Features
- Measures absolute dose of beta radiation and X-rays in soft tissue equivalent material very precisely
- Includes a micrometer screw for the depth adjustment of the sensitive volume down to zero
- 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) and secondary standard dosimetry laboratories (SSDL) 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.
Specifications
| Type of product | extrapolation chamber according to Böhm |
|---|---|
| Application | absolute dosimetry of beta radiation and X-rays |
| Measuring quantity | absorbed dose in soft tissue |
| Nominal sensitive volume | (0.353 … 7.422) cm3 |
| Design | not waterproof, vented, fully guarded |
| Reference point | in chamber center of entrance foil underside |
| 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 and max. dose rate | dependent on electrode distance |
|---|
Useful Ranges
| Temperature |
(10 … 40) °C (50 … 104) °F |
|---|---|
| Humidity | (10 … 80) %, max 20 g/m3 |
| Air pressure |
(700 … 1060) hPa |
Parts
T23392 Böhm extrapolation chamber
T23392/U5 Connection cable for Böhm extrapolation chamber, connecting system M
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