HIGH TEMPERATURE SCINTILLATORS FOR BOREHOLE LOGGING

HIGH TEMPERATURE SCINTILLATORS ARE NEEDED FOR GAMMA-RAY DETECTION IN BOREHOLE LOGGING. ZINC SULFIDE HAS LONG BEEN KNOWN AS A VERY EFFICIENT SCINTILLATOR; AS A THIN POWDER LAYER, IT IS CURRENTLY USED FOR -PARTICLE DETECTION. AS A LARGE TRANSPARENT BOULE, THIS COMPOUND WOULD ALSO BE USEFUL FOR GAMMA-RAY DETECTION. AN ECONOMICALTECHNIQUE FOR THE GROWTH OF LARGE TRANSPARENT BOULES OF HIGHBAND GAP II-VI COMPOUNDS SUCH AS ZINC SELENIDE AND CADMIUM SULFIDE HAS BEEN DEVELOPED. PRELIMINARY EXPERIMENTS WITH UNDOPED ZINC SULFIDE INDICATE THAT THIS MATERIAL, WHICH HAS THE HIGHEST BAND GAP AND HIGHEST MELTING POINT FOR A II-VI COMPOUND, CAN BE GROWN IN TRANSPARENT FORM WITH GOOD LUMINESCENCE. THE LUMINESCENCE EFFICIENCY OF HIGH TEMPERATURE FIRED COPPER-DOPED ZINC SULFIDE INCREASES WITH INCREASING TEMPERATURE TO BEYOND 200 DEGREES CENTIGRADE AND RETAINS 60% OF ITS ROOM TEMPERATURE VALUE UP TO 350 DEGREES CENTIGRADE. THIS PROJECT'S OBJECTIVE IS TO DEVELOP A PROCESS FOR MAKING TRANSPARENT COPPER-DOPED ZINC SULFIDE BOULES WITH LUMINESCENCE THAT INCREASES WITH TEMPERATURE. PHASE I INVOLVES FABRICATION OF CYLINDERS 2.5 CM DIAMETER X 2.5 CM HIGH FOR TESTING BY A COMMERCIAL PARTNER.