HIGH TEMPERATURE SEMICONDUCTOR SENSOR FOR BORE HOLE LOGGING

FOR MANY YEARS, NUCLEAR MEASUREMENT TECHNIQUES HAVE BEEN AN IMPORTANT ASPECT OF DOWNHOLE GEOLOGICAL BORE HOLE LOGGING. APPROCHES RANGE FROM GAMMA RAY BACKSCATTER USED FOR GAUGING DENSITY TO NEUTRON ACTIVATION ANALYSIS TO DETERMINE COMPOSITION. THE CONDITIONS WHICH SEVERLY LIMIT THE PERFORMANCE OF THESE DETECTORS ARE: 1) THE VERY SMALL SPACE AVAILABLE FOR THE INSTRUMENTATION DOWN IN A BORE HOLE AND 2) THE HIGH AMBIENT TEMPERATURE FOUND BELOW THE EARTH'S SURFACE. THESE CRITERIA INTERACT SINCE COOLING APPARATUS ALONG WITH THE MECHANICAL ISOLATION NEEDED FOR PROTECTION FROM VIBRATION BECOMES BULKY VERY QUICKLY AS THE HEAT LOAD INCREASES. THE IDEAL SOLUTION TO THIS PROBLEM WOULD BE A HIGH Z (ATOMIC NUMBER), HIGH DENSITY SOLID STATE NUCLEAR DETECTOR WHICH COULD OPERATE WITH LITTLE OR NO COOLING. AN EXAMINATION OF THE PROPERTIES OF THE PRESENTLY KNOWN COMPOUND SEMICONDUCTORS HAS SHOWN THAT NONE WOULD BE IDEAL; ONE SEMICONDUCTOR DETECTOR, ZNTE, SHOWS PARTICULAR PROMISE. ZNTE IS A HIGH Z, HIGH DENSITY SEMICONDUCTOR WHICH IS THEORETICALLY CAPABLE OF OPERATING AT OR ABOVE 200 DEGREES C. THUS, WE PROPOSED TO INVESTIGATE ZNTE SENSORS WHICH SHOW GAMMA-RAY RESPONSE AT HIGHER TEMPERATURES AND TO IDENTIFY THE AREAS OF RESEARCH WHICH NEED TO BE STRESSED IN ORDER TO BRING ABOUT THE SUCCESSFUL DEVELOPMENT OF THIS HIGH TEMPERATURE SENSOR.