JPS5916700B2 - X-ray fluorescence multiplier tube - Google Patents

Description

[Detailed description of the invention] This invention relates to improvements in X@fluorescence multiplier tubes.

Among image tubes, X-ray fluorescence intensifier tubes are used in a wide range of applications, mainly for medical purposes, but also for industrial non-destructive testing, in combination with X@Industrial Television.

This type of X-ray fluorescence multiplier tube is constructed as shown in FIG. It is arranged as follows.

On the other hand, a solar umbrella 4 is disposed inside the output side of the envelope 1, and an output fluorescent surface 5 is formed therein, and a focusing electrode 6 is further formed along the side wall inside the envelope 1. .

After the incident X-ray 1 is once converted into light by the input fluorescent surface 2, the light causes the photocathode 3 to emit photoelectrons 8,
The photoelectrons 8 are accelerated and focused by the anode 4 and the focusing electrode 6 and collided with the output phosphor surface 5 to excite the phosphor and emit light, thereby observing an optical image 9 with enhanced brightness.

By the way, in the above-mentioned X-ray fluorescence multiplier tube, the input surface has conventionally been constructed as shown in FIG.

That is, on the concave side of a substrate 10 mainly made of aluminum and having a certain curvature, a phosphor layer 11 made of cesium iodide as a matrix and added with sodium, thallium, etc. as an activator is formed by vacuum evaporation or the like. On this phosphor layer 11 is a photocathode 12 made of antimono and cesium.
However, this is also formed by a vacuum evaporation method or the like.

However, since the phosphor layer 11 made of cesium iodide is not sufficiently stable with respect to cesium as a substrate for forming a photocathode, the photocathode 12 made of antimony and cesium formed on the phosphor layer 11 has a photoelectric sensitivity. However, the maximum output is only about 10 microamperes/lumen.

Also. Under normal usage conditions, a phenomenon is observed in which the photoelectric sensitivity gradually decreases due to the instability of the substrate.

As a result, the light emitted from the phosphor layer 11 is sufficiently absorbed into the photoelectron 8.
(See FIG. 1), the brightness is low, and the brightness further decreases as the usage time increases.

Another drawback is that a photocathode made of antimony and cesium cannot be formed unless a large amount of cesium is introduced into the tube and reacted with antimony.

That is, the phosphor 5 used on the output surface (see Figure 1)
is mixed with some of the highly concentrated cesium vapor introduced during the formation of the photocathode, leading to a decrease in brightness, and if it progresses further, the phosphor particles on the output surface turn black, resulting in a completely poor output screen quality. It is to be.

This invention was made to improve the above-mentioned drawbacks, and it improves the photoelectrode intensity, brightens the brightness, and further improves the life characteristics. It also does not deteriorate the output screen quality during the formation of the photocathode, so it can produce X-rays with clear image quality. The purpose of this invention is to provide a fluorescence multiplier tube.

An embodiment of the present invention will be described below with reference to FIG.

That is, on the input surface of the X-ray fluorophore multiplier according to the present invention, a low-resistance intermediate layer 13 is disposed between the phosphor layer 11 and the photocathode 14, and the photocathode 14 is made of conventional antimony and cesium. Instead, a material consisting of antimony, potassium and cesium is used.

The low-resistance intermediate layer 13 functions to prevent a chemical reaction between the phosphor layer 11 and the photocathode 14 mainly due to transfer of cesium, and to increase the conductivity in the plane direction of the photocathode.

That is, a phosphor layer 1 made of cesium iodide as a matrix and added with sodium or thallium as an activator is formed on the concave surface of a substrate 10 made of aluminum or the like and having a certain curvature.
1 is formed, and on this phosphor layer 11 there is an intermediate layer made of a metal such as AttAu, which is controlled to be almost transparent to the light emitted from the phosphor layer 11. A layer 13 is applied, on which a photocathode 14 of antimony, potassium and cesium is formed.

Note that since the configuration other than the input surface is the same as that in FIG. 1, detailed explanation will be omitted.

A method of manufacturing such an input fluorescent surface will be described below.

In the first method, cesium iodide 11 to which sodium has been added as an activator is deposited on a clean aluminum substrate 10 having a certain curvature to a thickness of 100 to 150 microns by vacuum evaporation.

After that, an activation treatment is performed at a temperature of 200 to 400°C.

At this point, the surface of the phosphor layer 110 has grown perpendicularly from the substrate 10 and has a very uneven shape due to grain boundaries formed by crystals each having a diameter of about 20 microns.

