Measuring device, measuring 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 apparatus, a measurement method, and a program for measuring the SEU (Single Event Upset) cross section of epithermal neutrons and thermal neutrons (neutrons having an energy of 0.1 [MeV] or less).

Background Art

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

[0003] Non-Patent Document 1 discloses separating thermal neutrons and neutrons having higher energies by using a shielding material (for example, cadmium) capable of shielding an energy band equal to or lower than that of thermal neutrons. That is, it is disclosed that the SEU cross section in the thermal neutron region is measured by calculating the difference between the SEU cross section measured without installing the shielding material and the SEU cross section measured with the shielding material installed.

[0004] Non-Patent Document 2 discloses a method of measuring the SEU cross section in the thermal neutron region by focusing on the fact that the velocity of neutrons changes according to energy, identifying thermal neutrons by detecting the timing at which SEU occurs.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

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

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

[0008] This disclosure is made in view of the above circumstances and aims to provide a measuring device, a measuring method, and a program that can measure the SEU crosssection and its energy dependence in the thermal neutron region with a simple configuration. [Means for solving the problem]

[0009] A measuring apparatus in one aspect of the present disclosure comprises: a neutron generating unit that generates neutrons; a switching unit equipped with a shielding material that shields against thermal neutrons, which switches between a shielded state that shields against thermal neutrons contained in the neutrons generated by the neutron generating unit and an open state that does not shield against thermal neutrons; a counting unit that counts the number of SEUs generated when a device is irradiated with neutrons; and a calculation unit that derives a calculation formula showing the relationship between neutron energy in the thermal neutron region and the SEU cross-section based on the number of first SEUs generated when the device is irradiated with neutrons with the switching unit in the open state and the number of second SEUs generated when the device is irradiated with neutrons with the switching unit in the shielded state, wherein the calculation unit calculates a neutron energy-dependent SEU cross-section from the thermal neutron region down to 0.1 [Mev] based on the calculation formula when neutron energy is input.

[0010] A measurement method in one aspect of the present disclosure involves irradiating a target with accelerated particles to generate thermal neutrons and neutrons with higher energies than thermal neutrons, counting the number of first SEUs generated when the device is irradiated with the thermal neutrons and neutrons with higher energies than thermal neutrons, counting the number of second SEUs generated when the thermal neutrons are shielded and only neutrons with higher energies than thermal neutrons are irradiated with the device, deriving a calculation formula showing the relationship between neutron energy in the thermal neutron region and the SEU cross-section based on the number of first and second SEUs generated, and calculating a neutron energy-dependent SEU cross-section from the thermal neutron region down to 0.1 [Mev] based on the calculation formula when neutron energy is input.

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

[0012] According to this disclosure, it becomes possible to measure the SEU crosssection and its energy dependence in the thermal neutron region with a simple configuration. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a block diagram showing the configuration of a measuring device and its peripheral equipment according to an embodiment. [Figure 2] Figure 2 is a graph showing the relationship between neutron energy and the nuclear cross-section of boron. [Figure 3] Figure 3 is a graph showing the relationship between neutron energy and SEU cross-section. [Figure 4] Figure 4 is a flowchart showing the processing procedure of the measuring device according to the embodiment. [Figure 5] Figure 5 is a block diagram showing the hardware configuration of this embodiment. [Modes for carrying out the invention]

[0014] The measuring device according to the embodiment will be described below with reference to the drawings. Figure 1 is a block diagram showing the detailed configuration of the measuring device 100 and its peripheral equipment according to the embodiment. As shown in Figure 1, the measuring device 100 comprises an irradiation device 1 and a calculation device 2.

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

[0016] The accelerator 111 generates accelerated particles p1 and irradiates the target 112 with them.

[0017] Target 112 is made of materials such as tungsten, beryllium, lithium, and lead, and generates neutrons p2 when irradiated with accelerated particles p1. The majority of the neutrons p2 generated in 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 moderates neutrons generated at the target 112. By providing the moderator 113, part of the high-energy neutrons p2 generated at the target 112 is moderated to thermal neutron energy. For this reason, the neutrons generated in the moderator 113 are in a state where thermal neutrons p4 and neutrons p3 with higher energy than thermal neutrons coexist.

