WO2005120342A1

WO2005120342A1 - Polarized xenon freezing and re-gasifying device and polarized xenon producing system

Info

Publication number: WO2005120342A1
Application number: PCT/JP2005/010379
Authority: WO
Inventors: Atsushi Wakai; Kazuhiro Nakamura; Iwao Kanno
Original assignee: Japan Science And Technology Agency
Priority date: 2004-06-07
Filing date: 2005-06-06
Publication date: 2005-12-22
Also published as: JP2005342426A; JP3863154B2

Abstract

A polarized xenon freezing and re-gasifying device comprising a magnetic field generating means (1) having a cavity having a magnetic field applied thereto, a sealed vessel (3) disposed in the cavity of the magnetic field generating means (1), an introduction tube (6) and a discharge tube (9) for a warmed medium which are connected to the sealed vessel (3), a sealed type freezing cell (14) stored in the sealed vessel (3), a supply tube (18) and an exhaust tube (19) for diluted gas including polarized xenon which pass through the sealed vessel (3) and are connected to the freezing cell (14), and a cooling tube (24) which is closely wound around the freezing cell (14) and through which a cooling medium is passed.

Description

Specification

Polarized xenon freezing and regasification equipment and polarized xenon generation system

The present invention relates to an apparatus for freezing and regasifying polarized xenon and a system for producing polarized xenon.

Background art

[0002] The xenon 129 ⁽¹²⁹ Xe) is capable of 100,000 times or more of the enhancement of polarization of the thermal equilibrium state by the light bombing method of the alkali metal vapor. The degree of polarization of the spin of this polarized ¹²⁹ Xe (hereinafter, simply referred to as polarized xenon) is defined as the polarization rate.

[0003] Polarized xenon is attracting attention as a gas that improves the positional resolution of MR imaging of a human body. In particular, improvement of the polarization rate of polarized xenon is important for improving the position resolution. By applying such polarized xenon to MR imaging, it will be possible to measure the oxygen saturation distribution, temperature distribution, and blood flow distribution of human brain tissue in the future.

[0004] Polarized xenon is generated by the following method. First, a polarizing cell composed of a non-magnetic material such as stainless steel has windows at both ends that can transmit circularly polarized light such as laser light, for example, quartz glass. To place. A piece of rubidium having a spin conversion function to xenon is put in the polarization cell and heated to generate, for example, about 100 ppm of rubidium vapor. ¹²⁹ Xe alone or ¹²⁹ Xe gas diluted with helium or nitrogen is supplied into the polarization cell, and laser light is made to enter the polarization cell through one window and bombed in the polarization cell. At this time, vapor-like rubidium is excited, and the excitation energy causes spin conversion between the xenon atoms in the cell and polarized xenon.

[0005] Here, focusing on the polarization rate of the polarized xenon gas, xenon gas having a high polarization rate is obtained by polarizing a mixed gas obtained by adding a small amount of nitrogen gas and a large amount of helium gas to xenon gas. It is possible to generate gas. In fact, the polarization process of a mixed gas consisting of 98% by volume of He gas, 0.6% by volume of ¹²⁹ Xe gas, and the balance of N gas has resulted in more than 65% polarization.

2

It has been reported that xenon gas having a porosity can be obtained. Such a high polarization rate Xenon gas can be obtained by adding a large amount of helium as a buffer gas, although the xenon atoms polarized during the polarization process of xenon atoms are scattered with each other to destroy the polarization. It is thought that this is to reduce the chance of this scattering.

[0006] Polarized xenon, which can obtain a mixed gas power containing a large amount of helium gas together with xenon gas, has an extremely low concentration. Therefore, the helium gas is removed when applied to a predetermined application. Need to be concentrated.

[0007] For these reasons, a method of freezing and accumulating polarized xenon to remove helium gas has been adopted. In this method, a mixed gas containing polarized xenon gas (melting point: 166K) together with a buffer gas such as helium (melting point: 4K) is passed through a liquid nitrogen trap to freeze only the polarized xenon gas. It is. When a sufficient amount of polarized xenon is frozen and trapped in the liquid nitrogen trap, heating is performed to regasify the frozen polarized xenon.

