JPS6359435B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention relates to rare earth-doped ceramic scintillators for computerized x-ray tomography (CT) and other x-ray, gamma ray, and nuclear radiation detection applications. More specifically, the present invention relates to a polycrystalline yttriated gadolinia (Y ₂ O ₃ --Gd ₂ O ₃ ) ceramic scintillator doped with rare earth elements.

A computer-processed X-ray tomography scanner is an apparatus for medical diagnosis, according to which a substantially planar X-ray beam is irradiated onto a subject. The intensity of such an x-ray beam varies proportionally to the degree of energy absorption along multiple paths within the subject's body. By measuring the X-ray intensity (i.e., X-ray absorption) along their path from multiple different angles or viewpoints, the The linear absorption coefficient can be calculated. Such areas typically consist of approximately square sections of approximately 1 mm x 1 mm.
By using the absorption coefficient thus obtained, for example, a tomographic image of an internal organ scanned by an X-ray beam can be obtained.

One of the important parts incorporated into such scanners is an x-ray detector for detecting the x-rays modulated by passing through the subject to be examined. Generally, an x-ray detector includes a scintillator material that emits radiation at optical wavelengths when excited by incident x-rays. In typical medical or industrial CT applications, an electrical output signal is generated by directing the optical output from a scintillator material onto a photoelectrically responsive material. The amplitude of the electrical signal thus obtained is proportional to the intensity of the incident X-rays. After such electrical signals are digitized, absorption coefficients are determined by processing in a digital computer and then displayed on a cathode ray tube screen or recorded on some other permanent medium.

Due to the demanding requirements specific to computed tomography techniques, all scintillator materials that emit optical radiation upon excitation by X-rays or gamma rays are
It is not necessarily suitable for CT applications. Useful scintillator materials convert x-rays with high efficiency into optical radiation in the visible and near-visible range of the electromagnetic spectrum, which is most efficiently detected by optical sensors such as photomultiplier tubes and photodiodes. It has to be something. Additionally, scintillator materials do not efficiently transmit and capture optical radiation, so optical radiation generated deep inside the scintillator material cannot be correctly detected by an externally located optical sensor. It is desirable that This indicates sufficient quantum detection efficiency and high
This is particularly important in medical diagnostic applications where it is desired to receive as little radiation dose as possible to the patient while maintaining the signal-to-noise ratio.

Other desirable properties for scintillator materials include short afterglow, low hysteresis phenomena, high X-ray stopping power, and spectral linearity. Afterglow is the tendency of the scintillator material to continue emitting optical radiation even after excitation by X-rays has ended, which can cause information-containing signals to become unclear in the temporal direction. Therefore, in applications that require high-speed continuous scanning, such as when photographing moving internal organs, it is desirable that the afterglow be short. The hysteresis phenomenon refers to a property of scintillator materials in which the optical output for the same X-ray excitation changes based on past irradiation history. In CT, it is necessary to accurately and repeatedly measure the light output from each scintillator cell, and the
Hysteresis phenomena are undesirable since the light output must be substantially the same for the same dose. Typical detection accuracy is on the order of 1/1000 for multiple consecutive measurements taken at a relatively fast rate. Further, in order to efficiently detect X-rays, it is also desirable that the X-ray blocking ability is large. X-rays not absorbed by the scintillator material escape detection. Furthermore, since incident X-rays have various frequencies, spectral linearity is also an important property for scintillator materials. That is, the response of the scintillator material must be substantially uniform at all x-ray frequencies.

Among the scintillator fluorescers considered for CT applications are cesium iodide (CsI), bismuth germanate (Bi ₄ Ge ₃ O ₁₂ ), cadmium tungstate (CdWO ₄ ), and sodium iodide (NaI). is included. Many of the above materials are typically
It has one or more disadvantages (eg excessive afterglow, low light output, cleavage, low mechanical strength, hysteresis phenomenon and high price). Many single crystal scintillators also exhibit hygroscopic properties. Known polycrystalline scintillators are efficient and economical. However, as a result of being polycrystalline, such materials have poor light transmission efficiency and are therefore susceptible to significant light trapping. Because the internal optical path is extremely long and tortuous, the degree of attenuation of the optical output is disadvantageously high.

Producing single crystal scintillators from multicomponent powder compositions is typically not economical and is often impractical. That is, the multicomponent powder composition must be heated above its melting point and an ingot of dimensions larger than each detector channel must be grown from the melt. Such an operation is inherently difficult given the required dimensions of the scintillator bar and the required temperatures. Additionally, some materials exhibit phase changes upon cooling, which may result in cracking of the crystals upon cooling from the growth process. Furthermore, in single crystals, lattice defects tend to spread along crystal planes.

DACusano et al., U.S. Pat. No. 4,242,221, assigned to the same assignee as the present invention, discloses that
A method for fabricating ceramic-like scintillators for CT is described.

The present invention provides an improved ceramic scintillator mainly composed of yttriated gadolinia and containing various rare earth oxide activators to improve luminous efficiency.

The terms "transparent" and "translucent" as used herein refer to the degree of optical clarity of the scintillator material. Ceramic scintillators of the present invention exhibit a
It is customary to exhibit an optical attenuation coefficient of less than cm ⁻¹ . The most desirable ceramic scintillator is
It has a smaller attenuation coefficient and therefore higher optical clarity.

SUMMARY OF THE INVENTION A rare earth doped polycrystalline yttriated gadolinia ceramic scintillator having high optical clarity, high density, high degree of uniformity and cubic crystal structure and useful in CT is a ) about 5 to about 50 (mol)% gadolinia (Gd ₂ O ₃ ), (b) Eu ₂ O ₃ , Nd ₂ O ₃ , Yb ₂ O ₃ , Dy ₂ O ₃ ,
about selected from the group consisting of Tb ₂ O ₃ and Pr ₂ O ₃
0.02 to 12 (mol)% of at least one rare earth oxide activator, and (c) the balance yttria (Y ₂ O ₃ )
It consists of

The present invention also relates to a method of manufacturing an ittria gadolinia ceramic scintillator.

The first method includes (a) about 5 to 50 (mol)% Gd ₂ O ₃ ,
(b) at least _one of about 0.02 to 12 (mol)% selected from the group consisting of Eu _{2 O 3} , Nd _{2 O 3 , Yb 2 O 3} , Dy ₂ O ₃ , Tb 2 O ₃ and Pr ₂ O ₃ species of rare earth oxide activators,
and (c) preparing a multicomponent powder containing the remainder Y ₂ O ₃ . A powder compact is formed by compressing such multi-component powder at room temperature,
A polycrystalline ceramic scintillator is then formed by sintering it.

