JP2013053870A - Neutron detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutron detector having the same spatial resolution as a conventional neutron detector, with a less number of detection elements arranged in matrix.SOLUTION: A neutron detector 100 includes; an X-coordinate detection element group comprising a plurality of parallelly-arranged first particle detection elements 1x made of a superconducting material whose electronic state changes upon receiving heat energy of one of at least two particles radiated in different directions by heat energy released from nuclear reactions of neutrons with a neutron detecting substance; and a Y-coordinate detection element group comprising a plurality of parallelly arranged second particle detection elements 1y made of a superconducting substance whose electronic state changes upon receiving heat energy of the other particle. An X coordinate of a position where the nuclear reaction occurred is identified based on detection of the first particle detection elements, and a Y coordinate of the position where the nuclear reaction occurred is identified based on detection of any of the second particle detection elements.

Description

  The present invention relates to a neutron detection apparatus.

  The neutron imaging technique (neutron radiography) is a technique for observing the inside of a substance by utilizing the property that neutron rays pass through the substance, as in the analysis technique using X-rays and gamma rays. Neutron radiography is suitable for observation of light elements such as hydrogen and carbon, unlike X-rays suitable for photographing heavy elements such as metals, and enables observation of substances containing a lot of organisms and moisture. In addition, since it has high sensitivity, it has a feature that it can be observed in real time as an image, and it is possible to observe the movement of moisture in a living organism. Furthermore, taking advantage of the fact that ordinary metals absorb less neutrons, it is possible to observe the state of fuel and oil moving inside the machine. It is also possible to investigate the magnetic distribution by utilizing the property of having a magnetic moment.

  There is a demand for observing the dynamics of water in a fuel cell as a high spatial resolution movie by taking advantage of such neutron beam characteristics. In addition, if a large pixel can be realized with submicron resolution, a spin-polarized neutron source can be used to observe the state of spin motion in a magnetic material at high speed. Become. Therefore, the realization of large pixels, particularly neutron radiography technology that can be observed in real time with high spatial resolution of submicron is required. At the Japan Proton Accelerator Research Complex (J-PARC) User Council, the high-intensity proton accelerator facility J-PARC has a spatial resolution of 1 μm in 2015 and a frame time of 10 ms in 2030 in the “fuel cell” and “power storage device” fields. It is raised as.

  By the way, as a detection device for neutron radiography, there are various types such as those using a gas discharge method, those using a scintillation method, and those using an imaging plate. As a high-resolution, high-speed neutron detector capable of responding to the above-mentioned concept, a neutron detector is known in which detection elements made of superconducting elements microfabricated into nanowires are arranged in a matrix form vertically and horizontally (for example, patents) Reference 1). The change in the electronic state of the detection element due to the heat generated by the nuclear reaction between these detection elements and neutrons is measured as the change in the electrical resistance value.

WO2006-095659

  However, when trying to realize a large pixel using a neutron detection device using a high-temperature superconductor, for example, when trying to construct a neutron detection system of 1 million pixels, 1 million detector elements are combined vertically and horizontally. It is necessary to arrange in a matrix. Then, it is necessary to pass a drive current to each detection element. Even if simply estimated, a total of 2 million cables are required, that is, 1 million for the drive current and 1 million for the output. Realization is extremely difficult if not impossible.

  Also, when detecting changes in electrical resistance caused by the heat generated by the nuclear reaction between the detection element and the neutron, the superconducting state of the detection element is broken due to the heat generated by the detection device accompanying the nuclear reaction or the inflow of heat from the cable. It may interfere with the normal operation of the device. As the number of detection elements increases, the aforementioned problems associated with heat generation and heat inflow become apparent.

  The present invention has been made in view of the above-described problems, and realizes a neutron detection apparatus having the same spatial resolution with a smaller number of detection elements than the conventional configuration in which detection elements are arranged in a matrix.

  In the present invention, when the thermal energy of one particle is received among at least two particles generated with a thermal energy by a nuclear reaction between one neutron and a neutron detection substance and emitted in different directions. An X coordinate detection element group in which a plurality of first particle detection elements in which a change in electronic state occurs is arranged in parallel, and a second particle detection element in which a change in electronic state occurs when the thermal energy of another particle is received Are arranged in parallel, each first particle detecting element is a superconducting material having a region extending long in the vertical direction, and the X coordinate detecting element group is a first of them. The particle detection elements are arranged in a horizontal direction, and the X coordinate of the position where the nuclear reaction has occurred is detected based on which first particle detection element has detected a change in the electronic state of the one particle. 2-particle detector , A superconducting material having a region extending in the lateral direction, and the Y-coordinate detection element group has the second particle detection elements arranged in the vertical direction, and any second particle detection element is an electron related to the other particles. The present invention provides a neutron detection apparatus that detects a Y coordinate of a position where the nuclear reaction has occurred based on whether a change in state is detected.

In the present invention, a specific example of the substance for detecting neutron includes magnesium diboride (MgB ₂ ). In that case, the particles emitted by the nuclear reaction are ⁴ He (alpha rays) and ⁷ Li (lithium rays).
Accepting thermal energy means that the characteristics of the first or second particle detecting element, particularly the electronic state, change due to the thermal energy of the particles. The detection method is not particularly limited as long as the change in the electronic state can be detected by some means, but in the embodiments described later, the change in the electronic state is detected as the change in the motion inductance.

  The neutron detection apparatus according to the present invention includes an X coordinate detection element group in which a plurality of first particle detection elements are arranged in a lateral direction, and a nuclear reaction occurs depending on which of the first particle detection elements has a change in an electronic state. The X coordinate of the selected position is detected. In addition, a Y coordinate detection element group in which a plurality of second particle detection elements are arranged in the vertical direction is provided, and the Y coordinate of the position where the nuclear reaction has occurred is determined depending on which of the second particle detection elements has an electronic state change. To detect.

