WORKERS INSTALL THE MARK III MAGNETIC DETECTOR AT THE SPEAR STORAGE RING.

THE SPEAR STORAGE RING IS ONE OF TWO OPERATIONAL ELECTRON POSITRON STORAGE RINGS LOCATED AT THE SLAC. BEAMS OF ELECTRONS AND POSITRONS CIRCULATE WITHIN THE RING, IN OPPOSITE DIRECTIONS, AND COLLIDE AT SEVERAL POINTS, CREATING VARIOUS SUBATOMIC PARTICLES IN THE PROCESS. RESEARCHERS STUDY THE BEHAVIOR OF THESE NEW PARTICLES, GAINING INSIGHT INTO THE NATURE AND STRUCTURE OF THE SUBATOMIC WORLD AND THE FORCES THAT OPERATE THEREIN. THE MARK III MAGNETIC DETECTOR IS ONE DEVICE USED TO MONITOR THIS BEHAVIOR. THE ELECTRON AND POSITRON BEAMS PASS THROUGH A VACUUM PIPE IN THE CENTER OF THE MARK III, AND THE PARTICLES PRODUCED IN THE COLLISION, WHICH SCATTER IN ALL DIRECTIONS, PENETRATE THE DETECTOR'S ELEMENTS. THE DRIFT CHAMBER FILLING THE CENTRAL REGION MEASURES THE DEFLECTION OF THESE PARTICLES OFF A MAGNETIC FIELD GENERATED BY A LARGE COIL LOCATED NEAR THE OUTSIDE OF THE UNIT, THUS DETERMINING THEIR ENERGY.