Jones, A. Adekola, D.
Priv.-Doz. Dr. Tilman Enss
Bardayan, et al. Nature , copyright Portions of the figure caption are extracted from K. Jones, W. Nazarewicz, Designer nuclei making atoms that barely exist, The Physics Teacher The nuclei colored in darker red are those whose binding is most enhanced by quantum effects. The nuclei predicted to be stable to beta decay are marked by dots. Bender, W.
Nazarewicz, and P. Reinhard, Shell stabilization of super- and hyperheavy nuclei without magic gaps, Physics Letters B 42, Copyright , with permission from Elsevier. Japanese National Laboratory for High Energy Physics KEK , of hypernuclei—nuclei that contain at least one hyperon, a strange baryon, in addition to nucleons. By adding a hyperon, nuclear physicists can explore inner regions of nuclei that are impossible to study with protons and neutrons, which must obey the constraints imposed by the Pauli principle.
The experimental work goes hand in hand with advanced theoretical calculations of hyperon-nucleon and hyperon-hyperon interactions, with the ultimate goal being the comprehensive understanding of all baryon-baryon interactions. An important challenge is to delineate the proton and neutron drip lines—the limits of proton and neutron numbers at which nuclei are no longer bound by. For example, experiments at MSU have produced the heaviest magnesium and aluminum isotopes accessible to date and have shown that magnesium, aluminum, and possibly aluminum exist.
Nuclei near the drip lines are very weakly bound quantum systems, often with extremely large spatial sizes. With the advanced-generation Facility for Rare Isotope Beams FRIB it should be possible to extend such studies and to delineate most of the drip line up to mass using the high-power beams available and the highly efficient and selective FRIB fragment separators. Drip line nuclei often exhibit exotic decay modes. An example is the extremely proton-rich nucleus iron that decays by beta decay or by ejecting two protons from its ground state. Moving toward the drip lines, the coupling between different nuclear states, via a continuum of unbound states, becomes systematically more important, eventually playing a dominant role in determining structure.
Many aspects of nuclei at the limits of the nuclear landscape are generic and are currently explored in other open systems: molecules in strong external fields, quantum dots and wires and other solid-state microdevices, crystals in laser fields, and microwave cavities. Radioactive nuclear beam experimentation will answer questions pertaining to all open quantum systems: What are their properties around the lowest energies, where the reactions become energetically allowed reaction thresholds?
What is the origin of states in nuclei, which resemble groupings of nucleons into well-defined clusters, especially those of astrophysical importance? What should be the most important steps in developing the theory that will treat nuclear structure and reactions consistently? What are the heaviest nuclei that can exist? Is there an island of very long-lived nuclei in the N-Z plane? What are the chemical properties of superheavy atoms? These questions present challenges to both experiment and theory.
As discussed earlier, the repulsive electrostatic Coulomb force between protons grows so much. Not only did this work discover a new element but new information obtained on the half lives of several nuclei in its decay path provided experimental support for the existence of the long-predicted island of stability in superheavy nuclei. However, there is a range of options for synthesizing heavy elements with exotic beams. By using neutron-rich radioactive targets and beams a highly excited system can be formed, which would decay into the superheavy ground state via evaporation of the excess neutrons.
Neutron-Rich Matter in the Laboratory and the Cosmos. Neutron-rich matter is at the heart of many fascinating questions in nuclear physics and astrophysics: What are the phases and equations of state of nuclear and neutron matter? What are the properties of short-lived neutron-rich nuclei through which the chemical elements around us were created? What is the structure of neutron stars, and what determines their electromagnetic, neutrino, and gravitational-wave radiations?
To explain the nature of neutron-rich matter across a range of densities, an interdisciplinary approach is essential in order to integrate laboratory experiments with astrophysical theory, nuclear theory, condensed matter theory, atomic physics, computational science, and electromagnetic and gravitational-wave astronomy. Figure 2.
In heavy neutron-rich nuclei, the excess of neutrons predominantly collects at the nuclear surface creating a skin, a region of weakly bound neutron matter. The upper-left diagram shows the deformation energy in MeV defined as a difference between the ground state energy and the energy at the spherical shape. The region of anticipated long-lived superheavy nuclei is schematically marked.
Tilman Enss - Ruprecht-Karls-Universität Heidelberg
Lower left: contour map of predicted ground-state quadrupole deformations and nuclear shapes for selected nuclei. Prolate shapes are red-orange; oblate shapes, blue-green; and spherical shapes, light yellow. The symbols , , , and refer to unnamed nuclei having the given number of nucleons superscript and protons base.
Its chemistry suggests it is a member of the metallic group 12 containing zinc, cadmium, and mercury. Heenen, and W. Nature ; right K. One of the main science drivers of FRIB is to study a range of nuclei with neutron skins several times thicker than is currently possible. Studies of high-frequency nuclear oscillations giant resonances and intermediate-energy nuclear reactions will help pin down the equation of state of nuclear matter.
