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Direct mass measurements of neutron-deficient nuclides around the N=50 shell closure below $^{100}$Sn were performed at the FRS Ion Catcher (FRS-IC) at GSI, Germany. The nuclei were produced by projectile fragmentation of $^{124}$Xe, separated in the fragment separator FRS and delivered to the FRS-IC. The masses of 14 ground states and two isomers were measured with relative mass uncertainties down to 1×10−7 using the multiple-reflection time-of-flight mass spectrometer of the FRS-IC, including the first direct mass measurements of $^{98}$Cd and $^{97}$Rh. A new QEC=5437±67 keV was obtained for $^{98}$Cd, resulting in a summed Gamow-Teller (GT) strength for the five observed transitions (0+⟶1+) as B(GT)=2.94−0.28+0.32. Investigation of this result in state-of-the-art shell model approaches accounting for the first time experimentally observed spectrum of GT transitions points to a perfect agreement for N=50 isotones. The excitation energy of the long-lived isomeric state in $^{94}$Rh was determined for the first time to be 293±21 keV. This, together with the shell model calculations, allows the level ordering in $^{94}$Rh to be understood.

Mass measurements of the $^{69}$As, $^{70,71}$Se and $^{71}$Br isotopes, produced via fragmentation of a $^{124}$Xe primary beam at the FRS at GSI, have been performed with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher with an unprecedented mass resolving power of almost 1,000,000. For the $^{69}$As isotope, this is the first direct mass measurement. A mass uncertainty of 22 keV was achieved with only 10 events. For the $^{70}$Se isotope, a mass uncertainty of 2.6 keV was obtained, corresponding to a relative accuracy of $\delta$m/m = 4.0$\times 10^{-8}$, with less than 500 events. The masses of the $^{71}$Se and $^{71}$Br isotopes were measured with an uncertainty of 23 and 16 keV, respectively. Our results for the $^{70,71}$Se and $^{71}$Br isotopes agree with the 2016 Atomic Mass Evaluation, and our result for the $^{69}$As isotope resolves the discrepancy between previous indirect measurements. We measured also the mass of $^{14}$N$^{15}$N$^{40}$Ar (A=69) with a relative accuracy of $\delta$m/m = 1.7$\times 10^{-8}$, the highest yet achieved with a MR-TOF-MS. Our results show that the measured restrengthening of the proton-neutron interaction ($\delta$V$_{pn}$) for odd-odd nuclei at the N=Z line above Z=29 (recently extended to Z=37) is hardly evident at N-Z=2, and not evident at N-Z=4. Nevertheless, detailed structure of $\delta$V$_{pn}$ along the N-Z=2 and N-Z=4 lines, confirmed by our mass measurements, may provide a hint regarding the ongoing $\approx$500 keV discrepancy in the mass value of the $^{70}$Br isotope, which prevents including it in the world average of ${Ft}$-value for superallowed 0$^+\rightarrow$ 0$^+$ $\beta$ decays. The reported work sets the stage for mass measurements with the FRS Ion Catcher of nuclei at and beyond the N=Z line in the same region of the nuclear chart, including the $^{70}$Br isotope., Comment: 11 pages, 4 figures, accepted for publication at Physical Review C

Physics letters / B 802, 135200 (2020). doi:10.1016/j.physletb.2020.135200, Published by North-Holland Publ., Amsterdam

Background: The γ softness of 136Nd makes it possible to study the shape changes induced by two-proton or two-neutron excitation. Purpose: We measure the lifetimes of two-quasiparticle states of the bands based on the 10+ states at 3296 and 3279 keV to investigate the shape change induced by the alignment of two protons or two neutrons in the h11/2 orbital. Methods: The recoil-distance Doppler shift method was used for the study of 136Nd studies, which was formed by the fusion reaction 120Sn(20Ne, 4n)136Nd, at Ebeam = 85 MeV. Calculations were performed within the microscopic-macroscopic approach, based on the deformed Woods-Saxon single-particle potential and the Yukawa-plus-exponential macroscopic energy. Results: The lifetime of the 10+ state at 3279 keV of 136Nd was measured to be T 10+1/2 = 1.63(9) ns. The lifetimes of the 2+ state at 374 keV and of the 12+ state at 3686 keV of the ground band were also measured to be T 2+1/2 = 26.5(14) ps and T 12+1/2 = 22.5(14) ps. Conclusions: The measured lifetime of 10+ the state at 3279 keV together with other observables confirm the structure change in 136Nd. A rather small reduced hindrance of the electromagnetic decay of the 10+ state at 3279 keV would be consistent with its K-mixed character.

