Radioactivity Flashcards
What is radioactivity?
The random and spontaneous emission of a particle or wave from an unstable nucleus
What is the mass number in an atom?
Sum of protons and neutrons in the nucleus of an atom
What is the atomic number in an atom?
The number of protons in the nucleus of an atom
What is an isotope?
Atoms of the same element with same amount of protons but a different amount of neutrons in the nucleus of the atom
What is ionisation?
The remove of an electron/ electrons from a neutral atom to leave an ion
What is background radiation?
It’s all around us, from natural and man-made sources.
What are some man-made sources of background radiation?
Fallout of nuclear weapons, medical procedures and agriculture
What are some natural sources of background radiation?
Cosmic rays from the sun and radioactive rocks
What is the atomic number and mass number of an alpha particle?
Atomic number - 4
Mass number - 2
Same as a helium nucleus
What is the range of alpha particle and why?
10cm in the air and 1 sheet of paper because it’s slow and heavy - low penetrating power
How ionising is an alpha particle?
Very ionising as it has a large charge
Are alpha particle dangerous?
Yes, inside of the body
What is the speed of an alpha particle?
0.1C
Is an alpha particle affected by an electric field?
Yes, goes towards negative
Is an alpha particle affected by a magnetic field?
Yes
What are alpha particles detected by?
GM tube and photographic film
What is the atomic number and mass number of a beta particle?
Atomic number - 0
Mass number - -1
High speed electron
What is the range of a beta particle?
1m in air and 6mm in aluminium as they are faster and lighter than alpha - medium penetrating power
Are beta particles ionising?
Yes but less than alpha
Are beta particles dangerous?
Yes but less than alpha
What is the speed of a beta particle?
0.5C
Is a beta particle affected by an electric field?
Yes, goes towards positive side faster because it’s light
Is a beta particle affected by a magnetic field?
Yes
What are beta particles detected by?
GM tube
Photographic film
What is the atomic mass and mass number of a gamma ray?
Atomic mass - 0
Mass number - 0
High energy EM wave
What is the range of a gamma ray?
Thick lead as it has a high penetrating power
Are gamma rays ionising?
Yes, but less than beta
Are gamma rays dangerous?
Yes, but less than beta
What is the speed of gamma rays?
C
Are gamma rays affected by electric fields?
No (no charge)
Are gamma rays affected by magnetic fields?
No (no charge)
What are gamma rays detected by?
GM tube and photographic film
What is activity?
The rate of disintegration/ decay
What is activity measured in?
Becquerels (1Bq = 1 disintegration per second)
What is radioactive decay and where does it occur?
Occurs in unstable nuclei
Parent nucleus ejects a particle to form a new daughter nucleus, daughter nucleus is excited and loses energy given off as gamma rays
What is alpha decay?
When a nucleus ejects a helium nucleus/ alpha particle
What is beta decay?
When a nucleus ejects a high speed electron/ beta particle and nucleus turns into a proton
What does half life refer to?
The time it takes for the mass of a the sample to become half of the original mass
When recording activity what must we consider?
Background radiation, this is called corrected count rate
What are alpha particles used in?
Smoke detectors
How does a smoke detector work?
Radioactive isotope americium-241 releases alpha particles and ionises the air molecules which forms a current between the plates
The detector of current measures the high current
If smoke enters the smoke detector it goes between the plates and slows down the ions decreasing the current
This causes the alarm to sound
What’s the hazard of alpha particles?
If ingested it can do immense damage to living cells
What are beta particles used in?
Checking the thickness of a paper sheet in manufacturing
Radioactive tracers in medical research and diagnosis
How does a thickness controller work?
Controlled by how much beta radiation passes through the paper to the counter
Counter control the pressure of the rollers to give the correct thickness
How do radioactive tracers work?
Small amount of a source which emits beta or gamma is injected into someone
Radiation can be detected externally and doctors can check if organs are working properly
Sources have a short half-life
What are the hazards of beta particles?
Some risk of tissue damage but nothing in comparison to alpha
What are gamma rays used in?
Radio therapy
Sterilisation
Detecting leaks in underground pipes
How does radiotherapy work?
Kills cancer cells and stop the dividing
High dose of gamma directed at cells in tumour
How does sterilisation work?
Food and medical equipment can be irradiated with a high dose of gamma rays to kill microbes
How are leaking pipes found?
A small amount of a radioactive source is injected into the pipe
It’s detected with a GM detector above ground
What is irradiation?
Objects that are exposed to a radioactive source (doesn’t make it radioactive)
How to reduce the risk of irradiation of a radioactive source?
Putting the source in lead lined boxes
Standing behind barriers or being in a different room to the source
Using remote controlled arms
What is contamination?
Objects that have radioactive atoms on them or in them (they may decay, release radiation and cause harm)
How to reduce the risk of contamination of a radioactive source?
Gloves and tongs (stops particles stuck in skin or under nails)
Protective suits and masks (prevents particles being breathed in)
What are some examples of ‘low-level’ radioactive waste?
Waste from nuclear power stations and hospitals
E.g. clothing, syringes…
How can low-level waste be disposed of?
Burying the waste in secure landfill sites
How can high-level waste be disposed of?
Stays radioactive for tens of thousands of years
Sealed in glass blocks which are then sealed in metal canisters - which are buried underground
What must the place be to be suitable of disposing of the waste?
Geologically stable (doesn’t suffer from earthquakes) which disturbs canisters and radioactive material will be leaked out
What is fission?
The splitting of a large unstable nucleus into two less massive daughter nuclei (also radioactive and unstable)
What is induced fission?
When a stable nucleus splits into two daughter nuclei due to the absorption of a slow moving neutron
What is a chain reaction?
When induced fission causes more nuclei to split into daughter nuclei and the daughter nuclei split more nuclei
What is nuclear fusion?
The combining of two light nuclei into an even more massive nucleus
How does the massive the individual nuclei change in nuclear fusion?
They have more mass when they are separate in comparison to when they are combined into a nucleus
Does fission or fusion release more energy?
Fusion releases more energy
What are the conditions required for nuclear fusion?
Really high pressures
Really high temperatures (about 10,000,000°C)
Why are these conditions required for nuclear fusion?
Positively charge nuclei have to get very close to fuse, so they have to move very fast and overcome strong forces due to electrostatic repulsion
What is Einsteins mass-energy equivalence equation?
e=mc^2
Why do neutrons need to be slowed down in a nuclear reactor?
They have a lot of energy
To absorbed by uranium nuclei
To sustain the chain reaction
What is the moderator made of and what does it do?
Graphite or water
Absorbs some of the kinetic energy from neutrons to slow them down
What are the control rods made of and what do they do?
Boron or cadmium
They absorbs excess neutrons, thus can slow down or speed up the rate of reaction
Why is shielding used and what is it made of?
High energy neutrons and gamma rays are highly penetrating ionising radiation, shielding absorbs the ionising radiation
Thick concrete, lead or other metals
How does the nuclear reactor work?
A substance (e.g. CO2) is pumped around the reactor and transfers the energy (by heating) to water in the heat exchanger. The water turns to steam which turns a generator and generates electricity.
What are the positives of nuclear reactors?
Doesn’t produce any pollutant gases
Produces a lot of energy
What are the negatives of nuclear reactors?
Very dangerous to surrounding areas if not controlled properly
Waste material can’t be disposed of easily (stored underground)
