摘要：Man has always been exposed to natural radiation arising from the earth as well as from outside the earth.No human activity or practice is totally devoid of associated risks.Radiation should be viewed from the perspective that the benefit from it to mankind is less harmful than from many other agents.In general,the basic principles of radiation protection (jutification and optimization of a procedure) need to be respected to help counteract the unjustified exposure in the number of procedures being performed.However ALARA(As Low as Reasonably Achievable) doses should be the guiding principle in dealing with radiation.
