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The field of nuclear science has considerably advanced since its beginning just over a century ago. Today, the science of rare isotopes is on the cusp of a new era with theoretical and computing advances complementing experimental capabilities at new facilities internationally. In this article we present a vision for the science of rare isotope beams (RIBs). We do not attempt to cover the full breadth of the field; rather, we provide a perspective and address a selection of topics that reflect our own interests and expertise. We focus in particular on systems near the drip lines, where one often finds nuclei that are referred to as exotic and where the role of the nuclear continuum is only just starting to be explored. An important aspect of this article is its attempt to highlight the crucial connections between nuclear structure and the nuclear reactions required to fully interpret and leverage the rich data to be collected in the next years at RIB facilities. Further, we connect the efforts in structure and reactions to key questions of nuclear astrophysics. [ABSTRACT FROM AUTHOR]

Facilities equipped with two major types of isotope separators—Isotope Separation On-Line (ISOL) and in-flight separators—have produced many types of unstable nuclei and have provided opportunities to study their exotic properties successfully. Gas-cell systems have been developed for both types of radioactive-ion (RI) facilities, enabling the performance of a great variety of nuclear-spectroscopic measurements by compensating for their respective disadvantages in the production and purification of the RI beams. Although many nuclear-spectroscopic studies have been performed in both types of RI facilities by applying 238 U target (ISOL) or 238 U beam (in-flight), two major unexplored regions remain on the nuclear chart located in the regions of the refractory elements in the vicinity of Z = 73–78 and N = 126 and in the actinide elements. Because it is hard or almost impossible to produce the neutron-rich nuclei, which require specific nuclear reactions for the productions, in these unexplored regions. To access these regions and perform nuclear spectroscopy there, the KEK Isotope Separation System (KISS)—an argon-gas-cell-based laser ion source—has been developed and operated. The gas-cell system at the KISS facility is dedicated to multinucleon transfer (MNT) reactions for producing heavy, neutron-rich nuclei in the unexplored regions. Here, we introduce some of the experimental results and discuss a plan to upgrade the facility to promote further nuclear spectroscopy of the nuclei in the unexplored regions. [ABSTRACT FROM AUTHOR]

The paper reviews the recent progress in the description of isospin-symmetry breaking within the nuclear shell model and applications to actual problems related to the structure and decay of exotic neutron-deficient nuclei and nuclei along the N = Z line, where N is the neutron number and Z the atomic number. The review recalls the fundamentals of the isospin formalism for two-nucleon and many-nucleon systems, including quantum numbers, the spectrum's structure and selection rules for weak and electromagnetic transitions; and at the end, summarizes experimental signatures of isospin-symmetry breaking effects, which motivated efforts towards the creation of a relevant theoretical framework to describe those phenomena. The main approaches to construct accurate isospin-nonconserving Hamiltonians within the shell model are briefly described and recent advances in the description of the structure and (isospin-forbidden) decay modes of neutron-deficient nuclei are highlighted. The paper reviews major implications of the developed theoretical tools to (i) the fundamental interaction studies on nuclear decays and (ii) the estimation of the rates of nuclear reactions that are important for nuclear astrophysics. The shell model is shown to be one of the most suitable approaches to describing isospin-symmetry breaking in nuclear states at low energies. Further efforts in extending and refining the description to larger model spaces, and in developing first-principle theories to deal with isospin-symmetry breaking in many-nucleon systems, seem to be indispensable steps towards our better understanding of nuclear properties in the precision era. [ABSTRACT FROM AUTHOR]

One of the most complicated problems of experimental nuclear physics is the synthesis of exotic nuclei near the boundaries of stability. These nuclei, as a rule, are 10 or more neutrons awayfrom stable nuclei, have a short lifetime (less than 1 ms) and low binding energy. All this determines special requirements to the choice of reactions for the synthesis of such nuclei and the method of their transportation and registration. Mainly, for the synthesis of exotic nuclei, reactions of fragmentation of the bombarding heavy ion, direct reactions of the types ( p,d) , (d, p) , (d,n) ,( d , 3 He), etc., as well as reactions of fission and deep inelastic transfer are used.

