CN110988971B - Wide-energy-spectrum white-light neutron resonance photography detector and detection method - Google Patents
Wide-energy-spectrum white-light neutron resonance photography detector and detection method Download PDFInfo
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- CN110988971B CN110988971B CN201911388864.4A CN201911388864A CN110988971B CN 110988971 B CN110988971 B CN 110988971B CN 201911388864 A CN201911388864 A CN 201911388864A CN 110988971 B CN110988971 B CN 110988971B
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- G01T3/00—Measuring neutron radiation
- G01T3/06—Measuring neutron radiation with scintillation detectors
Abstract
The invention discloses a wide-energy spectrum white-light neutron resonance photography detector and a detection method, wherein the detector is internally provided with a cavity structure, an incidence window and a rear window are respectively arranged at two ends of the detector, a neutron-sensitive MCP, a common high-performance MCP and a position-sensitive anode strip array circuit board are arranged along the direction from the incidence window to the rear window, a vacuum extraction opening is arranged on the side wall of the detector body close to the rear window, the position-sensitive anode strip array circuit board is connected with a signal extraction electrode, and one end of the signal extraction electrode is arranged on the side wall of the detector body. Neutron beam is injected from an incidence window, firstly reacts with boron in the neutron-sensitive MCP to generate charged particles, the charged particles excite electrons, the electrons drift to the position-sensitive anode strip array circuit board after being subjected to electron cascade amplification generated by the common high-performance MCP to form electric pulse signals, and then the electric pulse signals are output from a signal extraction electrode. The invention can realize resonance photography for resolving all resonance nuclides on a high-intensity wide-energy spectrum neutron source.
Description
Technical Field
The invention relates to the technical field of neutron resonance imaging, in particular to a wide-energy-spectrum white-light neutron resonance photographic detector and a detection method.
Background
The neutron-substance interaction is closely related to the nuclear structure of substance atoms, and neutrons with different energies have greatly different action cross sections on different nuclides and are generally accompanied by a resonance peak reflecting characteristic information of the nuclide in an epithermal-fast neutron energy region (0.5eV-10 MeV). Theoretically, the neutron resonance imaging technology not only provides a gray level map of conventional transmission photography, provides nuclide composition of a measured object through formant analysis, but also provides a position distribution image of each resonant nuclide, and the neutron resonance imaging technology has wide application prospects in fields of scientific research, industrial detection, social safety and the like.
The neutron source of neutron resonance imaging generally adopts a pulse type accelerator neutron source, neutron beam current depends on the characteristics of the neutron source, and the covered neutron energy regions are different. The small accelerator neutron source mainly provides fast neutrons from dozens of keV to dozens of MeV, and high-flux neutrons generated by the large accelerator neutron source can cover a wide energy spectrum region from the MeV to hundreds of MeV after being properly moderated. The neutron beam flies for a long distance and passes through the collimation hole to form a beam spot with a proper size. Before the resonance photography of the sample, the profile distribution, the neutron energy spectrum and the flux intensity of the neutron beam spot need to be calibrated by using a position sensitive detector with time resolution. Wherein the neutron spectrum is measured using a time-of-flight method. The neutron beam passing through the tested sample can react with the sample through elastic scattering, inelastic scattering, resonance absorption and the like, and flux changes of different positions of the neutron beam are caused. The neutron interaction cross-section of different nuclides has a strong resonance cross-section peak in a specific energy interval, as shown in fig. 1, which is a full cross-section resonance peak of several nuclides such as gold, silver, tungsten, tantalum, indium, and the like.
After the neutron beam passes through the sample, the neutron flux is sharply reduced near the characteristic resonance peak of the nuclide (i.e. an extremum appears on the neutron reaction cross section), and an absorption valley is formed on the case rate spectrum obtained by the downstream neutron detector. The formants of different nuclides have different characteristics (including different intensities and energy regions), so that the neutron beam flux before and after the sample is placed is compared by the high-resolution detector, the different nuclides contained in the sample can be identified, the density distribution condition of the different nuclides in the sample can be given by the imaging function of the neutron detector, and the resonance photography of the sample is completed. Based on the principle, the neutron resonance photography requires that the neutron energy spectrum of each pixel point is obtained on the basis of certain position resolution (the neutron energy spectrum is obtained by a flight time measuring method), so that the efficiency of a neutron detector has high requirements.
Compared with thermal neutron transmission imaging, white-light neutron resonance imaging requires that a detector system simultaneously meets several key indexes of position resolution, energy resolution, detection efficiency, energy spectrum response range and the like of wide-energy-spectrum neutron measurement, and the detection efficiency of high-energy neutrons is far lower than that of low-energy neutrons, so that the detection technology is very difficult to realize, and is still in an exploration stage at home and abroad at present.
