JPS5820449B2 - photoelectron emission cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION There is no filter that blocks light with wavelengths longer than a specific wavelength in the vacuum ultraviolet region.

For this reason, conventionally, when detecting vacuum ultraviolet rays, it has been impossible to arbitrarily select the wavelength of the long wavelength side detection end of the detected light.

Therefore, the present invention is sensitive to vacuum ultraviolet rays and can detect ultraviolet rays in any wavelength range by setting the longer wavelength end of the spectral sensitivity curve to a desired wavelength.

FIG. 1 shows an example of a phototube equipped with a photoelectron emitting cathode 1 according to an embodiment of the present invention, in which a cylindrical vacuum glass container 2
A metal ring 3 is sealed to the end of the metal ring 3, and an ultraviolet transmitting window 4 made of the metal iK magnesium fluoride (Mg F2) is sealed.

Inside this container, a conductive substrate 5 such as nickel is placed on the window 4.
A thin layer 6 made of a mixed crystal of potassium bromide and potassium chloride is formed on the surface of the substrate 5, and the substrate 5 is led out of the container through an introduction wire 7.

Further, a mesh-shaped anode 8 is attached to the inner surface of the window 4, and this anode is connected to the metal ring 3.

Further, in the container 2, a vapor deposition source 9 made of a tungsten coil for vapor depositing the thin layer 6 of the mixed crystal and a shielding plate 10 covering the window side of the vapor deposition source are provided, and both ends of the coil are connected to lead-in wires 11, 12 is a guide to the outside of the container 2.

That is, the thin layer 6 forms a photocathode sensitive to ultraviolet rays, and if the composition ratio of the mixed crystal of potassium bromide and potassium chloride is X, it is expressed as KBrxCe (x-1), and
The value of determines the position of the long wavelength end of the spectral sensitivity curve.

When manufacturing a phototube as described above, for example, 38 g of potassium bromide and 11 g of potassium chloride are placed in a quartz tube.
The quartz tube is evacuated to 0 Torr or less and heated to 400°C to seal off the quartz tube from the exhaust system.

The quartz tube is further heated to 800° C. to dissolve potassium bromide and potassium chloride in vacuum, and then cooled to room temperature to obtain highly transparent mixed crystals KBro, 7CeO03.

That is, the mixed crystal having a composition ratio X of 0.7 is taken out from the quartz tube, placed in a tungsten coil serving as a small amount of vapor deposition source, and sealed in a container 2 as shown in FIG.

The exhaust port 13 of this container is connected to the exhaust system as shown by the chain line to exhaust the air to 10-7 Torr, and the lead-in wires 11 and 12 are connected to the power source 15 via the resistor 14 to coil K.
A flow of N is applied to sufficiently discharge the gas contained in the mixed crystal.

Further, by connecting a DC tE source 16 and an ammeter 17 between the metal ring 3 and the lead-in wire 7, and gradually increasing the current flowing through the evaporation source 9, potassium bromide and potassium chloride are deposited on the substrate 5. A thin layer 6 is formed by depositing a mixed crystal of .

At the same time, the surface of the substrate 5 is irradiated with ultraviolet light through the window 4, the photocurrent is observed with an ammeter 17, and when the photocurrent exceeds the maximum value, the deposition is stopped and the container 2 is cut out from the exhaust system.

Figure 2 shows the spectral sensitivity curve of the photoelectron-emitting cathode prepared in this way. be.

The long wavelength end a of the above spectral sensitivity curve is 150 nm,
The short wavelength end is determined by the transmittance characteristics of the magnesium fluoride forming the window 4, and is 113 nm.

That is, the wavelength of the long wavelength end a is determined by the bromide power and the composition ratio X of the mixed crystal of lithium and potassium chloride, and when this composition ratio X is 0.7, it is 150 nm as described above, It changes depending on the value as shown by the chain line.

FIG. 3 shows this relationship, with the horizontal axis representing the wavelength λ at the long wavelength end of the spectral sensitivity curve, and the vertical axis representing the composition ratio X.

The dotted line is for the case where the composition ratio X is 0.7 as mentioned above,
There is a linear relationship between this composition ratio X and the wavelength λ at the long wavelength end, as shown in the figure. It is nm.

As mentioned above, the photoelectron emitting cathode of the present invention has a thin layer made of a mixed crystal of potassium bromide and potassium chloride formed on a conductive substrate, and the spectral sensitivity curve can be adjusted by changing the composition ratio of the mixed crystal. Long wavelength end k 140 nm to 155
It can be any value between nm.

Therefore, by selecting this value to a desired wavelength and using it in conjunction with an ultraviolet filter that blocks short wavelengths, it is possible to selectively detect light in any wavelength range in the ultraviolet region.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a phototube equipped with a photoelectron emitting cathode according to an embodiment of the present invention, FIG. 2 is a spectral sensitivity curve of the phototube shown in FIG. 1, and FIG. 3 is a composition of a mixed crystal forming the cathode of the present invention. FIG. 3 is a diagram showing the relationship between the ratio and the long wavelength end of the spectral sensitivity curve. In the figure, 1 is a photoelectron emitting cathode, 5 is its substrate,
6 is a thin layer of mixed crystal, and 8 is an anode.

Claims (1)

[Claims] 1. A photoelectron emitting cathode characterized in that a thin layer made of a mixed crystal of potassium bromide and potassium chloride is formed on a conductive substrate.