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Resonances in s-d shell nuclei

Description: It appears that the system we have studied here, /sup 24/Mg(/sup 16/O,/sup 12/C)/sup 28/Si representing /sup 40/Ca as the composite nucleus, is perhaps the heaviest one that exhibits strong enough resonances that quantitative measurements may be contemplated. But we have uncovered only a small corner of what is there and even within this system a huge amount of work remains. The nature of these resonances is not yet clear. The sequence may perhaps have an explanation that is schematically outlined, namely that there are several families of quasistationary states in /sup 40/Ca, but that the slopes of these families do not necessarily coincide with the slope of the grazing partial waves that provide us with a narrow transparent strip of a window on the underlying structure of the nucleus. We must concentrate a lot of effort and ingenuity in order to maximize the information we gather through this window and only then may we hope to sensibly attempt forming hypotheses about the underlying simple pattern.
Date: January 1, 1981
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Order in cold ionic systems: Dynamic effects

Description: The present state and recent developments in Molecular Dynamics calculations modeling cooled heavy-ion beams are summarized. First, a frame of reference is established, summarizing what has happened in the past; then the properties of model systems of cold ions studied in Molecular Dynamics calculations are reviewed, with static boundary conditions with which an ordered state is revealed; finally, more recent results on such modelling, adding the complications in the (time-dependent) boundary conditions that begin to approach real storage rings (ion traps) are reported. 14 refs., 19 figs., 2 tabs.
Date: January 1, 1988
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

A condensed state in a system of stored and cooled ions

Description: In heavy-ion storage rings a beam of particles with uniform mass and (positive) charge, is confined to a narrow region around an equilibrium orbit. The internal temperature in the co-moving reference frame for such beams may be lowered by stochastic or electron cooling to very low values: 1/sup 0/K has been reported for proton beams. If such conditions are indeed realized in heavy-ion beams, new types of condensation phenomena should appear. For laser cooling techniques even lower temperatures are anticipated.Progress is reported on studies of computer simulations of such systems using the method of Molecular Dynamics. 11 figs., 8 refs., 2 tabs.
Date: January 1, 1987
Creator: Rahman, A. & Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Possibility of achieving a condensed crystalline state in cooled particle beams

Description: Calculations have shown that when a plasma of one kind of particle (one-component plasma or OCP) is below a certain temperature, it will undergo a phase transition and the particles will form a crystalline (bcc) array. The relevant parameter is GAMMA = (q/sup 2//a)kT (where a is the average spacing and T the temperature) and the transition takes place at GAMMA = 170. the properties of proposed storage rings for heavy ions with q >> e, are such that an ordered array may actually be realized.
Date: January 1, 1986
Creator: Schiffer, J.P. & Rahman, A.
Partner: UNT Libraries Government Documents Department

The physics of crystalline beams

Description: It seems that the time has come in the pursuit of lower and lower beam temperatures to start focusing more detailed attention to the reality of storage rings--conventional cooling techniques and measures of temperature are generally not the appropriate ones at the lowest temperatures. Finding solutions to these serious problems does not appear to be impossible, but these considerations must be kept in mind in designing new storage rings with the aim to approach the regime of ordered three-dimensional beams. In particular, such rings will have to: Use calculations of the lattice with the full effects of space charge included. (N.B. averaged over time, space charge exactly cancels the focusing fields for a cold beam and therefore must be explicitly included.) Find technical solutions and incorporate several of; cooling to introduce a longitudinal velocity gradient and favor constant angular velocity; high multiplicity in bending and focusing elements; stronger focusing (high betatron tune); and high symmetry in the ring design. Finally, simulations should try to incorporate as much realism as possible, with larger repeating cells and more detailed descriptions of the lattice.
Date: December 31, 1995
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Ordered one-component plasmas: Phase transitions, normal modes, large systems, and experiments in a storage ring

Description: The property of cold one-component plasmas, confined by external forces, to form an ordered array has been known for some time both from simulations and from experiment. The purpose of this talk is to summarize some recent work on simulations and some new experimental results. The author discusses some experimental work on real storage rings, magnetic storage devices in which partials circulate with large kinetic energies and for which laser cooling is used on partially ionized ions to attain temperatures ten or more orders of magnitude lower than their kinetic energies.
Date: December 31, 1994
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Order in very cold confined plasmas

