Thermal neutron capture cross-section of <Superscript>76</Superscript>Ge

The thermal neutron capture cross-sections of the ⁷⁶Ge(n,)⁷⁷Ge and the ⁷⁶Ge(n,)^77m Ge reactions have been measured by activating targets of isotopically enriched GeO₂ through cold neutrons. The -decay spectra after the -decay of ⁷⁷Ge and ^77m Ge were measured with HPGe detectors. From these spectra the cross-sections for the ⁷⁶Ge(n,) reactions were derived relative to the cross-section of ¹⁹⁷Au using the absolute emission probabilities of the observed -ray energies. The methods used in this work result in smaller systematic uncertainties than those obtained in previous experiments.     

Light-charged-particle emission from hot <Superscript>32</Superscript>S<Superscript>*</Superscript>formed in <Superscript>20</Superscript>Ne + <Superscript>12</Superscript>C reaction

Inclusive energy distributions for light charged particles (p , d , t and have been measured in the ²⁰Ne (158, 170, 180, 200 MeV) + ¹²C reactionsintheangularrange$10^°$ - - $50^°$.Exclusivelight-charged-particleenergydistributionmeasurementswerealsodoneforthesamesystemat158 MeVbombardingenergybyin - planelightchargedparticle - - fragmentcoincidence.Pre - equilibriumcomponentshavebeenseparatedoutfromprotonenergyspectrausingthemovingsourcemodelconsideringtwosources.ThedatahavebeencomparedwiththepredictionsofthestatisticalmodelcodeCASCADE.Ithasbeenobservedthatsignificantdeformationeffectswereneededtobeintroducedinthecompoundnucleusinordertoexplaintheshapeoftheevaporated$d$,$t$energyspectra.Forprotons, evaporatedenergyspectrawereratherinsensitivetonucleardeformation, thoughangulardistributionscouldnotbeexplainedwithoutdeformation.Thedecaysequenceofthehot$³²S$nucleushasbeeninvestigatedthroughexclusivelight - - charged - particlemeasurementsusingthe$²⁰Ne$$(158 MeV) + $¹²C reaction. Information on the sequential decay chain has been extracted through a comparison of the experimental data with the predictions of the statistical model. It is observed from the present analysis that exclusive light-charged-particle data may be used as a powerful tool to probe the decay sequence of hot light compound systems.     

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.     

Instabilities of the Conventional Nucleus-Nucleus Interactions for (<Superscript>3</Superscript>H<Superscript>4</Superscript>He) Proton Pickup Cross-Sections

The angular distributions of the ²⁶Mg, ²⁸Si, ³⁰Si(³H, ⁴He) reactions have been analyzed using the exact finite-range DWBA calculations. The optical model potential is assumed to have the conventional spin-orbit potential. The obtained cross-sections with the spin-orbit potential are not significantly different from those calculated using the phenomenological Woods–Saxon form factors in the forward angle regions. The inclusion of the spin-orbit potential gives the best fit to the data and greatly improves the large angle cross-sections. Different reasonable spectroscopic factors are found to account well for the cross-section magnitudes.     

A 3-quasiparticle isomer in neutron-rich <Superscript>183</Superscript>Ta

Excited states in neutron-rich ¹⁸³Ta have been studied using a two-neutron transfer reaction of ¹⁸¹Ta(¹⁸O,¹⁶O) . In-beam -rays were measured in coincidence with scattered ions detected by a high-resolution E -E Si telescope for reaction channel selection. Previously known 1-quasiparticle bands are extended to higher spins, and several levels including a T _1/2 = 0.9(3) μs 3-quasiparticle isomer are identified.     

Cluster structure of <Superscript>16</Superscript>O

A folding potential describing the -scattering on ¹⁶O over a broad energy range 25.8-146.0 MeV is constructed on the basis of -like cluster and unclustered-nucleon configurations of ¹⁶O. The resulting potential does not need any renormalization to fit the angular distribution of elastic cross-sections. The effects of the repulsive part of - and -nucleon interactions are investigated. The analysis suggests that both the - repulsive potential and the unclustered nucleonic configuration in the target are important to describe the scattering data over a broad range of incident energies. The root-mean-square radius for the ¹⁶O nucleus is deduced.Received: 5 December 2002, Published online: 9 October 2003PACS: 25.55.Ci Elastic and inelastic scattering - 24.10.Ht Optical and diffraction models - 21.60.Gx Cluster models     

