absorption spectra
When a continuous spectrum of light is shone through an element in gaseous form, specific frequencies are preferentially absorbed (the frequencies of the element's emission spectrum). The resulting spectrum (i.e. most frequencies with some specific ones m
emission spectra
When an element is hot enough (given enough energy) it emits light. Analysis of this light shows that each element only emits specific frequencies. These specific frequencies form the element's emission spectrum.
photons
Light energy is not emitted as a continuous wave but comes in small 'packets' of energy. Each 'packet' is called a photon. The energy of one photon depends on the frequency of light being considered.
photon energy
The energy of a single photon is given by:
E = hf or E = hc / ?
E = Energy of the released photon (J)
h = Planck's constant (6.63 x 10?�? Js)
f = frequency of emitted photon (Hz)
c = speed of light in vacuum (3x10? m/s)
? = wavelength f emitted photon (m)
electron energy levels
Electrons can only exist in certain energy levels in an atom. In order to move between levels they must emit or absorb a photon. The lowest energy level is called the ground state.
electronvolt
A unit of energy used when dealing with very small amounts of energy - the energy of an electron when accelerated through a voltage of 1 V
1 eV = charge on an electron x 1 volt
= 1.6 x 10?�? Joules
ionizing radiation
Alphs, Beta or Gamma particles emitted from a nucleus that can remove electrons from atoms and molecules with which they collide. Removing electrons ionizes the molecule.
alpha particles
Alpha particles are helium nuclei (two protons and two neutrons) emitted as a result of a decaying unstable nucleus.
Due to their large size alpha particles are easily stopped by air and thin paper, but are strongly ionising.
beta- decay
?- decay is the emission of a fast-moving electron when a neutron decays into a proton, a ?- particle, and an antineutrino.
beta+ decay
?+ decay is the emission of a fast-moving positive electron (positron) when a proton decays into a neutron, a ?+ particle, and a neutrino.
beta particles
Beta particles are fast-moving electrons or positrons that have been emitted as a result of a decaying unstable nucleus.
Beta particles are more penetrating than alpha particles. Can be stopped by thin aluminium.
gamma radiation
Gamma radiation is photons of high-energy electromagnetic radiation emitted as a result of a nucleus changing from an excited state into a lower energy state.
Gamma radiation is highly penetrating. Can be stopped by thick sheets of lead.
neutrino, existence of
The energy spectra in ? decay (both ?+ and ?-) are continuous (the ? particles are observed to have a range of possible energies). The neutrino was postulated to account for these spectra. The hypothesis being that in addition to the observed ? particles
Einstein's mass-energy equivalence relationship
Einstein's mass-energy equivalence relationship allows us to calculate the energy that is in the form of mass:
E = mc�
E is the energy equivalent (J)
m is the mass (kg)
c is the speed of light (3 � 10E8 m s-1).
An alternative unit of mass can be used to m
mass defect
The mass of any nucleus is less than the mass of the component nucleons that go to make it up.
The difference between the mass of a nucleus and the masses of its component nucleons is called the mass defect.
binding energy
The binding energy is the amount of energy that is released when a nucleus is assembled from its component nucleons. It is also the amount of energy that needs to be added in order to separate a nucleus into its individual nucleons.
binding energy per nucleon
The binding energy per nucleon is the total binding energy for a particular nucleus divided by the number of nucleons contained in the nucleus. A larger binding energy per nucleon represents a nucleus that is more energetically stable.
isotope
Isotopes are nuclides that contain the same number of protons (and are thus the same element) but different numbers of neutrons.
nucleon
A nucleon is the collective name for protons and neutrons - the particles that make up the nucleus.
nuclide
A nuclide is the name given to a particular species of atom - one whose nucleus contains a specific numbers of protons and neutrons.
nucleon number, A
The nucleon number, A is the total number of protons and neutrons in a given nuclide.
proton number, Z
The proton number, Z, is the total number of protons in a given nuclide
neutron number, N
The neutron number, N, is the total number of neutrons in a given nuclide.
artificial (induced) transmutation
Artificial (induced) transmutation can take place when a nucleus is bombarded by a nucleon, an alpha particle, or other small nucleus. The target nucleus first 'captures' the incoming object and then an emission or decay takes place.
For example, when nit
nuclear fission
Nuclear fission is a nuclear reaction in which large nuclei are induced to break up into small nuclei and release energy in the process.
nuclear fusion
Nuclear fusion is a nuclear reaction in which small nuclei are induced to join together into larger nuclei and energy is released in the process. Nuclear fusion is the main source of the Sun's energy.
radioactive decay
Radioactive decay is the spontaneous emission of ionizing radiations (alpha, beta, or gamma) from an unstable nucleus. It is a random and spontaneous process. As a result, the rate of decay decreases exponentially with time.
N = N?e ^(-?t)
N is the number
radioactive half-life
The time taken for the number of nuclei that are available to decay to halve to its original value is known as the half-life.
Equivalent definitions are possible in terms of other quantities, as the result of exponential decay is that many quantities (num
unified atomic mass unit
The unified atomic mass unit, u, is a unit appropriate for nuclear mass calculations. 1 u is approximately the mass of one proton or one neutron but is defined to be exactly one twelfth the mass of a carbon-12 atom.
1u = 1.66 � 10?�� kg = 931.5 MeV/c�
Thi
Models of the atom
Representations of the atom. Beginning over 2000 years ago with the Greek idea that matter is composed of tiny, indivisible particles called atoms, in the last 200 years our understanding of the atomic structure has changed considerably.
Dalton's Atom
Atoms are small, indivisible objects. Each chemical element is composed of a unique type of atom.
Plum Pudding model
Atoms consist of individual electrons embedded in a sea of negative charge. Proposed by J.J Thompson after he discovered the electron.
Nuclear Model
A small, positively charged nucleus which contains nearly all the mass of an atom is orbited at great distance by electrons. Most of the atom is empty space. Proposed by Ernest Rutherford.
Bohr Model
Schrodinger model of the atom
Gold leaf alpha-scattering experiment
Standard Model
the presently accepted model of elementary particles and interaction for quarks and leptons
Fermions
Particles that make up matter.
Quarks and Leptons are Fermions
Hadrons
Particles that are affected by strong nuclear force, and contain quarks.
Mesons and Baryons are both types of Hadron.
Quarks
Smaller particles that make up protons and neutrons
Mesons
Hadrons which contain an anti quark-quark pair. e.g. pions ??, ?+, ?-
Baryons
Hadrons which contain 3 quarks, such as protons and neutrons
Bosons
Particles that carry forces
Leptons
Particles that don't interact via the strong interaction (e.g. Electrons and neutrinos )
Large Hadron Collider (LHC)
A large collider that collides Hadrons
Very Large Hadron Collider (VLHC)
A proposed collider that collides Hadrons that is larger than the larger hadron collider (very large in fact).
Conservation of Charge
In an interaction the total initial charge is equal to the total final charge.
Conservation of Baryon number
A Baryon has a Baryon number of 1. Baryon number is conserved in an interaction.
Conservation of Lepton number
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