Q: A patient receives a 100 mg dose of iodine-131, which has a half-life of 8.0 days. How much of the isotope remains after 24 days?

$$100 \times (\frac{1}{2})^3$ = 12.5 mg$$

Q: A radioactive isotope has a half-life of 3 hours. If you start with 80 mg, how much remains after 9 hours?

$$80 \times (\frac{1}{2})^3$ = 10 mg$$

Question 1

Which of the following statements best explains why atoms are electrically neutral?

Accepted Answer

Atoms have equal numbers of protons and electrons.

Question 2

A fluorine atom has an atomic number of 9 and a mass number of 19. How many neutrons does it have?

Accepted Answer

$$19 - 9 = 10$$ neutrons

Question 3

Which of the following is the correct symbolic notation for an atom with 17 protons, 20 neutrons, and 17 electrons?

Accepted Answer

$$\displaystyle \frac{37}{17}Cl$$

Question 4

Which statement correctly distinguishes between mass number and atomic mass?

Accepted Answer

Mass number is the sum of protons and neutrons in a specific atom; atomic mass is the weighted average of all isotopes of an element.

Question 5

Chlorine has two naturally occurring isotopes: chlorine-35 and chlorine-37. The atomic mass of chlorine is 35.45 amu. Which isotope is more abundant and why?

Accepted Answer

Chlorine-35, because the atomic mass is closer to 35.

Question 6

Which of the following types of radiation has the greatest penetrating power and requires thick lead or concrete for shielding?

Accepted Answer

Gamma rays

Question 7

What is the balanced nuclear equation for the alpha decay of americium-241 ($$^{241}_{95}Am$$)?

Accepted Answer

$$^{241}_{95}Am \$$rightarrow ^{4}$$_{2}He $$+ ^{237}$$_{93}Np$$

Question 8

A patient receives a 100 mg dose of iodine-131, which has a half-life of 8.0 days. How much of the isotope remains after 24 days?

Accepted Answer

$$100 	imes (\frac{1}{2})^3$ = 12.5 mg$$

Question 9

Which of the following best describes a beta particle?

Accepted Answer

A high-energy electron emitted from the nucleus

Question 10

Which SI unit is used to measure the biological effect of radiation exposure?

Accepted Answer

Sievert (Sv)

Question 11

What is the main reason radioisotopes used in medical imaging are chosen to have short half-lives?

Accepted Answer

To minimize the patient's exposure to radiation

Question 12

Which of the following nuclear equations represents the beta decay of manganese-56 ($$^{56}_{25}Mn$$)?

Accepted Answer

$$^{56}_{25}Mn \$$rightarrow ^{0}$$_{-1}e $$+ ^{56}$$_{26}Fe$$

Question 13

A radioactive isotope has a half-life of 3 hours. If you start with 80 mg, how much remains after 9 hours?

Accepted Answer

$$80 	imes (\frac{1}{2})^3$ = 10 mg$$

Question 14

Which of the following statements about gamma rays is correct?

Accepted Answer

They are high-energy electromagnetic radiation with no mass or charge.

Question 15

What is the effect of ionizing radiation on living cells?

Accepted Answer

It can eject electrons from atoms, making them more reactive and potentially damaging genetic material.

Question 16

Which of the following is a real-world application of positron emission tomography (PET) scans?

Accepted Answer

Detecting functional abnormalities in the brain using fluorine-18

Question 17

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 18

Which of the following best describes the process of radioactive decay?

Accepted Answer

An unstable nucleus emits radiation to become more stable.

Question 19

A hospital technician needs to prepare a dose of technetium-99m (half-life = 6 hours) for a scan. If the initial activity is 32 mCi, what will the activity be after 18 hours?

Accepted Answer

$$32 	imes (\frac{1}{2})^3$ = 4$$ mCi

Atoms and Radioactivity: Structure, Properties, and Applications

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