Topic 11 - Radioactivity Flashcards
Ionisation
Process by which electrons can be added or removed from an atom to create an ion
Types of ionising radiation
Alpha (α), Beta (β) and Gamma (γ)
These are emitted from unstable nuclei in a random process
Alpha (α)
- Most ionising
- Least penetrating
- Middle activity
- Blocked by paper, aluminium and lead
- Particle is a helium nucleus
- +2 charge
- mass of 4
Beta (β)
- Moderate ionising
- Moderate penetrating
- Highest activity
- Blocked by aluminium and lead
- Particle is a fast-moving electron
- -1 charge
- mass of 1/2000
Gamma (γ)
- Least ionising
- Most penetrating
- Lowest activity
- Blocked by lead
- An EM wave
- No charge
- No mass
Penetration powers practical
- Set up Geiger-Muller tube and counter
- Measure background radiation in 10 seconds
- Place source in front of detector (use gloves and tweezers)
- Measure count rate in 10 secs and take background radiation away
- Place materials in order, paper then aluminium then lead
- Count rate will significantly decrease if radiation is stopped
Effect on atomic and mass numbers (alpha decay)
- 2 protons and 2 neutrons are lost (helium nucleus)
- Mass number decreases by 4
- Atomic number decreases by 2
Effect on atomic and mass numbers (beta decay)
- neutron is converted into a proton and an electron
- mass number is unchanged
- atomic number increases by 1
Effect on atomic and mass numbers (gamma decay)
- Energy is lost from an atom in the form of an electromagnetic wave
- Mass number is unchanged
- Atomic number is unchanged
Effect on atomic and mass numbers (neutron decay)
- neutron is emitted
- mass number decreases by 1
- atomic number unchanged
Photographic film
radiation causes photographic film to darken
Background radiation
The radiation that is naturally found in the environment and exists around us all the time
Sources of background radiation
- Radon gas (50%)
- Rocks and building materials (15%)
- Medical (e.g. X-rays) (13%)
- Food (11%)
- Cosmic rays (10%)
- Other (1%)
Nature of activity of radioactive sources
- Decreases over a period of time
- Measured in Becquerels (Bq)
Activity
The rate at which the unstable nuclei from a source of radiation decays
Half-life
The time it takes for the number of nuclei of the isotope in a sample to halve
Calculating half-life graphically
- find the starting number and halve
- draw a line going across from that value until the trend line is reached
- draw a line down to the time
Ionisation smoke alarm
without smoke: alpha particles knock electrons free from air molecules, causing them to flow to the positive plate, creating a small current
with smoke: smoke particles attach to ions, rendering them neutral, disrupting the flow of current and initiating the alarm
Uses of radioactivity
- diagnosis and treatment of cancer
- sterilising food
- sterilising medical equipment
- determining age of artefacts
- checking thickness of materials
- smoke detectors
Contamination
when an object has a radioactive material introduced INTO it
object becomes radioactive and emits radiation
Irradiation
when an object is exposed to a source of radiation OUTSIDE the object
object is exposed to radiation but does not become radioactive
Dangers of ionising radiations
- radiation can cause mutations in living organisms
- radiation can damage cells and tissue
Disposal of radioactive waste
- an isotope may have a long half-life, meaning a sample of it will decay slowly
- it will remain radioactive for a very long time, therefore presenting risk of contamination for longer
- it is buried underground to prevent it from being released into the environment
Ionising radiation
Radiation that is able to remove electrons from atoms or molecules to produce cations.
