41601

Background Radioactivity of Environment

Лабораторная работа

Экология и защита окружающей среды

Shchetynsk ICS 405 Lbortory work Bckground Rdioctivity of Environment im: to lern the methods of mesure of bckground rdioctivity simply gmmrdition. Theoreticl informtion Mny forms of “rdition†re encountered in the nturl environment nd re produced by modern technology. Even sunlight the most essentil rdition of ll cn be hrmful in excessive mounts. Most public ttention is given to the ctegory of rdition known s “ionizing rdition.

Английский

2013-10-24

19.23 KB

0 чел.

Done by T. Shchetynska, IACS 405

Laboratory work #1

Background Radioactivity of Environment

Aim: to learn the methods of measure of background radioactivity simply gamma-radiation.

Theoretical information

Many forms of “radiation” are encountered in the natural environment and are produced by modern technology. Most of them have the potential for both beneficial and harmful effects. Even sunlight, the most essential radiation of all, can be harmful in excessive amounts. Most public attention is given to the category of radiation known as “ionizing radiation.” This radiation can disrupt atoms, creating positive ions and negative electrons, and cause biological harm. Ionizing radiation includes x-rays, gamma rays, alpha particles, beta particles, neutrons, and the varieties of cosmic rays.

All ionizing radiations, at sufficiently large exposures, can cause cancer. Many, in carefully controlled exposures, are also used for cancer therapy. Whether harmful or beneficial, exposures to ionizing radiation have been an inevitable part of the environment throughout the Earth's history. The nucleosynthesis processes that produced the elements created both stable and unstable nuclides. The unstable nuclides with very long half-lives, together with their radioactive progeny, constitute the natural radioactivity on Earth today. In addition, violent processes in the sun and elsewhere lead to the bombardment of the Earth by cosmic rays. Thus, radiation is an old and familiar, if unrecognized, pollutant.

Radiation is measured in terms of its effects on people and materials. Radiations such as ultra violet, infra-red, microwaves etc. are not considered here but only those emitted by radioactive materials. These are known as ionising radiations. For man the unit used to measure ionising radiation dose is the millisievert (mSv). Radiation from radioactive materials can be in the form of three main types namely:

1) Alpha particles which are positively charged helium nuclei, which are of very low penetration and hence do not give rise to a measurable external radiation dose but can give higher doses when incorporated into the body by inhalation or ingestion.

2) Beta particles which are equivalent to electrons. These can give an external dose, particularly those of high energy which will penetrate through two cm of aluminium.

3) Gamma-rays. These are very penetrating passing through up to 6m of concrete. X-rays are equivalent to low energy gamma-rays.

Radiation Sources

Cosmic radiation

This is gamma radiation which has emanated from the sun and other terrestrial bodies and travelled to our planet. On its journey it has not had to pass through any substantial matter only space. Hence it can travel large distances without being absorbed. Once the radiation reaches our atmosphere it begins to be absorbed by the air, thus reducing the radiation level on the ground. The radiation dose will be higher if you live or work at any altitude and will be highest for people in aircraft or spaceship.

Ground

Rocks and soil contain uranium, thorium and potassium. The former two are part of an elaborate decay scheme producing a range of radioactive elements which emit alpha, beta and gamma radiation. Potassium has a naturally occurring isotope, potassium-40 which emits beta and gamma radiation.

Buildings

The buildings in which we work, study, play and live have all been constructed of materials which contain radioactivity that is uranium, thorium and potassium. In addition wood and any other material which at one time was living will contain carbon-14. This is a very weak beta emitter and does not give a measurable dose.

Air

The air which we breathe also contains radioactive material which will give both an external dose to our bodies as a whole and an internal dose to our lungs. The major radionuclides are of radon gas; radon-222 which is produced from the decay of uranium and radon-220 from the decay of thorium.

The carbon dioxide in the air we breathe contains carbon-14 a weak beta-emitter. Carbon-14 is produced in the upper atmosphere by the interaction of cosmic rays with nitrogen-14. The radioactive isotope carbon-14 hence enters every carbon cycle involving living organisms. It is subsequently trapped when organisms die and it is a measure of its decay which allows us to perform carbon dating.

Food

Any radioactivity present in air or more importantly the ground and soil may transfer into food grown on it. Some of the food producing the highest concentrations of radioactivity are tea, coffee and Brazil nuts. The dose to man will vary depending on the quantities consumed and the rate at which the body excretes the radioactivity.

Medical

The X-ray equipment used by hospitals and dentists is the best known source of medical radiation. Nowadays hospitals use a wide range of radioactive materials for diagnostic as well as therapeutic purposes. Examples of radioactive nuclides used are Iodine-131, Iodine-129 and Technetium-99. Besides giving a dose when administered, the hospital, like all other establishments handling radioactive material, has an authorisation to discharge small quantities to the local environment. This will add to background radiation. Medical sources of radiation account for approximately 95% of the average dose to the public from artificial (man-made) radiation.

Fallout

As a result of nuclear weapon testing in the past our atmosphere contains radioactive material primarily Caesium-137 and Strontium-90 which can be detected in current rainfall and is present in sea-water and soils. The initial explosions transferred radioactive­debris to the upper stratosphere from where it will take decades to return to earth. This is the reason why radioactivity from weapon testing is still measurable in rainfall. Levels were substantially increased as a result of the Chernobyl accident, but these have now mainly been deposited on the ground and form part of the ground source as these discharges were confined to low altitude.

Laboratory procedure

1. The principal of action of given device is based on the registration of gamma-radiation by the gas glow counter Glyger-Muller. It converts the energy of gamma-quant into electric impulses. The frequency of their input is directly proportional to the power of equivalent dose of radiation.

2. The range of measurement of external radiation power mZV/hour is divided into 3 parts:

0.10-9.99

0.1-99.9

1-999

3. Switch on the dosemeter.

4. The initial data on the screen should be 0.00.

5. After getting the state mode (1 or 2 sec) dosemeter starts the measuring cycles and finishes with the result on the screen. Time of the measuring on the first and second ranges is 35 sec. And the fixation of the results takes 5 sec.

6. The measuring cycle contains changes on the screen of dosemeter and some sounds. The frequency of the sounds is directly proportional to the intensity of registrated gamma-radiation.

7. The sign ”=” shows us that the cycle is finished.

8. The dosemeter acts in cycling automatic mode. If the time of result fixation has flown then all data is returned back to 0.And the dosemeter starts the next cycle.

9. The power of the equivalent dose that is proportional to the gamma-radiation usually lies in the range 0.10-0.30 mZV/hour depending on the measuring objects.

10. The upper boundary of radiation that acts on the population is 1mZV/year.

11. Build table of measuring results.

Object of researching

Radiation power,

mZV/hour

1.

Cake

0.9

2.

Flesh card

0.14

3.

Headphone

0.15

4.

Face cream

0.14

5.

Monitor

0.13

6.

Mobile phone Nokia

0.11

7.

Dirty apple

0.17

8.

Washed apple

0.13

 

Conclusion:

During our experimental work we determined that the highest index of radiation power in our case is the dirty apple, but after that the apple was washed, its radiation decreases. So it can be explained in such way: any radioactivity present in air or in ground and soil may transfer into food grown on it. Some of the food producing the highest concentrations of radioactivity influence on our health, although on our future generations. So that we conclude that food is one of the radiation sources.

   


 

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