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The nucleus of an atom consists of protons and neutrons. The protons and neutrons are bounds together by a strong force and the nucleus is stable. Some nuclei are unstable. They emit radioactive radiation to become more stable nuclei. Medium-sized are more stable than heavy nuclei and light nuclei.

Radioactive substances are elements with unstable nuclei with undergo spontaneous decay to become more stable elements while emitting dangerous and invisible radioactive radiation. The isotopes carbon -14, cobalt -60 and iodine -131 are examples of radioactive substances whereas carbon -12, cobalt -59 and iodine -132 are not radioactive substances. All natural isotopes above the element bismuth in the Periodic Table are highly unstable and radioactive.

Radioactive Decay

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Radioactive decay or radioactivity is a process where an unstable atom becomes a more stable atom by emitting particles or radiation. Radioactive decay is a random process. It is not possible to tell when a particular atom will give out radioactivity. However it is possible to know the time taken for half of a large number of unstable atoms to decay.

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The radioactive decay of uranium was first discovered by Antoine Henri Becquerel in 1896. The Paris physician accidentally discovered that photographic plates wrapped in dark paper were blackened by invisible radiation was capable of discharging an electroscope. In 1898, a France couple, Marie and Pierre Curie, discovered the radioactive elements radium and polonium. Marie Curie also discovered the radioactive element thorium.

Radioactive Radiation

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There are three types of radioactive radiations emitted during nucleus decay. They are: a) Alpha radiation or α – radiation b) Beta radiation or β – radiation c) Gamma radiation or γ – radiation. Alpha, beta and gamma radiations are emitted from the nuclear of an atom at high speeds.  The nucleus will release of an alpha particle, resulting in the formation of a new nucleus which is lighter than the original by four mass units. 

Radium -226 will decay with the release of an alpha particle to become radon -222. Beta radiation is a stream of electrons. An electron is produced when a neutron (in a nucleus) turns into a proton. Sodium -24 will release a beta particle and turn into magnesium -24. Gamma radiation is usually found in association with alpha and beta radiations. Gamma radiation possesses no charge or mass; thus the emission of gamma radiation by an unstable nucleus only results in the loss of certain amount of radiant energy in new nucleus. Table below shows the types of radioactive radiations emitted by radioactive substances:

Radioactive substances	Types of radiation
Uranium -238	Alpha Radiation
Iodine -131	Beta radiation
Cobalt -60	Gamma radiation
Radium -226	Alpha, beta and gamma radiations

Alpha Radiation

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Alpha radiation or α – radiation is a stream of alpha particles which consist of charged helium ions. The helium nucleus has two protons and two neutrons. Alpha radiation is positively charged and is deflected in a magnetic field. It is also deflected towards the negatively charged plate in an electric field. The deflection in both the magnetic and electric fields is small because the mass of alpha particles is heavier than beta particles. Alpha radiation as the highest ionizing power and ionizes air molecules along its path into positive and negative ions. It has the weakest penetrating power. It can only penetrate a few centimeters in the air and can be blocked by a thin sheet of paper.

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Beta Radiation

Beta radiation or β – radiation is a stream of beta particles which consist of negatively charged electrons. Beta radiation is deflected in a magnetic field. It is also deflected towards the positively charged plate in an electric field. The deflection is large because the mass of beta particles is small compared to alpha particles. Beta radiation has weal ionizing power. It has average penetrating power. It can be blocked by a sheet of copper one millimeter thick.

Gamma Radiation

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Gamma radiation or γ – radiation consist of high frequency electromagnetic waves with very short wave lengths. It is neutral and is not deflected in both magnetic and electric fields. It has the weakest ionizing power. It has the highest penetrating power and can be blocked only by a sheet of thick lead or a thick concrete wall.

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Radioisotopes

 

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Isotopes are atoms of the same elements which contain the same number of protons but different number of neutrons. Radioisotopes are isotopes of radioactive substances which are unstable and undergo radioactive decay while emitting heat and radiation. Artificial radioisotopes are produced by bombarding the atoms of certain elements with high speed particles such as neutrons or protons.

Elements	Radioisotopes
Uranium	Uranium -235, Uranium -238
Radium	Radium -226
Carbon	Carbon -14
Cobalt	Cobalt -60
Hydrogen	Hydrogen -3(tritium)
Polonium	Polonium -209
Phosphorus	Phosphorus -32
Iodine	Iodine -131
Sodium	Sodium -24

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Uses of Radioactive Substances

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Radioisotopes will emit alpha, beta or gamma radiations. Detectors such as the Geiger-Muller counter are used to trace the presence of radiations. The Malaysian Nuclear Agency (previously known as The Malaysian Institute of Nuclear Research and Technology (MINT) is the government body responsible for the development of nuclear science and technology in Malaysia. Radioactive radiations are used in the fields of: i) agriculture ii) medicine iii) archaeology iv) industry v) food preservation.