The second method uses (a) Y ₂ O ₃ , (b) Gd ₂ O ₃ and (c)
Eu ₂ O ₃ , Nd ₂ O ₃ , Yb ₂ O ₃ , Dy ₂ O ₃ , Tb ₂ O ₃ and
The method includes preparing a multicomponent powder containing at least one rare earth oxide activator selected from the group consisting of Pr ₂ O ₃ . A powder compact is formed by compacting such multicomponent powders, which is then sintered to a closed porosity state. A polycrystalline ceramic scintillator is formed by subjecting the thus obtained sintered compressed body to gas high temperature isobaric compression at a predetermined temperature.

A third method includes (a) about 5 to 50 (mol)% Gd ₂ O ₃ ,
(b) at least _one of about 0.02 to 12 (mol)% selected from the group consisting of Eu _{2 O 3} , Nd _{2 O 3 , Yb 2 O 3} , Dy ₂ O ₃ , Tb 2 O ₃ and Pr ₂ O ₃ species of rare earth oxide activators,
and (c) preparing a multicomponent powder containing the remainder Y ₂ O ₃ . Such multicomponent powders are compacted in a vacuum at a first temperature and pressure. A polycrystalline ceramic scintillator is then formed by increasing and maintaining temperature and pressure.

The ceramic scintillator of the present invention may also contain 0.1 to 2 (mol)% strontia (SrO) or calcia (CaO) to reduce afterglow.

Thus, it is one of the objects of the present invention to provide a polycrystalline yttriar-gadolinia ceramic scintillator having large X-ray stopping power and high radiation efficiency.

Rare earth-doped polycrystalline yttriants also have high optical clarity, high density, high degree of uniformity and cubic crystal structure and are particularly useful in CT and other X-ray detection applications. It is also an object of the present invention to provide a gadolinia ceramic scintillator.

Furthermore, it is another object of the present invention to provide a polycrystalline yttriar-gadolinia ceramic scintillator that exhibits less afterglow and hysteresis phenomena.

Furthermore, rare earth materials such as those having a cubic crystal structure, large X-ray stopping power, high density, high degree of uniformity and high radiation efficiency and are useful in radiation detectors for CT and digital radiography. It is also an object of the present invention to provide a sintering process for producing doped transparent to translucent polycrystalline yttriated gadolinia ceramic scintillators.

Furthermore, rare earth materials such as those having a cubic crystal structure, large X-ray stopping power, high density, high degree of uniformity and high radiation efficiency and are useful in radiation detectors for CT and digital radiography. It is also an object of the present invention to provide a combined sintering-gas high-temperature isostatic compression method for producing doped transparent to translucent polycrystalline yttriated gadolinia ceramic scintillators.

Furthermore, it is another object of the present invention to provide a sintering method for producing a polycrystalline Yttri-Gadolinia ceramic scintillator with less afterglow.

Furthermore, the addition of rare earth elements has a cubic crystal structure, large X-stopping power, high density, high degree of uniformity and high radiation efficiency, and is useful in radiation detectors for CT and digital radiography. It is also an object of the present invention to provide a vacuum hot pressing method for producing transparent to translucent polycrystalline yttriated gadolinia ceramic scintillators.

Furthermore, it is another object of the present invention to provide a vacuum high-temperature compression method for producing a polycrystalline yttriated gadolinia ceramic scintillator with little afterglow.

DETAILED DESCRIPTION OF THE INVENTION The features of the invention believed to be novel are pointed out with particularity in the appended claims. The structure and manner of carrying out the invention, as well as additional objects and advantages, may, however, be best understood from the following description, taken in conjunction with the accompanying drawings.

U.S. Pat. No. 3,640,887 to RC Anderson, assigned to the same assignee as the present invention, describes a method for making transparent polycrystalline ceramic materials.
Such materials include oxides of thorium, zirconium and/or hafnium and oxides of 58
Contains oxides of rare earth elements from No. 71 to No. 71. Such materials may also optionally contain itria. The average ionic radius of rare earth oxides is approximately 0.93 Å with or without ittria
, and the ionic radii of the component oxides should not differ by more than about 0.22 Å. The polycrystalline ceramic materials thus obtained are used in high temperature applications and/or applications requiring light transmission. Examples of such applications include high temperature microscopes, light bulb casings, laser applications and furnace windows.

According to the above patent specification, such polycrystalline ceramic materials contain about 2-15 (mol)% thoria (ThO ₂ ), zirconia (ZrO ₂ ), hafnia (HfO ₂ ) or mixtures thereof. hand,
It is stated that these components act as densifying agents during sintering.

However, the present inventors have discovered that when ThO ₂ , ZrO ₂ or HfO ₂ is incorporated into the scintillator material of the present invention in the amount specified in the above-mentioned Anderson patent specification, the resulting material has high radiation rays such as X-rays. It has been found that the light output when excited by energy beams is significantly reduced, making such materials unsuitable for CT applications. Looking at Figure 1,
Approximately 58.7 (mol)% Y ₂ O ₃ , 38 (mol) % Gd ₂ O ₃ ,
3 (mol)% Eu ₂ O ₃ and 0.3 (mol) % Yb ₂ O ₃
A graph is shown in which the relative light output (vertical axis) of a polycrystalline ceramic scintillator consisting of a polycrystalline ceramic scintillator is plotted against the molar percentage of ThO ₂ (horizontal axis). Note that as the ThO ₂ content increases, the Y ₂ O ₃ content decreases accordingly. The average ionic radius and the difference between the ionic radii of the ceramic components are as defined in the Anderson patent specification. As is clear from Figure 1, 2 (mol)%
ThO ₂ (minimum amount prescribed by Anderson)
The light output of a scintillator material containing _ThO2 is only 5% of the light output of the same scintillator material without ThO2. In fact, 0.5 (mole) is far below the lower limit specified in Anderson's patent specification.
% ThO ₂ alone reduces the light output to about 18% of that measured for scintillator materials without ThO ₂ .
Scintillator materials useful in CT include ThO ₂
Approximately 35% of the light output of scintillator materials that do not contain
It is necessary to have a light output corresponding to the above.

Substantial reductions in light output have also been observed with additives such as cerium oxide (CeO ₂ ), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), and tantalum oxide (Ta ₂ O ₅ ). for example,
55.5 (mol)% Y ₂ O ₃ , 38 (mol) % Gd ₂ O ₃ , 1
The relative light output of scintillator materials containing (mol)% Eu ₂ O ₃ , 0.5 (mol) % Yb ₂ O ₃ and 2 (mol) % ZrO ₂ is the same except that it does not contain ZrO ₂ was found to be 4% of the light output of the scintillator material. These tetravalent ( ⁴⁺ ) and pentavalent ( ⁵⁺ ) additives have a suppressive effect on light output. It should be noted that the optical output referred to here refers to light emission due to X-ray excitation. It is important to make a clear distinction because some ceramic materials, for example, emit light when excited by ultraviolet light but not by excitation with X-rays.