[0019] The switching unit 12 includes a shielding material 12A that shields thermal neutrons. For example, cadmium can be used as the shielding material 12A. The switching unit 12 can switch to either a shielding state in which the shielding material 12A is disposed or an open state in which the shielding material 12A is not disposed, in response to a user's switching operation. When the switching unit 12 is set to the shielding state, among the neutrons emitted from the moderator 113, the thermal neutrons p4 are shielded, and the neutrons p3 with higher energy than thermal neutrons pass through. On the other hand, when the switching unit 12 is set to the open state, the neutrons (thermal neutrons p4 and neutrons p3 with higher energy than thermal neutrons) emitted from the moderator 113 pass through without being shielded. The neutrons that have passed through the switching unit 12 are applied 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 emitted from the accelerator 111. The measurement unit 21 outputs the counted number of accelerated particles to the arithmetic unit 22.

[0022] The arithmetic unit 22 calculates the neutron flux (number of neutrons) emitted from the target 112 based on the number of accelerated particles. The arithmetic unit 22 includes correspondence data indicating 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 arithmetic unit 22 outputs the calculated neutron flux data to the calculation unit 24.

[0023] The counting unit 23 counts the number of SEUs generated when device 3 is irradiated with neutrons. An "SEU" is an event in which a single particle (neutron, proton, heavy particle, etc.) is incident on device 3 such as an LSI, and the charge generated by the nuclear reaction causes the data (bits) stored in the LSI to be reversed. SEUs are also called soft errors.

[0024] As described above, the switching unit 12 switches between an open state without the shielding material 12A and a shielded state with the shielding material 12A installed, and irradiates the device 3 with neutrons. The counting unit 23 counts the number of SEUs generated in the open state (hereinafter referred to as the "first SEU generation count") and the number of SEUs generated in the shielded state (hereinafter referred to as the "second SEU generation count"). The counting unit 23 outputs the first SEU generation count and the second SEU generation count to the calculation unit 24.

[0025] The calculation unit 24 derives a formula for calculating the neutron energy-dependent SEU cross-section based on the number of first SEUs and the number of second SEUs. The "SEU cross-section" is a value obtained by dividing the number of SEUs generated when the device is irradiated with a particle beam (e.g., neutrons) by the irradiated neutron fluence. Neutron fluence refers to the total number of neutrons that passed per unit area.

[0026] The derivation method of the above calculation formula is explained below. Figure 2 is a graph showing the relationship between neutron energy and the nuclear cross-section of boron (B10). As shown in Figure 2, in the region where the neutron energy is 0.1 [MeV] or less, the slope of 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. Figure 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 curve s2 is "1 / √E). The region around 0.1 [MeV] neutron energy is called the "epothermic neutron region". Therefore, neutrons in the region where the neutron energy is 0.1 [MeV] or less include epithermic neutrons and thermal neutrons.

[0027] If we denote the SEU crosssection with a neutron energy of 0.1 [MeV] or less as "σSEU(E)", then we can consider "σSEU(E)" and "1 / √E" to be proportional. "σSEU(E)" can be expressed by the following equation (1).

[0028]

number

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

[0030] In this embodiment, the number of first SEUs generated (referred to as "Nwo shield") is measured with the switching unit 12 in the open state. The number of second SEUs generated (referred to as "Nw shield") is measured with the switching unit 12 in the shielded state. Assuming that the SEU cross-section "σSEU(E)" is given by equation (1) above, the following (2) holds true.

[0031]

number

[0032] In equation (2), "Th" is the threshold energy of the shielding material 12A. For example, if 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 that pass through 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 the above equation (2).

[0033] By substituting the variable A calculated using equation (2) above into equation (1) above, a calculation formula is derived that shows the relationship between the neutron energy E and the SEU cross-section "σSEU(E)" in the region where the neutron energy is 0.1 [MeV] or less (the region below the epithermal neutron). That is, the calculation unit 24 derives the above calculation formula based on the relationship that when the neutron energy is E, the SEU cross-section in the region below the epithermal neutron is proportional to 1 / √E.

[0034] By using the calculation formula derived in 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 calculation formula. Furthermore, it is possible to measure the SEU cross-section from the thermal neutron region down to 0.1 [MeV] and its energy dependence.

[0035] Next, the procedure for deriving the calculation formula for the SEU cross-section "σSEU(E)" using the measuring device according to this embodiment will be explained with reference to the flowchart shown in Figure 4.

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

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

[0038] Since the switching section 12 is in an open state and no shielding material 12A is installed, both neutrons p3 and thermal neutrons p4, which have higher energies than thermal neutrons, are irradiated onto the device 3.