Triple differential cross-sections of Ne (2s<Superscript>2</Superscript>) in coplanar to perpendicular plane geometry

The distorted wave Born approximation (DWBA) with the spin averaged static exchange potential has been used to calculate the triple differential cross-sections (TDCSs) for Ne (2s ²) ionization by electron impact in coplanar to perpendicular plane symmetric geometry at 110.5 eV incident electron energy. The present theoretical results at gun angles (coplanar symmetric geometry) and (perpendicular plane geometry) are in satisfactory agreement with the available experimental data. A deep interference minimum appears in the TDCS in the coplanar symmetric geometry and a strong peak at scattering angle caused by the single collision mechanism has been observed in the perpendicular plane geometry. The TDCSs at the gun angles , and are predicted.Received: 16 July 2002, Published online: 22 July 2003PACS: 34.80.Gs Molecular excitation and ionization by electron impact - 34.80.Dp Atomic excitation and ionization by electron impact     

Low-lying magnetic and electric dipole strength distribution in the <Superscript>176</Superscript>Hf nucleus

In this study the QRPA approach with the rotational and translational invariant Hamiltonians has been carried out to describe magnetic and electric dipole excitations in ¹⁷⁶Hf . Calculations show that the ¹⁷⁶Hf nucleus demonstrates a very rich B(M1) strength structure and in some aspects nicely confirm the experimental data. It has been shown that the main part of spin-1 states, observed at 2-4MeV in ¹⁷⁶Hf , may be attributed to have a M1 character and may be interpreted as the main fragments of the scissors mode. The agreement between the calculated mean excitation energies as well as the summed B(M1) values of the scissors mode excitations and the available experimental data is quite good. The constructive interference between the orbit and the spin part of M1 strength has been found to be below 3.5MeV. The calculations indicate the presence of a few prominent negative-parity states in the 2-4MeV energy interval. This suggests that the supposition of the experiment “all stronger K = 1 low-lying dipole excitations were of magnetic character” cannot be generalized.     

The photoresponse of <Superscript>45</Superscript>Sc up to 7 MeV

High-resolution photon scattering experiments have been performed on the nucleus ⁴⁵Sc at the Darmstadt superconducting electron accelerator S-DALINAC using bremsstrahlung beams with end point energies of 5.0 and 7.0MeV. Energies, absolute cross-sections and decay widths of 50 states, most of them previously unknown, have been determined. The results are compared to (γ, ) experiments on the neighbouring closed proton shell isotope ⁴⁴Ca .     

On the momentum correlations in the fragmentation of <Superscript>197</Superscript>Au + <Superscript>197</Superscript>Au reactions

We aim to present the formation of fragments using static as well as momentum-dependent interactions and larger nucleonic cross-sections. We shall also examine, in detail, the role of momentum correlations in these situations which are close to the fire-ball as well as to the spectator matter decay. The role of momentum correlations will be studied by imposing an additional cut in the momentum space. A clear need of a momentum cut is demonstrated in both fire-ball as well as spectator matter physics. The momentum-dependent interactions and larger cross-sections play a drastic role in peripheral reactions, whereas the role of momentum cut remains the same in these situations.     

Hyperfine quenching of the 4s4p <Superscript>3</Superscript>P<Subscript>0</Subscript> level in Zn-like ions

In this paper, we used the multiconfiguration Dirac-Fock method to compute with high precision the influence of the hyperfine interaction on the [Ar] P₀ level lifetime in Zn-like ions for stable and some quasi-stable isotopes of nonzero nuclear spin between Z=30 and Z=92. The influence of this interaction on the [Ar] P P₀ separation energy is also calculated for the same ions.     

Multiplicity correlations of intermediate-mass fragments with pions and fast protons in <Superscript>12</Superscript>C + <Superscript>197</Superscript>Au

