JPS62277587A - Neutron converter - Google Patents

Abstract

PURPOSE:To obtain a high-sensitivity converter with improved definition by specifying the particle size of <6>LiF of a converter made of a mixture of <6>LiF and a fluorescent material of zinc sulfide with silver and cadmium. CONSTITUTION:This converter has a base and a fluorescent material layer provided on the base and the fluorescent material layer consists of the mixture of <6>Lif dispersed in a binder and the fluorescent material (Zn1-x, Cdx)S:Ag (X: number satisfying 0<=X<=0.6) of zinc sulfide with silver and cadmium. The mean particle size of <6>LiF has its center value preferably within a range of 5-20mum as to sensitivity and sharpness and more preferably within a range of 8-15mum. This <6>LiF, (Zn1-x, Cdx)S:Ag fluorescent material, and the binder are added to a solvent, and a dispersant, a plasticizer, etc., are added and mixed to prepare fluorescent material coating liquid. This fluorescent material coating liquid is applied uniformly over the base and dried to form the fluorescent material layer. Further, a protection layer is provided to the fluorescent layer and then the high-sensitivity converter with improved sharpness is obtained.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a neutron converter (hereinafter simply referred to as "converter") used in neutron radiography and the like. More specifically, the present invention relates to an improvement in a converter for efficiently converting neutron transmittance information of an object into near-ultraviolet light or visible light, transmitting it to a light detection means such as a film or an image pickup tube, and converting it into an image.

[Conventional technology]

Neutron radiography takes advantage of the fact that the attenuation characteristics of thermal neutrons when they pass through a material are different from those of X-rays and γ-rays used in normal non-destructive testing, and can be used to detect hydrogen-containing compounds and other compounds that are difficult to inspect with X-rays and γ-rays. It is effective for inspecting composite materials consisting of metals and light element materials, and is used for inspecting nuclear reactor materials, rocket carpentry, aircraft jet engine parts, etc.

For neutron radiography, there is a photographic film method that combines a converter made of a material that has a large neutron absorption cross section and contains an element that easily causes a nuclear reaction with neutrons, or a converter made of a mixed material with a phosphor and a photographic film. Mainly used, the converter materials in this case include a mixture of Gd methanoben BN and ZnS:Ag phosphor, Gd2O,S:Tb phosphor, 6LiF and Zns.
: Mixture of Ag fluorophores, Gd2O3 and ZnS :
A mixture with Ag phosphor or the like is used, and these materials are laminated on one side of a support made of plastic, aluminum, or the like.

[Problem that the invention seeks to solve]

Among these conventionally known converters, Gd
A converter that does not use a phosphor instead of a metal converter can provide images with excellent sharpness, but the sensitivity is low, and even when neutrons from a nuclear reactor are used as a radiation source, for example, the flux amount is L 2 X 10' n/cof
Irradiation with a neutron flux of /sec requires 10 to 20 minutes of irradiation to obtain a sufficient image, and if a small cyclotron, which emits less neutron flux, is used as a radiation source, the time required for imaging will be even longer. It's time. On the other hand, Gd2O□S has a large neutron absorption cross section from the phosphor layer.
; Converters made of a mixture of a fluorophore and a substance with a large neutron absorption cross section, such as Tb fluorescer or BN, Gd2O3, 6LiF, etc., have relatively high sensitivity; among these, 6LiF and 2nS : A converter made of a mixture with Ag phosphor has a sensitivity several tens to 100 times higher than a converter made of Gd metal, so it can significantly shorten the imaging time, but the quality of the obtained neutron image is poor, making it impractical. Because of these unsatisfactory conditions, it has been desired to develop a converter that can provide images with higher sensitivity and sharpness than these conventional converters.

The present invention has been made in view of the above-mentioned situation, and it is an object of the present invention to provide a converter with particularly high sensitivity and improved sharpness compared to conventional converters.