In 2012, Mor et al utilized a capillary array based on liquid flash filling and a multi-anode photomultiplier tube (PMT) scheme to perform fast neutron imaging, but the position resolution of this mode based on a flash array is usually in the millimeter order, which is difficult to achieve the ideal effect for imaging. Further improving the position resolution requires reducing the wire diameter and increasing the number of photomultiplier devices and electronic readout circuits, which not only reduces the probability that the detection is affected by the light signal collection efficiency, but also increases the difficulty of scintillation array bundling and the difficulty of photomultiplier device docking, and the cost, volume and power consumption of multi-channel signal readout electronics are very large, greatly increasing the practical cost thereof, so that the scheme is not successfully applied to neutron resonance imaging experiments so far.
In 2015 Dangendorf et al attempted fast neutron resonance imaging using a hydrogen-containing material as the neutron conversion layer in combination with a position sensitive gas detector (GEM), although a better transmission spectrum was obtained, the desired C element distribution image did not appear. The position resolution of the position sensitive gas detector can reach dozens of micrometers, and the position sensitive gas detector can be used for energy-resolved position imaging in principle, but the maximum limitation is that the detection efficiency of a neutron conversion layer is too low (the thickness of the conversion layer cannot be too large due to charged particle detection), and the neutron resonance imaging requirement cannot be met.
Professional CCD cameras used for scientific research are widely used for neutron photography experiments as general photographic means. In recent years, screening neutrons with specific energy by using shutter delay and gate width of a camera has been reported in realizing specific nuclide imaging. Although the CCD camera has the advantages of high pixel and good position resolution, when used for nuclear resonance photography, the CCD camera does not have neutron energy spectrum measurement capability, so that only a neutron energy region of a certain width can be selected. On the other hand, the greatest restriction in neutron imaging is that it is based on photon quantity accumulation rather than neutron case number accumulation, so the imaging effect of neutrons in different energy regions is seriously influenced by the energy sensitivity of light yield.
The data acquisition chip Timipix is derived from a Medpix chip which is derived from a large hadron collider LHC and then is used for medical imaging, has the capability of being matched with a high-pixel position resolution (usually reaching 55 mu m) detector, and can independently extract time information from each pixel point. In recent years, the combination of Timipix and boron-doped microchannel plate (MCP) for epithermal neutron resonance photography has achieved great success, but is limited by its technical characteristics (for example, Timipix has low time resolution (about 100ns), and Timipix needs to be placed on a neutron beam together with a detector, and has poor irradiation resistance as a high-integration modulus hybrid chip), and its application is limited to the epithermal neutron energy region (<100eV), and has not been successfully applied to fast neutron imaging.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a wide-energy-spectrum white-light neutron resonance photography detector which can realize resonance photography for resolving omnipotent-region resonance nuclides on a high-intensity wide-energy-spectrum neutron source (eV-MeV).
Another object of the present invention is to provide a method for detecting wide-spectrum white-light neutron resonance photography by the above detector.
The technical scheme of the invention is as follows: the utility model provides a wide energy spectrum white light neutron resonance photographic detector, including the detector body, the sensitive MCP of neutron, ordinary high performance MCP, position sensitive anode strip array circuit board and signal extraction electrode, the inside cavity structure that is of detector body, the both ends of detector body are equipped with incident window and rear window respectively, along incident window to rear window direction, the inside sensitive MCP of neutron that sets gradually of detector body, ordinary high performance MCP and position sensitive anode strip array circuit board, be equipped with the vacuum extraction opening on the detector body lateral wall that is close to the rear window, position sensitive anode strip array circuit board is connected with the signal extraction electrode, and the one end of signal extraction electrode is located on the detector body lateral wall. Wherein, the vacuum pumping port is externally connected with a vacuum pumping device, so that a vacuum packaging structure is formed in the detector body, and the signal extraction electrode is externally connected with an electronic reading circuit; the incident window, the neutron-sensitive MCP, the common high-performance MCP and the position-sensitive anode strip array circuit board are arranged in parallel and located in a range covered by the neutron beam, a plane where a sensitive area is located is perpendicular to the direction of the neutron beam, and the plane belongs to a sensitive area part of a detector and needs to work in vacuum; the electronic reading circuit receives the electric pulse signal induced on the position-sensitive anode strip array circuit board, and the electric pulse signal is processed by an operational amplifier and position decoding in the circuit to give a data packet with neutron energy (flight time information) and position information. The electronics reading circuit is arranged outside the detector, so that direct irradiation of neutron beam current can be avoided, and the problem of radiation damage is avoided.
The neutron-sensitive MCP is a boron-doped microchannel plate (namely the neutron-sensitive MCP contains10B nuclide), the common high-performance MCP is a high-gain uniformity microchannel plate, and the high-gain uniformity microchannel plate is an existing microchannel plate; the thickness of the neutron-sensitive MCP is 0.5-3 mm, and the thickness can be adjusted within the range according to actual requirements.
A plurality of first multiplication pore channels are distributed on the neutron-sensitive MCP, and the average wall thickness of each first multiplication pore channel is 2-3 mu m.
