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Direct-Reading Dosimeter - Low-Range Models

All models are available with a protective hard (sapphire) window to prevent the lens from being scratched in a harsh environment.

Licensed from the U.S. Government under Patent No. 5,426,305

The Direct-Reading Dosimeter is a pocketsize, carbon-fiber electroscope with a thinwalled chamber for detecting exposure to Gamma and X-Ray radiation.

The low energy feature has hospital applications including fluoroscopy, portable radiography and angiography.

This pocket-size instrument is lightweight and has a sturdy metal clip to attach to an individual’s pocket. The entire unit is hermitically sealed and waterproof.
Low Range Models include:
Model Range
138 0- 200mR
138-S 0- 2mSv
500 0- 500mR
500-S 0- 5mSv

Radiation Detected Gamma and X-Ray from 16 keV to 6 MeV
Ranges 0 -200 mR, 0 - 500 mR, 0 - 2 mSv, 0 - 5 mSv
DetectorFiber electrometer mounted in an electrically conductive plastic ion chamber
Detector HousingVery low permeability plastics-hermetically sealed
AccuracyWithin + or - 10% of true exposure
Rate ResponseDose rate independent for gamma and x-ray
Electrical LeakageLess than 1.0% of full scale for 24 hours at 50 C
Temperature Range-20 degrees C to + 50 degrees C
Relative HumidityUp to 90%
DimensionsLength : 4.5” (12.4 cm) Diameter .6 “ (1.5 cm)
Weight1.0 oz (25 grams)
FinishBarrel and End Caps are Natural Matte Black with Metal Clip
Warranty2 Year Limited Warranty

All dosimeters are tested for compliance with ANSI specifications and customer specification requirements. All test equipment is calibrated, with documentation of traceability to NIST standards. All dosimeters are identified as to model number, range, manufacturer’s name, and unique serial number.

Accumulated radiation is read directly on an internal calibrated scale. A Dosimeter Charger is required in order to return the dosimeter to zero after each exposure or when desired.

A conductive fiber dosimeter is a rugged precision instrument consisting of an ionization chamber (5) sensitive to radiation. A conductive fiber electrometer (4) which measures the charge: and a microscope to read the shadow of the fiber on a reticle(scale) (8).

Direct-Reading Dosimeter Operation

Item Description
1Diaphragm Switch
2 Electrostatic Shield
3 Charging Pin
4 Electrometer
5 Ionization Chamber
6 Objective Lens Holder
7 Objective Lens
8 Eye Piece/Reticle
9 Eyepiece Spacer
10 Eyepiece Lens ? 2
11 Upper Barrel
12 Upper End Cap
13 Lower Barrel
14 Lower End Cap
15 Window
16 Metal/Pocket Clip
17 Frame
19 Conductive Fiber
20 Upper Barrel Insert
25 Decal/Label

The electrometer embodies two electrodes, one of which is a moveable conductive fiber. When the electrometer is charged to a predetermined voltage, the electrodes assume a calibrated separation.

As the dosimeter is exposed to radiation, ionization occurs in the surrounding chamber decreasing the charge on the electrodes in proportion to the exposure. The deflection of the moveable conductive fiber electrodes is projected by a light source, through an objective lens (7) to the calibrated reticle and read through a microscope eyepiece (8, 9, 10).

Illumination for the optical system is obtained by pointing the dosimeter at any convenient light source. Light passes through the clear plastic electrostatic shield (2) to illuminate the reticle.

The bottom is sealed by the clear plastic diaphragm switch (1) containing an insulated charge pin (3). When charging, the charge pin moves up to contact the electrometer closing the circuit. Sufficient voltage is applied to recharge the system.

The entire system is encased in a liquid crystal polymer (LCP) barrel (11 & 13) with all joints hermetically sealed with epoxy.

Licensed from the U.S. Government under Patent No. 5,426,305

Arrow-Tech, Inc. recommends a yearly calibration of the Direct Reading Dosimeter which is generally consistent with good health physics practices. More frequent calibration may be necessary should the user’s license require a shorter calibration interval

Dosimeters are extremely sensitive instruments. Although they are constructed for rugged use, they should receive the same care as a wristwatch. Since dosimeters are hermetically sealed at the factory, they cannot be repaired or adjusted in the field. Therefore, if instrument malfunctioning is experienced, the instrument should be returned to the factory or your dealer. Dosimeters may be maintained in operating condition simply by cleaning the eyepiece lens and the charging switch insulator with clean water and a cloth that is free of lint and grit. Make sure the charging switch insulator is absolutely free of lint and moisture at all times.

Caution: Do not insert any sharp objects into, or tamper with parts in the charging switch recess. Irreparable damage may be done