IONISATION CHAMBERS
NE2571 FARMER 0.6CC IONISATION CHAMBER
The Farmer NE2571A cylindrical ionisation chamber is the original 0.6 cm3 chamber designed by Professor F. T. Farmer. It is constructed from a thin-walled, high purity graphite thimble and aluminium electrode, with a detachable build-up cap which also protects the thimble. Careful guarding of the signal conductors and cable has ensured low post-irradiation leakage. The NE2571A is used throughout the world for the measurement of photon and electron beam dosimetry. It is also possible to purchase the graphite thimble replacements and water proof sheaths (please refer to the sales office).
NE2571A is delivered as standard with a detachable build-up cap, 10 metre cable, Triax TNC plug; and carry case. Variations to this are available upon request.
| Physical Characteristics | |
| Sensitive Volume:
Sensitive Length: |
0.69cm3
24.1mm |
| Thimble materials:
Inner diameter: Wall thickness: |
99.99% graphite
6.3mm 0.36mm |
| Inner electrode:
Length: Outer diameter: |
99.99% aluminium
20.6mm 1.0mm |
| Build-up cap:
Wall thickness: Outside diameter Density: |
Delrin CH20
3.87mm 15.1mm 1.425gm cm-3 |
| Stem: Outside diameter | 2MV to 35MV |
| Energy range for electrons: In suitable phantom (measures absorbed dose to water) | 8.62mm |
| Length of connecting cable: | 10m |
| Specification | |
| Sensitive Volume: | 0.69cm3 |
| Sensitivity for X-rays of 1mm Cu HVL | 4.6 R.nC-1 275 R.min-1.nA-146 Gy.μC-1 2.75 Gy.min-1.nA-1 |
| Energy range for X and gamma radiation: (a) Without build-up cap: (measures exposure) |
50kV to 300kV |
| (b) With build-up cap: (measures exposure) | 0.3MV to 35MV |
| (c) In suitable phantom (measures absorbed dose to water) | 2MV to 35MV |
| Energy range for electrons: In suitable phantom (measures absorbed dose to water) | 5MeV to 35MeV |
| Leakage current:
Typical: Maximum: |
5 x 10-15A
1.5 x 10-14A |
| Maximum exposure rate (approx) or 99% collection efficiency: | |
| Polarising potential—250V | 4 kR.min-1, continuous 25 mR/Pulse, pulsed40 Gy.min-1, continuous 0.25 mGy/Pulse, pulsed |
| Polarising potential—400V | 10 kR.min-1, continuous 40mR/Pulse, pulsed100 Gy.min-1, continuous 0.4 mGy/Pulse, pulsed |
NE2581 ROBUST FARMER 0.6cc IONISATION CHAMBER
The 0.6 cm3 NE2581A is a robust Shonka Plastic version of the Graphite based NE2571A with similar applications but using a tissue equivalent inner electrode and thimble. This is particularly suitable for routine output checks of X-ray, 60Co and Linacs.
NE2571A is delivered as standard with a detachable build-up cap, 10 metre cable, Triax TNC plug; and carry case. Variations to this are available upon request.
Associated and Peripheral equipment includes:
- Chamber repair kit
- NPL2611 Secondary Standard Chamber
- NE2566A Intercomparison Phantom (see picture)
- NE2528/3 Small Water Phantom for NE2571
- PEP small Photon Electron Water Phantom
- Dosimetry Extension Cables
- Solid Water
The NE2581A is delivered as standard with a detachable build-up cap, 10 metre cable, TNC plug; carry case – variations available upon request.
