JP4806742B2 - Magnetic field generator and nuclear magnetic resonance apparatus - Google Patents

Description

  The present invention relates to a magnetic field generator and a nuclear magnetic resonance apparatus using the same. More particularly, the present invention relates to a magnetic field generator that generates a strong static magnetic field with a uniform distribution comparable to that of a conventional superconducting magnet without using liquid helium, and a nuclear magnetic resonance apparatus using the same.

  The applicant of the present invention has previously proposed a nuclear magnetic resonance apparatus including a magnetic field generation apparatus using a superconducting bulk body (see Patent Document 1). This nuclear magnetic resonance apparatus magnetizes a cup-shaped superconducting bulk body having a hollow cylindrical shape or a hollow cylindrical portion cooled in a vacuum heat insulating container to a temperature not higher than the superconducting transition temperature in the axial direction. A magnetic field generator that generates a static magnetic field in the direction of the cylindrical axis is used to detect an NMR signal of an object to be measured in the magnetic field with a detection coil and a spectrometer.

  In such a magnetic field generator, a magnetic field is generated by utilizing the property that a massive superconducting bulk body retains a magnetic flux provided by a pinning effect. This pinning effect is mainly due to the presence of fine insulating phase particles dispersed in the superconducting phase. The finer the insulating phase particles, the higher the insulating phase particles below a certain limit, the higher the effect. . Also, the stronger the pinning effect, the higher the critical current density. Ideally, if the applied magnetic field is uniform, the captured magnetic field is also uniform within a certain range, and the current distribution is automatically maintained in the magnetized superconducting bulk to maintain such a magnetic field distribution. It is formed. However, in reality, a phenomenon called creep (called magnetic flux creep) occurs in which the trapped magnetic flux gradually moves and the magnetic field decreases, and the magnetic field distribution changes. Since the magnetic flux creep increases as it approaches the both ends of the superconducting bulk body in the axial direction, the distribution of the trapped magnetic field is generally strongest near the center in the axial direction of the cylindrical shape and weakens as it approaches both ends.

  For this reason, the uniformity of the magnetic field necessary for the observation of the conventional NMR signal cannot be obtained, or the range becomes narrow. In a nuclear magnetic resonance apparatus equipped with such a magnetic field generator, the spectrum width of the NMR signal of the object to be measured placed in the magnetic field is widened, and as shown in FIG. There was a problem that the sensitivity and resolution decreased with the passage of time.

FIG. 11 shows a superconducting bulk of a hollow cylinder having an outer diameter of 60 mm, an inner diameter of 10 mm, and a thickness of 40 mm by laminating two Gd-Ba-Cu-O-based Gd-based superconducting bulk bodies G0 and G0. It is a conceptual diagram which shows the distribution of a static magnetic field when forming the body 120 (refer FIG. 10) and magnetizing this superconducting bulk body 120 in a predetermined procedure. The horizontal axis in FIG. 11 is the position of the hollow cylindrical portion 120a in the axial direction, and the vertical axis indicates the magnetic field strength at that position. The magnetic field distribution immediately after magnetization indicated by the solid line F is high at the central portion C in the axial direction and decreases toward both ends. As time passes, the magnetic field distribution changes from a solid line to a broken line and further to a dotted line due to magnetic flux creep. As can be seen from FIG. 11, in the superconducting bulk body 120, the decrease in the magnetic field strength at the central portion C is small, but the decrease in the magnetic field strength at both ends is large. For this reason, the uniform range of the magnetic field intensity was narrowed, and when the proton NMR spectrum was measured in such a magnetic field, the peak width was about 20 ppm, which did not show satisfactory sensitivity and resolution.
Japanese Patent Laid-Open No. 2002-6021

  The present invention has been made to solve the above problems, and provides a magnetic field generator having a wide uniform magnetic field range near the central portion of a superconducting bulk body, and using it, the peak width of an NMR signal is provided. It is an object of the present invention to provide a nuclear magnetic resonance apparatus having a narrow, high sensitivity and high resolution.

