National 5- Nuclear Chemistry past paper revision 1. The diagram shows the paths of alpha, beta and gamma radiations as they pass through an electric field. Which line in the table correctly identifies the types of radiation which follow paths X, Y and Z? 2. Some smoke detectors make use of radiation which is very easily stopped by tiny smoke particles moving between the radioactive source and the detector. The most suitable type of radioisotope for a smoke detector would be A. An alpha-emitter with a long half-life. B. A gamma-emitter with a short half-life. C. An alpha-emitter with a short half-life. D. A gamma-emitter with a long half-life.
3. Which particle will be formed when an atom of emits an α-particle and the decay product then emits a β-particle? 4. An atom of 227Th decays by a series of alpha emissions to form an atom of 211 Pb. How many alpha particles are released in the process? A. 2 B. 3 C. 4 D. 5 5. The half life of the isotope 210 Pb is 21 years. What fraction of the original 210 Pb atoms will be present after 63 years? A. 0.5 B. 0.25 C. 0.125 D. 0.0625 6. Radioactive 14 C decays by beta particle emission. Which statement is true of the new nucleus formed? A. It has a mass number of 13. B. It has 6 protons. C. It has 7 neutrons. D. It is a carbon nucleus.
7. 24 Na is a beta emitter with a half life of 15 hours. What percentage of the original isotope would remain after 45 hours? A. 12.5 B. 25 C. 75 D. 87.5 8. 14 C has a half life of 5600 years. An analysis of charcoal from a wood fire shows that its 14 C content is 25% that of living wood. How many years have passed since the wood for the fire was cut? A. 1400 B. 4200 C. 11200 D. 16800 9. After 48 years the level of radioactivity in a sample of an isotope was found to be 1/8 th of the level originally. What is the half-life of the isotope? A. 6 years B. 12 years C. 16 years D. 24 years 10. 215 Th is a beta emitter with a half life of 4.2 minutes. What percentage of the original isotope would remain after 8.4 minutes? A. 12.5 B. 25 C. 50 D. 75
11. Technetium-99m is used in medicine to detect damage to heart tissue. It is a gamma-emitting radioisotope and is injected into the body. a) The half-life of Technetium-99m is 6 hours. How much of a 2g sample of Technetium-99m would be left after 12 hours? b) Suggest one reason why Technetium-99m can be used safely in this way. c) Technetium-99m is formed when Molybdenum-99 decays. The decay equation is: 99 Mo 99 Tc + X Identify X. 12. Different types of radiation have different penetrating properties. An investigation was carried out using three radioactive sources. a) Name the type of radiation emitted by source 2. b) The half-life of source 3 is 8 days. Calculate the fraction of source 3 that would remain after 16 days. c) Radioisotopes can be made by scientists. The nuclear equation shows how a radioisotope of element X can be made from aluminium. Name element X.
13. Americium-241, a radioisotope used in smoke detectors, has a half-life of 432 years. a) The equations for the decay of Americium-241 is Name element X. b) Name the type of radiation emitted by the Americium-241 radioisotope. c) Another radioisotope of Americium exists which has an atomic mass of 242. Americium-242 has a half-life of 16 hours. i. A sample of Americium-242 has a mass of 8g. Calculate the mass, in grams, of Americium-242 that would be left after 48 hours. ii. Suggest why Americium-241, and not Americium-242, is the radioisotope used in smoke detectors. 14. Carbon dating can be used to estimate the age of wood found in archaeological sites. The decay curve shows the decrease in the percentage of Carbon-14 against the number of half lives.
a) A piece of wood was found to contain 5% of the original Carbon-14 content. The half-life of Carbon-14 is 5700 years. Calculate the age of the wood, in years. b) Suggest a reason why Carbon-14 is unsuitable for dating samples that are more than 50 000 years old. 15. 75% of the Potassium-40 atoms originally present in a rock sample were found to have undergone radioactive decay. The half-life of Potassium-40 is 1.26x10 9 years. Calculate the age of the rock, in years. 16. Phosphorus-32 and Strontium-89 are two radioisotopes used to study how far mosquitoes travel. a) Strontium-89 decays by emission of a beta particle. Complete the nuclear equation for the decay of Strontium-89 b) In an experiment, 10g of Strontium-89 chloride was added to a sugar solution used to feed mosquitoes. i. The Strontium-89 chloride solution was fed to the mosquitoes in a laboratory at 20 C. When the mosquitoes were released, the outdoor temperature was found to be 35 C. What effect would the increase in temperature have on the half-life of the Strontium-89? ii. Calculate the mass, in grams, of Strontium-89 present in the 10g sample of Strontium-89 chloride, SrCl 2. iii. A mosquito fed on a solution containing Phosphorus-32 is released. Phosphorus-32 has a half-life of 14 days. When the mosquito is recaptured 28days later, what fraction of the Phosohorus-32 will remain?
17. The element Iodine has only one isotope that is stable. Several of the radioactive isotopes of Iodine have medical used, Iodine-131, for example, is used in the study of the thyroid gland and it decays by beta emission. a) Why are some atoms unstable? b) Complete the balanced nuclear equation for the beta decay of Iodine- 131. c) The graph shows how the mass of Iodine-131 in a sample changes over a period of time. What is the half life of this isotope? 18. A sample of 11 C had an initial count of 640 counts min -1. After 1 hour the count rate had fallen to 80 counts min -1. Calculate the half-life, in minutes, of 11 C.
19. Thorium-227 decays by alpha emission. a) Complete the nuclear equation for the alpha decay of Thorium-227. b) A sample of Thorium-227 was placed in a wooden box. A radiation detector was held 10cm away from the box. Why was alpha radiation not detected? c) Thorium-227 has a half life of 19days. If 0.42g of Thorium-227 has decayed after 57 days, calculate the initial mass of Thorium-227, in grams. 20. All the isotopes of Technetium are radioactive. a) Technetium-99 is produced as shown. Identify X.