When a semiconductor is used to measure the range of photon energies produced by a radionuclide, what unit may be displayed?

When a semiconductor is used to measure the range of photon energies produced by a radionuclide, what unit may be displayed?

• A. sieverts (Sv)
• B. gray (Gy)
• C. kilo-electron volts (keV)
• D. counts per minute (CPM)

Answer: (C)

The main idea is that this measurement focuses on the energy carried by each photon, not on dose or how many photons arrive per minute. A semiconductor detector converts each incoming photon into a charge pulse, and the pulse height is proportional to the photon’s energy. After calibration, the spectrum is displayed with energy on the scale, typically in electronvolts, kiloelectronvolts, or MeV. For radionuclide gamma rays, energies are commonly in the keV–MeV range, so kiloelectronvolts is a natural unit to show the photon energies detected. The other units relate to different quantities. Sieverts and grays measure dose (biological effect and energy deposited, respectively), not the photon energy. Counts per minute is a rate of detected events, not the energy of each photon.

The main idea is that this measurement focuses on the energy carried by each photon, not on dose or how many photons arrive per minute. A semiconductor detector converts each incoming photon into a charge pulse, and the pulse height is proportional to the photon’s energy. After calibration, the spectrum is displayed with energy on the scale, typically in electronvolts, kiloelectronvolts, or MeV. For radionuclide gamma rays, energies are commonly in the keV–MeV range, so kiloelectronvolts is a natural unit to show the photon energies detected.

The other units relate to different quantities. Sieverts and grays measure dose (biological effect and energy deposited, respectively), not the photon energy. Counts per minute is a rate of detected events, not the energy of each photon.