Physics particles

Atomic radius

1x10^-10m

Nuclear radius

1x10^-15m

Nucleon number

number of protons plus the number of neutrons in an atom

• Always a whole number

Isotopes

elements with the same number of protons and electrons, but a different number

of neutrons.

• Same charge as each other

Radioisotope

radioactive isotope of an element

Ions

different charges to their equivalent atom (electron gained or lost)

Four fundamental forces

• Strong nuclear

• Weak nuclear

• Electromagnetic

• Gravity

Strong Nuclear force

• Both attractive and repulsive

• Attractive over short-range (up to 3 fm)

• Repulsive over very short range (under 0.5 fm)

• Prevents electromagnetic repulsive forces between protons causing nucleus to fly apart

Unstable nucleus

nucleus that will change (by undergoing fission, fusion or emitting radiation)

electron anti-neutrino

by product of beta decay

• fundamental, nearly massless particles

• Second most common particle in the universe

Specific charge [C]

the relative charge of a particle divided by its mass (the ratio of its total charge to its mass)

Antiparticles

subatomic particles that have the same mass as their corresponding matter particle but with the opposite electric charge

• An antiparticle has the exact same mass as its corresponding particle.

• The electric charge is opposite to the particle

• Have opposite spin and colour (for quarks)

• often denoted with a bar over their symbol or a different symbol

Annihilation

when a particle and the corresponding antiparticle meet and their mass is converted into radiation energy.

• This process releases 2 photons (a single photon cannot ensure a total momentum of 0 after the collision)

• The minimum energy of each photon, hf_min ,is given by equating the energy of the two photons, 2hf_min, to the rest energy of the particle and antiparticle

• I.e. 2hf_^min = 2E0, where E0 is the rest energy of the particle

• Minimum energy of each photon produced hf_min = E₀

• Usually gamma-ray photon produced

Pair production

when a photon creates a particle and the corresponding antiparticle, and vanishes in the process

• For a particle and antiparticle, with both rest energy E0, you can calculate the minimum energy hf_min and minimum frequency F_min that the photon must have to produce the particle-antiparticle pair

• Minimum energy of photon needed = hf_min = 2E₀

• Starts with a gamma photon, and branches out to produce a particle and anti-particle, nearly always a electron and a positron

Nucleon

a proton or neutron in the nucleus

Nuclide

each type of nucleus

• Labelled using isotope notation

Strong nuclear force

a force that holds a nucleus together and overcomes the electrostatic force of repulsion between the protons in the nucleus, keeping the protons and neutrons together

• Same effect between two protons as it does between two neutrons or a proton and a neutron

Strong nuclear force effect

Attraction from around 3fm to 0.5 fm, less than 0.5 fm it is a repulsive force

Beta decay

when a neutron in the nucleus changes into a proton

Neutrinos

subatomic particles which carries some energy away from the nucleus during beta decay

Antimatter

the counterpart to ordinary matter, consisting of particles with the same mass but opposite charge

• When antimatter and matter particles meet they destroy each other and radiation is released

• Can make use of this in a positron emitting tomography (PET) hospital scanner

positron

antiparticle of the electron

Positron emission

takes place when a proton changes to a neutron in an unstable nucleus with too many protons

PET Scanner used for brain scan

• Positron emitting isotope administered to patient and some reaches brain via blood

• Each positron emitted travels no further than a few millimeters before it meets electron and annihilate each other, causing two gamma photons to be produced and are sensed by detectors

• This builds up an image in a computer and an image is built up from the detector signal of where the positron emitting nuclei are inside the brain

Rest energy

mass of a particle when it is stationary

Dirac’s theory of antiparticles

• Annihilates the particle and itself if they meet, converting total mass into photons

• Has exactly the same rest mass as particle

• Has exactly opposite charge to particle if particle has a charge

Millions of electron volts [MeV]

Energy of a particle / Antiparticle unit

• 1MeV = 1.6 x10-13J

• Defined as the energy transferred when an electron is moved through a potential difference of 1 volt

• Can be calculated using E=mc2

Minimum energy of each photon produced equation

hƒ_min = E₀

• hƒ_min being minimum energy of each photon produced

• E₀ being rest energy

Minimum energy of each photon needed equation

hƒ_min = 2E₀

• hƒ_min being minimum energy of each photon needed

• E₀ being rest energy

Exchange particles

particles that exist temporarily to cause ‘particle interactions’

e.g.

