Pr-containing scintillator single crystal, method of manufacturing the same, radiation detector, and inspection apparatus
09834858 · 2017-12-05
Assignee
Inventors
- Akira Yoshikawa (Miyagi, JP)
- Hiraku Ogino (Miyagi, JP)
- Kei Kamada (Miyagi, JP)
- Kenji Aoki (Miyagi, JP)
- Tsuguo Fukuda (Miyagi, JP)
Cpc classification
G21K4/00
PHYSICS
G01T1/2985
PHYSICS
C30B29/28
CHEMISTRY; METALLURGY
G01T1/1644
PHYSICS
International classification
C30B15/00
CHEMISTRY; METALLURGY
C30B29/28
CHEMISTRY; METALLURGY
G21K4/00
PHYSICS
G01T1/29
PHYSICS
Abstract
The present invention provides an oxide-base scintillator single crystal having an extremely large energy of light emission, adoptable to X-ray CT and radioactive ray transmission inspection apparatus, and more specifically to provide a Pr-containing, garnet-type oxide single crystal, a Pr-containing perovskite-type oxide single crystal, and a Pr-containing silicate oxide single crystal allowing detection therefrom light emission supposedly ascribable to 5d-4f transition of Pr.
Claims
1. A scintillator single crystal expressed by (Pr.sub.xLu.sub.1−x).sub.3Al.sub.5O.sub.12 where 0.002≦x≦0.02; and the scintillator single crystal emits fluorescence having a wavelength of 200 to 350 nm when excited by gamma ray and having a decay time at room temperature of 1 to 50 nsec, and wherein the scintillator single crystal is a crystal formed by Czochralski method.
2. The scintillator single crystal according to claim 1, wherein the scintillator single crystal has an emission peak at a wavelength of 200 to 350 nm.
3. The scintillator single crystal according to claim 1, wherein the scintillator single crystal has an emission peak at a wavelength of about 300 nm.
4. The scintillator single crystal according to claim 1, wherein a fluorescence decay time of the scintillator single crystal is shorter than 20 nsec.
5. The scintillator single crystal according to claim 1, wherein the scintillator single crystal is expressed by (Pr.sub.xLu.sub.1−x).sub.3Al.sub.5O.sub.12 where 0.002≦x≦0.003.
6. A method of manufacturing the scintillator single crystal of claim 1, comprising charging Pr into a molten liquid expressed by (Pr.sub.xLu.sub.1−x).sub.3Al.sub.5O.sub.12 where 0.002≦x≦0.02, to an amount 5 to 15 times as much as a target amount of incorporation of Pr, and allowing said single crystal to grow by the micro-pulling-down process, using a molybdenum (Mo) crucible, or an iridium (Ir) crucible, or a crucible composed of an alloy of Ir and rhenium (Re).
7. A radiation detector having a scintillator composed of the scintillator single crystal according to claim 1, and configured as having a radiation detection unit detecting radioactive ray, and as being combined therewith a light receiving unit receiving fluorescence output as a result of detection of radioactive ray by said radiation detection unit.
8. A radiation inspection apparatus comprising the radiation detector according to claim 7.
9. The radiation inspection apparatus according to claim 8, being a positron emission tomography (PET) apparatus adoptable to a medical image processing apparatus.
10. The radiation inspection apparatus adoptable to a medical image processing apparatus according to claim 9, wherein said PET is two-dimensional PET, three-dimensional PET, time-of-flight-type (TOF-type) PET, depth-of-interaction-type (DOI-type) PET, or combinations thereof.
11. The radiation inspection apparatus according to claim 10, wherein said radiation inspection apparatus adoptable to said medical image processing apparatus is any one of stand-alone apparatus, magnetic resonance imaging apparatus (MRI), computed tomography apparatus (CT) and single photon computed tomography (SPECT), or combination thereof.
12. A radiation inspection apparatus adoptable to non-destructive inspection having the radiation detector according to claim 7, being either one of X-ray computed tomography apparatus (CT) and radiographic apparatus for radioactive ray transmission inspection, or combination thereof.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The above and other objects, advantages and features of the present invention will be more apparent from the preferable embodiments described below, and the accompanying drawings.
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BEST MODES FOR CARRYING OUT THE INVENTION
(45) Embodiments of the present invention will be explained below.
(46) A scintillator single crystal according to the embodiments of the present invention is a scintillator single crystal expressed by general formula (PrRE).sub.aM.sub.b(O.sub.pF.sub.1−p).sub.c: (where, RE is any one of, or two or more species selected from Y, Sc, Yb, Lu, La and Ce, M is any one species, or more species selected from Al, Ga, Si, Li, Na, K, Cs, Rb, Mg, Ca, Sr, Ba, Sc, Zr, Hf, Mn, Fe, Co, Ni, Cu, Zn, Pd, Cd and Pb, wherein 0<a<10, 0<b<10 and 0<c<50, and p is 0 or 1.)
(47) This embodiment is supposed to make use of light emission ascribable to 5d-4f transition of Pr by contribution of Pr-containing scintillator single crystal, and makes it possible to largely improve the absolute light yield ratio above from 8,200 photons/MeV of BGO.
(48) The scintillator single crystal, capable of emitting fluorescence at 200 to 350 nm, more preferably 200 to 310 nm, when excited by gamma ray, can preferably be used for the purpose of rapid-response radioactive detection.
(49) This sort of scintillator single crystal can be exemplified by oxide-base single crystal and fluoride-base single crystal.
(50) The oxide-base scintillator single crystal of this embodiment is characterized by p=1 in the scintillator single crystal expressed by the above-described general formula, wherein RE is any one species, or two or more species selected from Y, La, Sc, Yb and Lu, M is at least one species selected from Al and Ga, and (a,b,c) is any one of (3,5,12), (1,1,3) and (2,1,5).
(51) A first embodiment of this sort of oxide-base scintillator single crystal relates to a scintillator single crystal composed of a garnet-type oxide expressed by (Pr.sub.xRE.sub.1−x).sub.3(Al.sub.1−yGa.sub.y).sub.5O.sub.12, where, RE is any one of, or two or more species selected from Y, Sc, Yb and Lu, Pr concentration x falls in the range of 0.0001≦x<0.02, preferably 0.001≦x≦0.02, more preferably 0.002≦x≦0.02, and still more preferably 0.002≦x≦0.003. Ga concentration y falls in the range of 0≦y≦1, preferably 0≦y≦0.25 or 0.75≦y≦1, and more preferably y=0 or 1.
(52) This sort of scintillator single crystal composed of a garnet-type oxide is specifically exemplified by a scintillator single crystal composed of a garnet-type oxide expressed by (Pr.sub.xY.sub.1−X).sub.3Al.sub.5O.sub.12 or (Pr.sub.xLu.sub.1−x).sub.3Al.sub.5O.sub.12 (where, Pr concentration x falls in the range described in the above), scintillator single crystal composed of a garnet-type oxide expressed by (Pr.sub.xRE.sub.1−x).sub.3Ga.sub.5O.sub.12 (where, RE is any one species, or two or more species selected from Y, Sc, Yb and Lu, Pr concentration x falls in the range described in the above), and so forth.