Another insight is being provided by electron scattering experiments. This measurement should have broad implications for nuclear structure, astrophysics, and low-energy tests of the Standard Model. Precise data from PREX would provide constraints on the neutron pressure in neutron stars at subnuclear densities. Important insights come from experiments with cold Fermi atoms that can be tuned to probe strongly interacting fluids that are very similar to the low-density neutron matter found in the crusts of neutron stars see Box 2.
Rather than tackling the nuclear problem from the femtoscopic perspective of nucleon motions and interactions, one can focus on a complementary view of the atomic nucleus as a mesoscopic system characterized by shapes, oscillations, and rotations and described by symmetries applicable to the nucleus as a whole. In this way, properties and regularities, which might not be explicit in a description in terms of individual nucleons, are highlighted, providing insights that can inform microscopic understanding.
Such a perspective focuses on identifying what nuclei do and what that tells us about their structure, while the femtoscopic approach is essential to understanding why they do it. The mesoscopic approach is motivated by the recognition of, and search for, regularities and simple patterns in nuclei that signal the appearance of many-body symmetries and associated emergent collective behavior. Despite the fact that the number of protons and neutrons in heavy nuclei is rather small, the emergent collectivity they show is similar to other complex systems exhibiting self-organization, such as those studied by condensed matter and atomic physicists, quantum chemists, and materials scientists.
While few if any nuclei will exhibit idealized symmetries exactly, such a conceptual framework provides important benchmarks. In this perspective, an important goal is to determine the experimental signatures that spotlight these patterns and the interactions responsible for them. Already, research with exotic nuclei is showing the breakdown of traditional patterns see discussion of Figure 2. Box 2. A team of U. The new superheavy element, born in a Russian accelerator laboratory at JINR, in Dubna, required coordinated collaborative efforts between four institutions in the United States and two in Russia and more than 2 years to achieve, highlighting what international cooperation can accomplish.
Analysis of the experimental data was performed independently at Dubna and Lawrence Livermore National Laboratory, providing nearly round-the-clock data analysis by virtue of the to hour time difference between Russia and California. The measured half-lives of new superheavy nuclei were observed to increase with larger neutron number. This work represents an experimental verification for the existence of the predicted island of enhanced stability. Scientists and students at Vanderbilt University and the University of Nevada also contributed to this successful experiment.
Ogannessian, F. Abdullin, P. Bailey, et al. Physical Review Letters The inset shows 22 mg of berkelium in the bottom of a centrifuge cone after chemical separation green solution. The californium contamination was reduced about 10 8 times during the purification process at the Radiochemical Engineering Development Center at ORNL. Nazarewicz and K. Rykaczewski, Oak Ridge National Laboratory. The study of neutron skins and the PREX experiment are discussed in the text. The anticipated discovery of gravitational waves by the Laser Interferometer Gravitational Wave Observatory LIGO and the allied European detector Virgo will help understanding large-scale motions of dense neutron-rich matter.
Finally, advances in computing hardware and computational techniques will allow theorists to perform calculations of the neutron star crust. The binding of nucleons in the nucleus contains integral information on the interactions that each nucleon is subjected to in the nuclear environment. Differences in nuclear masses and nuclear radii give information on the binding of individual nucleons, on the onset of structural changes, and on specific interactions.
Examples of recent measurements of charge radii in light halo nuclei were discussed above. With exotic beams and devices such as Penning and atomic traps, storage rings, and laser spectroscopy the masses and radii of long sequences of exotic isotopes are becoming available, extending our knowledge of how nuclear. The inset displays the energy required to remove the last two neutrons from the nucleus.
These energies have sharp drops after magic numbers but approximately linear behavior in between. Subtracting an average linear behavior therefore magnifies structural changes as seen in the color-coded contours in the two-dimensional plot in the proton-neutron plane. Changes in nuclear properties as a function of nucleon number can signal quantum phase transitions between regions characterized by different symmetries. Although the behavior of such transitions is muted in finite nuclear systems, experimental studies have provided evidence for their existence and tested simple theoretical schemes for nuclei at the critical points.
Gamma-ray spectroscopy is a basic tool for studying nuclear structure, shapes, and their changes—both from the energies and decay paths of excited nuclear states and by measuring nuclear level lifetimes from Doppler effects. Recently, a great diversity of phenomena has been discovered as increasingly sensitive instrumentation reveals unexpected behavior in our quest to observe higher excitation energies and angular momentum states in nuclei. Since gamma-ray spectroscopy is one of the most powerful experimental approaches to unraveling. Nuclear systems—from atomic nuclei to the matter in neutron stars to the matter formed in ultrarelativistic heavy ion collisions—are complex many-particle systems that exhibit a great range of collective behavior such as superfluidity.
This facet of nuclear systems, shared with matter studied by condensed matter physicists, atomic physicists, quantum chemists, and materials scientists, has opened up splendid opportunities for productive and valuable cross-fertilization among these fields. Of growing importance is the intersection of nuclear physics and ultracold atomic gases.
