The solid solutions of Li2Mn4O8-Li1Fe5O8

A solid solution of (1 ?x)(Li₂Mn₄O₈)x(Li₁Fe₅O₈) for 0<x<1 has been investigated by Mössbauer spectroscopy at room temperature and at 80 K. The saturated magnetic moment has been measured forx>0.6. The results are explained by a change of site preference of the Li ion from the tetragonal (A) site atx=0 to the octahedral [B] site atx=1.     

Structure functions of bound nucleons: From the EMC effect to nuclear shadowing

We describe the nuclear structure functions in the whole range of the Bjorken variablex, by combining various effects in a many-step procedure. First, we present a QCD motivated model of nucleons, treated, in the limit of vanishingQ ², as bound states of three relativistic constituent quarks. Gluons and sea quarks are generated radiatively from the input valence quarks. All parton distributions are described in terms of the confinement (or nucleon's) radius. The results for free nucleons are in agreement with the experimental determinations. The structure functions of bound nucleons are calculated by assuming that the main effect of nucleon binding is stretching of nucleons. The larger size of bound nucleons lowers the valence momentum and enhances the radiatively generated glue and sea densities. In the small-x region the competitive mechanism of nuclear shadowing takes place. It also depends on the size of the nucleons. By combining stretching, shadowing and Fermi motion effects (the latter confined to very largex), the structure function ratio is well reproduced. Results are also presented for theA-dependence of the momentum integral of charged partons, the nuclear gluon distribution and the hadron-nuclei cross sections.     

Dynamical parton distributions of the proton and small-x physics

The perturbative properties of parton distributions generated radiatively from a valence-like input at some low resolution scale are discussed with the aim of explaining the physical aspects underlying the reliability of the predicted distributions in the small-x region. Aspects of higher-twist (shadowing) effects as well as small-x resummations are discussed. Utilizing recent improved data atx?10^?2 and a factorization scheme in which the heavy quarksc, b, ..., arenot entailed among the intrinsic (massless) parton distributions, we readjust our valencelike input and provide parametrizations of the slightly modified dynamical LO and NLO $(\overline {MS} ,DIS)$ predictions for parton distributions.     

J/Ψ suppression in relativistic heavy ion collisions through final state interactions with excited nucleons

TheJ/Ψ suppression in relativistic heavy ion collisions through final state interactions with excited state nucleons is estimated in a manner analogous to that of Gerschel and Hüfner for ground state nucleons. If excited state nucleons are larger in size than nucleons in their ground state, theJ/Ψ absorption cross section is increased. Because of relativistic time dilation this effect does not significantly alter theJ/Ψ suppression previously found.     

New aspects of the rotational model in25Mg

Spin assignments have been made to the²⁵Mg levels in theE _x=5–6 MeV region fromγ-ray angular distributions measured in the²²Ne(α, n y) reaction atE _α=8.0 and 8.8 MeV and fromp-γ angular correlations measured in the²⁴Mg(d, p γ) reaction atE _d=6 MeV. Unique spin assignments ofJ=7/2, 5/2, 5/2, and 9/2 could be made to the levels atE _x=5005, 5511, 5851, and 5967 keV, respectively. Ambigious assignments have been made to the levels atE _x=5245, 5524, 5785, 6032 keV (J=11/2, 7/2), 5455 keVJ=13/2, 9/2), and 5738 keV (J=3/2, 5/2). The present data confirm previous assignments ofJ=1/2 to the levels atE _x=5108 and 5466 keV, respectively. Lifetime estimates have been obtained, using the Doppler-shift attenuation method, for the levels atE _x=5245 keV (τ=30–60 fs), 5785 keV (τ=50–100 fs), 5967 keV (τ=50–100 fs), and 5455 keV (τ>1ps). All other levels in theE _x=5–6 MeV region haveτ<60 fs. A breakdown of theK-selection rule has been observed in theγ-decay of some high spin states, indicating a deviation from the strong coupling model.     

Roles of survival probability and barrier reduction in heavy ion fusion induced by break up

Shadowing effects in deep-inelastic lepton-nucleus scattering probe the mass spectrum of diffractive leptoproduction from individual nucleons. We explore this relationship using current experimental information on both processes. In recent data from the NMC and E665 collaboration, taken at small x ? 0.1 and Q ² ? 1 GeV ², shadowing is dominated by the diffractive excitation and coherent interaction of low mass vector mesons. If shadowing is explored at small x ? 0.1 but large Q ² ? 1 GeV ² as discussed at HERA, the situation is different. Here dominant contributions come from the coherent interaction of diffractively produced heavy mass states. Furthermore we observe that the energy dependence of shadowing is directly related to the mass dependence of the diffractive production cross section for free nucleon targets.     

