Narrow Results

The upcoming FAIR facility in Darmstadt, Germany, will produce intense high energy beams of exotic nuclei, which will be used to explore the properties of new regions of the chart of nuclides of key importance for both nuclear structure and nuclear astrophysics. In the EXL project, heavy ion beams are first cooled in the New Experimental Storage Ring (NESR) and then used to induce reactions on windowless thin Hydrogen, Deuterium and Helium gas targets in the ring. High luminosities can be achieved because of the recirculation of the beam with a frequency of about 1 MHz. The EXL system will be ideal for high resolution reaction studies at low momentum transfer. The design of the detector system considered is universal in the sense that it should allow the use of a large variety of nuclear reactions, addressing numerous physics questions. The detector system provides the capability of fully exclusive kinematical measurements, with target recoil detectors, fast ejectile forward detectors and an in-ring heavy-ion spectrometer. The physics case and detector design considerations for EXL along with tests experiments performed at KVI and GSI, paving the way to the full EXL detection system, are presented in this contribution.

The Facility for Rare Isotope Beams (FRIB) will be a world-leading laboratory for the study of nuclear structure, reactions and astrophysics. Experiments with intense beams of rare isotopes produced at FRIB will guide us toward a comprehensive description of nuclei, elucidate the origin of the elements in the cosmos, help provide an understanding of matter in neutron stars and establish the scientific foundation for innovative applications of nuclear science to society. FRIB will be essential for gaining access to key regions of the nuclear chart, where the measured nuclear properties will challenge established concepts, and highlight shortcomings and needed modifications to current theory. Conversely, nuclear theory will play a critical role in providing the intellectual framework for the science at FRIB, and will provide invaluable guidance to FRIB's experimental programs. This review overviews the broad scope of the FRIB theory effort, which reaches beyond the traditional fields of nuclear structure and reactions, and nuclear astrophysics, to explore exciting interdisciplinary boundaries with other areas.

The use of radioactive beams opens a new frontier for fusion studies. The coupling to the continuum can be explored with very loosely bound nuclei. Experiments were performed with beams of nuclei at or near the proton and neutron drip-lines to measure fusion and associated reactions in the vicinity of the Coulomb barrier. In addition, the fusion yield is predicted to be enhanced in reactions involving very neutron-rich unstable nuclei. Experimental measurements were carried out to investigate if it is feasible to use such beams to produce new heavy elements. The current status of these experimental activities is given in this review.

TETRA long neutron counter has proven to be an unique tool to identify and to measure delayed neutron emission from photo-fission fragments produced at ALTO ISOL facility. TETRA uses robust technology based on ³He filled-counters operating in the proportional mode. The cross-section of the reaction (n, ³He) is very larger for the thermal neutron energy range. Thus, β-delayed neutrons are moderated and can be detected with a high efficiency. However, due to the moderation process, information on the initial neutron energy is typically lost. Energy of emitted neutrons is needed for detailed description of the process of delayed (multi) neutron emission from neutron rich nuclei. In the present paper we discuss one of a method which can be used to recover information on the initial neutron energy.

Nuclear astrophysics is a active, rapidly developing field that addresses fundamental scientific questions. Advances in astronomy have to be matched with advances in nuclear physics to address these questions in the future. I discuss some of the major open questions and future directions, using as examples supernovae, the rapid neutron capture process, and processes on the surface of accreting neutron stars. In all cases nuclear physics is needed to interpret observations and to guide and constrain theoretical models. While a wide range of experimental facilities is required, one of the major challenges for the future is the study of unstable nuclei that play a central role in many of the major open questions. Therefore, an advanced radioactive beam facility such as the proposed Rare Isotope Accelerator (RIA) is of particular importance for the future of this field.

The dipole response of neutron-rich nuclei has been investigated in a series of experiments at the R3B/LAND facility at GSI utilizing the heavy-ion induced electromagnetic excitation process at high energy. Pronounced changes of the dipole response have been observed compared to stable nuclei. The present article summarizes the experimental results covering a wide mass range.

Magnetic moments provide a microscopic description of the structure of wave functions of nuclear states. The advent of radioactive beam has opened the possibility of exploring nuclear properties in nuclei far from stability where new phenomena, not described by extant theoretical models, might become observable. Over the last few years, techniques have been developed to extend the measurements of g factors of low-lying excited states with lifetimes of picoseconds to these regions of the periodic table. The transient field technique, coupled to Coulomb excitation of beams in inverse kinematics, represents an approach with broad applicability. The experiments are difficult and each nucleus imposes new challenges. The first two experiments, one on proton-rich ⁷⁶Kr carried out at the LBNL and one on neutron-rich ¹³²Te nuclei performed at the HRIBF laboratory at ORNL, will be described. The future direction of such measurements will be discussed in the context of the existing and planned radioactive beam facilities.

The ALTO facility consists of two accelerators in the same area. A Tandem accelerator dedicated to stable (ions and cluster) beam physics and a linear electron accelerator dedicated to the production of radioactive beams. This gives a unique opportunity to have in the same place cluster beams for interdisciplinary physics and stable and radioactive beams for astrophysics and nuclear physics.

ISOLDE is the CERN facility dedicated to the production of radioactive ion beams for many different experiments in the fields of nuclear and atomic physics, materials science and life sciences. By a clever combination of target and ion source units pure beams of over 1000 different nuclei of 74 elements have been produced and delivered to experiments. Since more than ten years ISOLDE offers the largest variety of post-accelerated radioactive beams in the world today. The HIE-ISOLDE intensity and energy upgrade has finished its phase 1 dedicated to upgrade the energy up to 5.5 MeV/u, producing the first radioactive beams at this energy in September 9th 2016. The results from this campaign of post-accelerated beams will be described together with very recent ISOLDE highlights of neutron-rich nuclei.

