World War II is introducing X-rays into U.S. industry with the same momentous impact with which World War I introduced them into every hospital and doctor's office. Today X-rays are looking for flaws in parts of airplanes, tanks, warships and cannon as systematically as they are used to examine the lungs of new Army recruits.
Ten years of industrial X-ray development have been telescoped into one urgent year of armsmaking. Six months ago, for example, there was only one giant 1,000,000-volt industrial X-ray machine capable of clearly radiographing seven inches of steel. Today there are upwards of half a dozen in use. Similarly, in the last year manufacturers have booked more orders for 200,000-and 400,000-volt X-ray machines than in the six previous years; more than 100 are now in industrial use.
X-rays can be imagined as streams of infinitesimal sub-atomic particles. They are similar to radium rays and they work in exactly the same way to destroy living cells. They are created when a powerful electric current—i.e., a stream of electrons —jumps through a vacuum tube and hits a "target,", usually a piece of tungsten. The electrons batter from the tungsten a secondary stream of chargeless particles, X-rays, whose wave lengths are thousands of times shorter than those of ultraviolet light and almost as short as those of radium's gamma rays. The shorter waves are the farther they penetrate into matter before their energy is dispersed. The stronger the voltage the shorter the resulting X-ray wave length and the greater the penetration. Thick Navy steels can be radiographed with 400,000-volt machines; but the pictures are not clear and require an hour of exposure for every minute required by the 1,000,000-volters.
Bones to Battleships. Ordinary clinical X-ray machines operate at about 90,000 volts for diagnosis, 200,000 volts for therapy. Early high-voltage machines, ranging up to about 800,000 volts, were such towering contraptions that they had to be housed in special buildings, so unwieldly and immobile that their rays could be beamed only at a fixed spot.
About four years ago, 1,000,000-volt machines began appearing in a few great U.S. hospitals on a new, more compact model, weighing about 4,000 pounds, one-quarter of this weight being lead to keep the rays from getting out into the hospitals. Costing some $40,000 apiece, every 1,000,000-volter is the equivalent of $90,000,000 worth of radium.* (Radium is still widely used in therapy because of its compactness: it can even be planted inside a patient and left there for a while to do its work.)
Industrial use of 1,000,000-volt machines had to wait until they became compact and light (1,500 lb.) enough to be slung easily from a crane and aimed this way & that upon intricate pieces of machinery. The new giants have two great industrial advantages: 1) they can see through thicker metals, 2) they can do the work of smaller machines in less time.