N'afọ 1925, ọ chọpụtara na-adịghị ike radioactivity na a sample nke potassium, ọzọ alkali metal, na-ezighị ezi kwubiri na eka-caesium na-emetọ sample (na radioactivity si sample bụ site ndammana na-ewere ọnọdụ potassium radioisotope, potassium-40). O bipụtara a tesis na amụma ya nke Njirimara nke eka-caesium, nke ọ aha ya bụ russium mgbe ya n'ụlọ mba. N'oge na-adịghị anya mgbe nke ahụ gasịrị, Dobroserdov malitere ilekwasị anya na ya na-akụzi ọrụ na Polytechnic Institute of Odessa, na ọ bụghị na-achụso ndị ọzọ mmewere. N'afọ na-esonụ, English chemists Gerald F. Druce na Frederick H. Allison chọpụtara na-adịghị ike radioactivity na a sample nke potassium, ọzọ alkali metal, na-enyocha na-adịghị ike radioactivity na a sample nke potassium, ọzọ alkali metal. N'afọ 1936, onye ọkà mmụta sayensị bụ́ onye America bụ́ Allison Hirsch na-eji igwe nchọpụta ya nke na-enyocha ihe
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