Abstract: A UO2 target for use in the manufacture of 99Mo, the target comprising: a porous matrix; wherein the matrix comprises particles of UO2 or of UO2 and CeO2 with a size of less than 7.15 ?m; and a molar ratio of 235U to Ce and 238U is less than 3%. The particles may comprise UO2 and the UO2 comprise uranium with a 235U to 238U ratio of less than 3% 235U enrichment. Also, a method of producing 99Mo, comprising: (a) irradiating such a UO2 target with thermal neutrons, with an irradiation time of between 3 and 7 days; then (b) extracting 99Mo from the target. The method includes performing steps (a) and (b) 2 or more times.