Alkali halide scintillators and uses thereof

Abstract

The present application relates to alkali halide scintillators and uses thereof. A scintillator can include a single crystal compound having the general formula Na (1‑y) Li y X, where 0

Description

[0001] This application is a divisional application of a patent application with an application date of March 30, 2017, an application number of 201780021100.4, and an invention title of "Alkali Halide Scintillators and Their Uses". Technical Field

[0002] The present disclosure relates to scintillators and methods of using such scintillators. Background Art

[0003] Scintillator-based detectors are used in various applications, including nuclear physics research, oil exploration, field spectroscopy, container and baggage scanning, and medical diagnostics. When the scintillator material of a scintillator-based detector is exposed to ionizing radiation, the scintillator material captures the energy of the incident radiation and scintillates, emitting the captured energy in the form of photons. The light sensor of the scintillator-based detector detects the emitted photons. Radiation detection devices can analyze pulses for many different reasons. Continuous improvement is needed. Summary of the Invention

[0004] In one aspect, the present application provides a scintillator comprising a single crystal compound having the general formula Na (1-y) Li y X, where 0 < y < 1 and X is at least one halogen or any combination of multiple halogens.

[0005] In another aspect, the present application provides a scintillator having a pulse shape discrimination figure of merit of at least 1.5 at a temperature of 25 °C.

[0006] In yet another aspect, the present application provides a scintillator having a pulse shape discrimination figure of merit of at least 1.5 at a temperature of 150 °C.

[0007] In still another aspect, the present application provides a radiation detector comprising the scintillator according to any one of the above embodiments, wherein the radiation detector is a dual-mode radiation detector. Brief Description of the Drawings

[0008] The embodiments are illustrated by way of example and are not limited to the drawings.

[0009] Figure 1 Diagrams including pulse shape discrimination parameters as a function of the left pulse height and as a function of the right scintillation count.

[0010] Figure 2 Depiction of a scintillator installed within a radiation detection device according to an embodiment described herein.

[0011] Figure 3This includes a description of a measurement-while-drilling device according to embodiments described herein.

[0012] Figure 4 include Figure 3 A description of the analyzer device of the measurement while drilling (MSD) system.

[0013] Figure 5 Including the use Figure 3 A flowchart of a method for a drilling measurement-while-drilling device.

[0014] Figure 6 Pulse shape discrimination density diagram of all scintillation pulses for sample 1 used in the example section.

[0015] Figure 7 This includes pulse shape discrimination spectra of γ and neutron pulses for Sample 1 in Example 1.

[0016] Figure 8 This includes a graph showing the estimated pulse discrimination quality factor of sample 2 for Example 2 within a certain temperature range.

[0017] Figure 9 The diagram includes a representation of the relative light yield of samples 2 and 3 used in Example 2 within a certain temperature range.

[0018] Figure 10 The diagram includes a representation of the relative light yield of samples 2 and 3 used in Example 2 within a certain temperature range.

[0019] Figure 11 Includes a diagram showing the energy resolution at Li concentrations for Example 3.

[0020] Figure 12 Includes illustrations of pulse shape discrimination at Li concentrations used in Example 4.

[0021] Those skilled in the art will understand that the components in the figures are shown for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some components in the figures may be enlarged relative to other components to aid in understanding the embodiments of the invention. Detailed Implementation

[0022] The following embodiments, taken in conjunction with the accompanying drawings, are provided to aid in understanding the teachings disclosed herein. The following discussion will focus on specific implementations and examples of the teachings. This focus is provided to aid in describing the teachings and should not be construed as limiting the scope or applicability of the teachings.

[0023] As used herein, the terms “comprises / comprising,” “includes / including,” “has / having,” or any other variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of characteristics is not necessarily limited to those characteristics, but may include other characteristics not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, unless expressly stated to the contrary, “or” means inclusive or not exclusive. For example, conditions A or B are satisfied by any of the following: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); and both A and B are true (or exist).

[0024] The term "a / an" is used to describe the elements and components described herein. This is used merely for convenience and to give a general understanding of the scope of the invention. Unless otherwise clearly stated, this description should be understood to include one or at least one, and the singular includes the plural, or vice versa.

[0025] Unless otherwise stated, the contents of the different components of the scintillator compounds described herein refer to the contents of the crystals that are opposite to the melt.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Materials, methods, and examples are illustrative only and are not intended to be limiting. To the extent not described herein, many details regarding specific materials and processing behaviors are conventional and can be found in textbooks and other sources within the field of scintillation and radiation detection techniques.

[0027] As described herein, a scintillator can achieve improved differentiation between neutrons and gamma radiation by exhibiting an increasing difference in the decay time between a neutron pulse and a gamma radiation pulse. For example, in one embodiment, the scintillator can exhibit a difference in the decay time between a neutron pulse and a gamma radiation pulse, the absolute value of which is at least 33 ns, at least 35 ns, at least 37 ns, or at least 39 ns. In one embodiment, the scintillator can exhibit a difference in the decay time between a neutron pulse and a gamma radiation pulse, the absolute value of which is at most 55 ns, at most 53 ns, or at most 51 ns. Furthermore, the absolute value of the difference in decay time between a neutron pulse and a gamma radiation pulse can be within any of the aforementioned minimum and maximum values, such as 33 to 55 ns or 35 to 53 ns. For example, the decay time of a neutron pulse can be faster than the decay time of a gamma radiation pulse.

[0028] In view of the above, the scintillators described herein can be used in dual-mode neutron and gamma radiation detection devices and can provide suitable pulse shape discrimination (PSD) over a wide range of temperatures, including temperatures from -40°C to 200°C or even higher temperatures, such as at least 25°C or at least 50°C or at least 100°C to at least 125°C or at least 150°C or at least 175°C or at least 200°C or even higher temperatures. When exposed to a wide range of temperatures, including temperatures from -40°C to 200°C or even higher temperatures, such as at least 25°C or at least 50°C or at least 100°C to at least 125°C or at least 150°C or at least 175°C or at least 200°C or even higher temperatures, the radiation detection device can exhibit suitable light output performance.

[0029] In one embodiment, the scintillator compound includes an alkali halide. The alkali halide can be doped with an activator. Additionally, the alkali halide can be co-doped with an alkali metal and an activator. Co-doping with an alkali metal can improve the decay time, light yield, energy resolution, proportionality, another suitable scintillation parameter, or any combination thereof. In one embodiment, the concentration of the alkali dopant, the activator, or the ratio of the alkali dopant to the activator can be controlled to obtain good scintillation performance.

[0030] In one embodiment, the alkali of the alkali halide can include sodium, and the alkali of the alkali dopant can include lithium. For example, the scintillator compound can have the following general formula (i):

[0031] (i)Na (1-y) Li y X, where 0 < y < 1 and X is at least one halogen or any combination of multiple halogens.

[0032] In one embodiment, 'y' can be at least 0.005 or at least 0.01 or at least 0.02 or at least 0.03. In additional embodiments, 'y' can be at most 0.1 or at most 0.09 or at most 0.08. Additionally, 'y' can be within any of the above minimum and maximum ranges, such as 0.005 to 0.1.

[0033] In a more specific embodiment, the scintillator compound can include 6 Li enriched such that 6 Li accounts for more than 7% of the total Li content. In a specific embodiment, 6 Li accounts for at least 70% or at least 80% or at least 90% of the total Li content. In another embodiment, the scintillator compound can include Li, where 6 Li accounts for at most 7% of the total Li content. In one embodiment, the scintillator compound has a stoichiometric composition, while in another embodiment, the scintillator compound has a non-stoichiometric composition.

[0034] Furthermore, the scintillator compound may include an activator dopant. The activator dopant may be present in the scintillator compound in an amount of at least 0.03 mol%, at least 0.1 mol%, at least 0.2 mol%, or at least 0.3 mol%. In one embodiment, increasing the concentration of the activator in the scintillator compound may reduce the performance of the scintillator relative to the PSD. Therefore, in some embodiments, the amount of activator dopant present, by weight of the scintillator compound, may be at most 1 mol%, at most 0.9 mol%, or at most 0.8 mol%. Furthermore, the activator dopant may be present in the scintillator compound in a range within any of the aforementioned minimum and maximum values, such as 0.03 mol% to 1 mol% or 0.1 mol% to 0.8 mol%. In some embodiments, the activator dopant may include a late transition metal, such as thallium, or a lanthanide element such as europium, but not a combination of thallium and europium. In one embodiment, the γ-radiation pulse decay time of the scintillator described herein may be affected by the concentration of co-dopersant in the scintillator compound. In one embodiment, the gamma-radiation pulse decay time of a scintillator compound comprising Li-doped NaI:Tl can be longer than that of a scintillator compound comprising NaI:Tl with the same Tl concentration but without Li co-doping. Furthermore, the gamma-radiation pulse decay time can decrease with increasing Li content in the scintillator compound. For example, the gamma-radiation pulse decay time of Li-doped NaI:Tl at 22°C can be at least 230 ns, at least 250 ns, or at least 300 ns. In another embodiment, the gamma-radiation pulse decay time of a scintillator compound comprising Li-doped NaI:Tl can be shorter than that of a scintillator compound comprising NaI:Tl with the same Tl concentration but without Li co-doping. For example, in a particular embodiment, the gamma radiation pulse decay time of Li-doped NaI:Tl with at least one additional co-doperb may be at most 200 ns, at most 190 ns, at most 180 ns, or at most 170 ns.

[0035] In one embodiment, as described above, the scintillator compound comprising Li-doped NaI:Tl or NaI:Eu may further comprise at least one additional co-doperant. The additional co-doperant may comprise alkali metals such as K, Rb, Cs; alkaline earth elements such as Mg, Ca, Sr, Ba; rare earth elements such as La, Lu, Yb, Ce, Tb, Sc, or Y; transition metals such as Cr; post-transition metals such as In; or any combination thereof.

[0036] In one embodiment, the scintillator compound can be grown in crystalline form according to Bridgman-Stockbarger, Czochralski, Kyropoulos, Edge-defined Film Growth (EFG), Gradient Freeze technique, etc. In a particular embodiment, crystal growth can be performed using a continuous feed in melt or powder form. Furthermore, the growth method can produce a single-crystal compound. In one embodiment, the single-crystal compound can be finished and used as a single-crystal scintillator compound. In another embodiment, the single-crystal compound can be plastically deformed to prepare a polycrystalline scintillator compound. For example, crystals can be formed according to the method disclosed in U.S. Patent No. 8,871,115 entitled "Method for Forming a Luminescent Material" by Vladimir Ouspenski, which is incorporated herein by reference in its entirety.

[0037] In one embodiment, a single-crystal scintillator compound comprising Li co-doped NaI:Tl can achieve unexpectedly improved performance compared to polycrystalline scintillator compounds comprising Li co-doped NaI:Tl. Furthermore, polycrystalline scintillator compounds derived from the initially formed single-crystal compound comprising Li co-doped NaI:Tl can achieve unexpectedly improved performance compared to the initially formed polycrystalline compound comprising Li co-doped NaI:Tl. Prior art has not successfully obtained PSD suitable for gamma radiation and neutrons using scintillators comprising polycrystalline NaI scintillator compounds. (See "Using Alkali Halide Scintillators") 6 Li and pulse shape discrimination thermal neutron detection using alkali halidescintillators 6In their paper "Li and pulse shape discrimination" (2011 IEEE Nuclear Science Symposium Conference Record), Brubaker et al. ("Brubaker") found that scintillators including polycrystalline NaI (Li, Tl) scintillator compounds exhibited poor neutron light yield and PSD, concluding that polycrystalline NaI (Li, Tl) scintillator compounds exhibited insufficient γ-ray filtering. Similarly, in their paper "Lithium alkali halides – new thermal neutron detectors with n-γ discrimination" (2013 IEEE Nuclear Science Symposium Conference Record), Nagarkar et al. ("Nagarkar") disclosed that scintillators including polycrystalline NaI (Li) scintillator compounds exhibited similar decay characteristics to neutron and γ-ray radiation, and therefore did not exhibit adequate PSD.

