CN115637148A - Lithium-thallium co-doped sodium iodide scintillation crystal, and preparation method and application thereof - Google Patents
Lithium-thallium co-doped sodium iodide scintillation crystal, and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a lithium thallium codoped sodium iodide scintillation crystal, a preparation method and application thereof, wherein the composition general formula of the lithium thallium codoped sodium iodide scintillation crystal is as follows: (Na) 1‑a‑b‑c 6 Li a Tl b M c ) X; x is one or more of F, cl, br and I; m is Ca, sr, mg or Ba; wherein 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 c is more than 0 and less than or equal to 0.05. According to the lithium thallium codoped sodium iodide scintillation crystal, alkaline earth metal ions are introduced for doping besides lithium and thallium dopants are concentrated, and the gamma energy resolution and the neutron-gamma discrimination capability can be synchronously improved by introducing the alkaline earth metal ions. The scintillation crystal has the advantages of high light output, 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.
Description
Technical Field
The invention relates to the field of crystal growth technology and radiation detection, in particular to an alkaline earth metal doped lithium thallium codoped sodium iodide scintillation crystal, a preparation method and application.
Background
The neutron detection technology has important functions in the aspects of homeland security, petroleum exploration and the like. 3 The He gas neutron detector has the advantages of high detection efficiency, simple structure, stable performance and the like, and is widely used. Fast development of neutron detection technology 3 He gas demand has proliferated and is restricted by national exports such as usa and russia, 3 he gas deficiency, commonly used 3 He detectors may be replaced in the future. Therefore, neutron detection materials are being studied in large numbers, for example: lithium glass, 6 LiF and ZnS (Ag) powder, 6 LiI is Eu crystal, etc. The lithium glass is transparent, low in production cost and short in response time, but the neutron light yield is 4,000photons/neutron (photon/neutron). 6 Under neutron irradiation, the light yield of LiF and ZnS (Ag) powder is as high as 160,000photons/neutron, but the response time is long, the LiF and ZnS (Ag) powder cannot be prepared into single crystals, and the neutron detection efficiency is not 20%. 6 The LiI Eu crystal has high thermal neutron detection efficiency, but has the decay time as long as 1.4s and strong deliquescence.
On the other hand, almost all neutron radiation is accompanied by gamma radiation, and the development of neutron technology has put new demands on neutron detection technology. The neutron/gamma double detection material with high detection efficiency, strong discrimination capability and low cost becomes an important requirement of the market. In the recent past, it has been possible to select, 6 LiCaAlF 6 :Eu、Cs 2 6 LiYCl 6 a series of neutron/gamma dual detection scintillation crystals, ce, etc., are reported. 6 LiCaAlF 6 Eu crystal in 252 The neutron light yield at Cf is 29,000photons/neutron, but the gamma detection capability is weak. Cs 2 6 LiYCl 6 Ce crystal has excellent detection and discrimination ability of gamma ray, fast neutron and slow neutron, and has attracted extensive attention and realized commercialization. However, cs 2 6 LiYCl 6 Ce also faces problems of high raw material cost, inconsistent melting and the like. Tl is the scintillation crystal material for gamma ray detection which is most widely used at present, and in 2017, yang et al, st.Goban, france will 6 Tl scintillation crystal is introduced into NaI in a co-doping mode by Li, and the dual-mode detection of neutrons/gammas is realized.Tl, naI prepared by the Bridgman method, 6 the Li crystal performance is equivalent to that of a standard NaI Tl crystal and is 2 percent 6 Neutron-gamma discrimination capability of Li-doped crystal and Cs with same size 2 6 LiYCl 6 The Ce crystal is close to the Ce crystal, and the screening quality factor is about 4. The NaI is the Tl, and the NaI, 6 the Li crystal has low raw material cost and simple crystal structure, and has commercial prospect of large-scale application. However, the energy resolution of the crystal is poor, further optimization is needed for high-requirement neutron-gamma double detection, and the discrimination quality factor is further improved.
