center of the window
Direction of incidence radial
Nominal response dependent on electrode distance
Chamber voltage dependent on electrode distance 500 V maximal
Leakage current ≤ ± 1 pA
Cable leakage ≤ 1 pC/(Gy·cm)

Materials and measures

Entrance window PET, graphite coated
Total window area density 0.75 mg/cm2
Measuring electrode diameter 30 mm
Rear electrode PMMA, graphite coated
  diameter 60.5 mm
Distance between electrodes (0.5 ... 10.5) mm

Ion collection efficiency at nominal voltage

Ion collection time max. dose rate dependent on electrode distance

Ranges of use

Temperature (10 ... 40) °C
  (50 ... 104) °F
Humidity (10 ... 80) %, max 20 g/m3
Air pressure (700 ... 1060) hPa
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