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In the same way, Professors Rutherford and Soddy have discovered a so-called thorium X to be the stage through which ordinary thorium has to pass in order to produce its emanation. Since the above was written, another product has been found to intervene between the X substance and the emanation in the case of actinium and thorium. They have been named radio-actinium and radio-thorium respectively.
"This twelfth series is interesting. So far only radium, thorium, and uranium are generally known. We know that the radioactive elements are constantly breaking down, and one often hears uranium, for instance, called the 'parent' of radium. Radium also gives off an emanation, and among its products is helium, quite another element.
Kemp sliced another round block of thorium out of a near-by crystal and fitted the second wedge of plutonium into it. At first Rip had worried about the two pieces of plutonium making a good enough contact, but Kemp’s skillful hand and precision eye removed that worry. The torchman finished fitting the plutonium and carried the block to the tube opening.
He sliced off the inner side where it tapered to a cone, then, working only by eye estimate, cut out a hole in which the wedge of fission material would fit. He wasn’t off by a thirty-second of an inch. Skillful application of the torch melted the thorium around the wedge and sealed it tightly. Koa was ready with a sheet of nuclite.
Here and there, pyramids of metal thrust up from the asteroid, sometimes singly, sometimes in clusters. They were metal crystal formations. He guessed that once, long ages ago, the asteroid had been a part of something much bigger, perhaps a planet. One theory said the asteroids were formed when a planet exploded. This asteroid might have been a pocket of pure thorium in the planet.
Back at ground level, he turned up his communicator. "Koa, is everything ready at the boat?" "Ready, sir." The Planeteers had already carried away the torch and its fuel and oxygen supplies. The area was clear of pieces of thorium. Rip announced, "We’re setting the explosion for ten minutes."
Scralabus primus was the scientific name of the creature, but the fact that it looked like a silicon armadillo had given it the popular name of "silly dilly." Apart from its desire for oxygen, it was harmless. Koa reported, "Sir, the block of thorium is ready. We've hung it on a line behind the landing-boat. The blast won't hurt it, and it's too big to get inside the boat." "Fine, Koa.
The chunks of thorium he had ordered thrown in to block some of the radiation made walking a little difficult. "Santos," he said, "we’re in the second crater." "Sir, I’m beyond the first, between two crystals. Pederson is near you somewhere." "Good. When I give the word, turn up your helmet light until they can see a pretty good glow. Keep watching them."
We’re already working on it." "Anything yet?" "No, sir. We’ll have the albedo measurement in a few minutes. It will take longer to figure the mass." The asteroid’s efficiency in reflecting sunlight was its albedo. The efficiency depended on the material of which it was made. The albedo of pure metallic thorium was known. If the asteroid’s albedo matched it, that would be one piece of evidence.
The radio-activity of salts of uranium was proved not to be increased or diminished when these salts had been shielded for five years from the action of light by keeping them in leaden boxes. Shortly after Becquerel's discovery, experiments proved that salts of the rare metal thorium are radio-active.
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