It is to be noted that the information disclosed in the above background section is only for enhancement of understanding of the background of the present invention and therefore may include information that does not constitute prior art known to a person of ordinary skill in the art.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a lithium thallium-codoped sodium iodide scintillation crystal, a preparation method and application thereof.
The invention provides a lithium thallium codoped sodium iodide scintillation crystal, which has a general composition formula as follows: (Na) 1-a-b-c 6 Li a Tl b M c )X；
X is one or more of F, cl, br and I;
m is Ca, sr, mg or Ba;
wherein 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 c is more than 0 and less than or equal to 0.1.
According to the first aspect of the invention, 0.001 < c.ltoreq.0.05.
According to a first aspect of the invention, the scintillation crystal is (Na) 1-a-b-c 6 Li a Tl b Sr c ) I, wherein c is more than 0 and less than or equal to 0.001.
According to a first aspect of the invention, the scintillation crystal has an energy resolution of a full energy peak at 662keV of 5.4% or less.
According to a first aspect of the invention, the scintillation crystal is (Na) 1-a-b-c 6 Li a Tl b Ca c ) X, wherein c is more than 0 and less than or equal to 0.002.
According to the first aspect of the present invention, the FOM value of the scintillator crystal is 5.85 or more.
According to a first aspect of the invention, the lithium thallium co-doped sodium iodide scintillation crystal is a single crystal.
According to a second aspect of the invention, a preparation method is provided for preparing the lithium thallium-codoped sodium iodide scintillation crystal, and comprises the following steps:
according to the general formula (Na) 1-a-b-c 6 Li a Tl b M c ) X respectively weighing sodium iodide, lithium halide, thallium halide and alkaline earth metal halide;
mixing the weighed raw materials, putting the mixture into a crucible and sealing the crucible;
vertically placing the sealed crucible in a growth furnace and heating the crucible to 700-900 ℃;
after the raw materials are melted, the crucible descends in the growth furnace at a descending speed of 2 mm/h-6 mm/h;
after the crystal growth is finished, the growth furnace is cooled to room temperature, and the crucible is taken out to obtain the lithium thallium codoped sodium iodide scintillation crystal.
According to a second aspect of the invention, the crucible bottom has a capillary for holding a seed crystal.
According to a third aspect of the invention, the lithium thallium codoped sodium iodide scintillation crystal is applied to neutron detection or gamma-neutron dual-mode detection.
According to the lithium-thallium co-doped sodium iodide scintillation crystal, alkaline earth metal ions are introduced for doping besides the concentrated lithium and thallium dopants, the gamma energy resolution and the neutron-gamma discrimination capability can be improved by introducing the alkaline earth metal ions, the scintillation crystal has the advantages of high light output, high energy resolution, excellent neutron/gamma ray discrimination capability and the like, and can be applied to the fields of petroleum exploratory wells, security inspection, industrial detection and the like.
Drawings
Other features, objects, and advantages of the invention will be apparent from the following detailed description of non-limiting embodiments, which proceeds with reference to the accompanying drawings and which is incorporated in and constitutes a part of this specification, illustrating embodiments consistent with the present application and together with the description serve to explain the principles of the application. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. Furthermore, the drawings are merely schematic illustrations of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and thus their repetitive description will be omitted. Some of the block diagrams shown in the figures are functional entities and do not necessarily correspond to physically or logically separate entities.
