Ionisation Chambers

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.

NE2571-NE2581 Ionisation Chamber Master

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: 10mm
NE2571 Farmer
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.

NE2581 Robust Farmer 0.6cc Ionisation Chamber

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.

NPL2611

 

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

NPL2611

 

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 left picture
  • 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/cm3high 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

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