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In Agriculture

In agriculture, radioisotopes are used as a tracer to determine the uptake of fertilizers by plants.  This can be done by adding the radioisotope phosphorus -32 to the fertilizers. The rate and amount of fertilizer absorbed by the plants are determined by the radiation emitted by the phosphorus -32. A higher reading on the counter shows that the plants have absorbed more fertilizer.

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Gamma radiation is used to kill or sterilize insect pests that destroy plants. This will control the population of pests that are harmful to the plants. Gamma radiation also used to alter plant genes. This produces new strains of plants that will increase both production and quality. The carbon -14 isotope is mixed with insecticides to trace their action on plants. The effectiveness of the insecticides is traced by radiation from the carbon -14.

In Medicine

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In radiotherapy (also called radiation therapy), gamma radiation emitted by cobalt -60 is used in the treatment of cancer. The radiation will destroy cancerous cells and shrink tumors. Radioactive tracers are used to check the function of body organs: a) Iodine -131 or strontium -89 is injected into a patient’s body or taken orally to detect damage to the thyroid gland b) Sodium -24 is injected into blood vessels to detect to clotting of blood during a head injury c) Barium -138 or iodine -131 are injected into a patient’s body to detect brain tumors.

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The plutonium -238 battery is used in heart pacemakers to help stabilize the heartbeat of heart patients. Gamma radiation is used to sterilize medical apparatus such as rubber gloves, syringes and surgical equipment which are non-heat resistant. Another application of radioisotopes in medicine is its use in determining the volume of blood in a patient. For example, a radioisotope of sodium is injected into the vein of a patient. Later a small volume of blood is drawn and the activity of the radioisotope is measured. From this, the volume of blood is estimated.

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In Archaeology

 

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Carbon dioxide in the air contains a small amount of the natural radioactive carbon -14. Plants absorb carbon -14 during the process of photosynthesis and transfer it to animals through the food chain. When plants and animals die, the supply of carbon -14 stops and the carbon -14 content in deed plants and animals will decrease due to radioactive decay. Archaeologists can estimate the edge of an artifact through a method known as carbon dating. Through this method, the percentage of carbon -14 remaining in an ancient artifact is determined to estimate its age.

In Industry

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Gamma radiation is used to detect whether the volume of content in a container is within an acceptable range. A reading recorded by a detector outside the acceptable range means that the volume of content in the container is rejected. Sodium -4 is added to water in underground water pipes to detect pipe leakages. The detector will record a sudden increase in reading at places where leakages have occurred.

Beta radiation is used to determine the thickness of paper, plastic and metal sheets. A non-uniform reading detected by a detector shows variance in the thickness of the substances. In the mining and petroleum industries, radioisotopes are used to locate and quantify minerals and petroleum deposits.

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Alpha radiation is used in the textile industry to prevent creases in fabrics caused by static electricity. The static charges are neutralized by the positive and negative ions produced by the ionization of alpha radiation.

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The amount of wear on the gear box and piston of a car engine is determined by adding a small quantity of radioactive iron into the piston. The amount of radioactive iron worn from the piston which is found in the lubrication oil it measured by a detector.

In Food Preservation    

 

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Irradiation is a process which uses radiation to kill microorganisms such as bacteria and fungi which cause food to decay. Gamma radiation is used to kill any bacteria trapped in sealed food cans and bottles such as sauces and cereals. The preservation of food using gamma radiation is suitable for food that is not prepared at a high temperature like fruits and vegetables. Radiation is also used to delay the ripening of stored fruits and vegetables, as well as to destroy bacteria in meat, enabling it to keep fresh for a longer period of time.

Info Gallery

 

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Natural radioactivity is common in the rocks and soils that make up our planet, in water and oceans, in the food we eat, in the building materials at our homes and in human body. There is nowhere on Earth that natural radioactivity cannot be found.

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Internal radiotherapy is where radioisotopes are taken orally or injected into the body to treat cancer of the thyroid gland and adult non-Hodgkin’s lymphoma. External radiotherapy uses radiation from a machine outside the body to treat cancer of the bladder, brain, breast, cervix, larynx, prostate and vagina.