In a high temperature superconducting material, a material having a higher critical temperature (Tc) has a higher critical current density (Jc). More specifically, when the superconducting bulk body is an oxide superconducting bulk body whose main component can be represented by RE-Ba-Cu-O, the ionic radius of RE (average ionic radius in the case of a mixed system) is The larger the value, the higher the critical temperature (Tc), and the smaller the value of δ in the superconducting phase REBa ₂ Cu ₃ O _7- δ (0 <δ <1), the higher the critical temperature (Tc). The critical current density (Jc) also changes depending on the amount and particle size of the insulating phase that becomes the pinning point. The smaller the particle size of the insulating phase, or the larger the amount of insulating phase within a predetermined limit, the more critical It is known that the current density (Jc) is high.

  It is also known that the high temperature superconducting material has a higher critical current density (Jc) as the temperature is lower.

  The inventor has paid attention to the fact that the object can be achieved by changing these elements between both ends and the center of the superconducting bulk material. That is, a combination of a plurality of superconducting bulk bodies having different characteristics, a superconducting bulk body having partially different characteristics, or a partial temperature difference in the superconducting bulk body during magnetization. It is to give.

  That is, in the magnetic field generator using the cylindrical superconducting bulk as described above, in order to reduce the magnetic flux creep and increase the uniform magnetic field range, the magnetic field distribution at both ends is higher than that at the center. If magnetized so as to be captured, a wide uniform magnetic field can be maintained even if magnetic flux creep occurs.

A magnetic field generator according to the present invention generates a magnetic field in a hollow portion of a superconducting bulk body by capturing the magnetic field in a hollow cylindrical superconducting bulk body cooled to a superconducting transition temperature or lower in a vacuum vessel. in the superconducting bulk body, the opposite axial ends of the superconducting bulk body is trapped magnetic field in a state not critical current density is higher than the axial center portion, the magnetic field strength after magnetization axial central portion It is characterized in that the axial both ends show a higher magnetic field distribution .

  A magnetic field generator of the present invention includes a hollow cylindrical superconducting bulk body that is magnetized at a superconducting transition temperature or less and captures a magnetic field in the center, a cooling device that cools the superconducting bulk body, and a superconducting bulk. It is desirable to provide a vacuum container for housing the body.

  As a preferred embodiment of the magnetic field generator of the present invention, the superconducting bulk body is made of a material having a critical temperature higher at both ends of the superconducting bulk body than at the central portion.

  Moreover, the other preferable aspect of the magnetic field generator of this invention has a temperature control means which makes both ends temperature lower than a center part, when magnetizing a superconducting bulk body. Such temperature adjusting means is desirably a heater for heating the central portion or a cooling member for sandwiching the superconducting bulk body and cooling both ends thereof.

  Here, the superconducting bulk material is an oxide superconductor whose main component can be represented by RE-Ba-Cu-O, and contains one or more of silver, platinum, or cerium in an amount of 0 to 50 mass%, RE is yttrium (element symbol Y), samarium (Sm), lanthanum (La), neodymium (Nd), europium (Eu), gadolinium (Gd), erbium (Er), ytterbium (Yb), dysprosium (Dy), holmium (Ho) is a combination of at least one or two or more of them, and has a superconducting phase having a superconducting transition temperature of 90 ° K to 96 ° K in absolute temperature and an insulating allotrope in the super conducting phase. It is preferable to include a structure dispersed with a particle size of 50 μm or less, desirably 10 μm or less.

  In the magnetic field generator of the present invention, the superconducting bulk body can be made of a material containing an element having an average ionic radius of the RE larger than that of the central portion at both ends of the superconducting bulk body. Alternatively, the superconducting bulk body may be made of a material including an insulating phase in which both end portions of the superconducting bulk body have an average particle size smaller than that of the central portion. It is also possible to configure the both ends of the material with a material having a larger volume fraction of the insulating phase than the central portion. In such a superconducting bulk body, the thickness of the central portion is preferably 30 to 70% when the thickness of the entire superconducting bulk body is 100%.

