Section 3 - Radioactivity and Astronomy Flashcards
What did JJ Thomson discover?
The atom has smaller bits
How did JJ Thomson discover what he discovered?
The atom can lose an electron
What did JJ Thomson suggest?
The ‘plum-pudding’ model
What did Rutherford do?
Fired alpha particles at a thin gold foil
What did Rutherford find following his experiment?
That most particles went straight through
Some were deflected more than they expected
Some were deflected back the way they had come
What did Rutherford theorise based off his findings?
That the mass of the atom was concentrated in the center which was positive and most of the atom is empty space
Whats part of our current model of the atom?
Protons and neutrons in the nucleus
Electrons in fixed orbits at set distances from the nucleus
What is the relative mass of an electron?
0.0005
Describe how the radius of an atom compares to the radius of its nucleus?
The radius of the atom is about 10,000 times bigger than the radius of the nucleus
How do electrons move up to a higher energy level?
By absorbing EM radiation
What will happen to an electron once it moves up a shell?
It will quickly fall back to its original energy level and in doing so will lose the same amount of energy it absorbed
How is the energy carried away once an electron falls down an energy level?
EM radiation
What determines the type of EM wave involved in electron levels?
The energy emitted
The higher the energy, the higher the frequency
What is most often released when electrons move back to their original level?
Visible light
Compare the energy difference from third - second and second - first electron level?
Third -> Second will release less energy, so a lower frequency wave than Second -> First
As you move further out from the nucleus, the energy level get _________
As you move further out from the nucleus, the energy level get closer together
As you move further out from the nucleus, the difference in energy gets ________
As you move further out from the nucleus, the difference in energy gets smaller
What will happen to an electron if it absorbs too much radiation?
It will leave the atom
What is ionising radiation?
Any radiation that can knock electrons from atoms
What is a positive ion and how is one formed?
An atom with more protons than electrons
A positive ion is formed when an outer electron absorbs enough energy that it leaves the atom
What are isotopes?
A type of an element with the same number of protons but a different number of neutrons
How many elements have isotopes?
All of them
How many stable isotopes are there usually per element?
One or two
What happens to unstable isotopes?
They tend to decay into other elements and give out radiation
Why do unstable isotopes decay?
To attempt to become more stable
What do radioactive substances ‘spit out’?
Gamma radiation
Alpha radiation
Beta radiation
Neutrons
What are alpha particles?
Helium nuclei (two protons and two nuetrons)
What is alpha radiation?
Alpha particles emitted from the nucleus of an atom
Describe how penetrative alpha radiation is?
Very weak
What stops alpha radiation?
A few cm of air
Thin sheet of paper
Describe how ionising alpha radiation is?
Strongly ionising
What makes alpha radiation so ionising?
It’s size
What can beta particles be?
Electrons or positrons
What is a beta-minus particle?
A fast moving electron released by the nucleus
What is a beta-plus particle?
A fast moving positron released from the nucleus
What is a positron?
The antiparticle of the electron
Describe the ionisingness of beta radiation?
Moderately ionising
Describe how ionising beta decay is?
Moderately ionising
What stops beta-minus decay?
Few meters of air
Absorbed by a sheet of aluminium (5mm thick)
What stops beta-plus decay?
Electrons
Compare the range of beta-plus to beta-minus decay?
Beta-plus’ range is much smaller
Why is the range of beta-minus much smaller?
Because when a positron hits an electron they destroy each other and produce gamma rays
What is annihilation?
The collision of a positron and an electron resulting in the destruction of both and the production of gamma rays
What happens to a nucleus once it has decayed?
It undergoes nuclear rearrangement and releases energy
Describe how penetrative gamma rays are?
Extremely
What stops gamma rays?
Thick sheets of lead
Meters of concrete
Describe how ionising gamma radiation is?
Weakly ionising
Why are gamma rays so ‘un-ionising’?
