CA1089117A - Reducing noise in uranium exploration - Google Patents
Reducing noise in uranium explorationInfo
- Publication number
- CA1089117A CA1089117A CA283,624A CA283624A CA1089117A CA 1089117 A CA1089117 A CA 1089117A CA 283624 A CA283624 A CA 283624A CA 1089117 A CA1089117 A CA 1089117A
- Authority
- CA
- Canada
- Prior art keywords
- porous medium
- housing
- soil
- barrier
- gases
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/17—Circuit arrangements not adapted to a particular type of detector
- G01T1/178—Circuit arrangements not adapted to a particular type of detector for measuring specific activity in the presence of other radioactive substances, e.g. natural, in the air or in liquids such as rain water
Abstract
ABSTRACT OF THE DISCLOSURE
A method and apparatus are described for reducing or removing the background noise caused by thoron gas (220Rn) in uranium exploration conducted by the detection of radon gas (222Rn) emanating from the ground.
This is accomplished by the use of a number of alpha particle detectors, each of which is disposed in a protective enclosure. A barrier which permits, but deliberately retards, the passage therethrough of gases is disposed in the path to be traversed before such gases can reach the alpha particle detector. The increase in the transit time made necessary by requiring soil gases to move through the barrier should be sufficiently long to allow the decay of most of the thoron, thereby eliminating its contribution to the total signal reflected by the dectector.
A method and apparatus are described for reducing or removing the background noise caused by thoron gas (220Rn) in uranium exploration conducted by the detection of radon gas (222Rn) emanating from the ground.
This is accomplished by the use of a number of alpha particle detectors, each of which is disposed in a protective enclosure. A barrier which permits, but deliberately retards, the passage therethrough of gases is disposed in the path to be traversed before such gases can reach the alpha particle detector. The increase in the transit time made necessary by requiring soil gases to move through the barrier should be sufficiently long to allow the decay of most of the thoron, thereby eliminating its contribution to the total signal reflected by the dectector.
Description
10~ 117 One method and apparatus by which the presence and concentration of radon and its alpha-emitting daughters can be effectively detected and monitored is disclosed in U.S. Patent No. 3,665,194 - Alter et al., dated May 23, 1972 (Canadian Patent 911,622 - October 3, 1972). A sheet of solid state track-registration material (the alpha particle detector) is disposed in a protective environment at a location to be checked for the emission of radon. If the track-registration material becomes irradiated by alpha particles, minute damage "tracks" are created therein, which tracks can be enlarged and made visible by contact with a reagent to which the tracks display preferential chemical reactivity.
Ordinarily this uranium exploration is carried out by burying in the earth inverted cup-shaped housings containing the track-registration material. The housings are set forth in a predetermined arrangement (e.g. a grid system) and permitted to remain for a preselected period of time (e.g.
.~ .
four weeks). Thereafter the housings and detectors are re-~ 20 moved, the detectors are subjected to a chemical etching ;~ solution and the number of tracks etched on each detector is counted by microscopic inspection. Correlation of the results from the various housing are made in order to deter~
mine whether subsurface uranium ore is present and where.
Another method of uranium exploration substitutes an electronic solid state detector of alpha particles for the track registration material of the method described herein-above. These electronic detectors may be used repetitively either in the same or new locations.
;~ 30 A method and apparatus are described for reducing or ;~
removing the background noise caused by thoron gas (220Rn) '~ in uranium exploration conducted by the detection - " lV~117 of radon gas ( 22Rn) emanating from the ground~ This is accomplished by the use of a number of alpha particle de-tectors, each of which is disposed in a protective enclosure.
A barrier which permits, but deliberately retards, the passage therethrough of gases is disposed in the path to be traversed before such gases can reach each alpha particle if~
detector. The increase in the transit time made necessary by requiring soil gases to move through the barrier should be sufficiently long to allow the decay of most of the thoron, thereby eliminating its contribution to the total signal ~ ~
indicated at the detector. ~ ~ ;
The barrier should not in itself be a source of sub-stantial quantities of either Rn or Rn. Thé material of which the barrier is made should not be soluble in water whereby it can remain stable when in contact with soil. The enclosure, e.g. cup, should have imperforate side and (in the inverted position) top areas.