[0008] FIG. 1 of "PHYSICAL REVIEW LETTERS" Volume 88, No 14, pp. 147602-1-4, 8 April 200 2 discloses an apparatus for freezing and regasification of polarized xenon. I have. This device is equipped with a superconducting magnet having a cylindrical cavity in the height direction to which a magnetic field is applied. The accumulator, whose upper and lower ends are sealed vertically, is placed in the cavity of the superconducting magnet. This accumulator has a double cylinder structure having a glass outer cylinder and an inner cylinder whose upper and lower ends are sealed. The upper end of the inner cylinder is connected to the upper end sealing plate of the outer cylinder, and the lower end is separated by a desired distance from the lower end sealing plate of the outer cylinder. The introduction pipe of the helium dilution gas containing polarized xenon is connected to the upper end sealing plate corresponding to the inner cylinder of the accumulator. The discharge pipe is connected to an upper end sealing plate between the inner cylinder and the outer cylinder of the accumulator. A cylindrical low-temperature maintenance container having a bottom is disposed in the hollow portion, and the storage device is inserted into the container. The cooling gas inlet pipe is connected to the bottom of the low temperature maintenance vessel. The heater is wound on the outer peripheral surface near the bottom of the low temperature maintenance container.

The operation of the apparatus for freezing and regasifying polarized xenon having such a structure will be described.

[0010] A cooling gas obtained by evaporating liquid helium is introduced into the bottom of the low-temperature maintenance container through a cooling gas introduction pipe, and the accumulator in the container is cooled. In the cavity by superconducting magnet A predetermined strong magnetic field is applied to the disposed storage device. After the accumulator is sufficiently cooled, a helium diluent gas containing polarized xenon is supplied to the inner cylinder through the introduction pipe, and flows out from the lower end of the inner cylinder to between the inner cylinder and the outer cylinder, and the cooling gas is discharged. And rises along the inner surface of the cooled outer cylinder made of glass to discharge the pipe. As the dilution gas rises and cools, the polarized xenon in the dilution gas is frozen near the bottom of the outer cylinder.

[0011] The re-gasification of ice-polarized xenon is achieved by stopping the introduction and cooling of a cooling gas in which liquid helium is vaporized, heating a heater wound near the bottom of the low-temperature maintaining vessel, and transferring the heat to the accumulator. This is accomplished by heating the frozen polarized xenon generated on the inner surface of the outer cylinder by transmitting it to the outer cylinder.

[0012] Meanwhile, in the above-described apparatus, the regasification of the ice-polarized xenon heats a heater wound near the bottom of the cryostat, and the heat is passed through the cryostat and the air layer of the accumulator. Since the power is transmitted to the outer cylinder, the heating speed of the frozen polarized xenon generated on the inner surface of the outer cylinder becomes slower. As a result, the frozen polarized xenon melts and the transit time of the melting point during gasification becomes relatively long. For this reason, there was a problem in that polarization collapse, that is, relaxation of polarization occurred during the melting process, and the polarization rate of regasified polarized xenon was considerably reduced as compared with frozen polarized xenon.

Disclosure of the invention

[0013] An object of the present invention is to provide an apparatus for freezing and regasifying polarized xenon that can suppress a decrease in the polarization rate during regasification of frozen polarized xenon.

[0014] The present invention includes polarized xenon by arranging a polarization cell of a xenon polarization device and an ice cell of a polarization xenon freeze / regasification device in the cavity of the same magnetic field generating means. Polarization capable of suppressing a decrease in the polarization rate when the dilution gas is transported from the polarization cell to the frozen cell, and suppressing a decrease in the polarization rate during regasification of the frozen polarized xenon. It is an object to provide a xenon generation system.

According to the present invention, a magnetic field generating means having a cavity to which a magnetic field is applied,

A sealed container arranged in the cavity of the magnetic field generating means,

An inlet tube and an outlet tube of the heating medium connected to the closed container,

A closed ice cell stored in the closed container, A supply pipe and an exhaust pipe for a dilution gas containing polarized xenon, which are connected to the ice cell through the closed container;

A cooling pipe through which a cooling medium is wrapped in close contact with the icing cell.

The present invention provides an apparatus for freezing and regasifying polarized xenon, comprising:

[0016] Further, according to the present invention, there is provided a polarized xenon generation system including a xenon polarizing device and a polarized xenon freeze / regasification device,

The xenon polarization device is disposed in a cavity of a magnetic field generating means, and has a polarization cell having laser light transmission windows at both ends, and causes laser light to enter the polarization cell through the laser light transmission window. And a supply pipe for a dilution gas containing xenon connected to the polarization cell, and

The polarized xenon freezing and regasification apparatus comprises: a sealed container juxtaposed with the polarized cell in the cavity of the magnetic field generating means; and an introduction pipe and discharge of a heating medium connected to the sealed container. A tube, a closed type icing cell housed in the closed container, and one end connected to the exhaust pipe of the polarized cell, and the other end connected to the icing cell through the closed container. A system for producing polarized xenon, comprising: a supply pipe for a dilution gas containing polar xenon; an exhaust pipe connected to the icing cell; and a cooling pipe wound tightly around the icing cell and through which a cooling medium flows. Is provided.

