CN114481320A - Method for growing lithium thallium codoped sodium iodide scintillation crystal by non-vacuum Bridgman-Stockbarge method - Google Patents
Method for growing lithium thallium codoped sodium iodide scintillation crystal by non-vacuum Bridgman-Stockbarge method Download PDFInfo
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- FVAUCKIRQBBSSJ-UHFFFAOYSA-M sodium iodide Chemical compound [Na+].[I-] FVAUCKIRQBBSSJ-UHFFFAOYSA-M 0.000 title claims abstract description 187
- 239000013078 crystal Substances 0.000 title claims abstract description 123
- 235000009518 sodium iodide Nutrition 0.000 title claims abstract description 62
- 238000000034 method Methods 0.000 title claims abstract description 40
- DVJXWGUUOPZAMD-UHFFFAOYSA-N lithium thallium Chemical compound [Li].[Tl] DVJXWGUUOPZAMD-UHFFFAOYSA-N 0.000 title claims abstract description 20
- 239000002994 raw material Substances 0.000 claims abstract description 21
- 238000010438 heat treatment Methods 0.000 claims abstract description 8
- 238000001816 cooling Methods 0.000 claims abstract description 4
- 239000007788 liquid Substances 0.000 claims abstract description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 40
- 229910052744 lithium Inorganic materials 0.000 claims description 22
- 229910052697 platinum Inorganic materials 0.000 claims description 20
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 18
- 238000001514 detection method Methods 0.000 claims description 16
- 239000000203 mixture Substances 0.000 claims description 12
- -1 polytetrafluoroethylene Polymers 0.000 claims description 11
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 9
- 229910021392 nanocarbon Inorganic materials 0.000 claims description 9
- 229910003481 amorphous carbon Inorganic materials 0.000 claims description 6
- 239000006229 carbon black Substances 0.000 claims description 6
- 239000004810 polytetrafluoroethylene Substances 0.000 claims description 6
- 229920001343 polytetrafluoroethylene Polymers 0.000 claims description 6
- 239000011734 sodium Substances 0.000 claims description 6
- 230000005251 gamma ray Effects 0.000 claims description 5
- 229910052794 bromium Inorganic materials 0.000 claims description 4
- 229910052801 chlorine Inorganic materials 0.000 claims description 4
- 229910052731 fluorine Inorganic materials 0.000 claims description 4
- 229910052740 iodine Inorganic materials 0.000 claims description 4
- 229910052736 halogen Inorganic materials 0.000 claims description 3
- 125000005843 halogen group Chemical group 0.000 claims description 2
- 238000001228 spectrum Methods 0.000 description 10
- 229910052716 thallium Inorganic materials 0.000 description 9
- 239000000155 melt Substances 0.000 description 7
- 230000005284 excitation Effects 0.000 description 6
- 238000002284 excitation--emission spectrum Methods 0.000 description 6
- 238000005303 weighing Methods 0.000 description 6
- 238000002844 melting Methods 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 238000011056 performance test Methods 0.000 description 5
- 230000002285 radioactive effect Effects 0.000 description 5
- BKVIYDNLLOSFOA-UHFFFAOYSA-N thallium Chemical compound [Tl] BKVIYDNLLOSFOA-UHFFFAOYSA-N 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 4
- 239000011888 foil Substances 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- AMXOYNBUYSYVKV-UHFFFAOYSA-M lithium bromide Inorganic materials [Li+].[Br-] AMXOYNBUYSYVKV-UHFFFAOYSA-M 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 230000005855 radiation Effects 0.000 description 3
- 230000006978 adaptation Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 150000004820 halides Chemical class 0.000 description 2
- 150000002366 halogen compounds Chemical class 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 238000007689 inspection Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Inorganic materials [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000011812 mixed powder Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000003208 petroleum Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- GBECUEIQVRDUKB-UHFFFAOYSA-M thallium monochloride Chemical compound [Tl]Cl GBECUEIQVRDUKB-UHFFFAOYSA-M 0.000 description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000012190 activator Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000012894 bi-exponential function Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000002109 crystal growth method Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 239000002019 doping agent Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 230000009643 growth defect Effects 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 229910000450 iodine oxide Inorganic materials 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- AFSVSXMRDKPOEW-UHFFFAOYSA-N oxidoiodine(.) Chemical compound I[O] AFSVSXMRDKPOEW-UHFFFAOYSA-N 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000005240 physical vapour deposition Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