Atomic gas clouds allow physicists to control experimental conditions such as particle densities and interaction strengths, a control intrinsically unavailable to nuclear physicists. Such control has inspired nuclear physicists to develop more unified pictures of nuclear matter, beyond the constraints of laboratory nuclear systems, and to see commonalities with atomic systems. The experimental flexibility of cold atom systems makes them ideal to explore exotic phases and quantum dynamics in these strongly paired Fermi systems.
The quark-gluon plasmas in ultrarelativistic heavy ion collisions are the hottest materials one can produce in the laboratory, with temperatures of trillions of degrees. On the other hand, clouds of ultracold trapped atoms are the coldest systems in the universe, reaching temperatures as low as one billionth of a degree above absolute zero.
The transition observed in strongly interacting cold fermionic atom clouds from paired superfluid states, analogous to superconducting electrons in a metal, to BEC states of molecules consisting of two fermion atoms, captures certain aspects of the transition from a quark-gluon plasma to ordinary hadronic matter made of neutrons, protons, and mesons.
Superfluid pairing in low-density strongly interacting fermionic atomic systems is very similar to that pairing in low-density neutron matter in neutron stars. Although the energy scales are vastly different, the attractive interactions between fermions in both systems produce extremely large superfluid pairing gaps, on the order of one-third to one-half the Fermi energy, and in this sense these systems are the highest temperature superfluids known.
Experiments in cold atoms illustrated in the inset of Figure 2. These properties are key to understanding the limits of stability and pairing in neutron-rich nuclei and the cooling of neutron stars. One can also study analogues of nuclear and quark-gluon plasma states with cold atoms: Simple examples include the binding of fermionic atoms in three distinct hyperfine states, as in lithium-6, analogous to quarks of three colors of quarks, into three-atom molecules, the analogs of nucleons; or the binding of bosonic atoms with fermionic atoms into molecules.
One can also exploit similarities of the tensor interaction between nucleons to the magnetic interaction between atoms with large magnetic dipole moments, e. Strongly interacting ultracold atomic plasmas also present unusual opportunities to study the dynamics of strongly interacting quark-gluon plasmas. Further examples include the formation and interaction of vortices and possible exotic superfluid. Future experiments with optical traps will allow one to study the properties of the inhomogeneous matter that exists in the crust of neutron stars.
And, strongly interacting clouds of atoms with differing densities of up and down spins, as can be engineered in optical traps, share some common features with strongly interacting quark matter with differing densities of up, down, and strange quarks. In both contexts, superfluid pairing gaps that are modulated in space in a periodic pattern may develop, yielding a superfluid and crystalline phase of matter, hints of which may have been seen in very recent cold atom experiments.
The images from upper left to lower right correspond to increasing strength of the pairing obtained by varying the magnetic field. Lower left: Comparison between the energies of cold atoms and neutron matter at very low densities. The energies are given relative to those of a noninteracting Fermi gas, E FG , and are plotted as a function of the product of Fermi momentum, k F , and scattering length a, representing the interaction strength.
Gezerlis and J. Carlson, Physical Review C , , Figure 1. Copyright by the American Physics Society.
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Removing a smooth reference from the bare values shown in the inset highlights the collective contributions attributed to the valence nucleons. Based on data available through The excitation energies of various states in erbium, with respect to a simple quantum rotor reference, are plotted as a function of angular momentum. A sequence of shape transitions, from weakly deformed prolate, to nearly spherical oblate, to well deformed triaxial is seen.
The future challenge will be to reach the region of extremely high nuclear rotations at which erbium cannot withstand the huge centrifugal force and fissions into fragments. The timeline indicates some of the significant milestones in this evolutionary path. Lower panel: This timeline, and the rapid development of more sophisticated instrumentation, are further echoed here, where the intensity of a particular gamma-ray transition normalized to unity for transitions between low angular momentum states between specific energy levels, as the nucleus de-excites, is plotted as a function of spin.
Riley, Florida State University. These prospects are supported by the advances already obtained with existing current-generation instruments. Nucleonic superfluidity plays a large role in nuclear structure. A generic feature of superfluidity is that elementary particles called fermions such as protons or neutrons combine to form specially constructed pairs Cooper pairs that are bosons and exhibit very different behavior and interactions than their constituent particles.
In loosely bound nuclei, pairing may be the decisive factor for stability against particle decay. A striking example is the unbound nature of odd-neutron He nuclei while their even-neutron neighbors are bound. Nucleonic pairing is also important for the structure of neutron star crust. As the number of nucleons can be controlled experimentally, nuclei far from stability offer new opportunities to study pairing.
For instance, it has been suggested that, in neutron-rich nuclei, neutron pairs di-neutrons are well localized in the skin region.
