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The
FWT EIC-1 is a tissue equivalent parallel plate ionization chamber
specifically designed for skin sparing measurements. The electrode
spacing is continuously adjustable, making it a true extrapolation
chamber.
The detecting volume (which includes one-half of the insulator thickness
on each side) is a right circular cylinder whose height is adjusted
by turning an aluminum ring on which the entrance window is mounted.
This ring turns on a brass sleeve, and a reference mark permits
repeatable settings.
The entrance window is conductive polyethylene. An optional thin
dag-coated polypropylene window is also available. The collecting
electrode and the guard ring are made of conducting tissue equivalent
plastic, and the signal insulator is polyethylene. The inner wall
of the adjustable ring carrying the entrance window has a 0.150-inch-thick
polyethylene liner to prevent electron contamination from the aluminum
wall . No metal is exposed to the chamber interior.
Chamber voltage should be 50V or less at the nominal 0 turn spacing
and 250 V at greater spacing. Both positive and negative polarities
may be used on the high voltage. The window and support ring are
at this high voltage and caution must be used. At 20 rads per minute,
saturation is achieved with a chamber voltage of 20 V or greater
at the 2-turn (2-3 mm) spacing.
The optional gas provision flow will allow tissue equivalent (TE)
gas to be used in a flow mode. (A flow rate of 5 cc per minute or
less is recommended; higher rates may cause window bulging or modulation.)
Typical chambers have a sensitivity of 0.16 esu/rad with TE gas
and a spacing of 2.3 mm.
Applications
 Skin sparing
measurements, gamma rays, and neutrons
Soft x-ray
dosimetry
Beta source
dosimetry
Depth dose
data with a thin (0-3 mm) ionization chamber (either beta, gamma,
or neutron).
Electron
beam dosimetry
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Specifications
Type: Ionization
Chamber Parallel plate, guarded three terminal design, tissue equivalent
conducting plastic; one cm diameter sensitive volume; plate spacing
continuously variable from 0.3 mm to 4.5 mm.
Window: Conductive
polyethylene is standard, 6.9 mg/cm2; graphite coated polypropylene
is available at 0.2 mg/cm2.
Signal Connector:
BNC, mates with UG 260 B/U or equivalent.
Signal Output:
0.16 esu/rad with methane based T.E. gas and a plate spacing of
2.3 mm.
Signal Cable
Recommended: RG-59/U or equivalent.
Signal Connector:
Low noise coax, e.g. MALCO 250-3834-000.
High Voltage
Requirements: Positive or negative polarity, 20 to 500V. MHV mates
with UG 932 A/U or equal; optional SHV, mates with Star-Tronics
5135 or equal.
Overall Size
and Weight: Length including connectors 13.75 inches (35.0 cm);
stem is 11.5 inches (29.2 cm) long; weight 150 grams; wooden storage
box weight 1540 grams.
Calibrations
Furnished: Nominal esu/rad at one plate spacing; plate spacing at
zero turns.
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Ordering Information
EIC-1: Extrapolation
Chamber with storage box and calibration
EIC-1-GF:
Extrapolation Chamber with Gas flow provision, storage box, and
calibration
EIC-1-BD:
8 plastic buildup discs, 2 ea. 30, 2 ea. 60, 1 ea. 120, 240 , 600
and 1200 mg/cm2
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