Global properties of radial wave functions in Schwarzschild's space-time

The radial factorR(x, x _s ) of a scalar field in Schwarzschild's space-time satisfies a second order ordinary differential equation with two regular singular points atx=0 andx=x _s and one irregular singular point atx=∞. The analytical properties of four solutions ?₁, ?₂, ?₃, and ?₄ (defined by their power series expansions aboutx=0 andx=x _s ) with respect tox _s are studied. An analytical continuation is given for each solution outside its circle of convergence. Relations to the flat-space solutions are established. Finally the coefficients relating linearly any three of these solutions are determined and studied as functions of the parameterx _s .     

Phenomenology of nuclear shadowing in deep-inelastic scattering

We investigate shadowing effects in deep-inelastic scattering from nuclei at small valuesx < 0.1 of the Bjorken variable. Unifying aspects of generalized vector meson dominance and color transparency we first develop a model for deep-inelastic scattering from free nucleons at smallx. In application to nuclear targets we find that the coherent interaction of quark-antiquark fluctuations with nucleons in a nucleus leads to the observed shadowing atx < 0.1. We compare our results with most of the recent data for a large variety of nuclei and examine in particular the Q² dependence of the shadowing effect. While the coherent interaction of low mass vector mesons causes a major part of the shadowing observed in the Q² range of current experiments, the coherent scattering of continuum quark-antiquark pairs is also important and guarantees a very weak overall Q² dependence of the effect. We also discuss shadowing in deuterium and its implications for the quark flavor structure of nucleons. Finally we comment on shadowing effects in high-energy photon-nucleus reactions with real photons.     

Shadowing,dipions and the EMC effect

The EMC effect is thought to be a compound phenomenon that appears when nucleons are bound in a nucleus. The shadowing effect shows up in a very low-x range. It is possible that in low- and medium-x ranges there exist weak-binding regions caused by the nucleon distortion in the nucleus as well as by exchange pions among the nucleons and other pions in weak-binding regions. Both these types of pions will be in the dipion state because of the Coulomb field. The dipion effect contributes to the structure function of the nucleus. Nuclear binding energy and Fermi motion in medium- and higher-x ranges cause a shift of the ratio of the nucleus structure function to the deuteron one. Calculations show that better agreement with recent data is obtained if the above three effects are mixed.     

Re-entrant magnetic behaviour in amorphous Fe-rich Fe100−x Zr x alloys

We report results of⁵⁷Fe Mössbauer measurements on the magnetically concentrated re-entrant amorphous Fe₁₀₀?xZr _x alloys (8≤x≤12) which give convincing evidence for a microscopic origin of the low-temperature magnetization anomaly atT _f<T _c. This is shown by an anomalous increase in the magnetic hyperfine field and in the relative intensities of the (?m=0)-Mössbauer lines belowT _f upon cooling. No evidence was found for an antiferromagnetic phase. The shape of the hyperfine-field distribution atT=4.2 K in zero external field and in a field of 3 T is unchanged, indicating homogeneous behaviour of all Fe moments near saturation. Ferromagnetic order is not long-ranged, but determined by exchange-coupled magnetic clusters. The cluster moment nearT _c is found to decrease strongly with increasing Fe content and extrapolates to zero atx≈96.     

The role of nucleon-nucleon short-range correlations in the nuclear structure function in thex > 1 region

By using the Jastrow correlation wave function, the role of nucleon-nucleon short-range correlations in the nuclear structure function in thex > 1 region is reanalyzed. The result shows that, with the proper energy-momentum distribution of nucleons in the nucleus including the effect of nucleon-nucleon short-range correlations, the experimental data of the nuclear structure function in thex > 1 region can not be well explained. It seems that additional components which go beyond the conventional nuclear physics are necessary to describe the effect.     

Inclusive Pomeron-Pomeron interactions at the CERN ISR

Data are presented for the first time on inclusive Pomeron-Pomeron interactions which produce a central systemX (composed mainly of multimeson states) in proton-proton collisions at \(\sqrt s \) at the CERN ISR. The systemX has a Feynman-x distribution which is sharply peaked atx _f=0, is inconsistent with any significant contributions from Reggeon exchange processes, and has an invariant mass dependence in good agreement with the predicted formM _x ^?2 . Kaon production is about 15% of pion production, nearly independent ofM _x, while proton-antiproton production averages about 5% of pion production and increases withM _x. The structure of the central systemX develops into a jetlike shape, asM _x increases, as would be expected from a model of Pomeron fragmentation. The shape of thex _f(π) distribution in the center of mass of theX system (although not proving existence) is consistent with asoft partonic substructure of the Pomeron.     

Rising inelastic cross-section and the attenuation of cosmic rays nucleons in the atmosphere

The intensity of C.R. nucleons in the atmosphere is calculated at high energies for energy dependent inelastic cross-section. It is found that the spectrum of C.R. nucleons becomes steeper with atmospheric depth (xgr/cm²) and behaves like E^?γ^?xB/λ_o.     

Distribution of valence quarks in hadrons at small x in QCD

Valence u- and d-quark distributions in nucleons and pions at small x corresponding to ? and ω Regge pole exchanges have been obtained on the basis of the QCD sum rule method.     

