Nuclear Physics Definitions Flashcards
Define activity
The rate of decay of the radioactive nuclei in a given isotope. It is proportional to the total number of nuclei in the sample and is measured in Becquerels.
Define alpha decay
The emission of an alpha particle (2 protons and 2 neutrons) from an unstable nucleus (usually one with too much mass) to make it more stable. Alpha radiation is strongly ionising and is stopped by a few centimetres of air or a sheet of paper
Define atomic mass unit
A unit mass to express atomic masses. One AMU is equal to the one twelfth of the mass of a carbon atom.
Define background radiation
Radiation that is found in small quantities all around us. It originates from natural sources such as rocks and cosmic rays as well as man-made sources such as nuclear accidents and medical sources.
Define beta decay
The emission of a beta particle when a proton turns into a neutron (or vice versa) in an unstable nucleus. Beta minus radiation is weakly ionising. Bet plus radiation is immediately annihilated by electrons.
Define binding energy
The amount of energy required to split a nucleus into all its separate consistent nucleons. It is equivalent to the mass defect.
Define chain reaction
The process of the neutrons released by a fission reaction inducing further fissile nuclei to undergo fission
Define closest approach
A method of estimating a nuclear radius by firing an alpha particle at it. It involves calculating the distance at which all the alpha particle’s kinetic energy is converted to electric potential energy
Define contamination
The introduction of radioactive material to another object. The object is consequently radioactive
Define control rods
Rods found in nuclear reactors to absorb neutron and control the rate of reaction. They can be raised or lowered depending on the rate required.
Define coolant
A substance that passes through nuclear reactors and is responsible for removing heat from the core. This heat is then used to generate energy.
Define critical mass
The smallest mass of fissile material required in a fission reactor for a chain reaction to be sustained.
Define electron capture
A process that occurs in proton-heavy nuclei, in which an electron is drawn into the nucleus, causing a proton to transition into a neutron. An electron neutrino is also produced.
Define fission
The splitting an nucleus, to form two smaller daughter nuclei, neutrons and energy
Define fusion
The joining of two smaller nuclei to form a larger nucleus and to release energy
Define gamma decay
The emission of gamma rays from an unstable nucleus that has too much energy. Gamma radiation is only very weakly ionising but requires several centimetres of lead to be stopped.
Define half-life
The average time it takes for the number of radioactive nuclei in a sample to halve
Definitely the inverse square law
A law that governs the intensity of gamma radiation. It means that the intensity of radiation at any point is inversely proportional to the square of the distance from its source
Define irradiation
The exposure of an object to radiation. The exposed object does not become radioactive
Define mass defect
The difference in mass between a nucleus and the sum of the masses of its constituent nucleons
Define moderator
A material in nuclear reactors that absorbs energy from fast moving neutrons, to slow them down to speeds that can be absorbed by fissile neutrons to induce fission
Define radioactive dating
The use of radioactive isotopes with known half-lives to date objects. The isotope that is usually used is carbon-14
Define radioactive waste
The waste produced from the products of fission reactions. Since the waste is unstable and radioactive, it must be stored and handled carefully.
Define random nature of radioactive decay
Radioactive decay is random - you can’t predict when a nucleus will decay or which nucleus will decay next.
Define Rutherford scattering
An experiment involving firing alpha particles at a thin gold foil and observing their deflections. It showed the existence and nature of the nucleus
