Rare-earth halide scintillating material and application thereof

Abstract

The present invention provides a rare-earth halide scintillating material and application thereof. The rare-earth halide scintillating material has a chemical formula of RE.sub.aCe.sub.bX.sub.3, wherein RE is a rare-earth element La, Gd, Lu or Y, X is one or two of halogens Cl, Br and I, 0≤a≤1.1, 0.01≤b≤1.1, and 1.0001≤a+b≤1.2. By taking a +2 valent rare-earth halide having the same composition as a dopant to replace a heterogeneous alkaline earth metal halide in the prior art for doping, the rare-earth halide scintillating material is relatively short of a halogen ion. The apparent valence state of a rare-earth ion is between +2 and +3. The rare-earth halide scintillating material belongs to non-stoichiometric compounds, but still retains a crystal structure of an original stoichiometric compound, and has more excellent energy resolution and energy response linearity than the stoichiometric compound.

Claims

1. A rare-earth halide scintillating material having a chemical formula of RE.sub.aCe.sub.bX.sub.3, wherein RE is a rare-earth element La, Gd, Lu or Y, X is one or two of halogens Cl, Br and I, 0.9≤a≤1, 0.02≤b≤0.2, and 1.0001≤a+b≤1.1.

2. The rare-earth halide scintillating material according to claim 1, wherein RE is La, and X is Br.

3. The rare-earth halide scintillating material according to claim 1, wherein RE is La, and X is Cl.

4. The rare-earth halide scintillating material according to claim 1, wherein RE is Gd, Lu ear Y, and X is I.

5. The rare-earth halide scintillating material according to claim 1, wherein the scintillating material is a single crystal.

6. The rare-earth halide scintillating material according to claim 5, wherein the rare-earth halide scintillating material is obtained by the Bridgeman-Stockbarge method.

7. A scintillation detector, comprising a scintillating material, wherein the scintillating material is the rare-earth halide scintillating material of claim 1.

8. A positron emission tomography, a gamma spectrometer, an oil logging instrument or a lithology scanning imager, comprising the scintillation detector of claim 7.

9. The scintillation detector according to claim 7, wherein RE is La, and X is Br.

10. The scintillation detector according to claim 7, wherein RE is La, and X is Cl.

11. The scintillation detector according to claim 7, wherein RE is Gd, Lu or Y, and X is I.

12. The rare-earth halide scintillating material according to claim 1, wherein the scintillating material is a single crystal.

13. The rare-earth halide scintillating material according to claim 12, wherein the rare-earth halide scintillating material is obtained by the Bridgeman-Stockbarge.

Description

DETAILED DESCRIPTION

(1) It should be noted that in case of no conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be illustrated in detail below with reference to the embodiments.

(2) To achieve the above objective, according to one aspect of the present invention, there is provided a rare-earth halide scintillating material having the chemical formula of RE.sub.aCe.sub.bX.sub.3, wherein RE is a rare-earth element La, Gd, Lu or Y, X is one or two of halogens Cl, Br and I, 0≤a≤1.1, 0.01≤b≤1.1, and 1.0001≤a+b≤0.2.

(3) According to the rare-earth halide scintillating material provided by the present invention, by taking a +2 valent rare-earth halide (for example, LaBr.sub.2) having the same composition as a dopant to replace a heterogeneous alkaline earth metal halide (for example, SrBr.sub.2) in the prior art for doping, not only can the same doping effect be achieved but also the problems of uneven segregation, etc. caused by introduction of a heterogeneous alkaline earth metal ion can be effectively avoided. The rare-earth halide scintillating material is relatively short of a halogen ion. The apparent valence state of a rare-earth ion is between +2 and +3. The rare-earth halide scintillating material belongs to non-stoichiometric compounds, but still retains a crystal structure of an original stoichiometric compound, and has more excellent energy resolution and energy response linearity than the stoichiometric compound.

