The trouble is that understanding this complexity often requires a tremendous amount of computational power. The results are freely available to the nuclear physicists' community so that other groups can perform their own nuclear structure calculations, even if they have only limited computational resources.
The idea outlined in this work is to describe the quantum mechanical states of nuclei in terms of relative coordinates, which makes it possible to describe the correlations between nucleons more easily. This approach also helps to separate out the motion of the centre of mass, thus further reducing the complexity of the problem.
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To date, most nuclear structure calculations have been performed using single particle basis states, as in keeping with what is referred to as the Pauli exclusion principle two identical elementary particles cannot occupy the same basis state--an aspect that is tremendously difficult to address in relative coordinates Now, in the new work, the authors generate sets of basis states for nucleons in complex nuclei, which feature anti-symmetrical relative coordinates. The authors introduce an algorithm designed to reflect the anti-symmetrized nature of the nucleon states using standard harmonic oscillator states for the light p-shell nuclei.
The states are produced along with their corresponding recoupling coefficients, making it possible to include two- and three-nucleon operators. The study focuses on several p-shell nuclei and examines their dependence on the harmonic oscillator frequency. Subsequently, the authors extract the binding and excitation energies of these nuclei. Materials provided by Springer. Note: Content may be edited for style and length. Science News. Story Source: Materials provided by Springer. The accelerator is based on superconducting cavities for acceleration.
Beams are recirculated and accelerated up to 5 times to provide intense continuous electron beams of GeV, polarized and unpolarized, to three target areas simultaneously. The photo insert shows assembly of a superconducting cavity section in the clean room. Accelerator Center SLAC , and continue to be involved in measurements at Fermilab and other high-energy facilities around the world. Two current key objectives of nuclear physics, understanding the quark structure of nucleons and nuclei and the search for the quark-gluon plasma, have demanded higher energies, beam currents, and duty factors for electrons, and much higher energies for heavy ions.
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Most of the accelerator facilities in nuclear physics have developed in close association with the science on the one hand and with the more general research and development in accelerator science and technology on the other. Superconducting magnet development at Michigan State University has led to compact, powerful cyclotrons for heavy-ion beams; superconducting beam bending and focusing magnets for the highest-energy beams, originally developed for proton accelerators in particle physics, have been extended for use with heavy-ion beams at RHIC.
Superconducting radio-frequency rf cavities have been successfully developed over the past two decades for acceleration of low-velocity heavy ions and of high-velocity electrons. Cavities for heavy ions, first developed and implemented at Argonne National Laboratory in the early s and soon after at the State University of New York at Stony Brook and other universities, provide cost-effective and versatile postaccelerators for high-quality ion beams that cover the full mass range from protons to uranium.
The successful operating experience with this new technology bolstered its development and application to the higher velocities required in the accelerators for particle physics. The development of high-charge-state electron cyclotron resonance ECR ion sources is revolutionizing the acceleration of heavy-ion beams both at cyclotrons and at heavy-ion linacs. Since energy gains increase with ionic charge state, acceleration of highly charged ions makes the most efficient use of accelerator voltages.
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The development of polarized beams and targets has made major strides. Developments in atomic-beam techniques at the University of Wisconsin are providing polarized gas targets and polarized ion sources, and long-lived frozen polarized targets have been developed at various facilities. Laser polarized targets have been developed for hydrogen, helium, and lithium ions at various universities and national laboratories.
So-called Siberian snakes and spin rotators. Schematics of the two principal concepts for the generation of energetic beams of short-lived nuclei radioactive beams. The ISOL isotope separator online approach illustrated at the bottom employs two independent accelerators: a high-power driver accelerator for production of the short-lived nuclei in a thick target that is directly connected to an ion-source and a postaccelerator. Radioactive atoms diffuse out of the hot target into the ion source where they are ionized for acceleration in the postaccelerator.
This scheme provides for excellent beam quality since it allows full control over beam energy and time structure. Electron cooling of ion beams in storage rings has greatly advanced, allowing precision in-beam nuclear physics measurements in storage rings with internal targets. The low emittance of the cooled, stored proton beam at the Indiana University Cyclotron Facility IUCF has proved to be an excellent tool to study threshold reactions for nuclear physics on the one hand and nonlinear, single-particle beam dynamics effects of interest to accelerator physicists on the other.