According to the present invention, a transparent or translucent rare earth ceramic scintillator can be produced without adding a densifying agent such as the one described above that suppresses luminescence. The optical output generated by the ceramic scintillator of the present invention in response to X-ray excitation is sufficient for use in CT.

The ceramic scintillator of the present invention comprises a rare earth matrix of yttriated gadolinia and a trivalent rare earth oxide activator. Such ceramic scintillators are manufactured by several methods, including sintering, combined sintering and gas high temperature isostatic compression (GHIP), and high temperature compression (all described in detail below). In a finished ceramic scintillator with optimal overall properties, the chemical components exist as a cubic solid solution, as confirmed by X-ray diffraction techniques.

europium, neodymium, itterbium, as activators to increase scintillator efficiency.
Oxides of trivalent rare earth elements such as dysprosium, terbium and praseodymium (i.e.
Eu ₂ O ₃ , Nd ₂ O ₃ , Yb ₂ O ₃ , Dy ₂ O ₃ , Tb ₂ O ₃ and
Pr ₂ O ₃ ) is added to the basic system of Ittria gadolinia. Ittrian gadolinis scintillator material containing Eu ₂ O ₃ exhibits excellent luminous efficiency. Generally, the content of the rare earth oxide activator may be in the range of 0.02 to 12 (mol)%. The optimum content of Eu ₂ O ₃ is about 1-6 (mol)%. Because, as shown in Figure 2, the highest relative light output (vertical axis) over Eu ₂ O ₃ content (horizontal axis) of about 1-6 (mol)%
This is because it can be obtained. The curve shown in Figure 2 is based on 25 (mol)% Gd ₂ O ₃ and the balance Y ₂ O ₃
This was determined by varying the Eu ₂ O ₃ content in the scintillator material containing .

An illustrative example of an yttriar gadolinia scintillator material using a neodymium oxide (Nd ₂ O ₃ ) activator is 30 (mol)% Gd ₂ O ₃ , 0.25 (mol) %
Those consisting of Nd ₂ O ₃ and the balance Y ₂ O ₃ are mentioned. Preferably _{, Nd2O3} is added in a content of 0.05-1.5 (mol)%. In addition, 0.1 to 0.5 (mol)
Most preferred is the addition of Nd ₂ O ₃ in a content of %. The preferred content of terbium oxide (Tb ₂ O ₃ ) activator is
0.05-3.0 (mol)%, while the preferred content of dyspsium oxide (Dy ₂ O ₃ ) activator is 0.03-1.0 (mol)%. Illustrative examples of Yttriar gadolinia scintillator materials with Tb ₂ O ₃ or Dy ₂ O ₃ activators include 40 (mol)% Gd ₂ O ₃ , 0.15 (mol)
% Tb ₂ O ₃ and balance Y ₂ O ₃ and 40 (mol) % Gd ₂ O ₃ , 0.2 (mol) % Dy ₂ O ₃ and balance Y ₂ O ₃ . It will be done.

The preferred content _{of Yb2O3} activator is about 0.10-2.0 (mol)
%. The preferred content _{of Pr2O3} activator is 0.02~
It is 0.05 (mol)%.

It should be noted that the effect of the activator is independent of the composition ratio of Y ₂ O ₃ and Gd ₂ O ₃ . A preferred activator is Eu ₂ O ₃ followed by Nd ₂ O ₃ and Dy ₂ O ₃ in that order.

Figure 3a shows that in an yttria-gadolinia scintillator material containing 3 (mol)% Eu ₂ O ₃ , the scintillator efficiency, expressed by the relative light output, depends on the relative contents of yttria and gadolinia. ing. In the figure, the mole percentages of Gd ₂ O ₃ and Y ₂ O ₃ are shown on the horizontal axis, and the relative light output is shown on the vertical axis. 50 (mol)
The dashed lines drawn at %Gd ₂ O ₃ and 50 (mol)% Y ₂ O ₃ represent the position where the crystalline phase of the scintillator material begins to gradually transition from cubic to monoclinic. . It will be appreciated that high relative light output can be obtained from scintillator materials containing up to about 50 (mol)% Gd ₂ O ₃ . 50-65 (mol)%
Scintillator materials containing Gd ₂ O ₃ provide moderate relative light output, but are prone to grain boundary cracking and a decrease in relative light output due to the progression of the cubic to monoclinic crystal phase transition. .

The cubic crystal phase is characterized by a high degree of symmetry in the crystal structure. Scintillator materials with such crystal structures are particularly desirable for CT applications. Scintillator materials with a large amount of monoclinic crystalline phase are characterized by a reduction in relative light output and optical clarity due to grain boundary cracking and non-uniform crystal structure. In scintillator materials with such non-cubic crystal structures, light scattering and reabsorption occurs to a significant extent due to the long effective relative optical path length, thus making it difficult for detection by external optical sensors. The amount of available light decreases.

When considering the usefulness of scintillator materials in CT applications, the X-ray stopping ability of the material must also be considered. FIG. 3b shows that for transparent and efficient scintillator materials, the X-ray blocking distance for 73 keV X-rays depends on the composition ratio of yttriated gadolinia. X-ray stopping power is measured as the X-ray stopping distance (ie, the distance that an X-ray photon penetrates into the scintillator material before being converted to a photon of an optical wavelength detectable by a photosensor). The X-ray stopping distance is mainly
It depends on the Gd ₂ O ₃ content and decreases as the Gd ₂ O ₃ content increases, as shown in Figure 3b. Generally speaking, about 5 to 50 (mol)%
Preference is given _to using _Gd2O3 . Approximately 5 (mol)
Scintillator materials containing less than 50 (mol)% Gd ₂ O ₃ have X-ray stopping power that is too small for most practical detectors, and scintillator materials containing less than 50 (mol) % Gd ₂ O ₃ Scintillator materials exhibit progressively lower optical clarity due to an increase in non-cubic crystal structure. A more preferred range of Gd ₂ O ₃ content is 20-40 (mol)%. Also, the most preferred range of Gd ₂ O ₃ content is 30-40 (mol)%, which corresponds to an X-ray blocking distance of about 0.45 mm.
For a 2 mm thick scintillator material with an X-ray stopping distance of 0.45 mm, approximately 99 of the incident X-ray photons
% will be converted into photons of optical wavelength.

Certain additives are useful in the Yttriar gadolinia scintillator system of the present invention to reduce afterglow, which can lead to undesirable distortions and artifacts in the reconstructed image. Afterglow reduction can be classified into primary afterglow (or basic afterglow) and secondary afterglow. The primary afterglow has a relatively short duration (approximately 3 milliseconds or less), whereas the secondary afterglow has a decay time that is several times or even much longer than the primary decay time. The primary afterglow of a phosphor is believed to be intricately related to the type of activator and the local environment of the activator in the matrix (in this case, Yttriar gadolinia). Secondary afterglow, the most unfavorable type of afterglow, may involve more subtle changes in the activator environment and may also involve additional electrons caused by natural defects and/or low-level impurities. It may also be related to the presence of hole-trapping centers elsewhere in the base material. Afterglow of either type can be reduced by appropriate purification operations or by the use of compensating additives. Additives used to reduce afterglow create killer centers that compete with the activator center for electron-hole pairs that would otherwise bind while emitting light at the activator center. It is believed that it will form.

