On the surface, it would seem so. But, according to Einstein's famous identity, E=mc^2, mass and energy are the same thing. one could, in principle, plot a mass spectrum in energy units rather than in mass units. That this is not done in practice does not overshadow the interchangeability of the units. Particle physicists, for instance, do you energy-derived units as a measure of mass--speaking of how many electron-volts a particle masses, for instance.
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