SP6 Radioactivity Flashcards
What’s the particle theory / kinetic theory
Is the model that helps explain properties of liquids and gases and solids
Particles usually represented with spheres
When do chemical reactions occur
When atoms in substances become joined in different ways
What did J.J Thomson do
Carried out experiments to show atoms contain much smaller subatomic particles called elections - these have a negative charge and hardly any mass
Described as a pudding made of positron charged material with negatively charged electrons (plums) scattered through it
What did Ernest Rutherford do
Carried out experiments involving a study of what happened when positively charged subatomic particles (alpha particles) passes through various substances
He discovered most of a particles went through gold foil but a few bounces back - the plum pudding model could not explain this
What did Rutherford change about the plum pudding model
Suggested atoms were mostly space with most of mass in the central nucleus with a positive charge and electrons around the nucleus and so would allow some particles to be deflected by a small amount
What the radius of a nucleus
1 X 10^-15 m radius
1 X 10^-10 for the atom so atom itself 100,000 times bigger than nucleus inside it
What are nucleons
Particles in nucleus
They are protons or neutrons
Protons have a mass of 1 and neutrons a mass of 1
What’s the atomic number
The proton number = number of electrons too
What’s the mass number or nucleon number
The total number of protons and neutrons in the nucleus
Numbers of neutrons can vary
What are isotopes
Two atoms of the same element have different mass numbers as a result of different numbers of neutrons
Tell me about electrons shells
Electrons can only exist in certain orbits around the nucleus
Each electron shell is at a different energy level so If ask atom absorbs energy an electron can move to a higher orbit
When does an atom emit light
When an atom emits energy it moves to a lower orbit and emits visible light of a particular wavelength
What’s the emission spectrum
It’s different for each element
An electron can move down 1 sheep at a time, even 2, maybe 3 or more at a time so different wavelengths are produced which show up on emission spectrum
What’s the absorption spectrum
The visible spectrum that passes through an atom
The wavelengths of light that neon gas absorb are the same wavelengths it emits
What did Niels Bohr amend about Rutherfords model of the atom
Suggesting electrons can only be in certain shells around the nucleus and can’t be in between so that’s why they are lines on emission and absorption spectra
When does ionisation happen
When an atom gains so much energy one or more of the electrons can escape from the atom all together
Radiation that causes electrons to escape is called ionising radiation
This means it has a positive charge as there are more protons so it’s a positive ion
What’s backround radiation
We are constantly being exposed to ionising radiation at a low level, from space and naturally radioactive substances in the environment
What are the sources of backround radiation
49% radon gas - produced by rocks that contain small amounts of uranium- it diffuses into the air and can build up in houses. Rock type varies so does amount of radon
15% medical 13% ground and buildings 12% cosmic rays 10% food and drink 1% nuclear and other
What are cosmic rays
High energy charged particles from the sun and other stars
They are stopped by the upper atmosphere but some still reach the surface
How can radioactivity be detected using photographic film
It becomes darker and darker as more radiation reaches it
However the film has to be developed in order to measure the amount of radiation (the dose)
Dosimeters are often work to check how much radiation they have been exposed to (badge)
Newer dosimeters use materials that change colour without needing to be developed
How can the radioactivity or a source be measured
Using a Geiger müller (GM) tube
Radiation passing through the tube ionises the gas inside it and allows a short pulse of current to flow
The tube can be connected to a counter to count the pulses of current or the GM tube may give a click each time radiation is detected
The count rate is the number of clicks per second or minute
What do scientists do before they measure radioactivity of a source
They need to measure the backround radiation first by taking several readings and finding the mean - the mean value is then subtracted from the measurements!!
