A Systematic Study on 1neutron and 2neutron Halo Nuclei Using Coulomb and Nuclear Proximity Potential

The halo-structure of a nucleus is analyzed on the basis of potential energy consideration and separation energy calculations and thereby characterized a nucleus as a halo nucleus. The separation energy analysis showed that ¹¹Be, ¹⁴B, ^{15, 17, 19}C, ²²N, ²³O, ^{24, 26}F, and ²⁹Ne are 1n-halo nuclei since the 1n separation energy S(n) is the lowest and ^{6, 8}He, ¹¹Li, ¹⁴Be, ¹⁷B, ²²C, and ²⁹F are 2n-halo candidates as 2n separation energy S(2n) is the lowest. The potential energy calculations are consistent with the predictions based on separation energy calculations except for ¹²Be, ¹⁹B, and ²⁷F which can be considered as 2n-halo candidates by potential energy consideration. Also, a discrepancy is noticed in the case of the proposed 2n-halo ⁸He and ¹⁷B nuclei. Further, the possibility of emitting halo nucleus via heavy particle decay of heavy nuclei, within the range 82?≤?Z?≤?102, has been studied using the Coulomb and proximity potential model (CPPM). It is observed that the probability of emission of a halo nucleus is lower than that of a normal cluster Nevertheless, there is a finite chance of emission of a halo nucleus in the decay of a heavy nucleus.     

Multiple Coulomb excitation of198Hg and200Hg

Multiple Coulomb excitation measurements on^{198, 200}Hg have been performed with 5MeV/amu²⁰⁸Pb projectiles andB(E2)-values are determined for transitions between states up to spin 8⁺. In¹⁹⁸Hg a reduction of theB(E2)-value for the yrast transition 8⁺→6⁺ by a factor of 3 as compared to the rigid rotor prediction is observed, which supports the earlier proposed idea that the ground state band is crossed between the 6⁺ and 8⁺ state by a weakly interactingvi ₁₃ ^2/2 rotation aligned band. In each of the two nuclei,¹⁹⁸Hg and²⁰⁰Hg, a state with a possibleI ^π=8⁺ assignment is observed, which is tentatively interpreted as the 8⁺ member of the ground state band.     

15N excitation contribution to 48Ca(16O, 15N)49Sc reaction

The effect of ¹⁵N excitation process is studied in the reaction ⁴⁸Ca(¹⁶O, ¹⁵N)⁴⁹Sc. The excitation process is included into a generalized non-local optical potential for a scattersing ¹⁵N-⁴⁹Sc and is found to be responsible for a shift of a grazing peak in the exact finite-range DWBA calculation.     

Neutron periphery in light nuclei

A spatial configuration of light nuclei that involves two excess neutrons (⁶He, ¹⁰Be, and ¹²B) is studied by analyzing cross sections for various reactions on these nuclei: ⁶He(α, α)⁶He, ⁹Be(d, p)¹⁰Be, and ¹⁰B(t, p)¹²B. Pole dineutron-transfer mechanisms (dineutron configuration of the neutron periphery) and second-order mechanisms involving sequential neutron transfer (cigar-like configuration of the neutron periphery) are taken into account in the calculations. It is shown that the neutron periphery is drastically different in the nuclei in question: in ⁶He, there is a halo receiving a contribution from both configurations; in ¹⁰Be, there is an only slightly noticeable halo featuring a contribution of practically one neutron from the cigar-like configuration; and, in ¹²B, there is a neutron skin.     

Traces of Landau-Zener transitions in the fusion cross section of heavy nuclei?

Nucleus-nucleus collisions with center-of-mass energies E_c.m. close to the Coulomb barrier are investigated within the framework of time-dependent two-center shell-model states. The influence of Landau-Zener transitions on the nucleus-nucleus potential is studied in detail as a function of E_c.m. Dynamical barrier shifts and barrier fluctuations are evaluated for central collisions of ⁹⁰Zr + ⁹⁰Zr, ⁹²Zr + ⁹²Zr, ⁹⁶Zr + ⁹⁶Zr and their effect on the fusion probability is discussed explicitly. While for ⁹⁰Zr + ⁹⁰Zr no modification of the barrier penetration is found a relative enhancement (reduction) of the fusion probability up to a factor of 4 is obtained for ⁹²Zr + ⁹²Zr and⁹⁶Zr + ⁹⁶Zr.     

Detection of the Rydberg states of rubidium using a frequency doubled CW dye laser

A sensitive method of detecting Rydberg atoms of Rb is described. The excitation source is a continuous-wave frequency doubled dye laser and detection is by a spacecharge limited thermionic triode. By applying a small electric field ²S, ²P and ²D series can be excited directly from the ground state. Term value for the ²S and ²D series up to 54 ²S and 52 ²D have been measured using the ²P states as references.     

