JP4013563B2 - Neutron detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to neutrons used in personal alarm dosimeters for managing radiation doses of workers working in radiation control areas such as nuclear power plants and dosimeters for monitoring radiation doses in the environment. It relates to a detector.
[0002]
[Prior art]
Neutrons are radiation that has no electric charge and is difficult to detect directly because of its weak interaction with matter. Therefore, a neutron detector employs a method of detecting neutrons via protons and α rays generated by interaction with a substance having a large cross-sectional area of interaction with neutrons. Fast neutrons and medium neutrons are detected by recoil protons from a radiator such as polyethylene containing hydrogen at high density.^TenB or⁷Detected by alpha rays emitted by nuclear reaction with Li. A semiconductor detecting element that uses a depletion layer formed in a diode to which a reverse bias is applied is commonly used as a means for detecting recoil protons and α rays.
[0003]
FIG. 7 is a conceptual diagram showing a configuration of a neutron detector for high and medium speed neutrons provided with the radiator 2, and FIG. 8 is a pattern diagram showing an example of the electrode shape of the detection element 1.
This neutron detector includes a semiconductor detection element (hereinafter abbreviated as a detection element) 1 in which a depletion layer 12 is formed on the side of an upper surface electrode (simply an electrode in FIG. 7) 11 applied with a reverse bias, and a surface thereof. A radiator 2 made of a material containing hydrogen at a high density such as polyethylene disposed adjacently, an amplifier 3 that integrates and amplifies the current pulse flowing through the electrode 11 and outputs a signal corresponding to the charge amount of the current pulse; Whether or not the output level of the amplifier 3 is equal to or higher than a predetermined value is identified and a peak value identification circuit 4 that outputs a signal when the output level is equal to or higher than a predetermined value; And a counting circuit.
[0004]
As the detection element 1, a pn junction type silicon diode, a hetero junction type silicon diode in which an amorphous silicon layer is formed on a p type silicon crystal, or the like is generally used. The detection element 1 shown in FIGS. 7 and 8 is a heterojunction type silicon diode, and an electrode 11 is formed on the entire surface except the outer peripheral portion of the upper surface thereof, and the formation region of the electrode 11 is almost depleted layer formation. It is an area. p⁺In the case of an n-junction silicon diode, p⁺The formation region of the layer corresponds to the formation region of the electrode 11 in FIGS. 7 and 8, and the electrode is usually formed in a part thereof. n⁺n for p-junction silicon diodes⁺Layers have similar functions.
[0005]
The radiator 2 is a member for generating recoil protons by elastic collision between neutrons and protons, which are hydrogen nuclei, when neutrons pass through them. Therefore, as the material of the radiator 2, a material containing hydrogen at a high density, for example, polyethylene is adopted.
The energy of recoil protons differs depending on the scattering direction after elastic collision, but since the mass of neutrons and the mass of protons are almost the same, it is most likely that the neutrons are scattered in the same direction as the incident neutrons. It becomes the same as the energy of the neutron just before the collision, and decreases as the scattering direction is tilted from the incident direction and becomes a continuous distribution up to zero.
[0006]
When recoiled protons enter a substance, they generate electron-hole pairs by interaction with the substance and move through the substance while consuming energy. Since the proton mass is three orders of magnitude greater than the electron mass, the recoil proton moves through the material with almost no change in its direction, and the electron-hole pair generated by the recoil proton is the recoil proton's mass. It is distributed in a high density only in the very vicinity of the passage route.
[0007]
For reference, the range of protons in silicon is about 18 μm when the energy is 1 MeV, about 48 μm at 2 MeV, about 150 μm at 4 MeV, about 730 μm at 10 MeV, and about 1500 μm at 15 MeV.
The range of protons in the air is about 20 mm at 1 MeV and about 70 mm at 2 MeV, so if the distance between the radiator 2 and the detection element 1 is about 1 mm, the energy loss of recoil protons in the air layer Is slight.
[0008]
Therefore, when the material of the detection element 1 is silicon, even if recoil protons are incident on the detection element 1 perpendicularly, if the depletion layer 12 having a thickness of 50 μm is formed, energy of 5 MeV or less is applied. A charge signal corresponding to 1 MeV or more can be obtained by the recoil proton.