[Means for solving problems]

In order to achieve the above object, the present inventors have developed 'LiF and silver-activated zinc sulfide cadmium-based phosphors ((Zn, 8, Cd,
)S:Ag) is particularly sensitive, and 6LiF and (Zn
+-,,Cd, )S: As a result of detailed research on the mixing ratio of Ag, particle size distribution, and their preparation method, we found that 6Li, which is one of its constituents and does not emit any light on its own,
Depending on the particle size distribution of F, (2nl-x, Cd
,,)S: The sensitivity and sharpness of the converter, which are also affected by the particle size distribution of the Ag phosphor, change greatly.In particular, by using 'LiF, which has a larger particle size than the conventional one, By using a (2J-x, CdX)S:Ag phosphor with a smaller particle size, a more sensitive and sharper converter can be obtained, while also reducing the amount of binder resin in the phosphor layer. The inventors have discovered that a converter with high sensitivity and high sharpness can also be obtained by the following methods, and have completed the present invention.

That is, the converter of the present invention has a support and a phosphor layer provided on the support, and the phosphor layer contains 6LiF and silver-activated zinc sulfide/cadmium dispersed in a binder. System phosphor ((Zn+-x, Cd, )S: Ag
, where X is a number that satisfies the condition 0≦X≦0.6. The same applies hereinafter), and the 6Li
It is characterized in that the average particle diameter of F is 5 μm to 20 μm.

The converter of the present invention is manufactured, for example, by the following method.

First, 6LiF of a specific particle size, (2n, , Cd,
)S:Ag phosphor and binder are added to a suitable solvent, and if necessary, a dispersant, a plasticizer, etc. that are commonly used in preparing the phosphor layer of an intensifying screen are added to this. In addition, these are sufficiently mixed to prepare a phosphor coating solution. mixing ratio〔
6IF and (2n1-,,CdX)S in the phosphor coating solution
: total weight with Ag phosphor]; [weight of binder] can generally be used in the range of 1:1 to 100:1. However, 6LiF and (Zn+-x, CdX)S:A
When the weight of the binder increases relative to the total weight of the phosphor, the sensitivity of the converter decreases due to absorption and scattering of neutrons by the binder, and at the same time, the sharpness (resolution) also tends to decrease. If the amount of binder is too small, the strength of the converter will be significantly reduced. Therefore, in order to obtain an excellent converter with particularly high sensitivity and high sharpness, it is necessary to combine 6LiF and (Zn+-X N
More preferably, the mixing ratio of the total weight of the CdjS diAg phosphor to the binder is selected in the range of 5:1 to 20:1.

Next, the phosphor coating solution prepared as described above is coated on ordinary paper, baryta paper, pigment paper containing pigments such as carbon, titanium dioxide, etc. by ordinary coating means using a roll coater, knife coater, etc. It is coated uniformly onto a support made of a material such as aluminum foil and dried to form a phosphor layer. Furthermore, a protective film made of a transparent plastic thin film that can transmit light may be provided on the surface of the phosphor layer in order to protect the phosphor layer. , apply a solution prepared by dissolving a transparent polymer substance such as nitrocellulose, polymethyl methacrylate, polyvinyl butyral, vinyl chloride/vinyl acetate copolymer in an appropriate solvent and dry it to form a protective film, or polyethylene terephthalate,
A transparent thin film of polyethylene, polyamide, etc. is laminated on the surface of the phosphor layer to obtain the converter of the present invention.

The 6LiF used in the converter of the present invention is obtained by dissolving commercially available 6LiF with a high 6L1 content or lithium salts such as 6L1□CO3, 6LiN03, etc. with an extremely high 6Sil content in water, acid, etc., and then adding KF, f46LiF is used by adding a fluorine-containing compound soluble in water or acid such as HF to precipitate it as a fluoride. If the 6LiF used in the converter of the present invention is smaller than 5 μm, the resulting converter will not have sufficient sensitivity, as in conventional converters, and if it is larger than 20 μm, the sensitivity of the converter will not decrease significantly but the sharpness will deteriorate. Therefore, from the viewpoint of sensitivity and sharpness, it is preferable that the average particle diameter of 6F used in the converter of the present invention is in the range of 5 μm to 20 μm, and preferably 8 μm to 20 μm. More preferably, the thickness is in the range of 15 μm. In order to obtain 6LiF with such a specific particle size, ready-made 6LiF may be classified using a sieve, water sieve, etc.;
According to the method for synthesizing F, the desired particle size can be obtained by controlling reaction conditions such as the concentration of hexabiion, concentration of F- ion, pH value, liquid temperature, and addition rate of the fluorine-containing compound in the reaction solution. This is particularly preferable since it is possible to produce 61F having the following properties.