On the neutron-sensitive MCP, a layer of boron material is deposited on the inner wall of each first multiplication pore channel, a secondary electron emission layer (the secondary electron emission layer is the same as that of the conventional MCP) covers the surface of the boron material layer, and the deposition thickness of the boron material layer is 0.5-2 microns. In the neutron-sensitive MCP, the material is selected10B material (Gd material may be used as well) as neutron converter, which generates alpha particles and7the average range of Li particles in neutron-sensitive MCP is 3.5 μm and 2 μm, respectively, and one or at most two adjacent channels in the neutron-sensitive MCP can be excited. In order to obtain high detection efficiency, the neutron-sensitive MCP adopted by the invention can deposit a layer on the inner wall of each first multiplication pore channel of the MCP through an atomic layer deposition technology10And B, the thickness is 0.5-2 mu m, and the structural mode breaks through the limitation of nuclide doping concentration and can effectively improve the detection efficiency. The thickness of the conventional MCP is generally 0.5mm, in order to further improve the surface density of the neutron sensitive material, the thickness of the neutron sensitive MCP can be adjusted to be 0.5-3 mm, meanwhile, the included angle between the first multiplication pore channel and the normal line of the MCP plane is reduced, and the position resolution of neutron detection is prevented from being influenced.
A plurality of second multiplication pore channels are distributed on the common high-performance MCP; the common high-performance MCP and the neutron-sensitive MCP are arranged in a parallel superposition mode, and a first multiplication channel and a second multiplication channel are stacked in a V shape between the two MCPs (namely, in a general situation, a plurality of multiplication channels with the same inclination angle are distributed on each MCP, and when the two MCPs are stacked, the V shape is formed between the multiplication channels of the two MCPs). The neutron sensitive MCP converts neutrons into detectable electrons, primarily amplifies the electrons, and secondarily amplifies the electrons by the common high-performance MCP to form a strong electron cloud. The mode can solve the problem of high detection efficiency difficulty of resonance photography, and can simultaneously keep the position resolution of a neutron signal amplified by an MCP detector sensitive area in the order of mum, which is far higher than the requirement of photography on the position resolution.
Furthermore, the surface of the neutron-sensitive MCP close to one side of the entrance window is covered with a plastic scintillation screen. The neutron-sensitive MCP added with the plastic scintillation screen is used as a neutron conversion material, high-energy neutrons are converted into fluorescence, photons can excite electrons in the neutron-sensitive MCP, and high enough detection efficiency for MeV or higher-energy neutrons can be obtained, so that all white-light neutron resonance energy regions (<20MeV) are covered, but the problem of position resolution reduction caused by diffusion effect of scintillation light due to the addition of the plastic scintillation screen is solved, and therefore, in actual use, selection is carried out according to actual detection requirements.
The position-sensitive anode strip array circuit board comprises an upper layer anode strip array and a lower layer anode strip array which are arranged in a crossed mode, the upper layer anode strip array comprises upper layer rectangular conductive strips and upper layer insulating channels which are distributed in an alternating mode, and the lower layer anode strip array comprises lower layer rectangular conductive strips and lower layer insulating channels which are distributed in an alternating mode.
In the upper-layer anode strip array, each upper-layer rectangular conductive strip and an adjacent upper-layer insulated channel form an upper-layer array period; in the lower-layer anode strip array, each lower-layer rectangular conductive strip and an adjacent lower-layer insulating channel form a lower-layer array period;
the width of the upper layer array period is equal to that of the lower layer array period;
the width of the upper layer rectangular conductive strip is smaller than that of the lower layer rectangular conductive strip;
the width of the upper layer insulation channel is larger than that of the lower layer insulation channel.
The gap between the position-sensitive anode strip array circuit board and the common high-performance MCP is 1.5 mm.
In the position-sensitive anode strip array circuit board, the electron cloud amplified by the neutron-sensitive MCP and the common high-performance MCP drifts to the position-sensitive anode strip array circuit board under the action of an electric field, and simultaneously, a plurality of anode strips (including the upper rectangular conductive strips and the lower rectangular conductive strips) are caused to catch fire. In order to reduce the space diffusion effect of the electron cloud, the position-sensitive anode strip array circuit board should be as close to the MCP as possible, and high-voltage ignition should be avoided, and the gap between the two is generally about 1.5 mm. In the upper layer anode strip array and the lower layer anode strip array, a charge center decoding algorithm (the algorithm is an existing algorithm) can be adopted to determine the position information of the neutron case, the positioning precision can reach about 10 mu m, and therefore the position resolution does not depend on the number of the upper layer rectangular conductive strips or the lower layer rectangular conductive strips. Generally, in the lower anode strip array, the width of the lower rectangular conductive strip is 0.4mm, the strip gap (i.e. the lower insulating channel) is 0.1mm, and in order to ensure that the charge distribution on the upper and lower strips is equal, the width of the upper rectangular conductive strip is smaller than that of the lower rectangular conductive strip. The widths of the upper layer array period and the lower layer array period are equal and are 0.5mm, and the array patterns of the upper and lower 128 paths can meet the photographic requirements of most neutron sources. Since the position resolution requires charge distribution decoding, the arrangement precision of the conductive strips (including the upper rectangular conductive strips and the lower rectangular conductive strips) reaches the mum order, the surface flatness of the conductive layer is controlled within 100nm, and the absolute insulation of the two layers of electrodes is ensured and the signal crosstalk between electrodes is prevented. The use of the position-sensitive anode strip array circuit board can keep high position resolution, and the highest detection case rate of the array accommodation is higher than 10MHz/cm2And the requirement of high-fluence rate neutron detection can be better met.
