Search

Isotopic distributions were measured for the light fragment group in the transition region from asymmetric to symmetric fission for thermal neutron induced fission of $^{239}\mathrm{Pu}$ and $^{241}\mathrm{Pu}$ using the novel technology of calorimetric low temperature detectors in combination with the passive absorber method. Nuclear charge distributions were determined for 24 masses in the range $A=89$ to $A=112$ for $^{241}\mathrm{Pu}({n}_{\mathrm{th}},f)$ for the first time with the LOHENGRIN mass spectrometer. Moving from asymmetric to symmetric fission, known data were supplemented for masses from $A=110$ to $A=112$ for $^{241}\mathrm{Pu}({n}_{\mathrm{th}},f)$ and from $A=109$ to $A=113$ for $^{239}\mathrm{Pu}({n}_{\mathrm{th}},f)$. The isotopic yields were used to evaluate the charge polarization $\mathrm{\ensuremath{\Delta}}Z$ and the proton odd-even effect $\ensuremath{\delta}p$ with emphasis on the borderline between asymmetric and symmetric fission. This highlighted a virtual shell effect near $Z=44$ which mirrors the effect of the $Z=50$ shell in the complementary heavy fragment group of the two Pu isotopes $(Z=94)$ studied.

Differential cross sections for elastic $p\text{\ensuremath{-}}^{6}\mathrm{He}$ and $p\text{\ensuremath{-}}^{8}\mathrm{He}$ scattering, measured in inverse kinematics at high momentum transfer up to the first diffraction minimum and at projectile energies around 700 MeV/u at GSI Darmstadt, are analyzed applying the sum-of-Gaussians (SOG) method based on the Glauber multiple-scattering theory. The rms point matter radii of $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$ are deduced to be 2.29(6) fm and 2.53(7) fm, respectively, in close agreement with those from former analyses using phenomenological parametrizations for describing the matter distributions. With the aid of the measurement at high momentum transfer, the overall radial density distributions of $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$ are precisely deduced using the SOG method, in particular at small radii. A pronounced core rearrangement by adding the valence neutrons to an $\ensuremath{\alpha}$-like core to form $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$ is elucidated, and briefly discussed.

Physics letters / B 809, 135776 (2020). doi:10.1016/j.physletb.2020.135776, Published by Elsevier, Amsterdam

The momentum distribution of 11Be fragments produced by the breakup of 12Be interacting with a proton target at 700.5 MeV/u energy has been measured at GSI Darmstadt. To obtain the structure information on the anomaly of the N = 8 neutron shell, the momentum distribution of 11Be fragments from the one-neutron knockout Be 12 ( p , p n ) reaction, measured in inverse kinematics, has been analysed in the distorted wave impulse approximation (DWIA) based on a quasi-free scattering scenario. The DWIA analysis shows a surprisingly strong contribution of the neutron 0 d 5 / 2 orbital in 12Be to the transverse momentum distribution of the 11Be fragments. The single-neutron 0 d 5 / 2 spectroscopic factor deduced from the present knock-out data is 1.39(10), which is significantly larger than that deduced recently from data of 12Be breakup on a carbon target. This result provides a strong experimental evidence for the dominance of the neutron ν ( 0 d 5 / 2 ) 2 configuration in the ground state of 12Be.

A new experimental system for precise determination of electronic stopping powers of heavy ions has been set up at the accelerator laboratory of the University of Jyvaskyla. The new setup, combining an established B-ToF system and an array of calorimetric low temperature detectors (CLTDs), has been used for the determination of electronic stopping powers of 0.05–1 MeV/u 131Xe ions in carbon, nickel and gold. Thereby advantage of the improved linearity and energy resolution of CLTDs as compared to the previously used ionization detector was taken to reduce energy calibration errors and to increase sensitivity for the energy loss determination, in particular at very low energies. The total uncertainties of 3–4% for C- and Ni-targets, and 5–7% for Au-targets, respectively, are dominated by the target properties, i.e. thickness determination and inhomogeneities. The results are compared to data from literature and to predictions of different theoretical computer codes. In the high energy part of the examined energy range the results are in good agreement with previously published data, while new stopping power data for very heavy ions in different Z2-materials have been obtained at lower energies. Moreover, unexpectedly strong channeling effects for the transmission of the 131Xe ions in thin, partly polycrystalline nickel and gold target foils have been observed and investigated.

