Abstract: An apparatus for detecting neutrons includes a cerium activated scintillation crystal containing .sup.10 B, with the scintillation crystal emitting light in response to .alpha. particles emitted from the .sup.10 B(n,.alpha.)Li* reaction. The apparatus also includes a gamma scintillator positioned adjacent the crystal and which generates light in response to gamma rays emitted from the decay of Li*. The apparatus further includes a first and a second light-to-electronic signal converter each positioned to respectively receive light from the crystal and the gamma scintillator, and each respectively outputting first and second electronic signals representative of .alpha. particles from the .sup.10 B(n,.alpha.)Li* reaction and gamma rays from the .sup.10 B(n,.alpha.)Li* reaction. The apparatus includes a coincidence circuit connected to receive the first and second signals and which generates a coincidence signal when the first and second signals coincide.

Abstract: A photon detector includes an activated lanthanide beryllate crystal, such as activated lanthanum beryllate, as a scintillator to detect photons. In one embodiment, the lanthanide beryllate crystal is doped with cerium.

Abstract: An apparatus to survey subsurface formations includes a sonde which is configured to move through a borehole. The sonde includes a neutron generator that emits neutrons into the subsurface formations. A crystal detector connected to the sonde monitors the neutron output of the neutron generator. The crystal detector can comprise an yttrium silicate crystal, an yttrium aluminate crystal, a lanthanum phosphate crystal, or a lutetium phosphate crystal. A lanthanum phosphate crystal or a lutetium phosphate crystal can also be used to detect photons coming from the subsurface formations. The sonde pressure casing can be fabricated from borated stainless steel to shield the internals of the sonde from thermal neutrons.

Abstract: A method of downhole neutron monitoring using an oxygen containing scintillating material to generate scintillator light as a function of electrons and gamma rays emitted from the product of the .sup.16 O (n,p) reaction in a scintillator, converting the generated scintillator light to an electrical signal, and using the electrical signal to record the flux of measured neutrons.

Abstract: Mine roof competency is determined by injecting a pressurized gas into a borehole drilled in the roof of the mine and measuring the rate of pressure loss. A high rate of pressure loss is indicative of a dangerous mine roof. A tracer gas may also be injected into the borehole to determine the extent of cracks in the roof if a dangerous condition has been determined.