WO2022037730A1 - Device for measuring the content of natural radioactive isotopes in rock sample - Google Patents

Device for measuring the content of natural radioactive isotopes in rock sample Download PDF

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Publication number
WO2022037730A1
WO2022037730A1 PCT/CZ2021/050083 CZ2021050083W WO2022037730A1 WO 2022037730 A1 WO2022037730 A1 WO 2022037730A1 CZ 2021050083 W CZ2021050083 W CZ 2021050083W WO 2022037730 A1 WO2022037730 A1 WO 2022037730A1
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Prior art keywords
ring
sample
shielding
shaped
evaluation unit
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PCT/CZ2021/050083
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French (fr)
Inventor
Karel BLAŽEK
Tomáš Marek
Jan TOUŠ
Tomáš Brunclík
Petr Mašek
Ondřej Hynek
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Crytur, Spol.S R.O.
GEORADIS s.r.o.
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Application filed by Crytur, Spol.S R.O., GEORADIS s.r.o. filed Critical Crytur, Spol.S R.O.
Publication of WO2022037730A1 publication Critical patent/WO2022037730A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/24—Earth materials
    • 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
    • G01T1/167—Measuring radioactive content of objects, e.g. contamination
    • 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
    • G01T1/20—Measuring radiation intensity with scintillation detectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V5/00—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity
    • G01V5/04—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging
    • G01V5/06—Prospecting or detecting by the use of nuclear radiation, e.g. of natural or induced radioactivity specially adapted for well-logging for detecting naturally radioactive minerals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material

Definitions

  • the invention relates to a geological analysis of the content of natural radionuclides in drill cores from exploratory drilling using KUTh gamma logging to describe the geological profile and geological activity of the area explored by means of exploratory drilling.
  • logging based on ionizing radiation, for example according to the principle they use.
  • Known logging includes, for example, spectral gamma logging as well as gamma-gamma logging, neutron-neutron logging, neutron-gamma logging, which is otherwise known to the professional public under its English abbreviation PGNAA (Prompt Gamma Neutron Activation Analysis), neutron logging, or for example gamma neutron logging.
  • PGNAA Prompt Gamma Neutron Activation Analysis
  • neutron logging or for example gamma neutron logging.
  • the ionizing radiation used during logging is either naturally emanating from the rock, or purposefully generated ionizing radiation is used, and then its reflection and scattering on the rock are measured, or secondary ionizing radiation generated by the rock is measured.
  • the above logging methods are categorize. For example, it is a measurement of radioactivity during the borehole drilling process, in which the detection means are part of the drilling body, moving through the rock together with the drilling head.
  • Another known method of application is to dive the detection means into an already drilled borehole, which can be reinforced by casing, but at the cost of changing the conditions of permeability of some components of natural ionizing radiation.
  • Another mode of application of logging with the use of ionizing radiation is measurement outside the borehole, in which the subject of measurement is the material obtained from the borehole, the so-called drill cores.
  • gamma logging measurements of weak natural gamma radioactivity of rocks are performed to determine the quality of mineral deposits.
  • the measured natural gamma radioactivity of rocks comes from the primordial radionuclides 40 K, 238 U, and 232 Th contained in them, and which gave it the name “KUTh gamma logging”.
  • the known detection units used for KUTh gamma logging either measure only the total radioactivity or have spectrometric properties.
  • the energy resolution in known detection units enables to determine the ratio of the mentioned radionuclides, and thus determine the geological composition of lithologically separated areas, or even the mineralogical composition of sediments. It is possible, for example, to characterize the type and composition of clay, or to distinguish micaceous sand from shale, etc.
  • a scintillator is a material in which a flash of light is generated by excitation of ionizing radiation. The intensity of light flash is proportional to the energy deposited by the quantum of ionizing radiation in the scintillator. This light flash is converted by the photosensitive element into an electrical signal. The signal is then processed and digitized by an electronic chain and transferred to the evaluation unit. The information obtained from the scintillator is of better quality the better the ionizing quanta deposit their energy therein. In general, therefore, the scintillator should have the highest possible density, and should contain the heaviest elements, i.e. elements with the highest possible proton number Z.
  • the photosensitive element is usually a photomultiplier, a photodiode, an avalanche photodiode (APD), or a so-called silicon photomultiplier (SiPM). Experts may include other light-sensitive elements in this category, for example based on graphene, etc.
  • the electronic chain usually includes a signal preamplifier and amplifier, a multi-channel analyzer, a data bus, a voltage source for the photosensitive element and possibly other components.
  • thallium-doped sodium iodide NaETl
  • thallium-doped sodium iodide NaETl
  • scintillation materials based on monocrystalline aluminates and silicates are also beginning to be used.
  • Examples of such newly used scintillation aluminates, without claim to completeness, are perovskites and garnets doped with cerium, praseodymium, neodymium and europium, as well as lutetium-yttrium silicate, and others.
