Radioactivity & Particles Flashcards
Components of an atom
Protons, neutrons, electrons, electron shells
Location, relative mass and relative charge of protons, neutrons and electrons
- protons = 1mu, +1, nucleus
- neutrons = 1mu, 0, nucleus
- electrons = 1/1836mu, electron shells
How does an atom become an ion
Electron loss or gain
Which number is unique to each element?
Proton/atomic number
Define atomic number
Number of protons in atom
Define mass number
Total number of protons and neutrons
Define isotope
An atom with the same number of protons but different number of neutrons
What never changes in an isotope?
Atomic number
Why do nuclei decay?
To become more stable, due to a variety of reasons :
- too many neutrons
- too big (too many protons + neutrons)
- too much energy
What type of process is decay and why?
Decay is a random process ; we cannot predict which unstable nucleus in a radioactive isotope will decay or when that decay will occur
What happens to unstable nuclei when they decay and why?
They give off radiation in the form of alpha, beta or gamma in order to release energy
What makes radiation ionising?
They have enough energy to ionise atoms by stripping electrons off them when they interact
Properties of alpha
- 2 protons + 2 neutrons
- charge = +2
- relative mass = 4
- ionising power = high bc they lose energy quickly + interact w/ atoms a lot due to size and energy
- penetrating power = low
- stopped/absorbed by = paper or card
- range in air = 2-3cm
Properties of beta
- high energy electron
- charge = -1
- relative mass = 1/1836mu
- ionising power =moderate
- penetration = moderate
- stopped/absorbed by = thin aluminium foil
- range in air = around 1m
Properties of gamma
- electromagnetic wave
- relative mass = almost 0
- charge = 0
- ionising power = low
- penetration = high
- stopped/absorbed by = thick lead + concrete but it’s hard to stop
- range in air = 1km+
Alpha damaging and penetration
As it’s a big heavy particle, it loses a lot of its energy very quickly. This means that, whilst it does cause lots of damage, it cannot penetrate very far
Beta damage and penetration
As it’s small, it has a greater penetration than alpha but won’t cause as much damage
Gamma damage and penetration
Electromagnetic wave means that it’s not very ionising but has lots of penetration and can travel for miles before being fully absorbed
Describe the investigation about penetration of different radiation
- measure the cps of each source beforehand over 5 minutes to compare against
- place alpha source with paper, beta with thin foil, gamma with thick lead
- they will all drop to background radiation as the materials all absorb those radiations
What does the GM tube do?
Geiger-muller tube detects radiation
What does the radioactive source do?
Emit radiation
What does the counter do?
Records the quantity of radiation penetrating through the materials
Define background radiation
Radiation that is ever present and cannot be removed
What is the purpose of measuring over a long period of time?
As decay is random, a longer count period improve accuracy by reducing random error
Activity level is measured in…
Counts per second (cps)
Range in air of alpha
A couple of centimetres
Range in air of beta
25cm-1m
Range in air of gamma
Km+
What happens to the nucleus in an alpha decay
2 protons + 2 neutrons are ejected from nucleus so atomic number decreases by 2 and mass number decreases by 4
What happens to the nucleus in a beta decay?
A high energy electron is ejected from the nucleus and a neutron has tuned into a proton , meaning that the atomic number increase by 1 and mass number stays the same
What happens to the nucleus when gamma passes through it?
Nothing
What happens to the nucleus during a neutron decay?
Neutron(s) leave the nucleus meaning that the proton number is unchanged and the mass number decreases by however many neutrons are emitted
How is ionising radiation detected in a lab?
By a GM tube detects radiation
What does the radiation badge do? How do they work?
- monitor exposure and warn if there are unsafe levels of radiation
- photographic film changes colour when exposed to different types of radiation
What percentage of background radiation sources are artificial and natural?
80% are natural and 20% are artificial
What are the sources of artificial background radiation?
- 17.5% medical
- 0.5% nuclear power + weapons testing
- 2% other
What are the sources of natural background radiation?
- 40% radon gas from the ground
- 15% buildings + ground
- 10% cosmic rays
- 15% humans + food + drink
What happens to number of undecayed nuclei of a radioactive source over time?
Decreases
What happens to decay rate over time?
