Storage-cooler Ring ESR Research Articles

Recent Precision Experiments with Exotic Nuclei Produced with Uranium Projectiles and Experimental Prospects at Fair

Precision experiments with relativistic fragments separated in-flight require special ex- perimental methods to overcome the inherent large emittance from the creation in nuclear reactions and atomic interactions in matter. At GSI relativistic exotic nuclei have been produced via uranium projectile fragmentation and fission and investigated with the in- flight separator FRS directly, or in combination with either the storage-cooler ring ESR or the FRS Ion Catcher. 1000 AMeV 238 U ions were used to create 60 new neutron-rich isotopes separated and identified with the FRS to measure their production cross sections. In another experimental campaign the fragments were separated in flight and injected into the storage-cooler ring ESR for accurate mass and lifetime measurements. In these exper- iments we have obtained accurate new mass values analyzed via a novel method which has reduced the systematic errors for both Schottky Mass Spectrometry (SMS) and for Isochronous Mass Spectrometry (IMS). Pioneering experiments have been carried out with the FRS Ion Catcher consisting of three experimental components, the dispersive magnetic system of the FRS with a monoenergetic and a homogeneous degrader, a cryo- genic stopping cell filled with pure helium and a multiple-reflection time-of flight mass separator. The FRS Ion Catcher enables high precision spectroscopy experiments with eV to keV exotic nuclides. Results from these different FRS experiments are presented in this overview together with prospects for the next-generation facility Super-FRS. The novel features of the Super-FRS compared with the present FRS will be discussed in addition.

New results on mass measurements of stored neutron-rich nuclides in the element range from Pt to U with the FRS-ESR facility at

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.

Discovery and investigation of heavy neutron-rich isotopes with time-resolved Schottky spectrometry in the element range from thallium to actinium

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.

Observation of non-exponential orbital electron-capture decay of stored hydrogen-like ions

In experiments conducted recently at the ion storage-cooler ring ESR of the GSI Helmholtzzentrum, Darmstadt, the two-body orbital electron-capture (EC) decay of stored and cooled hydrogen-like 140Pr and 142Pm ions has been investigated. On top of the exponential decay, periodic modulations with a period T = 7 s and an amplitude A = 0.2 were found for both systems. Tentatively these observations were explained as a kind of “quantum beats”, due to the fact that the electron neutrino, generated in these strict two-body decays, is a flavor—but neither a mass- nor energy- nor momentum-eigenstate. This interpretation has raised many objections. In order to discuss them reasonably, the first section of this paper after the introduction aims for a precise description of the experimental technique and the observables revealed in our experiments. It will be proven that many of the objections are entirely irrelevant, because they are based on a misinterpretation of our experiments and, in particular, of the observables addressed there. In the last section, the actual experimental status will be summarized, including preliminary results of the EC decay of hydrogen-like 122I ions. An outlook is presented on forthcoming experiments which could corroborate or disprove our observations and their explanation.

Experiments with the FRS facility at GSI

Exotic nuclear beams produced via projectile fragmentation and fission at relativistic energies (400–1500MeV/u) are separated in flight with the FRS. Experiments are performed in three separator branches: directly at the FRS, in combination with the storage-cooler ring ESR, and with the ALADIN-LAND reaction setup. The FRS has been successfully used as a powerful separator and also as a versatile high-resolution magnetic spectrometer. Novel technical developments are recently installed in the FRS motivated by the experimental program and by the increasing projectile intensity of the driver accelerators. In this contribution, we give an overview on the recent experimental program at the FRS with the emphasis on experiments with stored and cooled rare isotopes performed in the FRS Ring Branch.

Direct mass measurements of neutron-deficient 152Sm projectile fragments at the FRS-ESR facility

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.

Beta decay of highly charged ions

Ion storage rings and ion traps provide the very first opportunity to address nuclear beta decay under conditions prevailing in hot stellar plasmas during nucleosynthesis, i.e. at high atomic charge states. Experiments are summarized that were performed in this field during the last decade at the ion storage-cooler ring ESR in Darmstadt. Special emphasis is given to the first observation of bound-state beta decay, where the created electron remains bound in an inner orbital of the daughter atom. The impact of this specific ‘stellar’ decay mode for s-process nucleosynthesis as well as for nuclear ‘eon clocks’ is outlined. Finally, a new technique, single-ion decay spectroscopy, is presented, where one observes two-body beta decay characteristics (i.e. orbital electron capture or bound-state beta decay) of highly charged, single ions for well-defined nuclear and atomic quantum states of both the mother – and the daughter – ion.