Brief Description of Drawings

FIG. 1 is a schematic diagram showing an apparatus for freezing and regasifying polarized xenon according to a first embodiment of the present invention.

[FIG. 2] FIG. 2 is a cross-sectional view showing a sealed container incorporating the frozen cell of FIG.

[FIG. 3] FIG. 3 is a partially cutaway perspective view showing a sealed container incorporating the frozen cell of FIG. 1.

FIG. 4 is a schematic diagram showing a polarized xenon generation system according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view showing the polarization cell of FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a polarized xenon freeze regasification apparatus and a polarized xenon generation system according to the present invention will be described in detail with reference to the drawings. (First Embodiment)

FIG. 1 is a schematic diagram showing a device for freezing and regasifying polarized xenon according to the first embodiment, FIG. 2 is a cross-sectional view showing a sealed container incorporating the ice cell of FIG. 1, and FIG. FIG. 2 is a partially cutaway perspective view showing a closed container having a frozen cell therein.

The horizontally placed superconducting magnet 1 as a magnetic field generating means has, for example, a cylindrical hollow portion 2 to which a magnetic field is applied. The closed container 3 is disposed horizontally in the hollow portion 2 of the superconducting magnet 1. As shown in FIGS. 2 and 3, the closed container 3 has a structure in which disks 5a and 5b are hermetically attached to left and right ends of a cylindrical container body 4. The container body 4 and the disks 5a and 5b that constitute the closed container 3 are made of a non-magnetic material, for example, SUS316 or copper.

A heating medium, for example, a hot water inlet pipe 6 is connected to the container body 4 near the right circular plate 5b of the closed container 3. The heating medium may be, for example, heated alcohol instead of hot water. A valve 7 is interposed in the hot water introduction pipe 6. The other end of the hot water inlet pipe 6 is connected to a hot water tank 8. The discharge pipe 9 for hot water is connected to the vicinity of the bottom of the left circular plate 5a of the closed vessel 3 facing the inlet pipe 6 for hot water. The hot water discharge pipe 9 is provided with a valve 10. The other end of the hot water discharge pipe 9 is connected to a hot water recovery tank 11. A branch pipe 13 is connected to a portion of the hot water discharge pipe 9 located between the valve 10 and the closed vessel 3. The branch pipe 13 is provided with a knob 12. The other end of the branch pipe 13 is connected to an exhaust means (not shown), for example, a vacuum pump. The hot water inlet pipe 6, the discharge pipe 9, and the branch pipe 13 are made of stainless steel, for example. The hot water inlet pipe 6 is arranged on the upper side of the horizontal sealed container 3 and the hot water discharge pipe 9 is arranged on the bottom side of the closed vessel 3, respectively. The hot water is discharged from the discharge pipe 9 while being introduced into the closed vessel 3 through the introduction pipe 6. At this time, the diameter of the hot water discharge pipe 9 is designed to be smaller than the diameter of the hot water inlet pipe 6 so that the hot water stays in the closed vessel 3 and is filled. In other words, the hot water discharge pipe 9 is designed so that the hot water can stay in the closed container 3 with a discharge amount smaller than the supply amount of the hot water from the hot water inlet pipe 6.

The icing cell 14 is arranged coaxially and horizontally in the closed container 3. this The icing cell 14 has a structure in which disks 16a and 16b are hermetically attached to left and right ends of a cylindrical cell body 15. The cell body 15 and the disks 16a, 16b constituting the frozen cell 14 are made of a non-magnetic material, for example, SUS316 or copper. The cell body 15 and the disks 16a and 16b are plated with a highly heat-conductive metal, for example, gold on the inner and outer surfaces. In particular, it is preferable that the inner surface of the cell body 15 is mirror-finished to have a smooth surface.