Physics letters / B 763, 16 - 19 (2016). doi:10.1016/j.physletb.2016.10.015, Published by North-Holland Publ., Amsterdam

The very first in-ring reaction experiment at the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR), namely proton elastic scattering on stable $^{58}\mathrm{Ni}$ nuclei, is presented. The circulating $^{58}\mathrm{Ni}^{19+}$ ions with an energy of 95 MeV/u were interacting repeatedly with an internal hydrogen gas target in the experimental storage ring (CSRe). Low-energy proton recoils from the elastic collisions were measured with an ultra-high vacuum compatible silicon-strip detector. Deduced differential cross sections were normalized by measuring $k$-shell x rays from $^{58}\mathrm{Ni}^{19+}$ projectiles due to the $^{58}\mathrm{Ni}^{19+}\text{\ensuremath{-}}{\mathrm{H}}_{2}$ ionization collisions. Compared to the experimental cross sections, a good agreement has been achieved with the theoretical predictions in the measured region, which were obtained by using the global phenomenological optical model potentials. Our results enable new research opportunities for optical model potential studies on exotic nuclides by using the in-ring reaction setup at the HIRFL-CSR facility.

The absolute differential cross sections for small-angle proton elastic scattering off the nuclei $^{12,14-17}$C have been measured in inverse kinematics at energies near 700 MeV/u at GSI Darmstadt. The hydrogen-filled ionization chamber IKAR served simultaneously as a gas target and a detector for the recoil protons. The projectile scattering angles were measured with multi-wire tracking detectors. The radial nuclear matter density distributions and the root-mean-square nuclear matter radii were deduced from the measured cross sections using the Glauber multiple-scattering theory. A possible neutron halo structure in $^{15}$C, $^{16}$C and $^{17}$C is discussed. The obtained data show evidence for a halo structure in the $^{15}$C nucleus.

Calorimetric low temperature detectors (CLTD’s) for heavy-ion detection have been combined with the LOHENGRIN recoil separator at the ILL Grenoble for the determination of nuclear charge distributions of fission fragments produced by thermal neutron-induced fission of $$^{235}$$ U. The LOHENGRIN spectrometer separates fission fragments according to their mass-to-ionic-charge ratio and their kinetic energy, but has no selectivity with respect to nuclear charges Z. For the separation of the nuclear charges, one can exploit the nuclear charge-dependent energy loss of the fragments passing through an energy degrader foil (absorber method). This separation requires detector systems with high energy resolution and negligible pulse height defect, as well as degrader foils which are optimized with respect to thickness, homogeneity, and energy loss straggling. In the present, contribution results of test measurements at the Maier Leibnitz tandem accelerator facility in Munich with $$^{109}$$ Ag and $$^{127}$$ I beams with the aim to determine the most suitable degrader material, as well as measurements at the Institut Laue–Langevin will be presented. These include a systematic study of the quality of Z-separation of fission fragments in the mass range $$82\le A \le 132$$ and a systematic measurement of $$^{92}$$ Rb fission yields, as well as investigations of fission yields toward the symmetry region.

X-ray spectroscopy on highly charged heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields. One limitation of the current accuracy of such experiments is the energy resolution of available X-ray detectors for energies up to 100 keV. To improve this accuracy, a novel detector concept, namely the concept of microcalorimeters, is exploited for this kind of measurements. The microcalorimeters used in the present experiments consist of silicon thermometers, ensuring a high dynamic range, and of absorbers made of high-Z material to provide high X-ray absorption efficiency. Recently, besides an earlier used detector, a new compact detector design, housed in a new dry cryostat equipped with a pulse tube cooler, was applied at a test beamtime at the experimental storage ring (ESR) of the GSI facility in Darmstadt. A U 89 + beam at 75 MeV/u and a 124 Xe 54 + beam at various beam energies, both interacting with an internal gas-jet target, were used in different cycles. This test was an important benchmark for designing a larger array with an improved lateral sensitivity and statistical accuracy.