(53) A second embodiment of this sort of oxide-base scintillator single crystal relates to a scintillator single crystal composed of a perovskite-type oxide expressed by (Pr.sub.xRE.sub.1−x)AlO.sub.3, where, RE is any one of, or two or more species selected from Y, La, Yb and Lu, Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, and more preferably 0.002≦x≦0.02.
(54) This sort of scintillator single crystal composed of a perovskite-type oxide is specifically exemplified by a scintillator single crystal composed of a perovskite-type oxide expressed by (Pr.sub.xY.sub.1−x)AlO.sub.3, (Pr.sub.xLa.sub.1−x)AlO.sub.3 or (Pr.sub.xLu.sub.1−x)AlO.sub.3 (where, Pr concentration x falls in the range described in the above).
(55) Although not covered by the above-described general formula of the scintillator single crystal composed of a perovskite-type oxide, also those having Lu replaced at the site of Al are adoptable, examples of which include (Pr.sub.xLa.sub.1−x)LuO.sub.3.
(56) A third embodiment of this sort of oxide-base scintillator single crystal relates to a scintillator single crystal composed of a silicate oxide expressed by (Pr.sub.xRE.sub.1−x).sub.2SiO.sub.5, where, RE is any one of, or two or more species selected from Y, La, Yb and Lu, Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, and more preferably 0.002≦x≦0.02.
(57) This sort of scintillator single crystal composed of a perovskite-type oxide is specifically exemplified by a scintillator single crystal composed of a silicate oxide expressed by (Pr.sub.xY.sub.1−x).sub.2SiO.sub.5 or (Pr.sub.xLu.sub.1−x).sub.2SiO.sub.5 (where, Pr concentration x falls in the range described in the above).
(58) The scintillator single crystal of this embodiment composed of other oxide is characterized by p=1 in the scintillator single crystal expressed by the above-described general formula, wherein RE is any one species, or two or more species selected from Y, Sc, Yb and Lu, M is at least one species selected from Al, Ga, Mg, Ca, Sr, Sc, Zr and Hf, and (a,b,c) is (3,5,12).
(59) The scintillator single crystal composed of this sort of oxide is specifically exemplified by a scintillator single crystal composed of a garnet-type oxide expressed by (Pr.sub.xY.sub.1−x).sub.3(Al.sub.1−ySc.sub.y).sub.5O.sub.12 or (Pr.sub.xLu.sub.1−x).sub.3(Al.sub.1−ySC.sub.y).sub.5O.sub.12, where, Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, more preferably 0.002≦x≦0.02, Sc concentration y falls in the range of 0≦y≦0.4, more preferably 0≦y0.01.
(60) In addition, also a scintillator single crystal expressed by (Pr.sub.xRE.sub.1−x).sub.3(M.sup.1.sub.yM.sup.2.sub.1−2yM.sup.3.sub.y).sub.5O.sub.12 can preferably be used, where, RE is any one species, or two or more species selected from Y, Sc, Yb and Lu, M.sup.1 is any one species, or two or more species selected from Mg, Ca and Sr, M.sup.2 is any one species, or two or more species selected from Al, Ga and SC, M.sup.3 is one species or two or more species selected from Zr and Hf, Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, more preferably 0.002≦x≦0.02, and concentration y falls in the range of 0≦y≦0.5, and more preferably 0≦y≦0.1.
(61) As the oxide-base scintillator single crystals, the scintillator single crystals of rare earth oxides described below are also adoptable.
(62) As this sort of scintillator single crystal composed of a rare earth oxide, a scintillator single crystal composed of a rare earth oxide expressed by (Pr.sub.xRE.sub.1−x).sub.2O.sub.3 is adoptable, where RE is anyone species, or two or more species selected from Y, Sc, La, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, and still more preferably 0.002≦x≦0.02.
(63) This sort of scintillator single crystal composed of a rare earth oxide is specifically exemplified by a scintillator single crystal composed of a rare earth oxide expressed by (Pr.sub.xY.sub.1−x).sub.2O.sub.3, (Pr.sub.xSc.sub.1−x).sub.2O.sub.3, (Pr.sub.xLa.sub.1−x).sub.2O.sub.3 or (Pr.sub.xLu.sub.1−x).sub.2O.sub.3 (where, Pr concentration x falls in the range described in the above).
(64) As the scintillator single crystal composed of still another rare earth oxide, a scintillator single crystal composed of a rare earth oxide expressed by Pr.sub.xRE.sub.1−xVO.sub.4 is adoptable, where, RE is any one species, or two or more species selected from Y, Sc, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, and more preferably 0.002≦x≦0.02.
(65) As the scintillator single crystal composed of still another rare earth oxide, a scintillator single crystal composed of a rare earth oxide expressed by (Pr.sub.xRE.sub.1−x)RE′O.sub.3 is adoptable, where, RE and RE′, differing from each other, are any one species, or two or more species selected from La, Gd, Y, Sc, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, and more preferably 0.002≦x≦0.02.
(66) As the scintillator single crystal composed of still another rare earth oxide, a scintillator single crystal composed of a rare earth oxide expressed by (Pr.sub.xRE.sub.1−x).sub.2Si.sub.2O.sub.7 is adoptable, where, RE is any one species, or two or more species selected from Y, Sc, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.3, more preferably 0.001≦x<0.05, and more preferably 0.002≦x≦0.02.
(67) The fluoride-base scintillator single crystal of this embodiment corresponds to the case of p=0 in the scintillator single crystal expressed by the above-described general formula. RE is any one species, or two or more species selected from La, Ce, Yb, Lu and Y, and among others, Y, Yb or Lu is particularly preferable. M is any one species or more selected from Li, Na, K, Cs, Rb, Mg, Ca, Sr, Ba, Al, Mn, Fe, Co, Ni, Cu, Zn, Pd, Cd, Pb, Zr and Hf.
(68) A first embodiment of such fluoride-base scintillator single crystal relates to a scintillator single crystal expressed by Pr.sub.wM.sub.xRE.sub.yF.sub.z, where, RE is any one of, or two or more species selected from La, Ce, Yb, Lu and Y, and M is any one or more species selected from Li, Na, K, Cs, Rb, Mg, Ca, Sr, Ba and Al. w, x and z respectively satisfy 0.0001≦w<0.3, 0<x<10, 0<y<10 and 0<z<50.
(69) This sort of fluoride-base scintillator single crystal can be exemplified by those having K (potassium atom) as M in the above-described general formula fluoride-base scintillator single crystal, and more specifically by a scintillator single crystal expressed by K(RE.sub.1−wPr.sub.w).sub.3F.sub.10 (where, RE is any one species, or two or more solid solutions selected from La, Ce, Yb, Lu and Y, and 0.0001≦w<0.3.)