In addition, the signal strength of the neutron case is related to the charge amount of the electron cloud. The electrical pulse signals formed on the position sensitive anode strip array circuit board need to be read out and electronically and data acquisition for further processing, and finally neutron identification, position and energy (flight time) information of each case is given. Therefore, the electric pulse signals are sent to an electronic system (namely the electronic reading circuit) through the signal extraction electrodes to carry out threshold crossing discrimination on each signal, a charge center position decoding algorithm is adopted for online analysis, and a data packet after positioning calculation is output (X, Y, T), so that the storage amount needing later data processing is reduced. For the interference of the simultaneous arrival case, X, Y direction orientation matching analysis and elimination can be performed by adopting a method of comparing the number of ignition strips and the signal amplitude (the method is also an existing calculation method).
The invention realizes a wide-energy spectrum white-light neutron resonance photography detection method through the detector, which comprises the following steps: neutron beam current is emitted into the detector body from the incident window, firstly reacts with boron element in the neutron-sensitive MCP to generate charged particles, the charged particles are subjected to electronic cascade amplification generated by the common high-performance MCP, drift to the position-sensitive anode strip array circuit board to form electric pulse signals, and finally the electric pulse signals are output from the signal extraction electrode. The signals finally obtained by the detection method can reflect the change of the section density distribution and the energy spectrum of the neutron beam after respectively passing through the empty sample and the actual sample.
Compared with the prior art, the invention has the following beneficial effects:
the wide-energy spectrum white-light neutron resonance photography detector and the detection method can realize resonance photography for resolving all resonance nuclides on a high-intensity wide-energy spectrum neutron source (eV-MeV), and can obtain the high neutron case rate of a single pixel under the conditions of high position resolution (10 mu m magnitude) and time resolution (10ns magnitude), thereby meeting the requirements of wide-energy spectrum neutron resonance photography and simultaneously meeting the technical conditions of neutron case number cumulative imaging, irradiation resistance, large-area manufacturing and the like.
In the wide-spectrum white-light neutron resonance photography detector, the doping10A neutron-sensitive MCP of a few millimeters thickness of B is very high10B-plane density, for a typical white light neutron spectrum, can achieve a relatively high enough neutron case rate for neutrons in the (eV-MeV) energy region.
In the wide-spectrum white-light neutron resonance photographic detector, the number of crossed anode array electronic paths of the position-sensitive anode strip array circuit board is generally hundreds of channels for accommodating neutronsThe sample rate can reach 10MHz/cm2The above.
In the wide-spectrum white-light neutron resonance photography detector, for the detection of neutrons in an energy region more than several MeV, a plastic scintillation screen can be additionally arranged on the surface of the neutron-sensitive MCP, so that the neutron detection efficiency is improved, the identification conditions of all nuclide formants are met, and the wide-spectrum white-light neutron resonance photography detector is flexible and convenient to use.
In the wide-energy spectrum white-light neutron resonance photographic detector, the electronics reading circuit is arranged outside the detector, so that the electronics chip module avoids the direct irradiation of a high-current neutron beam, and the neutron-sensitive MCP, the common high-performance MCP and the position-sensitive anode strip array circuit board have the radiation resistance characteristic, so that the whole detector device has good applicability of the high-current neutron beam.
Drawings
FIG. 1 is a schematic diagram of the resonance cross-sectional peak of a common nuclear species.
Fig. 2 is a schematic structural diagram of the wide-energy spectrum white-light neutron resonance photography detector in embodiment 1.
Fig. 3 is a partial structural schematic diagram of the neutron-sensitive MCP.
Fig. 4 is a schematic structural diagram of a position-sensitive anode strip array circuit board.
Fig. 5 is a schematic structural diagram of the wide-energy spectrum white-light neutron resonance photography detector in embodiment 2.