The present paper describes the development of in-ring reaction measurements at the Cooler-Storage Ring of the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR). A Silicon (Si) detector has been developed with cost-efficient methods to meet the requirements of Ultra-High Vacuum (UHV) conditions in a storage ring. The UHV-Si detector and luminosity monitor Si(Li) detector were installed at the experimental cooler storage ring (CSRe). The pilot in-ring reaction experiment about proton elastic scattering on 58Ni 19 + ions has been operated successfully with the basic detector system in inverse kinematics , which opens an opportunity for in-ring reaction measurements at the HIRFL-CSR. This is an important step towards realizing in-ring reaction measurements with large Si detector arrays at the next generation High Intensity heavy ion Accelerator Facility (HIAF).

Physics letters / B 780, 200 - 204 (2018). doi:10.1016/j.physletb.2018.03.013, Published by North-Holland Publ., Amsterdam

Atoms 6(4), 59 - (2018). doi:10.3390/atoms6040059 special issue: "Perspectives of Atomic Physics with Trapped Highly Charged Ions)", Published by MDPI, Basel

A novel method for measuring nuclear reactions in inverse kinematics with stored ion beams was successfully used to extract the nuclear-matter radius of $^{58}\mathrm{Ni}$. The experiment was performed at the experimental heavy-ion storage ring at the GSI facility using a stored $^{58}\mathrm{Ni}$ beam at energies of 100 and 150 MeV/u and an internal helium gas-jet target. Elastically scattered $\ensuremath{\alpha}$-recoils at low momentum transfers were measured with an in-ring detector system compatible with ultrahigh vacuum. Experimental angular distributions were fitted using density-dependent optical model potentials within the eikonal approximation. This permitted the extraction of the point-matter root-mean-square radius of $^{58}\mathrm{Ni}$ with an average value of 3.70(7) fm. Results from this work are in good agreement with several experiments performed in the past in normal kinematics. This pioneering experiment demonstrates a major breakthrough towards future investigations with far-from-stability stored beams using the present technique.

Calorimetric low temperature detectors (CLTD’s) have been included in a B-ToF setup, that has already been used several times to perform energy loss measurements at the accelerator laboratory of the University of Jyvaskyla. The new experimental setup enabled a precise determination of stopping power data for 0.05–1 MeV/u $$^{131}$$ Xe ions in carbon, nickel and gold. The results are presented and compared to data from literature and theoretical predictions. As a by-product, due to the excellent energy resolution of CLTD’s for heavy ions at low energies, an observation of channeling effects in very thin polycrystalline targets and a determination of the channeling energy loss for 0.1–0.5 MeV/u $$^{131}$$ Xe-ions in Ni- and Au-absorbers was possible.

The precise determination of the transition energy of the Lyman- $$\alpha $$ 1 line in hydrogen-like heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields. We report the determination of the Lyman- $$\alpha $$ 1 transition energy of gold ions (Au $$^{78+}$$ ) with microcalorimeters at the experimental storage ring at GSI. X-rays produced by the interaction of 125 MeV/u Au $$^{79+}$$ ions with an internal argon gas-jet target were detected. The detector array consisted of 14 pixels with silicon thermistors and Sn absorbers, for which an energy resolution of 50 eV for an X-ray energy of 59.5 keV was obtained in the laboratory. The Lyman- $$\alpha $$ 1 transition energy was determined for each pixel in the laboratory frame, then transformed into the emitter frame and averaged. A Dy-159 source was used for energy calibration. The absolute positions of the detector pixels, which are needed for an accurate correction of the Doppler shift, were determined by topographic measurements and by scanning a collimated Am-241 source across the cryostat window. The energy of the Lyman- $$\alpha $$ 1 line in the emitter frame is $$E(Ly-\alpha 1,Au^{+78})=(71563 \pm 4_{stat} \pm 7_{syst})$$ eV, in good agreement with theoretical predictions. The systematic error is dominated by the uncertainty in the position of the cryostat relative to the interaction region of beam and target.

The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm (Abrahamsson et al. 1993) and at the Test Storage Ring (TSR) at Heidelberg (Baumann et al. 1988). For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum fur Schwerionenforschung (GSI) in Darmstadt (Franzke 1987) where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei (Xia et al. 2002).