• electrostatic attraction/repulstion

• ß- decay

• Electromagnetic force: exchange particles = photon

• Weak nuclear force exchange: exchange particles = W+, W-, Z+

Feynman diagram

represents particle interactions

• Charge must be conserved at each vertex

W bosons and Z bosons

name of the exchange particle for a weak nuclear force

• Non-zero rest mass

• Very short range (no more than 0.001 fm)

• Positively or negatively charged (W⁺ or W^-)

Quarks

make up particles like protons and neutrons

• Twelve quarks

• 6 particles, 6 anti-partiles

• Negative name particles are negatively charged

• Does interact via / experience a strong nuclear force

• Fractional charged

Fundamental particles

particles which cannot be broken down into smaller particles

• E.g. neutrinos, anti-neutrino, electrons, positrons, leptons, tau, quarks

Protons quark structure

made up from 3 quarks (2 up quarks and 1 down quark )

• p = u + u + d

Neutron quark structure

made up from 3 quarks (2 down quarks and 1 up quark)

• n = u + d + d

Leptons

• Twelve leptons

• Six particles, six antiparticles

• Don’t interact via / experience a strong nuclear force

• Have integer charge

• Lighter than hadrons

List of particle Leptons

• Electron

• Electron Neutrino

• Muon

• Muon Neutrino

• Tau 

• Tau Neutrino

List of antiparticle Leptons

• Positron

• Electron anti-neutrino

• Anti-muon

• Muon anti-neutrino

• Anti-tau

• Tau anti-neutrino

List of particle Quarks

• Up

• Down

• Top

• Bottom

• Strange

• Charm

List of particle anti-quarks

• Anti- Up

• Anti - Down

• Anti - Top

• Anti - Bottom

• Anti - Strange

• Anti - Charm

Hadrons

• Heavy

• Not fundamental particles

• Subject to the strong interaction

• Two types:

  • Baryons

  • Mesons

Baryons

• made of 3 quarks

• Protons are the only stable baryon which other baryons eventually decay to

• E.g protons and neutrons

Mesons

made of 1 quark and 1 anti-quark

• E.g pions and kaons

  • Kaons - have to have a strange or anti-strange quark

Quantum numbers

numbers that must be conserved in particle interactions (value before an interaction = value after interaction)

• Charge

• Mass-energy

• Hadron number

• Baryon number

• Strangeness

Baryon number

• Baryon Number = 1 (e.g. proton)

• Anti-Baryon = -1 (e.g. anti-proton)

• Baryon number of quark = ⅓

• Baryon number of anti-quark = -⅓

• Non-baryon = 0 (e.g. electron)

Lepton number

• Lepton number = 1

• Anti-lepton number = -1

• Lepton number of quark and anti-quark = 0

• Non-lepton = 0 (anything else)

Strangeness

• Strange quark = -1

• Anti-strange quark = 1

Hadrons

• Pion - another exchange particle of the strong nuclear force, between proton (p+) and neutron (n0)

  • Kaons can decay to pions

• Gluons - holds together the quarks within hadrons such as protons and neutrons

General information about particles

• Particles beginning with ‘p’ are the most stable

• Many exist for very short periods of time due to being unstable

• Decay is a weak interaction

Strange quarks

• Strange quarks produce via strong nuclear interactions

• Created in pairs

• Strangeness conserved in the strong interactions

• Can change by 0, +1, -1 in weak interactions

Lepton decay

• Taus decay into muons

• Muons decay into electrons

Electromagnetic waves

consists of an electric wave and a magnetic wave, which travel together and vibrate

• Travel and vibrate at right angles to each other and to the direction in which they are travelling

• Travel and vibrate in phase with each other

• Emitted as short bursts of waves, with each burst leaving the source in a different direction

Photons

a packet of electromagnetic waves that are emitted by a charged particle when it loses energy

• Happens when a fast moving electron is stopped, slows down or changes direction

• Happens when an electron in a shell of an atoms moves to a different shell of lower energy

• Established by Einstein when he used his ideas to explain the photoelectric effect

Photon energy equation

E = hf

• h as plancks constant

Laser beams

consists of photons of the same frequency

• Power of laser beam is the energy pers second transferred by photons

• Laser beam power equation: power of beam = nhf

• n = number of photons in beam passing a fixed point per second

• hf = energy in each photon

Nature of light

Light sometimes behaves like a particle

Particles of light are called photons and have zero rest mass

Can be:

