The Dragon
A neutron is a subatomic particle found in
the nucleus of all known elements except
one—hydrogen, whose nucleus consists of a lonely proton. A neutron has a
mass nearly that of a proton but has no electrical charge (the proton carries a
positive charge). In the early years of nuclear physics, neutrons and protons
could be thought of as sub-atomic billiard balls, solid and hefty. Now we know
otherwise. Quantum physics tells us that a neutron is made up of two
down-quarks and one up-quark. And quarks are thought to be made up of squiggles
in n-dimensional space where n may vary from 4 to 10 or 11 or 26 depending upon
your version of String Theory. I prefer the billiard ball analogy myself. Let
it just be said that a neutron, with no electrical charge, can enter a nucleus
of certain atoms, such as uranium 235 or plutonium 239, and create quantum havoc.
The aftermath of that havoc is nuclear fission.
In 1938, German physicists Otto Hahn and
Fritz Strassman bombarded a sample of uranium metal with neutrons. At the time,
uranium, atomic number 92, was at the tail end of the periodic table of all
known elements. By absorbing a neutron in its nucleus, it was thought that the
uranium might be transformed into a new, unknown element of atomic number 93.
However, their results were baffling. Instead of a newer, heavier element, they
found several lighter elements that hadn’t been there before.
Lise Meitner, an Austrian physicist,
suggested to them that the uranium nucleus had split, releasing great energy,
and leaving behind the lighter atoms as fragments. Shortly thereafter Meitner’s
nephew, Otto Frisch, also a physicist and a colleague of Neils Bohr, came to
visit her and he suggested the term “nuclear fission” to describe the
phenomenon.
I was two years old when this was happening.
Thirty-one years later I listened to Otto Frisch, in person, give a lecture
about a fission experiment he designed for the Manhattan Project. That
experiment bore similarities to a project where I was working at the time.
In 1944 Frisch was recruited to work in the
Manhattan Project at Los Alamos. In early 1945 he proposed a rather risky
experiment which entailed dropping a piece of fissionable uranium 235 through a
sub-critical mass of the same material, making it supercritical for an instant.
The burst of fissions would help in refining calculations for the final
critical mass needed for the atomic bomb. At the meeting where the presentation
was made for the experiment, the famed physicist Richard Feynman began
chuckling. When asked why he thought it humorous he said, “That’s like tickling
the tail of a sleeping dragon.” Thereafter it was called The Dragon Experiment.
Months after the successful tests, the Dragon killed two physicists.
Fourteen
years later I came to work in a project that was a direct descendant of that
Dragon Experiment.