What’s the nucleus of a radioactive substance like
It’s unstable so it fan easily change or decay
Tell me about decay
When it occurs radiation is emitted which causes the nucleus to lose energy and become more stable - it’s a random process and you can’t predict it
What are alpha particles
Alpha particles contain two protons and two neutrons
- just like nucleus of helium atom
They have a relative mass of 4 with no electrons
Charge of +2
Can be written as fish symbol / weird a
Or 4 with 2 under and He by the side
Tell me about Beta particles
They are high energy, high speed electrons
They have a relative mass of 1/1835 and a charge of -1 they can be written as a welter B with a - minus sign top right corner of it
Or 0 with -1 under and e next to it
The electrons that are beta particles come from the nuclei of atoms when a neutron transforms into a proton
Beta particles do not ionise the atoms as they leave them
Tell me about positrons
They are high energy high speed particles with the same mass as electrons but a charge of +1
They can be written as B^+ or 0 with +1 under and e
Opposite to beta particles
Tell me about gamma rays
written as weird y
They are a high frequency electromagnetic waves (they travel at the speed of light)
They don’t have an electric charge
Tell about neutrons is radioactive decay
Neutrons can also be emitter from an unstable nucleus
They have a relative mass of 1 and no electric charge
What type of radiation are positrons, gamma rays, beta particles and alpha particles
Ionising radiation
So they can all penetrate materials
Tell me about Alpha particles passing through materials
They are emitted at high speeds
Due to this and their high relative mass, they transfer a lot of energy and so are good at ionising atoms they encounter
Each time they ionise an atom they lose energy - since they produce many ions in a short distance, they lose energy quickly and have a SHORT PENETRATION DOSTANCE
THEY CAN BE STOPPED BU PAPER
How far can alpha particles travel
Can be stopped by a few centimetres in air
Very ionising
Can be stopped by a sheet of paper
Tell about beta particles being ionising
Beta particles are much less ionising than alpha particles so it can penetrate further in to matter
What can stop beta particles
Will travel a few metres in air
Moderately ionising
Can be stopped by 3mm thick aluminium
Tell me how ionising gamma rays are
They can penetrate much further in to matter they are about 10 times less ionising than beta particles and can penetrate matter easily
What can stop gamma rays
They will travel a few km in air
Weakly ionising
Need thick lead or several metres of concrete to stop them
They can use gamma rays to check the inside of lorries to help prevent movement of illegal goods
How can an atom become a different element
When an unstable nucleus changes and emits particles, the atomic number can change
If this happens to atoms becomes a different element
Eg when alpha is emitted th mass number goes down 4 and atomic number by 2
When happens to a neutron in beta decay
A neutron changes in to a proton and electron
The electron is ejected from the atom. Atomic number increase by 1 mass number don’t change
Beta particle is the electron
What happens in positron decay
A proton becomes a neutron and a positron
The atomic number goes down by 1 by mass number don’t change
What happens with gamma radiation
Nuclei may lose energy as gamma radiation when the subatomic particles in the nucleus are rearranged which helps makes them more stable
What’s a nuclear equation
Shows what’s happened during radioactive decay
The equation must be balanced and the total mass number and total charges must be the Same on both sides
Look page 101 (just like a half equation in chemistry ish)
What did Marie curie do
Made important discoveries with radioactivity
Before dangers were known - notebooks are still radioactive
What’s the ACTIVITY of any radioactive substance
The number of decays per second and is measured in becquerels )Bq£
One becquerel is one nuclear decay each second
What’s the half life of a radioactive substance
It’s the time taken for half the unstable nuclei in a sample of a radioactive isotope to decay
We can’t predict individual nucleus because it’s a random process
However the half life does allow us to predict the activity of a large number of nuclei
The half life is the same for any mass of a particular isotope
Wh Carbon-14 is 5730 years
The more stable a nuclei a sample of a substance contains the lower its…
Activity
The half life of an isotope is therefor also a measure of how long it takes tor the activity to halve
I
How can half like be recorded
It can be found by recording the activity of a sample over a period of time
Take a break
;)
How can gamma rays be used to kill microorganisms
Some bacteria also cause food poisoning, food can be irradiated by gamma rays to kill bacteria
- makes it safer to eat do you can store it for longer
Also surgical instruments need to be sterilised to kill microorganisms- heat Them but plastic ones are irradiated with gamma rays
Tell me about tracers
Radioactive isotopes can be used as tracers - a gamma source added to water is used to detect leaks in water pipes buried underground
Where ther is a leak the water flows into the surrounding earth. A Geiger-müller tube following the path of the pipe will detect higher levels of radiation where there is a leak
How can radioactivity be used for cancer tracers
It can be used a tracer in the body to find cancer
Similar to a leaking pipe
How can radioactivity be used to check thickness of paper
A detector is below he paper and a beta source on other side
If paper is too thin more beta particles penetrate the paper and the detector records a higher count rate and so rollers to squash paper reduces force to make it thick and oppose happens when paper too thick
Tell me about using radioactivity for smoke alarms
It contains a source of alpha particles, there’s a gap in an electrical circuit between 2 electrically charged plates and alpha Partjcles ionise air and attract move to opposite charge plate and allow a small electrical current to flow
When smoke gets in to gap - air is not ionises as smoke particles slow down jons and so alarm sounds when the current drops below a certain level
What can ionising radiation do to your skin m8 this ain’t difficult
Damage your tissue - reddened skin from radiation burns
Small amount over long time can damage DNA in a cell - may cause cancer - if they occur in gametes they can be passed on to the next generation; not all mutations harmful and cells often capable of repairing damage if the dose is low
Why are radioactive sources always handled with tongs
