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铀为锕系元素,地壳中含量为3mg/kg。天然铀由234U、235U和238U三种同位素组成,丰度分别为0.0058%、0.714%、99.274%。铀系有多种同位素,除232U、233U、236U和238U为长半衰期α辐射体外,其他均为短半衰期的α或β辐射体,有些伴有γ射线。尽管含量极低,但是234U的放射性比活度远
Uranium is an actinide, with a crust content of 3 mg / kg. Natural uranium is composed of three isotopes 234U, 235U and 238U with abundances of 0.0058%, 0.714% and 99.274%, respectively. Uranium has a variety of isotopes, with the exception of 232U, 233U, 236U and 238U, which are alpha or beta emitters with short half-lives and long gamma-rays, respectively. Despite its low content, 234U’s radioactivity is far more specific