Such a neutron detector for high and medium speed neutrons is used in an environment where not only neutrons but also γ rays and β rays are mixed. Moreover, the above detection element generates electron-hole pairs by electrons, positive electrons and β-rays by Compton effect by γ-ray generation and electron pair generation, etc., and similar to electron-hole pairs by recoil protons, Generate a current pulse. Especially in nuclear power plants, etc., it is generated by the reaction of nitrogen and neutrons in water.¹⁶There is a 6.1 MeV gamma ray emitted by N, and it is necessary to distinguish this high energy level gamma ray signal from the neutron signal. In the prior art, in order to discriminate between 6.1 MeV γ rays and neutrons, the discriminating level of the peak value discriminating circuit 4 is set to be equivalent to 1 MeV, for example. This identification level is determined based on the result of measuring 6.1 MeV gamma rays by the detection element 1 so that the detection element 1 does not detect 6.1 MeV gamma rays.
[0009]
Thus, in the conventional neutron detector for high and medium speed neutrons, the discrimination level of the peak value discrimination circuit 4 is set to a high energy level equivalent to, for example, 1 MeV. Cannot be detected, and the detection sensitivity of neutrons with energy higher than the identification level is also lowered.
on the other hand,^TenB or⁷A neutron detector of a type that detects neutrons by α rays emitted by a nuclear reaction with Li is usually called a thermal neutron detector. With neutrons^TenThe cross-sectional area of interaction with B or the like is the maximum in the case of thermal neutrons, and gradually decreases as the energy increases. Therefore, the neutron detection sensitivity of the thermal neutron detector is greatest for thermal neutrons, and decreases as the energy increases.
[0010]
In general, a neutron detector for high and medium speed neutrons using a radiator 2 and a thermal neutron detector are used in combination for detecting neutrons. As described above, the sensitivity of a neutron detector for high and medium speed neutrons is high. When it becomes zero at 1 MeV or less, the detection sensitivity of neutrons in the vicinity of 1 MeV is significantly lower than other energy regions in this combination, and if there are many low energy neutrons, the exposure dose by neutrons is too low. It has the problem of evaluating.
[0011]
Since silicon, which is a material of the detection element used in these neutron detectors, is a material that exhibits a large piezoelectric effect, when an impact is applied to the neutron detector and the detection element vibrates and deforms with the impact, The deformation changes the capacitance of the detection element. As a result, the amplifier 3 outputs a noise having a waveform corresponding to the deformation. If this noise is less than the discrimination level of the peak value discriminating circuit 4, there will be no problem, but if it exceeds the discrimination level, it will be counted by the counting circuit and cause an erroneous count. In order to avoid such erroneous counting, the detection element is used by being attached to a highly rigid substrate, a ceramic package, or the like.
[0012]
On the other hand, personal alarm dosimeters for managing radiation exposure doses of workers working in radiation control areas such as nuclear power plants have been reduced in size, weight and thickness to improve portability. Strong demand. For this reason, in the case of personal alarm dosimeters, it has become difficult to ensure that the detection element is attached to a highly rigid substrate or ceramic package as described above. In the conventional detector of the shape and size of the device, when the personal alarm dosimeter is subjected to an impact, an erroneous count of several counts may occur as described in the next paragraph. In the case of a thermal neutron detector,^TenSince the cross-sectional area of the interaction with B or the like is large, the detection sensitivity of thermal neutrons is high, and a count value corresponding to a management level such as an alarm level is sufficiently large. Therefore, such miscounting hardly causes a problem. However, in the case of neutron detectors for high and medium speed neutrons, the cross section of the interaction between high and medium speed neutrons and hydrogen nuclei is^TenCompared with the case of a detector of the same size, the detection sensitivity is about 1/100 that of a thermal neutron detector, and the number of counts is as above. Even the miscounting of is greatly affected, and the required measurement accuracy cannot be ensured.
[0013]
FIG. 11 is a recording chart showing an output waveform output by an amplifier of a neutron detector for high and medium speed neutrons when an impact is applied to a personal alarm dosimeter that is small, light, and thin. The horizontal axis of the recording chart is the elapsed time since the impact was applied. (A) is one scale of 200 μs, and (b) is 1 scale of 1 ms. The vertical axis represents the amplifier output, and the dotted line corresponds to the discrimination level of the peak value discrimination circuit. To apply impact to the personal alarm dosimeter, place the personal alarm dosimeter on a steel desk and place an iron piece weighing about 1.8 g on the outer surface where the neutron detector for high and medium speed neutrons is stored. It is a method of dropping from a height of 10cm. This method is almost equivalent to a case where a personal alarm dosimeter standing on a steel desk is brought down.