(70) The fluoride-base scintillator single crystal can specifically be exemplified by a scintillator single crystal expressed by Ba.sub.x(RE.sub.1−wPr.sub.w)F.sub.z (where, RE is any one species, or two or more solid solutions selected from La, Ce, Yb, Lu and Y, and 0.0001≦w<0.3.)
(71) For these fluoride-base scintillator single crystals, those having Y, or a solid solution of Y and Lu as RE are preferable.
(72) As another fluoride-base scintillator single crystal, a scintillator single crystal expressed by Pr.sub.wM.sub.xF.sub.z can specifically be exemplified (where, M is any one species, or more species selected from Li, Na, K, Cs, Rb, Mg, Ca, Sr, Ba and Al, and 0.0001≦w<0.3, 0<x<10, 0<z<50.)
(73) Of the above-described fluoride-base scintillator single crystals of this embodiment expressed by Pr.sub.wM.sub.xRE.sub.yF.sub.z or Pr.sub.wM.sub.xF.sub.z, particularly preferable examples include (Pr.sub.w(Lu,Y).sub.1−w)KF.sub.10, (Pr.sub.w(Gd,Y).sub.1−w)KF.sub.10, (Pr.sub.wRE.sub.1−w)Ba.sub.xF.sub.z, (Pr.sub.wYb.sub.2−w)BaF.sub.8 or Ba.sub.2(Pr.sub.wYb.sub.1−w)F.sub.7, and specific examples thereof include the followings.
(74) K(Y.sub.0.99Pr.sub.0.01).sub.3F.sub.10, K(Y.sub.0.59Yb.sub.0.4Pr.sub.0.01).sub.3F.sub.10, K(Y.sub.0.59Gd.sub.0.4Pr.sub.0.01).sub.3F.sub.10, K(Y.sub.0.59Lu.sub.0.4Pr.sub.0.01).sub.3F.sub.10, Ba(Y.sub.0.97Pr.sub.0.03).sub.2F.sub.8, Cs.sub.3(Y.sub.0.99Pr.sub.0.01)F.sub.6) Ba(Lu.sub.0.999Pr.sub.0.001)F.sub.8, Li(Lu.sub.0.95Pr.sub.0.05)F.sub.4, K(Y.sub.0.89Ce.sub.0.10P.sub.r0.01).sub.3F.sub.10, K(Y.sub.0.89La.sub.0.10Pr.sub.0.01).sub.3F.sub.10, (Y.sub.0.89Gd.sub.0.10Pr.sub.0.01).sub.3F.sub.10, Pr.sub.0.01Mg.sub.0.99F.sub.2.01, Pr.sub.0.03Ca.sub.0.97F.sub.2.03, Pr.sub.0.05Sr.sub.0.95F.sub.2.05, Pr.sub.0.001Ba.sub.0.999F.sub.2.001, Pr.sub.0.01Mn.sub.0.99F.sub.2.01, Pr.sub.0.001LiCaAlF.sub.6, P.sub.r0.001LiSrAlF.sub.6, Pr.sub.0.001NaCaAlF.sub.6, Pr.sub.0.001BaMgF.sub.4, Ba.sub.2(Pr.sub.0.01La.sub.0.99)F.sub.7, Ba.sub.2(Pr.sub.0.01Ce.sub.0.99)F.sub.7, Ba.sub.2(Pr.sub.0.01Gd.sub.0.99)F.sub.7, Ba.sub.2(Pr.sub.0.01Yb.sub.0.99)F.sub.7, Ba.sub.2(Pr.sub.0.01Lu.sub.0.99)F.sub.7, Ba.sub.2(Pr.sub.0.01Y.sub.0.99)F.sub.7, Ba(Pr.sub.0.01Yb.sub.1.99)F.sub.8, KLu.sub.3F.sub.10, etc.
(75) With respect to the composition of the fluoride-base scintillator single crystals of this embodiment expressed by Pr.sub.wM.sub.xRE.sub.yF.sub.z or Pr.sub.wM.sub.xF.sub.z, an absolute light yield ratio (photons/MeV) of 1,000 to 200,000 (photons/MeV) or around is achievable, preferably 8,000 to 200,000 (photons/MeV), more preferably 80,000 to 200,000 (photons/MeV), and in particular 8,000 to 120,000 (photons/MeV) is preferable, 16,000 to 80,000 (photons/MeV) is more preferable, representing an extremely high energy of light emission of the fluoride-base scintillator crystal. More specifically, the absolute light yield ratio relative to that of BGO is expressed by a factor of 0.125 to 25, preferably 1 to 25, and more preferably 10 to 25. The ratio is preferably expressed by a factor of 1 to 15, and more preferably 2 to 10, in view of technical effect when correlation with elongation of the fluorescence lifetime due to energy transition is taken into consideration.
(76) In the composition of the fluoride-base scintillator single crystal expressed by Pr.sub.wM.sub.xRE.sub.yF.sub.z or Pr.sub.wM.sub.xF.sub.z, Pr concentration w falls in the range of 0.0001≦w<0.3000, preferably 0.0010≦w<0.0500, and more preferably 0.0020≦w≦0.0200. Because x, y and z are arbitrarily determined depending on the crystal composition, and are therefore not specifically limited, wherein they are preferably 0<x<10.0000 and more preferably 0<x<4.0000, 0<y<10.0000 and more preferably 0<y<4.0000, and 0<z<50.0000 and more preferably 0<z<20.0000. More specifically, for the case where M is K, x=1, y=3 and z=10 preferably, that is, K(Pr.sub.wRE.sub.1−w).sub.3F.sub.10 is preferable. Also in this case, Pr concentration w falls in the range of 0.0001≦w<0.3000, preferably 0.0001≦w<0.0500, and more preferably 0.0020≦w≦0.0200, wherein RE is one species or two or more rare earth elements selected from La, Ce, Gd, Lu, Y and Yb, and among others, Y, Gd, Yb or Lu is particularly preferable.
(77) For the case where M is Ba, x=2, y=1 and z=7 preferably, or x=1, y=2 and z=8 preferably, that is, Ba.sub.2(Pr.sub.wRE.sub.1−w)F.sub.7 or Ba(Pr.sub.wRE.sub.1−w).sub.2F.sub.8 is preferable. Also in this case, Pr concentration w falls in the range of 0.0001≦w<0.3000, preferably 0.0010≦w<0.0500, and more preferably 0.0020≦w≦0.0200, wherein RE is one species, or two or more species of rare earth element selected from La, Ce, Gd, Lu, Y and Yb, and among others, Y, Gd, Yb or Lu is preferable.
(78) Next, the method of manufacturing the oxide or fluoride-base scintillator single crystal according to the present invention will be explained.
(79) The method of manufacturing according to this embodiment is characterized by charging Pr into a molten crystal having a composition expressed by (PrRE).sub.aM.sub.b(O.sub.pF.sub.1−p).sub.c, to an amount 5 to 15 times as much as a target Pr content, and allowing a single crystal to grow by the micro-pulling-down process using a molybdenum (Mo) crucible, or a iridium (Ir) crucible, or a crucible composed of an alloy of Ir and rhenium (Re).
