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Abstract The Laser Laboratory for Acceleration and Applications (L2A2) is a new facility, recently built at the University of Santiago de Compostela in Spain, to investigate laser–plasma acceleration technologies. This facility is equipped with a 50 TW laser system and a radio-protected area where different laser–plasma induced radiation sources are being implemented. In this paper we use Monte Carlo radiation transport simulations based on the code Fluka to validate the radiation shielding installed at L2A2 for proton, neutron and electron sources generated with the present laser system, but also for future possible upgrades increasing the laser power to 100 and 200 TW. Particular attention is paid to the determination of the radiation source term describing the acceleration of electrons, protons and neutrons using over-dense and under-dense plasmas. [ABSTRACT FROM AUTHOR]

One-neutron knockout data for 18-22N are analyzed in the eikonal approximation of the Glauber model. The role of the s-d shell and the crossing of the N = 14 neutron subshell are discussed. Of particular interest is the nucleus 22N, where the knockout data provide a sensitive experimental test for a possible halo structure of its ground state. The observation of a narrow momentum distribution of the 21N fragments, together with an essential 1s1/2 contribution needed to describe the observed longitudinal-momentum distribution, allow the firm conclusion that the ground state of 22N is a well-developed nuclear halo. The results also show that the N = 14 subshell in 22N is somewhat reduced as compared to that of 23O. [ABSTRACT FROM AUTHOR]

Abstract: One-neutron knockout reactions of 24–28Ne in a beryllium target have been studied in the Fragment Separator (FRS), at GSI. The results include inclusive one-neutron knockout cross-sections as well as longitudinal-momentum distributions of the knockout fragments. The ground-state structure of the neutron-rich neon isotopes was obtained from an analysis of the measured momentum distributions. The results indicate that the two heaviest isotopes, 27Ne and 28Ne, are dominated by a configuration in which a neutron is coupled to an excited state of the 26Ne and 27Ne core, respectively. [Copyright &y& Elsevier]

One-neutron knockout reactions have been studied in a systematic way for a set of neutron-rich projectiles. The goal of the experiment, performed at GSI, was to explore the evolution of the nuclear structure close to the neutron drip line, in the region between C and Al. The momentum distributions of the surviving fragments and the cross-sections of the knockout process have been measured and used as physical observables. This report focuses on oxygen and nitrogen isotopes around N = 14. In particular, we discuss the case of 22N, for which the mentioned observables have been determined for the first time. We will consider 23O, already studied in earlier experiments, as a reference. [ABSTRACT FROM AUTHOR]

Breakup reactions were used to study the ground-state configuration of the neutron-rich isotope 23O. The 22O fragments produced in one-nucleon removal from 23O at 938 MeV/nucleon in a carbon target were detected in coincidence with de-exciting γ rays, allowing to discern between 22O ground-state and excited-states contributions. From the comparison of exclusive experimental momentum distributions for the one-neutron removal channel to theoretical momentum distributions calculated in an Eikonal model for the knockout process, and spin and parity assignment of Iπ = 1/2+ was deduced for the 23O ground state. This result solved the existent experimental discrepancy. [ABSTRACT FROM AUTHOR]

We have measured production cross-sections and longitudinal momentum distributions of fragments from neutron-deficient 36Ar at 1.05A GeV. The production cross-sections show excellent agreement with the predictions of the semiempirical formula EPAX. We have compared these results, involving extremely neutron deficient nuclei, with model calculations to extract information about the response of these models close to the driplines. The longitudinal momentum distributions have also been extracted and are compared with the Goldhaber and Morrissey systematics. [Copyright &y& Elsevier]

One-proton removal reactions of 936 MeV/u 8B have been studied with carbon and lead as breakup targets. Using the FRS at GSI, the longitudinal momentum distributions of the 7Be fragments and the one-proton removal cross section of 8B were measured. The relative contributions of the breakup channels leading to 7Be in its ground state and excited state at 429 keV (7Be*) have been determined from measurements of γ rays in coincidence with the fragments from the one-proton removal reaction. The experimental breakup data are discussed in the context of a theoretical (α+3He+p) three-body model. The combined data from the two targets allow a determination of the weight of the 7Be* component in the 8B ground state wave function as (13.3±2.2%) [Copyright &y& Elsevier]