[0014]
Judging from this chart and other similar charts, the amplifier output waveform is a damped vibration in which higher-order vibration is superimposed on the vibration of 5 kHz to 10 kHz, and the influence of the impact is almost disappeared in 5 to 10 ms. However, as can be seen from (a), the portion exceeding the discrimination level of the peak value discrimination circuit has occurred several times, and this is an erroneous count, so it is a large neutron detector for high and medium speed neutrons. It is a problem.
[0015]
[Problems to be solved by the invention]
The object of the present invention is to detect even lower energy neutrons in order to eliminate the underestimation of the neutron exposure dose as described above, and erroneously count depending on the degree of impact on the desk. It is to provide a neutron detector for high and medium speed neutrons that has a stable measurement accuracy.
[0016]
[Means for Solving the Problems]
The present invention includes a situation in which recoil protons by neutrons generate electron-hole pairs, a situation in which scattered electrons or generated electrons by γ rays generate electron-hole pairs, and a situation in which noise is generated by impact. Based on the difference, the current pulse signal due to γ rays and the noise due to impact are identified.
[0017]
The situation where neutron recoil protons generate electron-hole pairs, as explained in the section of “Prior Art”, is limited to the very vicinity of the passing path of recoil protons that travel almost straight. High density electron-hole pairs are generated. Moreover, the range is as short as about 18 μm when the energy is 1 MeV, about 48 μm at 2 MeV, about 150 μm at 4 MeV, about 730 μm at 10 MeV, and about 1500 μm at 15 MeV. Therefore, the region where the detection element detects the electron-hole pair by the recoil proton is limited to the vicinity of the recoil proton incident position.
[0018]
On the other hand, the state of generation of electron-hole pairs by γ-rays is due to the interaction of electrons having the same mass due to the Compton effect, electrons by electron pair generation, etc., and a distribution state spread over a wide region.
FIGS. 9 and 10 show such a situation as a model.
The recoil protons ejected from the radiator 2 by the neutrons travel straight within the electrode 11 and the depletion layer 12 of the detection element 1 while maintaining the original direction, and move only by the range corresponding to the energy, and are closest to the movement path. High density electron-hole pairs.
[0019]
On the other hand, the generation region of electron-hole pairs by electrons scattered or generated by γ-rays, when modeled, shows the direction in which electrons etc. first jumped from the position where the electrons etc. were generated as the starting point. It becomes a spherical shape with a diameter corresponding to the initial energy of electrons and the like. FIGS. 9 and 10 show a case where electrons and the like are ejected in the same direction as the incident direction of γ-rays. This corresponds to the case where the electron with the largest energy is scattered in the case of the Compton effect. A small circle indicates a case where the γ-ray energy is small (on the order of 100 KeV), and a large circle indicates a case where the γ-ray energy is large (around 5 MeV).
[0020]
As shown in FIG. 9, when γ rays enter the electrode 11 of the detection element 1 near the vertical, the electron-hole pair generation region does not extend over the entire depletion layer 12 of the detection element 1, but FIG. When γ rays are incident on the electrode 11 of the detection element 1 in a tilted manner as described above, the generation region of electron-hole pairs may cover the entire depletion layer 12 of the detection element 1, and in such a case, , The number of electron-hole pairs generated in the depletion layer 12 is maximized, as explained in the prior art section,¹⁶The detection element 1 detects a current pulse corresponding to 1 MeV at the maximum value by the 6.1 MeV γ-ray generated by N.
[0021]
The above description is for a heterojunction type silicon diode, but the same is true for a pn junction type silicon diode.
For reference, the range of electrons in silicon is approximately 13 μm when the electron energy is 50 KeV, approximately 54 μm at 100 KeV, approximately 190 μm at 200 KeV, approximately 770 μm at 500 KeV, approximately 1.7 mm at 1 MeV, and approximately 2 mm at 2 MeV. About 4.0mm, about 11mm at 5MeV,¹⁶The maximum energy electron (5.9 MeV) produced by 6.1 MeV gamma rays in which N is generated is about 13 mm.