One of the components of the converter of the present invention (Zn
l Fluorophores containing co-activators may be used as well. (
The Zn + - The sensitivity of the imaging system including the converter may change depending on the spectral sensitivity of the photodetector used, but from the viewpoint of sensitivity, x = 0 (Zn+-11, C
L)S'Ag fluorophore, i.e. ZnS:Ag)
are particularly recommended as converters for the present invention.

Moreover, the sensitivity of the converter of the present invention is (Zllll-M,
CdX)S: Average particle diameter of Ag phosphor and (Zn
, -M%Cd) S:Ag It changes depending on the relative relationship between the average particle diameter of the phosphor and the 6-IF, and is used in terms of sensitivity (2n+ -x, Ccl+)S:Ag
The average particle diameter of the phosphor is in the range of 3 μm to 7 μm,
Furthermore, it is particularly preferable to use a material that is equal to or lower than that of 6LiF. That is, the ratio of the average particle diameter of 6LiF to the average particle diameter of the silver-activated zinc sulfide/cadmium phosphor is 1.
It is preferable that it is above.

Furthermore, the converter of the present invention has 6LiF in the phosphor layer and (
Zn, )l, Cdx)S: The sensitivity changes greatly depending on the mixing weight ratio with Ag phosphor, and regardless of the size of each particle, the mixing weight ratio of both (silver-activated zinc sulfide/cadmium It is preferable that the ratio of 6LiF to the system phosphor is approximately 0.5 to 2.0, and from the viewpoint of sensitivity, it is more preferable that this ratio is in the range of 0.6 to 1.3. Particularly preferred.

Binders used in the converter of the present invention include nitrocellulose, ethylcellulose, vinyl chloride/vinyl acetate copolymer, polyvinyl acetate, polyvinyl butyral, polymethyl methacrylate, acrylic polyol, polyurethane, cellulose acetate/butyrate, etc. Binders commonly used for layer formation are used.

FIG. 1 illustrates the correlation between the particle size of 6LiF used in a converter made of 6LiF and a znS:Ag phosphor and the sensitivity of the resulting converter. In Figure 1, the relative sensitivity on the vertical axis was determined by measuring the degree of blackening of the film when the film was placed in close contact with each converter and irradiated with neutrons of a partial flag amount for a certain period of time, and 6LiF with an average particle size of 12 μm was used. It is expressed as a relative value when the degree of blackening of the converter is set to 100, and the particle size of the ZnS:Ag phosphor used at this time was constant.

As is clear from Figure 1, the particle diameter is approximately 5 μm to 2 μm.
It has a sensitivity of 90% or more of the maximum sensitivity when the particle size is in the range of 0 μm, and it is especially more sensitive than when the particle size is 8 μm to 15 μm, both of which are more sensitive than conventional converters using LiF with an average particle size of 3 to 4 μm. Even a highly sensitive converter (asked).

Figures 2 and 3 are the same (6LiF and ZnS
A graph illustrating the relationship between the average particle diameter of the ZnS:Ag phosphor and the relative sensitivity of the resulting converter used in a converter consisting of a ZnS:Ag phosphor and the mixing weight ratio of 6LiF and lnS:Ag phosphor and the obtained 2 is a graph illustrating the relationship between the relative sensitivity of the converter and the relative sensitivity of the converter, and the relative sensitivity on the vertical axis of each graph is obtained in the same manner as in FIG. 1.

As is clear from FIG. 2, in the converter of the present invention composed of 61F and lnS:Ag fluorophores, when the particle diameter of 61F used is constant, the ZnS:Ag fluorescer used together with 61F and lnS:Ag fluorophores The average particle diameter of the converter peaks at about 5 μm, and the sensitivity decreases as the particle size becomes larger or smaller, and a converter with a sensitivity of 90% or more of the maximum sensitivity in the range of 3 μm to 7 μm can be obtained.