A nuclear magnetic resonance apparatus of the present invention includes a hollow cylindrical superconducting bulk body that is magnetized at a superconducting transition temperature or less and traps a magnetic field in a hollow portion, a cooling apparatus that cools the superconducting bulk body, and the superconducting apparatus. A magnetic field generator including a vacuum container that accommodates a bulk body, and a detection coil that detects an NMR signal of an object to be measured inserted into a hollow portion of the superconducting bulk body, the superconducting bulk body comprising: the axial ends of the superconducting bulk body is trapped magnetic field in a state not high critical current density than the central portion in the axial direction, is more field strength after magnetization of both axial ends than the central portion in the axial direction It is characterized by showing a high magnetic field distribution . The magnetic field generator in the nuclear magnetic resonance apparatus of the present invention is preferably the magnetic field generator of the present invention described above.

  According to the magnetic field generator of the present invention, when a superconducting bulk body captures a magnetic field in a state where the critical current density at both ends is high, both ends of the superconducting bulk body have a higher magnetic field distribution than the central portion. Become. For this reason, even if magnetic flux creep occurs, the magnetic field distribution having a higher peak than the central portion can be maintained at both ends, so that the uniformity of the magnetic field in the vicinity of the central portion is improved.

  Therefore, the nuclear magnetic resonance apparatus of the present invention can use a magnetic field having a wide uniform range as described above, and therefore can improve sensitivity and resolution as compared with the conventional technique.

  Also, in the case of magnetic field distribution with a shape that is lower in the center than at both ends, it is easy to increase the uniformity of the magnetic field distribution by placing a coil in the center, so when using as a high-resolution nuclear magnetic resonance apparatus A necessary correction coil can be easily manufactured, and a nuclear magnetic resonance apparatus having higher resolution can be provided.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(1) First Embodiment of Magnetic Field Generating Device FIG. 1 is a diagram showing the overall configuration of the nuclear magnetic resonance apparatus 1 of the present invention, and the range of the dotted line is the magnetic field generating apparatus 10 of the preferred embodiment of the present invention. is there.

  In the magnetic field generator 10, the superconducting bulk body 20 is accommodated in a vacuum vessel 22 and connected to the cooling unit 23 of the pulse tube refrigerator 25 through a copper rod. By using the pulse tube refrigerator 25 as a cooling device, the vibration of the superconducting bulk body 20 can be reduced and the influence on the NMR signal can be suppressed.

  The vacuum vessel 22 containing the superconducting bulk body 20 is disposed in the hollow portion of the superconducting magnet 28 that applies a magnetic field to the superconducting bulk body 20 so that the axis of the superconducting bulk body 20 matches the center of the magnetic field. ing.

  The vacuum vessel 22 can be evacuated by a vacuum pump 24, and the superconducting bulk body 20 can be cooled below its critical temperature by the pulse tube refrigerator 25 by operating the compressor 26.

  In the magnetic field generation device 10 having such a configuration, the superconducting bulk body 20 is applied with the magnetic field generated by the superconducting magnet 28, and the superconducting bulk body 20 is cooled to a predetermined temperature below the critical temperature and held. Thereafter, the magnetic field generated by the superconducting magnet 28 is gradually decreased and finally set to 0, whereby the superconducting bulk body 20 can be magnetized. Then, the temperature of the superconducting bulk body 20 can be further lowered to the operating temperature by the pulse tube refrigerator 25, and a uniform and strong static magnetic field can be generated in the axial direction in the hollow portion of the superconducting bulk body 20. That is, the superconducting bulk body 20 captures the magnetic field by the pinning effect, and a magnetic field of almost the same magnitude as the superconducting magnet 28 is initially generated is maintained in the space of the hollow cylindrical portion 20a. is there.