The neutron detection apparatus of the present invention is based on the premise that neutrons collide only at one point at a certain point in time, and normally neutrons do not collide simultaneously at a plurality of points (even if such an event occurs). If the probability is low, collisions occur sequentially and the position of the nuclear reaction is detected.
For example, when the neutron detection substance is MgB ₂ and the particles emitted by the nuclear reaction are alpha rays and lithium rays, it does not matter which of them is the first particle. Furthermore, when the collision between neutrons and MgB ₂ occurs sequentially, it is not limited that the first particle detecting element consistently detects alpha rays or lithium rays, and in some cases, the first particle detecting element emits alpha rays. Then, the lithium wire may be detected.

  According to the neutron detection apparatus of the present invention, one of the two particles radiated in different directions accompanying the nuclear reaction between the neutron and the neutron detection substance is detected by the X coordinate detection element group, and the other By detecting the particles with the Y coordinate detection element group, neutron detection having the same spatial resolution can be realized with a smaller number of detection elements than in the configuration in which the detection elements are arranged in a matrix.

It is explanatory drawing which shows schematic structure of the neutron detection apparatus which concerns on 1st Embodiment of this invention. It is explanatory drawing of the conventional neutron detection apparatus. It is explanatory drawing which shows an example of the neutron measurement by the neutron detection element which concerns on 1st Embodiment of this invention. It is AA arrow direction sectional drawing of the neutron detection apparatus of FIG. Is an explanatory diagram showing an example of the nuclear reaction between the neutrons and ¹⁰ B. Is an explanatory diagram showing an example of the nuclear reaction between the neutrons and ¹⁰ B in the neutron detector according to the first embodiment of the present invention. It is a circuit diagram which shows the SFQ (single magnetic flux quantum) circuit and likelihood determination circuit of the neutron detection apparatus which concern on 1st Embodiment of this invention. It is a block diagram which shows the structure of the SFQ circuit and likelihood determination circuit which concern on 1st Embodiment of this invention. It is sectional drawing which shows the structure of the neutron detection apparatus which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows the manufacturing process of the neutron detection apparatus which concerns on 1st Embodiment of this invention. It is sectional drawing which shows the structure of the neutron detection apparatus which concerns on 2nd Embodiment of this invention. Is an explanatory diagram showing an example of the nuclear reaction between the neutrons and ¹⁰ B in the neutron detector according to a second embodiment of the present invention. It is explanatory drawing which shows the neutron detection element which concerns on 3rd Embodiment of this invention. It is a circuit diagram which shows the modification of the neutron detection element which concerns on 1st Embodiment of this invention.

In the neutron detection apparatus according to the present invention, the neutron detection substance may be used for the first particle detection element and / or the second particle detection element.
If it does in this way, 1st particle | grains will be detected by any 1st element detection element among the particles radiated | emitted when a 1st particle | grain detection element and / or 2nd particle | grain detection element, and a neutron react. Then, the X and Y coordinates of the position where the nuclear reaction has occurred can be specified by detecting the second particles with any of the second particle detection elements.

In the neutron detection apparatus according to the present invention, the neutron detection substance is between the adjacent first particle detection element and the first particle detection element, between the adjacent second particle detection element and the second particle detection element, or It may be arranged at least between any of the first particle detection elements and each second particle detection element.
In this way, between the adjacent first particle detecting element and the first particle detecting element, between the adjacent second particle detecting element and the second particle detecting element, or between each first particle detecting element and each of the first particle detecting elements. A first particle is detected by any one of the first element detection elements among the particles emitted when a neutron reacts with a neutron detection substance disposed at least between the two particle detection elements. Then, the X and Y coordinates of the position where the nuclear reaction has occurred can be specified by detecting the second particles with any of the second particle detection elements. Moreover, since the 1st particle | grain detection element and the 2nd particle | grain detection element do not need to contain the substance for neutron detection, arbitrary high-temperature superconductors can be used as those detection elements.

In the neutron detection apparatus according to the present invention, each first particle detection element detects a change in an electronic state in which a superconducting electron pair decreases due to reception of thermal energy of the first particle as a change in motion inductance, and each second particle The detection element may detect a change in an electronic state in which a superconducting electron pair decreases due to reception of thermal energy of the second particle as a change in motion inductance.
In this way, each first particle detection element and each second particle detection element receive the thermal energy of the first and second particles not by a change in electrical resistance accompanying the generation of Joule heat, but by a change in motion inductance. Since each is detected, almost no heat is generated.

The neutron detector according to the present invention further includes an SFQ (single magnetic flux quantum) circuit formed by forming a Josephson junction in a part of the superconducting ring, and the SFQ circuit has a predetermined magnetic flux every predetermined time T1. A detection SFQ pulse input unit that inputs a detection SFQ pulse, and a motion inductance detection element group that detects a change in the motion inductance based on a change in the Josephson current in the superconducting ring due to a change in the motion inductance. Further, it may be magnetically coupled to one of the first particle detection element or the second particle detection element.
In this way, by using a neutron detector equipped with an SFQ circuit capable of detecting a weak magnetic field change, the reduction of the superconducting electron pair that occurs when the thermal energy is received becomes highly sensitive as a change in motion inductance. It can be detected.

In the neutron detection apparatus according to the present invention, the SFQ circuit includes a likelihood determination circuit, and the likelihood determination circuit inputs a determination SFQ pulse every predetermined time T2 longer than the time T1. When the determination SFQ pulse is input, the number of the detection SFQ pulses detected from the number of the detection SFQ pulses input by the detection SFQ pulse input unit is a predetermined number. When it is more than a few, you may provide the detection determination part which determines with the change of the said movement inductance being detected.
In this way, the likelihood determination circuit can count the number of SFQ pulses indicating the change in motion inductance, and the change in motion inductance can be detected with higher sensitivity by the principle of majority decision.

The neutron detection apparatus according to the present invention further includes an address generation circuit that outputs the X and Y coordinates detected by the X coordinate detection element group and the Y coordinate detection element group as digitized address values. Also good.
In this way, by outputting the detected X coordinate and Y coordinate values as digitized address values, for example, when the X coordinate detection element group has N X coordinate detection elements, It is possible to reduce the number of signal lines for sending signals to the room temperature region to N ₂ log ₂ compared to N when not digitizing.

In the neutron detection apparatus according to the present invention, the neutron detection substance contains ¹⁰ B, and the particles are generated by a nuclear reaction between neutrons and ¹⁰ B and are emitted in two opposite directions, alpha rays and lithium rays. It may be.
In this way, ¹⁰ B, which is known to react with neutrons and emit two particles, alpha and lithium, in opposite directions, and two particles emitted in opposite directions, By using it, the X and Y coordinates can be specified regardless of the radiation direction of the two particles, so that the neutron detection efficiency can be increased.

In the neutron detection apparatus according to the present invention, the neutron detection substance may include MgB ₂ .
In this way, a neutron detector can be realized using MgB ₂ which is a high-temperature superconductor that is easy to process as the neutron detection substance.

  The various preferable aspects shown here can also be combined. Hereinafter, a neutron detector according to a first embodiment of the present invention will be described in detail with reference to the drawings. In addition, the following description is an illustration in all the points, Comprising: It should not be understood as limiting this invention.

<< first embodiment >>
A neutron detector according to a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is an explanatory diagram showing a schematic configuration of a neutron detection apparatus according to the first embodiment of the present invention.
As shown in FIG. 1, the neutron detection apparatus 100 according to the first embodiment of the present invention is characterized in that it includes a plurality of linear neutron detection elements arranged in a grid pattern in the vertical and horizontal directions. A plurality (N) of neutron detection elements extending along the vertical direction (Y-axis in FIG. 1) correspond to first particle detection elements that detect positions in the horizontal direction (X-axis direction). These first particles A set of detection elements corresponds to an X coordinate detection element group. In FIG. 1, one of these N neutron detection elements is represented by a reference numeral 1x. A plurality (N) of neutron detection elements extending along the horizontal direction (X-axis in FIG. 1) correspond to second particle detection elements that detect positions in the vertical direction (Y-axis direction). A set of two particle detection elements corresponds to a Y coordinate detection element group. In FIG. 1, one of the N neutron detection elements is represented by a reference numeral 1y. The neutron detection elements 1x and 1y are made of a high-temperature superconducting material containing MgB ₂ as a neutron detection substance, and are below a superconducting transition temperature T _c (about 39K in the case of MgB ₂ ) by a refrigerator using liquid helium ( In the case of the first embodiment, it is cooled to about 4K) to be in a superconducting state. In addition, in order to maintain a superconducting state, the neutron detection apparatus 100 is put in a refrigerator and kept in a vacuum.
The X-axis, Y-axis, arrows indicating the direction in which neutrons fly, and the letters 1 to N are given for explanation. The same applies to FIG.
FIG. 2 is an explanatory diagram of a conventional neutron detector. That is, the configuration in which the neutron detection elements are arranged in a matrix form in the vertical and horizontal directions is shown for easy comparison with the configuration in FIG.

FIG. 3 is an explanatory diagram showing an example of neutron measurement by the neutron detection apparatus 100 according to the first embodiment of the present invention.
As shown in FIG. 3, the sample 103 is irradiated with neutrons emitted from the neutron source 101 through the slits 102a and 102b. Currently available neutron sources in Japan include pulsed neutron sources such as J-PARC. Neutrons are generated by colliding a high energy beam such as a proton beam generated by such an accelerator with a mercury nucleus.

  Part of the neutrons irradiated to the sample 103 passes through the sample 103 and penetrates to the back side of the sample 103. Others are absorbed or scattered inside the sample 103. Therefore, when the neutron detector 100 is installed on the back side of the sample 103 and neutrons are measured, the state of the sample 103 can be known. This is the principle of neutron radiography.

  The neutron detection apparatus 100 is installed so that the neutrons that have passed through the sample 103 are irradiated substantially perpendicularly onto the surface formed by the lattice-like neutron detection elements 1x and 1y. Here, the neutron detection device is installed inside a heat insulating container 105 having a window portion 104, and the neutron reaches the neutron detection device 100 through the window portion 104. The window 104 is made of a neutron permeable material such as a thin aluminum alloy.

4 is a cross-sectional view of the neutron detector of FIG.
FIG. 5 is an explanatory diagram schematically showing a state in which a nuclear reaction occurs when a neutron collides with ¹⁰ B, and two particles of alpha rays and lithium rays radiate in opposite directions.
¹⁰ B is an ¹¹ B isotope having a mass number of 11 that exists mainly in nature, and is known to perform a nuclear reaction that absorbs neutrons to produce ⁴ He and ⁷ Li. This nuclear reaction is used to detect neutrons that are difficult to detect because they have no charge. ¹⁰ B is known to have a high reaction probability especially for cold neutrons.

When neutron n undergoes a nuclear reaction with ¹⁰ B,
¹⁰ B + n → ⁷ Li + ⁴ He
By the reaction, two particles, ⁴ He (alpha ray) and ⁷ Li (lithium wire) are generated and emitted. At this time, about 2.3 MeV of nuclear reaction heat is generated, but this thermal energy is carried away by ⁴ He and ⁷ Li. The thermal energy of ⁴ He and ⁷ Li are 0.88 MeV and 1.47 MeV, respectively. The feature of this nuclear reaction is that ⁴ He and ⁷ Li are radiated in directions opposite to each other in accordance with the law of conservation of momentum, and this feature is used in the present invention.
The direction in which ⁴ He and ⁷ Li are radiated is not constant but is determined probabilistically (randomly), and is different for each nuclear reaction. In the superconducting MgB ₂ , the ranges of ⁴ He and ⁷ Li are about 4 μm and 2 μm, respectively.

In the neutron detection elements 1x and 1y according to the first embodiment of the present invention, the width of each element is 0.5 μm, and the interval between adjacent elements is about 1 μm. The intermediate layer between the neutron detection elements 1x and 1y has a thickness of about 1 μm at the maximum. For this reason, even if ⁴ He, ⁷ Li flies to the neutron detection element on the other side of the intermediate layer, the deviation of the detection position from the nuclear reaction position may be large if the range limit is considered. It is only about 1 to 3 μm.

