5.2. Radioactivity
A subsection of Physics, 5054, through 5. Nuclear physics
Listing 10 of 187 questions
The proton number (atomic number) of the element lead is 82. The isotope lead-209 (209 82Pb) is radioactive and decays by the emission of beta-particles. Describe the composition and structure of a neutral atom of lead-209. A nucleus of lead-209 emits a beta-particle. State how the composition of the nucleus produced differs from the original nucleus. Complete the table in to show the relative ionising effects of the three types of ionising radiation produced by radioactive decay. least strongly ionising most strongly ionising A sample containing lead-209 nuclei is used to produce a beam of beta-particles. The beta-particles enter a magnetic field. The magnetic field is perpendicular to the direction of travel of the beta-particles. The beta-particles travel from left to right. shows that the direction of the magnetic field is out of the page. magnetic field out of the page beam of beta-particles On , sketch the path of the beta-particles in the magnetic field. An industrial technician uses a detector to measure the background count rate in a laboratory. State what is meant by background radiation. Suggest two major sources of background radiation. 1. 2. The average reading for the background count measured by the technician is 16 counts / minute. He then brings a sample that contains a radioactive isotope of lead close to the detector and he finds that the new count rate is 92 counts / minute. The half-life of this isotope is 3.3 hours. Determine the count rate measured using the detector after 6.6 hours. count rate =
5054_w15_qp_22
THEORY
2015
Paper 2, Variant 2
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Plutonium-238 is a radioactive isotope that decays by alpha-particle emission. It also emits gamma-rays. The nuclide notation for plutonium-238 is 238 94 Pu. Describe the structure and composition of a neutral atom of plutonium-238. Alpha-particles, beta-particles and gamma-rays all cause ionisation. The ionisation of substances in the human body can be hazardous. State how the ionising effect of beta-particles compares with 1. the ionising effect of alpha-particles, 2. the ionising effect of gamma-rays. State two precautions that are taken when radioactive substances are moved in a safe way. 1. 2.
5054_w16_qp_22
THEORY
2016
Paper 2, Variant 2
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A sample of the radioactive isotope radon-222 decays by the emission of alpha-particles. As alpha-particles travel through air, the air is ionised. Describe the composition of an alpha-particle. Explain how an alpha-particle ionises air. State how the relative ionising effect of alpha-particles compares with that of 1. beta-particles, 2. gamma rays. The half-life of radon-222 is 3.3 × 105 s. The number of radon-222 atoms in the sample is 4.8 × 104. Determine the time that it takes for the number of radon-222 atoms in this sample to decrease to 1.5 × 103. time = Suggest one reason why, in practice, the time for the number of radon-222 atoms to decrease to 1.5 × 103 may differ slightly from the value obtained in .
5054_w17_qp_21
THEORY
2017
Paper 2, Variant 1
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shows a radiation detector placed on a laboratory bench. 000031 counts / minute radiation detector point P The detector is switched on and six readings of the count rate are recorded. The table in shows the readings obtained. reading number count rate counts / minute Using all the readings obtained, determine an average value for the background count rate. background count rate = shows a point P which is a very short distance from the end of the radiation detector. A sample of the radioactive isotope cobalt-60 is placed at P. The average value of the count rate obtained is now 975 counts / minute. The average count rate is determined with different objects between the radiation detector and the sample. The table in shows the results obtained. object average count rate counts / minute no object four sheets of paper 0.50 mm thickness sheet of aluminium 2.0 cm thickness sheet of lead Indicate, by placing ticks (✓) in the appropriate boxes, the radiation emitted by cobalt-60. alpha-particles beta-particles gamma rays This radiation is produced when a nucleus of cobalt-60 ( 60 27Co) decays into a nucleus of the daughter product X. Product X is not radioactive. Determine 1. the number of protons in a nucleus of X, number of protons = 2. the number of neutrons in a nucleus of X. number of neutrons = The half-life of cobalt-60 is 5.3 years. State what is meant by half-life. When there is a lead sheet between the detector and the sample, the average count rate is obtained from six readings taken at one-minute intervals. The six readings are given in the table in . reading number count rate counts / minute There are reasons for suggesting that the variation in these readings is random and not because the number of cobalt-60 atoms in the sample is decreasing. State two of these reasons. 1. 2.
5054_w18_qp_22
THEORY
2018
Paper 2, Variant 2
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All the isotopes of the gas radon are radioactive. State one similarity and one difference between the nuclei of two different isotopes of radon. similarity difference The isotope radon-222 decays by alpha-particle emission to an isotope of polonium (Po). The proton number (atomic number) of polonium is 84. Determine the number of neutrons in an atom of the polonium isotope. number of neutrons = Determine the number of protons in an atom of radon-222. number of protrons = Describe how a neutral atom of helium ( 4 2He ) differs from an alpha-particle. In an experiment to collect a small quantity of helium, a sample of radon-222 is enclosed in an inner glass tube which has a very thin wall. shows that this tube is placed inside a container that is initially evacuated. inner glass tube vacuum container seal radon-222 Both the container and the inner glass tube are sealed. As the radon-222 decays, alpha-particles pass through the thin wall of the inner glass tube. shows how the total number of alpha-particles produced by the radioactive decay of the radon-222 changes as time passes. time / days number of alpha-particles 1.0 × 1010 2.0 × 1010 3.0 × 1010 Use to determine the number of alpha-particles produced in 7.6 days. Initially, there are 2.8 × 1010 atoms of radon-222 in the inner glass tube. As each radon- 222 atom decays, it produces an alpha-particle. Calculate the number of radon-222 atoms that remain after 7.6 days. number of atoms remaining = Using the number of radon-222 atoms present initially and the number present after 7.6 days, calculate the half-life of radon-222. half-life = The alpha-particles become helium atoms which are collected in the vacuum shown in . Explain, in terms of the properties of alpha-particles, why the wall of the inner glass tube must be extremely thin. In some parts of the world, radon-222 accumulates in the air in buildings and is breathed in by people. Explain why the presence of an alpha-emitter in the lungs is particularly hazardous.
5054_w19_qp_22
THEORY
2019
Paper 2, Variant 2
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The isotope yttrium-90 ( 90 39 Y ) is radioactive. It is a beta-particle emitter that decays to product Q. Product Q is stable. State one feature that is common to all isotopes of yttrium. Describe how a neutral atom of Q differs from a neutral atom of yttrium-90. A sample of yttrium-90 is placed close to a radiation detector in a laboratory. There are no other radioactive samples in the laboratory. A counter records the count rate. is a graph of the count rate plotted against time. time / s time / hours count rate counts / minute Using , determine the average background count rate. average background count rate = Suggest two different origins for the background count. 1. 2. Using , determine the half-life of yttrium-90. Show how the answer is obtained. half-life = Many of the points plotted in do not lie on the best-fit line. Explain why. A beam of beta-particles, travelling in a vacuum, enters the region between two parallel, metal plates. One plate is negatively charged and the other is positively charged. shows the arrangement. beam of beta-particles + + + + + + – – – – – – On , draw the path taken by the beta-particles as they travel between the two plates.
5054_w21_qp_21
THEORY
2021
Paper 2, Variant 1
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Questions Discovered
187