- 229910052722 tritium Inorganic materials 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/12—Halides
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
- C30B11/02—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method without using solvents
-
- 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
- G01T1/202—Measuring radiation intensity with scintillation detectors the detector being a crystal
- G01T1/2023—Selection of materials
Abstract
The invention relates to a method for growing a lithium thallium codoped sodium iodide scintillation crystal by a non-vacuum Bridgman method, which comprises the following steps: (1) selecting NaI,6LiX and TlX are used as raw materials, mixed with a deoxidizer and then placed in a crucible and sealed; (2) vertically placing the sealed crucible in the middle of a crystal growth furnace, then heating to 700-1000 ℃, and preserving heat for a certain time to completely melt the raw materials; (3) setting the temperature gradient of a solid-liquid interface to be 10-50 ℃/cm, and the descending speed of a crucible to be 0.1-10mm/h, and starting the growth of the lithium thallium codoped sodium iodide scintillation crystal; (4) and after the growth is finished, cooling to room temperature.
Description
Technical Field
The invention relates to a preparation method of a lithium thallium co-doped sodium iodide scintillation crystal, in particular to a method for growing the lithium thallium co-doped sodium iodide scintillation crystal by a non-vacuum Bridgman-Stockbarge method, belonging to the fields of crystal growth technology and radiation detection.
Background
The thallium-doped sodium iodide (NaI: Tl) scintillation crystal born in the middle of the last century becomes an evergreen tree in a radiation detection material due to the advantages of high light output, good energy resolution, easy low-cost manufacture of large-size crystals and the like, and in 2013, the Finnish radiation and nuclear safety Bureau bases on the NaI crystal127I and23na absorption of neutrons followed by production128I and24na, with simultaneous gamma ray emission, using 4 'x 16' (inch) NaI crystals to make a portal neutron-gamma detector, and measuring the pair252The absolute detection efficiency of Cf is 0.84cps/ng, which is lower than3He detection efficiency (1.1cps/ng) was analyzed and it was believed that this difference was due to the low abundance of neutron-sensitive species in the NaI crystal. Without changing the composition, the crystal volume would need to be increased to 12 liters to meet the actual demand, which is clearly an unacceptable challenge for crystal growth.
To improve the efficiency of neutron capture, Brubaker, et al, Levermore national laboratory, USA, superimposes lithium foil of 50 microns thickness with NaI (Tl) scintillation crystal face-to-face to form a simple "sandwich" neutron detector, using lithium foil with a scintillation crystal in the foil6Tritium and alpha particles emitted after the Li isotope absorbs neutrons excite NaI (Tl) scintillation crystals, the neutron detection efficiency of the combination of natural lithium and lithium-enriched 6 foil and NaI (Tl) crystals is 10%, and the result shows that6Li-doped alkali-halide scintillators have the ability to detect both neutrons and gamma rays. In 2015, national laboratories of Nagarkar and Oak Ridge, Inc. of RMD USA6Li is used as a doping agent and classical scintillation crystal NaI is used as a substrate, a physical vapor deposition method is used for preparing a LixNa1-xI Tl Eu micro-columnar polycrystalline solid solution scintillation film, and Li is foundxNa1-xTl, the light output of the Eu film to gamma rays and neutrons is respectively 25, 100ph/MeV and 102, 500ph/n, the equivalent electron energy (GEE) to gamma is respectively 2.9 and 4.1MeV, the Pulse Shape Discrimination (PSD) of the Eu film under the excitation of 241Am/Be neutron source is studied by a charge integration method, and the Li film is confirmed to Be excited by 241Am/Be neutron sourcexNa1-xTl, Eu micro-columnar polycrystalline scintillation film has high neutron/gamma discrimination capability, and can realize simultaneous monitoring of neutrons and gamma rays.