Tilman Enss group | Ruprecht-Karls-Universität Heidelberg
In heavier nuclei with similar neutron and proton numbers, pairing carried by deuteron-like proton-neutron pairs with nonzero angular momentum is expected. Pairing can be probed with a variety of nuclear reactions that add or subtract pairs of nucleons. Because of finite-size effects and different polarization effects in nuclei and nuclear matter, a theoretical challenge will be to relate experiments on nucleonic superfluidity in finite nuclei to pairing fields in neutron stars see Box 2. These studies precisely probed nuclear interactions on short distance scales, showing that energetic protons are about 20 times more likely to pair up with energetic neutrons than with other protons in the nucleus when nucleons overlap see Figure 2.
As discussed earlier, in studies of pair correlations at lower energies, such proton-neutron predominance has not been observed. This can be traced back to variations in the nuclear interaction when changing the relative distance between the two nucleons. Knocking out a proton by an energetic electron causes a high-momentum correlated partner nucleon to be emitted from the nucleus, leaving the rest of the system relatively unaffected.
Right: Depiction of the experimental results from JLAB and BNL that demonstrate the large momentum nucleons in nuclei are primarily coming in proton-neutron pairs. Different symbols and colors mark results of different reactions used. Subedi, R. Shneor, P. Monaghan, et al. Reprinted with permission from AAAS. Toward a Comprehensive Theory of Nuclei. An understanding of the properties of atomic nuclei is essential for a complete nuclear theory, for an explanation of element formation and properties of stars, and for present and future energy and defense and security applications.
Nuclear theorists strive for a comprehensive, unified description of all nuclei, a portrait of the nuclear landscape that incorporates all nuclear properties and forces and can deliver maximum predictive power with well-quantified uncertainties. Such a framework would allow for more accurate predictions of the nuclear processes that cannot be measured in the laboratory, from the creation of new elements in exploding stars to the reactions occurring in cores of nuclear reactors.
Developing such a theory requires theoretical and experimental investigations of rare isotopes, new theoretical concepts, and extreme-scale computing, all carried out in partnership with applied mathematicians and computer scientists see Box 2. There is a well-delineated path toward such a description at the nucleonic level across the nuclear chart that merges three approaches: 1 ab initio, 2 configuration-interaction CI , and 3 nuclear density functional theory DFT.
Ab initio methods use basic interactions among nucleons to fully solve the nuclear. One of the trends in science today is the increasingly important role played by computational science. All of this computing power will provide an unprecedented opportunity for nuclear science see Figure 2. Scientific computing, including modeling and simulation, has become crucial for research problems that are insoluble by traditional theoretical and experimental approaches, too hazardous to study in the laboratory, too time-consuming, or too expensive to solve.
High-performance computing provides answers to questions that neither experiment nor analytic theory can address. As such, it becomes a third leg supporting the field of nuclear physics. Nuclear physicists perform comprehensive simulations of strongly interacting matter in the laboratory and in the cosmos.
These calculations are based on the most accurate input, the most reliable theoretical approaches, the most advanced algorithms, and extensive computational resources.
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Until recently working with petascale resources was hard to imagine, and even at the present time such an ambitious endeavor is beyond what a single researcher or a traditional research group can carry out. Computational resources required for these calculations are currently obtained from a combination of dedicated hardware facilities at national laboratories and universities, and from national leadership-class supercomputing facilities. Collaborative frameworks such as SciDAC will need to continue in order to prepare for, and to fully utilize, computing resources beyond the petascale when they become available to nuclear physicists.
Given the scale of the computational facilities, it is clear that one should view these numerical efforts like experiments in their style of operation. Currently, the nuclear physics community can efficiently use between 1 and 10 sustained petaflop resources; hence a staged evolution to the exascale seems appropriate. In summary, the field of nuclear physics is poised to be transformed through the deployment of extreme-scale computing resources. Such resources will provide nuclear physics with unprecedented predictive capabilities that are needed for the systematic exploration of fundamental aspects of nature that are manifested in the structure and interactions of nuclei and.
Future high-performance computing resources will generate enhancements to nuclear physics program that cannot be imagined today. Deriving internucleon interactions from quantum chromodynamics QCD is a fundamental problem that bridges hadron physics and nuclear structure. Meanwhile, QCD-inspired interactions derived within the framework of effective field theory and precise phenomenological forces carefully adjusted to scattering data are commonly used in nuclear structure and reaction calculations. Configuration-interaction methods adopt the notion of a nuclear potential, which the nucleons themselves both create and move in.
This approach has promise up through the region of mid-mass nuclei and heavy near-magic systems. The nuclear DFT focuses on nucleon densities and currents instead of on the particles themselves and is applicable throughout the nuclear chart. The road map for this effort involves the extension of ab initio approaches all the way to medium-heavy nuclei, the development of configuration interaction approaches in a variety of model spaces, and the quest for a nuclear density functional for all nuclei up to the heaviest elements see Figure 2.
Special, related challenges are the description of the role of the continuum in weakly bound nuclei and the development of microscopic reaction theory that is integrated with improved structure models. The nuclear many-body problem is of broad intrinsic interest. The phenomena that arise—shell structure, superfluidity, collective motion, phase transitions—and their connections with many-body symmetries, are also fundamental to fields such as atomic physics, condensed matter physics, and quantum chemistry.
