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
Outside the body, whats the most dangerous radiation?
Gamma and beta
Why are gamma and beta the most dangerous outside the body?
Because they can penetrate the body and get to the delicate organs
Inside the body, whats the most dangerous?
Alpha
Why is alpha the most dangerous inside the body?
Because alpha particles are strongly ionising so they do damage in a very localised area
What is the main worry with alpha sources?
Contamination or irradiation?
Contamination
Give three sources of background radiation?
Any three from: Fallout from nuclear explosions Nuclear waste Cosmic rays Foods Building materials Rocks
What do the hazards associated with a radioactive source depend on?
It’s half-life
The ____ the activity of a radioactive source, the safer it is to be around
The lower the activity of a radioactive source, the safer it is to be around
What must be considered when choosing a radioactive source for an application?
The activity of the source
The half life of the source
Disposal and storage of the source
What type of radiation is used for fire alarms?
Alpha
Where is the radiation placed, in the smoke alarm?
Between two electrodes
How do smoke alarms work?
The source of alpha radiation causes ionisation and a current of charged particles to flow meaning if there is a fire the smoke will absorb the charged particles meaning the current stops and the alarm sounds
Why is irradiation better than using high temperatures?
Because fresh fruit and plastic instruments can be sterilised without being damaged
What sources are used for tracers?
Beta or gamma
What can beta radiation be used in?
Thickness control
When measuring thickness control, why is beta radiation used?
Because the paper will partly block the radiation
Explain why radioactive sources that emit alpha radiation are not used as medical tracers?
Alpha radiation is highly ionising so would damage cells in the body. Alpha radiation can’t penetrate through tissue, so it wouldn’t be detected outside the body with the radiation detector
What can PET scanning help do?
Diagnose illnesses
What is PET scanning?
A technique used to show tissue or organ function and can be used to diagnose medical conditions
How can you detect cancer tumours?
By looking for high metabolic activity in tissue
Describe how you can undergo PET scanning?
Inject the patient with a substance used by the body containing a positron-emitting radioactive isotope
Positrons are emitted by the isotope which would meet electrons in an organ and annihilate which would emit high-energy gamma rays
Detectors outside the body then recieve the rays, undergoing triangulation to find the location of the source
What does the distribution of radioactivity equal?
The metabolic activity
Why does the metabolic activity = radioactivity?
Because the cells that have a higher metabolic rate will take in more gucose meaning there will be more gamma rays from that area
What are the isotopes used in PET scanning like?
Short half-lives
What makes isotopes?
Cyclotron
Because of the short half-lives what must hospitals do with the isotopes?
Use them quickly and make sure they’re made close
What source is typically used when treating tumours?
Alpha
What source is typically used when treating implants?
Beta
What source can be used to treat tumours externally?
By aiming gamma rays at the tumour
Explain how a PET scan can detect a cancerous tumour in a patient?
The patient is injected with a substance that contains a radioactive isotopes
This isotope decays and produces positrons which annihilate with nearby electrons and produce gamma rays
These gamma rays are then detected outside of the body
Areas of high metabolism can indicate the presence of a cancerous tumour
What is nuclear fission?
The splitting up of an atoms nucleus
Briefly describe how to start nuclear fission?
A slow-moving neutron is fired at a large unstable nucleus which absorbs the neutron and causes the atom to become more unstable and eventually split
Once the atom splits, in nuclear fission, what happens next?
The atom splits to form two new lighter elements, energy and neutrons
What is produced once a Uranium-235 is split apart?
Two daughter cells
Neutrons
Energy
What element is often used in nuclear fission?
Uranium-235
What are thermal neutrons?
Slow-moving neutrons
What do control rods do in nuclear fission?
Limit the rate of fission by absorbing excess neutrons
What do moderators do in nuclear fission?
Limit the rate of fission by slowing down thermal neutrons
What could happen if the rate of fission is left unchecked?
Large amount of energy will be released in a very short time potentially resulting in an explosion
How do nuclear power stations get the energy from the fission?
The energy heats the coolant which is heated into steam which is then used to rotate a turbine which releases kinetic energy
What is nuclear fusion?
The joining of small nuclei
Briefly describe how nuclear fusion occurs?
Two light nuclei collide at high speed and join to create a larger, heavier nucleus
Compare the mass of the heavy nuclei to the two light nuclei?
The total mass of the light nuclei is slightly more as there is some mass converted to energy which is then released as radiation
What is the problem with fusion?
It requires extremely high temperature and pressure
What temperature is needed for fusion?
10,000,000 *C
Why are such high temperatures needed for nuclear fusion?