Miniball has been used since September 2001 in a variety of experiments with radioactive beams ranging from ¹⁷F to ²²⁴Ra at the REX-ISOLDE facility (CERN). A few of the highlights of this decade of activity are presented here as well as an outlook for the future.

New g-factor measurements by the recoil in vacuum method are discussed. The stable even tin isotopes, neutron-rich ^126,128Sn, and tellurium isotopes including neutron-rich semimagic ¹³⁴Te, have been studied. The experiments were performed at the Holifield Radioactive Ion Beam Facility (HRIBF) by Coulomb exciting ~ 3 MeV/u beams in inverse kinematics on C and Ti targets, and using the CLARION+HyBall arrays to observe the perturbed particleangular correlations. The measurements, including those on the neutron-rich radioactive beams, have sufficient precision to distinguish between alternative models.

I attempt to experimentally evaluate the prospects of synthesizing new neutronrich superheavy nuclei. I consider three possible synthetic paths to neutronrich superheavy nuclei: (a) the use of neutron-rich radioactive beams. (b) the use of damped collisions and (c) the use of multi-nucleon transfer reactions. I consider the prospects of synthesizing new n-rich isotopes of Rf-Bh using light n-rich radioactive beams and targeted beams from ReA3, FRIB and SPIRAL2. For the damped collision path, I present the results of a study of a surrogate reaction, ¹⁶⁰Gd + ¹⁸⁶W. These data indicate the formation of Au (trans-target) fragments and the depletion of yields of target-like fragments by fission and fragment emission. The data are compared to predictions of Zagrebaev and Greiner. For the multi-nucleon transfer reactions, the results of a study of the ¹³⁶Xe + ²⁰⁸Pb reaction are discussed. I consider the possibility of multi-nucleon transfer reactions with radioactive beams.

The project of a new in-flight fragment separator ACCULINNA-2 at the U-400M cyclotron in FLNR, JINR is being realized to upgrade the research done at the existing separator ACCULINNA. The new separator will offer high intensity RIBs with Z=1÷36 in the lowest energy range (10–50 MeV/amu) attainable for in-flight separators. The long-range program for experiments and further development of this facility are discussed.

Isoscalar giant resonances in exotic nuclei can be studied using inelastic alpha scattering in inverse kinematics. In particular, the compression modes, i.e. isoscalar giant monopole and dipole resonances, are very interesting because they can furnish information on the different terms of the nuclear incompressibility, especially if measured in long isotopic chains including nuclei far from the valley of stability. As beams of exotic nuclei have relatively low intensities thick targets have to be used in order to get a reasonable yield. However, this leads to degradation of the energy resolution and stops low-energy recoil particles. Two good alternatives exist. The first method is to use an active target, such as MAYA, which is a time-projection chamber and therefore can be used for detection of low-energy recoil particles. Furthermore, its thickness can be increased by increasing the length of the detection volume or the gas pressure without severe loss of energy resolution. The second method is to use a storage ring for storing the exotic nuclei, which then interact with target nuclei from a gas-jet target. Here, the luminosity and hence the yield are increased because the exotic nuclei circulate in the ring at a frequency of around 10⁶ turns/s. Low-energy recoil particles traverse the gas-jet with little loss of energy and can be detected in solid-state detectors. Pioneering experiments with both methods have been performed for inelastic scattering of secondary ⁵⁶Ni beam off helium nuclei. Here, preliminary results of the experiment with the active target MAYA will be presented.

We present an analysis of the ⁶He+⁹Be elastic scattering angular distributions at two energies above the Coulomb barrier, E_cm= 9.72 and 12.78 MeV. The analysis was performed using an approach based on a cluster optical model for the ⁶He projectile. The total reaction cross sections have been obtained from the elastic scattering and a considerable enhancement has been observed in comparison with stable systems.

We propose to search for the ⁷H g.s. using the quasifree (α,2α) knockout reaction from ¹¹Li having a spatially extended halo. In the quasi-free scattering ⁴He(¹¹Li,2α)⁷H reaction an α-particle is knocked out from ¹¹Li by the alpha target nucleus and the detection of these two α-particles is sufficient to extract the missing mass of ⁷H. The use of telescopes composed of a set of micro-strip Si deterctors provides a reconstruction of the vertex position inside the target with an accuracy of about ±100 μm. This accuracy also allows a very thick target which is only limited by the energy loss of the outgoing α-particles.

The Texas A&M Cyclotron Institute has been studying nuclear science with radioactive beams for the past two decades with in-flight production and separation using the MARS spectrometer. The TREX upgrade to the facility will augment this fast beam capability with the ability to deliver both stopped and reaccelerated radioactive ions. This paper will discuss the present capabilities and future plans of the Texas A&M Cyclotron Institute.

The ALTO facility consists of two accelerators in the same area. A Tandem accelerator dedicated to stable (ions and cluster) beam physics and a linear electron accelerator dedicated to the production of radioactive beams. This gives a unique opportunity to have in the same place cluster beams for interdisciplinary physics and stable and radioactive beams for astrophysics and nuclear physics.

The project of a new in-flight fragment separator ACCULINNA-2 at the U-400M cyclotron (FLNR, JINR) is being realized to enhance the research opportunities offered by the existing fragment separator ACCULINNA. The new facility will produce high intensity RIBs with Z=1÷36 in the lowest energy range (~8÷50 MeV/nucleon) attainable for in-flight separators. We discuss the “first day” experiments (commissioning of ACCULINNA-2 is planned for 2015) and long-range program (seven year plan for 2017-2023), as well as further developments of this facility.