Nuclear Decay and Radioactive Isotopes

1. Approximately how many radioactive atoms are present in a tritium sample with an activity of 0.4 x 10-6 Ci and a half-life of 12.3 years? (1 Ci = 3.7 x 1010 decays/s) • 13 x 107 • 7 x 108 • 3 x 1010 • 8 x 1012

2. What is the binding energy per nucleon of Au-197 (atomic number = 79)? (The following information regarding atomic masses will be needed: Au-197, 196.966560; hydrogen, 1.007825; neutron, 1.008665; also 1 u x c2 = 931.5 MeV) • 7.3 MeV • 7.7 MeV • 7.9 MeV • 8.3 MeV

3. Approximately how many half-life periods must elapse if the activity of a radioactive isotope sample is to be reduced to 0.004 of the original value? • 3 • 6 • 8 • 60

4. Tritium has a half-life of 12.3 years. What proportion of its original radioactivity will a sample have after 9 years? • 0.55 • 0.60 • 0.73 • 0.84

5. The activity of a newly discovered radioactive isotope reduces to 96% of its original value in an interval of 2 hours. What is its half-life? • 10.2 hrs • 34.0 hrs • 44.0 hrs • 68.6 hrs

6. If there are 128 neutrons in Pb-210, how many neutrons are found in the nucleus of Pb-206? • 122 • 124 • 126 • 130

7. The existence of the neutrino was postulated to account for which basic conservation laws during the beta decay process? • conservation of energy • conservation of momentum • both of the choices are valid • none of the choices are valid

8. A radioactive isotope which emits a gamma quantum will change in what respect? • atomic number increases by one • atomic number decreases by one • atomic mass number decreases by one • none of the choices are valid

9. A radioactive isotope which emits an alpha particle will change in what respect? • atomic number decreases by four • mass number decreases by four • both atomic number and mass number decrease by four • none of the choices are valid

10. Tritium has a half-life of 12.3 years. How many years will elapse when the radioactivity of a tritium sample diminishes to 10% of its original value? • 31 years • 41 years • 84 years • 123 years

11. A pure sample of Ra-226 contains 2.0 x 1014 atoms of the isotope. If the half-life of Ra-226 = 1.6 x 103 years, what is the decay rate of this sample? (1 Ci = 3.7 x 1010 decays/s) • 2.7 x 10-12 Ci • 3.4 x 10-10 Ci • 7.5 x 10-8 Ci • 9.6 x 10-6 Ci

12. What energy must be added or given off in a reaction where one hydrogen atom and two neutrons are combined to form a tritium atom? (atomic masses for each: hydrogen, 1.007825; neutron, 1.009665; tritium, 3.016049; also, 1 u x c2 = 931.5 MeV) • 8.5 MeV added • 8.5 MeV given off • 10.3 MeV given off • 10.3 MeV added

13. An ancient building was known to have been built 3000 years ago. Approximately what proportion of C-14 atoms are yet in the building's wooden framing compared to the number which were present at the time of its construction? (half life of C-14 = 5800 years) • 0.425 • 0.500 • 0.517 • 0.698

14. The isotope Zn-64 has a nuclear radius of 4.8 x 10-15 m. Which of the following is the mass number of an isotope for which the nuclear radius is 7.2 x 10-15 m? • 144 • 96 • 125 • 216

15. A pure sample of Ra-226 contains 2 x 1014 atoms of the isotope. If the half-life of Ra-226 = 1.6 x 103 years, what is the decay rate of this sample? • 6.7 x 109 decays/yr • 8.7 x 1010 decays/yr • 9.4 x 1010 decays/yr • 12.6 x 10-10 decays/yr

16. The beta emission process results in the daughter nucleus differing in what manner from the parent? • atomic mass increases by one • atomic number decreases by two • atomic number increases by one • atomic mass decreases by two

17. The gamma radiation first detected by Becquerel was in fact which of the following? • helium nuclei • high energy quanta • electrons • positrons

