JPH08262144A - Radiation detecting element and radiation detector - Google Patents

Abstract

PURPOSE: To measure the deviation of the incident position of radiation from a central junction by measuring the time difference between the signals generated from a series junction surrounding a dead zone by phonons generated by the radiation absorbed to a substrate and the central junction or the ratio of the magnitude of the signals and to improve the energy resolution by correcting the incident position dependency of the magnitude of the signals from the series junction around the dead zone by using the deviation. CONSTITUTION: A central junction 5 is provided by connecting in series a plurality of superconducting tunnel junctions on a substrate 1. A dead zone 2 having an area which is ten or more times larger than that of the central junction 5 and no superconducting tunnel junction is provided around the junction 5 and one or a plurality of series junctions 3 are provided around the zone 2 so as to surround the zone 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detecting element. More specifically, the present invention relates to a detection element for detecting radiation such as X-rays, γ-rays and charged particles, and infrared rays.

[0002]

2. Description of the Related Art A large number of superconducting tunnel junctions are connected in series on a substrate so that phonons generated in the substrate due to the incidence of radiation on the substrate are absorbed by the superconducting tunnel junction, whereby a series of superconducting tunnel junctions are obtained. In a radiation detection element using a series superconducting tunnel junction (Fig. 1) (Japanese Patent Application No. 2-73430), in which a signal charge is extracted from the junction and the magnitude of the radiation energy is measured from the magnitude of the charge, If the conduction tunnel junction is evenly arranged on a certain part of the substrate, the signal strength greatly depends on the incident position of the radiation, and the energy resolution is greatly impaired. .

One of the reasons for this is that the proportion of phonons contributing to the signal varies depending on the incident position of the radiation. For example, the phonon due to the radiation incident on the end of that portion is not absorbed by the junction and is emitted from that portion. This is because the rate of dissipation is high. Another reason is that the phonons are mainly absorbed in different junctions depending on the incident position of the radiation, but the uniformity of the junction sensitivity is not sufficient.

A radiation detecting element in which a dead region without a superconducting tunnel junction is provided on a substrate, and one series superconducting tunnel junction is provided further around the dead region so as to surround the dead region (FIG. 2) (special feature). In Japanese Patent Application No. 4-150981), it is considered that the phonons generated near the center of the dead region diffuse in the dead region and are absorbed by almost all the junctions at the same time. Therefore, the dependency of the signal intensity on the radiation incident position is significantly reduced as compared with the element having no dead region. However, it was not enough to realize high energy resolution.

Further, as shown in FIG. 3, it has been known that when two series superconducting tunnel junctions are provided, one-dimensional position detecting ability in the lateral direction can be obtained. Since there is no resolution and the signal size and waveform differ depending on the incident position in the vertical direction, the horizontal position resolution was also limited, and it is difficult to improve the energy resolution by using that position resolution. It was In addition, the series superconducting tunnel junction referred to here is Japanese Patent Application No. 2-73430.
As described in (1), not only a single row of serially connected junctions but also a plurality of series connected in parallel are included.

[0006]

The problem to be solved by the present invention is to improve the energy resolution of a radiation detector using a series superconducting tunnel junction. Further, another problem to be solved by the present invention is, in addition to the above problem, a radiation detector in which the radiation within the plane of the substrate is
It is to add a function capable of measuring the incident position of a dimension.

[0007]

The above-mentioned problems can be solved by the following means. A large number of superconducting tunnel junctions are connected in series on the substrate, and the phonons generated in the substrate due to the incidence of radiation on the substrate are absorbed by the superconducting tunnel junctions, so that the signal charges from the series superconducting tunnel junctions are absorbed. In a radiation detecting element using a series superconducting tunnel junction in which the magnitude of the radiation energy is extracted from the magnitude of the electric charge, a dead region having no superconducting tunnel junction is provided on the substrate as shown in FIG. A radiation detecting element, further comprising four or more series superconducting tunnel junctions that operate independently so as to surround the dead region, further around the dead region.

It is provided with means for independently amplifying the signals from the above-mentioned devices and respective series superconducting tunnel junctions, and means for measuring the time difference between these signals or means for measuring the ratio of the signal magnitudes. A radiation detector characterized by the above.

A large number of superconducting tunnel junctions are connected in series on a substrate, and the phonons generated in the substrate due to the incidence of radiation on the substrate are absorbed by the superconducting tunnel junctions, whereby the superconducting tunnel junctions are connected in series. In a radiation detecting element using a series superconducting tunnel junction for extracting a signal charge and measuring the magnitude of the radiation energy from the magnitude of the charge, as shown in FIG. 5, FIG. 6 or FIG. A central junction consisting of one or more superconducting tunnel junctions connected in series is provided, a dead region without a superconducting tunnel junction is provided around it, and a dead region is surrounded further around the dead region. A radiation detecting element comprising one series superconducting tunnel junction or a plurality of independently operating series superconducting tunnel junctions.

