GSI Darmstadt Research Articles

Radiation damage in single crystal CVD diamond material investigated with a high current relativistic 197Au beam

Single-crystal Chemical Vapor Deposition (ScCVD) diamond based prototype detectors have been constructed for the high intensity heavy ion experiments HADES and CBM at the future FAIR facility at GSI Darmstadt. Their properties have been studied with a high current density beam (about 2–3×106/s/mm2) of 1.25AGeV Au69+197 ions. Details of the design, the intrinsic properties of the detectors and their performance after irradiation with such a beam are reported.

Deep Inelastic Transfer Reactions – A New Way to Exotic Nuclei?

We studied deep inelastic multinucleon transfer reactions in collisions of 64Ni+207Pb and 48Ca+238U at energies around the Coulomb barrier. The experiments were performed at the velocity filter SHIP at GSI Darmstadt. One of the goals was to investigate if deep inelastic transfer is superior to fragmentation reactions for producing neutron-rich isotopes in the astrophysically interesting region of nuclei along the magic neutron number N = 126. With both collision systems, rather neutron-rich transfer products were populated, some of them reaching out to the limits of the present chart of nuclides. New isotopes could not be identified. A comparison of the measured transfer cross-sections and yields with those from fragmentation reactions allowed for interesting conclusions.

Proton-induced fission of181Ta at high excitation energies

Total fission cross sections of ${}^{181}$Ta induced by protons at different relativistic energies have been measured at GSI Darmstadt using the inverse kinematic technique. These data contribute to solve inconsistencies in previously reported measurements, but also help to benchmark state-of-the-art reaction codes. The energy range covered with these measurements allowed us to investigate the onset and temperature dependence of dissipative and transient effects at small deformation.

Decay of201–203Raand200–202Fr

Decay properties of the neutron-deficient nuclides ${}^{201--203}\mathrm{Ra}$ and ${}^{200--202}\mathrm{Fr}$ were investigated using $\ensuremath{\alpha}$- and $\ensuremath{\gamma}$-decay spectroscopy. The nuclei were produced in fusion-evaporation reactions of ${}^{56}$Fe projectiles with enriched ${}^{147}$Sm and ${}^{149}$Sm targets at the velocity filter SHIP at GSI in Darmstadt (Germany). The $\ensuremath{\alpha}$ decay from the (3/2${}^{\ensuremath{-}}$) state in ${}^{201}$Ra was identified with an energy ${E}_{\ensuremath{\alpha}}=7842(12)$ keV and half-life ${T}_{1/2}={8}_{\ensuremath{-}4}^{+40}$ ms. Ambiguous decay properties for ${}^{202}$Ra from previous measurements were clarified by remeasuring with significantly improved precision, resulting in values of ${E}_{\ensuremath{\alpha}}=7722(7)$ keV and ${T}_{1/2}=3.{8}_{\ensuremath{-}0.8}^{+1.3}$ ms. New short-lived isomeric states were identified in ${}^{200}$Fr and ${}^{201}$Fr with half-lives of 0.6${}_{\ensuremath{-}0.2}^{+0.5}$ $\ensuremath{\mu}$s and 0.7${}_{\ensuremath{-}0.2}^{+0.5}$ $\ensuremath{\mu}$s, respectively. A tentative spin and parity of 13/2${}^{+}$ were assigned to the latter. One event attributed to $\ensuremath{\beta}$-delayed fission of ${}^{200}$Fr was observed.

48Ca+249Bk fusion reaction leading to element Z = 117: long-lived α-decaying 270Db and discovery of 266Lr.

The superheavy element with atomic number Z=117 was produced as an evaporation residue in the (48)Ca+(249)Bk fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their α-decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub-μs and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope (294)117 and its decay products. A hitherto unknown α-decay branch in (270)Db (Z = 105) was observed, which populated the new isotope (266)Lr (Z = 103). The identification of the long-lived (T(1/2) = 1.0(-0.4)(+1.9) h) α-emitter (270)Db marks an important step towards the observation of even more long-lived nuclei of superheavy elements located on an "island of stability."

Perspectives for low energy antiproton physics at FAIR

The CRYRING accelerator, previously located at the Manne Siegbahn Laboratory of Stockholm University, has been chosen by the FLAIR collaboration as the central accelerator for the planned facility. It has been modified to allow for high-energy injection and extraction and is capable of providing fast and slow extracted beams of antiprotons and highly charged ions. It is currently being installed at the ESR of GSI Darmstadt where it can be used with highly charged ions. The future possibilities for its use with slow antiprotons will be discussed.

