Directional gamma ray spectrometer
 This disclosure is directed to a scintillation crystal surrounded by a sleeve and having a window formed therein. The scintillation crystal has end located first and second photomultiplier tubes which provide output signals. A scintillation event observed in the crystal is seen by both photomultiplier tubes and both form output signals. The output signals have a relationship determining the point of impingement along the length of crystal of the photon gamma radiation; in turn, that photon is located relative to a surrounding shield having a helical window formed therein so that the relative angle of impingement can be determined. The relative angle is then converted into the absolute angle relative to the well borehole by referencing a north seeking gyroscope supported by the sonde. The output signals are also used to determine the energy of the impinging gamma radiation using well known pulse height analysis spectroscopy techniques. 
Halliburton Logging Services, Inc.
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inventional inventional inventional
Dan McCay
Arnold