Radioactive Decay And Acid Dissociation Constant Chap. 9 And 10 Worksheet With Answers - Middle Tennessee State University Page 19
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20decay for 138 days. What was the mass in grams of the original sample?
Assume all alpha particles formed by the decay escape, and the daughter nuclei
remains in the sample as nonradioactive isotopes, then calculate the mass of
the sample in grams after 138 days.
Solution
20
23
Original mass is 6.02x10
atoms/6.02x10
atoms/mol*210g/mol = 0.210 g.
At 138 days, 50% of the Po-210 has decayed to daughter product by alpha
emission. 50% of the Po-210 remains (0.105g) and the daughter has lost 4
out of 210 amu per decay (1.90%). The mass of the daughter would be
0.103 g. Total final mass at 138 days would be 0.208 grams.
10.55 At one time, nuclear bombs were tested by exploding them above ground. The
fallout from such tests contained some Sr-90, a radioactive isotope of strontium.
If Sr-90 gets into the food supply, it can be incorporated into the bones of
humans and other animals. Explain how this can happen though strontium is
not a normal component of bones.
Solution
Strontium is not normally available in the food chain but, if introduced in any
manner, can behave as described. This is because it is chemically similar to
calcium.
ALLIED HEALTH EXAM CONNECTION
10.57 Rank the following from highest penetrating power to lowest penetrating power.
a) alpha particles; b) beta particles; c) gamma rays; d) X rays
Solution
Gamma rays = X rays > beta particles > alpha particles
10.59 If a sample of a radioactive element with a half-life of 100 years has a mass of
31.5 kg remaining after 400 years, what was the mass in kg of the original
sample.
Solution
After each half-life, 50% of the material remains. After 4 half-lives have
passed, only 6.25% would remain. The original amount would be found by:
31.5 kg / 0.0625 = 504 kg.
10.61 Which of the following statements best expresses the fundamental principle of
2
the mass-energy equivalency represented by the Einstein equation, E=mC
?
a) small mass = much energy
b) small mass = little energy
c) little energy = great mass
Solution
Item a comes closest. Any mass will equate to a large amount of energy.
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