[0038] Surprisingly, the inventors have developed a single-crystal compound comprising Li co-doped NaI:Tl that exhibits improved performance. In one embodiment, the single-crystal compound can have increased transparency. Additionally, the polycrystalline scintillator compound derived from the single-crystal compound can have reduced porosity while maintaining increased transparency. In one embodiment, the porosity of the scintillator compound, expressed as a percentage of the scintillator compound's material density, can be at most 0.1%, 0.5%, or 2%. Without being bound by any particular theory, the inventors believe that the increased transparency in the scintillator compound contributes to achieving improved PSD that Brubaker and Nagarkar could not achieve.

[0039] The improved performance of bimode applications combined with PSD can be demonstrated using the PSD quality factor (FOM). The scintillator can be exposed to a neutron source, and the electron pulses received by the analyzer device are processed using a Fast Fourier Transform (FFT) to obtain PSD parameter values. The PSD parameter can be determined by the time it takes for the electron pulse to rise from 2% to 60% of its maximum intensity. Other integration ranges can be used for other scintillator compounds. For example, the PSD parameter can be determined by the time it takes for the electron pulse to rise from 2% to 50% or from 10% to 90% of its maximum intensity. For illustration, Figure 1Including pulse height ratio closer Figure 1 The graph of the PSD parameters on the left is closer to the pulse count ratio. Figure 1 The PSD parameters are illustrated on the right. Figure 1 In the middle, if closer Figure 1 As shown in the right-hand diagram, H1 corresponds to the peak value of the gamma radiation pulse, and H2 corresponds to the peak value of the thermal neutron pulse. H1 and H2 are represented in PSD parameters using the Y-axis of the left-hand diagram. Therefore, H1 is 700 (in PSD parameters), and H2 is 594 (in PSD parameters). The full width at half maximum (FWHM) can be obtained from the peak values ​​in the right-hand diagram and can also be represented in PSD parameters. FWHM1 corresponds to the FWHM of H1 and has a value of 37 (in PSD parameters), and FWHM2 corresponds to the FWHM of H2 and has a value of 42 (in PSD parameters).

[0040] As used in this article, the PSD FOM is defined by the following equation:

[0041] |(H1 – H2)| / (FWHM1 + FWHM2).

[0042] H1, H2, FWHM1, and FWHM2 are all in units of PSD parameters; therefore, the PSD FOM is dimensionless. Figure 1 In the figure, the PSD FOM of the sample scintillator is 1.34. The PSD FOM of the compositions described herein can be analyzed in a similar manner. As the PSD FOM becomes larger, the PSD is more accurate and the possibility of pulse misclassification decreases. On the other hand, as the PSD FOM becomes smaller, the PSD becomes more difficult to determine and the possibility of pulse misclassification increases.

[0043] In one embodiment, the PSD FOM of the scintillator compound described herein can be greater than that of a NaI:Tl scintillator having the same Tl concentration but without Li co-doping. For example, the PSD FOM of the scintillator compound described herein at 25°C can be at least 1.1, at least 1.3, or at least 1.5. In one embodiment, the PSD FOM of the scintillator compound at 25°C can be at most 6, at most 5, or at most 4. The scintillator compound can have the above-described PSD FOM at 25°C at a Li concentration of at least 0.5 mol%, at least 2 mol%, at least 4 mol%, or at least 8 mol%.

[0044] Furthermore, the PSD FOM of the scintillator compound may be at least 1.5 at a temperature of at least 50°C, at least 75°C, at least 100°C, at least 125°C, at least 150°C, or at least 175°C. In one embodiment, the PSD FOM of the scintillator compound described herein at 50°C may be at least 2, at least 2.5, or at least 3. In one embodiment, the PSD FOM of the scintillator compound described herein at 75°C may be at least 2, at least 2.5, or at least 3. In one embodiment, the PSD FOM of the scintillator compound described herein at 100°C may be at least 2, at least 2.5, or at least 3. In one embodiment, the PSD FOM of the scintillator compound described herein at 125°C may be at least 1.7, at least 2.1, or at least 2.5. In one embodiment, the PSD FOM of the scintillator compound described herein at 150°C may be at least 1.1, at least 1.3, or at least 1.5.

[0045] Furthermore, certain embodiments of the scintillators described herein offer advantages including the introduction of neutron sensitivity into NaI, NaI:Tl, or NaI:Eu scintillators by doping the scintillator compound with Li. In one embodiment, the Li-co-doped NaI scintillator compound can achieve a PSD suitable for dual-mode detection of neutrons and gamma radiation at both room temperature and high-temperature environments (e.g., at temperatures from about 50°C to at least about 200°C).

[0046] Another advantage of certain embodiments of the scintillators described herein includes that, compared to a NaI:Tl scintillator with the same Tl concentration but without Li co-doping, Li-co-doped NaI, NaI:Tl, or NaI:Eu scintillator compounds exhibit substantially no reduction in performance relative to light output and gamma-ray energy at 25°C, and an increase in such performance at higher temperatures in the range of about 50°C to about at least 200°C. In one embodiment, the scintillator compound comprising Li-co-doped NaI:Tl exhibits greater light output at temperatures of 25°C or higher, such as at at least 50°C, at at least 75°C, at at least 100°C, at at least 125°C, at at least 150°C, at at least 175°C, or at at least 200°C than the light output of a NaI:Tl scintillator with the same Tl concentration but without Li co-doping.

