Particles and Radiation - Unit 1

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Particles and Radiation ­ Victoria Halloran
Constituents of an atom
An atom is made up of protons, neutrons and electrons.
Ion ­ A charges atom caused by the gain or loss of electrons.
Specific charge
charge to mass ratio ­ Q/M
For a neural atom you have to remember the specific charge is 0
For an ion, only use the excess charge (either positive or negative) but the total mass
Stable and unstable nuclei
-Every particle has a corresponding antiparticle. An antiparticle has the same mass as its
corresponding particle, however it is opposite in ways such as charge and direction of spin.
Proton ­ antiproton
Electron- positron
Neutron- antineutron
Neutrino ­ antineutrino
1 ev = 1.6 x10^-19 J
The strong force
Fundamental force with a short range
Repulsive at very short separations- below 0.5fm
Attractive at short separations ­ 3fm
Responsible for the stability of nuclei and interactions between hadrons.
Attractive force between nucleons that holds the nucleons in the nucleus.

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Alpha decay
Beta decay
Photon model of electromagnetic radiation
Emitted in short `bursts' each burst leaving the source in a different direction.
Are emitted by a charged particle when it loses energy.
This can happen when a fast moving electron is stopped ­ eg. X-rays
This also happens when an electron in a shell of an atom moves to different shell of lower
energy.…read more

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Pair production
A process of converting energy to mass in which a gamma
ray photon has enough energy to produce a
particle-antiparticle pair.
Hfmin= 2E0
The process by which a particle and its antiparticle meet and their
mass gets converted in the form of a pair of gamma ray photons.
Hfmin= E0
Particle interactions
Weak interaction
A fundamental force that has a short range and can change the character of a quark.…read more

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Classification of particles
Subject to the strong force and weak interaction
Can be split into two sub groups; baryons and mesons
Type of hadron made up of 3 quarks.…read more

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Rutherford Scattering Experiment
Demonstrated that every atom contains a positively charged nucleus which is much smaller
than the atom where all the positive charge and most of the
mass of the atom is located.
Rutherford proposed a model of the atom to consist of :
-A heavy, positively charges nucleus at the centre
-A much lighter, negatively charged electron field in orbit
around it.
Rutherford made 3 observations;
MOST of the fast, highly charged alpha particles went straight
though the foil- undefeated.…read more


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