5. Nuclear Physics Flashcards
Atom
The smallest unit of an element, made from neutrons, protons and electrons.
Proton - (Symbol, charge, mass, location)
Symbol = p
Charge = +1
Mass = 1
Location = In the nucleus
Nucleus
The central part of an atom that contains all the protons and neutrons, and so all the mass and positive charge. (pl. nuclei)
Neutron - (Symbol, charge, mass, location)
Symbol = n
Charge = 0
Mass = 1
Location = In the nucleus
Electron - (Symbol, charge, mass, location)
Symbol = e
Charge = -1
Mass = 0 (1/2000) (tiny mass)
Location = Orbit the nucleus
Testing the atomic model
In 1911, Ernest Rutherford proposed the atomic model based on the Rutherfords Gold Foil experiment (aka Alpha Scattering experiment.)
- Beam of alpha particles was directed through a slit in a flourescent screen towards a piece of thin gold foil (1 atom thick)
- Experiment carried out in vaccum so particles didn’t hit any air particles –> only collided with foil
- When the particles hit the circular flourescent screen surrounding the model there was a flash of light
Result of alpha scattering experiment
Most particles passed through the gold foil. Some were deflected slightly but still passed out the other side. Very few were completely deflected and hit behind where they were emitted.
All 4 atom features
- The number of protons and electrons are equal.
- Most of an atom is empty space. The size of the nucleus is incredibly small compared to the size of an atom.
- The nucleus is positively charged.
- The nucleus accounts for nearly all the mass.
Explanation of Alpha scattering results - (The number of protons and electrons are equal.)
Atoms do not have an overall charge
Explanation of Alpha scattering results - Most of an atom is empty space. The size of the nucleus is incredibly small compared to the size of an atom
Most of Rutherford’s α - particles went straight through the gold foil without changing their direction.
Explanation of Alpha scattering results - The nucleus is positively charged.
Alpha particles are positive. When some particles come close to the nucleus of the gold foil, they were repelled. The nucleus must therefore also be positive.
Explanation of Alpha scattering results - The nucleus accounts for nearly all the mass.
In one experiment the α - particle was deflected back in the opposite direction when a direct hit occurred. This change in momentum could only happen if the tiny nucleus also contains most of the mass.
Nuclide
An atom or nucleus characterised by a specific number of protons and neutrons.
Nuclide Notation
A notation using symbols for elements along with atomic number and nucleon number to describe the composition of an element’s nucleus.
A
Z X
A - Mass number
Z - Proton number
X - Element
Z (proton number) - In relation to charges
Z = relative charge of the nucleus
A (mass number) - In relation to mass
A = relative mass of the nucleus
Isotope
Atoms of the same element that have different nucleon numbers due to a varied number of neutrons.
Nuclear Fusion
Small nuclei fuse to form larger nuclei and release energy.
This is what happens in the sun
Eg.
2 2 4
1 H + 1 H –> 2 He
Total mass is conserved
Nuclear fission
Large nuclei split up into smaller nuclei and release energy.
Nuclei with very large nucleon numbers have heavy nuclei and are often unstable. This is why large nuclei often split up.
This can happen independently or can be caused by a single neutron colliding with the nuclei.
Total mass is conserved
Eg. A neutron is fired into the uranium-235 nucleus, causing the nucleon number to increase. A larger mass makes the nucleus unstable. Nuclear fission then occurs and the heavy nucleus splits into krypton and barium with three spare neutrons.
Background Radiation
The average level of radiation detectable as part of everyday life, due to a combination of natural and man-made sources.
Types of background radiation
Food - (eg. bananas –> dosage of 0.1 micosieverts)
Building materials + rocks - (eg. granite, concrete both contain elements such as uranium, radium and thorium)
Radon gas - (naturally found in atmosphere because of uranium decay)
Cosmic ray - (high radiation waves travelling from outside of our solar system)
Medical procedures - (eg. X-rays, CT scans)
Geiger–Müller (GM) tube
Detects alpha, beta and gamma radiation. A ‘click’ can be heard as the radiation is detected and a digital count is recorded.
Spark Counter
Detects alpha, beta and gamma radiation with an audible click.
Cloud Chamber
Shows the paths of alpha and beta particles by producing a vapour trail behind each particle.