Nuclear physics Flashcards
Nuclear decay is said to be random and spontaneous. What is meant by random?
Random: you cannot identify which nucleus will decay next/ when an individual nucleus will decay
Nuclear decay is said to be random and spontaneous. What is meant by spontaneous?
Spontaneous: decay cannot be influenced by any external factors
What is meant by ionising radiation?
Ionising radiation removes electrons from atoms/ molecules
What is an alpha particle, its mass and its charge?
Helium nucleus
Mass 4u
Charge +2
What is the ionising ability, speed and penetration power of alpha particles?
Strong ionising ability
Slow
Not very penetrating- absorbed/ stopped by paper or a few cms of air
When a nucleus is unstable, it will break down to become more stable. Explain why an alpha particle is emitted and what happens to the proton number and nucleon number?
Too many nucleons in total / nucleus too heavy
The proton number decreases by 2 and the nucleon number decreases by 4
Why aren’t alpha particles very penetrating?
Alpha particles are strongly positive so can easily pull electrons off atoms/ are strongly ionising
When an alpha particle ionises an atom it transfers some of its energy to the atom
Alpha particles quickly ionise lots of atoms and lose all their energy quickly so can’t travel very far/ have a low penetrating power
What is a beta-minus particle, its mass and its charge?
Electron, negligible mass, -1
What is a beta-plus particle, its mass and its charge?
Positron, negligible mass, +1
State ionising ability, speed and penetration power of beta-minus particles.
Weak/ moderate ionising ability
Fast
Moderately penetrating- absorbed/ stopped a few mm of aluminium
When a nucleus is unstable, it will break down to become more stable. Explain why a beta- minus particles is emitted, what happens when it is emitted and what happens to the proton number and nucleon number.
Emitted due to nucleus being neutron-rich/ has too many neutrons
One of the neutrons in the nucleus decays into a proton and ejects a beta-minus particle/ electron and an electron antineutrino
Proton number increases by one and nucleon number stays the same
Explain why a beta-plus particle is emitted, what happens when it is emitted and what happens to the proton number and the nucleon number.
Emitted due to the nucleus having two few neutrons
One of the protons in the nucleus changes into a neutron and releases a beta-plus particle/ positron and an electron neutrino
Proton number decreases by one and nucleon number stays the same
Explain why beta-minus particles are more penetrating than alpha particles.
Beta-minus particles are moderately ionising because they travel at high speed
They are less ionising than alpha particles because they have a lower mass
This means they lose less energy so can travel further and are more penetrating
State why beta-plus particles have virtually zero range.
After being produced they are almost immediately annihilated by an electron
State what gamma radiation is, its mass and its charge.
Short-wavelength, high frequency electromagnetic wave/ photon.
0
0
State ionising ability, speed and penetration power of gamma radiation.
Very weak ionising ability
Speed of light
Very penetrating- absorbed/ stopped by many cm of lead/ several m of concrete
When a nucleus is unstable, it will break down to become more stable. Explain why a gamma ray is emitted and how gamma emission affects the nuclear equation.
Nucleus is excited/ has excess energy
This energy is lost by emitting a gamma ray
Nuclear equation is unchanged because there is no change to the nuclear constituents- the nucleus just loses excess energy
Explain why gamma radiation is very penetrating.
Gamma radiation isn’t/ is very weakly ionising
Because it has no charge or mass/ it is photons of light
This means it loses barely any energy when travelling so can travel very far and is very penetrating
State why and how readings from a Geiger counter must be corrected when you take readings from a radioactive source.
Because you have to subtract the background count rate from each reading to get the actual radiation count for the source.
Measure the background radiation in absence of the source
State the 3 things conserved in nuclear equations and the 2 things conserved in nuclear reactions.
Nuclear equations: charge, nucleon number and electron lepton number
Nuclear reactions: energy and momentum
State the other type of radiation and why it would not be detected by a film badge that relies on ionisation.
Neutron emission
Uncharged particles are not ionising so would not be detected
State what is meant by the activity of a radioactive source.
Rate of decay of unstable nuclei/ the number of nuclei that decay per second/ per unit of time
Explain why it is necessary to repeat the radioactive count when taking readings.
So you can take an average as nuclear decay is random so fixed count for a period will vary
State why external exposure to gamma radiation is dangerous.
