Gamma Iodine Detector

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Gamma Iodine Detector

The Model RD-55 detector assembly measures concentrations of gamma-emitting I¹³¹ isotopes adsorbed into an activated charcoal or silver zeolite filter. It can operate in a gamma flux background. The shield assembly consists of a steel-jacketed, horizontal, cast-lead cylinder with a center stainless-steel sleeve. An easily removable lead plug and an iodine-collection-cartridge assembly cap the front end of the shield. The opposite end is capped by a lead plug and an Am²⁴¹-doped NaI (TI) detector assembly. The cylindrical shield and end plug provide full 4π shielding. There is an easily removable lead plug and an iodine collection cartridge assembly that cap the front end of the shield.

Specifications:

FILTER: TEDA-impregnated charcoal-filter or silver zeolite cartridge

SHIELDING: 3- and 4-in. (7.6- and 10.2-cm) full 4π solid cast lead

WEIGHT: Depends on shield thickness (see table of dimensions, back page)

DETECTOR: 2-in. (5-cm) –diam x 2-in. (5-cm) –thick spectrometer-grade NaI (TI) crystal, optically coupled to 2-in. (5-cm) –diam photomultiplier tube. Am²⁴¹ doped for thermal stability

CHECKSOURCE: <10 μCi Ba¹³³

SAMPLE PRESSURE: 15 psi (1.05 kg/cm²) gauge max

SAMPLE HUMIDITY: Up to 95% relative humidity (noncondensing)

SAMPLE TEMPERATURE: 35° to 120°F (2° to 49°C)

SAMPLE FLOW: 3 scfm (14 liters/min) nominal

INLET/OUTLET: 0.5-in. (1.3-cm) –diam stainless-steel tubing

SAMPLER MATERIAL: Type 304 stainless steel or carbon steel except aluminum foil detector windows and selected other materials including O-ring seals

PRESSURE DROP ACROSS INLET/OUTLET: Approximately 4-in. (10-cm) Hg with clean filters at nominal flow

ELECTRICAL CONNECTORS: High voltage – MHV; signal – BNC

Calibration

No energy response curve is provided, since only one energy level is of interest. The gamma spectrum of I¹³¹ shows the major photo peak at 364 keV and the digital signal processor single-channel analyzer 40 keV window. Detector I¹³¹ sensitivity is determined for this window.

*Average, rather than end-point, beta energies better represent actual detector operation, since beta particles from most isotopes are not

Phosphor Size [in. (cm)]	Lead Thickness [in. (cm)]/Model No.	cpm* ambient	cpm/mR/hr Co⁶⁰	cpm/µCi I¹³¹
2 (5) diam. X 2 (5) thick	3 (7.6)/RD-55-30	17	54	1.01 x 10⁵
2 (5) diam. X 2 (5) thick	4 (10.2)/RD-55-40	09	16	1.01 x 10⁵

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

Minimum Detectable Activity (MDA) and Minimum Detectable Concentration (MDC) for RD-55-30.

Iodine Detector:

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

MDA: 2.10 x 10^-5 µCi (7.77 x 10^-1 Bq) I¹³¹

MDC: 1.05 x 10^-12 µCi/cm³ (3.89 x 10^-2 Bq/m³) I¹³¹