Радиоактивті сәулелердің биологиялық әсері. Радиациядан қорғану. Физика, 11 сынып, қосымша материал, 45-46 сабақ.

The nuclear medicine department of hospital uses radioactive materials every day. They uses to help doctors understand what's happening inside people's bodies first a radioactive material called a tracer is prepared in a specially protected area. It's designed to accumulate in a certain part of the body. This syringe contains a tracer called technetium-99 m it emits gamma radiation and is one of the most commonly used radioactive materials in nuclear medicine. Once the tracer is ready it's injected into the patient in just a few minutes it'll accumulate in the target organ in this case the kidneys. The doctors are trying to find out if this patient’s kidney’s are functioning properly. Gamma radiation is very penetrating it easily passes out through her body. She’s carefully positioned over a machine called a gamma camera. It detects the radiation and pinpoints where it’s coming from. A series of images are collected at regular intervals. The first image captured by the camera clearly shows the size and shape of the two kidneys. Now watch what happens over the next 15 minutes, the radioactivity in the kidney on the right has almost disappeared. This kidney has quickly got rid of the tracer but there’s still a high level of radiation being emitted from the kidney on the left. There’s probably a blockage the left is struggling to get rid of the tracer

How do we know how old something is? For people we'd ask to see their birth certificate. For trees we'd count the rings. But how do we know how old a fossil is? Fossils have their own internal clock. Scientists can read it by looking at the ratio of two different types of carbon atoms. Of course, every living thing is made of carbon. Plants grab carbon dioxide from the atmosphere and use it to form complex organic molecules. Animals get their

carbon by eating these plants. But there's more than one form of carbon. Most carbon atoms have 6 protons and 6 neutrons. We call this carbon-12. High up in the atmosphere, sometimes cosmic rays hit nitrogen atoms.

This creates carbon with six protons and eight neutrons. We call this carbon-14.

Carbon-12 and carbon-14 behave alike. But

carbon-14 has one unique and important

attribute: it's unstable. So once an animal dies, the carbon-14 in his body

will start to go away. Every 5730 years on average, about half of the carbon-14

atoms will decay into nitrogen. This is its half-life. After one half-life the

animal will have about half the amount of carbon-14 it started with. After

another half-life it will have about a quarter. And after another half life it will have about an eighth. By contrast the amount of carbon-12, that has in its

body will stay the same. By measuring the ratio of carbon 14 to carbon-12, we can measure how many thousands of years have passed since the animal died. Carbon dating works for fossils up to about 60,000 years old. For older fossils scientists use unstable elements that have much longer half-lives.

Electromagnetic radiation covers a broad spectrum of wavelengths and includes

sunlight which is vital to life on earth. The waves have different uses according

to their energy: radio waves enable us to communicate and share information.

microwaves cook our food; infrared radiation warms us; visible light illuminates our lives and is essential for food production; ultraviolet radiation gives us Sun tans and bone strengthening vitamin D; x-rays enable us to diagnose and treat illnesses and to check our luggage; and gamma rays are used to sterilize medical equipment. Irradiation using x-rays and gamma-rays can also be used to treat food. By choosing the right wavelength and dosage, these rays can prevent sprouting of vegetables, like potatoes, maintain their freshness and taste; and destroy harmful bacteria that could be present in spices, meat seafood; They also can read fresh fruits and vegetables of insects that might otherwise hitchhike -spreading to other regions of the world. Where they could have devastating effects on the environment and agriculture. Food irradiation evolves shining electromagnetic ray's or beams of electrons onto food - the energy is transferred at an intensity necessary to give the desired effect. It is a cold process, so spices retain their unique flavors and aromas that would be diminished by heating. It also avoids reliance on chemical methods such as illumination or pesticides to combat bacteria, insects or other spoilage organisms. In addition those irradiation beams pass through packaging - so the food remains protected from bacteria or insects after treatment and will remain fresh longer. Food irradiation offers a chemical free and heat free approach. It maintains fresh food quality reduces the risk of foodborne diseases and prevents the spread of exotic insects through globalized trade.