JPH0555831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention fabricates a radiation detector using a superconducting tunnel junction, and in particular detects the signal of the diffusion of energy imparted from radiation to the superconducting tunnel junction from the superconducting tunnel junction to an electrode. By reducing the effect on size, it can be used as a high-resolution radiation detector.

Conventional radiation detectors include gas counters that utilize the ionization of gas by radiation, scintillation radiation detectors that utilize scintillation light caused by radiation, and radiation detectors that utilize the generation of electron-hole pairs by radiation in semiconductors. Semiconductor radiation detectors and other equipment were used. The present invention utilizes the destruction of Cooper pairs by radiation in a superconductor and the accompanying excitation of electrons, and is based on a completely different principle from that of conventional radiation detectors.

Conventional radiation detectors detect electrons in semiconductors.
Because the average energy required to generate hole pairs, ionize gas, and emit a single scintillation beam is large, ranging from several ev to several hundred ev, statistical fluctuations in the signal magnitude due to radiation were large. In superconductors, the average energy required to excite one electron with radiation is extremely small, about 1 mev, and the number of excited electrons is extremely large. Therefore, in a superconducting radiation detector, the ratio of statistical fluctuations in the signal magnitude to radiation of a constant energy is extremely small, that is, the energy resolution can be extremely high. Furthermore, since conventional semiconductor radiation detectors with high resolution use single crystals, they have had a major limitation in use in that they are susceptible to radiation damage due to disturbance of crystallinity due to radiation. Superconducting radiation detectors can use polycrystalline superconductors, so they have the advantage that disturbance of crystallinity due to radiation poses almost no problem compared to semiconductor radiation detectors.

When radiation enters a superconducting tunnel junction,
Since the electrons in the superconductor are excited, the current and voltage characteristics change temporarily, and the energy of the radiation can be determined by the magnitude of the change. For example, if the current flowing through a superconducting tunnel junction (bias current) is kept constant, the voltage across the superconducting tunnel junction will change, and if the voltage across both ends (bias voltage) is kept constant, the current will change. These changes can then be extracted as signals.

In the present invention, by covering the periphery of the junction with a collimator (see Figures 1 and 2), the energy applied to the superconducting tunnel junction from the radiation is diffused to the electrodes, which increases the signal magnitude. By reducing the effect, or by making electrodes with thin conductor wires or thin strip-shaped conductors as shown in Figure 3, the energy given to the superconducting tunnel junction by the radiation can be diffused from the superconducting tunnel junction. By making it difficult for the particles to escape to the electrodes, high resolution can be obtained. By stacking the junctions as shown in FIG. 4, it is also possible to know how much energy the radiation has lost in each layer.

The superconducting tunnel junctions used in these superconducting radiation detectors can be fabricated by using a glass plate or quartz plate as a substrate and creating a superconducting tunnel junction on it, or directly on a superconductor plate without a substrate. It is also possible to create joints. Furthermore, it can also be used without a substrate by, for example, producing it on a substrate and then peeling it off from the substrate.

Next, one embodiment of the present invention will be described.

In this example, a superconducting tunnel junction made of tin-tin oxide-tin was used. The superconducting tunnel junction was fabricated as follows. First, a thin film of tin with a width of 0.3 mm, a length of 20 mm, and a thickness of 1500 Å is created by vacuum evaporation on a glass substrate through a metal mask. Next, 0.3 Torr of oxygen gas is introduced into the vacuum evaporation equipment, and a high voltage of 600V-60Hz is applied to the high voltage terminal provided in the vacuum evaporation equipment to cause the oxygen gas to glow discharge for several minutes. The surface of the tin thin film was oxidized to form a tin oxide layer that would serve as a tunnel barrier layer. Finally, after replacing the metal mask, a strip of tin thin film with a width of 0.2 mm and a length of 20 mm was placed so as to intersect with the thin strip of tin that had already formed an oxide layer on the surface.
A thin film of tin with a thickness of 1500 Å is made by vacuum evaporation. Tin-tin oxide-tin layered area: 0.3 x 0.2 mm ² , thickness
The 3000 Å section becomes a superconducting tunnel junction. The parts other than the superconducting tunnel junction of the band-shaped tin thin film and the band-shaped thin film whose surface is covered with tin oxide serve as electrodes.
In this embodiment, as shown in FIGS. 1 and 2,
A collimator is installed above the superconducting tunnel junction so as to cover the periphery of the superconducting tunnel junction. The distance between the superconducting tunnel junction and the collimator was about 0.1 mm. An α-ray source with a diameter of 3 mm was placed 15 mm away from the collimator and directly above the collimator. As a result, the α particles only enter the vicinity of the center of the superconducting tunnel junction through the hole in the collimator. If there is no collimator, α particles will also be incident on the periphery of the junction in the superconducting tunnel junction, and in the case of this example, which consists of two band-shaped superconductors, Much of the energy given to the superconducting tunnel junction by the particles escapes to the electrodes by diffusion, and the signal in this case is smaller than the signal caused by the alpha particle incident on the center of the junction.
Therefore, in that case, the magnitude of the signal varies depending on the incident position, and high energy resolution cannot be obtained.

