Final answer:
The gamma energy of Tc-99 is 140 keV (Option A).
Step-by-step explanation:
Gamma rays are high-energy photons emitted during radioactive decay. Tc99m is a widely used medical isotope that emits gamma rays with an energy of 140 keV when it decays.
The gamma energy of Tc-99 is primarily 140 keV, which is a common nuclear transition energy for the medical imaging isotope Technetium-99m. This is based on the nuclear transition of the metastable isotope Technetium-99m (Tc-99m) which is commonly used in medical imaging. It decays by gamma ray emission, and 140 keV is the energy most frequently associated with this isotope's decay. Nuclear physics often deals with energies at this scale, utilizing units such as kiloelectronvolts (keV) or megaelectronvolts (MeV) to describe these processes.
Thus, the correct option is A.