Patent Number: 
Section: claims

1. A MgF2—CaF2 binary system sintered body for a radiation moderator, comprising MgF2 containing CaF2 from 1.5% by weight to 80% by weight inclusive, having a compact polycrystalline structure with a bulk density of 2.96 g/cm3 or more and having radiation moderation performance. 2. The MgF2—CaF2 binary system sintered body for a radiation moderator according to claim 1, wherein the radiation moderation performance is neutron moderation performance. 3. The MgF2—CaF2 binary system sintered body for a radiation moderator according to claim 1, having a bending strength of 15 MPa or more and a Vickers hardness of 90 or more as regards mechanical strengths. 4. A method for producing the MgF2—CaF2 binary system sintered body for a radiation moderator according to claim 1, comprising the steps of:mixing a MgF2 powder with a CaF2 powder of 1.5-80% by weight and further adding 0.02-1% by weight of a sintering aid thereto to mix;molding the raw material powder compounded in the preceding step at a molding pressure of 5 MPa or more using a press molding device;molding the press molded article at a molding pressure of 5 MPa or more using a cold isostatic pressing (CIP) device;conducting preliminary sintering by heating the CIP molded article in a temperature range of 600° C.-700° C. in an air atmosphere;conducting sintering by heating in a temperature range from (Tn-100)° C. to (Tn)° C. when the starting temperature of foaming of the preliminary sintered body is (Tn)° C., in an air atmosphere or in an inert gas atmosphere; andforming a sintered body having a compact structure by heating in a temperature range of 900° C.-1150° C. in the same atmosphere as the preceding step. 5. The method for producing a MgF2—CaF2 binary system sintered body for a radiation moderator according to claim 4,wherein the shape of a particle size distribution curve of the compound shows a sub-1-peak-type or 1-peak-type particle size distribution, the maximum particle diameter is 50 μm or less and the median diameter of the particles is 6 μm or less. 6. The method for producing a MgF2—CaF2 binary system sintered body for a radiation moderator according to claim 4,wherein the inert gas atmosphere in the sintering step comprises one kind of gas or a mixture of plural kinds of gases, selected from among nitrogen, helium, argon and neon. 7. The method for producing a MgF2—CaF2 binary system sintered body for a radiation moderator according to claim 5,wherein the inert gas atmosphere in the sintering step comprises one kind of gas or a mixture of plural kinds of gases, selected from among nitrogen, helium, argon and neon.