Neutron position detector

Abstract

The neutron position detector according to the embodiment includes a tubular peripheral as a cathode, an anode disposed at the center of the peripheral, and a gas containing 3 The gas enclosed in the peripheral includes He gas and an additive gas. The additive gas contains nitrogen as a quenching gas and contains argon as a shortening gas for neutrons and 3 The gas containing a reaction product of the He gas.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to a neutron position detector for measuring a position distribution of neutrons. BACKGROUND

[0002] The neutron position detector is used, for example, in an accelerator facility, to irradiate neutrons to a sample to be investigated, to investigate a characteristic of the sample by detecting scattering of the neutrons, and the like.

[0003] The neutron position detector includes a position sensitive neutron detecting proportional counter (PSD) that is a neutron position detector, and a processing circuit that processes output charges from the neutron position detector and calculates an incident position of the neutrons.

[0004] The neutron position detector includes a tubular peripheral device that is a cathode, an anode disposed at an axis of the peripheral device, and a gas containing 3 He gas and an additive gas enclosed in the peripheral device. When neutrons are incident in the peripheral device, the 3 He in the gas performs a nuclear reaction with the neutrons to generate protons and tritium, and the protons and tritium fly out into the gas to ionize the surrounding gas, and the ionization-generated charges are collected at the anode. Then, in the processing circuit, the incident position of the neutrons is detected based on the output charges from both ends of the anode.

[0005] In such a neutron position detector, in a case where the neutron intensity is high, the additive gas is easily deteriorated, so that the life is shortened.

[0006] Therefore, it is desirable that the neutron position detector can extend the life while ensuring the detection accuracy of the incident position of the neutrons, i.e., the position resolution.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT DOCUMENTS

[0009] Patent Document 1: Japanese Patent No. 6228340 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] An object of the present application is to provide a neutron position detector that can extend the life while ensuring the detection accuracy of the incident position of the neutrons, i.e., the position resolution.

[0012] TECHNICAL SOLUTION

[0013] The neutron position detector according to the present embodiment includes: a tubular peripheral device that is a cathode; an anode disposed at an axis of the peripheral device; and a gas containing 3He gas and an additive gas and is enclosed in a peripheral vessel. The additive gas contains nitrogen as a quenching gas and contains argon as a shortening gas for neutrons and 3 a gas that is a reaction product of the He gas. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a structural diagram of a neutron position detection device using a neutron position detector according to one embodiment.

[0015] Figure 2 is an explanatory diagram that sequentially explains the action of ionization of a gas from a neutron incident in the neutron position detector according to (a) (b) (c) in order.

[0016] Figure 3 is a graph that shows the relationship between the position and the density of the electric charge generated in the neutron position detector according to the above.

[0017] Figure 4 is a table that shows the relationship between the kind of additive gas and the range in the neutron position detector according to the above.

[0018] Figure 5 is a table that shows the relationship between the kind of additive gas and the action voltage in the neutron position detector according to the above. DETAILED DESCRIPTION

[0019] Hereinafter, one embodiment will be described with reference to the drawings.

[0020] As shown in Figure 1 , a neutron position detection device 10 includes a neutron position detector 11, a high-voltage power supply 12, and a processing circuit 13. The processing circuit 13 includes preamplifiers 14a, 14b, an AD converter 15, and an arithmetic unit 16, and the like.

[0021] The neutron position detector 11 is a proportional counter tube (PSD) for one-dimensional position-sensitive neutron detection. The neutron position detector 11 includes a tubular peripheral vessel 20 as a cathode, an anode 21 disposed at the axial center of the peripheral vessel 20, terminal portions 22a, 22b provided at both ends of the peripheral vessel 20, and a gas 23 enclosed in the peripheral vessel 20.

[0022] The peripheral vessel 20 is a circular tube, is long in the axial direction, and is closed at both ends. A closed space 24 is provided in the inside of the peripheral vessel 20.