The instant invention conslsts of radon detection apparatus for ura~ium-ore prospecting, comprlsing in ~ combination: an imperforate protective housing defining an ~;
enclosed volume and having an opening therein, said housing ~
being adapted for burial in the earth with said opening ~;
disposed at the underside of said housing; a body of alpha par~icle detection material disposed within said housing and ~;
secured thereto for exposure to irradiation by alpha particles from soil gases entering said enclosed volume through said opening; and a quantity of a porous medium so disposed be- ~ -tween said body and the soil that soil gases leaving the -~
soil and entering said housing must traverse the thickness
Ordinarily this uranium exploration is carried out by burying in the earth inverted cup-shaped housings containing the track-registration material. The housings are set forth in a predetermined arrangement (e.g. a grid system) and permitted to remain for a preselected period of time (e.g.
.~ .
four weeks). Thereafter the housings and detectors are re-~ 20 moved, the detectors are subjected to a chemical etching ;~ solution and the number of tracks etched on each detector is counted by microscopic inspection. Correlation of the results from the various housing are made in order to deter~
mine whether subsurface uranium ore is present and where.
Another method of uranium exploration substitutes an electronic solid state detector of alpha particles for the track registration material of the method described herein-above. These electronic detectors may be used repetitively either in the same or new locations.
;~ 30 A method and apparatus are described for reducing or ;~
removing the background noise caused by thoron gas (220Rn) '~ in uranium exploration conducted by the detection - " lV~117 of radon gas ( 22Rn) emanating from the ground~ This is accomplished by the use of a number of alpha particle de-tectors, each of which is disposed in a protective enclosure.
A barrier which permits, but deliberately retards, the passage therethrough of gases is disposed in the path to be traversed before such gases can reach each alpha particle if~
detector. The increase in the transit time made necessary by requiring soil gases to move through the barrier should be sufficiently long to allow the decay of most of the thoron, thereby eliminating its contribution to the total signal ~ ~
indicated at the detector. ~ ~ ;
The barrier should not in itself be a source of sub-stantial quantities of either Rn or Rn. Thé material of which the barrier is made should not be soluble in water whereby it can remain stable when in contact with soil. The enclosure, e.g. cup, should have imperforate side and (in the inverted position) top areas.
The instant invention conslsts of radon detection apparatus for ura~ium-ore prospecting, comprlsing in ~ combination: an imperforate protective housing defining an ~;
enclosed volume and having an opening therein, said housing ~
being adapted for burial in the earth with said opening ~;
disposed at the underside of said housing; a body of alpha par~icle detection material disposed within said housing and ~;
secured thereto for exposure to irradiation by alpha particles from soil gases entering said enclosed volume through said opening; and a quantity of a porous medium so disposed be- ~ -tween said body and the soil that soil gases leaving the -~
soil and entering said housing must traverse the thickness
- 2 -.~
o~ said quantity of said porous medium whereby said porous medium functions as a diffusion barrier that retards the passage of gases, said porous medium being substantially free of content emitting either ORn or Rn.
The invention also provides in a method of prospecting for alpha-emitting ore bodies involving burying a series of protective housings in the earth in a predetermined series of locations, each housing defining an enclosed volume and containing a body of alpha particle detection material mounted therein spaced from said opening, each housing being buried with said opening disposed at the underside thereof, and after a predetermined exposure period making a determination of the extent of exposure of said alpha particle detection material to alpha particles during said exposure period, the improvement comprising the step of: disposing at each housing a retarding barrier interposed between the earth and said alpha particle detection material, said barrier delaying passage of soil gases therethrough a - sufficiently long period of time to allow decay of sub-stantially all of any Rn content in said soil gases. ~ -The description below sets forth the manner and process of making and using an embodiment of the invention and the accompanying drawing forms part of the description for schematically illustrating the invention and the best mode.