18. The alpha emission process results in the daughter nucleus differing in what manner from the parent? • atomic mass increases by one • atomic number decreases by two • atomic number increases by one • atomic mass decreases by two

19. If the sum total mass of reactants in a nuclear reaction is greater than that of product particles, then which of the following statements best describes the conditions of the reaction? • reaction is exothermic • reaction is endothermic • atomic number of each reactant must be greater than 40 • atomic number of each reactant must be less than 80

20. The isotope Zn-64 has a nuclear radius of 4.8 x 10-15 m. Approximately what is the nuclear radius of an isotope of Al-27? • 2.0 x 10-15 m • 2.7 x 10-15 m • 3.6 x 10-15 m • 4.0 x 10-15 m

21. The ratio of the numbers of neutrons to protons in the nucleus of naturally occurring isotopes tends to vary with atomic number in what manner? • increases with greater atomic number • decreases with greater atomic number • is maximum for atomic number = 60 • remains constant for entire range of atomic numbers

22. The atomic mass number of a nucleus is equivalent to which of the following numbers? • # neutrons present • # protons present • difference in neutron and proton numbers • sum of neutron and proton numbers

23. Of the main types of radiation emitted from naturally radioactive isotopes, which of the following is the most penetrating? • alpha • beta • gamma • positron

24. Samples of two different isotopes, X and Y, both contain the same number of radioactive atoms. Sample X has a half life twice that of Y. How do their rates of radiation compare? • X has a greater rate than Y • X has a smaller rate than Y • rates of X and Y are equal • rate depends on atomic number, not half life

25. The beta radiation first detected by Becquerel was in fact which of the following? • helium nuclei • high energy quanta • electrons • positrons

26. The alpha radiation first detected by Becquerel was in fact which of the following? • helium nuclei • high energy quanta • electrons • positrons

27. The atomic number of a given element is equivalent to which of the following? • proton number in the nucleus • neutron number in the nucleus • sum of the protons and neutrons in the nucleus • number of electrons in the outer shells

28. Chromium-55 (54.9279 u) emits an electron (0.0005 u) leaving a daughter nucleus of manganese-55 (54.9244 u). How much energy is released in this reaction? (1 u x c2 = 931 MeV) • 5.59 MeV • 2.79 MeV • 1.40 MeV • 0.70 MeV

29. An endothermic nuclear reaction occurs as a result of the collision of two reactant nuclei. If the Q value of this reaction is -2.17 MeV, which of the following describes the minimum kinetic energy needed in the reactant nuclei if the reaction is to occur? • equal to 2.17 MeV • greater than 2.17 MeV • less than 2.17 MeV • exactly half of 2.17 MeV

30. If a fossil bone is found to contain 1/8th as much Carbon-14 as the bone of a living animal, what is the approximate age of the fossil? (half-life of C-14 = 5800 years) • 8,000 years • 17,400 years • 23,000 years • 46,400 years

31. Rutherford's experiments involving the use of alpha particle beams directed onto thin metal foils demonstrated the existence of which of the following? • neutron • proton • nucleus • positron

32. The components of natural radiation, in order of least to most penetrating, are which of the following choices? • alpha, beta and gamma • gamma, beta and alpha • beta, gamma and alpha • alpha, gamma and beta

33. A radioactive material initially is observed to have an activity of 800 counts/sec. If four hours later it is observed to have an activity of 200 counts/sec, what is its half life? • 1 hour • 2 hours • 4 hours • 8 hours

34. The experiment which gave the first evidence for the existence of the atomic nucleus involved which of the following? • X-ray scattering • radioactive dating • cosmic ray detection • alpha scattering

35. The nucleus of an atom is made up of which of the following? • electrons and protons • electrons and neutrons • protons, electrons and neutrons • protons and neutrons

36. Radium-226 decays to Radon-222 by emitting which of the following? • beta • alpha • gamma • positron

37. When bismuth-214 emits a beta particle, the remaining daughter nucleus is which of the following? • lead-213 • actinium-215 • polonium-214 • bismuth-215

