Detector

The RO-20 AA detector is an air-filled ionization chamber. It has a diameter of 7.32 cm (2.88“) and a volume of 220 cm³ (13.4 in³).
The detector has 640 mg/cm² phenolic walls inside a 1.6 mm (0.063”) aluminum wall case for a total thickness of approximately
1,000 mg/cm². A 7.9 mm (5/16”) 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 AA resting on slab,
slide open. 90Sr90Y: Approximately 93 % of true mrad/h field at 30 cm with slide open.
Fast Neutron Response (PuBe): Reads approximately 8% in mR/h of true neutron field in mrem/h.

Radiological
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; see options below for faster response.
Linearity: Within ± 5 % of full scale.
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. Light switch, for meter light.
Internal Controls: Five calibration controls, one for each range.
Batteries: Main power: Five “AA” cells.
Chamber Bias: Three 12 volt standard “23A” alkaline cells, 36 volts.

Battery Life: “AA” cells, widely variable according to RO-20 AA usage. Typical Alkaline: mR/h ranges, 2500 hrs.
All other positions, 125 hrs. Frequent or continuous use of the light will reduce battery life significantly. 36 volt chamber bias battery life: Totally dependent upon the usage of “Battery 2″position of the range 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
Temperature: Operable from -40 °C to 60 °C (-40 °F to 140 °F).
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 3.3 pounds (1.47 kg) with alkaline AA cells.
Size: 201 L x 107 W x 196 H mm (7.9” L x 4.2” W x 7.7” H), including handle.
Testing: The RO-20 AA has been successfully tested to ANSI N42.17A
Options: 137Cs gamma check source: CS-7A
Carrying strap: ZP11466031