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1．Radioactivity occurs naturally. The main sources are in space, rocks, soil, water and even the human body itself. This is called background radiation and levels vary from place to place, though the average dose is fairly constant. The radiation which is of most concern is artificial radiation which results from human activities. Sources of this include the medical use of radioactive materials, fallout and contamination from nuclear industry, and the storage and dumping of radioactive waste.
1、辐射在自然界中普遍存在。（radioactivity n. 放射性；放射；occur vi.存在；发生；出现）主要的辐射源存在于空间、岩石、土壤、水、甚至是人体之中（even the human body itself）。这叫做背景辐射（be called 被叫做…；被称为…）。辐射强度会因地点而异（vary vi. 变化；变异; from place to place 各地，到处），但平均辐射量实则(does, 强调，加强语气的作用)大致相同（fairly adv. 相当地；公平地；constant n. 常数；恒量）。最令人担忧（which is of most concern定语从句修饰the radiation）的是人类活动造成(which results from human activities定语从句修饰artificial radiation)的人工辐射（artificial adj. 人造的；虚伪的；武断的）。辐射源包括医用放射性材料（radioactive materials）、核工业的放射性沉降物和污染物（fallout and contamination），以及辐射废弃物(radioactive waste)的积存和倾倒(the storage and dumping)。
2. While artificial radiation accounts for a small proportion of the total, its effects can be disproportionate. Some of the radioactive materials discharged by human activities are not found in nature, such as plutonium, while others which are found naturally may be discharged in different physical and chemical forms, allowing them to spread more readily into the food-chain.
2、虽然(while)人工辐射只占辐射总量的一小部分，其后果却很严重。（accounts for 占…比例；proportion n.比例；部分；disproportionate adj. 不成比例的）人类活动所排放（discharged by human activities过去分词作定语，修饰some of the radioactive materials；discharge vt. 放出）的一些放射性物质本在自然界中无处可寻(are not found被动语态否定形式)，比如说钚（plutonium）。然而(while)另外一些本来天然存在(which are found naturally)的物质却以各种不同的物理或化学形式(in different physical and chemical forms)被释放出来，致使它们能更轻易地(more readily; readily adv. 容易地)进入食物链。
3. For all these reasons, simple comparisons of background and artificial radioactivity may not reflect the relative hazards. Equally important, it has never been shown that there is such a thing as a safe dose of radiation and so the fact that we are progressively raising global levels should be of as much concern to us as the possibility of another major nuclear test, nuclear reactor or shipment of plutonium means an additional and unnecessary health risk.
3、基于这些原因，也许仅仅拿背景辐射和人工辐射作简单比较（simple comparisons of background and artificial radioactivity）并不能够反映相关的危险性（the relative hazards）。同样重要的是(Equally important)，从来也没有过辐射存在安全摄入量(there is such a thing as a safe dose of radiation; dose n. 剂量)这种说法（such… as… 像…这种的；诸如…之类的）。因此(so)，事实上：就像处理另一场大型核试验、核反应堆的制造、钚材料的运送等可能发生的事情（possibility n.）会对健康形成潜在威胁一样，不断増加辐射总量(we are progressively raising global levels; progressively adv.日益增多地)也应该引起我们足够重视。（that……health risk是同位语从句，进步一说明the fact；从句是一个比较句，比较的内容是两个句子；可译为：我们不断増加的辐射总量（现在进行时；在比较句中做主语）和处理另一场大型核试验、核反应堆的制造、钚材料的运送等可能发生的事情会对健康形成潜在威胁（一般现在时）一样，它们都应引起我们足够多的关心）
4. In general, the effects of radiation can be divided into those which affect the individuals exposed and those which affect their descendants. Somatic effects are those which appear in the irradiated or exposed individual. These include cancer and leukaemia. Hereditary or genetic effects are those which arise in subsequent generations.