FIG. 6 is an explanatory diagram showing an example of a nuclear reaction between ¹⁰ B and neutrons in the neutron detection element according to the first embodiment of the present invention.
As shown in FIG. 6, when neutron A collides with ¹⁰ B in neutron detection element 1y, ⁴ He and ⁷ Li are radiated in the opposite directions due to the nuclear reaction, and ⁷ Li is in the vicinity (within range) Collide with the neutron detection element 1x.
By detecting which of the N neutron detection elements has collided in the X axis direction, the X coordinate of the position where the nuclear reaction has occurred can be detected. Similarly, in the Y-axis direction, the Y coordinate of the position where the nuclear reaction has occurred can be detected by detecting which of the N neutron detection elements has collided.
However, the ^{direction 4} and He and ⁷ Li is radiated for a random, ⁷ Li is ^{sometimes 4} He without colliding neutron detecting element 1x collide with neutron detection element 1x. However, even in this case, since ⁴ He and ⁷ Li are radiated in opposite directions, even if any of ⁴ He or ⁷ Li collides with the neutron detection element 1x, a change in kinetic inductance occurs, so that detection is possible. .
When the radiation directions of ⁴ He and ⁷ Li are substantially parallel to the neutron detection element 1x, no collision with the neutron detection element 1x occurs. Therefore, in that case, the X coordinate of the nuclear reaction cannot be detected. However, since the distance between the neutron detection elements 1x and 1y is about 1 μm, the probability that neither ⁴ He nor ⁷ Li collides with the neutron detection element 1x is low. In radiography, a sample is observed using a large number of neutrons, so it is not a problem if some neutrons cannot be detected.
In the measurement using the neutron detector of the present invention, the time from detection of one neutron to detection of the next neutron is sufficiently long, and neutrons are detected simultaneously at a plurality of locations. There are almost no. This assumption is reasonably reasonable in light of the neutron generation frequency of available accelerators since the time required to detect one neutron is as short as nanoseconds. Moreover, the generation of neutrons may be controlled to satisfy this premise.

On the other hand, the inner side when colliding with ¹⁰ B neutron detector elements in 1x of ⁴ and He and ⁷ Li are radiated in the opposite directions by the nuclear reaction slip through between the neutron B neutron detecting element 1y in FIG 6 , ⁴ He collides with the nearby neutron detection element 1y.
As described above, regardless of the direction in which ⁴ He and ⁷ Li are radiated by the nuclear reaction, collision occurs with high probability in one or both of the neutron detection elements 1x and 1y arranged in the orthogonal direction.

When the neutron C passes between the neutron detection elements 1y and 1x, no nuclear reaction occurs and no neutron is detected. However, such a probability is detected in the conventional matrix form as shown in FIG. It is sufficiently low as compared with a configuration in which elements are arranged. Further, as will be described later in the second embodiment, such non-detection is avoided by including ¹⁰ B between the neutron detection elements.

  Note that the number of particles emitted is not limited to two, and three or more particles emitted by a nuclear reaction may be used. It is only necessary to emit particles having such a direction as to collide with the neutron detection elements 1x and 1y by one nuclear reaction.

  In this way, N neutron detection elements 1x extending in the X-axis direction and N neutron detection elements 1y extending in the Y-axis direction are arranged in a total of 2N in a lattice shape, so that neutrons can be obtained with an N × N resolution. Can be detected. According to the present invention, the number of neutron detection elements can be remarkably reduced as compared with the conventional configuration in which N × N neutron detection elements are arranged in a matrix form vertically and horizontally as shown in FIG.

  In the first embodiment, in order to achieve a spatial resolution of 1 million pixels, 1000 neutron detection elements 1x and 1y may be arranged in the X and Y directions, respectively. That is, a spatial resolution of 1 million (= 1000 × 1000) pixels can be realized with a total of 2000 neutron detection elements.

Heretofore, in order to simplify the description, the detection condition is that ⁴ He and ⁷ Li collide with either or both of the neutron detection elements 1x and 1y. However, if the electronic state of the neutron detection elements 1x and 1y changes due to the reception of thermal energy, detection is possible. The particles do not necessarily have to collide with the neutron detection elements 1x and 1y. For example, detection is possible even when a particle having thermal energy passes through the vicinity of the neutron detection elements 1x and 1y to cause a change in the electronic state of the neutron detection elements 1x and 1y.

Next, a method for detecting the change in the electronic state will be described.
FIG. 7 is a circuit diagram showing the SFQ circuit and the likelihood determination circuit of the neutron detection apparatus according to the first embodiment of the present invention.
FIG. 8 is a block diagram showing the configuration of the SFQ circuit and likelihood determination circuit according to the first embodiment of the present invention. Corresponding elements in FIG. 7 and FIG. In FIG. 7, the terminal portion indicated as “100 GHz sampling” corresponds to “detection SFQ pulse input unit 111” in FIG. The terminal portion indicated as “1 GHz sampling” in FIG. 7 corresponds to “determination SFQ pulse input unit 121” in FIG. 7, the superconducting loop in the SFQ circuit 110 corresponds to the detection unit 112 in FIG. 8, and the superconducting loop in the likelihood determination circuit 120 in FIG. 7 corresponds to the detection determination unit 122 in FIG.

In the neutron detection apparatus 100 according to the first embodiment, the mode in which the electric inductance hardly occurs and the motion inductance increases is detected using the SFQ circuit. This avoids the problem of heat generation due to the occurrence of electrical resistance as in the conventional configuration.
Specifically, a change in the electronic state in which the superconducting electron pair decreases due to the reception of thermal energy is detected as a change in motion inductance.

Conventionally, a method of detecting a change in electric resistance value has been used. This technique is to generate an electric resistance by transferring a superconducting electron pair flowing in a neutron detecting element to a normal conducting state by receiving thermal energy by a nuclear reaction. For example, in MgB ₂ , such a phenomenon is confirmed at 30 K near the superconducting transition temperature T _c (about 39 K). However, with this technique, the problem of heat generation due to Joule heat becomes obvious as the resolution increases.