A supply pipe 18 for diluent gas containing polarized xenon, in which a valve 17 is interposed, penetrates through the left circular plate 5a of the closed container 3 and is connected to the left circular plate 16a of the frozen cell 14. . One end of the exhaust pipe 19 is connected to the right circular plate 16b of the frozen cell 14. The other end of the exhaust pipe 19 passes through the right circular plate 5b of the closed vessel 3 and is connected to a gas bag 20 disposed outside. A knurl 21 is interposed in an exhaust pipe 19 near the gas bag 20. A branch pipe 23 is connected to a portion of the exhaust pipe 19 located between the valve 21 and the icing cell 14. The branch pipe 23 is provided with a valve 22. The other end of the branch pipe 23 is connected to an exhaust means (not shown), for example, a vacuum pump. The supply pipe 18, the exhaust pipe 19, and the branch pipe 23 are made of, for example, stainless steel.

The cooling pipe 24 is wound around the outer peripheral surface of the cell body 15 of the frozen cell 14 at a desired pitch. A cooling medium, for example, liquid nitrogen of 77 K flows through the cooling pipe 24. The cooling medium is not limited to liquid nitrogen, and liquid neon (23K) and liquid helium (4K) can be used. The cooling pipe 24 is made of a material having high thermal conductivity, for example, copper. The inner and outer surfaces of the cooling pipe 24 are plated with a high heat conductive metal, for example, gold. The cooling pipe 24 has a perfect circular cross section, but may have a flat elliptical cross section in order to increase the contact area with the cell body 15.

[0025] The liquid nitrogen supply pipe 25 has one end penetrating through the left disk 5a of the closed vessel 3, and one end of the cooling pipe 24 located in the cell body 15 near the right disk 16b of the frozen cell 14. It is linked to In other words, the liquid nitrogen supply pipe 25 is connected to one end of the cooling pipe 24 located downstream of the flow of the diluent gas containing polarized xenon (flow from left to right in FIG. 2) flowing through the icing cell 14. Are linked. A valve 26 is interposed in the liquid nitrogen supply pipe 25. The other end of the supply pipe 25 is connected to a liquid nitrogen tank 27. One end of the liquid nitrogen discharge pipe 28 passes through the left circular plate 5a of the The cooling pipe 24 is connected to the other end of the cooling pipe 24 located in the cell body 15 near the left circular plate 16a. That is, the liquid nitrogen exhaust pipe 28 is connected to the other end of the cooling pipe 24 located on the upstream side of the flow of the diluent gas containing polarized xenon flowing in the icing cell 14. A valve 29 is interposed in the liquid nitrogen discharge pipe 28. The other end of the discharge pipe 28 is connected to a liquid nitrogen recovery tank 30. The liquid nitrogen supply pipe 25 and the discharge pipe 28 are made of, for example, stainless steel.

A plurality of ring-shaped baffles 31 are fitted on the outer peripheral surface of the cell body 15 of the frozen cell 14 at desired intervals in the length direction of the cell body 15. These baffles 31 are made of a material having high thermal conductivity, for example, copper. Each of the baffles 31 has a plurality of holes 32 in order to increase a contact area with a heating medium, for example, hot water. An insertion tube 33 for inserting a temperature sensor (not shown) into the closed container 3 is connected to the right circular plate 5b of the closed container 3.

[0027] Next, the operation of the above-described apparatus for refreezing and regasifying polarized xenon will be described.

[0028] The supply pipe 18, the exhaust pipe 19, the branch pipe 23, the hot water inlet pipe 6, the hot water discharge pipe 9, and the branch pipe 13 valves 17, 21, 22, 22, shown in Fig. 1, for the diluted gas containing polarized xenon. Close valves 7, 11, and 12, and open valves 26 and 29 of liquid nitrogen supply line 25 and discharge line 28 which are liquid nitrogen supply lines. With such an operation, the liquid nitrogen in the liquid nitrogen tank 27 is supplied through the supply pipe 25 into the cooling pipe 24 wound around the outer peripheral surface of the cell body 15 of the icing cell 14. The supplied liquid nitrogen flows from the downstream side to the upstream side of the flow of the diluent gas containing polarized xenon (flow from left to right in the drawing) in the cooling pipe 24, and The freezing cell 14 is cooled during the distribution process. At this time, the outer peripheral surface of the cell body 15 of the icing cell 14 is plated with high thermal conductivity, and the inner and outer surfaces of the cooling pipe 24 are plated with high thermal conductivity. The cooling efficiency by the liquid nitrogen at the contact portion of the cooling pipe 24 is further improved. Therefore, the icing cell 14 can be cooled more efficiently. In addition, the valve 12 of the branch pipe 13 connected to the hot water discharge pipe 9 is opened, and the vacuum pump connected to the branch pipe 13 is operated to exhaust the gas in the closed vessel 3 and to raise the inside of the closed vessel 3. By setting the vacuum state, the cooling pipe 24 is vacuum-insulated with respect to the space of the closed vessel 3. Therefore, the frozen cell 14 can be more efficiently cooled by the liquid nitrogen flowing through the cooling pipe 24. become.

