Radiation Flashcards
What is radioactive decay?
When nuclear radiation is emitted by unstable atomic nuclei to become more stable.
What sort of process is radioactive decay?
Random
What is ionisation?
When radioactive decay causes electrons to be expelled from atoms
What is an alpha particle?
Two protons, two neutrons
What happens to the nucleus when an alpha particle is expelled?
Loses 2 protons and 2 neutrons
What is the ionising power of alpha particles?
Highest
What is the range of alpha particles?
Travels a few cm in air
What are alpha particles stopped by?
A sheet of paper
What are beta particles?
Fast moving electrons
What happens to the nucleus when a beta particle is expelled?
A neutron becomes a proton and an electron
What is the ionising power of beta particles?
High
What is the range of beta particles?
Travels ~1m in air
What are beta particles stopped by?
A few mm of a aluminium
What is gamma radiation?
Short wavelength, high frequency EM radiation
What happens to the nucleus when gamma radiation is expelled?
Energy is transferred away from nucleus
What is the ionising power of gamma radiation?
Low ionising power
What is the range of gamma radiation?
Virtually unlimited range in air
What is gamma radiation stopped by?
Several cm of thick lead, metres of concrete
What is the decay equation for an alpha particle?
A,ZX -> (A-4),(Z-2)Y + 4,2α
What is the decay equation for a beta particle?
A,ZX -> A,(Z+1)Y + 0,-1β
What is the decay equation for gamma radiation?
A,ZX -> A,ZX + 00γ
What is activity?
The rate of decay of an unstable nucleus
What is activity measured in?
Bq (becquerel)
What is count rate?
The number of decays detected per second
How do we calculate count rate?
Count rate after n half-lives = initial count rate/2ⁿ
What is half life?
The time it takes for:
1. Half the number of unstable nuclei in a sample to decay
2. Cours rate or activity of a source to halve
How do you calculate net decline?
Reduction in activity/original activity
What is irradiation?
When an object is exposed to nuclear radiation
What is contamination?
When atoms of a radioactive material are in or on an object
How can you prevent irradiation?
Shielding, removing, moving away from source of radiation
How can you remove contamination?
It is very hard to remove - object remains exposed to radiation as long as it is contaminated
How can we protect against irradiation and contamination?
- Maintain distance from radiation source
- Limit time near source
- Shielding from radiation
What should be done on all studies of radiation published?
Peer review
Why is ionising radiation dangerous?
Can kill or damage living cells
What does the risk of a radioactive source depend on?
Its half-life, type of radiation
Why is alpha radiation more dangerous inside the body than on the outside?
Inside: affects all surrounding tissue
Outside: only affects skin and eyes as cannot penetrate further
What is radiation dose?
Measure of health risk of exposure to radiation
What is radiation dose measured in?
Sieverts (Sv)
What is background radiation?
Radiation around us all the time
Where does background radiation come from?
- Natural sources (rocks, cosmic rays)
- Nuclear weapons, accidents
Name 2 ways nuclear radiation is used in medicine.
- Tracers
- Control or destruction of unwanted tissue (e.g: tumours)
How are tracers used in medicine?
- Gamma-emitting tracers injected or swallowed by patient
- Gamma cameras create image showing path of tracer
Why must the half life of a tracer be short?
So most nuclei will decay shortly after image is taken -> limit reaction dose
Describe 1 way radiation is used to control/destroy unwanted tissue.
Narrow beams of gamma radiation focused on tumour cells to destroy them.
Why is gamma radiation used to destroy tumour cells?
Can penetrate from outside body - high penetrative ability
Describe another way radiation is used to control or destroy unwanted tissue.
Beta or gamma-emitting implants surgically placed inside/next to tumours
Why is the half life of beta/gamma-emitting implants important?
Half lives must be long enough to be effective, but short enough to not irradiate patient after treatment.
What is nuclear fission?
When a large, unstable nucleus absorbs an extra neutron, then divides into two smaller nuclei.
What happens during nuclear fission?
- Gamma radiation emitted and energy released
- 2-3 neutron emitted -> can cause chain reaction
How are chain reactions in power stations controlled?
Absorbing neutrons
What are nuclear explosions?
Uncontrolled chain reactions
What is spontaneous fission?
When an unstable nucleus splits apart without absorbing a neutron
