Nuclear Flashcards
Describe Rutherford’s experiment
He fired a beam of alpha particles at thin gold foil, which was surrounded by a circular screen detector, which was used to detect alpha particles deflected at any angle
What did Rutherford find and what did he expect
They expected that the alpha particles would be deflected, instead 99.5% of the alpha particles went straight through the foil, while a small number were deflected by a large angle.Some were even deflected by more than 90 degrees
From Rutherford’s experiment what did he conclude
- Atoms have a small positively charged nucleus at the centre
- Most of the atom must be empty space because most of the alpha particles passed straight through
- The nucleus must have a large positive charge
- The nucleus must be small
- Most of the mass must be in the nucleus
How does J.J Thomson’s theory differ to Dalton’s
Dalton believed that matter was made up of tiny spheres that couldn’t be broken up, and that each element was made up of a different type of atom
Whereas Thomson suggested that atoms were spheres of positive charge with tiny negative electrons (Plum Pudding Model), and that electrons could be removed
Factors that affected the accuracy of Rutherford’s experiment
- The location of the alpha source meant that it was impossible to detect a head on collision resulting in a scattering angle of 180
- He assumed the only force between the alpha particle and gold nucleus was electrostatic, but alpha particles contain Hadrons meaning they will also interact via the strong force
- The finite size of the alpha particles introduces an uncertainty in the calculation of the closest approach
What is Alpha’s range in air
Up to 10cm
What is Beta’s range in air
About 1m
What is Gamma’s range in aie
10’s-100’s of metres
How are the types of radiation effected by magnetic fields
Alpha= Deflected as charged Beta= Deflected significantly as low mass Gamma= No effect
Uses of alpha
Smoke Detector
Uses of Beta
PET scanners
Rolling out metals
Uses of Gamma
Radiotherapy
Medical Tracers
Sterilisation of Equipment
Define Intensity
Intensity of electromagnetic radiation is the radiation energy passing per second through an area of 1m^2 normal to the radiation
What is the inverse square law for Gamma radiation, and what does it assume
I=k/x^2
As it spreads out in a spherical direction
It assumes that while the gamma intensity is being measured the source activity is unchanged so only works for sources with a long enough half-life
Origins of background radiation
- Radioactive Radon gas released from some rocks such as Granite
- Cosmic Rays
- Medical Applications
- Radioactive isotopes in living things
- Waste from nuclear industry and fallout from nuclear weapons testing
Define Background Radiation
A radiation does rate at a specified location, which is generated by natural and artificial ionising radiation sources existing in the environment
How do you calculate corrected count rate
Corrected Count rate= Measured count rate - Background Count Rate
What is radioactive decay
It is the process by which an unstable nucleus loses energy by emitting radiation. The decay is a random event, however if a large enough number of atoms are studied it is possible to predict the most likely proportion of them that will decay in a given time
What is the decay constant
The probability of an individual nucleus of a particular radioisotope decaying per second
What is activity and what’s its symbol
The number of decays per second, Bq
Define Half-Life
The average time taken for half of the radioactive nuclei in a sample to decay
2 formulas to calculate number of moles
No. of Moles= Mass/Molar Mass
No. of Moles= No. of Particles/ Avogadro’s Number
When is a nucleus unstable
- It has too many neutrons
- It has too few neutrons
- Its too heavy
- It has too much energy
Typical value for nucleus radius
x10^-15
How can we estimate nuclear radius
- Closest approach of alpha particles
- Through electron diffraction
What does the formula E=mc^2 show
That the mass of a body is a measure of its energy content, if the energy is transferred to or from a body, its mass changes
Define the atomic mass unit
Being 1/12th of the mass of 12g of Carbon-12
state what is meant by binding energy, and explain how it arises,
The binding energy of a nucleus is the energy needed to separate the nucleus into its constituent nucleons.(or the energy released when the nucleus is formed from individual nucleons) The potential energy of the nucleons decreases when they come together under the strong force.
What is the critical mass of fuel
The minimum mass required to establish a self-sustaining chain reaction
Why is energy released during fission
Because the new smaller nuclei will have a higher binding energy per nulceon
What is fission
It is splitting nucleons into smaller parts
`How can you induce fission
By making a neutron enter a Uranium-235 nucleus, causing it to become unstable- only thermal neutrons can be captured in this way
What is the function of a moderator in a thermal reactor plant
-It absorbs excess energy, slowing down the fast fission neutrons
What materials are used for moderators and why
Carbon Dioxide, Water and Lithium
The must have a low probability of absorbing neutrons. Choosing a moderator with a similar mass to the neutrons is more efficient at slowing neutrons down
What is the function of control rods
Absorbs neutrons to control the rate at which fission occurs
What material is used for control rods and why
Commonly Boron as it has a high probability of absorbing neutrons
What is the function of the coolant
It is the material that passes through the reactor, and absorbs the heat energy generated by fission. The heat energy is transferred to convert water into high pressure steam
What material is used for the coolant and why
Water or Carbon Dioxide gas
The material must have a high specific heat capacity or be able to be pumped very quickly around the system
What’s the difference between a fast neutron and a thermal neutron
A thermal neutron is in thermal equilibrium with its surroundings,, is much slower and has less KE than a fast neutron
How is High Level Waste Stored
Stored as liquid in water cooled tanks. Requires thick concrete to shield operators from high levels of radiation
His is Intermediate Level Waste stored
Some stored in vaults, and some mixed in cement inside stainless steel drums. Requires thick concrete walls to shield operator
How is Low Level Waste Stored
Compacted to a fraction of its original volume and stored in steel drums in concrete vaults