The afterglow of the rare earth-doped itria gadolinia ceramic scintillators of the present invention can be substantially reduced through the use of several additives.

If ytterbium oxide (Yb ₂ O ₃ ) is used alone in the yttri-gadolinia matrix, it will act as an activator as mentioned above, but its addition will cause undesirable secondary effects, although it will cause some decrease in luminous efficiency. Helps to reduce afterglow. As shown in Figure 4, when the Yb ₂ O ₃ content is increased from 0 (mol) % to 2 (mol) %, 3 (mol) % of Eu ₂ O ₃
The primary afterglow (τ) of scintillator materials containing activators is reduced from 1.1 ms to 0.82 ms. Increasing the Yb ₂ O ₃ content from 0 (mol)% to 2 (mol)% is also accompanied by a decrease in luminous efficiency of about 50%, as shown in FIG. In addition, the fifth
The figure is a graph in which relative light output is shown on the vertical axis and Yb ₂ O ₃ content is shown on the horizontal axis.

Curves A, B, C and D shown in Figure 4
indicates the proportion of secondary afterglow remaining (vertical axis) after a time of 10 milliseconds or more (horizontal axis) has elapsed since the stop of X-ray excitation. 30 (mol)%
Gd ₂ O ₃ , 3 (mol)% Eu ₂ O ₃ and 67 (mol)%
For a scintillator material containing Y ₂ O ₃ but no Yb ₂ O ₃ , it is clear from curve A that about 3% of the luminescence present immediately after X-ray interruption occurs 10 ms after X-ray interruption. It remains in the. Curves B, C and D are 0.2 (mol)% and 0.5, respectively.
Figure 2 shows the afterglow ratio for similar scintillator materials containing (mol)% and 2 (mol)% Yb ₂ O ₃ (as well as less Y ₂ O ₃ ).
It is clear that the secondary afterglow is reduced with increasing Yb ₂ O ³ content. For example, about 10% of X-ray blocking
After milliseconds, the afterglow ratio for the scintillator material without Yb ₂ O ₃ (curve A) is about 3% (3 × 10 ^-2 ) of the value immediately after the cessation of X-ray excitation. The afterglow rate for the scintillator material containing 2 (mol)% Yb ₂ O ₃ (curve D) is approximately
It is only 0.7% (7×10 ^-3 ). 66.7 (mol)% Y ₂ O ₃ , 30 (mol) % Gd ₂ O ₃ and 3
scintillator material consisting of (mol) _{% Eu2O3}
Addition of 0.3 (mol)% Yb ₂ O ₃ provides an extremely excellent scintillator material for CT with a short decay time. In addition, suitable for reducing afterglow
_{Yb2O3 content} is about 0.15-0.7 (mol)%.

Another additive that is effective in reducing afterglow in scintillator materials is strontium oxide (SrO).The addition of SrO primarily reduces secondary afterglow, albeit with a relatively small decrease in luminous efficiency. It helps to make it happen. In the Yttriar gadolinia scintillator system, the content of SrO useful for afterglow reduction has generally been found to be between 0.1 and 2 (mol)%. As shown in Figure 6, SrO
Increasing the content from 0 (mol)% to 2 (mol)% has little effect on the primary afterglow (τ) (1.08 ms and 1.10 ms, respectively). however,
As shown by curves E and F, there is a significant effect on secondary afterglow. 30 (mol)
For a scintillator material containing % Gd ₂ O ₃ , 2 (mol) % Eu ₂ O ₃ and 68 (mol) % Y ₂ O ₃ but no SrO (curve E), the X-ray blocking Approximately 0.8% (8×10 ⁻³ ) of the immediately present emission remains approximately 150 milliseconds after X-ray interruption.
However, for a scintillator material (curve F) of the same composition except for containing 2 (mol)% SrO (and correspondingly less Y ₂ O ₃ ), the residue shown on the vertical axis in FIG. The proportion of light is only about 0.03% (3×10 ⁻⁴ ) after the same elapsed time.

It has been found that adding calcium oxide (CaO) to the scintillator material (instead of SrO) can provide the same afterglow reduction effect as SrO. The content of CaO useful when used as an afterglow reducer is
It is 0.1 to 2 (mol)%.

The above-mentioned rare earth-added yttriar gadolinia ceramic scintillator can be produced using a sintering method.
It can be manufactured by a combination of sintering and gas high-temperature isobaric compression and a high-temperature compression method. Incidentally, when manufacturing such a ceramic scintillator, it is preferable and most economical to use a sintering method.

When producing ceramic scintillators by any of the above methods, it is required as a preliminary step to prepare a suitable powder containing the desired scintillator components. According to the first method for preparing such a powder, for example 99.99 to
Ittria (Y ₂ O ₃ ) and Gadolinia (Gd ₂ O ₃ ) submicron to micron particle size powders with a purity of 99.9999% should be added as activators for rare earth oxides, oxalates, carbonates, and nitrates. or mixed with mixtures thereof. Mixing of these components may be carried out in an agate mortar or ball mill using water, heptane or alcohol (eg ethyl alcohol) as the liquid medium. Dry milling can also be employed for mixing and crushing the powder agglomerates. When dry grinding is used, a
It is necessary to use a grinding aid such as % stearic acid or oleic acid. Clarity improver
SrO is also oxidized prior to ball milling.
It may be added in the form of nitrate, carbonate or oxalate. When the various additives are used in the form of nitrates, carbonates or oxalates, the corresponding oxidation is carried out by a calcination step prior to the production of ceramic scintillators by any of the methods described below. It is necessary to obtain things.

A second means for preparing the desired scintillator raw material powder can be a wet chemical oxalate method. According to this method,
Nitrates of desired rare earth elements selected from Y, Gd, Eu, Nb, Dy, Tb, Pr and Sr are dissolved in water at predetermined molar percentages, and then they are coprecipitated in oxalic acid. Thus, the respective oxalates are produced. Such an oxalate coprecipitation step consists of adding an aqueous nitrate solution of the desired scintillator component to, for example, an 80% saturated oxalic acid solution at room temperature. The coprecipitated oxalate thus obtained, after washing, neutralization and further drying in air at about 100° C. for about 8 hours. The corresponding oxide is then produced by calcining (pyrolysis) the oxalate in air at a temperature of about 700-900°C for 1-4 hours. Typically, heating at 800°C for 1 hour is sufficient. When producing ceramic scintillators using hot compression or sintering methods, oxalate and/or Preferably, the oxide produced therefrom is milled. It has been found that it is sufficient to mill such powders over a period of 1/2 to 10 hours. It should be noted that, regardless of the manufacturing method used, milling the oxalate and/or oxide generally improves the optical clarity of the resulting ceramic scintillator.