[0029] After the icing cell 14 is sufficiently cooled in the process of continuing the supply of liquid nitrogen to the cooling pipe 24, the valve 22 of the branch pipe 23 connected to the exhaust pipe 19 of the dilution gas containing polarized xenon is opened. The gas (mainly air) in the icing cell 14 is exhausted by operating a vacuum pump connected to the branch pipe 23. While continuing to supply and exhaust liquid nitrogen to the cooling pipe 24, the valve 17 of the supply pipe 18 is opened, and the dilution gas containing polarized xenon is supplied into the ice cell 14 through the supply pipe 18. The diluent gas, for example, polarized xenon; 1-5 volume ^_0/0, N;

2 It has a gas composition of the same amount to twice that of polarized xenon and the balance He. As the dilution gas is cooled in the freezing cell 14, the polarized xenon therein is selectively frozen and accumulated on the inner surface of the freezing cell 14 (mainly the inner surface of the cell body 15). At this time, since a magnetic field is applied to the frozen cell 14 by the superconducting magnet 1, the polarized xenon is prevented from undergoing polarization collapse (relaxation of polarization) during the freezing process, and a decrease in the polarization rate is suppressed. I do. In particular, by applying a strong magnetic field of 3 T or more from the superconducting magnet 1 to the icing cell 14, it is possible to remarkably suppress a decrease in the polarization rate. Further, when flowing the liquid nitrogen through the cooling pipe 24, the liquid nitrogen is caused to flow from the downstream side to the upstream side of the flow of the diluent gas containing polarized xenon (the flow toward the left side and the flow toward the right side in the figure). . That is, the liquid nitrogen is circulated so as to cross the flow of the dilution gas. As a result, the dilution gas is uniformly cooled in the entire lengthwise direction of the polarization cell 14 to efficiently freeze and accumulate polarized xenon on the entire inner surface of the frozen cell 14 (mainly, the inner surface of the cell body 15). It becomes possible. In addition, the inside of the frozen cell 14 (mainly the inner surface of the cell body 15) is mirror-polished to a smooth surface, so that the spin of polarized xenon is applied to the inner surface of the frozen cell 14 (mainly the inner surface of the cell body 15). It is possible to suppress the adsorption of the disturbing impurity gas and suppress the decrease in the polarization rate more effectively.

[0030] After the freezing and accumulation of the polarized xenon in the freezing cell 14 is sufficiently performed, the operation of the vacuum pumps connected to the branch pipes 23 and 13 is stopped, and the supply pipe 18 for the dilution gas and the supply of liquid nitrogen are supplied. Close pipes 25, 26, 29, 22, and 12 of pipe 25, discharge pipe 28, branch pipe 23 connected to exhaust pipe 19, and branch pipe 13 connected to hot water discharge pipe 9, and introduce hot water that is a hot water supply line. Open valves 7, 11, 21 of pipe 6, hot water discharge pipe 9 and exhaust pipe 19. By this operation, the warm water in the warm water tank 8 is introduced into the closed vessel 3 through the introduction pipe 6. The introduced hot water is sealed While being filled in the container 3, it is discharged through the hot water discharge pipe 9 and collected in the hot water recovery tank 11. During this time, the polarized xenon that has frozen and accumulated on the inner surface of the frozen cell 14 (mainly the inner surface of the cell body 15) is heated with warm water, regasified, and stored in the gas bag 20 through the exhaust pipe 19. At this time, warm water is directly contacted with the frozen cell 14 in which the polarized xenon freezes and accumulates, and heat is transferred, so that the frozen xenon is quickly heated. For this reason, the frozen polarized xenon is melted, and the melting point at the time of gasification can be passed in a short time, and the polarization collapse in the process, that is, the relaxation of the polarization can be suppressed. As a result, it becomes possible to store the regasified polarized xenon having a polarization rate close to the state of frozen polarized xenon in the gas bag 20. The regasified polarized xenon is removed and used every 20 gas bags.

[0031] In particular, the outer peripheral surface of the cell body 15 of the frozen cell 14 is plated with high thermal conductivity, so that the frozen xenon inside the frozen cell 14 is heated more quickly and re-heated. It can be gasified.

