Particles and radioactivity

radioactive decay in which an atomic nucleus emits an alpha particle (helium-4 nucleus)

conversion of matter into energy, especially the mutual conversion of a particle and an antiparticle into electromagnetic radiation.

hadron consisting of three antiquarks. Antibaryons have a baryon number of -1.

positively-charged antiparticle of the muon.

antiparticle of the neutron.

opposite of a particle, have the same rest mass and, if charged, have opposite charge. They are given the same symbol as the particle but with opposite charge or, if uncharged or a quark, a bar on top: e.g. 𝜈̅ (anti electron-neutrino) and u̅ (anti-up quark).

smallest constituent of ordinary matter that retains the properties of a chemical element.

unit of atomic mass, equal to one twelfth of the mass of an atom of carbon-12. Its value is given on the data sheet as 1.661 x 10-27 kg.

hadron consisting of three quarks. See neutron and proton. Baryons have a baryon number of +1.

quantum number equal to the number of baryons in a system of subatomic particles minus the number of antibaryons. Quarks and antiquarks respectively have baryon numbers of + 1/3 & - 1/3 .

radioactive decay in which an atomic nucleus emits a beta particle along with an electron antineutrino or electron neutrino.

Beta negative particles are fast-moving electrons emitted by unstable, neutron-rich nuclei or the decay of a free neutron. Beta positive particles are positrons, the antiparticle of the electron, emitted by proton-rich nuclei.

electric charge causes matter to experience the electromagnetic interaction. Positive and negative, an absence of which is referred to as neutral.

simple detector revealing the paths of alpha particles in (usually) ethanol-saturated air. The ionisation of the air causes instantaneous formation of condensation trails along the radiation path

conservation of energy, momentum, charge, baryon number and lepton number apply to all particle interactions. Conservation of strangeness applies to strong interactions only.

effective wavelength of a matter particle

sub-atomic particle, the lightest lepton.

a force that occurs between electrically charged particles.

atom inner-shell electron captured by the nucleus, effectively reverse beta decay.

observation that a beam of electrons fired through a suitable target (thin metal or graphite) will behave like waves, diffracting through the gaps between atoms to certain angles only.

unit of energy, equal to the amount transferred when one electron is accelerated through a potential difference of 1 V. From the definition of p.d., 1 eV = 1.6 x 10-19 J

given as... h𝑓 = 𝐸1 − 𝐸2

virtual particles that interact between particles to give rise to forces of attraction or repulsion

when an atom absorbs energy without becoming ionised as a result of an electron transition rom a lower to a higher energy level.

pictorial representations describing the behaviour of subatomic particles, but they are not trajectories of the interacting particles in space and time. Generally, read left to right. Particles are represented by straight lines with arrows, exchange particles are wavy lines, time is usually on the x-axis. Particles are created/annihilated at the vertices between the lines

instrument for measuring ionising radiation (including alpha, beta and gamma) count or count rate in a Geiger-Müller tube, based on principle discovered in the Cavendish Laboratory in 1908.

particles and antiparticles which can interact through the strong nuclear interaction.

creation of ionised atoms (ions) due to the loss (or gain) of one or more electron

nuclei of the same element with a different number of neutrons but the same number of protons. Hence they have the same proton number but a different nucleon number

short for K meson, they consist of a strange quark or antiquark and another quark or antiquark. They will decay into pions.

fundamental particle that does not interact through the strong nuclear interaction. Electrons, muons, neutrinos and associated antiparticles all interact through the weak nuclear interaction and, except for neutrinos/antineutrinos, through the electromagnetic interaction.

assigned to every lepton (+1) and antilepton (-1) such that the total lepton number is always conserved.

set of dark or bright spectral lines in an otherwise uniform absence of light or a continuous spectrum. They result from emission (bright) or absorption (dark) of light of a certain photon energy. Line spectra can be used to identify atoms and molecules from their characteristic lines which are associated with transitions between energy levels

of an emitted electron (sometimes called a photoelectron) from a metal surface via the photoelectric effect

unit of energy, the mega electron-volt is equal to 106 eV or 1.6 x 10-13J and is commonly used.

neutral sub-atomic particle, a hadron, quark composition: udd.

in an atomic nucleus, a neutron may decay into a proton, leading to the emission of a electron and an anti electron-neutrino. A free neutron (on its own) will also decay (equation should be known: 0n 1 →1p 1 +-1e 0 +𝜈̅𝑒) in this way with a half-life of about 10 minutes.

sub atomic particles that lack an electric charge and have zero rest energy. The two symbols indicated here are for electron-neutrino and muon-neutrino respectively.

total number of nucleons in the nucleus of an atom. Sometimes called mass number

type of nucleus with a certain number of protons and neutrons

creation of a particle and its antiparticle

emission of electrons when light is shone onto a material.

electrons emitted by the photoelectric effect can be called photoelectrons.

quantum of electromagnetic radiation and the force carrier for the electromagnetic interaction (even when static via virtual photons). Zero rest mass, they always move at the speed of light. Photons have energy given as... 𝐸 = ℎ𝑓 = ℎ𝑐⁄𝜆 where h is the Planck constant and c is the speed of light.

they consist of an up or down quark together with an up or down antiquark.

proportionality constant between the energy of a photon and the frequency of electromagnetic radiation. Value: 6.63×10-34 Js

antiparticle of the electron.

positive sub-atomic particle, a hadron, quark composition: uud. Opposite in charge to an electron. Protons are the only stable baryon, as they are the lightest. All other baryons decay into protons.

the number of protons in an atomic nucleus. Sometimes called atomic number.

minimum amount of a physical entity involved in an interaction. Some properties can be 'quantised', such as the energy levels of electrons in atoms, where only certain values are possible.

one of a number of conserved quantities associated with particle interactions.

six types exist: up (u), down (d), strange (s), charmed, top and bottom

energy due to the rest mass

highly visible (and audible) way of showing and counting ionisation of the air caused by alpha radiation (or a match). It is a useful step towards understanding the Geiger counter.

ratio of charge to mass for a particle

subatomic particle classified as having a non-zero value for strangeness. Produced through the strong interaction they decay through the weak interaction. E.g. kaons.

assigned to every particle and antiparticle, strangeness is always conserved in the strong nuclear interaction, but not in a weak nuclear interaction (can change by 0, 1 or -1), or a decay involving a strange quark or antiquark.

minimum p.d. that needs to be applied to a metal plate to attract emitted photoelectrons back to the surface.

attractive force between nucleons that holds the nucleus together, an attraction solely between two hadrons.

minimum frequency of radiation incident on a metal surface which will cause electrons to be emitted from that metal in the photoelectric effect.

change from one state to another, for electrons in atoms from one energy level to another. Associated with the absorption or emission of a photon.

carrier of the electromagnetic interaction (force), a photon exchanged between two charged particles when they interact.

matter particles have a wave-like nature (given by the de Broglie wavelength) as well as particle-like. Similarly, photons have particle-like nature as well as wave-like

between two leptons or a lepton and hadron. Responsible for beta decay.

(energy) of a metal is the minimum energy required by an electron to escape (called a photoelectron) from the surface of the metal. Commonly expressed in either eV or J.