“Alpha decays” of <Stack><Subscript>Λ</Subscript><Superscript>10</Superscript></Stack>Be and <Stack><Subscript>Λ</Subscript><Superscript>10</Superscript></Stack>B hypernuclei: Phenomenological analysis and role of nuclear structure

Hypernuclei are used to study the baryon-baryon weak interaction and associated effective weak Hamiltonian. We will show how the proper choice of hypernucleus can be used to pick out components of the effective weak Hamiltonian. It is well known that removing one nucleon from ⁹Be or ⁹B results in ⁸Be* with a subsequent αα decay. Through this unique process, it would be possible to identify final states of the residual nucleus. So, due to these specific properties of the core nuclei ⁹Be and ⁹B, it may be possible to measure the branching fractions Γ _ααi ^n(p) for the exclusive decays of the _Λ ¹⁰ Be ( _Λ ¹⁰ B) hypernuclei.     

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.     

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     

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.     

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.     

Absorption spectrum of H<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> near 1.06 μm

The absorption spectra of molecular hydrogen plasma excited by electric hollow-cathode and high-frequency discharges are measured. The spectra in the region of 1.06 μm were recorded using a neodymium intracavity laser spectrometer with a resolution of 0.03 cm^?1 and an absorption sensitivity of 10^?8 cm^?1. The absorption lines that can be attributed to the transitions to vibrational states in the molecule are recorded.     

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.     

Krein Regularization of <Emphasis Type="Italic">λϕ</Emphasis><Superscript>4</Superscript>

We calculate the four-point function in λϕ ⁴ theory by using Krein regularization and compare our result, which is finite, with the usual result in λϕ ⁴ theory. The effective coupling constant (λ _μ ) is also calculated in this method.     

Detailed Investigations of Neutron–Neutron Angular Correlations in Slow-Neutron-Induced Fission of <Superscript>233</Superscript>U, <Superscript>235</Superscript>U,and <Superscript>239</Superscript>Pu

An experiment devoted to studying neutron–neutron angular correlations in the slow-neutroninduced fission of ²³³U, ²³⁵U and ²³⁹Pu nuclei was performed. The experimentally determined angular dependence of the number of neutron–neutron coincidences was compared with the results of a Monte Carlo simulation for various values of the neutron-detection threshold in the range between 490 and 2080 keV. It was found that the experimental angular distributions in question can be described well under the assumption that 2% to 5% of all prompt fission neutrons are emitted isotropically in the laboratory frame. Probably, such neutrons can be interpreted as so-called scission neutrons directly associated with the nuclear-rupture instant. Energy distributions of this component were also obtained from the present analysis.     

Broadening and shift of lines of the ν<Subscript>2</Subscript> + ν<Subscript>3</Subscript> band of water vapor induced by helium pressure

The broadening and shift coefficients of more than 100 absorption lines of the ν₂ + ν₃ band of water vapor that are induced by the pressure of helium are measured and calculated. The broadening and shift coefficients are obtained from analysis of the room-temperature absorption spectra of an H₂O-He mixture measured with a resolution of 0.007 cm^?1 on a Fourier spectrometer in a large range of helium pressures. The specific features in the rotational dependence of the line center shifts are determined, which, in contrast to the broadening induced by other gases, are mainly positive. The calculated coefficients of the line broadening and shift of line centers are determined by a semiclassical method. An unusual dependence of the shift coefficients is explained by the rotational dependence of the intermolecular isotropic interaction potential.     

A study of the neutrino production of <Emphasis Type="Italic">φ</Emphasis> and <Emphasis Type="Italic">D</Emphasis><Stack><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript><Superscript>+</Superscript></Stack> mesons

The charged current neutrino production of φ and D _s ⁺ mesons is studied, using the data obtained with the SKAT bubble chamber exposed to the Serpukhov accelerator neutrino beam. It is found that the φ production occurs predominantly in the forward hemisphere of the hadronic c.m.s. (at x _F > 0, x _F being the Feynman variable), with the mean yield strongly exceeding the expected yield of directly produced φ mesons and varying from 〈n _φ(x _F s 0)〉 = (0.92 ± 0.34) × 10^?2 at W > 2 GeV up to (1.23 ± 0.53) × 10^?2 at W > 2.6 GeV and (1.44 ± 0.69) × 10^?2 at W > 2.9 GeV, W being the invariant mass of the hadronic system. For the first time, the inclusive yield of leading D _s ⁺ mesons carrying more than z = 0.85 of the current c-quark energy is estimated: 〈n _{D s} ⁺ (z > 0.85, W > 2.9 GeV)〉 = (6.64 ± 1.91) × 10^?2. It is shown that the shape of measured φ meson differential spectrum on xF is reproduced by that expected from the D _s ⁺ → φX decays. An indication was obtained that this expected spectrum underestimates the measured φ yield.     

Mössbauer spectroscopy of <Superscript>57</Superscript>Fe in <Emphasis Type="Italic">α</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> following implantation of <Superscript>57</Superscript>Mn<Superscript>*</Superscript>

Two Fe/MCM-41 systems, one of them sylilated, were obtained to be used as catalysts in Fischer–Tropsch reaction. They have more than 90% of the iron species located inside the support channels, leading to a narrow crystal size distribution accessible to reactive gases. The samples were characterized by X-ray diffraction, atomic absorption spectroscopy, N₂ adsorption, Mössbauer spectroscopy and Fourier transformer infrared spectroscopy. Mössbauer spectroscopy allowed us to demonstrate that the catalytic active species were the same in both catalysts. The only difference between them was the surface hydrophobicity, which decreases the “water gas shift reaction” in the sylilated catalyst. Besides, this solid is more active for hydrocarbon production, with a lower methane yield.     

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.     

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.     

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.     

Measurement of the Dalitz-decay branching ratio of the π<Superscript>0</Superscript>

The ratio is measured by comparing the production rates of the π⁰ in the two decay channels. The analysis is based on approximately four million hadronic decays of the Z boson recorded by the ALEPH detector in the years 1991 to 1995. The value of is determined to be . A recalculation of the Particle Data Group world average gives rise to a slightly improved error, and moves the world average closer to the theoretical value.     

Laser control of low-temperature reaction <Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> + O<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

A theory is developed to describe dissociative recombination of a slow electron with a ground-state molecular ion of oxygen driven by a strong monochromatic electromagnetic field. Mathematically, the theory is based on the time-independent formalism of radiative scattering matrix whose poles correspond to dressed intermediate states of the complex. The analysis embraces both transitions to dissociative states and laserinduced nonadiabatic transitions to intermediate bound states of valence configurations. Key reaction mechanisms are considered, and a classification is given of all allowed transitions to dissociative states. Partial and total reaction cross sections are calculated by taking into account the contributions from Rydberg, valence, and dissociative states of O₂^**. A detailed discussion of results is presented, and feasibility of laser control of the reaction is demonstrated.