In the above figures, the components indicated by the respective reference numerals are as follows: the detector comprises a detector body 1, a neutron sensitive MCP2, a common high-performance MCP3, a position sensitive anode strip array circuit board 4, a signal extraction electrode 5, an entrance window 6, a rear window 7, a vacuum extraction opening 8, a first multiplication hole channel 9, an upper rectangular conductive strip 10, an upper insulating channel 11, a lower rectangular conductive strip 12, a lower insulating channel 13, a neutron beam, an electron cloud 15, a plastic scintillation screen 16 and an included angle between the first multiplication hole channel and an MCP plane normal line.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
Example 1
The embodiment provides a wide-energy spectrum white-light neutron resonance photography detector, as shown in fig. 2, including detector body 1, neutron-sensitive MCP2, ordinary high performance MCP3, position-sensitive anode strip array circuit board 4 and signal extraction electrode 5, the inside cavity structure that is of detector body, the both ends of detector body are equipped with incident window 6 and rear window 7 respectively, along incident window to rear window direction, detector body is inside to set gradually neutron-sensitive MCP, ordinary high performance MCP and position-sensitive anode strip array circuit board, be equipped with vacuum extraction opening 8 on the detector body lateral wall that is close to the rear window, position-sensitive anode strip array circuit board is connected with the signal extraction electrode, and the one end of signal extraction electrode is located on the detector body lateral wall. Wherein, the vacuum pumping hole is externally connected with a vacuum pumping device, so that a vacuum packaging structure is formed in the detector body, and the signal extraction electrode is externally connected with an electronic reading circuit.
The neutron-sensitive MCP is a boron-doped microchannel plate (namely the neutron-sensitive MCP contains10B nuclide), the common high-performance MCP is a high-gain uniformity microchannel plate, and the high-gain uniformity microchannel plate is an existing microchannel plate; the thickness of the neutron-sensitive MCP is 0.5-3 mm. As shown in FIG. 3, a plurality of first multiplication channel 9 are distributed on the neutron-sensitive MCP, and the average wall thickness of each first multiplication channel is 2-3 μm. On the neutron-sensitive MCP, a layer of boron material is deposited on the inner wall of each first multiplication channel, a secondary electron emission layer (the secondary electron emission layer is the same as that of the conventional MCP) covers the surface of the boron material layer, and the deposition thickness of the boron material layer is 0.5-2 microns. In neutron-sensitive MCP, the material is selected10B material as neutron converter, alpha particle of product of capture reaction with neutron and7the average range of Li particles in neutron-sensitive MCP is 3.5 μm and 2 μm, respectively, and one or at most two adjacent channels in the neutron-sensitive MCP can be excited. In order to obtain high detection efficiency, a layer of material can be deposited on the inner wall of each first multiplication channel of the neutron-sensitive MCP by the atomic layer deposition technology10And B, the thickness is 0.5-2 mu m, and the structural mode breaks through the limitation of nuclide doping concentration and can effectively improve the detection efficiency. The thickness of the conventional MCP is generally 0.5mm, and in order to further improve the area density of the neutron sensitive material, the conventional MCP is prepared by carrying out MCP on neutronsThe thickness is adjusted to be 0.5-3 mm, and meanwhile, the included angle a between the first multiplication pore channel and the normal line of the MCP plane is reduced, so that the position resolution of neutron detection is prevented from being influenced.
A plurality of second multiplication pore channels are distributed on the common high-performance MCP; the common high-performance MCP and the neutron-sensitive MCP are arranged in a parallel superposition mode, and a first multiplication channel and a second multiplication channel are stacked in a V shape between the two MCPs (namely, in a general situation, a plurality of multiplication channels with the same inclination angle are distributed on each MCP, and when the two MCPs are stacked, the V shape is formed between the multiplication channels of the two MCPs). The neutron sensitive MCP converts neutrons into detectable electrons, primarily amplifies the electrons, and secondarily amplifies the electrons by the common high-performance MCP to form a strong electron cloud. The mode can solve the problem of high detection efficiency difficulty of resonance photography, and can simultaneously keep the position resolution of a neutron signal amplified by an MCP detector sensitive area in the order of mum, which is far higher than the requirement of photography on the position resolution.