In the α particle detection test of this example, the superconducting tunnel junction, collimator, and α-ray source were housed in a ³ He cryostat, and the superconducting tunnel junction was cooled to 0.32K to bring the tin into a superconducting state. did. A magnetic field of several Gauss is applied to the superconducting tunnel junction.
The DC Josephson current is not allowed to flow, and a constant current is allowed to flow through the superconducting tunnel junction through the upper and lower electrodes. irradiate 5.3 Mev alpha particles only to
The voltage change across the junction was extracted as a signal. In the case of the superconducting tunnel junction used in this example, the total film thickness is as thin as 3000 Å, and the α particles only give about 1/50th of that energy, or about 100 KeV, to the superconducting tunnel junction, and other large Although some energy was lost in the glass substrate,
The energy resolution obtained is approximately 7% (approximately 7KeV)
It was expensive.

As described above, the present invention is a radiation detector based on a completely different principle from conventional radiation detectors. Energy resolution comparable to that of semiconductor radiation detectors, which have the highest energy resolution to date, can be easily obtained.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an embodiment of the invention, FIG. 2 is a front view thereof, FIG. 3 is a side sectional view of an embodiment of the invention, and FIG. 4 is a side sectional view of an embodiment of the invention. Code, 1...collimator, 2...electrode, 3...
...Superconductor, 4...Tunnel junction, 5...Current -
voltage terminal.

Claims (1)

[Claims] 1. One superconducting tunnel junction or two or more superconducting tunnel junctions sandwiching a tunnel barrier layer that creates a tunnel effect between superconductors or between a superconductor and another conductor. From the multilayer junction in which superconducting tunnel junctions are stacked, the means for applying bias current or bias voltage to the junction or multilayer junction, and the magnitude of the change in transient current-voltage characteristics due to the tunnel effect when radiation is incident. A superconducting radiation detector having means for measuring the energy of radiation, and characterized by having a structure in which the peripheral part of the boundary between a conductor and a junction for applying a bias current or bias voltage is covered with a collimator. superconductor radiation detector. 2. One superconducting tunnel junction or stacking of two or more superconducting tunnel junctions with a tunnel barrier layer that creates a tunnel effect between superconductors or between a superconductor and another conductor. The energy of the radiation is measured from the magnitude of the change in transient current-voltage characteristics due to the tunneling effect when the radiation enters the multilayer junction, the application means for applying a bias current or bias voltage to the junction or the multilayer junction, and the tunnel effect when the radiation is incident. What is claimed is: 1. A superconducting radiation detector comprising means for applying a bias current or bias voltage to a superconducting tunnel junction, the superconducting radiation detector having a conductor having an elongated shape. 3 One superconducting tunnel junction or stacking of two or more superconducting tunnel junctions with a tunnel barrier layer that creates a tunnel effect between superconductors or between a superconductor and another conductor The energy of the radiation is measured from the magnitude of the change in transient current-voltage characteristics due to the tunneling effect when the radiation enters the multilayer junction, the application means for applying a bias current or bias voltage to the junction or the multilayer junction, and the tunnel effect when the radiation is incident. A superconducting radiation detector comprising: means and means for cooling the junction or multilayer junction using liquid ³ He.