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  • 放射性同位素

    Fossil skull of an ancient human ancestor displayed in a museum setting.

    This fossil skull came from an ancient human ancestor. Scientists used carbon-14 dating to estimate its age. Carbon-14 is one of several radioisotopes that scientists use to estimate the ages of fossils and other ancient materials.
    ::这个化石头骨来自一个古老的人类祖先,科学家用碳-14来估计其年龄。碳-14是科学家用来估计化石和其他古老材料年代的若干放射性同位素之一。

    What Are Radioisotopes?
    ::什么是放射性同位素?

    All the atoms of a given have the same number of in their nucleus , but they may have different numbers of . Atoms of the same element with different numbers of neutrons are called isotopes. Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes . Their nuclei are unstable, so they break down, or decay, and emit radiation.
    ::给定原子的核中原子数量相同,但它们可能具有不同的数量。 具有不同数量中子的同一元素的原子被称为同位素。 许多元素含有一种或多种放射性同位素。 这些同位素被称为放射性同位素。 这些同位素的核是不稳定的,因此它们分解或衰变,并释放辐射。

    Q: What makes the nucleus of a radioisotope unstable?
    ::问题:什么使放射性同位素核心不稳定?

    A: The nucleus may be unstable because it has too many protons or an unstable ratio of protons to neutrons. For a nucleus with a small number of protons to be stable, the ratio of protons to neutrons should be 1:1. For a nucleus with a large number of protons to be stable, the ratio should be about 1:1.5.
    ::A:核心可能不稳定,因为它有太多质子或质子与中子之间的不稳定比率。 质子数量少的核心要保持稳定,质子与中子的比例应该是1:1。 质子与中子的比例应该是1:1。 质子数量大的核心要稳定,比例应该是1:1.5。

    An Example: Carbon-14
    ::实例:碳-14

    Find carbon in the Figure , and you’ll see that its is 6. This means that all carbon atoms have 6 protons per nucleus. Almost all carbon atoms also have 6 neutrons per nucleus. These carbon atoms are called carbon-12, where 12 is the number of protons (6) plus neutrons (6). This gives carbon-12 nuclei a 1:1 ratio of protons to neutrons, so carbon-12 nuclei are stable.
    ::在图中找到碳,你会看到它的是6。 这意味着所有的碳原子每个核都有6个质子。 几乎所有的碳原子每个核都有6个中子。 这些碳原子被称为碳-12,其中12个是质子数量(6)+中子数量(6)。 这使得碳-12核的质子对中子比例为1:1,因此碳-12核是稳定的。

    Some carbon atoms have more than 6 neutrons, either 7 or 8. Carbon atoms with 8 neutrons are called carbon-14 (6 protons + 8 neutrons). The nuclei of carbon-14 atoms are unstable because they have too many neutrons relative to protons, so they gradually decay.
    ::有些碳原子有超过6个中子,有7个或8个,有8个中子的碳原子称为碳-14(6个质子+8个中子 ) 。 碳-14原子核心不稳定,因为它们相对于质子有太多的中子,因此它们逐渐衰减。

    Q: What is the proton-to-neutron ratio of carbon-14 nuclei?
    ::问题:碳-14核的质子对中子比率是多少?

    A: With six protons and 8 neutrons, the ratio is 6:8, or 1:1.3.
    ::A:有6个质子和8个中子,比率为6:8或1:1.3。

    Q: How is carbon-14 used to estimate the ages of fossils?
    ::问题:碳-14如何用来估计化石的年代?

    A: Living things take in carbon, including tiny amounts of carbon-14, throughout life. The carbon-14 constantly decays, but more carbon-14 is taken in all the time to replace it. After living things die, no new carbon-14 is taken in, and the carbon-14 they already have keeps decaying. The older a fossil is, the less carbon-14 it still has, so the remaining amount can be measured to estimate the fossil’s age. 
    ::问题:生命在生命中吸收碳,包括微小数量的碳-14。碳-14在不断衰减,但更多的碳-14在不断被取代。 生命死后,碳-14不再被吸收,碳-14已经不断衰减。 化石老化,碳-14仍然少,因此剩余数量可以测量来估计化石的年代。

    Periodic table highlighting elements, particularly focusing on carbon-14 and radioisotopes.

    Periodic Table of the Elements
    ::要点定期表格

    Radioactive Elements
    ::放射性元素

    In elements with more than 83 protons, all of the isotopes are radioactive. In the Figure , these are the elements with a yellow background. The force of repulsion among all those protons makes the nuclei unstable. Elements with more than 92 protons have such unstable nuclei that they don’t even exist in nature. They have only been created in labs.
    ::在超过83个质子的元素中,所有同位素都是放射性的。在图中,这些元素是黄色背景的元素。所有这些质子的反弹力使得核不稳定。92个质子以上的元素有如此不稳定的核,以至于它们根本不存在自然。它们只是在实验室中产生的。

    Summary
    ::摘要

    • Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes. An example of a radioisotope is carbon-14.
      ::许多元素含有一种或多种放射性同位素。这些同位素被称为放射性同位素。放射性同位素的例子之一是碳-14。
    • The nuclei of radioisotopes are unstable, so they constantly decay and emit radiation.
      ::放射性同位素的核心是不稳定的, 所以它们不断腐烂和释放辐射。
    • In elements with more than 83 protons, all of the isotopes are radioactive.
      ::在超过83个质子的元素中,所有同位素都是放射性的。

    Review
    ::回顾

    1. What is a radioisotope? Give an example.
      ::放射性同位素是什么?
    2. Why do radioisotopes have unstable nuclei?
      ::为什么放射性同位素有不稳定的核?
    3. Which elements in the periodic table have only radioactive isotopes?
      ::周期表中哪些元素只有放射性同位素?

    Explore More
    ::探索更多

    Watch the video about radioisotopes and then answer the questions below. 
    ::观看关于放射性同位素的视频,然后回答下面的问题。

    1. Describe the analogy in the video for stable and radioactive isotopes.
      ::描述视频中稳定与放射性同位素的类比。
    2. Complete the following table :
      ::填写下表:
    Atomic Number Proton-to-Neutron Ratio for a Stable Nucleus
    1 - 19  
    20 – 82  
    > 82  
    1. How can radioisotopes become stable? List three ways and state when each way occurs.
      ::放射性同位素如何稳定?列出三种方法,说明每种方法发生的时间。