The decay pattern of the Pygmy Dipole Resonance of ¹⁴⁰Ce

The decay properties of the Pygmy Dipole Resonance (PDR) have been investigated in the semi-magic N=82 nucleus ¹⁴⁰Ce using a novel combination of nuclear resonance fluorescence and γ–γcoincidence techniques. Branching ratios for transitions to low-lying excited states are determined in a direct and model-independent way both for individual excited states and for excitation energy intervals. Comparison of the experimental results to microscopic calculations in the quasi-particle phonon model exhibits an excellent agreement, supporting the observation that the Pygmy Dipole Resonance couples to the ground state as well as to low-lying excited states. A 10% mixing of the PDR and the [2+1×PDR]is extracted

Coulomb dissociation of N 20,21

Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N20,21 are reported. Relativistic N20,21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the N19(n,γ)N20 and N20(n,γ)N21 excitation functions and thermonuclear reaction rates have been determined. The N19(n,γ)N20 rate is up to a factor of 5 higher at

Coulomb dissociation of O-16 into He-4 and C-12

We measured the Coulomb dissociation of O-16 into He-4 and C-12 within the FAIR Phase-0 program at GSI Helmholtzzentrum fur Schwerionenforschung Darmstadt, Germany. From this we will extract the photon dissociation cross section O-16(alpha,gamma)C-12, which is the time reversed reaction to C-12(alpha,gamma)O-16. With this indirect method, we aim to improve on the accuracy of the experimental data at lower energies than measured so far. The expected low cross section for the Coulomb dissociation reaction and close magnetic rigidity of beam and fragments demand a high precision measurement. Hence, new detector systems were built and radical changes to the (RB)-B-3 setup were necessary to cope with the high-intensity O-16 beam. All tracking detectors were designed to let the unreacted O-16 ions pass, while detecting the C-12 and He-4

Coulomb dissociation of 16O into 4He and 12C

We measured the Coulomb dissociation of 16O into 4He and 12C at the R3B setup in a first campaign within FAIR Phase 0 at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The goal was to improve the accuracy of the experimental data for the 12C(a,?)16O fusion reaction and to reach lower center-ofmass energies than measured so far. The experiment required beam intensities of 109 16O ions per second at an energy of 500 MeV/nucleon. The rare case of Coulomb breakup into 12C and 4He posed another challenge: The magnetic rigidities of the particles are so close because of the same mass-To-charge-number ratio A/Z = 2 for 16O, 12C and 4He. Hence, radical changes of the R3B setup were necessary. All detectors had slits to allow the passage of the unreacted 16O ions, while 4He and 12C would hit the detectors' active areas depending on the scattering angle and their relative energies. We developed and built detectors based on organic scintillators to track and identify the reaction products with sufficient precision

Entwicklung eines Detektors für gepulste Schwerionenstrahlen

Die Arbeitsgruppe Laser- und Plasmaphysik im Institut für Kernphysik an der Technischen Universität Darmstadt erforscht die Wechselwirkung von Schwerionen mit heißen und dichten lasererzeugten Plasmen. Der dabei im Plasma auftretende relativ zu kalter Materie erhöhte Energieverlust wird über die Flugzeitänderung von einzelnen Ionenpulsen zueinander nach einer Driftstrecke von ca. 12m mit einem Stoppdetektor bestimmt. Ziel der vorliegenden Diplomarbeit war es, für diese Experimentiermethode einen neuen Stoppdetektor, also ein Timing-Detektorsystem mit sowohl hoher Zeitauflösung und Zählratenkapazität wie auch mit hoher Empfindlichkeit zu entwickeln. Dazu wurden insgesamt vier einzelne Detektoren basierend auf dünnen Schichten (13-60 μm) aus synthetischem polykristallinem Diamant entworfen, konstruiert und erfolgreich getestet: Die Detektoren wurden in einem Experiment mit einem bei 108,408MHz gepulsten54Cr21+-Schwerionenstrahl bei einer Teilchenenergie von 4,75AMeV und bei mittleren Strahlströmen zwischen 280 nA und 3,6 μA eingesetzt und zeigten sich den gestellten Anforderungen gewachsen.Die zeitliche Antwort der Detektoren ist charakterisiert durch Signalbreiten von 2-4 ns, Anstiegszeiten von etwa 1,3 ns, und die Abfallszeit liegen zwischen 2 ns und 4 ns. Für die Bestimmung der Ankunftszeit eines Schwerionenpulses wurde eine erreichbare Zeitauflösung von 40 ps ermittelt; das entspricht einer relativen Energieauflösung von etwa 2 · 10−4 . Hierbei ist wichtig, dass diese Zeitauflösung nicht nur durch die intrinsischen Eigenschaften des Detektors bestimmt wird, sondern auch durch eine geringe Teilchenstatistik, die im Experiment zur Verfügung stand. Somit ist der genannte Wert als obere Grenze für die Zeitauflösung zu betrachten.In der Konsequenz ist die Empfindlichkeit der Detektoren hervorragend geeignet für die Anforderungen der Wechselwirkungsexperimente mit lasererzeugtem Plasma; selbst bei niedrigen mittleren Strahlströmen von etwa 300 nA liefern die Detektoren verwertbare Signale und sind damit um Gröÿenordnungen besser als der Vorgängertyp einer Micro Sphere Plate (MSP); es können prinzipiell einzelne Ionen nachgewiesen werden. Die Signalqualität bei positiven Detektorspannungen ist höher. Um Polarisationseffekte im Detektormaterial zu minimieren, sollte dessen Schichtdicke niedriger sein als die Eindringtiefe der zu untersuchenden Ionen. Der Detektorbetrieb wird durch den aus lasererzeugtem Plasma stammenden Röntgenblitz nicht beeinträchtigt; dessen Zeitpunkt ist messbar und in Form einer zusätzliche Referenz dienlich

