Approximately how many half-life periods must elapse if the activity of a radioactive isotope sample is to be reduced to 0.003 of the original value?
a. 5
b. 4
c. 9
d. 16
e. 8
[Ques. 2] Approximately how many radioactive atoms are present in a tritium sample with an activity of 0.20 106 Ci and a half-life of 12.3 years? (1 Ci = 3.7 1010 decays/s)
a. 1.3E+5
b. 1.1E+2
c. 3.5E6
d. 4.1E+12
e. 2.9E+12
[Ques. 3] Tritium has a half-life of 12.3 years. What proportion of its original radioactivity will a sample have after 2 years?
a. 0.01
b. 0.89
c. 0.37
d. 0.16
e. 0.25
[Ques. 4] Tritium has a half-life of 12.3 years. How many years will elapse when the radioactivity of a tritium sample diminishes to 35 of its original value?
a. 1.2E1 years
b. 1.9E+1 years
c. 4.3E+0 years
d. 6.3E+1 years
e. 8.1E+0 years
[Ques. 5] A pure sample of 226Ra contains 1.5 1013 atoms of the isotope. If the half-life of 226Ra = 1.6 103 years, what is the decay rate of this sample? (1 Ci = 3.7 1010 decays/s)
a. 8.0E9 Ci
b. 2.1E+2 Ci
c. 5.6E9 Ci
d. 1.8E1 Ci
e. 2.5E1 Ci
[Ques. 6] A pure sample of 226Ra contains 2.3 1013 atoms of the isotope. If the half-life of 226Ra = 1.6 103 years, what is the activity of this sample?
a. 1.4E+10 decays/yr
b. 1.0E+10 decays/yr
c. 3.2E+2 decays/yr
d. 3.7E+16 decays/yr
e. 6.2E+6 decays/yr
[Ques. 7] An ancient building was known to have been built 3 000 years ago. Approximately what proportion of Carbon-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 14C = 5 730 years)
a. 0.425
b. 0.500
c. 0.517
d. 0.696
[Ques. 8] There are 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 decay rates compare?
a. X has a greater rate than Y.
b. X has a smaller rate than Y.
c. The rates of X and Y are equal.
d. The rate depends on atomic number, not half-life.
[Ques. 9] If a fossil bone is found to contain 1/32 as much Carbon-14 as the bone of a living animal, what is the approximate age of the fossil? (half-life of 14C = 5 730 years)
a. 1.83E+5 years
b. 2.87E+4 years
c. 1.15E+3 years
d. 5.55E+3 years
e. 1.79E+2 years
[Ques. 10] A radioactive material initially is observed to have an activity of 1 600 decays/s. If six hours later it is observed to have an activity of 400 decays/s, what is its half-life?
a. six hours
b. three hours
c. twelve hours
d. seven hours
e. not enough information
Quick Reply
