JP2009198439A - Neutron position measurement device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a neutron position measurement device 11 capable of improving a positional resolution. <P>SOLUTION: A plurality of neutron detection elements 12 for detecting an input neutron are juxtaposed. A neutron shield body 15 having a neutron shield section 16 for shielding a neutron and a neutron pass-through section 17 for allowing a neutron to path therethrough as a slit 18 is provided at a neutron incident face side of the neutron detection elements 12. A neutron passing through the slit 18 of the neutron shield body 15 is detected by means of the neutron detection elements 12 by moving the neutron detection elements 12 for every width of the slit 18. It is possible to obtain the positional resolution having a degree equal to the width of the slit 18 of the neutron shield body 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a neutron position measurement apparatus that measures the position of a neutron.

  Neutron position measuring equipment is mainly used in a reactor or accelerator facility with a powerful neutron source to irradiate the sample to be examined with neutrons and measure and analyze the scattering to examine the characteristics of the sample. . Representative facilities of this type include J-PARC in Ibaraki Prefecture, JRR-3 from JAEA, SNS in the US, and ILL in France.

  In this neutron position measuring device, a neutron proportional counter, a position sensitive neutron proportional counter, or a neutron multi-wire proportional counter (MWPC) is often used as a neutron detection element (for example, Non-patent document 1). A schematic configuration of a neutron position measuring apparatus using these will be described below.

  As shown in FIG. 5, the neutron proportional counter 1 includes a cathode 2 that is a cylindrical container, and an anode 3 is disposed at the axial center of the cathode 2, and 3He that easily reacts with neutrons in the cathode 2. Alternatively, a neutron absorbing gas 4 such as 10B is enclosed, and a connector 5 for outputting a signal to the outside is provided at one end of the anode 3. Then, neutrons enter the neutron proportional counter 1 and react with the neutron absorption gas 4 to generate electrons. The electrons are drawn to the anode 3 by the potential difference applied between the cathode 2 and the anode 3, and the connector The number of incident neutrons can be counted by outputting the signal from 5 to the outside.

  However, the position of the neutron cannot be specified from the output signal of the neutron proportional counter 1. Therefore, when used for neutron position measurement, a large number of neutron proportional counters 1 are arranged and the neutron position is measured by observing from which neutron proportional counter 1 the signal is output.

  As shown in FIGS. 6 and 7, the position sensitive neutron proportional counter 6 is similar to the neutron proportional counter 1, but the anode 3 at the center is made of a material having a large electrical resistance such as nichrome. In addition, a connector 5 for outputting a signal to the outside is provided at both ends of the anode 3. Then, the electric charge output at both ends of the anode 3 is amplified and waveform-shaped by the pre-processing unit 7, and the ratio of the electric charges output at both ends of the anode 3 is obtained by the arithmetic unit 8, thereby detecting the position where the neutron is detected. Recognize. Reference numeral 9 denotes a high-voltage power supply supplied to the pre-processing unit 7.

  The position-sensitive neutron proportional counter 6 is a one-dimensional neutron detection element that can determine the position of neutrons only in the direction parallel to the anode 3, but a two-dimensional distribution is often required in actual applications. Therefore, a two-dimensional neutron position measuring device is configured by arranging a large number of position sensitive neutron proportional counters 6.

  The neutron multi-wire proportional counter (MWPC) is in principle the same as the neutron proportional counter 1 and the position sensitive neutron proportional counter 6, but has a large number of anodes and cathodes inside. Normally, the position where the neutron is detected can be known in two dimensions from more than four output signals.

  In general, a neutron position measuring device for detecting the position of neutrons is preferably as small as the position resolution is small.

  However, the three types of neutron position measuring devices listed above have the following lower limit of position resolution.

  In a neutron position measuring device in which a large number of neutron proportional counters 1 are arranged, the position resolution cannot be made smaller than the outer shape of the neutron proportional counter 1. Normally, the neutron proportional counter 1 is cylindrical, but is small and has a diameter of about 5 mm and a length of about 5 to 10 cm. Therefore, the position resolution in this neutron position measuring device is about 5 mm × 5 cm. .

