Creating models Flashcards
What is radioactive decay?
When the nuclei of atoms are unstable and so break down to emit particles of three distinct types (alpha, beta, gamma)
What is activity?
The number of nuclei decaying per second
Bq (s-1)
What is half life?
Time required for the number of nuclei in a sample to fall to the half of the original value
(Time taken for activity to half)
In L half lives what factor is the number of nuclei reduced by?
2^L
What is the decay constant (λ)?
The probability of a nucleus decaying in a given time (usually per second)
What equation links activity, number of nuclei and decay constant?
A=λN
How do you calculate the half life from the decay constant?
T(1/2) = ln2 / λ
Why is radioactive decay an example of exponential decay?
The rate of change is proportional to the value of the quantity
ΔN/ΔT ∝ -N
What does the minus sign in the equation ΔN/ΔT = -λN mean?
Indicates that after each decay fewer original nuclei remain
Why are the lines between each value calculated using iteration a straight for radioactive decay?
The model assumes that the activity is constant during each time interval
How can you improve a model of radioactive decay that uses iterations?
Reduce the time interval between calculations
Explain how these statements are true for a sample containing many nuclei and a short half life:
Radioactive decay is random
The number of nuclei in a sample that will decay in 1s can be accurately predicted
The decay constant gives the probability of a nucleus decaying in a unit time. It is impossible to predict which nuclei will decay in any time interval, so radioactive decay is random
However knowing the probability of a decay of a nucleus and the number of nuclei in a sample allows the number decaying in unit time to be accurately predicted
Explain why the statement ‘The number of nuclei in a sample that will decay in 1s can be accurately predicted’ doesn’t hold for a sample with few nuclei and a half life considerably greater than one second?
If few nuclei are present, the random nature of decay becomes more apparent making the prediction much less certain
When half life greater than one second it makes it even harder to predict when exactly a nuclei will decay
How can you find the activity at any given time given the original activity and decay constant?
A = A0 e^(-λt)
How are activity and number of undecayed nuclei present related?
proportional
