2. 职称考试
  3. 下面的短文后列出了 7 个句子，请根据短文的内容对每个句子做出判断：如果该句提供的是正确信息，请选择A ; 如果该句提供的是错误信息，请选择B ; 如果该...

下面的短文后列出了 7 个句子，请根据短文的内容对每个句子做出判断：如果该句提供的是正确信息，请选择A ; 如果该句提供的是错误信息，请选择B ; 如果该...

admin2020-12-24  29
问题 下面的短文后列出了 7 个句子，请根据短文的内容对每个句子做出判断：如果该句提供的是正确信息，请选择A ; 如果该句提供的是错误信息，请选择B ; 如果该句的信息文中没有提及，请选择C。

Radiocarbon Dating  
Nowadays scientists can answer many questions about the past through a technique called radiocarbon （放射性碳）， or carbon-14， dating. One key to understanding how and why something happened is to discover when it happened.
Radiocarbon dating was developed in the late 1940s by physicist Willard F. Libby at the University of Chicago. An atom of ordinary carbon, called carbon-12, has six protons（质子）and six neutrons（中子）in its mKJteus（原子核）.Carbon-14, or C-14, is a radioactive.
unstable form of carbon that has two extra neutrons. It returns to a more stable form of carbon through a process called decay ( 衰减）. This process involves the loss of the extra neutrons and energy from the nucleus.
In Libby’s radiocarbon dating technique, the weak radioactive emissions （放射） from this decay process are counted by instruments such as a radiation detects and counter. The decay rate is used to determine the proportion of C-14 atoms in the sample being dated.
Carbon-14 is produced in the Earth’s atmosphere when nitrogen （氮）-14，or N-14, interacts with cosmic rays （宇宙射线）. Scientists believe since the Earth was formed，the amount of nitrogen in the atmosphere has remained constant. Consequently, C-14 formation is thought to occur at a constant rate. Now ratio of C-14 to other carbon atoms in the atmosphere is known. Most scientists agree that this ratio is useful for dating items back to at least 50, 000 years.
All life on Earth is made of organic molecules （分子） that contain carbon atoms coming from the atmosphem. So all living things have about the same ratio of C-14 atoms to other carbon atoms in their tissues （组织）. Once an organism （有机体） dies it stops taking in carbon in any form, and the C-14 already present begins to decay. Over time the amount of C-14 in the material decreases, and the ratio of C-14 to other carbon atoms goes down. In terms of radiocarbon dating, the fewer C-14 atoms in a sample, the older that sample is.
An atom of ordinary carbon has six protons and eight neutrons.
选项 A Right
B Wrong
C Not mentioned
答案B
解析
转载请注明原文地址:https://ti.zuoweng.com/ti/t6sQKKKQ
相关试题推荐
随机试题