New results from the HAPPEX Experiments at Q<Superscript>2</Superscript> = 0.1GeV/c<Superscript>2</Superscript>

The nucleon's strange electric and magnetic form factors G _E ^s and G _M ^s can be probed via parity-violating electron scattering. The HAPPEX Collaboration has made new measurements of the parity-violating asymmetry A _PV in elastic scattering of 3GeV electrons off hydrogen and ⁴He targets with 〈θ_lab〉 ≈ 6.0^° . For ⁴He the preliminary result is A _PV = (+ 6.43±0.23(stat)±0.22(syst))×10^-6 . For hydrogen the preliminary result is A _PV = (- 1.60±0.12(stat)±0.05(syst))×10^-6 . From these values we extract G ^s _E = 0.004±0.014±0.013 at 〈Q ²〉 = 0.077 GeV/c^2 , and G ^s _E +0.09G ^s _M = 0.004±0.011±0.005 at 〈Q ²〉 = 0.109 GeV/c^2 , both consistent with zero, providing stringent new limits on the role of strange quarks in the vector structure of the nucleon.     

The pp→K<Superscript>+</Superscript><Emphasis Type="Italic">Σ</Emphasis><Superscript>+</Superscript>n cross-section from missing-mass spectra

We utilize existing inclusive data on K⁺-meson momentum spectra of the reaction pp→K ⁺ X at T _p = 2.3-2.85GeV to deduce total cross-sections for pp→K ⁺ Σ ⁺ n. The method used to extract those cross-sections is explained and discussed in detail. Our result for T _p = 2.85GeV is consistent with the data point from a direct measurement at the same beam energy. The cross-section obtained for T _p = 2.3GeV is with 13.7±2.3μb considerably smaller than the value found in a recent experiment by the COSY-11 Collaboration at a somewhat lower beam energy, indicating that the pp→K ⁺ Σ ⁺ n reaction cross-section could exhibit a rather unusual energy dependence.     

Application of Boltzmann Equation on Spin Diffusion of Ferromagnetic Superfluid <Superscript>3</Superscript>He: Near Critical Temperature

Different scattering processes of quasiparticles containing a binary process, a coalescence process and a decay process in transition probabilities are taken into account. In the meantime, interaction between Bogoliubov quasiparticles as well as that between normal and superfluid components (spin up-spin down quasiparticles) of ferromagnetic superfluid ³He-A ₁ are considered. Pfitzner procedure is used in the calculation of triplet and singlet quasiparticle scattering amplitude existing in transition probabilities of the collision integral of standard Boltzmann equation at melting pressure. Pfitzner procedure is extended beyond s-p approximation by adding higher angular momentum components. Then, using the results of Boltzmann equation and considering smallness of the gap close to T _c↑, the change of the spin diffusion coefficients tensor of the A ₁-phase of superfluid ³He close to critical temperature and melting pressure is calculated. Temperature dependence of the spin diffusion coefficient change, i.e., δD _xyxy /D⌈=(3/2)(δD _xzxz /D)⌉, is −0.71(1−(T/T _c↑))^1/2. It is also shown that interaction between normal and Bogoliubov quasiparticles (normal-superfluid components interaction) is very important to transport properties such as spin diffusion close to critical temperature. Furthermore, using s-p approximation, the prefactor of δD _xyxy /D is plotted in terms of pressure; hence, the pressure dependence of δD _xyxy /D is also determined.     

Phase shift analysis of the <Superscript>6</Superscript>He+<Superscript>208</Superscript>Pb and the <Superscript>6</Superscript>He+<Superscript>197</Superscript>Au systems

We present the elastic scattering of the ⁶He+²⁰⁸Pb and the ⁶He+¹⁹⁷Au systems at the laboratory energy of E _lab=27 MeV within the framework of the McIntyre parametrization, and systematically investigate χ ²/N analysis of both systems to obtain an excellent agreement between the theoretical results and the experimental data. We find large diffusivity parameters indicating long range absorption mechanisms. We also show that both systems lack both the nuclear and the Coulomb rainbow scattering for obtained S-matrix parameters.     