The physics program at the super-conducting fragment separator (Super-FRS) at FAIR, being operated in a multiple-stage, high-resolution spectrometer mode, is discussed. The Super-FRS will produce, separate and transport radioactive beams at high energies up to 1.5 AGeV, and it can be also used as a stand-alone experimental device together with ancillary detectors. Various combinations of the magnetic sections of the Super-FRS can be operated in dispersive, achromatic or dispersion-matched spectrometer ion-optical modes, which allow measurements of momentum distributions of secondary-reaction products with high resolution and precision. A number of unique experiments in atomic, nuclear and hadron physics are suggested with the Super-FRS as a stand-alone device, in particular searches for new isotopes, studies of hyper-nuclei, delta-resonances in exotic nuclei and spectroscopy of atoms characterized by bound mesons. Rare decay modes like multiple-proton or neutron emission and the nuclear tensor force observed in high momentum regime can be also addressed. The in-flight radioactivity measurements as well as fusion, transfer and deep-inelastic reaction mechanisms with the slowed-down and energy-bunched fragment beams are proposed for the high-resolution and energy buncher modes at the Super-FRS. (C) 2016 Elsevier B.V. All rights reserved.

An array of calorimetric low temperature detectors (CLTD’s) for energy sensitive detection of heavy ions was combined with time-of-flight (TOF) detectors to obtain a detector system for high resolution mass identification of low energy heavy ions. In addition the same setup was used to prove the ability of CLTD’s to be used in electronic stopping power measurements for heavy ions in matter. Experiments with 50 MeV 63Cu and 65Cu ions at the tandem accelerator at the MPI at Heidelberg, and with 25 to 250 MeV 238U ions at the UNILAC accelerator at GSI at Darmstadt have been performed. For 63,65Cu at 50 MeV a mass resolution of Δm(FWHM)=0.9 amu, and for 238U in an energy range of 65 to 150 MeV a resolution of Δm(FWHM)=1.28 amu, was obtained. The results for stopping powers of 238U in carbon and gold are presented and compared with theoretical predictions and data from the literature.

We report on a new experimental setup for the investigation of proton induced reactions on exotic nuclei in inverse kinematics. It was installed and successfully used in the scattering study of intermediate-energy protons ( ∼ 700 MeV / u ) on neutron-rich nuclei 6,8He produced with the FRagment Separator (FRS) at the GSI facility, Darmstadt. A new pure liquid-hydrogen target was successfully adapted allowing to obtain low-background data as compared to commonly used (CH2)n targets. Absolute differential cross-sections for elastic (p,6,8He) scattering were obtained at angles corresponding to 0.05 ⩽ | t | ⩽ 0.125 (GeV/c)2 of the four-momentum transfer squared (−t) leading to the first diffraction minimum and spanning more than two orders of magnitude. They complement an earlier measurement at smaller angles 0.0025 ⩽ | t | ⩽ 0.05 (GeV/c)2 performed at the same energy with an active target. Both data sets agree well in the overlap region t ≈ 0.05 (GeV/c)2 and enable a refined and comparative study of the radial distribution of the nuclear matter density.

We have measured the nuclear-matter distribution of the doubly-magic N = Z nucleus Ni-56 by investigating elastic proton scattering in inverse kinematics. The radioactive beam of Ni-56 was injected and stored in the experimental storage ring (ESR, GSI) and interacted with an internal hydrogen gas-jet target. The high revolution frequency of the ions in the ring enabled a high luminosity, despite the low density of the target being used. This way, measurements at very low momentum transfers became possible. By measuring the energy and the scattering angle of the recoiling protons, we were able to separate the elastic reaction channel from inelastic scattering to the first excited 2(+) state of Ni-56 and deduced the differential cross section of Ni-56 (p, p)(56) Ni. The data were analyzed within the framework of the Glauber multiple-scattering theory in order to extract the nuclear-matter radius and radial matter distribution of Ni-56. Parameterizing the matter distribution with the phenomenological Symmetrized Fermi distribution, a preliminary value of 3.5 fm for the rms matter radius was deduced. This experiment was part of an EXL (EXotic nuclei studied in Light-ion induced reactions at storage rings) campaign at GSI in 2012 and was the first successful investigation of nuclear reactions with a stored radioactive beam ever.

