首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Radioactivity occurs naturally. The main source comes from natural sources in space, rocks, soil water and even the human body i
Radioactivity occurs naturally. The main source comes from natural sources in space, rocks, soil water and even the human body i
admin
2018-10-19
24
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.
选项
答案
fatal
解析
(由第六段末尾“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”可知它的面积可能最终扩大到足以形成可探测的癌症,在某些情况下通过在局部或身体的其他部分传播会导致死亡。因此填fatal,表示“致命的”。)
转载请注明原文地址:https://kaotiyun.com/show/JiyK777K
本试题收录于:
A类竞赛(研究生)题库大学生英语竞赛(NECCS)分类
0
A类竞赛(研究生)
大学生英语竞赛(NECCS)
相关试题推荐
—YoumaythinkI’mmad,butafteragreatdealofthought,I’venowfinallycometoadecision:IwanttostudyinEngland.—__
Thedeathwatchbeetleisthoughtofasthedevil’spestinchurchesandoldhouses,butinnaturalhabitatsitinfestsawidera
Thedeathwatchbeetleisthoughtofasthedevil’spestinchurchesandoldhouses,butinnaturalhabitatsitinfestsawidera
WhatdoesVetusuallydotodealwithstressanddepression?
WhatdoesVetusuallydotodealwithstressanddepression?
Thenumbersontherightareformedfromthenumbersontheleftusingthesamerules.Discovertheruleusedandreplacethequ
Writeonthefollowingtopic.It’swhileyouarepatientlytoilingatthelittletasksoflifethatthemeaningandshapeofgre
Inthetwonumericalsequencesbelow,onenumberthatappearsinthetopsequenceshouldappearinthebottomsequenceandvice
LatertheGreeksmovedeastfromCumaetoNeapolis,theNewCity,alittlefartheralongthecoastwheremodemNaplesnowstands
A、It’smanufacturedtobestrong.B、Itbendswithoutbreaking.C、Thatchersnailitdownsecurely.D、Thewindscanpassthroughi
随机试题
彼特拉克的抒情诗《歌集》歌咏的爱情对象是【】
When______oursportsmeetisstillaquestion.
某校在2006年8月底突然发生大批腹泻病人,不少人需住院治疗,临床诊断为细菌性痢疾。立即进行流行病学调查,查了4194人,共查出病例769人。最好用下列哪种指标
下列说法正确的是:
社会政策的行动主体是指制定和实施社会政策的责任承担者或行动者。下列不属于社会政策行动主体的是( )。
考试是否达到了测验目的,即是否测出了所要测出的东西是指()。
被公认为是行为主文学习观与认知主文学习观相结合的代表是()
(2016年真题)2013年5月,某外国人在我国境内运输毒品2千克,人民法院依据《中华人民共和国刑法》判处其无期徒刑。该案所体现的我国法律效力的原则是
设数据结构B=(D,R),其中D={a,b,c,d,e,f},R={(a,b),(b,c),(c,d),(d,e),(e,f),(f,a)}。该数据结构为()
【B1】【B11】
最新回复
(
0
)