  On the other hand, when the transition to the normal state due to thermal energy remains in some superconducting electron pairs, that is, when only some of the superconducting electron pairs in the neutron detection element transition to the normal state, normal electrons Has electrical resistance, but the current in the neutron detector flows exclusively through superconducting electron pairs without electrical resistance. Therefore, although generation of heat due to electrical resistance due to normal electrons occurs slightly, Joule heat is not generated as much as when all superconducting electron pairs are transferred to normal electrons.

In such a state in which a part of the superconducting state remains, a superconducting electron pair having no electrical resistance is transferred to a normal conducting electron pair having a part of electrical resistance, thereby causing a change in motion inductance. The kinetic inductance is inertia with respect to electrons. In such a state in which a part of the superconducting state remains, a part of the superconducting electron pair shifts to a normal conducting electron, resulting in a change in motion inductance ΔL. It has been confirmed that such a change in kinetic inductance occurs at a temperature much lower than the superconducting transition temperature T _c (about 39 K), and is observed at least at 16 K in the case of MgB ₂ . In addition, the result of numerical calculation of the superconducting electron density dynamics based on the Ginzburg-Landau theory also shows that a change in motion inductance can be detected at 25K. In the neutron detector according to the first embodiment of the present invention, detection is performed in a 4K superconducting state.

  However, the change in motion inductance ΔL due to one neutron reaction is about 1 pH, which is smaller than the change in magnetic inductance. Because the detection circuit itself is not so small as to ignore the thermal noise of the detection circuit itself and the electromagnetic noise from room temperature (even if the thermal noise itself becomes zero by integration), it is very useful as a detection circuit for motion inductance. High sensitivity is desired. In addition, since the time width of the change of the kinetic inductance is as extremely short as about 1 nanosecond, none of the conventional MKID (microwave kinetic inductance change) method, the microwave SQUID frequency multiplex reading method, and the time domain division method can be used. Therefore, in the neutron detection apparatus according to the first embodiment of the present invention, an SFQ circuit is used as a highly sensitive detection method for motion inductance.

In the method of detecting motion inductance using the SFQ circuit, when neutrons enter MgB ₂ , the loop inductance of QOS (Quasi One Junction SQUID) changes equivalently. The change in motion inductance can be detected in a non-contact manner by a detection circuit and magnetic coupling. Details of the magnetic coupling will be described later.

The SFQ circuit is a single flux quantum circuit formed by forming a Josephson junction in a part of a superconducting ring. When a ring is made of a superconductor, the amount of magnetic flux passing through the hole of the ring takes a discrete value of 1 or 0. A Josephson junction is a structure in which a very thin insulating film is sandwiched between superconductors and is weakly coupled. By inserting a Josephson junction into a superconducting ring and flowing a DC bias current, Manipulate the flux quanta. For example, when a current more than a certain amount of current called a critical current value flows, the magnetic flux quantum passes through the insulating film, moves to the adjacent superconducting ring, and propagates sequentially. When SFQ passes through the superconducting ring, a voltage pulse (SFQ pulse) is generated.
Details of the SFQ circuit are described in, for example, JP-A-2007-104332.

  In the first embodiment of the present invention, one neutron detecting element (N neutron detecting elements as shown in FIG. 1, N in the X-axis direction, N in the Y-axis direction, or 2N in total) One SFQ circuit 110 and one likelihood determination circuit 120 perform detection correspondingly. That is, one neutron detection element (one of 1x or 1y) corresponds to one SFQ circuit 110 and likelihood determination circuit 120. If the environmental noise or the like is sufficiently small, the likelihood determination circuit 120 may not be provided, and only the SFQ circuit 110 may be provided. As shown in FIG. 1, if there are 2N neutron detection elements in total, assuming that one SFQ circuit 110 and likelihood determination circuit 120 correspond to each neutron detection element, a total of 2N neutron detection elements The SFQ circuit 110 and the likelihood determination circuit 120 are required.

The SFQ circuit 110 includes a detection SFQ pulse input unit 111 and a detection unit 112. The detection unit 112 has a circuit characteristic represented as a Josephson junction shown in FIG.
The likelihood determination circuit 120 includes a determination SFQ pulse input unit 121 and a detection determination unit 122. The detection determination unit 122 has a second Josephson junction magnetically coupled to the superconducting loop of the Josephson junction of the detection unit 112.
The likelihood determination circuit 120 transmits a determination result to the address generation circuit 130 described later.

The detection SFQ pulse input unit 111 inputs a detection SFQ pulse of the magnetic flux Φ ₀ every predetermined time T1 (10 picoseconds in FIG. 7) (100 GHz sampling). For example, the SFQ pulse is input as follows. When a small magnetic field is applied to the superconducting ring at the end when a DC bias current is applied to the Josephson transmission path composed of superconducting rings connected by superconducting wires, one SFQ is formed in the superconducting ring. enter. The SFQ that has entered the superconducting ring receives force from the current flowing in the superconducting ring and moves to the adjacent superconducting ring. The time required for the movement of this SFQ is an extremely short time of about 2 to 3 picoseconds. Therefore, by applying a small magnetic field to the superconducting ring at the end every 10 picoseconds (ie, at 100 GHz) with a DC bias current flowing in the SFQ circuit, the detection SFQ pulse is periodically sent to the SFQ circuit. Can be generated.

In the first embodiment of the present invention, for example, using a Gifford-MacMahon (GM) refrigerator, the temperature of the SFQ circuit is maintained at 4K together with the neutron detection elements 1x and 1y.
Further, the magnetic coupling method is realized by taking a superconducting contact between the neutron detection elements 1x and 1y and the SFQ circuit. For example, an MgB ₂ coil and electrode pad, a niobium (Nb) coil and electrode pad are precisely microfabricated and bonded with a flip chip bonder to realize a superconducting contact.

