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A 410 MeV/u 238 U projectile beam was used to create cadmium isotopes via abrasion-fission in a beryllium target placed at the entrance of the in-flight separator FRS at GSI. The fission fragments were separated by the FRS and injected into the isochronous storage ring ESR for mass measurements. Isochronous Mass Spectrometry (IMS) was performed under two different experimental conditions, with and without B ρ -tagging at the high-resolution central focal plane of the FRS. In the experiment with B ρ -tagging the magnetic rigidity of the injected fragments was determined with an accuracy of 2 ⋅ 10 − 4 . A new method of data analysis, which uses a correlation matrix for the combined data set from both experiments, has provided experimental mass values of 25 rare isotopes for the first time. The high sensitivity and selectivity of the method have given access to nuclides detected with a rate of a few atoms per week. In this letter we present for the 129,130,131 Cd isotopes mass values directly measured for the first time. The experimental mass values of cadmium as well as for tellurium and tin isotopes show a pronounced shell effect towards and at N = 82 . Shell quenching cannot be deduced from a single new mass value, nor by a better agreement with a theoretical model which explicitly takes into account a quenching feature. This is in agreement with the conclusion from γ -ray spectroscopy and confirms modern shell-model calculations. [ABSTRACT FROM AUTHOR]

Abstract: The core-excited isomer in fully-ionized 133Sb has been directly studied for the first time by applying the novel technique of isochronous mass spectrometry at GSI. The neutron-rich nuclides in high charge states were produced by projectile fission of 411 MeV A 238U ions, separated in flight by the fragment separator (FRS) and stored in the isochronous storage ring (ESR). The measured excitation energy is 4.56(10) MeV. The neutral-atom half-life is known to be 17 μs. This is the shortest-lived isomer measured directly with mass spectrometry techniques. The extended in-flight half-life of the bare ions in the ESR, which is due to the exclusion of the strong internal conversion, demonstrates that there should be another nuclear level above that identified from isomer-decay spectroscopy, in support of shell-model calculations. This measurement opens up a new half-life domain for storage-ring measurements. [Copyright &y& Elsevier]

Precise mass measurements of short-lived exotic nuclei are very important for the understanding of basic nuclear structure physics and astrophysical nucleosynthesis in nature, as well as for the test and the development of theoretical nuclear mass models. At GSI, the Isochronous Mass Spectrometry (IMS) dedicated to mass measurements of short-lived nuclides was developed. In this contribution, the IMS technique is briefly reviewed. Recently, the first large-scale measurement on the 238U fission fragment was done successfully. The measured mass values are in excellent agreement with the recent Penning trap data, however, they show a systematical deviation from the values in the latest atomic mass evaluation. Some representative results from this experiment will be presented, including their impact on nuclear structure physics and astrophysical r-process nucleosynthesis. [ABSTRACT FROM AUTHOR]

Abstract: The previously pioneered Isochronous Mass Spectrometry (IMS) has been extended by an additional precise magnetic-rigidity determination to enable accurate large-scale measurements of stored short-lived relativistic nuclei with the FRS-ESR facility at 382 MeV/u. With this novel experimental tool the mass resolving power and accuracy have been improved by a factor of about 3. The recorded broad-band revolution time spectrum corresponds to the mass-over-charge range of about 6%. A mass resolving power of 200 000 (FWHM) and a typical accuracy of 120 keV have been achieved almost over the entire spectrum. The masses of 35 neutron-rich nuclides have been directly measured in the element range from aluminum to barium. The Masses of 8 nuclides (85,86As, 89Se, 123Ag, 138Te, 140,141I, 143Xe) have been measured for the first time. The results are compared with previous experimental data and theoretical predictions. The evolution of the shell closure towards doubly-magic 78Ni is discussed. [Copyright &y& Elsevier]

Projectile fragments separated in flight with the FRS have been injected into the storage ring ESR. Operating the ESR in the isochronous mode has enabled high-resolution mass measurements of short-lived isotopes. Already in our pilot experiments the Isochronous Mass Spectrometry (IMS) has provided accurate results for a restricted isotope range in the neighborhood of a selected isotope characterized by the best isochronous condition. In the present experiment this restriction has been overcome by precise external magnetic rigidity determination (1.5·10–4) at the dispersive midplane of the FRS. In this way the mass resolving power for neutron-rich fission fragments covering a large mass-over-charge ratio in one spectrum has been improved by up to one order of magnitude and the accuracy by more than a factor of two. [ABSTRACT FROM AUTHOR]