A spectrometer on chemical vapour deposition-diamond basis for the measurement of the charge-state distribution of heavy ions in a laser-generated plasma

This article reports on the development and the first applications of a new spectrometer which enables the precise and time-resolved measurement of both the energy loss and the charge-state distribution of ion beams with 10 < Z < 30 at energies of 4–8MeV/u after their interaction with a laser-generated plasma. The spectrometer is based on five 20 × 7mm2 large and 20μm thick polycrystalline diamond samples produced via the Chemical Vapour Deposition (CVD) process and was designed with the help of ion-optical simulations. First experiments with the spectrometer were successfully carried out at GSI using $^{48}Ca$ ions at an energy of 4.8MeV/u interacting with a carbon plasma generated by the laser irradiation of a thin foil target. Owing to the high rate capability and the short response time of the spectrometer, pulsed ion beams with 103–104 ions per bunch at a bunch frequency of 108MHz could be detected. The temporal evolution of the five main charge states of the calcium ion beams as well as the corresponding energy loss values could be measured simultaneously. Due to the outstanding properties of diamond as a particle detector, a beam energy resolution E E ≈ 0.1% could be reached using the presented experimental method, while a precision of 10% in the energy loss and charge-state distribution data was obtained

Cold test results of the FAIR super-FRS first-of-series multiplets and dipole

International audienceWithin the collaboration between GSI and CERN, a dedicated cryogenic test facility has been built at CERN (Geneva, Switzerland) in order to perform the site acceptance tests of the 56 Superconducting FRagment Separator cryomodules before their installation at the the Facility for Antiproton and Ion Research (Darmstadt, Germany). Two of the three benches of the CERN test facility were successfully commissioned with the powering tests of the first-of-series multiplets and dipole. The long multiplet, with a warm bore radius of 192 mm, is composed of nine magnets of different type (quadrupole, sextupole, steering dipole and octupole) assembled with Nb-Ti racetrack and cosine-theta coils, mounted in a cold iron yoke and in a common cryostat. This work presents the first results of the cold powering tests at 4.5 K during which dedicated measurements have been implemented for the magnetic characterization of the single magnets up to nominal current (300 A for a long quadrupole) and the study of their crosstalk effects. The results of the acceptance tests will be presented together with the challenges and lessons learnt during the facility commissioning

Exclusive measurements of quasi-free proton scattering reactions in inverse and complete kinematics

Quasi-free scattering reactions of the type (p, 2p) were measured for the first time exclusively in complete and inverse kinematics, using a 12C beam at an energy of ∼400 MeV/u as a benchmark. This new technique has been developed to study the single-particle structure of exotic nuclei in experiments with radioactive-ion beams. The outgoing pair of protons and the fragments were measured simultaneously, enabling an unambiguous identification of the reaction channels and a redundant measurement of the kinematic observables. Both valence and deeply-bound nucleon orbits are probed, including those leading to unbound states of the daughter nucleus. Exclusive (p, 2p) cross sections of 15.8(18) mb, 1.9(2) mb and 1.5(2) mb to the low-lying 0p-hole states overlapping with the ground state (3/2−) and with the bound excited states of 11B at 2.125 MeV (1/2−) and 5.02 MeV (3/2−), respectively, were determined via γ -ray spectroscopy. Particle-unstable deep-hole states, corresponding to proton removal from the 0s-orbital, were studied via the invariant-mass technique. Cross sections and momentum distributions were extracted and compared to theoretical calculations employing the eikonal formalism. The obtained results are in a good agreement with this theory and with direct-kinematics experiments. The dependence of the proton–proton scattering kinematics on the internal momentum of the struck proton and on its separation energy was investigated for the first time in inverse kinematics employing a large-acceptance measurement

A New Cryogenic Test Facility for Large and Heavy Superconducting Magnets

CERN has recently designed and constructed a new cryogenic facility for testing large and heavy superconducting magnets at liquid helium temperatures. The facility, erected in a large assembly hall with cranes capable of up to 100 t, provides a cooling capacity of 1.2 kW at 4.5 K equivalent, 15-kW LN$_2$ cooling and warming capabilities for up to three magnets in parallel. The facility provides the required technical infrastructure for continuous and reliable operation. Test capabilities comprise electrical, cryogenics, vacuum and mechanical verification, and validation at ambient and liquid helium temperatures. A comprehensive survey and magnetic measurement system, comprising a hall-probe mapper, a rotating-coil magnetometer, a stretched wire, a translating fluxmeter, and a laser tracker, allows the detailed measurement of the magnetic field strength and quality on a large volume. The magnetic axes of the quadrupoles can be established within $\pm 0.2$ mm at $1 \sigma$ accuracy. The facility has been equipped with power supplies, three converters of $\pm 500$ A/120 V, and six converters of $\pm 600$ A/40 V, as well as the required energy extraction, quench protection, data acquisition, and interlocks for the testing of superconducting magnets for the FAIR project, currently under construction at the GSI Research Center, in Darmstadt, Germany. The versatile design of the facility, its layout, and testing capabilities complements CERN's other test infrastructures for large superconducting magnets. We report on the design, construction, and commissioning of the facility as well as the expected capabilities and performances for future tests of large and heavy superconducting magnets