FIG. 1 is a flow chart of a method for preparing a lithium thallium co-doped sodium iodide scintillation crystal according to an embodiment of the invention;
FIG. 2 is a diagram of a lithium thallium-codoped sodium iodide scintillation crystal prepared by a preparation method according to a different embodiment of the invention;
FIG. 3 shows (Na) according to an embodiment of the present invention 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) I crystal and undoped NaI: 6 an X-ray excitation emission spectrum of the Li, tl crystal;
FIG. 4 shows (Na) according to an embodiment of the present invention 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) I crystal and undoped NaI: 6 gamma energy spectrogram of Li and Tl crystals;
fig. 5 and 6 are undoped NaI: 6 neutron spectrogram and gamma spectrogram of Li, tl crystal and FOM value scatter spectrogram of discrimination capability of the neutron spectrogram and the gamma spectrogram calculated from the neutron spectrogram and the gamma spectrogram;
FIGS. 7 and 8 show (Na) in accordance with an embodiment of the present invention 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) A neutron spectrogram and a gamma spectrogram of the I crystal and FOM value scatter-point spectrograms of the discrimination ability of the neutron spectrogram and the gamma spectrogram calculated from the neutron spectrogram and the gamma spectrogram;
FIG. 9 shows an embodiment of the present invention(Na 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) I crystal and undoped NaI: 6 scintillation decay time diagrams of Li, tl crystals;
FIG. 10 shows (Na) according to an embodiment of the present invention 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) X and undoped NaI: 6 an X-ray excitation emission spectrum of the Li, tl crystal;
FIG. 11 shows (Na) according to an embodiment of the present invention 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) And (3) mixing the X crystal with undoped NaI: 6 gamma energy spectrogram of Li and Tl crystals;
FIG. 12 and FIG. 13 show (Na) in accordance with an embodiment of the present invention 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) Neutron spectrogram and gamma spectrogram of the crystal and FOM value scatter spectrogram of the discrimination capability of the neutron spectrogram and the gamma spectrogram of the crystal calculated from the neutron spectrogram and the gamma spectrogram;
FIG. 14 shows (Na) according to an embodiment of the present invention 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) And (3) mixing the X crystal with undoped NaI: 6 scintillation decay time plot of Li, tl crystals.
Detailed Description
Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
Reference in the specification to expressions of "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the specification. Furthermore, the particular features, structures, materials, or characteristics shown may be combined in any suitable manner in any one or more embodiments or examples. Moreover, various embodiments or examples and features of different embodiments or examples presented in this specification may be combined and combined by those skilled in the art without contradiction.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or to implicitly indicate the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the feature. In the expressions of the present specification, "plurality" means two or more unless specifically defined otherwise.
Throughout the specification, when a device is referred to as being "connected" to another device, this includes not only the case of being "directly connected" but also the case of being "indirectly connected" with another element interposed therebetween. In addition, when a device "includes" a certain component, unless otherwise stated, the device does not exclude other components, but may include other components.
Terms representing relative spatial terms such as "lower", "upper", and the like may be used to more readily describe one element's relationship to another element as illustrated in the figures. Such terms are intended to include not only the meanings indicated in the drawings, but also other meanings or operations of the device in use. For example, if the device in the figures is turned over, elements described as "below" other elements would then be oriented "above" the other elements. Thus, the exemplary terms "under" and "beneath" all include above and below. The device may be rotated 90 or other angles and the terminology representing relative space is also to be interpreted accordingly.
Although the terms first, second, etc. may be used herein to describe various elements in some instances, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, the first interface and the second interface are represented. Also, as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used in this specification, specify the presence of stated features, steps, operations, elements, components, items, species, and/or groups, but do not preclude the presence, or addition of one or more other features, steps, operations, elements, components, items, species, and/or groups thereof. The terms "or" and/or "as used herein are to be construed as inclusive or meaning any one or any combination. Thus, "a, B or C" or "a, B and/or C" means "any of the following: a; b; c; a and B; a and C; b and C; A. b and C ". An exception to this definition will occur only when a combination of elements, functions, steps or operations are inherently mutually exclusive in some way.
Although not defined differently, including technical and scientific terms used herein, all terms have the same meaning as commonly understood by one of ordinary skill in the art to which this specification belongs. Terms defined in commonly used dictionaries are to be additionally interpreted as having meanings consistent with those of related art documents and the contents of the present prompts, and must not be excessively interpreted as having ideal or very formulaic meanings unless defined.