  • Examples of known detection units are the inventions disclosed in CN 110 018 510 (A) and CN 106 019 358 (A). Both inventions measure rock samples in the form of drill cores.
  • the invented devices include shielded irradiation tables into which the drill cores are fixed.
  • the disadvantages of the above-mentioned devices are that they are robust devices.
  • the robustness of both devices is due to the need to sufficiently shield the ubiquitous natural radiation background, as the solution used, with the detectors with large NaLTl scintillators in the devices, is too sensitive to this background radiation.
  • the work cycle on the devices is time consuming because it requires the following operational steps: open the shielding of the device, place the drill core on the irradiation table, close the shielding of the device, perform measurements, open the shielding of the device, remove the measured drill core, and repeat the cycle with a new drill core.
  • the object of the invention is to provide a device for measuring the content of natural radioactive isotopes in rock sample, in particular represented by a drill core, provided with a detector capable of distinguishing between desirable natural ionizing radiation emanating from radionuclides contained in rock and natural radiation background present behind shielding, which was easy to transport and assemble even in conditions of use outside laboratory buildings, and which could shorten the work cycle by steps associated with opening and closing of the shield.
  • the stated object is solved by providing a device for measuring the content of natural radioactive isotopes in rock sample, in particular in drill core according to the invention below.
  • the device for measuring the content of natural radioactive isotopes in rock sample, in particular in drill core comprises at least one detection means for measuring the ionizing radiation emanating from the sample.
  • the detection means comprises a detector which consists of a scintillator, a photosensitive means and an electronic chain.
  • the device further comprises at least one means for positioning the sample.
  • the device comprises at least one shielding of the sample and/or the detection means against the influence of the radiation background.
  • An integral part of the device is at least one evaluation unit, which is communicatively connected to the detection means by a data bus, e.g. USB, CAN, or another.
  • the core of the invention is based on the fact that the detection means is composed of at least one ring-shaped assembly composed of at least three ring-shaped segments arranged side by side.
  • Each ring-shaped assembly comprises at least one segment with detectors arranged in the middle of the ring-shaped assembly and at least two shielding segments, each arranged at the edge of the ring-shaped assembly.
  • the ring-shaped assembly may include several segments with detectors and several shielding segments interposed between adjacent detection segments.
  • the shielding ring-shaped segments form the shielding from the radiation background.
  • the detector segment is provided with at least one ionizing radiation detector.
  • the sample positioning means is adapted to move the sample through the ring-shaped assembly.
  • the detector comprises a rod scintillator and at least one photosensitive means for collecting light flashes from the rod scintillator.
  • the scintillator is made of monocrystalline or poly crystalline material from the group of aluminates doped with cerium, praseodymium, europium, neodymium.
  • Proven material candidates are materials from the group, LuYAG:Ce, GAGG:Ce, GYGAG:Ce, LuGAGG:Ce.
  • the scintillator of the invention has a number of advantages.
  • the use of a scintillator from the group of aluminates or silicates, in particular of the GAGG:Ce material has the advantages that each of the detectors has sufficient detection efficiency even at a small size.
  • the small size of the detector then brings advantages in the lower natural background.
  • the use of the GAGG:Ce scintillator gives a better signal/background ratio than other traditional scintillators, such as thallium-doped sodium iodide (NaETl). This is because the proton number of iodine is 53, while the proton number of gadolinium is 64.
  • the benefit of the invention is, firstly, its modular construction.
  • the ring-shaped assembly can be disassembled into individual segments, which facilitates the installation/disassembly and transport of the device.
  • Another great advantage of the invention is that it is possible to use it in a series of several ring-shaped assemblies for one sample.
  • the more assemblies used the more accurate the measurement will be, or the shorter the measurement time of the sample will be while maintaining the accuracy.
  • a ring shape is advantageous because the samples are inserted and removed from the side, thus saving time with the opening and closing of the shielding above the area of measurement.
  • the means for positioning the sample is preferably provided with a sample displacement sensor. Data from sensors, especially if sent directly to the evaluation unit, can help to better assign the associated location and status of the sample to the measured data.
  • the photosensitive means consists of at least one photomultiplier, or a photodiode, or an avalanche photodiode, or a silicon photomultiplier (SiPM).
  • the device is provided with at least one means for monitoring the effects of temperature changes on the function of the ionizing radiation detector. This means can be based on measuring the temperature in different parts of the detector, measuring other characteristics of the detector, e.g. dark current or thermal noise, or detecting short-term deviations of the positions of selected photopeaks of KUTh nuclides in the spectrum of ionizing radiation.
  • the detection of deviations of positions of photopeaks of KUTh nuclides works with dose rate at the level of natural background and does not require the use of other radiation sources.
  • the device includes hardware or software implemented continuous correction of the effect of temperature, either by changing the voltage that supplies the photosensitive means, or by changing the gain of the electronic chain.
