The half-life of 19N is 0.42 s. What is the decay constant for this isotope?
a. 1.7 1011 Ci
b. 1.7 s1
c. 1.1 s1
d. The decay constant is not defined for a half-life of less than one second.
[Ques. 2] The half-life of radioactive Technetium-99 is 6.0 hours. Find the number of 99Tc nuclei necessary to produce a sample of activity 18 Ci. (1 Ci = 3.7 1010 decays/second)
a. 1.2 109
c. 8.0 108
b. 3.4 1011
d. 2.1 1010
[Ques. 3] Tritium is radioactive with a half-life of 12.33 years decaying into 3He with low-energy electron emission. If we have a sample of 2.35 1019 tritium atoms, what is its activity in decays/second? (1 year = 3.16 107 s)
a. 6.64 107/second
c. 3.69 108/second
b. 5.35 109 /second
d. 4.18 1010/second
[Ques. 4] 1010 Bq = ______ Ci?
a. 2.7 10-11
c. 0.27
b. 3.7
d. 3.7 1010
[Ques. 5] Over the course of 6 hours, 15 of a radioactive material decays. What is its half-life?
a. 12.8 hrs
c. 4.1 hrs
b. 25.6 hrs
d. 68.6 hrs
[Ques. 6] Approximately how many half-life periods must elapse if the activity of a radioactive isotope sample is to be reduced to 0.03 of the original value?
a. 5
c. 8
b. 3
d. 60
[Ques. 7] Approximately how many radioactive atoms are present in a tritium sample with an activity of 0.6 10-6 Ci and a half-life of 12.3 years? (1 Ci = 3.7 1010 decays/s)
a. 4 1010
c. 7 108
b. 2 108
d. 1 1013
[Ques. 8] Tritium has a half-life of 12.3 years. What proportion of its original radioactivity will a sample have after 6 years?
a. 0.55
c. 0.84
b. 0.60
d. 0.71
[Ques. 9] Tritium has a half-life of 12.3 years. How many years will elapse when the radioactivity of a tritium sample diminishes to 30 of its original value?
a. 29 years
c. 86 years
b. 21 years
d. 57 years
[Ques. 10] 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 decay rate of this sample? (1 Ci = 3.7 1010 decays/s)
a. 2.7 10-12 Ci
c. 3.4 10-10 Ci
b. 11 10-8 Ci
d. 7.4 10-8 Ci
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