JP5521273B2 - Single crystal for scintillator, heat treatment method for producing single crystal for scintillator, and method for producing single crystal for scintillator - Google Patents

Description

  The present invention relates to radiation medicine such as gamma rays in the fields of radiology such as positron CT (PET) for medical diagnosis, cosmic ray observation and underground resource search, physics, physiology, chemistry, mineralogy, and oil exploration. The present invention relates to a single crystal for a single crystal scintillation detector (scintillator), a heat treatment method for producing a single crystal for a scintillator, and a method for producing a single crystal for a scintillator, and more specifically, a cerium-activated orthosilicate compound. The present invention relates to a scintillator single crystal, a heat treatment method for manufacturing a scintillator single crystal, and a method for manufacturing a scintillator single crystal.

  A scintillator made of cerium activated gadolinium orthosilicate compound has been put to practical use as a radiation detector such as positron CT because it has a short fluorescence decay time and a large radiation absorption coefficient. However, although the fluorescence output is larger than that of the BGO scintillator, it is only about 20% of the NaI (Tl) scintillator, and its improvement is desired.

In recent years, a scintillator using a single crystal of cerium-activated lutetium orthosilicate represented by the general formula Lu _{2 (1-x)} Ce _2x SiO ₅ (see Patent Documents 1 and 2), the general formula Gd _{2− (x + y)} Ln _x Ce _y SiO ₅ (Ln is Sc, Tb, Dy, Ho, Er, Tm, at least one element selected from the group consisting of Yb and Lu) scintillator (patent documents using a single crystal of a compound represented by 3 and 4), and a scintillator using a single crystal of cerium-activated lutetium yttrium orthosilicate represented by the general formula Ce _2x (Lu _1-y Y _y ) _{2 (1-x)} SiO ₅ (Patent Document 5, 6) is known. In these scintillators, it is known that not only the crystal density is improved, but also the fluorescence output of a single crystal containing a cerium-activated orthosilicate compound is improved and the fluorescence decay time can be shortened.

Further, Patent Documents 7 and 8 are scintillation materials based on silicate crystals containing lutetium (Lu) and cerium (Ce), which include oxygen vacancies α, and the chemical composition thereof is represented by the general formula: Lu _{1-y Me y A 1-} x Ce x SiO 5-z α z
x is 1 × 10 ^{−4 to} 0.2
y is 1 × 10 ^{−5 to} 0.05
[Wherein A is at least one element selected from the group consisting of Lu, Gd, Sc, Y, La, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb. , Me are H, Li, Be, B, C, N, Na, Mg, Al, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, Hf, Ta, W, Re, Os, Ir, At least one element selected from the group consisting of Pt, Au, Hg, Tl, Pb, Bi, U, and Th. ] Is described. In Patent Documents 7 and 8, 50 or more elements from H to Th are described as Me to be substituted for Lu, and these are effective in preventing scintillation element cutting and crystal cracking during manufacture, and waveguides. It is described that it is effective to create waveguide characteristics within the device.

Among these, when ions having an oxidation degree of +4, +5, +6 (for example, Zr, Sn, Hf, As, V, Nb, Sb, Ta, Mo, W, Th) are present in the original reagent, or Adding the necessary amount to the scintillation material not only improves the fluorescence characteristics of the crystal by suppressing the generation of Ce ⁴⁺ by the charge compensation action, but also suppresses the generation of cracks and vacancies in the oxygen sublattice. It also describes that it prevents the formation of. As a result, ions having an oxidation degree of +4, +5, +6 (for example, Zr, Sn, Hf, As, V, Nb, Sb, Ta, Mo, W, Th) are present or necessary in the original reagent. It is described that when a small amount is added to the scintillation material, for example, even when an inexpensive raw material containing 50 or more elements as impurities is used and a low-priced low-priced material is used, good fluorescence characteristics can be obtained. .

General formula: Ce _2x Ln _2y Lu _{2 (1-xy)} SiO ₅ (wherein Ln is at least one element of lanthanoid elements excluding Lu, and 2 × 10 ⁻⁴ ≦ x ≦ As a scintillator single crystal of cerium activated lanthanoid silicate represented by 3 × 10 ⁻² , 1 × 10 ⁻⁴ ≦ y ≦ 1 × 10 ⁻³ ), Ce and Tm co-activated lutetium silicate single crystal is disclosed in Patent Document 9. It is described that variation in fluorescence output, decay time, and energy resolution is improved by coactivation of Tm.

  In the scintillator whose base material is a rare earth silicate crystal, the rare earth element is selected from the group consisting of Sc, Y, La, Gd, and Lu, and includes Ti and Ce as the luminescent central element, preferably a molar ratio of Ti to Ce As a rare earth silicate scintillator single crystal having a ratio of 1/10000 to 1/10, Ce and Ti co-activated gadolinium silicate single crystal is described in Patent Document 10, and the fluorescence output is improved by co-activation of Ti. It is described that the decay time becomes faster.

General formula: Ce _x Ln _y Si _z O _u (Ln represents at least two elements selected from Y, Gd and Lu, and 0.001 ≦ x ≦ 0.1, 1.9 ≦ y ≦ 2. 1, 0.9 ≦ z ≦ 1.1, 4.9 ≦ u ≦ 5.1) as a scintillator single crystal having a chemical composition represented by a range where the maximum peak wavelength of the fluorescence intensity spectrum is 450 nm or more and 600 nm or less Patent Document 11 discloses a Ce-activated gadolinium lutetium silicate (Lu composition 20%) single crystal.

General formula: Ln _2x Gd _{2 (1-xy)} Ce _2y SiO ₅ (where Ln is at least one element of Sc, Y, and Lu, and 0.1 ≦ x ≦ 0.5, 0 .01 ≦ y ≦ 0.1), the peak wavelength of fluorescence intensity when excited at any wavelength between 360 nm and 400 nm is longer than 450 nm, and the half width is 112 nm. Patent Document 12 discloses a Ce-activated gadolinium silicate lutetium silicate (Lu composition 20%) single crystal characterized by being larger than that.

Japanese Patent No. 2852944 US Pat. No. 4,958,080 Japanese Examined Patent Publication No. 7-78215 US Pat. No. 5,264,154 US Pat. No. 6,624,420 US Pat. No. 6,921,901 Japanese Patent No. 3668755 US Pat. No. 6,278,832 JP 2006-199727 A JP 2005-350608 A JP 2007-2226 A JP 2006-257199 A C. L. Melcher et al., IEEE Transactions on Nuclear Science, Vol. 47, no. 3, June 2000, p965-968

As described so far, single crystals can have greatly different properties even if they use elements that seem to be similar in nature as elements that serve as raw materials. For example, the general formula is described in Patent Documents 7 and _8: In _{Lu 1-y Me y A 1} -x Ce x SiO 5-z α rare earth silicate single crystal represented by _z, is represented as element A As such, select the degree of oxidation +4, +5, +6 (for example, Zr, Sn, Hf, As, V, Nb, Sb, Ta, Mo, W, Th) and make ions having these present in the original reagent When added to the scintillation material, it has been found that the crystals may be colored and the fluorescence output may deteriorate.

  Patent Documents 7 and 8 describe more than 50 elements as effective in preventing scintillation element cutting and crystal cracking during manufacturing, and in creating waveguide characteristics in the waveguide element. However, it has been found that some of them do not have the effect of improving the fluorescence output or reducing the influence of oxygen deficiency.

  For example, according to the study by the inventors, in the silicate single crystal containing Lu and Ce represented by the chemical formulas of Patent Documents 7 and 8, oxygen deficiency is particularly obtained when the orthosilicate compound single crystal containing Lu ( An orthosilicate compound in which the other rare earth elements are Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc having an ion radius smaller than that of Tb. It has been found that oxygen deficiency (corresponding to oxygen lattice defects) is more likely to occur in crystals because the crystal structure has a C2 / c structure. Furthermore, in Patent Documents 7 and 8, the periodic table group 2 (group IIa) described as a harmful element which makes the valence of Ce tetravalent is more effective in suppressing oxygen defects, and among them, ions It has been found that Mg and Ca are particularly effective in terms of radius. In addition, since these elements can suppress the change in the valence of Ce ions even in an atmosphere containing a small amount of oxygen, the occurrence of oxygen deficiency can be further reduced by adjusting the atmosphere of the heat treatment during or after the growth. These are known and described in Japanese Patent Application Laid-Open No. 2007-16197. As described above, a single crystal is limited in the types of elements constituting it, but the basic composition and the material to be added must be changed according to the purpose and desired effect.

