Re: Are gamma and x-rays determined by origin or energy?

The frequency and hence size (wavelength) of an electromagnetic wave
is its defining characteristic aside from iits speed in a vacuum 
(c=3x10E8 m/s).  Regions of the electromagnetic spectrum have been given
arbitrary names just as the regions of the visible spectrum 
(i.e. ROYGBIV; Radio, Microwave, IR, UV, X-ray, Gamma-ray).
The breaking points are somewhat arbitrary and do have overlap.
Origin is not the defining characteristic.

But size does matter.  If you need to create an electromagnetic wave
of small size (say X-rays and gamma rays), things of similar size
do the creating like atomic nuclei.  Radio wave on the other hand
are created (and detected) by large things because their wavelengths
are large.