JPH01121784A - Radiation detecting element consisting of multi-layered film superconductor - Google Patents

Abstract

PURPOSE:To obtain a detecting element which is strong to heat cycles, etc., and has high stopping power to radiations by using multi-layered films formed by alternate laminations of the superconductor having an average atomic number Z1 and the superconductor or nonsuperconductor having an average atomic number Z2 as the superconductor of a superconductive tunnel bond. CONSTITUTION:The superconductor having the average atomic number Z1 and the superconductor or nonsuperconductor having the average atomic number Z2 are formed to the layer thicknesses at least either of which is smaller than the coherent length of at least one thereof. These superconductors or nonsuperconductors are then alternately laminated and the multi-layered films formed in such a manner are used as the superconductor of the superconductive tunnel bond in the superconductor radiation detector. The above-mentioned superconductors are used and are multi-layered with the material which is strong to the heat cycles or the superconductor or nonsuperconductor of the large effective atomic number which is weak to the heat cycles, etc., and has a high radiation heat effect. The detecting element which is strong to the heat cycles and has the large stopping function to radiations is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a multilayer superconductor radiation detection element. To explain in detail, 1 (prior technology)' Radiation detection with high energy resolution; occupies an important position in fluorescent X-ray analyzers, etc. .゛However, conventional radiation detectors include a gas force detector that uses the ionization of gas by radiation, a lentil radiation detector that uses scintillation light caused by radiation, and an electrophotometer that uses radiation in semiconductors. - Semiconductor radiation detectors that take advantage of the generation of holes before are used. However, in these radiation detectors, the average energy required to generate electron-hole pairs in the semiconductor, ionize gas, and emit one scintillation light is large, ranging from several eV to several hundred eV. There was a large statistical fluctuation in the signal magnitude due to the line.

In order to improve the drawbacks of conventional radiation detectors, a radiation detector using a superconducting tunnel has been proposed (Japanese Patent Laid-Open No. 59-95-484). Therefore, with a compact detector, the average energy required for the superconductor to excite the potato with radiation tA radiation is 1 meV.
Since the number of excited electrons is extremely small, the proportion of statistical fluctuations in the superconducting signal is very small, and therefore the energy resolution can be extremely high. Further, since a polycrystalline superconductor can be used in a superconducting radiation detector, there is also an advantage that disturbance of crystallinity due to radiation poses almost no problem compared to the case of a semiconductor radiation detector. Therefore, a radiation detector using a superconducting tunnel junction may have an energy resolution that is several tens of times better than a radiation detector using a conventional semiconductor (Applyed Physics, Vol. 53, No. 6). 532-537Jj, 1984). In fact, about 5
．． 9keV.

There are also experimental results that clearly show better resolution than semiconductors for X-rays [Europhysics Letter (Eu
Volume 1, No. 5, pp. 209-214 (1986)].

(Problems to be Solved by the Invention) In general, in a radiation detector, in order to increase the detection efficiency of radiation (for example, X-rays), the material constituting the detector itself is
It is better to be made of an element with a large atomic number (Z).

This is particularly important for superconductor radiation detectors, for which only thin-film detectors are available so far. That is, when Z is small, a large proportion of radiation passes through the detector.

However, superconducting tunnel junctions made of lead, for example, which has a large atomic number of 2 (<2=82), have a drawback of being susceptible to thermal cycles between room temperature and low temperature.

On the other hand, superconducting tunnel junctions made of At) or Nb are resistant to thermal cycles, but their atomic numbers are 13° and 14, respectively, and they have the problem of low radiation detection efficiency.

The purpose of the present invention is to provide a superconducting tunnel junction that has a high atomic number, but is strong against thermal cycles, and has high radiation detection efficiency, even if it contains materials that have drawbacks such as being weak against thermal cycles and having large leakage currents. The object of the present invention is to provide a radiation detection element made of a superconducting tunnel junction with a small leakage current.

(Means for Solving the Problems) The purpose of these developments is to combine a superconductor having an average atomic number Z1 and a superconductor or non-superconductor having an average atomic number Z2 different from zl by increasing the layer thickness of at least one of them. Multilayer film superconductor radiation detection using a superconducting tunnel junction, characterized in that a multilayer film made thinner than the coherence length of at least one of the superconductors and laminated alternately is used as the superconductor of the superconducting tunnel junction. This is achieved by the element.

If a material (such as an alloy) made by homogeneously mixing an element with a large atomic number, such as lead (Pb), and other elements becomes a superconductor with good characteristics for a superconducting tunnel junction, the above problems will be solved. Of course it can be solved. However, so far no such substances are known. for example,
Although superconducting tunnel junctions using Pb1n are more resistant to thermal cycles than those using Pb, they are much more susceptible to thermal cycling than those using Nb or Afl.

Another method to solve the above problem is to use a superconductor layer for a superconducting tunnel junction, in which a superconductor with a small energy gap (for example, A9) is placed near the tunnel barrier, and a superconductor with a larger energy gap is placed outside of that layer. It is conceivable to use a stack of bodies (for example, pb). However, in this case, unless a superconductor with a small energy gap is used near the tunnel barrier, it will be difficult for electrons excited by radiation to flow. That is, for example, if Nb is used closer to the tunnel barrier and Pb is used outside of it, electrons excited in Pb will be less likely to flow toward the adhesive because Nb has a larger energy gap. On the other hand, if 89, which has a smaller energy gap than Pb, is used instead of Wb near the tunnel barrier, electrons will not flow more easily. However, in that case, All with a small energy gap, that is, a low superconducting transition temperature
(C = 1.3K), the operating temperature of the detection element becomes low, which is not preferred in practice. As described above, there are many restrictions on the composition of each layer.

