Nuclear and Particle physics

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.

Alpha particles

A type of particle consisting of two protons and two neutrons.

Alpha particles are emitted in alpha decay and are strongly ionising, but weakly

penetrating.

Alpha Scattering

An experiment that involved firing alpha particles at a thin gold

foil and detecting their subsequent motion. It provided evidence for the currently

accepted model of the atom.

Annihilation

The process of a particle and its antiparticle colliding and being

converted into energy. The energy is released in two photons to conserve

momentum.

Antiparticles

All particles have a corresponding antiparticle with the same mass

but opposite charge and conservation numbers.

Beta particles

An electron or positron. Beta particles are emitted during beta

decay and have medium ionising and penetrating capabilities.

Beta-minus decay

The process of a proton inside a nucleus turning into a

neutron, and emitting a beta-minus particle (an electron) and a neutrino.

Beta-plus decay

The process of a neutron inside a nucleus turning into a

protron, and emitting a beta-plus particle (a positron) and a neutrino.

Binding energy

The amount of energy required to split a nucleus into all its

separate constituent nucleons. It is equivalent to the mass defect.

Chain reaction

The process of the neutrons released by a fission reaction

inducing further fissile nuclei to undergo fission.

Control rods

Rods found in nuclear reactors to absorb neutrons and control the

rate of reaction. They can be raised or lowered depending on the rate required.

Decay constant

The probability of decay in a unit time.

Einsteins mass-energy equivalence

Mass and energy are equivalent, with the

energy equivalent of a given mass being equal to the product of the mass and the

speed of light squared.

Electron

A negatively charged fundamental particle that is found in energy levels

surrounding a nucleus.

Gamma rays

A type of radiation emitted in gamma decay. Gamma rays are

weakly ionising but very strongly penetrating.

Hadrons

A class of subatomic particle that experiences the strong nuclear

interaction.

Half-Life

The average time it takes for the number of radioactive nuclei in a

sample of an isotope to halve.

Isotopes

A form of an element with the same number of protons but different

numbers of neutrons.

Leptons

A group of elementary subatomic particles, consisting of electrons,

muons and neutrinos.

Mass defect

The difference in mass between a nucleus and the sum of the

masses of its constituent nucleons.

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.

Neutron

A neutrally charged nucleon, found in the nucleus of an atom. Neutrons

are a form of hadron.

Nuclear fission

The splitting a nucleus, to form two smaller daughter nuclei,

neutrons and energy.

Nuclear fusion

The joining of two smaller nuclei to form a larger nucleus and to

release energy.

Nucleon number

The sum of the number of protons and neutrons in a given

nucleus.

Positiron

A positively charged particle that is the antiparticle of an electron.

Proton number

The number of protons present in the nucleus of a given

element.

Proton

A positively charged nucleon, found in the nucleus of an atom. Protons

are a form of hadron.

Quarks

Fundamental particle that interacts with other quarks via the strong

interaction. They change flavour via the weak interaction and annihilate with

antiquarks to form photons via the electromagnetic interaction.

Radioactive dating

The use of radioactive isotopes with known half-lives to date

objects. The isotope that is usually used is Carbon-14.

Random nature of decay

Radioactive decay is random - you cannot predict

when a nucleus will decay or which nucleus will decay next.

Strong nuclear force

A force that acts between nucleons in a nucleus to keep it

stable. It is attractive at distances of up to 3fm and repulsive at separations less

than 0.5fm.