Radio Activity

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In today’s class, we will be talking about radioactivity. Enjoy the class!

Radio Activity

Henri Becquerel, a French scientist, accidentally discovered radioactivity in 1896. He found out that uranium compounds emit radiations without an external source of energy by using photographic plates. Marie Curie, a female scientist who together with her husband, coined the term radioactivity, Pierre Curie began investigating the process recently discovered by Henri Becquerel.

Meaning of radioactivity

Radioactivity is the spontaneous emission of radiation. The emitted radiation is from the decay or disintegration of unstable atomic nuclei of a radioactive element. Radioactivity is a nuclear process that is not affected by temperature change unlike in chemical reactions, which are mostly affected by temperature changes.

Generally, the radiations from the decay or disintegration of unstable atomic nuclei emit the following radiations: alpha particle, beta particles and gamma-ray

Radioactive elements

A radioactive element is an element whose isotope is subjected to spontaneous degeneration by emitting alpha, beta or gamma rays. All elements with atomic number greater than 83 are radioactive Examples of radioactive elements include: uranium, radium, thorium, polonium, etc Radioactive elements can either occur naturally such as uranium or can be artificially made by bombarding stable elements with subatomic particles in a cyclotron.

Types of radioactive elements

Radioactivity occurs because of an element with an unstable nucleus. There are two types of radioactive elements, these are

1. Natural radioactive element
2. Artificial radioactive element

• Natural radioactive element:

Old radioactive elements such as uranium or any of their decay products have always been present in the earth’s crust, atmosphere, and any other place. Lord Rutherford and Soddy later discovered and put forward a theory about the spontaneous decay of some natural radioactive elements with an unstable nucleus (those with atomic number greater than 83).

• Artificial radioactive elements:

These are elements that do not occur naturally on earth but are artificially made by bombarding stable elements with subatomic particles in a cyclotron.

Geiger – Muller (GM) tube

Geiger Muller counter is an instrument used for detecting ionizing radiation.

Types of radiation and their properties

The radiations emitted by radioactive elements as discovered by Ernest Rutherford are:

1. Alpha
2. Beta
3. Gamma-ray

In his experiment, he placed a small sample of radium at the bottom of a small hole drilled in a block of lead. The radiation emitted from this radiation merged from the hole in a narrow beam.

The radiation was subjected to a strong magnetic field placed at the side of the beam A photographic plate placed at the side of the radiation received the lead and showed the path. Some rays were observed to be bent to the right, some to the left and some went straight unbent.

The rays that bent toward the south pole of the magnetic field were called alpha particle and the rays that bend toward the magnetic north pole were named beta. Moreover, the unbent radiation was named gamma radiation.

Properties of alpha particles (α)

Some of the properties of alpha particles are:

1. They are helium particles with a mass number of 4 and an atomic number of 2.
2. It has little penetrating power. A sheet of paper can stop it.
3. They can only travel a short distance (a few centimetres) in the air with high speed.
4. They are heavier and lose energy easily.
5. Alpha rays are deflected by electric and magnetic fields.
6. They have very high ionizing power
7. They are all emitted at the same speed.
8. It causes fluorescence in ZnS

Properties of beta particles

Some of the properties of a beta particle are:

1. They have an intermediate penetrating power
2. They have moderate ionizing PO which is much lesser than that alpha particles
3. Beta radiation may travel several feet in the air.
4. They are deflected more than alpha particles due to their small mass.
5. They can be deflected by electric fields but deflected more by magnetic fields.
6. Beta particles can be stopped by a quarter-inch-thick sheet of aluminium.
7. They lose energy at a slower rate.
8. It does not cause fluorescence in ZnS.

Properties of gamma rays

Some of the properties of gamma rays are:

1. Gamma rays are not deflected by electric and magnetic fields.
2. They travel at high speed in air.
3. They have a very large penetrating power, i.e. they can penetrate through several centimetres of iron and lead.
4. Gamma rays give interference and diffraction effects
5. Gamma rays can travel for a long time in the air
6. They have the smallest ionizing power.
7. They have no mass.

