Peggy McMahan
Lawrence Berkeley
Laboratory, Nuclear
Science Division
http://www.lbl.gov/abc/
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M.A.M.A. McMahan, February 2002
Outline
I. A Bit of History
II. Cyclotrons and other accelerators: The
Legacy of E.O. Lawrence
III. A Walk Around the Nuclear Wallchart:
Nuclear Science in the 21st Century
IV. Applications of Nuclear Science
V. Resources
a. Wallchart
b. Web pages
c. Cosmic Ray Detectors
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I saw in a dream a table
where all the elements
fell into place as required.
Awakening, I immediately
wrote it down on a piece
of paper. Only in one place
did a correction later appear
necessary.
-Dmitri Mendeleev, 1869
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The Beginning of Nuclear Science
Poised on the threshold
of a new century,
scientists in the late
1800’s made
discoveries which
would change the
course of science,
history and medicine in
the 20th Century.
Henri Becquerel
Marie and Pierre Curie
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The Discovery of Radioactivity
Henri Becquerel discovered radioactivity in
1896 when he was doing experiments on
fluorescence of uranium-containing minerals.
He was wrapping the minerals together with
photographic plates in black paper and
putting them in the sun. He thought the
minerals absorbed energy from the sun and
then emitted “x-rays” which gave an image
of the minerals on the plate. But one cloudy
week he put the samples in his desk drawer
and a few days later developed the plate. Lo
and behold, he saw a strong image anyway.
The minerals were emitting x-rays without a
source of external energy. Becquerel had
discovered natural radioactivity.
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Marie Curie
Marie Curie ca 1920. Inset: Pierre Curie
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Marie Curie, working on her
thesis at the Sorbonne in
Paris, together with her
husband Pierre isolated
the elements polonium
and radium from ore
containing uranium in
1898. In 1903, both Curies
were awarded the physics
Nobel prize for their
discoveries. In 1911, Marie
won an unprecedented
second prize, in chemistry
this time, for her chemical
studies of the new
elements.
M.A.M.A. McMahan, February 2002
Types of Radioactivity
In studies of natural radioactivity, Ernest Rutherford
determined there were 3 kinds of radioactivity:
In alpha decay, a nucleus
emits an alpha particle (4He
nucleus) with 2 neutrons and 2
protons
In beta decay, a proton (or
neutron) inside the nucleus
transforms to a neutron (or
proton), emitting a electron
(or positron) and a neutrino
(or antineutrino).
In gamma decay, a nucleus
keeps the same neutron and
proton numbers, but de-excites
by emitting gamma rays.
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Proton #
The Chart of the Nuclides: A “2-D” Periodic
Table
Neutron #
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Nuclei have shells similar
to the electron shells in an atom.
The electron shells determine the
atomic and chemical properties;
the nuclear shells determine the
nuclear properties. Nuclei with
filled shells (a “magic” number of
neutrons or protons) are more stable.
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Ernest Orlando Lawrence
Lawrence at the controls of the 27”
Cyclotron, about 1938.
Lawrence’s first cyclotron, a few inches
in diameter
Ernest Orlando Lawrence invented
the first cyclotron in 1929-31 in a
small laboratory on the Berkeley
campus. This was the foundation
of the “Radiation Laboratory”.
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Lawrence only thought he invented the
cyclotron
From a stone in a 200 BC Greek
“hospital” in Asia Minor (modern
Turkey)
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What is an accelerator?
If a charged particle goes
through an electric
field it gets accelerated. The
amount of acceleration
depends on the strength of
the electric field.
A simple vacuum tube accelerator
Scientists/engineers tried to put more and more voltage across a gap to
make an electron field to accelerate a particle to 1 million electron volts
(MeV). When they couldn’t get any higher, they tried to put a bunch of gaps
together, so that the particle would get successively accelerated.
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Lawrence’s breakthrough
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Lawrence took the idea
of successive
accelerations from
Wideroe and suggested
“rolling up” the linear
accelerator into a circle.
Lawrence’s 11”
cyclotron reached the
sought-after goal of 1
MeV acceleration.
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A Bit of Local History
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E.O. Lawrence invented the Cyclotron in 1931 on
campus
He rapidly moved up in size to 27”, 36” and finally
60” cyclotrons. The 60” cyclotron was built to make
medical isotopes.
LBNL came into being when he conceived the 184”
Cyclotron, too large to build on campus
The 88-Inch Cyclotron, in operation since 1962, is a
third generation, “sector-focused” cyclotron
Many years later, the 88-Inch Cyclotron is the last
nuclear physics accelerator left on the site
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How a cyclotron works
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The 88-Inch Cyclotron Facility
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Gammasphere - the world’s most powerful
detector array to measure gamma rays
A beam particle hits
a target nucleus inside
Gammasphere
The two nuclei fuse to
make a hot “compound
nucleus” which can be
elongated and rotating
The compound nucleus
cools down by emitting
neutrons and protons
The rotating nucleus
emits gamma rays which
are detected in Gammasphere
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The Expansion of the Universe
Relativistic
Collisions (RHIC)
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Medium Energy
(JLAB)
Low Energy
(small accelerators; RIA)
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Nuclear Astrophysics
(small accelerators; nonaccelerator)
Phases of Nuclear Matter
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The Structure of the Nucleus
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Nuclei at the Extreme of Mass
Natural Radioactivity
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Man-made Radioactivity: the
heaviest elements
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Nuclei at the neutron and
proton “driplines”
Proton #
The formation of elements in
supernovae explosions follows
this path (maybe)
Neutron #
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The Rare Isotope Accelerator, RIA, the
next proposed large accelerator at the
DOE, will accelerate radioactive species in
order to study nuclear astrophysics and the
formation of the elements.
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Neutrinos from the Sun
•Nuclear reactions in the sun produce
photons and electron neutrinos
•Early experiments measured too few
neutrinos to be explained by reaction
models.
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•First results from SNO (2001) show
that the electron neutrinos are
oscillating into other flavors (µ,τ)
before reaching the detector. This
proves neutrinos have mass!
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Applications of Nuclear Science
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Resources for Teachers
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The Cosmic Connection http://www.lbl.gov/abc/cosmic/
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Viewing the x-ray spectrum of 63 elements
http://ie.lbl.gov/xray/
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