• reflected

• refracted

• diffracted

• Interference

Planck’s constant

 6.63 x 10^-34 Js

Electron volt (eV)

the amount of energy gained by an electron as it accelerates through a potential difference of 1 volt

• an alternative unit to the joule for energy

• 1eV = 1.6 x 10^-19J

• 1eV has the same magnitude as the charge of single electron

Photon emissions

• Emitted when an electron (in an atom) moves from a high energy level to a low energy level

• Energy it loses is emitted as a photon

• Can also be atoms in a sample going from high energy level to a low energy level

Energy levels diagram

• Negative value imply it is bound to something

• Photons lose energy to move to a lower energy level (if the levels were given positive values, they would be gaining energy)

• Must have 0 energy when they are far away from the nucleus (no longer bound to the atom at this highest 0eV energy level)

Range of wavelength for visible light

400nm to 700nm

Photon emission

• Electrons becom excited (gain energy when the gas is heated to a high temperature)

• emitted when an electron (in an atom) moves from a higher energy level to a lower energy level. 

• The energy that it loses is emitted as a photon

Two types of atomic line spectra

• Emission spectra

• Absorption spectra

Emission spectra

certain wavelengths / colours of light are given out / emitted

• Appears as bright coloured lines on a dark background

• Can be produced by heating a gas

• Certain wavelengths (colours) of light will be emitted

Absorption spectra

certain wavelength / colours of light are taken in / absorbed.

• Will appear as dark lines on a spectrum when viewed with a spectrometer

• Can be produced by shining light through a sample of an element (normally as a gas) and observing the wavelengths that have been absorbed

Energy levels

quantised places for electrons(electron shells)

Ionisation

when the electron moves to 0eV energy level , the electron is no longer bound to the atom (leaving the atom)

Photoelectric effect

process of electrons being emitted from a material

• When a photon is absorbed by an electron it will excite the electron to a higher energy level

• If the energy of an incoming photon is big enough, then the electron will escape the atom and the atom is now ionised

• It is evidence of the particle theory of light

Photoelectric effect Process

• Ultraviolet light photons excite electrons in the zinc / ionise the zinc

• Electrons leave the zinc plate making it positively charged

• Electrons from the bass rod are attracted towards the zinc

• Leaves brass rod with a positive charge at the bottom

• Which attracts the negatively charged gold leaf

Work function

the minimum energy needed to ionise a material

• Usually defined from the ground state

Threshold frequency

the minimum frequency associated with the work function energy, if a photon has a lower frequency than the threshold frequency then it cannot ionise the atom

• When over threshold frequency, the extra energy becomes kinetic energy of the photoelectron

Photoelectric effect equations

ɸ = hf_t

• h - planck’s constant [Js]

• f_t - the threshold frequency [Hz]

• ɸ (phi) - the work function [J]

Conservation of energy equation

hf = ɸ + E_{k max}

• hf - the energy of an incident photon [J]

• ɸ (phi) - the work function [J]

• E_{k max} - the maximum kinetic energy of the emitted electron

higher intensity light on photoelectric effect

• More intense light hitting a metal, more photons per second hit the metal

• More photoelectrons emitted per second

• No change to velocity or kinetic energy of electrons

Higher frequency light on hitting a metal (shorter wavelength)

• Each photon has more energy (coming in)

• Each emitted photoelectron has greater kinetic energy

• No effect on number of electron emitted per second

Stopping potential

the minimum potential required to stop photoelectric emission

• Depends on the metal, intensity and frequency of incident light

• Kinetic energy of electrons is zero because extra work needs to be done against the potential difference 

• Kinetic energy maximum of emitted electrons = electronic charge x velocity

Wave-particle duality

light sometimes behaves as a wave and sometimes as a particle

• Particles only display wave properties only when they are small and relatilistic (moving at a significant proportion to speed of light)

Particle properties of light

• Photoelectric effect

• Line spectra

Louis de Broglie discovery

said that when a particle has momentum it has a corresponding wavelength

Formula for de Broglie wavelength

λ_db = h / p or λ_db = h / mv

• λ_db - de Broglie wavelength (of a particle)

• h - planck’s constant

• p or mv - the momentum

Wave properties of light

• Reflection

• Refraction

• Diffraction 

• Interference