Regarding the production of ceramic scintillators by the sintering method, after preparing a desired powder composition by any of the above methods, a powder compact is formed from a predetermined amount of the powder composition. for that purpose,
The powder composition may be subjected to die compaction or die compaction followed by isobaric compaction to further increase the green density; Preferably, a mold material is used. Suitable mold materials include alumina, silicon oxide, and metals such as molybdenum, hardened steel, and nickel-based alloys. Powder compacts are formed by mold compaction under pressures of about 3,000 to 15,000 psi. Furthermore, in order to further increase the unsintered density of the powder compact,
The mold compacted powder compact may be subjected to isostatic compression under a pressure of about 10,000 to 60,000 psi. If grinding aids or compaction aids (friction reducers such as waxes) are used, an oxidation treatment to remove all organic additives is preferred prior to sintering. During the sintering process, the powder compact is heated at a rate of about 100-700°C/hour to 1800-2100°C in a vacuum or a reducing atmosphere such as a wet hydrogen atmosphere (e.g. dew point about 23°C), for example by using a high-temperature tungsten furnace. is heated to the sintering temperature of Significant densification and optical clarity is then achieved by maintaining the sintering temperature for 1 to about 30 hours.
After completion of the sintering process, the resulting ceramic scintillator is cooled from the sintering temperature to room temperature over a period of about 2 to 10 hours.

Sintered ceramic scintillators can also be produced by heating operations involving holding at a temperature below the final sintering temperature. Typically, powder compacts are heated to approximately 1600-1700°C at a rate of 300-400°C/hour.
heated to a holding temperature of Retention time is 1-20
As long as it's within the time range. Then reduce the temperature to approx.
After increasing the temperature to 1800-2100°C, final sintering is performed for 1-10 hours. The increase from the holding temperature to the final sintering temperature takes place at a rate of about 25-75°C/hour. A suitable heating operation is to heat the powder compact to a holding temperature of 1660°C for 5 hours, and then
Maintained for 10 hours, then 1950 in 6 hours.
℃ and sintering at 1950℃ for 2 hours.

Following the preferred sintering operation, 59.85 (mol)%
_Y2O3 , 40 ₍ mol)% _Gd2O3 and _0.15 (mol)%
a first ceramic scintillator consisting of Tb ₂ O ₃ and 59.8 (mol) % Y ₂ O ₃ , 40 (mol) %
A second consisting of Gd ₂ O ₃ and 0.2 (mol)% Dy ₂ O ₃
A ceramic scintillator was manufactured. In either case, the oxalates of the desired components are prepared by the oxalate coprecipitation method, and then they are heated at 800°C for 1
The corresponding oxide was obtained by calcination for a period of time. The oxide was first cold pressed at 3500 psi to form a powder compact, then isostatically pressed at 29000 psi to further increase the green density. after that,
The powder compact was placed in a wet hydrogen atmosphere for 5 hours.
It was heated to 1660℃. After maintaining the temperature at 1660°C for 10 hours, the temperature was increased to 1950°C and maintained for 2 hours. Thereafter, the obtained ceramic scintillator was cooled to room temperature in a furnace.

Yttriar gadolinia ceramic scintillators for luminescent applications can also be produced by a combination of sintering and gas hot isostatic pressing (GHIP). A powder composition of raw oxide is prepared according to any of the above methods. For this purpose, it is preferable to use the oxalate coprecipitation method. By way of illustration and not limitation, examples of useful Yttriar gadolinia scintillator materials include 66.7 (mol)% Y ₂ O ₃ , 30 (mol)%
Gd ₂ O ₃ , 3 (mol)% Eu ₂ O ₃ and 0.3 (mol)%
of Yb ₂ O ₃ and 49.7 (mol)% of
Y ₂ O ₃ , 45 (mol)% Gd ₂ O ₃ , 5 (mol)%
Mention may be made of a composition consisting of Eu ₂ O ₃ and 0.3 (mol) % Yb ₂ O ₃ . Unlike the aforementioned sintering methods, which preferably require milling of oxalates and/or oxides to obtain transparent ceramic scintillators, the combined sintering-gas hot isopressing method requires milling. A transparent ceramic scintillator can be manufactured from a powder composition that is not subjected to any process.

When manufacturing Yttriar gadolinia ceramic scintillators using a combination of sintering and gas high-temperature isostatic compression, after preparing the desired powder composition,
Cold compression under ~10000psi pressure and then
Powder compacts are formed by isostatic compression under pressures of 15,000 to 60,000 psi. Then about 1500
The powder compact is presintered by heating at temperatures of ~1700° C. for 1 to 10 hours until it reaches 93 to 98% of its theoretical value. The presintered powder compact is subjected to gas high temperature isobaric compression at an argon gas pressure of 1000 to 30000 psi and a temperature of 1500 to 1800° C. for 1 to 2 hours.

To describe an example of manufacturing a ceramic scintillator using a combination of sintering and gas high-temperature isostatic compression, about 20 g of a powder composition is poured into a rectangular mold.
Powder compacts were formed by cold compaction under a pressure of 4000 psi. Next, the powder compact is
The green density was increased to 49% of the theoretical value by isobaric compression under a pressure of 30,000 psi. After such cold compaction, closed porosity was achieved by sintering the powder compact at 1660° C. for 2 hours in a humid hydrogen atmosphere (dew point 23° C.). The density of the sintered compacted powder body at this stage was measured by the water immersion method, and the theoretical value was 93.
It was found to be equal to ~98%. In order to achieve further densification and improved optical clarity, such powder compacts are processed in a carbon resistance furnace.
The gas was subjected to hot isostatic compression for 1 hour under an argon gas pressure of 25000 psi and a temperature of 1750°C. During gas hot isobaric compression, the temperature was increased stepwise to a final value of 1750°C. First, the powder compact was heated to 1400°C in one hour, and then raised to 1750°C in the next hour. The ceramic scintillator obtained by maintaining the temperature at 1750° C. for 1 hour had a black color due to the reduction caused by the reducing atmosphere in the furnace. in the air
By applying a suitable oxidation treatment, such as heating at 1200° C. for 32 hours, such ceramic scintillators became transparent to visible light. A comparison of the physical dimensions of the powder compacts before and after the gas hot isostatic compression process shows that the powder compacts contracted during the gas hot isostatic compression process, thus resulting in further densification. The completed ceramic scintillator had a density higher than 99.9% of the theoretical value.

