|1. alpha particles
|Alpha particles are Helium nuclei carrying positive charges. There are 2 protons and 2 neutrons in each Helium nucleus. Because of their larger mass, they have very little penetration power. They can easily be stopped by a sheet of paper.
||All materials are made up of tiny particles called atoms. At the centre of an atom is the nucleus. The nucleus consists of uncharged neutrons and positively charged protons. It makes up virtually all the mass of the atom. Revolving round the nucleus are negatively charged electrons.
|3. background radiation
||The radiation constantly present in the environment and be normally received by our body is called the "background radiation". On average, about 85% of this comes from natural sources, 14% from medical applications and 1% from other sources.
In Hong Kong, the normal background radiation levels may vary between 0.06 and 0.30 microsievert per hour.
|4. background ambient gamma radiation levels in Hong Kong
||From readings taken at various locations in Hong Kong during the period 1987-2010, the background ambient gamma radiation levels may vary between 0.06 and 0.30 microsievert per hour. (1 microsievert = 0.000001 sievert = 0.001 millisievert)
|5. becquerel (Bq)
||Becquerel is the SI unit of radioactivity. One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. 1 µBq = 1 microbecquerel = 1 millionth of a becquerel.
Keep on inhaling the air with 828 µBq/m3 of iodine-131 for one year gives a radiation dose of about 0.05 µSv to a human being.
|6. beta particles
|Beta particles are high speed electrons. They are more penetrating than alpha particles. Thicker shields made up of dense materials, such as lead or paraffin, are required to protect ourselves from radiation.
|7. biological half-life
||Inside our body, a particular radioactive element by virtue of its chemical property tends to accumulate in a certain organ (critical organ). For example, radioactive strontium may concentrate in the bones because it is chemically similar to calcium.
The time required for the radioactive element in the body to be reduced to half its original amount is called the "biological half-life".
|8. chain reaction
||When neutrons produced in the fission of a nucleus bombard other nuclei, it can cause fissions of these nuclei producing more neutrons and nuclear fissions to recur. The continuing process for a series of nuclear fissions to take place in such manner is called a chain reaction. For example, the neutrons produced by fission may strike other uranium nuclei and produce more neutrons. This multiplication process, or chain reaction, happens in a split second and results in a release of a large amount of heat.
|9. curie (Ci)
||The curie was used as a unit of radioactivity, which was named in honour of Madame Curie.
It was replaced by the becquerel in 1975 as the official unit in the International System of Units (SI). The latter unit has been named after the French physicist, Henri Becquerel, who shared the Nobel Prize in Physics with Marie and Pierre Curie (her husband) in 1903 for their work in radioactivity.
One curie is the radioactivity level measured by observing the decay rate of approximately one gram of radium (Ra-226). One curie of radioactive material will have 37 billion atomic transformations (disintegrations) in one second. 1 Ci = 3.7 x 1010 Bq
||The nucleus of the smallest atom - the hydrogen atom, contains one proton only. But those of the larger atoms contain many protons and neutrons. A uranium-238 nucleus contains 92 protons and 146 neutrons.
The nucleus of most atoms is stable, but some nuclei, in particular those larger ones, are unstable.
An unstable (radioactive) nucleus can become more stable by emitting particles (such as alpha particles, beta particles, gamma rays or neutrons) and energy (in the form of electromagnetic waves). The process of emitting particles and energy by an unstable nucleus is called "decay".
|11. derived intervention level (DIL)
||The concentration level required for taking protective actions is called Derived intervention level (DIL). The DIL for inhalation of Iodine-131 and Caesium-137 from the air is 661.38 and 2,480 Bq/m3 respectively.
||Dose is the amount of energy that the ionizing radiation (alpha, beta or gamma) imparts to the organs of an individual and is a measure of the health risk or effect due to exposure to radiation. The various types of radiation produce different health effects on different parts of our body. It is normally expressed in units of millisievert (mSv). The average annual dose is about 3 mSv per person in Hong Kong.
The health effect of radiation depends on its intensity, the length of exposure, the type of radiation and the kind of body cells exposed. When a person receives a high radiation dose of more than 1000 mSv in a short time, he/she may suffer from nausea, vomiting, fatigue and loss of hair. In addition, radiation can cause genes to mutate or change permanently and increase the risk of cancer.
Radiation workers are permitted to receive up to 20 mSv per year.
The world average background radiation dose is about 3 mSv per year per person. It varies from place to place and depends on the life style.
|13. electromagnetic radiation
||The traveling wave motion resulting from oscillating magnetic and electric fields. It consists of waves of energy associated with electric and magnetic fields resulting from the acceleration of an electric charge.
