CN1200351A

CN1200351A - Single crystals of lead tungstate

Info

Publication number: CN1200351A
Application number: CN 98106681
Authority: CN
Inventors: 薄善行
Original assignee: Furukawa Co Ltd
Current assignee: Furukawa Co Ltd
Priority date: 1997-04-22
Filing date: 1998-04-20
Publication date: 1998-12-02
Anticipated expiration: 2018-04-20
Also published as: JPH10291898A; CN1092148C; RU2145648C1

Abstract

Lead monocrystals are obtained through use of tungsten trioxide and lead dioxide or lead tungstate which contain lanthanum in amount from 3.10-7 mole to 10.10-3 mole per mole of lead tungstate. Thus lead tungstate monocrystals may be obtained, possibility of obtaining crystals used as scintillator for radiation detector increasing amount of used light due to increased light transmission coefficient and reduced self-absorption.

Description

Single crystals of lead tungstate

The present invention relates to be used as the single crystals of lead tungstate of scintillator, this scintillator is used for radioactive ray, such as X ray or gamma-ray detector.

For the scintillator that is used for high energy the various features requirement is arranged, wherein particularly importantly: (1) high-density, the radiation hardness that (2) bob optical attenuation time and (3) are excellent.

Up to the present, Bi ₄Ge ₃O ₁₂Being used as the material that satisfies above-mentioned requirements uses.

, require scintillator to have higher performance characteristic in recent years.According to above-mentioned viewpoint, for searching has more the material of performance characteristics multiple material is studied, people such as Derenzo find, in these materials, plumbous tungstate PbWO ₄Can be used for radioactivity prospecting.Then, at PbWO ₄The measurement of the production of monocrystalline, their characteristics and make them enter the practical application aspect to have carried out research.

Usually, PbWO ₄Monocrystalline is produced with rotary pulling method (Czochralsky method).Use plumbous oxide (PbO) and tungstic oxide (WO exactly ₃) or PbWO ₄Do initial material, be placed on the fusion of platinum crucible internal heating, PbWO ₄Monocrystalline is just produced with the Czochralsky method.

The PbWO that obtains ₄Usually can satisfy aforesaid three features., because parent material purity is not enough, impurity is brought into monocrystalline makes crystal present yellow.PbWO ₄The emission peak of monocrystalline is positioned at 400nm near 420nm, and because near the light of yellow absorption wavelength its, the light part of emission is sponged by the crystalline self-absorption, when light when crystal penetrates, the loss of light is just inevitable.

To PbWO ₄, light is output as Bi ₄Ge ₃O ₁₂3% (PbWO ₄Value comprise self-absorption).

From the angle of three features above-mentioned, PbWO ₄Be much better than existing Bi ₄Ge ₃O ₁₂, but its luminous quantity is less.Therefore reduce PbWO ₄In self-absorption, it is extremely important also promptly reducing crystalline painted.

In any case, carried out multiple trial for the minimizing crystalline is painted.One of them is exactly a purity of improving parent material.Even but when the purity of parent material reaches 99.999%, also do not obtain satisfied result.On the other hand, also try the overdoping agent for opaque, but same not success.If the adding molybdenum occurs increasing at weak radiation zone luminous quantity, but then identical with the crystal that those do not add molybdenum at severe radiation district luminous quantity, and also has, the adding of molybdenum degenerates luminescence decay time.

As mentioned above, do not sacrifice other characteristic and reduce also achieving success of coloring of crystal.

The accelerator that use in the high energy field needs higher energy.So, the scintillator of radiation detector just needs better temporal resolution.Therefore, the crystal that is used as scintillator just needs shorter fall time (recommendation is less than several nanoseconds) and excellent radiation hardness (recommendation is greater than 10 ⁸Rad).On the other hand, from the angle of surveying instrument sensitivity, luminous quantity is big more to have superiority more.The present PbWO that produces ₄Monocrystalline is not enough to the requirement that reaches such.

The invention is intended to overcome foregoing problems, its purpose is to provide the single crystals of lead tungstate of the scintillator that is used as radiation detector.

