Nuclear vertex constants for the virtual decay <Superscript>7</Superscript>Be → <Superscript>3</Superscript>He + <Superscript>4</Superscript>He of the 7Be bound states from a phase-shift analysis in the effective-range theory

The phase-shift-analysis data for the ³He⁴He scattering are analyzed using the effective-range theory, with the Coulomb interaction taken into account. We find both the renormalized nuclear vertex constants for the vertex ⁷Be → ³He + ⁴He in the ground (3/2⁻) and in the first excited (1/2⁻) bound states of ⁷Be, and the corresponding asymptotic normalization constants of the radial wave functions in these states. The results obtained can be used in an astrophysical S-factor calculation for radiative capture reaction ⁴He(³He, γ)⁷Be     

Study of the parameters of the He(3 <Superscript>3</Superscript>S)-He(2 <Superscript>3</Superscript>P) line *

We have observed emission spectrum in dense plasmas of helium excited by a corona discharge at 706.69 nm. In continuation of an analysis of spectra obtained in gaseous helium at 300 K, we report on a study of the line parameters of the observed spectra. We discuss the major importance of temperature and perturber density in the broadening, shift and asymmetry measured from calculated profiles within a unified line shape semi-classical theory. The comparison is done with existing data derived from experimental spectra at 300 K. The theoretical work is extended at lower temperatures down to 40 K.     

Concentration dependence of the thermal boundary resistance between dilute<Superscript>3</Superscript>He−<Superscript>4</Superscript>He solutions and sintered silver powder

We have measured the³He concentration dependence of the thermal boundary resistanceR _B between³He?⁴He dilute mixtures and submicron sintered silver between 10 and 150 mK. For concentrations greater than one percent, the results for the boundary resistance per inverse volume are insensitive to the concentration and have a magnitude similar to that predicted by the acoustic mismatch theory. For concentrations less than one percent, we observe an increase ofR _B for decreasing concentrations.     

Role of various mechanisms in the formation of a <Superscript>12</Superscript>C nucleus in the reaction <Superscript>13</Superscript>C(<Superscript>3</Superscript>He, <Emphasis Type="Italic">α</Emphasis>)<Superscript>12</Superscript>C

The contributions of various mechanisms to the production of the final nucleus ¹²C in the reaction ¹³C(³He, α)¹²C are estimated. These are neutron stripping and the transfer of the heavy cluster ⁹Be in the pole approximation or via a sequential transfer of virtual ⁸Be and a neutron. It is shown that the sequential mechanism of heavy-cluster transfer must be taken into account in order to describe correctly experimental data over the whole angular range.     

Characteristics of the discrete and continuous spectra of the <Superscript>4</Superscript>He + Λ system

In view of projected experiments on the production of relativistic hypernuclei and the investigation of reactions induced by them, the characteristics of the hypernucleus and low-energy parameters of the _Λ ⁵ He hyperon scattering from ⁴He were calculated. The interaction of the Λ hyperon and the α particle is described by the effective Λα potential in two different forms. The root-mean-square radius of the Λ hyperon in the _Λ ⁵ He hypernucleus, the vertex constant for the _Λ ⁵ He ? ⁴He + Λ process, and the corresponding asymptotic normalization coefficient of the _Λ ⁵ He wave function were calculated by solving the radial Schrödinger equation. The scattering length and the effective radius for the scattering of Λ from ⁴He were calculated by two methods. The calculated characteristics turn out to be sensitive to the form of the Λα potential.     