Because in order to join the nuclei you must overcome the strong force due to electrostatic repulsion as they are both positive
Why are the conditions for fusion so hard?
Because no material can withstand that kind of temperature as it would just be vapourised
Why are the no fusion reactors at the moment?
Because it takes more power to get up to the temperature than the reactor releases
What are the cons of nuclear power?
Bad public perception
Nuclear waste is hard to dispose of
Leaks (eg. Chernobyl and Fukushima)
What are the pros of nuclear power?
Pretty safe when done right
Very reliable
No greenhouse gases released
Fuel is cheap and readily available
Why is the cost of nuclear power so high?
Because of the inital cost of the power plant
Explain why fusion only occurs at high temperatures and pressures?
Because all nuclei have positive charges so when they are close they repel each other meaning high pressures/temperatures are needed to overcome this electrostatic repulsion and fuse the two nuclei together
What is solar system?
The stuff that orbits out Sun
What are planets?
Large objects that orbit a star
What are dwarf planets?
Planet-like objects that aren’t big enough to be planets
What are moons?
Natural satellites that orbit planets with almost circular orbits
What type of orbits do moons have?
Almost circular
What type of orbits do artificial satellite have?
Fairly circular
What are asteroids?
Lumps of rock and meetals that orbit the Sun
What are comets?
Lumps of ice and dust that orbit the Sun.
What type of orbits do comets have?
Highly elliptical
What provides the force that creates orbits?
Gravity
What type of orbits do planets have?
Almost circular
Where does centripetal act?
Towards the centre of the circle
What affects graviational field strength?
The mass of the object
The distance from the object
What must happen to the instantaneous velocity as the gravity increases?
The velocity must increase to balance it
What happens to an object the close it gets to a star or a planet?
The faster the object must go
For an object in a stable orbit, what must happen if the speed changes?
The radius of the orbit
What did the geocentric model involve?
The theory that the Sun, Moon, planets and stars all orbited the Earth in perfect circles
Why did the geocentric model arise?
Because we didn’t have telescopes and saw the Sun andMoon travelling across the sky in the same way every day and night
What did the heliocentric model involve?
The theory that the Sun was at the centre of the solar system and that all the planets orbited the Sun in perfect circles
Who found evidence for the heliocentric model?
Galileo
What evidence did Galelio find for the heliocentric model?
There were ‘stars’ around Jupiter that never moved, meaning not everything orbited the Earth
These ‘stars’ are the moons of Jupiter
What is the difference between our current model of the solar system and the heliocentric model?
Orbits are elliptical rather than circular
The Sun isn’t the centre of the Universe
What does the Steady State theory say?
That as the Universe expands new matter is constantly being created meaning the density remains roughly the same because of this there is no beginning or end to the Universe
What does The Big Bang theory say?
All the matter in the Universe occupied a very small space which eventually ‘exploded’ causing space to expand
What does the Big Bang theory provide us with?
A start and an end
An age of the universe
What is the estimated age of the universe?
13.8 billion years
What was the small space of all the matter in the Universe like?
Extremely dense and very hot
Explain the difference between the geocentric and heliocentric models of the Solar System?
In the geocentric model everything orbits the Earth, whilst, in the heliocentric model everything orbits the Sun
The Big Bang theory puts a finite age on the Universe, whereas, the Steady State theory assumes there is no beginning and no end to the Universe
In the Steady State Theory, matter is constantly being created. In the Big Bang theory, all of the matter in the Universe occupied a small, dense region of space at the start of the Universe, which then ‘exploded’ outwards
What does red-shift suggest?
The Universe is expanding
Different elements absorb ______ frequencies of light
Different elements absorb different frequencies of light
What do we see when we look at light from different galaxies?
We see the same patterns but at slightly lower frequencies meaning there’s an observed increase in the wavelength of light coming from the galaxies
What is the red-shift but for sound?
Doppler effect
What happens to the sound of a car as it gets closer to you?
Higher pitched as the frequency increases
Compare more distant galaxies to closer galaxies in terms of red-shift?
Distant galaxies have greater red-shifts than closer galaxies
What does the distant galaxies and closer galaxies having different red-shifts show you?
That the whole universe is expanding
What is CMB radiation?
Low frequency electromagnetic radiation coming from all parts of the Universe
What is CMB evidence for?
The Big Bang
What is red-shift evidence for?
The Big Bang and Steady State
What is red-shift evidence for?
The Big Bang and Steady State
Why does red-shift only support the Big Bang theory?
Because it shows the Universe had a beginning
What is red-shift?
