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Proton-proton and proton- $ \eta$ invariant-mass distributions and the total cross-section for the pp $ \rightarrow$ pp $ \eta$ reaction have been determined near the threshold at an excess energy of Q = 10 MeV. The experiment has been conducted using the COSY-11 detector setup and the cooler synchrotron COSY. The determined invariant-mass spectra reveal significant enhancements in the region of low proton-proton relative momenta, similarly as observed previously at higher excess energies of Q = 15.5 MeV and Q = 40 MeV. [ABSTRACT FROM AUTHOR]

The production of K+-mesons in proton-nucleus collisions from 1.0 to 2.3 GeV is analyzed with respect to one-step nucleon-nucleon (NN?NYK+) and two-step ?-nucleon (?N?K+ YN) or pion-nucleon (pN?K+ Y) production channels on the basis of a coupled-channel (CBUU) transport approach including the kaon final-state-interactions (FSI). Momentum-dependent potentials for the nucleon, hyperon and kaon in the final state are included as well as K+ elastic rescattering in the target nucleus. The transport calculations are compared to the experimental K+ spectra taken at COSY-Jülich. Our systematic analysis of K+ spectra from12C,63Cu,107Ag and197Au targets as well as their momentum differential ratios gives a repulsive K+ potential of 20±5 MeV at normal nuclear matter density. [ABSTRACT FROM AUTHOR]

The production of the ?- and S0-hyperons has been measured via thepp?pK+?/S0 reaction at the internal COSY-11 facility in the excess energy range between 14 and 60 MeV. The transition of the ?/S0 cross-section ratio from about 28 atQ=13 MeV to the high-energy level of about 2.5 is covered by the data showing a strong decrease of the ratio between 10 and 20 MeV excess energy. Effects from the final-state interactions in thep-S0 channel seem to be much smaller than in thep-? channel. Estimates of the effective range parameters are given for theN? and theNS systems. [ABSTRACT FROM AUTHOR]

The n' -meson production in tne reaction pp → ppn' has been sturnea at excess energies o Q 26.5, 32.5 and 46.6 MeV using the internal beam facility COSY-11 at the cooler synchrotron COSY. The total cross-sections as well as one angular distribution for the highest Q-value are presented. The excitation function of the near-threshold data can be described by a pure s-wave phase space distribution with the inclusion of the proton-proton final-state interaction and Coulomb effects. The obtained angular distribution of the n'-mesons is also consistent with pure s-wave production. [ABSTRACT FROM AUTHOR]

The production of η- and η′-mesons in elementary nucleon-nucleon collisions has been investigated at the synchrotrons CELSIUS, COSY and SATURNE. The high-quality proton beam with low emittance and small momentum spread permits to study the creation of these mesons very close to the kinematical threshold, where -due to the rapid growth of the phase space volume- the total cross-section increases by orders of magnitude over a few MeV range of the excess energy. The magnitude and energy dependence of the total cross-section as well as the occupation distribution of the phase space serve as observables for investigating the mechanisms underlying the production processes and the interaction of mesons with nucleons. The precise data on the η and η′ creation via the pp → ppη(η′) reactions allowed to settle the general features of the η and η′-meson production and revealed the sensitivity of the mentioned observables to the nucleon-nucleon-meson final-state interaction. The particular production properties, like for example, the determination of the dominating exchange processes which lead to the excitation of the S11 nucleon isobar in the case of η creation, must be established by confrontation with other observables. The present status of this investigation with an emphasis on the results of the COSY-11 Collaboration is briefly presented. The available data are interpreted in view of the production mechanism and the meson-nucleon interaction. [ABSTRACT FROM AUTHOR]