Terms used in radioactivity

The following are the terms used in radioactivity

1. Radioactive decay: Radioactive decay occurs when an unstable atomic nucleus loses its energy by emitting radiation such as alpha particles, beta particles, gamma rays. Radioactive decay is a spontaneous process that cannot be controlled. The decaying nucleus of an element is called the parent radioisotope.
2. Half-life: This is the time taken for a radioactive element to decay to half of its original mass. Half-life is a characteristic property of unstable atomic nuclei and i.e. way it decays. It is not affected y temperature change, which indicates that every radioactive element has its own definite time of decay.
3. Activity: The activity of a radioactive element is the average number of disintegration per second.

Radiation detectors

Some of the radioactive detectors are:

1. Scintillation detector
2. Photographic plate
3. The gold-leaf electroscope
4. The spark counters
5. Geiger Muller tube
6. The cloud chambers

Uses of radioactivity

Some of the uses of radioactivity are:

1. Radiotherapy: Radiotherapy is the use of radiation to treat cancer and tumour. It treats cancer by destroying cancer cells in the area that is being treated.
2. Sterilization: Medical instruments and foods are subjected to concentrated radiations such as gamma radiation to kill microorganisms that can cause various infections and diseases.
3. Nuclear power: Nuclear power can be generated using a nuclear reactor.
   

4. A nuclear reactor is a device that uses a fission reaction to generate energy. Some nuclear power plants use uranium in fission reaction as a fuel to produce electricity
5. Smoke detectors: Smoke detectors use the ionizing property of alpha particles to measure changes in the ionization of the air immediately around the detector.
6. Carbon dating: By measuring the amount of carbon – 14 left in a dead organism, its time of death can be approximately predicted. This technique is best for dating an organism that died in the range of 1000 to 1,000,000 years ago.
   

7. Tracers: Radioactive tracers are substances that carry molecules that contain a radioactive atom that allows easy detection and measurement of various elements. Radioactive tracers are mostly used in nuclear medicine to diagnose and treat diseases, e.g. to detect the activity of a thyroid gland, detect intestinal bleeding, etc. A radioactive tracer can be administered into a patient through injection, ingestion and inhalation. Radioactive tracers are also used agriculture to carry out various researches on plants and animals such as plant growth rate, the performance of bodily functions, plants hydration rate, etc.
   

8. Dating rock: Some types of rock contain small traces of radioactive elements such as uranium. By calculating the uranium half-life, the approximate age of the rock can be predicted.
9. Radiation detection is used to check and detect leakages and blockages in underground pipes that are carrying petroleum.
10. Plants photosynthesis rate can be calculated by using radioactive carbon-14.

Dangers of radioactive rays

1. Exposure to concentrated radioactive rays can lead to death.
2. Exposure to radioactive rays might destroy healthy living cells which might lead to the abnormal growth of cells.
3. Radioactive rays can cause different types of eye defect, e.g. cataract.
4. Exposure to radioactive rays can cause gene mutation-change in DNA
5. Exposure to excess radioactive rays can cause cancer, e.g. leukaemia.

Safety precautions

Some of the safety measures to take against the harmful effect of radioactive rays are:

1. When handling radioactive materials, always wear appropriate clothing such as gloves, laboratory clothes, shoe covers, etc.
2. Dispose of all radioactive waste in an enclosed container made of steel.
3. Use appropriate radiation shield such as lead, concrete walls, etc.
4. Replace contaminated materials.
5. Do not hold radioactive materials close to the eye.
6. Apply radiation sign to any radioactive container.
7. The weak radioactive sources cited in schools should be lifted by forceps.
8. Strict hygiene such as the prohibition of eating, smoking in the radioactive lab, etc., is very essential when handling radioactive materials to avoid internal contamination.
9. Regularly check the radiation level which you are exposed to by wearing a dose badge

 

In our next class, we will be talking about Ethical Issues in Science and Development.  We hope you enjoyed the class.

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