  In the magnetic generator as described above, in the first embodiment, as will be described in detail in specific examples 1 to 5 described later, the superconducting bulk body 20 is divided into a plurality of superconducting bulk bodies (S, G) having different characteristics. , D, etc.), and a superconducting bulk body having a critical temperature Tc higher than that of the central superconducting bulk body is disposed and laminated at both ends of the superconducting bulk body 20.

(Specific example 1)
Specific example 1 is superconducting bulk body 201 shown in the schematic cross-sectional view of FIG. 2, and is configured to sandwich superconducting bulk body G with superconducting bulk body S. The superconducting bulk body 201 is composed of two superconducting bulk bodies S and one superconducting bulk body G. The superconducting bulk body S is an Sm-based material mainly composed of Sm, Ba, Cu, and O. It is a superconducting bulk body and is a hollow cylinder (perforated disk shape) having an outer diameter of 60 mm, an inner diameter of 10 mm, and a thickness of 10 mm. The superconducting bulk body G is a Gd-based superconducting bulk body mainly composed of Gd, Ba, Cu, and O, and is a hollow cylinder (perforated disk shape) having an outer diameter of 60 mm, an inner diameter of 10 mm, and a thickness of 20 mm. is there. Since the ionic radius of the Sm system is larger than that of the Gd system, the critical temperature (Tc) is high, and the critical current density (Jc) is high even at the same temperature. These were laminated in the order of superconducting bulk body S-superconducting bulk body G-superconducting bulk body S in the axial direction as shown in FIG. 2 to form a hollow cylinder having an outer diameter of 60 mm × inner diameter of 10 mm × thickness of 40 mm.

  The superconducting bulk body 201 is placed in the vacuum container 22 of FIG. 1, the vacuum container 22 is evacuated, and the superconducting bulk body 201 is placed in the magnetic field generated by the 3T superconducting magnet 28 by the pulse tube refrigerator 25 to 50K. Cooled to. Thereafter, the generated magnetic field of the superconducting magnet 28 was gradually decreased to finally become 0, and the superconducting bulk body 201 was further lowered to 40 K, which is the lowest temperature reached by the refrigerator.

  The distribution of the magnetic field in the direction of the axis L in the hollow portion 20a of the superconducting bulk body 201 magnetized as described above was measured with a gauss meter. The results are shown in FIG. In FIG. 3, the horizontal axis represents the measurement position in the direction of the axis L, and the vertical axis represents the magnetic field strength at that position. The solid line a is the magnetic field distribution immediately after magnetization, the broken line i is the magnetic field distribution during the magnetic flux creep, and the dotted line u shows the magnetic field distribution when the magnetic flux creep has almost ended.

  In the superconducting bulk body 201, a magnetic field distribution having peaks P at both ends (superconducting bulk body S) is formed immediately after magnetization as shown in FIG. 3, and the magnetic fields at both ends (S) are reduced by magnetic flux creep. Even so, it can be seen that the strength of the magnetic field in the central portion (superconducting bulk body G) is maintained uniformly in the thickness direction of the superconducting bulk body G although it is somewhat reduced.

  FIG. 4 schematically shows the axial distribution of the critical current density (Jc) of the superconducting bulk body 201 showing the magnetic field strength distribution as described above. Since the internal structure of each superconducting bulk body S, G is substantially uniform in the axial direction, the critical current density (Jc) is substantially constant in the axial direction of each superconducting bulk body S, G. The superconducting bulk body G in the central portion has a concave distribution with a lower step than the bulk body S. Also, depending on the manufacturing method of the superconducting bulk body, the internal structure of each superconducting bulk body may not be uniform in the axial direction, but even in this case, by making the axial distribution of the critical current density concave. The effects of the present invention can be obtained.

