Q: A radioactive isotope has a half-life of 8 hours. If you start with a 100 mg sample, how much remains after 24 hours?

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

Q: A patient receives a dose of 15 millisieverts (mSv) of radiation during a medical procedure. How many sieverts (Sv) is this?

$$15 \times 10$$^{-3}$$ = 0.015 Sv$$

Question 1

Which of the following statements best explains why most of the mass of an atom is concentrated in its nucleus?

Accepted Answer

Because protons and neutrons, which have significant mass, are located in the nucleus, while electrons have negligible mass and occupy the surrounding space.

Question 2

An atom of sodium has an atomic number of 11 and a mass number of 23. How many neutrons does it contain?

Accepted Answer

$$23 - 11 = 12$$ neutrons

Question 3

Which of the following best describes isotopes?

Accepted Answer

Atoms of the same element with the same number of protons but different numbers of neutrons.

Question 4

Which type of radiation is most likely to cause ionization in living cells, potentially leading to cancer?

Accepted Answer

Alpha, beta, gamma, positron, and neutron radiation, as they are all forms of ionizing radiation.

Question 5

A radioactive isotope has a half-life of 8 hours. If you start with a 100 mg sample, how much remains after 24 hours?

Accepted Answer

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

Question 6

Which of the following statements about radioisotopes used in medicine is correct?

Accepted Answer

Radioisotopes with short half-lives are preferred for diagnostic imaging to minimize radiation exposure to the patient.

Question 7

Which nuclear equation correctly represents the alpha decay of uranium-238 ($$^{238}_{92}\mathrm{U}) to $$thorium-234 ($$^{234}_{90}\mathrm{Th}$$)?

Accepted Answer

$$^{238}_{92}\mathrm{U} \$$rightarrow ^{234}$$_{90}\mathrm{Th} $$+ ^{4}$$_{2}\alpha$$

Question 8

A patient receives a dose of 15 millisieverts (mSv) of radiation during a medical procedure. How many sieverts (Sv) is this?

Accepted Answer

$$15 	imes 10$$^{-3}$$ = 0.015 Sv$$

Question 9

Which of the following best explains why all isotopes of elements with atomic number 83 or higher are radioactive?

Accepted Answer

Their nuclei are too large to be stable, leading to spontaneous radioactive decay.

Question 10

A laboratory produces a radioisotope by bombarding a stable isotope with neutrons. On which side of the nuclear equation does the neutron appear?

Accepted Answer

On the reactant side, because it is used to initiate the reaction.

Question 11

Which of the following is the SI unit for measuring the number of radioactive disintegrations per second?

Accepted Answer

Becquerel (Bq)

Question 12

A sample of a radioisotope has a physical half-life of 10 days and a biological half-life of 5 days. Which of the following statements is true about its effective half-life in the body?

Accepted Answer

The effective half-life will be shorter than either the physical or biological half-life.

Question 13

Which of the following best describes the process of positron emission in PET scans?

Accepted Answer

A positron is emitted from a radioisotope, collides with an electron, and produces gamma radiation detected by the scanner.

Question 14

Which of the following is a real-world example of a radioisotope used as a tracer in medical diagnostics?

Accepted Answer

Technetium-99m, which is used in imaging because it concentrates in specific tissues and has a short half-life.

Question 15

Which of the following best explains why the loss of electrons from atoms in living cells due to ionizing radiation can be harmful?

Accepted Answer

It makes the atoms more reactive and less stable, potentially damaging cell chemistry and genetic material.

Question 16

A patient is treated for thyroid cancer with a dose of iodine-131 that is 1000 times higher than the dose used for diagnostic imaging. What is the main reason for using such a high dose?

Accepted Answer

To destroy diseased or cancerous thyroid tissue through the emission of beta particles.

Question 17

Which of the following statements about the increase in human exposure to radiation since the 1980s is correct?

Accepted Answer

It has increased by about 40%, mainly due to the increased use of radiation in medical procedures.

Question 18

Which of the following is a correct calculation for converting 250 millirems to sieverts?

Accepted Answer

$$250 	imes \frac{1}{100,000} = 0.0025 Sv$$

Question 19

Which of the following best describes brachytherapy?

Accepted Answer

Implanting small titanium seeds containing radioisotopes directly into a tumor to destroy cancerous tissue.

Atoms and Radioactivity: Structure, Isotopes, and Medical Applications

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