By investigating the intersections between these theoretical strategies, one aims at developing a unified description of the nucleus. Bottom: Three examples of theoretical calculations involving high-performance computing—proton densities of carbon obtained in the ab initio quantum Monte Carlo method compared with experimental results left ; numerical simulations of neutrino flavor evolution in a hot supernova environment, where the oscillation probability of neutrinos is shown as a function of neutrino energy and the direction of emission from the surface of a collapsing star middle ; two-dimensional total energy of fermium in MeV using nuclear DFT explaining the phenomenon of bimodal fission observed in this nucleus, where nuclear shapes are shown as three-dimensional images that correspond to calculated nucleon densities right.
Last accessed on April 12, The aim of nuclear astrophysics is to understand those nuclear reactions that shape much of the nature of the visible universe. Nuclear fusion is the engine of stars; it produces the energy that stabilizes them against gravitational collapse and makes them shine. Spectacular stellar explosions such as novae, X-ray bursts, and type Ia supernovae are powered by nuclear reactions.
While the main energy source of core collapse supernovae and long gamma-ray bursts is gravity, nuclear physics triggers the explosion. Neutron stars are giant nuclei in space, and short gamma-ray bursts are likely created when such gigantic nuclei collide. And last but not least, the planets of the solar system, their moons, asteroids, and life on Earth—all owe their existence to the heavy nuclei produced by nuclear reactions throughout the history of our galaxy and dispersed by stellar winds and explosions.
Among the open questions that will guide nuclear astrophysics in the coming decade are these:. Answering these questions requires understanding intricate structural details of thousands of stable and unstable nuclei, and so draws on much of the work described in the preceding section on nuclear structure.
This can be seen in Figure 2. Each step of each process depends on the nature of that particular nucleus. As an example, a small change of just 10 percent in the energy of a single excited state of one particular nucleus, the famous Hoyle state in carbon, would make heavy elements, planets, and life as we know it disappear.
Unraveling the nuclear physics of the cosmos, therefore, requires a broad range of experimental and theoretical approaches. In the last decade, ever more sensitive laboratory measurements of low-energy nuclear reactions enabled precise solar models revealing a deficit of solar neutrinos detected on Earth. Knowledge of this. Stable nuclei are marked as black squares, nuclei that have been observed in the laboratory as light gray squares.
The horizontal and vertical lines mark the magic numbers for protons and neutrons, respectively. A very wide range of stable, neutron-deficient, and neutron-rich nuclei are created in nature. Many nuclear processes involve unstable nuclei, often beyond the current experimental limits.
Laboratory precision measurements also revealed that the nuclear reactions that burn hydrogen in massive stars via the carbon-nitrogen-oxygen CNO cycle proceed much more slowly than had been anticipated, changing the predictions for the lifetimes of stars. A few key isotopes in the reaction sequence of the rapid neutron capture process r-process responsible for the origin of heavy elements in nature have now been produced by rare isotope facilities. Advanced experimental techniques also enabled measurements of the nuclear properties that characterize their role in the r-process, despite short lifetimes and small production quantities.
The same sensitive techniques enabled precision mass and decay measurements of the majority of the extremely neutron-deficient rare. The results explain the existence of two classes of X-ray bursts, short and long bursts. In addition, a new rare class of X-ray bursts, so-called superbursts, were discovered and nuclear physics provided the likely explanation of a deep carbon explosion. New multidimensional core collapse supernova models included much more realistic weak interaction physics and nuclear matter properties owing to new results from laboratory experiments and nuclear theory calculations.
Contrary to earlier work, some of these supernova models do now explode although many questions about the explosion mechanism remain. In these supernova explosion models, a new type of nuclear process producing heavy elements, the so called neutrino-p process, was found. The discovery of the most massive neutron star to date has eliminated many theoretical predictions about the nature of nuclear matter.
Future nuclear astrophysics efforts are emerging along two frontiers: 1 the study of unstable isotopes that exist in large quantities inside neutron stars and are copiously produced in stellar explosions but difficult to make in laboratories and 2 the determination of extremely slow nuclear reaction rates, which are important for the understanding of stars.
Enabled by technical advances, dramatic progress is expected in the coming decade at both frontiers. The FRIB facility in the United States will, together with other rare isotope laboratories around the world, provide unprecedented access in the laboratory to the same unstable isotopes that play crucial roles in cosmic events. And a new generation of high-intensity stable beam accelerators to be located deep underground, as has been proposed for the United States, will enable the measurement of extremely slow stellar nuclear reactions without disturbance from cosmic radiation.
A precision frontier also has emerged in the area of measuring neutron-induced reaction rates using neutron beams. Work is needed at this frontier not only on understanding the origin of those elements produced by neutron capture reactions, but also on applications of nuclear science that depend on neutron capture processes. These applications include the design of novel nuclear reactors and stockpile stewardship, as discussed in Chapter 3. Nuclear theory is of special importance for nuclear astrophysics for many reasons:.
