Measurement device, measurement method, and program

Abstract

To provide a measurement device, a measurement method, and a program that are capable of measuring an SEU cross section of a thermal neutron region and its energy dependence with a simple configuration.SOLUTION: A measurement device includes: a neutron generation unit 11; a switching unit 12 that includes a shielding material 12A for shielding thermal neutrons and switches between a shielding state in which thermal neutrons contained in neutrons generated by the neutron generation unit 11 are shielded and an open state in which thermal neutrons are not shielded; a counter 23 that counts the number of SEUs that occur when a device 3 is irradiated with neutrons; and a calculation unit 24 that derives an arithmetic expression showing a relation between neutron energy in a thermal neutron region and an SEU cross section based on the number of first SEUs that occur when the device 3 is irradiated with neutrons with the switching unit 12 in the open state, and the number of second SEUs that occur when the device 3 is irradiated with neutrons with the switching unit 12 in the shielding state. When the neutron energy is input, the calculation unit 24 calculates the SEU cross section from the thermal neutron region to 0.1 [MeV] based on the arithmetic expression.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a measurement device, a measurement method, and a program for measuring a cross-section of a single event upset (SEU) caused by epithermal and thermal neutrons (neutrons having an energy of 0.1 [Mev] or less). [Background technology]

[0002] Neutrons generated by accelerators are a mixture of thermal neutrons (neutrons with energies around 25 [meV]) and neutrons with higher energies. Therefore, in order to measure the SEU cross-section of thermal neutrons and neutrons with energies close to that (hereinafter referred to as the "thermal neutron region"), it is necessary to separate the thermal neutrons from the neutrons generated by the accelerator.

[0003] Non-Patent Document 1 discloses that a shielding material (e.g., cadmium) capable of shielding the energy band below thermal neutrons is used to separate thermal neutrons from neutrons with higher energy. That is, it discloses that the SEU cross section in the thermal neutron region is measured by calculating the difference between the SEU cross section measured without installing a shielding material and the SEU cross section measured with the shielding material installed.

[0004] Non-Patent Document 2 discloses a method that focuses on the fact that the speed of neutrons changes depending on the energy, identifies thermal neutrons by detecting the timing at which an SEU occurs, and measures the SEU cross-section of the thermal neutron region. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] JEDEC JESD89BMeasurement and reporting of particle alphaand terrestrial cosmicray-induced soft errorsin semiconductor devices(P.53) [Non-Patent Document 2] "Energy-Resolved SEU Cross SectionFrom 10-meV to 800-MeV Neutronsby Time-of-Flight Measurement," in IEEE Transactions on Nuclear Science Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method disclosed in Non-Patent Document 1 can measure the SEU cross-section in the thermal neutron region, but cannot measure the energy dependence within the thermal neutron region or above the thermal neutron region.

[0007] In the method disclosed in Non-Patent Document 2, the accelerator facility capable of measuring neutron energy is large-scale, and available facilities are limited worldwide. Therefore, there are problems such as high costs for measurement and limited time for using the facility.

[0008] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide a measurement device, a measurement method, and a program capable of measuring the SEU cross-section of the thermal neutron region and its energy dependence with a simple configuration. [Means for solving the problem]

[0009] A measurement device according to one embodiment of the present disclosure includes a neutron generating unit that generates neutrons, and a shielding material that blocks thermal neutrons, and a switching unit that switches between a shielded state in which thermal neutrons contained in the neutrons generated by the neutron generating unit are shielded, and an open state in which the thermal neutrons are not shielded, a counting unit that counts the number of SEUs that occur when a device is irradiated with neutrons, and a calculation unit that derives an arithmetic equation that indicates the relationship between neutron energy in the thermal neutron region and an SEU cross-section based on the number of first SEUs that occur when the device is irradiated with neutrons with the switching unit in the open state and the number of second SEUs that occur when the device is irradiated with neutrons with the switching unit in the shielded state, and the calculation unit calculates a neutron energy-dependent SEU cross-section from the thermal neutron region to 0.1 Mev based on the arithmetic equation when neutron energy is input.

[0010] A measurement method of one embodiment of the present disclosure includes irradiating a target with accelerated particles to generate thermal neutrons and neutrons with higher energy than the thermal neutrons, counting the number of first SEUs that occur when a device is irradiated with the thermal neutrons and the neutrons with higher energy than the thermal neutrons, and counting the number of second SEUs that occur when the device is irradiated with only neutrons with higher energy than the thermal neutrons by shielding the thermal neutrons, deriving an equation showing the relationship between neutron energy in the thermal neutron region and an SEU cross-section based on the number of first SEUs and the number of second SEUs, and calculating a neutron energy-dependent SEU cross-section from the thermal neutron region to 0.1 Mev based on the equation when neutron energy is input.

