JP4097845B2 - Tunnel junction radiation detector - Google Patents
Tunnel junction radiation detector Download PDFInfo
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- JP4097845B2 JP4097845B2 JP14471099A JP14471099A JP4097845B2 JP 4097845 B2 JP4097845 B2 JP 4097845B2 JP 14471099 A JP14471099 A JP 14471099A JP 14471099 A JP14471099 A JP 14471099A JP 4097845 B2 JP4097845 B2 JP 4097845B2
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- magnetic field
- superconductor
- columnar
- thin film
- tunnel junction
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Description
【０００１】
【発明の属する技術分野】
本発明はＸ線、γ線等の電磁波や電子線、α線等の粒子線等の放射線のエネルギースペクトルを測定するための放射線検出器に使用する放射線検出素子に関するものである。
【０００２】
【従来の技術】
超伝導トンネル接合を用いた放射線検出素子においては、トンネル接合に平行に磁場をかけないとジョセフソン効果によりトンネル接合間に超伝導トンネル電流が流れるため、放射線による信号電流が検出できない。
従来の超伝導トンネル接合を用いた放射線検出素子は、図２のようにトンネル接合に平行に磁場をかけるために磁場発生用電磁石を用いていた。図２で、３はバイアス用電極、４は出力電極、６は基板、７は従来の第１の超伝導体薄膜、８は従来の第２の超伝導体薄膜、９はヘルムホルツコイルである。
【０００３】
トンネル接合に平行に均一な磁場をかけるための磁場発生用電磁石としてはヘルムホルツコイルがよく用いられている。
【０００４】
【発明が解決しようとする課題】
超伝導トンネル接合を用いた放射線検出素子は冷凍機を用いて極低温状態で動作させることが多いが、必要な大きさの磁場を発生するためには、磁場発生用電磁石に大電流を流す必要があり、磁場発生用電磁石のコイル材料に超伝導材料を用いたとしてもその励磁には大電流が必要である。また冷凍機内の超伝導転移温度以上の温度部分にある配線に流れる電流はジュール熱を発生するため冷凍機の負荷が大きいという課題があった。
【０００５】
またはトンネル接合に平行に均一な磁場をかけるために形状、大きさ、配置に制約をうけるので、冷凍機内の空間を小さくできないという課題と、磁場の方向が単一磁場発生用電磁石では外部から制御できないという課題があった。
【０００６】
【課題を解決するための手段】
本発明の放射線検出素子は、柱状の超伝導体の側面に酸化膜を形成し、その上に超伝導体薄膜を設け、超伝導体薄膜が酸化膜付きの柱状の超伝導体の側面の一部を覆う構造とした。
さらに柱状の超伝導体に超伝導電流を流すための磁場発生用電極を設けたので、柱状の超伝導体中に超伝導電流を流すと自動的にトンネル接合に平行に磁場がかかる。
【０００７】
超伝導体薄膜が酸化膜付きの柱状の超伝導体の側面の一部ではなく全部を覆う構造にしてもトンネル接合に平行に磁場がかかるが、トンネル接合間の超伝導トンネル電流の大きさは柱状の超伝導体に流れる超伝導電流に従って周期的に変化し、トンネル接合間の超伝導トンネル電流を充分に小さくすることはできない。柱状の超伝導体として直径が充分に小さい材料が工業的に得られるので、柱状の超伝導体の側面には小さい電流で充分に大きい磁場を発生させることが可能であり、冷凍機の負荷を小さくできる。
【０００８】
また磁場発生用に追加する部品は磁場発生用電極および電線１本のみであるので、冷凍機内の空間を大きくする必要がなく、磁場の方向は自動的にトンネル接合に平行となるので、外部から磁場の方向を変える必要がない。
【０００９】
【発明の実施の形態】
図１に本発明による第１の実施例の断面図を示す。寸法は見やすさのために正確には図示していない。
柱状の超伝導体１は、直径５０μｍ、長さ８ｍｍの円柱状の多結晶アルミニウムよりなる。アルミニウムは約１．２Ｋ以下の温度で超伝導体である。 本実施例では柱状の超伝導体１として多結晶アルミニウム薄膜を用いたがスズ、ニオブ、タンタル、レニウムなどの多結晶超伝導体もしくは単結晶超伝導体を用いてもよく、多結晶アルミニウムに限定されるものではない。
【００１０】
柱状の超伝導体１であるアルミニウムの表面を酸素雰囲気中に置くことによって、図示しない酸化膜を円柱状超伝導体１の全体表面に形成する。そして、さらに柱状の超伝導体１の酸化膜の上に超伝導体薄膜２として厚さ０．１μｍのアルミニウム薄膜を全周蒸着した。本実施例ではアルミニウム薄膜の蒸着領域の長さは３ｍｍである。
【００１１】
放射線は超伝導体薄膜２の蒸着領域の長さの中央部付近の側面から入射させる。柱状の超伝導体１の内部で発生した準粒子は、バイアス電極３にバイアス電圧をかけておくことによって、トンネル効果により超伝導体薄膜２であるアルミニウム薄膜に収集される。収集された電荷は出力電極４を通して取り出される。
柱状の超伝導体１には磁場発生用電極５が接続されている。本実施例では磁場発生用電極５として厚さ０．１μmの金を柱状の超伝導体１にメタルマスクを用いて蒸着した。出力電極４も同じ方法で作製した。
【００１２】
磁場発生用超伝導電流は、バイアス電極３から磁場発生用電極５の方向またはその逆方向に流す。
本実施例の場合、磁場発生用超伝導電流が１００ｍＡの時、柱状の超伝導体の表面に発生する磁場の大きさはは０．８ｍＴである。通常、０．８ｍＴの磁場があればトンネル接合間のジョセフソン効果による超伝導トンネル電流は充分に小さくできる。
【００１３】
０．８ｍＴの磁場をヘルムホルツコイルで発生するためには、コイル間距離を１０ｍｍとし、巻数を１００回として１００ｍＡの電流を流せば良い計算であるが、トンネル接合に平行な方向と磁場の方向は正確には合わせられないので、その数倍の電流が必要となる。
【００１４】
【発明の効果】
本発明によれば、柱状の超伝導体の側面に酸化膜を形成し、その上に超伝導体薄膜を形成し、超伝導体薄膜が酸化膜付きの柱状の超伝導体の側面の一部を覆う構造とし、さらに柱状の超伝導体に磁場発生用超伝導電流を流すための磁場発生用電極を設けたので、柱状の超伝導体中を流れる磁場発生用超伝導電流によって自動的に接合に平行に磁場がかかる。
【００１５】