The 7Be fragments produced in one-proton removal from relativistic 8B nuclei of 936 MeV/nucleon in a carbon target have been detected in coincidence with γ rays emitted by these fragments at the reaction target. It is found that 13±3% of the 7Be fragments are released in the 429 keV excited state, 7Be*, which gives direct experimental information on the ground state configuration of 8B. The longitudinal momentum distributions (p∥) of the 7Be fragments have been measured, both inclusively and in coincidence with de-excitation γ-rays from 7Be*. The widths and cross sections of the respective p∥ distributions are compared with calculations in a three-body cluster model. [Copyright &y& Elsevier]

The R³B experiment (Reactions with Relativistic Radioactive Beams) at FAIR (Facility for Antiproton and Ion Research) is a versatile setup dedicated to the study of reactions induced by high-energy radioactive beams. It will provide kinematically complete measurements with high efficiency, acceptance and resolution, making possible a broad physics program with rare-isotopes. CALIFA (CALorimeter for In-Flight detection of gamma-rays and high energy charged pArticles), is a complex detector based on scintillation crystals, that will surround the target of the R³B experiment. CALIFA will act as a total absorption gamma-calorimeter and spectrometer, as well as identifier of charged particles from target residues. This versatility is its most challenging requirement, demanding a huge dynamic range, to cover from low energy gamma-rays up to 300 MeV protons. This fact, along with the high-energy of the beams determine the conceptual design of the detector, presented in this paper, together with the technical solutions proposed for its construction. [ABSTRACT FROM AUTHOR]

We report the development of a stable high-average power X-ray source generated by the interaction of ultrashort laser pulses (35 fs, 1 mJ, 1 kHz) with a solid target in air. The achieved source stability, which is essential for the applications foreseen for these laser-driven plasma accelerators, is due to the combination of precise positioning of the target on focus and the development of a fast rotating target system able to ensure the refreshment of the material at every shot while minimizing positioning errors with respect to the focal spot. This vacuum-free laser-plasma X-ray source provides an average dose rate of 1.5 Sv/h at 30 cm and a repeatability better than 93% during more than 36 min of continuous operation per target. [ABSTRACT FROM AUTHOR]

Nucleon knockout experiments using beryllium or carbon targets reveal a strong dependence of the quenching factors, i.e., the ratio ( R s ) of theoretical to the experimental spectroscopic factors ( C 2 S ), on the proton-neutron asymmetry in the nucleus under study. However, this dependence is greatly reduced when a hydrogen target is used. To understand this phenomenon, exclusive 1 H (17 Ne , 2 p 16 F) and inclusive 12 C (17 Ne , 2 p 16 F) X , 12 C (17 Ne , 16 F) X as well as 1 H (17 Ne , 16 F) X (X-denotes undetected reaction products) reactions with 16 F in the ground and excited states were analysed. The longitudinal momentum distribution of 16 F and the correlations between the detached protons were studied. In the case of the carbon target, there is a significant deviation from the predictions of the eikonal model. The eikonal approximation was used to extract spectroscopic factor values C 2 S . The experimental C 2 S value obtained with C target is markedly lower than that for H target. This is interpreted as rescattering due to simultaneous nucleon knockout from both reaction partners, 17 Ne and 12 C . [ABSTRACT FROM AUTHOR]

Abstract: Longitudinal fragment-momentum distributions resulting from one-neutron knockout of 40 different neutron-rich exotic species (Z ranging from 6-13) have been recently measured at high-energy (700 A MeV) using the FRS at GSI. This paper concentrates on results obtained for the Ne isotopic chain where five isotopes (24Ne-28Ne) have been studied. The comparison of those experimental results with simple model calculations shows the evolution of the nuclear structure across neutron numbers N=14,16 in this transitional region in the neighbourhood of the island of inversion. [Copyright &y& Elsevier]

