Topic 6 - Radioactivity Flashcards
The current model of the atom consists of
A positive nucleus of protons and neutrons
Surrounded by shells of negative electrons
The nucleus makes up almost all the mass but is tiny in comparison to the atom
Atoms and small molecules size
1 x 10^-10
Isotopes are
Atoms of an element with the same number of protons but a different number of neutrons. This means the atomic number stays the same but the mass number changes
Proton relative mass and charge
Mass: 1
Charge: 1
Neutron relative mass and charge
Mass: 1
Charge: 0
Electron relative mass and charge
Mass: 0 or 0.0005
Charge: -1
What is a positron
The antiparticle of an electron
Positron relative mass and charge
Mass: 0 or 0.0005
Charge: 1
Atoms are always neutral because
There is the same amount of protons and electrons
Electrons change orbit/shell when
It absorbs or emits EM radiation
If an electron absorbs EM it
Gets excited to higher shells which are higher energy levels. Then it quickly falls back.
When an electron falls back after being excited it
Emits the same amount of EM and energy as it originally absorbed
Atoms become positive ions when
They lose an electron
When an isotope nucleus is unstable it
Decays and gives out radiation. They emit one or more of alpha, beta and gamma. They can also emit neutrons
Beta particles can be either
Beta-minus particles: fast moving electrons released by the nucleus
Beta-plus particles: fast moving positrons
Alpha, beta and gamma rays are
Ionising
Background radiation is
Low-level radiation that is around us all the time
Sources of background radiation
Naturally occuring unstable isotopes
Radiation from space that is not stopped by the atmosphere
Radiation due to human activity
The two ways of measuring radiation
Geiger-muller tubes: Clicks every time it detects radiation, connected to counter for count-rate
Photographic film: It becomes darker with more exposure to radiation
Alpha particles are equivalent to
A helium nucleus: two neutrons and two protons
Alpha particles penetration
Dont penetrate far into materials and are highly ionising
Beta particles are
Moderatley ionising and can’t penetrate very far
Gamma rays are an
EM wave with a short wavelength
Gamma rays penetration
Penetrate far into materials and are weakly ionising
JJ Thompson model name and year
Plum pudding model 1897
JJ thompsn discovered
that electrons could be removed from atoms
Plum pudding model features
Spheres of positive charge with negative electrons inside it
Rutherford experiment and year
Fired alpha particles at thin gold foil. Some particles unexpectedly bounced back in same direction. 1909
Rutherford experiment showed that
Most of the mass is in the nucleus and the nucleus has a positive charge.
Rutherfords experiment led which model
The nuclear model
What did Bohr do to the atomic model
Tweaked rutherfords model where the electrons are at fixed orbits from the nucleus called energy levels(shells).
Beta minus decay leads to
A neutron becoming a proton and an electron
Beta plus decay leads to
A proton becoming a neutron and a positron
Nuclear equations are
a way of showing radioactive decay using element symbols
Nuclear equation form
Atom before decay –> Atom after decay + Radiation emmited
Alpha decay leads to
A nucleus emitting an alpha particle
Gamma decay leads to
No change other than the nucleus losing energy in its excited state to become more stable
Alpha decay equation
Atom before decay –> Atom after decay + a(mass number 4 atomic number 2)
Beta minus decay equation
Atom before decay –> Atom after decay + B(mass number 0, atomic number -1)
Beta plus decay equation
Atom before decay –> Atom after decay + B(mass number 0, atomic number 1)
Neutron emission equation
Atom before decay + Atom after + n(mass number 1, atomic number 0)
Gamma ray decay equation
No change to atom after decay
After undergoing radioactive decay, nuclei often
Lose energy to become more stable through gamma radiation
Over time, activity of radioactive sources
Decreases because all the unstable nuclei are being decayed
The unit of activity of a radioactive source
Becquerels/ Bq
Activity in radioactivity is
The rate at which a source decays
1 Bq =
1 decay per second
A half life is
The average time taken for the number of radioactive nuclei in an isotope to halve
The process of decay is
Completely random
Half-lives allow us to
Predict the activity of a very large number of nuclei
Half life calculation:
a source takes 2 hours for activity to fall from 640Bq to 40Bq. What is the half life
30 mins
How to find half-life on a activity/time graph
Find the amount of time taken for the activity to reduce by half
Household fire alarms use
Alpha radiation. A weak source is placed close to two electrodes. This means there is a current of charged particles. If there is smoke, it absorbs the charged particles and stops the current, sounding the alarm
Food and equipment can be sterilised using
A high dose of gamma rays which kill microbes.