Investigation of the reaction D(<Superscript>4</Superscript>He, γ)<Superscript>6</Superscript>Li at ultralow energies

The cross section of the reaction D(⁴He, γ)⁶Li with titanium and zirconium deuterides as targets is measured for incident ⁴He⁺ ion energies of 30 and 36 keV, respectively. The ion beam is generated by a Hall pulsed plasma accelerator. For the first time, upper limits on the cross section of the reaction D(⁴He, γ)⁶Li at ultralow energies are imposed (at 90% confidence level): σ ≤ 1.2 × 10^?35 cm² for the TiD₂ target and E(⁴He⁺) = 30 keV, and σ ≤ 7 × 10^?36 cm² for the ZrD₂ target and E(⁴He⁺) = 36 keV     

Emission spectroscopy of the A<Superscript>1</Superscript>Π–X<Superscript>1</Superscript>Σ<Superscript>+</Superscript> system of AlH

The high-resolution emission spectrum of the A¹ Π–X¹Σ⁺ transition of AlH was observed in the 18 000–25 000 cm^-1 spectral region using a conventional spectroscopic technique. The AlH molecules were excited in an Al hollow-cathode lamp filled with a mixture of Ne carried gas and a trace amount of NH₃. The emission from the discharge was observed with a plane grating spectrograph and recorded by a photomultiplier tube. In total 163 transition wave numbers belonging to six bands (0-0,1 and 1-0,1,2,3) were precisely measured and rotationally analysed. In the final fit the present data have been combined with available high-resolution measurements of the vibration-rotation bands by White et al. [J. Chem. Phys. 99, 8371 (1993)]. This procedure enabled extracting molecular constants for the A¹ Π and X¹ Σ⁺ states of AlH. A very slight local perturbation has been discovered in the v=1 vibration level of the A¹ Π state at J=5. This was probably caused by the interaction with the a³Π state.     

The evaluation of the branching ratios of the decays φ(1020)→2π<Superscript>+</Superscript>2π<Superscript>−</Superscript>π<Superscript>0</Superscript>, π<Superscript>+</Superscript>π<Superscript>−</Superscript>3π<Superscript>0</Superscript>

Combining the Okubo-Zweig-Iizuka rule in the decay φ→ρπ→π⁺π^?π⁰ with the ρ→4π decay amplitudes, we calculate the φ→2π⁺2π^?π⁰ and φ→π⁺π^?3π⁰ ones. The partial widths of the above φ decays are evaluated, and the excitation curves in e⁺e^? annihilation are obtained, assuming reasonable particular relations among the parameters characterizing the anomalous terms of the HLS Lagrangian. The evaluated branching ratios B_φ→π⁺_π^?_3π⁰ ≈ 2 × 10^?7 and B_φ→2π⁺_2π^?_π⁰ ≈ 7 × 10^?7 are such that, with the luminosity L=500 pb^?1 attained at DAΦNE φ factory, one may already possess about 1685 events of the decays φ→5π.     

The construction of wave functions in the <Superscript>7</Superscript>Li → d + <Superscript>5</Superscript>He channel by the projection method

Relative motion wave functions in the d + ⁵He channel were constructed by the projection method using the two-body αt model of ⁷Li nucleus. The asymptotic constants in this channel were calculated using various models of ⁵He{αn} wave function.     

Resonant parameters of <Superscript>5</Superscript>He and <Superscript>5</Superscript>Li states and nucleon-α scattering

A new method of analysis of resonant parameters in the framework of the J-matrix inverse scattering formalism is proposed. The method is applied to analysis of Nα scattering in various partial waves. The obtained 1/2^? and 3/2^? resonance energies and widths in ⁵He and ⁵Li nuclei are in good agreement with the results of other approaches. The eigenenergies entering the J-matrix phase shift parameterization are shown to correlate well with the respective results of no-core shell model calculations, in particular, in the case of non-resonant s-wave scattering.     

Mechanism of independent neutron transfer in elastic <Emphasis Type="Italic">α</Emphasis><Superscript>6</Superscript>He scattering and structure of the <Superscript>6</Superscript>He nuclear wave function

The presence of two topologically different configurations, a dineutron and a cigar-like one, in the spatial wave function for the neutron-rich nucleus ⁶He is predicted. In elastic α ⁶He scattering, the dineutron configuration leads to the appearance of backward maxima in the cross section for elastic α ⁶He scattering. The cigar-like configuration is responsible for the scattering mechanism involving independent sequential neutron transfer and the formation of the ⁵He-⁵He virtual system. In order to estimate the contribution of this mechanism, the matrix element for the two-step sequential particle transfer is calculated by a method that takes into account delay in the interaction and which is realized in the QUADRO code. Calculations performed on this basis make it possible to estimate the weight of the cigar-like component in the wave function for the ⁶He nucleus.     

