Section 3 - Radioactivity & Astronomy Flashcards
Who suggested the plum pudding model of the atom?
J.J Thomson, 1897
What did Rutherford do to an atom that proved the plum pudding model wrong?
He fired a beam of alpha particles at thin gold foil. If the plum pudding model was correct, then this should’ve passed straight through
Although most particles did go through, some were deflected back more than expected. The plum pudding model could not explain this
What did Rutherford discover from the gold foil experiment?
That most of the atom’s mass was concentrated in the centre in a tiny nucleus
He also realised that most of the atom was empty space, and that the nucleus must have a positive charge, since it repelled the positive alpha particles
What subatomic particles are currently believed in an atom?
Protons, neutrons and electrons
What is in the nucleus of an atom?
Protons and neutrons
Where are electrons in an atom?
Going around the nucleus in energy levels / shells
If an atom loses an electron, what does it become?
A positive ion
If an atom gains an electron, what does it become?
A negative ion
What is a molecule?
Two different atoms joined together
What is the current model of atom called?
The Bohr Model
If an electron absorbs electromagnetic radiation, what can it do?
It can move up to a higher energy level / shell
What happens when an electron moves up to a higher energy level?
The electron will quickly move back down to its original energy level and by doing so it will emit the same amount of energy it absorbed
The energy is carried away by EM radiation
What causes an atom to be ionised?
If it loses an electron
What type of radiation ionises atoms?
Nuclear radiation
What are isotopes?
Different forms of the same element
What makes isotopes all different?
All isotopes of a particular element have the same amount of protons as this makes it the particular element
Isotopes have different amounts of neutrons in the nucleus. This does not change the charge, however it does change the mass number
What are the three types of ionising radiation?
Alpha
Beta
Gamma
What is an alpha particle?
When an alpha particle is emitted from the nucleus. An alpha particle consists of two neutrons and two protons, making the overall charge +2
They do not penetrate very far into materials, and they can only travel a few cm in air
Because of their size, they are highly ionising
What is a beta particle?
Simply a fast moving electron released by the nucleus. A beta-minus particle has virtually no mass and has a relative charge of -1
A beta-plus particle is a fast moving positron. This has the same mass of an electron, but has a charge of +1
Both moderately ionising
What happens when a positron hits an electron?
The electron and positron destroy each other and produce gamma rays. This is called annihilation
Used in PET scanning
What are gamma rays in radioactivity?
Gamma rays are EM waves with a short wavelength
After a nucleus has decayed, it undergoes nuclear rearrangement and releases some energy . These are gamma rays
They are almost unstoppable, but can be stopped through thick concrete or lead
They are weakly ionising because they tend to pass through materials rather than collide with atoms
What does alpha decay do to the nucleus?
Decreases the charge and the mass
Mass number decreases by 4
Atomic number decreases by 2
What does beta decay do to the nucleus?
Increases the charge of the nucleus
Mass number - no change
Atomic number increases by 1
What does positron emission do the the nucleus?
Decreases the charge of the nucleus
Mass number - no change
Atomic number decreases by 1
What does neutron emission do to the nucleus?
Decreases the mass number of the nucleus
Mass number decreases by 1
Atomic number - no change
What do gamma rays do to the nucleus?
Gamma rays do not change the charge or the mass number.
The atom stays completely the same
Radioactivity has a set rate of decay
True or false?
False - radioactivity is a completely random process
What happens to a radioactive source over time?
It decreases over time
How can the activity of the decay be measured?
Using a Geiger-Müller tube
This clicks each time it detects radiation It is connected to a counter, which displays the number of clicks per second
How can you detect radiation using photographic film?
The more radiation it is exposed to, the darker it becomes
What do all radioactive sources contain?
Radioactive isotopes?
What is the half-life?
The average time taken for the number of radioactive nuclei to halve
What does it mean if a radioactive substance has a short half-life?
It means that the activity falls quickly because the nuclei are very unstable. These sources are dangerous because they emit a high amount of radiation, but they quickly become safe
What does it mean if a radioactive substance has a long half-life?
The activity falls more slowly because most of the nuclei don’t decay for a long time. These sources can still be dangerous because nearby areas are still exposed for years
How can you measure half-life?
