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Flashcards in Particle Physics Deck (52)
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Describe the nuclear model of the atom

A positive nucleus containing protons and neutrons with electrons found in shells orbiting the nucleus


State the relative charge of all sub atomic particles

Proton +1 Neutron 0 Electron -1


State the relative masses of all sub atomic particles

Proton 1 Neutron 1 Electron almost 0 (1/1840)


How can you calculate the specific charge? Giving all units

Specific charge (C/kg) = charge (C) / mass (kg)


Define atomic (proton number)

The number of protons in a nucleus = the number of electrons for an uncharged atom


Define nucleon number

The number of nucleons (protons + neutrons)


Define an isotope

An isotope is the same element with the same number of protons but different number of neutrons


Why is the strong nuclear force important?

It keeps nucleus stable


When is the strong nuclear force attractive

between 0.5 fm up to approximately 3 fm


When is the strong nuclear force repulsive

A distances closer than 0.5 fm


Describe some properties of the strong nuclear force

Very strong - overcomes repulsion between positive protons Very short range - only acts between adjacent nucleons Acts on any nucleon (proton or neutron) and is independent of charge Can be attractive or repulsive Is repulsive if nucleons gets too close - stops nuclei collapsing


How does the strong nuclear force cause particles to be in equilibrium?

Increase in nucleon separation leads to an attractive force Decrease in nucleon separation leads to a repulsive force In both situations, force will return nucleons back to equilibrium position.


What are the three types of radioactive decay?

Alpha, Beta and Gamma


Describe an alpha particle

2 protons and 2 neutrons Helium nucleus Relative mass of 4 Relative charge of +2 highly ionising Stopped by skin, paper, 5 - 10 cm of air


Describe a beta particle

fast moving electron ejected from the nucleus Relative mass of almost 0 Relative charge of -1 moderately ionising Stopped by mm's aluminium or 1 meter of air


Describe a gamma wave

Electromagnetic wave that moves at the speed of light through a vacuum Relative mass of 0 Relative charge of 0 very weakly ionising Reduced by cm's lead or m's of concrete


Describe the evidence that neutrinos exist

Experimental data shows that as a beta particle is emitted in beta decay it will have a range of energies from nearly zero up to a maximum All decays must have the same energy (conservation of energy) The total energy and momentum of the beta particle and recoiling nucleus was not constant Energy has to be conserved Wolfgang pauli (1930) predicted a particle that could carry away the extra energy/momentum so they would be conserved. This particle was discovered and named the antineutrino


Describe the changes that take place in beta decay

A neutron decays into a proton creating the beta particle and an electron antineutrino For a neutron to decay into a proton a down quark decays into a up quark


Describe the changes that take place in positron emission

A proton decays into a neutron creating the positron and an electron neutrino For a proton to decay into a neutron a up quark decays into a down quark.


Define a fundamental particle

Fundamental particles cannot be divided into other particles. They have no internal structure.


Give some examples of fundamental particles

Electron, neutrino, all quarks


What are the 6 types of quark

Up, down, top, bottom, strange, charm


What is the quark structure of a proton?

u u d


What is the quark structure of a neutron?

u d d


What is an antiparticle

particles with the same mass but opposite charge


State the name of the anti electron



Define a hadron

Hadrons are any particle made up of quarks Hadrons are not fundamental Hadrons can be either Baryons or mesons Hadrons are subject to the strong nuclear force


Define a baryon

Baryons are made up of three quarks Common baryons are protons and neutrons have a baryon number of 1


Which is the most stable baryon?



Define a meson

Mesons are classified as hadrons as they are made of quarks Mesons contain a quark and an antiquark have a baryon number of 0