Moreover, as is clear from Fig. 3, 6-IF and ZnS
: A converter consisting of a mixture of Ag fluorophores
LiF and ZnS: 6LI relative to the weight of Ag phosphor
The sensitivity peaks when the F weight mixing ratio is approximately I (1/1), and this ratio is approximately 0.5 to 2.0 (
1/2 to 2/1), the maximum sensitivity is 80
% or more.

In addition, in a converter made of 6LiF and ZnS:Ag phosphor, the relationship between the particle size of LiF and the relative sensitivity of the resulting converter is as follows:
Regardless of the particle size of the Ag phosphor, the relationship is roughly similar to that illustrated in Figure 1, and 2nS: Ag
It was confirmed that the relationship between the particle size of the phosphor and the relative sensitivity of the resulting converter is similar to the relationship illustrated in FIG. 2, regardless of the particle size of 6LiF used at the same time.

In addition, the relationship between the mixing weight ratio of 6LiF and 2nS:Ag phosphor and the relative sensitivity of the resulting converter is also used. Similar to the correlation, the most sensitive converter was obtained when the mixed weight ratio of both was close to 1. Furthermore, although not exemplified, when (Znl K , Cdx )S:Ag fluorophores other than ZnS:Ag are used, the relative sensitivity and 61i of the resulting converter
F or (Zn14, Cdx)S: Ag phosphor particle size and 6 silF and (Zn1-x, Cd,,)S
: The correlation with the mixing weight ratio with the Ag phosphor showed a tendency roughly similar to the correlation illustrated in FIGS. 1 to 3.

Next, the present invention will be explained with reference to examples. However, these Examples do not limit the present invention.

〔Example〕

(Example 1) Lithium carbonate (6t,
12CO,) 1 part by weight was added to 1.5N hydrochloric acid (llc1
Ammonium hydroxide (NH,OH) dissolved in 20 parts by weight
After adjusting the pH to 5 with
6LI by adding a 10% aqueous solution in which parts by weight were dissolved at room temperature.
F was precipitated, filtered and dried to yield 6LiF. The particle size of the obtained 6LiF was measured by microscopy, and the average particle size was 8 μm.

'LiF with an average particle size of 8 μm produced in this way
5 parts by weight of ZnS with an average particle size of 4 μm: 5 parts by weight of A,g phosphor and 1 part by weight of nitrocellulose (binder) were mixed with a solvent (a mixture of acetone and ethyl acetate in a weight ratio of 1:9). A phosphor coating solution having a viscosity of approximately 100 centistokes was prepared by mixing.

Next, this phosphor coating solution was applied onto a 150 μm thick paper support having a carbon black light absorption layer on the surface using a knife coater so that the phosphor coating weight after drying was approximately 50 mg/ctl. The phosphor layer was formed by applying the film uniformly and drying it.

Next, a coating solution prepared by dissolving cellulose acetate in acetone is applied onto this phosphor layer so that the film thickness after drying is approximately 5 μm, and is dried to form a protective film.
I] was produced.

(Example 2) Same as Example 1 except that instead of the 10% aqueous solution containing 2 parts by weight of potassium fluoride (KF), a 6% aqueous solution containing 2 parts by weight of potassium fluoride (KF) was used. 61iF with an average particle diameter of 12 μm was obtained.

Next, instead of 61iF with an average particle diameter of 8 μm, 6iIF with an average particle diameter of 12 μm obtained as described above was used,
Furthermore, a ZnS:Ag phosphor with an average particle size of 5 μm was used in place of the 2nS:Ag phosphor with an average particle size of 4 μm, and the coating weight of the phosphor after drying was 60 mg/day on the support.
Converter [II] was produced in the same manner as in Example 1, except that the phosphor coating liquid was applied so as to be cTII.

(Example 3) Same as Example 1 except that instead of the 10% aqueous solution containing 2 parts by weight of potassium fluoride (KF), an 8% aqueous solution containing 2 parts by weight of potassium fluoride (KF) was used. 6LiF having an average particle diameter of 10 μm was obtained.

Next, 61iF with an average particle diameter of 10 μm obtained as described above was used in place of 61iF with an average particle diameter of 8 μm, and the phosphor coating weight after drying was 35 mg/
A converter ClID was manufactured in the same manner as in Example 1, except that the phosphor coating liquid was applied so as to achieve cr+l.

