DENSE HIGH-SPEED SCINTILLATOR MATERIAL OF LOW AFTERGLOW

Abstract

The invention relates to an inorganic scintillator material of formula Lu .sub.(2−y) Y .sub.(y−z−x) Ce.sub.xM.sub.zSi.sub.(1−v) M′ .sub.vO.sub.5, in which:

M represents a divalent alkaline earth metal and

M′ represents a trivalent metal,

(z+v) being greater than or equal to 0.0001 and less than or equal to 0.2;

z being greater than or equal to 0 and less than or equal to 0.2;

v being greater than or equal to 0 and less than or equal to 0.2;

x being greater than or equal to 0.0001 and less than 0.1; and

y ranging from (x+z) to 1.

In particular, this material may equip scintillation detectors for applications in industry, for the medical field (scanners) and/or for detection in oil drilling. The presence of Ca in the crystal reduces the afterglow, while stopping power for high-energy radiation remains high.

Claims

1. (canceled)

2. An inorganic LYSO-type scintillator material comprising Lu, Y, Si, O, Ce, M, and optionally M′ wherein: the relative amounts of Lu, Y, Si, O, Ce, M, and M′ satisfy formula (1):
Lu.sub.(2−y)Y.sub.(y−z−x)Ce.sub.xM.sub.zSi.sub.(1−v)M′.sub.vO.sub.5  (1) M represents a divalent alkaline earth metal and M′ represents a trivalent metal; (z+v) is greater than or equal to 0.0001 and less than or equal to 0.2; z is greater than 0 and less than or equal to 0.2; v is greater than or equal to 0 and less than or equal to 0.2; x is greater than or equal to 0.0001 and less than 0.1; and y is from (x+z) to 1.

3. The inorganic scintillator material according to claim 2, wherein (z+v) is greater than or equal to 0.0002.

4. The inorganic scintillator material according to claim 2, wherein (z+v) is less than or equal to 0.05.

5. The inorganic scintillator material according to claim 2, wherein (z+v) is less than or equal to 0.01.

6. The inorganic scintillator material according to claim 2, wherein (z+v) is less than 0.001.

7. The inorganic scintillator material according to claim 2, wherein x is greater than 0.0001 and less than 0.001.

8. The inorganic scintillator material according to claim 2, wherein z is at least 0.0001.

9. An inorganic LYSO-type scintillator material comprising Lu, Y, Si, O, Ce, M, and optionally M′ wherein: the relative amounts of Lu, Si, O, Y, Ce, and M or M′ satisfy formula (1):
Lu.sub.(2−y)Y.sub.(y−z−x)Ce.sub.xM.sub.zSi.sub.(1−v)M′.sub.vO.sub.5  (1) M represents a divalent alkaline earth metal and M′ represents a trivalent metal; (z+v) is greater than or equal to 0.0001 and less than or equal to 0.2; z is greater than 0 and less than or equal to 0.2; v is greater than or equal to 0 and less than or equal to 0.2; x is greater than or equal to 0.0001 and less than 0.1; y is from (x+z) to 1; and the inorganic scintillator material is a single crystal.

10. The inorganic scintillator material according to claim 9, wherein (z+v) is greater than or equal to 0.0002.

11. The inorganic scintillator material according to claim 9, wherein (z+v) is less than or equal to 0.05.

12. The inorganic scintillator material according to claim 9, wherein (z+v) is less than or equal to 0.01.

13. The inorganic scintillator material according to claim 9, wherein (z+v) is less than 0.001.

14. The inorganic scintillator material according to claim 9, wherein x is greater than 0.0001 and less than 0.001.

15. The inorganic scintillator material according to claim 9, wherein z is at least 0.0001.

16. A radiation detector comprising an inorganic LYSO-type scintillator material comprising Lu, Y, Si, O, Ce, M, and optionally M′ wherein: the relative amounts of Lu, Si, O, Y, Ce, and M or M′ satisfy formula (1):
Lu.sub.(2−y)Y.sub.(y−z−x)Ce.sub.xM.sub.zSi.sub.(1−v)M′.sub.vO.sub.5  (1) M represents a divalent alkaline earth metal and M′ represents a trivalent metal; (z+v) is greater than or equal to 0.0001 and less than or equal to 0.2; z is greater than 0 and less than or equal to 0.2; v is greater than or equal to 0 and less than or equal to 0.2; x is greater than or equal to 0.0001 and less than 0.1; and y is from (x+z) to 1.

17. The radiation detector according to claim 16, wherein an inorganic scintillator material is a single crystal.

18. The radiation detector according to claim 16, wherein the radiation detector is a positron emission tomography detector.

19. The radiation detector according to claim 16, wherein the radiation detector is a time-of-flight positron emission tomography detector.

20. The radiation detector according to claim 16, wherein the inorganic scintillator material is coupled to a light detector which produces an electrical signal proportional to a number of light pulses received by the light detector and the intensity of the light pulses received by the light detector.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is a diagram showing the amount of light detected in the form of the number of events (or counts) per mg of scintillator material as a function of time, under X-ray excitation for a few hours.

[0019] FIG. 2 is a diagram showing the amount of light measured as a function of temperature.

[0020] FIG. 3 is a schematic diagram of an automated TL-DA-15 instrument, manufactured by RISO (Denmark).

[0021] FIG. 4 is a diagram comparing the afterglow values of compositions 1 and 2 with a conventional LSO.