(80) In this case, RE is any one of, or two or more species selected from Y, Sc, Yb, Lu, La and Ce, M is any one species, or more species selected from Al, Ga, Si, Li, Na, K, Cs, Rb, Mg, Ca, Sr, Ba, Sc, Zr, Hf, Mn, Fe, Co, Ni, Cu, Zn, Pd, Cd and Pb, 0<a<10, 0<b<10 and 0<c<50, and p is 0 or 1.
(81) The method of manufacturing the scintillator single crystal is given herein as a method of manufacturing a scintillator single crystal composed of an oxide, when p=1 in the composition of the molten crystal expressed by the above-described general formula.
(82) This sort of method of manufacturing can specifically be exemplified by a method of manufacturing a scintillator single crystal composed of a garnet-type oxide, wherein the molten crystal has a composition allowing a single crystal expressed by (Pr.sub.xRE.sub.1−x).sub.3(Al.sub.1−yGa.sub.y).sub.5O.sub.12 to produce, and has a Pr concentration of 5x to 15x, where, RE is any one species, or two or more species selected from Y, Sc, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.02, preferably 0.001≦x≦0.02, more preferably 0.002≦x≦0.02, and still more preferably 0.002≦x≦0.003. Ga concentration y falls in the range of 0≦y≦1, preferably 0≦y≦0.25 or 0.75≦y≦1, and more preferably y=0 or 1.
(83) In this sort of method of manufacturing a scintillator single crystal composed of a garnet-type oxide, the molten crystal preferably has a composition allowing a single crystal expressed by (Pr.sub.xY.sub.1−x).sub.3Al.sub.5O.sub.12, (Pr.sub.xLu.sub.1−x).sub.3Al.sub.5O.sub.12, or (Pr.sub.xRE.sub.1−x).sub.3Ga.sub.5O.sub.12 to be obtained, and has a Pr concentration of 5x to 15x, where, RE is any one of, or two or more species selected from Y, Sc, Yb and Lu. Pr concentration x falls in the range described in the above.
(84) This sort of method of manufacturing can specifically be exemplified by a method of manufacturing a scintillator single crystal composed of a perovskite-type oxide, wherein the molten crystal has a composition allowing a single crystal expressed by (Pr.sub.xRE.sub.1−x)AlO.sub.3 to produce, and has a Pr concentration of 5x to 15x.
(85) In this case, RE is any one of, or two or more species selected from Y, La, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, and more preferably 0.002≦x≦0.02.
(86) In this sort of method of manufacturing a scintillator single crystal composed of a perovskite-type oxide, the molten crystal preferably has a composition allowing a single crystal expressed by (Pr.sub.xY.sub.1−x)AlO.sub.3, (Pr.sub.xLa.sub.1−x)AlO.sub.3 or (Pr.sub.xLu.sub.1−x)AlO.sub.3 to produce, and has a Pr concentration of 5x to 15x. Pr concentration x falls in the range described in the above.
(87) This sort of method of manufacturing can specifically be exemplified by a method of manufacturing a scintillator single crystal composed of a silicate oxide, wherein the molten crystal has a composition allowing a single crystal expressed by (Pr.sub.xRE.sub.1−x).sub.2SiO.sub.5 to produce, and has a Pr concentration of 5x to 15x.
(88) In this case, RE is any one of, or two or more species selected from Y, La, Yb and Lu. Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, and more preferably 0.002≦x≦0.02.
(89) In this sort of method of manufacturing a scintillator single crystal composed of a silicate oxide, the molten crystal preferably has a composition allowing a single crystal expressed by (Pr.sub.xY.sub.1−x).sub.2SiO.sub.5 or (Pr.sub.xLu.sub.1−x).sub.2SiO.sub.5 to produce, and has a Pr concentration of 5x to 15x. Pr concentration x falls in the range described in the above.
(90) This embodiment also relates to a method of manufacturing a scintillator single crystal composed of a rare earth oxide, characterized by growing the single crystal from a molten crystal having a composition which allows a single crystal expressed by (Pr.sub.xRE.sub.1−x).sub.2O.sub.3 to produce, and having a Pr concentration of 5x to 15x, by the micro-pulling-down process using a Re crucible.
(91) In this case, RE is any one species, or two or more species selected from Y, Sc, La, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.3, preferably 0.001≦x<0.05, and more preferably 0.002≦x≦0.02.
(92) In this sort of method of manufacturing a scintillator single crystal composed of a rare earth oxide, the molten crystal may have a composition allowing a single crystal expressed by (Pr.sub.xY.sub.1−x).sub.2O.sub.3, (Pr.sub.xSc.sub.1−x).sub.2O.sub.3, (Pr.sub.xLa.sub.1−x).sub.2O.sub.3 or (Pr.sub.xLu.sub.1−x).sub.2O.sub.3 to produce, and a Pr concentration of 5x to, 15x (where, Pr concentration x falls in the range described in the above).
(93) The method of manufacturing a scintillator single crystal composed of an oxide of this embodiment also includes the followings.
(94) (1) A method of manufacturing a scintillator single crystal composed of a garnet-type oxide, characterized by growing a single crystal from a molten crystal having a composition which allows a single crystal expressed by (Pr.sub.xY.sub.1−x).sub.3(Al.sub.1−ySc.sub.y).sub.5O.sub.12 or (Pr.sub.xLu.sub.1−x).sub.3(Al.sub.1−ySc.sub.y).sub.5O.sub.12 to produce, and having a Pr concentration of 5x to 15x, by the micro-pulling-down process using a Mo crucible, or an Ir crucible, or a crucible composed of an alloy of Ir and Re (where, Pr concentration x falls in the range of 0.0001≦x<0.3, and Sc concentration y falls in the range of 0≦y≦0.4):
(95) (2) A method of manufacturing a scintillator single crystal composed of a garnet-type oxide, characterized by growing a single crystal from a molten crystal having a composition which allows a single crystal expressed by (Pr.sub.xRE.sub.1−x).sub.3(M.sup.1.sub.yM.sup.2.sub.1−2yM.sup.3.sub.y).sub.5O.sub.12 to produce, and having a Pr concentration of 5x to 15x, by the micro-pulling-down process using a Mo crucible, or Ir crucible, or a crucible composed of an alloy of Ir and Re (where, RE is any one species, or two or more species selected from Y, Sc, Yb and Lu, M.sup.1 is any one species, or two or more species selected from Mg, Ca and Sr, M.sup.2 is any one species, or two or more species selected from Al, Ga and Sc, M.sup.3 is one species, or two or more species of metal selected from Zr and Hf, Pr concentration x falls in the range of 0.0001≦x<0.3, and concentration y falls in the range of 0≦y<0.5):
(96) (3) A method of manufacturing a scintillator single crystal composed of a rare earth oxide, characterized by growing a single crystal from a molten crystal having a composition which allows a single crystal expressed by RePr.sub.xRE.sub.1−xVO.sub.4 to produce, and having a Pr concentration of 5x to 15x, by the micro-pulling-down process using a Mo crucible, or Ir crucible, or a crucible composed of an alloy of Ir and Re (where, RE is any one species, or two or more species selected from Y, Sc, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.3):
(97) (4) A method of manufacturing a scintillator single crystal composed of a rare earth oxide, characterized by growing a single crystal from a molten crystal having a composition which allows a single crystal expressed by (Pr.sub.xRE.sub.1−x)RE′O.sub.3 to produce, and having a Pr concentration of 5x to 15x, by the micro-pulling-down process using a Mo crucible, or Ir crucible, or a crucible composed of an alloy of Ir and Re (where, RE and RE′, differing from each other, are any one species, or two or more species selected from La, Gd, Y, Sc, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.3):
(98) (5) A method of manufacturing a scintillator single crystal composed of a rare earth oxide, characterized by growing a single crystal from a molten crystal having a composition which allows a single crystal expressed by (Pr.sub.xRE.sub.1−x).sub.2Si.sub.2O.sub.7 to produce, and having a Pr concentration of 5x to 15x, by the micro-pulling-down process using a Mo crucible, or Ir crucible, or a crucible composed of an alloy of Ir and Re (where, RE is any one species, or two or more species selected from Y, Sc, Yb and Lu, and Pr concentration x falls in the range of 0.0001≦x<0.3).
