On-line production of neutron rich isotopes from uranium carbide targets

Experiments done using on-line mass separation of neutron-rich nuclei produced by 1 GeV proton beam on natural U by spallation reactions are performed to study the characteristics of different UCx targets. Special attention is devoted to reliably extract isotopic yields in case of complex decay schemes and to the valuation of release efficiency of some isotopic chains. New gamma-branching measuremet for ⁹²Rb are obtained. In addition, a formalism is developed to disantangle the contribution of β-decay in the target from direct production by fission and to provide more consistent data for the interpretation of release curves. Some results are shown for the Cs and Rb isotopic chains.     

The symmetry energy in nuclei and in nuclear matter

We discuss to what extent information on ground-state properties of finite nuclei (energies and radii) can be used to obtain constraints on the symmetry energy in nuclear matter and its dependence on the density. The starting point is a generalized Weizs?cker formula for ground-state energies. In particular, effects from the Wigner energy and shell structure on the symmetry energy are investigated. Strong correlations in the parameter space prevent a clear isolation of the surface contribution. Use of neutron skin information improves the situation. The result of the analysis appears consistent with a rather soft density dependence of the symmetry energy in nuclear matter.     

Determination of the elemental contents in stream sediments collected from Cheongju city by instrumental neutron activation analysis

Sediment samples were collected from seven locations of the MeeHo stream in Cheongju city, strained out by a sieve, dried by an oven and pulverized by an agate mortar. Instrumental neutron activation analysis (INAA) was applied for the determination of the elemental contents in the sediment samples by using the NAA #1 and #2 irradiation holes of the HANARO research reactor and HPGe gamma-ray spectrometers. Twenty-five elements were determined by a relative method with NIST SRM 2711-Montan Soil and the ranges of the elemental contents for the seven locations were identified. The contamination levels for elements such as As, Ba, Cr, Mn, Fe and Zn were compared with the guidelines of USEPA. The detection limits and combined uncertainties for the hazardous elements such as As, Ba, Cr, Mn, Sb, V and Zn were estimated under the given analytical conditions.     

Determination of sulfur forms in wine including free and total sulfur dioxide based on molecular absorption of carbon monosulfide in the air–acetylene flame

A new method for the determination of sulfur forms in wine, i.e., free SO₂, total SO₂, bound SO₂, total S, and sulfate, is presented. The method is based on the measurement of the carbon monosulfide (CS) molecular absorption produced in a conventional air–acetylene flame using high-resolution continuum source absorption spectrometry. Individual sulfur forms can be distinguished because of the different sensitivities of the corresponding CS molecular absorption. The sensitivity of free SO₂ is about three times higher than the value for bound SO₂ and sulfate. The method makes use of procedures similar to those used in classic reference methods. Its performance is verified by analyzing six wine samples. Relative standard deviations are between 5 and 13% for free SO₂ and between 1 and 3% for total SO₂. For the validation of the accuracy of the new method, the results are compared with those of reference methods. The agreement of the values for total SO₂ with values of the classic method is satisfactory: five out of six samples show deviations less than 16%. Due to the instability of free SO₂ in wine and the known problems of the used reference method, serious deviations of the free SO₂ results are found for three samples. The evaluation of the limits of detection focuses on the value for free SO₂, which is the sulfur form having by far the lowest concentration in wine. Here, the achievable limit of detection is 1.8 mg L⁻¹. Figure Detection of non-metal elements using continuum source flame absorption spectrometry     

Magnetic structure and electronic study of complex oxygen-deficient manganites

Neutron diffraction and X-ray absorption near-edge structure (XANES) studies have been performed in La0.5Ca0.5MnO2.5, La0.5Sr0.5MnO2.5 and Nd0.5Sr0.5MnO2.5 oxygen-deficient perovskite compounds obtained by topotactic reduction. They all exhibit a brownmillerite structure with G-type antiferromagnetic ordering. Mn2+, Mn3+ and Mn4+ coexist at the octahedral sites, whereas only Mn2+ is placed in the tetrahedral positions. A magnetic moment of 1.6 microB has been detected at the tetrahedral layers, which can be explained by assuming Mn2+ is in a low-spin configuration.     