[0011] One aspect of the present disclosure is a program for causing a computer to function as the counting unit and the calculating unit of the above-mentioned measuring device. Effect of the Invention

[0012] According to the present disclosure, it is possible to measure the SEU cross section of the thermal neutron region and its energy dependence with a simple configuration. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing the configuration of a measurement device and its peripheral devices according to an embodiment. [Diagram 2] FIG. 2 is a graph showing the relationship between neutron energy and the nuclear cross section of boron. [Diagram 3] FIG. 3 is a graph showing the relationship between neutron energy and SEU cross-section. [Figure 4] FIG. 4 is a flowchart showing a processing procedure of the measurement device according to the embodiment. [Diagram 5] FIG. 5 is a block diagram showing a hardware configuration of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a measurement device according to an embodiment will be described with reference to the drawings. Fig. 1 is a block diagram showing a detailed configuration of a measurement device 100 according to an embodiment and its peripheral devices. As shown in Fig. 1, the measurement device 100 includes an irradiation device 1 and a calculation device 2.

[0015] The irradiation device 1 includes a neutron generating unit 11 that generates neutrons, and a switching unit 12. The neutron generating unit 11 includes an accelerator 111, a target 112, and a moderator 113.

[0016] The accelerator 111 generates accelerated particles p 1 and irradiates the target 112 with the particles.

[0017] The target 112 is made of, for example, tungsten, beryllium, lithium, lead, or the like, and generates neutrons p2 when irradiated with accelerated particles p1. Most of the neutrons p2 generated in the target 112 are high-energy neutrons of 1 [MeV] or more.

[0018] The moderator 113 is, for example, a substance containing hydrogen, water, polyethylene, liquid hydrogen, or solid methane. The moderator 113 slows down the neutrons generated in the target 112. By providing the moderator 113, some of the high-energy neutrons p2 generated in the target 112 are slowed down to the energy of thermal neutrons. Therefore, the neutrons generated in the moderator 113 are a mixture of thermal neutrons p4 and neutrons p3 with higher energy than the thermal neutrons.

[0019] The switching unit 12 includes a shielding material 12A that blocks thermal neutrons. Cadmium, for example, can be used as the shielding material 12A. The switching unit 12 can be switched by a user's switching operation between a shielding state in which the shielding material 12A is installed and an open state in which the shielding material 12A is not installed. When the switching unit 12 is in the shielding state, thermal neutrons p4 among the neutrons irradiated from the moderator 113 are shielded, and neutrons p3 having higher energy than the thermal neutrons pass through. On the other hand, when the switching unit 12 is in the open state, neutrons irradiated from the moderator 113 (thermal neutrons p4 and neutrons p3 having higher energy than the thermal neutrons) pass through without being shielded. The neutrons that pass through the switching unit 12 are irradiated to the device 3. The device 3 is, for example, an LSI.

[0020] The arithmetic device 2 includes a measurement unit 21, an arithmetic unit 22, a counting unit 23, and a calculation unit 24.

[0021] The measurement unit 21 counts the number of accelerated particles irradiated from the accelerator 111. The measurement unit 21 outputs the counted number of accelerated particles to the calculation unit 22.

[0022] The calculation unit 22 calculates the neutron flux (number of neutrons) irradiated from the target 112 based on the number of accelerated particles. The calculation unit 22 has correspondence data showing the relationship between the number of accelerated particles and the neutron flux, and calculates the neutron flux based on this correspondence data and the number of accelerated particles. The calculation unit 22 outputs the calculated neutron flux data to the calculation unit 24.

[0023] The counter 23 counts the number of SEUs that occur when neutrons are irradiated onto the device 3. An "SEU" is an event in which a single particle (neutron, proton, heavy particle, etc.) enters the device 3 such as an LSI, and the data (bits) stored in the LSI are inverted due to the charge generated by the nuclear reaction. An SEU is also called a soft error.

[0024] As described above, the switching unit 12 switches between an open state in which the shielding material 12A is not installed and a shielded state in which the shielding material 12A is installed, and irradiates the device 3 with neutrons. The counting unit 23 counts the number of SEUs that occur in the open state (hereinafter referred to as the “first SEU number”) and the number of SEUs that occur in the shielded state (hereinafter referred to as the “second SEU number”). The counting unit 23 outputs the first SEU number and the second SEU number to the calculation unit 24.