According to the present invention, every mole that makes with tungstic oxide and plumbous oxide or plumbous tungstate contains 3 * 10 ^-7Mole is to 1 * 10 ^-3The single crystals of lead tungstate of mole lanthanum just can reach aforementioned purpose.

Aforementioned and further feature of the present invention and advantage are below with reference to the accompanying drawings to embodying in the description that preferential embodiment carried out.Here,

Fig. 1 shows the figure that concerns between wavelength and the transmissivity;

Fig. 2 shows the concentration of lanthanum and the figure that transmissivity increases relation between the ratio.

As to having the PbWO of less smooth self-absorption₄The conscientiously result of research of monocrystalline, the inventor finds existing PbWO₄The transmittance graph of monocrystalline has a depression near 420nm, it means big Near the self-absorption, ABSORPTION EDGE curvilinear motion is gentle, as shown in Figure 1. On the other hand, added lanthanum PbWO₄The transmittance graph of monocrystalline does not cave near 420nm, this means little self-absorption, And near the curve the ABSORPTION EDGE descends suddenly, this means that this characteristic is gratifying. At this On one basis of finding, the inventor has done kinds of experiments, has obtained according to lead tungstate list of the present invention Brilliant.

At PbWO₄In the monocrystalline, can utilize the amount of light to increase by increasing light transmission and minimizing self-absorption, this is realized that by lead tungstate mixing lanthanum the content of lanthanum is every mole of PbWO₄Contain 3 * 10^-7Mole is to 1 * 10^-3The mole lanthanum.

If the content of lanthanum is 3 * 10^-7Mole or still less, because painted self-absorption appears, otherwise, if the content of lanthanum is 1 * 10^-3Mole or more, because black appears in comprehensive self-absorption that lanthanum causes, and Transmissivity degenerates.

PbO and WO ₃Or PbWO ₄Be used as parent material, and be placed in the fusion of platinum crucible internal heating, PbWO ₄Monocrystalline is prepared with the Czochralsky method.PbWO ₄Lanthanum content in the monocrystalline is at every mole of PbWO ₄Contain 3 * 10 ^-7Mole is to 1 * 10 ^-3Between the mole.

For this purpose, be used as the PbO and the WO of parent material ₃Or PbWO ₄In lanthanum content be decided to be 3 * 10 ^-7The mole or still less.And then, PbO and WO ₃Or PbWO ₄In foreign matter content, do not comprise lanthanum, be decided to be 1 * 10 ^-4The mole or still less, recommendation is 1 * 10 ^-5Or still less.

PbWO when such acquisition ₄The size that monocrystalline is processed to be scheduled to is also done mirror polish, and when doing optical transmittance and observing, near optical transmission rate curve depression not 420nm, and curve descends suddenly near ABSORPTION EDGE, this means excellent characteristic.

Example 1

In the purity of mole numbers such as respectively weighing up 99.99% PbO powder and WO ₃Powder and their are mixed after, mixture is inserted diameter 70mm, the platinum crucible of high 70mm, the sensed heating and melting of initial powder shape material blends, PbWO ₄Monocrystalline is prepared into diameter 35mm with the Czochralsky method from the fused liquid state, the rod of long 65mm.Lanthanum is added into so that contain 3 * 10 in the crystal ^-7The lanthanum of mole.At PbO and WO ₃Lanthanum in the powder is 5 * 10 ^-8Or still less.

The PbWO of Huo Deing like this ₄Monocrystalline is cut into 1 * 1 * 2cm size, and by mirror polish, surveys the transmissivity of 300nm and 600nm then on the 1cm thickness direction.

The result is displayed among Fig. 1 and Fig. 2.Fig. 1 has shown the relation between wavelength and the transmissivity, and Fig. 2 has shown the content of lanthanum and the relation between the transmissivity increase ratio.

