Method and system for uranium exploration

• US 4,568,510 A
• Filed: 04/12/1983
• Issued: 02/04/1986
• Est. Priority Date: 09/22/1980
• Status: Expired due to Fees

• Current Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Original Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Inventors: Caldwell, Richard L.
• Primary Examiner(s): Cangialosi, Sal
• Application Number:
  US06/484,391
• Time in Patent Office: 1,029 Days
• Field of Search: 250/269, 376/154, 376/164
• US Class Current: 376/154
• CPC Class Codes: G01N 2223/071 combination of measurements, at least 1 secondary emission
• CPC Class Codes: G01N 2223/074 activation analysis
• CPC Class Codes: G01N 2223/301 portable apparatus
• CPC Class Codes: G01N 2223/616 earth materials
• CPC Class Codes: G01N 2223/626 radioactive material
• CPC Class Codes: G01N 23/222 using neutron activation analysis [NAA]
• CPC Class Codes: G01V 5/02 specially adapted for surface logging, e.g. from aircraft
• CPC Class Codes: G01V 5/06 for detecting naturally radioactive minerals

Abstract

A portable uranium analyzer employs a neutron source and a neutron detector for carrying out an uranium assay along the surface of the earth and a gamma ray detector for carrying out a natural gamma radiation assay along the surface of the earth. The neutron source irradiates the underlying earth formation along an exploration line in either a continuous scan mode or in a plurality of fixed assay points. Prompt or delayed neutrons resulting from neutron fission of any uranium present in the formation are detected and recorded during assaying. The uranium assay and the natural gamma radiation assay are correlated to identify formations suspected of containing uranium.

Claims

1. A method of carrying out a reconnaisance survey over an extended area of the earth'"'"'s surface for identifying zones suspected or containing uranium ore deposits, comprising the steps of:

(a) traversing the earth'"'"'s surface along at least one line of survey with a neutron source and a neutron detector,

(b) periodically operating said neutron source to irradiate the earth formations underlying said line of survey with repetitive bursts of fast neutrons spaced by time intervals greater than the time required for dissipation of neutrons originating in said bursts,

(c) during time intervals between said bursts and after the time required for dissipation of neutrons originating in said bursts operating said neutron detector to detect fission neutrons attendant to the presence of uranium in the earth formations,

(d) recording radiation detected in step (c) to obtain a neutron fission assay record delineating said line of survey whereby zones of interest over an extended area of the earth'"'"'s surface suspected of containing uranium ore may be identified,

(e) carrying out a natural gamma radiation assay along said line of survey simultaneously with said neutron fission assay,

(f) correlating said neutron fission assay with said gamma radiation assay at corresponding points along the line of survey,

(g) identifying the presence of a surface uranium deposit in which the uranium daughter products are out of equilibrium with the parent uranium when there is a gamma radiation measurement of a one-to-five-times increase over the natural background gamma radiation of the earth with no uranium present and a neutron fission count rate for delayed neutrons of at least a two-times increase in delayed neutrons over the oxygen background of the earth or at least a three-times increase in prompt neutrons over the background measurement for a 0.005 weight % U₃ O₈ content,

(h) identifying the presence of a subsurface uranium deposit in which the uranium daughter products are out of equilibrium with the parent uranium when there is a gamma radiation measurement of at least a five-times increase over the natural background radiation of the earth with no uranium present and a neutron fission count rate for delayed neutrons of a one-to-two-times increase in delayed neutrons over the oxygen background of the earth or for prompt neutrons of a one-to-three-times increase in prompt neutrons over the background measurement for a 0.005 weight % U₃ O₈ content, and

(i) identifying the presence of a surface uranium deposit in which the uranium daughter products are in equilibrium with the parent uranium when there is a gamma radiation measurement of at least a five-times increase over the natural background radiation of the earth with no uranium present and a neutron fission count rate for delayed neutrons of a one-to-two-times increase in delayed neutrons over the oxygen background of the earth or for prompt neutrons of a one-to-three-times increase in prompt neutrons over the background measurement for a 0.005 weight % U₃ O₈ content.

2. The method of claim 1 wherein said natural gamma radiation assay is spaced from said neutron fission assay such that said natural gamma radiation assay is unaffected by fast neutrons generated during said neutron fission assay.

3. The method of claim 1 wherein the depth of irradiation of the earth formations underlying said line of survey is in the order of one to two feet.

4. The method of claim 1 wherein a surface uranium deposit is in the order of one to two feet below the earth'"'"'s surface.

5. The method of claim 1 wherein a subsurface uranium deposit is in excess of about two feet below the earth'"'"'s surface.