This work presents a systematic study of the properties (Light Output Non-Uniformity (LONU) and energy resolution) of two CsI(Tl) scintillation units over a span of almost three years, under adverse conditions of humidity and temperature. These two crystals are part of the CALIFA detector, a highly segmented calorimeter and spectrometer for γ rays and light-charged particles, that is placed surrounding the reaction target at Cave C, the experimental cave of the R 3 B (Reactions with Radioactive Relativistic Beams) collaboration at the GSI-FAIR facilities in Darmstadt, Germany. The findings obtained after the experiment indicate that there was no significant impact on the performance in terms of resolution and LONU. This suggests that the employed wrapping for light collection effectively serves as an excellent barrier against humidity. As a result, the crystal is preserved in a far better condition than initially anticipated. [ABSTRACT FROM AUTHOR]

In the R 3 B experiment at FAIR, charged particles with energies up to 600 MeV and forward boosted γ -rays with energies up to 20 MeV need to be detected in scattering experiments. Calorimeters for nuclear physics experiments of this kind, using relativistic radioactive ion beams, require high energy resolution and high efficiency for simultaneous detection of strongly Doppler shifted γ -rays and high-energy charged particles. A calorimeter design that can meet these requirements, using CsI(Tl) scintillators, results in detector elements that may exhibit light output variations with crystal depth, which can limit the attainable resolution. In this paper we present results from a systematic study of 478 detector modules of CALIFA, the R 3 B calorimeter, in order to determine and minimize such variations. To facilitate further systematic studies we also present results for the total absorption length of the scintillation light, using spectrophotometry, light crosstalk between adjacent detector modules, and surface topography of the CsI(Tl) crystals from atomic force microscopy. [ABSTRACT FROM AUTHOR]

The quasi-free scattering reactions 11C (p , 2 p) and 10,11,12C (p , p n) have been studied in inverse kinematics at beam energies of 300–400 MeV/u at the R3B-LAND setup. The outgoing proton-proton and proton-neutron pairs were detected in coincidence with the reaction fragments in kinematically complete measurements. The efficiency to detect these pairs has been obtained from GEANT4 simulations which were tested using the 12C(p , 2 p) and 12C(p , p n) reactions. Experimental cross sections and momentum distributions have been obtained and compared to DWIA calculations based on eikonal theory. The new results reported here are combined with previously published cross sections for quasi-free scattering from oxygen and nitrogen isotopes and together they enable a systematic study of the reduction of single-particle strength compared to predictions of the shell model over a wide neutron-to-proton asymmetry range. The combined reduction factors show a weak or no dependence on isospin asymmetry, in contrast to the strong dependency reported in nucleon-removal reactions induced by nuclear targets at lower energies. However, the reduction factors for (p , 2 p) are found to be 'significantly smaller than for (p , p n) reactions for all investigated nuclei. [ABSTRACT FROM AUTHOR]

Abstract A thick neutron skin emerges from the first determination of root mean square radii of the proton distributions for 17−22N from charge changing cross section measurements around 900 A MeV at GSI. Neutron halo effects are signalled for 22N from an increase in the proton and matter radii. The radii suggest an unconventional shell gap at N = 14 arising from the attractive proton–neutron tensor interaction, in good agreement with shell model calculations. Ab initio , in-medium similarity re-normalization group, calculations with a state-of-the-art chiral nucleon–nucleon and three-nucleon interaction reproduce well the data approaching the neutron drip-line isotopes but are challenged in explaining the complete isotopic trend of the radii. [ABSTRACT FROM AUTHOR]

New experimental data for dissociation of relativistic 17 Ne projectiles incident on targets of lead, carbon, and polyethylene targets at GSI are presented. Special attention is paid to the excitation and decay of narrow resonant states in 17 Ne. Distributions of internal energy in the O 15 + p + p three-body system have been determined together with angular and partial-energy correlations between the decay products in different energy regions. The analysis was done using existing experimental data on 17 Ne and its mirror nucleus 17 N. The isobaric multiplet mass equation is used for assignment of observed resonances and their spins and parities. A combination of data from the heavy and light targets yielded cross sections and transition probabilities for the Coulomb excitations of the narrow resonant states. The resulting transition probabilities provide information relevant for a better understanding of the 17 Ne structure. [ABSTRACT FROM AUTHOR]

