High Spatial and Temporal Resolution Particle Detectors

In associated particle imaging (API) applications, an alpha particle detector is used to “tag” an alpha particle with an associated neutron in both space and time. To increase the efficiency and accuracy with which associated neutrons are tagged, faster alpha particle detectors with higher spatial and temporal resolution are desired. The combination of API with transmission imaging is sometimes referred to as associated particle neutron radiography (APNR). The use of time and direction tagging allows the APNR system to effectively remove measurement noise resulting from scattered neutrons (This technique is sometimes referred to as “electronic collimation.”). The elimination of scattered neutrons enables high-contrast images to be generated, even through thick objects (e.g., large cargo containers), without the need for any physical collimation or shaping of the neutron beam. The present alpha detector is a 100 to 500 micron-thick YAP:Ce scintillator that is mounted inside a deuterium-tritium (DT) generator adjacent to a fiber optic faceplate that transmits the scintillation light to the outside where it can be detected by a photomultiplier tube. The current configuration of a single crystal adjacent to a fiber optic faceplate results in a loss of approximately 67% of the light. In this work, we are fabricating and testing innovative high-resolution fiber optic scintillation detectors where one or more scintillation activator dopants (e.g., Ce3+) are optimally incorporated into one end of the fibers. Doping to form the sensitive region of the fiber is being conducted using ion implantation, thermal diffusion, and physical deposition methods. Increased light collection will improve both the spatial and temporal resolution. In addition, the proposed detector sensitive region is extremely thin (~5 microns for an alpha detector) and is, therefore, less sensitive to x-rays. This decreased sensitivity to xrays allows alpha-produced light pulses of lower magnitude to be discriminated from xrays, thus increasing the fraction of alpha pulses detected. Successful implementation of this method will lead to an improvement by a factor of ~4 in the spatial resolution and a factor of up to ~2 in the timing resolution (a property of most benefit to scatter imaging techniques).