This paper considers the possible existence of a bound diproton. The study was inspired by the predictions of Migdal (Sov. J. Nucl. Phys. 16, 238 (1973)), who solved a theoretical task for two identical particles to become bound in the potential field established by heavy nuclei. Earlier, the possibility of bound particles was confirmed experimentally in the case of the dineutron. We report the search for a bound diproton, or ²He nucleus, analyzing the results of irradiation of several samples with protons with energies just below the thresholds in the corresponding (p, 2p) nuclear reaction channel. The irradiated 159Tb and 181Ta samples were then counted by applying an HPGe gamma-spectrometer and featured a significant intensity of the 511 keV gamma-ray peaks. After acquiring data sets with peak intensities versus sample cooling times, the results were fitted with one or two exponential functions, and two experimentally determined half-lives were obtained for Ta sample, i.e., 6336±220 s and 1224±40 s. These values were in good agreement with the results of theoretical calculation based on the assumption of the 384 keV binding energy of the diproton. In addition, the radius and possible configuration and reaction mechanism were estimated and presented to serve together as a preliminary basis for confirming the existence of a bound diproton. [ABSTRACT FROM AUTHOR]

Tritiated titanium targets were irradiated by the short-pulse OMEGA EP laser (1.25 kJ, 10 ps) to generate a laser-accelerated pulsed beam of tritons by target normal sheath acceleration. Using a Thomson parabola, the beam was found to contain 1012 tritons per pulse, with a mean energy of 2.2 MeV and an exponential tail reaching up to 10 MeV. In a separate experiment, the triton beam was directed onto a secondary deuterated polyethylene (CD) target to induce deuterium–tritium (D–T) nuclear reactions. Using neutron time-of-flight spectrometers, approximately 108 D–T fusion neutrons were observed per laser pulse. This triton beam presents new research opportunities for the study of the 3H(t, 2n)4He reaction and di-neutron transfers to lithium and beryllium that may produce exotic neutron-rich nuclei of interest to basic nuclear science, astrophysics, and inertial confinement fusion technology. [ABSTRACT FROM AUTHOR]

A quantitative and predictive microscopic theoretical framework that can describe reactions induced by α particles (4He nuclei) and heavier projectiles is currently lacking. Such a framework would contribute to reducing uncertainty in the modeling of stellar evolution and nucleosynthesis and provide the basis for achieving a comprehensive understanding of the phenomenon of nuclear clustering (the organization of protons and neutrons into distinct substructures within a nucleus). We have developed an efficient and general configuration-interaction framework for the description of low-energy reactions and clustering in light nuclei. The new formalism takes full advantage of powerful second-quantization techniques, enabling the description of α - α scattering and an exploration of clustering in the exotic 12Be nucleus. We find that the 4He (α , α) 4 He differential cross section computed with non-locally regulated chiral interactions is in good agreement with experimental data. Our results for 12Be indicate the presence of strongly mixed helium-cluster states consistent with a molecular-like picture surviving far above the 6He+6He threshold, and reveal the strong influence of neutron decay in both the 12Be spectrum and in the 6He(6He, α)8He cross section. We expect that this approach will enable the description of helium burning cross sections and provide insight on how three-nucleon forces influence the emergence of clustering in nuclei. [ABSTRACT FROM AUTHOR]

In the following sections we describe the science topics and highlights of the recent GRETINA campaigns with fast beams at NSCL and with Coulomb-barrier beams at ATLAS. GRETINA will be initially installed on the S800 beam-line where experiments will focus on the structure of the most exotic nuclei accessible and where every single -ray count is precious. High-resolution -ray detector arrays have driven many scientific advances and discoveries in nuclear physics. The sixth campaign, the third at ATLAS, will finish in spring 2022 and GRETINA will then move back to Michigan State University, but this time to be the flagship -ray detector array at the Facility for Rare Isotope Beams (FRIB), which will begin operations early in 2022. [Extracted from the article]

H igh I ntensity heavy-ion A ccelerator F acility (HIAF) project is being constructed by the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS). An in-flight H igh energy FR agment S eparator (HFRS) at HIAF was designed to study the properties of rare isotopes far away from the line of beta stability and their involved nuclear reactions of astrophysics interests. HFRS is a two-stage magnetic system which consists of Pre-Separator and Main-Separator. The maximum magnetic rigidity of 25 Tm was designed in particular for experiments with very neutron-rich rare isotopes beams and studies of hypernuclei and Δ-resonances in exotic nuclei. A dispersive mode and an achromatic mode were designed for different experimental requirements. The HFRS device can be used to separate and purify the rare isotopes produced by the projectile fragmentation of all primary beams up to Uranium or by the projectile fission of Uranium ions via Bρ-ΔE-Bρ method. The detailed HFRS ion-optical design including the first order and the higher order, and the magnet specification were presented in this paper. [ABSTRACT FROM AUTHOR]

