Structure of theN=59 nucleus97Sr: coexistence of spherical and deformed states

A band with a rotational pattern based on a state at 585.1 keV has been identified in theN=59 neutron-rich nucleus⁹⁷Sr. Its properties lead to the [422] 3/2 Nilsson-orbital assignment for the band head. There is evidence for a second band with the head at 644.7 keV and the configuration [541] 3/2. Since the ground state and the lowest excited levels are spherical, shape coexistence is established for⁹⁷Sr. A deformed nature of several levels at 500–600 keV results also from QRPA-model calculations. The structure of the low-lying spherical levels has been studied in the frame of the IBF model. The results of the present investigations lead to a better understanding of theN=59 isotones which constitute the link between the spherical and deformed nuclei atA～100 as a species with shape coexistence but without any indications of particular softness.     

Half-lives andP n values of delayed-neutron precursors in the mass chains 85–87, 92, 135, 136 and 145

Further results are presented on half-lives and neutron emission probabilities (P _n ) of short-lived delayed-neutron precursors in the mass chains 85–87, 92, 135, 136 and 145 obtained with the recoil focussing parabola-type mass separator for unslowed fission products LOHENGRIN installed at the Grenoble high-flux reactor. A newP _n -value of (44±14)% is given for the (0.73±0.06)s⁸⁷As; theP _n -values of seven precursor nuclides have been redetermined: (1.9±0.1)s⁸⁵As with (22±8)%, 0.9s⁸⁶As with (10.5±2.2)%, (0.35±0.04)s⁹²Br with (21±8)%, (1.6±0.15)s¹³⁵Sb with (14±1)%, (0.9±0.1)s¹³⁶Sb with (19±9)%, (17.5±0.2)s¹³⁶Te with (2.0±1.0)% and 0.6s¹⁴⁵Cs with (12.5±3.0)%. The results are compared with the existing data, and the neutron emission probabilities are discussed within a simple semi-empirical picture.     

Gamma-ray competition with neutron emission in the decay of 137I

Gamma-rays with energies above the neutron binding energy in ¹³⁷Xe have been observed at 3907 and 3994 keV in the decay of ¹³⁷I. Their combined intensity amounts to about 25% of the delayed neutron intensity and demonstrates that γ-ray widths are an important factor in defining the magnitude and energy distribution of the delayed neutron spectrum.     

Zum Gültigkeitsbereich des zentralen Grenzwertsatzes und des Gesetzes der großen Zahlen

Ohne Zusammenfassung     

Evidence for a new low-lying resonance state in 7He

Low-lying resonance states in 7He(6He+n), formed after fragmentation reactions of a 227 MeV/nucleon 8He beam on a carbon target, have been studied. Coincidences between 6He nuclei and neutrons, corresponding to the one-neutron knockout channel in 8He, were selected. The relative energy spectrum in the 6He+n system shows a structure, which is interpreted as the 7He ( Ipi = 3/2(-)) ground state, unbound with 0.43(2) MeV relative to the 6He+n system and a width of Gamma = 0.15(8) MeV overlapping with an excited ( Ipi = 1/2(-)) state observed at 1.0(1) MeV with a width of Gamma = 0.75(8) MeV.     

Photoneutron cross sections for unstable neutron-rich oxygen isotopes.

The dipole response of stable and unstable neutron-rich oxygen nuclei of masses A = 17 to A = 22 has been investigated experimentally utilizing electromagnetic excitation in heavy-ion collisions at beam energies about 600 MeV/nucleon. A kinematically complete measurement of the neutron decay channel in inelastic scattering of the secondary beam projectiles from a Pb target was performed. Differential electromagnetic excitation cross sections d sigma/dE were derived up to 30 MeV excitation energy. In contrast to stable nuclei, the deduced dipole strength distribution appears to be strongly fragmented and systematically exhibits a considerable fraction of low-lying strength.     

Influence of programming strain rates on the shape‐memory performance of semicrystalline multiblock copolymers

Multiblock copolymers named PCL‐PIBMD consisting of crystallizable poly(ε‐caprolactone) segments and crystallizable poly[oligo(3S‐iso‐butylmorpholine‐2,5‐dione)] segments coupled by trimethyl hexamethylene diisocyanate provide a versatile molecular architecture for achieving shape‐memory effects (SMEs) in polymers. The mechanical properties as well as the SME performance of PCL‐PIBMD can be tailored by the variation of physical parameters during programming such as deformation strain or applied temperature protocols. In this study, we explored the influence of applying different strain rates during programming on the resulting nanostructure of PCL‐PIBMD. Programming was conducted at 50 °C by elongation to ε_m = 50% with strain rates of 1 or 10 or 50 mm min^?1. The nanostructural changes were visualized by atomic force microscopy (AFM) measurements and investigated by in situ wide and small angle X‐ray scattering experiments. With increasing the strain rate, a higher degree of orientation was observed in the amorphous domains. Simultaneously the strain‐induced formation of new PIBMD crystals as well as the fragmentation of existing large PIBMD crystals occurred. The observed differences in shape fixity ratio and recovery stress of samples deformed with various strain rates can be attributed to their different nanostructures. The achieved findings can be relevant parameters for programming the shape‐memory polymers with designed recovery forces. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1935–1943     

Fission in238U+238U collisions below the Coulomb barrier

Integral fission cross sections in the system²³⁸U+²³⁸U were measured at beam energies below the interaction barrierV _C. Scattering angle dependent probabilities and integral cross sections for Coulomb fission were calculated. It is concluded that earlier observed discrepancies between measured and calculated angular distributions for the one-neutron transfer product²³⁹U cannot be explained by sequential fission. Multi-nucleon transfer induced fission is observed down to energies (0.90±0.02)×V_C.