CN103245680A - Fast neutron imaging method and system based on time-of-flight method - Google Patents
Fast neutron imaging method and system based on time-of-flight method Download PDFInfo
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- CN103245680A CN103245680A CN2013101664490A CN201310166449A CN103245680A CN 103245680 A CN103245680 A CN 103245680A CN 2013101664490 A CN2013101664490 A CN 2013101664490A CN 201310166449 A CN201310166449 A CN 201310166449A CN 103245680 A CN103245680 A CN 103245680A
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Abstract
The invention relates to a fast neutron imaging technology, and in particular relates to a fast neutron imaging method and system based on a time-of-flight method. The method comprises the steps that: a plurality of scintillant units form a scintillant array to enable the scintillant array to be coupled with a position sensitive detector; the whole coupled detector array is arranged away from a neutron source; a sample is arranged close to the neutron source; the measurement is performed by using the neutron time-of-flight method; interference factors are eliminated by using a conforming method to obtain effective counting on each scintillant unit detector; and the effective counting on each scintillant unit detector is arrayed to obtain a two-dimensional image in which only acting source neutrons acts. The method and the system adopt a detector array design mode, so that the detection efficiency is improved; and the time-of-flight method measurement mode can effectively remove scattered sample neutrons, an environment diffuse scattering background and a gamma background, and a signal-to-noise ratio is increased.
Description
Technical field
The present invention relates to the fast neutron imaging technique, be specifically related to a kind of fast neutron formation method and system and device based on time-of-flight method.
Background technology
The fast neutron imaging technique is the important supplement means of x radial imaging and thermal neutron imaging as a kind of important Dynamic Non-Destruction Measurement, is current radial imaging technical research hot topic.The emphasis of foreign study concentrates on and improves the neutron source strength, develops new aspects such as imaging technique.Rfq accelerator is adopted in U.S. Lao Lunsiliwo More laboratory, windowless gas target, and the DD neutron yield reaches 10
12N/s surpasses 100g/cm to surface density
2The big article position resolution reach a millimeter magnitude.The about 0.8 millimeter moisture defective of the distinguishable 1.25 cm thick alloy body inside diameters of laboratory, Argonne fast neutron imaging system.The fast neutron formation method presents variation, and the transmission damped method is not only arranged, and has also developed scattering method, and fast neutron resonance image-forming method etc. are utilized as German PTB fast neutron imaging device
9(d, n) reaction neutron source and " resonance " method are chosen the different-energy neutron to the sample imaging to Be, can differentiate the Density Distribution information of multiple nucleic in the sample.Also have multiple ray formation method simultaneously, fast neutron imaging and γ/x imaging is carried out simultaneously, obtains 3-d photographs clearly through image reconstruction again, has remedied the careless omission that a kind of ray causes.Australia CSIRO has developed the model machine that is used for the fast neutron-γ imaging system of customs's safety check.
Though the fast neutron imaging technique can be applied to aspects such as safety check, national defence, industry, it can not get popularizing too widely all the time, even does not have industrial standard.This mainly contains two aspect problems: lack high current neutron source; Lack the measurement means of taking into account spatial resolution, detection efficiency and high s/n ratio.Existing fast neutron imaging research report show general during with the scintillator conversion screen best position resolution can reach about millimeter magnitude, but this moment, detection efficiency was generally less than 3%, image-forming principle has limited detector thickness, and the thickening detector can make position resolution reduce; Reach 10～100 micron dimensions (based on the MICROMEGAS/GEM technology) if fixed position is differentiated, detection efficiency is just lower, generally is lower than per mille.For thick sample measurement, scattered neutron and background composition are in the great majority, though traditional formation method touches the solution of far being far from being simultaneously.The fast neutron imaging technique lacks a kind of good measurement means at present in a word.
Summary of the invention
The present invention seeks to the defective at prior art, propose a kind of fast neutron formation method and system based on time-of-flight method, propose to adopt the mode of moulding sudden strain of a muscle detector array cooperation time-of-flight method to solve the imaging problem that spatial resolution is low under the existence conditions, detection efficiency is low and signal to noise ratio (S/N ratio) is low.
Technical scheme of the present invention is as follows: a kind of fast neutron imaging technique based on time-of-flight method, adopt polylith scintillator unit to form scintillator arrays, scintillator arrays and position sensitive photo-multiplier tube are coupled, whole detector after the coupling is arranged on apart from neutron source than distant positions, sample is arranged on apart from the neutron source closer locations, in the outside of collimating apparatus; Utilize the neutron time of flight method to measure, obtain the time of flight spectrum of each scintillator single-element detector, the power spectrum of each pixel is done the card threshold treatment, namely by access time window reject disturbing factor and obtain effective counting that the just source neutron on each scintillator single-element detector works, the effective counting on each scintillator single-element detector is obtained two dimensional image after by arrayed.