[0025] The calculation unit 24 derives an equation for calculating the neutron energy-dependent SEU cross section based on the number of first SEU occurrences and the number of second SEU occurrences. The "SEU cross section" is a value obtained by dividing the number of SEU occurrences when a particle beam (e.g., neutrons) is irradiated to a device by the fluence of the irradiated neutrons. The neutron fluence refers to the total number of neutrons passing through a unit area.

[0026] The method of deriving the above formula will be explained below. FIG. 2 is a graph showing the relationship between neutron energy and the nuclear cross section of boron (B10). As shown in FIG. 2, in the region where the neutron energy is 0.1 [MeV] or less, the slope of the curve s1 is (1 / √E). It is also known that the SEU cross section depends on the nuclear cross section of boron in the region where the neutron energy is 0.1 [MeV] or less. FIG. 3 is a graph showing the relationship between neutron energy and the SEU cross section, and in the region where the neutron energy is 0.1 [MeV] or less, the slope of the curve s2 is "1 / √E". The region where the neutron energy is around 0.1 [MeV] is called the "epithermal neutron region". Therefore, the neutrons in the region where the neutron energy is 0.1 [MeV] or less include epithermal neutrons and thermal neutrons.

[0027] If the SEU cross section with neutron energy of 0.1 MeV or less is defined as "σSEU(E)", then "σSEU(E)" and "1 / √E" can be considered to be proportional to each other. "σSEU(E)" can be expressed by the following equation (1).

[0028]

number

[0029] In equation (1), A is a variable (proportionality coefficient) and E is the neutron energy. A is a different value for each device that is irradiated with neutrons. Therefore, if the variable A in equation (1) can be determined, the formula for the SEU cross section, "σSEU(E)", can be derived, and the SEU cross section can be calculated based on the neutron energy E.

[0030] In this embodiment, the number of first SEU occurrences (referred to as "Nwo shield") is measured with the switching unit 12 in an open state. Also, the number of second SEU occurrences (referred to as "Nw shield") is measured with the switching unit 12 in a blocked state. Assuming that the SEU cross section "σSEU(E)" is expressed by the above formula (1), the following formula (2) is established.

[0031]

number

[0032] In formula (2), "Th" is the threshold energy of the shielding material 12A, and for example, when cadmium is used as the shielding material 12A, Th=0.4 [eV]. "Φwoshield(E)" is the neutron fluence when the shielding material 12A is not installed (open state). "Φwo shield(E)" can be measured by simulation or actual measurement. The neutron fluence is the total number of neutrons passing per unit area, and can be calculated based on the neutron flux output from the calculation unit 22. The variable A can be calculated using formula (2) above.

[0033] By applying the variable A calculated by the above formula (2) to the above formula (1), an equation is derived that indicates the relationship between the neutron energy E in the neutron energy region of 0.1 [MeV] or less (region of epithermal neutrons or less) and the SEU cross section "σSEU(E)". That is, the calculation unit 24 derives the above formula based on the relationship that when the neutron energy is E, the SEU cross section in the region of epithermal neutrons or less is proportional to 1 / √E.

[0034] By using the formula derived by the calculation unit 24, it becomes possible to calculate the SEU cross section based on the neutron energy E. That is, if the neutron energy E is known, the SEU cross section "σSEU(E)" can be calculated using the above formula. In addition, the SEU cross section from the thermal neutron region to 0.1 [MeV] and its energy dependence can be measured.

[0035] Next, a procedure for deriving an equation for the SEU cross section "σSEU(E)" using the measurement apparatus according to this embodiment will be described with reference to the flowchart shown in FIG.

[0036] First, in step S11 of FIG. 4, the user sets the switching unit 12 to the open state.

[0037] In step S12, the user operates the accelerator 111 to irradiate accelerated particles p1 onto the target 112. When the accelerated particles p1 are irradiated onto the target 112, high-energy neutrons p2 are generated in the target 112. When the high-energy neutrons p2 are irradiated onto the moderator 113, some of the neutrons are slowed down. As a result, neutrons p3 with higher energy than thermal neutrons and thermal neutrons p4 are generated.

[0038] Since the switching unit 12 is in an open state and the shielding material 12A is not installed, the device 3 is irradiated with both neutrons p3 and thermal neutrons p4, which have higher energies than thermal neutrons.

