DESIGN AND CONSTRUCTION OF A VIBRATING REED MODULATOR FOR THE STABILIZATION OF X-RAY BEAMS

X-RAY ABSORPTION SPECTROSCOPY STUDIES OF DILUTE BIOLOGICAL SYSTEMS OF THE EXAFS TYPE ARE INHERENTLY INSENSITIVE RELATIVE TO OPTICAL ABSORPTION METHODS, AND SYNCHROTRON ORBITAL RADIATION IS OFTEN UNSTABLE AND NOISY IN ITS INTENSITY AND POSITION. THEREFORE, ANY STEPS TAKEN TO ACHIEVE THE THEORETICAL MAXIMUM SIGNAL/NOISE RATIO ARE OF PARAMOUNT IMPORTANCE IN INCREASING THE SCIENTIFIC DATA OUTPUT FROM X-RAY ABSORPTION STUDIES AND IN MAXIMIZING THE EFFECTIVENESS OF LIMITED AND PRECIOUS BEAM TIME ASSIGNMENTS.FOLLOWING A RECENT STUDY OF FOCUSED AND UNFOCUSED X-RAY BEAMLINES, LOW-FREQUENCY NOISE IN THE RANGE 1 TO 20 HZ WAS FOUNDTO ORIGINATE FROM (1) AMPLITUDE MODULATION ARISING FROM VARIATIONS IN X-RAY BEAM INTENSITY; (2) POSITION MODULATION ARISING FROM VARIATIONS IN X-RAY BEAM POSITION; AND (3) STATISTICAL FLUCTUATIONS OF THE FLUORESCENT RADIATION FROM THE METAL ATOMS AND THE ELASTICALLY SCATTERED RADIATION OF VARIABLE ENERGY AS THE METAL ATOM K OR L EDGE IS SCANNED. NOISE FROM AMPLITUDE MODULATION CAN BE REDUCED BY IMPROVING LINEARITY OF DETECTORS AND THEIR ASSOCIATED ELECTRONICS AND BY CAREFULLY MATCHING REFERENCE AND SIGNAL DETECTOR CHARACTERISTICS. THE CORRECTION OF NOISE PROBLEMS IN THE ELECTRON BEAM OF A DEDICATED SOURCE IS CURRENTLY ATTEMPTED BY MAGNETIC STEERING OF THE BEAM INTO USER BEAM LINES FROM APOINT 20 M FROM THS USER END STATION. THIS PROJECT WILL PROVIDE INDIVIDUAL USER COMPENSATION FOR THE MAJOR COMPONENTS TO NOISE BY THE USE OF A CARRIER MODULATION SYSTEM OF GOOD NOISE IMMUNITY.