Nuclear A2 Flashcards by Chris Abraham

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.

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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

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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

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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

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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

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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

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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

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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

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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.

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How can the decay of count rate from a gamma source be modelled as

Inverse square graph

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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

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What are the hazards of ionising radiation

Damage cells and DNA. Cause cancerous cell mutations

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What is background radiation

Naturally occurring radiation from rocks, soil and the air. An example is radon gas.

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How should radioactive materials be safely stored away

Lead-line containers

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How should radioactive materials be used

No contact with the skin, tongs used, lead aprons

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What is the half life

Time taken for the number of decaying nuclei to halve

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What is the activity

The number of nuclei of the isotope that decays per second

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What happens to the activity after 1 half life

It halves

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What is the unit of activity

Bacquerel (Bq)

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What is the decay constant

Probability of a nuclei to decay in one second

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What are the axis on the N-Z graph

N is neutrons and Z is protons

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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