[0039] In step S13, the counting unit 23 counts the number of SEUs generated in device 3. The number of SEUs generated at this time (first SEU generation count) is referred to as "Nwo shield".

[0040] In step S14, the user determines whether the measurement of the number of SEUs in both the open and shielded states has been completed. If it has been completed (S14; YES), the process proceeds to step S16; otherwise (S14; NO), the process proceeds to step S15. Initially, the measurement in the shielded state is not yet completed, so the process proceeds to step S15.

[0041] In step S15, the user sets the switching unit 12 to the shielded state and then executes the process in step S12. Because the switching unit 12 is set to the shielded state, of the neutrons p3 and thermal neutrons p4 that have higher energies than the thermal neutrons generated by the moderator 113, thermal neutron p4 is shielded. As a result, neutrons p4 with higher energies than the thermal neutrons are irradiated onto the device 3.

[0042] In step S13, the counting unit 23 counts the number of SEUs generated in device 3. The number of SEUs generated at this time (second SEU generation count) is referred to as "Nw shield". Then, the process proceeds to step S14.

[0043] Since the measurement of the number of SEUs has been completed in both the open and shielded states (S14; YES), the process proceeds to step S16.

[0044] In step S16, the calculation unit 24 substitutes the first SEU generation number "Nwo shield" and the second SEU generation number "Nw shield" into equation (2) described above. Furthermore, based on the neutron flux data calculated by the calculation unit 22, it calculates the neutron fluence "Φwo shield(E)" and substitutes it into equation (2) to calculate variable A. By substituting variable A into equation (1) described above, the calculation unit 24 derives a calculation formula showing the relationship between the SEU cross-section and neutron energy. Given a neutron energy E in the energy region below the epithermal neutron (including the thermal neutron region), the calculation unit 24 can calculate the SEU cross-section "σSEU(E)" in the energy region below the epithermal neutron by substituting this neutron energy E into the above calculation formula.

[0045] As described above, the measuring device according to this embodiment is a measuring device 100 for measuring SEU cross-sections in the thermal neutron region, comprising: a neutron generating unit 11 that generates neutrons; a shielding material 12A that shields against thermal neutrons, and a switching unit 12 that switches between a shielded state that shields against thermal neutrons contained in the neutrons generated by the neutron generating unit 11 and an open state that does not shield against thermal neutrons; a counting unit 23 that counts the number of SEUs generated when the device 3 is irradiated with neutrons; and a switching unit 12 that switches between an open state and an open state. The system includes a calculation unit 24 that derives a calculation formula showing the relationship between neutron energy and SEU cross-sections in the thermal neutron region, based on the number of first SEUs generated when neutrons are irradiated to device 3 in a shielded state, and the number of second SEUs generated when neutrons are irradiated to device 3 with the switching unit 12 in a shielded state. The calculation unit 24 calculates neutron energy-dependent SEU cross-sections from the thermal neutron region down to 0.1 [MeV] based on the calculation formula when neutron energy is input.

[0046] In this embodiment, the SEU cross-section with respect to neutron energy E in the region below epithermal neutrons (the region where neutron energy is 0.1 [MeV] or less) can be calculated with a simple configuration without using a special accelerator. By extension, the SEU cross-section with respect to neutron energy E in the thermal neutron region can be calculated. Furthermore, as shown in equation (1) above, 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] Specifically, the variable A shown in equation (1) above is calculated based on the measurement results of the number of SEUs generated in two cases, when the switching unit 12 is in the open state and in the shielded state, and the "Φwo shield(E)" calculated by simulation or actual measurement. Based on variable A, a calculation formula showing the relationship between the SEU cross-section "σSEU(E)" and the neutron energy E can be derived. Therefore, by substituting the neutron energy E into this calculation formula, it becomes possible to easily calculate the SEU cross-section.

[0048] In this embodiment, accelerated particles generated in the accelerator 111 are irradiated onto the target 112 to generate high-energy neutrons, and these high-energy neutrons are irradiated onto the moderator 113 to slow down some of the high-energy neutrons to the energy of thermal neutrons. As a result, it is possible to generate neutrons that are a mixture of thermal neutrons and neutrons with higher energies 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 SEUs and the number of second SEUs generated.

