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EP-3985148-B1 - GROWTH METHOD FOR SCINTILLATION CRYSTAL WITH SHORTENED DECAY TIME

EP3985148B1EP 3985148 B1EP3985148 B1EP 3985148B1EP-3985148-B1

Inventors

  • WANG, YU
  • GUAN, WEIMING
  • LI, MIN

Dates

Publication Date
20260513
Application Date
20190821

Claims (8)

  1. A method for growing a crystal, comprising: weighting reactants based on a molar ratio of the reactants according to a reaction equation (1) or a reaction equation (2) after a first preprocessing operation is performed on the reactants: 1 − x − y Lu 2 O 3 + SiO 2 + 2 xCeO 2 + yCe 2 O 3 → Lu 2 1 − x − y Ce 2 x + y SiO 5 + x / 2 O 2 ↑ 1 − x − y − z Lu 2 O 3 + zY 2 O 2 + SiO 2 + 2 xCeO 2 + yCe 2 O 3 → Lu 2 1 − x − y − z Y 2 z Ce 2 x + y SiO 5 + x / 2 O 2 ↑ where x=0.15%, y=0.3%, a weight of SiO 2 exceeds 0.2% of its theoretical weight determined according to the reaction equation (1), x=0.16%, y=0.3%, z=20%, a weight of SiO 2 exceeds 2% of its theoretical weight determined according to the reaction equation (2), and the first preprocessing operation includes a roasting operation under 800°C ~ 1400°C; placing the reactants on which a second preprocessing operation has been performed into a crystal growth device after an assembly preprocessing operation is performed on at least one component of the crystal growth device, wherein the second preprocessing operation includes at least one of an ingredient mixing operation or a pressing operation at room temperature, the at least one component of the crystal growth device includes a crucible, and the assembly processing operation includes at least one of a coating operation, an acid soaking and cleaning operation, or an impurity cleaning operation; introducing a flowing gas into the crystal growth device after sealing the crystal growth device; and activating the crystal growth device to grow the crystal based on Czochralski technique.
  2. The method of claim 1, wherein the flowing gas includes a mixed gas of oxygen and at least one of nitrogen or inert gas.
  3. The method of claim 2, wherein a volume ratio of oxygen is 0.001% ~ 10% in an initial stage of the crystal growth.
  4. The method of claim 2 or claim 3, wherein the method further includes: during a cooling process of the crystal growth, increasing a volume ratio of oxygen in the flowing gas to 1% ~ 30% when a temperature drops to 1400°C ~ 800°C.
  5. The method of any of claims 2-4, wherein the method further includes: during a cooling process of the crystal growth, decreasing the volume ratio of oxygen in the flowing gas to 0.001% ~ 20% when the temperature drops below 800°C.
  6. The method of any of claims 1-5, wherein a flow rate of the flowing gas is 0.01 L/min ~ 50 L/min.
  7. The method of any of claims 1-6, wherein a distance between a seed crystal and an upper surface of the reactants is 5 ~ 10 mm during melting the reactants during the crystal growth.
  8. The method of any of claims 1-7, wherein the method comprises: sinking a seed crystal to 0.1mm ~ 50mm below a surface of a melt of the reactants by controlling a pulling rod during temperature adjustment.

