A pure sample of 226Ra contains 3.0 1014 atoms of the isotope. If the half-life of 226Ra = 1.6 103 years, what is the activity of this sample?
a. 13 1010 decays/yr
c. 6.7 109 decays/yr
b. 9.4 1010 decays/yr
d. 8.7 1010 decays/yr
[Ques. 2] An ancient building was known to have been built 4000 years ago. Approximately what proportion of Carbon-14 atoms are still in the building's wooden framing compared to the number which were present at the time of its construction? (half life of 14C = 5730 years)
a. 0.696
c. 0.500
b. 0.616
d. 0.425
[Ques. 3] There are samples of two different isotopes, X and Y. Both contain the same number of radioactive atoms. Sample X has a half-life half that of Y. How do their decay rates compare?
a. The rates of X and Y are equal.
b. X has a greater rate than Y.
c. The rate depends on atomic number, not half-life.
d. X has a smaller rate than Y.
[Ques. 4] If a fossil bone is found to contain 1/16th as much Carbon-14 as the bone of a living animal, what is the approximate age of the fossil? (half-life of 14C = 5730 years)
a. 7640 years
c. 45,800 years
b. 22,900 years
d. 17,200 years
[Ques. 5] A radioactive material initially is observed to have an activity of 1000 decays/sec. If nine hours later it is observed to have an activity of 125 decays/s, what is its half-life?
a. 1/2 hour
c. 3 hours
b. 8 hours
d. 1 hour
[Ques. 6] Neglecting recoil of the gold nucleus, how much kinetic energy must an alpha particle (charge = 2 1.6 10-19 C) have to approach to within 1.95 10-14 m of a gold nucleus (charge = 79 1.6 10-19 C)? (ke = 8.99 109 Nm2/C2 and 1 MeV = 1.6 10-13 J)
a. 14.6 MeV
c. 18.2 MeV
b. 11.7 MeV
d. 22.7 MeV
[Ques. 7] Gamma radiation is in fact which of the following?
a. electrons
c. positrons
b. high energy quanta
d. helium nuclei
[Ques. 8] Alpha radiation is in fact which of the following?
a. high energy quanta
c. helium nuclei
b. positrons
d. electrons
[Ques. 9] Two different nuclei emit alpha particles, the energy released in each of these decays being the same. Which of the following has the lowest resulting kinetic energy?
a. The alpha particle from the lighter nucleus.
b. The alpha particle from the heavier nucleus.
c. The heavier daughter nucleus.
d. The lighter daughter nucleus.
[Ques. 10] 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 M = 4.00 1030 kg collapsed into neutrons (mn = 1.67 10-27 kg), what would be the radius of such a star? (Hint: r = r0A1/3, where r0 = 1.20 10-15 m.)
a. 12.7 km
c. 16.1 km
b. 25.4 km
d. 18.5 km
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