[0047] In one embodiment, the energy resolution of the scintillator compound described herein can be comparable to that of the NaI:Tl scintillator compound, particularly when the Li concentration in the crystal is in the range of greater than 0 mol% to about 8 mol%. For example, the energy resolution of the scintillator compound described herein at 662 keV can be in the range of 6% to about 8%, or more particularly 6.2% to 7.6%.

[0048] In another embodiment, within the 2.0 to 4.0 MeV gamma-ray equivalent energy range, the gamma filtering of the scintillator can be up to 1 × 10⁻⁶ gamma rays per gamma-ray detection. -6 Or at most 5×10 -7 Or at most 1×10 -7 False neutron detection.

[0049] In one embodiment, the scintillator can be a large scintillator. In one embodiment, the width of the scintillator can be at least 15 mm, at least 25 mm, at least 50 mm, at least 75 mm, at least 90 mm, or at least 100 mm. In another embodiment, the volume of the scintillator can be at least 500 cm³. 3 Or at least 750 cm 3 Or at least 1000 cm 3 Or at least 1500 cm 3 Or at least 2000 cm 3 In one embodiment, the scintillator described herein does not include thin-film scintillators, such as scintillators with a thickness of no more than 10 mm.

[0050] Furthermore, in one embodiment, the scintillator described herein does not include size-limited crystals such as potassium cryolite. Rare earth potassium cryolite can have the general formula: M1 1+ 2M2 +1 REX6, including M1 1+ These are elements with relatively large cations, which belong to Group 1 elements, particularly Cs, Rb, K, and Na; M2 1+ X is an element with a relatively small cation, which belongs to Group 1 elements, particularly Li or Na. RE is one or more rare earth elements; and X is one or more halogen elements. The size of potassium cryolite crystals can be limited due to the variety of species in potassium cryolite.

[0051] Any of the scintillators described above can be used in a variety of applications, including nuclear physics research, oil exploration, field spectroscopy, container and baggage scanning, and medical diagnostics. Exemplary applications include radiation detectors for: security detection equipment, oil well logging equipment, gamma-ray spectroscopy equipment, isotope identification equipment, public area detectors, large-area survey equipment, baggage and cargo scanning equipment, single positron emission tomography (SPECT) or positron emission tomography (PET) equipment, x-ray imaging equipment, entrance monitor radiation detectors, handheld radiation detectors, and personal radiation detectors.

[0052] Figure 2 The description includes drilling equipment 10, which includes a top drive 12 connected to the upper end of a drill string 14 suspended within a wellbore 16 by a winch 17. A rotary table, including a pipe slide 18, is used to maintain proper drill string orientation connected to or replacing the top drive 12. A downhole telemetry and transmission device 20 (commonly referred to as a measurement while drilling (MWD) device) is part of a downhole tool connected to the lower end of the drill string 14. The MWD device transmits drilling-related parameters to the surface via mud pulses or electromagnetic transmission. These signals are received at the surface by a data receiving device 22. The downhole tool includes a bend 23, a downhole motor 24, and a drill bit 26. The bend 23 is adjacent to the MWD device to assist drilling in tilting the wellbore. The downhole motor 24, such as a positive-displacement motor (PDM) or a downhole turbine, powers the drill bit 26 and is located at the distal end of the downhole tool 26.

[0053] Downhole signals received by data receiving device 22 are provided to computer 28, output device 30, or both. Computer 28 may be located at the well site or remotely connected to the well site. Analyzer device may be part of computer 28 or may be located within downhole tools near MWD device 20. Computer 28 and analyzer device may include processors that can receive input from users. Signals may also be sent to output device 30, which may be a display device, hard copy recording and printing device, measuring instrument, visual and audible alarm, or any combination thereof. Computer 28 is operatively connected to the controller of winch 17 and control electronics 32 associated with top drive 12 and rotary table 18 to control the rotation of drill string and drill bit. Computer 28 may also be coupled to control mechanisms associated with drilling fluid pumps of drilling equipment to control drill bit rotation. Control electronics 32 may also receive manual input, such as from drilling operators.

[0054] Figure 3A depiction of a portion of an MWD device 20 within a downhole tool 16 is shown. The MWD device 20 includes a housing 202, a temperature sensor 204, a scintillator 222, an optical interface 232, an optical sensor 242, and an analyzer device 262. The housing 202 may include materials capable of protecting the scintillator 222, the optical sensor 242, the analyzer device 262, or combinations thereof, such as metals, metal alloys, other materials, or any combination thereof. The temperature sensor 204 is adjacent to the scintillator 222, the optical sensor 242, or both. The temperature sensor 204 may include a thermocouple, a thermistor, or other suitable means capable of determining the temperature within the housing at the normal operating temperature of the MWD device 20. The radiation detection device may include the scintillator 222, an optical sensor 242 optically coupled to the scintillator 222, and an analyzer device 262 optically coupled to the optical sensor 242. Although shown herein as part of an MWD device, those skilled in the art will recognize upon reading this disclosure that the radiation detection device can be used for other applications, such as those described above.

[0055] Scintillator 222 may include any of the scintillator compounds described above. In a particular embodiment, scintillator 222 may include a scintillator compound having a composition well-suited for high-temperature applications, such as applications operating at temperatures in the range of 50°C to 200°C or even higher, such as at least 50°C or at least 75°C or at least 100°C to at least 125°C or at least 150°C or at least 175°C or at least 200°C or even higher. In another embodiment, scintillator 222 may include a scintillator compound having a composition such that the PSD FOM is sufficiently high to allow for pulse shape discrimination so that neutrons and gamma radiation can be counted separately even at the aforementioned high temperatures.

[0056] In summary, scintillator 222 may have a PSD FOM that allows pulse shape discrimination, may have a composition that may include a Br- or I-containing alkali halide, or may have a PSD FOM and the composition therein.

[0057] Back Figure 3 The scintillator 222 and the photosensor 242 are optically coupled to the optical interface 232. The optical interface 232 may include a polymer, such as silicone rubber, to mitigate the refractive index difference between the scintillator 222 and the photosensor 242. In other embodiments, the optical interface 232 may include a gel or colloid comprising a polymer and additional elements.