In the first campaign of the exotic nuclei studied with light-ion induced reaction in storage rings (EXL) collaboration at the existing storage ring experimental heavy-ion storage ring (ESR) at Helmholtz Center for Heavy Ion Research (GSI), we performed the first experiments using a stored beam of 58Ni and an internal helium gas-jet target aiming for the investigation of isoscalar giant resonances in inverse kinematics. In this experiment, inelastically scattered recoil particles (at very forward angles, °) were detected with a dedicated setup, including ultra-high vacuum (UHV)-compatible double-sided silicon strip detector (DSSDs). Preliminary results show evidence for the excitation of the isoscalar giant monopole resonance (ISGMR) in the 58Ni nucleus. This opens the opportunity to study in the near future giant resonances also with stored radioactive beams, like 56Ni, and extract important information about the nuclear matter incompressibility. In the present work the current status of the data analysis and results are shown and discussed.

The Super-FRS at FAIR is a powerful superconducting in-flight separator and also a versatile high-resolution spectrometer system for exotic nuclei over a large energy range equivalent to a maximum magnetic rigidity of 20 Tm. In this contribution we present the physics program of the Super-FRS Collaboration. This program is partially based on the previous experimental results obtained with the FRS of GSI, but will also extend the research to directions not considered before.

The differential cross sections for small-angle proton elastic scattering on the 6,8,9,11 Li nuclei at energies near 700 MeV/nucleon were measured in inverse kinematics using secondary nuclear beams at GSI Darmstadt. The hydrogen-filled ionization chamber IKAR was employed as target and recoil proton detector. For determining the nuclear matter radii and radial matter distributions, the measured cross sections have been analysed with the aid of the Glauber multiple-scattering theory. The nuclear matter distribution deduced for 11 Li exhibits a very pronounced halo structure, the matter radius of 11 Li being significantly larger than those of the 6,8,9 Li isotopes. The data on 8,9 Li are consistent with the existence of sizable neutron skins in these nuclei. The obtained data allow for a test of various theoretical model calculations of the structure of the studied neutron-rich nuclei.

This paper presents the results of experimental investigations of ( p , p n ) , ( p , p α ) and ( p , p 6 He) reactions with relativistic 6 He and 8 He beams impinging on a hydrogen target. Information on the structure of extremely neutron-rich nuclei was obtained by using the unique characteristic of quasi-free scattering processes and inverse kinematics. For the first time, momentum distributions of complex clusters inside 6 He and 8 He were measured. Spectroscopic factors for valence neutrons, α - and 6 He clusters were deduced from the experimental data. They demonstrate that the filling of the p 1 2 shell is the essential feature of the 8 He structure. It is shown that the 8 He cluster structure can be considered as a 6 He core plus two valence neutrons.

Absolute differential cross sections for elastic p 4 He, p 6 He and p 8 He small-angle scattering were measured in inverse kinematics with secondary 4,6,8 He-beams at an energy near 0.7 GeV / u. The experiment was performed using beams from the heavy-ion synchrotron SIS and the fragment separator FRS of GSI Darmstadt. The hydrogen-filled ionization chamber IKAR served simultaneously as a gas target and a detector for the recoil protons. Projectile scattering angles were measured with multi-wire tracking detectors. For proton scattering from the neutron-rich isotopes 6 He and 8 He, differential elastic-scattering cross sections d σ/ d t were deduced in the range 0.002⩽|t|⩽0.05 (GeV /c ) 2 of the four-momentum transfer squared t . For elastic p 4 He scattering, the data obtained in the t -range 0.002⩽|t|⩽0.02 (GeV /c ) 2 supplement the results from an earlier work performed in direct kinematics. From the differential cross sections the integral elastic-scattering cross sections σ el , the total cross sections σ tot , and the total reaction cross sections σ r for the proton–nucleus strong interaction were evaluated. The data obtained on d σ/ d t allow the radial matter distributions in the 6 He and 8 He nuclei to be determined and the corresponding root-mean-square matter radii to be deduced.