Description: The study of the structure and dynamic properties of classical systems of charged particles confined by external forces, and cooled to very low internal energies, is the subject of this talk. An infinite system of identical charged particles has been known for some time to form a body-centered cubic lattice and is a simple classical prototype for condensed matter. Recent technical developments in storage rings, ion traps, and laser cooling of ions, have made it possible to produce such systems in the laboratory, though somewhat modified because of their finite size. I would like to discuss what one may expect in such systems and also show some examples of experiments. If we approximate the potential of an ion trap with an isotropic harmonic force F = {minus}Kr then the Hamiltonian for this collection of ions is the same as that for J. J. Thomson`s ``plum pudding`` model of the atom, where electrons were thought of as discrete negative charges imbedded in a larger, positive, uniformly charged sphere. The harmonic force macroscopically is canceled by the average space-charge forces of the plasma-, and this fixes the overall radius of the distribution. What remains, are the residual two-body Coulomb interactions that keep the particles within the volume as nearly equidistant as possible in order to minimize the potential energy. The configurations obtained for the minimum energy of small ionic systems [2] in isotropic confinement are shown in figure 1. Indeed this is an `Exotic Atom` and fits well into the subject of this symposium honoring the 60th birthday of Professor Toshi Yamazaki.
Date: December 31, 1995
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Ordering in classical Coulombic systems.

Description: The author discusses the properties of classical Coulombic matter at low temperatures. It has been well known for some time [1,2] that infinite Coulombic matter will crystallize in body-centered cubic form when the quantity {Lambda} (the dimensionless ratio of the average two-particle Coulomb energy to the kinetic energy per particle) is larger than {approximately}175. But the systems of such particles that have been produced in the laboratory in ion traps, or ion beams, are finite with surfaces defined by the boundary conditions that have to be satisfied. This results in ion clouds with sharply defined curved surfaces, and interior structures that show up as a set of concentric layers that are parallel to the outer surface. The ordering does not appear to be cubic, but the charges on each shell exhibit a ''hexatic'' pattern of equilateral triangles that is the characteristic of liquid crystals. The curvature of the surfaces prevents the structures on successive shells from interlocking in any simple fashion. This class of structures was first found in simulations [3] and later in experiments [4].
Date: January 22, 1998
Creator: Schiffer, J. P.
Partner: UNT Libraries Government Documents Department

Crystalline beams

Description: A beam of confined charged particles, that are cooled to the extreme of the space-charge dominated regime, where the relative motion of particles within the beam is small compared to their Coulomb potential energies, will crystallize in a unique form of condensed matter. Such a system of particles can be simulated using the method of Molecular Dynamics, which explicitly includes the interaction between all pairs of particles and uses repeating cells to simulate the effects of a long beam. Within the molecular dynamics simulations typically a few thousand particles are followed in time, allowed to equilibrate, and then the velocities are gradually scaled down while still allowing the system to maintain equilibrium. To reach a cold equilibrium value requires 10-100 thousand iterations, corresponding to real times on the order of a few thousand betatron periods.
Date: June 1, 1995
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Symmetries in confined classical Coulomb systems

Description: The properties of charged particles confined in a harmonic oscillator potential have become of increased interest lately in view of the development of techniques in ion traps and storage rings. The symmetries in such systems intrigued the imagination of Ted Hecht in connection with the storage ring at Heidelberg, and so perhaps it is an appropriate subject for this symposium.
Date: January 1, 1991
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Moessbauer-Like Absorption and Scattering of Light From Confined Crystalline Ionic Systems

Description: In recent years, the prediction of numerical simulations of the unique shell-structure in the crystallization of confined, cold ionic systems, has been confirmed in ion traps though it has not yet been observed in storage rings. These systems of up to tens of thousands of ions, constitute the sparsest known form of condensed matter (10[sup 7]--10[sup 9] ions/cm[sup 3]). The method for producing such systems involves cooling to mK temperatures using laser cooling'': The resonant absorption and reemission of laser light to shepherd the ions into having a very small velocity spread (i.e. temperature). The purpose of this note is to estimate some of the properties of such a system at low-temperatures: the condition for Bragg scattering of photons, and the Debye temperature.
Date: January 1, 1991
Creator: Schiffer, J. P.
Partner: UNT Libraries Government Documents Department

Heavy ion interactions

Description: Nuclear Physics has come a long way since its inception 70 years ago. We have learned a great deal about nuclear structure and nuclear interactions -- and we have a lot to learn yet. Our understanding of the substructure of protons and neutrons in terms of their elementary' constituents has also evolved to the present level of QCD and the Standard Model. Early work on nuclear reactions involving light projectiles did a great deal in elucidating the characteristic nuclear symmetries and the dynamic phenomena associated with nuclei. As accelerator and ion source technologies evolve it has become possible to accelerate heavier nuclei in addition to electrons, protons, and the very light nuclear systems. From these developments in the tools of our science we are deriving new knowledge: learning about otherwise inaccessible nuclear properties, of the dynamic characteristics of nuclear matter, and about the production of mesons, antiparticles, and other exotic objects in the collision of complex nuclear systems. The subject cuts across much of nuclear physics and it is difficult to give a cohesive overview talk. But I would like to attempt giving you the current flavors of the subject. 18 figs.
Date: January 1, 1989
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Static and dynamic properties of confined, cold ion plasmas: MD (molecular dynamics) simulations

