Section 3 - Radioactivity and Astronomy Flashcards
What is the solar system?
all the stuff that orbits our sun
What is included in the solar system?
Planets, Dwarf planets, Moons, Artificial satellites, Asteroids, Comets
Planets
Large objects that orbit a star.
What are the 8 planets in our solar system?
(from the sun, outwards)
Mercury, Venus, Earth, Mars, Jupiter, Saturn,Uranus, Neptune
My Very Educated Mother Just Served Us Nachos
Dwarf Planets
Planet like objects that arent large enough to be planets.
Moons
Orbit planets wiht almost circular orbits, natural sattelites
Asteroids
Lumps of rock and metals that orbit the sun, they are usually found in the asteroid belt
Comet
Lumps of ice and dust that orbit the sun. highly eliptical orbits
What is alpha radiation
Alpha radiation is when an alpha particle is emmitted fromthe nucleus (2 protons and 2 neutrons)
How far do alpha particles travel?
Few cm in air and stopped by thin paper because they are strongly ionising
How are B- particles created
when a neuton decays into an electron and a proton. That electron is then thrown out of the nucleus
How far do B- particles travel?
Few meters and absorbed by a sheet of aluminium, moderately ionising
How are gamma rays created?
A neucleus decaying and releasing energy in form of gamma rays
How far do gamma rays go
A very long distance, can penetrade deeply into materials, weakly ionsiing. Cna be stopped by lead or meteres fo cncrete
When can an electron move up energy levels/shells?
if it absorbs EM radiation with the right amount of energy
What happens when an electron moves up to a higher energy level?
It moves up to a partially filled shell or empty and is said to be “exited”
It then quickly falls back to its original energy level
What happens when an exited electron falls back to its original energy level?
It will emit the same amount of energy it absorbed, this energy is carried away by EM radiation
What happens to electron shells as they move further out?
They get closer togethe, so the differrence in the energy levels between the shells gets smaller
What is a positron?
An anti-electron
Same mass, positive charge
Why is a positron made?
When a nucleus have too few neutrons, a proton will turn into a neutron and emit a fast-moving positron
What is a Becquerel?
Bq
1 decay per second
How is radioactive decay mesured?
In a geiger-muller tube
Half -life
The average time taken for the number of radioactive nuclei in an isotope to halve
Backround radiation
The low level radiation thats around us all the time
What are the 3 main exposures to backround radiation?
Naturally occuring isotopes - air, some foods, buildings and rocks
Space - Cosmic rays from the sun most blocked by the atmosphere
Human activity - fallout from nuclear explosions
What is exposure to radiation called?
Irradiation
How to prevent irradiation
Keeping sources in lead-lined boxes/ standing behind barriers or different room.
Contamination
Unwanted Radioactive particles getting onto objects
How can radioactive contamination be harmfull?
if touching the object without gloves, you would them become contaminated. If the atoms may then decya, causing you harm
Ionisation
Radiation can enter living cells and ionise atoms and molecules within them leading to tissue damage
Hazard correlation with half-life
The lower the activity of a radioactive source, the safer it is to be around.
Longer half life = more dangerous
Uses of Alpha Radiation
Household fire alarms
Smoke absorbs small particles so when alpha radiation is no lenger detected, the alarm goes off.
Uses of Gamma Rays
Food and Equipment sterilisation
Gamma rays kill microbes
Food can be irradated
Uses of General Radiation
Tracers and thickness gauges
Some radiation can be injected into a patient and tracked by an external detector. - Used to detect and diagnose certain medical conditions e.g. cancer
The tracers have to be BETA OR GAMMA so they can pass through and out the body without causing too much damage.
Uses of Beta Radiation
Thickness gauges
e.g paper. Detector sense how much radiation gets through, when this changes the thickness has changed.
What does PET stand for
Positron emission tomography
What is a PET scan used for
To show tissue or organ function and can be used to diagnose medical conditions.
How can PETs diagnose cancer cells?
