Measurements of rating of equivalent dose, μSv/hour

Theoretical part

Ionizing radiation ? fast-moving alpha or beta particles or high-energy electromagnetic radiation emitted by radioisotopes that have enough energy to dislodge one or more electrons from atoms it hits to form charged ions, which can react with and damage living tissue.

Natural radioactivity ? a nuclear change in which unstable nuclei of atoms spontaneously shoot out ?chunks? of mass, energy, or both at a fixed rate.

The two most common types of ionizing particulate radiation are high-speed alpha particles (positively charged chunks of matter that consist of two protons and two neutrons) and beta particles (negatively charged electrons).

Radio waves, infrared light, and ordinary light are examples of nonionizing electromagnetic radiation, which does not have enough energy to cause ionization of atoms in living tissue. Although X rays are a form of high-energy ionizing radiation that can pass through the body and cause damage, they are not given off by radioisotopes. The most common form of ionizing electromagnetic radiation released from radioisotopes is high-energy gamma rays, which are even more penetrating than X rays. Some unstable nuclei emit only one type of ionizing radiation, others emit 2 or 3 types.

Dose is energy of ionizing radiation, which was absorbed (got) by unit of volume or mass during the time of exposure. Speed of getting ionizing radiation doze characterize rate of dose, which is determined as ratio of dose to exposure time.

Absorbed dose ? ratio of energy to mass of body, which got the energy. Unit of absorbed dose is Gray (1 Gr = 1 J/kg), and widely used nonsystem unit is rad.

To characterize the quality of radiation the equivalent dose is used. Equivalent dose - absorbed dose, which is multiplied by coefficient, which shows the possibility of particular type of ionizing radiation to damage the living tissues. Unit of equivalent dose is Sievert (Sv). Nonsystem unit is rem.

Exposure to any ionizing radiation can damage cells in the human body. The effects depend on the amount and frequency of exposure, the type of ionizing radiation, its penetrating power, and whether it comes from outside or inside the body.

From the outside, alpha particles and beta particles can cause burns at high levels of exposure, but cannot penetrate the skin to cause internal damage. However, if a radioactive isotope that emits alpha or beta particles is inhaled or ingested into the body, the particles can cause considerable damage to nearby vulnerable tissues. Gamma rays and high-energy neutrons are so highly penetrating that they pass through the body easily and inflict internal cellular damage from outside or inside the body.

Most damage occurs in tissues with rapidly dividing cells, such as the bone marrow (where blood cells are made), spleen, digestive tract (whose lining must be constantly renewed), reproductive organs, and lymph glands. Rapidly growing tissues of the developing embryo are also extremely sensitive, so pregnant women should avoid all exposure to radioactivity and X rays unless they are essential for the health or diagnostic purposes.

Small doses of ionizing radiation over a long period of time cause less damage than the same total dosage given all at once, because our body apparently has some ability to repair itself. Exposure to a large dose of ionizing radiation over a short time, however, can be fatal within a few minutes to a few months later, depending on the dose.

All living things are exposed to small amounts of ionizing radiation, known as natural, or background, ionizing radiation. Sources include cosmic rays from outer space; naturally radioactive isotopes, such as radon-222 found in certain types of rock and in bricks, stone and concrete used in construction; and other natural radioactivity that finds its way into air, water, and food. We receive additional exposure to ionizing radiation as a result of various human activities, most from dental and medical X rays and diagnostic tests involving the injection or ingestion of radioactive isotopes. The smallest amount of human-caused exposure to ionizing radiation comes from nuclear power plants and other nuclear facilities ? assuming that they are operating normally.

The standards of radiation safety used in Ukraine define the permissible level of equivalent dose for buildings with people as 0,5 μSv per hour.

Practical part

I.The principle of dosimeter operation is based on registration of gamma rays by Geiger counter, which convert energy of gamma rays to electrical impulses, frequency of which is proportional to rate of equivalent dose of this radiation.

Method of measuring

1.Hold the device at the distance of 10 cm from the surface of investigated object.

2.Switch the power in on-position.

3.The start information ? 0,00 μSv/hour appears on the dosimeter display.

4.After the setting the work mode dosimeter begins the cycle of measuring, which ends with the result presented on display. The end of each cycle of measurement is marked by ?=? in the extreme left corner of the display.

For example, information on display ?= 0,14? means, that in the previous cycle the result of measuring was 0,14 μSv/hour.

5.Dosimeter works in cycle automatic mode. After fixation of the previous cycle result the display information is upcasted and new cycle begins automatically.

II.1.Measure the level of radioactive background of environment with the dosimeter in the following point: on the soil surface (floor surface), window-sill, table. Quantity of measurements in each point is multiply 5.

2.Note the results in the table. Compare got received results with the safe (possible) level of rate of equivalent dose. Make conclusions.

Table

Measurements of rating of equivalent dose, μSv/hour

Date: 2016-06-12; view: 8