Topic 3 - Radioactivity and Atomic Structure Flashcards
What were the first ideas about atoms
- John Dalton thought that atoms were tiny balls of matter that couldn’t be broken up
Describe the plum pudding model
A ball of positive charge with negatively charged electrons embedded in it
What was the gold foil experiment
- Positively charged alpha particles were fired at a thin gold foil
- Circular detector screen surrounding gold foil detects alpha particles deflected
What results were Rutherford expecting?
- most of the alpha particles would pass straight through or some would be very slightly deflected ( < 1°)
Results of alpha particle experiment
- most alpha particles went straight through as expected
- however some were reflected more than expected
- a few alpha particles were reflected straight back at them
What did this explain?
- most of the atom was empty space because most alpha particles passed through
- nucleus must have large positive charge as some particles reflected/deflected by big angle
- nucleus must be small as very few particles were deflected/ reflected
2 differences between nuclear model and plum pudding
- nuclear model has positive charge concentrated in small nucleus but P.P has it spread out
- nuclear model is mostly empty space but P.P is a ‘ solid mass ‘
3 developments to nuclear model
- Niels Bohr discovered that electrons orbit nucleus at certain distances in shells : this stopped atom collapsing
- nucleus could be split into a group of atoms with positive charge(protons)
- James Chadwick proved existence of neutral atoms in nucleus( neutrons)
what happens when an atom absorbs/emits EM radiation?
- when an atom absorbs EM radiation electrons move to a higher energy level : further
- when an atoms emits EM radiation electrons move to a lower energy level : closer
ion
atom that has lost or gained electron(s)
isotopes
different form of same element with same no. of protons but different no. of neutrons
Radioactive decay
when unstable nuclei emit radiation to try and become stable
random nature of radioactive decay
- you don’t know which nuclei is going to decay
- and when they are going to decay
alpha particle
2 protons, 2 neutrons ( helium nucleus )
properties of alpha particles
- low penetration
- high ionising power
- travels few cm in air
- absorbed by a tissue/ skin cells
beta particle
electron ejected from unstable nucleus
properties of beta particles
- medium penetration
- medium ionising power
-travels few metres in air - absorbed by a sheet of aluminium
gamma decay
high frequency EM radiation released by unstable nucleus
properties of gamma decay
- high penetration
- low ionising power
-travels few miles in air - absorbed by thick layer of concrete
activity
how many radioactive decays happen per second ( Bq)
what is a Geiger Muller tube
records the amount of radiation counts detected per second and measures activity
half-life
The time it takes for the number of nuclei ( or activity ) of a radioactive isotope to halve
dangers of short half-life
- initially they can be dangerous due to the high amounts of radiation they emit at the start
- activity falls quickly and and they quickly become safe
dangers of long half-life
- in the short term they aren’t so dangerous
-in the long term this is dangerous because nearby areas are exposed to radiation for millions of years
irradiation
exposure to radiation from a radioactive source
how to minimise risk of irradiation
- keep sources in lead- lined boxes ,
- standing behind barriers
- using remote controlled arms to handle sources
contamination
unwanted presence of radioactive atoms on or in another material
how to minimise risk of contamination
- gloves and tongs when handling sources
- protective suits
Why is beta and gamma the main concern with irradiation
- beta and gamma have higher penetration power so can pass through the body and get to delicate organs
- alpha particles can’t penetrate skin and easily blocked by small air gap
- high levels of irradiation from bet and gamma are most dangerous
Why is alpha the main concern with contamination
- higher ionising power and do all their damage in localised area
- they don’t pass through the body so just stay in the body doing damage
- higher chance of causing mutations which can cause cancer
- beta and gamma pass through the body without doing much damage as they have a lower ionising power
radiation dose
measure of the risk of harm to the body due to radiation
background radiation
low-level radiation that is present at all times
sources of background radiation
- naturally occurring unstable isotopes ( air, rocks )
- cosmic rays from space
- man made sources ( nuclear disasters like chernobyl )
effect of location
-people who live in higher altitudes are exposed to more cosmic rays
-people living in places with a lot of radioactive rocks like Cornwall
effect of occupation
- uranium miners are exposed to a lot of radiation so need to wear face masks and protective clothing
- miners due to lots of rocks
ionising radiation effects on living cells
- knock electrons of cells and changes and damages DNA
- this causes mutant cells which divide uncontrollably
- making tumours and causing cancer if it spreads
- high dose can kill cells completely causing radiation sickness
using radiation - medical tracers
- radioactive isotopes injected into people
- their progress around the body is followed using detector which shows where the strongest reading come from
- this makes sure that internal organs are working properly
what type of isotopes should be used ( gamma )
- they aren’t highly ionising and won’t do damage in localised area
-they pass directly out of body as well
what type of isotopes should be used ( short half life )
- radioactivity inside patient quickly disappears
using radiation - medical tracers - radiotherpay
- focusing ionising radiation on cancer cells to kill them
- must be directed carefully and at right dosage to not kill too many helathy cells
nuclear fission
when a large unstable nucleus splits into two smaller ones ( usually has to absorb neutron)
nuclear chain reaction
- nucleus absorbs a neutron
- it releases energy and splits into two smaller nuclei, also releasing 2 or 3 neutrons
- those neutrons will collide with other nuclei and start the process over again
nuclear fusion
- two light nuclei combine to form a heavier, bigger nucleus and also releases energy