  Further, in the neutron position measuring device in which a large number of position sensitive neutron proportional counters 6 are arranged, the position resolution in the direction along the anode 3 is mainly the electrical resistance of the anode 3 and the signal output from the position sensitive neutron proportional counter 6. It is influenced by the S / N ratio determined from the above. In the practical application, the smallest is about 2 mm. On the other hand, the position resolution in the direction perpendicular to the anode 3 is the outer shape of the position sensitive neutron proportional counter 6. Usually, the outer shape of the position sensitive neutron proportional counter 6 is about 8 mm to 25 mm. Therefore, the position resolution in this neutron position measuring apparatus is about 2 mm × 8 mm, which is the best currently in practical use.

  Moreover, in the neutron position measuring apparatus using the neutron multi-wire proportional counter (MWPC), the position resolution can be reduced as the distance between the electrode lines provided in the inside is narrower. However, if the interval is narrow, the electric field strength around the anode is lowered and the required signal strength cannot be obtained. Therefore, when the interval is narrow, the applied voltage inevitably increases, or the pressure of 3He gas for detecting neutrons must be reduced, and the detection efficiency decreases. Also, the electrostatic force causes the anode / cathode to be displaced, resulting in poor accuracy. In practice, the electrode line spacing is limited to about 1 mm.

As described above, the neutron position measurement apparatus that has already been put into practical use has a lower limit in position resolution, but research and development of a new type of high-resolution neutron position measurement apparatus are currently underway. For example, a microstrip gas chamber (MSGC: Microstrip Gas Chamber) (see, for example, Non-Patent Document 2) can obtain a two-dimensional position resolution on the order of 0.1 mm.
Glenn F.M. Knoll Radiation Measurement Handbook 3rd Edition Nikkan Kogyo Shimbun P215-218 Glenn F.M. Knoll Radiation Measurement Handbook 3rd Edition Nikkan Kogyo Shimbun P218-220

  As described above, the neutron position measuring apparatus already in practical use has a lower limit in position resolution.

  In addition, a microsplit gas counter (MSGC), which is currently being researched and developed as a new type of high-resolution neutron position measurement device, has not yet been put into practical use. Construction of a large neutron scattering facility is already underway, and it is unlikely that a microsplit gas counter (MSGC) will be introduced from the beginning of the facility. On the other hand, neutron position measuring devices that have already been put into practical use have a track record of several decades since practical use and have high reliability. Therefore, even if the resolution is unsatisfactory, it has to be used.

  The present invention has been made in view of these points, and an object thereof is to provide a neutron position measuring apparatus capable of improving the position resolution.

  The present invention relates to a neutron detection element that detects incident neutrons, and a neutron provided with a neutron shielding part that shields neutrons and a neutron passage part that allows neutrons to pass, arranged on the neutron incident surface side of the neutron detection element And a shield.

  According to the present invention, since only the neutron that has passed through the neutron passage provided in the neutron shield can be detected by the neutron detector, the position of the neutron passage of the neutron shield and the output of the neutron detector are used. The position of the neutron can be easily identified, and the position resolution can be improved.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  In the present embodiment, the neutron position measuring apparatus using the position-sensitive neutron proportional counter 6 with the most adopted number will be described as an example. The configuration of the position-sensitive neutron proportional counter 6 has been described above. The description is omitted.

  FIG. 1 shows a perspective view of a neutron position measuring device 11, which uses a plurality of position sensitive neutron proportional counters 6 as neutron detection elements 12 and a plurality of these position sensitive neutron proportional counters. 6 are arranged in parallel in a radial direction intersecting with a direction along the anode 3 (hereinafter referred to as an axial direction).

  Further, a plate-like neutron shield 15 for shielding neutrons is disposed on the front surface of the position sensitive neutron proportional counter 6 on the neutron incident side. The neutron shield 15 is made of a material having high neutron absorption such as B, Cd, Gd, or is made by sticking a sheet-like neutron absorber to another member.

