Radioactivity Flashcards
What is radioactive decay?
Some isotopes have an unstable nucleus
To become stable, the nucleus gives out radiation
This process is radioactive decay
Can radioactive decay be predicted?
No, it is a completely random process and scientists cannot predict when it will occur
Activity
The rate at which a source of unstable nuclei decay
How do we measure activity and what’s the unit?
Using a Geiger-Muller tube
Becquerel (Bq)
What is the count rate in a Geiger-Muller tube?
Number of decays recorded each second by a detector
Ie the number of radioactive emissions picked up
But scientists can’t say for certain when this will happen
Alpha particles
A type of radiation
Consists of 2 neutrons and 2 protons
The same as a helium nucleus
Beta particles
A type of radiation
1 electron which is ejected from a nucleus at a very high speed when a neutron changes into a proton and electron
Gamma ray
Type of electromagnetic wave
Is radiation from the nucleus
Neutron radiation
Sometimes given off by an unstable nucleus, also a type of radiation
Properties of alpha particles
Large
Travels around 5cm in the air before stopping due to air particles
Stopped with a single sheet of paper
Strongly ionising - produces lots of ions when hitting an atom
Properties of beta particles
Travels around 15cm in the air
Stopped by a sheet of aluminium
Quite strongly ionising
Properties of gamma rays
Can travel several metres in the air before stopping
Has to be stopped by several cm of lead
Weak ionising
Ionising power
When radiation collides with atoms, that can cause atoms to lose electrons and form positive ions
Nuclear equations
Shows us what happens when a radioactive nucleus decays
Alpha decay equations
The atomic number decreases by 2
The mass number decreases by 4
Creates helium atom with a mass of 4 and number of 2
Beta decay equations
The atomic number increases by 1
The mass number does not change
Produced an electron with atomic number -1
Why does the atomic number in a beta decay increase by 1?
Because the neutron becomes a proton, increasing the atomic number
Risks of ionising radiation
Can penetrate skin cells, if it hits the DNA in the nucleus can cause a mutation and thus cancer
Uses of radiation in medicine as a tracer
Can be used as X-rays ro visualise damage to find tumours/ arthritis etc
To find problems in the thyroid gland which absorbs iodine. Drinking radioactive iodine then detecting the gamma rays that are emitted to see if too much/little has been absorbed
Count rate vs activity
Activity = rate at which unstable nuclei decay
Count rate = rate at which radioactive emissions are detected, effected by background radiation
What determines an isotope’s instability?
If it has too many or too few neutrons
Why is radioactive decay random?
A radioactive source has so many nucleus it’s impossible to predict when a particular one decays
Gamma decay equations
No change to atomic number or mass number
Half life
Because a nuclei’s radioactive decay is random,
Scientists can’t state when individual nucleus decay
So we find time taken for half of the nuclei in a source to decay
If nuclei have a short half life what does that show?
It is an unstable isotope
As it has to give out more radioactivity to achieve stability
Half life in terms of count rate
Time it takes for count rate/ activity of the sample to fall to half of its initial rate
How to find half life from a graph?
Find where half of the decays are on y axis
Draw lines from the y axis to the time using the graph at the x axis
Irradiation
Exposing an object to nuclear radiation
Can be either alpha, beta, gamma, neutrons
How can irradiation be used?
Sterilising medical equipment that can’t be heated normally
How does sterilisation of medical equipment work?
Place equipment in plastic wrapper to stop bacteria entering
Place near a radioactive isotope, releasing gamma radiation
Use protection from lead shield then withdraw it to expose the equipment to gamma waves
Ionising radiation risk
Can hit the atoms in our cells and form ions
Causing mutation in DNA and thus uncontrolled division = cancer
How to be protected from alpha radiation?
Gloves
How to be protected from beta or gamma radiation?
Lead apron
If the levels of radiation are too high how else can we be protected?
Lead screen and lead glass
Use a radiation monitor to avoid contact with radioactive isotopes
Radioactive contamination
When unwanted radioactive isotopes end up on materials
Causing the isotopes to decay and emit ionising radiation
Why is alpha radiation dangerous when inside the body?
Crash into living cells
Damage DNA = mutation
Is gamma radiation dangerous to humans?
Not too bad as it usually pases right through
Peer review
Studies are published on affects of things eg radiation to be checked by other scientists
Background radiation
Radiation around us all the time
Sources of background radiation
Radioactive rock eg granite
Cosmic rays from space (high energy particles) due to supernovas
Nuclear weapon testing fall out
Accidents at power stations
What affects exposure to background radiation?
Location eg places with a lot of granite
Occupation eg cabin crew with a lot of cosmic rays
What is radiation dose measured in?
Sieverts (Sv)
Radioactive isotopes as a medical tracer
Check how much iodine has been absorbed by the thyroid glands by swallowing radioactive iodine, decaying
Bone scans to visualise tumours off damage by arthritis
What must a medical tracer be like?
Must pass out body (not alpha)
Not strongly ionising = damage
Not decay into another isotope
Short half life so not present for a long time
Radiotherapy
Destroying cancer with ionising radiation
How does radiotherapy work externally ?
External source of ionising radiation
Gamma rays pass into body and destroy tumour from
Risks of external radiotherapy
Damages healthy tissue
How does radiotherapy work internally?
Radioactive rods put inside the body
Benefits of internal radiotherapy
Radiation precisely targets tumour
No damage to healthy tissue
What are the stages of nuclear fission?
Unstable nucleus absorbs a neutron
Nucleus split to form smaller daughter nuclei, gamma, neutrons
The neutrons are absorbed by other unstable nucleus
Repeats
Nuclear chain reaction
Nuclear fission
When unstable nucleus absorbs neutron which releases more neutrons to be absorbed by nucleus
Causing a large amount of energy to be released
Controlled chain reaction
Scientists controlling nuclear fission to release energy in a nuclear reactor
What causes a nuclear bomb?
Uncontrolled nuclear fission
Nuclear fusion
2 light nuclei such as hydrogen join to create a heavier nucleus
This mass of the nuclei converted to energy, released as radiation
What can nuclear fusion do?
Release energy in stars
