Replaceable thermal neutron absorbing sleeve for neutron detector

A downhole system, comprising:

• a downhole tubular having a body portion formed between a central bore and a radially outer surface of the downhole tubular;
• a neutron generator housed within the body portion and configured to emit neutrons;
• a gamma ray detector housed within the body portion and configured to detect gamma rays formed via interactions between the emitted neutrons and a downhole formation;
• a sleeve disposed about the radially outer surface of the downhole tubular, wherein the sleeve is axially positioned over at least a portion of the gamma ray detector, wherein the sleeve comprises a composite material, wherein the thermal neutron absorption layer is formed within the sleeve as part of the composite material, and wherein composite material includes a fiberglass material, a boron carbide powder, and an epoxy resin:
• a thermal neutron absorption layer disposed between a radially outer surface of the sleeve and the gamma ray detector.

A thermal neutron absorption sleeve, comprising:

• an inner tubular configured to be positioned over a portion of a downhole tubular that houses a gamma ray detector configured to detect gamma rays formed via interactions between neutrons emitted from a neutron generator and a downhole formation;
• a protective layer disposed about the inner tubular;
• a thermal neutron absorption layer disposed between the protective layer and the inner tubular, wherein the thermal neutron absorption layer is configured to reduce thermal neutron radiation for the gamma ray detector;
• a first end ring secured to a first end of the inner tubular;
• and
• a second end ring secured to a second end of the inner tubular, wherein the first end ring and the second end ring are configured to interface the downhole tubular to restrain axial movement of the thermal neutron absorption sleeve with respect to the downhole tubular.

A downhole system, comprising:

• a downhole tubular having a body portion formed between a central bore and a radially outer surface of the downhole tubular, and wherein the body portion includes at least one end slot formed in a radially outer surface of the body portion;
• a neutron generator housed within the body portion and configured to emit neutrons;
• a gamma ray detector housed within the body portion and configured to detect gamma rays formed via interactions between the emitted neutrons and a downhole formation;
• a sleeve disposed about the radially outer surface of the downhole tubular, wherein the sleeve is axially aligned with the gamma ray detector;
• at least one end ring secured to a corresponding axial end of the sleeve and having an axial protrusion feature extending axially from the at least one end ring, wherein the axial protrusion feature is configured to interface with the at least one end slot to restrain rotation of the sleeve with respect to the downhole tubular;
• and
• a thermal neutron absorption layer disposed between a radially outer surface of the sleeve and the gamma ray detector.