238 Physics Essentials Workbook Stage 2 Physics 15.1 2 Exercises P Explain why stable nuclei of high mass have a higher proportion of neutrons than stable nuclei of low mass. 2 Name four types of spontaneous radioactive decay process and identi9 the emissions in each. 3 The chart, at right, shows the neutron to proton ratio for stable isotopes up to an atomic number of 83. (1) Indicate, by writing the letter E on the chart several times, the region where you would expect to find a radioactive isotope that decays by beta minus emission. I) (2) Indicate, by writing the letter P on the chart several times, the region where you would expect to find a 2 radioactive isotope that decays by beta minus 0 L w emission. (3) Indicate, by writing the letter A on the chart several times, the region where you would expect to find a radioactive isotope that decays by beta minus emission. 120 y loo 7 80 5 60 + 5 40 (4) Explain why this chart does not extend beyond o 20 40 60 80 atomic number 83. Atomic number z 20 4 Radium-226 Rair spontaneously decays into the gas radon (Rn) by alpha decay. Wrote an equation for this decay, identifying all emissions.
5 A radioactive sample emits alpha, beta r&is and gmma radiation. When the radiations are directed through a magnetic field, they are deflected as in the diagram. (1) Which of the tracks is produced by alpha particles? (2) Which of the tracks is produced by beta particles? -4 magnetic field into page (3) Which of the tracks is produced by gamma ray photons? 6 Uranium-232 decays by alpha decay, as shown below Ug -+ 121: + He: [mass Ug2 = 3.851816x 1 ~ - ~ mass ~ k 121;" ~, 3.785277~ 10-~~k~, mass He: = 6.64489~ 10-27kg] (1) Calculate the loss of mass in this reaction. (2) Calculate the total kinetic energy of the thorium and the alpha particle. (3) Calculate the kinetic energy of the alpha particle, assuming that the UiF nucleus was initially stationary. 7 Explain how electrons can be emitted, as in beta minus decay, if there are no electrons in the nucleus.
The photograph at right shows the tracks made in a cloud chamber by alpha particles, emitted by a radioactive source. Explain why the tracks appear to have three distinct, discrete ranges. 9 Uranium-238 U;i8 decays through a chain of radioactive nuclei, leading eventually to the stable isotope of lead, namely lead-206 Pbiy. (1) How many alpha particles are emitted in the process of the decay of one nucleus of uranium-238 into lead-206? (2) How many beta particles are emitted in the same process? 10 The isotope of polonium Poi: decays into an isotope of lead ~b:;'. Write a nuclear equation for this decay, identifying all emissions. 11 (1) What happens to the mass number and atomic number of a nucleus if it emits an alpha particle? - - - (2) What happens to the mass number and atomic number of a nucleus in beta minus decay? (3) What happens to the mass number and atomic number of a nucleus if it emits a positron? (3) What happens to the mass number and atomic number of a nucleus if it emits a gamma ray photon only?
12 A nucleus of thorium Th: absorbs a neutron and the resulting nucleus undergoes two successive beta minus decays. Given that the atomic numbers of protactinium (Pa) and uranium (U) are 91 and 92 respectively, write nuclear equations for these three reactions. 13 Explain how the charge on a proton can be explained by combining up u and down d quarks. 14 (1) Explain what is meant by the term "elementary particle"? (2) Which are the elementary particles? 15 The half life of radon-222 is 3.8 days. A sample of radon-222 has a mass of 20g. (1) Draw a graph of the mass of radon-222 remaining against for the first 19 days. (2) Determine the mass of radon-222 remaining after 15.2 days. -- 16 A Geiger counter shows that the activity of a radioactive sample decreases to one quarter of its initial value in 22 hours. What is the half-life of that isotope?
Physics Essentials Workbook Stsage 2 Physics 17 The graph shows the fraction of radioactive 3 cn C c nuclei remaining in a sample, plotted against ;g;g time. What is the half life of the sample? q 1 "OF 5 c (I) 0-1 -= Q 1 "$ 4 2 1 8 time (s) 18 The half-life of thorium-234 is 24 days. A sample of this isotope initially contains 3.2~10~' atoms. (1) Determine how many atoms will remain after 72 days. (2) How long will it take for 3.2~10~' atoms to decay? 19 In beta plus decay, a proton converts into a neutron. Explain this change in terms of up and down quarks. 20 In an experiment to determine the half-life of a material two measurements were taken of its activity three days apart. The two recorded activities were 12Bq and 1-5Bq. What is the half-life of this material? 21 A Geiger counter records 300 decays in two minutes. What is the activity of the sample?
Radioactivity 22 The radioactive decay of thorium gas isotope was investigated in a laboratory. First of all the background count rate was recorded and this was 2Bq. Then the results of recordmg the count rate of the thorium were tabulated, as below: Time (seconds) 10 40 70 100 130 190 Activity (Bq) 199 103 75 56 43 33 (1) Use this data to plot a graph of activity against time. (2) From your graph estimate the half-life of thorium gas. Explain how you arrived at your answer. 23 The graph shows the activity, measured in counts per minute, of a radioactive sample of polonium Po;;8. (1) What is the half-life of Po;:8? (2) explain what is meant by the term "half-life" of a radioactive material. 24 Explain why gamma photons have a much greater penetrating power than alpha particles.
244 Physics Essentials Workbook Stage 2 Physics 25 Explain how carbon-14 is produced in the upper atmosphere. Include an equation to illustrate this. 26 When discussing radiation exposures explain what is meant by each of the following terms. Give the units in which they are measured, where appropriate. (1) Absorbed radiation dose. (2) The Q factor. (3) Equivalent radiation dose (4) Background radiation. -- -.- 2'7 Explain why alpha particles have a high Q factor. - 28 In beta minus decay, a neutron converts to a proton. Explain this in terms of up and down quarks.
29 List some of the effects that ionising radiations can have if they interact with the atoms and molecules of the human body. 30 The activity of carbon in living matter is 0.226Bq per gram. The half-life of carbon-14 is 5730 years. 10g of carbon from the bone of an ancient skeleton is found to have an activity of 0.28Bq. (1) What would be the activity of 10g of carbon from the bone of someone who died yesterday? (2) Approximately how old is the ancient skeleton? 31 A laboratory technician absorbed 10J of energy from gamma radiation during a faulty transfer of isotopes. His weight is 75kg. (1) Calculate his absorbed dose. (2) If the gamma rays had a Q factor of 1, what is his equivalent dose? (3) Explain why this dose would have been more dangerous to him if the radiation absorbed was alpha radiation and not gamma.
Physics Essentials Workbook Stage 2 Physics 32 Fred weighs 80kg and his friend Joe weighs 90kg. They both work in a nuclear facility. When an accident occurs Fred absorbs 20J of radiation in the form of protons with a Q factor of 5 and Joe receives 7 J of radiation in the form of alpha particles with a Q factor of 17. (1) Calculate the absorbed dose for each of them. (2) Calculate the equivalent dose for each of them. (3) Who received potentially the more dangerous dose of radiation? Explain your answer.