Cluster radioactivity leading to doubly magic <Superscript>100</Superscript>Sn and <Superscript>132</Superscript>Sn daughters

Decay of neutron-deficient ^{128 − 137}Gd parents emitting ⁴He to ³²S clusters are studied within the Coulomb and proximity potential model. The predicted half-lives are compared with other models and most of the values are well within the present experimental limit for measurements (T _1/2 < 10³⁰ s). The lowest T _1/2 value for ²⁸Si emission from ¹²⁸Gd indicates the role of doubly magic ¹⁰⁰Sn daughter in cluster decay process. It is also found that neutron excess in the parent nuclei slows down the cluster decay process. Geiger–Nuttal plots for all clusters are found to be linear with different slopes and intercepts. The α-decay half-lives of ^{148 − 152}Gd parents are computed and are in agreement with experimental data. The role of doubly magic ¹³²Sn daughter in cluster decay process is also examined for various neutron-rich Ba, Ce, Nd, Sm and Gd parents emitting clusters ranging from ⁴He to ³²Si. Alpha-like structures are most probable in the decays leading to ¹⁰⁰Sn, while non-α-like structures are probable in the decays leading to ¹³²Sn. The neutron–proton asymmetry in parent and daughter nuclei is responsible for the reduced decay rate in the decay leading to ¹³²Sn.     

Direct calculation of transition intensities in LiYF<Subscript>4</Subscript>: Nd<Superscript>3+</Superscript>

Duan’s simple model is extended to analyze the mixing of the 4f ^{N − 1}5d configuration with the 4f ^N states. The explicit static coupling and traditional dynamic coupling are considered, and the parameters are fitted according to the absorption spectrum in LiYF₄: Nd³⁺. The parameter values obtained are as follows: T ₃₂ = −28i × 10⁻⁷, T ₅₂ = −1151i × 10⁻⁷, A ₃₂² = 192i × 10⁻¹² cm, A ₅₂⁴ = i × 10⁻¹² cm, A ₇₂⁶ = 54i × 10⁻¹² cm, and A ₇₆⁶ = −680i × 10⁻¹² cm. Compared to the experimental measurements, the present model yields better results than those obtained from the Judd-Ofelt theory. The text was submitted by the authors in English.     

Analysis of <Superscript>4</Superscript>He+<Superscript>40</Superscript>Ca and <Superscript>4</Superscript>He+<Superscript>44</Superscript>Ti scattering using different optical model potentials

Elastic scattering of ⁴He+⁴⁰Ca and ⁴He+⁴⁴Ti reactions at backward angles has been analyzed using two differentmodels, microscopic and semimicroscopic folding potentials. The derived real potentials supplemented with phenomenological Woods–Saxon imaginary potentials, provide good agreement with the experimental data at energy E_c.m. = 21.8 MeV without need to renormalize the potentials. Coupledchannels calculations are used to extract the inelastic scattering cross section to the low-lying state 2+ (1.083 MeV) of ⁴⁴Ti. The deformation length is obtained and compared with the electromagnetic measurement values as well as those obtained from previous studies.     

Effect of Sr<Superscript>2+</Superscript> ion substitution with trivalent ions (Sc<Superscript>3+</Superscript>, In<Superscript>3+</Superscript>, La<Superscript>3+</Superscript>, Bi<Superscript>3+</Superscript>) on its ferroelectric instability in SrTiO<Subscript>3</Subscript>

The vibration frequencies of unstable ferroelectric and antiferrodistortion modes and the dependences of the energy on the ion displacement amplitude have been calculated within the generalized Gordon-Kim model for distortions along eigenvectors of these modes in the mixed compounds Sr_{1 − x} A _x Ti_{1 − x} /₄□ _x/4O₃ and Sr_{1 − y} A _2y /₃□ _y/3TiO₃ (A = Sc³⁺, In³⁺, La³⁺, Bi³⁺; □ is the vacancy). To compensate an excess positive charge, vacancies are introduced into the Ti⁴⁺ or Sr²⁺ site. Calculations have been performed in the “daverage” crystal approximation for impurity concentrations of 0.25 and 0.50. To this end, a set of 40 atomic superlattices with various orderings of heterovalent ions Sr²⁺ and impurity A ³⁺ has been considered. It has been found that each impurity type, independently of charge balance, induces ferroelectric instabilities in doped compounds. In the case of doping with In³⁺ and La³⁺ for concentration x = 0.25, the possibility of rotating the polarization vector has been shown.     