Heterodyne Interferometers Using Orthogonally Polarized and Two-Frequency Shifted Light Sources with Super-high Extinction Ratio

This paper describes heterodyne interferometers using orthogonally polarized and two-frequency shifted light sources of two types with super-high extinction ratio to reduce non-linearity of the interferometer due to polarization cross-talk. The acousto-optic modulators are used to shift light frequency. In the first interferometer the light source with Glan-Thomson prisms of very high extinction ratio (50 dB) is used to make the polarization cross-talk very small. In the second interferometer the light source of two-frequency shifted beams with small crossing angle (2.5 rnrad-10 mrad) is used to completely exclude non-linearity of the interferometer due to polarization cross-talk. By measuring the thickness of vacuum evaporation film, it was demonstrated that the interferometers are useful to measure thickness of a thin film in nanometer order.     

Application of SSNTD for maintenance of radiation and nuclear safety of the Sarcophagus

Object “Shelter” (known world-wide as the Sarcophagus) is a source of very high radiological and nuclear hazard. Transfer of the Sarcophagus into an ecologically safe site is a task not only for Ukraine but also for the world community. A composite approach to maintenance of radiation and nuclear safety of the Sarcophagus applying spectrometric methods using solid state nuclear track detectors (SSNTD) is suggested in this paper. The aspects are: (1) monitoring of transuranium element inhalation intake to a human body of nuclear workers; (2) neutron flux evaluation in some premises of the Sarcophagus; (3) fuel hot particle detection in air of working zones; (4) radon and thoron simultaneous measurements.     

Collapse of the magnetic ordering and structural anomalies in the U La S system: neutron diffraction and specific heat measurements

We report specific heat and neutron diffraction measurements of seven samples in the solid solution system U_xLa_1-xS. All samples have the simple fcc NaCl crystal structure. Both specific heat and neutron diffraction confirm the suggestion from the earlier magnetic measurements that the ferromagnetism disappears abruptly at 0.57. Near there is a doubling of the electronic contribution to the specific heat, as compared to the value of 23 mJ mol^-1K^-2 in pure US. Around the widths of the nuclear Bragg peaks show a considerable broadening, as well as anomalies in the mean lattice parameter, as compared to those expected from Vegard's law. A preliminary analysis suggests this broadening may be due to a loss of long range lattice order near . However, these changes are independent of temperature, so that further experiments are necessary before they can be associated with the changes in magnetic behavior at . Received 18 September 1998     

Reflection of cold atoms from an array of current-carrying wires

We report the realization of a new type of magnetostatic mirror for slowly moving atoms which comprises a planar array of parallel wires alternately carrying electric current in opposite directions. One of the features of this atomic mirror is that the magnetic field may be readily varied, switched or modulated by altering the current in the wires. Reflection signals close to 100% at a pulsed current of 3 A are demonstrated for a beam of free-falling laser-cooled cesium atoms at normal incidence. The current dependence of the reflection signals exhibits structure which is associated with the sequential onset of reflection of cesium 6² S _1/2 , F=4 atoms in the m=+4, +3, +2 and +1 magnetic states. Measurements of the spatial distribution of the reflected atoms indicate the reflection is predominantly specular at currents of 3 A. Received: 31 August 1998 / Accepted: 6 October 1998     

Synthesis and structure of the ternary and quaternary strontium nitride halides, Sr2N(X, X′) (X, X′=Cl, Br, I)

A number of new, layered nitride mixed halides have been synthesised in the quaternary phase systems Sr-N-Cl-Br and Sr-N-Br-I. The variation in structure with composition has been investigated by powder X-ray and powder neutron diffraction techniques and the structure of strontium nitride iodide, Sr₂NI, has been determined for the first time (rhombohedral space group R-3m, , , Z=3). A continuous solid solution exists between Sr₂NCl and Sr₂NBr with intermediate compounds adopting the same anti-α-NaFeO₂ structure (rhombohedral space group R-3m) as the ternary end members. A similar smooth and linear relationship between structure and composition is seen from Sr₂NBr to Sr₂NI and hence cubic close packing of metal-nitrogen layers is adopted regardless of halide, X (X′). While nitride and halide anions occupy distinct crystallographic sites, there is no ordering of the halides in the quaternary materials irrespective of stoichiometry or temperature (between 3 and 673 K).