Because they tend to pass through rather than collide
For each of alpha, beta-minus and gamma radiations, give an example of a material that could be used to absorb it
Refer to the material’s thickness in your answer
Alpha - A thin sheet of paper
Beta-minus - A 5mm thick sheet of aluminium
Gamma - A thick sheet of concrete or meters of concrete
What are nuclear equations of way of showing?
Radioactive decay
What is the golden rule of nuclear equations?
The total mass and atomic numbers must be equal on both sides
What does alpha decay do?
Decreases the charge by 2 and the mass by 4
What does beta-minus decay do?
Increases the atomic number by 1
What does beta-minus decay involve?
A neutron changing into a proton and an electron
What does beta-plus decay do?
Decreases the atomic number by 1
What does beta-plus decay involve?
A proton changing into a neutron and a positron
What does neutron emission do?
Decreases the mass number by 1
What does gamma radiation do?
Nothing
Why does gamma radiation do nothing?
Because its a way of getting rid of excess energy
What type of radiation is given off in this decay? 8 3 Li -> 8 4 Be?
Beta-minus
Write the nuclear equation for 219 86 Rn emitted an alpha particle?
219 86 Rn -> 215 84 Po + 4 2 α
What do radioactive sources contain?
Radioactive isotopes that give out radiation
How can you predict how many will have decayed in a given time?
By using the half-life of the source
What is the activity of a radioactive substance?
The rate at which a source decays
What is activity measured in?
Becquerels Bq
What is 1 Bq equal to?
1 decay per second
What measures activity?
A Geiger-Muller tube
What are methods of detecting radiation?
A Geiger-Muller tube
Photographic film
How can you use a Geiger-Muller tube?
Count how many times it clicks
How can you use photographic film to measure radiation?
The more radiation the film’s exposed to, the darker it becomes
What happens as the unstable nuclei all steadily disappear?
The activity as a whole will decrease
What is half-life?
The average time taken for the number of radioactive nuclei in an isotope to halve
What are the important parts of the half-life definiton?
Average for number of radioactive nuclei to halve
What does a short half-life mean?
The activity falls quickly
How dangerous are short half-life substances?
Very as there will be a high amount of radiation at the stary
What does a long half-life mean?
The activity falls slower
The activity of a radioactive sample is measured as 640 Bq
Two hours later it has fallen to 40 Bq
Find its half-life
640/2 = 320 1 320/2 = 160 2 160/2 = 80 3 80/2 = 40 4
Two hours / 4 = 30 minutes
What will a graph of activity against time be shaped like?
An inverse proportion graph
How do you find the half-life of a substance from a graph?
By finding the time interval on the bottom axis corresponding to a halving of the activity on the vertical axis
A radioactive source has a half-life of 60h and an activity of 480 Bq
Find its activity after 240h
240/60 = 4
480/2 = 240 240/2 = 120 120/2 = 60 60/2 = 30
What does background radiation come from?
Human activity Cosmic rays Foods Buildings Rocks
Where do most cosmic rays come from?
The Sun
What are examples of human activity that contribute to background radiation?
Fallout from nuclear explosions
Nuclear waste
What is irradiation?
Exposure to radiation
How do you prevent irradiation?
Using lead-lined boxes
Standing behind barriers
Remote-controlled control
What do medical staff wear?
Photographic film badges to monitor their exposure
What does it mean when an object is contaminted?
Unwanted radioactive atoms have stuck onto an object
How could you prevent contamination?
Wearing gloves and protective suits
Using tongs
How does radiation damage cells?
By ionisation
Describe how radiation damages cells by ionisation?
Radiation can enter living cells and ionise atoms and molecules within them
What can lower doses of radiation lead to?
Minor damage without killing the cells this can rise to mutant cells which divide uncontrollably (cancer)
What can higher doses of radiation lead to?
The death of cells which will cause radiation sickness if alot of cells all get blatted at once
What does radiation sickness lead to?
Vomitting
Tiredness
Hair loss