Mass measurements of exotic nuclei is a fast developing field which is essential for basic nuclear physics and a wide range of applications. The method of storage ring mass spectrometry has many advantages: (1) a large amount of nuclides can be simultaneously measured; (2) very short-lived (T1/2 ≳ 50 µs) and very rare species (yields down to single ions) can be accessed; (3) nuclides in several atomic charge states can be investigated; (4) half-life measurements can be performed with time-resolved mass spectrometry. In this contribution we concentrate on some recent achievements and future perspectives of the storage ring mass spectrometry. [ABSTRACT FROM AUTHOR]

We have measured for the first time simultaneously both the mean charge states and stopping powers of (35–280) MeV/u 208Pb ions in gases and solids with an accuracy of 1%. The existence at lower energies and disappearance at higher of density effects in the charge-state distribution and the corresponding stopping power are directly confirmed and comparisons with widely used theories and simulations for heavy ions demonstrate strong deviations of up to 27%. However, an unprecedented prediction power of better than 3% has been achieved for the energy loss when the measured mean charge-states are implemented in the Lindhard-Sørensen theory. Our present benchmark data contribute to an improved understanding of the basic atomic collision processes and to numerous applications in nuclear physics. Extending the GANIL data [1] to higher accuracy and energies, we can now answer at which velocities the Bohr-Lindhard density effect in stopping will vanish. [ABSTRACT FROM AUTHOR]

Abstract A thick neutron skin emerges from the first determination of root mean square radii of the proton distributions for 17−22N from charge changing cross section measurements around 900 A MeV at GSI. Neutron halo effects are signalled for 22N from an increase in the proton and matter radii. The radii suggest an unconventional shell gap at N = 14 arising from the attractive proton–neutron tensor interaction, in good agreement with shell model calculations. Ab initio , in-medium similarity re-normalization group, calculations with a state-of-the-art chiral nucleon–nucleon and three-nucleon interaction reproduce well the data approaching the neutron drip-line isotopes but are challenged in explaining the complete isotopic trend of the radii. [ABSTRACT FROM AUTHOR]

At the Low-Energy Branch (LEB) of the Super-FRS at FAIR, projectile and fission fragments will be produced at relativistic energies, separated in-flight, energy-bunched, slowed down and thermalized in a cryogenic stopping cell (CSC) filled with ultra-pure He gas. The fragments are extracted from the stopping cell using a combination of DC and RF electric fields and gas flow. A prototype CSC for the LEB has been developed and successfully commissioned at the FRS Ion Catcher at GSI. Ionization of He buffer gas atoms during the stopping of energetic ions creates a region of high space charge in the stopping cell. The space charge decreases the extraction efficiency of stopping cells since the high amount of charge distorts the applied DC electric drag fields. Thus the understanding of space charge effects is of great importance to make full use of the high yields at future RIB facilities such as the Super-FRS at FAIR. For this purpose a detailed study of space charge effects in the CSC was performed using experiments and simulations. The dependence of the extraction efficiency, the extraction time and the temporal ion extraction profile on the intensity of the impinging beam and the electric field strength was studied for two different 238 U projectile fragments produced at 1000 MeV/u and separated with the FRS. Good agreement between experiments and simulations was found. [ABSTRACT FROM AUTHOR]

Previously unknown isotopes 30Ar and 29C1 have been identified by measurement of the trajectories of their in-flight decay products 28S + p + p and 28S + p, respectively. The analysis of angular correlations of the fragments provided information on decay energies and the structure of the parent states. The ground states of 30Ar and 29C1 were found at 2.25-0.10+0.15 and 1.8 ±0.1 MeV above the two- and one-proton thresholds, respectively. The lowest states in 30Ar and 29C1 point to a violation of isobaric symmetry in the structure of these unbound nuclei. The two-proton decay has been identified in a transition region between simultaneous two-proton and sequential proton emissions from the 30Ar ground state, which is characterized by an interplay of three-body and two-body decay mechanisms. The first hint of a fine structure of the two-proton decay of 30Ar* (2+) has been obtained by detecting two decay branches into the ground and first-excited states of the 28S fragment. [ABSTRACT FROM AUTHOR]

