Methods and apparatus for gamma-ray spectroscopy and like measurements

A borehole photon logging scintillation detector comprising:

• a crystal of cerium-doped gadolinium orthosilicate having a polygonal cross-section;
• a photomultiplier tube having a transparent face disposed adjacent a surface of said crystal;
• an optical coupling medium between said photomultiplier tube face and said crystal surface;
• a layer of light reflective material covering said crystal except for said face;
• a layer of photon absorbing material around said crystal for attenuating photons having an energy below approximately 1 MeV;
• a layer of neutron absorbing material around said crystal and having a capture cross-section of at least 100 barns;
• and
• a housing around said crystal and said layers.

Apparatus for investigation of subsurface earth formations, comprising:

• a sonde adapted for movement through a borehole;
• neutron source means for irradiating material in the region of said borehole with neutrons capable of interactions with said material resulting in radiation having characteristics carrying information about said material;
• detector means carried by said sonde for detecting radiation, said detector means including a gadolinium orthosilicate scintillator and a layer of boron-10 in the order of two millimeters in thickness for absorbing neutrons;
• and
• means coupled to said detector means for generating and recording a signal representative of at least one characteristic of radiation detected by said detector means.

Apparatus for investigation of subsurface earth formations comprising:

• a sonde adapted for movement through a borehole;
• detector means carried by said sonde for detecting radiation and including a gadolinium orthosilicate scintillator;
• means for rendering said scintillator selectively responsive to a desired type of radiation;
• and
• means coupled to said detector means for generating and recording a signal representative of at least one characteristic of radiation detected by said detector means.

Apparatus for investigation of subsurface earth formations comprising;

• a sonde adapted for movement through a borehole;
• detector means carried by said sonde for detecting radiation and including a single crystal gadolinium orthosilicate scintillator of generally cylindrical shape;
• and
• means coupled to said detector means for generating and recording a signal representative of at least one characteristic of radiation detected by said detector means.

Apparatus for investigation of subsurface earth formations comprising:

• a sonde adapted for movement through a borehole;
• detector means carried by said sonde for detecting radiation and including a gadolinium orthosilicate scintillator;
• said scintillator being substantially exposed to and unprotected from the temperatures encountered in said borehole;
• and
• means coupled to said detector means for generating and recording a signal representative of at least one characteristic of radiation detected by said detector means.

Apparatus for investigation of subsurface earth formations comprising:

• a sonde adapted for movement through a borehole;
• source means carried by said sonde for irradiating material in the region of said borehole with penetrating radiation capable of interactions with said material resulting in radiation having characteristics carrying information about said material;
• detector means carried by said sonde for detecting radiation and including a gadolinium orthosilicate scintillator;
• means for rendering said scintillator selectively responsive to a desired type of radiation;
• and
• means coupled to said detector means for generating and recording a signal representative of at least one characteristic of radiation detected by said detector means.

A method of investigating subsurface earth formations comprising the steps of:

• moving a sonde carrying detector means including a gadolinium orthosilicate scintillator through a borehole in said formations;
• detecting radiation from material in the region of said borehole with said detector means;
• and
• generating and recording signals representative of at least one characteristic of radiation detected with said detector means.