Title: InkPhysics / Nuclear physics
On every note of this deck, unless a note says otherwise:
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Front: RECALL
State the half-life from the decay constant.
Back: T_½ = ln 2/λ.

Front: RECALL
State the closest-approach energy condition.
Back: At closest approach, all the alpha particle's kinetic energy has become electrostatic potential energy.

Front: DEFINITION
Define: Atomic mass unit.
Back: One twelfth of the mass of a carbon-12 atom, 1.661 × 10^−27 kg.

Front: DEFINITION
Define: Decay constant.
Back: The probability per unit time that a given nucleus decays: λ, in s^−1.

Front: RECALL
State how to find reaction energy from nuclear masses.
Back: Total mass before minus total mass after, in u, multiplied by 931.5 gives the energy released in MeV.

Front: DEFINITION
Define: Induced fission.
Back: A heavy nucleus splitting into two smaller nuclei after absorbing a neutron.

Front: RECALL
State the gradient of a ln N against t decay graph.
Back: A straight line of gradient −λ; the straightness is evidence the decay is exponential.

Front: DEFINITION
Define: Thermal neutron.
Back: A fission neutron slowed to the speeds at which it is most likely to be absorbed and cause further fission.

Front: SPOT THE ERROR
Say what is wrong with this claim: Mass is always conserved.
Back: Mass alone is not conserved; total mass-energy is. A nucleus has less mass than its separated nucleons, the difference having been released as binding energy via E = mc².

Front: EQUATION · NOT ON THE DATA SHEET
Activity falling with time:
A = ?\(A = \, ?\)A = ?
Back: A = A_0e^-λt\(A = A_{0}e^{-λt}\)A = A_0e^(-λt)

Front: RECALL
State where the binding energy per nucleon curve peaks.
Back: Iron-56, at about 8.8 MeV per nucleon: among the most tightly bound of all nuclei. The true maximum is a broad iron-nickel shelf, nickel-62 fractionally the highest, but iron-56 is the answer expected.

Front: DEFINITION
Define: Activity.
Back: The number of nuclei in a sample decaying per second: A = λN, in becquerels.

Front: RECALL
State the electron diffraction feature that fixes the nuclear radius.
Back: The angle of the first minimum of the intensity against angle graph.

Front: SPOT THE ERROR
Say what is wrong with this claim: After two half-lives, a sample has all gone.
Back: Each half-life halves what remains rather than removing it all: after two half-lives a quarter of the nuclei are still undecayed, and the sample never quite reaches zero.

Front: EQUATION · NOT ON THE DATA SHEET
Neutron energy kept in an elastic moderator collision:
fraction kept = ?\(\text{fraction kept} = \, ?\)fraction kept = ?
Back: fraction kept = (M - mM + m)^2\(\text{fraction kept} = (\frac{M - m}{M + m})^{2}\)fraction kept = ((M - m)/(M + m))^2

Front: SPOT THE ERROR
Say what is wrong with this claim: Bigger nuclei are packed tighter, so heavy elements have denser nuclei.
Back: Nuclear density is the same for all nuclei: R = R₀A^1/3 makes volume proportional to nucleon number, so every nucleus has a density of about 2 × 10¹⁷ kg m⁻³.

Front: SPOT THE ERROR
Say what is wrong with this claim: A nuclear reactor can explode like a nuclear bomb.
Back: A reactor cannot explode like a bomb: its low-enriched fuel and control rods keep exactly one neutron per fission causing another fission; the worst failure is a meltdown, not a nuclear explosion.

Front: EQUATION · NOT ON THE DATA SHEET
Nuclear density from R₀:
ρ = ?\(ρ = \, ?\)ρ = ?
Back: ρ = 3u4πR_0^3\(ρ = \frac{3u}{4πR_{0}^{3}}\)ρ = 3u/4πR_0^3

Front: RECALL
Explain the emergency shut-down of a reactor.
Back: The control rods drop fully into the core, absorbing enough neutrons to stop the chain reaction.

Front: RECALL
State how to find binding energy from mass defect.
Back: A nucleus's binding energy equals its mass defect multiplied by c^2: ΔE = Δmc^2.

Front: RECALL
Explain how to correct a count rate for background.
Back: Subtract the background count rate, measured with the source absent, from every reading before analysis.

Front: RECALL
State the absorber that stops beta radiation.
Back: A few millimetres of aluminium stop beta particles, which pass through paper.

