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Model 3-98

Ludlum's Model 3-98 is uniquely configured to optimize measurements for 125I and any alpha, beta, or gamma contamination. The dual detector design allows the user to select the detector for the task at hand. The internally-housed GM pancake detector can be used to measure gamma. This detector's face can be exposed via a slide located along the bottom of the instrument, thus making it sensitive to alpha and beta as well. The external NaI detector, Ludlum Model 44-3, is optimized for low-energy gamma from 125I.

The ratemeter is Ludlum's venerable Model 3-series, which employs a robust, cast aluminum instrument housing with a separate battery compartment for long-lasting protection and long instrument life. The front-panel controls include a rotary switch for selecting the 4-decade range, instrument shut-off and battery test, audio on/off switch, fast/slow response switch, count reset button, and internal/external detector switch. Also included are a standard 1-meter (39 inch) cable with series "C" connector (others available), detector clip, and two "D" cell batteries.

  • Dual Purpose Detection
  • 125I & Alpha-Beta-Gamma Contamination
  • 4-Range Analog Ratemeter
    • Rugged Construction
  • 0 to 500 kcpm
  • User-Selectable Internal and External Detectors
Indicated Use:
Alpha, beta, low-energy gamma survey
Internal Detector:
Type: Pancake-style GM detector with 1.7 ± 0.3 mg/cm² window; stainless steel protective screen (79% open) Active Area: 15.51 cm2 (2.4 in2) Open Area: 12.26 cm2 (1.9 in2) Efficiency (4π): 14C: 5%, 90Sr/90Y: 23%, 99Tc: 19%, 32P: 33%, 239Pu: 15% Sensitivity (137Cs gamma): Typically 3300 cpm per mR/hr Alpha-Beta Shield: Retractable 211 mg/cm2 phenolic slide
External Detector:
Type: Model 44-3: 125I and low-energy gamma scintillator Efficiency (4π): 125I: 33.5% (based on 129I efficiency of 18%) Sensitivity (125I): 675 cpm per μR/hr Energy Range: Recommended 5 keV to 60 keV Background (10 µR/hr): < 350 cpm
Reading within ±10% of true value with detector connected
Meter Dial:
0 - 5 kcpm, BAT TEST (Meter Faces tab lists other available meter faces)
6.4 cm (2.5 in.) arc, 1 mA analog type
Rotary Selector Switch: x0.1, x1, x10, x100 Response Switch: Toggle switch for FAST (4 s) or SLOW (22 s) from 10% to 90% of final reading Reset Push-Button: Push-button to zero meter Audio Switch: Built-in unimorph speaker with ON/OFF switch (greater than 60 dB at 0.61m [2 ft]) Calibration Controls: Accessible from front of instrument (protective cover provided) Int/Ext Switch: Selects the internal GM detector or the external detector
High Voltage:
Adjustable from 400 to 1500 V
-30 mV ± 10 mV
Temperature Range:
-20 to 50 °C (-4 to 122 °F)
2 "D" cell batteries (housed in sealed compartment that is externally accessible)
Battery Life:
Typically 600 hours with alkaline batteries (battery condition can be checked on meter)
Cast and drawn aluminum with beige powder coating
Series "C" (others available)
Size (H x W x L):
24.1 x 8.9 x 21.6 cm (9.5 x 3.5 x 8.5 in.) with handle
2.5 kg (5.6 lb) including batteries and detector
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