As shown in fig. 4, the position-sensitive anode strip array circuit board includes an upper anode strip array and a lower anode strip array which are arranged in a crossed manner, the upper anode strip array includes upper rectangular conductive strips 10 and upper insulating channels 11 which are alternately distributed, and the lower anode strip array includes lower rectangular conductive strips 12 and lower insulating channels 13 which are alternately distributed. In the upper-layer anode strip array, each upper-layer rectangular conductive strip and an adjacent upper-layer insulated channel form an upper-layer array period; in the lower-layer anode strip array, each lower-layer rectangular conductive strip and an adjacent lower-layer insulating channel form a lower-layer array period; the width of the upper layer array period is equal to that of the lower layer array period; the width of the upper layer rectangular conductive strip is smaller than that of the lower layer rectangular conductive strip; the width of the upper layer insulation channel is larger than that of the lower layer insulation channel. The gap between the position-sensitive anode strip array circuit board and the common high-performance MCP is about 1.5 mm. In the position-sensitive anode strip array circuit board, the electron cloud amplified by the neutron-sensitive MCP and the common high-performance MCP drifts to the position-sensitive anode strip array circuit board under the action of an electric field, and meanwhile, a plurality of anode strips (including the upper rectangular conductive strips and the lower rectangular conductive strips) are caused to catch fire. To reduce the effect of spatial diffusion of the electron cloud, a potential-sensitive anode stripThe array circuit board should be as close to the MCP as possible while avoiding high voltage sparking, with a gap of about 1.5 mm. In the upper layer anode strip array and the lower layer anode strip array, a charge center decoding algorithm (the algorithm is an existing algorithm) can be adopted to determine the position information of the neutron case, the positioning precision can reach about 10 mu m, and therefore the position resolution does not depend on the number of the upper layer rectangular conductive strips or the lower layer rectangular conductive strips. Generally, in the lower anode strip array, the width of the lower rectangular conductive strip is 0.4mm, the strip gap (i.e. the lower insulating channel) is 0.1mm, and in order to ensure that the charge distribution on the upper and lower strips is equal, the width of the upper rectangular conductive strip is smaller than that of the lower rectangular conductive strip. The widths of the upper layer array period and the lower layer array period are equal and are 0.5mm, and the array patterns of the upper and lower 128 paths can meet the photographic requirements of most neutron sources. Since the position resolution requires charge distribution decoding, the arrangement precision of the conductive strips (including the upper rectangular conductive strips and the lower rectangular conductive strips) reaches the mum order, the surface flatness of the conductive layer is controlled within 100nm, and the absolute insulation of the two layers of electrodes is ensured and the signal crosstalk between electrodes is prevented. The use of the position-sensitive anode strip array circuit board can keep high position resolution, and the highest detection case rate of the array accommodation is higher than 10MHz/cm2And the requirement of high-fluence rate neutron detection can be better met.
In the wide-energy spectrum white-light neutron resonance photographic detector, the incident window, the neutron-sensitive MCP, the common high-performance MCP and the position-sensitive anode strip array circuit board are arranged in parallel and positioned in a range covered by neutron beam current, a plane where a sensitive area is located is vertical to the direction of the neutron beam current, and the part belongs to a sensitive area part of the detector and needs to work in vacuum; the electronic reading circuit receives the electric pulse signals induced on the position-sensitive anode strip array circuit board, and the data packet with neutron energy (flight time information) and position information can be given out through the operational amplifier and position decoding processing in the circuit. The electronics reading circuit is arranged outside the detector, so that direct irradiation of neutron beam current can be avoided, and the problem of radiation damage is avoided. In addition, the signal strength of the neutron case is related to the charge amount of the electron cloud. The electrical pulse signals formed on the position sensitive anode strip array circuit board need to be read out and electronically and data acquisition for further processing, and finally neutron identification, position and energy (flight time) information of each case is given. Therefore, the electric pulse signals are sent to an electronic system (namely the electronic reading circuit) through the signal extraction electrodes to carry out threshold crossing discrimination on each signal, a charge center position decoding algorithm is adopted for online analysis, and a data packet after positioning calculation is output (X, Y, T), so that the storage amount needing later data processing is reduced. For the interference of the simultaneous arrival case, X, Y direction orientation matching analysis and elimination can be performed by adopting a method of comparing the number of ignition strips and the signal amplitude (the method is also an existing calculation method).
The method for realizing the wide-energy-spectrum white-light neutron resonance photography detection by the detector comprises the following steps: neutron beam 14 is emitted into the detector body from the incident window, firstly reacts with boron in the neutron-sensitive MCP to generate charged particles, the charged particles are subjected to electron cascade amplification generated by the common high-performance MCP to form an electron cloud 15, the electron cloud drifts to the position-sensitive anode strip array circuit board to form an electric pulse signal, and finally the electric pulse signal is output from the signal extraction electrode. The signals finally obtained by the detection method can reflect the change of the section density distribution and the energy spectrum of the neutron beam after respectively passing through the empty sample and the actual sample.
The following describes the operation of the detection method with the detected process of a neutron:
in the approximately parallel beam of the white light neutron source, the neutrons pass through the incident window of the detector after flying for a certain distance and are in contact with the neutrons in the neutron-sensitive MCP10B is subjected to a capture reaction to produce alpha and7li two charged particles excite electrons in the adjacent 1-2 first channels and form multiplication effect, and the multiplication coefficient is generally more than 107And then the electron cascade amplification is generated by the common high-performance MCP, and an electron cloud 15 is formed when the common high-performance MCP is separated. The electron cloud drifts towards the sensitive anode strip array circuit board under the action of the electric field between the sensitive anode strip array circuit board and the common high-performance MCP, and is formed by a plurality of anode strips (namely the upper layer rectangular strip) arranged in the direction of X, YConductive strips and underlying rectangular conductive strips) and form electrical pulse signals. An electronic readout circuit placed outside the detector receives the electrical pulse signal from the anode strip and performs threshold crossing discrimination. And (3) starting positioning analysis after the neutron case is determined by screening, and calculating a specific ignition position by using the distribution size of the charge quantity on the plurality of anode strips (the positioning precision can be far higher than the width of the anode strips and reaches 10 mu m magnitude). The neutron beam current generally adopts a pulse type accelerator neutron source, and the accelerator can give a signal of the neutron pulse generation time on a target as a starting time signal T0 of neutron flight time measurement; the signal on the anode strip is received by the electronic reading circuit and is used as a signal Ts for ending the flight time of the reaction neutron, the signal Ts is subtracted from T0 to obtain the flight time of the neutron, and then the kinetic energy E of the neutron is obtained according to the accurately positioned flight distance L. The uncertainty of the measurement of the flight time T is 10ns magnitude, and corresponding to the flight distance of dozens of m, the neutron energy resolution in a wide energy region (eV-MeV) can be ensured to be higher than 1%. Generally, the time-of-flight T to neutron energy E conversion calculation can be done off-line, with electronics and data acquisition systems outputting position and time-of-flight (i.e., X, Y, T) information packets for each neutron measured. The probability of the action of neutrons with different energies and nuclides in a sample is very different, namely the energy spectrum of the neutron beam changes after passing through an experimental sample, and if the sample contains different nuclides and has different shapes and thicknesses, the energy spectrum of the transmitted neutron beam is not single but related to the spatial position. By comparing the energy spectrum change of each position point before and after the neutron passes through the sample and contrasting the nuclide formant table, the nuclide components of the sample and the position distribution condition in a neutron irradiation area (sensitive detection area) can be analyzed. The whole process is neutron case number accumulation, and the measurement time depends on the requirement of statistical error analysis, including position analysis and energy spectrum analysis.
This is based on10B is used as a detection method of neutron detection materials, can keep high enough detection efficiency on a high-current white-light neutron source, has a coverage energy region from eV to about MeV magnitude, and can identify all nuclides except individual light elements through a resonance peak.
In this example, neutronsThe sensitive MCP is one of the core parts of the whole detector and determines the key index of neutron detection efficiency. In order to improve neutron-sensitive materials10The surface density of B may be doped by a combination of glass substrate doping (which is the same as that of the conventional boron-doped MCP) and the first layer of the multiple via plating. The plating process is generally first plating10B layer is then plated with MCP conductive layer and secondary electron emission layer10The B layer is below the secondary electron emission layer to avoid the effect on electron multiplication. Because electrons are multiplied in the first multiplication channel, the position resolution cannot be obviously reduced by properly increasing the thickness of the neutron-sensitive MCP, so that the thickness of the neutron-sensitive MCP can be 0.5-3 mm according to the process requirement, and the inclination angle of the channel is properly reduced to reduce the influence on the position resolution. The neutron sensitive MCP and the common high-performance MCP are stacked in parallel, and ion feedback interference is avoided by adopting a channel V-shaped stacking mode.
The position-sensitive anode strip array circuit board is also one of the core parts of the whole detector, and determines the key index of the position resolution of the neutron photograph. The arrangement precision of the upper rectangular conductive strips and the lower rectangular conductive strips reaches the order of mum, the surface flatness of the conductive layer is controlled within 100nm, and the absolute insulation of two layers of electrodes is ensured and the signal crosstalk between electrodes is prevented.
The white light neutron source adopts a pulse type strong current accelerator neutron source, and a neutron flight time starting signal T0 is used for triggering an electronic reading circuit and measuring and timing the neutron flight time. The neutron energy spectrum covers an eV-MeV energy region, and the energy spectrum shape is preferably that the fluence rate increases along with the neutron energy index.
The electronic reading circuit receives and processes the case trigger electric pulse signals from the position-sensitive anode strip array circuit board, the electronic reading circuit deviates from a neutron beam line, direct irradiation of neutrons is avoided, and the signal processing time resolution is 10ns magnitude.
A vacuum packaging structure is formed in the detector body, and the vacuum degree of the vacuum packaging structure is higher than 10-4pa, the sensitive part of the detector is all operated under vacuum.
Example 2
This embodiment is a wide-spectrum white-light neutron resonance photography detector, as shown in fig. 5, and compared with embodiment 1, the difference is that: the surface of the neutron-sensitive MCP close to one side of the entrance window is also covered with a plastic scintillation screen 16. The neutron-sensitive MCP added with the plastic scintillation screen is used as a neutron conversion material, high-energy neutrons are converted into fluorescence, photons can excite electrons in the neutron-sensitive MCP, and high enough detection efficiency for MeV or higher-energy neutrons can be obtained, so that all white-light neutron resonance energy regions (<20MeV) are covered, but the problem of position resolution capacity reduction caused by the diffusion effect of scintillation light due to the addition of the plastic scintillation screen is solved.