(4) Preferably, RE and X are combined in any of the following ways: La and Br, La and Cl, Gd and I, Lu and I, and Y and I. Rare-earth halides adopting the above combinations have more excellent performance than rare-earth halides adopting other combinations. Scintillating materials formed by the same rare-earth element and different halide ions have different scintillation properties. For example, in Ce.sup.3+-activated lanthanum halide, LaBr.sub.3 has a very high light yield, LaCl.sub.3 also has a relatively higher light yield which is obviously lower than that of LaBr.sub.3, and LaI.sub.3 almost does not emit light at room temperature. The light yields of Ce.sup.3+-activated Gd, Lu and Y iodides are obviously higher than those of corresponding bromides and chlorides. Therefore, the preferred combinations of La and Br, La and Cl, Gd and I, Lu and I, and Y and I have the best comprehensive scintillation properties and also have the characteristics of high light yield, high energy resolution and short decay time.

(5) It should be noted that the proportion of a rare-earth ion to a halide ion in a non-stoichiometric compound is only limited to a relatively narrower range. In the present invention, the value range of the rare-earth ion is 1.0001≤a+b≤1.2, preferably, 1.0001≤a+b≤1.1. An over high proportion of the rare-earth ion will cause a series of problems including decrease of the crystal light yield, increase of the crystal growth defect, etc., which may be related to the increase of halide ion vacancies, the change of a crystal energy band structure and phase segregation. Further preferably, 0.9≤a≤1, 0.02≤b≤0.2, and 1.0001≤a+b≤1.1 or a=0, 1.0001≤b≤1.1. From the perspective of the product comprehensive performance, the proportion of the rare-earth ion in the rare-earth halide scintillating material is within the above preferred range.

(6) The rare-earth halide scintillating material is in the form of powder, ceramics or single crystals, and is preferably applied in the form of single crystals obtained by the Bridgeman-Stockbarge method.

(7) The present invention further relates to a scintillation detector including the rare-earth halide scintillating material, as well as a PET, a gamma spectrometer, an oil logging instrument or a lithology scanning imager including the scintillation detector. Relevant devices adopting the rare-earth halide scintillating material provided by the present invention are relatively higher in consistency of crystal scintillation properties.

(8) It should be noted that the rare-earth halide scintillating material provided by the present invention is a non-stoichiometric compound. That is, the apparent valence state of the rare-earth ion is not generally +3, but between +2 and +3. In the present invention, the consistency of the scintillation property of the rare-earth halide scintillating material is improved by adjusting the proportion of the rare-earth ion to the halide ion.

(9) The present invention initially studies the doping modification solution of LaBr.sub.3:Ce to solve the problems of too complicated compositions, difficult crystal growth and poor consistency of the scintillation property, caused by co-doping of the halide ion and an alkaline earth metal ion in a conventional doping solution. At present, the function mechanism that the alkaline earth metal ion is doped to improve the scintillation property of a LaBr.sub.3:Ce crystal is not yet very clear. It is generally believed that this function mechanism is relevant to a valence transition of some Ce.sup.3+ to Ce.sup.4+ in the crystal arising from the doping of a +2 valent alkaline ion. The inventor proposes that by taking a +2 valent rare-earth halide (for example. LaBr.sub.2) having the same composition as a dopant to replace a heterogeneous alkaline earth metal halide (for example, SrBr.sub.2) in the prior art for doping, not only can the same doping effect be theoretically achieved but also the problems of uneven segregation, etc. caused by introduction of a foreign ion can be effectively avoided. A rare-earth halide obtained in this way is relatively short of a halogen ion. The apparent valence state of a rare-earth ion is between +2 and +3. Thus, the rare-earth halide is a non-stoichiometric compound.

(10) Since the +2 valent rare-earth halide with the unstable valence state, for example, LaBr.sub.2, is generally difficult to obtain, in practice, another equivalent solution is adopted in the present invention for replacement. That is, a small amount of a rare-earth metal (for example, La) is added into the stable stoichiometric rare-earth halide (for example, LaBr.sub.3) and high-temperature melting is performed to obtain a target non-stoichiometric rare-earth halide having a uniform composition. The stoichiometric rare-earth halide and the rare-earth metal, of which the production methods are mature, are readily available on the market, the alternative solution is relatively lower in cost and is operable.