The present invention solves the above problem by utilizing the proximity effect of superconductors.

In other words, as a material (substance) in contact with the tunnel barrier that is directly related to changes in characteristics due to thermal cycles and leakage current, there are materials such as AΩ and Nb, which have a small atomic number Z, but are used as materials for tunnel junctions and are directly related to changes in characteristics due to thermal cycles and leakage current. A material A with a small leakage current is used, and on the outside, a superconductor with a large Z value but difficult to form a good superconducting tunnel junction by itself, such as Pb1 or uranium U, which does not become superconducting by itself, is used. Substance B
A multilayer superconductor with overlapping films is used. Here, either one of substances A and 8 must be a superconductor. If one is a non-superconductor, its non-superconductor layer 1
The thickness per layer must be less than the coherence length of the superconductor, and if both are superconductors, the thickness per layer of at least one must be less than the coherence length of the other superconductor. Must be thin.

With this structure, due to the proximity effect of the superconductor,
The multilayer film can now be regarded as one superconductor, and the energy gap in the multilayer film has a nearly constant value regardless of its location. Therefore, as a material in contact with the tunnel barrier, it is possible to use a material with a small atomic number that changes little over time, has small characteristic changes due to thermal cycles, and has a small leakage current, regardless of whether it is a superconductor or a non-superconductor, and has a small atomic number due to the multilayer structure. A superconductor detector with high radiation-stopping power and at the same time operable at temperatures not too low (>1.3 K) is realized by averaging.

Note that the atomic number in the present invention refers to the atomic number of a superconductor or a non-superconductor layer if it is made of a single element, but if it is made of multiple elements, such as an alloy In some cases, it is the effective atomic number of the stopping power against radiation.

(Example) Next, the present invention will be roughly described in detail with reference to the drawings.

As shown in FIG. 1, a silicon substrate 2 having a thickness of 0.38# was introduced into an ultra-high vacuum deposition apparatus equipped with an electron gun for depositing silicon, niobium, and lead, respectively. The electron beam from this electron gun first deposits about 1 silicon on the silicon substrate.
After depositing a film with a thickness of 0A (=1 nm), it is heated to about 850°C to reduce the S! 02 to 5iO (=SiO
2+81 to about 10) and evaporated. Next, niobium and lead are evaporated by electron beam heating, and a thin niobium film wA3 (film thickness 1008) is made by alternately opening and closing shutters provided between each evaporation source and the silicon substrate.
A first multilayer film 5 of niobium and lead (thin film thickness of approximately 50,008 mm) was formed by alternately forming thin films 4 of niobium and lead (film thickness of approximately 500 mm). Next, oxygen on the surface of the niobium thin film 3 is introduced into the surface of the multilayer film thus formed to form a niobium oxide thin film 9 (
A film thickness of approximately 30 mm) was formed to form a tunnel barrier layer.

Roughly, a second multilayer film 8 is formed by alternately forming a niobium thin film 6 (thickness: 500) and a lead thin film 7 (thin film: 508) using the same method as in the case of the first multilayer film 5. (Thickness: 3,000 OOA) was formed on the surface of the tunnel barrier layer 9 to obtain a multilayer superconductor radiation detection element 1.

A magnetic field of about 100 Gauss is applied to the superconducting tunnel junction of the radiation detection element 1 obtained in this way to prevent the DC Josephson current from flowing, and the superconducting tunnel junction is passed through the collimator installed on the superconducting tunnel junction. Only the center portion was irradiated with α-rays of about 5 MeV, and voltage changes across the junction were taken out as signals by electrodes 10a and 10b.

The energy resolution obtained was 6%.

(Effects of the Invention) As described above, the present invention provides a multilayer film formed by alternately laminating a superconductor having an average atomic number @Z1 and a superconductor or non-superconductor having an average atomic number @Z2. This is a multilayer film superconductor radiation detection element using a superconducting tunnel junction, which is characterized by using a superconducting tunnel junction, so it uses a material that is resistant to thermal cycles, and a material that is resistant to thermal cycles but is sensitive to radiation. By multilayering with a superconductor or non-superconductor having a large effective atomic number and a large detection effect, a superconductor radiation detector that is resistant to thermal cycles and has a high stopping power against radiation can be realized.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining an embodiment of a multilayer film superconductor radiation detection element according to the present invention. DESCRIPTION OF SYMBOLS 1...Multilayer film radiation detection element, 2...Substrate, 3...Superconductor film having a small average atomic number, 4...
Superconductor or non-superconductor thin film with a large average atomic number, 5... First multilayer film, 8... Second multilayer film, 9... Tunnel barrier layer.

Claims (1)

[Claims] A superconductor having an average atomic number Z_1 and a superconductor or non-superconductor having an average atomic number Z_2 different from Z_1 are alternately formed with at least one layer thickness being thinner than the coherence length of at least one of the superconductors. A multilayer film superconductor radiation detection element using a superconducting tunnel junction, characterized in that a multilayer film formed by laminating the above is used as a superconductor of the superconducting tunnel junction.