Nuclear Physics Flashcards
What as the first model of the atom like
A plum pudding - a sphere of positive chafe with tiny negative electrons stuck in
What was rutherfords experiment
He fired a beam of electrons at thin gold foil, he used a circular detector screen to measure the angle that alpha was deflected at
What were the results of rutherfords experiment
- most particles went straight throug
- some were deflected
- a few were deflected back by 180
What could be shown from rutherfords experiment
- most of the atom is free space
- there must be a positively charged nucleus
- the nucleus must be small and contain lots of mass, therefore has a great sense
What is closest approach and how is it measured
The closest distance a particle can get to another particle before being repelled
When electric potential energy equal initial kinetic energy
What is the use of closest approach
To Estimate a maximum size of a nuclear radius
What is electron diffraction used for
Estimating nucleus radius
What must happen to electrons to get them to diffract
There wavelength must be around 10(-15), therefore they must have a high energy by accelerating them to a high speed
How do you get an electron beam to diffract
Fire it at a material 1 atom thick
What does the diffraction pattern look like for an electron
A central bright maxima, with dimmer circular rings, the intensity will never be zero
What is an approx radius of an atom
0.05nm
What is the approx radius of a nucleus
1fm
What is the relationship between radius and nucleon number
Radius is dp to the cube root of the nucleon number
What is alpha absorbed by
Paper or a few cm of air
What is the range of beta
It’s absorbed by 3mm of aluminium or a metre or so of air
What is gamma absorbed by
Many cm of lead or a several m of concrete
What is beta radiation used for
Thickness measuring
What is alpha radiation mainly used for
Smoke detectors
When is alpha very dangerous
If it’s ingested as it will ionise body tissue
What are two uses of gamma
- radioactive tracers
- treatment of cancerous cells by means of a rotating beam
What causes background radiation
1) radon gas in the air from rocks
2) rocks in building and the ground
3) cosmic rays
4) living things containing c-14
5) medical uses
6) radioactive power
7) radioactive weapons
What happens to the intensity of gamma with distance
Intensity is proportional to the square of the distance from the source
What is activity
The number of nuclei that decay per second
What is the unit of activity
Becquerels Bq
