LUDLUM Measurement Neutron Dose Survey Meter

The Ludlum Model 15 detects and measures alphas, betas, gammas, and neutrons. A GM detector can be selected by the user to obtain alpha-beta-gamma readings. The neutron count rate measurement is provided by a 3He proportional detector that is outfitted with a removable moderator.

The ratemeter is a four-decade, analog meter designed with a cast aluminum instrument housing, incorporating a separate battery compartment and accompanying metal handle. This design delivers industrial robustness and quality, promoting long-lasting protection and instrument life. The front-panel controls include a rotary switch for selecting the four-decade range, instrument shut-off, and battery test; an audio on/off switch; a fast/slow response switch; a GM/Neutron Detector switch; a count reset; and high-voltage test pushbutton. The Model 15 is a complete turn-key system and includes two "D" cell batteries.

Neutron Detector (Model 42-14H)
Detector Type: 2 atm ³He proportional detector with 7.6 cm (3 in.) diameter, cadmium-lined (removable) moderator for thermal neutrons
Sensitivity (bare ²⁴¹AmBe): 55 cpm per mrem/hr
Detection Range: Thermal to approximately 12 MeV
Energy Response: Not linear through energy spectrum (0.025 to 12.0 MeV)
Gamma Rejection (¹³⁷Cs gamma): < 10 cpm through 10 R/hr

Alpha-Beta-Gamma Detector (Model 44-7)
Detector Type: Thin end-window GM detector
Window: 2.0 ± 0.3 mg/cm² mica
Window Area: Active: 6.4 cm² (1 in²); Open: 5.2 cm2 (0.8 in²)
Efficiency (4π): ¹⁴C: 2%, ⁹⁰Sr/⁹⁰Y: 10%, ⁹⁹Tc: 7%, ²³⁹Pu: 7%
Sensitivity (¹³⁷Cs gamma): Typically 2100 cpm per mR/hr
Energy Response: Energy dependent
Background: Approximately 40 cpm

Controls:
Multi-Selector Switch: Range multiplers (x1, x10, x100, x1000), Battery Check, Off
Audio: On/Off switch
Response Time: Pushbutton to zero meter
Detector Switch: For displaying either the alpha-beta-gamma detector or neutron detector count rate
High Voltage: Test pushbutton
Reset: Count rate pushbutton