Physical review / C covering nuclear physics 99(6), 064313 (2019). doi:10.1103/PhysRevC.99.064313, Published by Inst., Woodbury, NY

Physics letters / B 754, 288 - 293 (2016). doi:10.1016/j.physletb.2016.01.039, Published by North-Holland Publ., Amsterdam

Journal of physics / Conference Series 875, 012008 (2017). doi:10.1088/1742-6596/875/2/012008, Published by IOP Publ., Bristol

Masses of uranium fission fragments have been measured with the FRagment Separator (FRS) combined with the Experimental Storage Ring (ESR) at GSI. A 410-415 MeV/u 238U projectile beam was fast extracted from the synchrotron SIS-18 with an average intensity of 109/spill. The projectiles were focused on a 1g/cm2 beryllium target at the entrance of the FRS to create neutron-rich isotopes via abrasion-fission. The fission fragments were spatially separated with the FRS and injected into the isochronous storage ring ESR for fast mass measurements without applying cooling. The Isochronous Mass Spectrometry (IMS) was performed under two different experimental conditions, with and without B $\rho$ -tagging at the high-resolution dispersive central focal plane of the FRS. The evaluation has been done for the combined data sets from both experiments with a new method of data analysis. The use of a correlation matrix has provided experimental mass values for 23 different neutron-rich isotopes for the first time and 6 masses with improved values. The new masses were obtained for nuclides in the element range from Se to Ce. The applied analysis has given access even to rare isotopes detected with an intensity of a few atoms per week. The novel data analysis and systematic error determination are described and the results are compared with extrapolations of experimental values and theoretical models.

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 newmass 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.

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.

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 238 U 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.

Highly charged radioactive ions can be stored for extended periods of time in storage rings which allows for precision measurements of their decay modes. The straightforward motivation for performing such studies is that fully ionised nuclei or few-electron ions can be viewed as clean quantum-mechanical systems, in which the interactions of the many electrons can be either excluded or treated precisely. Thus, the influence of the electron shell on the decay probability can be investigated. Another important motivation is stellar nucleosynthesis, which proceeds at high temperatures and the involved atoms are therefore highly ionised. Presented here is a compact review of the relevant experiments conducted at heavy-ion storage rings. Furthermore, we outline the perspectives for future experiments at new-generation storage-ring facilities.

A review and recent progress are presented from experiments on masses and lifetimes of bare and few-electron exotic nuclei at GSI. Relativistic rare isotopes produced via projectile fragmentation and fission were separated in flight by the fragment separator FRS and injected into the storage ring ESR. This worldwide unique experimental method gives access to all fragments with half-lives down to the microsecond range. The great research potential is demonstrated by the discovery of new isotopes along with simultaneous mass and lifetime measurements. Single particle decay measurements and the continuous recording of both stored mother and daughter nuclei open up a new era for nuclear spectroscopy. The study of bare and few-electron nuclei has also important astrophysical relevance with respect to the hot stellar conditions where reactions and decay are influenced by the degree of atomic ionization. The future international NUSTAR facility at FAIR consisting of a new large-acceptance in-flight separator (Super-FRS) and a dedicated storage ring system (CR–RESR–NESR) will be an ideal tool to study nuclei with new probes and to investigate the majority of relevant r- and rp-process nuclei which are not in reach with the present-day facilities.

Recently, much progress has been made with stored exotic nuclei at relativistic velocities ( v c = 0.7 ) . Fragments of 208Pb and 209Bi projectiles and fission products from 238U ions were produced, separated in flight with the fragment separator FRS, and injected into the storage-cooler ring ESR for precision measurements. 114 new masses of neutron-deficient isotopes in the lead region have been measured with time-resolved Schottky Mass Spectrometry (SMS). A new isospin dependence of the pairing energy was observed due to the improved mass accuracy of typically 1.5×10-7 (30 keV). New masses of short-lived neutron-rich fission fragments have been obtained with Isochronous Mass Spectrometry (IMS). An innovative field of spectroscopy has been opened up with lifetime measurements of stored bare and few-electron fragments after applying both stochastic and electron cooling.