The view shown in the drawing schematically illustrates utilization of the instant invention in uranium exploration.
In order to facilitate the description of this invention reference will be made to the application thereof in the method disclosed in the aforementioned U.S. 3,665,194 in which a solid state track-detector is - 2a -~, ;r ~ 117 RD 9059 used as the alpha particle detector. This invention is equally applicable when other forms of alpha particle detector are employed.
The uranium exploration by the method descrbied in U. S. 3,665,194 cup lO would be placed in excavation ll so as to rest on the soil 12 at the bottom thereo.
Typically a board would be used to cover the hole and this in turn would be covered with dirt from the excavation thereby burying cup 10. This procedure would be repeated -with a number of such cups in some desired pattern, the cups remaining buried for the test period. Mounted within each cup is a piece, or sheet, 13 of alpha particle track detector material, preferably cellulose nitrate, to measure the emanation from the ground below of the gaseous radon isotopes 220Rn and 222Rn. The 222Rn gas is a decay product of uranium and, therefore, the detection of such emanations would be an indication of the presence of uranium in the earth. The other alpha particle-emitting gas, 222Rn, is a decay product of thorium and, hence, tracks induced thereby in track detector 13 cons~tu~e an unwanted background caused by alpha particle emissions from thoron gas entering the mouth of cup lO, instead of permitting gases leaving the soil through sur~
face 12 to enter directly into the internal volume of cup ;
10, a layer 14 of a porous medium is disposed between surface 12 and sheet 13 (or other alpha particle detector).
The sides and top of cup 10 are imperforate in order to ~;
prevent the short-circuiting by soil gases around layer 14. Thus, any soil gases reaching the sheet of track detector material 13 must first pass through layer 14.
A zone, or volume, as least 6.0 centimeters thick must remain in the cup between the upper surface of layer 14 .. ' ~,'`` "' .
o~ said quantity of said porous medium whereby said porous medium functions as a diffusion barrier that retards the passage of gases, said porous medium being substantially free of content emitting either ORn or Rn.
The invention also provides in a method of prospecting for alpha-emitting ore bodies involving burying a series of protective housings in the earth in a predetermined series of locations, each housing defining an enclosed volume and containing a body of alpha particle detection material mounted therein spaced from said opening, each housing being buried with said opening disposed at the underside thereof, and after a predetermined exposure period making a determination of the extent of exposure of said alpha particle detection material to alpha particles during said exposure period, the improvement comprising the step of: disposing at each housing a retarding barrier interposed between the earth and said alpha particle detection material, said barrier delaying passage of soil gases therethrough a - sufficiently long period of time to allow decay of sub-stantially all of any Rn content in said soil gases. ~ -The description below sets forth the manner and process of making and using an embodiment of the invention and the accompanying drawing forms part of the description for schematically illustrating the invention and the best mode.
The view shown in the drawing schematically illustrates utilization of the instant invention in uranium exploration.
In order to facilitate the description of this invention reference will be made to the application thereof in the method disclosed in the aforementioned U.S. 3,665,194 in which a solid state track-detector is - 2a -~, ;r ~ 117 RD 9059 used as the alpha particle detector. This invention is equally applicable when other forms of alpha particle detector are employed.
The uranium exploration by the method descrbied in U. S. 3,665,194 cup lO would be placed in excavation ll so as to rest on the soil 12 at the bottom thereo.
Typically a board would be used to cover the hole and this in turn would be covered with dirt from the excavation thereby burying cup 10. This procedure would be repeated -with a number of such cups in some desired pattern, the cups remaining buried for the test period. Mounted within each cup is a piece, or sheet, 13 of alpha particle track detector material, preferably cellulose nitrate, to measure the emanation from the ground below of the gaseous radon isotopes 220Rn and 222Rn. The 222Rn gas is a decay product of uranium and, therefore, the detection of such emanations would be an indication of the presence of uranium in the earth. The other alpha particle-emitting gas, 222Rn, is a decay product of thorium and, hence, tracks induced thereby in track detector 13 cons~tu~e an unwanted background caused by alpha particle emissions from thoron gas entering the mouth of cup lO, instead of permitting gases leaving the soil through sur~
face 12 to enter directly into the internal volume of cup ;
10, a layer 14 of a porous medium is disposed between surface 12 and sheet 13 (or other alpha particle detector).
