New investigation of the decay of the high-spin isomer in 151Er

The decay of the T _1/2 = 420 ns isomer in ¹⁵¹Er has been reinvestigated. The multipolarities of the decaying transitions have been established by measuring the electron conversion coefficients. An I ^π = 67/2⁻ assignment is proposed for this isomer with a π[h ₁₁^2/4 d ₃^2/1 d ₅^2/−1]⊗ν[f _7/2 h _9/2 h ₁₁^2/−1] configuration.     

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.     

The heavy-ion magnetic spectrometer PRISMA

PRISMA is a magnetic spectrometer installed at Laboratori Nazionali di Legnaro (Italy) and designed for A=100–200, E=5–10 MeV-per-nucleon beams, and for possible use with the proposed radioactive beam facility SPES. The foremost features of the instrument are presented, along with the outline of two data analyses exemplifying the effectiveness of PRISMA-CLARA in studies of reaction dynamics.     

Structure of 231Ac: Measurements of level half-lives

There is lack of knowledge of the structure of the ²³¹Ac nucleus located in the upper border of the island of octupole deformation centered around A = 225. We have populated the excited states in ²³¹Ac by beta-decay from the parent ²³¹Ra produced at ISOLDE, CERN. The low-energy structure of ²³¹Ac has been investigated by means of γ, conversion electrons, γ-γ and γ-e^- spectroscopy. We report here in the precise determination in ²³¹Ac of the half-life of the most intensively populated states by the Advanced Time Delayed ββγ(t) technique.     

GSI experiments on synthesis and nuclear structure investigations of the heaviest nuclei

Isotopes of elements up to Z = 113 have been synthesized using medium heavy projectiles and target nuclei around doubly magic ²⁰⁸Pb. Synthesis of still heavier elements in reactions of ⁴⁸Ca projectiles with actinide target nuclei has been reported. To obtain more information about production mechanism of transfermium isotopes nuclear reaction studies including investigations of massive transfer were resumed at SHIP, GSI. Nuclear structure investigations at SHIP have been concentrated so far mainly on systematic investigations of low lying Nilsson levels in odd-mass nuclei. Recently this field has been extended to decay studies of isomeric states in nobelium nuclei at E^* > 1 MeV.     

Decay of 1.643 h <Superscript>95</Superscript>Ru and its daughter's level structure

The decay of ⁹⁵Ru has been investigated by means of γ-ray spectroscopy. The ⁹⁵Ru nuclei were produced by the reaction ⁹²Mo( α, n) ⁹⁵Ru at a beam energy of 17MeV. High-purity Ge detectors have been used singly and in coincidence to study γ-rays in the decay of ⁹⁵Ru to ⁹⁵Tc. 132 γ-rays are reported, among them, energies and intensities for 127 transitions have been determined. A decay scheme of ⁹⁵Ru with 31 levels is proposed which accommodates 127 of these transitions. Spins and parities for three new levels are proposed from calculated log ft values, measured γ-ray branching ratios, and in-beam experiment results of the daughter nucleus ⁹⁵Tc. Combining with the high-spin states observed by in-beam γ-ray spectroscopy of previous decay works, the structure of the excited states of ⁹⁵Tc is discussed in the framework of the projected shell model.     

Isomeric states in 214Th and 213Th

Isomeric states in ²¹⁴Th and ²¹³Th were identified by means of γ -rays measured in delayed coincidence with the implanted evaporation residues. These were produced in irradiations of ¹⁶⁴Dy with ⁵⁴Cr projectiles and separated in-flight by the velocity filter SHIP. An isomeric state of I ^π = 8⁺ with a half-life of (1.24±0.12) μs was identified in ²¹⁴Th . The configuration π[1h _9/2 ⊗ 2f _7/2] was assigned to this state. An isomeric state with a half-life of (1.4±0.4) μs was observed in ²¹³Th . Tentatively it was assigned to an I ^π = 13/2⁺ state.     

Qβ measurements of 158, 159Pm , 159, 161Sm , 160-165Eu , 163Gd and 166Tb using a total absorption BGO detector

Q _β values of the neutron-rich isotopes of ^160-165Eu and ¹⁶³Gd were measured for the first time using a total absorption bismuth germanate (BGO) detector, and previously obtained data on ^{158, 159}Pm , ^{159, 161}Sm and ¹⁶⁶Tb were re-analyzed. These radioactive sources were prepared by an on-line mass separator (Tokai-ISOL) following the ²³⁸U (p,f reaction. The deduced Q _β values are the following: 6085(80)keV for ¹⁵⁸Pm , 3805(65)keV for ¹⁵⁹Sm , 5460(140)keV for ¹⁵⁹Pm , 4705(60)keV for ¹⁶⁰Eu , 5065(130)keV for ¹⁶¹Sm , 3705(60)keV for ¹⁶¹Eu , 5575(60)keV for ¹⁶²Eu , 4690(70)keV for ¹⁶³Eu , 3170(70)keV for ¹⁶³Gd , 6430(70)keV for ¹⁶⁴Eu , 5800(120)keV for ¹⁶⁵Eu , and 4695(70)keV for ¹⁶⁶Tb . Moreover, the deduced mass excesses and two-neutron separation energies ( S _2n values) were compared with those of the atomic mass evaluations and theoretical predictions.     

Energetic and structural characterization of 2‐R‐3‐methylquinoxaline‐1,4‐dioxides (R = benzoyl or tert‐butoxycarbonyl): experimental and computational studies

The gaseous standard molar enthalpies of formation of two 2‐R‐3‐methylquinoxaline‐1,4‐dioxides (R = benzoyl or tert‐butoxycarbonyl), at T = 298.15 K, were derived using the values for the enthalpies of formation of the compounds in the condensed phase, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, using a quartz crystal oscillator. The three dimensional structure of 2‐tert‐butoxycarbonyl‐3‐methylquinoxaline‐1,4‐dioxide has been obtained by X‐ray crystallography showing that the two N? O bond lengths in this compound are identical. The experimentally determined geometry in the crystal is similar to that obtained in the gas‐phase after computations performed at the B3LYP/6‐311 + G(2d,2p) level of theory. The experimental and computational results reported allow to extend the discussion about the influence of the molecular structure on the dissociation enthalpy of the N? O bonds for quinoxaline 1,4‐dioxide derivatives. As found previously, similar N? O bond lengths in quinoxaline‐1,4‐dioxide compounds are not linked with N? O bonds having the same strength. Copyright © 2007 John Wiley & Sons, Ltd.     

A multichannel Raman spectrometry study of polyacetylene isomerization induced by laser irradiation

The multichannel Raman spectrometry has been used in the study of the isomerization reaction of an 80% cis PA film into a trans PA, using a laser beam for a double purpose. It is employed simultaneously as an activation agent inducing the isomerization reaction and the Raman diffusion. In each experience, the power of the laser beam Pⁱ(λ) was equivalent to the temperature. Twelve spectra have been recorded at different time periods tj = j·dt. The integrations of the Raman intensities related to two selected bands were numerically calculated.We also proposed an original method for the determination of the isomeric composition. A quantitative relationship between the equilibrium temperature and the laser beam power (in the range of laser power: 30 < Pⁱ(λ) < 300 mW) has been found. An estimate number of isomerized molecules N₀ and then a correction factors f_cis and f_trans were also obtained.