The Biological Effect of Large and Small Doses (p.102)

Date: 2015-10-07; view: 475.

Mechanism of Radiation Damage (p.98)

1. Any material undergoes some damage or change on irradiation.

2. In elements the only effect is a change of the crystal structure.

3. Living organisms undergo chemical change.

4. Ionizing radiations passing through living matter produce changes in the heredity of the cell.

5. Mechanism of radiation damage falls into two main groups – direct action and indirect one.

6. Direct action is the breaking of some part of the cell structure by the bombarding particles or photons.

7. In indirect action very active groups of atoms called free radicals are formed.

8. Thus the mechanism of the radiation damage has the following steps:

a) radiation energy absorption

b) free radicals formation

c) the breaking of biochemical reaction

d) the breaking of physiological reaction

1. Biological changes result from large doses of internal and external irradiation

2. They lead to radiation syndrome or radiation disease.

3. They distinguish acute radiation disease and chronic radiation disease.

4. Radiation disease is considered in units of the absorbed dose.

5. At free air exposure from 100 to 200 rads we observe light form of acute radiation disease.

6. At mid-line absorbed dose from 200 to 400 rads there is malfunction of the main system of the living organism.

7. At extremely high exposures 400-600 rads we observe heavy form of the acute radiation disease.

8. There are three effects of small doses to living matter.

9. Cells may not be killed by a given dose of radiation, they may be unable to divide or they may undergo mutation.

10. Mutation is a new form of gene which affects the following generation.

RADIATION MONITORING(p.108)

1. Monitoring may be defined as a detection and measurement of radioactive contamination.

2. The instruments differ in their construction depending on the type of radiation detected.

3. The main instruments used for alpha contamination detection are the air proportional counter, the gas-flow proportional counter and scintillation counter.

4. Beta-gamma radiations are considered together because most radioactive materials emit both radiations.

5. For beta-gamma radiation monitoring the ionization chamber and the Geiger-Muller (GM) counters are used.

6. Neutrons are among the most difficult radiations to measure.

7. They are not directly ionizing and must be detected indirectly from ionizing radiations produced.

8. Instruments for neutrons monitoring are: proportional-counter tube, a scintillation counter, or thermoluminescent dosimeters for fast neutrons.