Aiming at the problems in the prior art, the invention provides a lithium thallium codoped sodium iodide scintillation crystal, a preparation method and application thereof, wherein the lithium thallium codoped sodium iodide scintillation crystal has a general formula: (Na) 1-a-b-c 6 Li a Tl b M c ) X; x is one or more of F, cl, br and I; m is Ca, sr, mg or Ba; wherein 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 c is more than 0 and less than or equal to 0.05. The lithium thallium codoped sodium iodide scintillation crystal not only concentrates lithium and thallium dopants, but also introduces alkaline earth metal ions for doping, can realize the improvement of gamma energy resolution and neutron-gamma discrimination capability by introducing the alkaline earth metal ions, has the advantages of high light output, 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.
Fig. 1 is a flow chart of a preparation method of a lithium thallium-codoped sodium iodide scintillation crystal according to an embodiment of the invention, wherein the preparation method comprises the following steps:
s10: according to the general formula (Na) 1-a-b-c 6 Li a Tl b M c ) X respectively weighing sodium iodide, lithium halide, thallium halide and alkaline earth metal halide; in the actual preparation, sodium iodide (NaI), lithium halide (NaI), and (II) are preferable 6 The purity of LiX), thallium halide (TlX) and halogenated alkaline earth metal is more than or equal to 99.9 percent. In the invention, the 6 Li and Tl ions are used as an activator of the lithium thallium co-doped sodium iodide scintillation crystal, 6 the Li and Tl ions being in the form of halides, e.g. 6 LiI and TlI are incorporated into the feedstock. Likewise, alkaline earth metal ions (Ca, sr, mg, ba) are used as dopants of the lithium thallium-codoped sodium iodide scintillation crystal, and MX, in the form of halides, is incorporated into the starting material.
S20: mixing the weighed raw materials, putting the mixture into a crucible and sealing the crucible; the crucible can be a quartz crucible, the shape of the crucible can be cylindrical, square column or conical, and preferably, the bottom of the crucible is provided with a capillary for fixing a seed crystal, which is beneficial to the growth of the lithium thallium codoped sodium iodide scintillation crystal.
S30: vertically placing the sealed crucible in a growth furnace and heating the crucible to 700-900 ℃;
s40: after the raw materials are melted, the crucible descends in the growth furnace at the descending speed of 2 mm/h-6 mm/h;
s50: after the crystal growth is finished, the growth furnace is cooled to room temperature, and the crucible is taken out to obtain the lithium-thallium co-doped sodium iodide scintillation crystal.
FIG. 2 is a physical diagram of a scintillation crystal of lithium thallium-codoped sodium iodide prepared by the preparation method of different embodiments of the invention, and the scintillation crystal prepared by the method has a general composition formula: (Na) 1-a-b-c 6 Li a Tl b M c )X；
X is one or more of F, cl, br and I;
m is Ca, sr, mg or Ba;
wherein 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 c is more than 0 and less than or equal to 0.1. Preferably, 0.001 < c.ltoreq.0.05. The lithium thallium codoped sodium iodide scintillation crystal is a single crystal.
The lithium thallium co-doped sodium iodide scintillation crystal and the preparation method thereof of the present invention are further illustrated by the following examples. It is to be understood that the examples are for further illustration of the invention and should not be construed as limiting the scope of the invention.
Example 1: growing NaI:0.2at% of TlI,1.0at% 6 LiI，0.05at％SrI 2 Crystal of the general formula (Na) 0.9875 6 Li 0.01 Tl 0.002 Sr 0.0005 )I
Growth of 6 Li doping concentration of 1.0%, tl doping concentration of 0.2%, srI 2 Alkaline earth metal doped NaI with a doping concentration of 0.06%: 6 li and Tl crystals. 81.0g of NaI is weighed, 6 mixing LiI0.73 g, tlI0.36g and SrI 2.94 g, placing into a flat-bottom quartz crucible, and sealing;
vertically placing the welded and sealed quartz crucible in the middle position of a crystal growth furnace by a descent method; heating the crystal growth furnace to keep the temperature at 750 ℃ for a certain time until the raw materials are completely melted and uniformly mixed; and 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, and then reducing the quartz crucible in the furnace at a reduction speed of 2mm/h, so that the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized.
