X-rays

When electrons strike a material in the CRT, rays are produced which can cause fluorescence in fluorescent materials. These were called X-rays by its discoverer (Wilhalm Roentgen)(1895)
X-rays are produced effectively when electrons strike dense metal anode (called targets). These are not reflected by electric or magnetic fields (but they possess electro-magnetic character) and have very high penetrating power.
Wavelength = ~0.1 nm