Science, Form 3, Chapter 8
Who discovered radioactivity (2)
- Antoine Henri Becquerel in 1896 - French physicist - successfully discovered radioactivity - found the radioactive compound, Uranium and unintentionally produced rays that blackened a photographic plate even in the dark - caused by the ionising property - Nobel Prize of Physics in 1903
Units of radioactivity (2)
- Becquerel (Bq) - S.I. unit for radioactivity - 1 decay / second
Radioactive radiation device
- Geiger-Muller counter - used to detect radioactive radiations
Who discovered radioactivity (3)
- Marie Curie & Pierre Curie - Couple from Poland - discovered radioactive radiation through ionising power and not the photographic effect - with the uranium ore, they successfully extracted 2 radioactive elements, polonium and radium - Marie died at 67 due to leukaemia (cancer of white blood cells) due to the exposure to gamma rays - the discovery of radium have been used in medicine and cancer treatment
Measurement of background radiation
- Sievert (Sv) is the SI unit for the absorption of radiation by living tissues in the human body - 1Sv = 1 joule of energy from radiation absorbed by 1kg of human tissues - dose rate is measured as microsievert/hour -dosimeter is used to measure the μSv/h
Who discovered radioactivity (1)
- Wilhelm Roentgen in 1895 - German physicist - discovered X-ray (electromagnetic radiation) - unintentionally photographed an X-ray of his wife's hand - Nobel Prize in Physics 1901
Health risks of aircrew members (reason and ways to overcome)
- aircrews are exposed to more ionising radiation when they are at higher altitudes because the atmosphere is thinner and has less protection from cosmic radiation form space - pregnant aircrew member is prohibit to be exposed to more than 1 mSv - monitor the annual dosage of radiation for each aircrew member and make sure it doesn't exceed 20mSv/year - limit flight hours and take turns to reduce the exposure to ionising radiation - stay away from the ionising radiation from x-rays in the departure hall
Dalton's Atomic Theory
- an atom is the smallest particle and cannot be further divided - John Dalton in 1808 - development in science succeeded in discovering particles smaller than atoms called protons, electrons, neutrons and quarks
Uses of radioactive radiation (archeology and geochronology)
- archeologists use carbon dating method to find the age of an artefact by determining the remaining amount of carbon-14 - geochronologist use radioactive dating method to determine the geological time by measuring the age of the rock
Units of radioactivity (1)
- curie (Ci) - one curie is 3.7 x 10¹⁰ decays / second
Non-ionising radiation
- from non-radioactive resources - low frequency -low energy and cannot ionise other atoms - less harmful than ionising radiation - eg. microwaves, radio waves, ultraviolet rays, visible light, infrared
Ionising radiation
- from radioactive resources - high-frequency - high energy, can ionise other atoms - harmful and can damge the DNA in the cells - eg. alpha particles, beta particles, gamma rays, x-rays, cosmic rays
Uses of radioactive radiation (food irradiation)
- gamma ray is used to kill harmful bacteria like salmonella, E. coli in meats, fishes and poultry - gamma ray is used to prevent germination and kill pests in herbs - gamma ray is also used to delay the ripening of fruits so they will last longer
Uses of radioactive radiation (medicine)
- iodine-131 is used to treat thyroid cancers - sodium-24 is used to detect the location of blood clots in blood vessels - cobalt-60 is used to destroy cancer cells and sterilise medical equipment
Ions
- ions are charged particles - a neutral atom will become an ion if it donates or receives electrons - positive ions are called cations - negative ions are called anions
Radioactivity
- is a random and spontaneous decay process of an unstable nucleus through emitting radioactive radiation
Characteristics of Ionising Radiation (alpha particles)
- large in size - positively charged - high ionising power - low penetration power (blocked by a paper) -range in air is a few centimetres - magnetic field deflection, small deflection because it has a large mass (upwards) - electric field deflection, attracted to the negative plate because alpha particles are positively charged
Uses of radioactive radiation (agriculture)
- nitrogen and phosphorus is used to study the effectiveness of the uptake of fertilizers from the roots of the plant - gamma ray is used to sterile pests so they cannot reproduce - radioactive radiation is used to produce a better strain of crop by changing the DNA of the plant cells
Characteristics of Ionising Radiation (gamma rays)
- no applicable size - no charges (neutral) - low ionising power - high penetrating power (blocked by 10mm lead) - magnetic field deflection, no deflection because it has no charges - electric field radiation, no deflection because it has no charges
Sources of radiation (man-made)
- nuclear wastes - nuclear tests - testing of nuclear weapons - radioactive residue from industries and nuclear power plants - in medicine sector, radioisotopes in cancer treatment and diagnosis of illness
Radioactive decay
- random and spontaneous process where an unstable nucleus emits radioactive radiation until the nucleus becomes more stable - eg. Carbon-14, Thorium-234, Uranium-238, Radon-222
Uses of radioactive radiation (industries)
- sodium is used to detect leaks in pipes that carry gases and oils - beta particles are used to control the thickness of paper, plastic and metal sheets - radioactive substances are used to control the same amount of content in food containers
Sources of ionising radiation (natural resources)
- terrestrial radiation, the decay of radioactive minerals like uranium and thorium in the Earth's crust - cosmic radiation, from outside the Solar System and other galaxies - air, radon is a radioactive gas produced from the decay of uranium - food, animals and plants produce carbon-14 and potassium-40 - soil and rocks contain radioactive elements - ionising radiation from natural resources are also called background radiation
Uses of radioactive radiation (defense)
- uranium and plutonium is used to make nuclear weapons - uranium is used to fuel warships and submarines
Characteristics of Ionising Radiation (beta particles)
- very small in size - negatively charged - moderate ionising power - moderate penetration power (blocked by 3mm aluminium) - magnetic field deflection, large deflection because the mass is small (downwards) - electric field deflection, attracted to the positive plate because it is negatively charged
Precautionary steps when dealing with radioactive substances
- wear protective clothing and equipment like protective gloves and safety glasses - wear a radiation badge to ensure the radiation absorbed into the body does not exceed the safe amount - use robotic hands when handing strong radioactive substances - store radioactive substances in a lead box