211 Po ions in the ground and isomeric states were produced via 238 U projectile fragmentation at 1000 MeV/u. The 211 Po ions were spatially separated in flight from the primary beam and other reaction products by the fragment separator FRS. The ions were energy-bunched, slowed-down and thermalized in a gas-filled cryogenic stopping cell (CSC). They were then extracted from the CSC and injected into a high-resolution multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). The excitation energy of the isomer and, for the first time, the isomeric-to-ground state ratio were determined from the measured mass spectrum. In the subsequent experimental step, the isomers were spatially separated from the ions in the ground state by an ion deflector and finally collected with a silicon detector for decay spectroscopy. This pioneering experimental result opens up unique perspectives for isomer-resolved studies. With this versatile experimental method new isomers with half-lives longer than a few milliseconds can be discovered and their decay properties can be measured with highest sensitivity and selectivity. These experiments can be extended to studies with isomeric beams in nuclear reactions. [ABSTRACT FROM AUTHOR]

The first determination of radii of point proton distribution (proton radii) of B12-17 from charge-changing cross sections (σCC) measurements at the FRS, GSI, Darmstadt is reported. The proton radii are deduced from a finite-range Glauber model analysis of the σCC. The radii show an increase from 13B to 17B and are consistent with predictions from the antisymmetrized molecular dynamics model for the neutron-rich nuclei. The measurements show the existence of a thick neutron surface with neutron-proton radius difference of 0.51(0.11) fm in B. [ABSTRACT FROM AUTHOR]

Abstract: The periodic time modulations, found recently in the two-body orbital electron capture (EC) decay of both, hydrogen-like 140Pr58+ and 142Pm60+ ions, with periods near to and amplitudes of about 20%, were re-investigated for the case of 142Pm60+ by using a resonator cavity with a much improved sensitivity and time resolution. We observed that the exponential EC decay is modulated with a period , in accordance with a modulation period as obtained from simultaneous observations with a capacitive pick-up, employed also in the previous experiments. The modulation amplitudes amount to and for the resonator and the capacitive pick-up, respectively. These new results corroborate for both detectors exactly our previous findings of modulation periods near to , though with distinctly smaller amplitudes. Also the three-body decays have been analyzed. For a supposed modulation period near to we found an amplitude , compatible with and in agreement with the preliminary result of our previous experiment. These observations could point at weak interaction as origin of the observed -modulation of the EC decay. Furthermore, the data suggest that interference terms occur in the two-body EC decay, although the neutrinos are not directly observed. [Copyright &y& Elsevier]

Storage-ring mass spectrometry was applied to neutron-rich 197Au projectile fragments. Masses of 18l,183Lu, 185,186Hf, 187,188Ta, 191W, and 192,193Re nuclei were measured for the first time. The uncertainty of previously known masses of 189,190W and 195Os nuclei was improved. Observed irregularities on the smooth two-neutron separation energies for Hf and W isotopes are linked to the collectivity phenomena in the corresponding nuclei. [ABSTRACT FROM AUTHOR]

Long-lived isomers in 212Bi have been studied following 238U projectile fragmentation at 670 MeV per nucleon. The fragmentation products were injected as highly charged ions into a storage ring, giving access to masses and half-lives. While the excitation energy of the first isomer of 212Bi was confirmed, the second isomer was observed at 1478(30) keV, in contrast to the previously accepted value of >1910 keV. It was also found to have an extended Lorentz-corrected in-ring half-life >30 min, compared to 7.0(3) min for the neutral atom. Both the energy and half-life differences can be understood as being due a substantial, though previously unrecognized, internal decay branch for neutral atoms. Earlier shell-model calculations are now found to give good agreement with the isomer excitation energy. Furthermore, these and new calculations predict the existence of states at slightly higher energy that could facilitate isomer deexcitation studies. [ABSTRACT FROM AUTHOR]

