Ludlum’s Model 3-98 is uniquely configured to optimize measurements for ¹²⁵I and any alpha beta 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 read 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. An optional 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 aluminum cast 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), convenient detector clip, and two “D” cell batteries.