Validating a Methodology That Associates Minimum Detectable Activity with Detector Velocity

Abstract

Mobile radiation detection systems are used widely in remediation and nuclear security. However, their detection efficiency and thus their minimum detectable activity is not completely understood. It is recognized that the detector's velocity will affect its detection efficiency. At lower speeds, detection efficiency will be higher than a detector moving at higher speeds. The relationship describing how speed and efficiency are related was only recently quantified using a modified four-parameter logistic function (M4PL). The current research verifies the M4PL function in a controlled laboratory setting using a 5.08 cm  5.08 cm sodium iodide detector at speeds between 20-120 cm s −1 . As expected, the M4PL function indicates a detection system's highest efficiency at low speeds and its lowest efficiency at higher speed. In between is a transition region of decreasing detector efficiency. This decrease is gradual within initial speeds but quickly steepens and then approaches a minimum at higher detector speeds. This general shape was observed in the experimental data and validated the M4PL function as a predictive tool. To conclude this research and to demonstrate the function's usefulness, a relationship between speed and minimum detectable activity (MDA) was developed. Using this function and the methods described in this research, planners can now optimize surveys by controlling velocity to maintain MDA. It is also possible to use this technique to accelerate surveys while having the ability to predict the reduction in MDA. This foundational relationship between detector speed and detection efficiency has the potential to improve detector performance in various applications for both the academic and operational fields.