The principle is as follows:10the section of the capture reaction between the B-nuclide and the neutron decreases along with the increase of the neutron energy, and the high energy of the wide-energy-spectrum neutron beam current is (>1MeV) neutron due to10The low section of B capture neutrons leads to low detection efficiency and longer measurement time. Therefore, the solution of this embodiment is that a plastic scintillation screen is added as a neutron conversion material on the basis of embodiment 1, inelastic collision between high-energy neutrons and hydrogen nuclei in the scintillation screen excites recoil protons, the recoil protons deposit energy in the scintillation screen and excite fluorescence, the photons can also excite electrons in neutron-sensitive MCP, and MeV or higher energy neutrons can be detected with high enough detection efficiency to cover all white-light neutron resonance energy regions (i.e., (ii) (i.e., higher energy neutrons have enough detection efficiency to cover all white-light neutron resonance energy regions<20MeV)。
As mentioned above, the present invention can be better realized, and the above embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention; all equivalent changes and modifications made according to the present disclosure are intended to be covered by the scope of the claims of the present invention.
Claims (8)
1. A wide-energy spectrum white-light neutron resonance photographic detector is characterized by comprising a detector body, a neutron-sensitive MCP, a common high-performance MCP, a position-sensitive anode strip array circuit board and a signal extraction electrode, wherein the detector body is of a cavity structure, an incidence window and a rear window are respectively arranged at two ends of the detector body, the neutron-sensitive MCP, the common high-performance MCP and the position-sensitive anode strip array circuit board are sequentially arranged in the detector body along the direction from the incidence window to the rear window, a vacuum extraction opening is formed in the side wall, close to the rear window, of the detector body, the position-sensitive anode strip array circuit board is connected with the signal extraction electrode, and one end of the signal extraction electrode is arranged on the side wall of the detector body;
the neutron-sensitive MCP is a boron-doped microchannel plate, a plurality of first multiplication channels are distributed on the neutron-sensitive MCP, an included angle is formed between each first multiplication channel and the normal line of the MCP plane, and each first multiplication channel is doped with a glass substrate10In the mode B, a layer of boron material is deposited on the inner wall of the first multiplication pore channel, and a secondary electron emission layer covers the surface of the boron material layer;
the position-sensitive anode strip array circuit board comprises an upper layer anode strip array and a lower layer anode strip array which are arranged in a crossed mode, wherein the upper layer anode strip array comprises upper layer rectangular conductive strips and upper layer insulating channels which are distributed alternately, and the lower layer anode strip array comprises lower layer rectangular conductive strips and lower layer insulating channels which are distributed alternately;
the surface of the neutron-sensitive MCP close to one side of the entrance window is covered with a plastic scintillation screen.
2. The wide-spectrum white-light neutron resonance photography detector of claim 1, wherein the common high-performance MCP is a high-gain uniformity microchannel plate; the thickness of the neutron-sensitive MCP is 0.5-3 mm.
3. The wide-energy spectrum white-light neutron resonance photography detector of claim 1, wherein the average wall thickness of each first multiplied pore channel is 2-3 μm.
4. The white-light neutron resonance photography detector of claim 2, wherein the deposition thickness of the boron material layer on the neutron-sensitive MCP is 0.5-2 μm.
5. The wide-energy spectrum white-light neutron resonance photography detector of claim 2, wherein a plurality of second multiplication pore channels are distributed on the common high-performance MCP; the common high-performance MCP and the neutron-sensitive MCP are arranged in a parallel superposition mode.
6. The wide-energy spectrum white-light neutron resonance photography detector of claim 1, wherein in the upper-layer anode strip array, each upper-layer rectangular conductive strip and an adjacent upper-layer insulation channel form an upper-layer array period; in the lower-layer anode strip array, each lower-layer rectangular conductive strip and an adjacent lower-layer insulating channel form a lower-layer array period;
the width of the upper layer array period is equal to that of the lower layer array period;
the width of the upper layer rectangular conductive strip is smaller than that of the lower layer rectangular conductive strip;
the width of the upper layer insulation channel is larger than that of the lower layer insulation channel.
7. The white-light neutron resonance photography detector of wide energy spectrum according to claim 1, wherein the gap between the position-sensitive anode strip array circuit board and the ordinary high-performance MCP is 1.5 mm.
8. The method for realizing the wide-energy spectrum white-light neutron resonance photography detection through the detector according to any one of claims 1 to 7 is characterized in that a neutron beam is emitted into the detector body from an incidence window, firstly reacts with boron in the neutron-sensitive MCP to generate charged particles, the charged particles excite electrons, the electrons drift to the position-sensitive anode strip array circuit board to form electric pulse signals after being subjected to electron cascade amplification generated by common high-performance MCP, and finally the electric pulse signals are output from the signal extraction electrode.
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| CN112255664B (en) * | 2020-10-23 | 2022-11-18 | 中国工程物理研究院激光聚变研究中心 | Microchannel type fast neutron image detector |
| CN113341453B (en) * | 2021-07-06 | 2022-12-13 | 散裂中子源科学中心 | White-light neutron imaging method and system for nuclide identification |
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