You can plot activity against time on a graph
The half-life is found from the graph by finding the time interval on the x axis corresponding to a halving of the activity on the y axis
Give three sources of background radiation
1) Radioactivity of naturally occurring isotopes. These can be in the air, some foods, building materials. They are with us all the time
2) Radiation from space, which is known as cosmic rays. These mostly come out of the sun. Earth’s atmosphere protects us from this
3) Radiation due to human activity. e.g. fallout from nuclear explosions or nuclear waste. This is only a small proportion of the total radiation
What is exposure to radiation called?
Irradiation
Irradiating something does NOT make it radioactive
Give two ways to reduce the effects of irradiation
1) Keeping sources in lead-lined boxes
2) Medical staff who work with radiation wear photographic film badges to monitor their exposure, and know when it reaches dangerous levels
What is radioactive contamination?
Where radioactive particles get into objects
How does radiation damage cells?
By ionisation
What do low doses of of radiation do to a cell?
Tend to cause minor damage without killing the cells. This can cause cells to mutate, which then divide uncontrollably. This is cancer
What do high doses of radiation do to a cell?
Tend to completely kill cells, causing radiation sickness if a lot of cells are killed at once
What sources are the most dangerous outside of the body?
Beta and gamma because they can penetrate through the skin and delicate organs.
Why is alpha the least dangerous outside of the body?
Because it cannot penetrate the skin
Why is alpha sources the most dangerous inside the body?
Alpha particles are strongly ionising. so all their damage is focused in a very localised area. The alpha particles cannot pass through the skin, meaning it cannot escape when inside the body
How do household fire alarms use alpha radiation?
A weak source of alpha radiation is used in a smoke detector, close to two electrodes
The source causes ionisation, and a current flows
If there is a fire then the smoke will absorb the radiation - the current stops and the alarm sounds
How is food and equipment sterilised using gamma rays?
Food can be irradiated with a high dose of gamma rays which will kill all microbes.
Similarly, medical equipment can be sterilised using gamma rays as opposed to being boiled
Irradiation is a good sterilisation method because with fruit, it can be sterilised without being damages due to high temperatures if it was boiled
How is radiation used in tracers?
Certain radioactive isotopes can be used in tracers, such as medical tracers
A medical tracer can be injected or swallowed, and its progress is followed using an external detector. This can be used to detect and diagnose conditions such as cancer
All isotopes which are taken in the body must ALWAYS be beta or gamma, so that radiation passes out of the body without doing too much damage
What does PET scanning do?
PET scanning (positron emission tomography) can help diagnose illnesses
How does PET scanning work?
1) Inject patient with substance used by body e.g. glucose containing . a positron-emitting isotope with a short half-life e.g. 11 Carbon
2) Positrons emitted by the isotope meet electrons in the organ and annihilate, emitting high energy gamma rays in opposite directions. Detectors around the body detect each pair of gamma rays - the tumour lies along the same path as each pair. The location can then be determined using triangulation
3) The distribution of radioactivity matches up the metabolic activity, because more glucose or whatever substance used is taken up and used by cells that do more work
Radiation can only be used to treat tumours internally
True or false?
False - radiation can be used both internally and externally to treat tumours
How are alpha emitters used to treat tumours?
Alpha emitters are usually injected near to a tumour. Alpha particles are strongly ionising, they do lots of damage to the nearby cancerous cells, however the damage to normal cells is limited due to their short range
What kind of half-life should sources used in external radiotherapy have?
Long half-lives so that they do not have to be replaced as often
What kind of half-life should sources used in internal radiotherapy have?
Short half-lives to limit the time that the source is in the patients body for. and therefore reducing the damage that it does
What is nuclear fission?
The splitting up of big atomic nuclei
Used to release energy from uranium or plutonium atoms
What is the nuclear fission chain reaction?
A slow-moving neutron is fired at a large, unstable nucleus - often uranium 235
The neutron is absorbed by the nucleus - this makes the atom more unstable and causes it to split
This split produces two ‘daughter nuclei’ and energy is released
Each time uranium splits, it can produce two or three neutrons, which can hit other uranium nuclei, causing them to split also
Why must chain reactions be carefully controlled?
Because the neutrons released by fission reactions have a lot of energy
How can fission chain reactions be controlled?
Uranium fuel rods are placed in a moderator to slow down the fast-moving neutrons
Control rods, often made of boron, limit the rate of fission by absorbing excess neutrons. They are placed in between the fuel rods and are raised and lowered into the reactor to control the chain reaction
This creates a steady rate of nuclear fission, where one new neutron produces another fission
What could happen if fission chain reactions is left to continue unmonitored?