A transparent ittria gadolinia ceramic scintillator can also be produced by subjecting scintillator raw material powder, preferably prepared by the above-mentioned wet oxalate coprecipitation method, to high-temperature vacuum compression. According to this method, a predetermined amount of calcined oxalate powder (preferably ground) is compressed inside a graphite mold using molybdenum foil as a spacer between upper and lower graphite plungers. Alternatively, boron nitride coated graphite types can be used. Approximately 1000-1200psi at a temperature of approximately 600-700℃ in a vacuum less than 200 microns
of pressure is applied and maintained for about 1 hour. The pressure is then increased to about 4000-10000 psi and the temperature is increased to 1300-1600°C. Reduce the pressure and temperature above by 1/2 to 4
After holding for a period of time, the pressure is released and the resulting ceramic scintillator is cooled in the furnace to room temperature.

Ceramic scintillators manufactured according to the hot compression method may become discolored due to surface reactions with the molybdenum foil spacers. Discoloration may also occur due to oxygen deficiency in the furnace atmosphere during high-temperature compression. However, such ceramic scintillators can be made transparent by oxidation in air or an oxygen-containing atmosphere at temperatures of about 800 DEG to 1200 DEG C. for 1 to 20 hours. Any remaining discoloration may be removed by conventional grinding and polishing techniques.

An example of manufacturing a ceramic scintillator using a vacuum high-temperature compression method is to place oxalate obtained from the above oxalate coprecipitation method in air.
10 by baking at 800℃ for 1 hour.
An oxide of g was prepared. The oxide was first placed in a boron nitride coated graphite mold and then hot pressed in a vacuum of about 20 microns at a temperature of 700° C. and a pressure of 1200 psi for 1 hour. Then about
Temperature and pressure were increased to 1400° C. and 6000 psi, respectively, in a 100 micron vacuum.
After maintaining these conditions for 2 hours, the pressure was released and the resulting ceramic scintillator was cooled in the furnace.

Such ceramic scintillators had a gray or gray-black color due to the reducing atmosphere generated during high-temperature compression. Carbon attached to the surface of the ceramic scintillator was removed by lightly grinding the surface and then heating it at 950°C for 4 hours. The remaining dark discoloration was removed by oxidation at 1150° C. for 2 hours in air. The ceramic scintillator thus obtained had a light brown color, was optically translucent to transparent, and exhibited good relative light output in response to X-ray excitation.

As can be seen from the above description, rare earths have high density, high optical clarity, high degree of uniformity and cubic crystal structure and are useful in computed x-ray tomography and other x-ray detection applications. A polycrystalline yttriated gadolinia ceramic scintillator is provided by the present invention. Such ceramic scintillators also include:
It also has large X-ray stopping power and high radiation efficiency. As a result of the inclusion of specific additives, the afterglow and hysteresis phenomena of such ceramic scintillators are minimized.

As can be seen from the above description, it has a cubic crystal structure, large X-ray stopping power, high radiation efficiency, high density, high degree of uniformity and low afterglow, and is suitable for radiation detection for CT and digital radiography. Sintering, combined sintering with gas high temperature isostatic compression, and vacuum high temperature compression are also used to produce rare earth-doped transparent or translucent polycrystalline yttriated gadolinia ceramic scintillators useful in equipment. Provided by the present invention.

Although the invention has been described in connection with specific preferred embodiments, it will be obvious to those skilled in the art that many variations are possible. It is therefore to be understood that the appended claims are intended to cover all such modifications as do not depart from the spirit of the invention.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the effect of thorium (ThO ₂ ) content on the light output of a yttriated gadolinia ceramic scintillator containing 3 (mol)% Eu ₂ O ₃ , _{and FIG.} Graph illustrating the dependence of relative light output on Eu ₂ O ₃ activator content in ceramic scintillators of the invention containing O ₃ , Figure 3a shows the dependence of the relative light output on the Eu 2 O 3 activator content in ceramic scintillators of the invention containing 3 (mol)% Eu ₂ O ₃ . A graph showing that the scintillator efficiency of a ceramic scintillator depends on the composition ratio of yttriar gadolinia. Figure 3b is a graph plotting the X-ray stopping power (73 keV) of the ceramic scintillator of the present invention against the composition ratio of yttriated gadolinia. , FIG. 4 is a graph showing the effect of Yb ₂ O ₃ content on the afterglow of scintillator materials, FIG. 5 is a graph plotting the relative light output of the ceramic scintillator of the present invention against Yb ₂ O ₃ content, and FIG. Figure 6 is a graph showing the effect of SrO content on the afterglow of scintillator materials.

Claims (1)

