Radioactivity
Give 3 reasons why some isotopes are unstable
- Their size
- They have too many neutrons
- They have too little neutrons
Define 'radioactive decay'
The process of emitting radiation (A random process)
Give 3 features of radioactive decay
- There's an equal probabitily of any nucleus decaying
- The rate of decay is unaffected bythe surrounding conditions
- You can only estimate the proportion of nuclei decaying in a given period of time
What is used to measure the amount of radioactive decay
A Geiger-Muller Tube
What does the fluctuation in count rate of a geiger muller tube show
Provides evidence that radioactive decay is a random process
Give the formula for Activity
A = λN
A = Activity
λ = Decay constant
N = Number of Unstable nuclei
What is the decay constant
The probability that a nucleus will decay
Define 'Activity'
The rate of decay of a radioactive source
Give 2 formulas in relation to exponential decay
A = A0e^-λt
N = N0e^-λt
As we know half-life is the average time taken for half a sample to decay, give a formula involving the half life and ln(2)
λt1/2 = ln(2)
How does carbon dating work?
- The ratio of carbon-12 to carbon-14 is constant in all living things
- Once a living orgainsm dies, it stops absorbing carbon and the carbon-14 continues to decay
- The ratio of carbon-12 to carbon-14 is measured in a dead and living sample
What is the half-life of carbon-14
5700 years
Other than living organisms, how else can carbon-14 be produced?
In the atmosphere, via cosmic rays
Explain why we assume the ratio between carbon-12 and carbon-14 is constant
Carbon-14 can also sometimes decay back into Carbon-12 via beta decay.
Give limitations to carbon dating
We assume the ratio between carbon 14 and carbon 12 is constant, however we don't take into account other factors e.g. fossil fuels
It cannot be used to date extremely old objects as it has a half life of 5700 years which isn't long enough
Describe the experiment to measure radioactivity of different sources
- Measure the background countrate with the geiger muller tube & counter (1 min)
- Repeat 3 times to get an average
*Wear gloves and use tongs to handle radioactive sources.
*Don't stand in front of the sources
- Place the radioactive source at a fixed distance in front of the GM tube and measure the countrate (1 min)
- Subtract the background countrate from the countrate of the radioactive source to get the real countrate
- Place your test material between the tube and radioactive source and measure the countrate (if it stops then that material stops that radiation)