Nuclear A2 Flashcards
Describe Rutherford’s scattering experiment
He fired alpha particles at a thin gold foil. Detectors were placed at an equal distance around the gold foil to find how the alpha particles deflect.
What were some observations that Rutherford made
Most alpha particles passed straight through the foil. A small percentage of particles deflected by more than 90 degrees
So how was the atom described after Rutherford’s findings
The atom is mostly empty space and the centre of the atom contains all the positive charge as a nucleus
How was the deflection from the magnetic field used to describe different types of radiation
Alpha and beta particles deflect in opposite directions and gamma doesn’t deflect. This meant that alpha particles are positive, beta particles are negative and gamma doesn’t have a charge as they are photons
Describe the ionisation experiment
A radioactive source is directed at a closed chamber full of air particles. The radioactive particles produce ions and these are attracted to the electrode, allowing for electrons to travel through the circuit and create a current
What was learnt from the ionisation experiment
Alpha particles are more ionising but has a short range. Beta particles are less ionising but has a longer range. Gamma is least ionising due to the lack of charge
Describe the absorption test
A radioactive source is fired at a a abosrber then to a geiger tube. The geiger counts the number of particles of radiation. This is converted into count rate and drawn on a graph against thickness of the absorber
What was learnt from the absorption test
Alpha radiation is absorbed completely by paper. Beta particles are absorbed completely by 5mm of metal. Gamma radiation is absorbed completely by several centimeters of lead
What are the ranges of radiation
Alpha has a range up to 100mm. Beta has a range up to 1m. Gamma range is unlimited but the count rate decreases over time as the radiation spreads in all directions.
How can the decay of count rate from a gamma source be modelled as
Inverse square graph
How can the inverse square law be shown mathematically
Intensity of radiation = radiation energy per second/total area = nhf/4πr^2. So, intensity is proportional to 1/r^2
What are the hazards of ionising radiation
Damage cells and DNA. Cause cancerous cell mutations
What is background radiation
Naturally occurring radiation from rocks, soil and the air. An example is radon gas.
How should radioactive materials be safely stored away
Lead-line containers
How should radioactive materials be used
No contact with the skin, tongs used, lead aprons
What is the half life
Time taken for the number of decaying nuclei to halve
What is the activity
The number of nuclei of the isotope that decays per second
What happens to the activity after 1 half life
It halves
What is the unit of activity
Bacquerel (Bq)
What is the decay constant
Probability of a nuclei to decay in one second
What are the axis on the N-Z graph
N is neutrons and Z is protons
What occurs for lighter isotopes
They mostly follow the line N=Z
What occurs as Z increases above 20
Nuclei gain more N than Z to help bind the nucleons together and stop the repulsive electrostatic forces between protons
Where are the alpha emitters on the N-Z graph
Where Z is higher than 60, the nucleus is too large and the strong nuclear force is unable to overcome the electrostatic forces
Where are the beta- emitters on the N-Z graph
These are on the left of the stability belt where they are neutron rich
Where are the beta+ emitters on the N-Z graph
These are on the right of the stability belt where they are proton rich
What is technetium used for
This is used in a generator in hospitals to produce a source which emits gamma radiation only
What are the ways we can estimate the radius of the nucleus
Closest approach of alpha particles and electron diffraction
How can we estimate the radius of the nucleus using alpha particles
Alpha particles begin with a certain amount of energy and approach. As it gets closer to the nucleus, it slows down and gains potential energy. The closest distance from the nucleus is an upper limit for the radius
How can we estimate the radius of the nucleus using electron diffraction
Sin(θ) = λ/d where θ is angle to first minimum and d is the nucleus diameter
How to find the equation for density of a nucleus
Use the equation for radius in the nucleus. Volume is 4πR₀³/3. Mass as Am, where A is atomic number and m is mass of 1 nucleon
How does the graph of intensity against angle of deflection for electron diffraction look
Largest peak at θ=0. Goes down unit first minimum, then goes up but lower than max…
What is the binding energy
Work that must be done to separate a nucleus into its constituent neutrons and protons
What is the mass defect
Change in mass of separated nucleons and the mass of the nucleus
What is binding energy per nucleon
Average work done per nucleon to remove all nucleons from a nucleus (measures stability)
Describe the graph of mass number against binding energy per nucleon
Steep increase at the beginning, then slow decrease. Peak is 8.7MeV per nucleon at A = 56
Where do atoms undergo fusion and why
Atoms can fuse when A < 56 as fusing these to form a larger atom will increase its binding energy, therefore making it more stable
Where do atoms undergo fission and why
Fission undergoes when A >56 as a large nucleus splitting up will decrease the mass of each one, so increasing its binding energy, therefore making it more stable
What is the proof of fusion producing more energy than fission
The change in binding energy in fission is 0.5MeV and fusion can be more than 5MeV
What is an atomic mass unit
Equal to one twelfth of the mass of an carbon-12 isotope
What is induced fission
When thermal neutrons are fired at large nuclei, causing them to fission and split up
What is meant by a chain reaction
After fission, multiple daughter nuclei can be released causing further fission and so on
What is the energy released in fission
Equal to the change in binding energy
What is critical mass
Minimum mass of a fissile material to continue a chain reaction
What occurs if the mass is less than the critical mass
Too many of the neutrons will escape due to the much higher surface area to mass ratio
What are the main parts in a nuclear reactor
Reactor core, control rods, coolant and moderator
What is the function of control rods
To absorb neutrons and the height is controlled to keep the number of neutrons in the core constant
What is the function of the coolant
Used to remove heat and transfer it to electrical generators. Water at high pressure
What is the function of the moderator
So neutrons can be slowed down to actually cause fission. If neutrons travel too fast, this will not causing fission
Examples of materials used for coolant
CO2 and H2O
Examples of moderator
Graphite and water
Examples of control rods
Boron
What are some safety features of a nuclear reactor
Fuel stored in steel cans, reactor core is thick steel to absorb temp and radiation, remote handling of fuel, emergency shut down system of fulling submerging control rods to stop fission
How is radioactive waste stored
Firstly stored underwater, then stored in large steel casks, unused uranium stored for further use
