Photofission of americium isotopes in the energy range 6–12 MeV

By means of the reference method, the cross sections for the fission of the ²⁴¹Am, ^242m Am, and ²⁴³Am isotopes were measured at the microtron of the Institute of Physics and Power Engineering (Obninsk). These measurements, which employed the cross section for ²³⁸U photofission as a reference, covered the energy range 6–12 MeV scanned with a variable step of 50 to 200 keV. Data on ^242m Am photofission in the energy range 6–12 MeV and ²⁴³Am photofission in the region between 6 and 7 MeV were obtained for the first time. New results for ²⁴¹Am reveal that the cross sections for ²⁴¹Am photofission from previous studies of the present author were exaggerated. The new results for this isotope comply well with data of other authors. It is not confirmed that the fissility of ²⁴¹Am is less than the fissility of ²⁴³Am. The energy dependences of the fissilities of the americium isotopes from photofission data are compared with those that were obtained for these fissilities from data on direct reactions like ²⁴⁰Pu(³He, df)²⁴¹Am. The results of this comparison show that the observed fission thresholds and the plateaulike dependences at energies above 7.5 MeV from the two types of studies comply well. The present data show evidence that, in the energy region around 6 MeV, the photofission cross section has a maximum, which is associated, in all probability, with the low-energy resonance structure in the cross section for dipole photoabsorption.     

The spestroscopy and structure of odd-A Fr isotopes withA=213–225

The remarkable features of the spectra of the odd-A Fr isotopes from²¹³Fr (with 126 neutrons) through²²⁵Fr (with 138 neutrons) serve as a sequence of examples for the application of a variety of nuclear models. As the shapes vary from spherical to spherical with strong octupole correlations to octupole-deformed, the corresponding symmetry breaking leads to increasingly complex spectra. Of considerable interest is the fact that the²¹⁹Fr 9/2⁻ ground state has the character of an h_9/2 shell model state while still having the rotational properties appropriate as a legitimate member of a reflection asymmetric K=1/2⁻ band. It is also possible to follow the expansion of the more degenerate shell model states into the less degenerate reflection asymmetric states. This results from dramatic decreasing in decoupling parameters with increasing mass number.     

Fine structure in the α-decay of radium isotopes with mass numbers 209-212

Radium isotopes with mass numbers from 209 to 212 have been produced by heavy-ion fusion reactions ²⁰⁴Pb( ¹²C, xn) ^216-Ra. Radioactive decay properties were investigated by means of α- and α-γ-spectroscopy after in-flight separation of the evaporation residues from the projectile beam by the velocity filter SHIP and implantation into a 16-strip position-sensitive Si detector. For the even-even nuclei ^210,212Ra we identified α transitions into the first-excited 2⁺-state of the daughter nuclei ^206,208Rn. Weak α transitions into excited levels of the odd-A daughter nuclei ^205,207Rn were also observed. Received: 19 August 2002 / Accepted: 6 November 2002 / Published online: 18 February 2003 RID="a" ID="a"e-mail: f.p.hessberger@gsi.de Communicated by D. Guerreau     

Investigation of the 19F(n, α)16N reaction excitation function in neutron energy range of 4–7.35 MeV

New method based on ionization chamber with Frisch grid and digital signal processing was developed for experimental investigation of ¹⁹F(n, α)¹⁶N reaction. The chamber filling gas with CF₄ additive was used as the fluorine-containing target. The experimental investigation of ¹⁹F(n, α)¹⁶N reaction cross-section in 4–7.35 MeV energy range is represented in this work. The total cross section of ¹⁹F(n, α)¹⁶N reaction was measured as well as partial cross-section for sum of α₀-α₃ and sum of α₄ and α₅ reaction channels.     

