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| With the Wilson cloud chamber that she devised ca. 1957. |
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Dr. Yuasa's first project was to observe the path of
alpha particles in a Wilson cloud
chamber and explore their action on matter. The Joliot-Curies and
others at the institute were deeply impressed by her unwavering dedication
to her research amid the hardships of German-occupied France. The trust
and friendship Dr. Yuasa earned proved invaluable as she pursued her studies.
Her next topic of research was beta decay in artificial
radioactive elements. At that time the mechanism of beta decay, which was
still largely wrapped in mystery, was one of the most advanced and important
research topics in science. Dr. Yuasa observed the path of beta particles
emitted by radioactive arsenic and other substances in a Wilson cloud chamber
and carefully charted the energy levels to determine what sort of energy
caused the emission of beta particles. These studies contributed substantially
to our understanding of the mechanism of beta decay. Dr. Yuasa's work in
this area earned her the French national degree of doctor of science in
1943.
In 1944, as the war turned against Germany and Japan, Dr. Yuasa was forced
to relocate to Berlin. In the midst of constant air raids, she continued
her work and even succeeded in devising the world's first dual-focus beta-ray
spectroscope. In 1945 she returned home to a defeated Japan. Experimental
nuclear research was banned in occupied Japan, so for the next four years
Dr. Yuasa taught and pursued her nuclear research on a theoretical level.
Returning to France in 1949, Dr. Yuasa set to work analyzing the radiation
emitted by atomic nuclei, particularly beta rays, in order to shed light
on the internal energy structure of the nucleus. In the process she devised
another beta-ray spectrometer that proved extremely valuable for such analyses.
Her research yielded important findings, and before long she became internationally
known and was being invited to give lectures at scientific symposiums around
the world. Around 1958 she began using a particle accelerator called a cyclotron
to bombard the nuclei of carbon and other atoms with accelerated protons.
In an effort to understand the mechanism of the resulting nuclear
reaction, she carried out highly advanced experiments in which she
observed the path of the particles emitted, generally using a propane
bubble chamber. She continued her meticulous analysis, devising
her own improved bubble chambers and other observation apparatuses, until
she was able to publish findings that attracted the notice of the scientific
community. This research led her finally to an attempt to understand the
interaction of forces in few-nucleon systems. Dr. Yuasa proposed a joint
Japanese-French research project to pursue this goal, and thanks to her
efforts it eventually came to fruition.
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radioactivity: A process
of "decay" in which atoms emit particles (radiation). In alpha decay,
the atomic nucleus emits an alpha particle consisting of two protons
and two neutrons--in other words, a helium nucleus. The radioactive
element radium has 88 protons and 138 neutrons; when it undergoes
alpha decay, it turns into radon, which has 86 protons and 136 neutrons.
In beta decay, one of the neutrons in the nucleus turns into a proton,
which remains in the nucleus, while an electron and a neutrino (an
uncharged particle of almost zero mass) are emitted. When carbon,
which has six protons and eight neutrons, undergoes beta decay, it
turns into nitrogen, which has seven protons and seven neutrons. Another
form of radioactivity involves the emission of gamma rays, a form
of light.
nuclear reaction: A phenomenon in which the
nucleus of an atom undergoes a change when hit by a high-speed particle.
Nuclear reactions are widespread in nature, both here on earth and
in space. In the laboratory, scientists may bombard carbon atoms with
accelerated protons, for example, to yield boron plus a proton, or
beryllium plus an alpha particle.
Wilson cloud chamber: A device that made the
paths of electrically charged particles visible. A sealed container
with a piston in it was filled with a mixture of vapors, such as water
and alcohol, and the temperature was lowered until the gas was saturated.
As the electrically charged particle passed through the chamber, the
piston was released to quickly enlarge the space inside the chamber
to make the gas supersaturated. The charged particle ionized the molecules
in its path, and vapor condensed around those electrically charged
molecules, showing the path of the particle as a mist. Scientists
could observe the path directly or photograph it.
propane bubble chamber: Another device for
viewing the paths of subatomic particles. A sealed container was filled
with liquid propane, which was heated almost to the boiling point.
As an electrically charged particle passed through the chamber, the
pressure was quickly lowered. This caused bubbles to form around the
molecules that were ionized by the particle, allowing one to observe
the particle's path. |
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