Title: InkPhysics / Particles
On every note of this deck, unless a note says otherwise:
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Front: SPOT THE ERROR
Say what is wrong with this claim: Protons and neutrons are fundamental.
Back: Protons and neutrons are not fundamental: each is made of three quarks, uud for the proton and udd for the neutron, as shown by deep inelastic electron scattering.

Front: RECALL
State the exchange particles of the weak interaction.
Back: The W^+ and W^− bosons.

Front: DEFINITION
Define: Hadrons.
Back: Particles that feel the strong interaction.

Front: RECALL
State the quark composition of the proton.
Back: Up, up, down (uud).

Front: RECALL
State the members of the lepton family.
Back: The electron, the muon, their neutrinos and their antiparticles.

Front: SPOT THE ERROR
Say what is wrong with this claim: Atoms of the same element are identical.
Back: Atoms of one element share a proton number but not necessarily a neutron number: isotopes of the same element have different nucleon numbers and masses.

Front: RECALL
State the exchange particle of the strong force between nucleons.
Back: The pion.

Front: RECALL
Explain how a particle and its antiparticle compare.
Back: Same mass and rest energy, with charge, baryon number and lepton number all reversed. A neutral pair such as the neutron and antineutron shares the same zero charge.

Front: RECALL
State the quark change in beta-plus decay.
Back: An up quark becomes a down quark (u → d).

Front: RECALL
State the evidence that led to the neutrino hypothesis.
Back: Beta particles are emitted with a continuous range of energies up to a maximum, so an unseen particle must carry the remainder.

Front: RECALL
Explain kaon decay at quark level.
Back: A K^− is a strange quark with an anti-up. The strange quark becomes an up quark, emitting a W^−, and that W^− becomes a down quark with an anti-up, which is the π^−; the spectating anti-up pairs with the new up quark to make the π^0. Strangeness changes by one, so only the weak interaction can do it.

Front: RECALL
State the exchange particle of the electromagnetic interaction.
Back: The virtual photon.

Front: RECALL
State the role of the nucleus in pair production.
Back: Pair production usually happens near a nucleus, which recoils so that momentum is conserved.

Front: DEFINITION
Define: Proton number Z.
Back: The number of protons in a nucleus, which determines the element.

Front: DEFINITION
Define: Meson.
Back: A hadron made of a quark and an antiquark.

Front: DEFINITION
Define: Isotopes.
Back: Atoms with the same number of protons but different numbers of neutrons: the same element with a different nucleon number.

Front: RECALL
Explain why annihilation gives two photons.
Back: A single photon could not conserve momentum. For a pair annihilating at rest, two photons travelling in opposite directions conserve both momentum and energy.

Front: RECALL
State the relative mass of the electron.
Back: About 1/1800 of the mass of a proton.

Front: RECALL
State the quantities conserved in every particle interaction.
Back: Charge, baryon number, each lepton number, energy and momentum.

Front: DEFINITION
Define: The weak interaction.
Back: The only interaction that can change quark flavour, as when a down quark becomes an up quark in beta-minus decay.

Front: RECALL
State the minimum photon energy for electron-positron pair production.
Back: 1.022 MeV, the total rest energy of the pair.

Front: SPOT THE ERROR
Say what is wrong with this claim: Antimatter is science fiction.
Back: Antimatter is real and routinely produced: every particle has an antiparticle with the same mass and opposite values of charge and the other quantum numbers, a neutral particle's antiparticle being neutral too, and annihilation and pair production are observed in experiments.

Front: DEFINITION
Define: Leptons.
Back: Fundamental particles that do not feel the strong interaction.

Front: RECALL
State the four fundamental interactions.
Back: Gravity, electromagnetic, weak nuclear and strong nuclear.

Front: RECALL
State the specific charge of the neutron.
Back: Zero, because the neutron has mass but no charge.

Front: EQUATION · NOT ON THE DATA SHEET
Specific charge:
specific charge = ?\(\text{specific charge} = \, ?\)specific charge = ?
Back: specific charge = Qm\(\text{specific charge} = \frac{Q}{m}\)specific charge = Q/m

Front: RECALL
Explain how strange particles are produced and decay.
Back: Produced in pairs by the strong interaction; they decay by the weak interaction.

Front: RECALL
Explain why a free proton cannot decay.
Back: It is the lightest baryon and baryon number is conserved, so there is no lighter baryon for it to become.

Front: SPOT THE ERROR
Say what is wrong with this claim: In particle physics, anything can happen.
Back: Not every reaction is allowed: a particle interaction can only happen if charge, baryon number and each lepton number are conserved, and strangeness is also conserved in strong interactions.

