1.半衰期⑴定义:放射性元素的原子核有半数发生衰变所需的时间,叫做这种元素的半衰期,用τ表示.⑵公式:半衰期一般用τ表示,t表示衰变时间,N0表示放射性元素的初始原子核个数,N为经历了n个半衰期后所剩余放射性元素的原子核个数,ΔN表示已衰变的放射性元素原子核个数;m0表示放射性元素的初始质量,m为经历了n个半衰期后所剩余放射性元素的质量,Δm表示已衰变的放射性元素的质量.则有如下4个公式: 1. Half-life ⑴ Definition: The time required for decay half of the nuclei of radioactive elements, called the half-life of this element, expressed as τ. (2) Formula: Half-life is generally expressed as τ, t is the decay time, N0 is the initial radioactive element N is the number of nuclei of the remaining radioactive elements after n half-lives, ΔN is the number of nuclei of the decayed radioactive elements, m0 is the initial mass of the radioactive elements, m is the number of nuclei remaining after n half-lives The mass of the radioactive element, Δm, indicates the mass of the decaying radioactive element, then there are 4 formulas: