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Physics Partic+React
| Question | Answer |
|---|---|
| Mass defect | The difference in mass between the initial particle and the products in a reaction. It has been converted to energy. |
| What is u? | The atomic mass unit |
| How to write nuclei | Top number is the nucleon number (aka atomic mass), bottom number is proton number (aka atomic number). |
| Alpha particles | No electrons. 4 mass, 2 proton. Written as a normal nucleus with an alpha symbol (or sometimes He). Just ejected by nucleus. In general, alpha particles emitted from a given type of nucleus are monoenergetic = all have equal energy |
| Nuclear activity occurs between what? | Nuclei, not atoms. Don't factor in electrons for e.g. alpha decay. Also for mass defect not important because their mass isn't being turned into energy. |
| Why beta decay isn't just a neutron turning into a proton and electron | The mass defect gives the electron a velocity faster than light, so something else must be happening. |
| Cosmic radiation | Not just the sun |
| Theory prior to rutherford | JJ Thompson suggested plum pudding, which suggests that the positive charge is spread over a large area containing the electrons, so a positive alpha particle will have a low angle of deflection due to wide spread of positive charge of atoms |
| Rutherford scattering experiment overview | Alpha source (radium) through gold foil (~100 atoms thick) onto ring of scintillators (release photons when particles hit) Angle of deflection of alpha particles strangely high In vacuum so alpha not quick attenuated |
| Alpha deflection in rutherford scattering experiment | Very few deflect so nucleus small compared to atom (nucleus 10^-14m, atom 10^-10), so most of mass concentrated in nucleus. Very high deflection (sometimes >90) showing nucleus is very dense positive charge |
| Nuclear strong force overview | Protons repel so held in nucleus. Gravity too weak. Arises as residual effect of strong forces holding quarks inside nucleus. Very small range (about 3fm) - not outside nucleus |
| Nuclear strong force graph | Nuclear force on y, separation of nucleons on x Line starts very high positive (repulsive), sloping very quickly down to strongly negative (attractive. peaks at about 1fm), then gradually asymptoting towards zero again. Crosses axis at approx 0.5fm |
| Nuclear strong force graph explanation | Strong nuclear force repulsive below gap of 2r (as nucleons overlap), so doesnt collapse in. We know this because distance between adjacent nucleons not affected by size of nucleus (i.e. more strong force doesn't make nucleus smaller) |
| Show relationship between radius of nucleus and number of nucleons (in formula booklet) V = volume of nucleus v = volume of nucleon A = number of nucleons R = radius of nucleus r[subscript 0] = r0 = constant | Assume V = Av Assume spherical nucleus 4/3*pi*R^3 = A*4/3*pi*r0^3 R^3 = A*r0^3 R = r0*A^(1/3) |
| Show density of nucleus independent of nucleon number V = volume of nucleus A = number of nucleons m = mass of one nucleon R = radius of nucleus r[subscript 0] = r0 = constant p = density of nucleus | p = m/v mass = Am volume = 4/3*pi*R^3 = 4/3*pi*(r0*A^1/3)^3 p = Am/(4/3*pi*r0^3*A) Cancel A so p independent of A |
| e.g. find approx density of He-4 nucleus [where i think the Q gave r0 = 1.2x10^-15] V = volume of nucleus A = number of nucleons m = mass of one nucleon R = radius of nucleus r[subscript 0] = r0 = constant p = density of nucleus | V = 4/3*pi*R^3 = 4/3*pi*(r0*4^(1/3)) = 4/3*pi*r0^3*4 V = 4/3*pi*(1.2x10^-15)^3*4 = 2.895x10^-44 Mass of He-4 nucleus is 4u Density = V/4u = 2.3 x 10^17 For atoms, instead use the 10^-10 volume |
| Beta minus decay (normal beta decay. Remember tail on the beta and the superscript minus) | B- particle is an electron. Neutron in nucleus changes into a proton, an electron, and an antineutrino. Proton stays in nucleus and other two emitted Written like an element but with top number mass (zero), bottom number charge (-1). Then B or e symbol |
| B+ decay | B+ particle is a positron (antimatter equivalent of electron) Proton changes into a neutron, a positron, and a neutrino. Neutron stays in nucleus and two other two emitted Written with top number mass (zero), bottom number charge (+1). B or e symbol |
| Gamma | High energy EM Written like an element, with 0 top, 0 bottom, then like a proportional symbol with the two ears pointing up |
| After decays | Remember to change both the numbers and the element symbol when needed |
| How to write B- decay | 14/6 C -> 14/7 N + 0/-1 B + antineutrino Write the antineutrino as a curvy v (like velocity) with a bar above it to mean anti REMEMBER THE ANTINEUTRINO |
| B+ decay | 37/19 K -> 37/18 Ar + 0/+1 B + v |
| Why large particles harder to find | Tons of energy in particle accelerator needed to find them |
| Leptons | Fundamental particles such as electrons. 3 'flavours' of leptons, a lepton neutrino for each lepton, and an anti-particle version of all 6 of these. The 3 flavours are electrons (e), muons (μ), and tauons (τ), all with -1 charge. |
