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Model RD-59
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The Model RD-59 is an offline radiation detector assembly for use as a process or continuous air monitor (CAM). It has two separate scintillation detectors, iodine and gas. Both are contained in one compact 3-in.-thick, 4π solid-lead shield, providing significant reductions in physical size, weight, and cost over earlier designs without reducing performance. Each detector can be easily and quickly serviced by just one person. Solenoid-actuated checksources are provided for each detector to verify proper operation. Various scintillator sizes are available, providing a choice of sensitivities and ranges.

Specifications

IODINE FILTER: TEDA-impregnated charcoal-filter cartridge (standard); silver zeolite available as an option SENSITIVE VOLUME (GAS): 25 in.3 (410 cm3) DETECTORS: 2-in. (5-cm) –diam x 2.0-in. (0.5-cm) –thick spectrometer-grade NaI(TI) crystal doped with Am241, optically coupled to a 2-in. (5-cm) –diam photomultiplier tube (standard iodine detector); 2-in. (5-cm) –diam x 0.01-in. (0.03-cm) –thick beta phosphor, 2-in. (5-cm) –diam photomultiplier tube (standard gas detector) CHECKSOURCES: <9 µCi Ba133 (gamma), iodine detector; <0.05 µCi Cl36 (beta), gas detector SAMPLE PRESSURE: 15 lb/in.2 (1.05 kg/cm2) gauge (max) SAMPLE TEMPERATURE: 35° to 120°F (2° to 49°C)

SAMPLE FLOW: 3 ft3/min (1400 cm3/min) nominal SAMPLE HUMIDITY: Up to 95% relative humidity (noncondensing) PRESSURE DROP ACROSS INLET/OUTLET: Approximate 3 in. (7.6 cm) Hg with clean cartridge at nominal flow ELECTRICAL CONNECTORS (ON EACH DETECTOR): High voltage – MHV; signal – BNC SAMPLE CONDITIONING: Filtering (typically of particulates) provided upstream of the detectors to inhibit radioactive contamination of the detectors INLET/OUTLET: 0.5-in. (1.3-cm) –diam stainless steel tubing SAMPLE MATERIAL: Type 304 stainless steel or carbon steel except aluminum foil detector windows and selected other materials including O-ring seals

Calibration

The energy response curve for the gas detector is shown below. The gamma spectrum of I¹³¹ shows how the major photo peak at 364 keV is monitored with a window of 40 keV (~10%). Also shown is the Am²⁴¹ reference peak used for pulse height stabilization.

*Average rather than end-point, beta energies better represent actual detector operation since beta particles from most isotopes are not monoenergetic. Using end-point beta energies would appear in improved, although perhaps misleading, performance.

Channel Phospor size [in.(cm)] cpm*ambient cpm/mR/hr Co60 Sensitivity (Isotope) Iodine 2 (5) diam x 2 (5) thick NaI(TI) 17 54 1.01 x 105 cpm/µCi (I131)   Gas 2 (5) diam x 0.01 (0.03) thick plastic 36 39 3.58 x 107 cpm/µCi (I131) (Kr85) 1.84 x 107 cpm/µCi/cm3 (Xe133)

*Includes normal contributions from cosmic, natural, internal, and checksource background.

Minimum Detectable Activity (MDA) and Minimum Detectable Concentration (MDC)

Iodine Detector:

MDA and MDC for I¹³¹ in a 0.1-mR/hr Co⁶⁰ gamma field:

MDA= 2.10 x 10^-5 (2.10 x 10^-1 Bq) µCi I¹³¹

MDC= 1.05 x 10^-12 µCi/cm³ (3.90 x 10^-2 Bq/m³) I¹³¹

Gas Detector:

MDC for Xe¹³³ in a 0.1 mR/hr Co⁶⁰ gamma field:

MDC = 1.30 x 10^-7 µCi/cm³ Xe¹³³

MDA: 2.10 x 10^-5 µCi I¹³¹

MDC: 1.05 x 10^-12 µCi/cm3 I¹³¹

MDC = 1.30 x 10^-7 µCi/cm³ Xe¹³³