Method and apparatus for the verification of helium-3 proportional counters

An apparatus for nuclear logging a formation, comprising:

• a nuclear logging assembly, the assembly comprising
• a source of high energy neutrons;
• a radiation detection system, the radiation detection system being in spaced relation to the source of high energy neutrons and including a proportional counter radiation detector, the detector comprised of a sealed, high-pressure housing transparent to thermal and epithermal neutron flux, the detector further having an electrode disposed therein, the electrode being insulated from the detector housing and adapted to be connected to an external source of electrical potential, the detector further including a detector gas disposed within the housing, the detector gas composed primarily of helium-3 having less than one part in 10.sup.10 parts tritium, the detector further including a source of beta-minus particles therein, the source having a characteristic energy peak of less than 0.5 MeV and a predetermined radioactivity level of 100 nanocuries or less, and an amplification means for counting changes in electrical potential in the electrode induced by the reaction of atomic particles with the detector gas across a predetermined energy spectrum;
• means for verifying the operation of the detector;
• means for stabilizing the gain of the amplification means;
• means for positioning the nuclear logging assembly in an earth formation at a desired depth of investigation;
• means for transmitting the detector counts to surface equipment, the surface equipment including means for recording the number of counts in relation to the depth of investigation.

A method for verifying the operation of a proportional counter radiation detector, the detector being comprised of a sealed, high-pressure housing transparent to thermal and epithermal neutron flux, the detector further having an electrode disposed therein, the electrode being insulated from the detector housing and adapted to be connected to an external source of electrical potential, the detector further including a detector gas disposed within the housing, the detector gas composed primarily of helium-3 having less than one part in 10.sup.10 parts tritium, the detector further including amplification circuitry for counting changes in the electrical potential in the electrode induced by reaction of atomic particles with the detector gas across a predetermined energy spectrum, the steps including:

• introducing a beta-minus particle source into the detector housing, the betaminus source having an energy spectrum distribution with a characteristic energy peak of less than 0.5 MeV and a predetermined radioactivity level of 100 nanocuries or less;
• counting the beta particle emissions from the beta-minus source across its energy spectrum;
• and
• comparing the beta particle emission count at the known beta-minus source characteristic energy peak with the predetermined radioactivity level.