A large area on the mass surface of neutron-deficient nuclides (36≤Z≤85) was measured with time-resolved Schottky mass spectrometry at the FRS-ESR facilities. The masses of 114 nuclides were obtained for the first time from which 43 were determined via known decay energies. The improved mass accuracy of 30 keV allowed to study the isospin dependence of nuclear pairing, to precisely locate the one-proton dripline for odd-Z isotopes from Tb to Pa and to make crucial tests of the predictive powers of modern mass models.

Recent progress in experiments with exotic nuclear beams at the SIS-FRS-ESR facility is summarized. New results on gross properties of exotic nuclei like binding energy, half-lives, and decay modes are presented. A brief outlook to future experiments is given.

The half-lives of isomeric states of fully ionized 144Tb, 149Dy and 151Er have been measured. These nuclides were produced via fragmentation of about 900 MeV/u 209Bi projectiles, separated in flight with the fragment separator (FRS) and stored in the cooler ring (ESR). The decay times of the cooled fragments have been measured with time-resolved Schottky spectrometry. We observed for the first time drastic increases of the half-lives of bare isomers by factors of up to 30 compared to their neutral counterparts. This is due to the exclusion of the strong internal conversion and electron-capture channels in the radioactive decay of these bare nuclei. The experimental results are in good agreement with theoretical calculations.

We present results from two methods of direct mass measurements of relativistic exotic nuclei stored in the storage ring ESR. Schottky Mass Spectrometry (SMS) with electron-cooled ions is well suited for long-lived nuclei ( T 1/2 ⩾10 s), and the Isochronous mass measurements (IMS) for hot fragments ( T 1/2 ⩾1 μs). In addition, SMS provides information on nuclear lifetime for bare and highly ionized atoms.

The masses of 64 short-lived neutron-deficient nuclides covering the element range from tungsten to uranium have been obtained for the first time. They have been evaluated by combining directly measured masses from Schottky mass spectrometry with linked experimental Q-values in α-decay chains. Based on these new mass data we have determined the one-proton and two-proton drip-lines as well as the size of the “littoral shallow” of the sea of instability. No evidence of a Thomas–Ehrman shift has been found in the region of the investigated heavy nuclides. A peculiar behavior of two-proton separation energies has been observed in the lead region. The predictive power of various mass models is investigated.

The Isochronous Mass Spectrometry (IMS) developed at GSI is a very efficient method for direct mass measurements of short-lived nuclides. By taking a recent IMS experiment as an example, the identification procedure of the Time-of-Flight (TOF) spectrum measured in this experiment is discussed.

Storage-ring mass spectrometry was applied to neutron-rich ${}^{197}$Au projectile fragments. Masses of ${}^{181,183}$Lu, ${}^{185,186}$Hf, ${}^{187,188}$Ta, ${}^{191}$W, and ${}^{192,193}$Re nuclei were measured for the first time. The uncertainty of previously known masses of ${}^{189,190}$W and ${}^{195}$Os 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.

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 the GSI 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 halflife >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 unrecognised, 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 de-excitation studies., published in PRL 110, 122502

The electron shakeoff probability of 6Li2+ ions resulting from the β- decay of 6He+ ions has been measured with high precision using a specially designed recoil ion spectrometer. This is the first measurement of a pure electron shakeoff following nuclear β decay, not affected by multielectron processes such as Auger cascades. In this ideal textbook case for the application of the sudden approximation, the experimental ionization probability was found to be Psoexp=0.023 39(36) in perfect agreement with simple quantum mechanical calculations.

International audience; The half-lives of fully ionized and hydrogen-like (H-like) I-122 ions have been measured in a heavy-ion storage ring. The beta(+)-decay constants for both charge states and the electron capture (EC) decay constant of H-like ions have been determined. The EC-decay constant in H-like I-122 ions lambda(H-like)(EC) = 7.35(33) . 10(-4) s(-1) is, within the uncertainty, the same as the one in neutral atoms. This result is in agreement with the estimates of recent theoretical considerations on the EC-decay of few-electron ions that explicitly take into account the conservation of the total angular momentum of the nucleus plus lepton(s) system and its projections. No firm confirmation could be concluded from our results on the predicted effect that allowed Gamow-Teller transitions become forbidden if the initial and final total angular momenta are not equal.

One of the major problems in nuclear astrophysics concerns the estimation of electron screening effects on nuclear reaction rates. We have proposed investigating the electron screening effects of nuclear systems which decay via α-particles, using fragmented beams at relativistic energies produced at the present GSI FRS-ESR facility. By looking at the modification of the half-lives and Q -value of highly charged emitters, we expect to estimate the electron screening energies. © 2012 The Royal Swedish Academy of Sciences.

