P2.5 Radioactive Decay Flashcards
Describe the ‘plum pudding’ structure
The theory that atoms were spheres of positive charge with tiny negative electrons stuck in them like plums in a plum pudding
What experiments did Rutherford and Madsen carry out ?
- They fired alpha particles at a piece of gold foil
- Some passed through - the nucleus is actually very small and the rest of the atom is space
- Some deflected away slightly - the nucleus must have an overall positive charge as it repelled positive alpha particles
- Some reflected back - the nucleus is very dense
Define ‘isotope’
The atoms of an element with a different neutron number
Define ‘mass number’
The total number of protons and neutrons of an atom
Define ‘atomic number’
The total number of protons/electrons of an atom
What do radioactive substances do randomly?
Radioactive substances randomly give out radiation from their atom’s nuclei no matter what happens to them.
What are two types of background radiation?
- Natural sources
- Manmade sources
What are 5 examples of background radiation from natural sources?
- Air
- Rocks
- Food
- Building materials
- Cosmic rays from space
What are 3 examples of background radiation from manmade ?
- Fallout from nuclear weapon tests
- Dumped nuclear waste
- Nuclear accidents
What are the 3 types of radioactivity?
- Alpha particles
- Beta particles
- Gamma rays
Describe the properties of an alpha particle (5)
- Helium nucleus (2 protons and 2 neutrons)
- Positive charge
- Big, heavy, slow moving
- Not penetrating, can only travel a few cm in air (can be a stopped by paper)
- Strongly ionising, because of their size they bash into atoms and knock electrons off them, creating ions.
Describe the properties of a beta particle (5)
- An electron
- Negative charge
- They move quite fast and are quite small
- They can penetrate through air and paper, but stopped by aluminium
- Moderately ionising
Describe the properties of a gamma ray (5)
- No mass
- No charge
- Least ionising - doesn’t collide
- E.M wave with very short wavelength
- Most penetrating, only stopped by thick lead
Which types of radiation are affected by a magnetic field?
- Beta particles
- Alpha particles
Why are alpha and beta particles deflected by a magnetic field?
- Because they have charge they are deflected by a magnetic field.
- They are both deflected in opposite directions as they have opposite charges.
What are the two things that affect radiation dose?
- Location
- Occupation
What are the four examples of situation that increase radiation dose?
- Living near/working at underground rocks (e.g mining) - higher levels at the surface, releasing radon gas.
- Nuclear industry workers and miners so they wear protective clothing.
- Radiographers and X-rayers work using ionising conditions, they wear lead aprons and lead screens
- At high altitudes there are more cosmic rays, increasing the dosage
Name 3 uses of radiation
- Smoke detectors
- Tracers in medicine
- Radiotherapy in medicine
How is radiation used in smoke detectors?
- There is alpha radiation between two electrodes, this causes ionisation
- A current flows between the two electrodes
- If there is smoke it will absorb the radiation, stopping the current and the alarm sounds
How is radiation used in tracers and what should its properties be?
- Radioactive isotope is injected/swallowed by the patient
- Gives out radiation to be detected by an external detector
- It needs to be gamma/beta radiation so it can pass out of the body quickly (alpha isn’t penetrating enough)
- It needs to have a short half life so radioactivity in the patient quickly disappears
How is radiation used in radiotherapy?
- High doses of gamma rays kill all living cells
- These rays are directed carefully and at the right dosage to cancer cells (although some of the normal cells are still killed off)
How does radiation damage body cells?
By entering them and colliding with their molecules,
- In lower doses : minor damage to cell without destroying, causing mutant cells, causing cancer
- In higher doses: kill cells completely, causing radiation sickness if many are killed at once
What 2 things does the extent of the harmful effects of radiation depend on?
- How much exposure you have to it
- The energy and penetration of it
What 2 types of radiation are the most dangerous outside the body and why?
- Gamma
- Beta
- They are penetrating enough to get into delicate organs
What type of radiation is the most dangerous inside the body and why?
- Alpha
- The most ionising in a localised area
- The least penetrating so doesn’t pass out the body
Define ‘half life’
The average time it takes for the nuclei number in a radioactive isotope sample to halve
Describe 5 ways of safety when dealing with radioactive sources
- Using radioactive sources for a minimum amount of time
to keep exposure to a minimum - Handle sources with tongs, never allow skin contact
- Hold sources at arms length, decreasing radiation amount that hits you especially as alpha can’t travel far in air.
- Store sources in a lead box, if X-raying use a lead apron and stand behind a lead screen
