The CsI (Tl) crystal used in Radiation Alert® Probes has a higher atomic number, is more rugged, and less hygroscopic than a typical Nal detector. The improved gamma ray absorption allows a thinner crystal to be used, effectively reducing the background count rate.

Detector
Type-CsI (Tl) crystal (Cesium Iodide Thallium)
RAP47 - 1.0" dia. x .04" thick (25.4 x 1.0mm)
RAP200 - 1.0" dia. x .25" thick (25.4 x 6.35mm)
RAP640 - 1.0" dia x 1.0" thick (25.4 x 25.4mm)
Radiation Detected
RAP47 - gamma 8 keV to 1 MeV.
Typical Absorption 100% at 47keV, 80% at 100 keV
RAP200 - gamma 8 keV to 1 MeV.
Typical Absorption 97% at 1007keV, 77% at 185 keV
RAP640 - gamma 8 keV to 3 MeV.
Typical Absorption 70% at 600 keV, 50% at 840 keV
Probe Construction
Anodized aluminum housing. Approximate size: length 7-7.5 inches, diameter 1.5 inches. Connectors-Standard MHV. Cable (Optional)-Straight RG59/u, length 3.5 feet.
Temperature Range
-25°C to 40°C (-4°F to 104°F)
Humidity Range
0 to 90% Relative Humidity.
Weight
RAP47-Approx. 178 g (6.3 oz.) without cable
RAP200-Approx. 240 g (8.5 oz.) without cable
RAP640-Approx. 290 g (10.25 oz.) without cable
Warranty
One year limited.

RAP47: Thin-crystal (1 mm) optimizes sensitivity to low energy gamma radiation while minimizing sensitivity to higher energies. An excellent detector for Iodine-125 and suitable for thyroid uptake measurements	RAP200: A 0.25-inch crystal optimizes this for the detection of special nuclear material (SNM) such as U-235, or related isotopes such as Am-241, much like a mini-FIDLER.
RAP640: Superior to a 1 x 1-inch NaI detector, this is a great choice for an all-around gamma and x-ray detector. Optimal energy range of about 20 keV to 2 MeV. Highest efficiency for a broad spectrum of gamma-emitting isotopes.	All RAP Scintillation probes work with the URSA-II Universal Radiation Spectrum Analyzer.