Section 3: Radioactivity & Astronomy Flashcards
How has the atom structure developed over time?
- Believed to be a tiny sphere that can’t be broken up
- Electrons were discovered so ‘Plum Pudding’ model created - sphere of positive charge with negative electrons stuck in it
- Alpha scattering experiment was carried out so ‘nuclear model’ created - positively charged nucleus surrounded by a cloud of negative electrons
- Neil Bohr’s carried out theoretical calculations so ‘Bohr model’ created - electrons orbit the nucleus at certain distances
What was the alpha scattering experiment? What did it show?
When an experiment was carried out where some alpha particles deflected back when they hit gold foil but most passed through
Showed that:
-This showed that most of the mass of an atom was concentration at a central, tiny nucleus
-nucleus is positively charged
What are the relative charges and relative masses of protons, neutrons and electrons?
. | Relative charge | Relative mass |
————————————————
Protons | +1 | 1 |
Neutrons | 0 | 1 |
Electrons | -1 | 0.0005 |
What is the charge of the nucleus?
Positive
What is the size of an atom?
Size of atom ≈ 1 x 10^-10
What can electrons absorb and emit?
Can absorb: EM radiation and move to higher energy levels
Can emit: EM radiation and move to lower energy levels
What is an atoms overall electric charge?
0
number of electrons = number of protons
SO they cancel out
What happens if an atom loses one or more electrons?
Becomes a positively charged ion
What is an isotope?
An atom of the same element with the same number number of protons but a different number of neutrons and therefore also has a different mass
What is the mass number of an element?
Total number of protons and neutrons in an atom
(Protons + neutrons = mass number)
It’s the number at the top or often the larger number
What is the atomic number of an element?
The number of protons in an atom
(Atomic number = protons)
It’s the number on the bottom of the element or often the smaller one
What is radioactive decay?
When the nucleus of an unstable isotope decays, giving out radiation to become more stable
What is ionising radiation (alpha, beta & gamma)?
Radiation that knocks electrons off atoms, creating positive ions
What can unstable nuclei release (not decay)?
Can release neutrons when they decay
Alpha particles: what they consist of, what they’re absorbed by, their range in the air and their ionising power.
Consist of: 2 neutrons and 2 protons (nucleus of helium)
Absorbed by: sheet of paper
Range in air: a few cm
Ionising power: strong
Beta minus particles: what they consist of, what they’re absorbed by, their range in the air and their ionising power.
Consist of: fast moving electrons from the nucleus
Absorbed by: sheet of aluminium
Range in air: a few metres
Ionising power: moderate
Gamma particles: what they consist of, what they’re absorbed by, their range in the air and their ionising power.
Consist of: electromagnetic radiation from nucleus
Absorbed by: thick sheets of lead
Range in air: long distances
Ionising power: weak
What is the trend from alpha to beta to gamma (ABG)?
. ABG
most ionising least ionising
least penetrative most penetrative
What happens when a neutron become a proton?
Neutrons in a nucleus decay into a proton and eject a neutron
Called a positron or a beta minus particle
What happens when a proton becomes a neutron?
Protons in a nucleus decay into a neutron and eject a positron (positive electron)
Called a beta plus particle
What happens in alpha nuclear reactions?
Mass number decreases by 4
Atomic number decreases by 2
What happens in beta minus nuclear reactions?
Mass number stays the same
Atomic number increases by 1 (a neutron turns into a proton)
What happens in beta plus nuclear reactions?
Mass number stays the same
Atomic number decreases by 1 (a proton turns into a neutron)
What happens in gamma nuclear reactions?
Mass number stays the same
Atomic number stays the same
What happens in the nucleus for gamma radiation to be emitted?
When nuclear rearrangement occurs due to decay
Is radioactive decay random or no?
Yes it’s random
What is activity?
The rate at which a source decays, measured in becquerels (Bq)
What can radioactive decay be detected by?
Photographic film
What measures activity?
A Geiger-Muller tube and counter
What is background radiation?
Low level radiation that’s always around us
What are the two sources of background radiation?
- From earth - rocks, food, air, building materials, nuclear waste, fallout from nuclear explosions
- From space - cosmic rays
RADON GAS
What is radioactive contamination?
Getting unwanted radioactive atoms onto or into an object
What is irradiation?
The exposure of an object to ionising radiation (doesn’t make the object radioactive)
What is half life?
Time taken for the number of nuclei of an isotope in a sample to halve
If there are 20 nuclei of an isotope in a sample, how many will there be after 1 half life?
10 nuclei
What can half life be represented by?
A graph
What is on the x axis and y axis of a half life graph?
X axis - time
Y axis - activity
If the activity is 800 and after 10s, the activity is 400, then what is one half life? Why?