Abstract: Masses of 238U projectile fragments have been measured with time-resolved Schottky Mass Spectrometry (SMS) at the FRS-ESR facility at GSI. The exotic nuclei were created in the production target at the entrance of the fragment separator FRS, spatially separated in flight and injected into the storage-cooler ring ESR at about 70% light velocity. This means the ions were mainly bare or carried only a few electrons, e.g., the population of Li-like ions was below 1% for Pt fragments. Accurate new mass values of 33 neutron-rich, stored exotic nuclei in the element range from platinum to uranium have been obtained for the first time. In total more than 150 nuclides including references with well-known masses have been covered in this large-area SMS measurement. A novel data analysis has been applied which reduces the systematic errors by taking into account the velocity profile of the cooler electrons and the residual ion-optical dispersion in this part of the storage ring. The experiment, the data analysis, and the mass values are presented. The experimental data are compared with theoretical predictions demonstrating systematic deviations of up to 1500 keV from modern mass models. [Copyright &y& Elsevier]

The one-neutron removal cross sections of neutron-rich Al isotopes and longitudinal momentum distributions of the residues have been measured for A = 33 to 36 at relativistic energies (≈900 MeV/u). The inclusive data have been interpreted within the eikonal approximation. The evolution of the single-particle occupancy in the ground state of 33,34,35A1 has been studied and compared with shell model predictions. The inferred 2s1/2 neutron occupancy in the 33A1 ground-state wave function is 20% to 40% lower than the predicted one. The inclusive data do not exclude the presence of intruder states. Some intruder / = 1 occupancy is found in 34A1, similarly to 33Mg. The single-particle 1 f7/2 occupancy shows a gradual increase at N = 22. Correspondingly, a decrease of the lrf3/2 strength has been observed. [ABSTRACT FROM AUTHOR]

The interaction cross sections of 32-35Mg at 900A MeV have been measurmed using the fragment separator at GSI. The deviation from the r0A1/3 trend is slightly larger for 35Mg, signaling the possible formation of a longer tail in the neutron distribution for 35Mg. The radii extracted from a Glauber model analysis with Fermi densities are consistent with models predicting the development of neutron skins. [ABSTRACT FROM AUTHOR]

Abstract: 238U projectile fragments have been created at the entrance of the fragment separator FRS, spatially separated in flight within 0.45 μs and injected into the storage-cooler ring ESR at 7.9 Tm corresponding to about 70% light velocity. Accurate new mass values and lifetime information of the stored exotic nuclei in the element range from platinum to uranium have been obtained with single-particle Schottky spectrometry. In this experiment the new isotopes of 236Ac, 224At, 221Po, 222Po, and 213Tl were discovered. The isotopes were unambiguously identified and their masses measured. In addition, the time-correlated data have provided information on the lifetime of the new nuclides. The discovery of isotopes along with accurate mass measurement has been achieved for the first time at the FRS-ESR facility. The results will contribute to the knowledge of the decay products from the r-process nuclei and enable a crucial test of the predictive power of modern nuclear mass and half-life models. [ABSTRACT FROM AUTHOR]

Abstract: The first reaction spectroscopy on the ground state structure of 33Mg through the measurement of the longitudinal momentum distribution from the one-neutron removal reaction using a C target at is reported. The experiment was performed at the FRS, GSI. The distribution has a relatively narrow width ( (FWHM)) and the one-neutron removal cross-section is . An increased contribution from the orbital is required to explain the observation showing its lowering compared to existing model predictions. This provides new information regarding the configuration of 33Mg and the island of inversion. [Copyright &y& Elsevier]

Abstract: The and orbital electron-capture decays of stored hydrogen- and helium-like 142Pm ions have been measured. So far, such measurements have been performed with only one nucleus, namely 140Pr. The electron-capture decay constant of hydrogen-like 142Pm60+ ions is about 50% larger than that of helium-like 142Pm59+ ions, which is in excellent agreement with the previous measurements in 140Pr ions and with new theoretical predictions. [Copyright &y& Elsevier]

Abstract: At the FRS Ion Catcher at GSI, relativistic exotic ions produced by projectile fragmentation/fission are range-focused, slowed down and thermalised in a gas-filled stopping cell, extracted and made available to high-precision experiments with ions almost at rest. It is a prototype for a gas cell system at the Low-Energy Branch of the Super-FRS at FAIR. In an online experiment, the FRS Ion Catcher was commissioned successfully with relativistic nickel fragments. The overall efficiency of the system was measured as (1.8±0.3)% and can be divided into a stopping efficiency of (5.0±1.1)% and an extraction and transport efficiency of (35.8±9.4)%. The overall efficiency is hence limited mostly by the stopping efficiency, which could be increased in the future by operating at higher gas cell pressures. From extraction time measurements of polyatomic ions formed in the gas cell extraction times of atomic ions of 20–50ms can be derived. The potential of the system was illustrated by the half-life measurement of 54Co with a short half-life of 193ms only. [Copyright &y& Elsevier]

