Nuclear and Particle Physics Flashcards
How does the alpha-scattering experiment give evidence of a small, dense nucleus?
A few alpha particles bounce back
This wouldn’t happen if the positive charge in the atom was distributed evenly throughout (as in the Plum Pudding Model) which suggests they must be hitting dense positive charge. The fact it only happens to a very small number of alpha particles shows the nucleus must be small.
What are the the main constituents of an atom?
- Proton
- Neutron
- Electron
How many times bigger is an atom than a nucleus
Approximately 100,000 times
What is the letter associated with a proton number?
Z
What is a nucleon
A particle that makes up the nucleus, a protons or neutorns
What letter represents nucleon number
A
Which is the correct notation:
A……..Z
. X or X
Z……..A
A
. X
Z
What is the definition of an isotope?
- the same number of protons
- different mass number
What is the strong nuclear force?
The force that holds the nucleus together
It must overcome the electrostatic force of repulsion between protons, but not so much as to cause the nucleus to collapse
Describe the range of the strong force
Repulsive up to 0.5 fm
Attractive up to 3 fm
measuring nuclear sizes is the femtometre (fm) = 10^−15 metres
What is the equation relating radius of an atom and its nucleon number?
r = r0 A^1/3
r = radius r0 = constant (for all atoms) 1.2 femto meters A = nucleon number
Which has a higher density: an atom or a nucleus
Nucleus, as an atom includes the empty space the nucleus and the electrons
True or false
‘Every particle has an antiparticle’
true
Give a difference and a similarity between particle and antiparticles
Similarity = mass Difference = Charge
What is the name of the antiparticle of an electron?
Positron
What is a hadron?
A type of particle which is affected by the strong nuclear force
What are hadrons made of?
Hadrons are made up of quarks
What are the classes of hadrons?
- Baryon (three quarks)
- Mesons (two quarks)
What are two examples of baryons?
Protons and neutrons
What are the four fundamental forces?
- Strong nuclear
- Weak nuclear
- Electrostatic
- Gravity
Which forces are hadrons subject to?
it can be all 4
only charged hadrons, like protons, will be subject to electrostatic forces
What are leptons
Leptons are fundamental particles that are not subject to the strong nuclear force
(they do still interact via the weak nuclear force)
Give some examples of leptons
- electron
- muon
- neutrino
- and their corresponding antiparticles
What are the six types of quark?
- up (U)
- down (D)
- strange (s)
- charm (c)
- top (t)
- bottom (b)
- and their corresponding antiparticles
State the quark compositions of protons and neutrons
- proton (uud)
- neutron (udd)
True or false:
quarks can be found on their own, in pairs or in triplets
False, quarks are never found on their own (‘free’)
Give the charges of the up, down, and strange quarks ( in terms of the electron charge, e)
up = +2/3 e
down = -1/3 e
strange = -1/3 e
(the charges of corresponding antiparticles are the same number, but opposite sign
What is meant by beta minus decay
when a neutron turns into a proton, the atom releases an electron and an anti neutrino
Which quark decays in beta minus decay?
what does it turn into?
a down quark turns into an up quark
what quantities must be conserved during the decay of the particles
Charges, mass, baryon and lepton numbers
and energy - but you can’t show this in a symbol equation
what are the defining features of radioactive decay
radioactive decay is spontaneous and random you can’t predict when an individual nucleus will decay (or which nucleus will go next)
what features of a nucleus might cause it to radioactively decay
- too many or too few neutrons
- too heavy overall (too many nucleons)
- too much energy
name 4 types of radiation
- alpha
- beta (plus and minus)
- gamma
order alpha, gamma and beta radiation starting with the most ionising?