Front: RECALL
State how to convert a mass in MeV/c² into kilograms.
Back: Multiply by 1.60 × 10^−13 to turn the MeV into joules, then divide by c^2. One MeV/c^2 is 1.78 × 10^−30 kg. Reverse both steps to come back, so a mass in kilograms times c^2 and then divided by 1.60 × 10^−19 is a rest energy in eV. (Edexcel only.)

Front: RECALL
State the six flavours of quark and their charges.
Back: Up, down, strange, charm, top and bottom. Up, charm and top carry +2/3 e; down, strange and bottom carry −1/3 e; every antiquark carries the opposite charge. (CIE only: AQA, OCR and Edexcel examine u, d and s alone.)

Front: RECALL
State the quark composition of the neutron.
Back: Up, down, down (udd).

Front: DEFINITION
Define: Pair production.
Back: A single high-energy photon passing close to a nucleus converts into a particle and its antiparticle.

Front: RECALL
Explain why a neutral particle leaves no track in a detector.
Back: A track is the trail of ionisation a charged particle leaves in the medium it crosses, and a neutral particle ionises nothing. It is inferred instead from the gap between where it was made and where it decayed, which is why a decay of a neutral particle shows as a V with nothing leading into it. (Edexcel only.)

Front: RECALL
State what the curvature of a particle track tells you.
Back: Which way it curls gives the sign of the charge, because opposite charges bend opposite ways in the same field. How tightly it curls gives the momentum, through r = p/(BQ), so a wide arc is a fast particle and a tight one a slow particle. (Edexcel only.)

Front: RECALL
State what a mass of 1 MeV/c² means.
Back: The mass whose rest energy is 1 MeV. Rearranging E = mc^2 gives m = E/c^2, so an energy divided by c^2 is a mass and the number does not change: a rest energy of 0.511 MeV is a mass of 0.511 MeV/c^2. (Edexcel only.)

Front: RECALL
State the effect of alpha decay on A and Z.
Back: A decreases by 4 and Z decreases by 2.

Front: DEFINITION
Define: Annihilation.
Back: A particle and its antiparticle meet and their mass is converted to energy. For a pair annihilating at rest this is released as two photons back to back.

Front: RECALL
Explain why a particle track spirals inwards.
Back: The particle ionises as it travels and so loses energy, its momentum falls, and by r = p/(BQ) the radius falls with it turn by turn. The tight end is therefore the end reached last, which fixes the direction of travel and with it the sign of every charge in the picture. (Edexcel only.)

Front: DEFINITION
Define: Baryon.
Back: A hadron made of three quarks, such as the proton or the neutron.

Front: RECALL
State the effect of beta-minus decay on A and Z.
Back: A is unchanged and Z increases by 1.

Front: RECALL
State the range of the strong nuclear force.
Back: Attractive between nucleons out to about 3 fm, repulsive below about 0.5 fm.

Front: RECALL
Explain why the weak interaction has a very short range.
Back: Its exchange particles, the W bosons, are massive, so they exist only briefly and travel a tiny distance.

Front: DEFINITION
Define: Nucleon number A.
Back: The total number of protons and neutrons in a nucleus.

Front: RECALL
State the only stable free baryon.
Back: The proton; every other free baryon eventually decays into it. A neutron bound in a stable nucleus does not decay.

Front: RECALL
State the neutrino emitted in beta-minus decay.
Back: An electron antineutrino.

Front: SPOT THE ERROR
Say what is wrong with this claim: Positive charges can never stick together.
Back: Protons do repel electrically, but within about 3 fm the strong nuclear force is attractive and overpowers that repulsion, holding the nucleons of a nucleus together.

Front: RECALL
State the strangeness conservation rule.
Back: Conserved in strong interactions; can change by 0 or ±1 in weak interactions.

Front: DEFINITION
Define: Specific charge.
Back: The charge of a particle divided by its mass: Q/m, in C kg^−1.

Front: RECALL
Explain neutron decay at quark level.
Back: One down quark in udd becomes an up quark, giving uud, with a W^− boson emitted.

Front: SPOT THE ERROR
Say what is wrong with this claim: When two things repel, nothing passes between them.
Back: Repulsion is carried, not conjured at a distance: the particles exchange a virtual boson (a photon for electromagnetic repulsion) which transfers the momentum that pushes them apart.

Front: SPOT THE ERROR
Say what is wrong with this claim: Matter is just protons, neutrons and electrons.
Back: Protons, neutrons and electrons are not the whole of matter: accelerators and cosmic rays produce many other particles, classified as hadrons, which feel the strong interaction, and leptons, which do not.