A Glauber based analysis of the experimental cross sections for small-angle elastic p 6,8He scattering at 0.7 GeV has been performed. The radii and radial shape of the 6He and 8He nuclei have been determined using phenomenological nuclear density distributions with two free parameters. The deduced shapes of the 6He and 8He nuclear matter radial distributions conform with the concept that both nuclei consist of an α-particle core and a significant neutron halo. The accuracy of the theoretical analysis of the elastic-scattering cross-section data is discussed, and possible sources of systematic uncertainty related to some basic limitations in the applied method are outlined. The experimental p 6,8He elastic-scattering cross sections have also been utilized for probing the matter density distributions resulting from various nuclear microscopic models. Besides, the sensitivity of the total p 6,8He reaction cross sections to the size of the 6He and 8He nuclei has been considered.

Quantum electrodynamics in very strong Coulomb fields is one scope which has not yet been tested experimentally with suffcient accuracy to really determine whether the perturbative approach is valid. One sensitive test is the determination of the 1s Lamb Shift in highly-charged very heavy ions. The 1s Lamb Shift of hydrogen-like lead (Pb81+) and gold (Au78+) has been determined using the novel detector concept of silicon microcalorimeters for the detection of hard X-rays. The results of (260 +- 22) eV for lead and (208 +- 13) eV for gold are within error bars in good agreement with theoretical predictions. For hydrogen-like lead, this represents the most accurate determination of the 1s Lamb Shift to our knowledge., Comment: This paper has been withdrawn because some technical details need to be clarified

The investigation of light-ion induced direct reactions using stored and cooled radioactive beams, interacting with internal targets of storage rings, can lead to substantial advantages over external target experiments, in particular for direct reaction experiments in inverse kinematics at very low momentum transfer, q. This new and challenging experimental technique enables high-resolution measurements down to very low q and provides a gain in luminosity from accumulation and recirculation of the stored beams. For performing first experiments of this kind a dedicated experimental setup housing several DSSD (Double-sided Silicon Strip Detector) and Si(Li) detectors for recoil particles, well suited for meeting the demanding UHV (Ultra High Vacuum) conditions of a storage ring, was recently designed, constructed and installed at the internal target of the ESR storage ring at GSI. From the interaction of a stored 56Ni beam with an internal H2 target, good quality differential cross section data for elastic proton scattering, measured with the aim to determine the radial shape of the nuclear matter distribution of 56Ni, were obtained. Preliminary results are presented. Being the first reaction experiment ever performed with a stored radioactive beam on a world-wide scale, this experiment can be considered as a breakthrough for nuclear structure and astrophysics studies, and, in addition, as a successful proof-of-principle of the new experimental concept. In addition, preliminary results from a feasibility study on inelastic α-scattering from 58Ni in inverse kinematics, where it was demonstrated that the Isoscalar Giant Monopole Resonance in 58Ni can be investigated by the present technique down to CM angles below 1 degree, are discussed. Such an experiment, performed in the future with the doubly magic 56Ni, would provide important information on the EOS of nuclear matter.

The European physical journal / Web of Conferences 66, 03093 (2014). doi:10.1051/epjconf/20146603093, Published by EDP Sciences, Les Ulis

In the last two decades a number of nuclear structure and astrophysics experiments were performed at heavy-ion storage rings employing unique experimental conditions offered by such machines. Furthermore, building on the experience gained at the two facilities presently in operation, several new storage ring projects were launched worldwide. This contribution is intended to provide a brief review of the fast growing field of nuclear structure and astrophysics research at storage rings., XVIth International Conference on Electro-Magnetic Isotope Separators and Techniques Related to their Applications, December 2--7, 2012 at Matsue, Japan