The associated strangeness dissociation at threshold has been studied at the COSY-11 facility measuring the hyperon and the K+K,- meson pair production. Measurements of the near-threshold Λ and σ° production via the pp → pK+Λ/Σ° reaction (S. Sewerin et al., Phys. Rev. Lett. 83, 682 (1999)) at COSY-1 1 have shown that theΛΣ° cross-section ratio exceeds the value at high excess energies (Q &Ge; 300 MeV (A. Baldini et al., Total cross-Sections for Reactions of High-Energy Particles, Landolt-Börnstein, New Series, Vol. I/12 (Springer, Berlin, 1988))) by an order of magnitude. For a better understanding additional data have been taken between 13 MeV and 60 MeV excess energy. The near-threshold production of the charged kaon-antikaon pair is related to the discussion about the nature of the scalar states in the 1 GeV/c2 mass range, i.e. the fo(980) and ao(980) (0. Krehl, R. Rapp, J. Speth, Phys. Lett. B 390, 23 (1997)). The interpretation as a KK molecule is strongly dependent on the K-K interaction which can be studied via the production channel. A first total cross-section value on the reaction pp → ppK+&Kmacr;- at an excess energy of 17MeV (C. Quentmeier et al., Phys. Lett. B 515, 276 (2001)), i.e. below the &phil; production threshold, was measured. [ABSTRACT FROM AUTHOR]

Abstract. A stack of annular detectors made of high-purity germanium was used to measure p + d →3He +π0 and p + d → 3H + π+ differential and total cross-sections at beam momenta from 900 MeV/c to 1050 MeV/c. The total cross-sections are consistent with Sδ- excitation. The differential data consist of two components. One corresponds to large momentum transfer from the projectile to the pion, the other to small momentum transfer. The former shows an independence of the slope as a function of the momentum transfer t (scaling). The scale parameter is different for π+ and π0 emission which violates isospin symmetry. The second component which is almost isotropic is in agreement with isospin symmetry. It is approximately a quarter of the total yield in the Δresonance region. [ABSTRACT FROM AUTHOR]

The lifetime of the Λ-hyperon in heavy hypernuclei measured in proton-Au, -Bi and -U collisions by the COSY-13 Collaboration at COSY-Jülich has been analyzed to yield τΛ = (145±11) ps. This value for τΛ is compatible with the lifetime extracted from antiproton annihilation on Bi and U targets, albeit much more accurate. Theoretical models based on the meson exchange picture and assuming the validity of the phenomenological Δ I = 1/2 rule predict the lifetime of heavy hypernuclei to be significantly larger (2-3 standard deviations). Such large differences indicate that at least one of the assumptions in these models is not fulfilled. A much better reproduction of the lifetimes of heavy hypernuclei is achieved in the phase space model, if the Δ I = 1/2 rule is discarded in the nonmesonic Λ decay. [ABSTRACT FROM AUTHOR]

The production of K+-mesons in proton-nucleus collisions from 1.0 to 2.5GeV is analyzed with respect to one-step nucleon-nucleon ( NN → NYK+) and two-step Δ-nucleon ( Δ N → K+ YN) or pion-nucleon ( π N → K+ Y) production channels on the basis of a coupled-channel transport approach (CBUU) including the kaon final-state interactions. The influence of momentum-dependent potentials for the nucleon, hyperon and kaon in the final state are studied as well as the importance of K+ elastic rescattering in the target nucleus. The transport calculations are compared to the experimental K+ spectra taken at LBL Berkeley, SATURNE, CELSIUS, GSI and COSY-Jülich. It is found that the momentum-dependent baryon potentials affect the excitation function of the K+ cross-section; at low bombarding energies of ∼ 1.0GeV the attractive baryon potentials in the final state lead to a relative enhancement of the kaon yield, whereas the net repulsive potential at bombarding energies ∼ 2GeV causes a decrease of the K+ cross-section. Furthermore, it is pointed out that especially the K+ spectra at low momenta (or kinetic energy TK) allow to determine the in-medium K+ potential almost model independently due to a relative shift of the K+ spectra in kinetic energy that arises from the acceleration of the kaons when propagating out of the nuclear medium to free space, i.e. converting the potential energy to the kinetic energy of the free kaon. [ABSTRACT FROM AUTHOR]

