nuclear and particle physics Flashcards
how does the alpha - scattering experiment give evidence of a small dense nucleus
- few alpha particle bounce back
- this wouldn’t happen if the positive charge in the atom was distributed evenly throughout which suggests they must be hitting a 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 main constituents of an atom
- proton
- neutron
- electron
how many times bigger is an atom than a nucleus
approx 100000 times
what is the letter associated with a proton number
Z
what is a nucleon
a particle that makes up the nucleus: a proton or a neutron
what letter represents nucleon number
A
which is the correct notation
AZX
isotope
atoms of an element with the same number of protons with a different number of neutrons and therefore a different mass number
strong nuclear force
force that holds the nucleus together
- 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 0.5fm
attractive up to 3fm
which has a higher density: an atom or a nucleus
nucleus is much more dense than an atom because the atom includes a lot of empty space
equation relating radius of an atom and its nucleon number
r = r0A^1/3
r = radius
R0 = constant
A = nucleon number
true or false
every particle has an antiparticle
true
give a difference and a similarity between particles and antiparticles
similarity - mass
difference - charge
name of antiparticle of an electron
positron
hadron
type of particle which is affected by the strong nuclear force made of quarks
what are the classes of hadrons
baryons - three quarks
mesons - two quarks
two examples of baryons
protons and neutrons
four fundamental particles
- strong nuclear
- weak nuclear
- electrostatic
- gravity
which forces are hadrons subject to
all four only charge hadrons like protons will be subject to electrostatic forces
leptons
fundamental particles which are not subject to strong nuclear force
- they do still interact via the weak nuclear force
examples of leptons
- electron
- muon
- neutrino
- and their corresponding antiparticles
three types of quark
- up (u)
- down (d)
- strange (s)
- and tehir corresponding antiparticles
quark compesitions 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
what is meant by beta minus decay
when a neutron turns into a proton the atom releases an electron and an anti electron 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 particles
charge, mass, baryon and lepton numbers
what are the defining features of radioactive decay
spontaneous and random you can’t predict when an individual nucleus will decay
what features of a nucleus might cause it to radioactively decay
- too many or too few neutrons
- too heavy overall
- too much energy
4 types of radiation
- alpha
- beta minus
- beta plus
- gamma
order alpha, gamma, and beta starting with most ionising
- Alpha
- Beta
- Gamma
alpha particles
particle which contains two protons and two neutrons
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
- gamma = 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
nucleon number A-4
atomic number Z-2
in beta plus decay how Dows the atomic number change
decreases
- proton turns into a neutron and a positron so mass is constant but atomic number decreases
activity of a source
the number of radioactive decays per second
in the equation A = lambdaN what doe each of the letters/ symbols stand for
A activity
lambda = decay constant
N = number of radioactive nuclei
half life of an isotope
average time taken for the activity of a sample or the number of radioactive nuclei to halve
what isotope is commonly used to find out how old artefacts are
carbon 14
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 pf the particles will transform into the energy equivalent
pair production
gamma ray has enough energy to produce a particle and its antiparticle
why does beta plus decay have a very low penetration
it will annihilate with matter accost immediately
mass defect
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
binding energy
energy required to separate a nucleus into its constituent parts
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 much energy would be required to separate the nucleus
nuclear fission
where a 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 nuclei. the new nucleus has a larger binding energy per nucleon than the old nuclei therefore energy is released in the process
which precess (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 a 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. 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 on 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
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 ir decrease
how is nuclear waste disposed of
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 release of greenhouse gas, no contribution to global warming, doesn’t use fossil fuels
risk - leak or escape of material can be catastrophic