Isospin decomposition of 0+ → 2+ and 0+ → 3− transition matrix elements by Coulomb nuclear interference observed in inelastic α-scattering from the even Zr isotopes

Coulomb-nuclear interference in inelastic scattering of 35.4 MeVα-particles from the stable even Zr isotopes was studied. In the framework of a collective DWBA analysis isoscalar and electromagnetic transition rates for low lying 2⁺ and 3^? states were derived. The experimentalB (E2) values are in good agreement with results obtained by purely electromagnetic methods. The deducedM _n /M _p ratios of the 2 ₁ ⁺ levels exhibit a surprisingly large increase with increasing neutron number.     

Complete N=4 structure of low-energy effective action in N=4 super-Yang–Mills theories

Using the $\text{N}\text{=2}$ superfield approach, we construct full $\text{N}\text{=4}$ supersymmetric low-energy effective actions for $\text{N}\text{=4}$ SYM models, with both $\text{N}\text{=2}$ gauge superfield strengths and hypermultiplet superfields included. The basic idea is to complete the known non-holomorphic effective potentials which depend only on $\text{N}\text{=2}$ superfield strengths W and W̄ to the full on-shell $\text{N}\text{=4}$ invariants by adding the appropriate superfield hypermultiplet terms. We prove that the effective potentials of the form $\text{ln}\text{W}\text{ln}\text{W}\text{̄}$ can be $\text{N}\text{=4}$ completed in this way and present the precise structure of the corresponding completions. However, the effective potentials of the non-logarithmic form suggested in hep-th/9811017 and hep-th/9909020 do not admit the $\text{N}\text{=4}$ completion. Therefore, such potentials cannot come out as (perturbative or non-perturbative) quantum corrections in $\text{N}\text{=4}$ SYM models.     

Investigation of the structure of lower excited states of the 28Si nucleus in α scattering at Eα = 30.3 MeV

The differential cross sections of the ²⁸Si(α, αγ)²⁸Si reaction at E _α = 30.3 MeV, calculated according to the coupled channel method (CCM) with the FRESCO program, are presented for a wide α-particle scattering region with the excitation of the lower ²⁸Si states (0⁺, ground; 2⁺, 1.78 MeV; 4⁺, 4.62 MeV; 0⁺, 4.96 MeV; 3⁻ + 4⁺, 6.88 MeV + 6.89 MeV). The coupling factors are calculated in the Nilsson model.     

Evaporation residues from the fusion of 32S on 27Al at E = 142–227 MeV

The evaporation residues from the reaction ³²S on ²⁷Al were measured at 142, 153, 175, 187 and 227 MeV incident sulphur energies, using a time-of-flight spectrometer. The measured fusion-evaporation residue excitation function shows a maximum around E_lab = 170 MeV, which corresponds to a limiting angular momentum of 43 ħ. Several possible mechanisms were investigated as being responsible for this limitation. It was found that both fission and entrance channel effects could be the limiting factors for the fusion-evaporation cross section at high energies.     

Investigation of the neutron shell structure of the even-even isotopes <Superscript>40–56</Superscript>Ca within the dispersive optical model

Within the method of matching experimental data obtained in the neutron-stripping and neutron-pickup reactions on ^{40,42,44,46,48}Ca isotopes, the single-particle energies and probabilities that neutron states are filled are obtained for the even-even calcium isotopes. These data are analyzed within the dispersive optical model, and good agreement between the calculated and experimental values of the energies of states is obtained. The dispersive optical potential is extrapolated to the region of the unstable ^50,52,54,56Ca nuclei. The calculated single-particle energies of bound states in these isotopes are compared with the results of the calculations within the multiparticle shell model, the latter predicting a new magic number N = 34 for Z = 20 nuclei.     

