Natural sources account for most of the radiation Essays - Physics

Natural sources account for most of the radiation we all receive each year. The nuclear fuel cycle does not give rise to significant radiation exposure for members of the public, and even in two major nuclear accidents radiation has caused no harm. Radiation protection standards assume that any dose of radiation, no matter how small, involves a possible risk to human health. This deliberately conservative assumption is increasingly being questioned. Radiation is energy in the process of being transmitted, which may take such forms as light, or tiny particles much too small to see. Visible light, the ultra-violet light we receive from the sun and from sun-beds, and transmission signals for TV and radio communications are all forms of radiation that are common in our daily lives. These are all referred to as 'non-ionizing' radiation. Radiation particularly associated with nuclear medicine and the use of nuclear energy, along with X-rays, is 'ionizing' radiation, which means that the radiation has sufficient energy to interact with matter, especially the human body, and produce ions, i.e. it can eject an electron from an atom. X-rays from a high-voltage discharge were discovered in 1895, and radioactivity from the decay of particular isotopes was discovered in 1896. Many scientists then undertook study of these, and especially their medical applications. This led to the identification of different kinds of radiation from the decay of atomic nuclei, and understanding of the nature of the atom. Neutrons were identified in 1932, and in 1939 atomic fission was discovered by irradiating uranium with neutrons, and this led on to harnessing the energy released by fission. Types of radiation Nuclear radiation arises from hundreds of different kinds of unstable atoms. While many exist in nature, the majority are created in nuclear reactionsa. Ionizing radiation which can damage living tissue is emitted as the unstable atoms (radionuclides) change ('decay') spontaneously to become different kinds of atoms. The principal kinds of ionizing radiation are: Alpha particles These are helium nuclei consisting of two protons and two neutrons and are emitted from naturally-occurring heavy elements such as uranium and radium, as well as from some man-made transuranic elements. They are intensely ionizing but cannot penetrate the skin, so are dangerous only if emitted inside the body. Beta particles These are fast-moving electrons emitted by many radioactive elements. They are more penetrating than alpha particles, but easily shielded - they can be stopped by a few millimetres of wood or aluminium. They can penetrate a little way into human flesh but are generally less dangerous to people than gamma radiation. Exposure produces an effect like sunburn, but which is slower to heal. Beta-radioactive substances are also safe if kept in appropriate sealed containers. Gamma rays These are high-energy beams much the same as X-rays. They are emitted in many radioactive decays and are very penetrating, so require more substantial shielding. Gamma rays are the main hazard to people dealing with sealed radioactive materials used, for example, in industrial gauges and radiotherapy machines. Radiation dose badges are worn by workers in exposed situations to detect them and hence monitor exposure. All of us receive about 0.5-1 mSv per year of gamma radiation from cosmic rays and from rocks, and in some places, much more. Gamma activity in a substance (e.g. rock) can be measured with a scintillometer or Geiger counter. X-rays are also ionizing radiation, virtually identical to gamma rays, but not nuclear in origin. Cosmic radiation consists of very energetic particles, mostly protons, which bombard the Earth from outer space. Neutrons are mostly released by nuclear fission (the splitting of atoms in a nuclear reactor), and and hence are seldom encountered outside the core of a nuclear reactor. Thus they are not normally a problem outside nuclear plants. Fast neutrons can be very destructive to human tissue. Units of radiation and radioactivity In order to quantify how much radiation we are exposed to in our daily lives and assess potential health impacts as a result, it is necessary to establish a unit of measurement. The basic unit of radiation dose absorbed in tissue is the gray (Gy), where one gray represents the deposition of one joule of energy per kilogram of tissue. However, since neutrons and alpha particles cause more damage per gray than gamma or beta radiation, another unit, the sievert