Forward scintillation hodoscope for nuclear fragment detection at the high acceptance dielectron spectrometer (HADES) setup

The main characteristics of the forward scintillation hodoscope and readout electronics of the high acceptance dielectron spectrometer (HADES) at GSI (Darmstadt, Germany) are presented. Methods for adjustment and amplitude-time calibration of hodoscope detectors using cosmic rays and results of measurements of the Au + Au reaction at a beam energy of 1.24 GeV/nucleon are described. The use of the forward hodoscope for tagging the n + p reaction by means of the deuteron beam incident on a liquid hydrogen target is discussed. A procedure for determining the reaction plane angle in event-by-event analysis of the Au + Au reaction data (at 1.24 GeV/nucleon) is presented.

Electrophysiologic and molecular characteristics of cardiomyocytes after heavy ion irradiation in the frame of the ESA IBER-10 program

Since essentially no information is available on the effects of high linear energy transfer (LET) radiation on the heart, an assessment of possible late effects on the cardiovascular system is important with respect to the planning of manned long-term space missions [ 1, 2]. In order to examine if and to what extent heart muscle cells are affected by an exposure to heavy ions, primary avian cardiomyocytes were isolated, cultured in vitro and exposed at GSI (Darmstadt) to different ion species (carbon, titanium and nickel). Investigation of electrophysiologic radiation effects was performed on cells grown on a microelectrode array (MEA) allowing the monitoring of beat rate, spike shape, field action potential duration and signal conduction pathways across the electrode array. Data were analysed using the DrCell software [ 3]. In parallel, immunohistological stainings were conducted to examine cell cycle progression, DNA-damage repair and apoptosis.Our preliminary data indicate that primary cardiac cells possess a high robustness toward ionizing radiation as cultures receiving doses of up to 7 Gy still show unaltered electrophysiologic activity. This is exemplarily shown in Fig. 1, where the beat rate of cells irradiated with 2 and 7 Gy carbon ions has been plotted. Figure 1 also illustrates that within each treatment group, inter-sample variations are quite large and thus do not allow detection of subtle changes in cellular electrophysiology, probably due to the embryonic character of the cells.Interestingly, in terms of the formation of double-strand breaks (DSBs) and cell cycle progression delay, the cultures showed a dose-dependent reduction in proliferation and DSB accumulation.Taken together, our electrophysiologic studies indicate that the large variations within the same treatment group of avian embryonic cardiomyocytes obscure the detection of radiation effects. To account for this problem, we will use in further studies human cardiomyocytes differentiated from iPS cells, as these cells resemble more closely the condition of an adult human heart and do not undergo developmental changes as embryonic cell cultures do. Fig. 1.Normalized beat rates measured in samples before and after exposure to carbon ions. (spread-out Bragg peak, LET: 75 keV/µm). Average beat rates range from 22 to 53 beats/min.

The proton injector for the accelerator facility of antiproton and ion research (FAIR)

The new international accelerator facility for antiproton and ion research (FAIR) at GSI in Darmstadt, Germany, is one of the largest research projects worldwide and will provide an antiproton production rate of 7 × 10(10) cooled pbars per hour. This is equivalent to a primary proton beam current of 2 × 10(16) protons per hour. For this request a high intensity proton linac (p-linac) will be built with an operating rf-frequency of 325 MHz to accelerate a 35 mA proton beam at 70 MeV, using conducting crossed-bar H-cavities. The repetition rate is 4 Hz with beam pulse length of 36 μs. The microwave ion source and low energy beam transport developed within a joint French-German collaboration GSI/CEA-SACLAY will serve as an injector of the compact proton linac. The 2.45 GHz ion source allows high brightness ion beams at an energy of 95 keV and will deliver a proton beam current of 100 mA at the entrance of the radio frequency quadrupole (RFQ) within an acceptance of 0.3π mm mrad (norm., rms).

