* NORM. Naturally occurring radioactive materials and Technologically Enhanced Naturally Occurring Radioactive Materials consist of materials， usually industrial wastes or by-products enriched with radioactive elements found in the environment， such as uranium， thorium and potassium and any of their decay products， such as radium and radon. For example， coal， a combustible black or brownish-black sedimentary rock， contains a substantial amount of the radioactive elements uranium and thorium. According to the UNSCEAR， the average specific activity of both uranium-238 and thorium-232 in coal is generally around 20 Bq/kg . Coal mines in Freital， Germany， which have uranium concentrations of 15000 Bq/kg， are an exception. Burning coal gasifies its organic materials， concentrating its inorganic components into the remaining waste， called fly ash. Around 10% of coal is fly ash. Fly ash is hazardous and toxic to human beings and some other living things， and fly ash also contains the radioactive elements uranium and thorium， which are concentrated by a factor of 10.
根据宇宙射线的路线可以将其产生的射线分为三部分，宇宙射线对地球形成的辐射称为初级辐射，但是大气层、电离层、电磁层会保护我们，此阶段的射线只有当人类进入太空时才可能受到辐射，这是第一部分；第二部分射线是宇宙射线穿过大气层，与空气中的物质成分发生反应，产生次级粒子，形成次级辐射，这是
统计数据显示，世界范围内的不孕不育发生率高达15%~20%，越来越多的朋友开始关注和重视生殖健康。核燃料循环，放射性核素研究、生产和使用，X线探测仪、医疗影像检查，以及肿瘤放疗等，都是日常电离辐射的重要人工来源。