Further, a plurality of ring-shaped baffles 31 are fitted to the outer peripheral surface of the cell body 15 of the frozen cell 14 at a desired interval in the longitudinal direction of the cell body 15, thereby forming an inner surface of the frozen cell 14. The frozen xenon that has been frozen can be heated and regasified more quickly. Further, by opening a plurality of holes 32 in the baffles 31 to increase the contact area with hot water, the heating rate of the frozen xenon frozen inside the freezing cell 14 is significantly increased, and regasification is performed. It is possible to do.

As described above, according to the first embodiment, the frozen xenon can be quickly heated in the freezing of the frozen xenon in the freezing cell 14 and the regasification after accumulation. As a result, the frozen polarized xenon is melted, and the melting point at the time of gasification can be passed in a short time. For this reason, polarization decay during the melting process, that is, relaxation of polarization is suppressed, and it is possible to obtain regasified polarized xenon having a polarization rate close to that of frozen polarized xenon. Xenon freezing and regasification equipment can be provided. The re-gasified polarized xenon having such a high polarization rate can further improve the positional resolution when applied to MR imaging or the like of a human body.

[0034] Further, in a structure in which the cooling pipe 24 is wound around the outer peripheral surface of the icing cell 14, the supply of liquid nitrogen is provided. By connecting the supply pipe 25 to one end of the cooling pipe 24 so that liquid nitrogen flows to the cooling pipe 24 so as to intersect with the flow of the diluent gas containing polarized xenon, the entire length of the polarized cell 14 in the longitudinal direction is changed. By uniformly cooling the dilution gas, polarized xenon can be efficiently frozen and accumulated on the entire inner surface of the icing cell 14 (mainly the inner surface of the cell body 15).

Further, the cooling pipe 24 through which the cooling medium flows is wound around the outer peripheral surface of the icing cell 14, and the icing cell 14 is housed in the closed container 3 so that the heating medium uniformly covers the entire icing cell 14. It has a structure that can be heated quickly. In other words, the structure does not involve any mechanical operation during heating and cooling. For this reason, it is possible to realize a small-sized frozen xenon regasification apparatus. Further, by forming the icing cell 14 and the sealed container 3 into a cylindrical shape with both ends sealed, it is possible to more easily reduce the size. As a result, the polarized xenon icing and regasification apparatus according to the first embodiment is economically limited in terms of its power to a space having a diameter of, for example, about 30 cm. It has the advantage that it can be adapted.

[0036] In the first embodiment, liquid nitrogen is supplied to the cooling pipe. However, liquid nitrogen vapor having a higher cooling efficiency than the liquid nitrogen may be supplied to the icing cell. If liquid neon or liquid helium is used instead of liquid nitrogen, the frozen cell can be cooled more efficiently.

(Second Embodiment)

FIG. 4 is a schematic diagram showing a polarized xenon generation system according to the second embodiment, and FIG. 5 is a cross-sectional view showing the polarized cell of FIG. In FIG. 4, the same members as those in FIG.

[0038] This polarized xenon generation system includes a xenon polarizing device and the above-described polarized xenon freezing / regasification device. The xenon polarization device comprises a polarization cell 41 juxtaposed with a closed vessel 3 containing a frozen cell in a cylindrical cavity 2 to which a magnetic field of a common (identical) superconducting magnet 1 is applied.

As shown in FIG. 5, the polarized cell 41 includes a non-magnetic material having flanges 42a and 42b at both ends, for example, a cylindrical cell body 43 made of SUS316 or copper. Quartz glass windows 44a, 44b are attached to the flanges 42a, 42b through O-rings 45a, 45b. A plurality of, for example, four clamp members 47a, 47b each having an abutment screw 46a, 46b are abutted, and are fixed. A laser oscillation device, for example, an array type semiconductor laser (not shown) is arranged so as to face, for example, a left window 44a of the polarization cell 41.

The mixed gas introduction pipe 48 is connected to the cell body 43 of the polarization cell 41. A knurl 49 is inserted into the introduction pipe 48, and the other end is connected to a mixed gas generator 50. One end of an exhaust pipe 18 of the dilution gas containing polarized xenon (also serving as a supply pipe) is connected to the cell body 43 of the polarized cell 41 approximately point symmetrically with the introduction pipe 48, and the other end of the closed vessel 3 is provided. It passes through the left disk and is connected to the left disk of the frozen cell. The introduction tube 48 is made of, for example, stainless steel.

Next, the operation of the above-described polarized xenon generation system will be described.