Converters [I], [■] obtained in this way
, [■] and a commercially available converter [R] (Nuclea
r Enterprises, NE-4266Li
F (average particle size 2 to 3 μm) was brought into close contact with a film (FC manufactured by Fuji Photo Film Co., Ltd.),
This is irradiated with neutrons emitted from a small cyclotron,
When we measured the sensitivity, sharpness, and graininess of each, we obtained the results shown in the table below, and found that the sensitivity, sharpness, and graininess of converters CII, [■], and [, III) were superior to that of the conventional converter CR]. It was significantly better than that.

In addition, these converters [ID, (II), ClI
For D and [R], the rectangular wave test chart made of cadmium foil described above was irradiated with neutrons from a small cyclotron as a subject, and the image of the test chart appearing on each converter was displayed on a display using an image pickup tube. However, images that appear via converter (I), CITE and [■] are converted to converter [R].
The image was brighter and had better resolution than the image that appeared via .

〔Effect of the invention〕

As detailed above, 'LiF and (2n, -X, CcL
)S: In a converter consisting of a mixture with Ag fluorophore, 'LiF and (ln+-x, Cdx)S
: By specifying the particle size of Ag and the amount of binder resin, a converter with particularly excellent sensitivity and sharpness compared to conventional ones can be obtained, and is useful for non-destructive testing using neutrons such as neutron radiography.

[Brief explanation of the drawing]

Figure 1 shows 6Li, which is a component of the converter of the present invention.
2 is a graph illustrating the relationship between the particle diameter of F and the relative sensitivity of the resulting converter. Figure 2 shows ZnS, which is a component of the converter of the present invention.
: is a graph illustrating the relationship between the particle size of Ag phosphor and the relative sensitivity of the resulting converter. Figure 3 shows 61F, which is a component of the converter of the present invention.
(!: ZnS: This is a graph illustrating the relationship between the mixed type ratio with Ag phosphor and the relative sensitivity of the converter, which is increased by 1.

Claims (10)

[Claims] (1) ^6LiF, which has a support and a phosphor layer provided on the support, and the phosphor layer is dispersed in a binder.
and the composition formula is (Zn_1_-_x, Cd_x)S:Ag(
However, x is a number that satisfies the condition 0≦x≦0.6)
It consists of a mixture with a silver-activated zinc sulfide/cadmium phosphor represented by
A neutron converter characterized in that it is in the range of 20 μm to 20 μm. (2) The average particle diameter of the ^6LiF is 8 μm to 15 μm
2. A neutron converter according to claim 1, characterized in that the neutron converter is in the range of m. (3) The neutron converter according to any one of claims 1 to 2, wherein the x is a number that satisfies the condition that x=0. (4) The average particle diameter of the silver-activated zinc sulfide/cadmium-based phosphor is in the range of 3 μm to 7 μm. Neutron converter. (5) Claims 1 to 4 characterized in that the ratio of the average particle diameter of the ^6LiF to the average particle diameter of the silver-activated zinc sulfide/cadmium-based phosphor is 1 or more. A neutron converter according to any one of the above. (6) The ratio of the weight of the ^6LiF to the weight of the silver-activated zinc sulfide/cadmium phosphor is 0.5 to 2.0.
A neutron converter according to any one of claims 1 to 5, characterized in that the neutron converter falls within the range of . (7) A mixing ratio of the total weight of the ^6LiF and the silver-activated zinc sulfide/cadmium-based phosphor to the weight of the binder is 5 or more.
The neutron converter according to any one of Items 6 to 6. (8) The neutron rays according to any one of claims 1 to 7, wherein the support is made of a paper support having a light absorption layer at least on the side of the support that is in contact with the phosphor layer. converter. (9) Any one of claims 1 to 8, characterized in that a protective film consisting of a thin layer with a thickness of 10 μm or less is provided on the surface of the phosphor layer opposite to the support side. The neutron converter described in paragraph 1. (10) The above ^6LiF is ^6LiF produced by dissolving ^6LiF_2CO_3 containing 95 at% or more of ^6LiF in acid, and adding a fluorine-containing compound soluble in water or acid to this. A neutron converter according to any one of claims 1 to 9.