New insight in the level structure of <Superscript>153</Superscript>Er

The high-spin level structure of the ¹⁵³Er nucleus has been reinvestigated by in-beam γ-ray and electron spectroscopy with (¹⁴N,pxn) reaction. Excitation energies, spin and parity assignments are unambiguously established for the two lowest isomers T _1/2≃ 380 ns and T_1/2\simeq 10 ns. The characteristics of the third one (T _1/2≃ 250 ns) at 5.2 MeV are still questionable but its main decay modes are better known. An extension of the level scheme is proposed up to 8.4 MeV.Experimental results have been discussed in terms of shell model multiplets and compared with the other structures observed in N=85 neighbouring nuclei. Received: 8 November 1999 / Revised version: 13 December 1999     

Leading-order 2πγ exchange NN interaction: Central potentials proportional to g<Subscript>A</Subscript><Superscript>0</Superscript> and g<Subscript>A</Subscript><Superscript>2</Superscript>

We calculate at two-loop order in chiral perturbation theory the electromagnetic corrections to the leading-order 2π exchange NN interaction proportional to g _A ⁰ and g _A ². The resulting 2πγ exchange potential contains isospin-breaking components which reach up to about -2% of the corresponding isovector 2π exchange potential. With a value of only -17keV at r = m _π ^-1 = 1.4fm the charge-independence breaking central potential obtained here is negligibly small in comparison to the one generated by the isoscalar c₃ contact vertex. Our calculation confirms that the largest long-range isospin-violating NN potentials arise from the 2πγ exchange diagrams involving the large low-energy constants c ₄ ≃ - c ₃ ≃ 3.3GeV^-1 representing the important Δ(1232) dynamics.     

A high-pressure polarized <Superscript>3</Superscript>He gas target for nuclear-physics experiments using a polarized photon beam

Following the first experiment on three-body photodisintegration of polarized ³He utilizing circularly polarized photons from High-Intensity Gamma Source (HIg \gamma S) at Duke Free Electron Laser Laboratory (DFELL), a new high-pressure polarized ³He target cell made of pyrex glass coated with a thin layer of sol-gel doped with aluminum nitrate nonahydrate has been built in order to reduce the photon beam-induced background. The target is based on the technique of spin exchange optical pumping of hybrid rubidium and potassium and the highest polarization achieved is ∼ 62% determined from both NMR-AFP and EPR polarimetries. The phenomenological parameter that reflects the additional unknown spin relaxation processes, X , is estimated to be ∼ 0.10 and the performance of the target is in good agreement with theoretical predictions. We also present beam test results from this new target cell and the comparison with the GE180 ³He target cell used previously at HIg \gamma S. This is the first time that the sol-gel coating technique has been used in a polarized ³He target for nuclear-physics experiments.     

Charge distribution studies in the fast-neutron-induced fission of <Superscript>232</Superscript>Th, <Superscript>238</Superscript>U, <Superscript>240</Superscript>Pu and <Superscript>244</Superscript>Cm

Charge distribution studies for heavy-mass fission products were carried out in the fast-neutron-induced fission of ²³²Th, ²³⁸U, ²⁴⁰Pu and ²⁴⁴Cm using radiochemical and gamma-ray spectrometric techniques. The width parameter( σ_Z/σ_A), the most probable charge/mass ( Z _P/A _P), the charge polarization (ΔZ) and the slope of charge polarization [ δ(ΔZ)/δA ^′] as a function of the fragment mass (A ^′) were deduced. The average charge dispersion parameter ( 〈σ_Z〉) and proton odd-even effect ( δ_p) were also obtained for these fissioning systems. The 〈σ_Z〉 and δ_p values in the fissioning systems ²⁴¹Pu ^* and ²⁴⁵Cm ^* were determined for the first time. The δ(ΔZ)/δA ^′ value is also determined for the first time in the fissioning systems ²³⁹U ^* , ²⁴¹Pu ^* and ²⁴⁵Cm ^* . These data along with the literature data for even-Z fissioning systems such as ²³⁰Th ^* , ²³²Th ^* , ²³³U ^* , ²³⁴U ^* , ²³⁶U ^* , ²³⁸U ^* , ²³⁹Pu ^* , ²⁴⁰Pu*, ²⁴²Pu ^* , ²⁴⁶Cm ^* , ²⁵⁰Cf ^* and ²⁵²Cf(SF) are discussed in terms of nuclear structure effect and dynamics of descent from the saddle to the scission point. The role of the excitation energy in low-energy fission is also discussed. Received: 26 July 2002 / Accepted: 3 December 2002 / Published online: 3 April 2003 RID="a" ID="a"Present address: Emeritus Scientist (CSIR) Bhabha Atomic Research Centre, Nuclear Recycle Group, WIP Building, Trombay, Mumbai-400085, India; e-mail: rhiyer@magnum. barc.ernet.in Communicated by D. Schwalm     