The precise determination of the Lamb shift in heavy hydrogen-like ions provides a sensitive test of quantum electrodynamics in very strong Coulomb"elds, not accessible otherwise. For the investigation of the Lyman-a transitions in 208Pb81‘ or 238U91‘ with su$cient accuracy a high resolving calorimetric detector for hard X-rays (E)100 keV) is presently developed. The detector modules consist of arrays of silicon thermistors and of X-ray absorbers made of high Z material to optimize the absorption e$ciency. The detectors are housed in a specially designed 3He/4He dilution refrigerator with a side arm which "ts to the geometry of the internal target of the storage ring ESR at GSI Darmstadt. The detector performance presently achieved is already close to ful"ll the demands of the Lamb shift experiment. For a prototype detector pixel with a 0.3 mm2]66 lm Sn absorber an energy resolution of *E FWHM "75 eV is obtained for 60 keV X-rays. ( 2000 Elsevier Science B.V. All rights reserved. 1. Motivation The precise experimental test of the theoretical predictions of quantum electrodynamics (QED) on corrections to the classical Coulomb interaction potential is still } at least for high Z systems } one of the outstanding and most challenging problems of atomic physics. In the hydrogen atom, or in hydrogen like ions, the QED corrections give rise to the so-called Lamb shift, which is a small deviation of the binding energies from those predicted by the relativistic Dirac}Coulomb energy (see Fig. 1). Whereas in light systems, where QED

Nuclear matter and charge distributions, and the radii of light exotic nuclei have been calculated with the Dynamic Correlation Model and compared with those extracted from proton and electron scattering experiments.

The investigation of direct reactions with exotic beams in inverse kinematics gives access to a wide field of nuclear structure studies in the region far off stability. The basic concept and the methods involved are briefly discussed. The present contribution will focus on the investigation of light neutron-rich halo nuclei. Such nuclei reveal a new type of nuclear structure, namely an extended neutron distribution surrounding a nuclear core. An overview on this phenomenon, and on the various methods which gave first evidence and qualitative confirmation of our present picture of halo nuclei, is given. To obtain more quantitative information on the radial shape of halo nuclei, elastic proton scattering on neutron-rich light nuclei at intermediate energies was recently investigated for the first time. This method is demonstrated to be an effective means for studying the nuclear matter distributions of such nuclei. The results on the nuclear matter radii of 6He and 8He, the deduced nuclear matter density distributions, and the significance of the data on the halo structure is discussed. The present data allow also a sensitive test of theoretical model calculations on the structure of neutron-rich helium isotopes. A few examples are presented. The investigation of few-nucleon transfer reactions in inverse kinematics may provide new and complementary information on nuclear structure, as well as astrophysical questions. The physics motivation and the experimental concept for such experiments, to be performed due to momentum matching reasons at low incident energies around 5–20 MeV/u at the new generation low energy radioactive beam facilities SPIRAL, PIAFE, etc., is briefly discussed.

Calorimetric low-temperature detectors have been investigated for several applications in heavy ion physics within the last 15 years. The detectors used consist of sapphire absorbers of 2×3×0.33 mm 3 and superconducting aluminum transition edge sensors operated at T ≈1.5 K. To fully exploit the potential of such detectors for heavy ion physics, a detector array is developed. For this purpose, a specially adapted 4 He bath cryostat with a base temperature of 1.2 K, which allows an active detector area of 30×80 mm 2 , was constructed. As different detectors have different transition temperatures, each detector pixel has to be adjusted to its specific working point and temperature stabilized individually. First performance tests with a prototype array of two pixels have shown that the present concept can be used successfully also for larger arrays. In particular, the temperature stabilization of additional pixels does not affect the energy resolution. No cross talk between pixels was observed.

The energy sensitive detection of energetic heavy ions with calorimetric low temperature detectors is investigated. The temperature readout was done with an aluminum transition edge thermometer operated at T ≈ 1.5 K. For 20Ne-ions with an energy of E = 100 MeV/u from the SIS accelerator at GSI Darmstadt the best energy resolution obtained was ΔE E = 1.9 × 10 −3 . This value corresponds to the energy spread of the ion beam of the SIS. In a first application of such detectors the excitation of the giant resonance in lead nuclei via the reaction natPb(20Ne, 20Ne′)natPb∗ was investigated by separating inelastically from elastically scattered 20Ne-ions in the energy spectrum. At a scattering angle ΘLab = 3° the excitation energy and the strength of the giant resonance were found to be in good agreement with theoretical predictions. In a first test with an extracted cooled 238U-beam with an energy of E = 360 MeV/u from the storage ring ESR with an intrinsic beam energy spread of ΔE E ≤ 2 × 10 −4 an energy resolution of ΔE = 97 MeV ( ΔE E = 1.1 × 10 −3 ) was measured. The baseline noise was ΔE = 17 MeV. Further improvement of the energy resolution seems possible.

