Chapter 7: Atomic and nuclear physics Flashcards
Describe a model of the atom that features a small nuclear surrounded by electrons
- electrons kept in orbit around the nucleus as a result of the electrostatic attraction between the electrons and the nucleus
Evidence for that supported the nuclear model of the atom
Geiger Marsden/ Rutherford/ Gold-Foil experiment
Outline one limitation of the simple model of the nuclear atom
- The problem in this theory was that acceleration changes are known to lose energy. If the orbiting electrons were to lose energy they would spiral into the nucleus. The Rutherford experiment cannot explain to us how atoms are stable.
Outline evidence for the existance of atomic energy levels
Evidence is found in the emission and absorption spectra.
- Elements with enough energy can emit light by using either diffraction grating or a prism, it is possible to analyse the different colours within the given light.
- A continuous spectrum would mean that all frequencies of the electromagnetic spectrum are present - light from the sun contains all visible wavelengths of light.
- An emission spectrum is not continuous, but contains certain frequencies of light relative to the discrete energy levels present in the atom. Each possible combinations of drops in energy level emit differenr wavelengths of light enabiling us to deduce what element created that light
Nuclide
a particular species of atoms whose nucleus contains a specified number of protons and neutrons
Isotopes
atoms of the same element but have different atomic number (differ with the number of neutrons)
Nucleons
Protons and neutrons
Nucleon number (A)
mass number, number of protons and neutrons
Proton number (Z)
atomic number, number of protons in the nucleus
Neutron number (N)
Mass number, proton number, equal to the number of neutrons in the nucleus
Describe the interactions in a nucleus
- Coulomb interactions between protons and the strong, short-rangesd nuclear interaction between the nucleons
Natural radioactive decay
a random and spontaneous process in which an unstable nucleus emits a particle. (the element of the nucleus changes)
Alpha particle
- consists of 2 protons and 2 neutrons (=helium nucleus)
- has approximately 5MeV kinetic energy
- travels at approximately 5% of the speed of light
Beta minus particle
- consists of 1 electron
- often travels at close to the speed of light
- They have a range of speeds and KEs depending on the element and the anti-neutrino
Beta particle decay
In the nucleus, a neutron changes into a proton and electrin (which is emitted as a beta particle)
Anti-neutrino
- particle emitted with beta minus particle
- carries away some of the KE
Gamma ray
High energy (also frequency) electromagnetic radiation emitted by nucleus following alpha and beta decay (which left the nucleus in a excited state)
Describe the ionizing properties of alpha, beta particles and gamma radiation
Ionisation can be throught of as “damage” to teh medium that radiation is passing through. The greater the ionisation energy, the less the penetration into the medium, since the radiation more rapidly loses energy. Thus the most ionisation us by alpha and the least (almost none) by gamma
Strong nuclear force
the force that holds the particles of a ucleus together. It is strong enough to overcome electrostatic repulsion of protons and very short range so that the nuclei do not attract each other
Stability
the nucleus is under the effect of strong nuclear attraction and proton -proton repulsion. This is therefore more stable with an excess of neutrons
Radioactive half-life
the time taken for half of the nuclei in a sampleto decay
7.3.1 Describe and give an example of an artifical (induced) transmutation
We can alo induce large nuclei to decay and release large energy by bombarding them with smaller particles. This is called fission and is how our nuclear power stations work. If we induce a nuclear decay then the process is called an artifical (or induced) transmutation. A good example is the induced transmutation of Uranium-235
Unified atomic mass
the mass of 1/12 of the nucleus of a carbon-12 isotope
Apply the Einstein mass-energy equivalent relationship
E=mc^2
Binding energy
the amount of work required to pull apart the constituents of a nucleus. A large binding energy implies a stable nucles
Mass deflect
the mass of the particles of the seperated nucleus is greater than when they are combined. Mass deflect=mass of parts-mass of nucleus
Binding energy per nucleon
A graph is plotted for each isotope which shows which nuclides are the most stable. The graph can predict fission and fusion reactions
The process of nuclear fission
A process where large nucleus splits to make samller ones. This is permitted when the BE/nucleon of the products is higher than the initional nucleus. The difference in mass/energy is treleased
The process of nuclear chain reaction
A uranium nucleus can be split by an incident wneutron the fission reaction produces more neutrons. Of one of the products produced also causes fission, then a chain reaction will follow. If the number of fissions is greater than the one, the reaction wil go out of control
What is the main source of the sun
Nuclear fusion
Explain how atomic spectra provide evidence for the quantization of energy in atoms
When an electron moves between energy levels it must emit or absorbe energy. The energy emitted or absorbed corresponds to the difference between the two allowed energy levels. The enrgy is emitted or absorbed as photons. The lines in the atomic spectra correspond with the enrergy levels
calculate wavelength of spectral lines from energy level differences and vice verse
E=hf=hc
Heisenberg incertainty principle
the principle identifies a fundamental limit to the possibly accuracy of any physical measurement. Conjugate properties, position-momentum and energy-time, cannot be known precisely at the same time
Decay constant
the probability of decay of a nucleus per unit time
Methods of measuring the half-life of an isotope
activity against time