[0042] For example, after removing the clamp member 47a on the left side of the cell body 43 of the polarization cell 41 and removing the window 44a and the O-ring 45a from the flange 42a, the spin conversion to xenon is performed in a nitrogen atmosphere. Put the rubidium pieces into the cell body 43. The O-ring 45a and the window 44a are attached to the flange 42a again by the clamp member 47a, and the cell body 43 is sealed. The polarized cell 41 having the cell body 43 is heated to generate, for example, about 100 ppm of rubidium vapor in the polarized cell 41. The valve 49 of the mixed gas introduction pipe 48 is opened, the other valves are closed, and the mixed gas is supplied from the mixed gas generator 50 into the polarization cell 41 through the introduction pipe 48. The mixed gas is, for example ¹²⁹ Xe; ^l~5 vol%, N; ¹²⁹ Xe and Doryokakara 2 times

2

And the balance is He gas composition. Although not shown in the state where a magnetic field is applied to the polarization cell 41 by the superconducting magnet 1, the array-type semiconductor laser also emits laser light having a peak wavelength of 799.8 nm through one window (for example, the left window 44a). And bombed in the polarization cell 41. At this time, vapor-like rubidium is excited, and the excitation energy causes spin conversion between the xenon atoms in the polarization cell 41 to generate xenon (polarized xenon) having a high polarization rate. .

[0043] As in the first embodiment described above, the inside of the frozen cell in the closed vessel 3 is evacuated in advance, and liquid nitrogen is allowed to flow through a cooling pipe wound around the outer peripheral surface of the cell body of the frozen cell. After cooling the cell, the diluted gas containing polarized xenon in the polarized cell 41 is passed through the exhaust pipe (also serving as the supply pipe) 18 by opening the valve 17 of the exhaust pipe (also serving as the supply pipe) 18. The xenon is supplied to the frozen cell and freezes and accumulates polarized xenon on the inner surface of the frozen cell (mainly the inner surface of the cell body). After that, the polarized xenon frozen and accumulated on the inner surface of the frozen cell is heated by the same method as in the first embodiment described above, such as introducing hot water into the closed vessel 3, re-gasified, and passed through the exhaust pipe 19. Store in gas bag 20.

As described above, according to the second embodiment, the polarization cell 41 of the xenon polarization device and the ice cell of the polarization xenon freezing / regasification device are combined with the cavity of the superconducting magnet 1 as the same magnetic field generating means. When the diluent gas containing polarized xenon is transported from the polarized cell 41 to the icing cell by arranging it in parallel in the part 2, the magnetic field (for example, a strong magnetic field of 3 T or more) containing the polarized xenon is always diluted. Since it can be converted to gas, it is possible to suppress a decrease in the polarization rate.

[0045] Further, at the time of regasification of the frozen polarized xenon, it is possible to suppress a decrease in the polarization rate as described in the first embodiment.

[0046] Therefore, the polarized xenon generated by the xenon polarizing device can be stored in the gas bag 20 or the like as re-gasified polarized xenon while suppressing a decrease in the polarization rate. It is possible to provide a polarized xenon generation system that can further increase the positional resolution when used for MR imaging of a living body or the like.

Further, it has a configuration in which the closed vessel 3 containing the frozen cell and the polarized cell 41 are cylindrical and arranged in a magnetic field, and the polarization of the xenon gas in the polarized cell 41 The structure is such that there is no mechanical action during heating and cooling in the cell. For this reason, a small-sized polarized xenon generation system can be realized. As a result, the system for generating polarized xenon according to the second embodiment is applied to a 4.7 T or 9 T high-field nuclear magnetic resonance apparatus whose diameter is limited to a space of, for example, about 30 cm from an economic viewpoint. It has the advantage that it becomes possible.

In the first and second embodiments, the superconducting magnet is used as the magnetic field generating means, but an electromagnet may be used.

[0049] In the first and second embodiments, the frozen cell is formed in a cylindrical shape, and the cooling pipe through which the cooling medium flows is wound around the outer peripheral surface, but the present invention is not limited to this. For example, a structure may be adopted in which the outer peripheral surfaces are closely adhered to each other by twisting the ice cell and the cooling pipe. In the first and second embodiments, the superconducting magnet, the sealed container, and the force with the polarized cell placed horizontally may be placed vertically.

Industrial applicability

[0051] According to the apparatus for freezing and regasifying polarized xenon according to the present invention, it is necessary to regasify the frozen xenon when regasification is performed. In addition, it is possible to suppress a decrease in the polarization rate, and it is possible to further improve the positional resolution when regasified polarized xenon is used for MR imaging of a living body, etc. It can contribute to the diagnosis, especially to the application of the brain image to the diagnosis technology.