[0022]
In addition, as described in the section of “Prior Art”, the noise generated by the impact applied to the personal alarm dosimeter is the detection element associated with the impact applied to the personal alarm dosimeter. This is considered to be due to a change in the capacitance of the detection element 1 due to the deformation and vibration of 1. Therefore, the generation of this noise is not limited to the local area of the detection element as in the region where electron-hole pairs are generated by recoil protons, but may occur over the entire sensitive area of the detection element.
[0023]
This invention¹⁶Generation of N The distribution of electron-hole pairs by gamma rays with high energy such as 6.1 MeV gamma rays spreads over a wide area of the depletion layer 12 of the detection element 1 and generation of noise due to impact Is detected over a wide area using the fact that the detection element covers the entire sensitive part of the detection element, and a signal generated limited to a narrow area such as an electron-hole pair due to recoil protons. , So that only the signals from recoil protons are counted.
[0024]
According to the first aspect of the present invention, electron-hole pairs generated in the detection element by recoil protons generated by the interaction of a neutron with a radiator containing hydrogen at high density are separated by an electric field of a depletion layer of the detection element. A neutron detector that detects neutrons by taking out the current pulses and measuring the amount of charge of the current pulses,
  Corresponding to the first and second electrodes having a spiral shape in the planar shape seen from the recoil proton incident surface provided on the detection element so as to be fitted to each other, and the first and second electrodes,The depletion layer has a planar shape viewed from the recoil proton incident surface side.The first and second spirals fitted togetherDetection element divided into depletion layers, and the detection elementFirst and secondTwo sets of measurement / identification circuits connected to each of the depletion layers and measuring a charge amount of each current pulse and outputting a signal when the charge amount is a predetermined value or more, and the two sets of measurement / identification An arithmetic circuit that does not output a neutron detection signal when a signal is input simultaneously from both circuits and outputs a neutron detection signal when a signal is input from only one of the circuits.
[0025]
The depletion layers of the sensing elementsFirst and second fitting shapesWhen the current pulse is detected by dividing into the depletion layers, and the current pulses with the charge amount equal to or greater than the predetermined value are detected simultaneously in both depletion layers, the signal is not used as the neutron detection signal. The counting of current pulses of γ-rays generated over a wide area of hole pairs and the counting of noise due to impact are eliminated, and current pulses by γ-rays are reduced even if the peak value discrimination level is reduced to less than half of the conventional level. Counting is eliminated, neutrons with lower energy levels can be detected, and miscounting associated with impact is reduced.
[0026]
In particular,In the invention of claim 1The first and secondThe planar shape of the depletion layer is a spiral shape fitted togetherIt is said.When the spirals are fitted to each other, the shape is almost the same for γ rays incident from any direction, so that a detection element with excellent direction characteristics can be obtained, and two depletion layers are fitted. By being combined, the two depletion layers are subjected to equivalent deformation even with respect to higher-order vibration caused by impact, and noise including higher-order vibration can be eliminated.
[0027]
According to the second aspect of the present invention, electron-hole pairs generated in the detection element by recoil protons generated by the interaction of a neutron with a radiator containing hydrogen at high density are separated by an electric field of a depletion layer of the detection element. A neutron detector that detects neutrons by taking out the current pulses and measuring the amount of charge of the current pulses,
  Corresponding to the first and second electrodes having a comb tooth shape in a planar shape viewed from the recoil proton incident surface provided on the detection element so as to be fitted to each other, and the first and second electrodes. A detection element in which the depletion layer is divided into first and second depletion layers each having a comb-like shape fitted from both sides in a planar shape viewed from the recoil proton incident surface side; Two measurement / identification circuits connected to each of the first and second depletion layers, measuring the charge amount of each current pulse and outputting a signal when the charge amount is equal to or greater than a predetermined value; An arithmetic circuit that does not output a neutron detection signal when a signal is input simultaneously from both of the two measurement / identification circuits, and outputs a neutron detection signal when a signal is input from only one of the circuits It is equipped with.
