# Radioactive Decay with Half-Life Concept

I need some help in determining the half-life:

1. A radioactive source has a half life of 74 days and an activity of 370 MBq. what was the activity 30 days ago?

2. A radioactive source has a half life of 60 days. what is the relative activity after one week?

3. An 11- Ci Ir- 192 source is recieved on August 20. Regulatory requirementss do not allow use of the source until its activity is 10 Ci or less. On what date will the source reach activity?

4. A patient had a 25- mCi I - 125 permanent seed implant 3 years ago. what is the activity now?

5. For a prostate seed implant, I- 125 seeds with an activity of .350 mCi are needed on the day of the implant. the seeds are to be delivered one week prior to the implant. what activity should the seeds have on the day of delivery?

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#### Solution Summary

The solution solves several problems involving the law of radioactive decay with step-by-step workings and all formulas and explanations are shown.

Radioactive Decay Concept Questions

13. Which one of the following can be done to shorten the half life of the radioactive decay of uranium-238?

a. Oxidize it to the +2 oxidation state.

b. Heat it.

c. Freeze it.

d. Convert it to UF6.

e. None of these

14. The half-life for beta decay of strontium-90 is 28.8 years. A milk sample is found to contain 10.3 ppm strontium-90. How many years would pass before the strontium-90 concentration would drop to 1.0 ppm?

a. 131

b. 0.112

c. 92.3

d. 186

e. 96.9

15. The decay of a radionuclide with a half-life of 4.3 x 105 years has a rate constant (in yr-1) equal to ________.

a. 6.2 x 105

b. 5.9 x 10-8

c. 2.8 x 103

d. 2.3 x 10-6

e. 1.6 x 10-6

16. Consider the following data for a particular radionuclide:

Time Nt

0 min 1.23 g

3 1.15

6 1.08

9 1.01

12 0.940

What is the half-life (in min) of this radionuclide?

a. 30.9

b. 0.0242

c. 0.0224

d. 0.0324

e. 44.64

17. The mass of a proton is 1.673 x 10-24 g. The mass of a neutron is 1.675 x 10-24 g. The mass of the nucleus of an 56Fe atom is 9.289 x 10-23 g. What is the nuclear binding energy (in J) for Fe56?

(C = 3.00 x 108 m/s)

a. 7.72 x 10-8

b. 7.72 x 10-11

c. 6.07 x 106

d. 2.57 x 10-16

e. 8.36 x 10-9