The sides and top of cup 10 are imperforate in order to ~;
prevent the short-circuiting by soil gases around layer 14. Thus, any soil gases reaching the sheet of track detector material 13 must first pass through layer 14.
A zone, or volume, as least 6.0 centimeters thick must remain in the cup between the upper surface of layer 14 .. ' ~,'`` "' .
- 3 - ~
~ 91~7 RD 9059 and the underside of the surface of sheet 13 so that in passing through this zone of air, the alpha particles are slowed sufficiently that they can be detected by this form of alpha particle detector.
In the arrangement shown, the lip 16 of cup 10 is embedded in layer 14 so that the cups anchored and the mouth thereof is closed off by the porous medium.
If a solid porous disc is to be employed as porous medium 14, it may be preferable to rest the disc on surface 12 and, in turn, to rest the lip 16 of cup 10 on the upper surface of the disc.
The thickness of the porous medium 14 should be appreciably greater than the mean diffusion distance for 20Rn in the given porous material, (e.g. about ;~
2 cm. in loose soil) and appreciably less than the mean diffusion distance for 222~n in the same porous medium (e.g. 150 cm. in loose soil). Thus, the thickness will depend upon the porosity of the porous material and may be in the range of from about 0.1 cm. to about 150 cm.
The preferred thickness for the layer of porous medium would be in the range of from about 1 cm. to about 4 cm.
The thickness of the layer of porous medium should be sufficient to insure the decay of most of the alpha particles emitted by any 20Rn that may be presen~
while the thoron gas is diffusing through the medium.
Some radon may also decay in transit therethrough and `
the decay products produced collect in the porous material. By way of example, diffusion through a 4 cm.
thickness of a suitable medium having an Rn diffusion constant D = 0.05 cm.2/sec. will reduce the alpha particle ~ -emitting capability of the thoron component present in the soil gases to 13.5% of its initial value. Since the ~- ~ . . . ~
typical 220Rn contribution is less than 50% of the total signal encountered and, therefore, less than 50% of the total to which sheet 13 would be subject, the Rn contribution would be reduced to less than 7% of the total signal. This amount would be comparable to the statistical uncertainty with which radon measurements are normally made.
Almost any porous material, solid or particulate, insoluble in water and in which the pores are interconnecting may be used, e.g. sand, felt or other fibrous sheet or mat, porous plastic, fritted glass, porous silica body, etc. Ideally in order to determine whether the porous material to be employed is not a source of objectionable -~;
; quantities of 220Rn and/or 222Rn comparison is made with the background to be encountered (i.e. the activity of the soil where measurements are to be made.) As much as 59% of the background reading can be tolerated. The -comparison can readily be made by comparing the readout (e.g. ~ ~-, , ., ~
over a 30 day period) from the porous medium itself with the readout from a sample of the soil. Preferably the `
activity of the porous medium will be less than 10% of the ~;~
soild background activity. ~ 7 This invention, in addition to having the utility described hereinabove with respect to uranium -~
exploration, can also be advantageously utilized in thorium exploration. Thus, if readings are first made with the usual arrangement described hereinabove, and then measurements are repeated using the intervening ~ -porous medium according to this invention, the differences, -- ~
,:. . .
if any, recorded between the first and second sets of readings will supply the requisite information on the -~
Rn levels and, therefore, indicate the presence or ;', " ~' absence of thorium.
A hole about 2 feet deep is prepared in the soil. The bottom of the hole is covered with a layer about 4 cm. thick of high silica content sand. The content of uranium and/or thorium should be sufficiently low so that the emission of 220Rn and/or 2 2Rn will be less than 5% of the background activity for these gases.
