CN1434291A - Neutron phase contrast chromatographic imaging device - Google Patents

Abstract

The invention is a kind of neutron phase contrast chromatographic imaging equipment, including rotational platform, sparkling body, aluminium mirror, CCD camera, comuputer and camera bellows, the sparkling body, aluminium mirror and CCD camera placed in the camera bellows, and the neutron beam reaches the sample placed on the platform, the produced diffractive neutron makes vertical incidence and is received by the sparkling body and converted into the visible light with the sample information, which then is reflected onto the CCD camera by the aluminium mirror and after digital conversion inputted into the computer.

Description

Neutron phase contrast tomography device

Technical field:

The present invention relates to neutron phase contrast imaging technology, particularly a kind of neutron phase contrast tomography device.

Background technology:

In recent years, continuous development along with nuclear reactor art and accelerator neutron technology, neutron has obtained in a lot of fields to use very widely, particularly neutron chromatography imaging technique and neutron phase-contrast technique, can be used as a kind of effective tool of nondestructive test, can be used to study the three-dimensional density and the phase structure of object.

1. neutron phase contrast imaging technology

Perhaps be under the inspiration of X ray phase contrast imaging technology, an associating group of US and European, developed a kind of coaxial neutron phase contrast imaging method, they adopt cold neutron, corresponding de Brogile, wavelength is 0.433nm, successfully observes some details of leg joint and the wing of wasp.

We know, no matter are light wave or matter wave, when by object, produce scattering and absorption, from sample suitably distance will obtain absorption of sample contrast picture clearly, this is the imaging basis of conventional micro-and chromatography.

We know from X ray optics: the refractive index n of X ray _x=1-δ, δ=r ₀λ ²N _AtF/2 π, in the formula, λ is the X ray wavelength, r ₀Classical electron radius, N _AtAtomicity density in the unit volume, f is an atomic scattering factor.From neutron optics as can be known, the refractive index of neutron has the form identical with X ray, i.e. n _n=1-λ _n ²N (π of b ± p)/2, in the formula, N also is the proton number in the unit volume, and λ is a neutron wavelength, and b is the nuclear scattering coefficient, and p is because the magnetic scattering coefficient that electron spin causes.As can be seen from the above, two kinds of forms of refractive index n are almost consistent, for same wavelength, and neutron δ (λ _n ²N (b ± p)/2 π) is than the little magnitude of δ value of X ray.Although the difference of 1-δ and 1 has only 10 ^-6, but when using very little λ value, even the variation of not too big thickness or density also may produce sizable phase distortion.If when adopting coherent light or partially coherent light by object, except absorbing, also to produce phase change, the distortion of wavefront promptly takes place.This wavefront distortion causes the direction of propagation on part corrugated to change, make the corrugated overlapping and form to interfere, like this, phase change changes into Strength Changes, this is the physical basis of phase contrast imaging, also is the physical basis of phase contrast chromatography, what is more important, this image can directly obtain the phase change image without any reconfiguration technique.

The experimental provision of neutron phase contrast as shown in Figure 1.

The neutron beam that sends from neutron source 1 is after pin hole 2, becoming a spherical wave incides on the sample 3, at 31.8 meters of distance sample, place a detector 4, the phase contrast picture that just can obtain sample 3 (is seen technology formerly: B.E.Allman, P.J, McMahon etc., Nature, 2000, Vol408,9Nov.)

The shortcoming of said method is: the distributed in three dimensions that can not provide phase information in the sample.

2. neutron tomography

When neutron beam by attenuation coefficient mu, when thickness is the medium of l, Bill (Beer) law is followed in its decay

I＝I ₀exp(-μl)

When object when the projecting direction attenuation coefficient is inhomogeneous, line integral should be arranged: $I=I_0\exp [-{\∫}_{-\∞}^{+\∞}\mathrm{\μ}\left(l\right)\mathrm{dl}]$

When medium not only at projecting direction, and when the vertical direction of projection was also inhomogeneous, following formula became $I_{\mathrm{\φ}}\left(x_r\right)=I_0\exp [-{\∫}_{-\∞}^{+\∞}\mathrm{\μ}(x_r,y_r){\mathrm{dy}}_r]$

