describle the significance of the atomic spectra of elements

-rays are a type of electromagnetic radiation with wavelengths of around 10-10 meter。When medical X-rays are being produced,a thin metallic sheet is placed between the emitter and the target,effectively filtering out the lower energy (soft) X-rays。The resultant X-ray is said to be hard。Soft X-rays overlap the range of extreme ultraviolet。The frequency of hard X-rays is higher than that of soft X-rays,and the wavelength is shorter。Hard X-rays overlap the range of "long"-wavelength (lower energy) gamma rays,however the distinction between the two terms depends on the source of the radiation,not its wavelength:X-ray photons are generated by energetic electron processes,gamma rays by transitions within atomic nuclei。