And (3) reducing the furnace temperature at the rate of 15 ℃/h, and taking out the alkaline earth metal doped NaI: 6 li and Tl crystals. Likewise, the grown crystals were transparent and crack-free, without inclusions.
Note that the concentration of the alkaline earth doping in each example was obtained by the ICP-OES test.
Example 2: growing NaI:0.1at%, tlI,1.0at% 6 LiI，0.1at％SrI 2 Crystal of the composition formula (Na) 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 )I。
Growth of 6 Li doping concentration of 1.0%, tl doping concentration of 0.1%, srI 2 Alkaline earth metal doped NaI with a doping concentration of 0.1%: 6 li and Tl crystals. 81.93g of NaI is weighed, 6 LiI0.76 g，TlI 0.18g，SrI 2 0.19g of the mixture is fully mixed, and then the mixture is put into a flat-bottom quartz crucible and sealed;
vertically placing the welded and sealed quartz crucible in the middle position of a crystal growth furnace by a descent method; heating the crystal growth furnace to ensure that the temperature reaches 800 ℃ and is kept for a certain time until the raw materials are completely melted and uniformly mixed; and 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, and then reducing the quartz crucible in the furnace at a reduction speed of 4mm/h, so that the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized.
And (3) reducing the furnace temperature at the rate of 10 ℃/h, and taking out the alkaline earth metal doped NaI: 6 li and Tl crystals.
Grown (Na) 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) The crystal I is transparent and crack-free, and contains no inclusion. The crystal was cut, ground and polished before testing for its performance. FIG. 3 shows (Na) in example 1 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) I crystal and NaI doped crystal: 6 an X-ray excitation emission spectrum of the Li, tl crystal; as can be seen from FIG. 3, the structure of the alkaline earth doped crystal is similar to that of the doped crystal, (Na) 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) The X-ray excitation emission peak of the I crystal is at 415 nm. FIG. 4 shows (Na) 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) I crystal and undoped NaI: 6 gamma energy spectrogram of Li and Tl crystals; it can be seen that 137 (Na) in pulse height spectrum excited by Cs radioactive source 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) The energy resolution of the omnipotent peak of the I crystal at 662keV is about 5.4%; compared to undoped NaI: 6 the resolution (7.0%) of Li and Tl crystals is obviously improved.
Fig. 5 and 6 are undoped NaI: 6 neutron spectrum of Li, tl crystalThe graph and the gamma spectrogram and the FOM value scatter-point spectrogram of the discrimination capability of the graph and the gamma spectrogram calculated from the graph and the FOM value scatter-point spectrogram; FIG. 7 and FIG. 8 show (Na) respectively 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) The neutron spectrogram and the gamma spectrogram of the I crystal and FOM value scatter-point spectrograms of the discrimination ability of the neutron spectrogram and the gamma spectrogram calculated from the neutron spectrogram and the gamma spectrogram. Generally, the neutron-to-gamma ray resolving power of a crystal is characterized by the FOM value. It can be seen that (Na) 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) I crystal and undoped NaI: 6 FOM values corresponding to the Li and Tl crystals are 5.72 and 4.56 respectively, namely the discrimination capability of neutrons and gamma rays of the alkaline earth metal Sr-doped crystals is improved.
No change in other properties of the crystal, such as decay time, was observed after doping with alkaline earth metals. As shown in FIG. 9 is (Na) 0.988 6 Li 0.01 Tl 0.001 Sr 0.001 ) I crystal and undoped NaI: 6 the scintillation decay time of a crystal sample can be well fitted by a double-exponential function, and the fast component of the scintillation decay time is 210ns, which accounts for 8%; the slow component was 1250ns, accounting for 92%, compared to the undoped NaI: 6 the Li and Tl crystals have small performance difference, so that the doping of the alkaline earth metal forms a new defect in the lithium thallium codoped sodium iodide scintillation crystal, optimizes the energy nonlinear response of the crystal, well improves the energy resolution and the neutron/gamma discrimination capability of the scintillation crystal, but does not influence other performances.