Corrections to the ratio of electron capture (EC) rates in hydrogen- and helium-like ions are calculated. We find that the most significant contribution is the electron screening effect. The correction has a simple form (1 − 5/16Z)3(1 − δ3) which ranges from almost 50% in helium to 1% in heavier nuclei. We discuss also EC in helium-like ions accompanied by an emission of the remaining electron into the continuum, a new decay channel, for which we calculate the decay probability. It is a very exotic type of Auger electron emission.

The core-excited isomer in fully-ionized 133 Sb 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 238 U 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.

International audience; The [beta]+ 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.

Time-resolved Schottky mass spectrometry has been applied to uranium projectile fragments which yielded the mass value for the Hg-208 (Z=80, N=128) isotope. The mass excess value of ME=-13 265(31) keV has been obtained, which has been used to determine the proton-neutron interaction strength in Pb-210, as a double difference of atomic masses. The results show a dramatic variation of the strength for lead isotopes when crossing the N=126 neutron shell closure, thus confirming the empirical predictions that this interaction strength is sensitive to the overlap of the wave functions of the last valence neutrons and protons.

An open problem in Nuclear Astrophysics concerns the understanding of electron‐screening effects on nuclear reaction rates at stellar energies. In this framework, we have proposed to investigate the influence of the electron cloud on α‐decay by measuring Q‐values and α‐decay half‐lives of fully stripped, H‐like and He‐like ions. These kinds of measurements have been feasible just recently for highly‐charged radioactive nuclides by fragmentation of 238U at relativistic energies at the FRS‐ESR facility at GSI. In this way it is possible to produce, efficiently separate and store highly‐charged α‐emitters. Candidates for the proposed investigation were carefully selected and will be studied by using the Schottky Mass Spectroscopy technique. In order to establish a solid reference data set, lifetimes and Qα‐value measurements of the corresponding neutrals have been performed directly at the FRS, by implanting the separated ions into an active Silicon stopper.

The influence of the electron cloud on the $\ensuremath{\alpha}$ decay constant is estimated by using relativistic electron binding energies to be a few per mil with an uncertainty of about one per mil. A few nuclides are suggested for measuring this influence in a storage ring.

The orbital electron capture decay of hydrogen- and helium-like ions is analyzed theoretically. For the general case of allowed nuclear transitions, we calculate the ratio of the decay rate for a helium-like ion to the decay rate for a hydrogen-like ion. We demonstrate that in some cases the decay probability for a nucleus with a single bound electron can be larger than that for the same nucleus with two bound electrons. The possibilities of experimental verification of our predictions are briefly discussed.

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 N = 50 shell closure towards doubly-magic 78Ni is discussed.

We report on the first measurement of the {beta}{sup +} and orbital electron-capture decay rates of {sup 140}Pr nuclei with the simplest electron configurations: bare nuclei, hydrogenlike, and heliumlike ions. The measured electron-capture decay constant of hydrogenlike {sup 140}Pr{sup 58+} ions is about 50% larger than that of heliumlike {sup 140}Pr{sup 57+} ions. Moreover, {sup 140}Pr ions with one bound electron decay faster than neutral {sup 140}Pr{sup 0+} atoms with 59 electrons. To explain this peculiar observation one has to take into account the conservation of the total angular momentum, since only particular spin orientations of the nucleus and of the captured electron can contribute to the allowed decay.

The combination of the in‐flight separator FRS and the storage‐ring ESR at GSI offers unique possibilities for high accuracy mass and lifetime measurements of bare and few‐electron fragments. Operating the ESR in the isochronous mode allows for measurements of revolution frequencies of stored ions without cooling. Isochronous Mass Spectrometry (IMS) can be applied to fragments with half‐lives as short as several tens of microseconds. Newly developed magnetic rigidity tagging increases the resolving power of IMS to about 500000. IMS can be used to measure masses of nuclei with rates even lower than one ion per day, a property also needed for the purpose of the ILIMA project at the future facility FAIR.

High accuracy mass and lifetime measurements are performed with the combination of the in-flight separator FRS and the cooler-storage ring ESR at GSI. Exotic nuclei are produced via projectile fragmentation and fission at (400–900) MeV/u. This energy range is the basis for unique experimental conditions with bare and few-electron fragments and allows for the first time investigations for decay channels which are rare or strictly forbidden in neutral atoms. New experimental developments and data including the discovery of new isotopes are presented. The comparison of the experimental results with theoretical predictions indicates the potential for improvements of nuclear models. A new generation of experiments will be possible with the advent of the proposed international Facility for Antiproton and Ion Research (FAIR).