Description: Some four years ago it was suggested that in the new generation of heavy ion accelerator storage rings for multiply charged ions, being planned in Europe, one may well attain internal temperatures that would correspond to very cold plasmas. Since that time, the techniques of electron or laser cooling of such beams has evolved and it may well be possible to reach temperatures corresponding to a plasma coupling parameter {Gamma} >> 100. I was fortunate to have had an opportunity to collaborate during 1986-87 with my former colleague Aneesur Rahman, of Molecular Dynamics fame, and we adapted the MD method to the calculation of the properties of cold confined plasmas. After Rahman's premature death two years ago I have continued the exploration of these systems and would like to summarize the results here. 9 refs., 10 figs.
Date: January 1, 1989
Creator: Schiffer, J.P.
Partner: UNT Libraries Government Documents Department

Moessbauer-like absorption and scattering of light from confined crystalline ionic systems

Description: In recent years, the prediction of numerical simulations of the unique shell-structure in the crystallization of confined, cold ionic systems, has been confirmed in ion traps though it has not yet been observed in storage rings. These systems of up to tens of thousands of ions, constitute the sparsest known form of condensed matter (10{sup 7}--10{sup 9} ions/cm{sup 3}). The method for producing such systems involves cooling to mK temperatures using ``laser cooling``: The resonant absorption and reemission of laser light to shepherd the ions into having a very small velocity spread (i.e. temperature). The purpose of this note is to estimate some of the properties of such a system at low-temperatures: the condition for Bragg scattering of photons, and the Debye temperature.
Date: December 31, 1991
Creator: Schiffer, J. P.
Partner: UNT Libraries Government Documents Department

Delta-nucleus dynamics: proceedings of symposium

Description: The appreciation of the role in nuclear physics of the first excited state of the nucleon, the delta ..delta..(1232), has grown rapidly in the past decade. The delta resonance dominates nuclear reactions induced by intermediate energy pions, nucleons, and electromagnetic probes. It is also the most important non-nucleonic degree of freedom needed to resolve many fundamental problems encountered in the study of low-energy nuclear phenomena. Clearly, a new phase of nuclear physics has emerged and conventional thinking must be extended to account for this new dimension of nuclear dynamics. The most challenging problem we are facing is how a unified theory can be developed to describe ..delta..-nucleus dynamics at all energies. In exploring this new direction, it is important to have direct discussions among researchers with different viewpoints. Separate entries were prepared for the 49 papers presented. (WHK)
Date: October 1, 1983
Creator: Lee, T.S.H.; Geesaman, D.F. & Schiffer, J.P. (eds.)
Partner: UNT Libraries Government Documents Department

Some thoughts on opportunities with reactions using radioactive beams

Description: I was asked to talk about the use of radioactive beams for nuclear reactions. My overall perspective is that the scientific justification for such studies must be done carefully. To go to the added complexity of radioactive beams one must clearly demonstrate the need for obtaining information about nuclear structure or processes, information that is not otherwise available. On the other hand, much of what we know about nuclear structure comes from nuclear reactions with stable nuclear beams and targets. While a certain amount of information about far from stability nuclei may be obtained from the study of their radioactive decays, this is limited. Our knowledge and understanding of nuclear structure comes from stable nuclei: energy levels, their spins and parties, and very importantly the matrix elements characterizing them. These are largely determined by reaction studies with normal stable nuclei. The extension of such studies to unstable nuclei, far from stability, may well hold qualitative surprises, or at the very least give a firmer basis to our understanding of nuclear structure. Perhaps it is a matter of taste, but if one wishes to start on this endeavor then it is best to begin with simple, easily accessible features. The simplest'' nuclei are the ones that form doubly-closed shells and the easiest features to explore initially are the single-particle states and the collective excitations that one can build on these. I would like to emphasize that a unique facility for this type of study is about to come into operation in Darmstadt where the ESR storage ring will capture radioactive beams from fragmentation products and cool them to useful energies for reaction studies.
Date: January 1, 1990
Creator: Schiffer, J.P. (Argonne National Lab., IL (USA) Chicago Univ., IL (USA))
Partner: UNT Libraries Government Documents Department