Cross sections and vector-analyzing powers for four unspecific configurations of the 2H( p, pp) n breakup reaction at E lab p = 65MeV were measured in a kinematically complete experiment. Measured observables are compared with rigorous Faddeev calculations using four realistic charge-dependent interaction models, the CD Bonn, Argonne v18, Nijmegen I, and Nijmegen II potentials with or without inclusion of the Tucson-Melbourne three-nucleon force. Coulomb effects are completely omitted. A satisfactory agreement between theory and experiment has been found. There exist, however, some discrepancies between measured and calculated analyzing-power distributions in certain kinematical regions. The effects of the Tucson-Melbourne three-body force are either negligible or slightly increasing the disagreement. [ABSTRACT FROM AUTHOR]

The proton-deuteron breakup cross sections and analyzing powers A for three kinematically complete configurations in a quasi-free-scattering geometry have been measured at E = 65 MeV. The data are compared with predictions of rigorous Faddeev calculations using the Argonne AV14, Bonn-B, Nijmegen-78, and Paris potentials. A satisfactory agreement between theory and experimental data, both for cross sections and analyzing powers, has been found. [ABSTRACT FROM AUTHOR]

The elemental composition of rabbit liver was determined by the PIXE and micro-PIXE methods. The mean concentrations of P, S, Cl, K, Fe, Cu, Zn, and Rb measured by both methods were similar. The latter method also allowed for localization of elements within lobule territory. It has been found that some elements are more prevalent in the veins (Cl, Fe) and others in the liver parenchyma (P, Cu, Zn). Moreover, Zn showed the characteristic intralobular distribution. Some methodological aspects of microbeam application to biological materials were also discussed. [ABSTRACT FROM AUTHOR]

We study the production of Λ hyperons in p+ A reactions on the basis of a BUU transport approach for S, Cu, Sn, Au, Pb and U from 1.1 to 1.7 GeV beam energy and evaluate the properties of the hypernuclei produced with respect to excitation energy, transverse and longitudinal momentum, angular momentum and mass. Furthermore, the decay of the hypernuclei by particle emission in competition with fission channels is followed by a statistical model calculation. We find the system p+ Au at about 1.5 GeV to be optimally suited for the production of heavy hypernuclei, where the Λ-decay is expected to be dominated by nonmesonic decay channels. [ABSTRACT FROM AUTHOR]

We study the production of Λ hyperons in p + A reactions within the BUU transport approach including elastic Λ N rescattering and extract the Λ sticking probabilities and hypernucleus formation cross sections as a function of bombarding energy and target mass. At 1.5 GeV about 25% of the Λ hyperons are found to be bound in case of heavy nuclei likeU leading to large cross sections for Λ-hypernuclei. The respective hypernuclei show broad distributions in excitation energy, momentum and angular momentum. The decay of the Λ hyperon in case of heavy targets is found to be almost entirely due to nonmesonic decay channels, i.e. ΛN → NN processes. [ABSTRACT FROM AUTHOR]

The production of K mesons in proton-nucleus and deuteron-nucleus collisions is analyzed with respect to one-step nucleon-nucleon ( NN → N ΛK), Δ- nucleon ( ΔN → N Λ K) and two-step pion-nucleon ( πN → K Λ) production channels on the basis of experimental ground state momentum distributions and free on-shell production processes. Whereas for K production in proton-nucleus reactions the secondary channel πN clearly dominates at subthreshold energies, meson and nucleon induced channels are of similar magnitude in deuteron-nucleus reactions. Contrary to nucleus-nucleus collisions the Δ induced reaction channels are found to be of minor importance. The experimental differentiation of the underlying microscopic reaction channels appears possible via differential proton - K coincidence measurements as shown in detail by the microscopic simulations including proton rescattering. [ABSTRACT FROM AUTHOR]

