Word: iridium
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...more than 4 cm. (1½ in.) in diameter -doctors first excise the growth in a relatively simple surgical procedure called a lumpectomy. Larger tumors are left in place because their removal would destroy the shape of the breast. Then the radioactive material, usually the shortlived, man-made isotope iridium 192, is inserted into the tumor area. The technique requires extreme care; the iridium must be inserted precisely and in just the right quantity to avoid damage to nearby healthy tissue...
Typically, the physician pushes several hollow steel needles horizontally into the breast through the tumorous area and out the other side (see diagram). Thin plastic tubes are then threaded through the needles (which are subsequently removed) and anchored in place by small plastic buttons at either end. The iridium-in the form of tiny "seeds" embedded in a thin, stiff nylon ribbon -is inserted into the tubes. The outer layer of the seed is a steel sheathing; it blocks dangerous ionizing beta rays (electrons), but allows the escape of the high-energy gamma rays that destroy the tumor...
...technique was first used for examining welds and joints in everything from bridges to nuclear submarines. Then Technical Operations, Inc. of Burlington, Mass, helped Eastern solve the problem of getting radiographic equipment into the hollow rotor shaft of jet engines by using a 100-curie capsule of iridium 192 that is as small as a pencil eraser but emits gamma radiation powerful enough to pierce the engine's metal innards...
...mercury battery, cast in epoxy resin and encased in a double coating of silicone rubber. The instrument uses the timing effect of electrical surges in a closed circuit to measure off 60 beats a minute. To carry the impulses to the heart, Dr. Chardack uses two springs of platinum-iridium alloy, attached to the heart muscle...
Since the 19th century, science and industry have honored a holy of holies: a bar of platinum-iridium alloy, triple-locked in a subbasement at Sèvres on the outskirts of Paris. Near the ends of the bar were engraved two microscopically thin lines, and the distance between them was exactly one meter-by international agreement, the world standard of measurement. Around the globe, other countries had copies of the bar at Sèvres, and their traditional units of length-feet (3.28 to a meter), versts, li, or whatever -were defined by reference to it. But last week...