H. Paetz gen. Schieck

ANKE, a new facility for medium energy hadron physics at COSY-Jülich

Abstract ANKE is a new experimental facility for the spectroscopy of products from proton-induced reactions on internal targets. It has recently been implemented in the accelerator ring of the cooler synchrotron COSY of the Forschungszentrum Julich (FZ-Julich), Germany. The device consists of three dipole magnets, various target installations and dedicated detection systems. It will enable a variety of hadron-physics experiments like meson production in elementary proton–nucleon processes and studies of medium modifications in proton–nucleus interactions.

Study of the kinematically complete breakup reaction 2H(p̄, pp)n at Ep = 3 Mev with polarized protons

Abstract The breakup reaction 2 H(p, pp)n at E p = 13.0 MeV has been measured in a kinematically complete experiment with polarized protons in four special kinematical situations: np final-state interaction, pp quasi-free scattering, collinearity and symmetric space star. These configurations are identical to those of a corresponding 2 H(n, nn) 1 H experiment. The cross sections d 3 σ/ d Ω 3 d Ω 4 d S and the vector analyzing powers A 1 are presented as a function of the arclenght of the relevant kinematical loci. They are compared to the rigorous Faddeev calculations using realistic meson-exchange NN potentials, i.e. the Paris and Bonn potential. Comparison with the cross section data of the analog neutron experiment is made. In the quasi-free scattering and the space-star cross sections marked discrepancies with the theoretical predictions, in the latter case also with the neutron results are found. In the collinear and final-state interaction situations the agreement is rather good as well as for all analyzing powers and is even improved by taking the finite angular spread into account.

Precision Lamb-shift polarimeter for polarized atomic and ion beams

The Lamb-shift polarimeter described here enables the polarization of a beam of hydrogen (deuterium) atoms, or of a slow proton (deuteron) beam, to be measured with an absolute precision better than 1% within a few seconds. The polarimeter measures the intensity ratios of Lyman-α transitions after Stark quenching of metastable hyperfine substates that were selected in a spin filter. For that purpose the hydrogen (deuterium) atoms are ionized in a Glavish-type ionizer. By charge exchange of the protons (deuterons) in cesium vapor, atoms in the metastable 2S state are produced. For a hydrogen beam of 3×1016 atoms/s, ∼3×106 photons/s are registered in a photomultiplier, i.e., the polarimeter efficiency is about 10−10. The signal-to-background ratio in the Lyman-α spectrum is excellent, thus beam intensities of one to two orders of magnitude less would still be sufficient to carry out a precise measurement. The different components of the polarimeter affect the measured polarization in several ways. It was, t...

Experiments on four-nucleon reactions

The status of experimental evidence on four-nucleon reactions in the range from very low to medium energies (∼50 MeV) is reviewed. The recent progress of microscopic theories as well as computer capabilities, the renewed interest in astrophysical and the new fusion-energy aspects of the four-nucleon reactions, the emphasis on improved measurements of polarization observables especially at very low energies and on new types of studies such as break-up reactions with polarized projectiles prompt such a survey. The aim is to stimulate interest in the four-nucleon system. It is expected that the four-nucleon system will undergo a development similar to the three-nucleon system as a special testing ground for nuclear forces.

The polarized ion source for COSY

The polarized ion source for COSY‐Julich has been set in operation. The source produces H− or D− ion beams by means of a charge exchange reaction. For the first time beam acceleration in the injector cyclotron and a first measurement of the beam polarization downstream of the cyclotron took place. The working scheme of this colliding‐beam source and the latest results are discussed.

Position sensitivity by light splitting in scintillator arrays

Abstract A novel detector design of overlapping plastic scintillator elements in cylindrical geometry has been developed for detection of low multiplicity events of fast protons and other light charged particles: each particle traversing the detector from the axis outwards will produce light in several elements. The relative amounts of energy deposited in those elements allow one to interpolate on the particle trajectory beyond the resolution given by the granularity. The detector covers the angular range 10° ≤ Θ lab ≤ 72° and 0° ≤ ϕ ≤ 360° with an inner layer of scintillator bars of triangular cross section and an outer layer of rings. The material is BC408. Tests with minimum ionizing electron beams show that spatial resolutions of ΔΘ lab ≈ 1.5° and Δϕ 12 ≈ 1.5° (FWHM) can be obtained for electrons or proton pairs with energies in the GeV range. In the EDDA experiment the ultimate spatial resolution is then determined by the size of the interaction area rather than by the intrinsic pulse height resolution of the detector.

Quantitative evidence of weak isospin mixing in the low-lying isobaric analog resonances in 209Bi

Abstract The excitation functions of 208 Pb ( p , p 0 ) 208 Pb have been measured in the energy range E p = 14.2 to 17.4 MeV in 50 keV steps at θ lab = 120°, 140° and 160°. The isobaric analog resonances of the parent states in 209 Pb up to E x = 2.5 MeV and the optical-model background were fit simultaneously at all energies and angles. The spreading widths and the values of a parameter β 2 , which measures the isospin purity of the IAR, were determined for the g 9 2 , i 11 2 , j 15 2 , d 5 2 , and s 1 2 resonances. An average value of the isospin purity of β 2 = 66% was found.

The status of “polarized fusion”

After an introduction into the essentials of nuclear fusion reactions, being considered for future energy production in fusion reactors, different aspects of using “polarized” particles as fuel are discussed. Special emphasis is given to the four-nucleon system and the D+D reactions. The status of the theory and the experimental data are presented. Predictions for observables in the framework of existing theoretical approaches are given. The necessity of carrying out direct spin-correlated cross-section measurements is accentuated. Details of a future experiment are proposed.

Global optical model potentials for symmetrical lithium systems: 6Li+6Li, 7Li+7Li at Elab = 5–40 MeV☆

Abstract Angular distributions of 6 Li+ 6 Li elastic scattering were measured for E lab = 5–40 MeV. An optical model analysis of these data together with older data of 7 Li+ 7 Li elastic scattering taken at E lab = 8–17 MeV was performed with the aim to search for a “global” OM potential which describes elastic scattering in both LiLi systems in a broad energy range. Both surface and volume absorbing potentials can be found which fulfill this requirement if a linear energy dependence is assumed of the depths of the real as well as the imaginary potential. These depths, if fitted to individual angular distributions, are found to vary in a correlated manner with the beam energy. This is taken as indication of strong coupling between elastic, inelastic, and reaction channels. This is corroborated by the existence of resonances in reaction channels at these energies where the potential depths are most pronouncedly changing.

24 segment high field permanent sextupole magnets

We report on the design, construction, and magnetic field measurements of a system of high field sextupole magnets made from NdFeB compounds. The magnets are utilized as a focusing system for neutral hydrogen (or deuterium) atoms in a polarized atomic beam source based on Stern–Gerlach spin separation. Each magnet consists of 24 segments of permanently magnetized material differing in remanence and coercivity to reduce demagnetization. According to quadratic extrapolation to the pole tip the magnetic flux density reaches values of up to B0=1.69 T. Three-dimensional field calculations using the MAFIA code were carried out to optimize the magnet performance and to avoid demagnetization by selecting appropriate materials for the individual segments. Measurements of the radial, azimuthal, and longitudinal magnetic flux density distributions were carried out by means of a small Hall probe (100×200×15 μm3). The measurements with the small probe permitted to extract experimentally higher order multipole componen...