A theoretical study of the spectroscopic states of the CF molecule

LCAO-MO SCF calculations on the ground and excited states of CF are described. Close agreement with observed term values is obtained. The calculation of some molecular properties is discussed, and a very good result is obtained for the spin-orbit coupling in the ground state. The positive spin-orbit coupling in the ²Δ state is not explained. It is shown that the observed predissociation in the A state must be attributed to a curve crossing at a smaller internuclear distance than equilibrium, and that the ⁴Σ^- state from 5σ 2π² is responsible. Calculations show that a second-order treatment of the A ²Σ⁺-⁴∑^- interaction is necessary and sufficient to account for the predissociation.     

Cross sections for production of 43Sc, 44Sc, and 46Sc isotopes in the 45Sc + 3He reaction

Reactions ⁴⁵Sc(³He, αn)⁴³Sc, ⁴⁵Sc(³He, α)⁴⁴Sc, and ⁴⁵Sc(³He, 2p)⁴⁶Sc, resulting from the irradiation of scandium targets with a beam of ³He ions with energy from 5 to 24 MeV, are investigated in experiments on the U120M cyclotron of the Nuclear Physics Institute (Rez, Czech Republic). The activation technique is used to find the yield of the produced Sc isotopes. The induced γ activity in the targets is measured using a high-resolution HPGe detector. Despite the low binding energy of ³He and positive reaction Q values, which leads to formation of the ⁴⁴Sc and ⁴⁶Sc isotopes, the behavior of the excitation functions for the formation of these isotopes differs from the behavior of the excitation function for deuterons. Scandium-44 formation cross sections reach their maximum at the reaction Coulomb barrier. This is because not only ⁴⁴Sc but also a stable ⁴He nucleus is formed in the reaction.     

A microscopical DWBA description of the charge-exchange reactions (7Li, 7Be)

The charge-exchange reaction (⁷Li, ⁷Be is described in the frame of a microscopical DWBA with central effective forces. The transition density for ⁷Li-⁷Be is calculated in two ways: with a one-particle model and with a cluster model, taking full account of recoil effects. The formalism is used for the cases of (⁷Li, ⁷Be reactions with ⁶Li and ⁴⁰Ca. Further cross sections for reactions on ¹²C and ¹⁶O with $\text{E(}{}^7\text{Li) = 78 MeV}$ and excitation energies around 4.5 and 6.2 MeV, respectively, are compared to new data obtained at the Kurchatov Institute. Here particle-hole states in an oscillator model were used to characterize the heavy system. Angular distributions are well reproduced, but absolute cross sections are 6–7 times too small. This indicates that the assumption of a direct one-step process is correct, but that tensor forces should be included as a component of the effective nucleon-nucleon force.     

An α-Particle Model for 16O: Is There a New Four-Body Scale?

The ¹⁶O nucleus is modelled as a system of four α-particles. It is shown that a Hamiltonian that includes established two- and three-body forces reproducing the α-α phase shifts, the ⁸Be resonance, and the first and second 0⁺ states of ¹²C overbinds the ¹⁶O nucleus. To rectify this a novel four-body force is introduced, which then leads to a good agreement with the low-lying experimental spectrum of ¹⁶O.     

Bestimmung der 15N Häufigkeit bei nichtstatistischer 15N-verteilung in N2 sowie bei N2O in Bodenluftproben mittels GC-R-IRMS-Kopplung in einem Probenlauf

Abstract

An analysis technique based on GC-R-IRMS coupling (Gas-Chromatography-Reduction-Isotope Ratio Mass Spectrometry) is demonstrated. The ¹⁵N abundance of N² and N²O in atmospheric air or soil atmosphere from nitrification or denitrification processes with nonrandom distribution is determined in one run. The 12 ml sample is separated from CO² and transported by a helium gas stream through a cooling trap. The N²O is trapped in the cooling trap while the N² passes through it and enters the GC. After GC separation and O² removal in a reduction column, part of the N² enters an isotope mass spectrometer to determine the masses m/z 28,29 and 30. The interferences on mass 30 by the formation of NO in the ion source of the mass spectrometer are eliminated by a calibration and a correction procedure. Upon removing the cooling trap, the N²O is injected into the GC, where it is separated and then quantitatively reduced to N² in a reduction column. The measurement of one sample takes 16 minutes. The detection limit of the ³⁰R_t in alteration N₂ is Δ³⁰R_t = 5 · 10^?7. The detection limit of the N₂O is 3.6 nl.     

Effect of high doses of N<Superscript>+</Superscript>, N<Superscript>+</Superscript> + Ni<Superscript>+</Superscript>, and Mo<Superscript>+</Superscript> + W<Superscript>+</Superscript> ions on the physicomechanical properties of TiNi