10s
One half life is the time taken for the activity of a sample to halve (800/2 = 400)
What two things can happen to a cell that’s in the body if it’s ionised?
Cell can be mutated when radiation enters a living cell, ionising its atoms - the mutated cell can then multiply and become cancer
OR
Cell can be killed when radiation enters a living cell, ionising its atoms
What types of radiation are the most and least dangerous in the body?
Alpha is most dangerous
Gamma is least dangerous
What types of radiation are the most and least dangerous outside the body?
Gamma is the most dangerous
Alpha is the least dangerous
What are the 4 precautions to reduce radioactive exposure?
- Keep sources in lead lined boxes
- Stand behind barriers or be in a different room to the source
- Wear protective clothing and use tongs to handle sources
- Have limits to how much time can be spent around radiation expose
What happens in short half lives?
- Short half life
- Activity falls quickly
- Emits high amounts of radiation in short time
- Become safe quicker
What happens in long half lives?
- Longhalf life
- Activity falls slowly
- Emits small amounts of radiation over a long time
- Is hazardous for longer
What type of materials partially absorb beta minus?
Beta minus is partially absorbed by thin materials (e.g. paper)
How do fire alarms work?
There are alpha sources in fire alarms
These cause ionisation and therefore create current
However…
Smoke particles stop the current
This then causes the alarms to sound
What is gamma radiation used for? Why?
Can be used for sterilisation of food and medical equipment
This is because high doses of gamma kill microbes
What are the two ways of treating cancer?
- Externally
- Internally
How can cancer be treated externally?
Gamma sources from outside the body are directed at cancer cells
How can cancer be treated internally?
Alpha and beta sources are put inside the body next to cancer cells
What is the negative of cancer treatments?
They cause damage to both cancerous and healthy cells
What are the two ways to diagnose medical conditions?
- Medical tracers
- PET scans
What is a medical tracer?
A radioactive source that’s injected or swallowed to explore internal organs
What type of radioactive source is used in medical tracers? Why?
Gamma sources
So that when radiation passes out of the body, it won’t cause much damage
What are PET scans?
Scans that detect medical conditions
What radioactive source do PET scans use?
Positrons
What are the properties of the radioactive source PET scans use?
Positrons - short half lives SO must be produced near by
How do PET scanners work?
- positron electron annihilation in the body occurs
- Causes gamma rays to be emitted
- Gamma rays are detected in the machine and used to form an image of inside the body
What is nuclear fission?
Splitting a large, unstable nucleus into two smaller nuclei of approximately equal size
When does fission occur?
When an unstable large nucleus absorbs a neutron
What does fission release?
Energy
Smaller nuclei
2 or 3 neutrons
What happens to the neutrons released by fission?
Can be absorbed by another nucleus
This starts a chain reaction (often controlled in a nuclear reactor)
What are the 5 parts of a nuclear reactor? IN ORDER
- Coolant
- Uranium fuel rod
- Moderator
- Boron control rod
- Boiler
What happens to a coolant?
heated by energy that’s released by chain reaction
What’s an example of a coolant?
Water
What happen to the uranium fuel rod?
Undergoes the fission chain reaction
What does a moderator do?
Slows down neutrons so they can be absorbed by nuclei and cause fission
What does a boron control rod do?
Absorbs excess neutrons to control chain reaction, prevents runaway reaction that could cause an explosion
What happens in the boiler?
The coolant is made into steam
Steam drives the turbine and generator to make electricity
What are pros of nuclear power?
No CO2 emission
A lot of energy is generated from a small amount of fuel
Reliable
What are cons of nuclear power?
Has a negative public perception
Risk of catastrophe (e.g. Chernobyl)
Waste is radioactive and hard to safely dispose of
What is nuclear fusion?
When two light nuclei collide at high speed and join to create a larger, heavier nucleus
What is released in nuclear fusion?
Energy - some of the mass of the lighter nuclei is converted into energy and is released
Heavier nucleus
What conditions are needed for fusion to occur? Why?
High temperatures
High pressure
BECAUSE NUCLEI HAVE TO OVERCOME ELECTROSTATIC REPULSION TO GET CLOSE ENOUGH TO FUSE
What are some negatives of nuclear fusion?
Requires a lot of energy
Expensive
Therefore there hasn’t been an efficient fusion power station built yet
What is the order of the planets (from closest to the sun to the farthest)?
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
How to remember the order of the planets (from closest to the sun to the farthest)?
My
Very
Easy
Method
Just
Speeds
Up
Nothing
What do the planets orbit and in what type of orbits?
The planets orbit the sun in almost circular orbits
What are examples of natural satellites?
The moon
What does the moon orbit and how?
The Earth in almost circular orbits
How to artificial satellites orbit?
