Revision:OCR A Level Physics - Nuclear And Particle Physics

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Revision:OCR A Level Physics - Nuclear And Particle Physics

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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Physics > OCR A Level Physics - Nuclear And Particle Physics

1 Nuclear And Particle Physics
2 Useful figures and formulae
3 Plasma
4 JET fusion reactor
5 Comments

Nuclear And Particle Physics

Neutron-induced fission:
- The splitting of a nucleus into parts caused by absorption/capture of a neutron
- The reaction cannot start without neutrons
Thermal neutrons:
- Neutrons having KE comparable with KE of thermal molecular KE
- Slow moving, low energy
- So-called because the energies are due simply to their temperature (KE does not really contribute to their energies)
Accelerating charged particles:
- Use two oppositely charged electrodes with p.d. between them
- OR use electric field
- F = ma
Fast moving charged particle made to follow circular path:
- Particle moves inside magnetic field
- Field is uniform
- Force perpendicular to direction of motion and acts as centripetal force
- Force causes acceleration
Nuclear decay:
- Means loss of alpha/beta particles from nucleus, plus gamma radiation
- Spontaneous
Nuclear fission:
- Means splitting of nucleus into two (roughly equal) nuclei
- Neutron-induced
Coulomb barrier:
- Electrostatic repulsion between nuclei
Binding energy
- The loss in mass/energy when nucleons cluster together to form an atomic nucleus
- The energy that needs to be supplied to separate the nucleons
- Can be though of as the energy that binds them together
Hadrons:
- Particles made up from quarks
- Are affected by the strong force
- Two types: baryons and mesons
Leptons:
- Fundamental particles not affected by the strong force
- E.g. electrons
Baryons:
- Hadrons comprising three quarks
- E.g. protons and neutrons
Mesons:
- Hadrons that consist of a quark and an anti-quark
Nuclide:
- Atomic nucleus with a particular number of protons and neutrons
- Isotopes have same number of protons but different neutrons and so are different nuclides

Useful figures and formulae

1 u = 931.5 MeV

1 eV = 1.6 x10^-19 J

$\displaystyle E_K = \frac{3kT}{2}$

$\displaystyle F = \frac{mv^2}{r}$

$\displaystyle F = B q v$

$\displaystyle T = \frac{2\pi r}{v}$

Plasma

Definition:
- Electrons have separated from nuclei
- So plasma consists of free electrons and positive ions / is completely ionised
Confinement:
- Magnetic field: ions rotate around or follow magnetic field, so cannot escape
- Strong gravitational field: nucleons and electrons pushed together by pressure of material
- Inertial: laser beams directed inwards/converging and compress a fuel pellet

JET fusion reactor

Reaction:

$\displaystyle \mathsf{{}^2_1H} + \mathsf{{}^3_1H} \longrightarrow \mathsf{{}^4_2He} + \mathsf{10n}\ (+ \mathsf{energy})$

$\displaystyle \mathsf{Deuterium} + \mathsf{Tritium} \longrightarrow \mathsf{Helium} + \mathsf{neutron}\ (+ \mathsf{energy})$

Conditions:
- High temperature (of gases), over 10⁶K
- This energy is high enough for the nuclei to overcome the Coulomb barrier
- Gas becomes very dense plasma; electrons stripped from nuclei
- Plasma confined by magnetic field/’bottle’
Achieving above conditions:
- Materials contained in toroidal Tokamak
- Ohmic heating (large current) causes heating
- Plasma forms one-turn transformer secondary coil, leading to a low turns ratio and therefore a large current
- Heating also caused by neutral beam injection, radio frequency, and self-heating by alpha particles
Generating energy (note JET does not do this itself):
- $\displaystyle \mathsf{{}^1_0n} + \mathsf{{}^6_3Li} \longrightarrow \mathsf{{}^3_1H} + \mathsf{{}^4_2He}$ or,
- $\displaystyle \mathsf{{}_1^0n} + \mathsf{{}^7_3Li} \longrightarrow \mathsf{{}^3_1H} + \mathsf{{}^4_2He} + \mathsf{{}^1_0n}$
- Lithium ‘blanket’ surrounds reactor vessel
- The KE of neutrons is transferred to lithium, causing heating
- Coolant is circulated through the lithium
- This heats water and converts it to steam, which drives turbines and turns electrical generators, generating useful electrical energy