[0023] The anode 21 is a resistive wire (resistive metal wire) having a certain resistance value per unit length. The anode 21 is disposed along the axial center in the inside of the peripheral vessel 20 and is electrically connected while being connected to the terminal portions 22a, 22b at both ends.

[0024] Terminal portions 22a and 22b are disposed at both ends of the peripheral device 20 in an insulated state from the peripheral device 20. The two ends of the anode 21 are electrically connected to the terminal portions 22a and 22b.

[0025] Gas 23 is sealed within the enclosed space 24 of the peripheral device 20. Gas 23 contains neutron-absorbing and ionized... 3 He gas, and added to 3 Added gas to He gas.

[0026] 3 The partial pressure of He gas can be set arbitrarily according to the specifications of neutron detection efficiency, for example, in the range of 10 to 20 atm.

[0027] The added gases include nitrogen, a molecular gas, as a quenching gas, and gases used to shorten neutrons and... 3 The reaction products of He gas are argon gas, which contains protons and tritium. In this case, assuming the inner diameter of the peripheral device 20 is d [cm] and the partial pressure of nitrogen is pN2 [atm], it is preferable to have a relationship of d × pN2 > 0.03. Furthermore, adding... 3 The partial pressure of argon in He is preferably higher than that of nitrogen. Added 3 The partial pressure of argon in He is preferably in the range of 1 to 3 atm.

[0028] Regarding the composition of gas 23, the following is set: 3 The partial pressure of He gas and the partial pressure of the added gas make the sum of the ranges of protons and tritium in gas 23 in the range of, for example, 2.0 to 2.7 mm.

[0029] Furthermore, the high-voltage power supply 12 applies an operating voltage between the peripheral device 20, which serves as the cathode, and the anode 21. The operating voltage is set to, for example, a range of 2.0 to 2.5 kV, such that the output charge from the anode 21 is, for example, 2 to 5 pC.

[0030] Furthermore, the preamplifiers 14a and 14b of the processing circuit 13 convert the output charge from the two ends of the neutron position detector 11 (hereinafter referred to as the detector ends) into electrical signals and output them respectively. The preamplifiers 14a and 14b include coupling capacitors 30a and 30b that block the high-voltage component applied to the neutron position detector 11, and operational amplifiers 31a and 31b that convert the output charge of the blocked high-voltage component into a predetermined electrical signal. Additionally, the coupling capacitors 30a and 30b can be connected in parallel to correspond to an increase in the operating voltage of the neutron position detector 11, thereby achieving high capacitance and low impedance to reduce distortion. Further, preferably, the operational amplifiers 31a and 31b use JFET input type operational amplifiers to minimize operating delay distortion.

[0031] Furthermore, the AD converter 15 converts the electrical signals (analog signals) at both ends of the detectors output from the preamplifiers 14a and 14b into digital signals (waveform signals). The AD converter 15 uses components with a resolution of 14 bits or higher. For example, the AD converter 15 can use components with a resolution of 16 bits.

[0032] In addition, the arithmetic unit 16 calculates the wave height based on the waveform data of the electrical signals at both ends of the detector after being digitized by the AD converter 15, and calculates the neutron incident position in the axial direction of the neutron position detector 11 based on the ratio of these wave heights.

[0033] Next, the operation of the neutron position detection device 10 will be explained.

[0034] An operating voltage is applied between the peripheral device 20, which serves as the cathode, and the anode 21 via a high-voltage power supply 12.

[0035] Then, as Figure 2 As shown in (a)(b), after neutron n enters the peripheral device 20, neutron n and 3 He gas undergoes a nuclear reaction (n+) 3 He → p + T + 765 keV, producing protons p and tritium T. Additionally, Figure 2 (b) shows A as the location where the nuclear reaction occurs, and also the location where proton p and tritium T are produced.

[0036] like Figure 2 As shown in (c), proton p has an energy of approximately 574 keV, and tritium T has an energy of 191 keV. These proton p and tritium T particles fly out into gas 23 in opposite directions, colliding with the surrounding atoms and molecules of gas 23 and gradually losing energy until they stop. When proton p and tritium T collide with gas 23, a portion of the energy of proton p and tritium T is applied to gas 23, causing it to ionize and generate a charge e.

