首页
登录
职称英语
Radioactivity occurs naturally. The main source comes from natural sources in
Radioactivity occurs naturally. The main source comes from natural sources in
游客
2024-08-06
28
管理
问题
Radioactivity occurs naturally. The main source comes from natural sources 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 bomb tests, discharges from the nuclear industry, and the storage and dumping of radioactive waste.
While artificial radiation accounts for a small proportion of the total , its effects can be disproportionate. Some of the radioactive materials discharged by human activity are not found in nature, such as plutonium(钚)while others which are found naturally may be discharged in different physical and chemical forms, allowing them to spread more readily into the environment, or perhaps accumulate in the food-chain.
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 radioactive and one which is not. So radioactive elements can be absorbed into living tissues, bones or the bleed, 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, pausing leukemia.
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 situation is different. In many cases the effect of the cell damage may never become apparent. A few malfunctioning cell will not significantly affect an organ where the large majority are still behaving normally.
However, if the affected cell is a germ cell within the ovaries or testicles, 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 cells 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.
In the same way that a somatic cell(体细胞)in 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 tissue. It may ultimately increase sufficiently in size to form a detectable cancer and in some cases cause death by spreading locally or to other parts of the body.
While there is now broad agreement about the effects of high-level radiation, there is controversy over the long-term effect of low-level doses. This is complicated by the length of time it takes for effects to show up, the fact that the populations being studied are small and exact doses are hard to calculate.
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 there is a disproportionately high risk from low doses of radiation. Others assume a directly proportionate link between the received dose and the risk of cancer for all levels of dose, while there are some who claim that at low doses there is a disproportionately low level of risk.
Questions 56 to 60
Fill in the blanks below with information from the passage, using no more than three words for each blank.
[br]
选项
答案
an inheritable abnormality
解析
(由第五段末尾“The localized chemical alteration of DNA in a single cell may be expressed as an inherited abnormality in one or many future generations”可知在一个或多个后代中,单个细胞的局部DNA化学蚀变可能被表达为先天性异常。因此填an inheritable abnormality,表示“可遗传的异常”。)
转载请注明原文地址:https://tihaiku.com/zcyy/3708113.html
相关试题推荐
Activelearningoccurswhenalearnertakessomeresponsibilityforthedevel
Activelearningoccurswhenalearnertakessomeresponsibilityforthedevel
Activelearningoccurswhenalearnertakessomeresponsibilityforthedevel
Activelearningoccurswhenalearnertakessomeresponsibilityforthedevel
Activelearningoccurswhenalearnertakessomeresponsibilityforthedevel
Activelearningoccurswhenalearnertakessomeresponsibilityforthedevel
Naturalhistoryfanswillprobablybefamiliarwiththenineseasonsofthe
Naturalhistoryfanswillprobablybefamiliarwiththenineseasonsofthe
Naturalhistoryfanswillprobablybefamiliarwiththenineseasonsofthe
Radioactivityoccursnaturally.Themainsourcecomesfromnaturalsourcesin
随机试题
Therearealargenumberofreferencebooks______toyou;youcanmakeuseoft
老师占用体育课,你是体育老师怎么看?
按照现行的地下工程防水等级标准,2级防水的工业与民用建筑应符合下列()的规定
下列关于人禽流感实验室检查的叙述,错误的是()A.外周血白细胞减少
下图是某地区城市规划示意图,读图完成下题。 图中信息显示,城市的服务功能(
下列关于投资者需求关键因素的说法错误的是()。A.通常情况下,投资期限越长
(2016年)根据《测绘生产质量管理规定》,下列质量管理工作内容中,不属于单位法
有限责任公司整体变更为股份有限公司,其过去()年业绩可连续计算。 A.1
患者,女,70岁,因无牙颌戴全口义齿10年,因旧义齿折断要求重新制作,检查见上颌
(2011年)根据《环境影响评价技术导则声环境》,下列噪声预测范围或预测点中,符
最新回复
(
0
)