Radioactive decay and half-lifeAQA A-Level Physics: Flashcards

What these 14 flashcards ask

Why is radioactive decay described as random?
Define the decay constant.
What is activity and its unit?
Write the equation for activity in terms of λ and N.
State the decay law for the number of nuclei.
State the equation linking half-life and decay constant.
How do you find the number of nuclei from a mass of sample?
What does the gradient of a ln A against t graph give?
What does the intercept of a ln A against t graph give?
What fraction of a sample remains after four half-lives?
Which has the greater activity for equal numbers of nuclei: a long or short half-life isotope?
How is carbon-14 used to date a sample?
Why is a long-lived isotope a storage problem?
Why do small numbers of nuclei give an uneven decay curve?

Exam questions on Radioactive decay and half-life

A freshly prepared sample contains 4.0 × 10⁶ nuclei of a radioisotope. The decay constant of the isotope is 2.0 × 10⁻³ s⁻¹.
Calculate the number of undecayed nuclei remaining after 600 s.2 marks
A student measures the activity A of a sample of a radioisotope at regular intervals. She plots a graph of ln(A / Bq) against time t in minutes and obtains a straight line with a gradient of −0.080 min⁻¹ and an intercept of 8.0 on the ln(A / Bq) axis.
Determine the half-life of the isotope.2 marks
Carbon-14 has a half-life of 5730 years. Living wood contains carbon-14 and gives an activity of 0.230 Bq per gram of carbon, a value that stays constant while the tree is alive. A sample of carbon from an ancient wooden bowl gives an activity of 0.160 Bq per gram.
Calculate the decay constant of carbon-14 in year⁻¹.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).