Large amounts of energy are released in a very short time. Many new fissions will follow each fission, causing a runaway reaction which could lead to an explosion
What are nuclear power stations, and what happens in them?
They are powered by nuclear reactors that create controlled chain reactions
The energy released by fission is transferred to the thermal energy store of the moderator. This is then transferred to the thermal energy store of the water in the boiler, which causes the water to boil and energy to be transferred to the kinetic energy store of the steam
This energy is then transferred to the kinetic energy store of the turbine and then to the kinetic energy store of the generator. The energy is then transferred away from the generator electrically
What is nuclear fusion?
The joining of small nuclei
Two light nuclei collide at a high speed and fuse to create a larger, heavier nucleus
e.g. hydrogen will fuse together to make helium
What conditions are needed for nuclear fusion?
Extremely high temperatures and pressures
About 10,000,000 degrees
Why are high temperatures and pressures needed for fusion?
Because it takes a lot of energy to get the positively charged nuclei to get close enough to fuse, so the electrostatic forces of repulsion has to be overcome
Give two pros of using nuclear power
1) Nuclear power does not release greenhouse gases such as methane and carbon dioxide
2) Huge amounts of electricity can be generated from a small amount of nuclear material §
Give two cons of using nuclear power
1) Carries the risk of leaks directly from the power station, or explosions like Chernobyl and Fukashima
2) Public perception of nuclear power is extremely negative, and can be viewed as very dangerous to some
What are planets?
Large objects that orbit a star. There are eight planets in our solar system
e.g. Mercury, Venus, Earth, Mars
What is a dwarf planet?
These are objects that are not considered big enough to be planets
e.g. Pluto
What are moons?
Natural satellites that orbit planets with elliptical orbits.
e.g. the Earth has one moon, but Mars for example has two
What are artificial satellites?
Human-built objects that orbit in a fairly circular orbit
What are asteroids?
Lumps of rock and metal that that orbit the Sun. Their orbits are usually elliptical. They can be found in the asteroid belt between Mars and Jupiter, and it separates the inner planets from the outer planets
What are comets?
Lumps of ice and dust that orbit the Sun. Their orbits are highly elliptical. Some travel near to the sun and others travel on the outskirts of the solar system
How does gravity provide a force that creates orbits?
An object in a circular motion orbits at a constant speed and is constantly accelerating. This is the centripetal force. This force would cause the object to fall into the centre of whatever it was orbiting. Since the object is already moving, it changes direction
The object keeps accelerating towards what it’s orbiting but the instantaneous velocity (at a right angle to the acceleration) keeps it travelling in a circle
The force that makes this happen is provided by the gravitational force between the planet and the Sun (or between the planets and its satellites)
The force due to gravity depends on what two factors?
Mass and distance
The larger the mass of the body, the ________ its gravitational field
Stronger
The further away you get from a star or planet, the ______ the gravitational force is
Weaker
The stronger the force, the larger the instantaneous velocity needed to balance it
True or false?
True
Where did the Ancient Greeks think the Earth was in the solar system?
The centre
What is the name of the model that proposed that the Earth was in the centre of the solar system?
Geocentric
What is the name of the model that proposed that the Sun was in the centre of the solar system?
Heliocentric
Describe the geocentric model of the solar system
Theory suggested that everything, including the Sun, orbited the Earth
People didn’t have telescopes at this time, and they saw the Sun and Moon travelling across the sky each day
This theory was proposed by the Ancient Greeks, and was accepted until the 1500s
Describe the heliocentric model of the solar system
This proposed that the Sun was in the centre of the solar system, and it was in a fixed position.
The planets and their moons, including Earth, orbited the Sun
What pieces of evidence did Galileo find to support the heliocentric model?
Whilst looking at Jupiter through a telescope, he found that some stars were in a line near the planet.
He saw that these stars never moved away from Jupiter and seemed to be carried along with the planet. This showed that individual objects orbited planets, and not the Earth. These were later discovered to be moons
Who invented the first telescope?
Hans Lippershey
What are the two scientifical theories for the creation of the universe?
Steady State
The Big Bang
What does the Steady State theory say about how the universe began?
it says that the universe has always existed as it is now, and it always will. It is based on the idea that the universe appears practically the same everywhere
As the universe expands, new matter is constantly being created
This means that the density of the universe is roughly the same
In this theory, there is no beginning or end to the universe
What does the Big Bang theory say about how the universe began?
