Level lifetimes for the candidate chiral doublet bands of 80Br were extracted by means of the Doppler-shift attenuation method. The absolute transition probabilities derived from the lifetimes agree well with the M1 and E2 chiral electromagnetic selection rules, and are well reproduced by the triaxial particle rotor model calculations. Such good agreements among the experimental data, selection rules of chiral doublet bands and theoretical calculations are rare and outstanding in researches of nuclear chirality. Besides odd-odd Cs isotopes, odd-odd Br isotopes in the A≈ 80 mass region represent another territory that exhibits the ideal selection rules expected for chiral doublet bands.

Dipole and quadrupole excitations in the semimagic N=50 nucleus Sr-88 were investigated at the superconducting Darmstadt electron linear accelerator S-DALINAC with bremsstrahlung of an end-point energy of 6.8 MeV. Many new dipole excitations could be identified, and their reduced excitation probabilities were determined. The experimental findings are discussed in the context of quasiparticle-phonon-model and shell-model calculations. A breaking of the N=50 core is essential to describe the structure of the observed excitations. The two-phonon quadrupole-octupole J(pi)=1(-) state exhibits unusual features which are presently not understood.

This paper proposes a general discussion of the handling of imprecise and uncertain information in temporal reasoning in the framework of fuzzy sets and possibility theory. The introduction of fuzzy features in temporal reasoning can be related to different issues. First, it can be motivated by the need of a gradual, linguistic-like description of temporal relations even in the face of complete information. An extension of Allen relational calculus is proposed, based on fuzzy comparators expressing linguistic tolerance. Fuzzy Allen relations are defined from a fuzzy partition made by three possible fuzzy relations between dates ( approximately equal, clearly smaller, and clearly greater). Second, the handling of fuzzy or incomplete information leads to pervade classical Allen relations, and more generally fuzzy Allen relations, with uncertainty. The paper provides a detailed presentation of the calculus of fuzzy Allen relations ( including the composition table of these relations). Moreover, the paper discusses the patterns for propagating uncertainty about ( fuzzy) Allen relations in a possibilistic way.

Excited states of the nucleus Br-79 were investigated via the reaction Ge-76(Li-7,4n) at a beam energy of 35 MeV. Coincidence data of emitted gamma rays were measured with an arrangement of six EUROBALL CLUSTER detectors. The E2 bands built on the 9/2(+) and 3/2(-) states were extended up to J=37/2 at Eapproximate to8.8 MeV. The M1 band starting with a 15/2(-) state at 2.6 MeV was observed up to J=(29/2) at E=6.4 MeV. Crossover E2 transitions within this band were observed for the first time. Mean lifetimes of 17 levels were deduced using the Doppler-shift-attenuation method. The M1 band can be described within the tilted-axis-cranking model on the basis of the tilted three-quasiparticle configuration pi(g(9/2)) nu(g(9/2)) nu(fp) which has a triaxial shape. This band appears as a mixed case including contributions of both magnetic and collective rotation.

The wave function of a planar-channeled positron with energy 10MeV⩽E⩽100 MeV under the resonant influence of hypersound is calculated. It is found that the longitudinal hypersound changes the spectral distribution of the channeling radiation significantly. With decreasing wavelength λs of the hypersound, starting from λs=λE, where λE is the characteristic length related to one transverse oscillation of the channeled positron, a new type of radiative transition occurs. It is characterized by the stimulated enhancement of transverse energy of the positron at channeling (inverse radiative transition). When λs approaches λE/2 the inverse transitions show a resonant behaviour.

Dipole excitations in the spherical nucleus Sr-88, observed in the energy region 4.5 MeV less than or equal to E-x less than or equal to 5.5 MeV, are proposed to be scissors-like excitations on top of the dynamically deformed quadrupole vibrational state.

