2.1 Particles Flashcards
What are the main constituents of an atom?
● Proton
● Neutron
● Electron
What is meant by specific charge?
The charge to mass ratio:
Specific charge = charge / mass
Units C/kg.
What is the specific charge of a proton?
= 9.58 x 10^7 C/kg
What is the letter associated with a
proton number?
Z.
What is a nucleon?
A constituent of the nucleus: a proton or a neutron.
What letter represents nucleon number?
A.
What is an isotope?
A version of an element with the same number of protons but a
different number
of neutrons.
State a use of radioactive isotopes.
Carbon dating - the proportion of carbon-14 in a
material can be used to estimate its age
What is the strong nuclear force?
The fundamental force that keeps the nucleus stable
by counteracting the electrostatic force of repulsion between protons
Describe the range of the strong force?
● Repulsive up to 0.5fm
● Attractive from 0.5-3fm
● Negligible past 3fm
What makes a nucleus unstable?
Nuclei which have too many of either protons or
neutrons or both.
How do nuclei with too many nucleons decay?
Alpha decay (emission of a helium nucleus formed of 2 protons and 2 neutrons)
How do nuclei with too many neutrons decay?
Beta minus decay in which a neutron decays to a
proton by the weak interaction (quark character has
changed from udd to uud).
How was the existence of the neutrino hypothesised?
The energy of particles after beta decay was lower than before, a particle with 0 charge (to conserve charge) and negligible mass must carry away this excess energy, this particle is the neutrino.
What is meant by beta minus decay?
When a neutron turns into a proton, the atom releases an electron and an anti-electron neutrino.
What is an alpha particle?
A particle contains two protons and two neutrons, the same as a helium nucleus.
What is an antiparticle?
For each particle there is an antiparticle with the
same rest energy and mass but all other properties
are the opposite of its respective particle
True or false:
‘Every particle has a antiparticle’
True.
What is the name of the antiparticle of an electron?
Positron.
What is the antiparticle of π0 (pion with 0 charge) ?
π0, its antiparticle is itself.
What occurs when a particle and
antiparticle meet?
Annihilation
what is annihilation
The mass of the particle and antiparticle is converted back to
energy in the form of 2 gamma ray photons which go in
opposite directions to conserve momentum.
What is pair production?
A gamma ray photon is converted into a particle-antiparticle pair
What is the minimum energy of a photon required to make a proton-antiproton pair?
2 x proton rest energy
2 x 938.257 = 1876.514 MeV
Name the 4 fundamental forces?
● Gravity
● Electromagnetic
● Weak nuclear
● Strong nuclear
The virtual photon is the exchange
particle of which force?
The electromagnetic force
What type of particles are affected by the strong nuclear force?
Hadrons.
What is the exchange particle of the
weak nuclear force?
The W boson (W+ or W-).
What does the electromagnetic force act on?
It acts on charged objects,
When does weak nuclear interaction occur?
When quark character changes (a quark changes into another quark), it affects all types of particles.
Which properties must be conserved in particle interactions?
● Energy
● Charge
● Baryon number
● Lepton number
● Momentum
● Strangeness (only for strong interactions)
What is a hadron?
Both baryons and mesons are hadrons, hadrons are made of 2 or more quarks held together by the strong nuclear force.
What are the classes of hadrons?
● Baryons (three quarks)
● Mesons (1 quark, 1 antiquark)
The pion and kaon are both examples of
which class of particle?
Mesons.
The pion can be an exchange particle for
which force?
The strong nuclear force.
What particle does a kaon decay into?
A kaon decays into a pion
Give some examples of baryons?
● Proton - uud
● Neutron - ddu
What is significant about a proton?
● It is the only stable baryon
● All baryons will eventually decay into protons
What are some example of leptons?
● Electron
● Muon
● Neutrino
● (the antiparticles of the above)
What does a muon decay into?
An electron and two types of neutrino.
What is the strangeness value of a
strange quark?
-1
True or false:
‘Strangeness is always conserved in a weak interaction’
False.
Strangeness is only conserved in the strong
interaction, in weak interactions it can change by
0, -1 and +1.
Complete the sentence:
Strange particles are produced through the
_____________ and decay through the ___________
Strange particles as particles that are produced through the
strong interaction and decay through the weak interaction.
