tailieunhanh - Radiation and Health - Chapter 11

Nhiều thông tin về các tác động sinh học của liều lượng lớn bức xạ nhưng ít được biết về ảnh hưởng của liều lượng nhỏ. Trong hầu hết các thí nghiệm với các tế bào, thực vật và động vật, liều lượng lớn đã được áp dụng với kết quả rõ ràng và quan trọng. Khi liều lượng trở nên nhỏ hơn tác dụng giảm và trở nên ít rõ ràng hơn. Để bù đắp cho điều này, số lượng của các đối tượng (ví dụ, động vật) có thể được tăng lên. Tuy nhiên, đối với khu vực. | Chapter 11 Small Doses and Risk Estimates The Dose-Effect Curve Much is known about the biological effects of large doses of radiation but less is known about the effects of small doses. In most experiments with cells plants and animals large doses have been applied with clear and significant results. When the doses become smaller the effects decrease and become less clear. In order to compensate for this the number of subjects . animals can be increased. However for the region where very small doses are involved . from an annual dose of a few mGy up to an acute dose of about 50 mGy the number of animals or humans must be so large that it is very difficult usually impossible to conduct experiments and or epidemiological studies. In epidemiological studies attempts are made to correlate the radiation dose to the incidence of biological effects such as cancers in a large group of people. Some examples are the populations that have been exposed to radon those exposed to the bombs at Hiroshima - Nagasaki and those exposed during the Chernobyl accident. Such studies have yielded both conflicting and confusing results. They are however of considerable interest to scientists and to the public. In this chapter we will discuss known health effects and risks in the low dose region. We will concentrate on the incidence of cancer. The crucial factor is the dose-effect curve. The form of the dose-effect curve is essential for all risk estimates. A discussion of the dose-effect curve for the low dose region must include both experimental work and theoretical models. 2003 Taylor Francis 128 Radiation and Health The shape of the dose-effect curve must be known in order to evaluate the effects of small increments of dose. Consequently all risk estimates are closely linked to the assumed shape of this curve. Two very important alternatives are outlined in Figure and are discussed in this chapter. Figure . Two different dose-effect curves for the incidence of cancer. .