The energy resolution of calorimetric low-temperature detectors for heavy ions has been analyzed. It is shown that the contribution of base line noise is small. The energy resolution is determined by intrinsic fluctuations of the detector signal. An incomplete energy thermalization during the stopping process of the heavy ion, the dependence of signal shape on impact position and fluctuations of the Al-TES thermometer response are considered as main sources of detector line broadening. Test measurements with 5 MeV α-particles are presented.

21st International School on Nuclear Physics and Applications & the International Symposium on Exotic Nuclei, Varna, Bulgaria, 7 Sep 2015 - 12 Sep 2015; Journal of physics / Conference Series Conference Series 724(1), 012026 - (2016). doi:10.1088/1742-6596/724/1/012026, The EXL project aims to study nuclear structure by direct reactions in inverse kinematics at the storage rings of the future FAIR facility. In this contribution, we present the status of the project: the technical implementation at the ESR at GSI and preliminary results of the EXL campaign in 2012, the first using also a radioactive beam., Published by IOP Publ., Bristol

Nuclear matter distributions of the neutron-rich nuclei 6 He and 8 He were studied via proton-nucleus scattering in inverse kinematics using the recoil detector IKAR. The differential cross sections for p 4 He and p 8 He elastic scattering were measured with un uncertainty of ±2% for the absolute normalization for proton recoil energies from 1 to 20 MeV. The experimental techniques and the data analysis are described and first Glauber calculations presented. Data analysis is still in progress so only preliminary results are given.

Elastic and inelastic proton scattering to the first-excited 2+ state in the doubly-magic, unstable 56Ni nucleus has been investigated in inverse kinematics with a secondary 56Ni beam. At the SIS heavy ion synchrotron at GSI Darmstadt, the radioactive heavy-ion beam was produced via projectile fragmentation of a stable 58Ni beam and separated inflight, with a ΔE - TOF - Bρ-method, by the fragment separator FRS. For the transition between the 0+ groundstate and the first 2+ state a value B(E2) = 600 ± 120 e2 fm4 was derived, which corresponds to a deformation parameter β(56Ni) = 0.173 ± 0.017. This result completes the set of experimental data for the first-excited 2+ states of nuclei with magic neutron or proton number in the 1f2p-shell and provides a sensitive test for recent shell-model predictions in the region off stability. The 56Ni -data are well reproduced by these calculations based on 1 particle - 1 hole excitations in a truncated (1f7/2)h - (2p3/2, 1f5/2, 1p3/2)p model space.

We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report. ispartof: European Physical Journal. Special Topics vol:207 issue:1 pages:1-117 status: published

The electronion scattering experiment ELISe is part of the installations envisaged at the new experimental storage ring at the International Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany. It offers an unique opportunity to use electrons as probe in investigations of the structure of exotic nuclei. The conceptual design and the scientific challenges of ELISe are presented. © 2011 Elsevier B.V. All rights reserved., The authors acknowledge financial support from the EC via the INTAS pro- gramme, grants No. 03-54-6545 and 05-1000008-8272. This work was partially supported by the Hessian LOEWE initiative Helmholtz International Center for FAIR

Status and results of a research project are reported, which aims at developing calorimetric low temperature detectors of heavy ions. The special conditions for the detection of energetic heavy ions are discussed. The response of an aluminium transition edge calorimeter, operated at about 1.5K, to the impact of heavy ions was investigated. The observed energy resolutions [Delta]E/E = 3.9 x 10[sup [minus]3] for 5.9 MeV/u [sup 208]Pb-ions, [Delta]E/E = 1.6 x 10[sup [minus]3] for 4.8 MeV/u [sup 58]Ni-ions and [Delta]E/E = 4.3 x 10[sup [minus]3] for 100 MeV/u [sup 20]Ne-ions are most probably not yet limited by the intrinsic detector resolution. The present results already represent an improvement over conventional solid state detectors and ionization chambers.