細い柱状の超伝導体の側面には小さい電流で充分に大きい磁場を発生させることが可能であり、冷凍機の負荷を小さくできるという効果が得られた。
また磁場発生用に追加する部品は磁場発生用電極および電線１本のみであるので製作が容易あり、冷凍機内の空間を大きくする必要がなく、磁場の方向は自動的にトンネル接合に平行となるので、外部から磁場の方向を変える必要がないという効果が得られた。
【図面の簡単な説明】
【図１】本発明の実施例の断面図であり、（ａ）は、軸方向の断面図であり、（ｂ）は、（ａ）のＡ−Ａ'位置の断面図である。
【図２】従来の技術による放射線検出素子の配置図である。
【符号の説明】
１ 柱状の超伝導体
２ 超伝導体薄膜
３ バイアス用電極
４ 出力電極
５ 磁場発生用電極
６ 基板
７ 従来の第１の超伝導体薄膜
８ 従来の第２の超伝導体薄膜
９ ヘルムホルツコイル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation detection element used in a radiation detector for measuring the energy spectrum of radiation such as electromagnetic waves such as X-rays and γ-rays, electron beams, and particle beams such as α-rays.
[0002]
[Prior art]
In a radiation detection element using a superconducting tunnel junction, unless a magnetic field is applied in parallel to the tunnel junction, a superconducting tunnel current flows between the tunnel junctions due to the Josephson effect, so that a signal current due to radiation cannot be detected.
A conventional radiation detection element using a superconducting tunnel junction uses a magnetic field generating electromagnet to apply a magnetic field in parallel to the tunnel junction as shown in FIG. In FIG. 2, 3 is a bias electrode, 4 is an output electrode, 6 is a substrate, 7 is a conventional first superconductor thin film, 8 is a conventional second superconductor thin film, and 9 is a Helmholtz coil.
[0003]
A Helmholtz coil is often used as a magnetic field generating electromagnet for applying a uniform magnetic field in parallel to a tunnel junction.
[0004]
[Problems to be solved by the invention]
Radiation detectors using superconducting tunnel junctions are often operated at extremely low temperatures using a refrigerator, but in order to generate the required magnetic field, it is necessary to pass a large current through the magnetic field generating electromagnet. Even if a superconducting material is used for the coil material of the electromagnet for generating a magnetic field, a large current is required for excitation. Moreover, since the current flowing through the wiring in the temperature portion above the superconducting transition temperature in the refrigerator generates Joule heat, there is a problem that the load on the refrigerator is large.
[0005]
Or because the uniform magnetic field is applied in parallel to the tunnel junction, the shape, size, and arrangement are restricted, so the space in the refrigerator cannot be reduced, and the direction of the magnetic field is controlled from the outside with a single magnetic field generating electromagnet. There was a problem that it was not possible.
[0006]
[Means for Solving the Problems]
The radiation detection element of the present invention is formed by forming an oxide film on the side surface of a columnar superconductor, providing a superconductor thin film thereon, and the superconductor thin film is one side surface of the columnar superconductor with an oxide film. It was set as the structure which covers a part.