| Physical Characteristics | |
| Sensitive Volume:
Sensitive Length: |
0.56cm3
24.1mm |
| Thimble materials:
Inner diameter: Wall thickness: |
Shonka A-150
6.3mm 0.36mm |
| Inner electrode:
Length: Outer diameter: |
Shonka A-150
20.6mm 3.0mm |
| Build-up cap:
Wall thickness: Outside diameter Density: |
Lucentine CH
5.61mm 18.6mm 1.06gm cm-3 |
| Stem: Outside diameter | 8.62mm |
| Energy range for electrons: In suitable phantom (measures absorbed dose to water) | 8.62mm |
| Specification | |
| Sensitive Volume: | 0.56cm3 |
| Sensitivity for X-rays of 1mm Cu HVL | 5.9 R.nC-1 350 R.min-1.nA-159 Gy.μC-1 3.5 Gy.min-1.nA-1 |
| Energy range for X and gamma radiation: (a) Without build-up cap: (measures exposure) |
100kV to 300kV |
| (b) With build-up cap: (measures exposure) | 0.3MV to 2MV |
| (c) In suitable phantom (measures absorbed dose to water) | 2MV to 35MV |
| Energy range for electrons: In suitable phantom (measures absorbed dose to water) | 5MeV to 35MeV |
| Leakage current:
Typical: Maximum: |
5 x 10-15A
1.5 x 10-14A |
| Maximum exposure rate (approx) or 99% collection efficiency: | |
| Polarising potential—250V | 50 kR.min-1, continuous 100 mR/Pulse, pulsed50 Gy.min-1, continuous 1 mGy/Pulse, pulsed |
| Polarising potential—400V | 130 kR.min-1, continuous 150mR/Pulse, pulsed1.3 kGy.min-1, continuous 1.5 mGy/Pulse, pulsed |
NPL-2611 SECONDARY STANDARD THERAPY DOSIMETRY CHAMBER
The 2611A chamber consists of a thin walled high purity graphite thimble, amber insulators and a hollow pure aluminium electrode supported by a thin walled aluminium stem.
The stem terminates in a robust cable entry, by which the chamber is mounted to a 10 metre length of low noise triaxial cable to a BNC triaxial plug and is provided with a Triax TNC converter.
Key Features:
- Air Vented Chamber – so air density corrections are to be applied
- The chamber is manufactured in the UK by the ‘NPL’ (National Physical Laboratory)
- Maintenance and Calibration are carried out by NPL
- Secondary Standard calibrations for Electrons and Photons are carried out normally twice per annum and are available directly from NPL
Sleeve for 2611 in IBA CDC Check source
Performance
- Energy response — uniform +/- 1% from 1.0mm AL 20mm AL HVL (0.030mm Cu to 4.00mm Cu HVL)
- Sensitivity – 11nC/Gy nominal
- Better than +/- 0.35 over 3 years
- Polarising potential— 200V / Max +/-400 V DC
- Collection efficiency (HV@-200V) – continuous radiation better than 99.9% for dose/pulse values less than 43.5 microGy
- Leakage – better than +/-2X10E-14A
Accessories:
- NPLSL—Water Proof Sleeve (one delivered with each new chamber)
- NPLCDC – Sleeve to accommodate NPL-2611 into IBA CDC Check Source—see picture above
- NE2566A — Perspex Phantom for Intercomparison between Farmer Type and 0.33cc Secondary Standard Chambers
| Specification | |
| Active Dimensions | Sensitive Volume—325mm3 Length of volukme—9.22mm Thimble wall thickness– 0.5mm Diameter—7.35 mm |
| Exterior Dimensions | Length — 185mm
Diameter — 12.5 mm |
| Materials | Thimble—high density (1.80b/cm3) high purity extruded graphite Collecting electrode – aluminium 99.99% pure Main insulator — amber stem insulators P.C.T.F.E. HV insulator – Delrin The chamber stem is guarded to a point 15mm from the measuring Volume |
| Reference Point | The effective measurement point for positioning the chamber should be taken to be the axis of the chamber 5mm from the tip of the graphite thimble |
| Venting | To ensure that the chamber is equilibrated with the atmosphere the measuring volume is vented giving pressure equilibration times for just a few seconds |
| Build up Cap | Delrin, with external diameter of 17.0 mm and wall thickness of 600mg/cm2 |
| Cable | Suhner GO 233OHT connections Centre core—signal at HV Inner screen—guard at HV Outer screen—earth potential Length 10m |