Incidentally, the general formula _{Lu 2 (1-x) Ce} 2x single crystal of cerium-activated orthosilicate lutetium represented by SiO _5, depending impurities defects and in the raw materials due to exposure to oxygen-poor atmosphere during crystal growth In addition, there is a problem that the fluorescence characteristics tend to vary within the crystal ingot and between the ingots.

Meanwhile, with cerium represented by the general formula _{Lm 2- (x + y) Lu} x Ce y SiO 5 (Lm in the formula is at least one of element selected from among lanthanoid elements, and Sc, Y, except for Lu.) In the case of an active orthosilicate compound single crystal, there is a problem that the single crystal having the structure of Lu _{2 (1-x)} Ce _2x SiO ₅ exists in the same manner, and a melt by the Czochralski method or the like. In crystal growth or the like by the pulling-up method, void-like crystal defects may occur in the latter half of the crystal growth, and dust may be observed inside the crystal, or variations in the crystal diameter by automatic diameter control may be observed. In some cases, separation of the melt occurs and it may be difficult to continue crystal growth. In the case where the turbidity of the crystal is generated, there is a case where a decrease in the fluorescence characteristic difference becomes remarkable or a large number of cracks are generated. Further, even if the apparent transparency is not lowered so much, there is a problem that the difference in fluorescence characteristics becomes relatively large (fluorescence characteristics vary) depending on the upper and lower positions of the crystal ingot.

Cerium activated ortho represented by the general formula Lm _{2-(x + y)} Lu _x Ce _y SiO ₅ (where Lm is a lanthanoid element excluding Lu and at least one element selected from Sc and Y). It has been found that the above-mentioned problem observed in a silicate compound single crystal is caused because this single crystal is a mixed crystal of Lu ₂ SiO ₅ and Lm ₂ SiO ₅ . That is, it was found that the segregation phenomenon caused by a difference in crystal composition in the crystal ingot during single crystal growth due to the difference in ion radii between Lu and Lm.

  It is thought that the above-mentioned crystal dust produced in the latter half of the crystal growth is due to the generation of void-like defects due to cell growth accompanied by segregation. If the light transmittance decreases due to the crystal obscuration, the heat dissipation of the crystal will deteriorate, so the shape of the solid-liquid interface will fluctuate, making it difficult to control the automatic diameter of the crystal or causing the melt to separate. It is done. In general, in the growth of a single crystal containing a cerium-activated orthosilicate compound, the Czochralski method is performed by high-frequency heating using an Ir crucible because the melting point of the single crystal is high. In the pulling method from the melt using such seed crystals, defects due to segregation due to the difference in ionic radius are likely to occur.

Further, with cerium represented by the general formula _{Lm 2- (x + y) Lu} x Ce y SiO 5 (Lm in the formula is at least one element selected from among lanthanoid elements, and Sc, Y, except for Lu.) In the case of an active orthosilicate compound single crystal, in general, the higher the Lu composition ratio, the higher the fluorescence output. Therefore, if there is a difference in Lu concentration between the upper and lower ingots, it is considered that a single crystal piece cut out from the ingot also has a difference in fluorescence output depending on the location cut out from the ingot. Further, even when the level of crystal dust cannot be recognized, the phenomenon in which the fluorescence output decreases or the energy resolution decreases in the lower part of the ingot is considered to be due to the generation of minute defects inside the crystal.

_{Gd 2 (1-x) Ce} 2x SiO 5 ( cerium-activated gadolinium orthosilicate: GSO) in the case of the single crystal is a rare earth which can be a trivalent is only Ce of Gd and activator, the Gd and Ce Since the ionic radii are relatively close, the segregation coefficient of Ce into the gadolinium orthosilicate crystal is about 0.7. Here, the segregation coefficient is Cs = KoCo (1-g) ^ (Ko-1) (where Ko is the segregation coefficient, Cs is the concentration in the crystal, Co is the concentration in the melt, and g is the solidification rate). Is the value given as Although the fluorescence output at the upper part of the crystal tends to be slightly higher than that at the lower part of the crystal, the change in the concentration of Gd and Ce in the crystal ingot is relatively small so that the characteristic difference does not become a big problem. However, since the Ce concentration dependence of the fluorescence decay time is relatively remarkable, the fluorescence decay time at the upper part of the crystal ingot tends to be longer than that at the lower part of the ingot.

On the other hand, in the case of Lu _{2 (1-x)} Ce _2x SiO ₅ (cerium activated lutetium orthosilicate: LSO) single crystal, the only rare earth that can be trivalent is Lu and the activator Ce. The ionic radius of Ce is larger than the ionic radius, and the difference between the ionic radii of the two is relatively different from that of GSO. For this reason, the segregation coefficient of Ce into the lutetium orthosilicate crystal is about 0.2, and the concentration change of Lu and Ce in the crystal ingot becomes relatively large. However, the fluorescence characteristics such as fluorescence output and fluorescence decay time of Lu _{2 (1-x)} Ce _2x SiO ₅ (cerium activated lutetium orthosilicate) single crystal are the same as those of cerium activated gadolinium orthosilicate single crystal (GSO). Compared to the Ce concentration dependency, the difference in fluorescence characteristics in the crystal ingot is less likely to be a problem. On the other hand, the characteristic variation in the crystal ingot due to the occurrence of oxygen defects or other impurities is more likely to occur than the cerium activated gadolinium orthosilicate single crystal (GSO), and the fluorescence output at the bottom of the crystal is at the top of the crystal. It may be significantly lower than that. Such a phenomenon is described in Non-Patent Document 1 and the like, and is a simple substance of cerium-activated lutetium yttrium orthosilicate represented by the general formula Ce _2x (Lu _1-y Y _y ) _{2 (1-x)} SiO _5. It is described in Patent Documents 5 and 6 that the same tendency is observed in the crystal, and that the composition of y = 0.3 or more is improved over the cerium-activated lutetium orthosilicate) single crystal.

As described above, it is represented by the general formula Lm _{2− (x + y)} Lu _x Ce _y SiO ₅ (where Lm is a lanthanoid element excluding Lu and at least one element selected from Sc and Y). Problems with the cerium-activated orthosilicate compound single crystal include the problem of turbidity of the crystal due to the occurrence of void-like crystal defects, the difficulty of stable crystal growth, and the fluorescence characteristics within the crystal ingot. There is a problem of variation.

  The object of the present invention is to solve the above-mentioned problems of conventional single crystals for scintillators. Specifically, an object of the present invention is to provide a scintillator single crystal having improved fluorescence characteristics by reducing the segregation phenomenon between elements in the single crystal. The present invention also provides a heat treatment method for producing a scintillator single crystal having improved fluorescence characteristics by reducing the segregation phenomenon between elements in the single crystal, and a method for producing the scintillator single crystal. Objective.

  The present inventor has found that the above-mentioned problem of a cerium-activated orthosilicate compound single crystal is influenced by the difference in ionic radius between Lm and Lu, and cell growth due to segregation occurs in the latter half of single crystal growth. It has been found that the difference in crystal composition occurs in the crystal ingot), and that the greater the difference in the ionic radius of Lm and Lu, the greater the ionic radius of Lm, in particular, the greater the occurrence. In addition, the segregation phenomenon described above increases the pulling speed of the crystal as the crucible diameter at the time of single crystal growth by the Czochralski method is increased to increase the crystal diameter, and the temperature gradient in the raw material melt is decreased. It was also found that there is a tendency to become more prominent as the rotational speed of the crystal at the time of pulling is increased.

  The present invention has been made on the basis of the above knowledge, and has found that the segregation phenomenon can be reduced by including an element having a difference in ionic radius between Lm and Lu in the single crystal structure. It is a thing.