[0037] The generated charge e is collected at the anode 21 by the electric field formed between the peripheral device 20, which serves as the cathode, and the anode 21. As a result, output charges with ratios corresponding to the distances from the collection points of the charge e on the anode 21 to the two ends of the anode 21 are output from each end of the anode 21.

[0038] The output charge from both ends of the detector (both ends of the anode 21) is converted into an electrical signal by preamplifiers 14a and 14b. The electrical signal from both ends of the detector output from preamplifiers 14a and 14b is converted into a digital signal (waveform signal) by AD converter 15.

[0039] In the calculator 16, the wave height of the electric signal between the detectors after digitization by the AD converter 15 is calculated, and the incident position of the neutrons n in the axial direction of the neutron position detector 11 is calculated based on the ratio of these wave heights.

[0040] Next, the additive gas used in the neutron position detector 11 will be described.

[0041] The neutron position detector 11 is a kind of proportional counter. In the proportional counter, in order to stabilize the operation, in addition to the gas that reacts with the neutrons n, a gas that absorbs the ultraviolet rays generated when the He ions recombine is added. 3 In addition to the He gas, a molecular gas is added. As described in Reference 1 (Radiation Measurement Handbook, 3rd edition, p. 190, published by Nihon Keizai Shimbun, Inc.), the purpose of adding the molecular gas is to absorb the ultraviolet rays generated when the He ions recombine, thereby stabilizing the operation of the proportional counter. 3

[0042] The gas having such an effect is generally called a quenching gas. As long as it is a gas that absorbs ultraviolet rays, any gas can be used, and on the market, methane (CH4), carbon dioxide (CO2), and carbon tetrafluoride (CF4) are widely used, and in addition, nitrogen and hydrogen can also be used. For example, in Reference 2 (U.S. Patent No. 3092747), there is an example in which nitrogen is used as a quenching gas in a proportional counter.

[0043] On the other hand, up to now, there has been no product in which nitrogen is used as a quenching gas in the neutron position detector 11, and carbon dioxide and carbon tetrafluoride have been used.

[0044] Next, the reason why nitrogen is not used as a quenching gas in the neutron position detector 11 will be described.

[0045] (Reason 1)

[0046] The neutron position detector 11 is a detector for performing position detection of the neutrons n, but the position detection accuracy, i.e., the position resolution, which is an important item of the performance of the detector, is affected by the range of the reaction products, i.e., the protons p and the tritium T, in the gas 23.

[0047] As shown in (c), the electric charges e are generated in the range from the position A where the protons p and the tritium T are generated to the stopping. Since the mass and the energy of the protons p and the tritium T are different, the ranges from the position A where the nuclear reaction occurs to the stopping are different. Therefore, as shown in (d), the center of gravity of the electric charges e generated by the protons p and the tritium T is more biased toward the side of the protons p than the position A where the nuclear reaction occurs. Thus, the position A where the nuclear reaction occurs is deviated from the center of gravity of the electric charges e. In addition, the directions in which the protons p and the tritium T fly are random. Figure 2 Figure 3

[0048] ​​​Thus, even in the case where it is assumed that a plurality of neutrons n are reacted at one point of the neutron position detector 11, the center of gravity of the electric charges e generated in the gas 23 is not one point but is spread in a range having a correlation with the ranges of the protons p and the tritium T.

[0049] In the neutron position detecting device 10 using the neutron position detector 11, since the center of gravity of the electric charges e is found in order to detect the incident position of the neutron n, the greater the ranges of the protons p and the tritium T, the greater the influence on the detection accuracy, i.e., the position resolution, of the incident position of the neutron n.

[0050] Therefore, in order to improve the position resolution, it is sufficient to shorten the ranges of the protons p and the tritium T, and for this purpose, the added gas needs to be a heavy gas or the partial pressure of the added gas needs to be increased.

