Patent Number: 
Section: claims

1. A method of attenuating radiation comprising the step of mixing the following compounds to form a mixture:30 to 70% by mass of erbium or of a compound thereof;20 to 50% by mass of praseodymium or of a compound thereof; and0 to 50% by mass of bismuth or of a compound thereof;wherein the method comprises the step of incorporating the mixture in a composition that attenuates radiation. 2. The method according to claim 1, characterised in that the erbium compound is an erbium oxide. 3. The method according to claim 2, characterised in that the erbium oxide is sesquioxide of erbium (III), of formula Er2O3. 4. The method according to claim 1, characterised in that the praseodymium compound is a praseodymium oxide. 5. The method according to claim 4, characterised in that the praseodymium oxide is oxide of praseodymium (III-IV), of formula Pr6O11. 6. The method according to claim 2, characterised in that the mixture comprises 55 to 65% by mass of erbium oxide and 35 to 45% by mass of praseodymium oxide. 7. The method according to claim 6, characterised in that the mixture comprises (60±2)% by mass of erbium oxide and (40±2)% by mass of praseodymium oxide. 8. The method according to claim 2, characterised in that the mixture comprises 30 to 45% by mass of erbium oxide, 20 to 30% by mass of praseodymium oxide and 30 to 45% by mass of bismuth. 9. The method according to claim 8, characterised in that the mixture comprises 33 to 42% by mass of erbium oxide, 22 to 28% by mass of praseodymium oxide and 30 to 45% by mass of bismuth. 10. Radiation attenuating material comprising a matrix in which a radiation attenuating composition is dispersed, said composition being in the form of a powder, characterised in that said composition comprises:30 to 70% by mass of erbium or of a compound thereof;20 to 50% by mass of praseodymium or of a compound thereof; and0 to 50% by mass of bismuth or of a compound thereof. 11. Radiation attenuating material according to claim 10, characterised in that the erbium compound is an erbium oxide. 12. Radiation attenuating material according to claim 11, characterised in that the erbium oxide is sesquioxide of erbium(III), of formula Er2O3. 13. Radiation attenuating material according to claim 10, characterised in that the praseodymium compound is a praseodymium oxide. 14. Radiation attenuating material according to claim 13, characterised in that the praseodymium oxide is oxide of praseodymium(III-IV), of formula Pr6O11. 15. Radiation attenuating material according to claim 10, characterised in that the radiation attenuating composition comprises 55 to 65% by mass of erbium oxide, and 35 to 45% by mass of praseodymium oxide. 16. Radiation attenuating material according to claim 15, characterised in that the radiation attenuating composition comprises (60±2) % by mass of erbium oxide and (40±2) % by mass of praseodymium oxide. 17. Radiation attenuating material according to claim 10, characterised in that the radiation attenuating composition comprises 30 to 45% by mass of erbium oxide, 20 to 30% by mass of praseodymium oxide and 30 to 45% by mass of bismuth. 18. Radiation attenuating material according to claim 17, characterised in that the radiation attenuating composition comprises 33 to 42% by mass of erbium oxide, 22 to 28% by mass of praseodymium oxide, and 30 to 45% by mass of bismuth. 19. Radiation attenuating material according to claim 10, characterised in that the matrix represents 10 to 25% by mass of the mass of the material, whereas the radiation attenuating composition represents 75 to 90% by mass of the mass of the material. 20. Radiation attenuating material according to claim 10, characterised in that the matrix represents (15±2) % by mass of the mass of the material, whereas the radiation attenuating composition represents (85±2) % by mass of the mass of the material. 21. Radiation attenuating material according to claim 10, characterised in that the radiation attenuating composition is constituted of particles of which at least 90% by number have an average particle size less than or equal to 20 μm. 22. Article providing protection against ionising radiation, in particular X- and gamma-type electromagnetic radiation, comprising a radiation attenuating material according to claim 10. 23. Article providing protection according to claim 22, characterised in that it is a glove, an overall, a chasuble, a jacket, a skirt, an oversleeve, a thyroid protector, a gonad protector, an armpit protective clothing, an ocular protection headband, an operation area, a curtain, a sheet, a bedding, a panel or a protective screen.