Radioactivity File
Matter is made up of atoms. Each atom consists of a nucleus composed of protons and neutrons. The nucleus is surrounded by electrons which gravitate around it like satellites. Radioactive materials spontaneously emit Gamma or X rays and/or Beta or sometimes Alpha particles.
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Beta particles are electrons. Because of their charge, they react very strongly to matter. They cover a distance of a few centimeters to a few meters in the air. A sheet of aluminium can stop them. Alpha particles are helium nuclei (2 neutrons and 2 protons). They can cover a distance of a few centimeters in the air. A sheet of paper can stop them. Gamma rays are electromagnetic rays which are formed by physical phenomena occurring within the nucleus of the atom. Gamma rays can produce ions (atoms or molecules which have an electrical charge which is not nil) directly or indirectly when they pass through matter. They can cover a distance of dozens of meters in the air. They can penetrate quite far. A thick layer of lead or concrete can effectively diminish their power of penetration. X rays are similar to Gamma rays but are formed by physical phenomena occurring within the electronic structure of the atom. They are used for medical purposes and are rarely found in nature.
IThere is no threshold under which radioactivity is harmless. Any dose, even very slight, causes a health hazard. The greater the dose is, the greater the risk of cancer or genetic anomaly. The relation between the risk and the dose is considered to be linear. Indeed, the International commission on Radiological protection (ICRP) proposed in 1990 that the equivalent of the maximum dose should be of one millisievert per year, that is to say 11.4μRem/h on average. This norm concerns doses other than those due to medical examinations or natural radioactivity. The former norm which is still occasionally used was of 5millisieverts per year but it included all of these different types of radiation.
You must take into account the radiation levels corresponding to the places you are usually in and the amount of time you usually spend there in order to calculate an average dose.
The ionization of the molecules in the human body can cause disorders capable of causing cancerous tumours and genetic mutations likely to create hereditary abnormalities.
Cosmic rays are reduced by the atmosphere, their effects are thus increased with altitude. The level can reach 300μRem/h in an plane at an altitude of 10 000 m, especially near the North or South Pole.
The following diagram illustrates in a simple way how radioactive elements are propagated and how they can be concentrated in food.
ALARM CLOCKS AND WATCHES Twenty years ago the hands of an alarm clock or watch were luminescent. GAS LAMP INCANDESCENT MANTLES When camping you might have used gas lamps. A mantle is adapted to the lamp and once heated by the gas, it will emit light by incandescence. Levels measured vary from 15 to 360 Rem/h when in direct contact. At distances exceeding 50 cm, rays are no longer detected. You can protect yourself from radiations by keeping at a distance of more than 50 cm from a mantle. Avoid putting a mantle in your pocket. Fifty years after Benjamin Franklin discovered the lightning conductor in 1760, a Hungarian thought of placing a radioactive source at the tip of a lightning conductor. He thought that the radioactivity would ionize the air around the tip of the lightning conductor and make it conductive and that thunder bolts would in consequence be directed there. Although the efficiency of this process was uncertain, it was patented and commercialized in 1932. The radionuclides used are extremely radiotoxic and the period of radioactivity lasts for a very long time. The sources remain radioactive for years, sometimes thousands of years. For example, the radioactive period of Americium 241 is of 433 years. This is the amount of time it takes for radioactivity to be reduced by half. It can be calculated that for a source of 30 million Becquerels in 1987, there will be 15 million in 2420; 7.5 million in2863 and 3.7 million in 3296 etc. The radioactive period of Radium 226 is much longer: 16000 years. The rate at which it diminishes is thus much slower. Radioactive sources used in lightning conductors are thus going to remain dangerous for generations. It is important to look after their removal and place of storage to limit risks of dispersion.
RadWaste.org
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