The surface layer of an equiatomic TiNi alloy, which exhibits the shape memory effect in the martensitic state, is modified with high-dose implantation of 65-keV N⁺ ions (the implantation dose is varied from 10¹⁷ to 10¹⁸ ions/cm²). TiNi samples are implanted by N⁺, Ni⁺-N⁺, and Mo⁺-W⁺ ions at a dose of 10¹⁷–10¹⁸ cm⁻² and studied by Rutherford backscattering, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction (glancing geometry), and by measuring the nanohardness and the elastic modulus. A Ni⁺ concentration peak is detected between two maxima in the depth profile of the N⁺ ion concentration. X-ray diffraction (glancing geometry) of TiNi samples implanted by Ni⁺ and N⁺ ions shows the formation of the TiNi (B2), TiN, and Ni₃N phases. In the initial state, the elastic modulus of the samples is E = 56 GPa at a hardness of H = 2.13 ± 0.30 GPa (at a depth of 150 nm). After double implantation by Ni⁺-N⁺ and W⁺-Mo⁺ ions, the hardness of the TiNi samples is ∼2.78 ± 0.95 GPa at a depth of 150 nm and 4.95 ± 2.25 GPa at a depth of 50 nm; the elastic modulus is 59 GPa. Annealing of the samples at 550°C leads to an increase in the hardness to 4.44 ± 1.45 GPa and a sharp increase in the elastic modulus to 236 ± 39 GPa. A correlation between the elemental composition, microstructure, shape memory effect, and mechanical properties of the near-surface layer in TiNi is found.     

Unbounded generalizations of standard von Neumann algebras

The primary purpose of this paper is to study unbounded operator algebras called standard EW^#-algebras which are generalizations of standard von Neumann algebras to the unbounded case.The first part is an investigation of the weak, σ-weak, strong and σ-strong topologies on a standard EW^#-algebra. It is showed that the weak and σ-weak topologies on a standard EW^#-algebra coincide.The second part is a study of a locally convex topology called _∞L^ω₂-topology on a standard EW^#-algebra U. It is proved that U is a GB¹-algebra under the topology.The third part is an investigation of isomorphisms of standard EW^#-algebras. It is showed that if standard EW^#-algebras U and B are isomorphic then U and B are spatially isomorphic.     

Relaxation of the conductivity of CsI-Tl after excitation by subnanosecond electron pulses

The pulsed conductivity is investigated for a CsI-Tl crystal having a Tl⁺ concentration N=8×10¹⁷cm⁻³ and excited by an electron beam (0.2 MeV, 50 ps, 10²–10⁴ A/cm ²). It is shown that the amplitude of the conduction current pulse is almost an order of magnitude lower than for “pure” CsI crystals irradiated under like conditions. The conduction current relaxation time is preserved up to τ=100 ps in this case. Under the experimental conditions, therefore, the lifetime of electrons in the conduction band is controlled by trapping at Tl⁺ centers. The electron capture cross section at a Tl⁺ center is determined: σ=7×10⁻¹⁶ cm², which agrees in order of magnitude with estimates of the capture cross section for a neutral trapping center. Fiz. Tverd. Tela (St. Petersburg) 40, 66–67 (January 1998)     

Infrared spectra for co isotopes chemisorbed on Pt “111”: Evidence for strong absorbate coupling interactions

Previous results for ¹²C¹⁶O chemisorbed on a Pt“111” recrystallised ribbon revealed that the infrared absorption band due to the CO stretch appears at low coverages at 2063 cm^?1 and shifts to ~2100 cm^?1 at saturation coverage at 300 K. The cause of this shift is studied in the present work, by investigating the vibrational spectra from a variety of mixtures of ¹²C¹⁶O and ¹²C¹⁶O. The results show that there is a strong dipole-dipole coupling interaction between adsorbate molecules in the overlayer, and provide conclusive evidence that the 35 cm^?1 frequency shift observed with increasing coverage for ¹²C¹⁶O is attributable to coupling.     

Alpha transfer at sub-coulomb energies in the 9Be + 16O reaction

From a detailed comparison of the sub-Coulomb-barrier cross sections for the ⁹Be + ¹⁶O and ¹²C + ¹³C reactions, it is demonstrated that there is a strong α-transfer in the channel ⁹Be + ¹⁶O→²⁰Ne¹ + ⁵He, in accord with the near optimum Q-value for the α-transfer.     

First evidence for the 2+ level in the very neutron-rich nucleus102Sr

Evidence for the 2⁺ level in¹⁰²Sr is obtained from theβ-decay of¹⁰²Rb, mass separated at the ISOLDE facility. The energy of 126 keV and the collectivity of the 2⁺→0⁺ transition indicate that¹⁰²Sr is a strongly deformed rigid rotor. In addition, a sizeable lifetime is measured for the 94 keV transition in¹⁰²Y.     

Determination of the negative hydrogen ion concentration in a cesium-hydrogen discharge

The concentration N _H ⁻ of negative hydrogen ions in a low-voltage cesium-hydrogen discharge plasma N _H ⁻ is determined from experiments with laser radiation absorption caused by the photodetachment of electrons from the H⁻ ions. The resolution of a setup measuring the relative absorption is ≥10⁻⁵ for a signal-to-noise ratio of ∼10⁻² or less. A heated-cathode diode is used to initiate the discharge at a voltage of U≤10 V and a current density of j≤5 A/cm² (hydrogen pressure p _{H 2} is equal to several torr, and the cesium concentration in the plasma N _Cs ⁽⁰⁾ ∼10¹⁴ cm⁻³). The absorption due to the photoionization of excited Cs atoms is shown to be negligible. The measured concentration N _H ⁻ of the H⁻ ions is 10¹²–10¹³ cm⁻³. Experimental results are consistent with the theory.