  • the shielding of the middle ring-shaped segment consists of materials which absorb gamma radiation or slow down and absorb neutrons, or of a mixture of these materials, alloys or their composites (hereinafter referred to as “shielding materials” or “composites”).
  • Materials that absorb gamma radiation are from the group of metals: lead, tungsten, barium, copper, iron, nickel, chromium.
  • Materials, which slow down neutrons include organic substances and polymers. These include, but are not limited to, poly(methyl) methacrylate (PMMA), polyethylene (PE), polypropylene (PP), paraffin, bitumen and others.
  • the neutron absorbing materials are lithium and boron, their compounds, alloys, mixtures and composites. It is preferred if the end ring-shaped segments are made of the mentioned shielding materials or composites.
  • the list of advantages of the invention includes in particular a modular concept which facilitates transport, installation and disassembly. Furthermore, used scintillators, which make it possible to reduce the amount of material used for shielding, and thus to lighten the device as a whole, compared to known robust structures. A good signal/background ratio of the detector itself then represents a design advantage of the whole device, as only a small amount of shielding materials or composites of which the shielding of detectors from gamma radiation or neutrons from the natural background is made is sufficient to achieve the required detection efficiency. This is supported by another advantage that the device is light and therefore easy to transport.
  • the detector has the additional advantage that lead usually contains a small but measurable amount of natural isotope 210 Pb with a half-life of 22 years. If the shielding contains less material, such as lead, then the natural background radiation generated by this isotope will also be reduced.
  • the advantage in terms of significance is that it is possible to insert samples from the side of the device into the openings of the rings, so that it is not necessary to open the shielding around the area of measurement.
  • the rings may be adapted to be opened from above in order to insert the sample.
  • Fig. 1 schematically shows the concept of the invention
  • Fig. 2 schematically shows a normal section of a middle ring-shaped segment fitted with three detectors
  • Fig. 3 shows an example of a spectrum measured by the invention.
  • a model drill core with a diameter of 80 mm was measured, which contains 148 ppm of uranium, 22 ppm of thorium and their decay products.
  • the horizontal axis represents the energy of radiation in electron volts, and the vertical axis shows the counts of detected quanta of radioactive radiation of a given energy.
  • the measured spectrum contains peaks characteristic for individual isotopes of the decay series of uranium 238 and thorium 232.
  • Fig. 1 shows a diagram of a device to be used to measure the content of natural radioactive isotopes in a sample 1 of rock, in particular in drill core.
  • Sample 1 has the shape of a cylinder with a diameter usually greater than 50 mm and less than 95 mm and a length greater than 350 mm, or a long prism to which the said cylinder can be circumscribed.
  • the detection means of the device in Fig. 1 is formed by two ring-shaped assemblies 3, but Fig. 1 indicates that it is possible to include another one between the two ring-shaped assemblies 3 shown.
  • the number of ring-shaped assemblies 3 is selected by the operator of the device with regard to the required accuracy and rate of measurement.
  • the ring-shaped assemblies are arranged as follows:
  • Fig. 1 shows a portable computer as an example of an evaluation unit 2 to which digitized measurement signals are transmitted.
  • the evaluation unit 2 can be an industrial computer, a desktop computer, and other similar device, the hardware of which can receive, archive, evaluate the measurement signals, and convey the measurement data to the user in a readable form.
  • Sample 1 represented by the drill core is a longitudinal cylindrical body.
  • the drill core may be provided with a suitable packaging material or, if consistent, will remain bare.
  • Sample 1 is inserted into the ring-shaped assemblies 3 using the means for positioning the sample 1.
  • the means for positioning the sample 1 is not shown in Fig. 1 for the sake of clarity, but the movement of the sample 1 is indicated by arrow.
  • the means for positioning the sample 1 may be a linear rail, an industrial robotic arm, etc. An expert will be able to suggest the use of known positioning designs by routine engineering work.
  • the ring-shaped assembly 3 is composed of end ring-shaped segments 4, which are made of lead or another shielding material or composite to shield the natural background radiation.
  • the middle ring-shaped segment 5 of the assembly 3 is provided with at least one detector 6, but ideally with three detectors 6 arranged in the ring-shaped segment 5 at intervals of 120°, see Fig. 2. A higher number of detectors 6 in the middle ring-shaped segment 5 is possible.
  • the middle ring-shaped segment 5 consists of materials which absorb gamma radiation or slow down and absorb neutrons, or of a mixture of these materials, alloys or their composites.
  • Detectors 6 comprise a rod scintillator made of GYGAG:Ce material (gadoliniumyttrium gallium-aluminium garnet doped with cerium), or the rod scintillators are made of another aluminate. Rod means that their height is greater than their width. Other proven materials include LuYAG:Ce, GAGG:Ce, LuGAGG:Ce. This list applies to tested scintillators.
