Method and apparatus for stabilizing signals in radioactive well logging tools

A method for measuring radiation in a borehole comprising:

• providing in said borehole, a main scintillation crystal capable of scintillating responsive to the radiation to be measured;
• embedding a reference scintillation crystal in one end of said main scintillation crystal;
• inducing in said main scintillation crystal a first set of light flashes whose intensity is proportional to the intensity of said radiation to be measured;
• inducing in said reference scintillation crystal a second set of light flashes of a predetermined intensity;
• transmitting said first set of light flashes directly from said main scintillation crystal to a light sensing means optically coupled to said main scintillation crystal;
• transmitting said second set of light flashes directly from said reference scintillation crystal to said light sensing means optically coupled to said reference scintillation crystal;
• with said light sensing means, generating electrical pulses responsive to the light flashes of said first and second set of light flashes, wherein the height of each of said generated electrical pulses is proportional to the intensity of a respective light flash of said first and second set of light flashes;
• and
• transmitting said electrical pulses to a point removed from said borehole.

A method for determining a borehole characteristic in an oil well comprising:

• providing in said borehole a main scintillation crystal capable of scintillating responsive to gamma radiation;
• embedding a reference scintillation crystal in one end of said main scintillation crystal;
• with a source of neutrons, irradiating that portion of the borehole adjacent said main scintillation crystal;
• inducing in said main scintillation crystal a first set of light flashes whose intensity is proportional to the intensity of gamma radiation induced in the oil well by said neutron irradiation;
• inducing in said reference scintillation crystal a second set of light flashes of a predetermined intensity;
• transmitting said first set of light flashes directly from said main scintillation crystal to a light sensing means optically coupled to said main scintillation crystal;
• transmitting said second set of light flashes directly from said reference scintillation crystal to said light sensing means optically coupled to said reference scintillation crystal;
• with said light sensing means, generating electrical pulses responsive to the light flashes of said first and second set of light flashes, wherein the height of each of said generated electrical pulses is proportional to the intensity of a respective light flash of said first and second set of light flashes;
• transmitting said electrical pulses to a point removed from said borehole;
• and
• analyzing the electrical pulses generated responsive to said first set of light flashes with respect to the electrical pulses generated responsive to said second set of light flashes to determine a borehole characteristic.

An apparatus for determining a borehole characteristic in an oil well comprising:

• a main scintillation crystal capable of scintillating responsive to gamma radiation for giving a first set of light flashes whose intensity is proportional to the intensity of said gamma radiation;
• a reference scintillation crystal embedded in one end of said main scintillation crystal including a mono-energetic source of radiation embedded therein, for giving a second set of light flashes of a predetermined intensity;
• a source of neutrons for irradiating that portion of the oil well adjacent said main scintillation crystal and inducing gamma radiation therein;
• light sensing means optically coupled to said main scintillation crystal and said reference scintillation crystal for generating electrical pulses responsive to the light flashes of said first and second set of light flashes, wherein the height of each of said generated electrical pulses is proportional to the intensity of a respective light flash of said first and second set of light flashes;
• electrical data transmitting means electrically connected to said light sensing means for transmitting said electrical pulses to a point removed from said borehole;
• and
• means at said removed point for analyzing the electrical pulses generated responsive to said first set of light flashes with respect to the electrical pulses generated responsive to said second set of light flashes to determine a borehole characteristic.