Abstract A Triple-foil differential Plunger for Exotic Nuclei (TPEN) has been developed to measure the lifetimes of excited states in nuclei with small production cross-sections. TPEN utilises one target foil and two degrader foils to make differential lifetime measurements: directly determining the decay function and its derivative at a single plunger distance setting. The direct measurement of the decay function and its derivative removes the requirement to measure γ -ray intensities at several target-to-degrader distances, thereby reducing the beam-time required relative to a conventional plunger with a single-degrader foil. This paper describes the commissioning of TPEN in the lifetime measurement of the first excited 4 + state in 156Dy using this differential lifetime technique. The 46(2) ps measured lifetime was found to be in good agreement with the 45.6(5) ps deduced from a previous high-statistics experiment using a conventional two-foil plunger. A comparison between the differential mode with TPEN, and that using TPEN as a conventional two-foil plunger reveals that it achieves the same statistical accuracy with a ∼ 4 -fold reduction in beam-time in the differential mode, for the reaction and experimental setup used in this work. TPEN opens up new opportunities to study exotic nuclei with lower production cross-sections that were previously not accessible. [ABSTRACT FROM AUTHOR]

The best poster was awarded to the Ph.D. student Antía Graña (USC), the second to Charlie Paxman (Surrey), and the third to Gabriel Martínez (USC). This DREB conference is part of the biennial series, which began in 1999 at MSU, East Lansing, through the initiative of physicists from MSU, IPN-Orsay (Institut de Physique Nucléaire d'Orsay), and FSU (Florida State University) working in the field. The 11th international conference on Direct Reactions with Exotic Beams (DREB) was coorganized by the Institute of Estructura de la Materia (IEM-CSIC), University of Santiago de Compostela (USC), and University of Seville (USE) and took place on the north campus of USC from 26 June to 1 July 2022 (Figure 1). [Extracted from the article]

The radial wavefunctions of transformed harmonic-oscillator in the local scale transformation technique are used to calculate the root-mean square proton, charge, neutron and matter radii, nuclear density distributions and elastic electron scattering charge form factors of stable (10,11B) and (unstable) exotic (8,14,17B) Boron isotopes. For 10B and 11B, the transformed harmonic-oscillator wavefunctions are applied to all subshells in no-core shell model approach using wbp interaction. For 8,14,17B, the radial wavefunctions of harmonic-oscillator and THO are used to calculate the aforementioned quantities for the core and halo parts, respectively. The calculated matter and charge density distributions are found to be in very good agreement with experimental data for 8,14,17B and 10,11B, respectively. The calculated elastic electron scattering form factors of the longitudinal C0+C2 components for 10,11B are in very good agreement with experimental data. [ABSTRACT FROM AUTHOR]

The structure of exotic nuclei has only been studied from around 1985, because they are very short lived and because before that, it was not possible to produce and deliver them as beams on a target. They have large N ∕ Z or Z ∕ N ratios, are weakly bound and quite extended most of the time. Thus breakup, transfer and/or inelastic excitations of the surface are some of their most common reaction mechanisms. Direct reactions, for their simplicity, have played a fundamental role in the last thirty years in the process of understanding such “new” type of structures. On the other hand, direct reactions have been studied and understood for a much longer time, starting with the pioneering experiments in the early ’50 on deuteron-induced reactions and the reaction models developed by S.T. Butler and collaborators. Both subjects are extremely vast and there is a large literature available of books, review articles and original papers. I will discuss here only a few selected examples of the many interesting problems that have been encountered and solved in all those years. I consider them breakthroughs in the field and as such I hope they can inspire young generations of researchers. [ABSTRACT FROM AUTHOR]

Activation cross sections of the nat Er(d,x) 163,165,166,167,168,170 Tm and nat Er(d,x) 171,161 Er nuclear reactions have been measured in the 32–50 MeV energy range, above 40 MeV for the first time. The activation method with stacked foil irradiation technique and gamma-ray spectroscopy were used. The experimental cross sections were compared with the theoretical predictions in the TENDL-2015 library. [ABSTRACT FROM AUTHOR]

Cross sections and corresponding momentum distributions have been measured for the first time at zero degrees for the exotic nuclei obtained from a beam of 18 O at 8.5 MeV/A impinging on a 1 mg/cm 2 238 U target. Sizable cross sections were found for the production of exotic species arising from the neutron transfer and proton removal from the projectile. Comparisons of experimental results with calculations based on deep-inelastic reaction models, taking into account the particle evaporation process, indicate that zero degree is a scattering angle at which the differential reaction cross section for production of exotic nuclei is at its maximum. This result is important in view of the new generation of zero degrees spectrometers under construction, such as the S3 separator at GANIL, for example. [ABSTRACT FROM AUTHOR]

