Rare earth cold accumulating material particles, and refrigerator, superconducting magnet, inspection device and cryopump using same

1. A method of manufacturing a refrigerator for accumulating an ultralow temperature of 20 K or lower, the method comprising the steps of:

providing a cold accumulating vessel; and

packing a rare earth cold accumulating material particle in the cold accumulating vessel;

wherein the rare earth cold accumulating material particle consists essentially of a rare earth oxide or a rare earth oxysulfide;

wherein the rare earth cold accumulating material particle is a sintered body;

wherein an average crystal grain size of the sintered body is 0.5 to 5 μm;

wherein a porosity of the sintered body is 10 to 50 vol %; wherein an average pore size of the sintered body is 0.3 to 3 μm; and

wherein in an arbitrary cross section of the rare earth cold accumulating material particle, a number of pores per a unit area of 10 μm×10 μm is 20 to 70.

2. The method according to claim 1 , wherein a group of the rare earth cold accumulating material particles packed in the cold accumulating vessel includes the rare earth cold accumulating material particles in a content of 50% by mass or more and 100% by mass or less.

3. The method according to claim 1 , wherein the refrigerator is a GM refrigerator.

4. The method according to claim 1 , wherein the refrigerator is a Stirling refrigerator.

5. The method according to claim 1 , wherein the refrigerator is a pulse tube refrigerator.

6. The method according to claim 1 , wherein two or more stages of cold accumulating material-filled zones are formed which are divided by a metal mesh material in at least one cold accumulating vessel, and the rare earth cold accumulating material particles are packed in at least one stage of regenerator material-filled zones.

7. The according to claim 6 , wherein the metal mesh material comprises a metal mesh member composed of copper or a copper alloy is packed.

8. The method according to claim 7 , wherein the method further comprises the step of packing the mesh material comprising a metal mesh member composed of copper or a copper alloy.

9. The method according to claim 1 , wherein the refrigerator is used for obtaining an ultralow temperature of 10 K or lower.

10. The method according to claim 1 , wherein the rare earth cold accumulating particle has an average particle size of 100 to 500 μm.

11. The method according to claim 1 , wherein a filling factor of the cold accumulating material particles in the cooling stage of a refrigerator falls within a range from 55 to 70%.

12. The method according to claim 1 , wherein the rare earth cold accumulating material particle has an aspect ratio of 2 or less.

13. The method according to claim 1 , wherein when L represents a perimeter length of a projection image of each of the cold accumulating material particles constituting a group of rare earth cold accumulating material particles, and A represents the actual area of the projection image, in the group of rare earth cold accumulating material particles, a proportion of the rare earth cold accumulating material particles having a shape factor R being represented by L 2 /4πA and exceeding 1.5 is 5% or less.

14. The method according to claim 1 , wherein the rare earth cold accumulating material particle comprises gadolinium aluminum oxide (GdAlO 3 ) or gadolinium oxysulfide (Gd 2 O 2 S).

15. A method of manufacturing a pulse tube refrigerator for accumulating an ultralow temperature of 20 K or lower, the method comprising the steps of:

filling a Cu mesh cold accumulating material in a first cooling stage;

partitioning a filling space of a second cooling stage into a first to a third filling spaces;

filling a group of lead cold accumulating material particles into the partitioned first filling space;

filling a group of HoCu 2 cold accumulating material particles into the partitioned second filling space; and

filling a group of cold accumulating material particles into the partitioned third filling space wherein the rare earth cold accumulating material particle consists essentially of a rare earth oxide or a rare earth oxysulfide;

wherein the rare earth cold accumulating material particle is a sintered body;

wherein an average crystal grain size of the sintered body is 0.5 to 5 μm;

wherein a porosity of the sintered body is 10 to 50 vol %; wherein an average pore size of the sintered body is 0.3 to 3 μm; and

wherein in an arbitrary cross section of the rare earth cold accumulating material particle, a number of pores per a unit area of 10 μm×10 μm is 20 to 70.

16. The method according to claim 15 , wherein the pulse tube refrigerator is a 4K pulse tube refrigerator.

17. A method of manufacturing a superconducting magnet provided with a refrigerator for accumulating an ultralow temperature of 20 K or lower, wherein the refrigerator is manufactured by the method according to claim 1 .

18. A method of manufacturing an MRI provided with a refrigerator for accumulating an ultralow temperature of 20 K or lower, wherein the refrigerator is manufactured the method according to claim 1 .

19. A method of manufacturing an NMR provided with a refrigerator for accumulating an ultralow temperature of 20 K or lower, wherein the refrigerator is manufactured by the method according to claim 1 .

20. A method of manufacturing a cryopump provided with a refrigerator for accumulating an ultralow temperature of 20 K or lower, wherein the refrigerator is manufactured through the method according to claim 1 .