Evaluating Minimum Detectable Activity as a Function of Velocity

Abstract:

Radiation detectors are deployed for many different uses in a variety of different field conditions, and many of these detection systems are mobile. The efficiency of radiation detection systems is known to decrease as the speed of the detection system increases. Understanding how these systems perform under increasing speeds and in changing environments will help improve the system’s effectiveness and ultimately decrease the cost of performing a survey. This research is a combination of simulation and experimentation. We used computer models to simulate simple detection systems and derive the underlying relationship between efficiency and speed. We then conducted experiments to verify this relationship using real world data. Data was first gathered in a laboratory using a 2 x 2 inch sodium iodide detector attached to a robot traveling between 20-120 centimeters per second. Data was then gathered outdoors using a 2x4x16 inch sodium iodide detector attached to a vehicle traveling between 10-40 miles per hour. Finally, we tested the relationship using aerial data provided by two partner groups gathered using large multi-detector systems traveling between 70-140 knots. By comparing field data with the results of the computer simulations, we was able to validate the relationship between efficiency and speed. Understanding how speed effects detector efficiency allows surveyors to tailor their survey plans for maximum effectiveness. Using this relationship, surveyors can be confident in their survey results, conduct surveys in the most efficient way possible, or identify lower thresholds for their surveys given operational constraints on their detection system.