Advancement of the CALIFA calorimeter project has reached a new milestone with the construction of the first modules of the CALIFA Demonstrator, ultimately to be integrated into the final calorimeter. Aspects and methods of detector optimisation will be discussed, along with characterisation using proton beams of 70 < E kin < 230 MeV at the Bronowice Cyclotron Centre (CCB) in Krakow, Poland. Features such as the support structure, crystal geometry and digital electronics represent the final versions to be employed, enabling a full test of each component׳s performance. A study of caesium iodide quenching over the available proton energy range has been performed, to accompany a method for proton calibration scaled from the measured gamma-ray energies. [ABSTRACT FROM AUTHOR]

Quasi-free scattering reactions of the type ( p , 2 p ) were measured for the first time exclusively in complete and inverse kinematics, using a 12 C 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 , 2 p ) cross sections of 15.8(18) mb, 1.9(2) mb and 1.5(2) mb to the low-lying 0 p -hole states overlapping with the ground state ( 3 / 2 − ) and with the bound excited states of 11 B 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 0 s -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. [ABSTRACT FROM AUTHOR]

The nuclear level density is one of the main ingredients for the statistical description of the fission process. In this work, we propose to constrain the description of this parameter by using fission reactions induced by protons and light ions on 208Pb at high kinetic energies. The experiment was performed at GSI (Darmstadt), where the combined use of the inverse kinematics technique with an efficient detection setup allowed us to measure the atomic number of the two fission fragments in coincidence. This measurement permitted us to obtain with high precision the partial fission cross sections and the width of the charge distribution as a function of the atomic number of the fissioning system. These data and others previously measured, covering a large range in fissility, are compared to state-of-the-art calculations. The results reveal that total and partial fission cross sections cannot unambiguously constrain the level density at ground-state and saddle-point deformations and additional observables, such as the width of the charge distribution of the final fission fragments, are required. [ABSTRACT FROM AUTHOR]

The properties of nuclei with extreme neutron–to–proton ratios, far from those naturally occurring on Earth, are key to understand nuclear forces and how nucleons hold together to form nuclei. 7H, with six neutrons and a single proton, is the nuclear system with the most unbalanced neutron–to–proton ratio known so far. However, its sheer existence and properties are still a challenge for experimental efforts and theoretical models. Here we report experimental evidences on the formation of 7H as a resonance, detected with independent observables, and the first measurement of the structure of its ground state. The resonance is found at ∼0.7 MeV above the 3H+4n mass, with a narrow width of ∼0.2 MeV and a 1 / 2 + spin and parity. These data are consistent with a 7H as a 3H core surrounded by an extended four-neutron halo, with a unique four-neutron decay and a relatively long half-life thanks to neutron pairing; a prime example of new phenomena occurring in what would be the most pure-neutron nuclear matter we can access in the laboratory. [ABSTRACT FROM AUTHOR]

The two fragments produced in fission reactions induced by 208Pb projectiles impinging on a liquid hydrogen target at 500AMeV have been fully identified in coincidence. The experiment was performed at GSI Darmstadt, where the combined use of the inverse kinematics technique with an efficient detection setup permitted one to detect and to fully identify the fission fragments in a range from Z = 27 to Z = 52. The corresponding isotopic cross sections and velocities of the fission fragments were measured with high accuracy. The results are compared to state-of-the-art model calculations that reproduce the measured observables. Correlations between the two fragments were used to assess the role of charge polarization and the excitation energy gained by the nascent fragments using the neutron excess of the final fragments. The analysis of the average velocities of the fission fragments allowed us to parametrize the distance between the two fission fragments at scission as a function of the size of the fissioning system. [ABSTRACT FROM AUTHOR]

