The theory of radioactive decay Flashcards
Discuss whether a radioactive source can decay completely Define exponential decrease Explain why a radioactive decay is a random process
Define radioactive decay
A random process
Define the decay constant
The probability of a nucleus decaying per unit time
How do you work out the decay constant of a sample?
Change in the number of nuclei / time x initial number of nuclei
Radioactive decay can be described as…
exponential decay
Define half-life
The time taken for half the radioactive nuclei in a sample to decay
The time taken for the activity to halve
State and explain a more accurate way to measure half-life
plotting ln(N0) against time
- forms a straight line
- modulus of gradient is the decay constant
- this can be used to find the half life
Derive the equation T = ln(2) / decay constant
ln(N) = -dc x t + ln(N0)
ln(1/2N) = -dc x t + ln(N0)
ln(1) - ln(2) =-dc x t
T = ln(2) / dc
Define activity
The number of nuclei that decay per second
State the equation for activity
A = dc x N
Give examples of how the half-life of a radioactive nucleus affects how it is used
Carbon-14 - long half-life - used for carbon dating
Technetium-99m - short half-life - used for medical diagnosis
Why is Technetium-99m used for medical diagnosis?
- Pure gamma emitter
- Half-life of 6 hours
Short enough to limit exposure
Long enough for tests to be carried out - Easily prepared on site
Why would we store nuclei with long-half lives underground?
To prevent damage to the environment and the people living around them hundreds of years into the future
