Patent Number: 
Section: claims

1. A radiation shielding sheet comprising:a shielding material mixed with an organic polymer material,wherein said shielding material is an oxide powder containing at least one element selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu) and gadolinium (Gd), said oxide powder having an average grain size of 1 to 20 μm, andwherein a volumetric ratio of the shielding material in said radiation shielding sheet is 40 to 80 vol. %. 2. A radiation shielding sheet comprising:an organic polymer material; anda shielding material mixed with said organic polymer material,wherein said shielding material is an oxide powder of a single substance of metal element or metal compound, and has a composition containing lanthanum (La) and cerium (Ce), andwherein the metal compound powder has a composition containing 10 to 40 mass % of lanthanum (La) oxide and 30 to 60 mass % of cerium (Ce) oxide. 3. The radiation shielding sheet according to claim 2, wherein a volumetric ratio of the shielding material filled in said radiation shielding sheet is 40 to 80 vol. %. 4. The radiation shielding sheet according to claim 1, wherein the average grain size of said shielding material grains existing in a structure of the radiation shielding sheet is A μm, where A is no less than 1 μm and no more than 20 μm, such that a quantity of said shielding material grains existing within a straight line segment range having a length of 50 μm is at least equal to 30/A,wherein the straight line segment range is arbitrarily drawn on a surface of the structure of the radiation shielding sheet. 5. The radiation shielding sheet according to claim 1, wherein the organic polymer material is further mixed with at least one powder selected from the group consisting of tungsten (W), bithmus (Bi), tin (Sn) and compounds thereof. 6. The radiation shielding sheet according to claim 1, wherein the radiation shielding sheet is used as a material in a wall of an X-ray room. 7. The radiation shielding sheet according to claim 2, wherein the average grain size of said shielding material grains existing in a structure of the radiation shielding sheet is A μm, where A is no less than 1 μm and no more than 20 μm, such that a quantity of said shielding material grains existing within a straight line segment range having a length of 50 μm is at least equal to 30/A,wherein the straight line segment range is arbitrarily drawn on a surface of the structure of the radiation shielding sheet. 8. The radiation shielding sheet according to claim 2, wherein the organic polymer material is further mixed with at least one powder selected from the group consisting of tungsten (W), bithmus (Bi), tin (Sn) and compounds thereof. 9. The radiation shielding sheet according to claim 2, wherein the radiation shielding sheet is used as a material in a wall of an X-ray room. 10. The radiation shielding sheet according to claim 5, wherein when one of tungsten (W), bithmus (Bi), tin (Sn), or compounds thereof, is included in the radiation shielding material, a weight part ratio of the one of tungsten (W), bithmus (Bi), tin (Sn), or compounds thereof is not greater than 30 weight parts. 11. The radiation shielding sheet according to claim 8, wherein when one of tungsten (W), bithmus (Bi), tin (Sn), or compounds thereof, is included in the radiation shielding material, a weight part ratio of the one of tungsten (W), bithmus (Bi), tin (Sn), or compounds thereof is not greater than 30 weight parts. 12. The radiation shielding sheet according to claim 5, wherein when tin (Sn) is included in the radiation shielding material, a weight part ratio of the tin (Sn) is not greater than 40 weight parts. 13. The radiation shielding sheet according to claim 8, wherein when tin (Sn) is included in the radiation shielding material, a weight part ratio of the tin (Sn) is not greater than 40 weight parts.