(99) In the method of manufacturing all of these oxides, any general oxide materials can be used as the starting materials, but for the case where use as the scintillator single crystal is aimed at, use of high-purity source materials of 99.99% or above (4N or above) is particularly preferable, wherein these starting materials are weighed and mixed so as to attain a target composition when the molten crystal is formed. It is particularly preferable that these source materials are extremely low in the content of impurities other than target components (1 ppm or below, for example). It is particularly preferable to use source materials containing almost no elements (Tb, for example) showing light emission at around the emission wavelength.
(100) Growth of the crystal is preferably allowed to proceed under an atmosphere of an inert gas (Ar, N.sub.2, He, etc., for example). It is also allowable to use a mixed gas of an inert gas (Ar, N.sub.2, He, etc., for example) and oxygen gas. It is to be noted that, for the case where the growth of the crystal is allowed to proceed using the mixed gas, partial pressure of oxygen is preferably adjusted to 2% or below, in view of preventing oxidation of the crucible. In the post-processes such as annealing after the crystal growth, oxygen gas, inert gas (Ar, N.sub.2, He, etc., for example), and mixed gas of inert gas (Ar, N.sub.2, He, etc., for example) and oxygen gas can be used. When the mixed gas is used, the partial pressure of oxygen is not limited to 2%, allowing adoption of any ratio of mixing ranging from 0% to 100%.
(101) Besides the micro-pulling-down process, any of the Czochralski method (pulling-up process), the Bridgeman method, the zone melting process, or the edge-defined, film-fed growth process (EFG process) and so forth are adoptable without special limitation as the method of manufacturing the scintillator single crystal composed of the oxide according to this embodiment, wherein the Czochralski method or the Bridgeman method is preferable, in view of obtaining a large-sized single crystal for the purpose of improving the yield ratio and relatively reducing the process loss. On the other hand, so far as only a small-sized single crystal is used as the scintillator single crystal, the zone melting process, the EFG process, the micro-pulling-down process and the Czochralski method are preferable because there is no need, or only a small need of post-processing, wherein the micro-pulling-down process and the zone melting process are particularly preferable, for reasons of wettability with the crucible and so forth. The concentration of Pr in the molten crystal at the time of charging is adjusted to approximately 5 to 15 times as much as the target amount of incorporation, although being susceptible to change depending on the process of manufacturing to be adopted.
(102) It is also allowable to compose the crucible and after-heater adopted herein using platinum, iridium, rhodium, rhenium, or alloys thereof.
(103) Not only the high-frequency oscillator, but also a resistance heater is adoptable.
(104) Paragraphs below will describe the method of manufacturing the scintillator single crystal composed of the oxide of this embodiment, referring to an exemplary case of adopting the method of manufacturing the single crystal based on the micro-pulling-down process, without being limited thereto.
(105) The micro-pulling-down process is allowed to proceed using an atmosphere-adjustable, micro-pulling-down apparatus making use of high-frequency induction heating. The micro-pulling-down apparatus has a crucible, a seed holding jig holding a seed to be brought into contact with a molten crystal discharged from a fine orifice provided at the bottom of the crucible, a moving mechanism moving the seed holding jig downward, a moving speed control device for the moving mechanism, and an induction heating unit heating the crucible. The single crystal manufacturing apparatus is configured to manufacture a single crystal by forming the solid-liquid interface straight under the crucible, and by moving the seed crystal downward.
(106) The crucible is made of carbon, platinum, iridium, rhodium, rhenium, or alloy thereof, and an after-heater, which is a heating element composed of carbon, platinum, iridium, rhodium, rhenium, or alloy thereof, is disposed at the outer circumference of the bottom of the crucible. The crucible and the after-heater are configured as being adjustable in the energy of heat generation through adjustment of the output of the induction heating unit, so as to control the temperature and distribution thereof of the solid-liquid interface area of the molten crystal drawn out from the fine orifice provided to the bottom of the crucible.
(107) The apparatus is also configured as using SUS as a chamber material, using SiO.sub.2 window component, providing a rotary pump so as to enable atmospheric control, so that a degree of vacuum of 1×10.sup.−3 Torr or below can be achieved before the gas replacement. The chamber can be supplied with Ar, N.sub.2, H.sub.2, O.sub.2 gas or the like, after being precisely controlled in the flow rate thereof using an attached gas flow meter.
(108) Using this apparatus, the source material prepared according to the above-described method is placed in the crucible, the inner space of the furnace is evacuated to a high degree of vacuum, Ar gas or a mixed gas of Ar gas and O.sub.2 gas is introduced into the furnace so as to adjust the inner space of the furnace to an inert gas atmosphere or an atmosphere with low partial pressure of oxygen, the crucible is heated by gradually applying high-frequency power to a high-frequency induction heating coil, to thereby completely melt the source material in the crucible.
(109) Next, the crystal is grown according to the procedures below. The seed crystal is gradually elevated at a predetermined speed, the tip thereof is brought into contact with the orifice at the lower end of the crucible so as to thoroughly run it thereinto, and the crystal is grown by descending a pulling-down axis while controlling the temperature of the molten crystal. The seed crystal is preferably equivalent to a target substance to be grown up to a crystal, or such as having both of structure and composition close thereto, but is not limited thereto. The seed crystal used herein preferably has clearly defined orientation. The crystal growth comes to the end, when the entire portion of the available material crystallizes, leaving no residual molten crystal. On the other hand, a device for consecutive charging of the source material may be incorporated, for the purpose of keeping the composition uniform, and of producing a long crystal.
(110) Paragraphs below will describe a method of manufacturing the scintillator single crystal composed of the oxide of this embodiment, also exemplifying an embodiment of using the pulling-up process, without limiting the embodiment.