The wave function of a planar/axially channeled electron with energy 10 MeV less than or equal to E much less than 1 GeV under the influence of a longitudinal hypersonic wave excited in a single crystal is calculated. Conditions for the resonant influence of the hypersonic wave on the quantum state of the channeled electron are deduced. Expressions for the wave function that are applicable in the case of resonance are obtained.Angular and spectral distributions of the radiation intensity from the planar/axially channeled electron are also calculated. The possibility of significant amplification of channeling radiation by a hypersonic wave is substantiated. It is found that the hypersound can excite inverse radiative transitions through which the transversal energy of the channeled electron is increased. These transitions have a resonant nature and can lead to a considerable intensification of the electron channeling radiation. In the case of axial channeling, the resonance radiation is sustained also by direct radiative transitions of the electron. (C) 2001 Elsevier Science B.V. All rights reserved.

The electric dipole strength distributions below threshold in stable even-mass Pb isotopes have been extracted from photon scattering experiments at the superconducting Darmstadt electron linear accelerator S-DALINAC. Between 4 and 6.5 MeV excitation energy a resonance-like clustering of strength is observed. A strong evolution of a fragmentation of the dipole strength with opening the neutron shell is found. The fine structure of the strength is compared to microscopic quasiparticle-phonon model calculations that quantitatively reproduce the data quite well and explain the fragmentation of the dipole strength. Models suggesting the oscillation of excess neutrons with respect to an N≃Z core as a possible origin of low-lying E1 strength are critically examined.

We have studied the isotopes (82)Rb45, (83)Rb46, and (84)Rb47 to search for magnetic rotation which is predicted in the tilted-axis cranking model for a certain mass region around A = 80. Excited states in these nuclei were populated via the reaction (11)B + (76)Ge with E = 50 MeV at the XTU tandem accelerator of the LNL Legnaro. Based on a γ-coincidence experiment using the spectrometer GASP we have found magnetic dipole bands in each studied nuclide. The regular M1 bands observed in the odd-odd nuclei (82)Rb and (84)Rb include B(M1)/B(E2) ratios decreasing smoothly with increasing spin in a range of 13(-) ≤ J(π) ≤ 16(-). These bands are interpreted in the tilted-axis cranking model on the basis of four-quasiparticle configurations of the type [Formula: see text]. This is the first evidence of magnetic rotation in the A ≈ 80 region. In contrast, the M1 sequences in the odd-even nucleus (83)Rb are not regular, and the B(M1)/B(E2) ratios show a pronounced staggering.

A 4π silicon ball for detection and identification of light charged particles in large multidetector γ-arrays as EUROBALL is presented. The design is based on a N=42 ball with 12 pentagons and 30 hexagons as used in the GASP array. The absorptive material for γ-rays is minimized to the detector thickness of 300 or 500μm and a 0.63 mm ceramic backing. The geometrical coverage is designed for about 90% of 4π. A pulse shape discrimination method with totally depleted detectors working in the reverse mount allows identifying protons and α-particles above an energy threshold of about 2MeV. The performances of the ball were tested at the tandem – booster accelerator combination of the MPI Heidelberg in two experiments using the high-recoil reaction of 228MeV 58Ni+46Ti and the low-recoil reaction of 95MeV 16O+58Ni. The two-dimensional spectra of zero-crossing (ZC) versus energy confirmed an excellent discrimination of protons and α-particles in all the detectors at different angles. The energy spectra of protons and α-particles measured in the experiments are presented, too. The γ-spectra measured in coincidence with various combinations of emitted particles showed a high selectivity of the ball. The reduced total efficiency for protons of 59% and 55% and α-particles of 44% and 32% measured in a nuclear spectroscopy application is analyzed in a Monte-Carlo simulation (GEANT). It is due to a combined influence of a thick target needed to stop the recoiling residual nuclei and thick absorbers needed to protect the Si-detectors from scattered beam. The results along with the GEANT extrapolation to optimum experimental conditions confirm that RoSiB is a highly efficient and selective device for identification of rare reaction channels with heavy ions.