  The neutron shield 15 has a surface formed as a neutron shield 16 that shields neutrons, and a slit 18 is formed inside the neutron shield 16 as a neutron passage 17 that allows neutrons to pass. Yes. The slits 18 are elongated along the direction orthogonal to the axial direction of the position sensitive neutron proportional counter 6 and are formed at a predetermined interval in the axial direction of the position sensitive neutron proportional counter 6. Has been.

  A moving mechanism 21 is used to change the relative position between the position sensitive neutron proportional counter 6 and the neutron shield 15. In this moving mechanism 21, the neutron shield 15 can be moved in the axial direction of the position sensitive neutron proportional counter 6. The moving mechanism 21 can be easily configured by using a stepping motor or the like. Although the motor generates noise, there is no particular problem unless data is acquired during operation of the motor.

  Next, the operation of the neutron position measuring device 11 will be described.

  First, FIG. 8 shows a comparative example when the neutron shield 15 is not used. In the neutron intensity position distribution as shown in FIG. 8 (a), when the neutron is incident on the position sensitive neutron proportional counter 6 not using the neutron shield 15, the position sensitive neutron proportional counter 6 detects the neutron. The obtained position distribution is shown in FIG.

  In this comparative example, even if neutrons are incident on exactly the same position of the position sensitive neutron proportional counter 6, as shown in FIG. 8 (b), the position sensitive neutron proportional counter 6 is sensitive to the output. A width of at least about 2 mm is formed in the full width at half maximum (FWHM) in the axial direction of the type neutron proportional counter 6. Therefore, for example, when neutrons are incident on two different positions within a range of 2 mm or less, the incident positions of the two neutrons cannot be determined.

  On the other hand, FIG. 2 shows the case of the neutron position measuring device 11 using the neutron shield 15. For example, assuming that the position resolution of the position-sensitive neutron proportional counter 6 is 2 mm in full width at half maximum (FWHM), and the width of the slit 18 of the neutron shield 15 is about 0.5 mm, the full width at half maximum (FWHM) in position. Is about 2.5 mm. However, the neutron count by the position sensitive neutron proportional counter 6 is derived from neutrons that have passed through the slit 18 of 0.5 mm, and is incident on the position sensitive neutron proportional counter 6 within a range of 0.5 mm. It can be considered as a result.

  When one measurement is completed via the neutron shield 15, the neutron shield 15 is shifted in the axial direction of the position sensitive neutron proportional counter 6 by the width of the slit 18, as shown in FIG. And measure again. This is performed the number of times determined by the position resolution / slit width of the position sensitive neutron proportional counter 6 (in this example, 2 mm / 0.5 mm = 4 times). Then, the position resolution data of the slit width is obtained for the number of times described above.

  If this data is used, the position distribution every 0.5 mm which is the slit width can be reconstructed. Therefore, even if the position sensitive neutron proportional counter 6 whose position resolution is not so small is used, high position resolution can be realized.

  The position distribution is reconstructed from the data output from the plurality of position sensitive neutron proportional counters 6 by a signal processing system. As shown in FIGS. 2 (b) and 3 (b) Processing can be easily performed simply by obtaining the area of the distribution output from the sensitive neutron proportional counter 6 and arranging and arranging them at the slit positions as shown in FIG.

  As described above, the neutron shield 15 having the slit 18 narrower than the position resolution of the position sensitive neutron proportional counter 6 is used, and the distribution measurement is performed a plurality of times. Can be obtained.

  The neutron position measuring device 11 can increase the position resolution while using the neutron detection element 12 such as the highly reliable position sensitive neutron proportional counter 6 that has been proven so far. For this reason, there is no risk of introducing a microsplit gas counter (MSGC) whose life and reliability are not sufficiently evaluated, and it is possible to reduce costs during facility improvements and upgrades. is there.

