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