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Summary AQA A-level Physics: Section 2 - Particles and Radiation
AQA A-level Physics: Section 2 - Particles and Radiation This covers everything from the make-up of a partcle to how it decays.
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Nuclear Physics3.2.1 Particles
3.2.1.1 - Constituents of the atom
The nucleus has protons and neutrons inside of it, which are both known as nucleons. Orbiting the nucleus
are electrons.
These are the properties of each of the particles:
The proton/atomic number (Z) is the number of protons in the nucleus. No two elements have the same
number of protons. In a neutral atom, the number of protons is the same as the number of elections.
The nucleon/mass number (A) is the total number of protons and neutrons
Isotopes have a different number of neurons but the same number of protons.
Radioactive isotopes can be used to find out how old things are:
All things contain carbon-14 from the atmosphere. After they die, the amount of carbon decreases.
Scientists can use isotopic data to find % of radioactive carbon-14 that is left in the object.
Specific charge is the ratio of its charge to its mass (Ckg^-1)
3.2.1.2 - Stable and unstable nuclei
To hold the nucleus together there must be an attractive force stronger than the electrostatic force.
Nucleons can only be held together when they are separated by up to 1fm (1x10^-15) - size of a nucleus.
At very small separations, the strong nuclear force (SNF) must be repulsive or it would crush the nucleus at
this point.
, Unstable Nuclei
When a nucleus has too many of either proton, neutrons or both causing the SNF to not be enough to keep
them stable, therefore these nuclei will decay in order to become stable. The type of decay the nuclei will
experience depends on the amount of each nucleon in them.
Alpha emission only happens in very large nuclei, so it is too massive for the strong nuclear force to keep
them stable, so an alpha particle is emitted (2 protons and 2 neutrons).
Beta- emission happens in neutron rich nuclei (gain of a proton)
At the start scientists thought that only the electrons (beta minus particles) was emitted from the nucleus
during beta decay but when they looked at energy conservation, they found the energy was not conserved.
This meant they came up with a hypothesis that is was neutrinos were released and this was later
observed.
3.2.1.3 - Particles, antiparticles and photons
Anti-particles have the same rest energy and mass, but all the other properties are opposite. For every
type of particle there is an antiparticle.
E.g.
Photons are elecromagnetic radiation which travels in pockets that transfer energy and have 0 mass. The
energy of a photon ∝ the frequency of the elecromagnetic radiation. We use the equation:
Annihilation is where one particle and its
antiparticle collide and their masses are converted into energy. This energy as well as the kinetic energy of
both particles is released in the form of 2 photons which move in opposite directions.
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