Precision experiments with relativistic exotic nuclei at GSI

Exotic nuclei generated via projectile fragmentation and fission are characterized by a large phase-space population. Thus precision experiments based on kinematical observables are difficult and require special methods. The experiments described in this contribution are based on special ion-optical spectrometer modes or on phase-space reduction via cooling of stored ions. The studies are performed with the projectile fragment separator FRS and the storage-cooler ring ESR at GSI.

New results with stored exotic nuclei at relativistic energies

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.

Particle detectors for beam diagnosis and for experiments with stable and radioactive ions in the storage-cooler ring ESR

A survey of the 12 available detector positions and of their applications is given. Emphasis is on the new pneumatic linear drives with accelerator controlled positioning and on new detectors for the positions dedicated to experiments.

Present and future experiments with stored exotic nuclei at relativistic energies

Pioneering experiments with stored and cooled exotic nuclei at relativistic energies have been performed using the combination of the fragment separator FRS with the storage-cooler ring ESR. Exotic nuclei created in peripheral collisions are spatially separated in-flight and injected into the storage ring for high-precision mass and unique lifetime measurements. Lifetimes of stored bare and few-electron nuclei have been measured to study the influence of the electron density on the β decay. This condition, relevant for stellar plasma, can now be systematically investigated in the laboratory for the first time. Characteristic experiments of the present FRS-ESR system are presented and perspectives for a next-generation facility are briefly outlined.

Physics with Stored Exotic Nuclei at GSI

We discuss some key experiments with relativistic exotic nuclei which have been performed with the fragment separator FRS and storage-cooler ring ESR. Although the present facility has contributed much to the progress in the field of nuclear structure physics major improvements are possible in the future. The realization of the proposed next-generation facility at GSI will open up new fields of outstanding research and will simultaneously excess unknown regions of nuclei with new properties.

Bound-state beta decay and nuclear lifetime measurements at the storage-cooler ring ESR

Strong effects on nuclear half-lives have been observed due to stripping the nucleus of all its atomic electrons: For the 52Fe nucleus the electron-capture branch was switched off completely, and the eight-hours half-life increased by about 50%. For bare 163Dy and 187Re ions the empty K shells enabled β − decay into these atomic orbits (bound-state β decay) with half-lives of 48 ± 3 d or 32.9 ± 2.0 yr, respectively, while in the corresponding neutral atoms the nuclei are stable ( 163Dy) or live 10 9 times longer ( 187Re). This half-life reduction for the latter nucleus may have implications on the 187 Re 187 Os galactic-chronometer. Different methods are presented that use a storage ring to measure nuclear half-lives in the range from seconds to years. These techniques are based either on counting the daughter nuclei after magnetic separation from the stored mother nuclei or on measuring revolution frequencies and beam intensities of cooled beams by Schottky-noise analysis.

Experiments with relativistic exotic nuclei at the FRS-ESR facilities

The status and the upgrade of the secondary nuclear beam facility FRS at GSI are outlined. Besides its main task to provide monoisotopic spatially separated fragment beams, the FRS has been successfully used as a high-resolution energy-loss spectrometer. Precise momentum measurements contribute to the study of neutron-halo nuclei and lead to the identification of the extended proton distribution in the 8B nucleus. First experiments with stored radioactive beams on direct mass and lifetime measurements of fully ionized atoms are presented. Measurements were performed with relativistic Ni, Au, and Bi projectile fragments separated by the FRS and injected into the storage-cooler ring ESR. For the first time the mass difference of ground and isomeric states for cooled secondary beams has been measured. About 37 new masses have been measured for a large region of elements 52≤Z≤85 using Schottky spectrometry. The accuracy was about (50 – 200) keV and the resolving power 4.7·10 5. Lifetimes of stored and cooled bare nuclei have been measured to study the influence of the atomic charge states on the β decay.

First experiments at the Darmstadt storage-cooler ring ESR

A survey is presented of the activities taking place at the heavy-ion storage-cooler ring (ESR) in Darmstadt which has now been in service for one year. The first experiments conducted during the ring commissioning are presented. Special attention is given to the results of the electron cooling of stored bare Ne, Ar, and Kr ions. The fact that the momentum spread Δp/ p and emittance ϵ of the stored ions can be reduced to Δp p ≈ 10 −5 and ϵ ≈ 0.1 π mm mrad, respectively, opens the way for new and experiments in fields such as precision atomic spectroscopy, nuclear reactions and the spectroscopy of radioactive nuclei.