  As in the second aspect of the invention, the first and secondThe planar shape of the depletion layerBothWhen the teeth are comb-fitted from the side, there is a difference in the shape with respect to the incident direction, but the pattern can be easily densified, and the electrodes of this pattern are formed by a method using a mask such as mask vapor deposition. In some cases, it is easy to manufacture a mask for this purpose. Note that the directional characteristics due to the difference in shape with respect to the incident direction can be improved by making the pattern finer. In addition, billingItem 1As with the invention, the two depletion layers are fitted together, so that the two depletion layers are subject to the same deformation with respect to higher-order vibration caused by impact, and noise including higher-order vibration is also eliminated. can do.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, the neutron detector according to the present invention includes a radiator 2 that generates recoil protons by neutrons and two equal electrodes (first electrode 13 and second electrode 2) for detecting recoil protons. A heterojunction type detection element 1a having a plurality of electrodes 14), an amplifier 3 and a peak value discriminating circuit 4 connected to each electrode, and an anti-coincidence arithmetic circuit 5 to which signals from the two peak value discriminating circuits 4 are inputted. And a counting circuit (not shown).
[0029]
Although the two equal electrodes 13 and 14 are simply separated into left and right in FIG. 1, in reality, as shown in FIGS. 2 to 6, both electrodes are fitted to each other, which is much more complicated. It has a nice shape. This is because the electron-hole pairs generated in the detection element 1a by the γ-rays can be equally divided between the two electrodes as much as possible, and can be taken out as a pulse current. This is because deformation due to vibration including higher-order vibration is not so different between the two electrodes. A first depletion layer 15 and a second depletion layer 16 are formed corresponding to the two electrodes 13 and 14, respectively, and electrons in the depletion layer are formed by the high electric field strength of the depletion layers 15 and 16. -The hole pairs are separated into electrons and holes and extracted from each corresponding electrode 13 or 14 as a current pulse.
[0030]
Each current pulse taken out from the electrode 13 or 14 is integrated and amplified by the amplifier 3 and converted into a pulse signal having a peak value corresponding to the charge amount of the current pulse. When this pulse signal is input to the peak value identification circuit 4 and is identified whether or not it is greater than or equal to a predetermined peak value, if it is greater than or equal to the predetermined peak value, the peak value identification circuit 4 sends the count signal to the anti-coincidence calculation circuit 5. Output. The anti-coincidence calculation circuit 5 does not output the count signal to the counting circuit when the count signal is simultaneously input to both of the two input units, and the count signal is input to only one of the two input units. Only in some cases, a count signal is output. The function of the anti-coincidence calculation circuit 5 is that current pulses that are spread out over a wide area of the detection element 1a and are simultaneously extracted to both the electrodes 13 and 14 are derived from electron-hole pairs by γ rays, or are detected by impact Because it is associated with the deformation of the element 1a, it is not counted, and the current pulse extracted only to one of the electrodes 13 and 14 is limited to a narrow region and is derived from electron-hole pairs by neutrons. This is equivalent to counting.
[0031]
Here, the effect of reducing the influence of γ rays will be described first.
By adopting the configuration as described above, the conventional technology has reached about 1 MeV.¹⁶The maximum peak value due to N γ rays (6.1 MeV) can be reduced to a fraction of that. That is, by dividing the electrode into two, the charge amount of the current pulse taken out to each electrode is reduced to about ½, and when the electron-hole pair spreads over a wide region, that is, scattered electrons or generated electrons. When the energy is large, the current pulses taken out by the two electrodes that are equal to each other are almost equal, so that the counting signal is excluded from the counting target by the anti-coincidence calculation circuit 5, and the predetermined peak value of the peak value identification circuit 4 is obtained. The counting signal by γ rays will not be counted unless it is greatly reduced.
[0032]
Here, the electrode widths of the first electrode 13 and the second electrode 14 are both 0.1 mm, the first electrode 13 and the second electrode 14 are alternately arranged, and the distance between both electrodes is also 0.1 mm. Is estimated to what extent the predetermined peak value of the peak value identification circuit 4 can be reduced.
If the electron range exceeds 0.3 mm (energy is less than 300 KeV), the generation region of electron-hole pairs will always reach both the depletion layer 15 of the electrode 13 and the depletion layer 16 of the electrode 14. A current pulse is taken out by both electrodes 13 and 14. However, if it exceeds 0.3 mm, the generation region is not distributed equally to both electrodes, so there is a possibility that a considerable difference will be generated in the current values taken out by both electrodes depending on the scattering position and scattering direction of scattered electrons. is there. If the electron range is 0.8 mm (energy is about 500 KeV) or more, the generation region of electron-hole pairs reaches the electrodes 13 and 14 fairly equally, so that the anti-coincidence calculation circuit 5 is effective. Will work. Therefore, if both electrode width and electrode spacing are 0.1mm,¹⁶It can be considered that the distribution of electron-hole pairs by 6.1 MeV γ rays in which N is generated is sufficiently uniform, and the anti-coincidence calculation circuit 5 functions effectively.