| How to write lepton neutrinos | the curvy v with a subscript of the flavour |
| Muons | Mean lifetime of about 2 microseconds, but because they are travelling very fast time slows down for them. Same charge as electron but about 200x the mass |
| Tauons | Mean lifetime of 10^-13 seconds Same charge as electron but 17x the mass of a muon |
| Neutrons stability outside atom | Decay in about 15 minutes but weak nuclear stabilises them in atom. |
| Quarks | 6 flavours of quarks in 3 generations. Combine to form hadrons. Contains charge in fractions of elementary charge. m = E/c^2 |
| How to show antiparticle version | Line above symbols |
| Types of quarks (in order of increasing mass) and their charge | Up (u) = +2/3 Down (d) = -1/3 Strange (s) = -1/3 Charm (c) = +2/3 Bottom (b) = -1/3 Top (t) = +2/3 |
| Types of hadrons | Baryons and mesons |
| Baryons | System of 3 quarks e.g. proton (uud), neutron (udd) [remember this makeup] Confined in nuclei. Will hypothetically decay if isolated - neutrons do, but it is unconfirmed if protons do. |
| Beta decay in terms of quarks | Fundamentally d -> u (B-) or u -> d (B+) transformation of quarks via emission of leptons |
| Mesons | 2 quarks in a quark-anti quark pair. e.g. pion, kaon, etc. Very rarely the same type because normally would annihilate |
| What needs to be conserved in all decays and interactions | Charge, lepton number, baryon number. Also 'mass-energy' Under certain circumstances (generally, but not if decaying by weak nuclear) strangeness has to be conserved. |
| All we need to know about strangeness | Strange quarks have -1 strangeness. Anti-strange quarks have +1 |
| Radioactive decay | Can be described as spontaneous and random. Precise moment an unstable nucleus will decay can't be predicted, and isn't altered by changes in temperature, pressure, etc. |
| Half life of radioactive nuclide | The AVERAGE time taken for half the radioactive nuclei (of that type of nucleus) to have decayed/time for activity (of that type of nucleus) to reduce to half its original value/mass (of that type of nucleus) decreased to half of original |
| Exponential decay graph | No of nuclei on y, time on x Starts at N[subscript 0]. After each equally long half life, becomes N0/2, N0/4, etc Exponential shows rate of emission of particles proportional to number of radioactive nuclei in sample (rate prop to value so exponent) |
| Activity of a sample | Number of particles emitted per second, which is equal to dN/dt. Measured in Bq |
| Relationship between activity and number of nuclei (in formula booklet) | A = dN/dt, which is proportional to number of nuclei, so equals -lambda*N Remember the minus: indicates number of undecayed nuclei falls with time. Lambda is the decay constant |
| Decay constant | Probability of an individual nucleus decaying per unit time |
| Decay equations (in formula booklet) | N = N0 * e^-(decay constant*t) where N is the number of decayed nuclei after time t and N0 is the number of undecayed nuclei at t=0 Can switch out N for A |
| Relationship between half life (t subscript 1/2) and decay constant In formula booklet | After one half life, A/A0 = 1/2 A/A0 = e^-lambda*t[1/2] 1/2 = e^-lambda*t[1/2] ln1/2 = -lambda*t[1/2] ln2 = lambda*t[1/2) (minus removed) |
| Baryon number (and lepton number) | All baryons have a baryon number of 1. All anti-baryons have -1. Everything else 0. Leptons work the same way |
| Momentum calculations for alpha decay | Remember that the original nucleus is now smaller for calculations with mass |
| Why alpha not super dangerous | Stopped by layer of dead skin |
| Stability line position | Neutron number N on y, proton number Z on x (check acc this for each Q) From N = Z, the stability line is about equal for a while (until about 20), gradually curving up higher than N = Z. Stops ~60 Z kinda - none truly stable beyond here |
| Stability line different areas of decay | If slightly to the left of the line, B- decay so Z increases and N decreases If slightly right, B+ so Z down N up If more significantly right (specifically above ~80 Z), alpha decay so Z lots down and N lots down Always closer to line from decays |
| Carbon dating overview | C-14 is radioisotope in atmosphere (incredibly tiny amounts) Living tissue carbon comes from atmosphere carbon so C-14 in living tissue, so can be used to carbon date dead things. |
| How to carbon date | Known atmospheric ratio of C14 to C12 Calc sample C-12 mass, using atmospheric ratio to calc initial C-14 Calc initial activity: A0 = lambda*N0 Measure background and activity due to C14 A = A0*e^-lambda*t |
| Why carbon dating sometimes unreliable | Amount in atmosphere has changed significantly over time. Has half life of about 5700 years, so not too old either Needs decently large organism |
| How to date the earth | Uranium dating - much longer half life. |