Fast neutron imaging system based on time-of-flight method, comprise the neutron source that places in the barrier shield, barrier shield is provided with the collimation duct, be provided with sample over against described collimating aperture road outlet closer locations, be provided with scintillator detector over against the outlet of described collimating aperture road than distant positions, wherein, described scintillator detector comprises by polylith scintillator unit forms scintillator arrays, scintillator arrays and position sensitive photo-multiplier tube coupling, the anode signal output terminal of each scintillator unit is connected with the data acquisition and processing (DAP) system.
Further, aforesaid fast neutron imaging system based on time-of-flight method, wherein said scintillator unit is the cube of 3mm * 3mm * 100mm, the face of a 3mm * 3mm and position sensitive photo-multiplier tube coupling, and all the other 5 faces cover or aluminium-plated film with aluminum coating.
Further, aforesaid fast neutron imaging system based on time-of-flight method wherein, uses small size position sensitive photo-multiplier tube or diode to form array as position sensitive detector.
Further, aforesaid fast neutron imaging system based on time-of-flight method, wherein, described sample target surface tangential direction arranges with the collimating apparatus axis parallel mode of direction.
Further, aforesaid fast neutron imaging system based on time-of-flight method, wherein, detector is exported fast signal and is converted to the flight time signal by the data acquisition and processing (DAP) system, and the discrimination threshold rejecting undesired signal by regulating, determine position of detector by address scrambler then, thereby realize two-dimensional imaging.
Beneficial effect of the present invention is as follows: scintillator detector of the present invention adopts the design of detector array, overcome the intrinsic indistinctness problem of a monoblock conversion screen detector, but also can lengthen the length of detector, realized improving the effect of detection efficiency; The time-of-flight method metering system can be removed sample scattering neutron, environment diffuse scattering background and γ background effectively, has improved signal to noise ratio (S/N ratio); According to the principle of the proportional amplification of geometric similarity triangle, sufficiently long flying distance can remedy the not good shortcoming of position resolution that each pixel dimension is brought greatly.
Description of drawings
Fig. 1 is the fast neutron imaging system principle schematic that the present invention is based on time-of-flight method;
Fig. 2 is how much amplification principle synoptic diagram of position resolution of the present invention;
Fig. 3 is the data acquisition system (DAS) synoptic diagram of detector array elements;
Fig. 4 is experiment measuring 14MeV neutron time of flight spectrum.
Among the figure, 1. pulsed neutron source 2. composite shielding bodies (heavy water mud wall) 3. collimate duct 4. testing samples and support 5. scintillator arrays, 6. position sensitive photo-multiplier tubes and rear end electronics element.
Embodiment
Below in conjunction with drawings and Examples the present invention is described in detail.
The present invention proposes to adopt the little scintillator of polylith to form detector array, the sensitive photomultiplier of scintillator arrays co-located is coupled, detector is placed on apart from neutron source than distant positions, sample is placed on apart from the neutron source closer locations, measure the time of flight spectrum of each probe unit, discrimination threshold is set again rejects disturbing factor and obtains effective counting on each detector, effectively count the two dimensional image that has only source neutron to work by just obtaining after the arrayed, play the purpose that effective inhibition background improves signal to noise ratio (S/N ratio).Do pixel cell with independent scintillator simultaneously and can improve detection efficiency, if with the scintillator of 10 centimeter length the 14MeV neutron is surveyed, efficient can surpass 20%, and this is that additive method is beyond one's reach.Long range measurements not only can effectively utilize the time-of-flight method (can be with reference to " atomic nuclear physics experimental technique ", the Atomic Energy Press, the third edition, p316), can also utilize geometrical principle to play amplification and improve position resolution, realize the position resolution of millimeter even submillimeter magnitude.
Based on the basic structure of the fast neutron imaging system of time-of-flight method as shown in Figure 1, pulsed neutron source 1 is shielded from 1 meter thick heavy water mud wall 2, utilize Cockcroft-Walton accelerator collimation duct 3 to realize the collimated neutron bean outgoing, sample 4 is placed on apart from the neutron source closer locations, and sample target surface tangential direction arranges with the collimating apparatus axis parallel mode of direction.Detector is scintillator arrays 5, and scintillator arrays 5 and position sensitive photo-multiplier tube 6 couplings are positioned at apart from neutron source than amphi position, use small size position sensitive photo-multiplier tube or diode to form array.Source neutron is got on the sample, have the part source neutron can be with sample effect off-energy change direction or repeatedly effect, also have part not act on neutron and continue rectilinear flight till be detected.Provide anode signal by scintillation detector this moment, provides the neutron time of flight spectrum after meeting with accelerator signal.The neutron time spectrum is very complicated, has both comprised source neutron information, also has sample scattering neutron information to also have surrounding environment diffuse scattering composition and follows γ.