Electromagnetic radiation can also be understood as a stream of photons moving at the speed of light. Each photon is massless but contains a certain amount of energy.
|14. gray (Gy)
||It is a unit the unit of absorbed dose for the amount of energy per unit mass imparted by ionizing radiation to an affected object from a dose of radiation. One gray (1 Gy) is equal to one joule of radiation energy absorbed per kilogram of matter. [1 Gy = 1 J/Kg]
||When a radioactive element decays, the number of radioactive nuclei decreases with time. The time it takes for the number of radioactive nuclei to decrease to half its original amount is called its half-life. Each radioactive element has a characteristic half-life. The half-lives of various radioactive elements may vary from millionths of a second to billions of years.
Half-life of artificial radionuclide Iodine-131 is 8 days. This means that after 8 days, the radioactivity of Iodine-131 drops to half of its original level, and after 16 days to a quarter and so on. Half-life of artificial radionuclide Caesium-137 is 30 years. This means that after 30 years the radioactivity of Caesium-137 drops to half of its original level, and after 60 years to a quarter and so on.
|16. internal and external irradiation
||Radioactive material can affect our body through various paths. Some may be transported by winds or water to our environment and affect us through direct radiation. Others may enter our body when we breathe and eat.
|17. ionizing radiation
||In nuclear decay, energy is spontaneously emitted in form of particles or electromagnetic waves from an unstable nucleus. These particles or energy are collectively called "radiation".
Radiation can be "ionizing" or "non-ionizing". If the energy of radiation is high enough to remove electrons from atoms, thus creating positively charged ions, it is called "ionizing radiation".
|18. ionizing radiation
||Ionizing radiation includes alpha particles, beta particles, X-rays and gamma rays as well as neutrons.
|19. man-made (artificial) radiation
||Man-made radiation may come from medical X-rays, fallout from nuclear weapon tests and operation of nuclear power plants. Some consumer products, such as TV (those using CRTs) and luminous watches, contain man-made radioactive materials too.
|20. natural radiation
||Radiation can be natural or man-made. It is all around us.
Natural radiation may come from the outer space or from naturally occurring radioactive materials in air, food and water and on the earth crust.
||Uncharged particles and most penetrating. They can pass right through the body. Thicker shields made up of dense materials, such as lead, are required to protect ourselves from radiation.
|22. non-ionizing radiation (NIR)
||Non-ionizing radiation does not have sufficient energy to remove electrons from atoms. Examples include ultraviolet (UV), visible light, infrared, microwave and radio wave.
Although non-ionizing radiation has lower energy, too much of it may still affect our health, e.g. lengthy exposure to UV radiation may cause sunburn.
|23. nuclear disintegration
||Any process of nuclear decay that involves the splitting of a nucleus into nuclear fragments (smaller nuclei) or the emission of particles, which occurs either spontaneously or as a result of a collision. For example, bombarding a nucleus by a particle (such as alpha particle, proton, deuteron, neutron, etc.) causes the nucleus to emit a proton or neutron.
|24. nuclear fission
||When an unstable nucleus of a particular heavy element (e.g., uranium) is struck by a neutron, the nucleus will break up ("fission") into nuclei of lighter elements with the release of nuclear energy. The uranium nucleus will break up ("fission") and release two or three neutrons together with some energy.
|25. nuclear fusion
||It is a type of nuclear reaction for combining two atomic nuclei to form a heavier nucleus with energy being released. Deuterium and tritium, both heavy forms of hydrogen, are common candidates for nuclear fusion.
|26. nuclear power plant
||The large amount of heat released in the chain reaction of nuclear fissions is used to generate electricity in a nuclear power plant. A chain reaction can be controlled by limiting the number of neutrons available for fission by an absorber (e.g. boron). This results in a controlled release of energy - nuclear power generation.
||It refers to the energy spreading across some distance in space in the form of electromagnetic waves or particles (such as alpha particles, beta particles, gamma rays or neutrons).
Also, the particles or energy (in the form of electromagnetic waves) emitted by unstable nuclei are collectively called radiation.
|28. sievert (Sv)
||Sievert is the SI unit of dose (the committed effective dose in scientific terms), which is a measure of the biological effect to a person, taking into account factors such as the type and energy of radiation, the tissue or organ affected, the retention of the radioactive substance in the human body after intake, etc.
1 Sievert of radiation absorbed dose equivalent produces the same biological effect in a specified tissue as 1 gray of high-energy X-rays. 1 µSv = 1 microsievert = 1 thousandth of a millisievert (mSv) = 1 millionth of a sievert. The radiation dose of a chest X-ray is around 10 - 50 µSv.
|29. uranium pellet
||One uranium pellet (about 1 cm in diameter and 1.5 cm in length) generates the same amount of energy as:
800 kilograms of coal, or 570 litres of oil, or 450,000 litres of natural gas
|30. X-rays and gamma rays
||X-rays and gamma rays are electromagnetic waves with very strong penetrating power. They can pass right through the body. Thicker shields made up of dense materials, such as lead, are required to protect ourselves from radiation. They have extremely short wavelengths.
The wavelength of X-rays is between 0.1A and 100A. The wavelength of gamma rays is below 0.1A. (1A = 1 Angstron = 10-10m)