In the SFQ circuit according to the first embodiment of the present invention, a change in motion inductance in the neutron detection element is detected in a short period of about 1 nanosecond. Therefore, 100 times of sampling is performed with a sampling pulse (SFQ signal) of 100 GHz (10 picosecond interval) to obtain a detection result.
Here, when the SFQ signal having a magnetic flux of Φ ₀ passes through a Josephson junction that is a part of the superconducting ring including the inductance L, ΔL represents a change in the motion inductance L, and ΔL represents a change in the motion inductance ΔL. Assuming that the change in the Josephson current J in the superconducting ring due to ΔJ is ΔJ, when the change in motion inductance ΔL is smaller than L (ΔL / L << 1), the change in Josephson current ΔJ is ΔJ≈JΔL / L. Here, if Josephson current J≈Φ ₀ / L, ΔJ≈Φ ₀ ΔL / L ^2, and therefore ΔL≈L ² ΔJ / Φ ₀ , the change in motion inductance ΔL is greater than the change ΔJ in Josephson current. Desired.

If the superconducting loop by the SFQ circuit is large, magnetic noise may appear due to the influence of vibration or the like. In that case, as shown in FIG. 14, a capacitor C may be inserted to constitute a resonance circuit, and detection of a high S / N ratio may be performed by utilizing the fact that the resonance frequency shifts due to the incidence of neutrons.
In this case, a change in the motion inductance L that generates a voltage when an SFQ signal having a magnetic flux of Φ ₀ passes through a part of the Josephson junction of the superconducting ring including the inductance L is expressed as ΔL (ΔL / L << 1). When the change in the resonance frequency of the resonance circuit in which the capacitor C is inserted is ΔF, the change in the resonance frequency ΔF is ΔF≈ (1 / (2π (LC) ^1/2 ) (ΔL / 2L)). However, in order to obtain the sensitivity, it is necessary sampling frequency f _s is an integer multiple of the resonance frequency f _r. In the example shown in FIG. 14, f _s (100 GHz) is eight times f _r (12.5 GHz). For example, the capacitor is manufactured in an interdigital structure in which needle-like long and narrow metal patterns are alternately arranged in close proximity and is integrated as a chip, and is configured such that the resonance frequency is the same for all neutron detection elements.

The likelihood determination circuit enables high-sensitivity detection by determining whether the output is 1 or 0 by majority vote, and is in principle the same as the likelihood determination method used in digital wireless communication or the like. It is. In general, the influence of noise can be reduced to 1 / (N ^1/2 ) times by determining the likelihood of N trials. This is statistically attributed to the fact that the variation in measurement results (ie, standard deviation σ) for N measurements is proportional to 1 / (N ^1/2 ). In the case of the SFQ circuit, the noise, that is, the variation in the measurement result, includes the influence of Johnson noise caused by shunt resistance, thermal noise caused by the electrical resistance of some normal particles, and the like. The shunt resistor is a resistor connected in parallel with the Josephson junction in order to flow an ohmic current through the Josephson junction. The shunt resistor prevents destruction due to excessive voltage applied to the Josephson junction.

  The determination SFQ pulse input unit 121 inputs a determination SFQ pulse into the circuit every predetermined time T2 (1 nanosecond in FIG. 7) longer than the SFQ pulse interval T1 of the detection SFQ pulse input unit 111. For example, when a detection SFQ pulse is input at 100 GHz (ie, every 10 picoseconds) and a determination SFQ pulse is input at 1 GHz (ie, every 1 nanosecond) as shown in FIG. Between the input and the next input, 100 detection SFQ pulses are input to the detection unit 112. In this case, the influence of noise is reduced to 1/10. However, in order to make a good likelihood determination, it is necessary that the change in the kinetic inductance continues during the 100 trials (that is, for at least 1 nanosecond).

In the superconducting loop of the detection unit 112 due to the detection SFQ pulse input by the detection SFQ pulse input unit 111, the period in which the change of the motion inductance does not occur is zero, and the change of the motion inductance occurs. 1 generates a magnetic flux Φ ₀ . However, since the SFQ pulse is very small, the magnetic flux Φ ₀ may be 1 due to the influence of noise even during a period when there is no change in the kinetic inductance, and conversely, the magnetic flux Φ ₀ is changed even during a period when the change in the kinetic inductance occurs. Sometimes it becomes zero.
The magnetic flux Φ ₀ of 1 is accumulated in the superconducting loop of the detection determining unit 122 that is magnetically coupled to the superconducting loop of the detecting unit 112. However, as shown in FIG. 7, since the attenuation resistance R is inserted in the likelihood determination circuit, the magnetic flux Φ ₀ accumulated in the superconducting loop of the detection determination unit 122 disappears after a while. The time constant until disappearance is determined by the damping resistance R and the inductance component L related to magnetic coupling.
In a neutron detection element that has received the thermal energy of particles emitted by a nuclear reaction, a change in kinetic inductance occurs over a period of about 2 to 3 nanoseconds. If one magnetic flux Φ ₀ is generated 100 times in the superconducting loop of the detection unit 112 during that period, for example, the magnetic flux is accumulated in the superconducting loop of the detection determination unit 122. The magnetic flux Φ ₀ is gradually accumulated from the first occurrence and approaches 100. If the disappearance time constant is sufficiently long, 100 magnetic fluxes Φ ₀ will eventually be accumulated. Thereafter, the accumulated magnetic flux disappears until the same neutron detection element receives another particle.
The likelihood determination circuit 120 determines that the change in the motion inductance has been detected when the magnetic flux Φ ₀ accumulated in the superconducting loop of the detection determination unit 122 is greater than or equal to a predetermined number.
In the first embodiment, out of 100 detection SFQ pulses, if the counter has more than 50 trial results, the detection result is output to an address generation circuit described later, and if it is smaller, no detection result is output. The likelihood determination by majority decision is performed.

  The address generation circuit is based on the premise that the neutron detection device rarely collides with a plurality of locations at the same time and usually only collides with one location. Since pulse neutron sources such as J-PARC are not dense enough to be generated at the same time, it can be considered that each neutron individually collides with the neutron detection element.

