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.