Study of ground states of <Superscript>3</Superscript>H, <Superscript>3,4,6</Superscript>He, <Superscript>6</Superscript>Li,and <Superscript>9</Superscript>Be nuclei by Feynman’s continual integrals method

The ground-state energies and the squared moduli of the ground-state wave functions are calculated for the ³H, ^3,4,6He, ⁶Li, and ⁹Be nuclei by Feynman’s continual (path) integrals method. The results are in satisfactory agreement with experimental data.     

Spectroscopy of the <Stack><Subscript>Λ</Subscript><Superscript>7</Superscript></Stack>He nucleus in a three-cluster model

The _Λ ⁷ He hypernucleus is considered within the _Λ ⁵ He + n + n cluster model. The hyperon—nucleon interaction is described by a one-boson-exchange potential that is constructed on the basis of the NSC97f model. Phenomenological potentials are used to describe the αΛ and αN interactions. For the _Λ ⁵ Hen interaction, use is made of the folding-model potential. The calculations of the hyperon binding energy in the ground state of the _Λ ⁷ He hypernucleus on the basis of Faddeev equations in configuration space yield a result (5.35 MeV) that agrees well with preliminary experimental data (5.4 MeV). The problem of calculating the hyperon binding energy within the three-body approach is discussed. In calculating the energy spectrum of _Λ ⁷ He, use is made of a version of the method of analytic continuation in the coupling constant. Low-lying excited states of this nucleus can be classified as an analog of the corresponding states of the ⁶He nucleus with allowance for the clustering of the _Λ ⁵ He+n+n system in the ⁶He(J ^π)+Λ(s) form.     

Perturbative analysis of the 2νββ decays of <Superscript>100</Superscript>Mo and <Superscript>116</Superscript>Cd

We have performed a theoretical analysis of the ground-state-to-ground-state transitions in ¹⁰⁰Mo and ¹¹⁶Cd, based on the quasiparticle random-phase approximation and on a straightforward perturbative scheme. The results show that the single-state dominance found in the realistic calculations of the nuclear matrix elements, which is consistent with data, can be viewed as a result of the interference between few two-quasiparticle configurations. Received: 12 August 2002 / Accepted: 23 October 2002 / Published online: 18 February 2003 RID="a" ID="a"e-mail: civitarese@fisica.unlp.edu.ar Communicated by V.V. Anisovich     

Comparison of the Effects of Different <Superscript>19</Superscript>F <Emphasis Type="Italic">π</Emphasis> Pulses on the Sensitivity and Phaseability of the <Superscript>19</Superscript>F-<Superscript>13</Superscript>C HSQC

The ¹⁹F-¹³C heteronuclear single quantum coherence (HSQC) experiment is vital for the structural elucidation of polyfluorinated organic species, yet its sensitivity and phaseability are limited by difficulties in uniform excitation of the widely disperse ¹⁹F spectral window. Adiabatic pulses of different types have previously been employed to generate effective π pulses for inversion and refocussing, but a systematic comparison of various adiabatic and other inversion pulses has not been published. In this work, it was observed that the use of a broadband inversion pulse (BIP) during the t ₁ evolution period resulted in properly phaseable spectra for experiments optimized to detect ¹ J _CF, in contrast to CHIRP or WURST adiabatic pulses. For the INEPT and reverse-INEPT transfer segments of the HSQC, optimal sensitivity for resonances distant from the transmitter frequency was afforded by optimized universal rotation (BURBOP) or CHIRP pulses. In HSQC experiments with delays optimized for two-bond correlations, only the use of BURBOP pulses in INEPT and reverse-INEPT sequences afforded spectra cleanly phaseable across the F ₂ and F ₁ spectral windows. This observation is supported by off-resonance pulsed field gradient spin-echo experiments.     