Nuclear theory is needed to calculate the necessary corrections, such as thermal excitations and electron screening. Progress in nuclear astrophysics must also go hand in hand with progress in astrophysics and observational astronomy. Astronomical observations of the manifestations of nuclear processes in the cosmos provide the link between laboratory and nature.
The last decade has seen extraordinary progress in astronomy, with high-precision observations of the composition of very old stars at the largest telescopes on Earth and in space and with surveys scanning hundreds of thousands of candidate stars to find the targets. A new generation of X-ray space telescopes has opened up a novel era in the understanding of phenomena related to neutron stars.
Gamma-ray observatories detected the decays of rare isotopes in space, ejected by stellar explosions. Neutrino telescopes provided neutrino images of the sun and had earlier registered neutrinos from a nearby supernova. In the coming decade this progress is bound to continue. Any ongoing large-scale surveys to search for old stars will only pan out in the coming decade, and a new generation of larger ground-based telescopes will enable detailed spectroscopy on many of the resulting targets. Existing X-ray observatories will be complemented with new facilities that push observations toward harder X-rays and possibly gamma-rays and will provide new data on neutron stars and stellar explosions.
New-generation gravitational wave detectors are expected to detect signals from supernovae and neutron stars for the first time. Neutrino observatories are ready, and with a little bit of luck they might observe a galactic supernova, an achievement that would revolutionize our understanding of such an event. And a new thrust in astronomy toward wide-field. Astronomy, astrophysical modeling, and nuclear physics need to work together to achieve progress in nuclear astrophysics. Communication across field boundaries, coordination of interdisciplinary research, and exchange of data are essential for these fields to jointly address the open questions.
The Joint Institute for Nuclear Astrophysics, funded by the Physics Frontiers Center Initiative of the National Science Foundation NSF , has been critical in forming and maintaining a unique worldwide platform to foster such interdisciplinary collaboration between the different nuclear astrophysics communities. Finally, it will be important to strengthen efforts to coordinate research across field boundaries, to form broad interdisciplinary research networks that integrate the wide range of required expertise, and to facilitate the exchange of data and information between astrophysics and nuclear physics, and between experiment, observations, and theory.
Such interdisciplinary research networks are also needed to attract and educate the next generation of nuclear astrophysicists, who, with emerging new facilities in nuclear physics, astrophysics, and high-performance computing, are likely to make transformational advances in our understanding of the cosmos. Origin of the Elements. The complex composition of our world—some stable or long-lived isotopes of 83 elements—is the result of an extended chemical evolution process that started with the big bang and was followed by billions of years of nuclear processing in numerous stars and stellar explosions see Figure 2.
The steady buildup of heavier elements in stars by the successive fusion of hydrogen, helium, carbon, oxygen, neon, and silicon marks the beginning of a new round in the ongoing cycle of nucleosynthesis. The freshly synthesized elements are ejected by stellar winds or supernova explosions and then mixed with interstellar gas and dust from which a new generation of stars is born to repeat the cycle. Nuclear physics provides the underlying blueprint for this chemical evolution by determining the composition of new elements generated in each astrophysical event.
By deciphering the structure of the nuclei involved and by advancing observations, we can trace our chemical history back, step by step, perhaps all the way to the very first supernovae that illuminated the universe. Stars form out of interstellar gas and dust and evolve only to eject freshly synthesized elements into space at the end of their lives. The ejected elements enrich the interstellar medium to begin the cycle anew in a continuous process of chemical enrichment and compositional evolution.
Reynolds et al. Paresce, R. Jedrzejewski STScI. How were the first heavy elements created by the potentially extremely massive stars formed after the big bang? The pattern of the elements ejected in their deaths might still be observable today in the most iron-poor stars of the galaxy, survivors of an early second generation of stars.
Candidate stars with iron content a few , times lower than that of the sun have been found see Figure 2. Comparing the signatures of these elements with predictions from theoretical models of first stars requires a quantitative knowledge of the nuclear reaction sequences generating these elements.
This opens up an observational window into the properties of first stars that is complementary to the planned, very difficult direct observations with future infrared telescopes. The reward might be not only a deeper understanding of the beginnings of chemical evolution in our galaxy but also clues about the nature of the early universe and the formation of structure in the cosmos. It is believed to be extremely old, having formed shortly after the big bang.
The absorption spectrum, here compared to that of the sun, reveals the composition of the early universe at the time the star formed and might contain clues about the elements created by the very first supernovae. All rights reserved. Stars are the nuclear furnaces that forge many of the chemical elements in nature. The composition of the material that stars eject into space depends sensitively on the rate at which the various nuclear fusion reactions occur in their interior.
While the reaction sequences have been identified, many reaction rates are still not known accurately, limiting predictions of element formation and stellar evolution.