- alpha
- beta
- gamma
what is an alpha particle
a particle which contains two protons and two neutrons, the same as a helium nucleus
which type of radiation can only be stopped by lead or concrete
gamma
how far does a beta particle typically penetrate in air
50cm - 1m
what materials would be needed to investigate whether a radioactive source was releasing alpha, beta or gamma
- alpha = paper
- beta = 5mm thick aluminium
- gemma = thick lead sheet
a particle with nucleon number, A, and mass number, Z, undergoes alpha decay. what are the nucleon and mass numbers of the resulting particle? (in terms of A and Z)
Nucleon number = A - 4
Atomic number = Z - 2
in beta plus decay, how does the atomic number change
it decreases, a proton turns into a neutron and a positron, so mass is ‘constant’ but atomic number decreases
what is the activity of a source
the number of radioactive decays per second (measured in Becquerels, Bq)
In the equation A = λN, what do each of the letters/symbols stand for?
A = activity λ = decay constant N = number of radioactive nuclei
What is the half-life of an isotope
the average time taken for the activity of a sample (or the number of radioactive nuclei) to halve.
what is the equation linking the activity of a sample, A, at time, t to the original activity of the sample, A0?
A = A0 e^-λt
what isotope is commonly used to find out how old artefacts are?
carbon-14 (in radiocarbon dating)
what equation is used to convert mass to its energy equivalent
E = mc^2
What occurs when a particle and antiparticle meet
- annihilation
- when a particle and its antiparticle meet, they will annihilate each other and releases two gamma rays
- two rays are released in order to conserve momentum
- the mass of the particles will transform into the energy equivalent
what is pair production
when a gamma ray has enough energy to produce a particle and its antiparticle
why does beta plus decay have a very low penetration
because it will annihilate with matter almost immediately
what is the mass defect
the difference between the total mass of all the nucleons separately compared to the mass of the nucleus
why is there a mass defect
because energy is released as the nucleons bind together into a nucleus
what is binding energy
the energy requires to separate a nucleus into its constituent parts
(this will be the same numerical value as the energy released when the nucleus binds, and is equivalent to the mass defect)
true or false:
a low binding energy per nucleon will mean that an element is more stable
false: a low binding energy per nucleon means not as much energy would be required to separate the nucleus (its more likely to decay)
what is nuclear fission
where an unstable nucleus splits into 2 smaller nuclei. Often occurs with the larger nuclei.
the binding energy per nucleon increases when fission occurs therefore the overall process releases energy
what is fusion
when two small nuclei fuse together to create a larger nucleus. The new nucleus has a larger binding energy per nucleon than the old nuclei therefore energy is released in the process
which process (fission or fusion) releases the most energy?
Fusion releases a lot more energy per reaction
this is because the change in binding energy is very drastic
why is it difficult to make fusion occur on earth
there is a large repulsion between the two positively charged nuclei, therefore a lot of energy is required to overcome the repulsion and fuse them together.
it is hard to get material that can withstand the heat and be cost effective
how is fission used in nuclear reactors
rods of uranium-235 absorb neutrons and become unstable and then split into two daughter nuclei, this reaction is endothermic so it releases energy. it also releases 2 or 3 more neutrons. These then go on to be reabsorbed by another uranium- 235.
what is the purpose of a moderator
to slow down the neutrons so they travel slow enough to be absorbed by the uranium
they do this through elastic collisions between the moderator and the nucleus
why are control rods essential for a nuclear power station
they stop the chain reaction from being out of control
they absorb neutrons so that only 1 of the neutrons released in each reaction can go to be absorbed by another uranium
If not then the nuclear reactor would overheat as too many reactions would happen at once
give an example of a material that can be used as a moderator
water
what is a chain reaction
a chain reaction is when exactly one neutron from each decay goes on to cause another decay, so the amount of energy released is constant and doesn’t increase or decrease
how is nuclear waste (spent fuel rods) disposed of?
it is first stored in cooling ponds
it will then be put in sealed steel containers and potentially stored deep underground or underwater
give one environmental benefit and risk of nuclear power
benefit:
- no greenhouse gases, no contribution to global warming
risk:
- leak or escape of material can be catastrophic
