We propose a new approach for a high-density free-neutron target, primarily aimed at nuclear astrophysics reaction studies in inverse kinematics with radioactive ions circulating in a storage ring. The target concept integrates four key subsystems: a neutron production source driven by a supercompact cyclotron utilizing 9Be(p; xn) reactions, an optimized moderator/reflector assembly using either heavy water or beryllium oxide with a graphite reflector shell to thermalize fast neutrons, a cryogenic liquid hydrogen moderator to maximize thermal neutron density in the interaction region, and beam pipe geometries that enable neutron-ion interactions while maintaining vacuum conditions for ion circulation. This integrated approach focuses on feasibility by incorporating readily available technologies. Using a commercial supercompact cyclotron delivering a proton beam of 130 mu A, the design achieves thermal neutron areal densities of similar to 3.4 & times; 106 n/cm2 for a proof-of-concept demonstrator at the CRYRING ionstorage ring at GSI Darmstadt. This autonomous accelerator-target assembly design enables deployment at both in-flight and ISOL facilities to exploit their complementary production mechanisms. Potential upgrades based on higher-energy and/or higher-current cyclotrons will enable an increase in areal density to similar to 109 n/cm2. In combination with a customized low-energy storage ring and a radioactive ion-beam facility, the proposed solution could deliver luminosities above 1023 cm-2 s-1, thereby enabling neutron capture measurements of similar to mb cross sections within a few days of experiment. The proposed system represents a significant milestone toward enabling large neutron-capture surveys on short-lived nuclei, thereby opening a new avenue for understanding the synthesis of heavy elements in our universe.

The heaviest stable nuclei in the universe owe their existence to quantum shell structure, the grouping of protons and neutrons into discrete energy levels separated by gaps. The largest known neutron shell gap in stable nuclei, at N=126, stabilizes doubly-magic ^208Pb and is responsible for the characteristic abundance peak of heavy elements near gold and platinum produced by the rapid neutron-capture process (r-process). Whether this shell gap persists as protons are removed from lead is a question central to both nuclear structure and the modeling of heavy-element synthesis, yet it has remained unanswered due to the extraordinary difficulty of producing the relevant neutron-rich nuclei. Direct experimental knowledge in this region was essentially absent. Here we report the first precision mass measurements of ^203,204Pt and ^204,205,206Au, performed at GSI using a novel combination of Schottky and isochronous mass spectrometry in a heavy-ion storage ring. The N=126 isotones ^204Pt and ^205Au are more strongly bound than the extrapolated trend of the previously known mass surface by 403 and 464 keV, respectively, revealing an unexpectedly enhanced N=126 shell strength below doubly-magic ^208Pb. Furthermore, the proton-neutron interaction strength exhibits a hitherto unobserved bifurcation at N=126 as protons are removed from ^208Pb. Our results redefine the nuclear mass surface in the neutron-rich heavy-element region and provide direct experimental benchmarks for theoretical models whose extrapolations toward more exotic nuclei are essential for r-process nucleosynthesis calculations.

The NECTAR (Nuclear rEaCTions At storage Rings) experiment at the ESR heavy-ion storage ring at GSI/FAIR Darmstadt is dedicated to surrogate reaction studies of neutron-induced reactions on heavy nuclei in inverse kinematics. In this work, we report on the implementation and performance of a newly developed fission-fragment detection system integrated into the NECTAR experimental setup. The upgraded detector configuration enables, for the first time in a surrogate experiment, the simultaneous detection ofgamma-decay residues, multi-neutron-emission residues, and fission fragments. The full setup was used for the first time in an experiment where a stored beam of bare 238U92+ ions at 17.24 MeV/u interacted with a gas-jet deuterium target, populating excited 238U and 239U nuclei via the 238U(d,d') and 238U(d,p) reactions. We describe the geometry of the used fission fragment detectors, design constraints, and simulation-based efficiency determination. The target-like particle identification and beam-like residue spectra demonstrating the performance of the complete setup are also shown.

Using novel metallic magnetic calorimeter detectors at the CRYRING@ESR, we recorded X-ray spectra of stored and electron cooled helium-like uranium (U^90+) with an unmatched spectral resolution of close to 90 eV. This allowed for an accurate determination of the energies of all four components of the Kα transitions in U^90+. We find good agreement with state-of-the-art bound-state QED calculations for the strong-field regime. Our results do not support any systematic deviation between experiment and theory in helium-like systems, the presence of which was subject of intense debates in recent years.

Non-destructive Schottky detectors are indispensable devices widely used in experiments at heavy-ion storage rings.In particular,they can be used to accurately determine the masses and lifetimes of short-lived exotic nuclear species.Single-ion sensitivity-which is the highest level of sensitivity-has been regularly achieved in the past by utilizing resonant cavity detectors.Recent designs and analysis methods aim to push the limits of measurement accuracy by increasing the dimensionality of the acquired data,namely,the position of the particle as well as the phase difference between several detectors.This paper describes current methods and future perspectives for Schottky detection techniques,with a focus on their application to mass and lifetime measurements of the most rare and simultaneously short-lived radio nuclides.

