Theme E — Nuclear and Quantum Physics
Theme E — Nuclear and Quantum Physics — IB Physics SL Revision Notes & Topical Questions
5 min read 11 parts Lesson 1 of 30 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
Theme E — Nuclear and Quantum Physics — IB PHYSICS SL notes: Summarise atomic structure and spectra, radioactive decay, fission, fusion and stellar physics at SL level.Nuclear model — a small dense nucleus of protons and neutrons is surrounded by electronsNucleon number — the tot…
- Energy levels
- Transitions
- Fingerprint
- Binding energy
- Count rate
- Usefulness of a source
Section 1 of 11Structure of the atom
Structure of the atom
Nuclear model
- Nuclear model a small dense nucleus of protons and neutrons is surrounded by electrons
Nucleon number
- Nucleon number the total number of protons and neutrons in a nucleus
Evidence
- Evidence alpha particle scattering from thin gold foil
Section 2 of 11Spectra
Energy levels
- Energy levels electrons occupy discrete levels
Transitions
- Transitions emission and absorption spectra arise when an electron moves between levels
- A photon of energy E = hf equals the difference between the levels.
Fingerprint
- Fingerprint each element therefore has its own set of spectral lines
Section 3 of 11Radioactive decay and stability
Stability
- Stability light stable nuclei have roughly equal numbers of neutrons and protons
- Heavier stable nuclei need extra neutrons to offset the growing repulsion between protons.
- Nuclei away from the line of stability decay.
Binding energy
- Binding energy the energy required to separate a nucleus completely into its nucleons
Activity
- Activity the number of decays per second, in becquerel (Bq)
Half-life
- Half-life the time for half the radioactive nuclei, or the activity, to decay
- Decay is exponential because the rate is proportional to the amount present.
Count rate
- Count rate it is a fraction of the activity, and the corrected count rate has background subtracted
Section 4 of 11Half-life in practice
Usefulness of a source
- Usefulness of a source a medical tracer needs a half-life of hours, whereas waste with a half-life of thousands of years needs very long storage
Same number of nuclei
- Same number of nuclei a shorter half-life gives a larger activity but a shorter-lived source
Quantity that halves
- Quantity that halves the number of undecayed nuclei halves each half-life, but the mass of the sample does not, since daughter nuclei remain in it
Data analysis
- Subtract background from each reading.
- Plot corrected count rate against time and draw a smooth curve.
- Read two or three half-lives from different starting points and average them.
Exponential signature
- Exponential signature a constant ratio over equal time intervals shows exponential decay
Section 5 of 11Nuclear fission
1Process
- Process a heavy nucleus splits, and the products lie nearer the peak of the binding-energy-per-nucleon curve
- Their total mass is less than that of the reactants, so ΔE = Δmc2.
- About 200 MeV is released per fission, mostly as kinetic energy of the fragments.
2Key words
- Key words chain reaction, critical mass, moderator, control rod and thermal neutron
3Control rod
- Control rod a rod of neutron-absorbing material used to regulate the fission rate
Section 6 of 11Nuclear waste
Long half-life
- Long half-life such waste is not always more dangerous, since its activity per atom is lower, although it lasts longer
High-level waste
- High-level waste it is a small share of the volume but holds most of the radioactivity
Reprocessing
- Reprocessing it recovers fuel but still leaves waste
Spent fuel
- Spent fuel it generates heat
After one half-life
- After one half-life waste is not harmless, since only half of the activity has gone
Section 7 of 11Nuclear fusion
Conditions
- Conditions very high temperatures are needed to overcome the electrostatic repulsion so that nuclei approach closely enough for the strong force to act
Key terms
- Q value is the energy released.
- The D–T reaction fuses deuterium and tritium into helium and a neutron, releasing 17.6 MeV.
- A tokamak confines the plasma magnetically.
- The Lawson criterion sets the density, temperature and confinement time for net gain.
- Ignition is self-sustaining fusion.
Section 8 of 11Life of stars
Stability
- Stability a star is stable because of a balance between gravity inward and the pressure of the hot gas and radiation outward, called hydrostatic equilibrium
Self-regulation
- Self-regulation if the core heats up, fusion speeds up, the star expands and cools, and the rate falls
Helium burning
- Helium burning when core hydrogen is exhausted the core contracts and heats until helium fuses (3 42He → 126C at about 108 K)
Massive stars
- Massive stars they fuse heavier elements up to iron-56, where fusion stops releasing energy
End states
- End states a star much more massive than the Sun ends as a neutron star or black hole after a supernova
Section 9 of 11Distances to stars
Parallax angle
- Parallax angle half the apparent angular shift of a star over six months
Distance
- Distance d = 1/p in parsecs, with p in arcseconds
Units
- The astronomical unit is the mean Earth–Sun distance, 1.50 × 1011 m.
- The parsec is 3.09 × 1016 m.
- The light-year is 9.46 × 1015 m.
- The arcsecond is 1/3600 of a degree.
Apparent brightness
- Apparent brightness the intensity of starlight received, in W m−2
Section 10 of 11Key terms
| Term | Meaning |
|---|---|
| Nucleon number | The total number of protons and neutrons in a nucleus. |
| Binding energy | The energy required to separate a nucleus completely into its nucleons. |
| Activity | The number of decays per second; unit becquerel. |
| Half-life | The time for half the radioactive nuclei to decay. |
| Control rod | A neutron-absorbing rod used to regulate fission. |
| Tokamak | A magnetic confinement device with a doughnut-shaped plasma. |
| Parallax angle | Half the apparent angular shift of a star over six months. |
| Parsec | The distance at which the parallax angle is one arcsecond, 3.09 × 10¹⁶ m. |
Section 11 of 11Exam technique
1
Believing that waste with a long half-life is always more dangerous — its activity per atom is lower.
2
Thinking that the mass of a radioactive sample halves each half-life.
3
Confusing reprocessing with disposal of nuclear waste.
4
Saying waste is harmless after one half-life.
5
Forgetting that spent fuel generates heat.
Last updated:
\n