[0058] The light sensor 242 can be a photomultiplier tube (PMT), a semiconductor-based photomultiplier (SiPM), a hybrid light sensor, or any combination thereof. The light sensor 242 can receive photons emitted by the scintillator 222 and generate electronic pulses based on the number of photons received. The light sensor 242 is electrically coupled to the analyzer device 262. Although not explicitly stated... Figure 3 As shown, however, an amplifier can be used to amplify the electronic signal from the light sensor 242 before it reaches the analyzer device 262.

[0059] The analyzer device 262 may include hardware and may be implemented at least in part as software, firmware, or a combination thereof. In one embodiment, the hardware may include multiple circuits within a field-programmable gate array (FPGA), an application-specific integrated circuit (ASIC), another integrated circuit, or on a printed circuit board or another suitable device, or any combination thereof. The analyzer device 262 may also include buffers for temporarily storing data before it is analyzed, written to storage, read from, transferred to another component or device, performing another suitable action on the data, or any combination thereof. Figure 4 In the embodiment shown, the analyzer device 262 may include a light sensor 242 coupled to it. Figure 3 An amplifier 422 is used to amplify the electronic pulses from the light sensor 242 before analysis. The amplifier 422 may be coupled to an analog-to-digital converter (ADC) 424 capable of digitizing the electronic pulses. The ADC 424 may be coupled to a pulse shape discrimination (PSD) module 442. In a particular embodiment, the PSD module 442 may include an FPGA or an ASIC. In a particular embodiment, the PSD module 442 may include circuitry for analyzing the shape of the electronic pulses and determining whether the electronic pulses correspond to neutrons or gamma radiation. In a more particular embodiment, the PSD module 442 may use the electronic pulses, the temperature from the temperature sensor 204, or derived information from these information, and use a lookup table to determine whether the electronic pulses correspond to neutrons or gamma radiation. The lookup table may be part of an FPGA or ASIC or may be in another device, such as an integrated circuit, a disk drive, or a suitable permanent memory device.

[0060] The analyzer device 262 further includes a neutron counter 462 and a gamma radiation counter 464. If the PSD module 442 determines that the electron pulse corresponds to a neutron, then the PSD module 442 increments the neutron counter 462. If the PSD module 442 determines that the electron pulse corresponds to gamma radiation, then the PSD module 442 increments the gamma radiation counter 464.

[0061] In an alternative embodiment, some or all of the components or functions provided by the analyzer device 262 may be located outside the wellbore or at the drilling site or away from the drilling site, such as in an office building.

[0062] Figure 5 Including the use of devices such as MWD device 20 Figure 2 A flowchart of an exemplary method for drilling equipment shown in the diagram. The method will relate to... Figure 2 The drilling equipment shown, such as Figure 3 The MWD device 262 shown and as Figure 4 The components within the analyzer device shown are used for description. After reading this specification, those skilled in the art will understand that activities described with respect to a particular component can be performed by another component. Furthermore, activities described with respect to a particular component can be combined into a single component, and activities described with respect to a single component can be distributed among different components.

[0063] The method can be used Figure 5 The insertion of the downhole tool into the wellbore 16 begins at frame 502. (See reference.) Figure 2 The drill bit 26 can be activated by pumping drilling fluid down the drill string 14 to rotate the downhole motor 24. For directional drilling, the top drive 12 can be used to control the direction of the drill bit. When drilling continues in a straight line, the top drive 12 rotates the drill string 14 while downward pressure is applied by the winch 17. To change direction, the top drive 12 is used to position the tool face of the downhole tool. When the direction changes, the downward pressure can be reduced. After the tool face is in the correct position, the top drive 12 stops rotating the drill string because the bend 23 changes the drilling direction. The downward pressure on the drill bit 26 increases, and drilling continues as the direction changes. After the proper direction is achieved, the top drive 12 is activated to rotate the drill string 14, allowing further drilling to continue in the new direction. During drilling, a large amount of heat can be generated, and the resulting temperature can be above 120°C, at least 130°C, at least 140°C, at least 150°C, or even higher. Also during drilling, the MWD device 20 collects data. Scintillator 222 is selected such that, at such a temperature, depending on the type of radiation captured, scintillator 222 can produce different scintillating light corresponding to different types of radiation converted into different types of electronic pulses by photosensor 242.

[0064] The method may include: Figure 5 Radiation is captured and scintillation light is emitted at boxes 522 and 524. Radiation can be captured by scintillator 222, and scintillation light can be emitted by scintillator 222 in response to the captured radiation. The method may further include generating an electronic pulse at optical sensor 242 at box 542 in response to receiving scintillation light from scintillator 222. The electronic pulse can be provided to analyzer device 262 by optical sensor 242. The method may further include amplifying the electronic pulse at box 562. The electronic signal can be amplified by a preamplifier or amplifier within optical sensor 242 or analyzer device 262. The method may further include converting the electronic pulse from an analog signal to a digital signal at box 564.

[0065] The method may include processing data as necessary, and Figure 5At box 566, it is determined whether the electron pulse corresponds to a neutron or gamma radiation. In one embodiment, the determination can be performed by an FPGA, ASIC, or other suitable device. Pulse analysis may include processing data as necessary and determining the pulse's rise time, decay time, another suitable parameter that can be used to make the determination, or any combination thereof. The determination can be performed using a PSD module 442. The PSD module 442 may use temperature information from temperature sensor 204 as part of the determination. The method may further include incrementing an appropriate counter at box 568 in response to the determination. When it is determined that the electron pulse corresponds to a neutron, the neutron counter 462 increments. When it is determined that the electron pulse corresponds to gamma radiation, the gamma radiation counter 464 increments. This information can also be used to identify the source of gamma radiation.

