885131
| Questão | Responda |
| What is an atom made up of? | The basic structure of an atom is a small central nucleus composed of protons and neutrons surrounded by electrons. Candidates should appreciate the relative size of the nucleus compared to the size of the atom. |
| Numbers of particles in a neutral atom? | In an atom the number of electrons is equal to the number of protons in the nucleus. The atom has no overall electrical charge. |
| What is an ion? | Atoms may lose or gain electrons to form charged particles called ions. |
| What is the same for ALL atoms of an element? | Number of protons |
| What is atomic number? | The total number of protons in an atom |
| What is mass number? | The total number of protons and neutrons in an atom |
| What is an isotope? | Same number of protons, different number of neutrons |
| Origins of background radiation? | Knowledge and understanding should include both natural sources, such as rocks and cosmic rays from space, and man-made sources such as the fallout from nuclear weapons tests and nuclear accidents. |
| What can affect the radiation gives out by a radioactive substance? | NOTHING! |
| What is an alpha particle? | two neutrons and two protons |
| What is a beta particle? | an electron from the nucleus |
| What is a gamma ray? | electromagnetic radiation |
| Nuclear equations? (H) | Candidates will be required to balance such equations, limited to the completion of atomic number and mass number. The identification of daughter elements from such decays is not required. |
| Properties of alpha | Strongly ionising (2+) Penetrate thin paper Short range in air |
| Properties of beta | Medium ionising (1-) Penetrate thin Al Tens of cm in air |
| Properties of gamma | Weakly ionising Penetrates lead! Very long range in air |
| Deflection of radiation by electric and magnetic fields | All candidates should know that alpha particles are deflected less than beta particles and in an opposite direction. Higher Tier candidates should be able to explain this in terms of the relative mass and charge of each particle. |
| What is half-life? | The half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate from a sample containing the isotope to fall to half its initial level. |
| The uses of and the dangers associated with alpha | Smoke detector. Short-range means very dangerous inside the body, but limited danger outside. |
| The uses of and the dangers associated with beta | Thickness monitoring (paper, Al sheet). Longer-range means more dangerous from outside the body, less dangerous from inside. |
| The uses of and the dangers associated with gamma | Medical tracers (short half-life) Radio-therapy Sterilising surgical instruments. Cancer risk from over-exposure to lower-energy gamma. |
| Name two nuclear fuels? | There are two fissionable substances in common use in nuclear reactors: uranium-235 and plutonium-239. |
| What is nuclear fission? | Nuclear fission is the splitting of an atomic nucleus. |
| What does the fuel nucleus have to do before it can fissh? | For fission to occur the uranium-235 or plutonium-239 nucleus must first absorb a neutron. |
| What happens when a nucleus undergoes fission? | The nucleus undergoing fission splits into two smaller nuclei and two or three neutrons and energy is released. The neutrons may go on to start a chain reaction. Candidates should be able to sketch or complete a labelled diagram to illustrate how a chain reaction may occur. |
| What is nuclear fusion? | Nuclear fusion is the joining of two atomic nuclei to form a larger one. |
| How do stars form? | Stars form when enough dust and gas from space is pulled together by gravitational attraction. Smaller masses may also form and be attracted by a larger mass to become planets. |
| What is true for a 'main sequence' star | During the ‘main sequence’ period of its life cycle a star is stable because the forces within it are balanced. |
| Can you describe the life cycle of a star? |
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| Where do the elements come from? | Fusion processes in stars produce all of the naturally occurring elements. These elements may be distributed throughout the Universe by the explosion of a massive star (supernova) at the end of its life. Candidates should be able to explain how stars are able to maintain their energy output for millions of years. Candidates should know that elements up to iron are formed during the stable period of a star. Elements heavier than iron are formed in a supernova. |
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