In-flight separators have played a significant role in the physics of exotic nuclei. In the last decade, in particular, this field has expanded rapidly with the advent of the new-generation (3rd-generation) in-flight-separator facility, the RI-beam Factory (RIBF) at RIKEN that was commissioned in 2007. In addition, new experimental methods, techniques and state-of-the-art detectors at in-flight separators have developed rapidly, which has contributed considerably to this progress. One can now reach very far from the stable nuclei towards the drip lines, and even beyond in some cases. Hundreds of new isotopes have been identified, and new exotic isomers have been observed. β decays and relevant γ decays, including isomeric states, have clarified many new aspects of nuclear structures. A variety of direct reactions, making the best use of in-flight rare isotope (RI) beams at intermediate/high energies, have been applied for a wide range of rare isotopes. New experimental results using these methods have shown that one needs a new framework to understand structures and dynamics of exotic nuclei, such as new or lost magic numbers, novel neutron halo/skin structures and relevant reactions/excitations. A wide range of reactions associated with nucleo-synthesis in the Universe and the equation of state (EoS) of neutron-rich nuclear matter have also been studied through experiments using rare isotopes available at in-flight separators. This review article focuses its attention on how recent experimental techniques have been developed and applied to exotic nuclei at in-flight separators. We also make remarks on prospects for the near future: in the era when the 3rd-generation RI-beam facilities based on in-flight separators are being completed world-wide. [ABSTRACT FROM AUTHOR]

One-neutron removal ( p , p n ) reactions induced by two-neutron Borromean nuclei are studied within a Transfer-to-the-Continuum (TC) reaction framework, which incorporates the three-body character of the incident nucleus. The relative energy distribution of the residual unbound two-body subsystem, which is assumed to retain information on the structure of the original three-body projectile, is computed by evaluating the transition amplitude for different neutron-core final states in the continuum. These transition amplitudes depend on the overlaps between the original three-body ground-state wave function and the two-body continuum states populated in the reaction, thus ensuring a consistent description of the incident and final nuclei. By comparing different 11 Li three-body models, it is found that the 11 Li ( p , p n ) 10 Li relative energy spectrum is very sensitive to the position of the p 1 / 2 and s 1 / 2 states in 10 Li and to the partial wave content of these configurations within the 11 Li ground-state wave function. The possible presence of a low-lying d 5 / 2 resonance is discussed. The coupling of the single particle configurations with the non-zero spin of the 9 Li core, which produces a spin-spin splitting of the states, is also studied. Among the considered models, the best agreement with the available data is obtained with a 11 Li model that incorporates the actual spin of the core and contains ∼31% of p 1 / 2 -wave content in the n - 9 Li subsystem, in accord with our previous findings for the 11 Li ( p , d ) 10 Li transfer reaction, and a near-threshold virtual state. [ABSTRACT FROM AUTHOR]

Emerging radioactive beams and multi petawatt laser facilities are sturdily transforming our base concepts in instruments in nuclear physics. The changes are fuelled by studies of nuclei close to the drip-line or exotic reactions. This physics demands high luminosity, wide phase space cover with good resolution in energy, time, position and sampled waveform. By judiciously modifying the micro-world of the particle or space physics instruments (Double Sided Strip Si Detectors, Micro-Pattern Gas Amplifiers, microelectronics), we are on the path to initiate dream experiments. In the following a brief status in the domain is reported for selected instruments that highlight the present trends with silicon and the growing shift towards gas media for charged particle detection. [ABSTRACT FROM AUTHOR]

Isochronous mass spectrometry (IMS) in storage rings is a powerful tool for mass measurements of exotic nuclei with very short half-lives down to several tens of microseconds, using a multicomponent secondary beam separated in-flight without cooling. However, the inevitable momentum spread of secondary ions limits the precision of nuclear masses determined by using IMS. Therefore, the momentum measurement in addition to the revolution period of stored ions is crucial to reduce the influence of the momentum spread on the standard deviation of the revolution period, which would lead to a much improved mass resolving power of IMS. One of the proposals to upgrade IMS is that the velocity of secondary ions could be directly measured by using two time-of-flight (double TOF) detectors installed in a straight section of a storage ring. In this paper, we outline the principle of IMS with double TOF detectors and the method to correct the momentum spread of stored ions. [ABSTRACT FROM AUTHOR]