  • an array of photodiodes of the SiPM type i.e. the so-called “silicon photomultiplier”, or other photosensitive means known to the expert, is connected to the rod scintillator. For example, photomultipliers, avalanche photodiodes, etc.
  • the photosensitive means convert the scintillation signal of the crystal into the electronic pulse and the electronic chain 8 processes, digitizes and prepares this pulse for transmission via the data bus 7 to the evaluation unit.
  • Detector 6 further comprises a temperature control system in the SiPM region.
  • the temperature control system may include a temperature sensor, such as a thermistor, or uses some of the SiPM characteristics, such as dark current, displacement of the spectrum of calibration isotope, and the like.
  • Each of the detectors 6 comprises an electronic chain 8 for signal processing.
  • the electronic chain 8 comprises: a signal preamplifier and amplifier, a multichannel analyzer, a converter for communication with the evaluation unit via the data bus 7, a bias voltage source for SiPM photodiodes or other photosensitive means, a temperature control system, feedback for either adjustment of bias voltage, and/or adjustment of the amplification of the electronic chain 8 depending on the temperature of the photosensitive means, as well as feedback to adjust the temperature of the SiPM, e.g. by means of a Peltier cell.
  • An expert in electronics and electrical engineering will be able to suggest alternative types of hardware.
  • Evaluation unit 2 is provided with a data storage where software modules can be found which receive the measured operating quantities of detectors, on the basis of which the evaluation unit 2 can assess the effect of operating temperature on the operation of the device. Algorithms from software modules allow to compensate the effect of the operating temperature on the operation of the device by controlling the operating parameters of the device.
  • Detector 6 functions as a counter of pulses induced by particles of ionizing radiation, it can also be used as a spectrometer. Detector 6 thus makes it possible to generate histograms of the amplitude of the pulses induced by the particles of ionizing radiation in the energy range of 10 keV to 3000 keV. An example of such a spectrum is shown in Fig. 3.
  • the device for measuring the content of natural radioactive isotopes in rock sample, in particular in drill core, according to the invention will find its application in geological mapping of the rock environment and mineral deposits.

Abstract

The device for measuring the content of natural radioactive isotopes in a rock sample (1), especially in drill core. The device comprises at least one detection means for measuring the ionizing radiation emanating from the sample (1) and at least one means for positioning the sample (1). The device also comprises at least one shielding of the sample (1) and/or the detection means communicatively connected to at least one evaluation unit (2). The detection means consists of at least one ring-shaped assembly (3) composed of at least three ring- shaped segments arranged side by side so that the end ring-shaped segments (4) shield from the radiation background. At least one detection ring-shaped segment (5) is arranged between the end shielding ring-shaped segments (4), provided with at least one ionizing radiation detector (6). The means for positioning the sample (1) are adapted to move the sample (1) through the ring-shaped assembly (3).

Description

Device for measuring the content of natural radioactive isotopes in rock sample
Field of the Invention
The invention relates to a geological analysis of the content of natural radionuclides in drill cores from exploratory drilling using KUTh gamma logging to describe the geological profile and geological activity of the area explored by means of exploratory drilling.
Background of the Invention
The importance of the natural radioactivity of rocks was known to experts in the field of geology already at the beginning of the 20th century. More massive development of prospecting methods using the natural radioactivity of rocks and ionizing radiation occurs in particular after World War II. Already in the 1940s, the application for registration of the invention US 2 640 161 (A) disclosed a device for measuring radioactivity in a geological borehole. With the development of the field of geological exploration by means of radioactivity, number of known prospecting methods was increasing, for example, those published in the applications of the inventions under the designations GB 908 485 (A) and GB 1 160747 (A).
At present, it is possible to differentiate prospecting methods, so-called logging, based on ionizing radiation, for example according to the principle they use. Known logging includes, for example, spectral gamma logging as well as gamma-gamma logging, neutron-neutron logging, neutron-gamma logging, which is otherwise known to the professional public under its English abbreviation PGNAA (Prompt Gamma Neutron Activation Analysis), neutron logging, or for example gamma neutron logging. The ionizing radiation used during logging is either naturally emanating from the rock, or purposefully generated ionizing radiation is used, and then its reflection and scattering on the rock are measured, or secondary ionizing radiation generated by the rock is measured. At the same time, it is possible to categorize the above logging methods according to the method of application. For example, it is a measurement of radioactivity during the borehole drilling process, in which the detection means are part of the drilling body, moving through the rock together with the drilling head. Another known method of application is to dive the detection means into an already drilled borehole, which can be reinforced by casing, but at the cost of changing the conditions of permeability of some components of natural ionizing radiation. Another mode of application of logging with the use of ionizing radiation is measurement outside the borehole, in which the subject of measurement is the material obtained from the borehole, the so-called drill cores.
The above-mentioned development of prospecting methods concerned mainly their application inside boreholes, with surprisingly less attention being paid to the measurement of drill cores. This trend has changed in recent years and efforts are being made to accurately measure drill cores. One of the reasons is to obtain more accurate information from existing drilling archives and a comprehensive assessment using a combination of prospecting methods. Examples of such efforts are the known inventions, for example KR 2017/0121546 (A) and KR 101 552 954 (B).
As part of gamma logging, measurements of weak natural gamma radioactivity of rocks are performed to determine the quality of mineral deposits. The measured natural gamma radioactivity of rocks comes from the primordial radionuclides 40K, 238U, and 232Th contained in them, and which gave it the name “KUTh gamma logging”. The known detection units used for KUTh gamma logging either measure only the total radioactivity or have spectrometric properties. The energy resolution in known detection units enables to determine the ratio of the mentioned radionuclides, and thus determine the geological composition of lithologically separated areas, or even the mineralogical composition of sediments. It is possible, for example, to characterize the type and composition of clay, or to distinguish micaceous sand from shale, etc.
Geiger-Muller detectors were formerly used in detection units to measure ionizing radiation, however, but they have been currently replaced by scintillators with photosensitive elements. A scintillator is a material in which a flash of light is generated by excitation of ionizing radiation. The intensity of light flash is proportional to the energy deposited by the quantum of ionizing radiation in the scintillator. This light flash is converted by the photosensitive element into an electrical signal. The signal is then processed and digitized by an electronic chain and transferred to the evaluation unit. The information obtained from the scintillator is of better quality the better the ionizing quanta deposit their energy therein. In general, therefore, the scintillator should have the highest possible density, and should contain the heaviest elements, i.e. elements with the highest possible proton number Z.
The photosensitive element is usually a photomultiplier, a photodiode, an avalanche photodiode (APD), or a so-called silicon photomultiplier (SiPM). Experts may include other light-sensitive elements in this category, for example based on graphene, etc. The electronic chain usually includes a signal preamplifier and amplifier, a multi-channel analyzer, a data bus, a voltage source for the photosensitive element and possibly other components.
Currently, thallium-doped sodium iodide (NaETl) is the most widely used scintillation material in the above applications, however, scintillation materials based on monocrystalline aluminates and silicates are also beginning to be used. Examples of such newly used scintillation aluminates, without claim to completeness, are perovskites and garnets doped with cerium, praseodymium, neodymium and europium, as well as lutetium-yttrium silicate, and others.
Examples of known detection units are the inventions disclosed in CN 110 018 510 (A) and CN 106 019 358 (A). Both inventions measure rock samples in the form of drill cores. The invented devices include shielded irradiation tables into which the drill cores are fixed.
Another well-known example of existing methods are the solutions in the publications “Spectrometric gamma radiation of shale cores applied to sweet spot discrimination in Eastern Pomerania” (DOI: 10.1007/s 11600-017-0089-7) and “A new natural gamma radiation measurement system for marine sediment and rock analysis ” (DOI: 10.1016/j.jappgeo.2011.08.008), which address the problem of analysis in their own original way, but are not a completely applicable solution to the following object of the invention.
The disadvantages of the above-mentioned devices are that they are robust devices. The robustness of both devices is due to the need to sufficiently shield the ubiquitous natural radiation background, as the solution used, with the detectors with large NaLTl scintillators in the devices, is too sensitive to this background radiation. In addition, the work cycle on the devices is time consuming because it requires the following operational steps: open the shielding of the device, place the drill core on the irradiation table, close the shielding of the device, perform measurements, open the shielding of the device, remove the measured drill core, and repeat the cycle with a new drill core.
The object of the invention is to provide a device for measuring the content of natural radioactive isotopes in rock sample, in particular represented by a drill core, provided with a detector capable of distinguishing between desirable natural ionizing radiation emanating from radionuclides contained in rock and natural radiation background present behind shielding, which was easy to transport and assemble even in conditions of use outside laboratory buildings, and which could shorten the work cycle by steps associated with opening and closing of the shield.
Summary of the Invention
The stated object is solved by providing a device for measuring the content of natural radioactive isotopes in rock sample, in particular in drill core according to the invention below.
The device for measuring the content of natural radioactive isotopes in rock sample, in particular in drill core, comprises at least one detection means for measuring the ionizing radiation emanating from the sample. The detection means comprises a detector which consists of a scintillator, a photosensitive means and an electronic chain. The device further comprises at least one means for positioning the sample. At the same time, the device comprises at least one shielding of the sample and/or the detection means against the influence of the radiation background. An integral part of the device is at least one evaluation unit, which is communicatively connected to the detection means by a data bus, e.g. USB, CAN, or another.