The 26Si(p, γ )27P reaction, which might play an important role in the rp process, was studied by the Coulomb Dissociation method. The experiment was performed at GSI, Darmstadt. A secondary 27P ion beam of 500 MeV/nucleon was directed onto a Pb target. From this experiment, the Coulomb Dissociation cross section, σCoulex, will be deduced and then converted to the photoabsorption cross section, σphoto, and the radiative-capture cross section, σcap. Also information on the structure of 27P will be obtained. The analysis is in progress. [ABSTRACT FROM AUTHOR]

A new phoswich array, for the detection of high-energy protons and gamma rays from nuclear reactions, has been built. This new detector consists of four individual closely packed scintillator detectors, each of them made of 4 cm of LaBr 3 (Ce) and 6 cm of LaCl 3 (Ce) in phoswich configuration (optically coupled and with a common readout). In this paper we report on the results of a beam test performed at the Bronowice Cyclotron Centre (CCB) in Krakow, showing the response of this versatile instrument to high energy protons (70–230 MeV). Furthermore, for the first time we prove that we can reconstruct the original energy of fast protons ( E > 200 MeV ) which pass through the total length of the crystal while still retaining a good energy resolution. [ABSTRACT FROM AUTHOR]

The CALIFA calorimeter is an advanced detector for gamma rays and light charged particles, accordingly optimized for the demanding requirements of the physics programme proposed for the R 3 B facility at FAIR. The multipurpose character of CALIFA is required to fulfil challenging demands in energy resolution (5–6% at 1 MeV for gamma rays) and efficiency. Charged particles, e.g. protons of energies up to 320 MeV in the Barrel section, should also be identified with an energy resolution better to 1%. CALIFA is divided into two well-separated sections: a “Forward EndCap” and a cylindrical “Barrel” covering an angular range from 43.2° to 140.3°. The Barrel section, based on long CsI(Tl) pyramidal frustum crystals coupled to large area avalanche photodiodes (LAAPDs), attains the requested high efficiency for calorimetric purposes. The construction of the CALIFA Demonstrator, comprising 20% of the total detector, has already been initiated, and commissioning experiments are expected for 2014. The assessment of the capabilities and expected performance of the detector elements is a crucial step in their design, along with the prototypes evaluation. For this purpose, the Barrel geometry has been carefully implemented in the simulation package R3BRoot, including easily variable thicknesses of crystal wrapping and carbon fibre supports. A complete characterization of the calorimeter response (including efficiency, resolution, evaluation of energy and reconstruction losses) under different working conditions, with several physics cases selected to probe the detector performance over a wide range of applications, has been undertaken. Prototypes of different sections of the CALIFA Barrel have been modeled and their responses have been evaluated and compared with the experimental results. The present paper summarizes the outcome of the simulation campaign for the entire Barrel section and for the corresponding prototypes tested at different European installations. [ABSTRACT FROM AUTHOR]

Total fission cross sections of 208Pb induced by protons have been determined at 370A, 500A, and 650A MeV. The experiment was performed at GSI Darmstadt where the combined use of the inverse kinematics technique with an efficient detection setup allowed us to determine these cross sections with an uncertainty below 6%. This result was achieved by an accurate beam selection and registration of both fission fragments in coincidence which were also clearly distinguished from other reaction channels. These data solve existing discrepancies between previous measurements, providing new values for the Prokofiev systematics. The data also allow us to investigate the fission process at high excitation energies and small deformations. In particular, some fundamental questions about fission dynamics have been addressed, which are related to dissipative and transient time effects. [ABSTRACT FROM AUTHOR]

The first determination of radii of point proton distribution (proton radii) of B12-17 from charge-changing cross sections (σCC) measurements at the FRS, GSI, Darmstadt is reported. The proton radii are deduced from a finite-range Glauber model analysis of the σCC. The radii show an increase from 13B to 17B and are consistent with predictions from the antisymmetrized molecular dynamics model for the neutron-rich nuclei. The measurements show the existence of a thick neutron surface with neutron-proton radius difference of 0.51(0.11) fm in B. [ABSTRACT FROM AUTHOR]