3.2.1 Particles Flashcards
What is nuclide notation
a
X
z
Where
a = nucleon number(mass number)
X = the chemical symbol of the element
z = atomic number(proton number)
What is the equation and units for specific charge?
Specific charge(CKg^-1) = charge/mass
What are isotopes?
Atoms of the same element(defined by the number of protons), but different numbers of neutrons
What is the range of strong nuclear force at which it is;
Ineffective
Attractive
Repulsive
Above 3 fm
Between 0.5 - 3 fm
Below 0.5 fm
How does the snf keep the nucleus stable?
It prevents the nucleus from collapsing inwards when repulsive, it prevents constituents escaping when attractive, it avoids attracting other nucleus when completely ineffective
When and why does alpha decay occur?
When the nuclei are very large
This needs to happen as the nuclei are too massive for the snf to keep them stable
Describe what is emitted in alpha decay
An alpha particle of two protons and two neutrons (same as a helium nucleus)
It has a very short range (only a few cm in air)
all alpha particles travel at the same speed
(so have the same amount of KE)
When does beta minus decay occur?
When a nucleus is neutron rich
What happens during beta- decay?
A neutron changes into a proton
A beta particle (electron) is emitted from the nucleus
An massless and chargeless electron anti neutrino is also emitted
Why was the neutrino first hypothesised?
Beforehand the energy after beta - decay was less than the starting energy.
To account for this the neutrino was proposed as a massless and chargeless particle with KE which would equal the missing energy.
(This was later proven true)
What is the antiparticle of;
Electron
Proton
Neutron
Neutrino
Positrons
Anti proton
Anti neutron
Anti neutrino
When does gamma decay occur?
When nuclei have excess energy (normally as a result of alpha or beta decay)
What is emitted during gamma decay?
a high energy electromagnetic wave that does not change the nucleus at all known as a gamma ray
Particle and anti particle, Same or opposite? :
Mass
Charge
Rest energy
Same
Opposite (unless they have no charge)
Same
Define a photon
A packet of electromagnetic radiation with no mass or charge
Define an electron-volt and give its conversion to a joule
The energy gained by an electron that is travelling through a potential difference of one volt
1ev = 1.6*10^-19 J
What do particle physicists state must be conserved in interactions?
Mass-energy
What is pair production?
When a photon interacts with a nucleus and the energy of the photon is used to create a particle-antiparticle pair
What is the minimum energy a photon must have for pair production and why is it this?
2 * the rest energy of the particle it’s trying to pair produce
This is required as energy must be conserved
Describe annihilation
When a particle meets its equivalent antiparticle they are both destroyed as their mass is converted into energy.
This takes the form of at least two gamma ray photons which move apart in opposite directions to conserve momentum
How do you calculate the energy of one photon emitted during annihilation?
(Total Rest energy of the particles + total KE of the particles) / 2
Give an example of the use of annihilation.
PET Scanners
You can inject a patient with a medical tracer that emits positrons. This tracer is absorbed by cancerous cells at a faster rate than normal cells. Since the positrons emitted will annihilate with the natural abundance of electrons in the body there will be a large amount of gamma photons coming from this area allowing it to be located by a ring of scanners.
What are the four fundamental forces?
Gravity, electromagnetic, weak nuclear, strong nuclear/interaction.
How do exchange particles/ gauge bosons work?
When two particles interact it’s impossible for there to be instantaneous action at a distance. Gauge bosons are passed between the particles to inform the particles of each others presence
What does all exchange particles being virtual mean?
They only exist for a short time and cannot be detected because if they are then it would stop the force occurring
Describe the strong nuclear force
Exchange particle: pions
Particles affected: hadrons
Range: 10^-15 m
Strength: strongest
Describe the electromagnetic force
Exchange particle: virtual photon (lambda)
Particles affected:any with charge
Range: infinite
Strength: 2nd strongest
Describe the weak nuclear force
Exchange particle: w+ and w- bosons
Particles affected: every one
Range: 10^-18m
Strength: 3rd strongest
Describe gravity
Exchange particle: graviton
Particles affected: any with mass
Range: infinite
Strength: weakest
Describe the relationship between mass and range for gauge bosons
The larger the mass the shorter the range
(inversely proportional)
