What are thermal neutrons?
- thermal neutrons have low energies or speeds (e.g 0.03 eV)
What is meant by self sustaining chain reaction?
- fission reaction gives out neutrons
- neutrons (from fission) cause further fissions
- self-sustaining when one fission leads to (at least) one further fission
What is involved in the process of moderation?
- neutrons from fission are fast (high energy) neutrons
- fission most favourable with low energy neutrons
- moderation involves slowing down neutrons
- by collision with moderator atoms
- large number of collisions required
- collisions are elastic
- graphite/water as moderator
- moderator atoms should have (relatively) low mass
How is the rate of fission controlled in a nuclear reactor?
- control involves limiting number of neutrons
- excess neutrons absorbed by control rods
- boron/cadmium control rods
- control rods inserted into reactor to slow reaction rate
What is the binding energy of a nucleus?
- the amount of energy required to separate a nucleus
- into its separate nucleons
What is induced fission?
- splitting of nucleus into two smaller nuclei
- brought about by bombardment (of neutrons)
Explain what is meant by persistence of vision and state a practical situation where it is important
- image remains after stimulus is removed
- e.g optical illusions
Define the threshold of hearing, Io
- minimum intensity heard by a normal ear
- at 1kHz
How would you reduce contact resistance in an ECG trace?
- sandpaper skin to remove hair and some dead skin
- apply conducting gel
- securely attach more than one electrode
In an ECG trace how do remove any un wanted signals?
- electrodes should be non-reactive
- patient needs to remain relaxed and still
- shielded leads
Give properties of an amplifier in an ECG trace
- has large input impedance
- the frequency response should be even across the frequency range otherwise the output voltage from the amplifier will be distorted
Give the events in order that cause the maximum points on an ECG trace
- depolarisation of atria
- depolarisation of ventricles (and repolarisation of atria)
- repolarisation of ventricles
In an X-ray intensity vs photon energy graph, there are a few vertical peaks, Explain the process that cause them
- electrons strike anode and excite/ionise the target atoms
- excited electrons fall to inner energy level
- fixed energy gaps produce fixed energy photons
Explain how the intensifying screens achieve their purpose and state their benefit to the patient
- convert X-ray photons to light photons
- light photons expose film in the correct place due to the closeness of the screens to the film
- reduces the intensity of radiation to the patient due to less contact time
