X-Rays

X-Rays

X-rays and the rays of visible light both belong to that class of electromagnetic radiations that stretches from the longest Hertzian or radio waves to the exceedingly short gamma rays of radium and on beyond the cosmic rays. The only difference among those kinds of waves is in the wave length. X-rays are much shorter than the waves of visible light.

To understand how X-rays are produced, it is first necessary to consider the electron that negatively charged particle that is one of the fundamental building blocks of matter. So small is the electron that 30,000 trillion (30 followed by 27 zeros) electrons weight less than an ounce. Yet the electron can be a powerful thing. For when an electron is accelerated by a high electric voltage, it becomes a projectile traveling at an awesome speed. At 50,000 volts an electron attains a velocity of 77,200 miles per second; at 400,000 volts, its speed approximates 155,000 miles per second, or 83 per cent of the velocity of light.

When millions of tiny speeding electrons strike a metal target, they penetrate the very atoms of the metal. And they produce, deep within the atomic structure, dislocations and rearrangements which, in turn, release the radiations we know as X-rays. The faster the electrons are traveling when they hit that is, the higher the voltage in the X-ray tube the more penetrating is the radiation.

Roentgen made his discovery while experimenting with a Crookes tube. This is a pear shaped vacuum tube containing two metal electrodes a cathode and an anode. Each electrode is connected to one terminal of an induction coil. Electrons shoot out from the cathode, the negative pole, at speeds of approximately 30,000 miles per second. They travel so fast that most of them cannot turn the corner to get to the anode, the positive pole, but instead hit the glass at the end of the tube. This impact of electrons upon the glass produces the X-rays which Roentgen was first to observe.