BOOK: "CANADA AND THE ATOM: Sharing in the Triumph"

BOOK: "CANADA AND THE ATOM: Sharing in the Triumph"

Postby Oscar » Thu Nov 07, 2019 3:44 pm

"CANADA AND THE ATOM - Chapter One - Sharing in the Triumph" - The Glory Days at McGill

[ http://ccnr.org/Chapter_One.pdf ] 2019 Dr. Gordon Edwards www.ccnr.org

Atomic research in Canada began in 1899, before the existence of the atom was fully accepted as a scientific fact. In that year, a young New Zealand physicist arrived in Montreal from England. A Canadian tobacco merchant, W. C. Macdonald, had given McGill University a generous donation sufficient to build a brand new Physics lab and hire several new professors. This newcomer was selected to be one of them. Though no one could have guessed it at the time, he was destined to become “the Newton of atomic physics”. His name was Ernest Rutherford.

Rutherford was eager to explore the mysterious new world of radioactivity. Three years earlier, in Paris, Henri Becquerel had left a lump of uranium ore in a closed drawer containing some photographic plates that were well wrapped. Later, he found a pattern of intense light on the prints, radiating outward from the exact spot where the rock had been sitting. Becquerel was astonished. How can a rock unstimulated by sunlight or any other external agency spontaneously emit energy – an invisible kind of light that can’t even be blocked by thick black paper?

While in England, Rutherford had begun to investigate these peculiar rays, given off by ores containing uranium or thorium. “There are present at least two distinct types of radiation,” he wrote, “one that is very readily absorbed, which will be termed for convenience the alpha radiation, and the other of a more penetrative character, which will be termed the beta radiation.” A third type of atomic radiation, having far greater penetrating power than either the alpha or beta variety, was discovered by Paul Villard in France just one year later. It was called gamma radiation in keeping with Rutherford’s scheme of nomenclature.

By the time Rutherford’s observation had appeared in print, he was already busy in his new Montreal lab, which he declared to be “the best of its kind in the world.” In 1900, he detected a radioactive gas emanating from solid thorium. He enlisted the aid of a young Oxford chemist, Frederick Soddy, then working at McGill. Soddy found that it was a “noble gas” similar to argon. By its nature, such a gas cannot be produced by any kind of chemical reaction. That fact implied “the tremendous and inevitable conclusion,” wrote Soddy, “that the element thorium was slowly and spontaneously transmuting itself” into an entirely different element. It was one of the most earth-shattering discoveries of the century: the spontaneous transmutation of radioactive substances into new substances, later to be called “decay products”.

For several years, Soddy and Rutherford worked as a team at McGill. They found that each radioactive substance has its own characteristic “half-life” – the time required for half of its radioactivity to disappear. Simple multiplication shows that when two half-lives have elapsed, one quarter of the original radioactivity will still remain; and after ten half-lives, less than one part in a thousand is left. They calculated the half-life of uranium at 4.5 billion years, and the half-life of radium (a decay product of uranium) at 1,620 years. They identified one decay product of thorium with a half-life of 22 minutes, another with a half-life of 27 days. Some decay products, they observed, can appear and disappear in the blink of an eye.

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Oscar
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