Low-energy ( MeV) from ¹² C + ¹⁹⁷ Au collisions at incident energies from 300 to 1800 MeV per nucleon were detected with the Si-Si(Li)-CsI(Tl) calibration telescopes of the INDRA multidetector. The inclusive angular distributions are approximately isotropic, consistent with multiple rescattering in the target spectator. The multiplicity correlations of the low-energy pions and of energetic protons ( MeV) with intermediate-mass fragments were determined from the measured coincidence data. The deduced correlation functions for inclusive event samples reflect the strong correlations evident from the common impact parameter dependence of the considered multiplicities. For narrow impact parameter bins (based on charged-particle multiplicity), the correlation functions are close to unity and do not indicate strong additional correlations. Only for pions at high particle multiplicities (central collisions) a weak anticorrelation is observed, probably due to a limited competition between these emissions. Overall, the results are consistent with the equilibrium assumption made in statistical multifragmentation scenarios. Predictions obtained with intranuclear-cascade models coupled to the Statistical Multifragmentation Model are in good agreement with the experimental data.Received: 9 December 2003, Revised: 18 February 2004, Published online: 31 August 2004PACS: 25.70.Mn Projectile and target fragmentation - 25.70.Pq Multifragment emission and correlations - 25.75.Dw Particle and resonance production - 25.75.Gz Particle correlations     

Effect of Ta<Superscript>5+</Superscript> substitution for Mn on the ground state of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>

We report the charge state modification effects at the Mn site on the ground state properties of colossal magnetoresistive manganites. Ta⁵⁺ substitution results in an appreciable increase in the lattice parameters and unit cell volume due to increased Mn³⁺ concentration. The ferromagnetic-metallic ground state modifies to a cluster glass insulator for . The reduction in the transition temperatures with increasing x is ∼39 K/at.%. Besides the modification of majority carrier concentration due to increased Mn³⁺ concentration and enhanced local structural effects, the local electrostatic potential of the substituent seems to contribute to the unusually strong reduction of the transition temperatures of the compounds. Thermo magnetic irreversibility just below Curie temperature (T_c), non-saturation of magnetization, two distinct magnetic transitions in ac susceptibility in an appropriate static field: close to T_c and other at low temperature (the spin freezing temperature (T_g)) and non-stationary dynamics with a characteristic maximum in the magnetic viscosity close to T_g confirm a cluster glass state for . These results find additional support from a linear low temperature magnetic specific heat of x = 0.10 with a characteristic broad maximum close to T_g.     

Nuclear quadrupole moments of 5/2<Superscript>-</Superscript> and 9/2<Superscript>-</Superscript> states in <Superscript>169</Superscript>Ta

The nuclear spectroscopic quadrupole moments for the πh_9/25/2^-, 1/2^-[541] and the πh_11/29/2^-, 9/2^-[514] isomeric states in ¹⁶⁹Ta have been measured employing the time differential perturbed angular-distribution technique following the nuclear reaction ¹⁵⁹Tb(¹⁶O, 6nγ)¹⁶⁹Ta at beam energy 104 MeV. The ratio of the intrinsic quadrupole moments has been derived as 1.87(13) from the measured quadrupole precession frequencies of the corresponding states. The model-independent analysis of the equilibrium deformation indicates strong prolate- and oblate-driving nature of the 1/2^-[541] and 9/2^-[514] orbitals in ^169,171Ta isotopes, respectively.     

Isospin mixing in the 4<Superscript> + </Superscript> doublet of <Superscript>54</Superscript><Emphasis Type="Italic">Co</Emphasis>

The T = 1 admixture into the T = 0 member of a recently discovered isospin-doublet in ⁵⁴Co is obtained from the measured electromagnetic E2/M1 multipole mixing ratio, of the transition. Combining these data with shell model calculations for strong isovector M1 and isoscalar E2 electromagnetic matrix elements one obtains a value for the T = 1 admixture into the T = 0, 4 ⁺ state of . The corresponding mixing matrix element in the 4 ⁺ doublet is keV.Received: 31 October 2002, Published online: 9 March 2004PACS: 21.10.Hw Spin, parity, and isobaric spin - 21.60.Cs Shell model - 23.20.Gq Multipole mixing ratios     

Fast-electron ejection from C,Ni, Ag and Au foils by <Superscript>36</Superscript><Emphasis Type="Italic">Ar</Emphasis><Superscript>18 + </Superscript> (95 MeV/u): Measurements of absolute cross-sections