[0052] According to the polarized xenon generation system of the present invention, the polarization device power of the diluent gas xenon containing polarized xenon is controlled to suppress the decrease in the polarization rate when transported to the icing / regasification device. In addition, when re-gasifying frozen polarized xenon, it is possible to suppress the decrease in polarization rate, and when re-gasified polarized xenon is used for MR imaging of a human body, the position of the xenon can be reduced. The resolution can be further improved, and it can contribute to the application of MR imaging, especially brain imaging.

Claims

The scope of the claims

[1] magnetic field generating means having a cavity to which a magnetic field is applied;

A closed ice cell stored in the closed container,

A supply pipe and an exhaust pipe for a dilution gas containing polarized xenon, which are connected to the ice cell through the closed container;

Xenon freezing and regasification equipment equipped with

2. The apparatus for freezing and regasifying polarized xenon according to claim 1, wherein the magnetic field generating means is a superconducting magnet.

3. The apparatus for freezing and regasifying polarized xenon according to claim 1, wherein the discharge pipe of the heating medium also functions as an exhaust pipe during a freezing operation, and an exhaust means is attached to the other end.

4. The apparatus for freezing and regasifying polarized xenon according to claim 1, wherein the freeze cell has an outer surface coated with a metal having higher thermal conductivity than the cell material.

5. The frozen xenon freeze / regasifier according to claim 1, wherein the freeze cell has a smooth mirror surface on an inner surface.

6. The apparatus for freezing and regasifying polarized xenon according to claim 1, wherein the cooling pipe is made of copper, and the inner and outer surfaces are coated with a metal having higher thermal conductivity than copper.

[7] The cooling medium supply pipe has one end connected to one end of the cooling pipe located downstream of the flow of the diluent gas containing polarized xenon through the closed vessel, and discharging the cooling medium. 2. The apparatus for freezing and regasifying polarized xenon according to claim 1, wherein the pipe is connected to one end of the cooling pipe located on the upstream side of the flow of the dilution gas.

8. The polarized xenon icing / regasification apparatus according to claim 1, wherein a plurality of ring-shaped baffles are further provided on the icing cell at desired intervals in a length direction of the cell.

[9] The apparatus for freezing and regasifying polarized xenon according to claim 8, wherein each of the ring-shaped baffles is further provided with a plurality of holes.

[10] Polarized xenon equipped with xenon polarizer and polarized xenon freeze / regasifier A generation system,

The polarized xenon freezing and regasification apparatus comprises: a sealed container juxtaposed with the polarized cell in the cavity of the magnetic field generating means; and an introduction pipe and discharge of a heating medium connected to the sealed container. A tube, a closed type icing cell housed in the closed container, and one end connected to the exhaust pipe of the polarized cell, and the other end connected to the icing cell through the closed container. A system for producing polarized xenon, comprising: a supply pipe for a dilution gas containing polar xenon; an exhaust pipe connected to the icing cell; and a cooling pipe wound tightly around the icing cell and through which a cooling medium flows. .

11. The polarized xenon generation system according to claim 10, wherein the magnetic field generation means is a superconducting magnet.

12. The polarized xenon generation system according to claim 10, wherein a discharge pipe of the heating medium of the freeze / regasifier serves also as an exhaust pipe at the time of the freeze operation, and an exhaust means is attached to the other end.

13. The polarized xenon generation system according to claim 10, wherein the icing cell of the icing / regasification apparatus has an outer surface coated with a metal having higher thermal conductivity than the cell material.

14. The system for producing polarized xenon according to claim 10, wherein the freeze cell of the freeze 'regasifier has a smooth mirror surface on an inner surface.

15. The system for producing polarized xenon according to claim 10, wherein the cooling tube of the freeze / regasifier is made of copper, and the inner and outer surfaces are coated with a metal having higher heat conductivity than copper.

[16] The cooling medium supply pipe has one end connected to one end of the cooling pipe located at the downstream side of the flow of the diluent gas containing polarized xenon through the closed vessel, and discharging the cooling medium. 11. The system for producing polarized xenon according to claim 10, wherein a pipe is connected to one end of the cooling pipe located upstream of the flow of the dilution gas.

[17] A plurality of ring-shaped baffles are provided on the frozen cell at desired intervals in the length direction of the cell. 11. The polarized xenon generation system according to claim 10, further provided with a gap. Each of the ring-shaped baffles further has a plurality of holes respectively opened.

7. A system for producing polarized xenon according to 7.