[0066] refer to Figure 5 Some of the actions described in boxes 562, 564, 566, and 568 can be performed by analyzer device 262. All analyzer devices 262 can be located within MWD device 20 or outside of wellbore 16. In another embodiment, amplifier 422 and ADC 424 can be located within MWD device 20, and PSD module 442 and counters 462 and 464 can be located on the external surface of wellbore 16. After reading this specification, those skilled in the art will be able to determine the location of the analyzer device or components of analyzer device 262 based on the PSD FOM of the scintillator for normal operating temperature, computational requirements that may or may not depend on the PSD FOM or the composition of the scintillator, and specific applications.

[0067] Although a radiation detection device is described in relation to drilling equipment, the radiation detection device can be part of a logging device that does not perform drilling operations. Similar to a downhole tool with a drill bit 26, the logging device can include a downhole tool without a drill bit. A flexible drill string can be coupled to the downhole tool to allow the downhole tool to descend and rise within the wellbore 16. The drill string can be coupled to the downhole tool if needed or desired.

[0068] The concepts described herein allow for a better selection of a scintillator compound that includes a co-doped alkali halide, particularly a NaI:Tl scintillator compound co-doped with Li, which can have an acceptable PSD FOM at the normal operating temperature of the device (whether at room temperature or at the higher temperatures described herein). An acceptable PSD FOM allows for the use of pulse shape discrimination to discriminate between two different types of radiation and allows pulse shape discrimination to be dedicated to a particular portion of an electron pulse where the difference between different types of radiation is more distinct compared to other portions of the electron pulse. Additionally, the Li content in the co-doped NaI:Tl can be adjusted to achieve a scintillator compound for the scintillator that has a very suitable PSD FOM for a particular portion of an electron pulse where the distinction between different types of radiation is greater than other portions. The concepts described herein can be extended to other types of radiation, such as x-rays, alpha particles, beta particles, etc., and are not limited to neutron and gamma radiation.

[0069] Many different aspects and embodiments are possible. Some of those aspects and embodiments are described herein. After reading this specification, those skilled in the art will understand that those aspects and embodiments are merely illustrative and do not limit the scope of the invention. Additionally, those skilled in the art will understand that some embodiments that include analog circuits can be implemented similarly using digital circuits and vice versa. Embodiments can be consistent with any one or more of the embodiments listed below.

[0070] Embodiment 1. A scintillator comprising a single crystal compound having the general formula Na (1-y) Li y X, where 0 < y < 1 and X is at least one halogen or any combination of multiple halogens.

[0071] Embodiment 2. A scintillator having a pulse shape discrimination figure of merit of at least 1.5 at a temperature of 22°C.

[0072] Embodiment 3. A scintillator having a pulse shape discrimination figure of merit of at least 1.5 at a temperature of 150°C.

[0073] Embodiment 4. The scintillator according to any one of Embodiments 2 and 3, having the general formula Na (1-y) Li y X, where 0 < y < 1 and X is at least one halogen or any combination of multiple halogens.

[0074] Embodiment 5. The scintillator according to any one of Embodiments 1 and 4, where y is at least 0.005 or at least 0.01 or at least 0.02 or at least 0.03.

[0075] Example 6. A scintillator according to any one of Examples 1, 4 and 5, wherein y is at most 0.1 or at most 0.09 or at most 0.08.

[0076] Example 7. A scintillator according to any one of the foregoing embodiments, wherein the scintillator includes an additional dopant comprising at least one of K, Rb, Cs, In, Mg, Ca, Sr, Ba, Sc, Y, La, Lu, Yb, Ce, Tb, Cr and any combination thereof.

[0077] Example 8. The scintillator according to any one of the foregoing embodiments further comprises an activator dopant.

[0078] Example 9. The scintillator according to Example 8, wherein thallium is the only activator dopant.

[0079] Example 10. The scintillator according to Example 8, wherein europium is the only activator dopant.

[0080] Example 11. A scintillator according to any one of Examples 8, 9 and 10, wherein the activator dopant is present in an amount of at least 0.03 mol%, at least 0.1 mol%, at least 0.2 mol%, or at least 0.3 mol%.

[0081] Example 12. A scintillator according to any one of Examples 8 to 11, wherein the amount of the activator dopant is at most 1 mol%, at most 0.9 mol%, or at most 0.8 mol%.

[0082] Example 13. A scintillator according to any one of Examples 1 and 4 to 12, wherein the pulse shape discrimination quality factor of the scintillator at a temperature of 22°C is at least 1 or at least 1.2 or at least 1.3.

[0083] Example 14. A scintillator according to any one of Examples 1 and 4 to 12, wherein the pulse shape discrimination quality factor of the scintillator at a temperature of 150°C is at least 0.9 or at least 1.1 or at least 1.2 or at least 1.3 or at least 1.4.

[0084] Example 15. A scintillator according to any one of the preceding embodiments, wherein the pulse shape discrimination quality factor of the scintillator at a temperature of 22°C is at most 5 or at most 4 or at most 3.

[0085] Example 16. A scintillator according to any of the preceding embodiments, wherein the pulse shape discrimination quality factor of the scintillator at a temperature of 150°C is at most 5 or at most 4 or at most 3.

[0086] Example 17. A scintillator according to any one of the foregoing embodiments, wherein the scintillator has at most 1 × 10⁻⁶ gamma rays per gamma ray in the 2.0 to 4.0 MeV gamma ray equivalent energy range. -6 Or at most 5×10 -7 Or at most 1×10 -7 The gamma filtering ratio of pseudoneutron detection.

[0087] Example 18. A scintillator according to any one of the preceding embodiments, wherein the scintillator comprises Li-co-doped NaI:Tl, and its light output at a temperature of 22°C or higher, such as at a temperature of at least 50°C, or at a temperature of at least 75°C, or at a temperature of at least 100°C, or at a temperature of at least 125°C, or at a temperature of at least 150°C, or at a temperature of at least 175°C, or at a temperature of at least 200°C, is greater than the light output of a scintillator compound comprising NaI:Tl having the same Tl concentration but without Li co-doping.