C. SCHEIDENBERGERl, J. STADLMANN', M. STECK', D. VIEIRA5, G. VOROBJEV1i2, H. WEICK', M. WINKLER114, H. WOLLNIK4 AND T. YAMAGUCHII3 ' GSI, Darmstadt, Germany; 2PNPI, Gatchina, Russia; 3St. Petersburg State University, Russia; Justus Liebig University Giessen, Germany; Los Alamos National Laboratory, USA; Institute of Nuclear Chemistry, University Mainz, Germany €4 VISTARS; 'Institute of Physics, University Mainz, Germany; Niigata University, Japan; ' Faculty of Physics and Astronomy, University of Heidelberg, Germany; lo INS, Warsaw, Poland; "NSCL, MSU, East Lansing, USA; l2 Joint Institute for Nuclear Astrophysics; 13Saitama University, Japan c. KOZHUHAROV~, K.-L. KRATZ~ , s. LITVINOV~, YU. LITVINOV~

Two complementary mass measurement techniques have been developed utilizing the combination of Fragment Separator (FRS) [1] and Experimental Storage Ring (ESR) [2] at GSI. In both methods relativistic exotic nuclei are produced via projectile fragmentation (or fission), are separated by the FRS and are injected and stored in the ESR.

Projectile fragments of a 209Bi beam were separated in flight with the fragment separator FRS and injected into the experimental storage ring ESR. In the ESR a beam containing up to about 100 different isotopes was cooled to a relative velocity spread of δυ/υ = 10 by means of the electron cooler. The image currents of the ions induced in a Schottky pick-up probe at each turn were recorded. A subsequent Fast Fourier Transformation of these signals yields the revolution frequencies of the different isotopes stored in the ESR. Unknown masses of more than 150 neutron-deficient nuclides in the element range of 52 ≤ Z ≤ 85 have been measured directly by Schottky Mass Spectrometry and in addition more than 60 new masses have been obtained from α-decay chains. These new mass data allow the location of the one-proton dripline and the prediction of the two-proton dripline for heavy nuclides. The experimental masses are compared with different theoretical predictions.

SHIPTRAP will allow direct measurement of masses of transuranium nuclides. The method of choice is a Penning trap spectrometer coupled to the SHIP (Separator for Heavy Ion Products) facility at GSI, Darmstadt. In this paper the impact of the SHIPTRAP facility, with its capability of systematic mass measurements with high precision, is explored. Rather few masses of nuclides above uranium are presently known experimentally. In the region of nuclides above Z = 100 no ground state masses were measured directly. SHIPTRAP will play an important role in systematically mapping out this area. Possible candidates for direct mass measurements, even with small or very small production cross sections, are presented.

Schottky Mass Spectrometry turned out to be an excellent tool for systematic nuclear mass measurements. The newly developed data acquisition system [1] which yields several advantages for the data analysis, was used for the first time in Nov. 1997. Instead of online Fourier transformation as in former measurements [2,3] the signal is now digitized with a sampling rate of 640 kHz (16 bits of resolution) and stored as time-captures. With a continuous data rate of 1.2MB/s nearly 1TB of raw data were stored. The Fast Fourier Transformation offline analysis allows the study of the dynamical behavior of the stored ions in the ESR including cooling forces and decay. The new spectra contain enough reference nuclei to determine the deviations from the constant momentum compaction factor αp.

Beams of relativistic exotic nuclei were produced, separated and investigated with the combination of the fragment separator FRS and the storage ring ESR. The following experiments are presented: 1) Direct mass measurements of relativistic nickel and bismuth projectile fragments were performed using Schottky spectrometry. Applying electron cooling, the relative velocity spread of the circulating secondary nuclear beams of low intensity was reduced to below 10−6. The achieved mass resolving power of m/Δm=6.5⋅105 (FWHM) in recent measurements represents an improvement by a factor of two compared to our previous experiments. The previously unknown masses of more than 100 proton-rich isotopes have been measured in the range of 54⩽Z⩽84. The results are compared with mass models and estimated values based on extrapolations of experimental values. 2) Exotic nuclei with half-lives shorter than the time required for electron cooling can be investigated by time-of-flight measurements with the ESR being operated in ...