Consider supporting us on Patreon. Help us keep revisedeck free.
23.2. Radioactive decay
A subsection of Physics, 9702, through 23. Nuclear physics
Listing 10 of 67 questions
The element strontium has at least 16 isotopes. One of these isotopes is strontium-89. This isotope has a half-life of 52 days. State what is meant by isotopes. Calculate the probability per second of decay of a nucleus of strontium-89. probability = s–1 A laboratory prepares a strontium-89 source. The activity of this source is measured 21 days after preparation of the source and is found to be 7.4 × 106 Bq. Determine, for the strontium-89 source at the time that it was prepared, the activity, activity = Bq the mass of strontium-89. mass = g
9702_s12_qp_42
THEORY
2012
Paper 4, Variant 2
View
An isotope of an element is radioactive. Explain what is meant by radioactive decay. At time t, a sample of a radioactive isotope contains N nuclei. In a short time Δt, the number of nuclei that decay is ΔN. State expressions, in terms of the symbols t, Δt, N and ΔN for the number of undecayed nuclei at time (t + Δt), number = the mean activity of the sample during the time interval Δt, mean activity = the probability of decay of a nucleus during the time interval Δt, probability = the decay constant. decay constant = The variation with time t of the activity A of a sample of a radioactive isotope is shown in . A t ½ 2t ½ 3t ½ t The radioactive isotope decays to form a stable isotope S. At time t = 0, there are no nuclei of S in the sample. On the axes of , sketch a graph to show the variation with time t of the number n of nuclei of S in the sample. n t ½ 2t ½ 3t ½ t
9702_s15_qp_41
THEORY
2015
Paper 4, Variant 1
View
An isotope of an element is radioactive. Explain what is meant by radioactive decay. At time t, a sample of a radioactive isotope contains N nuclei. In a short time Δt, the number of nuclei that decay is ΔN. State expressions, in terms of the symbols t, Δt, N and ΔN for the number of undecayed nuclei at time (t + Δt), number = the mean activity of the sample during the time interval Δt, mean activity = the probability of decay of a nucleus during the time interval Δt, probability = the decay constant. decay constant = The variation with time t of the activity A of a sample of a radioactive isotope is shown in . A t ½ 2t ½ 3t ½ t The radioactive isotope decays to form a stable isotope S. At time t = 0, there are no nuclei of S in the sample. On the axes of , sketch a graph to show the variation with time t of the number n of nuclei of S in the sample. n t ½ 2t ½ 3t ½ t
9702_s15_qp_43
THEORY
2015
Paper 4, Variant 3
View
State what is meant by radioactive decay. An unstable nuclide P has decay constant λP and decays to form a nuclide D. This nuclide D is unstable and decays with decay constant λD to form a stable nuclide S. The decay chain is illustrated in . nuclide P nuclide D nuclide S decay constant λP λD decay constant The symbols P, D and S are not the nuclide symbols. Initially, a radioactive sample contains only nuclide P. The variation with time t of the number of nuclei of each of the three nuclides in the sample is shown in . number t On , use the symbols P, D and S to identify the curve for each of the three nuclides. The half-life of nuclide P is 60.0 minutes. Calculate the decay constant λP, in s–1, of this nuclide. λP = s–1 In the decay chain shown in , λP is approximately equal to 5λD. The decay chain of a different nuclide E is illustrated in . nuclide E nuclide F nuclide G decay constant decay constant λE λF The decay constant λF of nuclide F is very much larger than the decay constant λE of nuclide E. By reference to the half-life of nuclide F, explain why the number of nuclei of nuclide F in the sample is always small.
9702_s18_qp_42
THEORY
2018
Paper 4, Variant 2
View
Uranium-234 is radioactive and emits α-particles at what appears to be a constant rate. A sample of Uranium-234 of mass 2.65 µg is found to have an activity of 604 Bq. Calculate, for this sample of Uranium-234, the number of nuclei, number = ………………………… the decay constant, decay constant = ………………………… s–1 the half-life in years. half-life = ………………………… years Use Suggest why the activity of the Uranium-234 appears to be constant. Suggest why a measurement of the mass and the activity of a radioactive isotope is not an accurate means of determining its half-life if the half-life is approximately one hour.
9702_w06_qp_4
THEORY
2006
Paper 4, Variant 0
View
Radon-222 is a radioactive element having a half-life of 3.82 days. Radon-222, when found in atmospheric air, can present a health hazard. Safety measures should be taken when the activity of radon-222 exceeds 200 Bq per cubic metre of air. Define radioactive decay constant. Show that the decay constant of radon-222 is 2.1 × 10–6 s–1. A volume of 1.0 m3 of atmospheric air contains 2.5 × 1025 molecules. Calculate the ratio number of air molecules in 1.0 m3 of atmospheric air number of radon-222 atoms in 1.0 m3 of atmospheric air for the minimum activity of radon-222 at which safety measures should be taken. ratio =
9702_w11_qp_43
THEORY
2011
Paper 4, Variant 3
View
Questions Discovered
67