Angular distributions of cross sections have been measured for single nucleon transfer reactions induced by 344.5 MeVC ions on aC target. DWBA analyses have been performed for transitions to discrete final states. Spectroscopic information has been derived and is compared with results of other studies. [ABSTRACT FROM AUTHOR]

A classical dynamical alpha-cluster model has been developed and applied in order to get inclusive energy spectra of alpha particles produced in the collision ofC +C at the beam energy 28.7 MeV/A. Results of the calculations are compared with experimental data. The shapes of the experimental energy spectra and the absolute normalization at forward angles are approximately described without any free parameters. The model makes it possible to distinguish alpha particles originating from the compound system and from direct processes. The spectra at forward angles are dominated by projectile fragmentation processes. The cross section at larger angles is overestimated, which is partially due to emission of particles other than alpha particles in central collisions. The evaporation Hauser-Feshbach model predicts that alpha particles emitted from the compound nucleus constitute less than 26% of all emitted particles. [ABSTRACT FROM AUTHOR]

Constraints on the spin-averaged Λp scattering length and effective range have been obtained from measurements of the pp → pK+Λ reaction close to the production threshold by comparing model phase-space Dalitz plot occupations with experimental ones. The data fix well the position of the virtual bound state in the Λp system. Combining this with information from elastic Λp scattering measurements at slightly higher energies, together with the fact that the hyperdeuteron is not bound, leads to a new determination of the low energy Λp scattering parameters. [ABSTRACT FROM AUTHOR]

Angular distributions of protons, deuterons, tritons and alpha-particles emitted from the reactions in the d+Be-system at E=7 MeV as well as excitation functions at selected angles in the energy range E=6.5-7.5 MeV (LAB) were measured. The potential part of the elastic scattering is described by the phenomenological optical model. The compound nucleus contribution to all exit channels is determined using the Hauser-Feshbach model. The collective excitation of the 2.43 MeV excited state ofBe and transfer processes are analysed within the DWBA formalism. The analyses suggest a significant contribution of five-nucleon transfer to the ( d,He) channel. [ABSTRACT FROM AUTHOR]

Angular distributions of theC( d,Li)Be reaction to the ground and to the unresolved first excited states ofLi orBe nuclei were measured in the entire angular region in the centre of mass system at E=78.0 MeV. Both the one-step five-nucleon cluster transfer as well as two-step sequential transfers were considered in the theoretical analysis. The former mechanism was found to dominate, but the latter is also not negligible. [ABSTRACT FROM AUTHOR]

Angular distributions of theB( α,Li)Be reaction were measured at E = 91.8 MeV in the entire center of mass angular region. A DWBA analysis explains the reaction as triton and helion transfer in the forward and backward angular regions, respectively. [ABSTRACT FROM AUTHOR]

The proton induced X-ray emission method in combination with a proton microprobe was applied to study the intramembranaceous ossification. As material sections of mouse embryo skulls from the 17th and 19th day of gestation were used. The morphology of the sample was examined by routine histochemical procedure performed on the sections adjacent to that irradiated by the proton microprobe. The measurements were made in line scan and raster scan mode. The concentrations of P, S, Cl, K, Ca, Fe and Zn were determined at each irradiated point. The average element concentrations were calculated for four parts of each section (bone, cartilage, mesenchymal tissue close to the bone and mesenchymal tissue in other places). The distributions of Ca and P (less markedly than Ca) concentrations almost exclusively correlate with localization of the bone while S, Cl and K concentrations show preference to the cartilage. The amount of inorganic material in flat bones of the 17-day embryo amounts to 14% of the dry mass. The material is characterized by a Ca/P ratio of bout 1.6 In the embryo 2 days older the amount of the inorganic phase is practically the same (15%) while the Ca/P ratio approaches 2. This suggests the presence of the precursor phase in the flat bone calcification. It is possible that octacalcium phosphate (Ca/P ratio equals to 1.72) is formed at the onset of the flat bone mineralization which transforms rapidly (in 2 days) to a more stable mineral (defective hydroxyapatite). [ABSTRACT FROM AUTHOR]