Saint gobain (USA) company reported in 20176Working with LiI codoped NaI (Tl) bulk crystals, NaI (Tl) was discovered6Li, Tl) crystal can effectively realize the resolution of neutron and gamma ray, the light output can reach 34000ph/MeV, the energy resolution is 7% @662keV, the PSD quality factor is 2.8,however, no crystal growth method has been reported in the literature and patent.
Disclosure of Invention
Aiming at the problems, the invention abandons the traditional halide crystal vacuum growth technology, adopts platinum material as a crucible, eliminates oxygen-containing impurities by adding deoxidizer into the raw materials, and prepares the lithium-thallium co-doped sodium iodide crystal by utilizing a melt method. And preparing the large-size, colorless and transparent lithium thallium codoped sodium iodide crystal without cracking under a non-vacuum condition.
In one aspect, the invention provides a method for growing a lithium thallium-codoped sodium iodide scintillation crystal by a non-vacuum Bridgman-Stockbarge method, wherein the composition general formula of the lithium thallium-codoped sodium iodide scintillation crystal is (Na)1-a-b 6LiaTlb)(I1-a-b+Xa+b) Wherein X is halogen element selected from at least one of F, Cl, Br and I, a is more than 0 and less than or equal to 0.2, and b is more than 0 and less than or equal to 0.01;
the method for growing the lithium thallium-codoped sodium iodide scintillation crystal by the non-vacuum Bridgman-Stockbarge method comprises the following steps:
(1) selecting NaI,6LiX and TlX are used as raw materials, mixed with a deoxidizer and then placed in a crucible and sealed;
(2) vertically placing the sealed crucible in the middle of a crystal growth furnace, then heating to 700-1000 ℃, and preserving heat for a certain time to completely melt the raw materials;
(3) setting the temperature gradient of a solid-liquid interface to be 10-50 ℃/cm, and the descending speed of a crucible to be 0.1-10mm/h, and starting the growth of the lithium thallium codoped sodium iodide scintillation crystal;
(4) and after the growth is finished, cooling to room temperature.
Preferably, the purity of the raw material is not less than 99.9 wt%.
Preferably, the deoxidizer is at least one of carbon black, amorphous carbon, nano carbon, graphite powder and polytetrafluoroethylene.
Preferably, the deoxidizer is NaI,6The ratio of the total mass of LiX and TlX does not exceed 5: 1000.
Preferably, the bottom of the crucible is provided with a capillary tube, a conical bottom or a flat bottom for fixing the seed crystal; the crucible is made of a platinum crucible; the crucible is cylindrical, square cylindrical or conical in shape.
Preferably, the temperature is decreased to room temperature at a rate of 1-20 ℃/hr.
On the other hand, a lithium thallium codoped sodium iodide scintillation crystal grown according to the above method.
In still another aspect, the invention also provides an application of the lithium thallium codoped sodium iodide scintillation crystal in neutron detection, X-ray detection or gamma-ray detection.
Has the advantages that:
the invention realizes the growth of the crystal under the non-vacuum condition, and reduces the growth defects of oxide, iodine oxide or hydroxyl ions and the like by adding the high-efficiency deoxidizer into the raw materials; the grown crystal is colorless and transparent, and the transmittance reaches more than 70%; by adding seed crystals, large-size lithium ion and thallium ion co-doped NaI crystals can grow. The method has the advantages of less equipment investment, simple and convenient operation, low production cost and the like, thereby overcoming the defects of a vacuum method and being beneficial to promoting the low-cost mass production of the lithium thallium-codoped sodium iodide scintillation crystal.
Drawings
FIG. 1 is a photograph of a lithium thallium co-doped sodium iodide crystal grown according to the present invention;
FIG. 2 is X-ray excitation emission spectrum of the grown lithium thallium co-doped sodium iodide crystal of the invention;
FIG. 3 shows the scintillation decay time of the grown Li and Tl-codoped sodium iodide crystal;
FIG. 4 is the gamma energy spectrum of the lithium thallium co-doped sodium iodide crystal grown by the invention;
FIG. 5 is a pulse shape resolution spectrum of a lithium thallium co-doped sodium iodide crystal grown according to the present invention;
FIG. 6 is a FOM scattering spectrum of the grown lithium thallium co-doped sodium iodide crystal, wherein neutron is neutron, and Gamma is Gamma.