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A prominent example is the rate of capture of helium on carbon. With a few exceptions, which mark major milestones in nuclear astrophysics, a direct experimental determination of the low-energy stellar fusion rates has not yet been possible. Some of these pioneering measurements have been enabled by experiments in the low background environments of laboratories deep underground. Models of stars therefore employ uncertain theoretical nuclear reaction rates mostly derived by extrapolating experimental data obtained at higher energies or indirectly.
Addressing this problem will remain a formidable challenge in the coming decade. Advances in experimental techniques such as high-intensity stable beam accelerators in underground laboratories, intense rare isotope beams, and advanced detection and target systems will be needed see Figure 2.
On the theoretical. The challenge is to measure the extremely small fusion rates at the low relative energies that the particles have inside stars. The reduced background in underground accelerator laboratories LUNA data shown above in green compared to aboveground laboratories all other data enables the measurement of fusion rates that are smaller by a factor of approximately 1, This reduces the error when extrapolating the fusion rate to the still lower stellar energies. Theory also needs to address the impact of electrons, which always accompany nuclei and modify reaction rates differently in a laboratory target and in stellar plasma.
A large gap in our understanding of the chemical evolution of our galaxy surrounds the origin of the elements heavier than iron, such as gold, platinum, or uranium, which comprise more than half of the elements in the periodic table. The other half, including the heaviest elements found on Earth, such as uranium and thorium, require an astrophysical environment with an extraordinary density of neutrons. While such an environment has not been identified with certainty, theory predicts that under such conditions, captures of neutrons are very fast, enabling the synthesis of heavy elements beyond bismuth.
During the brief duration of this rapid neutron capture process r-process , exotic short-lived nuclei with extreme excesses of neutrons come into existence as part of the ensuing chain of nuclear reactions. Most of these exotic nuclei have never been made in the laboratory. This will change with the advent of next-generation rare isotope beam facilities like FRIB, which will allow experimental nuclear physicists to produce such nuclei and to determine their properties.
The goal is to finally understand how and where nature produces precious metals like gold and platinum and heavy elements like thorium and uranium. Physics questions concerning the neutron-induced processes that constitute the r-process are closely related to neutron-driven applications such as nuclear reactors. Although the ultimate goal—namely, to identify the astrophysical site of the r-process—has not been reached yet, progress in nuclear physics and astrophysics has been made in the past decade toward unraveling the origin of the r-process elements.
Existing radioactive beam facilities have provided experimental data on some of the key nuclei participating in the r-process. Important recent milestones include the half-life measurement of nickel see Figure 2. The production and identification of the r-process waiting point nucleus nickel was a challenge, though a sufficient number of isotopes were identified to determine a first measurement of its half-life.
Because most r-process isotopes are out of reach of current rare isotope facilities, their study must await a new generation of accelerators such as FRIB. Hosmer, H. Schatz, A. Aprahamian, et al. Copyright , American Physics Society. These data provide guidance for theoretical models, which are used to predict the properties of the many nuclei out of current experimental reach.
This has led to recognizing the importance of forbidden beta decay transitions and the direct mechanism in neutron captures and, accordingly, to a more realistic description of nuclear fission.
A variety of astrophysical models have been developed that might provide the conditions necessary for an r-process and eject sufficient amounts of matter into space to account for the observed element abundances. The most promising ones involve core collapse supernovae and the merging of two neutron stars. As a breakthrough, observations of the surface composition of iron-poor stars have opened an unprecedented window into the gradual enrichment of the early galaxy with r-process elements. These stars preserve the composition of the early, chemically less evolved galaxy at the time and location of their formation.
The observations tell us that r-process events must have started very early in the evolution of the universe, and that they generate a very robust and characteristic pattern for the abundance of elements throughout the history of the galaxy. Progress in nuclear physics is needed to connect advances in observations and theoretical astrophysics. In addition to new facilities, the data-driven advances expected in nuclear theory will allow predicting the properties of the nuclei that remain out of reach experimentally and quantifying the errors of such extrapolations.
This will reduce the uncertainty in astrophysical models related to nuclear physics to the point where various astrophysical assumptions can be rigorously tested against observations, enabling a data-driven approach to solving the r-process puzzle. New approaches in astrophysics are also needed because none of the existing models achieves the conditions and event frequencies inferred from observations for the r-process.
Future large-scale astronomical surveys, followed by high-resolution spectroscopy with the largest telescopes available, need to increase the sample of iron-poor stars formed in r-process-rich environments in the early galaxy to provide statistically relevant information on the frequency of r-process events and the nuclear abundance patterns they produce.
The slow neutron capture process is known to occur in red giant stars. But how does matter flow in the deep interiors of stars to generate the necessary free neutrons, and how have these processes changed over the history of chemical evolution? Progress has been achieved in the past decade by analyzing presolar. Analyzing the composition of these messengers from space, and comparing them with s-process models that include precise neutron capture rates for stable isotopes measured in an experimental tour de force over many decades, has now led to constraints on the flow of matter in the deep interiors of stars and the dependence of neutron capture rates on galactic age.
