Simple Two-PMT Directional Detector for Radiation Source Localization in Nuclear Security Applications

If lost or stolen, radioactive materials can be located and secured using various radiation detectors, though traditional radiation detectors and radiation imaging systems may not allow for the swift localization of lost sources in many measurement scenarios. A simple, low-cost, directional radiation detector that can quickly “point” towards the nearest radiation source is sought for source search scenarios. A simple directional detector can be constructed using a plastic scintillator coupled to dual-end readout photomultiplier tubes. The interaction position of scattering events in the dimension of orientation of the two photomultipliers can be determined by averaging the amount of light arriving at each of the photomultiplier tubes during coincidence counting. The detector system can then be rotated so the average interaction position within the detector volume can be found in other spatial dimensions. A “guess vector” drawn through the centroid of the detector and the point of intersection of the average intra-detector interaction positions across at least two dimensions should point in the direction of a nearby radiation source. An MCNPX-PoliMi model was used to guide the design of a detector using this concept and to validate the guess vector technique. A prototype system using a cube of an EJ-204 fast plastic scintillator and two photomultiplier tubes was constructed. The detector prototype efficiency and source direction convergence time are characterized. Applications for such as system are discussed in the context of nuclear and radiological security.