Patent Number: 
Section: claims

1. A neutron moderator comprising a fluoride sintered body, wherein the fluoride sintered body has a thickness of 60 mm or more and 64 mm or less and comprises MgF2 of a compact polycrystalline structure having a bulk density of 2.90 g/cm3 or more and 3.07 g/cm3 or less and a bending strength of 10 MPa or more and 25 MPa or less as regards mechanical strengths. 2. The neutron moderator according to claim 1, wherein the sintered body has a Vickers hardness of 71 or more and 120 or less as regards mechanical strengths. 3. The neutron moderator according to claim 1, wherein the sintered body has volume of 2,183 cm3 or more and 2,421 cm3 or less. 4. A neutron moderator comprising a fluoride sintered body, wherein the fluoride sintered body has a thickness of 60 mm or more and 64 mm or less and comprises MgF2 of a compact polycrystalline structure having a bulk density of 2.90 g/cm3 or more and 3.07 g/cm3 or less and a bending strength of 10 MPa or more and 25 MPa or less as regards mechanical strengths,wherein the sintered body is produced by a process comprising the steps of:pulverizing a high-purity MgF2 raw material and mixing it with 0.03-0.5% by weight of a sintering aid:molding the resulting mixture obtained after the mixing step at a molding pressure of 5 MPa or more using a uniaxial press device and subsequentlyat a molding pressure of 5 MPa or more using a cold isostatic pressing (CIP) device to obtain a molded article;conducting preliminary sintering of the molded article in the temperature range of 550° C.-600° C. for 4-10 hours in an air atmosphere;heating in the temperature range of 750° C.-840° C. for 5-12 hours in an inert gas atmosphere; andconducting main sintering by heating in the temperature range of 900° C.-1100° C. for 0.5-3 hours in the same atmosphere as the preceding step so as to form MgF2 sintered body having a compact structure. 5. The neutron moderator according to claim 4, wherein the sintered body has a Vickers hardness of 71 or more and 120 or less as regards mechanical strengths. 6. The neutron moderator according to claim 4, wherein the sintering aid is selected from the group consisting of carboxymethyl cellulose and calcium stearate. 7. The neutron moderator according to claim 4, wherein the sintered body has volume of 2,183 cm3 and 2,421 cm3 or less.