Detailed Description
The present invention is further illustrated by the following examples, which are to be construed as merely illustrative, and not a limitation of the present invention.
The disclosure provides a brand-new method for growing sodium iodide crystals, namely a non-vacuum crucible descent method (melt method), so as to overcome the defects and shortcomings of the traditional vacuum method and inert gas protection method, realize low-cost preparation of high-quality and high-performance lithium thallium-codoped sodium iodide crystals, and widely apply the crystals to the fields of gamma detection, neutron detection and gamma-neutron dual-mode detection, such as security inspection, petroleum exploration, industrial detection and the like.
The sodium iodide crystal has a composition general formula of (Na)1-a-b 6LiaTlb)(I1-a-b+Xa+b) Belongs to a cubic crystal system, wherein X is one or a mixture of more of halogen elements (F, Cl, Br and I); a is more than 0 and less than or equal to 0.2; b is more than 0 and less than or equal to 0.01. Wherein adopt6Li and Tl ions are used as activators of NaI crystals,6the Li and Tl ions being in the form of halides, e.g.6LiI and TlI are doped into the raw material with a doping concentration of 0.01-20 at.%.
The core of the invention is that: (1) one or the combination of amorphous carbon, nano carbon, graphite powder, polytetrafluoroethylene and the like is added into the raw materials to be used as a deoxidizer for expelling oxygen impurities in the raw materials and the crucible, so that the oxygen impurities are prevented from reacting with the components in the raw materials to form an inclusion in the crystal, the traditional vacuum method growth technology is completely abandoned, and the transparency and other scintillation properties of the crystal are obviously improved.
Selecting high-purity anhydrous sodium iodide (NaI) with the purity of not less than 99.9 percent and lithium halide (NaI)6LiX) and thallium halide (TlX) (X ═ at least one of F, Cl, Br, I) as raw materials, weighed and proportioned according to the following formula: (1-a-b) NaI + a6LiX+bTlX→(Na1-a-b 6LiaTlb)(I1-a-b+Xa+b) (a is more than 0 and less than or equal to 0.2; b is more than 0 and less than or equal to 0.01) and then put into a mortar. Then adding deoxidizer and mixing. Since the halogen compound has extremely strong deliquescence, the halogen compound cannot grow in a non-vacuum environment without a deoxidizer. Wherein the deoxidizer can be one or mixture of carbon black, amorphous carbon, nanocarbon, graphite powder and polytetrafluoroethylene with strong reducibility, and the deoxidizerThe weight ratio of the raw materials is not more than 5:1000, preferably 1/1000-5/1000.
Platinum is used as a crucible for loading raw materials and growing crystals, the shape of the crucible can be cylindrical, square column or conical, and the bottom of the crucible is provided with a capillary or a conical bottom or a flat bottom for fixing a seed crystal.
And growing the lithium thallium co-doped sodium iodide crystal by adopting a non-vacuum Bridgman-Stockbarge method. The non-vacuum crucible descending method abandons the traditional growth technology of a vacuum method and an inert gas protection method, and prepares the large-size, colorless and transparent and crack-free lithium-thallium co-doped sodium iodide crystal under the non-vacuum condition. The method has the advantages of simple and convenient operation, low cost, high light output of the grown crystal, high energy resolution, excellent neutron/gamma ray discrimination capability and the like, and can be applied to the fields of petroleum exploration, security inspection, industrial detection and the like.
Spontaneous nucleation is adopted or seed crystals are put into the capillary part of the crucible, then raw materials and deoxidizer are mixed and put into a platinum crucible, and the opening part of the crucible is sealed.
And vertically placing the welded and sealed platinum crucible in the middle of the crystal growth furnace. The temperature of the crystal growth furnace is raised to the temperature of 700-.