The femoral bone from the 18-day pregnancy embryo and an rib cartilage of mature mice have been investigated using PIXE (proton induced X-ray emission) in combination with a proton microprobe on snap frozen cryosectioned material. The localization and the results of quantitative measurement of P, S, Cl, K, Ca, Fe and Zn have been correlated with the histochemical localization of inorganic deposits. It has been found that in calcifying and degenerating cartilage of the growth plate there is substantial loss of S; this element being indicative for sulphate groups of glycosaminoglycans. This change seems to be an important factor conditioning the process of mineralization. Zn is found in higher concentration in mineralized tissues, both in embryonal and mature cartilage as well as in the bone, and this suggests that Zn is also involved in the mineralization process. The mineralization of rib cartilage exceeds that of embryonal bone, and the Ca/P ratio is higher in the former than in the hydroxyapatite of the latter. The method described is a useful analytical tool especially for such types of studies in which elements are not easily redistributed by freezing, cutting and drying; e.g. in investigations of mineral deposits. [ABSTRACT FROM AUTHOR]

The elemental composition of the human atheroselerotic popliteal artery was examined using the proton-induced X-ray-emission (PIXE) method. The application of a narrow proton beam (3×10 μm) enabled us to determine not only the concentrations of Cl, K, Ca, Fe, Cu, Zn, Br and Pb, but also their localization in different artery-wall regions. The highest mean concentrations of Cl, K, Zn and Br were found in the tunica media. In the investigated sections the distribution of Ca and Fe varied: sometimes, these elements were prevalent in the tunica intima, whereas in other cases, the highest concentrations were observed in the tunica media or tunica adventitia. The concentration profiles of each element were characterized by many sharp, narrow peaks. The highest concentrations of Ca and Fe showed such high levels that only one explanation is possible, i.e. the presence of crystals. The correlation of Ca peaks with those of Zn and Fe is discussed. The usefulness of the micro-PIXE method for the investigation of biomedical materials is also considered. [ABSTRACT FROM AUTHOR]

For the reaction Bi ( n, γ) Bi, the Q-value as determined from a suitablereaaction chain exceeds that indicated by the γ-line of maximum energy as measured with a magnetic pair spectrometer. Coincidence investigations have therefore been undertaken to search for γ-γ-cascades: transitions for 117, 165, 275, 396 and 507 keV have been detected in coincidence with the lines at 4 MeV. The intensities of the former lines have been elucidated and are discussed. The most probable value for the neutron binding energy is thereby indicated to be 4·56 MeV. [ABSTRACT FROM AUTHOR]

At the internal facility COSY-11 a first measurement of the reaction p′p → near the production threshold has been performed. Results for the analysing power will be presented and a comparison with one-meson exchange models will be discussed. [ABSTRACT FROM AUTHOR]

The predictions for the production of nuclides and particles in proton-induced reactions are important e.g. for the detailed design of spallation neutron sources or accelerator-driven-systems. Computational tools are required that are able to describe quantitatively the two-stage process i.e. intra-nuclear cascade followed by evaporation-fission. The first stage is a highly non-equilibrated process in which incoming proton deposits in hot residual nucleus both excitation energy and angular momentum. The CBUU transport model calculation for few targets, for the proton energy range 0.4-2.0 GeV are presented, with the idea to find global parametrizations for the distributions of charge, mass, excitation energy, angular momentum of hot residual nuclei. [ABSTRACT FROM AUTHOR]

It is shown that the mass dependence of the Λ-lifetime in heavy hypernuclei is sensitive to the ratio of neutron-induced to proton-induced non-mesonic decay rates Rn/R p. A comparison of the experimental mass dependence of the lifetimes with the calculated ones for different values of Rn/R p leads to the conclusion that this ratio is larger than 2 on the confidence level of 0.75. This suggests that the phenomenological Δ I= 1/2 rule might be violated for the nonmesonic decay of the Λ-hyperon. [ABSTRACT FROM AUTHOR]