[Claims] 1 (a) about 5 to 50 (mol)% Gd ₂ O ₃ , (b) Eu ₂ O ₃ ,
about 0.02 to 12 (mol)% of at least one rare earth oxide activator selected from the group _consisting of Nd ₂ O ₃ , Yb ₂ O ₃ , Dy 2 O 3 _, Tb ₂ O ₃ and Pr ₂ O ₃ ; and (c) a polycrystalline ceramic scintillator consisting essentially of the remainder Y ₂ O ₃ . 2 The rare earth oxide activator is about 1 to 6 (mol)
Claim 1 consisting essentially of % Eu ₂ O ₃
The polycrystalline ceramic scintillator described in Section 1. 3. The polycrystalline ceramic scintillator of claim 1 containing about 20-40 (mol)% Gd ₂ O ₃ . 4. The polycrystalline ceramic scintillator of claim 1 _, wherein said rare earth oxide activator consists essentially of about 0.05-1.5 (mol)% _Nd2O3 . 5 The rare earth oxide activator is about 0.1 to 0.5 (mol)
Claim 4 consisting essentially of % Nd ₂ O ₃
The polycrystalline ceramic scintillator described in Section 1. 6 The rare earth oxide activator is about 0.05 to 3 (mol)
Claim 1 consisting essentially of % Tb ₂ O ₃
The polycrystalline ceramic scintillator described in Section 1. 7 The rare earth oxide activator is 0.1 to 2 (mol)%
A polycrystalline ceramic scintillator according to claim 1, consisting essentially of Yb ₂ O ₃ . 8. The polycrystalline ceramic scintillator _of claim 7, wherein said rare earth oxide activator comprises about 0.15-0.7 (mol)% _Yb2O3 . 9 The rare earth oxide activator is about 0.03 to 1 (mol)
Claim 1 consisting essentially of % Dy ₂ O ₃
The polycrystalline ceramic scintillator described in Section 1. 10 The rare earth oxide activator is about 0.02 to 0.05
A polycrystalline ceramic scintillator as claimed in claim 1 consisting essentially of (mol)% Pr ₂ O ₃ . 11 (a) about 5 to 50 (mol)% Gd ₂ O ₃ , (b) Eu ₂ O ₃ ,
about 0.02 to 12 (mol)% of at least one rare earth oxide activator selected from the group _consisting of Nd ₂ O ₃ , Yb ₂ O ₃ , Dy 2 O 3 _, Tb ₂ O ₃ and Pr ₂ O ₃ ; (c) each selected from the group consisting of CaO and SrO, about 0.1 to
A polycrystalline ceramic scintillator characterized in that it consists essentially of 2 ₍ mol)% of at least one afterglow reducing agent, and (d) the balance _Y2O3 . 12 The rare earth oxide activator is about 1 to 6 (mol)
Claim 1 consisting essentially of % Eu ₂ O ₃
The polycrystalline ceramic scintillator according to item 1. 13. The polycrystalline ceramic scintillator of claim 11 containing about 20-40 (mol)% Gd ₂ O ₃ . 14. The polycrystalline ceramic scintillator of claim 11 _, wherein said rare earth oxide activator consists essentially of about 0.05-1.5 (mol)% _Nd2O3 . 15. The polycrystalline ceramic scintillator of claim 14 _, wherein said rare earth oxide activator consists essentially of about 0.1-0.5 (mol)% _Nd2O3 . 16. The polycrystalline ceramic scintillator of claim 11, wherein said rare earth oxide activator consists essentially of about 0.05-3 ( _mol )% _Tb2O3 . 17 The rare earth oxide activator is 0.1 to 2 (mol)
Claim 1 consisting essentially of % Yb ₂ O ₃
The polycrystalline ceramic scintillator according to item 1. 18. The polycrystalline ceramic scintillator of claim 17 _, wherein said rare earth oxide activator comprises about 0.15-0.7 (mol)% _Yb2O3 . 19. The polycrystalline ceramic scintillator of claim 11, wherein said rare earth oxide activator consists essentially of about 0.03-1 (mol)% Dy ₂ O ₃ . 20 The rare earth oxide activator is about 0.02 to 0.05
12. The polycrystalline ceramic scintillator of claim 11 consisting essentially of (mole) % Pr ₂ O ₃ . 21 (A) (a) about 5-50 (mol)% Gd ₂ O ₃ , (b)
Eu ₂ O ₃ , Nd ₂ O ₃ , Yb ₂ O ₃ , Dy ₂ O ₃ , Tb ₂ O ₃ and
Approximately 0.02 to 12 (mol) selected from the group consisting of Pr ₂ O ₃
% of at least one rare earth oxide activator, and ( _c ) the balance _Y2O3 ;
(B) forming a compacted powder body by compressing the multi-component powder at room temperature; and (C) forming a polycrystalline ceramic scintillator by sintering the compacted powder body. A method for producing a polycrystalline ceramic scintillator, characterized by: 22 The multi-component powder contains about 20 to 40 (mol)%
22. The method of claim 21 containing Gd ₂ O ₃ . 23 The multi-component powder contains about 1 to 6 (mol)%
22. The method of claim 21 containing Eu ₂ O ₃ . 24 The multi-component powder contains 0.1 to 2 (mol)%
22. The method of claim 21 containing Yb ₂ O ₃ . 25 The multi-component powder contains about 20 to 40 (mol)%
Claim 21 containing Gd ₂ O ₃ , about 1-6 (mol) % Eu ₂ O ₃ , 0.1-2 (mol) % Yb ₂ O ₃ and the balance Y ₂ O ₃ Method. 26 The multi-component powder contains about 0.05 to 1.5 (mol)%
22. The method of claim 21 containing Nd ₂ O ₃ . 27 The multi-component powder contains about 0.05 to 3 (mol)%
22. The method of claim 21 containing Tb ₂ O ₃ . 28 The multi-component powder contains about 0.03 to 1 (mol)%
22. The method according to claim 21, containing Dy ₂ O ₃ . 29 The multi-component powder is about 0.02 to 0.05 (mol)%
22. The method of claim 21, comprising Pr ₂ O ₃ . 30 The multi-component powder contains about 0.1 to 2 (mol)%
22. The method according to claim 21, further comprising SrO or CaO. 31 The step of preparing a multi-component powder comprises:
22. The method of claim 21, comprising the step of mixing micron to submicron particle size high purity powders of Gd ₂ O ₃ , Y ₂ O ₃ and at least one of said rare earth oxide activators. 32 The step of preparing a multicomponent powder comprises coprecipitating Y, Gd and the oxalate of at least one rare earth element to be added as an activator by a wet chemical oxalate method, and then adding the oxalate of the at least one rare earth element to be added as an activator. 22. A method according to claim 21, comprising the steps of obtaining the corresponding oxide by calcining the acid salt. 33. The method of claim 32, wherein said calcination step comprises heating said oxalate salt in air at a temperature of 700 to 900C for 1 to 4 hours. 34. The method of claim 32, further comprising the step of grinding the oxalate salt prior to the calcination step. 35 Claim 3 additionally includes a step of grinding the oxide obtained in the firing step
2 or 34. 36. Claims 21 and 3, wherein said step of cold compacting said multicomponent powder comprises the step of mold compacting said multicomponent powder under a pressure of about 3000 to 15000 psi.
33. The method according to item 1 or 32. 37 The step of compressing the multi-component powder at room temperature compresses the multi-component powder that has been mold-compressed in order to further increase the green density and uniformity of the compacted powder body.
37. The method of claim 36, further comprising the step of isobaric compression at a pressure of 10,000 to 60,000 psi. 38 The step of sintering the compacted powder body is performed by sintering the compacted powder body at a rate of about 100 to 700°C/hour.
38. The method of claim 37, comprising the steps of heating to a sintering temperature of 2100<0>C and then maintaining said sintering temperature for about 1 to 30 hours. 39 The step of sintering the compacted powder body may include sintering the compacted powder body at a rate of 300 to 400°C/hour to 1600 to
Heating to a holding temperature of 1700°C, maintaining said holding temperature for 1 to 20 hours, then increasing the temperature at a rate of 25 to 75°C/hour to a final sintering temperature of 1800 to 2100°C, and then final sintering. 38. The method of claim 37, comprising the steps of maintaining the freezing temperature for 1 to 10 hours. 40. The method of claim 38, wherein the heating step is performed in air or in a reducing atmosphere. 41. The method of claim 37, further comprising the step of cooling the resulting polycrystalline ceramic scintillator to room temperature for about 2 to 10 hours. 42 (A) (a) about 5-50 (mol)% Gd ₂ O ₃ , (b)