In the first embodiment, N neutron detection elements 1x shown in FIG. 1 are arranged in a range from 1 to N in the X-axis direction. “Ch.1” in FIG. 7 corresponds to the first neutron detection element and the SFQ circuit and likelihood determination circuit corresponding to the first neutron detection element. “Ch.2” corresponds to the second neutron detection element, SFQ circuit, and likelihood determination circuit. Therefore, from the correspondence with FIG. 1, the SFQ circuit and the likelihood determination circuit of FIG. 1-Ch. There are N channel pairs up to N, and Ch. 1-Ch. There are N channel pairs up to N.
The likelihood determination circuit determines the presence / absence of neutron detection for each channel using a determination SFQ pulse at 1 GHz (ie, every nanosecond). The address generation circuit sequentially scans each channel from 1 to N with a delay of 1 nanosecond, and checks the determination result. In the example of 1 million pixels, N = 1000. As a result, it can be seen in which channel one neutron was detected among the 1000 channels within 1 nanosecond × 1000 = 1 μsec. The scanning period of each channel, in this case 1 μsec, corresponds to the scanning period. In each scanning period, the detection result is output to the address generation circuit. In the address value, 10 bits (2 ¹⁰ = 1024) correspond to the values of each channel from 1 to 1000.

Therefore, when the sample is observed with the neutron detector of the present invention at a frame time of 1 ms, a maximum of 1000 neutrons per frame time can be observed at one frame. Note that the number of signal lines that communicate with the outside (room temperature region) is 10 bits (10 lines) in the X direction and 10 bits (10 lines) in the Y direction, for a total of 20. However, since a cable for a temperature element for monitoring the DC bias current of the SFQ circuit and temperature is necessary, a total of 40 to 50 cables are actually required.
The numerical values such as the frame time are not intended to limit the present invention, and can be changed according to the purpose of use, such as differences in observation objects.

Next, a manufacturing process for the neutron detector 100 according to the first embodiment of the present invention will be described with reference to FIGS.
FIG. 9 is a sectional view showing the structure of the neutron detector according to the first embodiment of the present invention.
FIG. 10 is an explanatory view showing the manufacturing process of the neutron detector according to the first embodiment of the present invention.

As shown in FIG. 10A, magnesium and boron are simultaneously sputtered using a carousel sputtering apparatus to form an MgB ₂ thin film 1 on a single crystal substrate 10 of sapphire (Al ₂ O ₃ ). In addition, the base material 10 is not limited to sapphire, and may be a nonmetal such as a dielectric. The deposition method of the MgB ₂ thin film may be a vapor deposition method. In FIG. 10, except for FIG. 10D, the description will be made assuming that the direction perpendicular to the paper surface is the Y axis and the direction along the paper surface is the X axis.
Details of the method of forming the MgB ₂ thin film are described in, for example, JP-A-2005-286245.

Next, as shown in FIG. 10B, a resist is applied on the MgB ₂ thin film 1, a resist pattern 11 is formed by electron beam lithography, and then electron cyclotron resonance (ECR) etching is performed. As a result, the neutron detection element 1x is formed in a stripe shape having a width of 0.5 μm extending in the depth direction of FIG.

Next, as shown in FIG. 10C, a protective film 3 is formed by depositing silicon oxide (SiO) on the neutron detection element 1x from which the resist pattern 11 has been removed. The protective film 3 prevents the surface of MgB ₂ from coming into direct contact with air.

  FIG. 10D shows the neutron detection element 1x shown in FIG. 10C viewed with the direction perpendicular to the paper surface as the X axis and the direction along the paper surface as the Y axis. Electrodes 4a are formed on both ends of the neutron detection element 1x. The electrodes 4a and 4b are conductors, and are formed of, for example, gold (Au), aluminum (Al), or titanium-gold (AuTi). Electrodes 4a are formed on both ends of the neutron detection element 1x.

Separately from these, a superconducting IC chip 2 in which circuits corresponding to the SFQ circuit 110, likelihood determination circuit 120 and address generation circuit 130 are integrated by a superconducting integrated circuit process formed by superposing Nb thin films as superconductors. Create An insulating layer 9 made of SiO ₂ is formed on the superconducting IC chip 2, and an electrode 4b is formed at a position corresponding to the electrode 4a of the neutron detection element 1x.

Next, as shown in FIG. 10E, the neutron detection element 1x is mounted (face-down) so as to face the surface on which the SFQ circuit of the superconducting IC chip 2 is formed. Specifically, the SFQ circuit of the superconducting IC chip 2 and the neutron detecting element 1x are bonded to the adhesive layer 5 so that the electrodes 4a and 4b face each other by flip chip bonding via the solder bumps 8 having superconductivity. Sandwich and join. As the adhesive layer 5, a thermocompression-bonding sheet may be used instead of the adhesive. In addition, as a material of the solder bump 8, a superconductive material such as a lead tin (Pb—Sn) alloy or a lead indium gold (Pb—In—Au) alloy is used, which is formed by a ball bonding method.
Further, alignment of the coil on the equivalent circuit of FIG. 7 made of MgB ₂ and the coil on the equivalent circuit of FIG. 7 made of Nb is also performed by the above-described flip chip bonding.

  Next, as shown in FIG. 10 (f), the neutron detection element 1y is further mounted on the neutron detection element 1x so that the extending directions of the neutron detection elements 1x and 1y are orthogonal to each other. Then, magnetic coupling is performed by superconducting IC chip 2 and superconducting contact.

  Finally, the neutron detection element 1x, the neutron detection element 1y, and the superconducting IC chip 2 are sealed with a sealing resin 6.

Note that the two neutron detection elements are bonded together so that the distance between the neutron detection elements 1x and 1y does not exceed the range of ⁴ He and ⁷ Li (4 μm and 2 μm, respectively). Should.
As a modification, the thin films 1x and 1y may be made of a superconducting material such as Nb, and the protective film 3 may contain MgB ₂ .