Transmittance graph does not cave near 420nm, and has shown unexpected decline near the ABSORPTION EDGE of curve.Transmissivity is 70.5% at the 420nm place, 19.5% increase occurred.Example 2

In the purity of mole numbers such as respectively weighing up 99.99% PbO powder and WO ₃Powder and their are mixed after, mixture is inserted diameter 70mm, the platinum crucible of high 70mm, the sensed heating and melting of initial powder shape material blends, PbWO ₄Monocrystalline is prepared into diameter 33mm with the Czochralsky method from the fused liquid state, the rod of long 70mm.Lanthanum is added into so that contain 2.2 * 10 in the crystal ^-5The lanthanum of mole.At PbO and WO ₃Lanthanum in the powder is 5 * 10 ^-8Or still less.

The result is displayed among Fig. 1 and Fig. 2.Transmittance graph does not cave near 420nm, and has shown unexpected decline near the ABSORPTION EDGE of curve.Transmissivity is 71% at the 420nm place, 20.3% increase occurred.Example 3

In the purity of mole numbers such as respectively weighing up 99.99% PbO powder and WO ₃Powder and their are mixed after, mixture is inserted diameter 70mm, the platinum crucible of high 70mm, the sensed heating and melting of initial powder shape material blends, PbWO ₄Monocrystalline is prepared into diameter 35mm with the Czochralsky method from the fused liquid state, the rod of long 70mm.Lanthanum is added into so that contain 7.5 * 10 in the crystal ^-4The lanthanum of mole.At PbO and WO ₃Lanthanum in the powder is 5 * 10 ^-8Or still less.

The result is displayed among Fig. 1 and Fig. 2.Transmittance graph does not cave near 420nm, and has shown unexpected decline near the ABSORPTION EDGE of curve.Transmissivity is 70% at the 420nm place, 18.6% increase occurred.Example 4

In the purity of mole numbers such as respectively weighing up 99.99% PbO powder and WO ₃Powder and their are mixed after, mixture is inserted diameter 70mm, the platinum crucible of high 70mm, the sensed heating and melting of initial powder shape material blends, PbWO ₄Monocrystalline is prepared into diameter 35mm with the Czochralsky method from the fused liquid state, the rod of long 60mm.Lanthanum is added into so that contain 1 * 10 in the crystal ^-3The lanthanum of mole.At PbO and WO ₃Lanthanum in the powder is 5 * 10 ^-8Or still less.

The result is displayed among Fig. 1 and Fig. 2.Transmittance graph does not cave near 420nm, and has shown unexpected decline near the ABSORPTION EDGE of curve.Transmissivity is 69% at the 420nm place, 16.9% increase occurred.

Owing to contain 3 * 10 ^-7Mole is to 1 * 10 ^-3The PbWO of mole lanthanum ₄Monocrystalline has high-transmission rate and less self-absorption, and the luminous energy of emission does not have absorption and penetrates from crystal when passing crystal.

In above-mentioned experiment, measure and carry out along the 1cm thickness direction.In any case because the material that uses has 23cm long in actual applications, the difference of every 1cm transmissivity can be brought extremely important influence in actual applications.

If resemble PbWO of the prior art ₄Monocrystalline is such, and transmittance graph has a depression near 420nm, and emission wavelength will be absorbed in the long traveling process of 23cm at the light between 400 to 430nm, and outside emergent light almost.Because existing PbWO ₄Monocrystalline is 59% in the transmissivity of the 420nm wavelength every 1cm in place, passing through certain-length, as available light behind the 23cm have only emission measure 1% or still less.

, because according to PbWO of the present invention ₄Monocrystalline does not almost have self-absorption, and radiative major part can be utilized.For example, if the transmissivity of every 1cm is 70%, the transit dose of light just is increased to 50 times.

Therefore, this PbWO ₄Monocrystalline can be effectively used to practical application.

As mentioned above, according to the present invention,, can obtain to do the single crystals of lead tungstate that the scintillator of radiation detector is used by improving optical transmittance and reducing the light emission amount that self-absorption increases single crystals of lead tungstate.

Claims

1. with the single crystals of lead tungstate of tungstic oxide and plumbous oxide or plumbous tungstate preparation, it is characterized in that each mole plumbous tungstate contains 3 * 10 ^-7Mole is to 1 * 10 ^-3The mole lanthanum.