Furthermore, since a magnetic field generating electrode for flowing a superconducting current is provided in the columnar superconductor, when a superconducting current is passed through the columnar superconductor, a magnetic field is automatically applied in parallel to the tunnel junction.
[0007]
Even if the superconductor thin film covers not all of the side surfaces of the columnar superconductor with oxide film, but a magnetic field is applied in parallel to the tunnel junction, the magnitude of the superconducting tunnel current between the tunnel junctions is It changes periodically according to the superconducting current flowing in the columnar superconductor, and the superconducting tunnel current between the tunnel junctions cannot be made sufficiently small. Since a material with a sufficiently small diameter can be obtained industrially as a columnar superconductor, it is possible to generate a sufficiently large magnetic field with a small current on the side surface of the columnar superconductor, which reduces the load on the refrigerator. Can be small.
[0008]
Moreover, since only the magnetic field generating electrode and one electric wire are added for generating the magnetic field, it is not necessary to enlarge the space in the refrigerator, and the direction of the magnetic field is automatically parallel to the tunnel junction. There is no need to change the direction of the magnetic field.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a cross-sectional view of a first embodiment according to the present invention. The dimensions are not shown accurately for ease of viewing.
The columnar superconductor 1 is made of cylindrical polycrystalline aluminum having a diameter of 50 μm and a length of 8 mm. Aluminum is a superconductor at temperatures below about 1.2K. In this embodiment, a polycrystalline aluminum thin film is used as the columnar superconductor 1, but a polycrystalline superconductor such as tin, niobium, tantalum, rhenium or a single crystal superconductor may be used, and is limited to polycrystalline aluminum. Is not to be done.
[0010]
An oxide film (not shown) is formed on the entire surface of the columnar superconductor 1 by placing the surface of aluminum as the columnar superconductor 1 in an oxygen atmosphere. Further, an aluminum thin film having a thickness of 0.1 μm was vapor deposited on the oxide film of the columnar superconductor 1 as a superconductor
[0011]
Radiation is incident from the side surface near the center of the length of the vapor deposition region of the superconductor
A magnetic field generating electrode 5 is connected to the columnar superconductor 1. In this example, gold having a thickness of 0.1 μm was deposited on the columnar superconductor 1 as a magnetic field generating electrode 5 using a metal mask. The output electrode 4 was also produced by the same method.
[0012]
The superconducting current for generating a magnetic field flows in the direction from the
In the case of this example, when the superconducting current for magnetic field generation is 100 mA, the magnitude of the magnetic field generated on the surface of the columnar superconductor is 0.8 mT. Usually, if there is a magnetic field of 0.8 mT, the superconducting tunnel current due to the Josephson effect between the tunnel junctions can be made sufficiently small.
[0013]
In order to generate a magnetic field of 0.8 mT with a Helmholtz coil, it is a calculation that the distance between the coils is 10 mm, the number of turns is 100, and a current of 100 mA is passed, but the direction parallel to the tunnel junction and the direction of the magnetic field are Since it cannot be accurately matched, several times as much current is required.
[0014]
【The invention's effect】
According to the present invention, an oxide film is formed on a side surface of a columnar superconductor, a superconductor thin film is formed thereon, and the superconductor thin film is a part of the side surface of the columnar superconductor with an oxide film. In addition, a column-shaped superconductor is provided with a magnetic field generating electrode for flowing a superconducting current for generating a magnetic field, so that it is automatically joined by the superconducting current for generating a magnetic field flowing in the columnar superconductor. A magnetic field is applied in parallel.
[0015]
It was possible to generate a sufficiently large magnetic field with a small current on the side surface of the thin columnar superconductor, and the effect of reducing the load on the refrigerator was obtained.
Moreover, since only the magnetic field generating electrode and one electric wire are added for generating the magnetic field, it is easy to manufacture and there is no need to increase the space in the refrigerator, and the direction of the magnetic field is automatically parallel to the tunnel junction. Therefore, the effect that there is no need to change the direction of the magnetic field from the outside was obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an embodiment of the present invention, (a) is a cross-sectional view in the axial direction, and (b) is a cross-sectional view at the position AA ′ in (a).
FIG. 2 is a layout view of radiation detection elements according to the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1
Claims (1)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14471099A JP4097845B2 (en) | 1999-05-25 | 1999-05-25 | Tunnel junction radiation detector |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14471099A JP4097845B2 (en) | 1999-05-25 | 1999-05-25 | Tunnel junction radiation detector |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2000332311A JP2000332311A (en) | 2000-11-30 |
| JP4097845B2 true JP4097845B2 (en) | 2008-06-11 |
Family
ID=15368497
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP14471099A Expired - Fee Related JP4097845B2 (en) | 1999-05-25 | 1999-05-25 | Tunnel junction radiation detector |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP4097845B2 (en) |
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1999
- 1999-05-25 JP JP14471099A patent/JP4097845B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JP2000332311A (en) | 2000-11-30 |
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