[0033]
on the other hand,¹⁶Of the electron-hole pairs generated by N-generated 6.1 MeV γ-rays that have been extracted to the conventional electrodes, they are divided approximately equally between the electrode part and the spacing part, and further divided into two parts. Therefore, the maximum value of the respective charge amounts taken out to the electrodes 13 and 14 corresponds to 1 MeV / (2 × 2) = 250 KeV, and most of these are excluded by the anti-coincidence calculation circuit 5. Therefore, the predetermined peak value of the peak value identification circuit can be set to less than 250 KeV.
[0034]
Naturally, if the electrode width and the electrode interval are reduced, the anti-coincidence calculation circuit 5 functions more effectively, so that the predetermined peak value can be set lower.
When the electrode area is reduced, the neutron detection area is reduced. In order not to reduce the neutron detection area, it is effective to reduce the ratio of the electrode spacing to the electrode width. However, in this case, the maximum value of the amount of charge extracted to the electrodes 13 and 14 is greater than 250 KeV depending on the area ratio between the electrode portion and the spacing portion. For example, in order to increase the area ratio of the electrodes, when a predetermined peak value is estimated when the width of both electrodes is 0.2 mm and the distance between the electrodes is 0.1 mm, 1 MeV × (2/3) × (1/2) ≈less than 333 KeV.
[0035]
The neutron detection sensitivity is determined by the neutron detection area and a predetermined peak value. When the predetermined peak value becomes low, recoil protons with low energy that could not be detected so far can also be detected, so that the detection probability of neutrons becomes high. Therefore, the neutron detection sensitivity does not decrease as much as the reduction in area, but increases in the low energy region close to 1 MeV even if it decreases in the high energy region.
[0036]
In the above, the case of a heterojunction diode in which the planar shape of the depletion layer is determined by the electrode shape has been described.⁺Layer or n⁺If the shape of the layer is replaced, the case of a pn junction diode is obtained.
In the above, the effect of reducing the influence of γ rays has been described, but the effect of reducing the influence of noise associated with an impact is almost the same as in the case of γ rays. That is, when the neutron detector receives an impact, a substrate or a ceramic package (not shown) on which the detection element 1a is mounted vibrates, and the detection element 1a is deformed by deformation accompanying the vibration. As described in the section of “Prior Art”, this deformation is presumed that higher-order vibration is superimposed on the vibration of about 5 to 10 kHz, and the entire detection element is deformed along with the vibration. It is thought that there is. Therefore, by using the two equal electrodes (first electrode 13 and second electrode 14) as described above, if the deformation of the detection element due to impact is received equally by both electrodes 13 and 14, this Even if the amplifier output due to the deformation exceeds the predetermined peak value of the peak value identification circuit 4, most of these are excluded by the anti-coincidence calculation circuit 5.
[0037]
Examples of the electrode shape of the detection element (heterojunction type) will be described below.
[First Example of Electrode Shape]
FIG. 2 is a pattern diagram showing a first embodiment of the electrode shape of the detection element used in the neutron detector according to the present invention.
In this embodiment, two spiral patterns having exactly the same shape are combined. When the first electrode 13 is rotated by 180 degrees around the center of the detection element 1a, the second electrode 14 is obtained.
[0038]
The feature of this electrode shape is that it has substantially the same shape when viewed from the top, bottom, left, and right directions, so that the directional characteristics do not deteriorate so much even if the electrode width is widened.
[Second Example of Electrode Shape]
FIG. 3 is a pattern diagram showing a second embodiment of the electrode shape.
In this embodiment, four spiral patterns having exactly the same shape are combined. When the first electrode 13b is rotated 90 degrees counterclockwise around the center of the detection element 1b, the second electrode 14b is obtained. The third electrode 17 and the fourth electrode 18 are formed. When these electrodes are connected to the amplifier 3, the first electrode 13b and the third electrode 17, and the second electrode 14b and the fourth electrode 18 are connected to the same amplifier 3, respectively. The first electrode 13b and the third electrode 17 correspond to the first electrode 13 in FIG. 1, and the second electrode 14b and the fourth electrode 18 correspond to the second electrode 14 in FIG.