It can identify active tumors by shwoing metabolic activity in tissue. Cancer cells havea much higher metabolic activity therefore can be identified.
How do PET scans work?
- Inject a sustance used in the body with a positron-emitting radioactive isotope with a short half used as a tracer.
- Positrons emmited by the isotope meet electrons in an organ and annihilate emmiting high energy gamma ray
- Distribution of radioactivity = metabolic activity
How does radiation therapy work?
Particles are injected near a tumor and kill the cells
Nuclear Fission
A type of nuclear reaction used to release energy from uranium or plutonium.
Chain reaction in nuclear fission
- a slow-moving neutron is fired at a large unstable nucleus
- this neutron is absorbed by the nucleus, making it more unstable, causing it to split
- The split atom forms 2 lighter daughter cells and energy is released.
- Some neutrons will be spit out in the reaction, moving into other large unstable nuclei, causing a chain reaction
Describe the energy transferrs in a nuclear power station
Energy relesed by fission is transferred to the thermal energy store of the moderator, then to the coolant, then to the cold water passing through the boiler. This causes the water to boil and the energy to be transferred to its kinetic energy store.
This then goes to a turbine, then a generator.
Centripedal force
Centre seeking force
What is the first stage of a star forming?
Stars initially form a cloud of dust and gas called a nebula
What is the second stage of a star forming?
After Nebula
The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the star gets denser and more particles collide with each other. When the temp gets high enough, hydrogen nuclei undergo nuclear fusion to form He nuclei. This gives out huge amounts of energy, which keeps the core of the star hot.
What is the third (main sequence) stage of a star forming?
After Protostar
The star enters a long stable period. During this, the outward pressure caused by thermal expansion balances the force of gravity, pulling everything inwards. This is called a main sequence star and typically lasts several billion years. The heavier the star, the shorter this time.
What is the fourth stage of a star forming?
After Main sequence star
Eventually, the H in the core begins to run out and the force due to gravity is larger than the pressure of thermal expansion. The star is compressed until it is dense and hot enough that hydrogen in its outer layers and helium in its core can undergo fusion; increasing pressure of thermal expansion - making the outer layers of the star expand
What is Thermal Expansion?
Life cycle of a star
The energy produced by nuclear fusion tries to expand a star
What does the star form into after the fourth stage?
After main sequence star
red giant (small star)
red supergiant (big star)
the outer surface gets red because it cools down
What does a red dwarf form after?
A white dwarf
- A small to medium sized star like the sun then becomes unstable and ejects it outer layer of dust and gas. This leaves behind a hot, dense solid core.
What do bigger stars form after red supergiant?
Big stars, start to glow brightly again as they undergo more fusion to make heavier elements. They expand and contract several times, as the balance between gravity and thermal expansion shifts. Eventually, they explode into a supernova.
What can supernovas form?
Neutron stars or black holes
- the exploding supernova throws the outer layer of dust and gas into space, leaving a very dense core called a neutron star.
- If the star is massive enough, it will collapse and form a black hole
What is a black hole?
A super dense point in space that not even light can escape from.
Where are electrons located in the model of the atom?
they sit in different energy levels orbiting the nucleus called shells
- Each energy level is a different distance from the nucleus
How can electrons move energy shells?
It can move up to a higher energy level if it absorbs EM radiation with the right amount of energy
What happens when electrons receive enough EM radiation to move up a higher energy level
It moves up to a higher energy level and is said to be “exited”
The electron will then quickly fall back to its original energy level, and in doing so will emit the same amount of energy it absorbed - the energy is carried away by EM radiation
What does the EM radiation released by electrons falling energy levels depend on?
Depends on the energy emitted - depends on the energy levels moved in-between. A higher energy means a higher frequency of EM radiation - often visible light is released
What happens to energy levels as you move out of the nucleus?
Further out from the nucleus, the energy levels gets closer ( so the difference in energy gets smaller)
How does the frequency of generated radiation (by electrons falling in energy levels) relate to the distance from the nucleus?
the frequency of generated radiation decreases as the energy levels get further from the nucleus
How does an atom become ionised?