That is, this invention is a single crystal for scintillators containing the cerium activated orthosilicate compound represented by following General formula (1).
Lm _{2− (x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (1)
(In the formula, Lm represents a lanthanoid element having an atomic number smaller than Lu and at least one element selected from Sc and Y, and Ln represents a lanthanoid element having an ionic radius between Lm and Lu. And at least one element selected from Sc, Y, B, Al, Ga and In, x represents a value greater than 0 and less than or equal to 0.5, y represents a value greater than 1 and less than 2, and z represents 0 Super value of 0.1 or less.)

  According to the scintillator single crystal of the present invention, while suppressing the segregation of Lm (change in composition ratio between Lm and Lu), there is also an effect of suppressing the segregation of Ce, reducing the variation in fluorescence characteristics in the single crystal, As a result, a scintillator single crystal having improved fluorescence characteristics can be provided. That is, it is possible to provide a single crystal that suppresses generation of crystal defects and realizes stable crystal growth, and reduces crystal dust, cracks, and abnormal growth (shape abnormality).

  In the scintillator single crystal of the present invention, Lm is Gd, and Ln is at least one element selected from Sc, Y, Yb, Tm, Er, Ho, Dy, Tb, B, Al, Ga, and In. It is preferable. According to this single crystal for scintillator, not only the generation of defects due to the segregation phenomenon of Gd and the abnormal growth in the latter half of the crystal growth, but also the difference in fluorescence characteristics between the upper and lower crystal ingots can be reduced.

  In the single crystal for scintillator, Ln is preferably Y. According to this single crystal for scintillator, not only the generation of defects due to the segregation phenomenon of Gd and the abnormal growth in the latter half of the crystal growth, but also the difference in the fluorescence characteristics above and below the crystal ingot can be further reduced. It can be improved further.

  In the single crystal for scintillator, x is greater than 0 and less than or equal to 0.2 and is smaller than [2- (x + y + z)], y is a value greater than 1.6 and less than 2, and z is 0. The value is preferably more than 001 and 0.02 or less. According to this single crystal for scintillator, not only the generation of defects due to the segregation phenomenon of Gd and the abnormal growth in the latter half of the crystal growth, but also the difference in the fluorescence characteristics above and below the crystal ingot can be further reduced. It can be improved further.

  In the scintillator single crystal of the present invention, Ln is an lanthanoid element having an ionic radius that is 2 pm or more smaller than the ionic radius of Lm and 4 pm or smaller than the ionic radius of Lu, and at least one selected from Sc and Y An element is preferable. According to the present single crystal for scintillator, segregation of Lm can be further suppressed, variation in fluorescence characteristics in the crystal ingot can be further reduced, and the fluorescence characteristics of the single crystal can be further improved.

  The single crystal for scintillator of the present invention contains 0.00005 to 0.1% by mass of at least one additive element selected from elements belonging to Group 2 (Group IIa) of the periodic table based on the total mass of the single crystal. Is preferred. According to the single crystal for scintillator, the decrease and dispersion of the fluorescence characteristics that are thought to be caused by oxygen defects are further reduced, thereby improving the fluorescence characteristics of the single crystal and the background (residual) of the fluorescence output caused by the crystal defects. Light (Afterflow) can also be reduced.

  The scintillator single crystal of the present invention preferably contains 0.00005 to 0.1% by mass of at least one additive element selected from elements belonging to Group 13 of the periodic table with respect to the total mass of the single crystal. According to the single crystal for scintillator, the effect of improving the fluorescence characteristics of the single crystal and reducing the background (afterglow) of the fluorescence output caused by crystal defects is more remarkable. By presenting at the same time as one or more additive elements selected from the elements to which they belong, a higher effect can be obtained.

  In the scintillator single crystal of the present invention, at least one element selected from elements belonging to Groups 4, 5, 6, 14, 15, and 16 of the periodic table is 0.002% by mass or less based on the total mass of the single crystal. It is preferable to contain. According to the scintillator single crystal, it is possible to further suppress the deterioration of the fluorescence characteristics.

A heat treatment method for producing a scintillator single crystal according to the present invention uses a raw material containing a constituent element of a scintillator single crystal containing a cerium-activated orthosilicate compound represented by the following general formula (1). In this heat treatment method, after the crystal is grown, the single crystal is heat treated at a temperature of 700 to 1300 ° C. in an atmosphere containing nitrogen or an inert gas having an oxygen concentration of 10 to 100% by volume.
Lm _{2− (x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (1)
(In the formula, Lm represents a lanthanoid element having an atomic number smaller than Lu and at least one element selected from Sc and Y, and Ln represents a lanthanoid element having an ionic radius between Lm and Lu. And at least one element selected from Sc, Y, B, Al, Ga and In, x represents a value greater than 0 and less than or equal to 0.5, y represents a value greater than 1 and less than 2, and z represents 0 The value is more than 0.1.)

  According to this heat treatment method, variations in single crystals (single crystal ingots) due to segregation between elements are reduced, and afterglow characteristics and characteristic degradation that may be caused by oxygen defects are reduced, thereby improving fluorescence characteristics. An improved single crystal can be provided.

A method for producing a scintillator single crystal according to the present invention comprises preparing a raw material containing a constituent element of a scintillator single crystal containing a cerium-activated orthosilicate compound represented by the following general formula (1): Czochralski method A step of growing a single crystal by:
And a step of heat-treating the single crystal at a temperature of 700 to 1300 ° C. in an atmosphere containing nitrogen or an inert gas having an oxygen concentration of 10 to 100% by volume. .
Lm _{2− (x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (1)
(In the formula, Lm represents a lanthanoid element having an atomic number smaller than Lu and at least one element selected from Sc and Y, and Ln represents a lanthanoid element having an ionic radius between Lm and Lu. And at least one element selected from Sc, Y, B, Al, Ga and In, x represents a value greater than 0 and less than or equal to 0.5, y represents a value greater than 1 and less than 2, and z represents 0 Super value of 0.1 or less.)

  This manufacturing method not only reduces defects and cracks during crystal growth due to segregation between elements, improves fluorescence characteristics, but also reduces afterglow characteristics and characteristic degradation that may be caused by oxygen defects. A method of manufacturing a scintillator single crystal that realizes scintillator characteristics (fluorescence characteristics) can be provided.

  According to the scintillator single crystal of the present invention, when a lanthanoid element having an atomic number smaller than that of Lu and at least one element selected from Sc and Y are contained as a base crystal, Lm is Lu. This improves the defects such as crystal defects due to segregation to crystals, and abnormal growth of crystals due to cell growth and crystal light transmittance reduction due to the occurrence of cell growth. Crystals can be provided.

  In addition, according to the heat treatment method for producing the scintillator single crystal of the present invention or the scintillator single crystal production method of the present invention, the scintillator single crystal having the above characteristics, that is, the segregation of Lm causes Thus, it is possible to provide a scintillator single crystal having improved fluorescence characteristics and variations in fluorescence output and energy resolution due to the difference in composition.

[Single crystal for scintillator]
The scintillator single crystal of the present invention is a scintillator single crystal containing a cerium-activated orthosilicate compound represented by the following general formula (1).
Lm _{2− (x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (1)
(In the formula, Lm represents a lanthanoid element having an atomic number smaller than Lu and at least one element selected from Sc and Y, and Ln represents a lanthanoid element having an ionic radius between Lm and Lu. And at least one element selected from Sc, Y, B, Al, Ga and In, x represents a value greater than 0 and less than or equal to 0.5, y represents a value greater than 1 and less than 2, and z represents 0 Super value of 0.1 or less.)

  Ion radii are Shannon and Prewitt (1969, 70) quoted from the homepage of the Earth Resources Research Laboratory at Hiroshima University (http://ome.hiroshima-u.ac.jp/er/Min_G2.html). ) Is an empirical radius (a part is due to Shannon (1976), and an estimated value according to Pauling (1960) or Ahrens (1952) is used as it is).