(111) The Czochralski (pulling-up) process is allowed to proceed using an apparatus based on high-frequency induction heating.
(112) The Czochralski method is a method of manufacturing a single crystal, by which a source material is placed into a crucible, the crucible is heated so as to melt the source material placed therein, and a seed crystal is dipped into the molten source material and pulled up so as to allow the single crystal to grow.
(113) More specifically, this is a method of manufacturing a single crystal based on the pulling-up process, wherein the ratio of temperature gradient between the center and outer end of the single crystal as viewed on the horizontal section over the span of length of pulling-up is controlled to as small as 1.25 or below, and particularly to 1 or around, by intercepting the radiation heat directed from the surface of the molten crystal to the single crystal grown up while being pulled up above the molten crystal, by promoting heat radiation from the upper solidified portion of the single crystal, so as to moderate the temperature gradient in the direction of axis of the single crystal over the span of length of pulling-up ranging from the lower portion, which falls on the melting point side, up to the top portion thereof, and by keeping the temperature of the single crystal through suppression of heat radiation from the outer circumferential surface portion thereof, over the span of length of pulling-up ranging from the lower portion, which falls on the melting point side, up to the top portion thereof.
(114) The method of manufacturing the scintillator single crystal is given as a method of manufacturing a fluoride-base scintillation single crystal, if p=0 is defined in the composition of the molten crystal expressed by the general formula described in the above.
(115) This sort of method of manufacturing can specifically be exemplified by a method of growing the single crystal based on the micro-pulling-down process, by adopting the molten crystal having a composition which allows a single crystal expressed by Pr.sub.wM.sub.xRE.sub.yF.sub.z to produce, and a Pr concentration of 5w to 15w.
(116) In this case, RE is any one species, or two or more species selected from La, Ce, Yb, Lu and Y, M is any one species, or more species selected from Li, Na, K, Cs, Rb, Mg, Ca, Sr, Ba and Al, and 0.0001≦w<0.3, 0<x<10, 0<y<10 and 0<z<50.
(117) It is to be noted herein that, as described previously, the Pr concentration w falls in the range of 0.0001≦w<0.3000, preferably 0.0010≦w<0.0500, and more preferably 0.0020≦w≦0.0200. Because x, y and z are arbitrarily determined depending on the crystal composition, and are therefore not specifically limited, wherein they are preferably 0<x<10.0000 and more preferably 0<x<4.0000, 0<y<10.0000 and more preferably 0<y<4.0000, and 0<z<50.0000 and more preferably 0<z<20.0000.
(118) In the method of manufacturing the fluoride-base scintillator single crystal, the starting materials applicable herein may be any general fluoride materials, but for the case where use as the scintillator single crystal is aimed at, use of high-purity source materials of 99.9% or above (3N or above) is particularly preferable, wherein these starting materials are weighed and mixed so as to attain a target composition. It is particularly preferable that these source materials are extremely low in the content of impurities other than target components (1 ppm or below, for example). The source materials used herein are preferably such as having an oxygen concentration of 1,000 ppm or below, and particularly preferably such as having an oxygen concentration of 100 ppm or below. However, even for the case where the source materials having high oxygen concentrations are used, a crystal of high quality can be obtained by pre-treating the materials under an atmosphere of a fluorine compound gas, or by adding a 10% or smaller amount of a fluorine compound as a scavenger, so as to produce a melt of low oxygen state (100 ppm or below, for example) at the time of crystal growth.
(119) The fluoride-base scintillator material expressed by Pr.sub.wM.sub.xRE.sub.yF.sub.z or Pr.sub.wM.sub.xF.sub.z, containing rare earth fluoride, can readily be converted into rare earth oxyfluorides if a trace amount of oxygen remains.
(120) The crystal growth is preferably allowed to proceed under a vacuum atmosphere, an inert gas atmosphere, extremely-low-oxygen atmosphere, and further in a fluorine-compound-containing atmosphere. The same will apply not only to the step of crystal growth (single crystal manufacturing step), but also to the pre-processes such as melting the source materials, and to the post-processes such as annealing. The fluorine-compound-containing gas used herein is particularly preferably CF.sub.4 which is generally used, whereas F.sub.2 gas, HF gas, BF.sub.3 gas and the like are also applicable. These gases may be used as being diluted with an inert gas (Ar, N.sub.2, He, etc., for example).
(121) As the method of manufacturing the fluoride-base scintillator single crystal expressed by Pr.sub.wM.sub.xRE.sub.yF.sub.z or Pr.sub.wM.sub.xF.sub.z of this embodiment, any of the micro-pulling-down process, the Czochralski method (pulling-up process), the Bridgeman method, the zone melting process, or the EFG process and so forth are adoptable without special limitation, wherein the Czochralski method or the Bridgeman method is preferable, in view of obtaining a large-sized single crystal for the purpose of improving the yield ratio and relatively reducing the process loss. On the other hand, so far as only a small-sized single crystal is used as the scintillator single crystal, the zone melting process, the EFG process, the micro-pulling-down process and the Czochralski method are preferable because there is no need, or only a small need of post-processing, wherein the micro-pulling-down process and the zone melting process are particularly preferable, for reasons of wettability with the crucible and so forth. The concentration of Pr contained in the molten crystal at the time of charging is adjusted to approximately 5 to 15 times as much as the target amount of incorporation, although being susceptible to change depending on the process of manufacturing to be adopted.
(122) Because the melting points of all of the fluoride-base source materials adopted herein are lower than 1,300° C., a temperature of lower than 1,300° C. is good enough in any of crystal growth techniques including the micro-pulling-down process, the Czochralski method, the Bridgeman method, the zone melting process and the EFG process. Therefore, output of the high-frequency oscillator can significantly be lowered, and the cost of manufacturing can consequently be reduced. Moreover, not only the high-frequency oscillator, but also a resistor heater is applicable. Although the crucible and the after-heater adopted may be composed of platinum, iridium, rhodium, rhenium, or alloy thereof, it is made possible herein to use carbon, which is not suitable for the step of forming the oxide crystal such as GSO, so that the cost of manufacturing can further be reduced.
(123) For example, K(Y.sub.0.99Pr.sub.0.01).sub.3F.sub.10 has a melting point of 1,050° C., indicating that it is extremely lower than 2,150° C. shown by Ce:LSO.
(124) Paragraphs below will describe the method of manufacturing the fluoride-base scintillator single crystal of this embodiment, referring to an exemplary method of manufacturing a single crystal based on the micro-pulling-down process, without limiting the invention.
(125) The micro-pulling-down process is allowed to proceed using an atmosphere-adjustable, micro-pulling-down apparatus making use of high-frequency induction heating. The micro-pulling-down apparatus has a crucible, a seed holding jig holding a seed to be brought into contact with a molten crystal discharged from a fine orifice provided at the bottom of the crucible, a moving mechanism moving the seed holding jig downward, a moving speed control device for the moving mechanism, and an induction heating unit heating the crucible. The single crystal manufacturing apparatus is configured to manufacture a single crystal by forming the solid-liquid interface straight under the crucible, and by moving the seed crystal downward.
