To improve internal environment of children’s body by keeping them away from radiation affected area for certain period. As biological half-life period of radioactive particles (The period in which radioactive particles stay within human body) is much shorter than those particles’ own half-life period, if children stay apart from the radiation affected area for certain period and do not inhale additional radioactive particles, the remained particles are eliminated from their bodies gradually. Thus, the dose of cumulative internal exposure of radiation of children will be decreased