In the coming decade experimental data of similar quality need to be obtained for lighter isotopes just slightly heavier than iron, and for so-called branch points. Branch points are unstable nuclei where, depending on nuclear properties, temperature, and neutron density, the reaction sequence splits, producing different isotopes. Once the nuclear properties are experimentally determined, the observed isotopic abundances can be used to infer temperature and neutron density deep inside red giant stars.
This is applied nuclear physics par excellence! However, to measure neutron captures on these unstable nuclei, radioactive beam facilities will have to work in concert with neutron beam facilities, where radioactive samples can be quickly irradiated to measure neutron capture rates. Where this is not possible, experimenters and theorists will have to develop new indirect techniques to extract the relevant information from other types of nuclear reactions.
The reactions producing neutrons for the s-process are also very uncertain and need to be measured in the coming decades at energies that are closer to the astrophysical conditions than has been possible so far. New radiation detection techniques as well as new high-intensity low-energy accelerators placed in underground facilities to shield experiments from background induced by cosmic rays provide a path forward. Neutron captures in stars also produce a long-lived radioactive iron isotope, iron, which is ejected in supernova explosions and decays with a half-life of a few million years.
Isotopic anomalies found in the solar system indicate that iron was present in the early solar system, and its decay heat might have contributed significantly to planetary melting. Using sensitive nuclear physics techniques, iron has also been discovered in deep sea sediments and on the surface of the moon, possibly indicating an interaction of the solar system with a nearby supernova 2 to 3 million years ago.
And the decay radiation of iron has now been detected by gamma-ray telescopes in space. Thus understanding the origin of iron holds the key to learning about conditions inside supernovae, the frequency of supernovae, the possible impacts of a nearby supernova on biological evolution, and the formation of the solar system and planetary systems in general. Developing that understanding requires knowing the efficiency with which nuclear reactions can produce and destroy iron in a given stellar model.
Progress has been. In addition, it has been shown that iron production is sensitive to the rate of various other nuclear reactions governing the evolution of stars, such as the triple alpha process or alpha capture on carbon. Despite decades of effort to measure these rates, the uncertainties surrounding them still prevent a precise prediction of the composition of elements produced in stars. The prevalent view of the origin of the elements heavier than iron and nickel has been that they are made by three distinct processes: the s-process, the p-process, and the r-process.
The observations of the composition of old stars show that this traditional picture is not complete as there must be at least one additional nucleosynthesis process producing elements heavier than iron but lighter than most r-process elements in the early galaxy: a so-called light element primary process. The nature of this process remains an open question. At the same time, theory has predicted an unexpected new process producing heavy elements to occur in core-collapse supernovae.
During a few seconds of the explosion, hot matter is ejected from the surrounds of the newly born neutron star in the center of the supernova. This matter has a completely unexpected and counterintuitive property: It has more protons than neutrons, caused by interactions with the overwhelming fluence of neutrinos accompanying the explosion.
Upon reaching colder temperatures after ejection, nuclei can be formed by combining protons and neutrons. The excess protons can then be captured together with additional neutrons created by proton-antineutrino collisions to produce heavy elements, a process dubbed the v p-process. In the coming decade it will have to be determined if the v p-process and the light element primary process are the same, what their contributions to the chemical evolution of the galaxy are, and what the underlying nuclear physics is.
The v p-process involves extremely neutron-deficient rare isotopes, which need to be studied at rare isotope facilities. Massive stars end their lives in a violent supernova explosion triggered by the collapse of their cores under their own weight. Core-collapse-induced supernovae can be brighter than billions of stars, and the associated neutrino burst is among the most powerful events in the universe.
Such supernovae play a central role in astrophysics. They create and eject most of the elements necessary for life see Figure 2. Show related SlideShares at end. WordPress Shortcode. Full Name Comment goes here. Are you sure you want to Yes No. Sasha Paul I recovered from bulimia. You can too! No Downloads. Views Total views. Actions Shares. Embeds 0 No embeds. No notes for slide. Major Religions in the U. Nurses may teach family planning. Sterilization is forbidden unless for medical reasons.
The Orthodox church discourages assisted deaths, autopsy, cremation, and organ donation. Illness and sin can be changed by altering the thoughts rather than by medical intervention. A sacred undergarment may be worn that should be removed only in an emergency. Circumcision is performed before puberty. All meat must be killed and blessed in a special way. Many may not eat traditional African American foods such as cornbread or collard greens. If family is unavailable, any practicing Muslim can provide this support.
After death the body must not be touched until the family has washed it, prepared it, and positioned it facing Mecca. Burial is performed as soon as possible. Cremation is forbidden. Autopsy is forbidden except for legal reasons. Organ donation is not permitted. Others believe that the woman should have only as many children as the husband can afford, and contraception is permitted. Privacy must be provided for prayer.
The Koran should not be touched by anyone ritually unclean, and nothing must be placed on top of it. Muslim women usually wear clothing that covers the entire body.