Electromagnetic induction in conductors accelerated in magnetic fields amplified by flux compression

The initial boundary-value problem for the electromagnetic induction in a conducting slab ats(t)≦x≦s(t)+a resulting from its accelerated motionv={s(t), 0, 0} across a transverse magnetic fieldB={0,B(x,t), 0} is treated, when the latter is amplified by orders-of-magnitude with respect to its initial valueB(x,t=0)=B ₀(x) by flux compression in the gap between the moving conductor surfacex=s(t) and an ideal resting conductor atx=0. Two initial (t=0) configurations are considered, assuming that (I)B ₀ (step-shaped) has not yet and (II)B ₀ (uniform) has completely diffused into the conductor atx=s(t=0). By means of a time-dependent coordinate transformation ξ=[x ? s(t)]/a and Fourier series expansions, the electromagnetic fields in the moving conductor are represented as integralfunctionals of the magnetic fieldB ₁ (t) in the gap 0≦x≦s(t).B ₁ (t) is given analytically as solution of a singular Volterra integro-differential equation. The theory is valid for arbitrary (nonrelativistic) speeds.(t) and accelerationss(t)) of the moving conductor. Applications to explosion driven electric induction generators and magnetic flux experiments are discussed briefly.     

The hyperfine magnetic field at57Fe and181Ta in Hf(Fe1−x Co x )2 system

The hyperfine magnetic field at⁵⁷Fe in the ferromagnetic Laves compounds Hf(Fe_1?x Co _x )₂ was measured by the Mössbauer effect method. The substitution of Fe atoms by Co atoms induces a gradual change ofB _hf(Fe) and a decrease in the magnetic moment values in Fe?Co sublattice. The perturbed angular correlation measurements of¹⁸¹Ta were carried out forX=0,X=0.1,X=0.55 at 300 K, andX=0.4 atT=400°C. An abrupt change ofB _hf (Ta) in 0<X<0.1 was observed.     

Structure of28Si from the spectroscopy of high-spin states

A search for high-spin states in²⁸Si has been performed byn?y coincidence measurements in the²⁵Mg(α,nγy) reaction atE _α=14 and 15.5 MeV. Spin-parity assignments of the observed levels were obtained fromn?γ angular correlation and lifetime measurements atE _α=14.5 MeV. Theγ-decay of the 9,164 keV level was investigated separately with the²⁷Al(p, γ) reaction at theE _p=2,160 and 2,312 keV resonances. Rotational bands withK ^π=3^? (comprising levels atE _x=6,879, 8,413, 10,188 and 12,204 keV),K ^π =5^? (comprising levels atE _x=9,702, 11,577 and 13,741 keV) andK ^π=0⁺ (comprising levels atE _x=6,691, 7,381, 9,164 and 11,509 keV) were observed. The finding of the latter band supports the idea of coexisting oblate and prolate shapes in²⁸Si. A level at 14,643 keV excitation energy has the properties of theI ^π=8⁺ member of the ground state band. There are additional positive-parity high-spin states which do not fit into rotational bands. All types of positive-parity states are well accounted for by shell model calculations.     

High-energy hadron-hadron collisions and internal hadron structure

As shown by many authors, central particle emission in pp collisions at centre-of-mass energies ? 20 GeV can be described in terms of independent cluster production. In ref. [1] this process has been related to the quark-gluon picture of nucleon structure. The present paper carries this relation further and links the leading particle spectrum of non-diffractive hadron-hadron collisions to the x distribution of quarks in the hadron. Thus, the flat leading particle spectrum, as observed in non-diffractive pp collisions, is found to be naturally related to the steeply falling x distribution of quarks in the nucleon, as deduced from the structure functions measured in deep inelastic scattering of electrons and neutrinos on nucleons. Our analysis is extended to meson-nucleon collisions and leads to a prediction of the general shape of the quark x distribution in a meson.     

Infrared contribution to the double-logarithmic small-x asymptotics of structure functions

The role playing by the “soft” (κ _T < 1 GeV/c) region in the small-x behaviour ofg ₁(x,Q ²) and the non-singlet structure functionf _{1, NS}(x, Q²) has been studied with the help of the effective QCD Lagrangian which takes into account the lightest degrees of freedom — the constituent quarks and the π-mesons (Goldstone bosons). It has been shown that the quark-quark interaction due to the pion exchange has a negative couplingg for the isovector component (I = 1 in thet-channel) off ₁(x,Q ²) and isosinglet component ofg ₁(x, Q²). Here the pion induced interaction changes mainly the normalization of the quark distribution (it decreasesf _1,NS ^{I = 1} (x,Q ²) two times atx < 3·10^?3) and changes slightly the effective exponents λ (?_1,NS ,g ₁ ～x ^?λ atx → 0). On the other hand due to a positive value of couplingg the value of λ increases by 15% for the isovector part ofg ₁ (x,Q ²) and up to λ ≈ 0.5 (instead of λ ≈ 0.2 without the pion contribution) for the isoscalar non-singlet structure functionf _1,NS ^{I = 0} (x,Q ²).