Some of the developments mentioned have occurred at the larger user facilities. But often smaller facilities, in particular those at universities, have provided the environment for generic developments that have important applications to the research programs at large accelerators. This exemplifies the symbiotic relationship between small university accelerators and large national and international facilities in nuclear physics.
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Several new projects are in progress or under consideration. A viable, bunched-beam, stochastic cooling system could potentially ameliorate the effects of intrabeam scattering in heavy-ion beams and thus significantly improve performance. Two superconducting cyclotrons are being upgraded to boost the energy and intensity of the primary production beam at this radioactive-beam facility of the in-flight fragmentation type. Radioactive-beam intensities will be increased by factors ranging from to 1, Figure 7.
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A list of present accelerators for nuclear physics research in the United States is given in Appendix A with a short summary of their respective performance characteristics. Major progress made in target and detector systems in recent years underlies many of the current advances in nuclear science. Polarized targets of light nuclei, produced either by atomic-beam techniques or by novel approaches using laser-induced polarization, have played an important role in fixed-target experiments, as well as in experiments using internal targets in storage rings.
Advances in particle detectors range from single detectors at low energies to complex detector arrays for the highest energies and the largest particle multiplicities. Most detectors are used in experiments with beams from accelerators, but stand-alone systems also play an important role and have undergone major developments. It is not possible to give a detailed discussion of all the recent developments within the limited space available in this report.
Rather, we will give selected examples from the various areas of nuclear physics research to provide a taste of the novel developments and genuine advances that these targets and detectors represent for the science. At the lowest energies, novel structure information on nuclei has been obtained by trapping nuclei, in particular short-lived, radioactive ones far from stability, in ion or atom traps and by measuring their masses and the properties of their radioactive decays.
Trapping atoms in magneto-optical traps with the help of lasers has made major advances over the last decade as shown in Figure 7. This technique promises unique advances in studying nuclear decays, allowing precision studies of fundamental symmetries under controlled conditions.
For example, atomic experiments can measure parity-violating matrix elements with significant precision. The heaviest alkali, francium, promises particularly large sensitivity to parity violations because of its simple structure, with only one electron outside of a spherical core. Francium has no stable isotopes, making it difficult to carry out this important class of measurements.
However, several laboratories have recently taken an important step in starting these measurements, by efficiently collecting the small number of francium atoms created in a nuclear reaction and cooling them sufficiently to confine them in a laser trap.
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To reach the intensities of trapped ions needed for the symmetry studies, major advances are needed in production yield and trapping. The next-generation ISOL facility will provide the required intensities. The use of ion traps in nuclear physics has proven equally exciting. Penning traps have been effective instruments for high-accuracy mass determinations.
With these devices, the mass ratios of a number of stable or long-lived light. Schematic layout of a magneto-optical trap, which uses a combination of a weak magnetic field and six intersecting polarized laser beams to capture radioactive atoms generated in a nuclear reaction.
These atoms are captured by neutralization and thermalization of a low-energy radioactive ion beam. Once captured in the trap, these atoms can become an ideal source for precision studies of nuclear decays that address aspects of fundamental symmetries and the Standard Model. High-accuracy measurements with radionuclides have been performed for an accurate determination of the binding energies of nuclei.
Novel high-precision mass measurements have also been made in a storage ring. Signals have been detected from as little as a single circulating ion of a specific isotope. Advanced detectors for nuclear reactions near the Coulomb barrier allow one to explore the behavior of the nucleus under the extremes of excitation, spin, and neutron-to-proton ratio.
High-sensitivity recoil systems allow identification of the rarest reaction products in heavy-ion fusion reactions at zero degrees, which are usually hidden in an overwhelming background from the incident particle beam. This has allowed nuclear physics, for example, to identify the new heavy elements up to , and a number of proton emitters, literally dripping protons, at the proton drip line.
New information about high-spin states in nuclei has been obtained with large, highly efficient germanium detector arrays.
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The Gammasphere array consists. Using its high efficiency for high-energy gamma rays, it has been possible to identify, unambiguously, the transitions linking states in the superdeformed and normally deformed potential minima. The combination of such powerful high-resolution detectors with the highly selective recoil systems shown in Figure 7.
Similarly, new high-resolution magnetic spectrometers allow precision nuclear structure studies in reactions with radioactive beams or polarized light-ion beams.
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