[0039]
The characteristics of this electrode shape are that the directional characteristics are further superior to those of the first embodiment, and the length of each spiral is ½ that of the first embodiment, so that vapor deposition using a metal mask is performed. When the electrode is formed by sputtering or sputtering, the metal mask can be easily manufactured and used.
[Third embodiment]
FIG. 4 is a pattern diagram showing a third embodiment of the electrode shape.
[0040]
In this embodiment, the spiral in the first embodiment is replaced with a combination of linear patterns. The features of this pattern are that the pattern can be easily formed and that the area of the detection element 1c can be effectively utilized. This embodiment has a slightly worse directional characteristic than the spiral pattern, but can be sufficiently improved by narrowing the electrode width somewhat.
[0041]
2, 3 and 4, the electrode width and the inter-electrode distance are shown to be the same. However, as described above, in order not to reduce the neutron detection sensitivity on the high energy side, the electrodes are as much as possible. It is desirable to narrow the distance.
[Fourth embodiment]
FIG. 5 is a pattern diagram showing a fourth embodiment of the electrode shape.
[0042]
In this embodiment, two comb-like patterns are combined, and when the first electrode 13d is rotated 180 degrees around the center of the detection element 1d, the second electrode 14d is obtained.
In this embodiment, unlike the spiral pattern, the pattern traversing method differs greatly depending on the direction, so that the directional characteristics are worse than those of the spiral pattern. However, if the electrode width and the distance between the electrodes are reduced in accordance with the range of electrons corresponding to a predetermined peak value, the direction characteristics can be improved by the expansion of the electron-hole pair generation region.
[0043]
The feature of this embodiment is that the metal mask can be easily manufactured and used when the electrode is formed by vapor deposition or sputtering using the metal mask. The reason for this is that the pattern is linear and that there are caps between the first electrode 13d and the second electrode 14d at both ends of the comb teeth. It is to support in.
[0044]
[Fifth embodiment]
FIG. 6 is a pattern diagram showing a fifth embodiment of the electrode shape.
This embodiment is effectively equivalent to the fourth embodiment formed by dividing the left and right regions into two regions, a second electrode 14e having comb teeth formed on both sides from the center, The first electrode 13e is fitted to the right half, and the third electrode 17e is fitted to the left half of the second electrode 14e. In this embodiment, there are three portions that support the fine pattern portion of the mask, making it easier to manufacture and use the metal mask. Note that the first electrode 13e and the third electrode 17e are connected to the same amplifier, and are equivalent to the electrode 13 in FIG.
[0045]
Such division of the region is effective when the electrode interval is narrowed, and if necessary, the division of the region is further refined to increase the number of holding portions for supporting the fine pattern portion of the mask. Good. In this case, at the time of connection with the amplifier, these divided electrodes are connected so as to be two equal electrodes in FIG.
[0046]
【The invention's effect】
Main departureIn the light, the depletion layer of the detection elementIn the plane shape seen from the recoil proton incident surface sideIniFirst and second fitting shapes (swirl or comb teeth)When the current pulse is detected by dividing into the depletion layers, and the current pulses with the charge amount equal to or greater than the predetermined value are detected simultaneously in both depletion layers, the signal is not used as the neutron detection signal. The counting of current pulses of γ-rays generated over a wide area of hole pairs and the counting of noise due to impact are eliminated, and current pulses by γ-rays are reduced even if the peak value discrimination level is reduced to less than half of the conventional level. Counting is eliminated, neutrons with lower energy levels can be detected, and miscounting associated with impact is reduced. Therefore, according to the present invention, it is possible to detect even lower energy neutrons, and for high and medium speed neutrons that have stable measurement accuracy without being erroneously counted due to the impact of being tilted on a desk. A neutron detector can be provided, and by using this neutron detector for high and medium speed neutrons and a thermal neutron detector in combination, a neutron detector having better energy characteristics can be provided.
[0047]
In particularDemandItem 1In the invention,1st and 2ndDepletion layerFrom the recoil-proton incident surface sideSince the surface shape is a spiral shape fitted to each other, the shape is almost the same for γ rays incident from any direction, a detection element with excellent direction characteristics can be obtained, and two depletions By fitting the layers together, the two depletion layers are subject to the same deformation even with higher-order vibrations caused by impact, and noise including higher-order vibrations can be eliminated, making it more stable. It is possible to provide a neutron detector for high and medium speed neutrons having the measured accuracy.