[0039] In step S13, the counting unit 23 counts the number of SEUs that occur in the device 3. The number of SEUs that occur at this time (the number of first SEUs) is designated as "Nwo shield."

[0040] In step S14, the user determines whether or not the measurement of the number of SEU occurrences in both the open state and the blocked state has been completed. If the measurement has been completed (S14; YES), the process proceeds to step S16. If not (S14; NO), the process proceeds to step S15. Initially, the measurement in the blocked state has not been completed, so the process proceeds to step S15.

[0041] In step S15, the user sets the switching unit 12 to the shielding state, and then executes the process of step S12. Since the switching unit 12 is set to the shielding state, the thermal neutrons p4 are shielded from the neutrons p3 and p4, which have higher energies than the thermal neutrons, generated in the moderator 113. Therefore, the device 3 is irradiated with the neutrons p4, which have higher energy than the thermal neutrons.

[0042] In step S13, the counting unit 23 counts the number of SEUs that have occurred in the device 3. The number of SEUs that have occurred at this time (the number of second SEUs) is set to "Nw shield." Then, the process proceeds to step S14.

[0043] Since the measurement of the number of SEU occurrences has been completed in both the open state and the blocked state (S14; YES), the process proceeds to step S16.

[0044] In step S16, the calculation unit 24 substitutes the number of first SEU occurrences "Nwo shield" and the number of second SEU occurrences "Nw shield" into the above-mentioned equation (2). Based on the neutron flux data calculated by the calculation unit 22, the calculation unit 24 calculates the neutron fluence "Φwo shield(E)" and substitutes it into equation (2) to calculate the variable A. The calculation unit 24 derives an equation indicating the relationship between the SEU cross-section and neutron energy by substituting the variable A into the above-mentioned equation (1). When neutron energy E in the energy region below epithermal neutrons (including the thermal neutron region) is given, the calculation unit 24 can calculate the SEU cross-section "σSEU(E)" in the energy region below epithermal neutrons by substituting this neutron energy E into the above-mentioned equation.

[0045] As described above, the measurement apparatus according to this embodiment is a measurement apparatus 100 for measuring an SEU cross section in the thermal neutron region, and includes a neutron generating unit 11 that generates neutrons, a shielding material 12A that blocks thermal neutrons, a switching unit 12 that switches between a shielded state in which thermal neutrons contained in the neutrons generated by the neutron generating unit 11 are shielded, and an open state in which thermal neutrons are not shielded, a counting unit 23 that counts the number of SEUs that occur when the device 3 is irradiated with neutrons, and a switching unit 24 that switches the switching unit 12 to an open state. a calculation unit 24 that derives an arithmetic expression showing the relationship between neutron energy in the thermal neutron range and the SEU cross-section, based on the number of first SEUs that occur when neutrons are irradiated to the device 3 with the switching unit 12 in a shielded state and the number of second SEUs that occur when neutrons are irradiated to the device 3 with the switching unit 12 in a shielded state, and the calculation unit 24 calculates the SEU cross-section dependent on neutron energy from the thermal neutron range to 0.1 MeV based on the above arithmetic expression when neutron energy is input.

[0046] In this embodiment, it is possible to calculate the SEU cross section for neutron energy E in the epithermal neutron range or less (neutron energy range of 0.1 MeV or less) with a simple configuration without using a special accelerator. Furthermore, it is possible to calculate the SEU cross section for neutron energy E in the thermal neutron range. Furthermore, as shown in the above-mentioned formula (1), since the SEU cross section is expressed as a function of neutron energy E, it becomes possible to measure the energy dependence of the SEU cross section.

[0047] That is, the variable A shown in the above formula (1) is calculated based on the measurement results of the number of SEU occurrences when the switching unit 12 is in the open state and the shielded state, and on "Φwoshield(E)" calculated by simulation or actual measurement. An equation showing the relationship between the SEU cross section "σSEU(E)" and neutron energy E can be derived based on the variable A. Therefore, by substituting the neutron energy E into this equation, it becomes possible to easily calculate the SEU cross section.

[0048] In this embodiment, accelerated particles generated in the accelerator 111 are irradiated onto a target 112 to generate high-energy neutrons, and these high-energy neutrons are irradiated onto a moderator 113 to moderate some of the high-energy neutrons to thermal neutron energy. This makes it possible to generate neutrons that are a mixture of thermal neutrons and neutrons with higher energy than thermal neutrons, and by operating the switching unit 12 to switch between installing and not installing the shielding material 12A, it becomes possible to easily measure the number of first SEU occurrences and the number of second SEU occurrences.