4、总的来说（in general），辐射的危害可以分为(be divided into)对辐射接收者本人(the individuals exposed; exposed 是过去分词作定语，修饰the individuals；expose vt. 暴露)的影响以及对其子孙后代的影响（descendant n. 子孙；后代）。身体（somatic adj. 躯体的；肉体的）伤害尤见于辐射接受者本身（those which appear in the irradiated or exposed individual是表语从句；appear in 出现在…；irradiated adj. 被辐射的；radiated adj. 辐射的），包括癌症和白血病（leukaemia）这类病症。遗传（hereditary adj. 遗传的; genetic adj. 遗传的）影响则发生（arise vi. 出现；生产）在其后代身上（in subsequent generations）。（本段中的those which在从句中做主语，指代前面提到的事情，它应该是集体代词，当它被看作整体时，谓语动词用单数形式，而着重强调组成该集体的各个成员时，谓语动词用复数形式，这里使用的是谓语动词的复数形式）
5. Many of the elements which our bodies need are produced by the nuclear industry as radioactive isotopes or variants. Some of these are released into the environment, for example iodine and carbon, two common elements used by our bodies. Our bodies do not know the difference between an element which is needed and which is not. So radioactive elements can be absorbed into living tissues, bones or the blood, where they continue to give off radiation. Radioactive strontium behaves like calcium—an essential ingredient in our bones—in our bodies. Strontium deposits in the bones send radioactivity into the bone marrow, where the blood cells are formed, causing leukemia.
5、我们身体所需要(which our bodies need是定语从句，修饰many of the elements)的许多元素是由核工业以放射性同位素或者变体的形式（as radioactive isotopes or variants）排放（或产生）出来的。其中有一些被释放到环境中，比如说碘(iodine)和碳(carbon)，这是我们身体所需的两种常见元素(two common elements used by our bodies)。我们的身体并不知道需要哪种元素，不需要哪种元素。所以放射性元素能够被我们的活细胞组织(living tissues)、骨骼和血液吸收(be absorbed into 被吸收到…)，而进入人体后其辐射并未停止(continue to give off… 继续释放…)。在我们体内的放射性元素锶(strontium)与人体骨骼中必需的元素（an essential ingredient; ingredient n. 原料；要素；组成部分）钙(calcium)具有类似的表现。在骨骼中锶的沉积物（deposits n. 沉积物）将放射能(radioactivity)传递至产生血液细胞（where the blood cells are formed）的骨髓（the bone marrow）之中，从而引发白血病。
6. There are three principal effects which radiation can have on cells: firstly cells may be killed; secondly the way cells multiply may be affected, resulting in the cells of the ovaries or testes, leading to the development of a child with an inherited abnormality.
6、辐射可以对细胞产生三大主要影响（which radiation can have on cells定语从句，修饰effects; principal adj. 最重要的；可直译为：辐射可以对细胞产生的影响有三大主要方面）：第一，细胞可能会被杀死；第二，细胞的繁殖可能会受影响，进而影响到卵巢或睾丸中的细胞（result in 导致，结果是），引起先天性胎儿畸形(lead to 导致；引起；abnormality 畸形；异常；两个现在分词短语做句子的状语，表结果)。；(thirdly ???)
7. In most cases, cell death only becomes significant when large numbers of cells are killed, and the effects of cell death therefore only become apparent at comparatively high dose levels. If a damaged cell is able to survive a radiation dose, the effects of the cell damage may never become apparent. A few malfunctioning cells will not significantly affect an organ where the large majority are still behaving normally.
7、在多数情况下，只有当大量细胞被杀死时（when large numbers of cells are killed），细胞死亡才会引起严重后果（significant adj. 重大的；值得注意的）。因此细胞死亡这一问题只有在辐射量相对较大的情况下（at comparatively high dose levels; comparatively adv. 相当地; dose不要看作does；dose n. 剂量；用量，在第1段已出现过：the average dose）才得以凸显（apparent adj. 显然的；明显的）。如果一个受损(damaged adj.)细胞在接触一定量的辐射后存活下来（be able to do sth. 能够做某事），那么细胞受损的危害(the effects of the cell damage)就不易被察觉。当大多数细胞在器官内正常运作时(where the large majority are still behaving normally, where指在器官内)，个别受损细胞（a few malfunctioning cells; malfunctioning adj. 出故障的）并不会对整个器官产生重大影响。
8. However, if the affected cell is a germ cell within the ovaries or testes, the situation is different. Ionizing radiation can damage DNA, the molecule which acts as the cell's "instruction book". If that germ cell later forms a child, all of the child's cell will carry the same defect. The localized chemical alteration of DNA in a single cell may be expressed as an inherited abnormality in one or many future generations.
