half-life造句

• It has a half-life of about 41/2 billion years .
  它的半衰期大约为45亿年。
• The half-life of francium is 22 minutes .
  钫的半衰期是22分钟。
• Evolutionists have recently learned that groups of species also have what might be called a half-life .
  进化论者最近发现生物属种也具有一种可以称为半死亡期的时期。