Saxet Surface Science — Department of Energy SBIR Phase I: Future experiments in nuclear (and particle) physics will require advances in detector tec

Description

Future experiments in nuclear (and particle) physics will require advances in detector technology in order to carry out planned measurements of QCD, electroweak interactions, studies of fundamental symmetries, understanding the spin properties of nucleons, and many other physics topics. Among the desired advancements is the development of robust, compact photomultiplier tube (PMT) capable of working in high magnetic fields. The Photocopia PMT takes advantage of two of the many unique properties of the hydrogenated amorphous silicon-germanium (a-SiGe) photoemitter material: its mechanical flexibility and mostly substrate-independent properties. The a-SiGe photoemitter has high secondary electron (SE) yield. It can be used both as the photocathode and as the gain medium. The active material can be grown on a flat, thin unibody substrate, formed and then rolled up ex situ. The completed structure would then be activated and sealed within a tube. The Ge component can be increased to enhance red-sensitivity. Compact sizes are possible, minimizing magnetic field effects. The Photocopia PMT will be a low cost alternative to MCPs for TOF detectors and provide better timing discrimination for Cherenkov detectors. Retention of the ability to activate to a normal photoyield state upon flexing (bending) the substrate of the a-SiGe material after growth, but prior to activation will be shown. The SE coefficient of the activated material also will need to be closely characterized over the voltage range suitable for utilization as the gain material. A demonstration standalone tube with an in situ activated a-SiGe photoemitter has been previously constructed and shown to exhibit a typical vacuum diode characteristic curve. Commercial Applications and Other Benefits: One need is enhancement and/or reduced cost for detectors employed in the positron emission tomography (PET) scanners used in PET imaging. This technique utilizes the positron-electron annihilation emission of paired gamma rays to generate 3D medical scans. The numbers of PMTs is multiplicatively reduced from that of the scintillators primarily as a cost saving feature. Reduced cost PMTs would allow higher density detectors and therefore greater resolution for more precise detection and differentiation between highly metabolic tissue (cancer) over normal tissue. Keeping the same number of PMTs would allow the manufacture of more affordable PET scanners and thereby serve the public by making the technique more available for medical applications and diagnoses. Reliable, lower cost PMTs will always find a ready market for their use in science and engineering applications as individual detectors. One inhibitor for the sale of PMTs has always been price.