| When can nuclear fusion happen | High temps and densities to overcome electrostatic repulsion between nuclei. In sun, conditions only met in core. In main sequence, it does fusion in a Proton-Proton chain |
| Proton-Proton chain hydrogen fusion | 4 H nuclei (protons) to 1 He (4/2) Protons collide into unstable 2/2 He, which then beta decays into deuterium. Then repeats with another proton for Tritium. 2 tritiums then collide into 4/2 He, which then releases the 2 spare protons. |
| Hydrogen fusion energy and equation | Four 1/1 H -> 4/2 He + energy (gamma rays) + neutrinos The mass of the helium nucleus is slightly less than the sum of the masses of the four H nuclei, so lots of energy (technically 6 protons in and 2 out, not just four in) |
| Types of hydrogen fusion | On earth we're researching D-T, but in sun it's T-T i think These last 3 flashcards really need some work done |
| Behaviour of hadrons and leptons | Hadrons experience strong and weak nuclear force and leptons only weak |
| Checklist points to hit when i have time: 'explain decay of particles in terms of quark model' and 'demonstrate quark transformation equations balanced in terms of charge' | |
| Define radioactive decay | Spontaneous and random event in which an unstable nuclei emits radiation to become more stable |
| Describe the techniques used to investigate the absorption of all three types of radiation | source safely in a tube pointed towards a geiger muller tube and counter at most 3cm away. Then place the various materials in the gap and for each record the readings in 1 minute. Also take a background count |
| Checklist points to hit when i have time: 'demonstrate the graphical methods and spreadsheet modelling of the equation dN/dt = -lambda*N' | |
| Gamma radiation relative ionising power | About 1000x less than beta and 10000x less than alpha |
| Beta deflection by magnetic/electric fields compared to alpha Also other beta vs alpha stuff | Alpha slight deviation, beta large deviation (also beta is about 0.9c, alpha is like 0.05 to 0.1c) Remember beta can be a positron |
| How to detect radiation | Photographic plates, Geiger-Muller tubes (ionising particle causes cascades of electrons), and solid state detectors |
| When does gamma happen | After other forms of decay, if daughter nuclide has excess energy |
| How each type of radiation falls off in intensity | Gamma not rlly absorbed by air so inverse square law (spreads out). Alpha and beta also do this in a vacuum In air (for a and b) and other materials they lose energy by ionising the atoms in their paths. Higher energy more readily absorbed |
| Why stability line curves up | The strong force is directly opposing electrostatic repulsion. As the size of the nucleus increases, more neutrons are needed than protons so strong force stronger than repulsion so still stable |
| Finding relative speeds of different particles | If A has twice the energy of B, then A = 2B. Nicely done with the complex algebra with that one. Express each in terms of the mass of one of them so you can cancel. |
| Alpha vs beta energy | Alpha all the same energy, but beta is a range of energies up to a maximum depending on the isotope |
| Smoke alarm | Can wear PPE for any spills to prevent contamination. Only open the plastic casing not the metal ionisation chamber one. |
| What do you call a bunch of decays in a row | A decay series/chain. Continues as long as it is resulting in lower energy states, where the final mass is always less than the initial mass. |
| Why baryon number conserved, not mesons | If baryon and anti-baryon combine, they have a baryon number of 0 and a lepton number of 0, but there still needs to be some mass-energy and charge. Mesons are how that balances (3 mesons from the 3 quarks and 3 anti-quarks) |
| Isotopes | Atoms of the same element with differing numbers of neutrons |
| Relative atomic mass number (decimal mass for each element) | Takes into account all of the isotopes with their relative abundance - not the actual mass of a given nucleus so dont use it - use the mass number |
| What fundamental force is responsible for radiation pressure | Electromagnetism |
| Weak nuclear basic info | the force responsible for beta decay. It acts to change quark types over very small distances Causes radioactive decay |
| Measuring mass | Because of mass-energy equivalence, fast objects have more mass (but only slight when at slow speeds because inverse of c^2). Therefore need to be measured at rest = rest mass. |
| 2 types of energy of binding energy | electrostatic potential energy and the potential energy that arises from the strong nuclear force |
| What principle does binding energy rely on | bound state having a more negative energy than the unbound state 'the minimum energy required to break a nucleus into its constituent components' |
| Why small elements gain binding energy per nucleon when fused unlike large elements | Large proton number causes a large repulsive electrostatic force and a relatively feeble strong attraction due to an increased average distance between the nucleons Smaller has big strong force increase but small electrostatic |