The core of the invention is based on the fact that the detection means is composed of at least one ring-shaped assembly composed of at least three ring-shaped segments arranged side by side. Each ring-shaped assembly comprises at least one segment with detectors arranged in the middle of the ring-shaped assembly and at least two shielding segments, each arranged at the edge of the ring-shaped assembly. Between the end shielding segments, the ring-shaped assembly may include several segments with detectors and several shielding segments interposed between adjacent detection segments. The shielding ring-shaped segments form the shielding from the radiation background. The detector segment is provided with at least one ionizing radiation detector. At the same time, the sample positioning means is adapted to move the sample through the ring-shaped assembly. It is also important that the detector comprises a rod scintillator and at least one photosensitive means for collecting light flashes from the rod scintillator. The scintillator is made of monocrystalline or poly crystalline material from the group of aluminates doped with cerium, praseodymium, europium, neodymium. Proven material candidates are materials from the group, LuYAG:Ce, GAGG:Ce, GYGAG:Ce, LuGAGG:Ce.
The scintillator of the invention has a number of advantages. For example, the use of a scintillator from the group of aluminates or silicates, in particular of the GAGG:Ce material, has the advantages that each of the detectors has sufficient detection efficiency even at a small size. The small size of the detector then brings advantages in the lower natural background. Thus, the use of the GAGG:Ce scintillator gives a better signal/background ratio than other traditional scintillators, such as thallium-doped sodium iodide (NaETl). This is because the proton number of iodine is 53, while the proton number of gadolinium is 64.
The benefit of the invention is, firstly, its modular construction. The ring-shaped assembly can be disassembled into individual segments, which facilitates the installation/disassembly and transport of the device. Another great advantage of the invention is that it is possible to use it in a series of several ring-shaped assemblies for one sample. As a rule, the more assemblies used, the more accurate the measurement will be, or the shorter the measurement time of the sample will be while maintaining the accuracy. Last but not least, a ring shape is advantageous because the samples are inserted and removed from the side, thus saving time with the opening and closing of the shielding above the area of measurement.
The means for positioning the sample is preferably provided with a sample displacement sensor. Data from sensors, especially if sent directly to the evaluation unit, can help to better assign the associated location and status of the sample to the measured data.
In a preferred embodiment of the device according to the invention, the photosensitive means consists of at least one photomultiplier, or a photodiode, or an avalanche photodiode, or a silicon photomultiplier (SiPM). Preferably, the device is provided with at least one means for monitoring the effects of temperature changes on the function of the ionizing radiation detector. This means can be based on measuring the temperature in different parts of the detector, measuring other characteristics of the detector, e.g. dark current or thermal noise, or detecting short-term deviations of the positions of selected photopeaks of KUTh nuclides in the spectrum of ionizing radiation. The detection of deviations of positions of photopeaks of KUTh nuclides works with dose rate at the level of natural background and does not require the use of other radiation sources. The device includes hardware or software implemented continuous correction of the effect of temperature, either by changing the voltage that supplies the photosensitive means, or by changing the gain of the electronic chain.
It is preferred that the shielding of the middle ring-shaped segment consists of materials which absorb gamma radiation or slow down and absorb neutrons, or of a mixture of these materials, alloys or their composites (hereinafter referred to as “shielding materials” or “composites”). Materials that absorb gamma radiation are from the group of metals: lead, tungsten, barium, copper, iron, nickel, chromium. Materials, which slow down neutrons, include organic substances and polymers. These include, but are not limited to, poly(methyl) methacrylate (PMMA), polyethylene (PE), polypropylene (PP), paraffin, bitumen and others. The neutron absorbing materials are lithium and boron, their compounds, alloys, mixtures and composites. It is preferred if the end ring-shaped segments are made of the mentioned shielding materials or composites.
The list of advantages of the invention includes in particular a modular concept which facilitates transport, installation and disassembly. Furthermore, used scintillators, which make it possible to reduce the amount of material used for shielding, and thus to lighten the device as a whole, compared to known robust structures. A good signal/background ratio of the detector itself then represents a design advantage of the whole device, as only a small amount of shielding materials or composites of which the shielding of detectors from gamma radiation or neutrons from the natural background is made is sufficient to achieve the required detection efficiency. This is supported by another advantage that the device is light and therefore easy to transport. In addition, reducing the amount of lead needed to shielding the detector has the additional advantage that lead usually contains a small but measurable amount of natural isotope 210Pb with a half-life of 22 years. If the shielding contains less material, such as lead, then the natural background radiation generated by this isotope will also be reduced. Last but not least, the advantage in terms of significance is that it is possible to insert samples from the side of the device into the openings of the rings, so that it is not necessary to open the shielding around the area of measurement. However, for measuring samples of less common dimensions, in particular short ones, the rings may be adapted to be opened from above in order to insert the sample.
