Radioactivity Flashcards
What is an isotope?
Atoms of a particular element with the same number of protons but different numbers of neutrons
What happens when an electron absorbs EM radiation?
It moves from a lower to higher orbit
What happens when an electron emits EM radiation?
It moves from a higher to lower orbit
How can electrons leave an atom?
- Absorbing enough EM radiation so they can escape the pull of the atom
- Being hit by a particle such as an alpha or beta particle
When will unstable nuclei decay?
When alpha, beta, gamma or neutron radiation is emitted
How does an nucleus change when it undergoes alpha decay?
The mass number decreases by 4 and the proton number decreases by 2
How does an nucleus change when it undergoes beta+ decay?
The mass number stays the same but the proton number decreases by 1
How does an nucleus change when it undergoes beta- decay?
The mass number stays the same and the proton number increases by 1
In beta- decay, what decays?
A neutron into a proton and an electron
In beta+ decay, what decays?
A proton into a neutron and a positron
What are the properties of alpha radiation?
- Very ionising
- Stopped by a sheet of paper
- Travels around 5cm in air
What are the properties of beta radiation?
- Mildly ionising
- Stopped by aluminium that is 3mm thick
- Travels a few metres in air
What are the properties of gamma radiation?
- Weakly ionising
- Stopped by thick lead
- Travels a few kilometres in air
What are the sources of background radiation?
- Radon gas 50%
- Ground and buildings 14%
- Medical 14%
- Nuclear power 0.3%
- Cosmic rays 10%
- Food and drink 11.5%
- Other 0.2%
How can radiation be measured?
Using a Geiger-Müller tube
How can radiation be detected?
Using photographic film, if radiation is present the photographic film will darken
What is the ‘plum pudding model’?
A model of the atom where there are negatively charged ‘electron plumbs’ embedded in a positively charged ‘dough’
What was Rutherford’s model?
Rutherford’s model had a positively charged nucleus which the electrons orbited
What is the Bohr model?
Electrons orbit a positively charged nucleus, in well defined energy levels, he stated that they could move between energy levels if they gained or lost energy
What does the activity of a radioactive source measure?
The amount of atoms that decay every second
What does the activity of a source depend on?
The amount of unstable atoms there are
What is half-life?
Time it takes for half of the unstable atoms to decay
What is activity measured in?
Becquerel (Bq)
If a source has an activity of 240Bq what will it’s activity be after 2 half-lives?
240/2 = 120 120/2 = 60Bq
What are the uses of gamma rays?
- Kill cancer cells
- Diagnose cancer
- Preserve food
What is the main use of alpha particles?
In smoke alarms
What is the main use of beta particles?
To control the thickness of paper
What is the danger of ionising radiation?
Ionising radiation causes atoms to turn into ions, these are very harmful to humans and can cause mutations which can lead to cancer
What precautions can be taken when coming into contact with ionising radiation?
- Limiting time of exposure
- Wearing protective clothing
- Increasing the distance between the person and the radioactive source
What is irradiation?
Ionising radiation from an external radioactive source travelling to the body
What is external contamination?
When radioactive materials come into contact with a person’s hair, skin, or clothing
What is internal contamination?
When a radioactive source is eaten or drunk
How do PET scanners work?
- Patient given a radioactive tracer that decays quickly by emitting positrons
- The positrons come into contact with electrons in the body, the two particles annihilate each other forming gamma rays
- These gamma rays are detected by a PET scanner and processed by a computer to produce an image on a screen
- The tracers need to be put into the body close to where they’re used as they decay quickly
How are tumors treated using gamma rays?
- Several beams of gamma rays are fired from different positions towards the cancer
- Each beam damages the tumor but doesn’t kill it
- Moving the beam ensures not too much ionising radiation comes into contact with the surrounding tissue
How are tumors treated internally?
- By injecting the radioisotope into the patient
- The patient eating or drinking something containing the radioisotope
What are the different types of nuclear reactions that can be a source of energy?
- Radioactive decay
- Nuclear fission
- Nuclear fusion
What nuclear fusion?
The fusing of two smaller nuclei to form a larger nuclei, this is what happens in the sun
What is nuclear fission?
When an unstable nuclei splits into two smaller ones resulting in huge amounts of energy being released
Is nuclear power efficient?
Yes, but nuclear power stations produce radioactive nuclear waste which can stay radioactive for thousands of years
What are the advantages of nuclear power?
- Carbon dioxide isn’t produced so it doesn’t contribute to climate change
- Supplies of nuclear fuels
What are the disadvantages of nuclear power?
- It’s expensive to store nuclear waste safely
- If an accident in a nuclear power station happens it can spread radioactive material over a large area
- Many people don’t want nuclear power stations to be built as they think that nuclear power is dangerous
When does a uranium-235 nucleus split?
When it absorbs a neutron
What does the fission of uranium-235 produce?
Two daughter nuclei and two or more neutrons
When neutrons are released following nuclear fission, other nuclei may absorb them and undergo fission, what is this called?
A chain reaction
How is electrical energy generated from power stations?
- Fuel rods containing uranium undergo nuclear fission and thermal energy is released
- Thermal energy is used to heat water and produce steam
- The steam causes turbines to rotate which turn the generator so it generates electricity
- The steam is cooled back into water in a cooler so it can be used again
- Extra thermal energy is released by cooling towers or into the sea
How are chain reactions controlled?
Using control rods that absorb neutrons
Why is nuclear fusion not a suitable source of energy?
It can only occur at very high temperatures and pressures because of electrostatic repulsion happens normally
Does nuclear fusion or fission happen in the sun?
Fusion, hydrogen nuclei are converted to helium nuclei
