Flashcards in Section 3 - Radioactivity and Astronomy Deck (93):
Where is the majority of an atom's mass located?
In the nucleus.
What size is the nucleus compared to the whole of the atom?
About 10,000 times smaller.
What is the rough size of an atom?
1 x 10⁻¹⁰
What happens if an electron is excited?
It shifts from one energy level to a higher one.
What happens when an electron drops to a lower energy level?
It will emit an EM wave with the same amount of energy as was used to raise the electron's energy level.
What happens with energy levels the further from the nucleus they get?
The distances between energy levels shrink.
What is ionising radiation?
Any radiation that can knock electrons off of an atom.
What are Isotopes?
Different forms of the same atom.
How can isotopes be written?
(Element name)-(Relative mass of atom)
What are the types of nuclear radiation?
Alpha, beta-minus, beta-plus, gamma and neutron.
What are alpha particles?
What does it take to stop alpha particles?
A few cm of air or a thin sheet of paper.
What does it take to stop beta-minus particles?
A few metres of air or a sheet of 5mm aluminium.
What does it take to stop beta-plus particles?
Anything with electrons.
What are beta-minus particles?
Fast moving electrons.
What are beta-plus particles?
Fast moving positrons.
What are positrons?
Antimatter, with virtually no mass and a positive relative charge of +1
What is nuclear radiation?
Any radiation that comes from an atom's nucleus.
What happens when a positron meets an electron?
They annihilate and produce gamma rays.
What are gamma rays?
A form of short wavelength EM radiation.
How does ionisation happen?
An atom looses or gains an electron.
What does it take to stop gamma rays?
Thick lead or metres of concrete.
How are nuclear equations written?
Atom before decay → atom after decay + radiation
How is an alpha particle written in an equation?
How is a beta-minus particle written in an equation?
How is a beta-plus particle written in an equation?
How is a neutron emission written in an equation?
How is gamma radiation written in equations?
How often does radiation occur?
What piece of equipment is used to measure radioactive activity?
A Geiger-Müller tube or Geiger counter.
What is radioactive activity measured in?
Becquerels, Bq, 1Bq = 1 decay per second.
What happens to photographic film exposed to radiation?
It becomes darker.
What is half life?
The average time taken for radioactive activity to decrease by half.
Describe a radioactive source's activity/time graph.
It will decrease exponentially.
What is background radiation?
The low levels of radiation around us all the time.
Where does background radiation come from?
The earth, space and human waste.
What is exposure to radiation called?
How can exposure to radiation be minimised when using radioactive materials?
By keeping sources in lead lined boxes, standing behind a barrier, being in a different room and using an RC arm or wearing a protective suit.
What is it called when radiation gets into an object?
What does a high dose of radiation do to cells?
It kills them.
What does a low dose of radiation do to cells?
It mutates them.
How is radiation used in fire alarms?
A weak alpha source is placed next to two electrodes.
The ionisation from the alpha particles causes a current to flow.
Smoke absorbs the alpha particles stopping the current.
The alarm sounds.
How is food and equipment sterilised by radiation?
A gamma source irradiates the food or equipment, killing all microbes and bacteria, this doesn't damage the food or equipment like heating would.
How is radiation used in tracers?
An isotope (always gamma or beta emitters) is ingested or injected.
The source is then followed around the body by an external tracker.
This can be used to diagnose conditions like cancer.
How is radiation used in thickness gauges?
A beta source is aimed through the thing that is being measured at a detector, which is a set distance away.
If not enough radiation reaches the detector, the object is too thick.
If too much radiation reaches the detector, the object is too thin.
How is radiation used in PET scanning?
Glucose containing short half life positron emitting isotopes act as tracers.
The positrons annihilate on contact with electrons, releasing high energy sets of gamma rays in opposite directions.
Detectors pick this up and locate the site of the annihilation.
Cancer cells have higher metabolisms, so areas of above average activity will release more radiation due to the higher concentrations of glucose, making the areas detectable.
How is radiation used to treat tumours internally?
Alpha emitters are injected near the cancerous tissues, they absorb it and are delivered high doses of radiation, killing the tumour off.
Beta emitters are implanted near the cancerous tissues, the beta particles can penetrate the implant's casing but deliver high doses of radiation to the tumour.
How is radiation used to treat tumours externally?
Gamma rays are aimed at the tumour to deliver large doses of radiation to the target tissues.
What is nuclear fission?
Where the atom splits into smaller atoms.