Explanation of drawings
The present invention will be explained in detail by means of the following figures where:
Fig. 1 schematically shows the concept of the invention,
Fig. 2 schematically shows a normal section of a middle ring-shaped segment fitted with three detectors,
Fig. 3 shows an example of a spectrum measured by the invention. By means of the invention, a model drill core with a diameter of 80 mm was measured, which contains 148 ppm of uranium, 22 ppm of thorium and their decay products. The horizontal axis represents the energy of radiation in electron volts, and the vertical axis shows the counts of detected quanta of radioactive radiation of a given energy. The measured spectrum contains peaks characteristic for individual isotopes of the decay series of uranium 238 and thorium 232.
Example of the invention embodiments
It shall be understood that the specific cases of the invention embodiments described and depicted below are provided for illustration only and do not limit the invention to the examples provided here. Those skilled in the art will find or, based on routine experiment, will be able to provide a greater or lesser number of equivalents to the specific embodiments of the invention which are described here.
Fig. 1 shows a diagram of a device to be used to measure the content of natural radioactive isotopes in a sample 1 of rock, in particular in drill core. Sample 1 has the shape of a cylinder with a diameter usually greater than 50 mm and less than 95 mm and a length greater than 350 mm, or a long prism to which the said cylinder can be circumscribed. The detection means of the device in Fig. 1 is formed by two ring-shaped assemblies 3, but Fig. 1 indicates that it is possible to include another one between the two ring-shaped assemblies 3 shown. The number of ring-shaped assemblies 3 is selected by the operator of the device with regard to the required accuracy and rate of measurement.
In other potential non-illustrated embodiments of the invention, the ring-shaped assemblies are arranged as follows:
• end shielding segment, detection segment, central shielding segment, detection segment, end shielding segment
• end shielding segment, detection segment, detection segment, central shielding segment, detection segment, detection segment, end shielding segment An expert is able to routinely design another set of variations in the arrangement of segments and ring-shaped assemblies according to the intended application of the invention, thanks to the modular nature of the invention.
Furthermore, Fig. 1 shows a portable computer as an example of an evaluation unit 2 to which digitized measurement signals are transmitted. The evaluation unit 2 can be an industrial computer, a desktop computer, and other similar device, the hardware of which can receive, archive, evaluate the measurement signals, and convey the measurement data to the user in a readable form.
Sample 1 represented by the drill core is a longitudinal cylindrical body. The drill core may be provided with a suitable packaging material or, if consistent, will remain bare. Sample 1 is inserted into the ring-shaped assemblies 3 using the means for positioning the sample 1. The means for positioning the sample 1 is not shown in Fig. 1 for the sake of clarity, but the movement of the sample 1 is indicated by arrow. The means for positioning the sample 1 may be a linear rail, an industrial robotic arm, etc. An expert will be able to suggest the use of known positioning designs by routine engineering work.
The ring-shaped assembly 3 is composed of end ring-shaped segments 4, which are made of lead or another shielding material or composite to shield the natural background radiation. The middle ring-shaped segment 5 of the assembly 3 is provided with at least one detector 6, but ideally with three detectors 6 arranged in the ring-shaped segment 5 at intervals of 120°, see Fig. 2. A higher number of detectors 6 in the middle ring-shaped segment 5 is possible. The middle ring-shaped segment 5 consists of materials which absorb gamma radiation or slow down and absorb neutrons, or of a mixture of these materials, alloys or their composites.
Detectors 6 comprise a rod scintillator made of GYGAG:Ce material (gadoliniumyttrium gallium-aluminium garnet doped with cerium), or the rod scintillators are made of another aluminate. Rod means that their height is greater than their width. Other proven materials include LuYAG:Ce, GAGG:Ce, LuGAGG:Ce. This list applies to tested scintillators. In detector 6, an array of photodiodes of the SiPM type, i.e. the so-called “silicon photomultiplier”, or other photosensitive means known to the expert, is connected to the rod scintillator. For example, photomultipliers, avalanche photodiodes, etc. The photosensitive means convert the scintillation signal of the crystal into the electronic pulse and the electronic chain 8 processes, digitizes and prepares this pulse for transmission via the data bus 7 to the evaluation unit.
Detector 6 further comprises a temperature control system in the SiPM region. The temperature control system may include a temperature sensor, such as a thermistor, or uses some of the SiPM characteristics, such as dark current, displacement of the spectrum of calibration isotope, and the like.
Each of the detectors 6 comprises an electronic chain 8 for signal processing. The electronic chain 8 comprises: a signal preamplifier and amplifier, a multichannel analyzer, a converter for communication with the evaluation unit via the data bus 7, a bias voltage source for SiPM photodiodes or other photosensitive means, a temperature control system, feedback for either adjustment of bias voltage, and/or adjustment of the amplification of the electronic chain 8 depending on the temperature of the photosensitive means, as well as feedback to adjust the temperature of the SiPM, e.g. by means of a Peltier cell. An expert in electronics and electrical engineering will be able to suggest alternative types of hardware.
