A NEGATIVE-ION SOURCE FOR HIGH-BRIGHTNESS MICROBEAMS

A NEGATIVE SPUTTER-ION SOURCE HAVING A HEMISPHERICAL IONIZER WILL BE FITTED WITH A SPUTTER TARGET OF NEW DESIGN, INTENDED TO ELIMINATE THE INSTABILITY AND SHORT LIFETIME OF PREVIOUS ION SOURCES OF THIS TYPE. A BRIGHTNESS OF 200 MICROAMPERES (PI-MILLIMETERS-MILLIRADIANS)(-2) (MEV)(-1) WILL BE SOUGHT, APPROXIMATELY 100 TIMES GREATER THAN EXISTING SOURCES HAVING HELICAL IONIZERS. HYDROGEN, OXYGEN, AND OTHER IONS WILL BE INVESTIGATED IN ORDER OF PRIORITY AS TIME PERMITS. THE BEAM WILL BE TRANSMITTED THROUGH A TANDEM ACCELERATOR HAVING 1.7-MEGAVOLT TERMINAL POTENTIAL, AND THE BRIGHTNESS OF THE ACCELERATED BEAM ESTIMATED BY TRANSMITTING IT THROUGH TWO SMALL APERTURES. ION BEAMS ARE PARTICULARLY EFFECTIVE IN THE MEASUREMENT OF QUANTITIES OF TRACE ELEMENTS BY THE PROTON-INDUCED X-RAY TECHNIQUE. MICROBEAMS OF 3-MICRON DIAMETER ARE CURRENTLY USED FOR INVESTIGATIONS OF DISEASES SUCH AS CANCER AND ALZHEIMER'S DISEASE. INCREASED RESOLUTION IN THIS TECHNIQUE, DOWN TO 0.1 MICRON, IS POSSIBLE, BUT PRACTICAL APPLICATION IS LIMITED BY THE BRIGHTNESS OF AVAILABLE ION BEAMS. IF SUFFICIENT BRIGHTNESS IS DEMONSTRATED, A MICROBEAM LINE CAPABLE OF PIXE AND RBS MEASUREMENTS AT HIGH RESOLUTION CAN BE CONSTRUCTED IN PHASE II OF THE RESEARCH.