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Fichas por Simran Nagra, actualizado hace más de 1 año
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Creado por Simran Nagra
hace más de 11 años
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| Pregunta | Respuesta |
| The nuclear model | Atoms contain three sub-atomic particles called protons, neutrons and electrons. The protons and neutrons are found in the nucleus at the centre of the atom. The nucleus is very much smaller than the atom as a whole. The electrons are arranged in energy levels around the nucleus. |
| Rutherford's scattering experiment | A beam of alpha particles was aimed at very thin gold foil and their passage through the foil detected. The scientists expected the alpha particles to pass straight through the foil, but something else also happened. Some of the alpha particles emerged from the foil at different angles, and some even came straight back. The scientists realised that the positively charged alpha particles were being repelled and deflected by a tiny concentration of positive charge in the atom. As a result of this experiment, the plum pudding model was replaced by the nuclear model of the atom. |
| Isotopes | Isotopes are the atoms of an element with different numbers of neutrons. They have the same proton number, but different mass numbers. |
| Background radiation | Most background radiation comes from natural sources, while most artificial radiation comes from medical examinations, such as x-ray photographs. Radiation can damage cells and make them cancerous. Radiation also has many practical uses. It can be used in medicine to trace where certain chemicals collect in the body, and also in industry, to control measuring equipment. |
| Natural sources | Natural sources of background radiation include: *Cosmic rays - radiation that reaches the Earth from space *Rocks and soil - some rocks are radioactive and give off radioactive radon gas *Living things - plants absorb radioactive materials from the soil and these pass up the food chain |
| Artificial sources | human activity has added to background radiation by creating and using artificial sources of radiation. These include radioactive waste from nuclear power stations, radioactive fallout from nuclear weapons testing and medical x-rays. |
| Geiger-Muller tube | The Geiger-Muller tube detects radiation. Each time it absorbs radiation, it transmits an electrical pulse to a counting machine. This makes a clicking sound or displays the count rate. The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Muller tube is absorbing. |
| Alpha radiation | Alpha radiation consists of alpha particles. An alpha particle is identical to the nucleus of a helium atom, which comprises two protons and two neutrons. |
| Beta radiation | Beta radiation consists of high energy electrons emitted from the nucleus. These electrons have not come from the electron shells or energy levels around the nucleus. Instead, they form when a neutron splits into a proton and an electron. The electron then shoots out of the nucleus at high speed. |
| Gamma radiation | Gamma radiation is very short wavelength - high frequency - electromagnetic radiation. This is similar to other types of electromagnetic radiation such as visible light and x-rays, which can travel long distances. |
| Electric fields | Alpha particles are positively charged, beta particles are negatively charged and gamma radiation is electrically neutral. This means that alpha radiation and beta radiation can be deflected by electric fields, but gamma radiation is not deflected. Remember that opposite charges attract. Beta particles are negatively charged so they will be attracted towards a positively charged plate. And positive alpha particles will be attracted towards a negatively charged plate. |
| Magnetic fields | Because they consist of charged particles, alpha radiation and beta radiation can also be deflected by magnetic fields. Just as with electric fields, gamma radiation is not deflected by magnetic fields. |
| Hazards of radiation | When radiation collides with molecules in living cells it can damage them. If the DNA in the nucleus of a cell is damaged, the cell may become cancerous. The cell then goes out of control, divides rapidly and causes serious health problems. Radiation warning symbol The greater the dose of radiation a cell gets, the greater the chance that the cell will become cancerous. However, very high doses of radiation can kill the cell completely. We use this property of radiation to kill cancer cells, and also harmful bacteria and other micro-organisms. |
| Alpha, beta and gamma radiation | The degree to which each different type of radiation is most dangerous to the body depends on whether the source is outside or inside the body. If the radioactive source is inside the body, perhaps after being swallowed or breathed in: *Alpha radiation is the most dangerous because it is easily absorbed by cells *Beta and gamma radiation are not as dangerous because they are less likely to be absorbed by a cell and will usually just pass right through it If the radioactive source is outside the body: *Alpha radiation is not as dangerous because it is unlikely to reach living cells inside the body *Beta and gamma radiation are the most dangerous sources because they can penetrate the skin and damage the cells inside |
| Half-life | The nuclei of radioactive atoms are unstable. They break down and change into a completely different type of atom. This is called radioactive decay. For example, carbon-14 decays to nitrogen-14 when it emits beta radiation. There are two definitions of half-life, but they mean essentially the same thing: The time it takes for the number of nuclei of the isotope in a sample to halve The time it takes for the count rate from a sample containing the isotope to fall to half its starting level |
| Using radiation | Here are some examples of how radiation is used: In smoke detectors For sterilising medical instruments For killing cancer cells For dating rocks and materials such as archaeological finds In chemical tracers to help with medical diagnosis For measuring the thickness of materials in, for example, a paper factory |
| Nuclear fission | Splitting atoms, 'Fission' is another word for splitting. The process of splitting a nucleus is called nuclear fission. Uranium or plutonium isotopes are normally used as the fuel in nuclear reactors because their nuclei are relatively large and easy to split. For fission to happen, the uranium-235 or plutonium-239 nucleus must first absorb a neutron. When this happens: *The nucleus splits into two smaller nuclei *Two or three neutrons are released * Some energy is released |
| Nuclear fusion | Nuclear fusion involves two atomic nuclei joining to make a large nucleus. Energy is released when this happens. The Sun and other stars use nuclear fusion to release energy. The sequence of nuclear fusion reactions in a star is complex, but overall hydrogen nuclei join to form helium nuclei. |
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