When an electron absorbs radiation with enough energy, it can move far enough to leave the electron
What is ionising radiation?
Any radiation that can knock electrons from atoms
What is nuclear fusion?
the opposite of nuclear fission
What happens in nuclear fusion?
two light nuclei collide at high speed and fuse to create a larger, heavier nucleus
e.g 2 hydrogen can create a helium nucleus
What happens to the mass of the nucleus created in nuclear fusion?
The created nucleus (heavier) does not have as much mass as the two seperate, light nuclei did. Some of the mass of the lighter nuclei is converted to energy and released.
What is the conditions needed for nuclear fusion?
- Needs really high pressures and temperatures
- Makes fusion reactors really hard and expensive to build
Why does nuclear fusion need really high pressures and temperatures?
The positively charged nuclei need to be very close to each other to fuse, so the strong force of electrostatic repulsion has to be overcome
Why are nuclear fusion reactors currently experimental?
it takes more energy to heat them up than energy produced by the fusion
What are the cons of nuclear power?
1) Public perception can be very negative - Dangerous, disposed of wrong and damaging environment
2) Nuclear power carries risks of leaks e.g. Chernobyl
What are the pros of nuclear power?
- Reliable and reduces the need for fossil fuels (reducing greenhouse gas emissions)
- Huge energy for small fuel amount
What are the two main theorys for creation of the universe?
steady state theory
the big bang
What is the steady state theory?
1) it says that the universe has always existed as it is now, and it always will do - based on the idea that the universe is the same everywhere
2) As the universe expands, new matter is constantly being created - density is always the same
3) In this theory there is no beginning or end to the universe
What is the big Bang theory
1) all matter in the universe initially occupied the small space - very dense and very hot
2) Then it exploded and expanded - and continues to do so
3) Gives a finite age to the universe
The current accepted theory on the universe
What are the 2 things that prove the universe is expanding?
Red-shift
Microwave radiation (CMB)
What is CMB?
Low frequency electromagnetic radiation coming from all parts of the universe (leftover energy from the initial big bang)
How has the model of the atom progressed
“plum-pudding model” - evidence: Electrons, Visual: Spheres of + charge with electrons stuck in them
Then Gold foil experiment - Alpha particles at foil (expected to pass through (or a abit deflected) and more were deflected)
- > Rutherford realised this meant that most of the mass of atom was concentrated in a nucleus + The centre had to have a + charge as it repelled the +alpha particles
How have ideas about the universe changed over time?
** (Greek) Geocentric model** - Sun,moon, planets and stars orbited earth in perfect circles - No telescopes and view of sun/moon orbiting earth everyday
**Heliocentric **- Earth and all planets orbited the sun in perfect circles
-> Evidence - Jupiters moons never moved away from it and therefore were orbiting it and not earth
**Current ** - Heliocentric but elliptical
What are telescopes used for?
Seeing distant things/observing the universe
They use refraction and reflection to see distant objects
What are optical telescopes?
Ones that detect visible light
How do you improve image quality whilst using telescopes?
Increase the apeture - this is the diameter of the objective lens - the big lens at the end of telescopes where light from distant telescopes enter the object
Use a higher quality objective lens
Why do space telescopes have a clearer view than telescopes on Earth?
- If trying to detect light, Earth’s atmosphere gets in the way - it absorbs alot of the light coming from space before it can reach us. To observe the frequencies absorbed, you have to go above the atmosphere
- Light Pollution - makes it hard to pick out dim objects
- Air Pollution - can reflect and absorb light coming from space
Where are telescopes positioned to get the best view of space?
Ontop of a mountain or in a dark place away from cities
- To avoid the problem entirely, place the telescope in space
What is used to get as full a picture of the universe as possible?
EM telescopes of all variation
What are X-ray and Radiotelescopes good for?
X-ray telescopes - good way to “see” violent, high temp events in space, e.g. exploding stars
Radiotelescopes - responsible for the discovery of CMB
