Question : 11) What mass of 14C (half-life = 5730 years) do : 2043773

11) What mass of 14C (half-life = 5730 years) do you need to provide a decay rate of 280.0 Bq?

A) 1.70 × 10-12 kg

B) 5.38 × 10-19 kg

C) 3.84 × 10-20 kg

D) 8.68 × 10-13 kg

12) Today, uranium contains 0.72% 235U  (half-life = 0.70 billion years) and 99.28% 238U (half-life = 4.5 billion years). At a time 1.9 billion years ago, what was the fraction of 235U in uranium?

A) 3.53%

B) 4.72%

C) 4.90%

D) 6.75%

13) The material used in nuclear bombs is 239Pu, with a half-life of about 20,000 years. How long must we wait for a buried stockpile of this substance to decay to 4% of its original 239Pu  mass?

A) 93 thousand years

B) 64 thousand years

C) 45 thousand years

D) 0.80000001 thousand years

14) An air sample is contaminated with 15O, which has a half-life of 2.03 minutes. You can pass it through a long pipe to allow it to decay until it can be safely released, at an air speed of

1.1 m/s.  How long must your pipeline be for the sample to decay to 3% of its original activity?

A) 678 m

B) 8 m

C) 7 m

D) 2 m

15) How much energy is released in the total fission of 2.0 g of 235U? The average energy per fission is 200.0 MeV.

A) 1.6 × 1011 J

B) 3.9 × 1013 J

C) 1.6 × 105 J

D) 3.9 × 1010 J

16) The decay constant of a radioactive nuclide is 1.6 ×10-3s-1. At a given instant, the number of atoms of the radioactive nuclide is 1.85 ×1012. The number of atoms of the nuclide that remain after a time interval of 30 minutes is closest to:

A) 1.04 × 1011

B) 1.14 × 1011

C) 1.26 × 1011

D) 1.38 × 1011

E) 1.52 × 1011

17) A nuclear bomb explosion results in a mass decrease of about 2.10 g between the initial and the final ingredients. How much energy is released?

A) 1.89 × 1014 J

B) 6.30 × 105 J

C) 1.89 × 1013 J

D) 2.25 × 1012 J

18) About how many days are required for a radioactive sample, with an initial activity of

105 Bq, to decay to an activity of 100 Bq? The half-life of the material is 4.5 days.

A) about 45 days

B) about 36 days

C) about 54 days

D) about 31 days

19) The maximum permissible workday dose for occupational exposure to radiation is 18 mrem. A 54 kg laboratory technician absorbs 2.6 mJ of 0.3 MeV gamma rays in a work day. The relative biological efficiency (RBE) for gamma rays is 1.00. The ratio of the equivalent dosage received by the technician to the maximum permissible equivalent dosage is closest to:

A) 0.27

B) 0.29

C) 0.32

D) 0.35

E) 0.37

20) The maximum permissible workday dose for occupational exposure to radiation is 11 mrem. A 77 kg laboratory technician absorbs 2.3 mJ of 0.5 MeV gamma rays in a work day. The relative biological efficiency (RBE) for gamma rays is 1.00. The number of gamma-ray photons absorbed by the technician in a workday is closest to:

A) 3 × 1010

B) 3 × 109

C) 3 × 108

D) 1 × 109

E) 1 × 108