8 Nuclear Physics Flashcards
Thompson’s plum pudding model
Atom made up of a sphere of positive charge with small areas of negative charge evenly distributed throughout
Equipment for Rutherford’s scattering experiment
Alpha source
Gold foil - gold chosen as it is very malleable so can be made very thin
Evacuated chamber - so the alpha particles don’t collide with air molecules
Rutherford’s scattering
An experiment that involved firing alpha particles at thin gold foil and observing their defelection
What would Rutherford’s scattering show if the plum pudding model was true?
positively charged alpha particles would be deflected by very small amounts
Rutherford scattering results
- Most particles passed straight through therefore the atom is mostly empty space
- small amount of particles deflected by a large angle therefore the center of the atom has a large positive charge
- very few particles were deflected by more than 90° therefore the center of the atom is very dense and positively charged. Also that the center is very small
Conclusions from Rutherford’s scattering
The atom has a small, dense positively charged nucleus and the centre and electrons orbit around it.
Alpha decay
The emission of an alpha particle (2 protons, 2 neutrons) from an unstable heavy nucleus.
Stopping alpha radiation
Stopped by a few cm of air or paper
Beta decay
Emission of a beta particle (fast moving electron) when a proton turns into a neutron in an unstable nucleus
Stopping beta minus decay
Around 1m of air or aluminium foil
Stopping beta plus decay
Annihilated by electrons, producing gamma rays
Gamma decay
Gamma rays emitted from an unstable nucleus with too much energy
Stopping gamma radiation
Infinite range in air so stopped by 1m of concrete or a few cm of lead
Inverse square law
Law that governs the intensity of gamma radiation. It means intensity of radiation at any point is inversely proportional to the square of the distance from the source
Identifying the type of radiation
Using a Geiger-muller (GM) counter. Find the background count and place a sheet of paper between the source and the counter. If the count rate drops, the source emits alpha radiation. Repeat using aluminium and lead.
How is radiation used to determine material thickness?
When a material is being rolled out, a beta source is placed on one side of the material and a detector on the other. If the material is too thick, the count rate decreases so the rollers can be adjusted
Gamma radiation uses in medicine
Gamma is used as a detector where a source with a short half is injected into the patient and can be detected outside the body.
It is also used to sterelise surgical equipment and to kill cancerous cells