  The atomic number and ionic radius of the lanthanoid element are as follows: La (atomic number: 57, ionic radius: 116 pm), Ce (58, 114 pm), Pr (59, 113 pm), Nd (60, 111 pm) , Pm (61, 109 pm), Sm (62, 108 pm), Eu (63, 107 pm), Gd (64, 105 pm), Tb (65, 104 pm), Dy (66, 103 pm), Ho (67, 102 pm), Er (68, 100 pm), Tm (69, 99 pm), Yb (70, 99 pm), Lu (71, 98 pm). The atomic numbers and ionic radii of Sc, Y, B, Al, Ga, and In are Sc (21, 87 pm), Y (39, 102 pm), B (5, 12 pm), Al (13, 53 pm), Ga (31). , 62 pm), and In (49, 80 pm). Note that 1 pm = 0.01 mm.

  In the above general formula (1), Lm is selected from La, Gd, Nd, Sm, Eu, Tb, Dy, Ho, Er, and Y because it is relatively easy to obtain a single crystal as a base crystal. It is preferably at least one element, more preferably La, Gd and Y, and particularly preferably Gd.

  Ln and other elements are considered to exist at the lattice positions of rare earth elements such as the elements Lu and Lm in the base crystal, the lattice positions of Si, or the interstitial positions. It is considered that an element having an ionic radius close to the element (Si: 40 pm, Lu: 98 pm) in the base crystal has a greater influence on the segregation characteristics, coloring, and fluorescence characteristics of the single crystal because the lattice position is more easily replaced.

In the above general formula (1), Ln is a lanthanoid such as Sc, Y, Yb, Tm, Er, Ho, Dy, Tb from the point that the ionic radius is relatively close to or smaller than Lu in the base crystal. It is preferably at least one selected from system elements, and selected from B, Al, Ga, and In that have an ionic radius smaller than Lu and can stably take a trivalent valence state (Ln ³⁺ ). It is also preferable that it is at least one kind. Since these elements are relatively less segregated with respect to the element Lu in the base crystal, an effect of suppressing the segregation of Lm in the base crystal is obtained. Ln is more preferably at least one of Sc, Y, and Yb from the viewpoint that single crystal growth is relatively easy even if a large amount exists in the crystal, and an effect can be obtained without deteriorating scintillator characteristics, or Y is particularly preferable because the scintillator characteristics can be improved.

  When Lm is Gd, Ln is preferably at least one element selected from Sc, Y, Yb, Tm, Er, Ho, Dy, Tb, B, Al, Ga, and In, and in particular, Sc, Y And at least one element selected from Ga and Ga, and most preferably Y.

  Ln is preferably a lanthanoid element having an ionic radius that is 2 pm or more smaller than the ionic radius of Lm and 4 pm or smaller than the ionic radius of Lu, and at least one element selected from Sc and Y. For example, when Lm is Gd, Ln is preferably Y.

  In the general formula (1), x represents a value of more than 0 and 0.5 or less, preferably a value of more than 0 and a value of 0.2 or less, and particularly preferably a value of more than 0 and 0.1 or less. y represents a value of more than 1 and less than 2, a value of more than 1.6 and less than 2 is preferable, and a value of more than 1.8 and less than 2 is particularly preferable. z represents a value greater than 0 and 0.1 or less, preferably a value greater than 0.001 and not greater than 0.02, and particularly preferably a value greater than 0.002 and not greater than 0.005. [2- (x + y + z)] is a value greater than 0 and less than or equal to 1, a value greater than 0 and less than or equal to 0.4 is preferable, and a value greater than 0 and less than or equal to 0.2 is particularly preferable.

  In the general formula (1), x is greater than 0 and less than or equal to 0.2 and smaller than [2- (x + y + z)], y is a value greater than 1.6 and less than 2, and z is The value is more than 0.001 and 0.02 or less. However, when Lm is an element having an ion radius sufficiently larger than Lu, such as La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd, x is more than 0 and less than 0.2, and [ 2- (x + y + z)] can be the same or larger.

  The single crystal of the present invention may contain at least one additive element selected from elements belonging to Group 2 (Group IIa) of the periodic table. The ionic radii of elements belonging to Group 2 (Group IIa) of the periodic table are Be (35 pm), Mg (72 pm), Ca (112 pm), Sr (125 pm), Ba (142 pm), and Ra (148 pm) in ascending order. From the viewpoint that the ionic radius is relatively close to Lu (98 pm) or smaller than Lu, Be, Mg, Ca, and Sr are preferable, Mg and Ca that have an ionic radius closest to Lu are more preferable, and Ca is particularly preferable. By containing these elements, it is possible to reduce a decrease or variation in fluorescence characteristics that may be caused by oxygen defects, and to reduce the background (afterglow) of fluorescence output caused by crystal defects.

  The total content of elements belonging to Group 2 of the periodic table (Group IIa) is 0.00005 to 0.1% by mass and 0.0001 to 0.05% by mass with respect to the total mass of the single crystal. Preferably, it is 0.0005-0.01 mass%. When the total content is less than 0.00005% by mass, it is difficult to obtain an effect due to the addition of an additive element of Group 2 (Group IIa) of the periodic table. If this total content is greater than 0.1% by mass, the addition of an additive element of Group 2 (Group IIa) of the periodic table increases lattice defects and crystal distortion, and increases crystal growth and crystal growth. It tends to be difficult, or the fluorescence output tends to decrease due to the formation of non-emission levels due to lattice defects.

  The single crystal of the present invention may contain one or more additive elements selected from elements belonging to Group 13 (Group IIIb) of the periodic table. B (12 pm), Al (53 pm), Ga (62 pm), In (80 pm), Tl (150 pm) in order of increasing ionic radii of Group 13 elements of the periodic table, but the ionic radii are Ce, Lu in the base crystal. B, Al, Ga and In are preferable, Al and Ga are more preferable, and the ionic radius is closest to Si from the point of being relatively close to Si (40 pm) or smaller than Si. Is particularly preferred. The presence of these elements simultaneously with one or more additional elements selected from the elements belonging to Group 2 of the periodic table further improves the effect of reducing the background (afterglow) of fluorescence output due to crystal defects. Become prominent.

  The total content of elements belonging to Group 13 (Group IIIb) of the periodic table is preferably 0.00005 to 0.1% by mass, and 0.0001 to 0.05% by mass with respect to the total mass of the single crystal. More preferably, it is 0.0005 to 0.01% by mass. When the total content is less than 0.00005% by mass, it is difficult to obtain the effect of adding the Group 13 element of the periodic table. On the other hand, if the total content is greater than 0.1% by mass, the addition of Group 13 elements of the periodic table increases lattice defects and crystal distortion, increasing the number of polycrystals and cracks, making crystal growth difficult. In addition, the fluorescence output tends to decrease due to the formation of non-light emitting levels due to lattice defects.

  The single crystal of the present invention contains at least one element selected from elements belonging to Groups 4, 5, 6, 14, 15 and 16 (Group IVa, Va, VIa, IVb, Vb and VIb) of the periodic table. May be. As additive elements belonging to Groups 4, 5, 6, 14, 15, and 16 of the periodic table, Group 4 Ti (ion radius: 61 pm), Zr (72 pm), Hf (71 pm), which is likely to be a tetravalent ion, and Group 14 Ge (54 pm), Sn (69 pm), Pb (78 pm), Group 5 V (64 pm), Nb (64 pm), Ta (64 pm), and Group 15 P (17 pm), which are likely to be pentavalent ions. ), As (34 pm), Sb (61 pm), Group 6 Cr (30 pm), Mo (60 pm), W (60 pm), and Group 16 S (12 pm), Se (29 pm), which are likely to be hexavalent ions. , Te (56 pm) and the like.

  The total content of elements belonging to groups 4, 5, 6, 14, 15 and 16 of the periodic table is preferably 0.002% by mass or less and 0.001% by mass or less with respect to the total mass of the single crystal. Is more preferably 0.0005% by mass or less, and most preferably 0.0002% by mass or less. Since the valence tends to deteriorate the fluorescence characteristics in the order of tetravalent, pentavalent and hexavalent elements close to the elements in the base crystal, if this total content is greater than 0.002% by mass, the ionic radius is particularly large. The deterioration of the fluorescence characteristics due to Zr, Hf, etc. of the periodic table group 4 which is a relatively large element cannot be ignored.