[0049] In this embodiment, when neutron energy is E, the variable A shown in equation (1) is specified based on the relationship that the SEU cross-section in the thermal neutron region (the region of energy below epithermal neutrons) is proportional to 1 / √E, making it possible to derive an arithmetic equation showing the relationship between neutron energy E and the SEU cross-section in a simple manner.

[0050] In this embodiment, when the number of first SEU occurrences is "Nwo shield" and the number of second SEU occurrences is "Nw shield," variable A is calculated based on the above-mentioned equation (2), and the above-mentioned equation is derived using this variable A as a proportionality coefficient between the SEU cross section and 1 / √E. This makes it possible to derive the above equation using an extremely simple method of measuring the number of SEU occurrences twice and then using "Φwo shield(E)" calculated by simulation or actual measurement.

[0051] The arithmetic device 2 of the present embodiment described above may be, for example, a general-purpose computer system including a CPU (Central Processing Unit, processor) 901, a memory 902, a storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), a communication device 904, an input device 905, and an output device 906, as shown in Fig. 5. The memory 902 and the storage 903 are storage devices. In this computer system, the CPU 901 executes a predetermined program loaded on the memory 902, thereby realizing each function of the arithmetic device 2.

[0052] The arithmetic device 2 may be implemented in one computer or in multiple computers, and may also be a virtual machine implemented in a computer.

[0053] The program for the arithmetic device 2 can be stored in a computer-readable recording medium such as a HDD, SSD, a Universal Serial Bus (USB) memory, a Compact Disc (CD), or a Digital Versatile Disc (DVD), or can be distributed via a network. The computer-readable recording medium is, for example, a non-transitory recording medium.

[0054] The present disclosure is not limited to the above-described embodiment, and various modifications are possible within the scope of the present disclosure. [Explanation of symbols]

[0055] 1 Irradiation device 2 Arithmetic unit 3 Devices 11 Neutron Generator 12 Switching section 12A shielding material 21 Measuring part 22 Arithmetic section 23 Counting Department 24 Calculation section 100 Measuring Equipment 111 Accelerator 112 Target 113 Moderator

Claims

1. A neutron generating unit that generates neutrons; a switching unit including a shielding material for blocking thermal neutrons, the switching unit being configured to switch between a blocked state for blocking thermal neutrons contained in the neutrons generated by the neutron generating unit and an open state for not blocking the thermal neutrons; A counting unit that counts the number of SEUs generated when the device is irradiated with neutrons; a calculation unit that derives an arithmetic expression showing a relationship between neutron energy in a thermal neutron region and an SEU cross-section based on a first number of SEUs generated when the device is irradiated with neutrons with the switching unit in an open state and a second number of SEUs generated when the device is irradiated with neutrons with the switching unit in a blocked state, The calculation unit calculates a neutron energy-dependent SEU cross section from a thermal neutron region to 0.1 [MeV] based on the arithmetic formula when the neutron energy is input. Measuring equipment.

2. The neutron generating unit includes: An accelerator that generates accelerated particles; a target that is irradiated with the accelerated particles to generate neutrons; A moderator that slows down neutrons generated in the target; The measuring device according to claim 1 ,

3. The calculation unit derives the calculation formula based on the relationship that the SEU cross section in the thermal neutron region is proportional to 1 / √E when the neutron energy is E.

3. The measuring device according to claim 1 or 2.

4. The calculation unit is When the number of first SEU occurrences is "Nwo shield" and the number of second SEU occurrences is "Nw shield", a variable A is calculated based on the following formula, and the formula is derived by setting the variable A as a proportionality coefficient between the SEU cross section and 1 / √E.

4. The measuring device according to claim 3. [0030]

5. Irradiating a target with accelerated particles to generate thermal neutrons and neutrons having higher energy than the thermal neutrons; counting the number of first SEUs generated when the device is irradiated with the thermal neutrons and neutrons having higher energy than the thermal neutrons; Counting the number of second SEUs generated when the thermal neutrons are shielded and the device is irradiated with only neutrons with higher energy than the thermal neutrons; deriving an arithmetic expression showing a relationship between neutron energy in a thermal neutron region and an SEU cross-section based on the first SEU generation number and the second SEU generation number; When the neutron energy is input, the neutron energy-dependent SEU cross section is calculated from the thermal neutron region to 0.1 [MeV] based on the above formula. Measurement method.

6. A program for causing a computer to function as the counting unit and the calculation unit mounted in the measurement device according to claim 1.

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