[0088] Example 19. A scintillator according to any one of Examples 1 and 4 to 18, wherein the Li comprises at least 30%, at least 60%, or at least 90% of the total Li content. 6 Lithium enrichment in Li.

[0089] Example 20. A scintillator according to any one of Examples 1 and 4 to 19, wherein the halogen comprises bromine or iodine.

[0090] Example 21. The scintillator according to Example 20, wherein the halogen comprises iodine.

[0091] Example 22. A scintillator according to any one of the foregoing embodiments, wherein the width of the scintillator is at least 75 mm, at least 90 mm, or at least 100 mm.

[0092] Example 23. A scintillator according to any one of the foregoing embodiments, wherein the volume of the scintillator is at least 500 cm³. 3 Or at least 750 cm 3 Or at least 1000 cm 3 Or at least 1500 cm 3 Or at least 2000 cm 3 .

[0093] Example 24. A scintillator according to any of the preceding examples, wherein the porosity of the scintillator is at most 0.1% or at most 0.5% or at most 2% based on the material density of the scintillator compound.

[0094] Example 25. A scintillator according to any of the preceding examples, wherein the scintillator comprises a polycrystalline scintillator compound derived from the initially formed single-crystal compound.

[0095] Example 26. A radiation detector comprising a scintillator according to any one of the foregoing embodiments.

[0096] Example 27. The radiation detector according to Example 26 further includes an optical sensor optically coupled to the scintillator.

[0097] Example 28. The radiation detector according to Example 27 further includes an analyzer device, wherein the analyzer device is adapted to distinguish a first pulse from the optical sensor from a second pulse from the optical sensor, wherein the first pulse corresponds to a neutron captured by the scintillator and the second pulse corresponds to gamma radiation captured by the scintillator.

[0098] Example 29. The radiation detector according to Example 28, wherein the analyzer device includes a discrimination module configured to use rise time, decay time or a combination thereof to distinguish between the neutron and the gamma radiation.

[0099] Example 30. A radiation detector according to any one of Examples 26 to 29, wherein the radiation detector is an entrance monitor radiation detector, a handheld radiation detector, or a personal radiation detector.

[0100] Example 31. A radiation detector according to any one of Examples 26 to 30, wherein the radiation detector is a dual-mode radiation detector.

[0101] Example 32. The radiation detector according to Example 31, wherein the dual-mode radiation detector detects neutrons and gamma radiation.

[0102] Example 33. A radiation detector according to any one of Examples 26 to 32, wherein the radiation detector is at least a part of: security detection equipment, oil well logging detection equipment, gamma-ray spectroscopy equipment, isotope identification equipment, public area detection equipment, large area survey equipment, baggage and cargo scanning equipment, single positron emission tomography (SPECT) equipment or positron emission tomography (PET) equipment, x-ray imaging equipment, entrance monitor radiation detector equipment, handheld radiation detector equipment, or personal radiation detector equipment.

[0103] Example 34. An apparatus comprising a downhole tool configured for insertion into a wellbore and including a scintillator according to any one of Examples 1 to 25.

[0104] Example 35. The device according to Example 34 further includes a light sensor optically coupled to the scintillator.

[0105] Example 36. The device according to Example 35 further includes an analyzer device coupled to the optical sensor, wherein the analyzer device is part of a downhole tool.

[0106] Example 37. The device according to Example 35 further includes an analyzer device coupled to the optical sensor, wherein the analyzer device is configured to operate outside the wellbore and spaced apart from the downhole tool.

[0107] Example 38. The device according to any one of Examples 35 to 37, further comprising a drill string coupled to the downhole tool.

[0108] Example

[0109] Examples are given by way of illustration only and do not limit the scope of the invention as defined in the appended claims.

[0110] Example 1

[0111] Data were collected on a single-crystal scintillator compound, namely Sample 1, which has NaI (0.05 mol% Tl, 0.5 mol% Li) in melt and NaI (0.06 mol% Tl, 0.4 mol% Li) in crystal. The scintillator was exposed to approximately 109 nanograms of... 252 Cf was placed approximately 30 cm away from the scintillator. Exposure was conducted at approximately 22°C. Radiation trapped by the scintillator caused the emission of scintillation light collected by a photosensor, which in turn generated electron pulses. Figure 6 Including PSD density maps of all flicker pulses, and Figure 7 PSD spectra including gamma and neutron pulses. From Figure 7 As can be seen, the separation between gamma radiation and neutrons is excellent. Specifically, the PSD FOM exceeds 1.5, which corresponds to a detection efficiency of 1 × 10⁻⁶ gamma rays per ray in the 2.0 to 4.0 MeV gamma-ray equivalent energy range. -8 The gamma filtering ratio of pseudoneutron detection.

[0112] Example 2

[0113] Data were collected from two samples (Sample 2 and Sample 3). Sample 2 was a single-crystal scintillator compound of the formula NaI (0.04 mol% Tl, 1 mol% Li) in crystal form. Sample 3 was a NaI:Tl crystal with the same Tl concentration but without Li co-doping. Each sample scintillator was exposed to approximately 10⁹ nanograms of [unclear - likely a specific type of material]. 252The Cf was placed approximately 30 cm from the scintillator. A quartz tube was used between the crystal and the PMT. This configuration was less efficient than the configuration in Example 1 without a quartz tube and reduced the measured PSD FoM by 50% (see Menge et al., Nuclear Science Symposium and Medical Imaging Conference (NSS / MIC), 2011 IEEE, pp. 1598, 1601, October 2011). The measurements were performed at temperatures ranging from -40°C to approximately 160°C. Figure 8 This includes an estimated PSD FOM plot of this temperature range for sample 2, and indicates that the measured value is twice as high to account for the efficiency reduction due to the light tube. Figure 9 Includes relative light yield plots (normalized to 25°C) over a given temperature range, with the forming time for samples 2 and 3 being 1 μs. Figure 10 Includes relative light yield plots (normalized to 25°C) over a given temperature range, with the forming time for samples 2 and 3 being 12 μs.