Example 3: growth NaI 0.1at% 6 LiCl，0.1at％CaI 2 Crystal of the general formula (Na) 0.918 6 Li 0.08 Tl 0.001 Ca 0.001 )X
Growth of 6 Li doping concentration of 8%, tl doping concentration of 0.1%, caI 2 Alkaline earth metal-doped NaI with a doping concentration of 0.1%: 6 li and Tl crystals. 80.72g of NaI is weighed, 6 LiCl1.95 g，TlI 0.19g，CaI 2 0.17g of the mixture is fully mixed, and then the mixture is put into a flat-bottom quartz crucible and sealed;
vertically placing the welded and sealed quartz crucible in the middle of a crystal growth furnace by a descent method; heating the crystal growth furnace to ensure that the temperature reaches 800 ℃ and is kept for a certain time until the raw materials are completely melted and uniformly mixed; and 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, and then reducing the quartz crucible in the furnace at a reduction speed of 3mm/h, so that the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized.
And (3) reducing the furnace temperature at the rate of 8 ℃/h, and taking out the alkaline earth metal doped NaI when the thermocouple shows that the temperature is reduced to the room temperature: 6 li and Tl crystals. The grown crystals were transparent and crack-free and contained no inclusions.
Example 4: growing NaI:0.2at% of TlI,1.0at% 6 LiI，0.2at％CaI 2 Crystal of the composition formula (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 )I
Growth of 6 Li doping concentration of 1.0%, tl doping concentration of 0.2%, caI 2 Alkaline earth metal doped NaI with a doping concentration of 0.2%: 6 li and Tl crystals. 81.61g of NaI is weighed, 6 LiI0.73 g，TlI0.37g,LaI 3 0.32g of the mixture, and after fully mixing, putting the mixture into a flat-bottom quartz crucible and sealing the crucible;
vertically placing the welded and sealed quartz crucible in the middle of a crystal growth furnace by a descent method; heating the crystal growth furnace to keep the temperature at 750 ℃ for a certain time until the raw materials are completely melted and uniformly mixed; and 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, and then reducing the quartz crucible in the furnace at a reduction speed of 2mm/h, so that the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized.
And (3) reducing the furnace temperature at the rate of 15 ℃/h, and taking out the alkaline earth metal doped NaI: 6 li and Tl crystals.
Grown (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) The X crystal is transparent and crack-free, and contains no inclusion. FIG. 10 shows (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) X and undoped NaI: 6 an X-ray excitation emission spectrum of the Li, tl crystal; (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) The X-ray excitation emission peak of the X-crystal is located at 420 nm. The experimental result proves that different dopants and different doping concentrations have no influence on the X-ray luminescence spectrum of the crystal. FIG. 11 shows (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) X crystal and undoped NaI: 6 gamma energy spectrogram of Li and Tl crystals; by 137 The pulse height spectrum excited by the Cs radioactive source is visible, (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) The energy resolution of the full energy peak of the X crystal at 662keV is about 6.1% higher than that of undoped NaI: 6 the Li and Tl crystals have 7.0% of resolution, and experimental results prove that the energy resolution of the crystals is effectively optimized by doping the alkaline earth metal Ca.
FIG. 12 and FIG. 13 show (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) FOM scatter plot of the crystals. As shown in FIG. 3, (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) The FOM value of the discrimination capability of the X crystal is 5.85, which is higher than that of the undoped NaI: 6 of Li, tl crystals (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) X (4.56), it can be seen that the doping of the alkaline earth metal Ca effectively enhances the neutron-gamma ray resolving power of the crystal.
Likewise, the other properties of the alkaline earth Ca-doped crystals did not show significant changes, as shown in fig. 14 (Na) 0.986 6 Li 0.01 Tl 0.002 Ca 0.002 ) X crystal and undoped NaI: 6 scintillation decay time diagrams of Li, tl crystals; the doping of the alkaline earth metal Ca shortens the scintillation decay time of the crystal, but has little effect. 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 215ns, accounting for 10%; the slow component was 1240ns, which accounted for 90%.