Two-neutrino positron double-beta decay of <Superscript>106</Superscript>Cd for the 0<Superscript>+</Superscript> → 0<Superscript>+</Superscript> transition

The two-neutrino positron double-beta decay of ¹⁰⁶Cd for the 0 ⁺ 0⁺ transition has been studied in the Hartree-Fock-Bogoliubov model in conjunction with the summation method. In the first step, the reliability of the intrinsic wave functions of ¹⁰⁶Cd and ¹⁰⁶Pd nuclei has been tested by comparing the theoretically calculated results for yrast spectra, reduced B(E2: 0⁺ 2⁺) transition probabilities, quadrupole moments Q(2⁺) and gyromagnetic factors g(2⁺) with the available experimental data. In the second step, the nuclear transition matrix element M₂ and the half-life T_1/2² for the 0 ⁺ 0⁺ transition have been calculated with these wave functions. Moreover, we have studied the effect of deformation on the nuclear transition matrix element M₂.     

Accurate characterisation of the C(3)<Superscript>1</Superscript>Σ<Superscript>+</Superscript> state of the NaRb molecule

We present a first detailed experimental study of the C(3)¹Σ⁺ state of the NaRb molecule converging to the Na(3p) + Rb(5s) states of separated atoms. Two different high resolution spectroscopic methods have been applied: the Fourier transform spectroscopy of laser induced fluorescence and the V-type optical-optical double resonance polarization labeling spectroscopy. The entire data field for the C¹Σ⁺ state of Na⁸⁵Rb and Na⁸⁷Rb consists of rovibrational levels with v'=0–64 and J'=4–123. The data were incorporated into a direct fit of a single potential energy curve to the level energies using the Inverted Perturbation Approach method. As the experimental data extend to the “shelf" region of the potential at large internuclear separations of 8.5 ?, the C state's suitability for photoassociation yielding cold heteronuclear NaRb is discussed. Electronic supplementary material Online Material     

Potential energy of <Superscript>∞</Superscript>H<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack>(<Superscript>2</Superscript>∑<Stack><Subscript>u</Subscript><Superscript>+</Superscript></Stack> in the bound-state region

An accurate calculation of the lowest negative electronic state of H ₂ ^- (fixed nuclei) is reported using the CCSD(T) method and doubly augmented cc-pv5z basis set. Comparison has been made with the reference data by Senekowitsch et al. [Chem. Phys. Lett. 111 (1984) 211]. Owing to larger size of the basisset and inclusion of triple excitations, no vertical shift in this work is necessary to reproduce the asymptotics of H + H ^-. In addition, the effect of basis-set truncation is estimated, based on the complete-basis-set extrapolation method. The contribution of correlated electron-proton motion to the electron-energy curve for H₂ ^– dynamics is pointed out.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday.     

On the energy of the 8<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> 1479-keV level in <Superscript>178</Superscript>Hf

The difference in the 332-and 326-keV transition energies from ¹⁷⁸Ta decay is measured with a magnetic β spectrometer and a γ spectrometer. The energy of the 332-keV transition (E(332) = 331 607 ± 4 eV) and the energy of the 8 ₂ ^? 1479-keV level in ¹⁷⁸Hf (E(1479) = 1479001 ± 6 eV) are determined with high accuracy.     

Scheme of the β-decay of <Superscript>234</Superscript>Th

The scheme of the β-decay of ²³⁴Th is still not completely clear. Only the upper bound (10 keV) of the energy of the isomeric transition from level T_1/2 = 1.17 min of the ²³⁴Pa nucleus is known, and the correspondence between gamma quanta of several energies emitted in the β-decay of ²³⁴Th and specific nuclear levels of ²³⁴Pa has not been established. In this work, the isomeric transition energy of 2.6 ± 0.5 keV is determined via the γ-spectrometry of a ²³⁴Th source in γγ-coincidences, and a new ²³⁴Pa level populated in the β-decay of ²³⁴Th is introduced.