  Next, a test tube containing ethanol and a probe were inserted into the uniform magnetic field (range of FIG. 3G), and the NMR signal of proton was measured. The results are shown in FIG. From FIG. 5, three independent peaks P1, P2 and P3 derived from differences in chemical shifts of hydrogen of three different binding partners can be discriminated. And the half width of each peak was about 3 ppm, and it turned out that very high resolution is shown.

(Specific example 2)
Superconducting bulk body 202 (not shown) of specific example 2 is composed of three superconducting bulk bodies as in specific example 1, and both end portions have an outer diameter of 60 mm × inner diameter of 10 mm × thickness of 10 mm (Nd, Eu, Gd) -Ba-Cu-O (Nd, Eu, Gd atomic ratio 1: 1: 1) as a main component, NEG-based superconducting bulk body N, the central part is an outer diameter 60 mm × inner diameter It consists of a Dy-based superconducting bulk body D whose main component is 10 mm × 25 mm thick Dy—Ba—Cu—O. The NEG-based superconducting bulk body N has a higher critical temperature (Tc) than the Dy-based superconducting bulk body D, and a high critical current density (Jc) because a fine insulating phase is precipitated. Accordingly, the superconducting bulk body 202 is magnetized in the same procedure as in the first specific example, thereby exhibiting a magnetic field distribution similar to FIG. 3 and a critical current density distribution similar to FIG.

(Specific example 3)
The superconducting bulk body 203 (not shown) of Example 3 is composed of a Dy-based superconducting bulk body in which all three superconducting bulk bodies are mainly composed of Dy-Ba-Cu-O. It contains certain Dy ₂ BaCuO ₅ particles. Both end portions are superconducting bulk bodies D1 having an outer diameter of 60 mm, an inner diameter of 10 mm, and a thickness of 15 mm including insulating phase particles having an average particle diameter of about 1 μm, and the central portion includes insulating phase particles having an average particle diameter of about 5 μm. A superconducting bulk body D2 having an outer diameter of 60 mm, an inner diameter of 10 mm, and a thickness of 20 mm. As already described, the critical current density (Jc) is higher in the superconducting bulk body D1 at both ends where the particles of the insulating phase are small. Accordingly, the superconducting bulk body 203 is magnetized in the same procedure as in the first specific example, thereby showing a magnetic field distribution similar to FIG. 3 and a critical current density distribution similar to FIG.

(Specific example 4)
The superconducting bulk material 204 (not shown) of Example 4 is composed of an Sm-based superconducting bulk material in which all three superconducting bulk materials are mainly composed of Sm—Ba—Cu—O, and is an insulating phase. It contains some Sm ₂ BaCuO ₅ particles. Both end portions are superconducting bulk bodies S1 having an outer diameter of 50 mm, an inner diameter of 10 mm, and a thickness of 15 mm containing 16.5% of the volume fraction of the insulating phase particles, and the central portion has the volume fraction of the insulating phase particles of 10%. It is a superconducting bulk body S2 having an outer diameter of 50%, an inner diameter of 10 mm, and a thickness of 25 mm. As already described, the critical current density (Jc) is higher in the superconducting bulk S1 at both ends containing a large number of particles of the insulating phase. Therefore, the superconducting bulk material 204 is magnetized in the same procedure as in the first specific example, thereby showing a magnetic field distribution similar to that in FIG. 3 and a critical current density distribution similar to that in FIG.

(Specific example 5)
The superconducting bulk body 205 of the fifth specific example is a modification of the first embodiment described above. As shown in FIG. 6, two superconducting bulk bodies S3 and S3 having the same characteristics are brought into contact with each other. Configured. That is, the superconducting bulk body S3 is formed such that the critical current density (Jc) gradually increases in the thickness t direction from the lower surface S3b toward the upper surface S3a (arrow Y). Then, the superconducting bulk body 205 is formed by laminating the lower surfaces S3b so as to contact each other.

For example, the superconducting bulk S3 is composed of an Sm-based superconducting bulk mainly composed of Sm—Ba—Cu—O having an outer diameter of 60 mm, an inner diameter of 16 mm, and a thickness of 20 mm, and is an insulating phase of Sm ₂ BaCuO _5. It contains particles. Then, the superconducting bulk body S3 is formed so that the volume fraction of the insulating phase particles increases from the lower surface S3b side toward the upper surface S3a side, and the lower surface S3b is disposed so as to contact each other. The superconducting bulk body 205 is continuously magnetized by being magnetized in the same procedure as in the first specific example so as to be higher at both end portions than in the central portion in the axial direction as schematically shown in FIG. It exhibits a critical current density (Jc) distribution and can show a magnetic field distribution similar to FIG.

  In the superconducting bulk bodies of Specific Examples 1 to 5 as described above, it is desirable that the thickness of the central portion where the critical current density (Jc) is low is 30 to 70% of the total thickness of the superconducting bulk body. If the thickness of the central portion is less than 30%, the peak position of the magnetic field is too close to the central portion, so that a good wide uniform magnetic field cannot be obtained. On the other hand, if the thickness of the central portion exceeds 70%, a high magnetic field distribution having a peak in the central portion may be formed, which is not desirable. The thickness of the central part is more preferably 40 to 60%.

(2) Second Embodiment of Magnetic Field Generator In a superconducting bulk body having the same composition, the critical current density (Jc) increases as the magnetization temperature decreases. That is, the magnetic field generator of the second embodiment has temperature adjusting means for lowering both ends of the superconducting bulk body at a temperature lower than that of the central portion.

  FIG. 8 is a schematic cross-sectional view showing the superconducting bulk body 206 to which the temperature adjusting means 40 a is attached. In FIG. 8, the temperature adjusting means 40 a is a heater H that heats the central portion of the superconducting bulk body 206.

  For example, the superconducting bulk body 206 is composed of a Gd-based superconducting bulk body mainly composed of Gd—Ba—Cu—O, and has three bulk superconductors each having an outer diameter of 60 mm, an inner diameter of 10 mm, and a thickness of 15 mm. The conductors G1, G2, and G3 are stacked. A heater H in which a 0.2 mmφ nichrome wire is wound a predetermined number of times is provided on the outer periphery of the superconducting bulk body G2 at the center.

  In this magnetic field generator, when the superconducting bulk body 206 is cooled to 50K in the magnetic field generated by the superconducting magnet 28 when magnetizing in the same procedure as in the first specific example, the superconducting bulk is heated by the heater H. The temperature of the body G2 was maintained to be 5K higher than both ends (G1, G3). Thereafter, the superconducting magnet 28 was demagnetized, the heater power supply was turned off, and the whole was cooled to 40K to complete the magnetization. Thereby, as shown in FIG. 7, the critical current density (Jc) of the central portion G2 can be made lower than both the end portions G1 and G3, so that the superconducting bulk body 206 can exhibit the same magnetic field distribution as in FIG. .

  Moreover, it is good also as a temperature control means to cool both ends instead of heating the center part of a superconducting bulk body. FIG. 9 shows an example of temperature adjusting means 40b for cooling both ends.

  FIG. 9 is a schematic cross-sectional view of the main part of the magnetic field generator 10 ′. In FIG. 9, the temperature adjusting means 40 b is a copper cooling case 44, which is in contact with the upper surface 20 f of the superconducting bulk body 207 and sandwiches and accommodates the superconducting bulk body 207 together with the copper cooling stage 42. The cooling stage 42 is connected to the cooling unit 23 of the pulse tube refrigerator through a copper rod 49. The temperature of the temperature adjusting means 40 b can be monitored by the temperature sensor 48 and controlled by adjusting the current applied to the heater 46.