Taken the logarithm in the following formula both sides, make the equation linearization, obtain new function: ${\mathrm{\λ}}_{\mathrm{\φ}}=-\ln \frac{I_{\mathrm{\φ}}\left(x_r\right)}{I_0}=\∫\mathrm{\μ}(x_r,y_r){\mathrm{dy}}_r$

The chromatography task is exactly with measured λ _φ(x _r) remove to obtain μ (x _r, y _r) distribution.Effort through several algebraists has developed various methods.Usually carry out image restoration with following two kinds of methods:

Δ algebraic approach: comprise process of iteration, return sciagraphy

Δ analytical method: comprise that La Dongfa, Fourier filtering method, convolution method, filtering returns sciagraphy etc.

An interesting phenomenon is, the absorption coefficient of hard X ray constantly increases along with the increase of atomic number, neutron beam but can not, except that several elements, beyond hydrogen, lithium, boron, cadmium, the absorption coefficient of neutron is well below hard X ray.

For most of heavy metal, the X ray penetration depth is restricted, and neutron really fully develops talents, and from certain meaning, neutron chromatography and X ray chromatography are to replenish mutually.What will propose especially is that protium has bigger absorption to neutron.Therefore, the neutron chromatography is to the detection of some hydrogeneous organic materials, very sensitive as the O-ring seal in: lubricating oil, plastics, the metal shell etc., to some complexity, require very harsh, be used on the automobile industry and the large-scale heavy metal element of aerospace industry, the neutron chromatography is also very valuable.

Neutron chromatography experimental provision

The experimental provision synoptic diagram as shown in Figure 2, parallel neutron beam 1 incides on the sample 3, sample 3 places on the rotatable platform 9, neutron is used scintillator 4[Z after absorption of sample _nS (Ag)- ⁶ZiF] projection value under the recorder different angles.Neutron of every incident, scintillator 4 will be converted to the cascade photon, reflex on the CCD camera 6 through aluminium mirror 5 then, being input to computing machine 7 gets on, read after the signal that comes from the CCD camera 6 when computing machine, control rotatable platform 9 rotates an angle, carries out the exposure of next round neutron beam.For fear of the influence of scattered light to CCD, scintillator 4, aluminium mirror 5 and CCD camera 6 all are placed in the camera bellows 8.

After obtaining enough data for projection, computing machine will provide the whole sample image (referring to technology: S.Koerner formerly, B.Schillinger, et al., " A neutron to mography facility at alow power researcu reactor ", Nuclear Instruments ﹠amp; Methods in PhysicsResearch, 2001, A471,69-74.)

The disadvantage of this chromatography is:

(1) can not provide the three-dimensional spatial distribution of sample meta phase;

(2) if two elements that absorption coefficient is close, this method is difficult to differentiate, for example for the test of biological tissue, poor contrast, resolution is low.

Summary of the invention:

The technical problem to be solved in the present invention is, overcomes the defective of above-mentioned prior art, proposes a kind of neutron phase contrast tomography device, the phase information of testing sample can be changed into strength information, and particularly three-dimensional phase structure and distribution reconstruct thereof are come out.Technical solution of the present invention is as follows:

A kind of neutron phase contrast tomography device, comprise rotatable platform, scintillator, aluminium mirror, CCD camera, computing machine and camera bellows, said scintillator, aluminium mirror and CCD camera are placed in the camera bellows, neutron beam incides on the sample that is placed on the rotatable platform, and neutron is received by scintillator by the diffraction neutron vertical incidence that sample produces, be converted into the visible light that contains sample message, entered on the CCD camera by the aluminium mirror reflection, be transferred to computing machine after the digitizing, be characterized in:

1. before rotatable platform, also be provided with the monochrome focusing instrument that aluminum single crystal orthogonal placement, that have certain curvature and aluminum single crystal constitute;

2. the step motor of described rotatable platform is subjected to the instruction of computing machine and rotates, and drives rotatable platform rotation or upper and lower motion.

Described CCD camera is placed in the liquid nitrogen.

