Radioactivity and exponential decay 4-5 Flashcards
What is a model?
A model is a set of assumptions that simplifies and idealises a problem. The assumptions mean you can write equations that describe the processes, and so make calculations and predictions. Without the assumptions, there would be too many factors to consider.
What is one of the benefit of having models?
Once you have a model that describes one process you can often extend it, or change it slightly, to describe another, unrelated process without having to start all over again.
When is an atom considered unstable?
If an atom has too many neutrons, not enough neutrons, or too much energy in the nucleus, it may be unstable.
What is radioactive decay?
Unstable atoms break down by releasing energy and/or particles, until they reach a stable form - this process is called radioactive decay.
If radioactive decay is a random process, how can models be made for the decay?
If you take a large enough sample of unstable atoms, the overall behaviour shows a pattern. You can’t predict the decay of an individual atom, but you can predict how atoms will decay in a given time.
What time of decay does radioactive decay have?
An exponential decay.
What is activity?
The number of unstable atoms that decay each second is called the activity of the sample.
What is the activity of a sample proportional to?
The activity of a sample is proportional to the size of the sample.
What is the decay constant?
The decay constant measures how quickly an isotope will decay-it’s the probability of a given nucleus decaying in a certain time. - The bigger the value of the decay constant, the more likely a decay is, so the faster the rate of decay.
What are the units of the decay constant?
Its unit is s-1.
What is the equation for activity?
activity = decay constant x number of atoms
What are the units of activity?
Activity is measured in becquerels(Bq):
1 Bq = 1 decay per second
What does the gradient tell you if you graph the number of unstable atoms remaining in a sample(N) against time?
Will the gradient of the graph be positive or negative?
The gradient of the graph is negative. The gradient is the change in the number of radioactive nuclei remaining in a given time (the rate of decay), which must also be negative.
Define the term half-life of an isotope.
The half-life (T1/2) of an isotope is the average time it takes for the numbr of undecayed atoms to halve.
What do you need to remember when measuring the activity and the half-life of a source?
You have ti remember background radiation. The background radiation needs to be subtracted from the activity readings to give the source acitivity.