<< Second Embodiment >>
Next, a neutron detector 100a according to a second embodiment of the present invention will be described with reference to FIGS.
FIG. 11 is a cross-sectional view showing the structure of a neutron detection element including a neutron detection element according to the second embodiment of the present invention.
The difference from the first embodiment is free of ¹⁰ B in the neutron detector 1x and 1y, a point comprising a nuclear reaction layer 7 containing those intermediate ¹⁰ B.
The nuclear reaction layer 7 may be formed on a MgB ₂ thin film. In that case, it can be used as a superconductive base plate. Further, it may be a thin film of ¹⁰ B itself. Specifically, it can be formed by vapor deposition using a K cell or an electron beam.

As shown in FIG. 12, when neutrons collide with ¹⁰ B in the nuclear reaction layer 7, ⁴ He and ⁷ Li are radiated in the opposite directions due to the nuclear reaction, and ⁴ He or ⁷ Li is in the vicinity (range) The inner neutron detection element 1x or 1y. When ¹⁰ B is uniformly included in the nuclear reaction layer 7, neutrons are detected reliably because they cause a nuclear reaction with ¹⁰ B in the nuclear reaction layer 7 even if the neutrons travel through the path through the neutron detection elements 1 x and 1 y. Is done. Further, since the neutron detection element 1x or 1y does not have to be a superconducting material containing ¹⁰ B, the neutron detection element 1x or 1y can be, for example, a superconductor of Nb or NbN, or a boron-doped diamond thin film (Tc = 11K)
High temperature superconductors such as can be used.

<< Third Embodiment >>
Next, a neutron detector 100b according to a third embodiment of the present invention will be described using FIG.

FIG. 13 is an explanatory view showing a neutron detector according to the third embodiment of the present invention.
As shown in FIG. 13, as the shape of the neutron detection elements 1x and 1y, a shape with a meandering path (hereinafter referred to as a meander shape) may be used. The change in the kinetic inductance can be detected efficiently only by the diffusion length of thermal energy, and the width of the superconducting wire should be about 1 μm. However, by making the meander shape, the width of the superconducting wire can be reduced. Since it is possible to increase the area while optimizing, it is possible to increase the nuclear reactivity with neutrons. Moreover, it is not limited to a shape like FIG. 13, According to a use, you may have various shapes, a magnitude | size, and a line | wire width.

1: MgB ₂ thin film 1x, 1y: Neutron detection element 2: Superconducting IC chip 3: Protective film 4a, 4b: Electrode 5: Adhesive layer 6: Sealing resin 7: Nuclear reaction layer 8: Solder bump 9: Insulating layer 10 : Substrate 11: Resist pattern 100, 100a, 100b: Neutron detector 101: Neutron source 102a, 102b: Slit 103: Sample 104: Window 105: Thermal insulation container 110: SFQ circuit 111: SFQ pulse input unit 112 for detection 112: Detection unit 120: Likelihood determination circuit 121: SFQ pulse input unit for determination 122: Detection determination unit 130: Address generation circuit

Claims (9)

Changes in electronic state when receiving the thermal energy of one of at least two particles that are generated with thermal energy by a nuclear reaction between one neutron and a substance for detecting neutrons and emitted in different directions A group of X-coordinate detection elements formed by arranging a plurality of first particle detection elements in parallel,
A Y-coordinate detection element group in which a plurality of second particle detection elements that change in the electronic state when receiving the thermal energy of other particles are arranged in parallel,
Each of the first particle detection elements is a superconducting material having a region extending in the longitudinal direction, and the X coordinate detection element group has the first particle detection elements arranged in the horizontal direction, and any of the first particle detection elements is The X coordinate of the position where the nuclear reaction has occurred is detected based on whether a change in the electronic state of one particle is detected, and each second particle detection element is a superconducting material having a region extending in the lateral direction. And the Y coordinate detection element group includes the second particle detection elements arranged in the vertical direction, and the nuclear reaction based on which second particle detection element detects a change in the electronic state of the other particles. A neutron detection device for detecting a Y coordinate of a position where an error occurs.   The neutron detection apparatus according to claim 1, wherein the neutron detection substance is used for a first particle detection element and / or a second particle detection element.   The neutron detecting substance is between the adjacent first particle detecting element and the first particle detecting element, between the adjacent second particle detecting element and the second particle detecting element, or each first particle detecting element and each The neutron detection apparatus according to claim 1, wherein the neutron detection apparatus is disposed at least between the second particle detection element and the second particle detection element. Each of the first particle detecting elements detects a change in an electronic state in which a superconducting electron pair is reduced by receiving thermal energy of the first particle as a change in motion inductance,
4. Each of the second particle detection elements detects a change in an electronic state in which a superconducting electron pair is reduced by receiving thermal energy of the second particle as a change in motion inductance. Neutron detector. An SFQ circuit formed by forming a Josephson junction in a part of the superconducting ring;
The SFQ circuit includes a detection SFQ pulse input unit for inputting a detection SFQ pulse having a predetermined magnetic flux every predetermined time T1, and a change in the Josephson current in the superconducting ring due to a change in the motion inductance. The neutron detection device according to claim 4, further comprising a motion inductance detection element group that detects a change in motion inductance, and being magnetically coupled to one of the first particle detection element or the second particle detection element. The SFQ circuit includes a likelihood determination circuit,
The likelihood determination circuit is input by a determination SFQ pulse input unit that inputs a determination SFQ pulse every predetermined time T2 longer than the time T1, and is input by the detection SFQ pulse input unit when the determination SFQ pulse is input. Detection of determining that a change in motion inductance has been detected when the number of detection SFQ pulses in which the change in motion inductance is detected is greater than or equal to a predetermined number among the number of detected SFQ pulses The neutron detection apparatus according to claim 5, further comprising a determination unit.   The address generation circuit which further outputs an X coordinate and a Y coordinate detected by the X coordinate detection element group and the Y coordinate detection element group as digitized address values. Neutron detector. The neutron detection material contains ¹⁰ B, and the particles are two particles of alpha rays and lithium rays generated by a nuclear reaction between neutrons and ¹⁰ B and emitted in opposite directions. The neutron detector as described in any one. The neutron detection apparatus according to claim 1, wherein the neutron detection substance contains MgB ₂ .