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# Determining the number of half-lives elapsed

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If a lab reports there are the same number of daughter as parent atoms, the number of half-lives elapsed are 1,2,3, or 4?

https://brainmass.com/earth-sciences/geology/determining-number-half-lives-elapsed-87056

#### Solution Preview

You can think of half-life as the time it takes for half of a given amount of radioactive material to decay into another element. The radioactive element is the parent, the product is the daughter. To put it in simple terms, fill a room ...

#### Solution Summary

Determining the number of half-lives elapsed by the number of daughter atoms present.

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## As the temperature of a sample of a radioactive element decreases, the half-life will

1) As the temperature of a sample of a radioactive element decreases, the half-life will

A. decrease
B. increase
C. remain the same
D. depends on the nucleus
E. none of the above

2) In a fusion reaction, reacting nuclei must collide. Collisions between two nuclei are difficult to achieve because the nuclei are

A. both negatively charged and repel each other
B. both positively charged and repel each other
C. oppositely charged and attract each other
D. oppositely charged and repel each other
E. none of the above

3) Heavy water and graphite are two examples of materials that are can be used in a nuclear reactor to slow down neutrons. These materials are called

A. fuels
B. shields
C. coolants
D. moderators
E. none of the above

4) Which reaction illustrates fusion?

A. 1H2 + 1H2 à 2He4
B. 0n1 + 13Al27 à 11Na24 + 2He4
C. 13Al27 + 2He4 à 15P30 + 0n1
D. 7N14 + 2He4 à 1H1 + 8O17
E. all of the above

5) Compared to chemical reactions, nuclear reactions produce:

A. proportionately far less energy
B. fewer changes in the nucleus
C. proportionately far more energy
D. different states
E. none of the above

6) Very large nuclei tend to be unstable because of the:

A. attraction of electrons for the positively charged nucleus
B. repulsive forces between electrons
C. attraction of protons for neutrons
D. repulsive forces between protons
E. repulsive forces between neutrons

7) The process in which a very heavy nucleus splits into more-stable nuclei of lesser mass is called:

B. a chain reaction
D. nuclear fusion
E. nuclear fission

8) An alpha (a) particle is essentially a ___________ nucleus.

A. carbon-12
B. uranium
C. hydrogen
D. plutonium
E. helium

9) Which of the following statements is true?

A. Some naturally occurring isotopes are radioactive
B. All naturally occurring isotopes are radioactive
C. No naturally occurring isotopes are radioactive
E. none of the above

10) For most common types of radioactive decay, the order of least penetrating to most penetrating to human tissue is:

A. beta, gamma, alpha
B. alpha, beta, gamma
C. gamma, alpha, beta
D. gamma, beta, alpha
E. alpha, gamma, beta

11) Gamma (g) rays are:

A. are very low energy, very short wavelength electromagnetic radiation
B. are very high energy, very short wavelength electromagnetic radiation
C. are very high energy, very long wavelength electromagnetic radiation
D. are very low energy, very long wavelength electromagnetic radiation
E. none of the above

12) An electron emitted from the nucleus during some kinds of radioactive decay is known as:

A. A positron
B. A beta (b) particle
C. A gamma ray
D. An alpha (a) particle
E. nuclear fusion

13) To make nuclear fission more efficient, which device is used in a nuclear reactor to slow the speed of neutrons?

A. internal shield
B. external shield
C. control rod
D. moderator
E. none of the above

14) In nuclear reactions:

A. small amounts of mass are converted to a large amount of energy
B. mass and energy are destroyed
C. large amount of energy are converted to small amount of mass
D. small amount of mass are converted to large amounts of mass
E. None of the above

15) Which radioactive emanations have a charge of -1?

A. neutrons
B. gamma rays
C. alpha particles
D. beta particles
E. none of the above

16) Which sample will decay least over a period of 30 days?

A. 10 g of Au-198
B. 10 g of I-131
C. 10 g of P-32
D. 10 g of Rn-222
E. cannot be determined

17) Which nuclide is a radioisotope used in the study of organic reaction mechanisms?

A. carbon-12
B. carbon-13
C. carbon-14
D. uranium-235
E. uranium-238

18) Complete the equation 82Pb211 à -1e0 + ­­­­­_______ by writing the symbol of the missing particle:

A. 81Tl211
B. 83Bi211
C. 82Pb210
D. 82Pb211 +
E. none of the above

19) Plutonium-242 decays via alpha emission, which equation represents this balanced nuclear equation?

A. 94Pu242 à 2He4 + 92U236
B. 94Pu242 à 2He4 + 92U238
C. 94Pu242 à 1n0 + 92U238
D. 94Pu242 à 2He4 + 92Pb238
E. none of the above

20) Complete the nuclear equation 73Ta177 electron capture à by writing the symbol of the missing particle:

A. 74W177
B. 74W178
C. 72Hf177
D. 72Hf178
E. none of the above

21) Magnesium-28 decays via beta emission, which equation represents the balanced nuclear equation?

A. 12Mg28 à -1e0 + 14Si28
B. 12Mg28 à 2He4 + 10Ne28
C. 12Mg28 à 1n0 + 13Al28
D. 12Mg28 à -1e0 + 13Al28
E. none of the above

22) Complete the nuclear equation by 86Rn220 à 2He4 + ______ writing the symbol of the missing particle:

A. 84Po216
B. 84Po214
C. 82Pb218
D. 82Pb222
E. none of the above

23) Silicon-26 decays via positron emission, which equation represents the balanced nuclear equation?

A. 14Si26 à -1e0 + 13Al26
B. 14Si26 à 2He4 + 13Al26
C. 14Si26 à 1e0 + 13Al28
D. 14Si26 à 1e0 + 13Al26
E. none of the above

24) Complete the nuclear equation 10Ne19 à 1e0 + ______ by writing the symbol of the missing particle:

A. 9F18
B. 10Ne18
C. 9F19
D. 10Ne19
E. none of the above

25) Argon-37 decays via electron capture emission, which equation represents the balanced nuclear equation?

A. 18Ar37 à -1e0 + 17Cl37
B. 18Ar37 + -1e0 à 17Cl37
C. 18Ar37 + 1e0 à 17Cl37
D. 18Ar37 + -1e0 à 16S37
E. none of the above

26) 131I decays with a t1/2 = 8.07 hrs. If we begin with 3.0 mg, how much remains after 6 half-lives?

A. 0.0469 mg
B. 0.0234 mg
C. 0.50 mg
D. 0.25 mg
E. 0.01875

27) The half-life of Pa-234 is 6.75 hr. Approximately what fraction of a sample of isotope remains after 20.25 hours?

A. 1/4
B. 1/8
C. 1/16
D. 1/3
E. 1/2

28) The half-life of Rn-222 is 3.823 day. What was the original mass of a sample of this isotope if 0.0500 g remains after 7.646 day?

A. 0.398 g
B. 0.199 g
C. 0.085 g
D. 0.800 g
E. 0.042 g

29) The half-life of Th-227 is 18.2 day. How many days are required for 0.70 of a given sample to decay?

A. 4 days
B. 16 days
C. 32 days
D. 64 days
E. 128 days

30) An object taken from a cave has a carbon-14 fraction which is 0.89 of the amount in a living organism. How old is the object? (half-life for C-14 is 5730 yr)

A. 240 yrs
B. 480 yrs
C. 960 yrs
D. 1920 years
E. 3840 years

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