Particles and nuclides (1)

Question 1

Atoms

Answer 1

made up of a very small central nucleus containing protons and neutrons, surrounded by orbiting electrons. They are electrically neutral overall, meaning they have the same number of protons and electrons.

Question 2

Proton (atomic) number

Answer 2

number of protons contained in the nucleus.

Question 3

Nucleon (mass) number

Answer 3

total number of protons and neutrons contained in the nucleus.

Question 4

Protons

Answer 4

positively charged particles with a relative charge of +1. Relative mass 1.

Question 5

Electrons

Answer 5

negatively charged particles with a relative charge of -1. Relative mass 1/1800.

Question 6

Neutrons

Answer 6

electrically neutral particles with a relative charge of 0. Relative mass 1.

Question 7

Ions

Answer 7

an atom which has lost or gained electrons (excess electrons = negatively charged ion, shortage of electrons = positively charged ion).

Question 8

Relative atomic mass

Answer 8

the RAM of an element compares the mass of atoms of the element with the carbon-12 isotope.

Question 9

Nucleon

Answer 9

the word used to describe protons or neutrons. These are particles that exist in the nucleus.

Question 10

Isotopes

Answer 10

nuclei with the same number of protons, but different numbers of neutrons.

Question 11

The strong nuclear force

Answer 11

one of the four fundamental forces of nature (including electromagnetic, weak and gravitational forces). It is a very short-range force and acts between nucleons (protons and neutrons) holding nuclei together.

Question 12

Neutrino, ν

Answer 12

a neutral, almost massless fundamental sub-atomic particle that rarely interacts with matter. There are three forms of the neutrino: the electron-neutrino, νe; the muon-neutrino, νµ; and the tau-neutrino, ντ.

Question 13

Antineutrinos

Answer 13

the antiparticles of the neutrino.

Question 14

Rest-mass energy

Answer 14

the amount of energy released by converting all of the mass of a particles at rest into energy using Einstein’s famous mass-energy equation, E=mc^2, where m is the rest mass of the particle and c is the speed of light.

Question 15

Mega electron-volts

Answer 15

the energy of nuclear particles is usually given in MeV, mega electron-volts. One electron-volt is a very small amount of energy, equivalent to 1.6×〖10〗^(-19)J. This is the same numerical value as the charge on an electron and is defined as the amount of energy needed to accelerate an electron of charge ‘e’, (1.6×〖10〗^(-19)C) through a potential difference of 1 volt. One MeV is a million electron-volts, equivalent to 1.6×〖10〗^(-13)J. This unit comes from the definition of the volt. A volt is the amount of energy per unit charge so energy = charge x volts.

Question 16

Annihilation

Answer 16

when a particle meets its antiparticle and their total mass is converted to energy in the form of two gamma ray photons, the particles annihilate each other.

Question 17

Antiparticles

Answer 17

fundamental particles with the same mass and energy as their particle counterparts, but have opposite properties such as charge. When a particle meets its antiparticle they annihilate, converting to gamma ray photons.

Question 18

Quarks

Answer 18

fundamental particles that make up particles such as protons and neutrons. They exert the strong nuclear force on one another.

Question 19

Gluons

Answer 19

one of the four exchange particles of the Standard Model. Gluons act between quarks holding them together. Gluons have an extremely short range of action of about 〖10〗^(-15)m.

Question 20

Deep-inelastic scattering

Answer 20

involves firing electrons at protons at very high energies (hence the word ‘deep’). Elastic scattering, for example, involves two particles such as two protons colliding with each other and rebounding off each other with the same kinetic energy – rather like two snooker balls hitting each other head-on and rebounding back. The word ‘elastic’ in this context means that no kinetic energy is lost. Inelastic scattering involves the conversion of kinetic energy into other forms. In this case the electrons penetrate into the proton and interact with the quarks (via exchange of photons); kinetic energy is converted into mass as the proton shatters, producing a shower of other particles. Using the snooker analogy, it would be as if one snooker ball entered the second ball causing it to break into other pieces as the first snooker ball scattered away from it.

Question 21

Exchange particles

Answer 21

particles involved with the interaction of particles via the four fundamental forces of nature on the quantum scale. Exchange particles are only created, emitted, absorbed and destroyed between the interacting particles.

Question 22

Macroscopic

Answer 22

means ‘large-scale’, as opposed to microscopic, quantum scale. Quantum effects operate at distances less than about 100nm, so anything above this scale is considered macroscopic, and classical (sometimes Newtonian) physics is applied.

Question 23

Feynman diagrams

Answer 23

used to represent reactions or interactions in terms of particles going in and out, and exchange particles.

Question 24

Particle lifetime

Answer 24

the average time that a particle exists from its creation to its decay.

Question 25

Mesons

Answer 25

hadron particles made up of a quark-antiquark pair.

Question 26

Virtual photon

Answer 26

the exchange particle for the electromagnetic interaction.

Question 27

Hadrons

Answer 27

particles subject to the strong interaction. There are two classes of hadrons:
• baryons (proton, neutron) and antibaryons (antiproton and antineutron)
• mesons (pion, kaon)

Question 28

Baryon number, B

Answer 28

a quantum number that describes baryons. Baryons have B = +1; antibaryons, B = -1; non-baryons, B = 0. Baryon number is always conserved in particle interactions.

Question 29

Free neutrons

Answer 29

are unstable and decay via the weak interaction forming a proton, β- particles and an electron neutrino.

Question 30

Pion

Answer 30

the exchange particle of the strong nuclear force between baryons.

Question 31

Kaon

Answer 31

a particle that can decay into pions.

Question 32

Leptons

Answer 32

particles that are subject to the weak interaction. Include electron, muon, neutrino (electron and muon types) and their antiparticles.

Question 33

Lepton number, L

Answer 33

a quantum number used to describe leptons. Leptons have L = +1; antileptons, L = -1; non-leptons, L = 0. Lepton number is always conserved in particle interactions.

Question 34

Muon

Answer 34

a particle that decays into electrons.

Question 35

Strange particles

Answer 35

particles that are produced through the strong interaction and decay through the weak interaction (e.g. kaons).

Question 36

Strangeness, S

Answer 36

a quantum number to describe strange particles. Strange particles are always created in pairs by the strong interaction (to conserve strangeness). In weak interactions, the strangeness can change by -1, 0 or +1.