Eu ₂ O ₃ , Nd ₂ O ₃ , Yb ₂ O ₃ , Dy ₂ O ₃ , Tb ₂ O ₃ and
Approximately 0.02 to 12 (mol) selected from the group consisting of Pr ₂ O ₃
% of at least one rare earth oxide activator, and ( _C ) the balance _Y2O3 ;
(B) forming a compacted powder body by compressing the multi-component powder; (C) presintering the compacted powder body to a closed pore-containing state; and (D) applying gas to the presintered body. 1. A method for producing a polycrystalline ceramic scintillator, comprising steps of forming a polycrystalline ceramic scintillator with higher density by subjecting the method to high-temperature isobaric compression. 43 The multi-component powder contains about 20 to 40 (mol)%
43. The method of claim 42 containing Gd ₂ O ₃ . 44 The multi-component powder contains about 1 to 6 (mol)%
43. The method of claim 42 containing Eu ₂ O ₃ . 45 The multi-component powder contains 0.1 to 2 (mol)%
43. The method of claim 42 containing Yb ₂ O ₃ . 46 The multi-component powder contains about 20 to 40 (mol)%
Claim 42 containing Gd ₂ O ₃ , about 1-6 (mol) % Eu ₂ O ₃ , 0.1-2 (mol) % Yb ₂ O ₃ and the balance Y ₂ O ₃ Method. 47 The multi-component powder contains about 0.05 to 1.5 (mol)%
43. The method of claim 42 containing Nd ₂ O ₃ . 48 The multi-component powder contains about 0.05 to 3 (mol)%
43. The method of claim 42 containing Tb ₂ O ₃ . 49 The multi-component powder contains about 0.03 to 1 (mol)%
43. The method of claim 42 containing Dy ₂ O ₃ . 50 The multi-component powder is about 0.02 to 0.05 (mol)%
43. The method of claim 42, comprising Pr ₂ O ₃ . 51 The multi-component powder contains about 0.1 to 2 (mol)%
43. The method according to claim 42, further comprising SrO or CaO. 52 The step of preparing a multi-component powder comprises:
43. The method of claim 42, comprising the step of mixing micron to submicron particle size high purity powders of Gd ₂ O ₃ , Y ₂ O ₃ and at least one of said rare earth oxide activators. 53 The step of preparing a multicomponent powder comprises coprecipitating Y, Gd and the oxalate of at least one rare earth element to be added as an activator by a wet chemical oxalate method, and then adding the oxalate of the at least one rare earth element to be added as an activator. 43. A method according to claim 42, comprising the steps of obtaining the corresponding oxide by calcining the acid salt. 54. The method of claim 53, wherein said calcination step comprises heating said oxalate salt in air at a temperature of 700 to 900C for 1 to 4 hours. 55. The method of claim 53, further comprising the step of grinding the oxalate salt prior to the calcination step. 56 Claim 5 additionally includes a step of grinding the oxide obtained in the firing step
3 or 55. 57. The step of compacting the multicomponent powder forms a pre-powder compact by cold compacting the multicomponent powder under a pressure of about 3000 to 10000 psi;
The preliminary powder compact is then heated to about 15,000 to 60,000 psi to increase the green density of the preliminary powder compact.
54. A method according to claim 42, 52 or 53, comprising both steps of isobaric compression under a pressure of . 58. The method of claim 57, wherein said step of pre-sintering said powder compact comprises the step of heating said powder compact at a temperature of about 1500-1700<0>C for 1-10 hours. 59 The step of subjecting the preliminary sintered body to gas high temperature isobaric compression is performed at a temperature of about 1500 to 1800°C and a temperature of about 1000 to
Claim 58 comprising heating under 30000 psi argon gas pressure for 1 to 2 hours.
The method described in section. 60 The step of subjecting the preliminary sintered body to gas high-temperature isobaric compression is more specifically performed by heating the pre-sintered body for one hour.
Raise the temperature to 1400℃, continue heating for 1 hour, raise the temperature to 1750℃, and then heat to 1750℃ for 1 hour.
It consists of various steps of maintaining the temperature at a temperature of
60. The method of claim 59 carried out under argon gas pressure of 25000 psi. 61 (A) (a) about 5-50 (mol)% Gd ₂ O ₃ , (b)
Eu ₂ O ₃ , Nd ₂ O ₃ , Yb ₂ O ₃ , Dy ₂ O ₃ , Tb ₂ O ₃ and
Approximately 0.02 to 12 (mol) selected from the group consisting of Pr ₂ O ₃
% of at least one rare earth oxide activator, and ( _c ) the balance _Y2O3 ;
(B) The multi-component powder is heated in a vacuum of 200 microns or less at a temperature of about 600 to 700°C and a temperature of about 1000 to
Compress for 1 hour under a pressure of 1200psi, then (C) increase the temperature to about 1300-1600℃, increase the pressure to about 4000-10000psi, then reduce the temperature and pressure after increasing by 1/2-4 1. A method for producing a polycrystalline ceramic scintillator, comprising steps of forming a polycrystalline ceramic scintillator by maintaining it over a period of time. 62 The multi-component powder contains about 20 to 40 (mol)%
62. The method of claim 61 containing Gd ₂ O ₃ . 63 The multi-component powder contains about 1 to 6 (mol)%
62. The method of claim 61 containing Eu ₂ O ₃ . 64 The multi-component powder contains 0.1 to 2 (mol)%
62. The method of claim 61 containing Yb ₂ O ₃ . 65 The multi-component powder contains about 20 to 40 (mol)%
Claim 61 containing Gd ₂ O ₃ , about 1-6 (mol) % Eu ₂ O ₃ , 0.1-2 (mol) % Yb ₂ O ₃ and the balance Y ₂ O ₃ Method. 66 The multi-component powder contains about 0.05 to 1.5 (mol)%
62. The method of claim 61 containing Nd ₂ O ₃ . 67 The multi-component powder contains about 0.05 to 3 (mol)%
62. The method of claim 61, comprising Tb ₂ O ₃ . 68 The multi-component powder contains about 0.03 to 1 (mol)%
62. The method of claim 61, comprising Dy ₂ O ₃ . 69 The multi-component powder is about 0.02 to 0.05 (mol)%
62. The method of claim 61, comprising Pr ₂ O ₃ . 70 The multi-component powder contains about 0.1 to 2 (mol)%
62. The method of claim 61, further comprising SrO or CaO. 71 The step of preparing a multi-component powder comprises:
62. The method of claim 61, comprising the step of mixing micron to submicron particle size high purity powders of Gd ₂ O ₃ , Y ₂ O ₃ and at least one of said rare earth oxide activators. 72 Said step of preparing a multicomponent powder comprises co-precipitating Y, Gd and the oxalate of at least one rare earth element to be added as an activator by a wet chemical oxalate method, and then adding said oxalate to said sulfur. 62. The method of claim 61, comprising the steps of obtaining the corresponding oxide by calcining the acid salt. 73. The method of claim 72, wherein said calcination step comprises heating said oxalate salt in air at a temperature of 700 to 900C for 1 to 4 hours. 74. The method of claim 72, further comprising the step of grinding the oxalate prior to the calcination step. 75 Claim 7 additionally includes a step of grinding the oxide obtained in the calcination step
2 or 74. 76 A step of oxidizing the obtained polycrystalline ceramic scintillator to remove discoloration is additionally included, and said oxidation step oxidizes said polycrystalline ceramic scintillator in an oxygen-containing atmosphere.
62. The method of claim 61, comprising heating at a temperature of 800-1200<0>C for about 1-20 hours.