Setting the temperature gradient of a solid-liquid interface to be 10-50 ℃/cm and the descending speed of the crucible to be 0.1-10 mm/h. The crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized. After the growth is finished, the furnace temperature is reduced at the speed of 1-20 ℃/h.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
Example 1: growth NaI 0.2 at% TlBr 0.5 at%6LiI crystal
(1) Growth of6The Li doping concentration is 0.5%, and the Tl doping concentration is 0.2%. Weighing NaI104.19g,60.47g of LiI, 0.39g of TlBr and 0.15g of graphite powder are fully mixed, and then the mixture is put into a flat-bottom platinum crucible and sealed;
(2) vertically placing the welded and sealed platinum crucible in the middle of a crystal growth furnace;
(3) heating the crystal growth furnace to ensure that the temperature reaches 700 ℃ and the temperature is preserved for a certain time until the raw materials are completely melted and uniformly mixed;
(4) adjusting the position of the crucible and the temperature of the furnace to reduce the temperature of the bottom of the crucible to about the melting point of the scintillation crystal, wherein the temperature gradient is 23.5 ℃/cm, then the platinum crucible is reduced in the furnace body at the reduction speed of 2mm/h, and the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized;
(5) and finally, reducing the furnace temperature at a speed of 10 ℃/h, and taking out the lithium and thallium co-doped sodium iodide crystal when the thermocouple shows that the temperature is reduced to the room temperature.
The grown crystals were transparent and crack-free and contained no inclusions. After the crystal is cut, ground and polished, performance test is carried out. As can be seen from the X-ray excitation emission spectrum, the X-ray excitation emission peak of the crystal is located at 433 nm. By137The pulse height spectrum excited by the Cs radioactive source can be seen, and the energy resolution of the full energy peak at 662keV is about 7%. The scintillation decay time of the crystal sample can be well fitted by a double-exponential function, and the fast component of the decay time is 210ns, accounting for 8%; the slow component is 1250ns, 92%. By analyzing the pulse shape resolution spectrum of the crystal, the neutron-gamma ray discrimination factor FOM of the crystal is 2.7.
Example 2: growth NaI 0.2 at% TlI,0.1 at%6LiI crystal
(1) Growth of6The Li doping concentration is 0.1%, and the Tl doping concentration is 0.2%. Weighing NaI178.61g of the mixture,60.16g of LiI, 0.79g of TlI and 0.3g of activated carbon powder are fully mixed, and then the mixture is put into a cylindrical platinum crucible and sealed;
(2) vertically placing the welded and sealed platinum crucible in the middle of a crystal growth furnace;
(3) heating the crystal growth furnace to ensure that the temperature reaches 900 ℃ and the temperature is preserved for a certain time until the raw materials are completely melted and uniformly mixed;
(4) adjusting the position of the crucible and the temperature of the furnace, reducing the temperature of the bottom of the crucible to about the melting point of the scintillation crystal, wherein the temperature gradient is 18.6 ℃/cm, then reducing the crucible in the furnace at a reducing speed of 5mm/h, and nucleating and growing the crystal from the bottom of the crucible until the melt is completely solidified and crystallized;
(5) and reducing the furnace temperature at the rate of 20 ℃/h, and taking out the lithium and thallium co-doped sodium iodide crystal when the thermocouple shows that the temperature is reduced to the room temperature.
The grown crystals were transparent and crack-free and contained no inclusions. After the crystal is cut, ground and polished, performance test is carried out. As can be seen from the X-ray excitation emission spectrum, the X-ray excitation emission peak of the crystal is located at 430 nm. By137The pulse height spectrum excited by the Cs radioactive source can be seen, and the energy resolution of the full energy peak at 662keV is about 7.5%. The scintillation decay time of the crystal sample can be well fitted by a double-exponential function, and the fast component of the decay time is 210ns, accounting for 20%; the slow component is 850ns, accounting for 80%. By analyzing the pulse shape-resolved spectrum of the crystal, the FOM of the crystal was 2.6.
