Final answer:
Modern x-ray tubes use metal enclosures for safety, a progression from the design of old-fashioned CRTs like those in early non-flat-screen TVs, which emitted light and X-rays when electrons collided with the internal components.
Step-by-step explanation:
Virtually all modern x-ray tubes now use metal enclosures in their construction. This advancement is in part a response to the fact that when cathode ray tubes (CRTs), which are found in older TV models and oscilloscopes, are in use, they employ an accelerating potential to direct electrons towards the screen. Once these electrons strike the screen's phosphor coating, light is emitted to create the images we see. Early models of CRTs generated X-rays when the accelerated electrons collided with the materials they encountered, such as the copper anode of the CRT.
In older TV tube technologies, which are a type of CRT, these electrons, while not harmful by themselves, posed a risk due to the X-rays that they would produce upon collision with the surface inside the tube. However, more recent models incorporated shielding to protect against X-ray emission, and current x-ray tubes using metal enclosures further mitigate this hazard.