  Furthermore, the single crystal of the present invention preferably contains no Zr or Hf of the periodic table group 4 from the above viewpoints among the elements belonging to the periodic tables 4, 5, 6, 14, 15 and 16 groups. It is more preferable not to contain Zr, Hf, Ti, Ta, V, Nb, W, Mo, and Cr belonging to Groups 5 and 6.

[Method for producing single crystal for scintillator]
A method for producing a scintillator single crystal according to the present invention comprises preparing a raw material containing a constituent element of a scintillator single crystal containing a cerium-activated orthosilicate compound represented by the following general formula (1): Czochralski method A step of growing a single crystal by:
And a step of heat-treating the single crystal at a temperature of 700 to 1300 ° C. in an atmosphere containing nitrogen or an inert gas having an oxygen concentration of 10 to 100% by volume. .
Lm _{2− (x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (1)
(In the formula, Lm represents a lanthanoid element having an atomic number smaller than Lu and at least one element selected from Sc and Y, and Ln represents a lanthanoid element having an ionic radius between Lm and Lu. And at least one element selected from Sc, Y, B, Al, Ga and In, x represents a value greater than 0 and less than or equal to 0.5, y represents a value greater than 1 and less than 2, and z represents 0 Super value of 0.1 or less.)

  The growth of the single crystal is not particularly limited, but may be, for example, according to the Czochralski method by high-frequency heating using an iridium (Ir) crucible. First, raw materials that are constituent elements of the compound of the general formula (1) are weighed and mixed according to the stoichiometric ratio, and charged into a crucible. The raw material is prepared in the form of an oxide (single oxide or composite oxide) or a salt (single salt or double salt) such as carbonate, and the form thereof is, for example, a solid powder. If necessary, other elements of Group 2 or Group 13 or Group 4, 5, 6, 14, 15 or 16 may be weighed and added. These elements may be added when the raw material is weighed, or may be added when the crucible is filled with the raw material. Any timing may be used as long as it is added to the raw material during crystal growth. Moreover, the aspect at the time of addition is not specifically limited, For example, you may add in a raw material in the state of an oxide or carbonate.

  Next, for example, the raw material charged in the crucible is melted by heating in a high-frequency induction heating furnace, seed crystals (seed crystals) are charged into the melt, and a cylindrical single crystal is grown while pulling up the seed crystals. At this time, in the single crystal growth step, the heating output of the heating furnace is adjusted, and the single crystal pulled up from the melt is grown until the cross section has a predetermined diameter. Thereafter, the heating output of the heating furnace is adjusted, the grown single crystal obtained after the crystal growth step is cooled, and a single crystal is formed.

After crystal growth, a scintillator single crystal of the present invention is obtained by heat treatment (annealing) at a temperature of 700 to 1300 ° C. in an atmosphere containing nitrogen or an inert gas having an oxygen concentration of 10 to 100% by volume. . At this time, the oxygen concentration is more preferably 20% by volume or more, and particularly preferably 50% by volume or more. The heat treatment temperature in the atmosphere containing nitrogen or an inert gas at the oxygen concentration is preferably 700 ° C. to 1300 ° C., more preferably 1000 ° C. to 1300 ° C., and particularly preferably 1100 ° C. to 1300 ° C. When the temperature is 700 ° C. or higher, a sufficient heat treatment effect can be obtained with an allowable processing time, and when the temperature is 1300 ° C. or lower, the deterioration of the fluorescence characteristics due to the valence change of Ce (Ce ³⁺ → Ce ⁴⁺ ) can be suppressed. However, only when the single crystal of the present invention contains an element of Group 2 (Group IIa) of the periodic table, the effect of suppressing the valence change of Ce (Ce ³⁺ → Ce ⁴⁺ ) is increased, and therefore, 1500 ° C. Up to this, the effect of improving the scintillator characteristics by heat treatment can be obtained. Further, when the single crystal of the present invention does not contain an element of Group 2 (Group IIa) of the periodic table, the above Ce valence change tends to occur, so the heat treatment temperature is set to 700 ° C. to 1150 ° C. It is preferably 900 ° C to 1150 ° C, more preferably 1000 ° C to 1150 ° C.

  As the heat treatment time, the effect is generally obtained in 5 hours to 48 hours. If the treatment time is less than 5 hours, sufficient effects may not be obtained, and if the treatment time exceeds 48 hours, the effect is saturated, which is not economical. However, if the sample size after processing is large or the heat treatment temperature is low In such a case, the longer the processing time, the higher the effect may be.

  Further, for example, the heat treatment method described in Japanese Patent Application Laid-Open No. 2007-1850 by the present inventors is also effective for the scintillator single crystal of the present invention. The timing for applying the heat treatment method is preferably after processing into a final shape used as a scintillator, and preferably before the surface mirroring treatment by chemical etching or mechanical polishing. In general, the larger the sample shape, the longer the time required to obtain a sufficient effect of heat treatment. In addition, if heat treatment is performed after the mirroring treatment, the mirrored surface may become cloudy and the light transmittance may be reduced.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example at all.

[Example 1]
Single crystals were grown according to the Czochralski method. First, diameter 150 mm, height 150 mm, in the iridium crucible of thickness _{3mm, Gd 2- (x + y} ) Y x Lu y Ce z SiO 5 (x = 0.02, y = 1.86, z = 0. 003) raw material was charged. Starting materials were 747.13 g of gadolinium oxide (Gd ₂ O ₃ , purity 99.99 mass%), lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 13,038.28 g, yttrium oxide (Y ₂ O _3, 99.99 wt% purity) 79.56G, silicon dioxide (SiO _2, purity of 99.9999% by mass) 2,127.43G, cerium oxide (CeO _2, 99.99 wt% purity) almost 18.19g The mixture was mixed so as to have a predetermined stoichiometric ratio, and the mixture was charged with a total of 16,011 g and 2.821 g of calcium carbonate (CaCO ₃ , purity 99.99% by mass) (0.007% by mass as the Ca component). A melt was obtained by heating to an melting point of about 2100 ° C. in an induction heating furnace. The melting point was measured with an electronic optical pyrometer (manufactured by Chino, Pyrosta Model UR-U). At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm.

Subsequently, seeding was performed by putting the tip of a pulling rod having a seed crystal (seed) fixed to the tip into a melt. The shoulder is pulled up at a rotation speed of 3 to ¹ min ⁻¹ at a crystal pulling speed of 1.0 mm / h, and parallel at a pulling speed of 1 mm / h and a rotation speed of 1 min ⁻¹ from the point when the diameter becomes φ85 mm. Department training started. After growing a predetermined parallel part by automatic diameter control by weight, the crystal was cut off from the melt and cooled to obtain a single crystal. During the growth and cooling of the single crystal, the gas flowing into the growth furnace was added to the N ₂ gas having a flow rate of 4 to 3 L / min, and the O ₂ gas having a flow rate of 10 to 15 mL / min was continuously supplied. At this time, the oxygen concentration in the furnace was measured by a galvanic cell diffusion type oxygen concentration indicator (manufactured by Taiei Denki Co., Ltd., model OM-25MS10), and was confirmed to be 0.2 to 0.4% by volume.

  The obtained single crystal had a crystal weight of about 11,500 g, a shoulder length of about 75 mm, and a parallel portion of about 235 mm. The appearance of the obtained single crystal was a crystal with high surface transparency, with no turbidity inside the crystal due to void defects up to the bottom of the parallel part.

From the obtained single crystal, the uppermost part (Top, crystallization rate by weight from seed: about 8% part) and the lowermost part (Bottom, crystallization rate by weight from seed): about 70% part ), 4 × 6 × 25 mm ³ samples were cut out. The obtained single crystal sample was put on a Pt plate and put into an electric furnace. The temperature was raised in air (oxygen concentration about 21% by volume) in about 4 hours, maintained at 1200 ° C. for 24 hours, and then cooled in about 10 hours. Thereafter, the sample was mirror-etched on the entire surface by chemical etching using phosphoric acid heated to 300 ° C., and the scintillator single crystal of Example 1 was obtained.