Evaluation unit 2 is provided with a data storage where software modules can be found which receive the measured operating quantities of detectors, on the basis of which the evaluation unit 2 can assess the effect of operating temperature on the operation of the device. Algorithms from software modules allow to compensate the effect of the operating temperature on the operation of the device by controlling the operating parameters of the device. Detector 6 functions as a counter of pulses induced by particles of ionizing radiation, it can also be used as a spectrometer. Detector 6 thus makes it possible to generate histograms of the amplitude of the pulses induced by the particles of ionizing radiation in the energy range of 10 keV to 3000 keV. An example of such a spectrum is shown in Fig. 3.
Industrial applicability
The device for measuring the content of natural radioactive isotopes in rock sample, in particular in drill core, according to the invention will find its application in geological mapping of the rock environment and mineral deposits.
List of reference numerals
1 sample
2 evaluation unit
3 ring-shaped assembly
4 end ring-shaped segment
5 middle ring-shaped segment
6 ionizing radiation detector
7 data bus
8 electronic chain of ionizing radiation detector

Claims

CLAIMS Device for measuring the content of natural radioactive isotopes in rock sample (1), in particular in drill core, comprising at least one detection means for measuring ionizing radiation emanating from the sample (1) equipped with an electronic chain, at least one means for positioning the sample (1), at least one shielding of the sample (1) and/or detection means against the influence of the radiation background, and at least one evaluation unit (2) communicatively connected to the detection means characterized in that the detection means consists of at least one ring-shaped assembly (3) composed of at least three ring-shaped segments arranged side by side so that the end ring-shaped segments (4) are shielding for shielding the radiation background, and at least one detection ring-shaped segment (5) is placed between the end shielding ring-shaped segments (4), which is provided with at least one ionizing radiation detector (6), which comprises a rod scintillator and at least one photosensitive means for collecting the scintillation flashes from the rod scintillator, with the scintillator being made of a monocrystalline or polycrystalline material from the group of cerium, praseodymium, europium, neodymium doped aluminates, and at the same time the means for positioning the sample (1) is adapted to move the sample (1) through the ring-shaped assembly (3). Device according to claim 1 characterized in that the ring-shaped assembly (3) comprises at least one central shielding ring-shaped segment arranged between the detection ring-shaped segments. Device according to claim 1 characterized in that the means for positioning the sample (1) is provided with a sample (1) displacement sensor. Device according to claim 1 characterized in that the scintillator is made of a material from the group LuYAG:Ce, GAGG:Ce, GYGAG:Ce, LuGAGG:Ce. Device according to any of claims 1 to 4 characterized in that the photosensitive means is formed by at least one photomultiplier or photodiode or avalanche photodiode or silicon photomultiplier (SiPM). Device according to any of claims 1 to 5 characterized in that it is provided with at least one means for measuring the temperature in the region of the ionizing radiation detector (6). Device according to any of claims 1 to 6 characterized in that the evaluation unit (2) is provided with at least one data storage provided with a software module for monitoring the electrical quantities of the photosensitive means and comprising an algorithm for determining the effect of temperature on the function of the device. Device according to any of claims 1 to 7 characterized in that the evaluation unit (2) is provided with at least one data storage provided with a software module for changing the sensitivity of the photosensitive element or for changing the setting of the electronic chain, including an algorithm for calculating the change in sensitivity/setting depending on the effect of temperature on the function of the device. Device according to any of claims 1 to 8 characterized in that the evaluation unit (2) is provided with at least one data storage provided with a software module for changing the supply voltage of the photosensitive means or for changing the amplification of the electronic chain, comprising an algorithm for calculating the compensation of the effect of temperature on the function of the device. Device according to claim 3 characterized in that the sample (1) displacement sensor is communicatively connected to the evaluation unit (2), with the evaluation unit (2) being provided with at least one data storage provided with a software module for sending information on sample (1) displacement into the automatic process of the results evaluation in the evaluation unit. Device according to claims 6, 7, 8 and 9 characterized in that the temperature measuring means is communicatively connected by feedback to other parts of the electronic chain, and/or is communicatively connected by feedback to the evaluation unit (2). Device according to any of claims 1 to 11 characterized in that the ring-shaped segment (5), which is provided with at least one ionizing radiation detector (6), is at least partly made of lead or another shielding material, or a mixture thereof, or a composite. Device according to any of claims 1 to 12 characterized in that the ring-shaped segments (4) intended to shield the radiation background are made of lead or another shielding material, or a mixture thereof, or a composite.
15
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EP0310303A1 (en) * 1987-09-28 1989-04-05 Amoco Corporation Beltless core conveyor system for wellsite analysis
US20140339409A1 (en) * 2013-05-15 2014-11-20 Schlumberger Technology Corporation Scintillation Detector Package Having Radioactive Reflective Material Therein
EP3074790A2 (en) * 2013-11-26 2016-10-05 FLIR Detection, Inc. SiPM-BASED RADIATION DETECTION SYSTEMS AND METHODS
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