How are fission reactors controlled?
Using boron control rods.
How are neutrons slowed down so they can cause fission in nuclear fission reactors?
Using a moderator, often water.
What is nuclear fusion?
Where two atoms join together.
What must there be for fusion to occur?
High pressures and high temperatures.
What are the pros of nuclear power?
Pretty safe, less polluting than fossil fuels, it is reliable, it generates a lot of energy and the fuel is cheap.
What are the cons of nuclear power?
It is seen negatively by the public, leaks are extremely dangerous, the waste products can last millions of years, overall cost is very high and dismantling a plant safely takes decades.
How many planets orbit our sun?
What are planets?
Large objects that orbit stars.
What are the planets of our solar system in order?
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
What are dwarf planets?
Planet-like objects that are too small to class as a planet.
What is our solar system's dwarf planet called?
What are moons?
Objects that orbit planets, they are a type of natural satellite.
What are artificial satellites?
Man-made objects that orbit planets.
What are asteroids?
Lumps of rock and metal that orbit stars.
What are comets?
Lumps of dust and ice that orbit stars.
Describe a comet's orbit.
What force causes objects to be drawn together?
What force causes moving objects to stay in orbit?
The centripetal force.
Why do objects orbit instead of plummeting towards the object they are orbiting?
The object has instantaneous velocity at a right angle to the centripetal force causing it to move in a circular motion.
What factors can affect gravitational field strength?
Mass and distance from the object.
What happens to gravitational field strength as you get closer to an object?
What happens to gravitational field strength as the mass increases?
What is the geocentric model of the solar system?
That everything orbited the earth in perfect circles.
What is the order of planets in the geocentric model of the solar system, starting from the centre.
Earth, the moon, Venus, Mercury, the Sun, Mars, Jupiter and Saturn.
What is Galileo's proof for the Heliocentric model of the solar system?
He observed Jupiter's moons.
What is the steady state theory?
The universe has always existed and always will, as it expands more matter is created, this means density is maintained everywhere.
What is the big bang theory?
In the beginning, the universe was condensed into a tiny space, making it very hot and dense, then it exploded out and the expansion is still continuing. This gives the universe an estimated age of about 13.7 billion years.
What is red shift?
The shift in an EM waves wavelength towards the red end of the spectrum because the source of the light is moving away from us.
What does a larger red shift mean?
The source is moving away faster.
What is cosmic microwave background radiation?
Low frequency EM waves coming from all parts of the universe.
What is the life cycle of a star?
Nebula, protostar, main sequence star, red giant, white dwarf.
Nebula, protostar, main sequence star, red supergiant, supernova, black hole.
Nebula, protostar, main sequence star, red supergiant, supernova, neutron star.
What is a nebula?
A cosmic cloud of dust and gas.
What occurs in the protostar phase of the star life cycle?
Gravity pulls a nebula together to form a protostar, the temperature raises as it gets denser, fusion begins to take place and large amounts of energy are released.
What occurs in the main sequence star phase of the star life cycle?
A long stabe period, where outwards presure is balanced by the gravity, it can last several billions of years.
What occurs in the red giant and red supergiant phases of the star life cycle?
The hydrogen in the core begins to run out and outwards pressure decreases, the core compresses under gravity and the heat released causes outer layers to expand.
Why do some stars become red supergiants?
The larger a star is, the larger its red giant phase is, so much larger stars can be many times the size of a normal red giant.
What occurs in the white dwarf phase of the star life cycle?
The star becomes unstable and ejects its outer layers, leaving a hot and dense core, which cools over time.
What occurs in the supernova phase of the star life cycle?
The star becomes unstable, expanding and contracting as the forces change, then the star explodes.
What occurs in the neutron star phase of the star life cycle?
The outer layers ejected by the supernova leaves behind an incredibly dense neutron star.
What occurs in the black hole phase of the star life cycle?
A large enough star's core collapses in on itself after a supernova leaving behind an inconceivably dense point in space where not even life can escape.
How can a telescope's image quality be improved?
By increasing the aperture, the diameter of the objective lens.
By increasing the quality of the objective lens.
Why do space telescopes have clearer views than those on earth?
Telescopes on earth don't achieve the same clarity as space ones because the atmosphere absorbs lots of the inbound EM radiation from space and light pollution makes it difficult to distinguish between space and dim objects.
What are X-ray telescopes good for?
'Seeing' violent, high-temperature events like supernovas.