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Farmer® Ionization Chamber 30012

Farmer chamber with graphite wall for reference dosimetry in high-energy photon, electron and proton beams

  • Graphite wall
  • Aluminum central electrode
  • Sensitive volume 0.6 cm3 , vented
  • Reference class in accordance with IEC 60731

The 30012 Farmer chamber is intended for reference dose measurements in radiation therapy.
Correction factors needed to determine absorbed dose to water or air kerma are published in the pertinent dosimetry protocols.
The graphite wall makes the chamber almost water equivalent, the aluminum central electrode improves the energy response at energies below 60Co.
The chamber is intended for the use in solid state phantoms and therefore not waterproof.

Type of product vented cylindrical ionization chamber
Application reference dosimetry in solid state
  phantoms and air
Measuring quantities absorbed dose to water, air kerma, exposure
Reference radiation quality 60Co
Design not waterproof, vented, guarded
Direction of incidence radial
Nominal sensitive volume 0.6 cm3
Nominal response 20 nC/Gy
Long-term stability ≤ 0.5 % per year
Chamber voltage 400 V nominal
  ± 500 V maximal
Polarity effect at 60Co < 0.5 %
Reference point on chamber axis, 13 mm from chamber tip
Photon energy response ≤ ± 2 % (70 kV ... 280 kV)
  ≤ ± 4 % (200 kV ... 60Co)
Directional response in solid state phantom ≤ ± 0.5 % for rotation around the chamber axis and for tilting of the axis up to ± 5°
Leakage current ≤ ± 4 fA
Cable leakage ≤ 1 pC/(Gy·cm)

Materials and measures

Wall of sensitive volume 0.425 mm graphite, 1.85 g/cm3
Total wall area density 79 mg/cm2
Dimensions of sensitive volume radius 3.05 mm
  length 23.0 mm
Central electrode Al 99.98, diameter 1.15 mm
Build-up cap PMMA, thickness 4.55 mm

Ion collection efficiency at nominal voltage

Ion collection time 140 μs
Max. dose rate for  
≥ 99.5 % saturation 5 Gy/s
≥ 99.0 % saturation 10 Gy/s
Max. dose per pulse for  
≥ 99.5 % saturation 0.46 mGy
≥ 99.0 % saturation 0.91 mGy

Ranges of use

Chamber voltage ± (100 ... 400) V
Radiation quality 60 kV ... 50 MV photons
  (10 ... 45) MeV electrons
  (50 ... 270) MeV protons
Field size (5 x 5) cm2 ... (40 x 40) cm2
Temperature (10 ... 40) °C
  (50 ... 104) °F
Humidity (10 ... 80) %, max 20 g/m3
Air pressure (700 ... 1060) hPa

Options

T48012 Radioactive check device 90Sr
T48002.3.003 Chamber holding device for check device
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