On top of this, aluminum was vapor-deposited in vacuum while controlling the transmittance until the transmittance decreased to 50-60%, resulting in a film thickness of several 1000 A0.
An intermediate layer 13 is formed.

The resistance value of the intermediate layer is what the tester needle can feel, that is, it is less than MΩ.

This input surface is attached inside the tube, and then attached to an exhaust stand to complete the prescribed baking process.

Next, while controlling the light transmittance of antimony, the first 80
%.

After that, potassium and antimony are added alternately and reacted until the photoelectric sensitivity reaches its maximum.

Next, when cesium and antimony are added alternately and reacted, the photoelectric sensitivity is further improved, and the reaction of antimony, potassium, and cesium photocathode 14 is completed until the maximum sensitivity is reached.

The brightness of the X-ray fluorescent multiplier tube formed by the above method was 40% brighter than that of the conventional one, and the decrease in brightness was by a factor of .theta..about.5 in the life test using the method described above.

The image quality of the output fluorescent surface 5 (see FIG. 1) was clear and was hardly poisoned by the alkali metal.

By the way, if the photocathode 14 made of antimony, potassium, and cesium is formed in the same way as above after forming another intermediate layer such as aluminum oxide, yttrium oxide, silicon oxide, etc. to a thickness of several thousand angstroms, the photocathode itself It was found that the charge supply did not go smoothly because the resistance was thin.

However, a method in which a conductive layer such as aluminum was further formed on the surface of the oxide intermediate layer gave good results as described in the first method.

The X-ray fluorophore multiplier of the present invention is constructed as described above and shown in the drawings, and since the low-resistance intermediate layer 13 is formed between the phosphor layer 11 and the photocathode 14, antimony and potassium It has become possible to use a photocathode 14 made of cesium.

In other words, since the resistance of the conventional photocathode made of antimony, potassium, and cesium is higher than that of the photocathode made of antimony and cesium, it has a large area like the input surface of an X-ray fluorescence multiplier tube. 5X-ray fluorescence multiplication (5X-ray fluorescence multiplication) As a pipe, it had a fatal flaw.

In particular, the above-mentioned drawbacks were noticeable on substrates with extremely uneven surfaces, such as cesium iodide phosphors.

On the other hand, the photocathode made of antimony, potassium, and cesium is well suited to the cesium iodide phosphor, and the peak wavelength of its emission spectrum matches well with the maximum sensitivity wavelength of the photocathode made of antimony, potassium, and cesium. At 400 nm, which is the peak wavelength of the emission spectrum, it has about twice the sensitivity as a conventional photocathode made of antimony and cesium. Optimal in combination.

Therefore, in the X-ray fluorophore multiplier made according to the structure of the present invention, chemical isolation between the phosphor layer and the photocathode is achieved by the action of the low-resistance intermediate layer, and the in-plane direction of the photocathode is The electrical conductivity has also been improved, so the brightness is 60-10% higher than the conventional one.
As a result of a compulsory test in which the brightness deterioration during use is equivalent to one year under normal usage conditions, the product of the present invention clearly has a lifespan of 5%, whereas the conventional product has a decrease of about 20%. The characteristics have also been improved.

Furthermore, even when the amount of incident X@ is large, an image with substantially uniform characteristics can be obtained over the entire screen.

Another advantage of using a photocathode made of antimony, potassium, and cesium is that the amount of alkali metal introduced into the tube when forming the photocathode has been reduced to less than half of the conventional amount, so the output fluorescent surface is not exposed to cesium, resulting in improved image quality. death,
Clear images can now be obtained.

As explained above, according to the present invention, it is possible to provide an X-ray fluorescence multiplier tube with improved brightness and life characteristics, and which has great practical value.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a conventional X-ray fluorescence multiplier tube used to explain an embodiment of the present invention, and FIG. 2 is an enlarged view of the input surface of the conventional X-ray fluorescence multiplier tube. FIG. 3 is a sectional view showing an enlarged input surface of an X-ray fluorescence multiplier tube according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 10... Substrate, 11... Fluorescent layer, 13... Intermediate layer, 14... Photocathode.

Claims (1)

[Claims] 1. An X-ray fluorophore intensifier comprising a substrate having a curvature, a cesium iodide-based phosphor layer formed on the concave surface of the substrate, and a photocathode formed on the phosphor layer. In the multiplier tube, a metal thin film made of at least AA or Au metal is formed between the phosphor layer and the photocathode in a controlled state so as to be almost transparent to light emitted from the phosphor layer. 1. An X-ray fluorescence multiplier tube having an intervening intermediate layer consisting of antimony and potassium.