The 2<Superscript>1/3</Superscript> rule for magnetic susceptibility of gadolinium

The dependences of the magnetization M and the magnetic susceptibility χ = ∂M/∂H of pure gadolinium (the concentration of foreign impurities is lower than 0.1 wt %) on the temperature T and the magnetic field H have been measured using a Quantum Design MPMS-5XL SQUID magnetometer. In this material, inhomogeneities of the atomic structure should not lead to a nonuniform distribution of the magnetic characteristics (including the Curie temperature T _C) over the volume of the sample. The obtained dependences of M and χ have been used to investigate the possibility of suppressing magnetic inhomogeneities of other types by magnetic fields with a strength of up to 50 kOe. It has been assumed that these inhomogeneities are suppressed when the specific relationship, namely, the 2^1/3 rule is fulfilled. The rule relates the portions of the dependence χ(T, H) which at the temperature T = T _C and at the maximum in the curve χ(T) (T = T _m ) depend on H in accordance with the H ^2/3 law. It has been shown that the portions separated from the experimental curves χ(T _C, H) and χ(T _m , H) obey the 2^1/3 rule.     

Re-dispersible Li<Superscript>+</Superscript> and Eu<Superscript>3+</Superscript> co-doped CdS nanoparticles: Luminescence studies

Re-dispersible CdS, 5 at.% Eu³⁺-doped CdS, 2 at.% Li⁺ and 5 at.% Eu³⁺ co-doped CdS nanoparticles in organic solvent are prepared by urea hydrolysis in ethylene glycol medium at a low temperature of 170°C. CdS nanoparticles have spherical shape with a diameter of ∼80 nm. The asymmetric ratio (A ₂₁) of the integrated intensities of the electrical dipole transition to the magnetic dipole transition for 5 at.% Eu³⁺-doped CdS is found to be 3.8 and this ratio is significantly decreased for 2 at.% Li⁺ and 5 at.% Eu³⁺ co-doped CdS (A ₂₁ = 2.6). It establishes that the symmetry environment of Eu³⁺ ion is more favored by Li-doping. Extra peak at 550 nm (green emission) could be seen for 2 and 5 at.% Eu³⁺ co-doped CdS. Also, the significant energy transfer from host CdS to Eu³⁺ is found for 5 at.% Eu³⁺-doped CdS compared to that for 2 at.% Li⁺ and 5 at.% Eu³⁺ co-doped CdS.      

High-spin states in <Superscript>36</Superscript>Ar and their underlying shell model configurations

Eight high-spin states in ³⁶Ar below 10MeV excitation energy, among them a prospective J ^π = 8^- state at 9408keV and the J? 8 levels of the recently discovered superdeformed rotational band, have been observed by n-γ coincidence measurements with the ³³S(α, nγ) reaction at E _α = 14.4 and 13.4MeV. High-spin assignments of, respectively, J ^π = 6⁺ and 5^- were obtained for the E _p = 1209 and 1462keV (E _x = 9682 and 9927keV) resonances of the ³⁵Cl (p,γ) reaction by a measurement of γ-ray angular distributions. The spectrum of the high-spin and of the E _x? 7.4MeV levels is decomposed according to the underlying shell model configurations with n = 0, 1, 2, 4 particles excited from the N = 2 into the N = 3 major shell. The role of four-particle excitations, all connected with large prolate distortions, is elucidated for the entire A = 36-40 mass region. Received: 21 December 2001 / Accepted: 25 March 2002     

Fine structure of the muonic <Superscript>4</Superscript>He ion

On the basis of quasi-potential approach to the bound state problem in QED we calculate the vacuum polarization, recoil and structure corrections of orders α⁵ and α⁶ to the fine splitting interval ΔE ^fs = E(2P _3/2) − E(2P _1/2) in muonic ₂⁴He ion. The resulting value ΔE ^fs = 146180.68 μeV provides reliable guideline in performing a comparison with the relevant experimental data.     