(126) The crucible is made of carbon, platinum, iridium, rhodium, rhenium, or alloy thereof, and an after-heater, which is a heating element composed of carbon, platinum, iridium, rhodium, rhenium, or alloy thereof, is disposed at the outer circumference of the bottom of the crucible. The crucible and the after-heater are configured as being adjustable in the energy of heat generation through adjustment of the output of the induction heating unit, so as to control the temperature and distribution thereof of the solid-liquid interface area of the molten crystal drawn out from the fine orifice provided to the bottom of the crucible.
(127) This precision atmosphere-controllable, micro-pulling-down apparatus can precisely control the atmosphere in the chamber, so as to enable growth of fluoride crystals. The apparatus is configured as adopting SUS and CaF.sub.2 as the materials composing the chamber and the window component, respectively, having a diffusion pump or a turbo molecular pump in addition to an already-equipped rotary pump, so as to enable evacuation to a high degree of vacuum which is most important in the growth of fluoride crystals, so that a degree of vacuum of 1×10.sup.−3 Torr or below can be achieved. The chamber can be supplied with CF.sub.4, Ar, N.sub.2, H.sub.2 gas or the like, after being precisely controlled in the flow rate thereof using an attached gas flow meter.
(128) Using this apparatus, the source material prepared according to the above-described method is placed in the crucible, the inner space of the furnace is evacuated to a high degree of vacuum, baking is carried out so as to remove moisture adhered on the surfaces, and a high-purity Ar gas (6N grade) or a high-purity CF.sub.4 gas (6N grade) is introduced into the furnace so as to adjust the inner space of the furnace to an inert gas atmosphere or a fluorine compound gas atmosphere, the crucible is heated by gradually applying high-frequency power to a high-frequency induction heating coil, to thereby completely melt the source material in the crucible.
(129) Next, the crystal is grown according to the procedures below. The seed crystal is gradually elevated at a predetermined speed, the tip thereof is brought into contact with the orifice at the lower end of the crucible so as to thoroughly run it thereinto, and the crystal is grown by descending a pulling-down axis while controlling the temperature of the molten crystal. The seed crystal is preferably equivalent to a target substance to be grown up to a crystal, or such as having both of structure and composition close thereto, but is not limited thereto. The seed crystal used herein preferably has clearly defined orientation. The crystal growth comes to the end, when the entire portion of the available material crystallizes leaving no residual molten crystal. On the other hand, a device for consecutive charging of the source material may be incorporated, for the purpose of keeping the composition uniform, and of producing a long crystal.
(130) Also in the method of manufacturing a fluoride-base scintillator single crystal of this embodiment, the above-described, pulling-up process is adoptable.
(131) The oxide or the fluoride-base scintillator single crystal of this embodiment can be configured to give a scintillator, and can further be combined with a radiation detection unit detecting radioactive ray, and with a light receiving unit receiving fluorescence emitted as a result of detection of the radioactive ray by the radiation detection unit, so as to make it available as a radiation detector. It is also allowable to compose a radiation inspection apparatus equipped with the radiation detector.
(132) The radiation inspection apparatus is suitable for applications of medical image processing apparatus, such as positron emission tomography apparatus (PET), X-ray CT, SPECT and the like. As for modes of PET, preferable examples include two-dimensional PET, three-dimensional PET, time-of-flight (TOF) PET and depth-of-interaction (DOI) PET. These may be used in combination.
(133) The light receiving unit used in the radiation detector of this embodiment can be exemplified by position-sensitive photomultiplier (PS-PMT), photodiode (PD) or avalanche-photodiode (APD).
(134)
(135) A PET apparatus 100 shown in
(136) Each radiation detector 110 is composed of a scintillator array 111, a photomultiplier 112 and an amplifier 113, so as to detect γ ray emitted out from a specific site, and to finally convert it into electric signals.
(137) The scintillator array 111 is configured as having a plurality of scintillators which functions as γ ray detection units arranged in an array. Each scintillator is excited by γ ray, and then causes transition to a more stable energy level, while emitting fluorescence in the ultraviolet wavelength range. The fluorescence is, as described in the above, supposedly ascribable to 5d-4f transition, and have a wavelength of 200 to 350 nm, wherein a fluorescence lifetime of 1 to 300 ns or around, as described later.
(138) Each photomultiplier 112 functions as a light receiving unit receiving the fluorescence. The photomultiplier 112 amplifies the fluorescence emitted from the correspondent scintillator array 111, and converts it into an electric signal.
(139) Thus converted electric signal is amplified by the amplifier 113. In this way, γ ray is detected by each radiation detector 110.
(140) The γ ray detection data of the individual radiation detectors 110 are then fetched by the coincidence counting circuit 120. The coincidence counting circuit 120 correlates these γ ray detection data to identification information of the radiation detector 110 which detected the γ ray, and data acquisition time, and sends the result to the energy discrimination circuit 130.
(141) The energy discrimination circuit 130 extracts preliminarily-determined specific energy data out of the γ ray detection data, and acquires the intensity data. For the case where a Lu-containing scintillator is used, the extracted energy data includes γ ray (511 KeV) emitted from positron, 420-KeV energy generated upon β decay of isotope .sup.176Lu contained to as much as approximately 2.6% in Lu, and because there is a need of discriminating these energies from those ascribable to γ decay (307 KeV) succeeding to the β decay, an energy window is typically set to 415 KeV, so as to extract only energies thereabove from the γ ray detection data. Also for the case where a Lu-free scintillator is used, there is a similar need of discriminating the positron-derived γ ray and naturally-occurring, high-energy particles such as the cosmic ray present in nature, and this raises a need of setting the energy window.
(142) The position calculation circuit 140 calculates position information of γ ray based on the discrimination information of the radiation detectors 110 detecting the individual γ ray detection data, correlates the result to the intensity data, and sends it to the image forming section 150.
(143) The image forming section 150 produces γ ray intensity distribution data in a tomographic image of a specified site, based on the intensity data correlated to the position information. The γ ray intensity distribution data is output as an image by the image output section 160.
(144) For the case where the radiation inspection apparatus is configured as having the radiation detector as described in the above, the radiation inspection apparatus may be used as a stand-alone apparatus, or may be used for magnetic resonance imaging apparatus (MRI), computed tomography apparatus (CT) and single photon computed tomography (SPECT), or combination-type apparatus.
(145) The radiation detector of this embodiment may be used also for X-ray CT, and radiographic apparatus for radioactive ray transmission inspection, or combination thereof.
(146) As has been described in the above, the scintillator single crystal used for the radiation detector of this embodiment is preferably adoptable to a rapid-response detection of radioactive ray in PET and SPECT, if the wavelength of fluorescence emitted under excitation by gamma ray falls in the range from 200 to 350 nm, and preferably from 200 to 310 nm.