The wave function of an electron of energy 10 MeV less than or equal to E less than or equal to 100 MeV axially channeled in a Longitudinal hypersonic superlattice has been obtained within the framework of a quantum mechanical approach. Conditions for the resonant influence of the hypersonic wave excited in the single crystal on the quantum states of the channeled electron have been deduced.

The solutions of the Dirac equation for a positron channeled in a single crystal which is excited by a longitudinal hypersonic wave have been obtained for the energy interval of 10 MeV < E less than or equal to 100 MeV, and the resonance condition for the interaction between hypersound and positron was deduced. It is shown that the total intensity of the channeling radiation emitted by the relativistic positron in the hypersonic field is formed by the partial. intensities of several dominating radiative transitions for which the appropriate conservation law and the Doppler shift of the photon frequency have been determined. Owing to the hypersound the transverse energy of the positron may increase which leads to a larger bandwidth of the emitted lines.

A nuclear resonance fluorescence experiment on 88Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy. The γ-ray linear polarisation has been measured with a EUROBALL CLUSTER detector used as a Compton polarimeter. The results indicate positive parity for the J= 1 state at 4.742 MeV in 88Sr, in contrast to the previous interpretation as a 1− two-phonon (2+1⊗ 3−1) state and in conflict with the predictions of the quasiparticle-phonon model. On the basis of such calculations the 1+ state at 3.486 MeV may be considered as the 1+1 one-phonon state and the very strong 1+1→ 0+1 deexcitation as proton spin-flip 2p1/2→ 2p3/2 transition.

The Forschungszentrum Rossendorf (FZR) is constructing a superconducting Electron Linac [F. Gabriel, J. Voigtländer, et al., ELBE Design Report 1998, http://www.fz-rossendorf.de/FWQ/report_d.htm; Annual Report 1996, FZR-179 (1997) 3; Annual Report 1997, FZR-215 (1998) 3] with high Brilliance and low Emittance (ELBE) which can deliver a 1 mA cw beam of 40 MeV. ELBE will be equipped with a free-electron laser (FEL) system for the production of infrared (IR) light in the range 5–300 μm and will thus cover the range from the infrared to the THz regime. The electron beam can also be used to generate X-rays, bremsstrahlung, positrons or fast neutrons.

We report on a nuclear resonance fluorescence experiment on the semi-magic odd-mass fp-shell nucleus 51V. The detected dipole strength distribution is discussed on the basis of modern shell-model calculations employing a model space allowing for excitations of protons and neutrons from the 1f7/2 to the (2p1/2,2p3/2,1f5/2) shells. The calculations indicate that the main body of transitions is of magnetic dipole type, and they are capable of reproducing the observed distribution well. Possible electric dipole and quadrupole contributions are also discussed.

The low-energy dipole strength distributions in 165Ho and 169Tm have been studied in nuclear resonance fluorescence experiments at the S-DALINAC utilizing a Euroball Cluster detector. In the energy interval between 2.5 and 4.0 MeV, where the scissors mode is expected, 35 ground state transitions could be observed in 165Ho and 53 in 169Tm. Assuming M1 character for all these transitions corresponds to ΣB(M1) ↑= 1.54(23), μN2 and ΣB(M1) ↑= 2.15(63), μN2 for 165Ho and 169Tm, respectively. A statistical analysis is applied to the measured spectra which is capable of reconstructing the complete strength, including contributions of transitions below the observation limit, with the ratio between M1 and E1 excitations and their total strengths taken as an average over the even-mass neighbours. This results in summed M1 transition strengths of ΣB(M1) ↑= 3.54−0.95+0.75, μN2 (165Ho) and ΣB(M1) ↑= 3.36−0.57+1.00μN2 (169Tm). The large variations of the summed dipole strength and the fragmentation in other deformed odd-mass nuclei can be reproduced by the same statistical ansatz. The total low-lying M1 strength in heavy deformed odd-mass nuclei is in agreement with the findings in the neighbouring even-mass nuclides as well as with sum-rule predictions.