(11) According to one embodiment of the present invention, a non-stoichiometric lanthanum bromide crystal obtained in the present invention has an extremely excellent scintillation property, and its comprehensive performance is obviously superior to that of a conventional undoped lanthanum bromide crystal, and is superior to those of alkaline-earth-doped and alkaline earth and halide ion co-doped lanthanum bromide crystals, wherein the superiority is embodied in that the light yield of the crystal is increased to some extent, the decay time is shortened significantly and the energy resolution is improved to some extent. This may be relevant to a halide ion vacancy in the non-stoichiometric crystal. On the one hand, the defect level contributed by the halogen ion vacancy may reduce the band gap of the crystal, resulting in an increase in the light yield of the crystal. On the other hand, the halogen ion vacancy makes it easier to form Ce.sup.4+ in the crystal, thereby shortening the luminescence decay time. Moreover, compared with the doped lanthanum bromide crystal, the non-stoichiometric lanthanum bromide crystal is free from impurity segregation and is greatly improved in homogeneity. Meanwhile, the growth process of the non-stoichiometric lanthanum bromide crystal is free from such crystal defects as an inclusion and a crack due to impurity enrichment. Thus, the yield of the crystal is improved significantly. The production cost of the crystal is effectively lowered.

(12) It is found that when the technical solution is applied to other rare-earth halide scintillating materials, a favorable implementation effect can also be achieved.

(13) Beneficial effects of the present invention will be further described below with reference to specific embodiments.

(14) It should be noted that in the following Embodiments and Comparative Examples, the light yield and the energy resolution are obtained through multichannel spectrum detection based on a .sup.137Cs radioactive source. The decay time is detected by the X-ray fluorescence spectrometry.

Comparative Example 1

(15) 119.89 g of anhydrous LaBr.sub.3 (the purity is 99.99%, that is, the mass content of LaBr.sub.3 is 99.99%, and the following purity means the same) and 6.33 g of anhydrous CeBr.sub.3 (with the purity of 99.99%) are accurately weighed in a glove box under atmosphere protection, and mixed uniformly. The obtained mixture is charged into a quartz crucible with the diameter of 25 mm. The quartz crucible is taken out of the glove box and quickly connected to a vacuum system to be vacuumized. When the vacuum degree is 1*10.sup.−3 Pa, an opening of the quartz crucible is sealed by fusing. The quartz crucible is placed in a Bridgeman crystal oven for single-crystal growth. The temperature of a high-temperature area is 850° C. The temperature of a low-temperature area is 700° C. A gradient area has a temperature gradient about 10° C./cm. The crucible descends at a rate of 0.5 mm/h to 2 mm/h. The total growth time is about 15 days. The obtained crystal is transparent and colorless and is about 5 cm in length. The crystal is cut and processed in the glove box into a cylindrical sample of Φ25 mm*25 mm. After that, tests of the light yield, the decay time and the energy resolution are performed.

Comparative Example 2

(16) 119.89 g of anhydrous LaBr.sub.3 (with the purity of 99.99%), 6.33 g of anhydrous CeBr.sub.3 (with the purity of 99.99%) and 0.041 g of anhydrous SrBr.sub.2 (with the purity of 99.99%) are accurately weighed in a glove box under Ar atmosphere protection, and mixed uniformly. The obtained mixture is charged into a quartz crucible with the diameter of 25 mm. Other operations are the same as those in Comparative Example 1.

Comparative Example 3

(17) 119.89 g of anhydrous LaBr.sub.3 (with the purity of 99.99%), 6.33 g of anhydrous CeBr.sub.3 (with the purity of 99.99%) and 0.048 g of anhydrous SrCl.sub.2 (with the purity of 99.99%) are accurately weighed in a glove box under Ar atmosphere protection, and mixed uniformly. The obtained mixture is charged into a quartz crucible with the diameter of 25 mm. Other operations are the same as those in Comparative Example 1.

