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The thin trail of the
positron is seen in the middle of the photo.
The positron moves upwards through a horizontal
3 mm lead plate and its trajectory is curved by
a magnetic field. The direction was determined
from the observation that the particle had lost
energy going through the lead plate and was
therefore curving more in the magnetic
field.
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In 1932 Carl Anderson observed
an intriguing particle in the cloud chamber which he
was using to study cosmic radiation. In the cloud
chamber charged particles give rise to a trail of
condensed droplets with which many properties of the
particle can be determined. There were several
interpretations possible. With the assumption that it
was a well-known particle, it was either an electron
moving downwards or a proton moving upwards. After
careful investigations it was possible to exclude
both possibilities. The electric charge was
determined to be positive, that is opposite to the
charge of the electron. This positive particle had a
mass close to that of the electron. Carl Anderson had
actually identified the first antiparticle, the
positron as he called it, the antiparticle of the
electron. In 1936 he received the Nobel Prize for his
discovery of the positron.
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The Nobel
Prize in Physics 1936 - Carl David Anderson
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