[0051] However, nitrogen gas has little effect on shortening the ranges of the protons p and the tritium T. Figure 4 The relationship between the kind of gas and the ranges of the protons p and the tritium T is shown in Table 1. In addition, in Table 1, Figure 4 In Table 1, the ranges of the protons p and the tritium T in each atmosphere of gas at 0°C are shown.

[0052] From Table 1, Figure 4 As is apparent from Table 1, carbon tetrafluoride and carbon dioxide have a remarkable effect on shortening the ranges of the protons p and the tritium T and are very excellent as the added gas of the neutron position detector 11.

[0053] On the other hand, although nitrogen gas can function as a quenching gas, since the ranges of the protons p and the tritium T are long, in order to obtain the desired ranges of the protons p and the tritium T, it is necessary to increase the partial pressure.

[0054] (Remaining reason 2)

[0055] When nitrogen gas is added as the added gas of the neutron position detector 11, the output electric charge with respect to the applied operating voltage is significantly decreased as compared with carbon tetrafluoride and carbon dioxide.

[0056] The higher the partial pressure of the added nitrogen gas, the lower the proportion of the output electric charge with respect to the applied operating voltage, and therefore, in order to obtain the desired output electric charge, it is necessary to apply a higher operating voltage.

[0057] Figure 5 The relationship between the kind of gas and the operating voltage is shown in Table 2. In addition, Figure 5 In Table 2, as an example, the increase in the operating voltage when the added gas is increased by 1 atm in a typical product of the neutron position detector 11 (cathode diameter 12.7 mm, anode diameter 3 He gas pressure 20 atm) is shown. He gas pressure 20 atm) is shown.

[0058] From Figure 5 the table, it is understood that the operating voltage of nitrogen is higher than that of other gases. If the operating voltage of the neutron position detector 11 is increased, problems such as the possibility of discharge between the peripheral vessel 20 and the anode 21, or the possibility of exceeding the withstand voltage of elements used in the processing circuit 13, can occur.

[0059] For the above reasons 1 and 2, in the case where nitrogen is added as the additive gas of the neutron position detector 11, although nitrogen functions as a quenching gas, the ability to shorten the range of protons p and tritium T is weak, and therefore, if the partial pressure of nitrogen is increased in order to shorten the range of protons p and tritium T, the operating voltage becomes high. Therefore, up to now, nitrogen has not been applied to products as the additive gas of the neutron position detector 11.

[0060] On the other hand, in the neutron detector 11 of the present embodiment, the additive gas contains nitrogen as a quenching gas, and contains argon as a gas that shortens the range of protons p and tritium T, which are reaction products of He gas. 3 He gas.

[0061] As for nitrogen, as described above, in the neutron position detector 11, since the range of protons p and tritium T is long and the operating voltage is high, nitrogen has not been used as a quenching gas, but the advantage of nitrogen is that it has a long lifetime. The bond energy of the triple bond of a nitrogen molecule is greater than that of the double bond of carbon dioxide and the single bond of carbon tetrafluoride, and has the characteristic of not being easily broken.

[0062] The disadvantage of nitrogen, in which the range of protons p and tritium T is long and the operating voltage is high, is eliminated by adding argon while adding nitrogen.

[0063] In this case, in the actual use of the neutron position detector 11, the inner diameter of the peripheral vessel 20 is assumed to be d [cm], and the partial pressure of nitrogen is assumed to be pN2[atm], and it is preferable that the partial pressure of nitrogen has a relationship of d x pN2> 0.03[atm-cm]. If the inner diameter of the peripheral vessel 20 is thin, it is necessary to absorb ultraviolet rays in a short distance, and therefore, if the inner diameter is thin, it is necessary to increase the partial pressure of nitrogen. If the partial pressure of nitrogen is lower than the partial pressure calculated by the above formula, the absorption of ultraviolet rays is not sufficient, the operation is unstable, or discharge can occur at a low voltage.

