SPACE
APPROACHING THE FINAL FRONTIER
NEAR
■ BY L. PAUL VERHAGE
THEY CAME FROM OUTER SPACE!
Atoms from another star and
possibly from another galaxy are
detectable right here on earth. What
are these mysterious rays and how
are they detected in near space?
THE DISCOVERY OF COSMIC RAYS
The Austrian physicist Victor Hess took a little balloon
ride in 1911 to discover the source of a mysterious
radiation. Previously, physicists had assumed this radiation
originated from elements on earth, but they were yet to
localize its source. They believed it originated from the
earth because early experiments indicated the radiation
decreased as one ascended in altitude. That’s what’s
expected if its source was indeed the earth. Hess’
experiment was designed to measure the background
radiation level as his balloon carried him higher and verify
if its source was terrestrial or cosmic.
In 1911, one of the few instruments capable of
accurately measuring radiation levels was the
electroscope. You’ll recall that an electroscope consists of
a container with an electrode on the top. Inside the
container and attached to the electrode are two thin metal
foil leaves. By bringing a charged object near an
electroscope, the electroscope’s two leaves acquire a
charge. The electric charge on both leaves is the same and
since like-charges repel one another, the leaves spread
apart. Over time, the leaves fall back together. “Where
does the charge go to?” asked the physicists. They
discovered that radioactive substances are capable of
neutralizing the charges, keeping the leaves spread apart.
They also discovered that the greater the “strength” of the
radioactive material, the quicker the leaves fell back
together. By measuring how quickly the charged
electroscope leaves fell back together, Hess was able to
measure the amount of background radiation as he
ascended in his balloon.
Hess rode balloons both day and night, during a solar
eclipse, and up to altitudes of 17,000 feet (which can be
dangerous). He discovered that the background radiation
decreased for the first 3,000 feet of the ascent. That’s
expected — if the mysterious background radiation
originated from radioactive elements in the earth’s crust.
Hess then observed that above 3,000 feet, the
background radiation began increasing with altitude. This
indicated a source of radiation originating from space and
that the radiation for the first 3,000 feet is just from
uranium and thorium in the earth’s crust. American
physicist Robert Millikan (he was the first to measure the
amount of electrical charge in the electron) later
confirmed this finding and gave the radiation the name we
call it today: cosmic rays.
Experiments indicate cosmic rays consist primarily of
energetic protons (the nucleus of the hydrogen atom) and
other atomic nuclei. Thrown into the cosmic ray mix are
electrons and occasional gamma ray photons. Because
cosmic rays consist primarily of energetic subatomic
particles rather than photons, it’s not correct to call them
rays. However, because of historical precedence, we still
refer to them as such.
The ratio of protons to heavier nuclei in cosmic rays
matches the ratio of elements found in the sun. Therefore,
the source of cosmic rays must be objects like stars. What
is responsible for giving cosmic rays their tremendous
energy? The first attempts to measure their direction of
travel indicated cosmic rays appear equally in all
directions. This shouldn’t be surprising; the magnetic fields
between their source and the earth will deflect, reflect,
and scramble the paths of cosmic rays. Fifty years ago,
Italian physicist Enrico Fermi hypothesized that interstellar
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