An element in which a plurality of series superconducting tunnel junctions are provided around the dead zone, a means for independently amplifying signals from the central junction and each series superconducting tunnel junction, and a time difference between the signals are shown. A radiation detector comprising: a means for measuring or a means for measuring a ratio of signal magnitudes.

[0011]

[Function] By providing four or more series superconducting tunnel junctions (series junctions), which operate independently so as to surround the dead area, by measuring the time difference between the signals from the respective series junctions, The incident position of the radiation incident on the dead region can be measured in two dimensions. Deviation of the incident position from the center of the element when measuring the time difference between the signal from the whole or a part of the series junction around the dead zone and the signal from the center junction or the ratio of the magnitudes of these signals Can be measured. Moreover, since the incident position can be measured, the incident position dependency of the signal magnitude can be corrected according to the incident position, and the energy resolution is improved.

More specifically, in the element of FIG. 4, for example, comparing the generation times of the signal from the upper series junction and the signal from the lower series junction, when the radiation enters the center of the element, it is generated by the radiation. Since the phonons arrive at both series junctions almost at the same time, the signals are generated almost at the same time, and when incident above the center, the signal from the upper series junction is generated earlier. Utilizing this fact, the Y-axis incident position of the radiation in the device of FIG. 4 can be measured, and the X-axis incident position can be measured by performing the same time difference measurement at the same time in the left and right series junctions. The incident position can be measured. The energy resolution can be improved by utilizing this two-dimensional position resolution. A signal that the sum of the magnitudes of the signals from all junctions due to the radiation incident on the position (X, Y) is A (X, Y) times that at the center when using the radiation having a constant energy. The radiation incident position dependence of the sum of the magnitudes of the signals is measured in advance, and in the actual measurement, the sum of the signal magnitudes is divided by A (X, Y) according to the incident position (X, Y) to obtain the signal. The energy can be measured with high accuracy even though the magnitude of γ depends on the incident position.

For example, in the element of FIG. 5, the time difference between the signal from the series junction and the signal from the central junction around the dead zone and the ratio of the magnitudes of these signals also depend on the deviation of the incident position from the element center. By providing a center junction at the center of the dead zone and measuring the time difference or magnitude ratio of the signals from the center junction and the series junction around the dead zone, the element center of the radiation incident position in the element with high symmetry can be measured. Can be accurately measured, and as a result, the incident position dependency of the signal magnitude can be corrected with higher accuracy according to the incident position.

[0014]

The present invention will be described in more detail below by showing examples of the present invention. In each of the examples, the joint has a thickness of about 400 μm and an area of 7 mm × 7 mm.
On the sapphire substrate as a lower electrode on the Nb film as Al
A film was provided, the surface of the Al film was oxidized to form a tunnel barrier, and the Nb film was used as an upper electrode on the tunnel barrier. As the radiation, α-particles of 5.3 MeV from ²¹⁰ Po were used, and the central portion of the device on the back surface of the substrate was irradiated. Moreover, the magnetic field was applied parallel to the substrate to suppress the direct current Josephson current.

(Embodiment 1) FIG. 4 shows a first embodiment.
Operates independently around a 3mm x 3mm dead zone 1
Four mm × 4 mm series junctions were produced. The α particles were irradiated from the back to a 1 mm × 1 mm area at the center of the dead area.

The energy of the radiation was measured by amplifying the signals from the four series junctions and adding up the magnitudes of the amplified signals. In that case, the energy resolution was equivalent to that of the conventional device of FIG. 2, and was about 70 keV.

By measuring the time difference of the signals from the top and bottom, and the left and right series junctions as seen in FIG.
It was possible to measure the two-dimensional incident position with an accuracy of 2 mm. Regarding the time difference between the signals from the upper and lower series junctions, one signal is delayed after amplifying the signals from the respective series junctions so that the time difference does not become negative. Time-to-peak converter (TAC) with the delayed signal as the start signal and the delayed signal as the stop signal
The time difference is converted into the magnitude of the output from the converter by inputting to. The signals from the left and right series junctions are similarly processed by another amplifier, delay device and TAC. The incident position in the plane is measured by these, and at the same time, the sum of the magnitudes of the signals from the amplifiers is also measured for each radiation. When the signal magnitude for each radiation was corrected using the incident position dependence data of the signal magnitude measured in advance by the same method, the energy resolution was improved to about 55 keV.

(Embodiment 2) One series junction is provided in a region having a width of 1 mm around a dead region having the same size as that of the device of Embodiment 1, and 50 μm × 50 μm junction is formed at the center of the dead region.
A central junction was provided, which was connected in series. The ground terminal of the central junction is common with that of the series junction. The structure is shown in FIG. The irradiated area and the like are the same as in Example 1.

By measuring the time difference between the signals from the central junction and the series junction, it was possible to measure the deviation of the radiation incident position from the element center with an accuracy of about 0.2 mm. In this case, since only the signals from the two amplifiers are processed, only one time-to-peak converter is required, and the only data required for each radiation is one time difference and the magnitude of the signal from the series junction. However, there is an advantage that the measurement is simpler than that of the first embodiment. However, in this case, there is no two-dimensional position resolution.