[0049] In this embodiment, when the neutron energy is E, the SEU cross-section in the thermal neutron region (the region of energy below the epithermal neutron) is proportional to 1 / √E. Based on this relationship, the variable A shown in equation (1) is determined, making it possible to derive a calculation formula 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", the variable A is calculated based on equation (2) above, and the above calculation formula is derived using this variable A as the proportionality coefficient between the SEU cross-section and 1 / √E. Therefore, it becomes possible to derive the above calculation formula in an extremely simple method by measuring the number of SEU occurrences twice and using "Φwo shield(E)" calculated by simulation or actual measurement.

[0051] As shown in Figure 5, the arithmetic unit 2 of this embodiment described above can be a general-purpose computer system comprising, for example, a CPU (Central Processing Unit, processor) 901, memory 902, storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), communication device 904, input device 905, and output device 906. The memory 902 and storage 903 are storage devices. In this computer system, each function of the arithmetic unit 2 is realized when the CPU 901 executes a predetermined program loaded onto the memory 902.

[0052] The arithmetic unit 2 may be implemented on a single computer or on multiple computers. Furthermore, the arithmetic unit 2 may be a virtual machine implemented on a computer.

[0053] The program for the arithmetic unit 2 can be stored on computer-readable storage media such as HDDs, SSDs, USB (Universal Serial Bus) memory, CDs (Compact Discs), and DVDs (Digital Versatile Discs), or it can be distributed via a network. Computer-readable storage media are, for example, non-transitory storage media.

[0054] This disclosure is not limited to the embodiments described above, and numerous modifications are possible within the scope of its essence. [Explanation of symbols]

[0055] 1 Irradiation device 2 Arithmetic unit 3 devices 11 Neutron generation section 12 Switching section 12A shielding material 21 Measuring part 22 Arithmetic section 23 Count section 24 Calculation Section 100 measuring devices 111 Accelerator 112 Target 113 Moderator

Claims

1. A neutron generator that produces neutrons, A shielding material for shielding thermal neutrons is provided, and a switching unit is provided to switch between a shielded state in which thermal neutrons contained in neutrons generated in the neutron generation unit are shielded, and an open state in which thermal neutrons are not shielded, A counting unit that counts the number of SEU generated when the device is irradiated with neutrons, The device is irradiated with neutrons with the switching unit in an open state, and the device is irradiated with neutrons with the switching unit in a shielded state, and the calculation unit derives a calculation formula that shows the relationship between neutron energy in the thermal neutron region and the SEU cross-section based on the number of first SEU generated and the number of second SEU generated when the device is irradiated with neutrons. The calculation unit calculates a neutron energy-dependent SEU cross-section from the thermal neutron region to 0.1 [MeV] based on the calculation formula when neutron energy is input. Measuring device.

2. The neutron generation unit is, Accelerators that generate accelerated particles, A target that is irradiated with the aforementioned accelerated particles to generate neutrons, A moderator for slowing down neutrons generated in the target, The measuring device according to claim 1, comprising:

3. The calculation unit derives the calculation formula based on the relationship that, when the neutron energy is E, the SEU cross-section in the thermal neutron region is proportional to 1 / √E. The measuring device according to claim 1 or 2.

4. The calculation unit described above, The number of occurrences of the first SEU is "N wo shield ", the number of occurrences of the second SEU is "N w shield When the threshold energy of the shielding material is "Th" and the neutron fluence when no shielding material is installed is "Φ wo shield (E)", the variable A is calculated based on the following formula, and the above calculation formula is derived using the variable A as the proportionality coefficient between the SEU cross-section and 1 / √E. The measuring device according to claim 3. [Math 3]

5. Accelerated particles are irradiated onto a target to generate thermal neutrons and neutrons with higher energies than said thermal neutrons, The number of first SEUs generated when the device is irradiated with thermal neutrons and neutrons with higher energy than the thermal neutrons is counted. The number of second SEUs generated when the thermal neutrons are shielded and only neutrons with higher energy than the thermal neutrons are irradiated onto the device is counted. Based on the number of first and second SEU generation, a formula is derived that shows the relationship between neutron energy in the thermal neutron region and the SEU crosssection. When neutron energy is input, the neutron energy-dependent SEU cross-section from the thermal neutron region to 0.1 [MeV] is calculated based on the above calculation formula. Measurement method.

6. A program that causes a computer to function as a counting unit and a calculation unit mounted on the measuring device described in claim 1.

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