Photodissociation of p-process nuclei studied by bremsstrahlung induced activation

A research program has been started to study experimentally the near-threshold photodissociation of nuclides in the chain of cosmic heavy element production with bremsstrahlung from the ELBE accelerator. An important prerequisite for such studies is good knowledge of the bremsstrahlung distribution which was determined by measuring the photodissociation of the deuteron and by comparison with model calculations. First data were obtained for the astrophysically important target nucleus 92-Mo by observing the radioactive decay of the nuclides produced by bremsstrahlung irradiation at end-point energies between 11.8 MeV and 14.0 MeV. The results are compared to recent statistical model calculations.Comment: 6 pages, 8 figures, Proceedings Nuclear Physics in Astrophysics II, May 16-20, 2005, Debrecen, Hungary. The original publication is available at www.eurphysj.or

Photon strength distributions in stable even-even molybdenum isotopes

Electromagnetic dipole-strength distributions up to the particle separation energies are studied for the stable even-even nuclides $^{92,94,96,98,100}$Mo in photon scattering experiments at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf. The influence of inelastic transitions to low-lying excited states has been corrected by a simulation of $\gamma$ cascades using a statistical model. After corrections for branching ratios of ground-state transitions, the photon-scattering cross-sections smoothly connect to data obtained from $(\gamma,n)$-reactions. With the newly determined electromagnetic dipole response of nuclei well below the particle separation energies the parametrisation of the isovector giant-dipole resonance is done with improved precision.Comment: Proceedings Nuclear Physics in Astrophysics 3, March 2007, Dresden Journal of Physics G, IOP Publishin

Slowing down of relativistic few-electron heavy ions

Abstract Experimental data on energy loss and energy-loss straggling of fully ionized relativistic heavy ions agree well with the theory of Lindhard and Sùrensen (LS). However, when heavy ions penetrate matter with many¯uctuating ionic charge states the theoretical description is more complicate and less accurate. A novel exploratory step to contribute to a better understanding of the slowing down of heavy ions has been done with the present experiment in an energy region where the atomic interaction is still dominated by bare and few-electron projectiles. In the energy range of 100±1000 MeV/u we measured with the high-resolution magnetic spectrometer FRS the stopping powers, the energyloss straggling and the charge-state distributions of 197 Au, 208 Pb and 209 Bi projectiles in charge-state equilibrium interacting with solids ranging from beryllium to lead targets. Additionally, charge exchange cross-sections have been measured to support a better analysis and interpretation of the energy-loss data. The experimental results on stopping power and energy-loss straggling clearly demonstrate the contribution of ions in dierent charge states. A novel application of the slowing down of relativistic exotic heavy ions is presented.

Search for Doubly-Charged Higgs Boson Production at HERA

A search for the single production of doubly-charged Higgs bosons H^{\pm \pm} in ep collisions is presented. The signal is searched for via the Higgs decays into a high mass pair of same charge leptons, one of them being an electron. The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment at HERA. No evidence for doubly-charged Higgs production is observed and mass dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only decays into an electron and a muon via a coupling of electromagnetic strength h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3, masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl

Study of Charm Fragmentation into D^{*\pm} Mesons in Deep-Inelastic Scattering at HERA

The process of charm quark fragmentation is studied using $D^{*\pm}$ meson production in deep-inelastic scattering as measured by the H1 detector at HERA. Two different regions of phase space are investigated defined by the presence or absence of a jet containing the $D^{*\pm}$ meson in the event. The parameters of fragmentation functions are extracted for QCD models based on leading order matrix elements and DGLAP or CCFM evolution of partons together with string fragmentation and particle decays. Additionally, they are determined for a next-to-leading order QCD calculation in the fixed flavour number scheme using the independent fragmentation of charm quarks to $D^{*\pm}$ mesons.Comment: 33 pages, submitted to EPJ

Jet production in ep collisions at high Q(2) and determination of alpha(s)