Beim nuklearen Zweiphotonenzerfall sendet ein angeregter Atomkern simultan zwei Photonen aus. Dieser sehr seltene Zerfallsmodus kann einerseits Informationen über eine Reihe von fundamentalen Eigenschaften des Atomkerns geben. Dazu zählt seine Polarisierbarkeit, je nachdem in welchem Anregungszustand er sich befindet. Andererseits kann er aber auch helfen, die nuklearen Grundlagen des doppelten Betazerfalls besser zu verstehen.

Schottky mass spectrometry utilizing heavy-ion storage rings is a powerful technique for the precise mass and decay half-life measurements of highly charged ions. Owing to the nondestructive ion detection features of Schottky noise detectors, the number of stored ions in the ring is determined by the peak area in the measured revolution frequency spectrum. Because of their intrinsic amplitude-frequency characteristic (AFC), Schottky detector systems exhibit varying sensitivities at different frequencies. Using low-energy electron-cooled stored ions, a new method is developed to calibrate the AFC curve of the Schottky detector system of the Experimental Cooler Storage Ring (CSRe) storage ring located in Lanzhou, China. Using the amplitude-calibrated frequency spectrum, a notable refinement was observed in the precision of both the peak position and peak area. As a result, the storage lifetimes of the electron-cooled fully ionized ^56 Fe ^26+ ions were determined with high precision at beam energies of 13.7 and 116.4 MeV/u, despite of frequency drifts during the experiment. When electron cooling was turned off, the effective vacuum condition experienced by the 116.4 MeV/u ^56 Fe ^26+ ions was determined using amplitude-calibrated spectra, revealing a value of 2× 10^-10 mbar, which is consistent with vacuum gauge readings along the CSRe ring. The method reported herein will be adapted for the next-generation storage ring of the HIAF facility under construction in Huizhou, China. It can also be adapted to other storage ring facilities worldwide to improve precision and enhance lifetime measurements using many ions in the ring.

Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth1,2. Among such nuclei whose decay signatures are found in the oldest meteorites, 205Pb is a powerful example, as it is produced exclusively by slow neutron captures (the s process), with most being synthesized in asymptotic giant branch (AGB) stars3-5. However, making accurate abundance predictions for 205Pb has so far been impossible because the weak decay rates of 205Pb and 205Tl are very uncertain at stellar temperatures6,7. To constrain these decay rates, we measured for the first time the bound-state β- decay of fully ionized 205Tl81+, an exotic decay mode that only occurs in highly charged ions. The measured half-life is 4.7 times longer than the previous theoretical estimate8 and our 10% experimental uncertainty has eliminated the main nuclear-physics limitation. With new, experimentally backed decay rates, we used AGB stellar models to calculate 205Pb yields. Propagating those yields with basic galactic chemical evolution (GCE) and comparing with the 205Pb/204Pb ratio from meteorites9-11, we determined the isolation time of solar material inside its parent molecular cloud. We find positive isolation times that are consistent with the other s-process short-lived radioactive nuclei found in the early Solar System. Our results reaffirm the site of the Sun's birth as a long-lived, giant molecular cloud and support the use of the 205Pb-205Tl decay system as a chronometer in the early Solar System.

In the last decade nuclear reaction measurements using heavy ion storage rings became an important tool for nuclear astrophysics studies. The new CRYRING Array for Reaction MEasurements (CARME), recently commissioned at the low energy CRYRING@ESR storage ring (GSI/FAIR), is designed to take this novel approach one step further and perform direct nuclear reaction measurements at stellar energies, as well as indirect studies of nuclear properties of interest for nuclear astrophysics. CRYRING is unique worldwide in being able to store high quality, isotopically pure, radioactive beams produced in-flight at the low energies required for nuclear astrophysics. This paper describes the first in-beam reaction measurement with CARME at CRYRING, the first beam on (conventional) target measurement for FAIR Phase-0, and the data analysis approach required by this unprecedented, unique experimental approach.

This contribution is based on our input to the NuPECC LRP on per-spectives of precision experiments at heavy-ion storage rings in the realm of nuclear structure, atomic-and astrophysics. A focus here is on experi-ments with secondary beams of heavy ions, which can either be stable or long-lived nuclei in specific, high atomic charge states, or unstable nuclides.

The mass and half-life of a nucleus are its basic properties which reflect its structure and decay properties. These data are among the most important nuclear physics inputs to astrophysical nucleosynthesis modelling. Tremendous experimental efforts are carried out to obtain yet unknown quantities, which are as a rule belong to short-lived nuclei far away from stability. Storage ring mass spectrometry is a technique ideally suited for addressing many different nuclear species at the same time. In the last few years it went through major developments regarding nuclear mass determinations, thereby boosting its efficiency, sensitivity and precision. A non-destructive detection capability is being presently implemented aiming at simultaneous mass, lifetime and decay branching measurements. Recent developments and future perspectives are briefly discussed.