Diffractive production of two ρ<Superscript>0</Superscript><Subscript>L</Subscript> mesons in e<Superscript>+</Superscript>e<Superscript>-</Superscript> collisions

We present an estimate of the cross-section for the exclusive production of a ρ_L ⁰-meson pair in e⁺e^- scattering, which will be studied in the future high-energy International Linear Collider. For this aim, we complete calculations of the Born order approximation of the amplitudes γ^* _L,T(Q₁ ²)γ^* _L,T(Q₂ ²)→ρ_L ⁰ρ_L ⁰, for arbitrary polarization of virtual photons and longitudinally polarized mesons, in the kinematical region s≫-t,Q₁ ²,Q₂ ². These processes are completely calculable in the hard region Q₁ ²,Q₂ ²≫Λ² _QCD, and we perform most of the calculations in an analytical way. The resulting cross-section turns out to be large enough for this process to be measurable with foreseen luminosity and energy, for Q₁ ² and Q₂ ² in the range of a few GeV².     

Saturation of Coulomb sum rules in the <Superscript>6</Superscript>Li case

The Coulomb sums S _L(q) of the ⁶Li nucleus have been obtained from electron scattering measurements at 3-momentum transfers q = 1.125–1.625 fm⁻¹. It is found that at q > 1.35 fm⁻¹ the Coulomb sum of the nucleus becomes saturated: S _L(q) = 1 .     

Kinetics of the sorption of <Superscript>3</Superscript>He by C<Subscript>60</Subscript> fullerite. The quantum diffusion of <Superscript>3</Superscript>He and <Superscript>4</Superscript>He in fullerite

The kinetics of the sorption and subsequent desorption of gaseous ³He in a C₆₀ fullerite powder has been studied in the temperature range of 2–292 K. The temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite have been plotted using the measured characteristic times of filling of octahedral and tetrahedral interstices, as well as previous data. These temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite are qualitatively similar. A decrease in the temperature from 292 to 79 K is accompanied by a decrease in the diffusion coefficients, which corresponds to the dominance of the thermally activated diffusion of helium isotopes in fullerite. A further decrease in the temperature to 8–10 K leads to an increase in the diffusion coefficients by more than an order of magnitude. The diffusion coefficients of ³He and ⁴He are independent of the temperature below 8 K, indicating the tunnel character of the diffusion of helium in C₆₀ fullerite. The isotope effect is manifested in the difference between the absolute values of the diffusion coefficients of ³He and ⁴He atoms at the same temperatures.     

Concentration of Cr<Superscript>4+</Superscript> impurity ions and color centers as an indicator of saturation of forsterite crystals Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript> with oxygen

The influence of the oxygen partial pressure P _{O 2} in the growth atmosphere on the coefficient of chromium distribution between the crystal and the melt of forsterite, the Cr³⁺ and Cr⁴⁺ ion contents in crystals, and the concentration of color centers induced by irradiation has been investigated. It has been established that the crystals grown at low oxygen partial pressures P _{O 2} (0.01–0.05 kPa) are characterized by low concentrations of Cr⁴⁺ ions and color centers. A change in the oxygen partial pressure to P _{O 2} ∼ 0.85 kPa leads to an increase in the Cr⁴⁺ center concentration by a factor of ∼10 and in the color center concentration by a factor of ∼5. A further increase in the oxygen partial pressure to P _{O 2} to 12 kPa remains the concentration of these centers almost unchanged. A model has been proposed according to which the intrinsic defects formed under conditions of a relative excess of oxygen leads to both the self-oxidation of chromium and the formation of color centers in the forsterite crystals under irradiation.