THE SIMULATION OF AN IMAGING GAMMA-RAY COMPTON BACKSCATTERING DEVICE USING GEANT4

A gamma-backscattering imaging device dubbed Compton Camera, developed at GSI (Darmstadt, Germany) and modified and studied at the Nuclear Physics Group of the National University of Colombia in Bogotá, uses the back-to-back emission of two gamma rays in the positron annihilation to construct a bidimensional image that represents the distribution of matter in the field-of-view of the camera. This imaging capability can be used in a host of different situations, for example, to identify and study deposition and structural defects, and to help locating concealed objects, to name just two cases. In order to increase the understanding of the response of the Compton Camera and, in particular, its image formation process, and to assist in the data analysis, a simulation of the camera was developed using the GEANT4 simulation toolkit. In this work, the images resulting from different experimental conditions are shown. The simulated images and their comparison with the experimental ones already suggest methods to improve the present experimental device

Nuclear Structure of the Heaviest Elements – Investigated at SHIP-GSI

The quest for the heaviest nuclei that can exist is a basic topic in natural science as their stability is characterized by a delicate interplay of short range nuclear forces acting between the nucleons (protons and neutrons) and long-range Coulomb forces acting solely between charged particles, i.e. the protons. As the stability of a nucleus is strongly correlated to its structure, understanding the nuclear structure of heaviest nuclei is presently a main challenge of experimental and theoretical investigations concerning the field of Superheavy Elements. At the velocity filter SHIP at GSI Darmstadt an extensive program on nuclear structure investigations has been started about a decade ago. The project covered both as well systematic investigations of single particle levels in odd-mass isotopes populated by α-decay as investigation of two- or fourquasi-particle states forming K isomers and was supplemented by direct mass measurements at SHIPTRAP and investigation of spontaneous fission properties. Recent experimental studies allowed to extend the systematics of low lying levels in N = 151 and N = 153 up to 255Rf and 259Sg, investigation of possible relations between nuclear structure and fission properties of odd-mass nuclei and investigation of shell strengths at N = 152 and towards N = 162.

Perspectives for laser spectroscopy of the element nobelium

Strong efforts are undertaken at GSI in Darmstadt preparing for laser spectroscopy of the synthetic element nobelium. Several excimer- and dye lasers will be used in the forthcoming search for the $^1$P$_1$ -level in 254No. Based on the highly-efficient Radiation Detected Resonance Ionization Spectroscopy (RADRIS) technique, the identification of this excited state predicted around 3.8 eV becomes possible within a relatively short period of beam-time. This will form the basis for future studies of the atomic structure of the heaviest elements.

Experimental study of nuclear fragmentation of 200 and 400 MeV/u 12C ions in water for applications in particle therapy

Carbon ion beams in the energy range of about 100–450 MeV/u offer excellent conditions for tumour therapy, in particular for the treatment of deep-seated radio-resistant tumours. Their depth-dose distribution is characterized by a low dose in the entrance channel, small lateral beam spread and an elevated biological effectiveness in the Bragg peak region. In comparison to protons the radiation field of heavier ions stopping in tissue is however more complex due to nuclear fragmentation reactions occurring along their stopping path. This results in an attenuation of the primary beam flux and a build-up of lower-Z fragments with longer ranges causing the characteristic dose tail beyond the Bragg peak. In the present work the characteristics of secondary charged particles at various depths of water were investigated experimentally using 12C ion beams of 200 and 400 MeV/u delivered by the heavy-ion synchrotron SIS-18 at GSI Darmstadt. The nuclear charge Zf of secondary fragments was identified by combining energy loss and time-of-flight (TOF) measurements. Energy spectra and yields were recorded at lab angles of 0° – 10° and at seven different water depths corresponding to the entrance channel, the Bragg peak region and the tail of the Bragg curve.

Average charge states of heavy and superheavy ions passing through a rarified gas: Theory and experiment

The average charge states $\overline{q}$ of heavy and superheavy ions (atomic numbers $Z=80$--114) passing through He gas are studied experimentally and theoretically. Experimental data were measured at the gas-filled recoil separator, i.e., the TransActinide Separator and Chemistry Apparatus (TASCA) at GSI Darmstadt, for ion energies of a few hundred keV/u at gas pressures of 0.2 to 2.0 mbar. An attempt is made to describe experimental $\overline{q}$ values by means of atomic calculations of the binding energies and electron-loss and electron-capture cross sections. The influence of the gas-density effect is included in the calculations. The calculated $\overline{q}$ reproduce the experimental values for elements with $Z=80$--114 within 20%. A comparison with different semiempirical models is presented as well, including a local fit of high accuracy, which is often used in superheavy-element experiments to estimate the average charge states of heavy ions, e.g., at the gas-filled recoil separator TASCA. The $\overline{q}$ values for elements with $Z=115$, 117, 119, and 120 at He-gas pressure of 0.8 mbar are predicted.