Front: RECALL
State the energy released per fission of uranium-235.
Back: About 200 MeV per fission.

Front: DEFINITION
Define: Mass defect.
Back: The difference between the mass of a nucleus and the total mass of its separate nucleons.

Front: RECALL
State the energy equivalent of 1 u.
Back: 1 u is equivalent to 931.5 MeV.

Front: SPOT THE ERROR
Say what is wrong with this claim: Splitting any atom releases energy.
Back: Fission only releases energy for nuclei heavier than iron, the most tightly bound nucleus. Splitting lighter nuclei would absorb energy; for them fusion is the energy-releasing process.

Front: RECALL
State the products of induced fission.
Back: Each fission releases energy and two or three further neutrons.

Front: DEFINITION
Define: Half-life.
Back: The time taken for the number of undecayed nuclei in a sample, and so its activity, to halve.

Front: DEFINITION
Define: Moderator.
Back: The reactor material that slows fission neutrons to thermal speeds by elastic collisions.

Front: RECALL
State the composition, mass and charge of each radiation.
Back: Alpha: two protons and two neutrons, 4u, +2e. Beta-minus: an electron, about u/1840, −1e. Beta-plus: a positron, about u/1840, +1e. Gamma: a photon, no mass and no charge.

Front: DEFINITION
Define: Coolant.
Back: The fluid, such as water or carbon dioxide, that transfers thermal energy from the core to raise steam for the turbines.

Front: RECALL
Explain why fusion needs very high temperatures.
Back: The positive nuclei must have enough kinetic energy to approach closely against their electrostatic repulsion. Even in a star they fall short of the barrier, and quantum tunnelling closes the remaining gap.

Front: EQUATION · NOT ON THE DATA SHEET
Closest approach: the alpha's kinetic energy:
E_k = ?\(E_{k} = \, ?\)E_k = ?
Back: E_k = Qq4πε_0r_min\(E_{k} = \frac{Qq}{4πε_{0}r_{min}}\)E_k = Qq/4πε_0r_min

Front: SPOT THE ERROR
Say what is wrong with this claim: An atom is a tiny solid ball, packed with matter all the way through.
Back: An atom is mostly empty space, not solid: most alpha particles passed straight through the foil, and nearly all the mass and all the positive charge sit in a tiny nucleus.

Front: RECALL
State the experimental evidence that radioactive decay is random.
Back: Counts recorded over successive equal intervals from an unchanging source do not repeat: they scatter about a mean. Those fluctuations in count rate are the evidence, because a regular process would return the same count every interval. The scatter is about √N for a count of N, so long counts have a smaller fractional error.

Front: RECALL
State the first stage of spent fuel storage.
Back: Cooling ponds, where water shields the radiation and carries away decay heat while short-lived isotopes decay.

Front: RECALL
State the quantity used to compare nuclear stability.
Back: Binding energy per nucleon, never total binding energy.

Front: RECALL
State how lead absorbs gamma radiation.
Back: By attenuation, each further thickness cutting the intensity by the same fraction, so thick lead reduces gamma to a safe level rather than halting it at a fixed range.

Front: RECALL
Explain the random nature of radioactive decay.
Back: Each nucleus has a constant probability of decay per unit time, unaffected by physical or chemical conditions.

Front: RECALL
State the most ionising radiation.
Back: Alpha: the most strongly ionising and least penetrating, stopped by paper or a few centimetres of air.

Front: DEFINITION
Define: Binding energy.
Back: The energy needed to separate a nucleus into its constituent nucleons.

Front: DEFINITION
Define: Critical mass.
Back: The minimum mass of fissile material in which, on average, one neutron per fission goes on to cause another fission.

Front: RECALL
Explain the half-life trade-off for a medical tracer.
Back: Long enough to image before the activity fades, short enough that the dose clears from the patient quickly.

Front: RECALL
State the constant in the nuclear radius equation.
Back: About 1.2 fm, the gradient of the straight-line graph of R against A^1/3.

Front: DEFINITION
Define: Control rods.
Back: Rods of boron or cadmium that absorb neutrons to control the rate of the chain reaction.

Front: DEFINITION
Define: Inverse-square law for gamma.
Back: The intensity of gamma radiation from a point source is I = k/x^2, so doubling the distance quarters the intensity.

Front: RECALL
Explain why electrons are used to measure nuclear radii.
Back: They do not experience the strong force, and their de Broglie wavelength can be made comparable to the nuclear diameter.