Red-shift is where the light we see from distant galaxies appears at a lower frequency than we would expect
What theory does CMB radiation support?
The Big Bang theory
State the cycle for a star bigger than the Sun?
Nebula Protostar Main Sequence Star Red Supergiant Supernova Neutron Star or Black hole
State the cycle for a star the same size as the Sun?
Nebula Protostar Main Sequence Star Red Giant White Dwarf
What is a nebula?
A cloud of dust and gas
How is a protostar formed?
Dust and gas is pulled together to form a protostar
What happens to a protostar as it gets denser?
The temperature rises and more particles collide with each other meaning when the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei which releases massive amounts of energy
What is thermal expansion of a star?
The energy produced by nuclear fusion trying to expand the star
What is the stable period of the star?
The main sequence star
What happens during the main sequence star stage?
The thermal expansion balances the force of gravity
The heavier the star, the _____ its time on the main sequence
The heavier the star, the shorter its time on the main sequence
What follows the main sequence star?
The supergiant
What happens after the main sequence star?
The hydrogen in the core begins to run out and the force due to gravity is larger than the pressure of thermal expansion
What happens once the force due to gravity is larger than the pressure of thermal expansion?
The star becomes compressed until it is dense and hot enough that the energy created makes the outer layers of the star expand
Why does the star become red?
The surface cools
What does a red giant turn into?
A white dwarf
How does a white dwarf form?
A small-to-medium-sized star like the Sun then becomes unstable and ejects its outer layer of dust and gas
What is a white dwarf?
A hot, dense solid core
What does a red supergiant turn into?
A supernova
What is a super nova?
An explosion
How does a super nova form?
A big star glowing brightly again as it undergoes more fusion to make heavier elements
They expand and contract several times as the balance shifts
What happens following a supernova?
A neutron star or a black hole
How is a neutron star formed?
The outer layer of dust and gas of a exploding supernova is thrown into space leaving a very dense core
How is a black hole formed?
If a star is massive enough it will collapse and become a black hole
What is a black hole?
A super dense point in space that not even light can escape
Describe the life cycle of a star much larger than our Sun, beginning from a nebula
A cloud of dust and gas is attracted together by gravity, forming a protostar
As the star gets denser, it gets hotter and hotter, until nuclear fusion of hydrogen nuclei starts to happen in its core
This nuclear fusion provides and outward pressure to balance the force of gravity, so the star remains a stable size, as a main sequence star
When the star runs out of hydrogen to fuse, it will expand and cool, becoming a red supergiant
It begins to glow brightly again and expands and contracts several times
What are optical telescopes?
Telescopes that detect light
What do telescopes use to allow you to see distant objects?
Refraction and reflection
How do you improve the quality of the image you can see through a telescope?
By increasing the aperature of the telescope
By using a higher quality objective lens
What is the aperature of a telescope?
The diameter of the objective lens
Whats the problem with using telescopes on Earth?
The Earth’s atmosphere absorbs light
Light and air pollution
How could you avoid the problems with atmosphere and light pollution when using telescopes?
Ontop of a mountain
A dark place away from cities
In space
Whats the main problem with optical telescopes?
Most objects in the Universe aren’t detectable using visible light
What are x-ray telescopes used to see?
Violent, high temperature events in space
What did radio telescopes help discover?
CMB radiation
What do computers allow us to do with telescopes?
Store huge amounts of data
Collect data 24 hours a day
No humans to rely on
Easier and quicker to analyse data
Give three ways of improving the image you can see through a telescope on Earth?
Any three from: Move the telescope to a darker location Move the telescope to a higher location Move the telescope to space Use a telescope with a larger aperture Use a telescope with a higher quality objective lens
True or False? Atoms are neutral?
True
What is the atomic number of an atom?
The number of protons (and electrons) in an atom
Name four things that may be emitted during radioactive decay
Alpha Beta-minus Beta-plus Gamma Neutron
Explain why alpha radiation can not be used to check the thickness of metal sheets?
Because the alpha radiation wouldn’t be able to penetrate the material
Describe the change to an atom’s mass and atomic number following alpha decay?
The mass number decreases by 4. the atomic number decreases by 2.
In what type of decay does a neutron change into a proton within the nucleus?
Beta-minus
What type of nuclear decay doesn’t change the mass or charge of the nucleus?
Gamma decay
Give three uses of radiation
PET scanning
Smoke sensors
Thickness control
What do asteroids orbit?
The Sun
What does CMB radiation stand for?
Cosmic Microwave Background radiation
List the life cycle stages a star the size of our Sun goes through?
Nebula Protostar Main Sequence Star Red Giant White Dwarf