Optionally extracted the three out of the samples obtained from the Top and Bottom position, wrapped PTFE tape is a reflective material five surfaces except the 4 × 6 mm ² surface side one face of 4 × 6 × 25 mm ³ sample The remaining 4 × 6 mm ² surface was fixed to the photomultiplier tube surface with optical grease, and the energy spectrum for gamma rays from 137Cs at 662 keV was measured. The energy spectrum is obtained by amplifying a signal from a dynode with a preamplifier (ORTEC, 113) and a waveform shaping amplifier (ORTEC, 570) in a state where a voltage of 1.45 kV is applied to the photomultiplier tube. Quantum MCA4000 (manufactured by PGT). The energy spectrum of each sample was measured, and the fluorescence output and energy resolution of each sample were evaluated. The signal from the anode was measured with a high-speed digital oscilloscope (Tektronix, TDS5052), and the fluorescence decay time and background (afterglow) were evaluated. As the background, the output value (mV) of the oscilloscope immediately after the sample was put in the dark box for measurement was measured. As a result, the average value of each three samples is shown in Table 1. The fluorescence decay time of the sample measured this time was 40 to 43 ns, and no clear difference was observed between the samples.

[Example 2]
As starting materials, gadolinium oxide (Gd2O3, purity 99.99 mass%) 621.29 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 13,077.64 g, yttrium oxide (Y ₂ O ₃ , purity) 99.99 mass%) 159.59 g, silicon dioxide (SiO ₂ , purity 99.9999 mass%) 2,133.85 g, cerium oxide (CeO ₂ , purity 99.99 mass%) 18.25 g were added to Gd _{2- ( x + y) Y x Lu y} Ce z SiO 5 (x = 0.04, y = 1.86, z = 0.003) were mixed to be substantially Ryoron composition, 16,011G and carbonate mixture in total calcium (CaCO _3, purity 99.99 wt%) 2.830g (as 0.007 wt% Ca component) except were charged, scintillator in the same manner as in example 1 To produce a crystal. At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm. The appearance of the obtained single crystal was a crystal with high surface transparency, with no dust inside the crystal due to void defects up to the bottom of the parallel part (Table 1).

[Example 3]
As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99 mass%) 867.26 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 13,001.15 g, gallium oxide (Ga ₂ O _3, purity 99.99 wt%) 2.63 g, silicon dioxide (SiO _2, purity of 99.9999 mass%) 2,121.37g, cerium oxide (CeO _2, the purity of 99.99 wt%) 18.14 g Gd _{2- (x + y)} Ga _x Lu _y Ce _z SiO ₅ (x = 0.0008, y = 1.86, z = 0.003) was mixed so that the composition was almost stoichiometric, A scintillator was prepared in the same manner as in Example 1 except that 011 g and 2.813 g of calcium carbonate (CaCO ₃ , purity 99.99% by mass) (0.007% by mass as the Ca component) were charged. A single crystal was prepared. At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm. As for the appearance of the obtained single crystal, a dust inside the crystal, which seems to be due to void defects, was observed at the lowermost 10 mm part of the parallel part, and the transparency of the crystal surface was also reduced in this part. The fluorescence properties such as energy resolution were at a high level (Table 1).

[Example 4]
As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99 mass%) 616.26 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 13,079.66 g, yttrium oxide (Y ₂ O ₃ , purity 99.99 mass%) 159.62 g, gallium oxide (Ga ₂ O ₃ , purity 99.99 mass%) 2.65 g, silicon dioxide (SiO ₂ , purity 99.9999 mass%) 2,134.18 g Cerium oxide (CeO ₂ , purity 99.99 mass%) 18.25 g Gd _{2-(x + y)} Y _x-0.0008 Ga _0.0008 Lu _y Ce _z SiO ₅ (x = 0.0408, y = 1 .86, z = 0.003), and the mixture was mixed with a total of 16,011 g and calcium carbonate (CaCO ₃ , purity 99.99% by mass). ) A scintillator single crystal was produced in the same manner as in Example 1 except that 2.830 g (0.007 mass% as a Ca component) was charged. At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm. The appearance of the obtained single crystal was a crystal with high surface transparency, with no dust inside the crystal due to void defects up to the bottom of the parallel part (Table 1).

[Example 5]
As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99 mass%) 494.68 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 13,117.24 g, yttrium oxide (Y ₂ O ₃ , purity) 99.99 mass%) 240.11 g, silicon dioxide (SiO ₂ , purity 99.9999 mass%) 2,140.32 g, cerium oxide (CeO ₂ , purity 99.99 mass%) 18.30 g were mixed with Gd _{2- ( x + y) Y x Lu y} Ce z SiO 5 (x = 0.06, y = 1.86, z = 0.003) were mixed to be substantially Ryoron composition, 16,011G and carbonate mixture in total calcium (CaCO _3, purity 99.99 wt%) 2.838g (as 0.007 wt% Ca component) except were charged, scintillator in the same manner as in example 1 To produce a crystal. At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm. The appearance of the obtained single crystal was a crystal with high surface transparency, with no turbidity inside the crystal due to void defects up to the bottom of the parallel part.

[Comparative Example 1]
As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99 mass%) 872.22 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 12,999.15 g, silicon dioxide (SiO ₂ , Purity 99.9999 mass%) 2,121.05 g, cerium oxide (CeO ₂ , purity 99.99 mass%) 18.14 g Gd _{2- (y + z)} Lu _y Ce _z SiO ₅ (y = 1.86 z = 0.003), and the mixture was 16,011 g in total and 2.813 g of calcium carbonate (CaCO ₃ , purity 99.99% by mass) (0.007% by mass as the Ca component) A scintillator single crystal was produced in the same manner as in Example 1 except that (2) was charged. As for the appearance of the obtained single crystal, a dust inside the crystal which seems to be due to void defects is seen in the lowermost 40 mm part of the parallel part, and the control of the crystal diameter by automatic diameter control deteriorates in that part, and the shape Disturbance occurred.

[Comparative Example 2]
As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99 mass%) 1,257.15 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 12,609.24 g, silicon dioxide (SiO ₂ ) ₂ , purity 99.9999 mass%) 2,126.01 g, cerium oxide (CeO ₂ , purity 99.99 mass%) 18.18 g was added to Gd _{2-(y + z)} Lu _y Ce _z SiO ₅ (y = 1.80). , Z = 0.003), and a total of 16,011 g of the mixture and 2.819 g of calcium carbonate (CaCO ₃ , purity 99.99 mass%) (0.007 as the Ca component) A single crystal for scintillator was produced in the same manner as in Example 1 except that (mass%) was charged. As for the appearance of the obtained single crystal, a dust inside the crystal, which is thought to be due to void defects, was observed in the lowermost 20 mm portion of the parallel portion, and the transparency of the crystal surface was also reduced in that portion.

[Example 6]
In an iridium crucible having a diameter of 180 mm, a height of 180 mm, and a thickness of 3 mm, Gd _{2- (x + y)} Y _x Lu _y Ce _z SiO ₅ (x = 0.06, y = 1.86, z = 0.003) The raw materials were input. Starting materials are gadolinium oxide (Gd ₂ O ₃ , purity 99.99 mass%) 881.15 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 23,365.08, yttrium oxide (Y ₂ O ₃ , purity 99.99 mass%) 427.70 g, silicon dioxide (SiO ₂ , purity 99.9999 mass%) 3,812.44 g, cerium oxide (CeO ₂ , purity 99.99 mass%) 32.60 g The mixture was mixed so as to obtain a predetermined stoichiometric ratio, and the mixture was charged with a total of 28,518.97 g and calcium carbonate (CaCO ₃ , purity 99.99 mass%) 5.056 g (0.007 mass% as a Ca component). The melt was obtained by heating to a melting point of about 2100 degrees in a high frequency induction heating furnace. The melting point was measured with an electronic optical pyrometer (manufactured by Chino, Pyrosta Model UR-U). At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm.

