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Nuclear and particle
| Question | Answer |
|---|---|
| Gold foil results | Most unaffected - mostly empty space. Some deflected at an angle less than 90 - small region of positive charge- Some more than 90, dense region of mass - nucleus. Very small compared to atom. |
| Nuclear strong force + range | Force between nucleons only. Short range, repulsive <0.5fm, attractive there to 3.0fm, otherwise no effect. Keeps the structure of the nucleus by binding the nucleons. |
| Standard model | Quarks, baryon number 1/3 Up +2/3, down -1/3 and strange, -1/3, -1 strangeness. Anti quarks have opposite charge, hadron number and strangeness. |
| Standard model cont. | Leptons, +1 lepton number weak nuclear force. Electrons, and electron neutrinos, positron and anti-electron neutrino. |
| Hadrons | Hadron is a combination of quarks. Meson is 1quark and 1 antiquark, baryon(heavy) is made of 3 quarks or 3 anti-quarks (technically antibaryon). Meson has baryon number of 0, baryon has baryon number of 1 or -1. |
| Strong and weak | Hadrons obey both strong and weak. Leptons only weak. |
| Beta decays | Proton-> neutron +positron+electron neutrino for beta plus, neutron->proton+electron+anti-electron-neutrino for beta minus. Changes proton number but not mass number. Can be d-> u or u->d when in terms of quarks. |
| Radioactive decay - words and definitions | Spontaneous - no obvious cause Random - no obvious pattern |
| Types of radiation | alpha,beta,gamma. charge mass obv. Ranges few cm, metre, very far. Stopped by paper, aluminium, thick lead or concrete. Only charge affected by electric and magnetic field. |
| Decay constant def and units. | Probability an individual nucleus decays in a given unit time. Units s^-1, but if kept consistent can use other time like years^-1 |
| Activity equations | A=lambda N - only in a small period time the instantaneous activity is lamda n. Exponential predicts activity for longer using differential. rate of change of number = -activity. |
| Half life | t1/2. Time taken for the activity and number of a sample to halve. Equal to ln(2)/lambda ensuring units match up. |
| How to check activity/half life | Geiger-Müller tube connected to a counter. Has an ionisable gas and a small hole for radiation to enter. When the radiation enters, a gas molecule is ionised. Electron goes to an anode causing the counter to increment. |
| Radioactive experiments | Wear gloves to prevent contamination. Only ever hold sample at arms length to minimise irradiation, especially of vital organs. Ensure no one pregnant is in the room. |
| Simulation using dice | Effectively decays constant of 1/6 per roll. Roll a large number of dice, remove all those which land on 6. Repeat for remaining dice. The number removed "activity" should decrease after every roll proportional to number of dice. |
| Spreadsheet modelling for radioactive decay | Presumably for each row, decrease the number of atoms by lambda times the number of atoms. |
| Radioactive dating | Carbon-14 isotopes form in the atmosphere consistently and are taken up by organisms. Therefore a living organism has a predictable proportion of carbon-14, and the mass will decrease over time predictably by a curve to give an age. |
| Mass defect | When nucleons bind together to form a nucleus, the mass of the nucleus is less.The difference is the mass defect, and the energy released when the nucleus is formed is the binding energy, using equivalence sameTo break a nucleus into its constituent parts |
| Pair production and annihilation | When a particle-antiparticle pair meat they can turn into energy in the form of a photon, whose energy is equal to the binding energies of the pair. A photon can become a pair spontaneously, but more often in a field, only when it has sufficient energy. |
| Binding energy per nucleon. | Binding energy being the energy equiv of mass defect of a nucleus. Per nucleon gives roughly the stability of a nucleus. Fe is the most stable nucleus as it has the highest binding energy per nucleon. In a nuclear reaction, this provides the change in e. |
| Fission | A large unstable nucleus decays into two nuclei of higher binding energy per nucleon, releasing energy. Can be induced by binding a neutron, making a heavier nucleus which is more likely to decay by fission. Daughters repel. |
| Fission reactor | Uses a self-sustaining induced fission (producing more neutrons) Fuel rods of the metal. Control rods, like graphite, absorb excess neutrons to control rate. Fission heats water which becomes water. This heats a separate flow of water into steam turbine |
| Water | Transfers heat, but also slows neutrons. Neutrons would otherwise pass nuclei without binding, but due to water they slow down allowing them to be captured by nuclei. |
| Nuclear waste | Daughter nuclei are often unstable with long half lives so are dangerous. Sealed in lead or concrete and buried or dropped in the ocean, but may cause environmental damage. |
| Nuclear fusion | Lighter nuclei than iron combine to form a heavier, more stable nucleus and release energy. Initial conditions must be high energy to get the nuclei to close enough to fuse. |
Created by:
pemmb