Shown in Fig. 4 experiment measuring, determine the wherein source neutron peak counting of detector pixel by analysis of spectrum, this has expressed the source neutron counting that its this pixel receives, thereby has eliminated the interference of this background greatly.Be generalized to two-way detector array, can obtain the image of high s/n ratio, so this method has the ability to measure the slight crack of big thick interior of articles.
In the present embodiment, whole detector is made up of scintillator arrays, and each scintillator unit is cube, is of a size of 3mm * 3mm * 100mm, and the face that stays next 3mm * 3mm is with the coupling of photoelectricity multiplier tube, and other 5 cover or aluminium-plated film with thin aluminium foil.Each has done some benefit like this: do not have adjacent probe unit optical crosstalk; Can be because of the thick inherent unsharpness problem that causes of screen; Survey scintillator element thickness raising detection efficiency thereby can increase.Can form the array of 16 * 16=256 pixel in every position sensitive photo-multiplier tube.Scintillator arrays is pressed in the thin aluminum top framework, play the fixed installation effect, two facets of array (pixel 3mm * 3mm face) are empty, accept the neutron end and can reduce diffuse transmission influence, do not plate aluminium foil surface and directly be coupled with silicone oil with the photoelectricity multiplier tube, and with support fixedly array and photomultiplier.
In order to improve position resolution, according to test its principle isosceles triangle as shown in Figure 2 as Fig. 1 mode.Because the collimation effect of body of wall collimating apparatus is fine, sample is far away relatively apart from neutron source, is similar to think the point source outgoing.In Fig. 2, sample 4 distance sources are made as 1 meter, and detector array 5 is 6 meters to the distance in source, according to similar triangle theory, the slight crack at sample place amplifies 6 times at detector place measurement size, and each flicker unit size is 3 millimeters, so can measure 0.5 millimeter slight crack.
Data acquisition modes of the present invention adopts special electronic to finish into, as shown in Figure 3, owing to will use the flight time method, the Back end data acquisition system needs time spent width of cloth metering circuit, and the threshold discriminator is set, provides the probe unit numbering by address scrambler simultaneously.Concrete thinking is as follows: each scintillator unit output anode signal enters discriminator, select suitable threshold of detectability output, two logical signals of each signal output, one of them is given scrambler and does geocoding, another realizes many group signal plus for " logical OR " unit, width of cloth converter was made commencing signal when signal was given after the addition, the time width of cloth converter stop signal provided by accelerator pulse bundle pickoff signals, thereby obtain many group detectors " or " the neutron time of flight spectrum, its amplitude is represented the time, by the time width of cloth converter output result and do later stage Cartridge threshold treatment, obtain having only source neutron time of flight spectrum event information.Position encoded information is provided by scrambler, the count information behind the cooperation time of flight spectrum card threshold, thus realize two-dimensional detection.The line construction of data acquisition and processing (DAP) system as shown in Figure 3.
Because excessive phenomenon of dead time far can not appear in detection range, is 10 by source strength
10/ s calculates, 6 meters far ultraviolet detection efficiencys 20%, and the about 4Hz of each detector per second 14MeV neutron count rate calculates each probe unit per second 20Hz counting rate according to signal to noise ratio (S/N ratio) 1:4.Whole detectors about 5000Hz that adds up, rear end electronics is enough handled.Because signal to noise ratio (S/N ratio) will improve greatly after utilizing time-of-flight method, each probe unit statistical counting only needs hundreds of just can satisfy the error needs, supposes that the effective counting rate of each probe unit is 4Hz, only needs a few minutes just can test and finishes one group.
Obviously, those skilled in the art can carry out various changes and modification to the present invention and not break away from the spirit and scope of the present invention.Like this, if of the present invention these are revised and modification belongs within the scope of claim of the present invention and equivalent technology thereof, then the present invention also is intended to comprise these changes and modification interior.
Claims (6)
1. fast neutron imaging technique based on time-of-flight method, it is characterized in that: adopt polylith scintillator unit to form scintillator arrays, scintillator arrays and position sensitive photo-multiplier tube are coupled, whole detector after the coupling is arranged on apart from neutron source than distant positions, sample is arranged on apart from the neutron source closer locations, utilize the neutron time of flight method to measure, obtain the time of flight spectrum of each scintillator single-element detector, the power spectrum of each pixel is done the card threshold treatment, by access time window reject disturbing factor and obtain effective counting on each scintillator single-element detector, the effective counting on each scintillator single-element detector is obtained the two dimensional image that source neutron just works after by arrayed.
2. fast neutron imaging system based on time-of-flight method, comprise the neutron source that places in the barrier shield, barrier shield is provided with the collimation duct, be provided with sample over against described collimating aperture road outlet closer locations, be provided with scintillator detector over against the outlet of described collimating aperture road than distant positions, it is characterized in that: described scintillator detector comprises by polylith scintillator unit forms scintillator arrays, scintillator arrays and position sensitive detector coupling, the anode signal output terminal of each scintillator single-element detector is connected with the data acquisition and processing (DAP) system.
3. the fast neutron imaging system based on time-of-flight method as claimed in claim 2, it is characterized in that: described scintillator unit is the cube of 3mm * 3mm * 100mm, the face of a 3mm * 3mm and position sensitive detector coupling, all the other 5 faces cover or aluminium-plated film with aluminium foil.
4. as claim 2 or 3 described fast neutron imaging systems based on time-of-flight method, it is characterized in that: use small size position sensitive photo-multiplier tube or diode to form array as position sensitive detector.
5. the fast neutron imaging system based on time-of-flight method as claimed in claim 2, it is characterized in that: described sample target surface tangential direction arranges with the collimating apparatus axis parallel mode of direction.
6. the fast neutron imaging system based on time-of-flight method as claimed in claim 2, it is characterized in that: detector is exported fast signal and is converted to the flight time signal by the data acquisition and processing (DAP) system, and the discrimination threshold rejecting undesired signal by regulating, determine position of detector by address scrambler then, thereby realize two-dimensional imaging.
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN104237270A (en) * | 2014-09-26 | 2014-12-24 | 同方威视技术股份有限公司 | Method and device for imaging object through photoneutron transmission |
| CN104502756A (en) * | 2014-12-16 | 2015-04-08 | 华南理工大学 | Electric energy quality detection method on basis of generalized morphological open-close and close-open wavelet transform |
| CN105988132A (en) * | 2014-09-23 | 2016-10-05 | 中国科学技术大学 | X-ray detector and packaging method thereof |
| CN106226339A (en) * | 2016-09-20 | 2016-12-14 | 清华大学 | Neutron produces equipment, neutron imaging equipment and formation method |
| CN109581474A (en) * | 2018-12-28 | 2019-04-05 | 中国原子能科学研究院 | The overlapping time window detection method of associated particle neutron detection |
| CN113456094A (en) * | 2021-07-02 | 2021-10-01 | 戴建荣 | Method for acquiring port images in time synchronization mode |
| CN114660096A (en) * | 2022-04-14 | 2022-06-24 | 中国工程物理研究院材料研究所 | Method for testing thermal neutron shielding performance of material |
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Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105988132A (en) * | 2014-09-23 | 2016-10-05 | 中国科学技术大学 | X-ray detector and packaging method thereof |
| CN104237270A (en) * | 2014-09-26 | 2014-12-24 | 同方威视技术股份有限公司 | Method and device for imaging object through photoneutron transmission |
| CN104502756A (en) * | 2014-12-16 | 2015-04-08 | 华南理工大学 | Electric energy quality detection method on basis of generalized morphological open-close and close-open wavelet transform |
| CN106226339A (en) * | 2016-09-20 | 2016-12-14 | 清华大学 | Neutron produces equipment, neutron imaging equipment and formation method |
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| CN109581474A (en) * | 2018-12-28 | 2019-04-05 | 中国原子能科学研究院 | The overlapping time window detection method of associated particle neutron detection |
| CN109581474B (en) * | 2018-12-28 | 2020-12-22 | 中国原子能科学研究院 | Method for detecting overlapping time windows accompanied by particle neutron detection |
| CN113456094A (en) * | 2021-07-02 | 2021-10-01 | 戴建荣 | Method for acquiring port images in time synchronization mode |
| CN113456094B (en) * | 2021-07-02 | 2023-11-21 | 戴建荣 | Method for collecting port images in time synchronization mode |
| CN114660096A (en) * | 2022-04-14 | 2022-06-24 | 中国工程物理研究院材料研究所 | Method for testing thermal neutron shielding performance of material |
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Application publication date: 20130814 |