Cancer can be detected using
Tracers(certain radioactive isotopes) swallowed into the body. they are tracked to see if there is a change in usual.
All isotopes passed through the body must be
Beta or gamma emitters, because alpha is highly ionising and will damage bodily cells
Leaks in underground pipes can be detected with
Gamma emittign tracers
Thickness control uses
Beta radiation. If the amount of radiation transmitted through a material changes then it is too thick or thin
Ionising radiation can lead to
Tissue damage. Either the cells die(high dose) or become mutated(low dose). These mutated cells can lead to uncontrolled division and therefore cancer.
The danger of ionising radiation depends on
Type of radiation
Irradiation or contamination
Half-life
Initial activity level
Irradiation is dangerous when
It is beta or gamma because they are less ionising and can penetrate the skin to get to the vital organs
Contamination is more dangerous when
It is alpha sources because they are very ionising and cant penetrate the skin. Thsi means if inside the body they can cause major damage to vital organs.
Internal tumour treatment methods
Alpha emitter injections
Beta emitter implant
Alpha to treat tumours
Alpha source is injected near to the tumour. kills tumour cells and does minimal damage to surroundign cells because of short range
Beta to treat tumours
Beta source is in an implant placed near a tumour. They penetrate the implant and reach the tumour cells. May do some damage to surounding healthy cells
External tumour treatment method
Gamma rays aimed at tumour
Gamma to treat tumours
It is aimed at the tumour. penetrates skin to tumour. can do some damage to surrounding cells.
PET scan process
Substance used by body and containing a positron-emitting isotope injected into body as tracer
They travel to organs and more travels to the tumour as it uses more of the substance.
The positrons colllide with electrons in the tumour and annihilate, emitting gamma.
Pairs of gamma rays are emitted in opposite directions, and the tumour must be on that line.
When three pairs are detected, traingulation can be used to accurately find the tumour location
Why do isotopes used for PET scanners need to be produced nearby
they have small half-lives, so wont be active enough if left for too long.
PET stands for
Positron Emission Tomography
Advantages of nuclear power
Quite safe
Very reliable
No greenhouse gases
Large amounts of energty from small amount of material
Disadvantages of nuclear power
Bad public perception
Radioactive waste products
Risk of major catastrophes
Nuclear reactions that produce energy
Fission
Fusion
Radioactive decay
Nuclear fission is
The splitting up of big atomic nuclei from uraniunm or plutonium atoms
Nuclear fission is a
Chain reaction
Nuclear fission chain reaction process
A slow-moving neutron is fired at uranium-235
This makes it more unstable, so it splits
It froms two lighter elements(daughter nuclei) and produces energy
The new nuclei are also radioactive
2 or 3 neutrons are released as well, which hit the next uranium nuclei
How is the the chain reaction of nuclear fission controlled
Fuel rods(containing uranium) are in moderators which slow down nuclei.
Control rods absorb excess neutrons to prevent uncontrolled fission(leads to explosion)
Fuel rods in nuclear fission are
The rods that store the uranium nuclei
Moderators in nuclear fission are
A substance such as graphite that slows down neutrons
Control rods in nuclear fission are
Made of boron, and limit the rate of fission by absorbing excess neutrons
How is energy transferred into electricity from nuclear fission
The thermal energy is transferred to water, which boils and produces steam. This spins a generator to produce electricity
The products of nuclear fission are
Radioactive
Nuclear fusion is
The joining of small nuclei to produce energy
Nuclear fusion process
Two light nuclei collide at a high speed and join to create a heavier nucleus
Some of the mass from the original nuclei is tranferred to energy.
Nuclear fusion is the enrgy source for
Stars
The difference between fission and fusion
Fission - Splitting up of large nuclei to release energy
Fusion - Joining up of small nuclei to release energy
Nuclear fusion only happens at
Very high temperatures and pressure
Why does nuclear fusion need such extreme conditions
The nuclei are positivley charged so repel eachother. Therefore extremely high forces are needed to overcome this repulsion and make them colide
The extreme conditions for fusion means that
Stations are very uneconomic and expensive, so there arent any effective ones