(147) The fluorescence emitted from the scintillator single crystal of this embodiment has a short lifetime, typically characterized by a decay time at room temperature of 1 to 300 nsec, and preferably 1 to 50 nsec.
(148) This sort of scintillator single crystal can successfully realize high energy emission and short fluorescence lifetime (short decay constant) in the ultraviolet region, which could not have been easy to realize, and is expected as being typically applicable to a time-of-flight (TOF) PET.
(149) More specifically, in the measurement (sampling) by PET, the scintillator crystal in the individual radiation detectors corresponded to a specific site is excited by gamma ray from the specific site, fluorescence is generated, and the fluorescence is detected for radiation detection. The next measurement will, therefore, be available only after waiting for sufficient attenuation of the fluorescence emitted from the single crystal of the individual scintillators. By composing the radiation detector with the scintillator using the single crystal described in this embodiment, it is made possible to allow the florescence to attenuate within a short period, and to obtain high-energy emission measurable even in a short period of time. Therefore, large time resolution can be realized, and the number of sampling per a unit time can be increased.
EXAMPLE
(150) Paragraphs below will detail specific examples of the present invention referring to the attached drawings, without limiting the present invention. In Examples below, Pr concentration will be determined either in terms of concentration in crystal or in terms of concentration in molten crystal (as charged), wherein in the individual Examples, the ratio of a concentration as charged to a concentration in crystal was found to follow a relation of approximately 1 to 5.
Example A1
(151) A garnet-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.001Y.sub.0.999).sub.3Al.sub.5O.sub.12 (Pr0.1%:YAG) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example A2
(152) A garnet-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002Y.sub.0.998).sub.3Al.sub.5O.sub.12 (Pr0.2%:YAG) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example A3
(153) A garnet-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.001Lu.sub.0.999).sub.3Al.sub.5O.sub.12 (Pr0.1%:LuAG) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example A4
(154) A garnet-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002Lu.sub.0.998).sub.3Al.sub.5O.sub.12 (Pr0.2%:LuAG) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example A5
(155) A garnet-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002Y.sub.0.998).sub.3Al.sub.5O.sub.12 (Pr0.2%:YAG) was manufactured by the pulling-up process. The obtained crystal is shown in
Example A6
(156) A garnet-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002Lu.sub.0.998).sub.3Al.sub.5O.sub.12 (Pr0.2%:LuAG) was manufactured by the pulling-up process. The obtained crystal is shown in
Example A7
(157) A silicate oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002Y.sub.0.998).sub.2SiO.sub.5 (Pr0.2%:Y.sub.2SiO.sub.5) was manufactured by the pulling-up process. The obtained crystal is shown in
(158)
(159) As is known from these results, emission of the scintillator single crystals composed of the Pr-containing oxides of the present invention show extremely large values of absolute light yield ratio. It is also found that the fluorescence decay time is shorter than 20 nsec, proving their great excellence as scintillator materials.
(160) It is to be noted that the emission of the scintillator single crystal composed of the Pr-containing oxides include also slow components. However, by virtue of their extremely large absolute light yield ratio, they prevail over BGO, GSO and so forth to a sufficient level only by contribution of the short-lifetime components, for the purpose of PET. It is suggested that, by using also emission ascribable to slow components for applications of non-destructive inspection such as X-ray CT, radioactive ray transmission inspection apparatus and so forth, they can be used as the scintillator single crystals having still larger values of absolute light yield ratio.
Example B1
(161) A garnet-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002Y.sub.0.998).sub.3(Sc.sub.0.01Al.sub.0.99).sub.5O.sub.12 (Pr0.2%, Sc1%:YAG) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example B2
(162) A garnet-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002Lu.sub.0.998).sub.3(Sc.sub.0.01Al.sub.0.99).sub.5O.sub.12 (Pr0.2%, Sc1%:LuAG) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example B3
(163) A garnet-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002Lu.sub.0.998).sub.3(Mg.sub.0.05Al.sub.0.90Hf.sub.0.05).sub.5O.sub.12 (Pr0.2%, Mg5%, Hf5%:LuAG) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example B4
(164) An oxide scintillator single crystal expressed by a composition of (PrY).sub.2O.sub.3 (Pr1%-as-charged:Y.sub.2O.sub.3) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example B5
(165) A perovskite-type oxide scintillator single crystal expressed by a composition of (PrY)AlO.sub.3 (Pr1%-as-charged:YAP) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example B6
(166) An oxide scintillator single crystal expressed by a composition of (PrLu)VO.sub.4 (Pr1%-as-charged:LuVO.sub.4) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example B7
(167) A perovskite-type oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002La.sub.0.998)LuO.sub.3 (Pr0.2%:LaLuO.sub.3) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example B8
(168) An oxide scintillator single crystal expressed by a composition of (Pr.sub.0.002Lu.sub.0.998).sub.2Si.sub.2O.sub.7 (Pr0.2%:Lu.sub.2Si.sub.2O.sub.7) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
(169)
(170)
(171)
(172) As is obvious from these results, emission of the scintillator single crystals composed of the Pr-containing oxides of the present invention show extremely large values of absolute light yield ratio. It is also found that the fluorescence decay time is shorter than 20 nsec, proving their great excellence as scintillator materials.
(173) It is to be noted that the emission of the scintillator single crystal composed of the Pr-containing oxides include also slow components. However, by virtue of their extremely large absolute light yield ratio, they prevail over BGO, GSO and so forth to a sufficient level only by contribution of the short-lifetime components, for the purpose of PET. It is suggested that, by using also emission ascribable to slow components for applications of non-destructive inspection such as X-ray CT, radioactive ray transmission inspection apparatus and so forth, they can be used as the scintillator single crystals having still larger values of absolute light yield ratio.
Example C1
(174) A fluoride scintillator single crystal expressed by a composition of K(PrY).sub.3F.sub.10 (Pr1%-as-charged:KYF) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
Example C2
(175) A fluoride scintillator single crystal expressed by a composition of K(PrYLu).sub.3F.sub.10 (Pr2%-as-charged:KYLuF) was manufactured by the micro-pulling-down process. The obtained crystal is shown in
(176)
(177) It was found that γ-ray-induced emission of Pr2%-as-charged:KYLuF single crystal was twice as large as that of Pr1%-as-charged:KYF single crystal, indicating that doping of Lu resulted in an extremely large absolute light yield ratio. On the other hand, the fluorescence lifetime was remained at an equivalent level.
(178) As can be seen from these results, emission of the scintillator single crystals composed of the Pr-containing oxides of the present invention show extremely large values of absolute light yield ratio. It is also found that the fluorescence decay time is shorter than 20 nsec, proving their great excellence as scintillator materials.
Comparative Example
(179) A garnet-type oxide scintillator single crystal expressed by a composition of (PrGd).sub.3Ga.sub.5O.sub.12 (Pr1%-as-charged:GGG) described in Patent Document 1, which has conventionally been used as a scintillator single crystal, was prepared, and emission characteristics under excitation by 285-nm ultraviolet radiation were measured.
(180) It is known from