Gamma rays will pass through skin because they are very penetrating
Gamma rays can damage healthy cells/ DNA
Suggest how a beta-minus source should be stored and handled so it poses minimal health risk.
Store in lead lined box
Handle with long tongs/ don’t handle directly/ point away from people
State what is meant by the decay constant.
The probability that a given nucleus will decay each second.
State what is meant by the half-life of an isotope.
The average time it takes for the number of undecayed/ unstable nuclei to halve
What is safest: a long/ short half life and a big/small decay constant?
Long half-life
Small decay constant- less activity
Explain what is meant by a radioactive atom.
A radioactive atom has an unstable nucleus, which emits alpha, beta or gamma radiation.
Suggest why it is safer to use a radioactive isotope with a short half life for a gamma trace in medicine.
Isotope decays quickly/ doesn’t produce radiation for long.
Patient doesn’t remain radioactive for long so is not a risk to others for long like children and pregnant women.
State what is meant by nuclear binding energy.
Energy equivalent to the mass deficit
When nucleons bind together to form an atomic nucleus/ when an atomic nucleus separates into all its constituent nucleons
Describe nuclear fusion and state what happens to total mass, energy released and binding energy per nucleon.
Nuclear fusion is when nucleons join together
Total mass decreases
Energy is released
Binding energy per nucleon increases
What does a high binding energy tell us about the amount of energy needed to remove nucleons from the nucleus and the nucleus’ stability?
The higher the binding energy:
The more energy is needed to remove nucleons from the nucleus.
The more stable the nucleus
State the most stable element according to the graph and give a reason why.
Iron because it has the highest binding energy
Describe nuclear fission in terms of splitting.
Nuclear fission is splitting a heavy nucleus
Into 2 smaller nuclei( and sometimes several neutrons)
During nuclear fission, what happens to total mass, energy released, binding energy per nucleon and why in terms of nucleon numbers.
Total mass decreases
Energy is released
Binding energy increases
Because the nucleon numbers of the 2 new nuclei are smaller than the original nucleus
Fission can be induced or is spontaneous. Fission happens when a heavy nucleus is what?
Unstable
State the 2 conditions for nuclear fusion. Explain why the kinetic energy of nuclei has to be so high for them to fuse in terms of forces and charge.
High density of matter
Very high temperature
High kinetic energy from high temperature needed because all nuclei are positively charged
So there will be an exponential force of repulsion between them
According to Coulomb’s law
Nuclei can only fuse if they overcome this electrostatic force and get close enough for the strong force/ interaction to act and hold them together
High density of matter
At very high temperatures, atoms don’t exist. Electrons are stripped away leaving positively charged nuclei and free electrons. State the name of this resulting mixture.
Plasma
State 2 advantages of nuclear power
No carbon dioxide released
For a particular amount of energy produced, a small amount of fuel is needed compared to fossil fuels
Lots of uranium left unlike fossil fuels
State 2 disadvantages of nuclear power
Most mined uranium is not U-235 so has to be processed
Radioactive waste produced
Uranium is not sustainable so will run out one day
State a problem with trying to do nuclear fusion on Earth referring to one of the conditions for fusion.
Confinement problems
Due to plasma created from very high temperatures
3 advantages of nuclear fusion over nuclear fission for generating power.
More energy released per unit mass for fusion
Fusion has fewer radioactive products- fission products cause disposal issues
Fission relies on a relatively limited resource whereas fusion fuel ( hydrogen) is virtually limitless.
Describe how nuclear fission produces power.
Low energy neutron absorbed by heavy U-235 nucleus
Nucleus becomes unstable
And splits into two daughter nuclei and 2 or 3 neutrons
So can go on to be absorbed by other nuclei causing more fission and creating a chain reaction
Control rods absorb some of the neutrons thus slowing down chain reaction and limiting fission
State the shape of fuel for greatest chance of self-sustaining reaction (bomb) and give a reason why in terms of surface area per unit mass
Sphere
Smallest surface area per unit mass possible so neutrons less likely to escape so more are available to create lots of fissions
State the shape of fuel for smallest chance of self-sustaining reaction (bomb) and give a reason why in terms of surface area per unit mass.
Pellets/ thin sheet/ fine wire
Largest surface area per unit mass possible so neutrons likely to escape instead of creating more fissions