The production of jets is studied in deep-inelastic e(+/-) p scattering at large negative four momentum transfer squared 150 LT Q(2) LT 15000 GeV2 using HERA data taken in 1999-2007, corresponding to an integrated luminosity of 395 pb(-1). Inclusive jet, 2-jet and 3-jet cross sections, normalised to the neutral current deep-inelastic scattering cross sections, are measured as functions of Q(2), jet transverse momentum and proton momentum fraction. The measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. The strong coupling as determined from these measurement

Gamma Production Cross Section Measurements for 76Ge via (n,n'gamma) at GELINA

This report describes the inelastic scattering data delivered to the Institute for Nuclear and Particle Physics of TU-Dresden. The GAINS setup was used for measurements of gamma production cross sections associated with the 69th excited state of 76Ge, using the (n, n'gamma) technique. The experimental work was performed at the GELINA facility at a 200 m flight path with eight high purity germanium detectors, using highly enriched 76Ge samples. A brief description of the experimental details and the results are presented.JRC.D.5-Nuclear physic

Status of D(n,n)D Elastic Scattering Data

An overview is presented of activities to reduce uncertainties in the neutron differential elasticscattering cross-section data for deuterium. The main subject is the amount of backscatter at energies below 3.2 MeV observed in different differential cross-section measurements and represented in various evaluations, together with the reactivity impact this has in simulations of relevant integral experiments. The scope encompasses fundamental nuclear-data measurements, three-body nuclear-theory calculations, evaluated nuclear-data libraries and associated data processing, and the simulation of critical experiments involving heavy water. The reactivity impact is illustrated using MCNP5 simulations of ZED-2 and other experiments. The simulations incorporate refinements, such as preparation of thermal-scattering-law data files for D-in-D2O to the nearest ºC using NJOY99 and inclusion of photonuclear data to account for the reactivity effects of (gamma,n) reactions. The analysis indicates that the energy grid ENDF/B-VII.0 uses to represent the angular distributions for deuterium elastic scattering should be refined. Additional work is planned, including new angular-distribution measurements at the GELINA facility at IRMM in Geel, Belgium using a CD2 (deuterated polyethylene) sample provided by AECL and scaling of new nuclear-theory-based elastic-scattering cross-section results. Preliminary GELINA findings using a C6D6 target indicate less backscatter than predicted by ENDF/B-VII.0, in contrast to the nuclear-theory results. It is expected that completion of the planned work will reduce the uncertainty of the energy-angle distributions for deuterium elastic scattering and contribute to an improved deuterium evaluation in a future release of ENDF/B-VII.JRC.DG.D.5-Nuclear physic

Neutron-Deuteron Elastic Scattering Measurements

Neutron-deuteron elastic scattering is important for critical systems involving heavy water, including the CANDU (Canada Deuterium Uranium) reactor. A change of the elastic scattering angular distributions included in the ENDF/BVI. 5 evaluated data file for deuterium (and retained in ENDF/B-VII) has led to significant changes in C/E for LANL critical benchmark experiments containing heavy water and a small, but noticeable, change in C/E for coolant void reactivity experiments relevant for CANDU reactors. Follow-up involved first principles nuclear model calculations to obtain revised angular distributions from Faddeev 3-body theory, state of the art nucleon-nucleon forces, three-body and magnetic moment interactions. The calculated differences which are most pronounced occur in the domain just above the onset of anisotropy at 50-100 keV. Here, earlier measurements show contradictory results about the magnitude of this anisotropy. At IRMM measurements are carried out in the energy range from 100 keV to 2 MeV to test the angular distributions of neutron deuteron elastic scattering at angles where predictions show the largest differences (backward angles). An enriched sample (99.999% purity of duterium ), consisting of a molded polyethylene disc 70 mm in diameter and 3 mm thick, was prepared and delivered through AECL. Measurements are performed at the GELINA facility using a new setup based on detection of scattered neutrons using two HPGe detectors. In front of each detector a 10B4C converter is used. Meanwhile we started another project to detect the recoiling deuterium using a state of the art TPC (time projection chamber) filled with deuterated P10 gas.JRC.DG.D.5-Nuclear physic