  In this magnetic field generator, when the superconducting bulk body 207 is cooled to 50K in the magnetic field generated by the superconducting magnet 28 when magnetization is performed in the same procedure as in the first specific example, the temperature adjusting means 40b superheats the superconducting bulk body 207. Since both end portions of the conductive bulk body 207 are cooled by heat conduction, the central portion is approximately 5K higher than both end portions. Thereafter, the superconducting magnet 28 was demagnetized, and the whole was cooled to 40K to complete the magnetization. As a result, the critical current density (Jc) at both ends can be made higher than that at the center, so that the superconducting bulk body 207 can exhibit a magnetic field distribution similar to that shown in FIG.

  In FIG. 9, reference numeral 50 denotes a sample space into which the object to be measured is inserted, the temperature in this space is room temperature, and the atmospheric pressure is atmospheric pressure.

(3) Embodiment of Nuclear Magnetic Resonance Apparatus FIG. 1 shows an example of a nuclear magnetic resonance apparatus provided with the magnetic field generator 10 of the present invention, and FIG. In FIG. 1, 13 is a high frequency generator, 14 is a pulse programmer (transmitter), 15 is a high frequency amplifier, 16 is a preamplifier (signal amplifier), 17 is a phase detector (receiver), 18 is an analog-digital converter, 19 Is a computer.

  In FIG. 9, the DUT 11 is inside the detection coil 12 wound around it. A high-frequency transmitter 13, a GATE unit that shapes the high-frequency pulse, and a power amplifier 15 that amplifies the high-frequency pulse, the pulse is given to the DUT 11 through the transmission coil, and free induction attenuation that occurs immediately after the pulse is generated. The signal received by the receiving coil, passed through the amplifier and the phase detector, and AD converted is stored in the computer 19. By Fourier transforming this data, the NMR analysis result can be displayed on the computer 19 or can be information mapped as MRI.

  The present invention is not limited to the above-described embodiment, and can be freely changed without departing from the gist of the present invention. For example, in Example 5, the superconducting bulk body S3 is formed so that the volume fraction of the insulating phase particles increases from the lower surface S3b side toward the upper surface S3a side, and the lower surface S3b is disposed so as to contact each other. However, the superconducting bulk body S3 ′ may be formed so that the size of the insulating particles decreases from the lower surface S3b side toward the upper surface S3a side. Alternatively, it may be formed so that the concentration of the RE element having a large ion radius increases from the lower surface S3b side toward the upper surface S3a side.

  In the above embodiment, the cooling means for the superconducting bulk body is a refrigerator, but a refrigerant such as liquid helium may be used. In such a magnetic field generator using a cryogenic refrigerant, a static magnetic field can be maintained even when the power supply is stopped, such as in the event of a power failure.

  The magnetic field generator of the present invention is suitable as a magnetic field generator for a nuclear magnetic resonance apparatus because it can generate a strong static magnetic field with a uniform distribution. In addition, since the nuclear magnetic resonance apparatus of the present invention has high sensitivity and high resolution, it can be suitably used for MRI apparatus in the medical field, components of industrial materials, agricultural products, and structural analysis.

1 is an overall configuration diagram showing an embodiment s of a nuclear magnetic resonance apparatus of the present invention. It is a cross-sectional schematic diagram explaining the superconducting bulk body of the specific example 1. It is a conceptual diagram which shows the magnetic field distribution by the superconducting bulk body of the specific example 1. It is a schematic diagram which shows the critical current density distribution of the superconducting bulk body of the specific example 1. 2 is a diagram showing an NMR spectrum of protons measured in a magnetic field of Example 1. FIG. It is a cross-sectional schematic diagram explaining the superconducting bulk material of Example 5. It is a schematic diagram which shows the critical current density distribution of the superconducting bulk material of Example 5. It is a cross-sectional schematic diagram explaining the temperature control means which heats the center part of a superconducting bulk body. It is a cross-sectional schematic diagram explaining the temperature control means which cools the both ends of a superconducting bulk body. It is a cross-sectional schematic diagram explaining the structure of the superconducting bulk body of a prior art. It is a conceptual diagram which shows the magnetic field distribution of the magnetic field generator by the superconducting bulk body of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Nuclear magnetic resonance apparatus 10: Magnetic field generator 11: To-be-measured object 12: Detection coil 20: Superconducting bulk body 20a: Hollow part 22: Vacuum vessel 23: Cooling part 25: Pulse tube refrigerator 40: Temperature control means 42 : Cooling stage 44: Cooling case 46: Heater 48: Temperature sensor 50: Sample space

