Studied by 7 people
Where in an atom are protons and neutrons found?
nucleus
where are electrons found
in shells around nucleus
define atomic number
number of protons in an atom
equal to the number of electrons
define mass number
number of protons + number of neutrons in the nucleus of an atom
how is the number of neutrons in an atom calculated
mass number - atomic number
what is an isotope
an atom of the same element with the same number of protons but a different number of neutrons
how may ionising radiation be emitted from an atom
random process
alpha beta gamma may be emitted from an unstable nucleus
what is an alpha particle
helium nucleus (2P, 2N)
what is a beta particle?
a fast moving electron
what is a gamma ray?
electromagnetic wave
how is alpha beta and gamma radiation stopped?
alpha - few cm of air, paper
beta - 10cm air, aluminium foil
gamma - several inches thick lead, metres of concrete
list alpha beta and gamma in order starting with the most penetrating
gamma > beta > alpha
define ionising
ability to remove an electron from an atom
list alpha beta and gamma in order, starting with the ionising
alpha > beta > gamma
what happens when a nucleus emits an alpha particle?
- Alpha is a helium nucleus
- 2 protons and 2 neutrons are emitted
- Mass number decreases by 4, atomic number (proton number) decreases by 2
Explain why an alpha particle is deflected when it passes the nucleus of an atom
- Alpha particle is a helium nucleus
- 2 protons and 2 neutrons - gives overall positive charge
- Nucleus of other atom also positive
- Like charges repel - deflects pathway of alpha particle
Why is it relatively safe to be in the same room as an alpha-emitting substance?
- Alpha radiation cannot penetrate skin
What happens when a nucleus emits a beta particle?
- A neutron turns into a proton, which stays in the nucleus
- Fast moving electron (β- particle) emitted
- Mass number unchanged, atomic number (proton number) increases by 1
What happens when a radioactive element emits a gamma ray?
- High energy electromagnetic wave released from atom
- No change to mass number of proton number
What device is used to measure the amount of ionising radiation (radioactivity)?
- Geiger-Muller detector
What is background radiation?
- Radiation which is always present
Give some sources of background radiation
- Cosmic rays from the Sun
- Medicine / medical devices
- Some food and drink (e.g. coffee, bananas)
- Granite rocks in ground and buildings / radon gas in air
- Nuclear waste / accidents
Describe the procedure to measure background radiation in order to correct a count measurement
- Remove the radioactive source
- Measure background count
- Repeat the measurement and calculate average
- Scaling background count to same time as count measurement
- Subtract background count from the non-corrected measurement
What is the unit for measuring radioactivity?
- Becquerel (Bq)
Define half life
- Time taken for half the radioactive nuclei to decay
Describe the nature of radioactive decay
- Random process
- Different for different radioactive isotopes
Why is tossing a coin a good model for radioactive decay?
- Random
- Unable to predict whether you will land on a head or tail - with radioactive decay you don’t know when the nuclei will breakdown (decay)
What are the limitations of tossing a coin as a model for radioactive decay?
- You can only toss the coin at most 1000 times really
- In radioactive material there are millions of nuclei that have the potential to decay
Describe how alpha radiation is used in smoke alarms
- Alpha radiation ionises the air creating small current
- Current picked up by a detector
- In a fire, alpha is stopped by smoke
- Current stops, alarm sounds
Describe the properties of radioactive medical tracers
- Short half-life
- Long enough to complete the procedure
- But falls to safe level quickly
- Usually emits gamma rays
- Gamma can penetrate out of the body and be detected
Discuss the risks of using radioactive medical tracers
- Harmful effect of gamma radiation
- e.g. cancer / cell damage
- Patient must have procedure very rarely to lower risk
- Doctors administer procedure regularly so risk is higher
- Doctor must limit time exposure to patient to reduce risk
Describe the use of radiation in carbon dating
- Carbon-14 is a radioactive isotope, found in carbon dioxide
- Small amount of radioactive carbon-14 in all living organisms because it enters food chain
- Once an organism dies, it stops taking in carbon-14
- Over time radioactivity of the material decreases
- Age of organism can be worked out by measuring the amount of carbon-14 left in its remans compared to the amount in living organisms
How can you reduce your risk of radiation?
- Limit exposure time
- Shielding e.g. lead, thick layer of concrete
- Using tongs to handle radiation
Discuss precautions that must be taken when disposing of radioactive waste with a long half-life
- Must use strong containers
- Containers can’t rust
- Rust-proof containers are expensive and difficult to manufacture
- Disposal site needs strong security
- Radioactive waste can potentially be diluted in sea water
- But must not leak into water table
What is the difference between irridation and contamination?
Contamination = when the radioactive source is on the object, whereas irridation = when an object is exposed to a source of radiation
Contamination = Radiation can not be blocked using lead shielding whereas irridation =radiation can be blocked using lead shielding
Contamination = The object is radioactive as long as the source is on the object whereas irradation doesn’t cause the object to become radioactive
Contamination = Radiation remains as long as the source is on it whereas irridation = radiation stops as soon as radioactive source is removed
List some examples of nuclear reactions which can provide energy
- Nuclear fission (in nuclear reactors)
- Nuclear fusion (occurs in stars)
- Radioactive decay
What fuel is used in a nuclear reactor?
- Uranium-235
What is nuclear fission?
- Splitting of atomic nuclei
Where is nuclear fission carried out?
- In a nuclear generator
How may a chain reaction be set up in a nuclear reactor?
- Fast moving neutron collides with uranium nuclei
- Nuclei split forming 2 radioactive daughter nuclei and 2-3 neutrons
- Neutrons hit other uranium nuclei
- Chain reaction set up
Describe what is meant by a chain reaction
- Fission releases neutrons
- Neutrons can be captured by other uranium nuclei
- These nuclei then undergo fission
What are the products of each reaction during nuclear fission?
- 2 radioactive daughter cells
- Small number of neutrons
state the type of energy released in a fission reaction
kinetic
What is the role of the control rods?
- Absorb extra neutrons
- Prevent uncontrolled chain reaction occurring
- Could lead to meltdown of reactor
What is the role of the moderator in a nuclear reactor?
- Slows the neutrons
- More likely that neutrons are absorbed by uranium
- Allows fission to continue
What is the role of the water/coolant in the nuclear reactor?
- Removes energy from reactor
What is the role of the lead shielding in a nuclear reactor?
- Stops radiation escaping
- Could cause cancer in employees
How does nuclear fission lead to the production of electricity?
- Thermal energy released used to heat water to create steam
- Steam turns a turbine
- Turbine turns a generator
What are the disadvantages of using a nuclear reactor?
- High decommissioning costs
- Radioactive waste - dangerous - may cause cancer
- Long term storage due to very long half lives of radioactive materials
What is nuclear fusion?
- Collision of atomic nuclei at high speed
- Creates larger nuclei, resulting in the loss of mass from small nuclei
- i.e. mass before > mass after
- Releases energy
What is the dfiference between nuclear fission and fusion?
Nuclear fission is the splitting of heavy atomic nuclei into smaller atomic nuclei, whereas nuclear fusion is the fusion of light nuclei to form a larger nucleus
Nuclear fission occurs in nuclear reactors, whereas nuclear fusion occurs in stars.
What is the source of energy for stars?
Nuclear fusion
Why does nuclear fusion not occur at low temperatures?
- Nuclear fusion involves 2 nuclei joining
- Nuclei are positively charged → electrostatic repulsion between like charges
- Needs extremely high temperature to overcome the repulsion
- These temperatures are only currently found in stars
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