Nuclear Flashcards
What do the top and bottom number of an element represent?
Top - nucleon number A
Bottom - proton number Z
Define an isotope
Atoms of the same element with the same number of protons but a different number of neutrons in the nucleus.
What is conserved in a nuclear reaction?
The nucleon number A and the charge (so proton number Z)
What is the equation used to find the distance from the centre of the alpha particle to the centre of the gold nucleus at closest approach?
1/2 mv^2 = Qq / 4πε0r
Loss of KE = gain in electrostatic PE
What is true about the density of all nuclei?
It is constant independent of the nucleon number.
What type of particles experience the strong nuclear force and which do not?
Hadrons do
Leptons do not
What are the fundamental particles?
Leptons: Electron, positron, neutrino, anti-neutrino.
What is true about fundamental particles?
They have no sub-structure.
What forces do both leptons and hadrons experience?
Gravitational, electromagnetic, weak nuclear.
What are the baryons?
Proton, antiproton, neutron, antineutron.
What is true about meson’s quarks?
They have a quark-antiquark pair.
Define a lepton
A fundamental particle with no sub-structure. They do not interact via the strong force.
What is true about a particle and its corresponding antiparticle?
They have the same mass and opposite charge (if charged particles)
What is true about the lepton or baryon number of an anti-particle and a particle?
The particle has a lepton/baryon number of 1. The antiparticle has a lepton/baryon number of -1.
Define a hadron
Not a fundamental particle, they have a sub-structure of quarks. They do interact via the strong force.
Define beta minus decay
When a nuclei has too many neutrons, a neutron decays into a proton plus an electron and anti-neutrino.
Define beta plus decay
When a nuclei has too many protons, a proton decays into a neutron plus a positron and a neutrino.
Define annihilation
When a particle meets its anti-particle they annihilate. They are both destroyed and their mass is converted into photon energy.
Define binding energy
The energy required to split a nucleus completely into separate protons and neutrons.
Define mass defect
(Mass of protons + mass of neutrons) - mass of nucleus
What conditions are needed for fusion?
Very high temperature so very high KE to overcome the force of electrostatic repulsion and very high density to give a high probability of head-on collisions.
Define spontaneous fission
A large nucleus splits into 2 smaller nuclei plus several neutrons and releases energy.
Define induced fission
A large nucleus absorbs a neutron and splits into 2 smaller nuclei plus several neutrons and releases energy.
Define nuclear fusion
2 small nuclei fuse to form a larger nucleus and releases energy.
Define a thermal neutron
A low KE and low speed neutron which when absorbed by an unstable nuclei causes it to undergo fission.
What is a moderator made of?
Solid carbon graphite
What do fuel rods contain?
Enriched Uranium with a higher % of U-235.
What are control rods made out of?
Cadmium or boron
Define radioactivity
The emission of ionising radiation from an unstable nucleus.
State the range of beta-minus, gamma and alpha particles in air.
Alpha: 5-10cm
Beta-minus: a few metres
Gamma: a few kilometres
State what absorbs beta-minus, gamma and alpha particles.
Alpha: thin paper
Beta-minus: a few mm of aluminium
Gamma: a few cm of lead or a few m of concrete
What is the decay equation for beta-minus?
A neutron becomes a proton and an electron and anti-neutrino are emitted.
What is the decay equation for beta-plus?
A proton becomes a neutron and a positron and neutrino are emitted.
Define a gamma ray
A high energy, high frequency photon.
When would a gamma ray be emitted in nuclear decay?
When the daughter nucleus has excess energy.
Define spontaneous in terms of radioactive decay
It is not affected by any external factors such as pressure, temperature or chemical reactions.
Define random in terms of radioactive decay
It cannot be predicted when a particular nucleus will decay, or which nuclei will decay in a given time period.
What is true about radioactive decay
It is spontaneous and random.
What do the letter in the equation A=λN represent?
A - activity, number of nuclei decaying per unit time
λ - decay constant, probability of a nucleus decaying per unit time
N - number of undecayed nuclei
Define half life
The average time taken for the activity (or undecayed nuclei) to reach half the initial value.
What is the equation for radioactive power?
Power = activity x decay energy (energy emitted per decay)
Why are alpha particles deflected by a nucleus?
Due to a force of electrostatic repulsion
What happens in terms of energy at closest approach?
All KE is transferred to electrostatic PE
What is the difference between the strong nuclear force and the force of electrostatic repulsion?
The strong nuclear force affects nearest neighbour nucleons only whereas the force of electrostatic repulsion is long range and acts between all protons inside a nucleus.
What is the difference between mesons and baryons?
Mesons contain a quark-antiquark pair whereas baryons contain 3 quarks.
What is the baryon number for quarks and anti-quarks?
Quarks - 1/3
Antiquarks - -1/3
What causes beta decay?
The weak nuclear force.
What is true about all nuclear reactions?
Total final mass < total initial mass
Released energy ΔE = Δmc^2 appears as kinetic energy of the products.
What is alpha-decay?
When a parent nucleus emits an alpha particle to become a more stable daughter nucleus.
What is element can be used to date the oldest rocks?
Uranium
What can convert the heat produced from radioactive power to electricity?
An RTG (radioisotope thermoelectric generator)