Embodiment 1

(18) 119.89 g of anhydrous LaBr.sub.3 (with the purity of 99.99%), 6.33 g of anhydrous CeBr.sub.3 (with the purity of 99.99%) and 1.852 g of metal La (with the purity of 99.99%) are accurately weighed in a glove box under Ar atmosphere protection, and mixed uniformly. The obtained mixture is charged into a quartz crucible with the diameter of 25 mm. Other operations are the same as those in Comparative Example 1.

(19) Other operations of Embodiments 2 to 13 are the same as those of Embodiment 1, except for raw material ratios.

(20) See Table 1 for detailed comparisons of all the Embodiments and Comparative Examples.

(21) TABLE-US-00001 TABLE 1 Decay Energy Light Yield Time Resolution Chemical Formula (ph/MeV) (ns) (@662 keV) Comparative La.sub.0.95Ce.sub.0.05Br.sub.3 56,000 32 3.2% Example 1 Comparative La.sub.0.95Sr.sub.0.0005Ce.sub.0.05Br.sub.3.001 62,000 30 2.7% Example 2 Comparative La.sub.0.95Sr.sub.0.0009Ce.sub.0.05Br.sub.3Cl.sub.0.0018 65,000 25 2.4% Example 3 Embodiment 1 La.sub.0.97Ce.sub.0.05Br.sub.3 75,000 24 2.0% Embodiment 2 La.sub.0.95Ce.sub.0.1Br.sub.2.7Cl.sub.0.3 74,000 20 2.1% Embodiment 3 La.sub.0.9901Ce.sub.0.01Br.sub.3 68,000 20 2.2% Embodiment 4 LaCe.sub.0.02Br.sub.2.1I.sub.0.9 69,000 23 2.4% Embodiment 5 La.sub.0.9Ce.sub.0.2Cl.sub.3 51,000 21 3.3% Embodiment 6 Ce.sub.1.0001Br.sub.3 60,000 17 2.9% Embodiment 7 Ce.sub.1.005Br.sub.3 65,000 16 2.8% Embodiment 8 Ce.sub.1.1Br.sub.3 61,000 15 2.9% Embodiment 9 Ce.sub.1.05Br.sub.2.8Cl.sub.0.2 63,000 18 2.9% Embodiment 10 Gd.sub.1.02Ce.sub.0.02Br.sub.3 49,000 31 3.8% Embodiment 11 Gd.sub.1.1Ce.sub.0.1I.sub.3 84,000 35 3.2% Embodiment 12 Lu.sub.1.01Ce.sub.0.08I.sub.2.5Br.sub.0.5 94,000 34 3.1% Embodiment 13 Y.sub.0.92Ce.sub.0.12I.sub.3 76,000 30 3.3%

(22) As can be seen from the above descriptions, compared with undoped or alkaline-earth-doped crystals and alkaline earth and halide ion co-doped crystals having the same composition, the non-stoichiometric crystal provided by the present invention has extremely excellent scintillation property and shows a relatively more remarkable performance advantage. While the high material performance is guaranteed, the material composition is remarkably simplified, which contributes to obtaining of the high-quality scintillating crystal with favorable consistency. The above embodiments achieve the following technical effect: by adjusting the proportion of the rare-earth ion to the halide ion, a conventional stoichiometric rare-earth halide scintillating material is converted into the non-stoichiometric compound, such that the scintillation property and the growth consistency of the rare-earth halide scintillating material are improved.

(23) The above descriptions are merely preferred embodiments of the present invention, and are not intended to limit the present invention. Various changes and modifications may be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included within the scope of protection of the present invention.

(24) The foregoing description of the exemplary embodiments of the present invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching.

(25) The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to activate others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.