An imperforate plastic cup is placed in the inverted position with the lip thereof embedded in the sand. Mounted in the cup (as shown in the drawing) is a sheet of cellulose nitrate as the alpha particle detector. The cup dimensions are such that the distance from the top layer of sand to the surface of cellulose nitrate is at least 6.0 cm. The cup with the layer of sand in place is buried as described above and the method comprising waiting about 4 weeks and then recovering the cups for readout applies.
" ~
.. .... . .
~ 91~7 RD 9059 and the underside of the surface of sheet 13 so that in passing through this zone of air, the alpha particles are slowed sufficiently that they can be detected by this form of alpha particle detector.
In the arrangement shown, the lip 16 of cup 10 is embedded in layer 14 so that the cups anchored and the mouth thereof is closed off by the porous medium.
If a solid porous disc is to be employed as porous medium 14, it may be preferable to rest the disc on surface 12 and, in turn, to rest the lip 16 of cup 10 on the upper surface of the disc.
The thickness of the porous medium 14 should be appreciably greater than the mean diffusion distance for 20Rn in the given porous material, (e.g. about ;~
2 cm. in loose soil) and appreciably less than the mean diffusion distance for 222~n in the same porous medium (e.g. 150 cm. in loose soil). Thus, the thickness will depend upon the porosity of the porous material and may be in the range of from about 0.1 cm. to about 150 cm.
The preferred thickness for the layer of porous medium would be in the range of from about 1 cm. to about 4 cm.
The thickness of the layer of porous medium should be sufficient to insure the decay of most of the alpha particles emitted by any 20Rn that may be presen~
while the thoron gas is diffusing through the medium.
Some radon may also decay in transit therethrough and `
the decay products produced collect in the porous material. By way of example, diffusion through a 4 cm.
thickness of a suitable medium having an Rn diffusion constant D = 0.05 cm.2/sec. will reduce the alpha particle ~ -emitting capability of the thoron component present in the soil gases to 13.5% of its initial value. Since the ~- ~ . . . ~
typical 220Rn contribution is less than 50% of the total signal encountered and, therefore, less than 50% of the total to which sheet 13 would be subject, the Rn contribution would be reduced to less than 7% of the total signal. This amount would be comparable to the statistical uncertainty with which radon measurements are normally made.
Almost any porous material, solid or particulate, insoluble in water and in which the pores are interconnecting may be used, e.g. sand, felt or other fibrous sheet or mat, porous plastic, fritted glass, porous silica body, etc. Ideally in order to determine whether the porous material to be employed is not a source of objectionable -~;
; quantities of 220Rn and/or 222Rn comparison is made with the background to be encountered (i.e. the activity of the soil where measurements are to be made.) As much as 59% of the background reading can be tolerated. The -comparison can readily be made by comparing the readout (e.g. ~ ~-, , ., ~
over a 30 day period) from the porous medium itself with the readout from a sample of the soil. Preferably the `
activity of the porous medium will be less than 10% of the ~;~
soild background activity. ~ 7 This invention, in addition to having the utility described hereinabove with respect to uranium -~
exploration, can also be advantageously utilized in thorium exploration. Thus, if readings are first made with the usual arrangement described hereinabove, and then measurements are repeated using the intervening ~ -porous medium according to this invention, the differences, -- ~
,:. . .
if any, recorded between the first and second sets of readings will supply the requisite information on the -~
Rn levels and, therefore, indicate the presence or ;', " ~' absence of thorium.
A hole about 2 feet deep is prepared in the soil. The bottom of the hole is covered with a layer about 4 cm. thick of high silica content sand. The content of uranium and/or thorium should be sufficiently low so that the emission of 220Rn and/or 2 2Rn will be less than 5% of the background activity for these gases.
An imperforate plastic cup is placed in the inverted position with the lip thereof embedded in the sand. Mounted in the cup (as shown in the drawing) is a sheet of cellulose nitrate as the alpha particle detector. The cup dimensions are such that the distance from the top layer of sand to the surface of cellulose nitrate is at least 6.0 cm. The cup with the layer of sand in place is buried as described above and the method comprising waiting about 4 weeks and then recovering the cups for readout applies.