Large acceptance spectrometers at in-flight RI separators have played significant roles in investigating the structure of exotic nuclei. Such spectrometers are in particular useful for probing unbound states of exotic nuclei, using invariant mass spectroscopy with reactions at intermediate and high energies. We discuss here the key characteristic features of such spectrometers, by introducing the recently commissioned SAMURAI facility at the RIBF, RIKEN. We also investigate the issue of cross talk in the detection of multiple neutrons, which has become crucial for exploring further unbound states and nuclei beyond the neutron drip line. Finally we discuss future perspectives for large acceptance spectrometers at the new-generation RI-beam facilities. [ABSTRACT FROM AUTHOR]

The spectra of neutrons from the reactions Ti( p, n)V and Fe ( p, n)Co were measured in the range of proton energies between 8 and 11 MeV along with their counterparts from the reactions Ti( d, n)V and Fe ( d, n)Co at the deuteron energies of 2.7 and 3.8 MeV. These measurements were conducted with the aid of a time-of-flight fast-neutron spectrometer on the basis of the EGP-15 pulsed tandem accelerator of the Institute for Physics and Power Engineering (IPPE, Obninsk). An analysis of measured data was performed within the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations based on the Hauser-Feshbach formalism of statistical theory were carried out with nuclear-level densities given by the generalized superfluid model of the nucleus, the backshifted Fermi-gas model, and the Gilbert-Cameron composite formula. The nuclear-level densities of V and Co and their energy dependences were determined. The results were discussed together with available experimental data and data recommended by model systematics. [ABSTRACT FROM AUTHOR]

Unbound positive-parity states in 10 Li have been populated with a two-proton removal reaction from a 71 MeV/u 12 B beam. The 9 Li fragments and emitted neutrons were measured with the MoNA-LISA-Sweeper setup. The measured decay energy spectrum was best fit with three states at 110 ± 40 , 500 ± 100 , and 1100 ± 100 keV decay energy. This is the second observation of a resonance below 200 keV. The lower two states likely belong to the expected 1 + , 2 + doublet. [ABSTRACT FROM AUTHOR]

We have analyzed elastic scattering angular distributions and total reaction cross sections of the exotic nuclei 9.11Li on 208Pb, at energies below and above the Coulomb barrier. For this purpose, we have used an optical potential with no adjustable parameters, composed by the nuclear Säo Paulo potential, derived from the nonlocal nature of the interaction, and the Coulomb dipole polarization potential, derived from the semiclassical theory of Coulomb excitation. Within this formalism, we identified an unusual long-range absorption for the 11Li 208Pb system, which is dominated by the Coulomb interaction. We compare it to the absorption mechanisms observed for 6He + 208Pb which, unlike those of 11Li + 208Pb, lake place at small interacting distances, where both Coulomb and nuclear interactions are important. The proposed approach shows to be a fundamental basis to study reactions involving exotic nuclei. [ABSTRACT FROM AUTHOR]

At radioactive ion beam facilities like ISOLDE at CERN, a high purity of the element of interest in the ion beam is essential for most experiments on exotic nuclei. Due to its unique combination of high ionization efficiency and ultimate elemental selectivity, the Resonance Ionization Laser Ion Source, RILIS, has become the most frequently used ion source at ISOLDE and at the majority of similar facilities worldwide. However, isobaric contamination predominantly stemming from unspecific surface ionization may still introduce severe limitations. By applying the highly selective resonance ionization technique inside a radio-frequency quadrupole ion guide structure, the novel approach of the Laser Ion Source and Trap, LIST, suppresses surface ionized isobaric contaminants by an electrostatic repelling potential. Following extensive feasibility studies and off-line tests, the LIST device has been adapted and refined to match the stringent operational constraints and to survive the hostile environment of the ISOLDE front-end region enclosing the highly radioactive nuclear reaction target. The LIST operation was successfully demonstrated for the first time on-line at ISOLDE during two experiments, attesting its suitability for radioactive isotope production under routine conditions. Data of these on-line characterization measurements confirm a suppression of surface-ionized isobars by more than a factor of 1000 in accordance to off-line studies that were carried out for the preparation of the on-line experiments. During the first on-line test, the suppression was associated with an efficiency loss of not more than a factor of about 50 with respect to normal RILIS operation. These losses could be further reduced to only about 20 during the second run. Results of the off-line studies in comparison to the first on-line characterization data are discussed here. [ABSTRACT FROM AUTHOR]