Retrievable subsurface nuclear logging system

A system for determining a property of a subsurface formation traversed by a borehole, comprising:

• a sub having an elongated body with tubular walls and an inner bore, the sub adapted for disposal within the borehole;
• the sub including at least one fully penetrating opening and at least one partially penetrating window along the tubular wall;
• the sub including a pressure barrier between the interior and exterior of the tubular wall at the at least one fully penetrating opening;
• a run-in tool adapted for disposal within the sub bore;
• the run-in tool including at least one radiation source or at least one radiation sensor;
• wherein at least one radiation source or at least one radiation sensor on the run-in tool is located near a partially penetrating window on the sub when said tool is disposed within the sub;
• and
• the sub wall including an inner passage adapted to direct radiation energy emitted from within the sub back toward the sub bore.

A method for determining a property of a subsurface formation traversed by a borehole, comprising:

• a)adapting a sub for disposal within the borehole, the sub having an elongated body with tubular walls and an inner bore, the sub wall including an inner passage adapted to direct radiation energy emitted from within the sub back toward the sub bore;
• b)disposing a run-in tool within the sub bore, said tool having at least one radiation source and at least one radiation sensor disposed thereon;
• c)emitting radiation energy into the formation from the at least one radiation source on the run-in tool;
• and
• d)detecting radiation energy with the at least one radiation sensor on the run-in tool to determine the formation property.