放射性同位素
维基百科，自由的百科全书
每個原子也有很多的同位素，每組同位素的原子序雖然是相同，但卻有不同的原子量。如果這原子是有放射性的話，它會被稱為物理放射性核種或放射性同位素。
放射性同位素是一個原子，而原子核是不穩定的。那個放射性同位素也將會進行放射性衰變，從而放射出伽瑪射線，和次原子粒子。放射性同位素天然地出現，但人工製造。
放射性同位素在英文中，會被化學家和生物學家分別稱為radioactive isotopes和radioisotopes，但也是放射性同位素的意思，化學家和生物學家都把放射性同位素的技術應用在我們的食品、水和身體健康等事項之。不過，他們也察覺到真正的危險，也有使用的安全規則。
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[编辑] 起源
天然存在的放射性同位素主要是恆星的內部。例如鈾，在星體內直接被形成。而當今仍然存在，是因為它們的半衰期的時間很長，而它們還沒有完全衰變。放射產生的同位素，如碳-14，是由長期衰變得出的。(這個也是全部目前氦形成方法： 雖然它沒有放射性，但是它容易逃離地球，因此氦被從地下倉庫等地方獲得。)
核反應堆和放射性同位素發電機的粒子加速器可人工製造放射性同位素。
放射性同位素生產核反應堆中的高流和大量的中子。 在核反應堆中，中子用來生激活放射性元素。 來自一個核回應堆的一種典型的生成物是鉈（Tl）-201。
Particle accelerators such as cyclotrons accelerate particles to bombard a target to produce radionuclides. Cyclotrons are used to accelerate protons at a target to produce positron emitting radioisotopes e.g. fluorine-18.
Radionuclide generators contain a parent isotope that decays to produce a radioisotope. The parent is usually produced in a nuclear reactor. A typical example is the technetium-99m generator used in nuclear medicine. The parent produced in the reactor is molybdenum-99.
Trace radionuclides are those that occur in tiny amounts in nature either due to inherent rarity, or to half-lives that are significantly shorter than the age of the Earth. Synthetic isotopes are not naturally occurring on Earth, but they can be created by nuclear reactions.
[编辑] 使用
放射性同位素的用途主要有两个：利用它们的化学特性以及作为辐射的来源。
Radionuclides of familiar elements such as carbon can serve as tracers because they are chemically very similar to the non-radioactive nuclides, so most chemical, biological, and ecological processes treat them in a near identical way. One can then examine the result with a radiation detector, such as a geiger counter, to determine where the provided atoms ended up. For example, one might culture plants in an environment in which the carbon dioxide contained radioactive carbon; then the parts of the plant that had laid down atmospheric carbon would be radioactive.
In medicine, radioisotopes are used for diagnosis, treatment, and research. Radioactive chemical tracers emitting gamma rays that can provide diagnostic information about a person's internal anatomy and the functioning of specific organs. This is used in some forms of tomography single emission computed tomography and positron emission tomography scanning. Radioisotopes are also a promising method of treatment in hemopoietic forms of tumors, while the success for treatment of a solid tumors has been limited so far. More powerful gamma sources are used to sterilise syringes and other medical equipment. About one in two people in Western countries are likely to experience the benefits of nuclear medicine in their lifetime.
In biochemistry and genetics, radionuclides are used to label molecules and allow tracing chemical and physiological processes occurring in living organisms, such as DNA replication or amino acid transport.
在食物的保存上，辐射可以阻止根块植物在收成之后发芽，杀除一些攀在植物上的寄生虫与害虫，还可以用来控制一些储存起来水果以及蔬菜的成熟度。
In agriculture and animal husbandry, radionuclides also play an important role. They are used to produce high intake of crops, disease and weather resistant varieties of crops, to study how fertilisers and insecticides work, and to improve the production and health of domestic animals.
Industrially, and in mining, radionuclides are used to examine welds, to detect leaks, to study the rate of wear of metals, and for on-stream analysis of a wide range of minerals and fuels.
Most household smoke detectors contain the radionuclide americium formed in nuclear reactors, saving many lives.
Environmentally, radionuclides are used to trace and analyse pollutants, to study the movement of surface water, and to measure water runoffs from rain and snow, as well as the flow rates of streams and rivers.
Natural radionuclides can be used in archaeology and in paleontology to measure ages. When radioactive carbon, for example, is in the atmosphere, it rapidly becomes separated from its decay products. Once it is bound up in a solid, such as wood or paper, its decay products must remain in place. So by measuring how much of these decay products has accumulated, one can estimate the time when the carbon was captured into solid form.
[编辑] 危險
如果放射性同位素被釋放到環境，透過一些事故、不良的處理或者其他方法，他們能潛在並引起有害的效應，放射性污染。如果過分地使用在醫療或生活應用上，也能導致危險，為放射性中毒。放射性同位素也能導致電器故障。
[编辑] 參考文獻
- Carlsson J et al.:Tumour therapy with radionuclides: assessment of progress and problems. Radiotherapy and Oncology, Volume 66, Issue 2, February 2003, Pages 107-117. PMID 12648782. Available online as full text.
