3.8.1.1-2 Rutherford scattering andα, β and γ radiation Flashcards
What was suggested through the Rutherford experiment?
Majority of the alpha particles went straight through, hence the atom is mostly empty space.
Some alpha particles were deflected through small angles under 10 degrees - positive nucleus in the centre, positive charges repel.
Only a small number of alpha particles went straight back at angles over 90 degrees - nucleus is extremely small, where mass and charge are concentrated.
What was Dalton’s model of matter?
Atoms are the smallest constituents of matter and cannot be broken down any further.
Atoms of a given element are identical to each other and atoms of different elements are different from one another.
When chemical reactions occur, atoms rearrange to make different substances
What was J.J. Thompson’s model of matter?
The atom consists of small positive and negative charges in equal amounts, so that it is neutral overall.
Modelled as spheres with positive and uniformly distributed charge density.
Negatively charged electrons were thought to be embedded in the positively charged sphere
What did Bohr’s model add to the model of matter?
Showed that electrons occupy energy levels around the nucleus at particular distances from the nucleus.
What did Schrodinger add to the model of matter?
Quantum mechanical model - portrayed as a nucleus surrounded by an electron cloud, where cloud is most dense, probability of finding an electron is greatest.
What are the properties of alpha radiation?
- 2 protons, 2 neutrons
- usually emitted from nuclei that are too large
- most ionising type of radiation (highest charge of +2e, so produces the greatest number of ion pairs per mm in air)
- least penetrating - travels around 5mm in air before being stoppedW
What are the properties of beta minus radiation?
- high energy electrons
- emitted by nuclei with too many neutrons
- moderately ionising
- moderately penetrating (range of around 1 m in air
What are the properties of beta+ radiation?
- high energy positrons
- emitted from nuclei with too many protons
-moderately ionising - moderately penetrating (range of around 1m in air)
What are the properties of gamma radiation?
- high energy electromagnetic waves
- emitted by nuclei with too much energy
- can hit other atoms and knock out electrons, ionising the atom (causing chemical changes in materials and damaging living cells)
- least ionising (no charge)
- most penetrating
- infinite range
What is the equation for the inverse square law of gamma radiation?
I = k/x^2
I = intensity of radiation (Wm^-2)
k = constant of proportionality
x = distance from source (m)
What is background radiation?
Low level radiation present in the surroundings at all times.
There are 2 types;
Natural sources
Man-made sources
What are natural sources of background radiation?
Radon gas from rocks and soil - heavy radioactive elements e.g. radon and uranium occur naturally, uranium decays to radon gas, which is an alpha emitter.
Cosmic rays - sun emits lots of protons every second, they enter the atmosphere at high speeds, when they collide with molecules in air, it produces gamma radiation.
C-14 in biological material
Radioactive material in food and drink
What are man-made sources of background radiation?
Medical sources - X-rays, CT-scans, radioactive tracers and radiation therapy.
Nuclear waste - dangerous for people handling it.
Nuclear fallout from nuclear weapons - residue material thrown into the air after a nuclear explosion.
Nuclear accidents - contribute large dose of radiation into the environment
What is corrected count rate?
When taking readings in a laboratory, background radiation must be accounted for - this is done by taking readings with no radioactive source present and subtracting it form the readings with the source present
What are the risks associated with working with radioative isotopes?
Amount and type of radiation are take into account. Big risks are exposure and contamination.
