Self-calibrating proportional counter
AssigneeSchlumberger Technology Corporation
InventorPeter D. Wraight
Life of this patent
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Abstract
The invention relates to a method and an apparatus for qualifying the operation of a radiation (e.g. neutron) detector containing an ionizable gas (e.g. He.sub.3), such as a detector disposed in a logging sonde designed to be lowered in a well, wherein a radioactive source capable of ionizing said gas is disposed inside the detector. From the counts of the ionization pulses, one qualifies the operation of the detector. The method provides either a verification (usually performed before the logging operation, outside the well) or, when carried out while the detector is operating in the well, a stabilization of the measured spectrum. Preferably, the internal source is an alpha source comprising uranium or americium and which is disposed inside the detector in the form of a thin foil.
Claims37
A radiation detector of the proportional counter type comprising a pressure-tight closed container pervious to transmission therethrough of neutrons in the thermal and epithermal energy regions, an electrode extending through said container is spaced relation with the enclosing walls and insulated therefrom, a detector gas within said container consisting substantially of helium-3 at a superatmospheric pressure and having a tritium content of less than one part in ten-to-the-ten parts, a source of radioactivity capable of ionizing said gas, said source being disposed within said closed container and selected so as to have a radioactivity level of less than 5 nanocuries, and circuit connections extending to said electrode and to said container for application thereto of an electric potential, said source of radioactivity having a characteristic peak at energies greater than 3 MeV.
A radiation detector of the proportional counter type comprising a pressure-tight closed container pervious to transmission therethrough of neutrons in the thermal and epithermal energy regions, an electrode extending through said container in spaced relation with the enclosing walls and insulated therefrom, a detector gas within said container of composition and pressure characterized by its sensitivity to neutrons in the thermal and epithermal regions and its insensitivity to gamma rays, a source located on a portion of the inside surface of said enclosing walls comprising a radioactive material which emits alpha particles by radioactive decay having a radioactivity level of less than 30 nanocuries, and circuit connections extending to said electrode and to said container for application thereto of an electrical potential, wherein said gas consists of high purity helium-3 present at a pressure of at least seven atmospheres absolute and having a tritium content of less than one part in ten-to-the-ten parts.
A radiation detector of the proportional counter type comprising a pressure-tight closed container pervious to transmission therethrough of neutrons in the thermal and epithermal energy regions, an electrode extending through said container in spaced relation with the enclosing walls and insulated therefrom, a detector gas within said container of composition and pressure characterized by its sensitivity to neutrons in the thermal and epithermal regions and its insensitivity to gamma rays, a source located on a portion of the inside surface of said enclosing walls comprising a radioactive material which emits alpha particles by radioactive decay having a radioactivity level of less than 30 nanocuries, and circuit connections extending to said electrode and to said container for application thereto of an electrical potential, wherein said gas consists of high purity helium-3 at a pressure of at least two and one-half atmospheres absolute and the radioactivity level of said source is less than 5 nanocuries.
A radiation detector of the proportional counter type comprising a pressure-tight closed container pervious to transmission therethrough of neutrons in the thermal and epithermal energy regions, an electrode extending through said container in spaces relation with the enclosing walls and insulated therefrom, a detector gas within said container of composition and pressure characterized by its high sensitivity to neutrons in the thermal and epithermal regions and its insensitivity to gamma rays, said gas consisting substantially exclusively of high purity helium-3 at a superatmospheric pressure, a source inside said container comprising a radioactive isotope which emits alpha particles by radioactive decay and has a radioactivity level of less than 30 nanocuries, and circuit connections extending to said electrode and to said container for application thereto of potential.
A logging tool comprising:
- an elongated external housing;
- a first radiation detector of the proportional counter type carried within said housing and comprising a pressure-tight closed container pervious to transmission therethrough of neutrons in the thermal and epithermal energy regions, an electrode extending through said container in spaced relation with the container walls and insulated therefrom;
- a detector gas within said container of helium-3 at a superatmospheric pressure;
- a source placed inside said container which emits particles by radioactive decay;
- the radioactivity level of said source outside of said housing being less than 5 nanocuries;
- circuit connections extending to said electrode and to said container for application thereto of an electrical potential;
- and means for monitoring variations in said electrical potential;
- wherein said source has an emission spectrum with a characteristic peak above 3 MeV.
Dependencies are inferred from the claim text.