Radioactivity Flashcards
Isotopes
Different number of neutrons
Alpha decay
- helium nucleus
A A-4 4
X -> Y + He
Z Z-2 2 - has a range of a few cm, absorbed by a thin sheet of paper.
Beta decay
- when a neutron changes into a proton and a high energy electron
A A 0
X -> Y + B
Z Z+1 -1
- range up to 1 metre
- absorbed by approx 5mm of aluminium
Gamma decay
- electromagnetic radiation, high-frequency
- absorbed by thick lead
Natural sources of radiation
- granite
- cosmic rays
- man made stuff (nuclear reactors)
Medical tracers
- Chemical compound which emits gamma radiation
- either swallowed or injected
- short half life
Medical treatment
Beta radiation to kill cancer cells
What detects radioactivity
Geiger - muller detector / photographic film
Radioactive decay
- Random process
- original element is patent
- New element is daughter
Half life
Measured in:
- counts per minute
- becquerels (Bq)
T = n x T1/2
T = time N = number of decays T1/2 = half life
Sterilisation
By heat, steam, gramma rays
- kills bacteria and other organisms
- fragile items like food/medical equipment is sterilised in its packaging with gamma radiation
Radiometric dating
When you compare the activity rate in a current sample of material to the activity rate in an older sample.
- age can be estimated using a half life curve
Radiocarbon dating
Specific radiometric process that uses carbon-14 (present in air and is radioactive)
- stays in living things where level stays constant as decaying atoms are replaced with new ones
- when something dies, carbon-14 decays but is not replaced so level falls and we are able to estimate the age of the material
Thickness control
Material absorbs radiation + changes levels detected
- Alpha: Thin sheets e.g cling film
- Beta: Sheets e.g card/rolled steel
- Gamma: Thick sheets e.g Lead/steel beams
Dangers of radiation
Burns + mutations:
Alpha particle stay in the body, destroy cells and cause mutations which can lead to death.
Handling:
- avoid handling, use robots
- checks every three months
- warning badges (they change colour)
- Dosimeters (display total radiation received)
- special protective clothing (lead lined)
Rutherford atom + experiment
He used an alpha emitter and fired alpha particles at thin gold leaf.
Most alpha particles went straight through, some particles got deflected and very few got reflected. Because of this he deduced that the atom was mostly made of space with a positive nucleus and negative electrons
Fission
- occurs when a slow-moving neutron is absorbed by the nucleus (fast moving neutrons will not be absorbed)
Neutron -> uranium nucleus -> splits into 2 daughter nuclei and more neutrons (1 or more)
- called a chain reaction, if it isn’t controlled, a nuclear explosion will occur
Contamination
- radiation is highly penetrating
- lead, steel or concrete lined containment vessel used to prevent radiation from escaping and to withstand an explosion
Waste products
- 97% fuel can be re-processed
- 3% is waste
- Sellafield, UK’s nuclear waste re-processing plant
Nuclear reactors
- use nuclear fission to generate heat
- The heat is used to create steam plus drive turbines
- The turbines are linked to generators
- work using fuel rods (the fuel is a radioactive isotope of uranium)
- uranium formed into cylindrical pellets which are stacked in hollow metal rods (4m long)
- 100 rods are bundled together into a fuel rod, 1000’s of fuel rods make a reactor core.
Moderators
E.g carbon/ graphite
- used to slow down the neutrons for fission
- absorbs neutrons
Control rods
E.g cadmium
- neutron absorbing material inserted into spaces between fuel rods to almost stop reaction
- fully lowered -> reaction nearly stops -> not much heat
Define half-life
It is the time taken for half of the radioactive atoms to decay
Why are the alpha particles most ionising
- alpha particles have less penetrating power
- alphas have more charge
- Alphas cause more ionisation
- alphas have more mass
- alpha particles are more likely to collide with atoms as they’re larger
- slowing force on alpha particles is larger
