Particle Physics Flashcards
What are isotopes?
atoms of the same element with a different number of neutrons.
what is specific charge?
charge divided by mass
what is the strong nuclear force?
force that overcomes the electrostatic force of repulsion between protons in the nucleus.
what is the range of the strong nuclear force?
3-4 fm
what do alpha particles consist of?
two protons and two neutrons
Why does beta radiation occur?
A neutron in a neutron rich nucleus changes into a proton. an electron and an anti-neutrino are also emitted as a result.
Discuss the differences between alpha, beta and gamma radiation
alpha radiation is highly ionising and weakly penetrating. has a very small range pf a few centimetres. beta radiation is less ionising and more penetrating. it can pass through paper but is stopped by metal foil. Gamma radiation is weakly ionising but highly penetrating, it is stopped by thick lead.
What is a photon?
a discrete packet of energy
what is the equation for the power of a laser beam?
nhf
What happens in annihilation?
a particle and anti-particle collide and two gamma photons are produced as a result.
Why does positron emission take place?
when a proton changes into a neutron in an unstable nucleus with too many protons. A positron and a neutrino are emitted as a result.
Describe pair production
a photon of sufficient energy can suddenly change into a particle anti-particle pair which then separates.
What is the weak nuclear force?
the weak nuclear force causes a neutron to change into a proton in B decay and a proton to change into a neutron in positron emission.
Draw Feynman diagrams for a neutron-neutrino reaction and a proton-antineutrino reaction.
See textbook
Draw the Feynman diagram for electron capture, B decay and positron emission.
See textbook
What are hadrons and leptons?
hadrons are particles that can interact through the strong iteraction and electromagnetic interaction if charged.
Leptons are particles that can interact through weak interaction.
What are baryons and mesons?
baryons are hadrons, they are protons and all other hadrons that decay into protons.
mesons are hadrons that don’t include protons in their product decay.
How many quarks make up a baryon?
3
How many quarks make up a meson?
2
In which interactions is strangeness conserved?
strong interaction
Describe the photoelectric effect
when light above a threshold frequency is incident on a metal surface, electrons are emitted from the surface.
What is the intensity of the incident radiation proportional to?
the number of electrons emitted per second.
What is the work function of a metal?
the minimum energy needed by an electron to escape from the metal surface.
What is the stopping potential?
the minimum potential needed to stop photoelectric emission from taking place.
What is the photoelectric current proportional to?
the intensity of the incident light
what is excitation?
the process of an absorbing energy without becoming ionised.
why is the excitation energy always less than the ionisation energy?
because the electron isn’t locked completely out of the atom in excitation.
How does the fluorescent tube work?
Ionisation and excitation of the mercury atoms occur as they collide with each other and the electrons in the tube. the mercury atoms emit UV photons during de-excitation. the UV photons are absorbs by the atoms of the fluorescent coating. the coating atoms then de-excite in steps and emit visible photons.
What is the wave like nature of light?
light can be diffracted, refracted and reflected.
What is the particle like nature of light?
the photoelectric effect
Matter like nature of a particle
electrons can be deflected by a magnetic field.
Wave like nature of a particle
a beam of electrons can be diffracted. They produce a pattern of rings on a fluorescent screen.
