Unit 5 Definitions

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Isotopes Atoms of the same element with the same atomic number or number of protons but different mass number or number of neutrons.

Half Life The half life of a radioactive isotope is the time taken for the mass of the isotope to decrease to half the initial mass.

Activity The activity of a radioactive isotope is the number of nuclei of the isotope that disintegrate per second. (unit is Becquerel, Bq)

Decay Constant The decay constant is the probability of an individual nucleus decaying per second.

Randon Nature of Decay Which nucleus decays when is by chance. It cannot be externally influenced.

Binding Energy The binding energy of a nucleus is the work that must be done to separate a nucleus into its constituent neutrons and protons.

The Mass Defect The mass defect of a nucleus is defined as the difference between the mass of the separated nucleons and the mass of the nucleus.

Internal Energy The internal energy of an object is the sum of the random distribution of the kinetic and potential energies of its molecules.

Absolute Zero This is zero Kelvin or -273 degrees celcius. At absolute zero, the internal energy of an object is a minimum.

Thermal Equilibrium Two objects in thermal equilibrium are at the same temperature. No overall heat transfer takes place between the two objects.

Specific Heat Capacity The specific heat capacity of a substance is the energy needed to raise the temperature of unit mass of a substance by 1K without a change of state.

Specific Latent Heat of Fusion The specific latent heat of fusion of a substance is the energy needed to change the state of unit mass of a substance from solid to liquid without a change in temperature.

Specific Latent Heat of Vaporisation of a substance is the energy needed to change the state of unit mass of a substance from a liquid to a vapour without a change in temperature.