Science: X-Rays in Overalls

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.

This week, for example, in General Electric’s Schenectady plant great turbine castings for U.S. warships are being Xrayed. Special photographic films are taped inside the castings (see cut p. 7.5). Then the X-ray machine is lowered into place and the operators retire behind an 18-inch concrete wall.* From a remote-control panel the machine is turned on, and for a minute or two the rays fall upon the six-inch steel. The developed films reveal cracks and pores deep inside the metal. Defective 40-ton castings are not junked: their flaws are gouged out and the holes welded full of solid metal. Since 1936 the Navy has demanded that General Electric X-ray its turbines, so that no invisible engine faults will ever make its warships helpless in battle.

The use of X-rays has made possible improved industrial technology. Sturdier boilers for the Navy are insured by X-ray tests. Bent out of six-inch steel plate, boilers were formerly riveted because reliable welds were unattainable. But with the help of 1,000,000-volt and lesser X-rays, engineers and welders of Babcock & Wilcox have learned how to eliminate flaws so that welded seams can now be relied on.

Ford Motor Co., which is speeding production of Pratt & Whitney aircraft engines by casting instead of forging their crankshafts, recently got a 1,000,000-volt machine to X-ray the crankshafts. Ford’s older 400,000-volters could X-ray 40 crankshafts a day; the new giant works six times as fast. Vital engine parts are all 100% Xrayed; at frequent intervals samples of other parts are X-rayed to make sure that quality does not fall off as it is apt to do in the furious pace of defense production. Founded in 1930, Ford’s X-ray department soon expects to have industry’s biggest collection of X-ray apparatus, to use many thousand films a day.

Principal use of big X-ray machines is to study castings and welds for flaws but there are hundreds of other uses for smaller machines ranging down as low as 5,000 volts, thousands of which have been turned out by Westinghouse, G.E., Picker X-Ray Corp. of Cleveland and Kelley Koett Corp. of Covington, Ky. For example :

> Inspecting tobacco, candy, nuts and canned foods for foreign objects. Usual method is by fluoroscopy. Instead of falling on photographic film the X-rays fall on chemically treated screens where they become luminous and form shadow pictures as the parade of examined materials goes by on conveyor belts. This inexpensive method is good where detail is not needed.

> Sorting fruits. In 1937 a frost-bitten California orange crop was ready to be thrown away completely when G.E. hurriedly developed X-ray machines which distinguished mottle-shadowed frozen oranges from the dark-shadowed good ones, saving fruit growers $10,000,000.

* World’s biggest X-ray machine—a 1,400,000-volter—began operation last fortnight at the U.S. Bureau of Standards in Washington.

* X-rays are literally death rays. A man ex posed to strong enough fays for a few minutes would die within a few months. A few seconds’ exposure could cause temporary and possibly permanent sexual sterility, as well as severe blood changes. These and other effects can be cumulative, picked up fatally second by second through several years. The machines at G.E. are housed in windowless buildings with 18-inch concrete walls to keep any death-dealing X-rays from getting out, and every worker in this laboratory carries an X-ray plate strapped to his wrist to give warning if he is unknowingly exposing him self.