Photoproduction of positive pions from hydrogen at large angles in the energy range 0.3–2.0 GeV

The differential cross-section for the reaction γp↦π ⁺ n was measured using the bremsstrahlung beam of the Bonn 2.5 GeV electron synchrotron. The pions were detected and momentum analysed in a multichannel magnet spectrometer. Data reduction resulted in 1278 measured cross-sections which are presented as energy distributions at six laboratory angles between 180° and 95°. The range of laboratory photon energies extended from 0.3 to 2.1 GeV. The statistical accuracy is better than 3 percent, the systematic error is about 5 percent. The data are compared with other experimental results and predictions of a phenomenological analysis. These cross-sections are the result of a measurement program which was started in the seventies. Further results will be reported in forthcoming publications. Received: 2 February 2000 / Accepted: 14 August 2001     

Hyperfine structure and isotope shift investigations in202–222Rn for the study of nuclear structure beyond Z=82

The hyperfine structure (hfs) and isotope shift (IS) in the isotopic chain of the radioactive element radon have been studied for the first time. The measurements were carried out by collinear fast-beam laser spectroscopy at the mass separator facility ISOLDE at CERN. The IS between 16 isotopes in the mass range 202A222 and the hfs of 7 odd-A isotopes were determined in the transitions 7s [3/2]₂-7p [5/2]₃ (745 nm) of Rn I. The nuclear spins and moments, as well as the observed inversion of the odd-even staggering for^218–222Rn, can be associated with the effects of octupole instability around N=134.This work was supported by the Bundesministerium für Forschung und Technologie and the Deutsche Forschungsgemeinschaft.     

Investigation of crystal/electronic structure effects on the photoluminescence properties in the BaO–SiO2:Eu2+ systems

BaO–SiO₂:Eu²⁺ phosphors with different Ba/Si mole ratio were prepared using a solid-state reaction method, and their crystal structure dependent-photoluminescence properties were investigated. The prepared phosphor powders were characterized using X-ray diffraction (XRD), field-emission electron microscopy (FE-SEM) and fluorescence spectroscopy. The emission band of the Eu²⁺ activator varied from orange to blue with varying crystal structure of the host materials, which was related to the crystal field splitting of the Eu 5d orbitals. These emission color changes were examined by calculating the electronic band structure properties such as the density of the state. Moreover, the host material with Ba/Si=1 (BaSiO₃) for Eu²⁺, which exhibited a yellow emission when excited with near UV light, was further characterized for enhancing its emission intensity.     

Stable carbon isotopes of glucose received from pine tree-rings as bioindicators of local industrial emission of CO2 in Niepołomice Forest (1950–2000)

The mass spectrometric investigations of carbon isotope composition of glucose received from α-cellulose samples derived from Scots pine (Pinus sylvestris L.) growing in Niepo?omice Forest were the main aim of this study. The annual rings covered the time span from 1950 to 2000. α-Cellulose samples were extracted from increment cores of four representative trees, and then acid hydrolysis was performed. The number of sunshine hours, thermal and pluvial conditions of the growing season and in the preceding months had a significant effect on pine. Also non-climatic factors, most likely by industrial pollution signal, have been recorded in the isotopic composition of glucose. The relationship between climatic conditions, carbon dioxide emission and annual tree-rings carbon isotopic composition was analysed, using methods of correlation and response function, and multiple regression function.     

Energy dependence of the optical potential for 16O + 28Si,elastic scattering in the energy range of E = 55–215 MeV

The energy dependence of an optical potential which reasonably fits all of the existing experimental data on ¹⁶O + ²⁸Si elastic scattering in the energy range of E = 54.7–215.2 MeV is studied. The real part of the potential found for this system shows a transition from a proximity to a double-folding type of the potential as a result of quenching of the Pauli principle effects with an increase of the incident energy. The imaginary part shows a transition from a surface-transparent to a strongly absorptive type of the potential.     

Angular Distributions and Anisotropy of Fragments from the Neutron-Induced Fission of 237Np in the Energy Range of 1–200 MeV: Measurement Data and Model Calculations

JETP Letters - The experimental data on the angular distributions of fragments from the fission of 237Np nuclei induced by 1–200 MeV neutrons have been presented. Such measurements for...