Biology Forums - Study Force

Uranium-238 decays to Thorium-234 by emitting which of the following?
 a. beta
  b. alpha
  c. gamma
  d. positron

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[Ques. 2] A radioactive sample has an activity R. For which of the following changes would the activity remain unchanged?
 a. The number of radioactive nuclei in the sample is doubled.
  b. The half-life of the radioactive nuclei is doubled.
 c. The decay constant is doubled.
 d. A time period equal to two half-lives is allowed to elapse.
  e. All of the above changes result in a change in the activity.

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[Ques. 3] About what fraction of the initial activity of a radioactive source remains after 10 half-lives?
 a. 1.0  1010 b. 9.8  104
  c. 5.0  102 d. 3.9  103

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[Ques. 4] Tritium (3H) has a half-life of 12.3 years and releases 0.018 6 MeV energy per decay. What is the rate at which energy is released for a 1.5-gram sample of tritium? (NA = 6.02  1023 mol1, 1 year = 3.16  107 s, 1 MeV = 1.6  1013 J, and mt = 3.016 05 u)
 a. 1.6 W
  b. 2.3 W
  c. 9.9E+12 W
  d. 5.0E+7 W
  e. 85.4 W

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[Ques. 5] Tritium (3H) has a half-life of 12.3 years and releases 0.018 6 MeV energy per decay. What is the activity of a 1.4-gram sample of tritium? (NA = 6.02  1023 mol1, 1 year = 3.16  107 s, 1 MeV = 1.6  1013 J, and mt = 3.016 05 u)
 a. 9.3E+12 Bq
  b. 1.5E+26 Bq
  c. 5.0E+14 Bq
  d. 5.8E1 Bq
  e. 1.7E+3 Bq

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[Ques. 6] The half-life of 18N is 0.62 s. What is the decay constant for this isotope?
 a. 0.43 s1
  b. 1.1 s1
  c. 1.7  1011 Ci
  d. The decay constant is not defined for a half-life of less than one second.

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[Ques. 7] The half-life of radioactive Technetium-99 is 6.0 hours. Find the number of 99Tc nuclei necessary to produce a sample of activity 1.9 Ci. (1 Ci = 3.7  1010 decays/second)
 a. 5.9E2
  b. 2.2E+9
  c. 1.5E+9
  d. 6.1E+5
  e. 4.2E+5

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[Ques. 8] 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 1.91  1018 tritium atoms, what is its activity in decays/second? (1 year = 3.15  107 s)
 a. 4.92E+9 decays/second
  b. 3.41E+9 decays/second
  c. 1.07E+17 decays/second
  d. 6.69E+16 decays/second
  e. 3.41E+10 decays/second

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[Ques. 9] 1 Bq = ________ Ci?
 a. 1
  b. 106
  c. 2.7  1011
  d. 3.7  1010

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[Ques. 10] Over the course of 2.0 hours, 44 of a radioactive material decays. What is its half-life?
 a. 3.45 hrs
  b. 2.39 hrs
  c. 1.12 hrs
  d. 0.88 hrs
  e. 1.69 hrs

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Thank you for taking the time to explain this