" ~
.. .... . .
Claims (12)
1. Radon detection apparatus for uranium-ore prospecting, comprising in combination:
an imperforate protective housing defining an enclosed volume and having an opening therein, said housing being adapted for burial in the earth with said opening disposed at the underside of said housing;
a body of alpha particle detection material disposed within said housing and secured thereto for exposure to irradiation by alpha particles from soil gases entering said enclosed volume through said opening; and a quantity of a porous medium so disposed between said body and the soil that soil gases leaving the soil and entering said housing must traverse the thickness of said quantity of said porous medium whereby said porous medium functions as a diffusion barrier that retards the passage of gases, said porous medium being substantially free of content emitting either 220Rn or222Rn.
an imperforate protective housing defining an enclosed volume and having an opening therein, said housing being adapted for burial in the earth with said opening disposed at the underside of said housing;
a body of alpha particle detection material disposed within said housing and secured thereto for exposure to irradiation by alpha particles from soil gases entering said enclosed volume through said opening; and a quantity of a porous medium so disposed between said body and the soil that soil gases leaving the soil and entering said housing must traverse the thickness of said quantity of said porous medium whereby said porous medium functions as a diffusion barrier that retards the passage of gases, said porous medium being substantially free of content emitting either 220Rn or222Rn.
2. The apparatus recited in claim 1, wherein said porous medium is sand having low uranium content and low thorium content.
3. The apparatus recited in claim 1, wherein said porous medium is a solid porous silica disk.
4. The apparatus recited in claim 1, wherein said thick-ness of said quantity of said porous medium is in the range of from about 0.1 cm to about 150 cm.
5. The apparatus recited in claim 1, wherein said thick-ness of said quantity of said porous medium is in the range of from about 1 cm to about 4 cm.
6. In a method of prospecting for alpha-emitting ore bodies involving burying a series of protective housings in the earth in a predetermined series of locations, each housing defining an enclosed volume and containing a body of alpha particle detection material mounted therein spaced from said opening, each housing being buried with said opening disposed at the underside thereof, and after a predetermined exposure period making a determination of the extent of ex-posure of said alpha particle detection material to alpha particles during said exposure period, the improvement comprising the step of:
disposing at each housing a retarding barrier inter-posed between the earth and said alpha particle detection material, said barrier delaying passage of soil gases therethrough a sufficiently long period of time to allow decay of substantially all of any 220Rn content in said soil gases.
disposing at each housing a retarding barrier inter-posed between the earth and said alpha particle detection material, said barrier delaying passage of soil gases therethrough a sufficiently long period of time to allow decay of substantially all of any 220Rn content in said soil gases.
7. The method improvement recited in claim 6, wherein said barrier is a porous medium which is substantially free of content emitting either 220Rn or 222Rn.
8. The method improvement recited in claim 7, wherein said porous medium is a layer of sand having low uranium content and low thorium content.
9. The method improvement recited in claim 7, wherein said porous medium is a solid porous silica disk.
10. The method improvement of claim 6 wherein the ore to be located is uranium ore.
11. The method improvement of claim 6 in which readings are taken at the same location both with and without the retard-ing barrier whereby the difference in the readings will indicate whether thorium ore is present.
12. The improvement of claim 1 wherein the porous medium closes off the opening.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA283,624A CA1089117A (en) | 1977-07-27 | 1977-07-27 | Reducing noise in uranium exploration |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA283,624A CA1089117A (en) | 1977-07-27 | 1977-07-27 | Reducing noise in uranium exploration |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1089117A true CA1089117A (en) | 1980-11-04 |
Family
ID=4109217
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA283,624A Expired CA1089117A (en) | 1977-07-27 | 1977-07-27 | Reducing noise in uranium exploration |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1089117A (en) |
-
1977
- 1977-07-27 CA CA283,624A patent/CA1089117A/en not_active Expired
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