What even is an x-ray?

I’ve always been taught the electromagnetic spectrum goes (in song form)…

Radiowaves, Microwaves, Infrared… Radiation, Visible light, Ultraviolet, X-rays, Gamma rays.

The assumption being that the higher the note sung (the later in the song), the higher the energy, the shorter the wavelength u.s.w.

Therefore why are we calling my LINAC friends x-ray units?! Their energy is way higher than a conventional diagnostic x-ray and way higher than the gamma rays required in say pair production of an electron and positron. Where has the system failed? What is the energy distinction between x-rays and gamma rays?!

Spoiler alert: There isn’t one…

X-rays are defined by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) as being produced when electrons strike a target or when electrons rearrange within an atom. Whereas Gamma rays originate from the settling process of an excited nucleus of a radionuclide after it undergoes radioactive decay.

And so method of production is the distinction between x-rays and gamma rays rather than energy.

In a linear accelerator, the photons are produced by accelerating electrons into a heavy metal target (e.g. Tungsten), therefore they are in fact x-ray units despite the colossal energies being worked with!