Topic 7: Atomic, Nuclear and Particle Physics Flashcards
Thomson’s Plum Pudding Model
Atoms were thought to be a cloud of positive charge with negative charges embedded in it (like a chocolate chip muffin).
Describe Rutherford’s experiment (method + expected results/actual results)
Alpha particles (helium nuclei) were fired at a thin gold foil. A fluorescent screen detected where they went.
If Thomson’s model was correct the alpha particles would pass straight through undeflected (as the charge was supposedly evenly distributed throughout the atom).
Most alpha particles were undeflected, a few were deflected slightly and a few bounced straight back.
What did Rutherford’s experiment conclude?
- That most of an atom is empty space.
- The positive charge of an atom is concentrated at the centre (the nucleus) and electrons orbit this.
- Most of the mass of an atom is in the nucleus.
Limitations of Rutherford’s model
The model was unable to show anything about the arrangement of electrons in the orbit.
Continuum Spectrum
A spectrum created from a light source producing photons of all wavelengths (and frequencies).
Emission Line Spectrum
Light is shone through hot gas (the element being studied), passed through a slit and then a prism. Electrons in the atoms will emit photons with the exact amount of energy to drop energy levels. So only photons of specific wavelengths (and frequencies) are emitted. This produces thin lines of colour in an otherwise spectrum of black.
Absorption Line Spectrum
Light is shone through a cold gas, passed through a slit and then a prism. Electrons in the atoms will absorb photons with the exact amount of energy required to jump energy levels. So only photons of specific wavelengths (and frequencies) are absorbed. This produces thin lines of black in an otherwise full spectrum of colour.
What is radioactive decay?
The nuclei of some elements are unstable bc of the wrong balance of protons and neutrons. Over time, these nuclei will spontaneously decay by emitting particles and energy. So they transform into the nuclei of another element.
How can electrons move to higher or lower energy levels? (physical processes)
To move to a higher energy level:
- The gas is heated
- Or a photon is absorbed
To move to a lower energy level:
- The gas is cooled
- Or a photon is emitted
Half-life
The time taken for half of the nuclei in a sample to decay (or the activity to fall to 50%).
Natural sources of background radiation
- Cosmic
- Terrestrial (eg. radioactive rocks/soil)
- Internal (eg. living organisms that have consumed radioactive substances in the food chain)
Artificial sources of background radiation
- Medical (eg. x-rays, radiation treatment)
- Industrial/occupational
- Nuclear fall out
Define transmutation
When nuclei are changed from one element to another by the addition of nucleons. Can occur naturally or artificially in nuclear fusion and nuclear fission.
Nuclear fission
The splitting of large nuclei into smaller nuclei by being bombarded by particles like neutrons or alpha particles. Occurs artificially in nuclear power stations.
Nuclear fusion
The joining of two nuclei to form a larger nuclei. Only occurs if temperature and pressure is high enough to give them the energy to overcome the electrostatic repulsion between them. It occurs naturally in stars, and is very hard to do artificially. Yields more energy than nuclear fission.
Why do both nuclear fission and nuclear fusion release large amounts of energy?
Because during these reactions mass is destroyed and converted to energy.
J to eV
eV to MeV
MeV to GeV
divide by 1.6 x 10^-19
divide by 10^6
divide by 1000
Define the unified atomic mass
The mass of 1/12th of a 12C atom.