| Unit for particle rest mass normally | MeV/c^2 Because in pair production photon must have energy greater than both rest masses combined. |
| Overview of particle model | Two classes: Hadrons and Leptons Hadrons have Baryons (3 e.g. proton) and Mesons (2 e.g. pion) |
| Why neutrinos hard to detect | Chargeless and VERY low mass so rarely interact with matter |
| What to block radiation with | Paper, aluminium, lead |
| Alpha emission can be thought of as | Spontaneous fission of unstable nuclei in which the strong nuclear force is not great enough to overcome the electrostatic repulsion between protons in the nucleus |
| Why alpha is a helium nucleus | high binding energy per nucleon of the helium nucleus so large energy loss from the unstable nuclei |
| What does the proportionality of deltaN to N, and thus the proportionality of A to N, rely upon | Very large sample |
| Background radiation | Cosmic radiation Naturally occurring radioactive materials Stuff like e.g. power plants nearby ALWAYS REMEMBER TO MEASURE AND REMOVE |
| How to calculate half life from just measuring activity at different times (if you can measure mass can just do A = constant*N) | Logarithmic scale of the A = A0e^-kt equation lnA against t gives a gradient of -k |
| Name for supernovae making heavy elements (prob dont need) | supernova nucleosynthesis |
| Name for giants making heavy elements (prob dont need) | Mainly CNO cycle in which carbon, nitrogen and oxygen are synthesised |
| Mass defect of fission | Combine, the KE of the nuclei, the KE of the neutrons, and the energy of the photons released |
| Fission reactor overview | Fuel rods (fissile material) in thermal coolant (gains KE, goes to turbine) Neutrons from fission slowed by moderator for higher chance of chain reaction Rate controlled by control rods - absorb thermal neutrons so rate not too high if overheating |
| Types of neutrons in reactor | Neutrons absorbed most when slow 'Thermal neutrons' are the slow ones, which are used to start the whole process, and are what we want so we use moderators to slow down fission neutrons Neutrons from fission released very fast so not easily absorbed |
| Moderator material | e.g. water or graphite |
| Control rod material | e.g. boron or cadmium |
| Products of fission | Typically radioactive and often have very long half lives (up to 10s of thousands of years) so need to be stored safely. |
| Alpha particle straight towards nucleus calculations | KE all to PE as it nears nucleus |
| R = r0 * A1/3 What is r0 | When A = 1, hydrogen, so r0 = radius of proton |
| How different radiations act in E fields and B fields | Beta always deflected lots, alpha slightly, and gamma not at all. Careful with direction of B+ and B- |
| Random meaning | Cannot predict WHICH nucleus will decay next Cannot predict WHEN any given nucleus will decay Each nucleus in a sample has an equal chance of decaying in a given time |
| Spontaneous meaning | Not affected by other nuclei in the sample Not affected by external factors (e.g. pressure) |
| C14 formation | Cosmic rays interacting with nuclei in atmosphere |
| Binding energy graph | y axis is (NEGATIVE) binding energy *per nucleon* x axis is atomic mass |
| For light nuclei: explanation of binding energy being that | To split apart a nucleus, takes lots of energy (to overcome binding energy). So putting nucleons together (fusing) releases energy because they have less (more strongly negative) energy once combined Opposite for heavy nuclei |
| 'Show beta decay in terms of quarks' | d -> u + e- + v[bar] Just the single quark, and include the electron and anti-neutrino |
| What is binding energy | Work done to separate a nucleus into its constituent nucleons to an infinite distance When binding energy per nucleon becomes more negative, energy released in fission/fusion Normally given as per nucleon |
| Defined mass of protons and neutrons | Only when isolated. When bound together, mass not equal to constituent parts, as some converted to balance out binding energy |
| Nuclear fission overview | Bombardment of U by neutrons splits into 2 large nuclei (roughly equal mass). Appreciable mass decrease - energy mainly as KE of products as they move apart. Other neutrons (called fissions) emitted in process. |
| Now nuclear power stations make energy | Fission products (fragments) collide with surrounding atoms - heat to make steam. Reactors like this are described as thermal reactors because fission caused by slow neutrons with thermal energies (i.e. same energy as avg KE of surrounding atoms) |
| Describing how to take count rate measurement | Take background. Over at least 3 mins. Measure with stopwatch. Calculate corrected count. Use Geiger-Muller tube and counter. Hold source at arms length when transferring. Keep in lead lined box at other times. Use tongs to hold. |
Created by:
Pyrogearos2