Nuclear Flashcards
Activity A
…of a radioactive isotope, the number of nuclei of the isotope that disintegrate per second. The unit of activity is the becquerel (Bq), equal to 1 disintegration per second.
Background radiation
Radiation due to radioactive substances in the environment (e.g. in the ground or in building materials or elsewhere). Background radiation is also caused by cosmic radiation.
Binding energy of a nucleus
The work that must be done to separate the nucleus into its constituent neutrons and protons. Binding energy = mass defect x c^2. Binding energy in MeV = Mass defect in u x 931.3
Binding energy per nucleon
The average work done per nucleon to separate a nucleus into its constituent parts. Defining energy per nucleon per the nucleus = the binding energy of the nucleus/mass number A. The binding energy per nucleon is greatest for iron nuclei of mass Number about 56. The binding energy curve is a graph of binding energy per nucleon against mass number A.
Chain reaction
A series of reactions in which each reaction causes a further reaction. The nuclear reactor each fission event is due to a neutron colliding with a uranium 235 nucleus Which splits and releases two or three further neutrons that can go on to produce further fission. A steady chain reaction occurs when one fission neutron on average from each fission event produces a further fission event.
control rods
rods made of a neutron-absorbing substance such as cadmium or boron that are moved in or out of the core of a nuclear reactor to control the rate of fission events in the reactor.
coolant
a fluid that is used to prevent a machine from becoming dangerously hot. The coolant of a nuclear reactor is pumped through the core of the reactor to transfer thermal energy from the core to a heat exchanger.
critical mass
the minimum mass of the fissile isotope (e.g., the uranium isotope 235 92 U) in a nuclear reactor necessary to produce a chain reaction. If the mass of the fissile isotope in the reactor is less than the critical mass, a chain reaction does not occur because too many fission neutrons escape from the reactor or are absorbed without fission.
decay constant λ
the probability of an individual nucleus decaying per second.
decay curve
an exponential decrease curve showing how the mass or activity of a radioactive isotope decreases with time.
dose equivalent
A comparative measure of the effect of each type of ionising radiation, defined as the energy that would need to be absorbed per unit mass of matter from 250 k of X-ray radiation to have the same effect as a certain ‘dose’ of the ionising radiation. The unit of dose equivalent is the sievert (Sv).
(In layman’s terms, dose equivalence is how ionising different radiation is to different parts of the body i.e 1 mSv of alpha radiation to the eye may have the same biological effect as 10 mSv of X-ray radiation)
fission neutrons
neutrons released when a nucleus undergoes fission and which may collide with nuclei to cause further fission
half-life
the time taken for the mass of a radioactive isotope to decrease to half of the initial mass or for its activity to halve. This is the same as the time taken for the number of nuclei of the isotope to decrease to half the initial number.
heat exchanger
a steel vessel containing pipes through which hot coolant in a sealed circuit is pumped, causing water passing through the steel vessel in separate pipes to turn to steam which is used to drive turbines.
induced fission
fission caused by an incoming neutron colliding with a235 235 92 U nucleus or a 94 Pu nucleus causing it to split into two approximately equal fragments.