The intensity of radiation decreases with distance from the source, risk can further be redirected by not pointing sources at people and storing them in lead lined containers
Tell me about radiation in hospital
Small doses
Sources with shortest half life used - minimise time patient is exposed
What’s irradiation
When someone is exposed to radiation from a nearby radioactive martial - once they move away the irradiation stops
Whats contamination
If they inhale, touch or ingest radioactive material - radiation will continue until material has decayed or is removed which isn’t always possible
Water and soils can be contaminated and spread in the food chain - many people concerned with accidents in nuclear power stations
Tell me about radioactive tracers - how they work
With gamma
The tracer often contains a radioactive isotope attached to molecules that will be taken up by particular organs in the body - the tracer emits gamma rays
It can be ingested, inhaled or injected into blood or organ
Gamma cameras detect the tracer
What can tracers be used for with gamma
They find sources of internal bleeding - gamma camera detect highest areas of gamma radiation when bleeding is occcuring
Gamma cameras also detect tumours - radioactive glucose molecules because cancer cells are very active and uptake glucose more quickly than other cells
Give me an example of a radioactive isoptope
Technetium-99m is attached to a drug that collects in the brain
Tell me about using tracers with positrons
A tracer emits a positron, when this meets an electron both the electron and positron are destroyed and 2 gamma rays are emitted in opposite directions
The detector in a PET scanner moves around the patient building up a set of images showing where the the different amounts of gamma radiation are coming from
Why must radioactive isotopes used in tracers have a short half life
So other parts of the body are affected as little as possible - since they lose there reactivity quickly they must be made close to a hospital and are often used within or even minutes of productions
Why are cancer cells more susceptible to being killed by radiation
They divide more rapidly than cells in the body and are so more susceptible
What’s internal radiotherapy
It uses a beta emitter placed close or in a tumour and the patient stays in the room alone whilst source in place
Doesn’t always require surgery
What’s external radiotherapy
Uses Beams of gamma rags or x Rays or protons directed at the tumour from outside the body
Serveral lower strength beams may be directed from different directions so that only the tumour absorbs a lot of the energy
What are the two types of nuclear reaction that are used as a source of energy on a large scale
Nuclear fission
Nuclear fusion
Tell me simply what’s nuclear fission
Large nuclei such as uranium-235 break up to form smaller nuclei and release energy
Fission reactions are used in nuclear power stations
Tell me simply what nuclear fusion is
Two small nuclei join together to from larger nucleus, fusion reactions release energy inside the sun
Tell me some pros of nuclear fuels
They store a lot more energy per kilogram than any other type of fuel, this makes them useful for naval ships and submarines
Nuclear fuels don’t burn and don’t need air to allow them to release energy and don’t produce co2 - most energy is used in power stations to generate electricity
Although uranium is non renewable but supplies estimated for over 200 years - much longer than other non renewable fuel
Tell me about radioactive waste
They do produce waste that will stay radioactive for millions of years - it’s also expensive to treat - sealed in concrete or glass and buried safely
Parts of a nuclear power station become radioactive as it is used and this makes it very difficult to decommission (dismantle safely)
Tell me about nuclear fission
Uranium 235 nucleus absorbs a nucleus and then splits into 2 smaller daughter nuclei - which are radioactive.
2 or more neutrons are released and both neutrons and nuclei store a lot of kinetic energy, energy also transferred by heating
If neutrons released are absorbed by other uranium 235 nuclei become unstable and release more nuetrons and so on
It’s an uncontrolled nuclear chain reaction
What are fuel rods
In a nuclear reactor the the fuel is made into fuel rods - at high speeds neutrons leave the fuel rods and are slowed down to increase chance they will be absorbed by any other uranium nuclear
Inside a reactor core, fuel rods are inserted into holes in a material called a moderator which slows down the neutrons
What’s a moderator
Holes in a material to slow down nuetrons in nuclear fission
How is the chain reaction nuclear fission controlled
Using control rods - which contain elements thag absorb nuetrons
They are placed in the reactor core, if rate of fission needs to increase, control rods moved out of the core and vice versa
When the control rods are fully lowered into the core, the chain reaction stops and the reactor shuts down
How is electricity generated from nuclear fission
Energy released from the core is transferred to a coolant - which is lumped through the reactor, coolant can be water, gas or a liquid metal
The hot coolant is pumped by a heat exchanger where it’s used to make steam which drives a turbine which turns a generator to produce electricity
Tell me about nuclear fusion
Occurs when smaller nuclei combine to form larger ones, the mass of the larger one is slightly less than 2 smaller nuclei - lost mass due to converted energy
Tell me about fusion in the sun
Hydrogen nuclei combine to form helium
Hydrogen-2 deuterium and hydrogen-3 tritium have to be forced together , the protons are positively charged and like charges repel; electrostatic repulsion
Sun has strong gravity so very high pressure in centre - so nuclei close together to be more likely to fuse + higher temps and so some can overcome electrostatic repulsion and fuse
Why aren’t we doing nuclear fusion on earth
A useful fusion reactor needs fusion to happen faster than it does in the sun
Very difficult to reproduce very high pressures on earth, so temperature needs to be very high - hotter then the sun so we can’t do this on earth or at least to make it efficient
Difficult to sustain extreme temps and pressures required - so far no experimental reactors have produced more energy than has been put in
Would fusion or fission reactors produce more energy
Fusion theoretically would produce more energy
Helium produced is not radioactive, but any materials used to contain fusion reactions do become radioactive - but far less problems with disposing radioactive waste from fusion reactors than fission