When the ratio of the signal magnitudes from the central junction and the series junction was measured, the deviation of the radiation incident position from the element center could be measured with an accuracy of about 0.1 mm. In this case, the energy resolution was about 50 keV when the signal magnitude and the incident position data were simultaneously measured to correct the incident position dependency. In this case,
The data required for each radiation is only the signal from the series junction and the signal from the central junction, and there is also an advantage that the time-to-peak converter is not required. However, even in this case, there is no two-dimensional position resolution.

(Embodiment 3) As an element of the third embodiment,
As shown in FIG. 6, 50 μm × 50 μ at the center of the dead area
An element similar to the element of Example 1 was prepared except that the central junction of m was provided. With this element, almost the same energy resolution as in Example 2 and almost the same two-dimensional incident position resolution as in Example 1 were obtained.

(Embodiment 4) Embodiment 4 is shown in FIG. The dead area is close to a circle with a diameter of about 3 mm, and the central joint has a diameter of 1
It is a circular joint of 00 μm, and each series joint is 0.6 mm ×
In an element consisting of two series of 1.25 mm, by the same means as in Example 2, the ratio of the signal magnitude from the central junction to the sum of the signal magnitudes from the four series junctions is When the magnitude of the signal was corrected, the energy resolution of this device was 45 keV. When the two-dimensional resolution was measured using the time difference of the signals from the four series junctions, the position resolution was about 0.1 mm.

[0023]

According to the present invention, the time difference or magnitude ratio between the signal generated from the series junction around the dead zone and the signal from the central junction due to the phonons generated by the radiation absorbed in the substrate is measured. The deviation of the incident position of the radiation from the central junction position can be measured, whereby the incident position dependency of the signal magnitude from the series junction around the dead region can be corrected to improve the energy resolution.

In addition, it operates independently around the dead zone 4
When three or more series junctions are provided, the radiation incident position in the two-dimensional plane of the substrate can also be measured from the time difference between the signals generated from the series junctions.

Note that if the area of the central junction is made too large, the proportion of phonons absorbed in the central junction increases, so that the magnitude of the signal from the series junction around the dead region is the element center at the radiation incident position. Since it depends too much on the deviation from, it becomes difficult to correct the energy of the radiation particularly near the central junction. Therefore, the area of the central junction is 10 times that of the dead zone.
It is preferably less than or equal to one-half, or less than or equal to the square of the thickness of the substrate.

Further, in order to obtain high positional resolution, it is preferable that the area of the dead region is four times or more the square of the thickness of the substrate. As a substrate to be used, a single crystal substrate of an insulator such as sapphire, a single crystal substrate of a semiconductor such as Si or GaAs, or a single crystal substrate of a metal such as Nb or gold is used so that phonons are not easily attenuated in energy during diffusion. Is preferred.

[Brief description of drawings]

FIG. 1 is an example of a structure of a conventional element.

FIG. 2 is an example of a structure of a conventional element.

FIG. 3 is an example of a structure of a conventional element.

FIG. 4 is a plan structure diagram of a first embodiment of the present invention.

FIG. 5 is a plan structure diagram of a second embodiment of the present invention.

FIG. 6 is a plan structure diagram of a third embodiment of the present invention.

FIG. 7 is a plan structural view of a fourth embodiment of the present invention.

[Explanation of symbols]

 1 substrate 2 dead region 3 series superconducting tunnel junction 4 bonding pad 5 center junction

Claims (3)

[Claims] 1. A large number of superconducting tunnel junctions are connected in series on a substrate, and phonons generated in the substrate due to incidence of radiation on the substrate are absorbed in the superconducting tunnel junction, whereby a series of superconducting tunnels. In a radiation detection element using a series superconducting tunnel junction that extracts the signal charge from the junction and measures the amount of radiation energy from the magnitude of the charge, a dead area without a superconducting tunnel junction is provided on the substrate A radiation detecting element, further comprising four or more series superconducting tunnel junctions, which operate independently so as to surround a dead region, around the region. 2. A plurality of superconducting tunnel junctions are connected in series on a substrate, and the phonons generated in the substrate due to the incidence of radiation on the substrate are absorbed by the superconducting tunnel junction, whereby the series superconducting tunnels. In a radiation detection element using a series superconducting tunnel junction that takes out a signal charge from the junction and measures the magnitude of the radiation energy from the magnitude of the charge, one or more superconducting tunnel junctions are connected in series on the substrate. The central junction is configured by connecting to, and a dead region without a superconducting tunnel junction is provided around it, and one series superconducting tunnel junction or independently so as to surround the dead region further around the dead region. A radiation detecting element comprising a plurality of series superconducting tunnel junctions that operate. 3. An element in which a plurality of series superconducting tunnel junctions are provided around the dead region according to claim 1 or 2, and signals from the central junction and each series superconducting tunnel junction are independently amplified. And a means for measuring the time difference between these signals or a means for measuring the ratio of the signal magnitudes.