Thereafter, seeding is performed, the shoulder is pulled up at a rotation speed of 1 min ⁻¹ at a crystal pulling speed of 1.0 mm / h, and when the diameter becomes 105 mm, the pulling speed is 0.8 mm / h. Parallel part growth was started at ¹ min ⁻¹ . After growing a predetermined parallel part by automatic diameter control by weight, the crystal was cut off from the melt and cooled to obtain a single crystal. During the growth and cooling of the single crystal, the gas flowing into the growth furnace was added to the N ₂ gas having a flow rate of 4 to 3 L / min, and the O ₂ gas having a flow rate of 10 to 15 mL / min was continuously supplied. At this time, the oxygen concentration in the furnace was measured by a galvanic cell diffusion type oxygen concentration indicator (manufactured by Taiei Denki Co., Ltd., model OM-25MS10), and was confirmed to be 0.2 to 0.4% by volume.

The obtained single crystal had a crystal weight of about 20,500 g, a shoulder length of about 80 mm, and a parallel portion of about 335 mm. The appearance of the obtained single crystal was a crystal with high surface transparency, with no turbidity inside the crystal due to void defects up to the bottom of the parallel part. From the obtained single crystal, the uppermost part (Top, crystallization rate by weight from seed: about 8% part) and the lowermost part (Bottom, crystallization rate by weight from seed): about 70% part ), 4 × 6 × 25 mm ³ samples were cut out. The obtained single crystal sample was put on a Pt plate and put into an electric furnace. The temperature was raised in air (oxygen concentration about 21% by volume) in about 4 hours, maintained at 1200 ° C. for 24 hours, and then cooled in about 10 hours. Then, the sample was made into a mirror surface entirely by chemical etching using phosphoric acid heated to 300 ° C., and a scintillator single crystal of Example 6 was obtained.

[Example 7]
As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99 mass%) 651.82 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 23,850.78 g, scandium oxide (Sc ₂ O _3, purity 99.99 wt%) 174.02g, silicon dioxide (SiO _2, purity of 99.9999 mass%) 3,790.80g, cerium oxide (CeO _2, the purity of 99.99 wt%) 32.58 g Gd _{2- (x + y)} Sc _x Lu _y Ce _z SiO ₅ (x = 0.04, y = 1.90, z = 0.003) was mixed so as to have an almost stoichiometric composition, and the mixture was 28, Scintillation was carried out in the same manner as in Example 6 except that 519 g and 5.052 g of calcium carbonate (CaCO ₃ , purity 99.99 mass%) (0.007 mass% as the Ca component) were charged. A single crystal was prepared. At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm. The appearance of the obtained single crystal was a crystal with high surface transparency, with no turbidity inside the crystal due to void defects up to the bottom of the parallel part.

[Example 8]
As starting materials, yttrium oxide (Y ₂ O ₃ , purity 99.99 mass%) 714.92 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 23,378.99 g, scandium oxide (Sc ₂ O _3, 99.99 wt% purity) 450.13G, silicon dioxide (SiO _2, purity of 99.9999% by mass) 3,922.25, cerium oxide (CeO _2, 99.99 wt% purity) of 33.71G Y _{2- (x + y)} Sc _x Lu _y Ce _z SiO ₅ (x = 0.10, y = 1.80, z = 0.003) are mixed so as to have an almost stoichiometric composition, and the mixture is 28, For scintillator in the same manner as in Example 6 except that 520 g and 5.227 g of calcium carbonate (CaCO ₃ , purity 99.99 mass%) were charged (0.007 mass% as Ca component). A single crystal was produced. At this time, the impurities contained in each raw material were all less than 1 ppm for 4, 5, and 6-valent elements. The appearance of the obtained single crystal was a crystal with high surface transparency, with no turbidity inside the crystal due to void defects up to the bottom of the parallel part.

[Comparative Example 3]
As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99% by mass) 2,239.30 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99% by mass) 22,460.21 g, silicon dioxide (SiO ₂ ) _2, a purity of 99.9999 mass%) 3,768.11g, cerium oxide (CeO _2, 99.99 wt%) 32.38g of _{Gd 2-y Lu y Ce z} SiO 5 (y = 1.80, z = 0.003), and the mixture was mixed in a total amount of 28,519 g and calcium carbonate (CaCO ₃ , purity 99.99 mass%) 5.022 g (0.007 mass% as the Ca component) A scintillator single crystal was produced in the same manner as in Example 6 except that was charged. At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm. However, in the automatic crystal diameter control during the parallel part growth of the single crystal, a phenomenon in which the amount of increase in crystal weight and the heating output fluctuate greatly was observed, so the crystal growth was stopped and cooling was performed.

  The obtained single crystal had a crystal weight of about 16,500 g, a shoulder length of about 80 mm, and a parallel portion of about 210 mm. In the appearance of the obtained single crystal, dust is generated inside the crystal due to void defects from near the middle of the parallel part, and the crystal outer diameter increases to about 120 mm near the lower part of the crystal and the inside becomes hollow. It was.

[ Reference Example 9]
As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99 mass%) 235.09 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%) 13,600.94 g, yttrium oxide (Y ₂ O ₃ , purity) 99.9979% by weight, silicon dioxide (SiO ₂ , purity 99.9999% by weight) 2,116.81 g, cerium oxide (CeO ₂ , purity 99.99% by weight) 18.10 g by Gd _{2- ( x + y) Y x Lu y} Ce z SiO 5 (x = 0.01, y = 1.95, were mixed so that substantially Ryoron composition of z = 0.003), were charged 16,011g mixture in total Except for the above, a scintillator single crystal was produced in the same manner as in Example 1. At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm. The appearance of the obtained single crystal was a crystal with high surface transparency, with no turbidity inside the crystal due to void defects up to the bottom of the parallel part.

[ Reference Example 10]
As a starting material, gadolinium oxide (Gd2 O3, 99.99 wt%) 1,301.51g, lutetium oxide _(Lu 2 _{O 3,} 99.99 wt%) 11,748.81g, yttrium oxide _(Y 2 _{O 3} , 740.77 g of silicon dioxide (SiO ₂ , purity 99.9999 mass%) 2,201.04 g, 18.82 g of cerium oxide (CeO ₂ , purity 99.99 mass%) Gd _{2 - (x + y) Y x} Lu y Ce z SiO 5 (x = 0.18, y = 1.62, z = 0.003) were mixed to be substantially Ryoron composition, 16,011G the mixture in total A single crystal for a scintillator was produced in the same manner as in Example 1 except that it was charged. At this time, all of the 4, 5, and 6-valent elements as impurities contained in each raw material were less than 1 ppm. As for the appearance of the obtained single crystal, a dust inside the crystal, which seems to be due to void defects, was observed in the lowermost 40 mm portion of the parallel portion, and the transparency of the crystal surface in this portion was slightly lowered.

[Comparative Example 4]
As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99% by mass) 2,422.81 g, lutetium oxide (Lu ₂ O ₃ , purity 99.99% by mass) 11,428.50 g, silicon dioxide (SiO ₂ ) ₂ , purity 99.9999 mass%) 2,141.03 g, cerium oxide (CeO ₂ , purity 99.99 mass%) 18.31 g Gd _{2-(y + z)} Lu _y Ce _z SiO ₅ (y = 1.62) , Z = 0.003), and a single crystal for scintillator was produced in the same manner as in Example 1 except that 16,011 g of the total mixture was charged. As for the appearance of the obtained single crystal, dust inside the crystal, which seems to be due to void defects, gradually begins to appear from around the central part of the parallel part, and the dust inside the crystal due to the void defect and the crystal surface toward the bottom of the parallel part The decrease in transparency was also remarkable. At the lower part of the parallel part, the control of the crystal diameter by the automatic diameter control deteriorates, and the shape is disturbed.

Table 1 shows experimental conditions, growth results, and evaluation results of fluorescence characteristics of Examples 1 to 5 and Comparative Examples 1 and 2. Table 2 shows the experimental conditions and the growth results of Examples 6 to 8 and Comparative Example 3. The experimental conditions and growth results of Reference Examples 9 and 10 and Comparative Example 4 are shown in Table 3. In addition, a present Example shows a suitable example and does not limit this invention.