A study of radiative double electron capture in bare chromium ions at the ESR

Radiative double electron capture is a fundamental atomic process which should be observed in collisions of bare ions with atoms, albeit with a much smaller cross-section than single radiative electron capture. A new experiment—to observe this rare process under single-collision conditions—has been performed at the internal gas jet target of the experimental storage ring at GSI in Darmstadt. X-ray spectra associated with single and double charge exchange have been observed in 30 MeV u−1 collisions of bare chromium ions (Cr24+) with helium and nitrogen target gases.

A beamline for x-ray laser spectroscopy at the experimental storage ring at GSI

By combining an x-ray laser (XRL) with a heavy-ion storage ring, precision laser spectroscopy of the fine-structure splitting in heavy Li-like ions will be possible. An initial study has been performed to determine the feasibility of a first experiment at the experimental storage ring at GSI in Darmstadt, which also has great potential for the experiments planned for FAIR. We plan to perform a unique, direct and precise measurement of a fine-structure transition in a heavy Li-like ion. Such a measurement will test state-of-the-art atomic structure calculations in strong fields. This endeavour will require that the existing infrastructure is complemented by a dedicated beamline for the XRL. In this paper, we will discuss the details of this project and outline a proof-of-principle experiment.

Cooling of highly charged ions—the HITRAP facility and Cooler trap

HITRAP is a facility at GSI in Darmstadt for decelerating, cooling and storing heavy, highly charged ions. It is designed to decelerate a beam of A/q < 3 particles with an energy of 4 MeV per nucleon as provided by the heavy ion storage ring ESR. HITRAP's decelerating linear accelerator (linac) will decelerate ions down to 6 keV per nucleon and then inject them into a Penning trap for cooling. The trap will capture bunches of up to 105 ions as heavy as U92+ in flight, cool and store them. After extraction from the cooler trap, the vertical beam line (VBL) transports the cold ions to the experiments. The linac has shown to decelerate ions down to 500 keV per nucleon on-line and to 6 keV per nucleon off-line. Recent tests with electrons and ions injected into the trap showed the necessity of a more careful electric and magnetic field alignment. An installed test ion source as well as a system of apertures and position sensitive diagnostics will be used to align the fields. A highly charged ion beam from a small room temperature electron beam ion trap was used for commissioning the VBL.

Combining Activity DSM with Temporal Logic for Collaborative Planning and Scheduling

This work presents an approach that implements enhanced scheduling algorithms to plan and schedule interventions in scientific facilities emitting various types of ionizing radiation such as the ones present at CERN in Geneva, (Switzerland) or at GSI in Darmstadt (Germany). To deal with the collaborative process of activity creation and submission used in those organizations, we propose a framework to set the appropriate sequence or skeleton for the activities. This framework combines Allen's Interval Algebra and DSM (Design Structure Matrix). It enables the sequence of activities to be automatically computed while gathering and taking into account the needs of users and testing their compatibility. It also deals with technical-type or resource-type constraints between activities as well as incompatible submissions. The work described in this paper includes details of the collaborative submission process and introduces suggestions for compromising as well as temporal calculations with the introduction of parameterized DSMs rather than binary ones.

A resonant Schottky pickup for the study of highly charged ions in storage rings

A resonant Schottky pickup was built into the experimental storage ring at GSI Darmstadt in 2010 and a similar one in the CSRe storage ring at IMP Lanzhou in 2011. Single-ion sensitivity was achieved at 400 MeV u−1. The pickup has also been used in many storage ring experiments ever since. A brief description of the pickup and its application in single-ion lifetime spectroscopy is provided in this work.

First particle identification with a Disc-DIRC detector

The PANDA experiment at the future FAIR laboratory at GSI in Darmstadt, Germany, will require excellent particle identification for its study of proton–antiproton reactions in the few GeV energy range. In the confined space of the PANDA Target Spectrometer, two RICH-type Cherenkov detectors mainly aim at pion–kaon separation: a Barrel-DIRC detector patterned after the BaBar-DIRC covering the central angles and a Disc-DIRC detector for the forward theta angle range from 5° to 22°. Such a Disc-DIRC design has not yet been used in particle physics experiments. A demonstrator prototype, one quarter segment scaled to 80% of the PANDA geometry, constructed at Giessen university and equipped with 480 sensor pixels, has measured particles of several GeV/c in a secondary mixed beam delivered by the PS T9 test beamline at CERN in October 2012. A first analysis of the recorded hit patterns is presented.