Example 5: growing NaI:0.2at% of TlCl,1.0at% 6 LiI，0.4at％BaI 2 The crystal composition has the general formula (Na) 0.984 6 Li 0.01 Tl 0.002 Ba 0.004 )X
Growth of 6 Li doping concentration of 1.0%, tl doping concentration of 0.2%, baI 2 Alkaline earth metal doped NaI with a doping concentration of 0.04%: 6 li and Tl crystals. 81.18g of NaI is weighed, 6 LiI 0.73g，TlCl0.26 g,SmI 2 0.86gg, and then putting the mixture into a cylindrical quartz crucible and sealing the quartz crucible;
vertically placing the welded and sealed quartz crucible in the middle of a crystal growth furnace by a descent method; 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; and 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, and then reducing the crucible in the furnace at a reducing speed of 5mm/h, so that the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized.
And (3) reducing the furnace temperature at the rate of 20 ℃/h, and taking out the alkaline earth metal doped NaI: 6 li and Tl crystals. Similarly, the crystal doped with alkaline earth metal Ba is transparent and crack-free, and contains no inclusion.
Example 6: 0.2at% of growing NaI, tlI,2at% 6 LiF,0.1at％MgI 2 A crystal having a composition of the formula (Na) 0.977 6 Li 0.02 Tl 0.002 Mg 0.001 )X
Growth of the seed 6 Li doping concentration of 2.0%, tl doping concentration of 0.2%, mgI 2 Alkaline earth metal-doped NaI with a doping concentration of 0.1%: 6 li and Tl crystals. 82.22g of NaI is weighed, 6 LiF0.82 g，TlI 0.37g，MgI 2 0.16g of the mixture is fully mixed, and then the mixture is put into a quartz crucible with a conical bottom and sealed;
vertically placing the welded and sealed quartz crucible in the middle of a crystal growth furnace by a descent method; 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; and 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, and then reducing the quartz crucible in the furnace at a reduction speed of 1mm/h, so that the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized.
And (3) reducing the furnace temperature at the rate of 15 ℃/h, and taking out the alkaline earth metal doped NaI: 6 li and Tl crystals.
Example 7: growth NaI 0.1at% 6 LiCl，0.1at％MgI 2 Crystal of the general formula (Na) 0.918 6 Li 0.08 Tl 0.001 Mg 0.001 )X
Growth of 6 Li doping concentration of 8%, tl doping concentration of 0.1%, mgI 2 Alkaline earth metal doped NaI with a doping concentration of 0.1%: 6 li and Tl crystals. 80.73g of NaI is weighed, 6 LiCl1.95 g，TlI 0.19g,MgI 2 0.16g, after fully mixing, putting the mixture into a quartz crucible with a conical bottom and sealing the quartz crucible;
vertically placing the welded and sealed quartz crucible in the middle position of a crystal growth furnace by a descent method; heating the crystal growth furnace to keep the temperature at 800 ℃ for a certain time till the raw materials are completely melted and mixed uniformly; and 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, and then reducing the quartz crucible in the furnace at a reduction speed of 3mm/h, so that the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized.
And (3) reducing the furnace temperature at the rate of 8 ℃/h, and taking out the alkaline earth metal doped NaI when the thermocouple shows that the temperature is reduced to the room temperature: 6 li and Tl crystals.
