Saturday, March 29, 2008


Sidebar: Ernest Rutherford

Father of Nuclear Physics

Born 1871 in Nelson, New Zealand, Ernest Rutherford entered Nelson Collegiate School at age 16; in 1889, he was awarded a University scholarship to University of New Zealand, Wellington where he entered Canterbury College. He graduated M.A. in 1893 with a double first in Math and Physical Science; and he continued research work at the College for a short time.

In 1851 (well prior to Lord Rutherford's birth), Prince Albert, husband of Queen Victoria, set up a scholarship fund during the 1851 Crystal Palace Exhibition. Prince Albert specifically wanted to increase opportunities for deserving students outside of England. In 1894, Rutherford was awarded this scholarship; he learned of this while working in his parent's garden and said "this is the last potato that I'll ever dig". Thus, he attended Trinity College, Cambridge as a research student at the Cavendish Laboratory.

His initial experience was not as friendly as he would have liked. As one of the first two nonCambridge graduates to enter their graduate program, he was subjected to some ridicule just for being a provincial. However, his genius quickly asserted itself, and his brilliance could not be denied for very long. For example, he was invited to demonstrate one of his experiments to an evening audience of students, faculty and guests, and Ernest Rutherford did very well. It also helped that he was taken under the wing of the then Cavendish Director, Dr. J. J. Thompson, a brilliant physicist in his own right. (Dr. Thompson discovered the electron.)

In 1898, Dr. Rutherford identified alpha and beta rays in uranium radiation and indicated some of their properties. During this time, he was described by his colleagues as "force of nature". He remained a strong influence on physics throughout his lifetime. Later that same year, he went to Canada to take the Chair of Physics at McGill University, Montreal. There, he discovered new gas, thoron, isotope of radon. With his colleague, Dr. Frederick Soddy, a chemistry professor, he discovered "half-life" of radioactivity.

Otto Hahn , who later discovered atomic fusion, worked under Rutherford in 1905-06.

In 1908, Rutherford was awarded Nobel Prize for Chemistry. By then, he had returned to England as Professor of Physics in University of Manchester . While working with H. Geiger, he invented a method of counting number of alpha particles emitted from radium. Couple of other items. From Manchester, he returned to Cavendish Lab as its director where he motivated many Nobel Prize winners toward their greater achievements.

Still acknowledged as a "force of nature", he obtained another handle, "battleship of physics", and all the brilliant physicists working for him freely acknowledged him as the flagship in the fleet of capable vessels in the scientific ocean of physics. He, himself, considered physics to be the true science, all other sciences were like "collecting stamps". Eventually, he focused on studying the nucleus of the atom and all other studies were relegated to the sidelines.

Lord Rutherford died at age 66; his ashes were buried in the nave of Westminster Abbey near the graves of Sir Isaac Newton and Lord Kelvin.

Source documents:
Engines of Discovery, A Century of Particle Accelerators, by Andrew Sessler and Edmund Wilson. page xii.
A Force of Nature, The Frontier Genius of Ernest Rutherford, by Richard Reeves.
The Fly in the Cathedral, How a Group of Cambridge Scientiests won the International Race to Split the Atom, by Brian Cathcart

Half Life

Term "half life" means a duration for which a certain substance declines by 50%. For example, radioactive thorium might decrease by 50% in 60 seconds.

This could be described by Mtho(1-Δ)sec = .5 * Mtho where Δ is % difference in mass per second and the exponent "sec" is the number of seconds.

Dividing both sides by Mtho and replacing sec by 60, we get following:
(1-Δ)60 = .5

Doing some manipulations with logarithms, we get:
60Log(1-Δ) = (Log .5)
Log(1-Δ) = (Log .5) / 60 = -0.005
1-Δ = 10-0.005 = 0.98855
Δ = .01145

Now, we determine amount of time for any amount of radioactive decay.
For example, how many seconds to decay to 10% of original.
(1-Δ)sec = .1
sec = (Log .1) / Log(1-.01145) = 200 seconds
Note the concept of radioactive half life is very similar to the concept of ever decreasing gross weight due to inflight fuel consumption.


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