PROTON MICROPROBE FOR TRACE ELEMENT ANALYSIS IN TISSUE

RECENT PROTON MICROPROBE STUDIES ON TRACE ELEMENTS IN SEVERAL HUMAN DISORDERS HAVE SHOWN THE SUPERIORITY OF THE PROTON AS COMPARED TO THE ELECTRON MICROPROBE. THIS HAS BEEN DRAMATICALLY DEMONSTRATED IN STUDIES OF ALUMINUM IN ALZHEIMER'S DISEASE. THE REASON FOR THE PROTON BEAM'S SUPERIORITY IS THE SUPPRESSION OF BACKGROUND X-RAY GENERATION WHEN LOOKING AT X-RAYS CHARACTERISTIC OF THE TRACE ELEMENTS. IT IS DESIRABLE TO HAVE A 2-MEV PROTON BEAM WITH 0.3-MICRON RESOLUTION (COMPARABLE TO AN ELECTRON MICROPROBE) WITH AT LEAST 100 PICOAMPERES OF CURRENT FOR THE TECHNIQUE OF PROTON-INDUCED X-RAY EMISSION. PRELIMINARY CALCULATIONS OF THE SECOND ORDER HAVE BEEN MADE FOR A FOCUSING SYSTEM TO MEET THESE CRITERIA. MEASUREMENTS HAVE ALSO BEEN MADE OF BEAM CURRENT FROM AN ACCELERATOR TO SHOW THAT THE DESIRED CURRENT CAN BE OBTAINED WITHIN THE CALCULATED FOCUSING SYSTEM ACCEPTANCE. WORK CARRIED OUT DURING PHASE I WILL SIMULATE PROTON TRAJECTORIES THROUGH THE PROPOSED FOCUSING SYSTEM TO ALL ORDERS AND, HENCE, FIRMLY ESTABLISH THE MERIT AND TECHNICAL FEASIBILITY OF THE TECHNIQUE. THE EFFECTS OF ABERRATIONS, MISALIGNMENTS, AND MANUFACTURING TOLERANCES WILL BE CALCULATED. AT PRESENT, THERE IS NO COMMERCIAL PRODUCTION OF PROTON MICROPROBES.