Ionizing radiation has many practical applications. In which of the following devices or processes is ionizing radiation not used? (A) Smoke detectors, (B) medical imaging, (C) radars, (D) disinfecting medical instruments, or (E) food irradiation.
Ionizing radiation is radiation that carries enough energy to remove electrons from atoms. There are different types of ionizing radiation, including part of the UV spectrum, X-rays, 𝛾 rays, 𝛼 particles, 𝛽 particles, and free neutrons.
X-rays can pass through the human body, and different tissues within the body absorb the rays in different amounts. So X-rays and 𝛾 rays can be used in medical imaging. So we know that option (B) medical imaging is not the answer to this question.
Both X-rays and 𝛾 rays can kill bacteria, so X-rays and 𝛾 rays can be used to kill harmful bacteria on food. So both of these types of ionizing radiation can be used in food irradiation. Therefore, option (E) food irradiation is not the answer to this question.
As the X-rays and 𝛾 rays can kill bacteria, they can also be used to disinfect medical instruments. So option (D) disinfecting medical instruments is not the answer to this question.
A source of 𝛼 particles is americium-241, which is commonly found in smoke detectors. 𝛼 particles emitted from americium-241 ionize air molecules. Two charged plates create a flow of charged ions. And when smoke enters the detector, the smoke breaks the flow of ions, decreasing the current and sounding the alarm. So we know that ionizing radiation can be used in smoke detectors. So option (A) smoke detectors is not the answer to this question.
The only option we’re left with is option (C) radars. Radar is a detection system that uses radio waves. Radio waves are part of the electromagnetic spectrum. Some of the electromagnetic spectrum is ionizing, and some is nonionizing. The divide is at ultraviolet or UV. Some UV is ionizing, and the parts of the spectrum with more energy than UV are also ionizing. This includes 𝛾 rays and X-rays.
Radio waves have a less energy than UV, so they are nonionizing. Thus, ionizing radiation is not used for radars. So the answer to the question “In which of the following devices or processes is ionizing radiation not used?” is (C) radars.