The radius-of-curvature range of choice of described aluminum single crystal is generally at 50～100 meters.

Described aluminium mirror is on the aluminium film on 2 millimeters glass substrates, is coated with that layer protecting film constitutes.

Described neutron beam (1) is from the radiation of fission reactor neutron source, and through the neutron beam of collimating apparatus outgoing, and this collimating apparatus is actually one and has that the steel box of rectangle or round section or steel cylinder constitute, and described collimating apparatus is that the ratio of length L and bore D is L/D ≈ 100.

Advantage of the present invention is:

(1) this neutron phase contrast tomography device has had both the advantage separately of phase contrast and chromatography, and the three dimensions position of energy high resolving power ground reconstruct testing sample distributes mutually.

(2) can test and differentiate the space structure of the very close sample of absorption coefficient, this point is very estimable.This is highly beneficial for biological tissue.

(3) do not adopt interferometry can measure the three-dimensional position phase-space distributions of sample.

Description of drawings:

Fig. 1 is the neutron contrast unit synoptic diagram in the technology formerly

Fig. 2 is the neutron chromatographic apparatus schematic diagram in the technology formerly

Fig. 3 is a neutron phase contrast tomography device synoptic diagram of the present invention

Embodiment:

See also Fig. 3 earlier.As seen from the figure, neutron diffraction laminated imaging device of the present invention is by neutron beam 1, aluminum single crystal 16,17, and rotatable platform 9, scintillator 4, aluminium mirror 5, CCD camera 6, computing machine 7 and camera bellows 8 are formed.

Parallel neutron beam 1 is after the monochromatic focuser monochromatization that a pair of aluminum single crystal 10,11 forms, incide on the sample 3 that is placed on the rotatable platform 9, neutron by the sample diffraction after, the scintillator 4 that diffracted signal is placed in the camera bellows 8 receives, and change into the visible light that contains sample message, reflexed on the CCD camera 6 by aluminium mirror 5, digitizing is input to computing machine 7 later on, carries out digital reconstruction by computing machine.

Said neutron beam 1 is from the radiation of fission reactor neutron source, and through the neutron of collimating apparatus outgoing.This fission reactor neutron source is that fissioners such as uranium and plutonium are made fuel, with the neutron is media, keep the device of controlled chain reaction of nuclear fission, be called fission reactor, this device can obtain high-throughout neutron irradiation, can reach for 1013～1020 neutron number/seconds, can long-time running, and by a steel box or a steel cylinder collimation with rectangle or round section, the neutron of outgoing from collimating apparatus, its divergence equals the ratio of aperture and length, obviously as long as reduced bore and increase length can be improved divergence greatly, obtains the quasi-parallel neutron beam.

Said aluminum single crystal 10 and aluminum single crystal 11, orthogonal placement mutual group monochromatizing focuser, owing to have certain curvature, therefore its R=100m had both had dispersion interaction, and focusing function is arranged again.During 10 one-tenth grazing angle θ of parallel incident neutron bundle 1 and aluminum single crystal, produce bragg reflection, when aluminum single crystal 11 during with aluminum single crystal 10 vertical placement, it can become a focus with the line that aluminum single crystal 10 focuses on, i.e. the astigmatism of usefulness aluminum single crystal 11 correction aluminum single crystals 10.Monochromatic neutron beam 1 enters into after the testing sample 3, and the diffraction that has only specific incident angle θ just to satisfy cloth loudspeaker lattice formula is strengthened.Therefore, by the selection of incident angle θ, can select that different elements carry out tomography in the sample.

Said rotatable platform 9 is subjected to the driving of a step motor (not shown) and rotatablely moves, and testing sample 3 is placed on this rotatable platform 9 and also rotatablely moves simultaneously.

Said scintillator 4 is ZnS (Ag)-LiF.Because neutron can not directly cause the ionization of atom in material, there is not electric current output, so adopt ZnS (Ag)-LiF among the present invention.The diffraction neutron beam that produces in the sample 3 impinges perpendicularly on the screen of scintillator 4, and each neutron produces the cascade optical photon.

