Nuclear Physics Exploring the Heart of Matter (2013) / Chapter Skim
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Pages 9-29
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From page 9... ...
There have been stunning accomplishments and major discoveries in nuclear science since the last decadal assessment. Like Rutherford, today's nuclear scientists find that the data from well-crafted experiments often challenge them to revise their ideas about the structure of matter.
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From page 10... ...
U.S. nuclear physicists often involve themselves in large collaborative efforts with scientists from many countries, carrying out experiments in the United States or abroad.
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From page 11... ...
Nuclear physics has Janus-like qualities, probing fundamental laws of nature that link it to particle physics while at the same time looking toward complex phenomena that emerge from the fundamental laws, as in atomic and condensed matter physics, and astrophysics and cosmology; zooming in on phenomena happening at the shortest distance scales that our best microscopes can see and zooming out to the stars and the cosmos. Because it sits in this liminal position between the fundamental and the emergent, between the microscopic and the astronomical, nuclear physics naturally addresses these central questions from varied angles, providing unique perspectives.
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From page 12... ...
Other elements were formed later in nuclear reactions occurring deep within the early stars. Cataclysmic explosions of these early stars dispersed these heavy nuclei throughout the galaxy, so that as the solar system formed it contained nuclei of carbon, nitrogen, oxygen, silicon, iron, uranium, and many more elements, which ended up forming our planet and ourselves.
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From page 13... ...
Significant advances in astronomy since the last decadal assessment have led to the discovery of very rare, very ancient stars whose composition reflects the production of elements by even earlier generations of stars, in some cases reaching back to stars formed from the debris of the very first generation of stellar explosions after the big bang. These ancient metal-poor stars are beginning to provide us with a chemical history of the galaxy, providing detailed information about the output of element-producing processes and in some cases hinting at previously unknown cycles of nuclear reactions responsible for making some of the elements heavier than iron.
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From page 14... ...
pointlike quarks, which are continually exchanging the force-carrying particles called gluons that pro vide the strong interactions binding the quarks into protons and neutrons (and pions and other short-lived complex structures)
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From page 15... ...
Examples of such bodies include novel superconductors, newly discovered topological patterns of quantum entanglement and quantum phase transitions in various condensed matter systems, warm dense plasmas, nuclear matter, quark-gluon plasma, and cold dense quark matter. One of the most exciting discoveries since the last decadal assessment is that the long-assumed periodicities in nuclear structure are, in fact, not always periodic.
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From page 16... ...
Many equally important emergent collective phenomena involving protons and neutrons in atomic nuclei will be studied at FRIB. Remarkably, the basic story of having new phenomena emerge when ele mentary constituents organize themselves into complex structures repeats itself within single protons and neutrons.
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From page 17... ...
This atomic periodicity, governed by the motion of the electrons in atoms, shows up in the behavior of the atomic ionization energy measured in electron volts of energy -- namely, the energy needed to remove one electron from an atom. The chemical reactivity of an atom is determined by this ionization energy.
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From page 18... ...
As described above, the formation of the first protons and neutrons about 10 µsec after the big bang represented the earliest instance of the emergence of complex structures from the previously featureless primordial fluid. Although featureless in the sense that it was the same everywhere in the universe, the liquid of quarks and gluons (called the quark-gluon plasma, or QGP)
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From page 19... ...
Witold Nazarewicz, University of Tennessee. microseconds-old universe -- and that is now being created and studied in experiments in which nuclei are collided at extreme energies -- turns out itself to have very interesting properties that are emergent, in the sense that characteristics of the macroscopic fluid are far from apparent from the fundamental laws that govern the fluid's elementary constituents.
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From page 20... ...
QCD is a rich and enormously complex theory that describes complex structures, phases, and phenomena at the femtoscale. Applying QCD, and the effective nuclear theories that emerge from it at longer length scales, to develop a full understanding of the structure and properties of stars, nuclei, protons, and neutrons, and of the liquid QGP, will be one of the most compelling contributions of nuclear physics to science.
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From page 21... ...
Nuclear phenomena occur on truly macroscopic distance scales in stars, in the nuclear reactions that drive certain classes of cataclysmic stellar explosions and in the description of the structure, formation, and cooling of neutron stars, which are basically gigantic nuclei. Building bridges of understanding between the physics at different spatial resolution scales is one of the paramount challenges facing contemporary nuclear science.
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From page 22... ...
(It could more descriptively be called the "Theory of Visible Matter.") By testing the predictions of this theory for nuclear phenomena to exquisite precision, nuclear physicists are challenging the Standard Model and seeking evidence for new interactions that go beyond it.
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From page 23... ...
For example, the symmetries of the Standard Model do allow a neutron to have a very tiny permanent separation between the center of mass of the positively charged quarks and the center of mass of the negatively charged quarks within it, but many ideas for the NSM allow for a possibly larger charge separation, known as the neutron dipole moment. In the coming decade, nuclear physicists are planning a campaign to detect such an effect or at least greatly reduce the experimental limits on it.
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From page 24... ...
But we do not yet have any fundamental understanding of the pattern of the masses of the 12 Standard Model matter particles, in particular of why the neutrinos are millions of times lighter than any of the other particles.
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From page 25... ...
homes, new medical diagnostic imaging methods, therapies using ion beams and new isotopes for cancer treatments, and new methods for assessing breaches in national and homeland security are just some of the ways that nuclear physics makes a difference to our safety, health, and security. Technological advances driven by advances in nuclear physics, which range from particle accelerators (most of which are now used either for medical purposes or in the semiconductor industry)
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From page 26... ...
The positron sources as well as the highly segmented crystalline detector elements come directly from nuclear physics research. Another example of synergy: Over the last two decades, nuclear physicists interested in the structure of the neutron have developed spin-polarized helium-3 targets, and it now turns out that these very techniques can be used to make spin-polarized helium-3 or xenon-129.
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From page 27... ...
Advancing nuclear science also drives innovations in computer architecture. For example, when IBM developed the Blue Gene line of computers that have become successful commercial machines with an impact on climate science, genomics, protein folding, materials science, and brain simulation, it employed a paradigm that had been developed first for lattice QCD machines -- in fact, IBM employed people who had previously designed a computer called the QCDOC (QCD on a chip)
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From page 28... ...
The Division of Nuclear Physics in the American Physical Society, one of the most active divisions, provides help with planning and outreach for the benefit of nuclear physics. Another effec tive element is the Long-Range Planning process organized by the Nuclear Science Advisory Committee (NSAC)
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From page 29... ...
Nuclear physics in the global context is described in Chapter 4. Resulting from remarkably productive international cooperation, the global program in nuclear physics combines competition, cooperation, and communication in a way that is benefiting all the participants and accelerating scientific progress.
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