In fairly circular orbits
What do comets orbit and how?
Comets orbit the sun in highly elliptical orbits
They travel faster the closer they get to the Sun
What was the first model of the solar system? When was it created?
The geocentric model
Created thousands of years ago
What did the geocentric model state?
Everything orbits the earth in perfect circles with a fixed background of stars
What is the current model of the solar system? How was it discovered?
The heliocentric model
Discovery: Galileo found out that Jupiter had moons using a telescope - not everything orbited Earth
What does the heliocentric model state?
Planets orbit the sun
What does gravitational field strength depend on?
Mass of the body - larger mass means a bigger gravitational field strength
Distance from it - the further away from it the smaller gravitational field strength
What is directly proportional to gravitational field strength?
Weight
What does does gravitational force do?
Keeps planets and satellites in a circular orbit
What happens in circular orbits?
The direction of the object is constantly changing
So the objects velocity constantly changes BUT the speed remains constant
What happens if the speed of an object, in stable orbit, changes?
The radius of the orbit changes
The smaller the orbit radius, the faster the object travels
What is the Doppler effect?
When a wave source is moving relative to an observer, there is a change in the observed frequency and wavelength
What happens to sound waves that move away from an observer in the Doppler effect?
They have a longer wavelength
They have a lower frequency
What happens to sound waves that move towards an observer in the Doppler effect?
They have a shorter wavelength
They have a higher frequency
What is red shift?
An observed increase in the wavelength of light (light is shifted towards the red end of the spectrum)
Observed when a galaxy moves away from Earth
What happens the more distant a galaxy gets in red shift?
It moves away faster
It’s red shift increases
What does CMB stand for?
Cosmic microwave background radiation
What is CMB radiation?
Low frequency electromagnetic radiation coming from all parts of the Universe
What 3 things does the Big Bang theory say about the universe?
- Universe has finite age
- All matter started in a dense and hot tiny space and ‘exploded’
- Space started expanding and still is
How does red shift provide evidence for the Big Bang theory?
Evidences that the universe is expanding
Supports this theory
How does CMB radiation provide evidence for the Big Bang theory?
Evidences that the universe had a beginning - explosion that released radiation
Supports this theory
What 3 things does the the steady state theory say about the universe?
- Universe is always expanding and always will be- no beginning or end
- Universe is expanding
- More matter is constantly being created - density stays constant
How does red shift provide evidence for the steady state theory?
Evidences that the universe is expanding
Supports this theory
How does CMB provide evidence for the steady state theory?
Doesn’t explain it
Doesn’t support this theory
What is the lifecycle of a star?
- Nebula (cloud of dust and gas) - gravity pulls the dust and gas together to form a star, the star gets denser and temp rises, hydrogen fusion then starts in the stars core then outward pressure from thermal expansion balances the inward force of gravity
- Main sequence star - hydrogen nuclei begin to run out and the star begins to fuse heavier elements, increasing pressure
FROM NOW ON THERE ARE TWO ROUTES:
ROUTE 1 - if mass of the star is greater than the Sun: red supergiant formed, supernova formed, then a neutron star or a black hole is formed
ROUTE 2 - if mass of the star is equivalent to the Sun: red giant formed, white dwarf formed
How has the universe been observed over the years?
- Optical telescope from 1600s
- Telescopes for other EM waves e.g. radio telescope from 1930s
- Telescopes in space from 1960s
What are properties of optical telescopes?
First telescope
Only detect visible light
What are properties of telescopes for other EM waves?
Detect other EM waves e.g. radio and x-ray
What are properties of telescopes in space?
Avoid light and air pollution
Detect EM waves that would be absorbed by earths atmosphere
Why have telescopes improved over time?
To give a better resolution and magnification to make sharper images
RADIATION CORE PRACTICAL: How can the emission of radiation be investigated?
- Get identical test tubes but wrap them in materials with different surfaces, cover the test tubes with bungs once the water has been poured in
- Boil water and fill each test with tube with the same volume
- Measure the temperature of water at regular intervals - temperature will drop faster if the surface is a better emitter
RADIATION CORE PRACTICAL: What 2 things can be gathered from the experiment investigating emission of radiation?
- A black surface is a better emitter than the white one - it dropped in temperature faster
- A matte surface is a better emitter than a shiny one - it dropped in temperature faster
RADIATION CORE PRACTICAL: What is the control, independent and dependent variable of the experiment investigating emission of radiation?
Control variable: volume of water and shape of test tube
Independent variable: surface that’s in the tube
Dependent variable: rate of decrease of water temperature
How does a Geiger muller tube work?
It gives an electrical signal each time radiation is detected - these signals can be converted into clicking sounds, giving a count rate in clicks per second or per minute