Atomic nuclei are many body systems composed of quantum particles termed nucleons,which are either positively charged pro-tons or electrically neutral neutrons.The nuclear force,which describes interactions between nucleons,is highly complicated.

Bound-state β−-decay is an exotic decay mode that produces temperature-dependent stability in nuclei. A striking example is 205Tl, in part because of its impact on the 205Pb/204Pb cosmochronometer—a short-lived ra-dionuclide clock that can provide unique constraints on s process material in the early solar system. The bound-state β−-decay of 205Tl was measured at GSI, where fully stripped 205Tl81+ ions were produced and stored in the Experimental Storage Ring. Decay occurred during storage producing increased 205Pb daughters with increased storage time. This contribution briefly outlines the experiment and describes analytical corrections required to extract the half-life.

229 Th with a low-lying nuclear isomeric state is an essential candidate for a nuclear clock as well as many other applications. Laser excitation of the isomeric state has been a long-standing goal. With relativistic 229 Th ions in storage rings

^229Th with a low-lying nuclear isomeric state is an essential candidate for a nuclear clock as well as many other applications. Laser excitation of the isomeric state has been a long-standing goal. With relativistic ^229Th ions in storage rings, high-power lasers with wavelengths in the visible range or longer can be used to achieve high excitation rates of ^229Th isomers. This can be realized through direct resonant excitation, or excitation via an intermediate nuclear or electronic state, facilitated by the tunability of both the laser-beam and ion-bunch parameters. Unique opportunities are offered by highly charged ^229Th ions due to the nuclear-state mixing. The significantly reduced isomeric-state lifetime corresponds to a much higher excitation rate for direct resonant excitation. Importantly, we propose electric dipole transitions changing both the electronic and nuclear states that are opened by the nuclear hyperfine mixing. We suggest using them for efficient isomer excitation in Li-like ^229Th ions, via stimulated Raman adiabatic passage or single-laser excitation. We also propose schemes for probing the isomers, utilizing nuclear radiative decay or laser spectroscopy on electronic transitions, through which the isomeric-state energy can be determined with an orders-of-magnitude higher precision than the current value. The schemes proposed here for ^229Th could also be adapted to low-energy nuclear states in other nuclei, such as ^229Pa.

We measured the Coulomb dissociation of 16 O into 4 He and 12 C within the FAIR Phase-0 program at GSI Helmholtzzentrum für Schwerionenforschung Darmstadt, Germany. From this we will extract the photon dissociation cross section 16 O(α,γ) 12 C, which is the time reversed reaction to 12C(α,γ) 16 O. With this indirect method, we aim to improve on the accuracy of the experimental data at lower energies than measured so far. The expected low cross section for the Coulomb dissociation reaction and close magnetic rigidity of beam and fragments demand a high precision measurement. Hence, new detector systems were built and radical changes to the R 3 B setup were necessary to cope with the high-intensity 16 O beam. All tracking detectors were designed to let the unreacted 16 O ions pass, while detecting the 12 C and 4 He.

The Gamma Factory (GF) is an ambitious proposal, currently explored within the CERN Physics Beyond Colliders program, for a source of photons with energies up to ≈400 MeV and photon fluxes (up to ≈1017 photons s−1) exceeding those of the currently available gamma sources by orders of magnitude. The high‐energy (secondary) photons are produced via resonant scattering of the primary laser photons by highly relativistic partially‐stripped ions circulating in the accelerator. The secondary photons are emitted in a narrow cone and the energy of the beam can be monochromatized, down to 10−3–10−6 level, via collimation, at the expense of the photon flux. This paper surveys the new opportunities that may be afforded by the GF in nuclear physics and related fields.

Neutron-induced cross sections of short-lived nuclei are highly relevant in many domains such as fundamental nuclear physics, astrophysics and applications in nuclear technology.In particular, these cross sections are essential for understanding the synthesis of elements via the s-and r stellar processes.However, the measurement of such cross sections with current techniques is very difficult or even impossible, because of the difficulties to produce and handle the necessary amounts of radioactive nuclei.Reaching the nuclei of interest is only possible by inverting the reaction kinematics with radioactive beams.In this contribution we present a project for indirectly determining neutron cross sections via the surrogate-reaction method.This project is based on the measurement of transfer-or inelastic-scattering-induced decay probabilities in inverse kinematics at storage rings.The measured probabilities are then used to tune nuclear-reaction models that will provide much more accurate predictions of the desired neutron cross sections.We also discuss a very ambitious, long-term project to directly measure neutron cross sections in inverse kinematics.It consists in the combination of a radioactive beam facility, an ion storage ring and a spallation neutron source.