38. Certain stars at the end of their lives are thought to collapse combining their protons and electrons together to form a neutron star. Such a star could be thought of as a giant atomic nucleus. If a star of mass equal to that of the sun (M = 2 x 1030 kg) collapsed into neutrons (mn = 1.67 x 10-27 kg), what would be the radius of such a star? (HINT: r = r0A1/3) • 25.4 km • 18.7 km • 12.7 km • 6.4 km

39. Calculate the binding energy of the tritium nucleus, given that the mass of the tritium nucleus is 3.01605 u. (mp = 1.007276 u, mn = 1.008665, and 1 u = 931.5 MeV/c2) • 2.24 MeV/nucleon • 2.45 MeV/nucleon • 2.66 MeV/nucleon • 2.86 MeV/nucleon

40. The half-life of radioactive iodine-131 is 8 days. Find the number of 131I nuclei necessary to produce a sample of activity 1.0µ Ci. (1 Curie = 3.7 x 1010 decays/second) • 4.6 x 109 • 3.7 x 1010 • 7.6 x 1012 • 8.1 x 1013

41. How much kinetic energy must an alpha particle (charge = 2 x 1.6 x 10-19 C) have to approach to within 10-14 m of a gold nucleus (charge = 79 x 1.6 x 10-19 C)? [k = 9 x 109 N-m2 /C2 and 1 MeV = 1.6 x 10-13 J] • 11.70 MeV • 14.55 MeV • 18.15 MeV • 22.75 MeV

42. Tritium is radioactive with a half-life of 12.33 years decaying into with low-energy electron emission. If we have a sample of 3 x 1018 tritium atoms, what is its activity in decays/second? (1 year = 3.15 x 107 s) • 4.20 x 1010/second • 5.35 x 109/second • 3.69 x 108/second • 6.64 x 107/second

43. An alpha particle (mass = 6.68 x 10-27 kg) is emitted from a radioactive nucleus with an energy of 5 MeV. How fast is the a-particle moving in m/s? (1 MeV = 1.6 x 10-13 J) • 2.40 x 107 m/s • 1.55 x 107 m/s • 3.70 x 106 m/s • 1.85 x 106 m/s

44. A 1-gram sample of petrified wood is taken from a petrified forest. If the Carbon-14 activity of the sample is 12.5% that of present-day organic material, what is the age of the petrified wood? (T1/2 for C-14 is 5,730 years) • 4,460 years • 8,600 years • 13,150 years • 17,200 years

45. In the beta decay of 14C, the existence of the anti-neutrino was required to maintain? • energy conservation. • charge conservation. • conservation of the number of nucleons. • all of the choices

46. The fact that the binding energy per nucleon doesn't depend very strongly on the volume of the nucleus indicates that? • the strong nuclear force saturates. • nucleons don't move throughout the nucleus. • all nuclei have the same volume. • the radius of a nucleus is directly proportional to the number of nucleons.

47. According to the shell model of the nucleus, radioactive decay which produces beta rays occurs because? • there is a vacant energy level for a neutron and as a neutron drops down to this lower energy level it gives up its energy to an electron. • there is no vacancy in a neutron energy level so the neutron goes to an energy level previously occupied by an electron. • the neutron must change to a proton before it can go to a lower energy level. • the neutron gets rid of excess angular momentum by giving it to ejected electron.

48. Some nuclei are not spherical and this can best be explained by the? • liquid drop model. • shell model. • collective model. • model of nuclear tunneling.

49. If the stable nuclei are plotted with neutron number vs. proton number, the curve formed by the stable nuclei does not follow the line N = Z. This is predicted by examining how the binding energy is influenced by? • the volume of the nucleus. • the size of the nuclear surface. • the Coulomb repulsion. • the proton-neutron mass difference.

50. The binding energy of a nucleus is equal to? • the energy needed to remove one of the nucleons. • the average energy with which any nucleon is bound in the nucleus. • the energy needed to separate all the nucleons from each other. • the mass of the nucleus times c2.