8、然而，如果受损（affected adj.）细胞是卵巢或者睾丸中的生殖细胞(germ cell )，情况就不容乐观了。电离辐射(ionizing radiation; ionizing adj. 电离的；离子化的)可以破坏在细胞中充当着“指令书”作用的DNA分子（molecule n. 分子；act as充当；the molecule… 是DNA的同位语；同位语是名词性的，两者的意思互相补充，也可以理解为主语或宾语的定语）。如果受损的生殖细胞之后发育形成了胎儿，那么这个孩子体内所有的细胞(all of the child's cell)都会带有同样的缺陷(the same defect; defect n. 缺点；缺陷)。单个细胞中DNA的局部化学成分的改变（the localized chemical alteration; localized adj. 局部的；地区的；alteration n. 修改；改变）将会在未来一代或者几代人身上以畸形的方式表现出来（be expressed as…表示为…）。
9. In the same way that a somatic cell in a body tissue is changed in such a way that it or its descendants escape the control processes which normally control cell replication, the group of cells formed may continue to have a selective advantage in growth over surrounding tissues. It may ultimately increase sufficiently in size to form a detectable cancer and in some cases （it many）cause death by spreading locally or to other parts of the body.
9、在体组织中的体细胞(a somatic cell in a body tissue)通过(in such a way that)逃脱(escape)控制细胞复制方式(which normally control cell replication定语从句，修饰the control processes)的控制过程来使体细胞自身或者后代（it or its descendants）发生改变，以同样的方式(in the same way)，新形成的细胞群体(the group of cells formed; formed 过去分词作定语，修饰the group of cells)在增殖过程中（in growth）来获得(continue to have)一种优于其周围组织(over surrounding tissues)的选择性优势(a selective advantage) (本句子翻译做了少许修改) 。最终(ultimately)它们可能在数量上急剧增加，以形成一种可检测性的（to form a detectable cancer不定式作目的状语; detectable adj.）癌症。在某些情况下(in some cases)，这些细胞的局部扩散或扩散到身体的其他部位(by spreading locally or to other parts of the body; spread vt. 传播; spread to 传到，蔓延到)还会导致死亡。
10. While there is now broad agreement about the effects of high-level radiation, they are complicated by the length of time it takes for effects to show up and the fact that（同位语从句） the populations being studied (bomb survivors, people exposed to nuclear industry) are small and exact doses are hard to calculate.
10、虽然(while)关于髙能辐射的危害性如今已达成广泛共识(broad agreement)，但由于辐射伤害往往要很长时间才得以显现（to show up），而且可供研究的对象（the populations being studied; being studied 现在分词被动语态）（爆炸幸存者、接触核工业的人群）人数很少，他们体内的辐射量很难(be hard to)被精确测算，这些都使问题变得更加复杂(complicated adj. 难懂的；复杂的)。
11. All that can be said is that predictions made about the effects of a given dose vary. A growing number of scientists point to evidence that（同位语从句） there is a disproportionately high risk from low doses of radiation. Others assume a directly proportionate link between the received doses and the risk of cancer for all levels of doses, while there are some who claim that at low doses there is a disproportionately low level of risk.
11、我们只能说，人们做出的关于特定辐射量对人体影响程度（made about the effects of a given dose过去分词作定语，修饰predictions预测）的猜测层出不穷且各不相同（vary vi.）。越来越多的科学家们指证说明，少量辐射会给身体带来难以想象的危害（disproportionately adv. 不成比例地）。另一些人则认为不管辐射是多是少（for all levels of doses，即对于所有剂量的辐射水平），人体受到的辐射量和癌症患病风险之间都存在着某种直接的比例关系（assume vt. 假设）。但是（while）也有一些人，他们声称辐射少则危害小（直译：在低辐射下存在着不成比例的低风险水平）。
