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Why are ionizing radiation energies often measured in electron volts?

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detector output connected to a measuring circuit — radiation measurement Figure 1: (A) A simple equivalent circuit for the development of a voltage pulse at the output of a detector. R represents the resistance and C the capacitance of the circuit; V(t) is the time (t)-dependent voltage produced. (B) A representative current pulse due to the interaction of a single quantum in the detector. The total charge Q is obtained by integrating the area of the current, i(t), over the collection time, t_c. (C) The resulting voltage pulse that is developed across the circuit of (A) for the case of a long circuit time constant. The amplitude (V_max) of the pulse is equal to the charge Q divided by the capacitance C.

In atomic and nuclear physics, the electron volt (eV) is the standard unit for measuring the energy of ionizing radiation because it is directly related to the fundamental processes of particle interaction. An electron volt is defined as the amount of energy gained by an electron when it is accelerated through an electrical potential difference of one volt.12

Because ionizing radiation involves the interaction of charged particles with atoms and molecules, the energy required to remove an electron—known as ionization energy—is conveniently expressed in this unit. While joules are the standard SI unit for energy, they are often inconveniently large for describing the energy scales of individual subatomic particles. Using electron volts allows physicists to work with numbers that are more practical for characterizing the energy of photons and particles across the electromagnetic spectrum.32