States that once, all matter in the universe was occupied in a very small space, and this space was incredibly dense and was very hot
Then it ‘exploded’ - space started to expand, and that expansion is still going on
This theory gives a finite age for the universe - around 13.7 billion years
This is the theory that is widely accepted today, and this is based on evidence such as redshift and CMB
What is redshift?
Most galaxies are moving away from each other, and this can be explained by redshift
Different elements produce different frequencies of light, and each element produces a specific pattern of dark lines (absorption lines) at the frequencies that it absorbs in the visible part of the EM spectrum
When we look at the light emitted from different galaxies, we see the same patterns but at slightly lower frequencies
There’s an increased observation in the wavelength of light coming from the galaxies and the patterns have been shifted towards the red ends of the spectrum. This is why it is called redshift
What is the Doppler effect?
This has the same effect as redshift
When an ambulance drives past you, the noise from the sirens sounds lower-pitched when it’s travelling away from you because it drops in frequency, and it sounds higher pitched when it’s travelling towards you due to the increase of frequency
What is CMB evidence for?
The Big Bang Theory
What is CMB?
Scientists have detected low frequency electromagnetic radiation coming from all parts of the universe
This is mainly the microwave part of the electromagnetic spectrum, and is therefore known as CMB (cosmic microwave background radiation)
What is the stellar life cycle, in order, for an average sized star?
Nebula Prostar Main sequence Red giant White dwarf Black dwarf
What is the stellar life cycle, in order, for a large star?
Nebula Prostar Main sequence Red supergiant Supernova Neutron star / black hole (depending on mass and size)
What is a nebula?
Stars that initially form from a cloud of dust and gas
What is a prostar?
Gravity pulls together the dust and gas from a nebula, and comes together to form a prostar
The temperature rises and the star gets denser - more particles collide with each other
When the temperature is high enough, nuclear fusion of hydrogen nuclei to form helium nuclei
What is a main sequence star?
This is when the star enters the period of stability where it will remain like this for a very long period of time - usually billions of years
During this period, the outward pressure caused by thermal expansion balanced the force of gravity, pulling everything inwards
The heavier the star, the shorter the time on the main sequence
What is a red giant / red supergiant?
When the hydrogen core begins to run out and the force due to gravity is larger than the pressure of thermal expansion, the star is compressed and the next heaviest element undergoes nuclear fusion
This causes the star to expand and become heavier. It becomes red because the surface cools
What is a white dwarf?
A small / medium star like the Sun that ejects its outer layers of dust and gas.
This leaves behind a hot, dense, solid core - a white dwarf
What is a black dwarf?
A white dwarf that has cooled down over a long period of time
What is a supernova?
Big stars undergo a supernova, which is when they start to glow brightly again due to ore nuclear fusion taking place of even heavier elements
They expand and contract several times, as the balance shifts between gravity and thermal expansion
Eventually, they explode into a supernova
What is a neutron star?
The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star
What is a black hole?
If the star is big enough (extremely big) then it will collapse in on itself and become a black hole
This is a super dense part of space where nothing can escape, not even light
What are telescopes used for?
Observe the universe
Who used the first telescope?
Galileo
How do telescopes work?
They use refraction and reflection to enable you to see distant objects
How can you increase the quality of telescopic images?
Increase the aperture of the telescope - diameter of the objective lens
Use a higher objective lens
Space telescopes have a better or worse view as opposed to those on Earth?
They have a better view - they escape the atmosphere, which allows them to detect light much more efficiently
They also escape light pollution, which makes it even worse when looking through a telescope
To get the best view, it should be placed on a mountain where there is less atmosphere above it, and a dark place away from cities
Different telescopes detect different types of what/
Electromagnetic waves
What type of telescope were the earliest telescopes?
Optical telescopes
They’re used to look at objects close by and in other galaxies
What are x-ray telescopes used for?
They are a good way to ‘see’ violent, high temperature events in space, like supernovas
What are more modern telescopes?
From the 1940s, telescopes could see all parts of the EM spectrum
Modern telescopes work alongside computers. Computers help to create clearer and sharper images, and makes it easier to capture them
Computers make it easier to analyse the data collected from the telescopes
Bigger telescopes give us what?
A better resolution. This means that they can gather a lot of light, and we can therefore see further than before
Because of this, we can see things that we could not see before, and as a result, more galaxies are being discovered
