Nuclear Fission and Fusion Flashcards
Define binding energy per nucleon
The average energy required to remove a nucleon from the nucleus
What is binding energy?
The energy required to separate an atom into its component parts
What is activity (Bq)?
The number of nuclei of the isotope that disintegrate per second
What is alpha decay?
Change in an unstable nucleus when it emits an alpha particle, consisting of 2 protons and 2 neutrons.
It is absorbs by paper, and has a range of a few centimetres and is the most ionising
What is atomic mass unit?
The unified atomic mass constant, 1/12th of the mass of an atom of carbon-12, equal to 1.667 x 10^-27kg
What is atomic number?
The number of protons in the nucleus of an atom
What is the Avogadro constant?
The number of atoms in 12g of Carbon-12, used to define the mole.
6.02 x 10^23
What is background radiation?
Radiation due to naturally occurring radioactive substances in the environment and cosmic radiation
What is beta-minus radiation?
B- emitted (and an antineutrino) by an unstable neutron-rich nucleus.
It is easily absorbed by aluminium, has a range of a few centimetres, and less ionising that alpha radiation, but more than gamma
What is beta-plus radiation?
B+ (and neutrino) emitted by an unstable proton-rich nucleus
Travels no more than 2mm before annihilated
What is binding energy per nucleon?
The average work done per nucleon to separate a nucleon into its constituent parts
E per nucleon = E / mass number
What is a chain reaction?
A series of reactions in which each reaction causes a further reaction
In an nuclear reactor, each fission event issue to a neutron colliding with a U nucleus, which splits and releases 2-3 further neutrons
What is a steady chain reaction?
One neutron on average from each fission event causes a further fission event
What are control rods?
Rounds made from a neutron absorbing substance (Cadmium) that are moved in or out of the core of a nuclear reactor to control the rate of nuclear fission events
What is coolant?
A fluid that is used to prevent a machine from overheating
In a nuclear reactor, the coolant is pumped through the core to transfer thermal energy to a heat exchanger
What is count rate?
The number of counts per unit time detected by a Geiger Muller tube
Count rates are corrected by measuring and subtracting the background radiation
What is critical mass?
The minimum mass of the fissile isotope in a nuclear reactor necessary to produce a chain reaction
What is the decay constant?
The probability of an individual nucleus decaying per second
The constant for an isotope that appears in the equation
A = lambda x N.
What is a decay curve?
An exponential decrease curve showing how the mass or activity of a radioactive isotope decreases with time
What is a dose equivalent (Sv)?
The energy that would need to be absorbed per unit mass of matter
What is electron capture?
A proton rich nucleus captures an inner shell electron, to change it into a neutron (neutrino emitted, and X-ray photon emitted when inner shell full)
What is an excited state?
An atom (or electron) not in it’s ground state
What is fission?
The splitting of a U or Pu nucleus into approximately equal fragments
What is induced fission?
Fission caused by an incoming neutron colliding with a U or Pu nucleus
What are fission neutrons?
Neutrons released when a nucleus undergoes fission and which may collide with nuclei to cause further fission
What is nuclear fusion?
The fusing of light nuclei to form a heavier nucleus
What is gamma radiation?
Electromagnetic radiation emitted by an unstable nucleus when it becomes more stable
Gamma radiation is the least ionising, but the most penetrative
What is ground state?
The lowest energy state of an atom (or electron)
What is a half life?
The time taken for the mass of a radioactive isotope to halve the initial mass or for its activity to halve — time taken for the number of nuclei to halve
What is a heat exchanger?
Hot coolant is pumped through this to cause water to turn into steam to drive turbines
What is intensity of radiation (Wm-2)?
The radiation energy per second per unit area at normal incidence to the surface
What is ionising radiation?
Radiation that produces ions in the substances it passes through
Destroys cell membranes and damages DNA
What is mass defect?
The difference between the mass of separated nucleons and the nucleus
What Rutherford’s alpha-particle scattering experiment reveal?
It demonstrated every atom contains a positively charges nucleus which is much smaller than the atom
What is strong nuclear force?
Force that holds the nucleons together. Range of 2-3fm, and below 0.5fm, it is repulsive
What is a thermal nuclear reactor?
Nuclear reactor which has a moderator in the core
Define the alpha particle
A particle comprising of two protons and two neutrons ejected from the nucleus during radioactive decay
Define annihilation
The process when a particle and antiparticle interact and their combined mass is converted to energy via E = mc^2
Define braking radiation
X-rays produced when electrons are decelerated
Why is it difficult to contain anti-hydrogen atoms, compared to anti-protons?
Atoms are not charged- magnetic/ electric fields have no effect.
Why has so little anti-matter been created?
Needs a large amount of energy to produce anti matter.
What happens to a capacitor when a switch is closed completing a circuit with it, a resistor and a cell?
The capacitor charges up gathering negative charges on one plate, repelling the negative charges on the othe plate giving that plate a positive charge.
This happens over a period of time. Eventually all charges are stored n the capacitor
How do neutral particles appear in an image taken from a bubble chamber?
No tracks, ot visible at all until it decays (decays into charged particles).
Explain the role of control rods in nuclear reactor
Control rods absorb some of the neutrons
The control rods are inserted into the reactor so as to allow, on average, one neutron from the previous reaction to cause subsequent fission
Explain the role of fuel rods in a nuclear reactor
Fuel rods contain the uranium
Explain the role of the moderator in a nuclear reactor
The moderator slows down fast moving neutrons and therefore lowers their KE
Slow moving neutrons have a greater chance of causing fission and sustaining a chain reaction
