by JOSEPH TREVITHICK
From television to Hollywood blockbusters, the “dirty bomb” — a device designed to spew radioactive material rather than set off a massive atomic explosion — has captured the public imagination as a potential terrorist weapon. But the U.S. Army once tried to make it into a real weapon of war.
In 1952, the ground combat branch conducted at least two live tests of prototype munitions at the Dugway Proving Ground in Utah. The experimental E-83 “radiological bomb” consisted of more than 70 pounds of tantalum 181 pellets wrapped around a high explosive charge, as technicians explained in one report:
The agent was composed of approximately 75 percent tantalum dust … and 25 percent fine copper wire to provide effective binding. The mixture was compressed … in cylindrical pellets. Each pellet had a diameter of 5/16 inch and a height of 5/16 inch.
The pellets were placed in aluminum tubes at the Chemical and Radiological Laboratories [in Maryland] and shipped to Oak Ridge, Tennessee, where the material was irradiated for a time calculated to produce an activation level of three to five curies per pound. The tubes were shipped to Dugway Proving Ground in lead-lined iron containers.
Scientists measure how fast radioactive materials decay using curies, named after pioneering nuclear physicists Pierre and Marie Curie. As these substances break down, they emit potentially hazardous alpha, beta or gamma rays.
The average person naturally produces around 0.1 curies from potassium-40 in the human body. A little more than a pound of uranium-235 — used to make the cores of the first atomic bombs — will generate one curie of radiation. A similar weight of material producing three to five curies is highly radioactive.
After World War II, the Pentagon had put the Army’s Chemical Corps in charge of cooking up chemical and biological agents. In the same vein, the service’s chemical arm established a radiological division to see if those substances would make useful weapons.
On May 20, 1952, the Army set off four “sectional munitions” at Dugway. A complete E-83 would have several 12-chamber sub-munitions, and steel “pusher” plates protected the pellets from the bomb’s main explosive core. When the bomb went off, the blast would propel the projectiles far and wide without shattering them.
Rather than drop the prototypes from planes, soldiers trucked the weapons out to various positions on Dugway’s “Target H” range. To protect the drivers from radiation, the Army installed lead-lined shields behind the truck’s cab.
After the test explosions, the Army discovered that size and shape of the explosive charges did not radically change where the tantalum pellets landed or how far they flew. In the future, they recommended sticking to one design and seeing if it produced the same effect.
Four months later, the ground combat branch trucked four more modified E-83 sections out to Dugway, along with a portion of another type, the E-59. Again, the Army blew each one up, and each weapon flung their payload in predictable patterns.
However, the Army was concerned about the reliability of the weapons since the pellets from the newest versions fell in completely different patterns from the designs in the first round. The explosive cores in three of the five bombs didn’t even work properly.
“Failure of … the jet-type initiators used in this test indicates some fault in the design or application of this type of initiator,” the technicians surmised in a second report.
We don’t know how long the Army continued to work on these dirty bombs. The Pentagon only declassified these two reports in 2000 as part of larger project to determine how many servicemen and women might have been exposed to dangerous radiation in such experiments over the years. The information had been kept secret under the Atomic Energy Act of 1946.
But the Pentagon seems to have quickly passed over the radiological weapons for increasingly powerful nuclear bombs. By the 1960s, American and foreign scientists had discovered how to produce similar “enhanced radiation” effects with small hydrogen bombs, more commonly known as neutron bombs.
Like a dirty bomb, the neutron bomb uses lethal doses of radiation to kill or otherwise incapacitate people. With these designs available, it’s unlikely — as far as we know — that the Pentagon would ever return to experimenting on cruder radiological weapons.