A High Sensitivity, High Resolution Imaging Detector for Alpha Particles

The storage photostimulable phosphor (SPP) technique has been demonstrated to be sensitive to ionization radiation. It is especially suited for detecting alpha particles since the efficiency is practically 100%. In addition to being able to quantify total ionization deposited in a SPP sensor, it also captures the radiation source distribution information in a digital image which can be readily analyzed. The high spatial resolution of the SPP imaging system provides an additional dimension to enhance the detectability of low-level alpha radiation. For example, SPP image of tracks left by single alpha particles is measurably different from those caused by other types of radiation, including cosmic rays. An image processing technique "grain counting" will be applied to utilize this feature to significantly improve the signal to noise ratio of alpha radiation measurement. The goal for Phase 1 is to be able to measure alpha activity of 10 dpm/100 cm2 or lower reliably in minutes. With modification in SPP sensor construction and the use of a shielded portable glove box in Phase 2, the lower detection limit can be pushed by two orders of magnitude or more to meet the stringent need of the electronic industry. To ensure the quality of measurement sets of reference sources will be designed and produced by incorporating NIST standard reference materials into thin electrical insulating polymers. The incorporation method researched here can be used to produce families of standard references for nuclear industry and environmental monitoring purposes.