Description

TECHNICAL FIELD The present disclosure generally relates to the field of crystal growth, and in particular, to methods and devices for growing scintillation crystals with short decay time. BACKGROUND Scintillation crystal is used as an energy conversion medium that can convert ionizing radiation energy (e.g., a gamma-ray, an X-ray) into light energy (e.g., visible light). The scintillation crystal (e.g., LSO, LYSO, BGO, BSO, GSO) is widely used in nuclear medicine field such as X-ray tomography (CT), positron emission tomography (PET), nuclear detection field such as industrial tomography (e.g., industrial CT), oil well exploration field, nuclear physics field, high-energy physics field, an environmental detection field, safety monitoring field, weapon fire control and guidance field, etc. In order to decrease a decay time of the scintillation crystal, some divalent or trivalent non-rare earth cations (e.g., Mg, Ca, Zn, Yb, Dy, Pb, Tb, Li, Na) may be co-doped into the crystal during the crystal growth. In this case, a lattice constant and a segregation coefficient of Ce in the crystal may be changed by introducing a lattice distortion, thereby affecting an energy band structure of luminescent ions and improving the efficiency and speed of capturing high-energy photons and converting them into visible light by the luminescent ions. However, the co-doped divalent or trivalent non-rare earth cations introduced into the crystal may affect the light yield of the crystal. In addition, the co-doped bivalent or trivalent non-rare earth cations may not be uniformly distributed in the crystal, which may cause a non-uniform distribution of light yield and decay time of the crystal and increase the cost of crystal production and screening. US 2014/291580 A1 discloses a scintillation material having emission maximum in the range of about 400-450 nm and based on cerium doped a rare-earth oxyorthosilicate including LFS, LSO, LYSO, LGSO, GSO crystals having defects in comparison with ideal crystal structure, and said defects change the optical transmission and absorption spectra in the range about of 200-340 nm. ZAGUMENNYI A I ET AL: "Czochralski growth and characterization of (Lu1-xGdx)2SiO5 single crystals for scintillators", JOURNAL OF CRYSTAL GROWTH, ELSEVIER, AMSTERDAM, NL, vol. 174, no. 1-4, 2 April 1997 (1997-04-02), pages 331-336, XP004113852, ISSN: 0022-0248, DOI: 10.1016/S0022-0248(96)01171-2 discloses the Czochralski growth of high quality single crystals of cerium doped mixed oxyorthosilicates. SUMMARY The invention is set out in the appended set of claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart illustrating an exemplary method for growing a crystal according to some embodiments of the present disclosure;FIG. 2 is a schematic diagram illustrating an exemplary temperature field device according to some embodiments of the present disclosure;FIG. 3 is a schematic diagram illustrating a top view of a cross-section of an exemplary temperature field device according to some embodiments of the present disclosure;FIG. 4 is a schematic diagram illustrating a top view of an exemplary first cover plate according to some embodiments of the present disclosure;FIG. 5 is a schematic diagram illustrating an exemplary observation unit according to some embodiments of the present disclosure; andFIG. 6 is a schematic diagram illustrating an exemplary image of a grown crystal according to some embodiments of the present disclosure. DETAILED DESCRIPTION Some embodiments of the present disclosure disclose a crystal. In some embodiments, a formula of the crystal may be X2x:M2m:Lu21−x−m−zY2zSiQ5−n2Nn, wherein X may consist of at least one of Ce, Cl, F, Br, N, P, or S, M may consist of at least one of Ca, Mg, Sr, Mn, Ba, Al, Fe, Re, La, Ce, Rr, Nd, Pm, Sm, Eu, Gd, Td, Dy, HO, Er, Yb, Tm, Lu, Sc, or Y, Z may consist of at least one of Sc, Y, Gd, or Lu, Q may consist of at least one of O, Cl, F, Br, or S, and N may consist of at least one of Cl, F, Br, or S. In some embodiments, when X and/or M consist of two or more elements, the crystal may be regarded as a doped crystal. Specifically, when X consists of Ce, the crystal may be regarded as Cerium-doped Lutetium oxyorthosilicate crystal or Cerium-doped Lutetium(-yttrium) oxyorthosilicate crystal, which may be used as a practical scintillation crystal. In some embodiments, a reactant consisting of Ce may include CeO2, Ce2O3, Ce(CO3)2, CeCl3, cerium fluoride, cerium(III) sulfate, or cerium(III) bromide, or the like, or any combination thereof. In some embodiments, X may consist of Lu, M may consist of Ce, and Q may consist of O. In this case, the formula of the crystal may be Lu21−mCe2mSiO5−n2Nn or Lu21−z−mY2zCe2mSiO5−n2Nn. In some embodiments, a value of x may be 0.000001 ~ 0.06. The value of x may be 0.00001 and 0.06. The value of x may be 0.0001 ~ 0.06. The value of x may be 0.001 ~ 0.06. The value of x may be 0.01 ~ 0.06. The value of x may be 0.02 ~ 0.05. The value of