Example 3: growth NaI 0.2 at% TlI,1 at%6LiF crystal
(1) Growth of6The Li doping concentration is 1%, and the Tl doping concentration is 0.2%. Weighing the NaI103.87g,60.15g of LiF, 0.46g of TlI and 0.1g of powder mixed by nano carbon and carbon black (the nano carbon and the carbon black are 2.5: 1) are fully mixed, and then the mixture is put into a flat-bottom platinum crucible and sealed;
(2) vertically placing the welded and sealed platinum crucible in the middle of a crystal growth furnace;
(3) heating the crystal growth furnace to keep the temperature at 850 ℃ for a certain time until the raw materials are completely melted and uniformly mixed;
(4) adjusting the position of the crucible and the temperature of the furnace to reduce the temperature of the bottom of the crucible to about the melting point of the scintillation crystal, wherein the temperature gradient is 30.6 ℃/cm, then the platinum crucible is reduced in the furnace body at the reduction speed of 1mm/h, and the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized;
(5) and reducing the furnace temperature at the rate of 15 ℃/h, and taking out the lithium and thallium co-doped sodium iodide crystal when the thermocouple shows that the temperature is reduced to the room temperature.
The grown crystals were transparent and crack-free and contained no inclusions. After the crystal is cut, ground and polished, performance test is carried out. As can be seen from the X-ray excitation emission spectrum, the X-ray excitation emission peak of the crystal was located at 435 nm. By137The pulse height spectrum excited by the Cs radioactive source can be seen, and the energy resolution of the full energy peak at 662keV is about 8.0%. The scintillation decay time of the crystal sample can be well fitted by a double-exponential function, and the fast component of the decay time is 210ns, accounting for 89%; the slow component is 1060ns, 11%.
Example 4: growth NaI 0.1 at% TlI,8 at%6LiCl crystal
(1) Growth of6The Li doping concentration is 8%, and the Tl doping concentration is 0.1%. Weighing NaI96.13g of NaI96,6LiCl 1.96g, TlI 0.23g and amorphous carbon, nano carbon, graphite powder and polytetrafluoroethylene mixed powder 0.35g (amorphous carbon, nano carbon, graphite powder and polytetrafluoroethylene are 1: 3.7: 5.2: 1) are fully mixed, and then the mixture is put into a flat-bottom platinum crucible and sealed;
(2) vertically placing the welded and sealed platinum crucible in the middle of a crystal growth furnace;
(3) heating the crystal growth furnace to ensure that the temperature reaches the temperature of 700-;
(4) adjusting the position of the crucible and the temperature of the furnace to reduce the temperature of the bottom of the crucible to about the melting point of the scintillation crystal, wherein the temperature gradient is 37.5 ℃/cm, then the platinum crucible is reduced in the furnace body at the reduction speed of 3mm/h, and the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized;
(5) and reducing the furnace temperature at the rate of 8 ℃/h, and taking out the lithium and thallium co-doped sodium iodide crystal when the thermocouple shows that the temperature is reduced to the room temperature.
The grown crystals were transparent and crack-free and contained no inclusions. After the crystal is cut, ground and polished, performance test is carried out. As can be seen from the X-ray excitation emission spectrum, the X-ray excitation emission peak of the crystal was located at 435 nm. By137The pulse height spectrum excited by the Cs radioactive source can be seen, and the energy resolution of the full energy peak at 662keV is about 10%. The scintillation decay time of the crystal sample can be well fitted by a double-exponential function, and the fast component of the decay time is 265ns, which accounts for 63%; the slow component was 1550ns, 37%.
Example 5: growth NaI 0.3 at% TlCl,12 at%6LiBr crystal
(1) Growth of6The Li doping concentration is 12%, and the Tl doping concentration is 0.3%. Weighing NaI91.74g, weighing,66.03g of LiBr, 0.50g of TlCl and 0.45g of mixed powder of carbon black, nano carbon and graphite (2.2: 3.7: 1) are fully mixed, and then the mixture is placed into a flat-bottom platinum crucible and sealed;
(2) vertically placing the welded and sealed platinum crucible in the middle of a crystal growth furnace;
(3) heating the crystal growth furnace to ensure that the temperature reaches 1000 ℃ and the temperature is preserved for a certain time until the raw materials are completely melted and uniformly mixed;
(4) adjusting the position of the crucible and the temperature of the furnace to reduce the temperature of the bottom of the crucible to about the melting point of the scintillation crystal, wherein the temperature gradient is 28.3 ℃/cm, then the platinum crucible is reduced in the furnace body at the reduction speed of 0.8mm/h, and the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized;
(5) and reducing the furnace temperature at the rate of 5 ℃/h, and taking out the lithium and thallium co-doped sodium iodide crystal when the thermocouple shows that the temperature is reduced to the room temperature.