Said aluminium mirror 5 is used for the visible light that scintillator 4 produces is reflexed to CCD camera 6, and CCD camera 6 is commerce CCD.

The course of work of apparatus of the present invention is roughly as follows:

One quasi-parallel neutron beam 1 is after aluminum single crystal 10,11 focusing and monochromatization, incide on the sample 3 that is placed on the rotatable platform 9, the neutron of outgoing is received by scintillator 4, and change into the visible light that contains sample message, reflex to through aluminium mirror 5 and to be placed on the CCD camera 6 that cools off in the liquid nitrogen, be input to after the digitizing on the computing machine 7.When computing machine 7 is received signal, drive step motor, drive rotatable platform 9 exposes automatically next time, up to finishing one-period, promptly on a section, finish the sampling in 0～180 °, afterwards rotatable platform 9 is driven sample 3 and do motion up or down, enter another section, repeat above-mentioned test, carry out digital reconstruction at last, obtain the three-dimensional position phase distribution plan of sample 3.

The neutron beam of sample 3 outgoing impinges perpendicularly on the screen of scintillator 4, scintillator be ZnS (Ag)- ⁶LiF.Each neutron produces cascade optical photon, reflexes on the CCD camera 6 through aluminium mirror 5, and aluminium mirror 5 is to select thickly to make the sheet base for the glass plate of 2mm; on the aluminium film, be coated with layer protecting film; select the purpose of aluminium mirror to be, do not allow neutron beam be directly incident on the chip of CCD camera 6, in order to avoid chip is damaged.In order to reduce the dark current of CCD camera 6, put it in the liquid nitrogen and cool off, this is extremely important for the experiment of using low neutron flux, time exposure, scintillator 4, aluminium mirror 5 and CCD camera 6 will be placed in the magazine 8, in order to avoid spuious visible light influences test data.Rotate rotatable platform 9, record each sample different section the position mutually after, be reconstructed with regard to available computers.

Among the present invention, neutron phase contrast tomography system also can be used for carrying out neutron phase contrast and the research of neutron tomography, there is very application prospects in this system at aspects such as biomedicine, material structure, archaeology, space flight and aviation, cosmochemistry and weapon industries, this new technology, new method provide a strong tool for people explore the new natural law.

Claims (5)

1, a kind of neutron phase contrast tomography device, comprise rotatable platform (9), scintillator (4), aluminium mirror (5), CCD camera (6), computing machine (7) and camera bellows (8), said scintillator (4), aluminium mirror (5) and CCD camera (6) are placed in the camera bellows (8), neutron beam (1) incides on the sample (3) that is placed on the rotatable platform (9), the diffraction neutron vertical incidence that neutron is produced by sample (3), received by scintillator (4), be converted into the visible light that contains sample message, entered on the CCD camera (6) by aluminium mirror (5) reflection, be transferred to computing machine (7) after the digitizing, it is characterized in that:

1. also be provided with the monochromatic focuser of aluminum single crystal orthogonal placement, that have certain curvature (10) and aluminum single crystal (11) formation before at rotatable platform (9);

The step motor of 2. described rotatable platform (9) is subjected to the instruction of computing machine (7) and rotates, and drives rotatable platform (9) rotation or upper and lower motion.

2, neutron phase contrast tomography device according to claim 1 is characterized in that described CCD camera is placed in the liquid nitrogen.

3, neutron phase contrast tomography device according to claim 1, the radius-of-curvature range of choice that it is characterized in that described aluminum single crystal (10,11) is generally at 50～100 meters.

4, neutron phase contrast tomography device according to claim 1 is characterized in that described aluminium mirror (5) is on the aluminium film on 2 millimeters glass substrates, is coated with that layer protecting film constitutes.

5, neutron phase contrast tomography device according to claim 1, it is characterized in that described neutron beam (1) is from the radiation of fission reactor neutron source, and through the neutron beam of collimating apparatus outgoing, this collimating apparatus is actually one and has that the steel box of rectangle or round section or steel cylinder constitute, and described collimating apparatus is that the ratio of length L and bore D is L/D ≈ 100.

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