DETAILED DESCRIPTION OF THE INVENTION

[0022] Surprisingly, the products according to the invention, thanks to the introduction of M, especially Ca, reduce the afterglow without affecting the density within the proportions considered.

[0023] The scintillator material according to the invention is of formula:

Lu.sub.(2−y)Y.sub.(y−z−x)Ce.sub.xM.sub.zSi.sub.(1−v)M′.sub.vO.sub.5  (Formula 1)

in which:

[0024] M represents a divalent alkaline earth metal, such as Ca, Mg or Sr, and M′ represents a trivalent metal, such Al, Ga or In, [0025] (z+v) being greater than or equal to 0.0001 and less than or equal to 0.2; [0026] z being greater than or equal to 0 and less than or equal to 0.2; [0027] v being greater than or equal to 0 and less than or equal to 0.2; [0028] x being greater than or equal to 0.0001 and less than 0.1; and [0029] y ranging from (x+z) to 1.

[0030] Preferably, (z+v) is greater than or equal to 0.0002.

[0031] Preferably, (z+v) is less than or equal to 0.05 and more preferably less than or equal to 0.01, and even less than 0.001.

[0032] Preferably, x is greater than 0.0001 and less than 0.001.

[0033] In particular, v may be zero (absence of M′), in which case z is at least 0.0001.

[0034] In particular, the scintillator material according to the invention may be such that v is zero. The scintillator material according to the invention may also be such that M is Ca, which corresponds to a particularly suitable composition. The combination of v being zero with M being Ca as particularly suitable. The composition according to the invention then has the following formula:

Lu.sub.(2−y)Y.sub.(y−z−x)Ce.sub.xCa.sub.zSiO.sub.5  (Formula II)

The scintillator material according to the invention may in particular also be such that z is zero. The scintillator material according to the invention may in particular also be such that M′ is Al. The combination of z being zero with M′ being Al is particularly suitable. The composition according to the invention then has the following formula:

Lu.sub.(2−y)Y.sub.(y−x)Ce.sub.xAl.sub.vSi.sub.(1−v)O.sub.5  (Formula III)

The molar content of the element 0 is substantially five times that of (Si+M′), it being understood that this value may vary by about ±2%.

[0035] The scintillator material according to the invention can be obtained in the form of a single crystal or a single crystal by Czochralski growth.

[0036] The invention also relates to the use of the scintillator material according to the invention as a component of a radiation detector, in particular a gamma-ray and/or X-ray detector, especially in CT (Computed Tomography) scanners.

[0037] The invention also relates to the use of the scintillator material according to the invention as a component of a scintillation detector, especially for applications in industry, for the medical field and/or for detection in oil drilling. In particular, this involves any scintillator system with continuous acquisition (which include CT tomography). Also involved is any scintillator system of the positron emission tomography type, especially with time-of-flight measurement), optionally combined with emission tomography.

[0038] Without the Applicant being tied down to any particular theoretical argument, it is assumed that the introduction of a divalent alkaline earth metal ion M substituting for a trivalent rare-earth ion, or of a trivalent metal ion M′ substituting for a tetravalent silicon atom, creates a positive charge deficit that limits the trapping of electrons responsible for the afterglow.

Examples

[0039] Three LYSO:Ce single crystals 1 inch in diameter were produced using the Czochralski method under conditions identical to those described in the aforementioned patents. To do this, raw materials corresponding to the following compositions were used:

[0040] Control (with no Ca):

[0041] Lu.sub.1.8Y.sub.0.1978Ce.sub.0.0022SiO.sub.4.9961

[0042] Composition 1:

[0043] Lu.sub.1.8Y.sub.0.1778Ca.sub.0.02Ce.sub.0.0022SiO.sub.4.9961

[0044] Composition 2:

[0045] Lu.sub.1.8Y.sub.0.1878Ca.sub.0.01Ce.sub.0.0022SiO.sub.4.9961

[0046] The charges were prepared from the corresponding oxides (Ca, Ce, Lu, Y oxides) so as to obtain the desired formulae. The actual Ce and Ca concentrations in the final crystal were lower than those introduced via the raw materials through segregation during crystal growth.

[0047] The single crystals finally obtained, of formula Lu.sub.(2−y)Y.sub.(y-z-x)Ce.sub.xCa.sub.zSiO.sub.5, had the following compositions at the top of the specimen:

TABLE-US-00001 Control (no Ca) Composition 1 Composition 2 x 0.00026 0.00031 0.00036 y 0.095 0.095 0.095 z 0 0.00041 0.00023

[0048] Composition 1 gave a significantly lower afterglow than the control composition (of the conventional LYSO type) and an estimated light level of 20 000 photons/MeV under excitation by a .sup.137Cs gamma-ray source, i.e. slightly less than the LPS composition (26 000 photons/MeV), the LYSO composition (34 000 photons/MeV) and the LSO composition (about 28 000 photons/MeV). Such a light level is far from unacceptable for most applications. Bismuth germanate (Bi.sub.4Ge.sub.3O.sub.12), very widely used, emits only 9 000 photons/MeV. Overall, composition 1 has as much stopping power as an LYSO-type composition without significantly losing out in terms of light level, while still significantly reducing the afterglow.

[0049] Composition 2 is even more advantageous, with a still lower afterglow and a light yield of 27 000 photons/MeV.

[0050] FIG. 4 compares the afterglow values of compositions 1 and 2 with a conventional LSO (the control).