Abstract: We report on time-modulated two-body weak decays observed in the orbital electron capture of hydrogen-like 140Pr59+ and 142Pm60+ ions coasting in an ion storage ring. Using non-destructive single ion, time-resolved Schottky mass spectrometry we found that the expected exponential decay is modulated in time with a modulation period of about 7 seconds for both systems. Tentatively this observation is attributed to the coherent superposition of finite mass eigenstates of the electron neutrinos from the weak decay into a two-body final state. [Copyright &y& Elsevier]

For the first time the electron capture and β+ decay rates of H-like 140Pr ions have been measured at the FRS-ESR facility by using the Schottky noise technique. The H-like 140Pr58+ decay rate was found to be larger by a factor of 1.5 than in the case of neutral atom. This non-intuitive result can be explained by taking into account hyperfine splitting of nuclear levels in the decaying nuclei and the conservation law of the total angular momentum of the system. [ABSTRACT FROM AUTHOR]

Schottky Mass Spectrometry (SMS) and Isochronous Mass Spectrometry (IMS) have been successfully applied for direct mass measurements of exotic nuclides at FRS-ESR facility at GSI. Both experimental methods are sensitive to single stored ions and can cover very efficiently a large number of nuclides in one run. Presently, more than 1100 masses of different nuclides have been covered by SMS and IMS in several FRS-ESR experiments whereby about 350 of them have been determined for the first time. In this paper, we present the status of our experimental program and use the experimental mass values to test the predictive power of modern mass models. [Copyright &y& Elsevier]

One important goal of the ILIMA project at FAIR is the study of masses and decay properties of relativistic isomeric beams stored and cooled in the planned storage-ring complex. A new scheme is described, where a storage-cooler ring is used for high-resolution mass separation. Experimental results on the separation of the isobaric pair 140Pr-140Ce are presented. [ABSTRACT FROM AUTHOR]

The FRS-ESR facility at GSI provides one of the most efficient methods for direct mass measurements. In the present experiment, exotic nuclei were produced via fragmentation of 152Sm projectiles in a thick beryllium target at 500-600 MeV/u, separated in-flight with the fragment separator FRS, and injected into the storage-cooler ring ESR. Time-resolved Schottky Mass Spectrometry was applied for mass measurements of stored and electron-cooled bare and few-electron ions. 373 different nuclides were identified by means of the spectra of their revolution frequencies. Masses for 18 nuclides (84Zr, 92Ru, 94Rh, 107,108,110Sb, 111,112,114I, 118Ba, 122,123La, 124Ce, 127Pr, 129Nd, 132Pm, 134Sm, 137Eu) have been determined for the first time. Masses for 111,112I and 113Xe have been obtained via known α-decay energies. The experiment and first results will be presented. [ABSTRACT FROM AUTHOR]

Proton radii of C12-19 densities derived from first accurate charge changing cross section measurements at 900A MeV with a carbon target are reported. A thick neutron surface evolves from ~0.5 fm in 15C to ~1 fm in 19C. The halo radius in 19C is found to be 6.4±0.7 fm as large as 11Li. Ab initio calculations based on chiral nucleon-nucleon and three-nucleon forces reproduce the radii well. [ABSTRACT FROM AUTHOR]

A new long-lived isomeric state in the near proton dripline nucleus 125Ce has been identified with Schottky mass spectrometry at GSI. The excitation energy E * = 103(12)keV and the decay time of 193(1)s have been obtained from a single stored fully ionized 125 m Ce58+ ion. The data implies an E3 transition and a 1/2+ assignment for the spin of the isomer. [ABSTRACT FROM AUTHOR]

Abstract: High precision direct mass measurements have shown strong potential to identify and determine new nuclear isomeric states, and therefore to add intriguing new nuclear physics information by going beyond γ-ray spectroscopy. The principle and characteristic experimental results of isomer investigations in the storage ring at GSI are discussed. [Copyright &y& Elsevier]