The grown crystals were transparent and crack-free and contained no inclusions. After the crystal is cut, ground and polished, performance test is carried out. As can be seen from the X-ray excitation emission spectrum, the X-ray excitation emission peak of the crystal is at 434 nm. By137The pulse height spectrum excited by the Cs radioactive source shows that the energy resolution of the full energy peak at 662keV is about 9%. The scintillation decay time of a crystal sample can be well fitted by a bi-exponential function,the fast component of the decay time is 285ns, accounting for 58%; the slow component is 1750ns, 42%.
Finally, it must be said here that: the above embodiments are only used for further detailed description of the technical solutions of the present invention, and should not be understood as limiting the scope of the present invention, and the insubstantial modifications and adaptations made by those skilled in the art according to the above descriptions of the present invention are within the scope of the present invention.
Claims (8)
1. The method for growing the lithium thallium-codoped sodium iodide scintillation crystal by the non-vacuum Bridgman-Stockbarge method is characterized in that the composition general formula of the lithium thallium-codoped sodium iodide scintillation crystal is (Na)1-a-b 6LiaTlb)(I1-a-b+Xa+b) Wherein X is a halogen element and is selected from at least one of F, Cl, Br and I, a is more than 0 and less than or equal to 0.2, and b is more than 0 and less than or equal to 0.01;
the method for growing the lithium thallium-codoped sodium iodide scintillation crystal by the non-vacuum Bridgman-Stockbarge method comprises the following steps:
(1) selecting NaI,6LiX and TlX are used as raw materials, mixed with a deoxidizer and then placed in a crucible and sealed;
(2) vertically placing the sealed crucible in the middle of a crystal growth furnace, then heating to 700-1000 ℃, and preserving heat for a certain time to completely melt the raw materials;
(3) setting the temperature gradient of a solid-liquid interface to be 10-50 ℃/cm and the descending speed of a crucible to be 0.1-10mm/h, and starting the growth of the lithium-thallium co-doped sodium iodide scintillation crystal;
(4) and after the growth is finished, cooling to room temperature.
2. The method of claim 1, wherein the feedstock has a purity of not less than 99.9 wt%.
3. The method of claim 1 or 2, wherein the deoxidizer is at least one of carbon black, amorphous carbon, nanocarbon, graphite powder, and polytetrafluoroethylene.
4. The method according to any one of claims 1 to 3, wherein the deoxidizer comprises NaI,6The ratio of the total mass of LiX and TlX does not exceed 5: 1000.
5. The method of any one of claims 1-4, wherein the bottom of the crucible has a capillary, conical bottom, or flat bottom to hold the seed crystal; the crucible is made of a platinum crucible; the crucible is cylindrical, square cylindrical or conical in shape.
6. The method according to any one of claims 1 to 5, wherein the temperature is reduced to room temperature at a cooling rate of 1 to 20 ℃/hr.
7. A lithium thallium-codoped sodium iodide scintillation crystal grown according to the method of any one of claims 1 to 6.
8. Use of the lithium thallium co-doped sodium iodide scintillation crystal of claim 7 for neutron detection, X-ray detection, or gamma ray detection.
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| CN115637148A (en) * | 2022-09-09 | 2023-01-24 | 中国科学院上海硅酸盐研究所 | Lithium-thallium co-doped sodium iodide scintillation crystal, and preparation method and application thereof |
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| CN115637148B (en) * | 2022-09-09 | 2023-09-12 | 中国科学院上海硅酸盐研究所 | Lithium thallium co-doped sodium-based halogen scintillation crystal, preparation method and application |
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