Super X Ray

A new X-ray tube which can shoot more concentrated radiation through twelve inches of steel than could all past commercial tubes combined plus all the radium ever mined, was announced last week at the Radiological Society of North America. It is the first commercial tube to operate at two million volts.

In any X-ray tube a stream of electrons from the cathode crashes into the target, impelled by the electrical voltage. Their speed goes up with the voltage--and the higher their speed, the more penetrating are the X rays produced when they collide with the metallic target. Low-voltage or "soft" X rays are sufficient to reveal cavities in teeth or the bones of the hand, because bone absorbs them and thus throws a "shadow" on the photograph. But to reveal gas bubbles or minute flaws in steel armor plate, very "hard" rays are needed, hence a very high voltage in the tube.

The new two-million-volt tube shows up a flaw only .01 inch thick as a clear shadow, even through 16 inches of steel. In penetrating thick steel, the tube is more effective in one hour's exposure than a one-million-volt tube would be in a week, or a half-million-volt tube in an exposure of 500 years.

There is another reason for this X-ray tube's phenomenal performance: it uses a "magnetic lens," similar to that in the electron microscope (TIME, Dec. 14, 1942), to focus the electron beam in the tube on a bull's-eye only .01 inch in diameter, instead of the usual quarter-inch focal spot. Thus the X rays emerge in a sharp beam and produce well-defined shadows even after passage through thick steel.

Present use of the tube is limited to Army ordnance and is secret. But its future uses in the metal industries and in medicine are legion. The design includes some 180 sections, to provide constant accelerating steps of 12,000 volts each. The tube is completely sealed-off, like an ordinary radio tube, needs no pumping to maintain the high vacuum. It is compact, portable so that it can be used to in spect the insides of machinery installed anywhere. In therapeutic use its advantage is that of radium over ordinary X rays: its rays are so penetrating that they can destroy internal cancers without harmful effect on the skin and fleshy tissues.

The man responsible for developing the new tube is keen, soft-spoken Raymond R. Machlett, Cornell-trained president of Machlett Laboratories of Springdale, Conn., largest manufacturers of X-ray tubes in the U.S. The firm was founded by Raymond's father, Robert, in 1897, just two years after the discovery of X-rays. Robert Machlett died in 1926 of prolonged and repeated X-ray burns, acquired in the pioneering period.

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