Unit 4 - Radioactivity Flashcards
What is the atomic number
The number of protons in the nucleus (bottom number on element card)
What is the mass number
Also know as the nucleon number, the mass number is the total of protons and neutrons in an atoms (top number on element card)
What are alpha particles, beta particles, and gamma rays
They are ionising radiations emitted from unstable nuclei in a random process
Properties of an alpha particle
Nature: a nucleus (2 protons, 2 neutrons)
Ionising: very strong
Penetrating: sheet of paper
What is an alpha particle made up of
2 protons, 2 neutrons
A helium nucleus
Properties of a beta particle
Nature: 1 electron
Ionising: medium
Penetrating: aluminium sheet (few mm thick)
Properties of a gamma ray
Nature: electromagnetic wave
Ionising: weak
Penetrating: thick lead
Effects of emitting an alpha particle
Mass number decreases by 4
Atomic number decreases by 2
Effect of emitting a beta particle
Atomic number increases by 1
Effect of emitting a gamma ray
No change in mass or atomic number
What device is used to detect radiation
A Geiger-Muller tube and counter
Photographic film can show its there but not measure it
What is background radiation
This is radiation detected with no source present
Causes of background radiation
Medical and industrial uses, rocks (radon gas), cosmic rays
What are the units of radioactivity
Activity is measured in Becquerels
1Bq = 1 emission per second
What is meant by the term ‘half life’
The half life of a radioactive source is the time taken for the activity to half
Uses of radioactivity in medicine
- Radioactive tracers let doctors see the inside of our bodies. The organ absorbs the tracer so it can be seen through a machine
- colbalt 60 emits very energetic gamma rays that kill bacteria (as well as cells) so it is used for sterilisation
Uses for radioactivity in industry
- tracers detect leaks in underground pipes (saving money + time)
- used to measure the thickness of paper
How does carbon dating work
Carbon-14 is a radioactive isotope found in the air and in all living organisms.
Once an organism dies, it stops taking in carbon-14. The carbon-14 it contained at the time of death decays over a long period of time, and the radioactivity of the material decreases.
The approximate time since the organism died can be measure by the amount of carbon-14 left in it and the half life of carbon-14
Risks of ionising radiation
Can cause mutations to DNA that cause cancer
Can cause damage to cells and tissue
How to reduce risk from radiation
Increase distance from source
Decrease exposure time
Use protective material
Problems with storing radioactive waste
It stays active for thousands of years and needs to be stored safely
Could be used by terrorists
Results of Geiger and Marsdens experiments with gold foil
It proved that an atom had a concentrated positive charge in there centre surrounded by lots of empty space.
How can we use uranium to make energy
The nucleus of U-235 can be split by collision with a neutron (fission), this process releases lots of energy in the form of kinetic energy (heats the water, steam, turns the generator) and fission products
How does carbon dating work
Carbon-14 is a radioactive isotope found in the air and in all living organisms.
Once an organism dies, it stops taking in carbon-14. The carbon-14 it contained at the time of death decays over a long period of time, and the radioactivity of the material decreases.
The approximate time since the organism died can be measure by the amount of carbon-14 left in it and the half life of carbon-14
Risks of ionising radiation
Can cause mutations to DNA that cause cancer
Can cause damage to cells and tissue
How to reduce risk from radiation
Increase distance from source
Decrease exposure time
Use protective material
Problems with storing radioactive waste
It stays active for thousands of years and needs to be stored safely
Could be used by terrorists
Results of Geiger and Marsdens experiments with gold foil
It proved that an atom had a concentrated positive charge in there centre surrounded by lots of empty space.
How can we use uranium to make energy
The nucleus of U-235 can be split by collision with a neutron (fission), this process releases lots of energy in the form of kinetic energy (heats the water, steam, turns the generator) and fission products
Fission of Uranium-235
- neutrons are fired at U-235 (found in fuel rods)
- U-235 absorbs these neutrons
- 2 daughter nuclei are produced, as well as some very fast moving electrons
- moderators slow down these electrons so that they can collide with more U-235
- control rods absorb neutrons, they can be lowered into the reactor to slow down/stop the chain reaction
Rutherfords nuclear model of the atom
Positive nucleus in the centre (protons and neutrons), surrounded by shells of electrons