[0048]
In addition,DemandItem 2In the invention,1st and 2ndDepletion layerFrom the recoil-proton incident surface sideComb tooth shape fitted from both sidesBecauseAlthough there is a difference in the shape with respect to the incident direction, it is easy to make the pattern finer, and when the electrode of this pattern is formed by a method using a mask such as mask vapor deposition, it is also easy to manufacture a mask for that purpose. is there. Note that the directional characteristics due to the difference in shape with respect to the incident direction can be improved by making the pattern finer. In addition, billingItem 1Similar to the invention, the two depletion layers are fitted to each other so that the two depletion layers are subjected to the same deformation with respect to higher-order vibrations, and noise including higher-order vibrations associated with impact is eliminated. Therefore, it is possible to provide a neutron detector for high and medium speed neutrons with more stable measurement accuracy.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing the configuration of a neutron detector according to the present invention.
FIG. 2 is a pattern diagram showing a first embodiment of an electrode shape of a detection element used in the neutron detector according to the present invention.
FIG. 3 is a pattern diagram showing a second embodiment.
FIG. 4 is a pattern diagram showing a third embodiment.
FIG. 5 is a pattern diagram showing a fourth embodiment.
FIG. 6 is a pattern diagram showing a fifth embodiment.
FIG. 7 is a conceptual diagram showing the configuration of a neutron detector according to the prior art.
FIG. 8 is a pattern diagram showing an example of the electrode shape of a detection element according to the prior art.
FIG. 9 is a conceptual diagram for explaining detection of neutrons and γ-rays by a detection element.
FIG. 10 is a conceptual diagram for explaining problems of a detection element according to the prior art.
FIG. 11 is an amplifier output chart showing an impact test result of a personal alarm dosimeter for explaining problems of a neutron detector according to the prior art
[Explanation of symbols]
1, 1a, 1b, 1c, 1d, 1e detector
11 electrodes
12 Depletion layer
13, 13b, 13c, 13d, 13e First electrode
14, 14b, 14c, 14d, 14e Second electrode
15 First depletion layer
16 Second depletion layer
17, 17e Third electrode
18 Fourth electrode
2 Radiator
3 Amplifier
4 Crest value discrimination circuit
5 Anti-coincidence arithmetic circuit

Claims (2)

Electron-hole pairs generated in the detection element by recoil protons generated by the interaction of neutrons with a hydrogen-containing radiator are separated by the electric field of the depletion layer of the detection element and taken out as a current pulse. A neutron detector that detects neutrons by measuring the charge amount of a current pulse,
Corresponding to the first and second electrodes having a spiral shape in the planar shape seen from the recoil proton incident surface provided on the detection element so as to be fitted to each other, and the first and second electrodes, first first, a detecting element which is divided into a second depletion layer, the detecting elements forming the depletion layer anti跳陽Ko incident surface fitted to each other Te planar shape odor viewed from the side together the spiral, the second 2 sets of measurement / identification circuits connected to each of the depletion layers, and outputting a signal when the charge amount of each current pulse is equal to or greater than a predetermined value, and the two sets of measurement / An arithmetic circuit that does not output a neutron detection signal when a signal is input simultaneously from both of the identification circuits, and outputs a neutron detection signal when a signal is input from only one of the circuits,
A neutron detector comprising: Electron-hole pairs generated in the detection element by recoil protons generated by the interaction of neutrons with a hydrogen-containing radiator are separated by the electric field of the depletion layer of the detection element and taken out as a current pulse. A neutron detector that detects neutrons by measuring the charge amount of a current pulse,
Corresponding to the first and second electrodes having a comb tooth shape in a planar shape viewed from the recoil proton incident surface provided on the detection element so as to be fitted to each other, and the first and second electrodes. Te, said first depletion layer forms a toothed comb was fitted to each other from both sides Te planar shape odor viewed from the anti跳陽Ko incident surface side, and a detecting element which is divided into a second depletion layer, the detection element Two measurement / identification circuits connected to each of the first and second depletion layers, and measuring a charge amount of each current pulse and outputting a signal when the charge amount is equal to or greater than a predetermined value; An arithmetic circuit that does not output a neutron detection signal when a signal is input simultaneously from both of the two sets of measurement / identification circuits, and outputs a neutron detection signal when a signal is input from only one of the circuits When,
A neutron detector comprising:

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