[0114] from Figure 8 As can be seen, the PSD FOM is greater than 2 from approximately -10°C to approximately 150°C. Furthermore, the PSD FOM increases significantly at approximately 25°C and is greater than 3.2 from approximately 50°C to approximately 110°C. Therefore, Li-co-doped NaI:Tl enables dual-mode detection.

[0115] from Figure 9 and 10 As can be seen, the relative light yield of Li-co-doped NaI:Tl compound sample 2 shows a smaller reduction than that of standard NaI:Tl scintillator compound sample 3 at temperatures ranging from 25°C to well above 140°C. Therefore, scintillator compounds containing Li-co-doped NaI:Tl perform better than scintillator compounds including standard NaI:Tl, especially at high temperatures.

[0116] Example 3

[0117] Data were collected on numerous samples of Li-co-doped NaI:Tl scintillator compounds. The Tl concentrations were the same as in the previous examples and consistent for each sample. The Li concentration for each sample varied from greater than 0 mol% to approximately 8 mol%. Each sample was exposed to approximately 10⁹ nanograms of [unspecified substance]. 252 Cf was placed approximately 30 cm from the scintillator. Energy resolution was measured at 662 keV and targeted at... Figure 11 Plotting the Li concentration in [the graph / data].

[0118] Example 4

[0119] Data were collected on numerous samples of Li-co-doped NaI:Tl scintillator compounds. The Tl concentrations were the same as in the previous examples and consistent for each sample. The Li concentration for each sample varied from greater than 0 mol% to approximately 8 mol%. Each sample was exposed to approximately 10⁹ nanograms of [unspecified substance]. 252 Cf was placed approximately 30 cm away from the scintillator. PSD FOM was measured at a temperature of approximately 25°C and targeted at... Figure 12 The Li concentration of each sample in the graph is plotted.

[0120] Note that not all activities described above in the general description or examples are required; a portion of a specific activity may not be necessary, and one or more additional activities may be performed besides those described. Furthermore, the order in which the activities are listed is not necessarily the order in which they are performed.

[0121] The benefits, other advantages, and solutions to problems have been described above with reference to specific embodiments. However, any benefits, advantages, solutions to problems, and one or more features that may lead to the existence or further apparent occurrence of any benefit, advantage, or solution should not be construed as critical, essential, or fundamental features of any or all claims.

[0122] The description and illustrations of the embodiments described herein are intended to provide a general understanding of the structure of various embodiments. The description and illustrations are not intended to be an exhaustive and comprehensive description of all elements and characteristics of devices and systems using the structures or methods described herein. Specific features described herein in the context of individual embodiments for clarity may also be provided in combination in individual embodiments. Conversely, various features described in the context of individual embodiments for brevity may also be provided individually or in any sub-combination. Furthermore, references to values ​​stated in range form include each value within the range. Many other embodiments will only become apparent to those skilled in the art after reading this specification. Other embodiments may be used and derived from this disclosure to allow for structural substitutions, logical substitutions, or other changes without departing from the scope of this disclosure. Therefore, this disclosure should be considered illustrative rather than restrictive.

Claims

1. A scintillator comprising a single crystal compound having the general formula Na (1-y) Li y X, where 0 < y < 0.1, where X is iodine, and where the scintillator further comprises an activator dopant: thallium.

2. A scintillator having a pulse shape discrimination figure of merit of at least 1.5 at a temperature of 25 °C, wherein the scintillator has the general formula Na (1-y) Li y X, where 0 < y < 0.1, where X is iodine, and wherein the scintillator further comprises an activator dopant: thallium.

3. A scintillator having a pulse shape discrimination quality factor of at least 1.5 at a temperature of 150°C. wherein the scintillator has the general formula Na (1-y) Li y X, where 0 < y < 0.1, where X is iodine, and wherein the scintillator further comprises an activator dopant: thallium.

4. The scintillator according to any one of claims 1 to 3, wherein y is at least 0.

005.

5. The scintillator according to any one of claims 1 to 3, wherein y is at most 0.

08.

6. The scintillator of claim 5, wherein the scintillator comprises a single activator dopant: thallium.

7. The scintillator of claim 5, wherein the scintillator comprises a single activator dopant: europium.

8. The scintillator according to any one of claims 1 to 3, wherein the scintillator comprises an additional dopant containing at least one of K, Rb, Cs, In, Mg, Ca, Sr, Ba, Sc, Y, La, Lu, Yb, Ce, Tb, Cr and any combination thereof.

9. The scintillator according to any one of claims 6 to 7, wherein the activator dopant is present in an amount of at least 0.03 mol.

10. The scintillator according to any one of claims 1 to 3, wherein the volume of the scintillator is at least 500 cm³. 3 .

11. The scintillator according to any one of claims 1 to 3, wherein the volume of the scintillator is at least 2000 cm³. 3 .

12. The scintillator according to claim 1, wherein the pulse shape discrimination quality factor of the scintillator at a temperature of 25°C is at least 1.

13. The scintillator according to claim 1, wherein the pulse shape discrimination quality factor of the scintillator at a temperature of 150°C is at least 1.

14. A radiation detector comprising a scintillator according to any one of claims 1 to 3, wherein the radiation detector is a dual-mode radiation detector.

15. The radiation detector of claim 14, wherein the radiation detector is at least a part of: security detection equipment, oil well logging detection equipment, gamma-ray spectroscopy equipment, isotope identification equipment, public area detection equipment, large area survey equipment, baggage and cargo scanning equipment, single positron emission tomography (SPECT) equipment or positron emission tomography (PET) equipment, x-ray imaging equipment, entrance monitor radiation detector equipment, handheld radiation detector equipment, and personal radiation detector equipment.

Images