[0064] Further, as for argon, from the table, it is understood that the range of protons p and tritium T is almost the same as that of nitrogen. Figure 4

[0065] However, the applied voltage at which argon and nitrogen obtain the same output charge is greatly different. From the table, it is understood that the applied voltage at which argon and nitrogen obtain the same output charge is greatly different. Figure 5 ​As is apparent from the table, in the case where argon and nitrogen are added at the same partial pressure, the influence of argon on the operating voltage is about 1 / 3 of that of nitrogen. Therefore, argon is superior to nitrogen as an added gas for shortening the range of protons p and tritium T. That is, even if the partial pressure of argon is increased in order to shorten the range of protons p and tritium T, the influence on the operating voltage is small. In this case, in order to shorten the range of protons p and tritium T, it is preferable to have a relationship in which the partial pressure of argon is higher than that of nitrogen.

[0066] However, compared with nitrogen, argon has a disadvantage in that it has a high sensitivity to γ-rays, and the influence on the operating voltage is not so small that it can be completely ignored, so the partial pressure cannot be increased without limit. Furthermore, the higher the partial pressure of argon, the shorter the range of protons p and tritium T, but the position resolution of the neutron position detector 11 is not determined only by the range of protons p and tritium T, but is also influenced by the thermal noise of the circuit system and the S / N ratio of the preamplifier, and merely increasing the partial pressure of argon does not increase the position resolution without limit. On the other hand, if the pressure of argon is too low, the range of protons p and tritium T does not become short, and the position resolution, which is important for the neutron position detector 11, does not become good.

[0067] Therefore, the partial pressure of argon has an appropriate range in actual use, and it is preferable to be 1 to 3 atm. The total of the ranges of protons p and tritium T is generally inversely proportional to the pressure, and is 13 mm at 1 atm of argon and 4.3 mm at 3 atm. On the other hand, the position resolution of the neutron position detector 11 in actual use is in the range of 4 mm to 20 mm, and if the argon is between 1 and 3 atm, the improvement in the position resolution is actually significant. If the partial pressure of argon is higher than this range, the range of protons p and tritium T becomes short, but other factors (thermal noise of the circuit, etc.) come to the fore, the position resolution does not improve, the sensitivity to γ-rays becomes high, the operating voltage rises, and only the disadvantages become significant. On the other hand, if the proportion of argon is lower than this range, the effect of adding argon becomes small, and the advantages obtained become small.

[0068] As described above, in the neutron position detector 11 of the present embodiment, since nitrogen is contained as a quenching gas and argon is contained as a gas for shortening the range of neutrons n and 3 The gas of the range of protons p and tritium T, which is the reaction product of He gas, can therefore extend the life while ensuring the detection accuracy of the incident position of neutrons n, i.e., the position resolution.

[0069] The present application has been described with several embodiments, but these embodiments are presented only as examples and are not intended to limit the scope of the present application. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the present application. These embodiments and variations thereof are included in the scope and gist of the present application, and are also included in the scope of the present application and the equivalent scope recited in the claims.

Claims

1. A neutron position detector, characterized in that, include: The tubular peripheral device serves as the cathode; Anode located at the center of the shaft within the peripheral device; as well as Include 3 He gas and the gas added and sealed within the perimeter. The added gas contains nitrogen as a quenching gas and argon as a shortening neutron and the 3 The reaction products of He gas have a range of gas.

2. The neutron position detector as described in claim 1, characterized in that, Let the inner diameter of the peripheral device be d, with the unit being cm, and the partial pressure of the nitrogen gas be pN2, with the unit being atm. The relationship d×pN2 > 0.03 is satisfied.

3. The neutron position detector as described in claim 1 or 2, characterized in that, Add to the 3 The partial pressure of argon in He is higher than the partial pressure of nitrogen.

4. The neutron position detector as described in any one of claims 1 to 3, characterized in that, Add to the 3 The partial pressure of the argon gas in He is in the range of 1 to 3, and its unit is atm.

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