  When using this neutron position measuring device 11 for the purpose of investigating the characteristics of a sample by irradiating the sample to be examined with neutrons and measuring and analyzing the scattering, the neutron shield provided with a plurality of slits 18 Using 15 is preferable because it takes less time for measurement, and when it is desired to specify the incident position of neutrons, a neutron shield 15 provided with one slit 18 may be used.

  Further, with respect to the radial direction, which is a direction orthogonal to the direction along the anode 3 of the position sensitive neutron proportional counter 6, the outer diameter of the position sensitive neutron proportional counter 6 becomes the position resolution. The distribution of incident positions of neutrons incident within the range is unknown. In this case, the neutron shield 15 provided with the slit 18 along the axial direction of the position sensitive neutron proportional counter 6 is used, and the slit width is smaller than the outer diameter of the position sensitive neutron proportional counter 6, that is, The position resolution of the position-sensitive neutron proportional counter 6 is made smaller than the position resolution in the outer diameter direction, and the neutron shield 15 is moved in the outer diameter direction of the position-sensitive neutron proportional counter 6 to perform distribution measurement several times, thereby making a slit. A high position resolution of about 18 widths can be obtained.

  Further, a neutron shield 15 having a slit 18 in the direction along the anode 3 of the position sensitive neutron proportional counter 6 and a direction orthogonal to the direction along the anode 3 of the position sensitive neutron proportional counter 6. By arranging the neutron shield 15 having the slits 18 in a certain radial direction so that the slits 18 are orthogonal to each other, the position resolution in the two directions can be improved.

  The neutron detection element 12 is not limited to the position sensitive neutron proportional counter 6 but may be a neutron proportional counter 1 or a neutron multi-wire proportional counter (MWPC).

It is a perspective view of the neutron position measuring device which shows one embodiment of this invention. Explains the measurement operation of the neutron position measurement device, (a) is an explanatory diagram showing the positional relationship between the actual neutron intensity position distribution and the slit of the neutron shield, (b) is a position sensitive neutron proportional counting It is a graph of the position distribution which a pipe | tube outputs. Fig. 2 shows the measurement operation of the neutron position measurement device with the neutron shield moved by the width of the slit. (A) shows the actual position distribution of neutron intensity and the slit of the neutron shield. Explanatory drawing showing the positional relationship, (b) is a graph of the position distribution output from the position sensitive neutron proportional counter. It is a graph of the slit position distribution of a neutron position measuring device same as the above. It is sectional drawing of a neutron proportional counter applicable as a neutron detection element of a neutron position measuring device same as the above. It is sectional drawing of a position sensitive type neutron proportional counter applicable as a neutron detection element of a neutron position measuring apparatus same as the above. It is a block diagram of the detection circuit using a position sensitive type neutron proportional counter same as the above. It explains the measurement operation of the neutron position measurement device of the comparative example, (a) is an explanatory diagram showing the positional relationship between the position distribution of actual neutron intensity and the position sensitive neutron proportional counter, (b) is position sensitive It is a graph of the position distribution which a type neutron proportional counter outputs.

Explanation of symbols

11 Neutron position measuring device
12 Neutron detector
15 Neutron shield
16 Neutron shield
17 Neutron passage
21 Movement mechanism

Claims (4)

A neutron detector for detecting incident neutrons;
A neutron position characterized by comprising a neutron shielding part disposed on the neutron incident surface side of the neutron detection element and provided with a neutron shielding part for shielding neutrons and a neutron shielding part for allowing passage of neutrons measuring device. The neutron position measuring apparatus according to claim 1, further comprising a moving mechanism that varies a relative position between the neutron shield and the neutron detection element. The neutron position measuring apparatus according to claim 1 or 2, wherein a substance containing at least one of B, Cd, and Gd is used for the neutron shield. The neutron position measuring device according to any one of claims 1 to 3, wherein any one of a neutron proportional counter, a position sensitive neutron proportional counter, and a neutron multi-wire proportional counter is used as the neutron detection element. apparatus.

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