Doubly differential electron velocity spectra induced by ³⁶Ar^{18 +} (95 MeV/u) from thin target foils (C, Ni, Ag, Au) were measured at GANIL (Caen, France) by means of the ARGOS multidetector and the time-of-flight technique. The main features observed in the forward spectra are convoy electrons, binary-encounter electrons, and (for the Au target only) a high-velocity tail which we attribute to a Fermi shuttle acceleration mechanism. Backward spectra do not show distinct structures. The spectra allow us to determine absolute singly differential cross-sections as a function of the target material and the emission angle. The convoy electron yield increases with the target atomic number, but for C their yield is so small that our experiment is not able to detect them. Absolute doubly differential cross-sections for binary-encounter electron ejection from C targets are well described by a transport theory which is based on the relativistic electron impact approximation (EIA) for electron production and which accounts for angular deflection, energy loss and energy straggling of the transmitted electrons.Received: 1 July 2003, Revised: 15 December 2003, Published online: 13 July 2004PACS: 34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization) - 79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces - 25.70.-z Low and intermediate energy heavy-ion reactions     

Quark-hadron duality and Q<Superscript>2</Superscript> evolution of the GDH integral in the HERMES experiment

First results on quark-hadron duality in the spin sector from the HERMES experiment are reported in the range GeV² and GeV². A complete set of measurements of the generalised GDH integrals for the deuteron, proton and neutron is also shown in the same Q² range and in the full W² range.Received: 1 November 2002, Published online: 15 July 2003PACS: 13.60.Hb Total and inclusive cross-sections (including deep-inelastic processes) - 12.38.Qk Experimental tests - 13.88.+e Polarization in interactions and scattering - 25.20.Dc Photon absorption and scatteringA. Fantoni: On behalf of the HERMES Collaboration     

Flavour-independent h<Superscript>0</Superscript>A<Superscript>0</Superscript> search and two Higgs doublet model interpretation of neutral Higgs boson searches at LEP

Upper limits on the cross-section of the pair-production process , assuming 100 branching fraction to hadrons, are derived from a new search for the hadrons final state, independently of the hadronic flavour of the decay products. This study, combined with previously published searches for the neutral Higgs bosons h⁰ and A⁰, is used to constrain the Type II Two Higgs Doublet Model (2HDM(II)) with no CP violation in the Higgs sector and no additional non-Standard Model particles besides the five Higgs bosons. The analysis combines LEP1 and LEP2 data collected with the OPAL detector up to the highest available centre-of-mass energies. The searches are sensitive to the and decay modes of the Higgs bosons. A benchmark scan of the 2HDM(II) parameter space is performed. Large regions of the 2HDM(II) parameter space explored are excluded at the 95% CL in the ( and planes, using both direct neutral Higgs boson searches and indirect limits derived from Standard Model high precision measurements. The region GeV and GeV is excluded at 95 % CL, independently of and for selected values of which are representative of a complete -scan.Received: 28 July 2004, Revised: 4 January 2005, Published online: 3 March 2005     

Alpha-gamma decay studies of <Superscript>251, 253</Superscript>No and their daughter products <Superscript>247, 249</Superscript>Fm

The isotopes ²⁵¹No and ²⁵³No were produced in nuclear reactions ²⁰⁶Pb(⁴⁸Ca,3n)²⁵¹No and ²⁰⁷Pb (⁴⁸Ca,2n)²⁵³No. Radioactive decay of these isotopes and their daughter products has been investigated by means of - and - - spectroscopy. An isomeric state ^251m No, having a half-life of s and decaying by emission of particles of keV was identified. The measured decay data allowed for the construction of partial level schemes for ²⁵¹No, ^247,249Fm and ^243,245Cf and an extrapolation of energy systematics of single particle levels of N = 145, 147 and 149 isotones with even Z towards higher atomic numbers up to Z = 102.PACS: 23.60. + e decay - 27.90. + b - 21.10.-k Properties of nuclei; nuclear energy levels     

Deformed shell model for T = 0, 1 and 2 bands in <Superscript>52</Superscript>Fe and <Superscript>72</Superscript>Kr

Deformed configuration mixing shell model based on Hartree-Fock states with extension to include isospin projection (DSMT) for two- and four-particle configurations (generated by particle-hole excitations) is applied to study the structure of the low-lying T = 0, 1 and 2 bands (or levels) in the even-even N = Z nuclei ⁵²Fe and ⁷²Kr. The pf-shell KB3 interaction for ⁵²Fe and a modified Kuos interaction for ⁷²Kr are employed in the calculations. In this first application of DSMT with four-particle T projection, low-spin (J 10) members of the T = 0, 1 and 2 bands in ⁵²Fe are compared with experiment including the known E2 transition strengths. The agreement between DSMT and experiment is reasonably good. Similarly, the low-spin members of the observed (prolate) yrast band in ⁷²Kr are also well described by DSMT.