Example 8: 0.2at% of grown NaI, tlBr,2at% 6 LiI，0.01at％MgI 2 A crystal of the formula (Na) 0.9779 6 Li 0.02 Tl 0.002 Mg 0.0001 )X
Growth of the seed 6 Li doping concentration of 0.1%, tl doping concentration of 0.2%, mgI 2 Alkaline earth metal doped NaI with a doping concentration of 0.01%: 6 li and Tl crystals. Weighing 82.09 g of NaI in a glove box, 6 LiI0.47 g，TlI 0.32g，ScI 3 0.16g of the mixture is fully mixed and put into a quartz crucible with a conical bottom；
Vertically placing the welded and sealed quartz crucible in the middle position of a crystal growth furnace by a descent method; heating the crystal growth furnace to keep the temperature at 850 ℃ for a certain time till the raw materials are completely melted and mixed uniformly; and 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, and then reducing the quartz crucible in the furnace at a reduction speed of 5mm/h, so that the crystal starts to nucleate and grow from the bottom of the crucible until the melt is completely solidified and crystallized.
And (3) reducing the furnace temperature at the rate of 5 ℃/h, and taking out the alkaline earth metal doped NaI when the thermocouple shows that the temperature is reduced to the room temperature: 6 li and Tl crystals. Examples 6 to 8 are lithium thallium-codoped sodium iodide scintillation crystals doped with different contents of alkaline earth Mg, and likewise, the crystals doped with alkaline earth Mg are transparent and crack-free and contain no inclusions. Therefore, the method provided by the invention can obtain the lithium thallium-codoped sodium iodide scintillation crystals doped with different alkaline earth metals, and the lithium thallium-codoped sodium iodide scintillation crystals doped with the alkaline earth metals have better resolution capability of neutrons and gamma rays.
The foregoing is a further detailed description of the invention in connection with specific preferred embodiments and it is not intended to limit the invention to the specific embodiments described. It will be evident to those skilled in the art that the application is not limited to the details of the foregoing illustrative embodiments, and that the present application may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Claims (10)
1. A lithium thallium codoped sodium iodide scintillation crystal is characterized in that the scintillation crystal has a general composition formula: (Na) 1-a-b- c 6 Li a Tl b M c )X；
X is one or more of F, cl, br and I;
m is Ca, sr, mg or Ba;
wherein 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 c is more than 0 and less than or equal to 0.1.
2. The lithium thallium co-doped sodium iodide scintillation crystal of claim 1, wherein 0.001 < c.ltoreq.0.05.
3. The lithium thallium-codoped sodium iodide scintillation crystal of claim 1, wherein the scintillation crystal is (Na) 1-a-b-c 6 Li a Tl b Sr c ) I, wherein c is more than 0 and less than or equal to 0.001.
4. The lithium thallium co-doped sodium iodide scintillation crystal of claim 3, wherein an energy resolution of a full energy peak of the scintillation crystal at 662keV is less than or equal to 5.4%.
5. The lithium thallium codoped sodium iodide scintillation crystal of claim 1, wherein the scintillation crystal is (Na) 1-a-b-c 6 Li a Tl b Ca c ) X, wherein c is more than 0 and less than or equal to 0.002.
6. The lithium thallium-codoped sodium iodide scintillation crystal of claim 1, having a FOM value of greater than or equal to 5.85.
7. The lithium thallium-codoped sodium iodide scintillation crystal of claim 1, wherein the lithium thallium-codoped sodium iodide scintillation crystal is a single crystal.
8. A preparation method for preparing the lithium thallium-codoped sodium iodide scintillation crystal of claim 1, comprising the steps of:
according to the general formula (Na) 1-a-b-c 6 Li a Tl b M c ) X respectively weighing sodium iodide, lithium halide, thallium halide and alkaline earth metal halide;
mixing the weighed raw materials, putting the mixture into a crucible and sealing;
vertically placing the sealed crucible in a growth furnace and heating the crucible to 700-900 ℃;
after the raw materials are melted, the crucible descends in the growth furnace at a descending speed of 2 mm/h-6 mm/h;
after the crystal growth is finished, the growth furnace is cooled to room temperature, and the crucible is taken out to obtain the lithium-thallium co-doped sodium iodide scintillation crystal.
9. The method of claim 8, wherein the bottom of the crucible has a capillary for holding the seed crystal.
10. Use of a lithium thallium codoped sodium iodide scintillation crystal according to any one of claims 1 to 7 for neutron detection or dual-mode gamma-neutron detection.
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