Edexcel Physics IGCSE Summary Notes on Radioactivity and Particles PDF

Edexcel Physics IGCSE Topic 7: Radioactivity and Particles Summary Notes (Content in ​bold​ is for physics only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-N...

Edexcel Physics IGCSE Topic 7: Radioactivity and Particles Summary Notes (Content in ​bold​ is for physics only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Radioactivity An atom consists of: A ​positively charged nucleus ​made of: o Positive ​protons o Neutral ​neutrons Surrounded by​ negatively charged electrons ​which orbit the nucleus The radius of the nucleus is a lot smaller than the radius of the entire atom. Almost all the mass of the atoms lies in the nucleus. Particle Relative Mass Relative Charge Proton 1 +1 Neutron 1 0 Electron 0.0005 -1 Atoms of the same element have the ​same​ number of protons. ​Isotopes​ are forms of an element’s atom with the ​same number of protons​ but a​ different number of neutrons. For a given nuclide (distinct nucleus): X is the ​symbol​ of the element A is the ​mass (nucleon) number​ (number of neutrons and protons) Z is the ​atomic (proton) number​ (number of protons) Radioactive decay is the ​spontaneous​ transformation of an ​unstable​ nucleus into a more ​stable one by the release of radiation. It is a ​random​ process which means one cannot know ​what nucleus will decay or ​when​ it will decay because it is down to chance. Decay processes: Alpha: o A heavy nucleus emits an ​alpha particle​ (helium nucleus - 2A, 4X). o The nucleus changes to that of a different element according to the following equation: Z AX→(X − 4A − 2Z) + α o They are ​highly ionising​ and ​weakly penetrating. ​They are stopped by a sheet of paper. Beta: o A neutron turns into a proton and emits a ​beta particle​ (electron) o The nucleus changes to that of a different element according to the following equation: ZAX→(X − A − Z ) + β − o They are ​moderately ionising​ and ​moderately penetrating. ​They are stopped by a thin sheet of aluminium. Gamma: o After a previous decay, a nucleus with excess energy emits a ​gamma particle. o Gamma particles are a form of electromagnetic radiation. o They are ​lowly ionising ​and ​highly penetrating. ​They are stopped by many centimetres of lead. Neutron radiation: o In neutron-rich nuclides, occasionally one or more ​neutrons​ are ejected. They are also emitted during nuclear fission. o The nucleus becomes a new isotope of the original element according to the following equation: Z AX→(X − A) + 1n https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Some ways of detecting radiation include: Photographic film: o The more radiation absorbed by the film, the ​darker​ it gets (the film is initially white). o They are worn as ​badges​ by people who work with radiation, to check how much exposure they have had. Geiger-Muller tube: o A Geiger-Muller tube is a ​tube​ which can detect radiation. o Each time it absorbs radiation, it transmits an electrical pulse to the machine, which produces a ​clicking sound.​ The greater the frequency of clicks, the more radiation present. Weak radiation that can be detected from​ external ​sources is called ​background radiation. Sources of background radiation include: From space: o Cosmic rays include high-energy charged particles penetrating the atmosphere From Earth: o Radioactive rocks which give off radioactive radon gas o Food and drink which contains radioactive isotopes (such as Carbon 14) o Fallout from nuclear weapons testing o Medical sources such as x-rays from MRI scanners o Nuclear power plants which produce radioactive waste The ​activity​ of a radioactive source is the ​number of decays ​which occur ​per unit time ​and is measured in ​becquerels (Bq where 1 Bq = 1 decay per second). ​The activity of a radioactive source ​decreases​ over a period of time. The ​half-life​ of an isotope is the ​time taken for half the nuclei to decay​, or the ​time taken for the activity to halve. ​It is different for different radioactive isotopes. In the graph, the count rate drops from 80 to 40 counts per minute in 2 days, which means the half-life is around 2 days. Or from 40 counts per minute to 20 counts per minute in the next two days. Half-life is ​constant ​(it does not depend on how many nuclei have decayed). Background radiation must be ​subtracted before attempting to perform half-life calculations Uses of radioactivity: Industry o Smoke detectors Long half-life ​alpha​ emitters are used in ​smoke detectors.​ Alpha particles cause a​ current​ in the alarm. If smoke enters the detector, some of the alpha particles are ​absorbed​ and the current drops,​ triggering the alarm. o Thickness monitoring Long half-life ​beta​ emitters can be used for ​thickness monitoring​ of metal sheets. A source and receiver are placed on either side of the sheet during its production. If there is a ​drop ​or ​rise​ in the number of beta particles detected, then the thickness of the sheet has changed and needs to be adjusted. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Medicine o Sterilisation of equipment Gamma​ emitters are used to ​kill ​bacteria or parasites on equipment so it is safe for operations (this means they can be sterilised through their protective packaging to eliminate the risk of contamination). o Diagnosis and treatment - Short half-life ​gamma​ emitters such as technetium-99m are used as ​tracers​ in medicine as they concentrate in certain parts of the body. The half-life must be long enough for diagnostic procedures to be performed, but short enough to not remain radioactive for too long. - Other gamma emitters such as cobalt-60 can be used to ​destroy​ tumours with a ​high dose of radiation. Contamination​ occurs when a ​radioactive source ​has been ​introduced into or onto ​an object. The contaminated object will be radioactive for as long as the source is in or on it. Irradiation​ occurs when an object is exposed to a ​radioactive source ​which is ​outside​ the object. The irradiated object does ​not​ become radioactive. Exposure to radiation can ​destroy living cell membranes​ by ​ionisation,​ causing the cells to ​die, or ​damage DNA ​which causes ​mutations​ that could lead to ​cancer. Safety measures include: Minimising the time​ of exposure to radiation, keeping as ​big a distance​ from the radioactive source as possible, and using ​shielding​ against radiation (such as protective clothing made from dense materials such as lead). Radioactive waste from nuclear reactors must be ​disposed of carefully,​ usually by burying it in sealed drums deep underground and ​remotely handling ​it after it has been thoroughly cooled. Fission and fusion Nuclear fission: The process of ​splitting a nucleus​ is called ​nuclear fission. When a ​uranium-235 ​nucleus ​absorbs a thermal ​(slow-moving) ​neutron,​ it splits into ​two daughter nuclei​ and ​2 or 3 neutrons,​ releasing ​energy​ in the process. The neutrons then can induce further fission events in a ​chain reaction ​by striking other uranium-235 nuclei. In a nuclear reactor: o Control rods ​(usually made of boron) are used to absorb neutrons ​and keep the number of neutrons such that only ​one​ fission neutron per event goes on to induce further fission. o The ​moderator ​(usually water) ​slows down neutrons by ​collisions​ so that they are moving slow enough to be absorbed by another uranium-235 nucleus. o A coolant (also water) is used to prevent the system from overheating. o The reactor core is a ​thick steel vessel ​which withstands the ​high pressures and temperatures​ and absorbs​ some of the ​radiation.​ The whole core is kept in a building with ​thick reinforced concrete walls ​that act as ​radiation shields ​to ​absorb ​all the radiation​ that escapes the reactor core. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Nuclear fusion: The process of ​fusing two nuclei​ to form a larger nucleus is called​ nuclear fusion. There is a very small ​loss of mass​ in the process, accompanied by a ​release of energy. Nuclear fusion is how the sun and other ​stars​ release energy. Nuclear fusion does ​not​ happen at ​low temperatures and pressures​ because the electrostatic repulsion ​of the ​protons​ is too great. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc