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 Features
• Measures gamma or x-ray exposure rate
• Temperature compensated measurements
• Sliding shield for beta measurements
• Large, backlit display
• 5 ranges up to 50 R/h
• Extended battery life
• Non-mechanical range switching
The Model RO-20 is a portable air ionization chamber instrument, used to detect beta, gamma, and x-radiation, with five linear ranges of operation to measure exposure from background to 50 R/h full scale.
The ionization chamber is vented to atmospheric pressure and is specifically designed to have a flat energy response into the x-ray region. The detector is fully temperature compensated, eliminating any need for temperature correction. Each instrument is factory calibrated to gamma radiation.
A single rotary switch turns the instrument off, checks the batteries, checks the zero setting, and selects the range of operation. An ergonomically located switch illuminates the meter. Internal switching of ranges is accomplished with reed relays, eliminating the mechanical swing arms typically used with portable ion chamber survey instruments.
Detector
The RO-20 detector is an air-filled ionization chamber. It has a diameter of 7.32 cm and a volume of 220 cm3. The detector has 640 mg/cm2 phenolic walls inside a 1.6 mm aluminum wall case for a total thickness of approximately 1,000 mg/cm2. A 7.9 mm thick phenolic sliding beta shield with a positive friction lock is mounted on the bottom of the chamber. The shield thickness is approximately 1,000 mg/cm2. The chamber window is comprised of two layers (one on the chamber, one on the can) 25 micron (0.001”) mylar, approximately 7 mg/cm2 total.
Energy Response
Photon Response: Reference to 137Cs measured through the bottom with the slide closed, the energy response is:
• ± 30% from 8 keV to 1.3 MeV with the open slide facing the source.
• ± 15% from 33 keV to 1.3 MeV with the closed slide facing the source.
• ± 15% from 55 keV to 1.3 MeV through the side of the instrument
Beta Response: Uranium Slab: 30% of true mrad/h field behind
7 mg/cm2 window with RO-20 resting on slab, slide open. 90Sr90Y:
Approximately 93% of true mrad/h field at 30 cm with slide open.
Fast Neurton Response (PuBe): Reads approximately 8% in mR/h of true neutron field in mrem/h.
Radiation Detected: Beta, gamma, and x-ray.
Ranges: Five linear ranges: 0-5, 0-50, 0-500 mR/h and 0-5, 0-50 R/h
Meter: Scale length, approx. 7.6 cm (3”), 2% accuracy. Linear markings from 0 to 5 in 50 minor increments. The meter is back- lit
Response Time: 90% of final reading within 5 seconds, Linearity: Within ± 5% of full scale
Battery Dependence: Reading is independent of battery voltage
when the battery check indication is in the green arc.
External Controls: Range switch, including Off, Zero, and Battery checking positions. Zero knob used to set meter to zero when Zero position of range switch is selected or when in no significant radiation field. Light switch, for meter light.
Internal Control: Five calibration controls- one for each range.
Batteries: Main Power: Five “C” cells
Battery Life: “C” cells, widely variable according to RO-20 usage and battery type. Typical ZnC: mR/h ranges, 2900 hrs. All other ranges, 150 hrs. Typical Alkaline: mR/h ranges, 6900 hours. All other positions, 350 hours. Frequent or continuous use of the light will reduce battery life significantly. Thirty volt chamber bias battery life: Totally dependent upon the usage of “Battery 2” position switch. The battery capacity should allow for at least 50,000 five second battery checks. The battery drain is negligible on all other positions of the range switch.
Chamber Bias: Ten 3 volt lithium coin cells, 30 volts
Temperature: Operable from -40 °C to 60 °C (-70 °F to 140 °F) For operation below -18°C (0°F), alkaline or nickel-cadmium “C” cells should be used.
Temperature Compensation: The detector is fully compensated
over the operational temperature range for output accuracy within
10% ± 0.5 mR/h
Moisture: Seals used at openings for dust and water resistance.
Detector is protected by a silica-gel dryer.
Humidity: Operable from 0 to 95%, non-condensing
Weight: Approximately 3.6 lbs with alkaline C cells
Size: 4.2” W x 7.9” L x 7.7” H
Testing: The RO-20 has been successfully tested to ANSI N42.17A and is CE Certified to European standard EN50082-1 (EN61000-4-2 & EN61000-4-3)
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