Decreases
Definition of half life in terms of undecayed nuclei
The average amount of time taken for the number of undecayed nuclei in a radioactive sample to halve
Definition of half life in terms of activity levels
The average time taken for the activity levels in counts per second to fall to half its original value
Irradiation
When something is exposed to the ionising radiation from a radioactive source. When the source is removed, the irradiation stops
Contamination
When the radioactive source gets into/ onto something so it’s being exposed continually
How do alpha emitter smoke detectors work?
- alpha emitter ionises air between charged plates that allow current to flow
- when detector senses current, the alarm doesn’t sound
- smoke enters the case and absorbs alpha = no ionsisation of air
- detector senses drop in current so the signal is sent for alarm to sound
Why is alpha suitable for smoke detectors? Why is a long HL required? Why can’t you dismantle an alpha emitter smoke detector?
- very ionising = effective ionisation of air + low penetrating power = can’t pass through the hard plastic case
- long HL = steady activity level + so doesn’t need replacement often
- dismantle = potential contamination by inhaling or ingesting accidentally
How is beta used in a foil factory?
If too much beta is detected, then the foil is too thin. If too little is detected, then it’s too thick
Why is beta good for foil factory usage? Why does it need a long HL?
- alpha wouldn’t penetrate foil and gamma would either way and beta does but less as thickness increases
- long HL = less replacement + more regular activity levels
How does gamma help in leaky pipe detection?
- gamma emitter is dissolved into water
- gamma radiation is detected on surface bc of high penetration
- higher levels of radiation = cracked pip as water is closer to surface
Why is gamma good for leaky pipe detection? Why does it need a short HL?
- weakly ionising = less danger posed + high penetration = more likely to pass through the ground
- short HL = quickly decays to a safe level by the time it reaches people’s homes
How is gamma used in sterilisation of surgical equipment?
- surgical equipment or food is sealed and remains sealed meaning that it is only irradiated
- gamma can kill unwanted bacteria and microorganisms
Why is gamma suitable for sterilisation of food and surgical equipment? Why is it safe to use these after?
- gamma can penetrate through package and kills bacteria
- Food and equipment has been irradiated not contaminated so it is not emitting radiation
How is gamma used in radiotherapy?
Gamma emitter is directed at cancerous cells repeatedly from multiple angles to ensure that healthy cells are not exposed
Why is gamma suitable for radiotherapy?
- it can penetrate through tissues to reach cancerous cells but is still not ionising so will not cause cell damage
- alpha would not penetrate and beta would be too ionising
What are the dangers of ionising radiation?
DNA is ionised which damages it and causes mutations and risks cancer. It can also kill cells
What are the three ways to limit exposure to ionising radiation?
- Increasing distance from radioactive source
- limiting exposure time and use of radioactivity detecting badges
- Shielding through the use of lead aprons for example
How does ionising radiation ionise a material?
Ionising radiation collides of atoms which become ionised because their electrons are stripped off causing the radiation to lose some of its energy
Why does alpha radiation have the strongest interaction with atoms in comparison to beta or gamma?
Alpha has the strongest interactions as it has the greatest charge of +2 in comparison to beta with minus one charge and gamma with no charge or or mass
Why is Alpha the most ionising?
Loses its energy at a faster rate as they lose more energy per interaction with other atoms in comparison to beta or Gamma
How are nuclear reactions used as a source of energy?
- thermal energy is released from nuclear reactions which can be used in power stations
- heat boils water into steam and the steam turns the turbine which turns the generator and generates electricity
Describe the process of nuclear fission
Parent nuclei absorbs a neutron, this causes it to become unstable. Parent nuclei then splits into smaller daughter nuclei and spare neutrons are also emitted as well as gamma radiation and excess energy
How how does one fission event cause a chain reaction?
Multiple spare neutrons from each fission event can go onto collide with other large nuclei causing an exponential growth in the number of events unless controlled
Nuclear fuel rod function
Rod containing radioactive material and allows spare neutrons to travel to neighbouring rods to continue fission events
Movable control rod function
Lowered into core to control the rate of chain reaction by absorbing excess neutrons
Graphite core/moderator
Absorb some energy of neutrons so that they are more likely to cause fission in next rod
Coolant function
Transfer thermal energy to nearby boiler to drive turbines and generators