From Table 1, in Examples 1, 2 and 5, in the general formula Lm _{2-(x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (where Lm is a lanthanoid element having a smaller atomic number than Lu, and Sc and Y In this case, the segregation of Gd is suppressed, and the dust at the lower part of the ingot is eliminated as compared with Comparative Example 1 that does not contain Y. In addition, fluorescence characteristics such as fluorescence output and energy resolution are improved. In particular, the fluorescence characteristics at the ingot bottom position are improved, and the characteristic difference due to the ingot vertical position is reduced. In Example 3, by containing Group 13 Ga as Ln, the effect is not as remarkable as in Examples 1 and 2 compared to Comparative Example 1, but the same effect is obtained. Moreover, in Example 3 and Example 4, the effect which reduces the fluorescence background (afterglow) is also acquired by Ga addition.

  Composition analysis of ingots Top and Bottom was performed on the same samples as those in which fluorescence characteristics were evaluated in Examples 1, 2, and 5 and Comparative Examples 1 and 2. The analysis was carried out by quantitatively analyzing the Lu, Gd, Y, and Ce components of the acid or alkali-fused sample by high frequency inductively coupled plasma emission spectroscopy (ICP-AES method). As a result, the difference between Gd components (Bottom−Top) between the ingot Top and Bottom (Bottom−Top) is in the order of Comparative Example 2> Comparative Example 1> Example 1> Example 2> Example 5, and Gd segregation is significantly reduced. I found out.

  On the other hand, in Comparative Examples 1 to 3, due to the segregation of Gd, crystal dust is generated in the lower part of the ingot, and in Comparative Example 2 having a relatively high Gd composition, dust is generated early in crystal growth, and automatic diameter control is performed. There were signs of abnormal growth worsening. In Comparative Example 3, the crystal composition is the same as in Comparative Example 2, but when the crucible diameter and the crystal diameter are increased, the timing of occurrence of dust inside the crystal tends to be earlier, and abnormal crystal growth occurs. I found it easy.

  In Examples 1 to 5 and Comparative Examples 1 and 2, a Group 2 element Ca is contained as an element, and since heat treatment is performed in air after processing a single crystal sample, the Lu element from the top of the ingot to the bottom Although there is a difference in characteristics due to a change in the concentration, a relatively stable and good fluorescence characteristic is obtained in a portion where the crystal is not blurred due to Gd segregation.

From Table 2, in Example 6 , Reference Examples 7 to 8 and Comparative Example 3, examples of single crystals having larger crystal diameters were shown. In the general formula Lm _{2− (x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (where Lm is a lanthanoid element having an atomic number smaller than Lu and at least one element selected from Sc and Y). In Comparative Example 3 that does not contain Ln that suppresses segregation of Lm, defects in crystal growth due to segregation of Gd become significant. On the other hand, in Example 6 and Reference Example 7 which are compositions containing Gd as Lm and Y or Sc as Ln, and Reference Example 8 which is a composition containing Y as Lm and Sc as Ln, segregation of Lm is suppressed. The dust at the bottom of the ingot has been eliminated. Therefore, the scintillator single crystals produced using the single crystals of Example 6 and Reference Examples 7 to 8 are expected to have high fluorescence characteristics.

From Table 3, in Reference Example 9, when Gd is relatively small as Lm and Y is contained as Ln, there is no defect in crystal growth due to segregation of Gd. In the comparative example 4 that does not contain Ln that suppresses the segregation of Gd in the case of a composition having a relatively large Gd as Lm, defects in crystal growth due to the segregation of Gd become remarkable. On the other hand, in Reference Example 10 containing Y as Ln, segregation of Gd is suppressed, and defects at the bottom of the ingot are improved. Therefore, the scintillator single crystals produced using the single crystals of Reference Examples 9 and 10 are expected to have high fluorescence characteristics.

  About the same sample as what evaluated the fluorescence characteristic in Examples 1, 2, 5 and Comparative Examples 1 and 2, composition analysis of Ingot Top and Bottom was performed. The analysis was carried out by quantitatively analyzing the Lu, Gd, Y, and Ce components of the acid or alkali-fused sample by high frequency inductively coupled plasma emission spectroscopy (ICP-AES method). The results are shown in Table 4. From Table 4, the difference in Gd component (Bottom-Top) between Ingot Top and Bottom is in the order of Comparative Example 1> Example 1> Example 2. In Examples 1 and 2, Gd segregation is significantly reduced. I found out.

The formula _{Lm 2- (x + y + z} ) Ln x Lu y Ce z SiO 5 ( here Lm is at least one element selected from among lanthanoid elements, and Sc, Y even atomic number is smaller than Lu of the present invention )) In addition to Examples 1 to 8 and References 9 to 10 , the combinations of Lm and Ln that can be applied are shown in Table 5 for typical combinations in which the effect of the present invention is remarkable.

Claims (7)

A scintillator single crystal comprising a cerium-activated orthosilicate compound represented by the following general formula (1), wherein at least one additive element selected from elements belonging to Group 2 of the periodic table is added to the total mass of the single crystal A scintillator single crystal containing 0.00005 to 0.1% by mass relative to the mass.
Lm _{2− (x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (1)
(Wherein, Lm is Gd, Ln is Y, and G a or al chosen represents at least one element, x is represents 0 ultra 0.5, inclusive, y is greater than 1 value less than 2 Z represents a value greater than 0 and less than or equal to 0.1.) Wherein Ln is Y, a scintillator single crystal according to claim 1, wherein. The x is greater than 0 and less than or equal to 0.2 and smaller than the [2- (x + y + z)], the y is a value greater than 1.6 and less than 2, and the z is greater than 0.001 and 0. .02 or less value, the scintillator single crystal according to claim 1, wherein. Containing 0.00005 wt% of at least one additive element with respect to the total mass of the single crystal selected from the elements belonging to the periodic table group 13, of any one of claims 1 to 3 Single crystal for scintillator. Containing 0.002% by mass or less based on the total weight of the at least one element selected from the elements belonging to the periodic table 4,5,6,14,15 and Group 16 single crystal, according to claim 1-4 The single crystal for scintillators according to any one of claims. A heat treatment method for producing the scintillator single crystal according to any one of claims 1 to 5 ,
The cerium-activated orthosilicate compound represented by the following general formula (1) is included, and at least one additive element selected from elements belonging to Group 2 of the periodic table is added to the total mass of the single crystal by 0.0. After growing a single crystal using a raw material containing a constituent element of a scintillator single crystal containing 00005 to 0.1% by mass, the single crystal is nitrogen or inert having an oxygen concentration of 10 to 100% by volume. A heat treatment method in which heat treatment is performed at a temperature of 700 to 1300 ° C. in an atmosphere containing a gas.
Lm _{2− (x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (1)
(Wherein, Lm is Gd, Ln is Y, and G a or al chosen represents at least one element, x is represents 0 ultra 0.5, inclusive, y is greater than 1 value less than 2 Z represents a value greater than 0 and less than or equal to 0.1.) A method for producing a scintillator single crystal according to any one of claims 1 to 5 ,
The cerium-activated orthosilicate compound represented by the following general formula (1) is included, and at least one additive element selected from elements belonging to Group 2 of the periodic table is added to the total mass of the single crystal by 0.0. Preparing a raw material containing a constituent element of a scintillator single crystal containing 00005 to 0.1% by mass, and growing a single crystal by the Czochralski method;
And a step of heat-treating the single crystal at a temperature of 700 to 1300 ° C. in an atmosphere containing nitrogen or an inert gas having an oxygen concentration of 10 to 100% by volume.
Lm _{2− (x + y + z)} Ln _x Lu _y Ce _z SiO ₅ (1)
(Wherein, Lm is Gd, Ln is Y, and G a or al chosen represents at least one element, x is represents 0 ultra 0.5, inclusive, y is greater than 1 value less than 2 Z represents a value greater than 0 and less than or equal to 0.1.)