Claims (13)

In a magnetic field generator for capturing a magnetic field in a hollow cylindrical superconducting bulk body cooled to a superconducting transition temperature or lower in a vacuum vessel and generating a magnetic field in a hollow portion of the superconducting bulk body,
The superconducting bulk body, both axial ends of the superconducting bulk body is trapped magnetic field in a state not critical current density is higher than the axial center portion, the magnetic field strength after magnetization is from said axial center portion The magnetic field generator is characterized in that both end portions in the axial direction show a higher magnetic field distribution .   A hollow cylindrical superconducting bulk body that is magnetized below the superconducting transition temperature and captures a magnetic field in the center, a cooling device that cools the superconducting bulk body, and the vacuum vessel that houses the superconducting bulk body The magnetic field generator of Claim 1 provided with these.   The magnetic field generator according to claim 1, wherein the superconducting bulk body is made of a material having a critical temperature higher at the both end portions than at the central portion.   3. The magnetic field generator according to claim 1, further comprising a temperature adjustment unit configured to magnetize the superconducting bulk body so that both end portions have a temperature lower than that of the central portion.   The magnetic field generator according to claim 4, wherein the temperature adjusting means is a heater that heats the central portion.   The magnetic field generator according to claim 4, wherein the temperature adjusting unit is a cooling member that sandwiches the superconducting bulk body and cools the both ends. The superconducting bulk material is an oxide superconductor whose main component can be represented by RE-Ba-Cu-O, and contains 0 to 50% by mass of one or more of silver, platinum or cerium. Yttrium (element symbol Y), samarium (Sm), lanthanum (La), neodymium (Nd), europium (Eu), gadolinium (Gd), erbium (Er), ytterbium (Yb), dysprosium (Dy), holmium (Ho) 1) or a combination of two or more thereof, and a superconducting phase having a superconducting transition temperature of 90 ° K to 96 ° K in absolute temperature and an insulative insulating phase of 50 μm magnetic field generating apparatus according to claim 1 comprising dispersed organizations granularity follows.   8. The magnetic field generator according to claim 7, wherein the superconducting bulk body is made of a material containing an element having an average ionic radius of the RE larger than that of a central portion at both ends of the superconducting bulk body.   The magnetic field generator according to claim 7, wherein the superconducting bulk body is made of a material including the insulating phase in which both end portions of the superconducting bulk body have an average particle size smaller than that of a central portion.   The magnetic field generator according to claim 7, wherein the superconducting bulk body is made of a material having a volume fraction of the insulating phase at both ends of the superconducting bulk body that is larger than that of a central portion.   The magnetic field generator according to any one of claims 8 to 10, wherein a thickness of the central portion of the superconducting bulk body is 30 to 70% of a thickness of the superconducting bulk body. A hollow cylindrical superconducting bulk body that is magnetized below the superconducting transition temperature and captures a magnetic field in the hollow portion, a cooling device that cools the superconducting bulk body, and a vacuum vessel that houses the superconducting bulk body And a detection coil for detecting an NMR signal of an object to be measured inserted into the hollow portion of the superconducting bulk body,
The superconducting bulk body, both axial ends of the superconducting bulk body is trapped magnetic field in a state not critical current density is higher than the axial center portion, the magnetic field strength after magnetization is from said axial center portion A nuclear magnetic resonance apparatus characterized in that both end portions in the axial direction show a higher magnetic field distribution .   The nuclear magnetic resonance apparatus according to claim 12, wherein the magnetic field generation apparatus is the magnetic field generation apparatus according to claim 3.

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