Variable thermal-conductance vacuum-walled container for scintillation detectors

Claim 1

APPARATUS FOR RADIOACTIVITY WELL LOGGING, SAID APPARATUS COMPRISING OF A SUBSURFACE INSTRUMENT HAVING A PRESSURE RESISTANT HOUSING, A DOUBLE-WALLED VACUUM FLASK MOUNTED IN SAID HOUSING, SAID FLASK HAVING AN INNER CHAMBER, A SCINTILLATION PHOSPHOR LOCATED IN SAID INNER CHAMBER, A PHOTOMULTIPLIER TUBE LOCATED IN SAID INNER CHAMBER AND OPTICALLY COUPLED TO SAID PHOSPHOR, A THERMAL MASS LOCATED IN SAID INNER CHAMBER TO MAINTAIN SAID PHOSPHOR AND SAID PHOTOMULTIPLIER TUBE AT A SUBSTANTIALLY CONSTANT TEMPERATURE, GAS RESERVOIR MEANS COMMUNICATING WITH THE SPACE BETWEEN THE WALLS OF SAID VACUUM FLASK, A QUANTITY OF GAS CONTAINED IN SAID RESERVOIR, REGULATING MEANS FOR RELEASING GAS FROM SAID RESERVOIR INTO SAID SPACE AND FOR EVACUATING GAS FROM SAID SPACE INTO SAID RESERVOIR, A SURFACE UNIT LOCATED AT THE SURFACE OF THE EARTH, A CABLE FOR SUSPENDING SAID SUBSURFACE INSTRUMENT IN A BOREHOLE TO BE LOGGED AND FOR TRANSMITTING ELECTRICAL SIGNALS BETWEEN SAID SUBSURFACE INSTRUMENT AND SAID SURFACE UNIT, MEANS LOCATED IN SAID SURFACE UNIT FOR RECEIVING SIGNALS FROM SAID PHOTOMULTIPLIER TUBE, AND MEANS FOR CONTROLLING SAID REGULATING MEANS.