Core lifter

A drilling system for collecting a core sample from a borehole, comprising:

• a drill string;
• an inner tube assembly configured for receipt within the drill string, the inner tube assembly comprising:
• a core lifter, comprising:
• a tubular body having an exterior surface and an interior surface;
• a gripping surface defined by the interior surface of the tubular body of the core lifter, the gripping surface being configured to grip a core sample;
• a plurality of longitudinally-oriented recesses formed in the exterior surface of the tubular body of the core lifter, the plurality of longitudinally-oriented recesses extending radially inwardly relative to the central axis, wherein the plurality of longitudinally oriented recesses do not extend radially through the tubular body between the exterior surface and the interior surface;
• a plurality of tapered recesses formed in the interior surface of the tubular body of the core lifter, the plurality of tapered recesses extending radially outwardly and being tapered relative to the central axis, wherein the plurality of tapered recesses do not extend radially through the tubular body between the exterior surface and the interior surface;
• a core lifter case configured to receive the core lifter, the core lifter case having a tapered inner wall, the tapered inner wall defining a shoulder configured for engagement with the core lifter;
• and
• an inner tube that is connected to the core lifter case, wherein the inner tube and the core lifter case are provided as a unitary, one-piece structure.