tailieunhanh - Radiation and Health - Chapter 8

Bức xạ trong Y học và nghiên cứu Nhân tạo hoặc con người (nhân tạo) nguồn bức xạ được sử dụng rộng rãi trong y học, nghiên cứu và công nghiệp, và các nguồn dưới sự kiểm soát quy định. Trong chương này và tiếp theo, việc sử dụng các nguồn bức xạ nhân tạo sẽ được kiểm tra tập trung vào đánh giá liều bức xạ cho những người làm việc với các nguồn này cũng như những người khác có thể được tiếp xúc | Chapter 8 Radiation in Medicine and Research Artificial or anthropogenic human made radiation sources are used extensively in medicine research and industry and these sources are under regulatory control. In this chapter and the next the use of artificial radiation sources will be examined with a focus on estimating radiation doses to those working with these sources as well as others who may be exposed. Radiation Sources X-ray machines are by far the most numerous and significant of the artificial radiation sources. Hospitals throughout the world use different x-ray machines for many diagnostic purposes. X-rays are also important in the practice of dentistry and chiropractory. In addition a number of hospitals have radiation producing equipment such as linear accelerators used for treating cancer. It is important to note that the radiation from x-ray sources can be turned on and off. There are therefore no problems with storage and during periods when the equipment is not in use. When these devices are in use the radiation field can be limited by lead screens and collimators. 2003 Taylor Francis 80 Radiation and Health X-ray diagnostics A few months after the discovery of x-rays the first x-ray pictures were published showing the possibility of seeing inside a living human. On the left is shown one of the first X-ray pictures taken in May 1896. On the right is a mammogram taken almost 100 years later. Note the differences in these two pictures. In the picture ofthe hand details ofthe bone structure and a ring are readily recognized. It is a lot more difficult in the mammogram to distinguish between cancer tissue and normal tissue. With knowledge about the absorption of x-rays the equipment can be used to achieve this goal. X-rays are absorbed more efficiently by heavy atoms than light atoms due to the increase in electron density see Chapter 2 . The large differences in electron density between bone and soft tissue are easy to see. The small difference in electron