Partial Dynamical SU(3) Symmetry and the Nature of the Lowest K=0 Collective Excitation in Deformed Nuclei

We discuss the implications of partial dynamical SU(3) symmetry (PDS) for the structure of the lowest K=0^{+} (K=0_2) collective excitation in deformed nuclei. We consider an interacting boson model Hamiltonian whose ground and gamma bands have good SU(3) symmetry while the K=0_2 band is mixed. It is shown that the double-phonon components in the K=0_2 wave function arise from SU(3) admixtures which, in turn, can be determined from absolute E2 rates connecting the K=0_2 and ground bands. An explicit expression is derived for these admixtures in terms of the ratio of K=0_2 and gamma bandhead energies. The SU(3) PDS predictions are compared with existing data and with broken-SU(3) calculations for ^{168}Er.Comment: 12 pages, 2 figure

Structure and diffusive dynamics of aspartate α-decarboxylase (ADC) liganded with D-serine in aqueous solution.

Incoherent neutron spectroscopy, in combination with dynamic light scattering, was used to investigate the effect of ligand binding on the center-of-mass self-diffusion and internal diffusive dynamics of Escherichia coli aspartate α-decarboxylase (ADC). The X-ray crystal structure of ADC in complex with the D-serine inhibitor was also determined, and molecular dynamics simulations were used to further probe the structural rearrangements that occur as a result of ligand binding. These experiments reveal that D-serine forms hydrogen bonds with some of the active site residues, that higher order oligomers of the ADC tetramer exist on ns-ms time-scales, and also show that ligand binding both affects the ADC internal diffusive dynamics and appears to further increase the size of the higher order oligomers

Multi-Phonon γ\gamma-Vibrational Bands and the Triaxial Projected Shell Model

We present a fully quantum-mechanical, microscopic, unified treatment of ground-state band and multi-phonon $\gamma$-vibrational bands using shell model diagonalization with the triaxial projected shell model. The results agree very well with data on the g- and $\gamma$-band spectra in $^{156-170}$Er, as well as with recently measured $4^+$ 2-phonon $\gamma$-bandhead energies in $^{166}$Er and $^{168}$Er. Multi-phonon $\gamma$-excitation energies are predicted.Comment: 4 pages, 4 figures, submitted to Phys. Lett.

Backbending region study in 160,162Dy using incomplete fusion reactions

18 págs.; 17 figs.; 3 tabs. ; PACS number(s): 23.20.Lv, 23.20.En, 27.70.1q, 21.60.CsThe incomplete fusion reactions 7Li→158,160Gd at beam energies of 8 MeV/nucleon have been used to study the first band crossing region in the heavy stable Dy isotopes 160,162Dy. The γ rays were detected in the GASP spectrometer in coincidence with fast charged particles detected in the ISIS silicon ball. We succeeded to observe the first backbending in 162Dy at a crossing frequency of ℏ ω ≈ 350 keV, a value much higher than expected from other nuclei in this mass region. Moreover, for the first time in a nucleus with a very large interaction strength, the yrare band in 160Dy could be established up to rather high spin (I= 20ℏ) allowing for a precise determination of the interaction strength between the ground state and the Stockholm band, |Vg-S| = 219(2) keV. Together with |Vg-S| = 14(2) kev determined for the corresponding interaction in 162Dy, a full oscillation of the strengths from one node to the next could be observed within an isotopic chain. In addition to the ground state and Stockholm bands, many other known bands in the two nuclei were considerably extended to higher spin and the experimental results are compared to calculations within the projected shell model. ©2002 The American Physical SocietyThis work has been supported by Deutsches Bundesministerium fur Bildung, Wissenschaft, Forschung und Technologie (BMBF). A.J. acknowledges support by the Deutsche Forschungsgemeinschaft (DFG).Peer Reviewe

Excited bands and signature dependent electromagnetic decay properties in neutron-rich 159,161,163Dy

14 págs.; 12 figs.; 3 tabs. ; PACS number(s): 23.20.Lv, 27.70.1q, 21.10.ReHigh-spin states of the neutron-rich odd nuclei 159,161,163Dy have been studied using the incomplete fusion reactions 158,160Gd(7Li,(p,d,t)xn). In 159Dy, the band crossing in the 11/2-[505] band has been observed for the first time. Moreover, 11 E1 transitions connecting both signatures of the 3/2-[521] band to the 5/2+[642] band have been observed in this nucleus; the deduced B(E1)/B(E2) ratios as well as the B(M1)/B(E2) ratios for transitions within the 3/2-[521] band show a pronounced signature dependence. In 161Dy and 163Dy, rotational bands have been extended to significantly higher spin values. In 161Dy, the sequences built on the neutron 5/2-[523] and 3/2-[521] states have been followed up to spin 49/2- and 33/2-, respectively, and in both cases upbends have been observed around hℏ ω ≈0.26 MeV. In addition, a new band most probably built on the 11/2-[505] single-particle state has been identified in this isotope. In 163Dy, both the 5/2-[523] ground state band and the structure built on the 5/2+[642] neutron orbit have been extended up to the 45/2- and 49/2+ states, respectively. However, no band crossing has been observed in this nucleus. The properties of the observed bands in 159,161,163Dy are discussed and compared to calculations performed within the projected shell model. ©2003 The American Physical SocietyThis work was supported by the Deutsches Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF). A.J. acknowledges support by the Deutsche Forschungsgemeinschaft (DFG) within the Heisenberg program.Peer Reviewe

Lifetime measurements in 80^{80}Br and a new region for observation of chiral electromagnetic selection rules

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

Protein Short-Time Diffusion in a Naturally Crowded Environment.

The interior of living cells is a dense and polydisperse suspension of macromolecules. Such a complex system challenges an understanding in terms of colloidal suspensions. As a fundamental test we employ neutron spectroscopy to measure the diffusion of tracer proteins (immunoglobulins) in a cell-like environment (cell lysate) with explicit control over crowding conditions. In combination with Stokesian dynamics simulation, we address protein diffusion on nanosecond time scales where hydrodynamic interactions dominate over negligible protein collisions. We successfully link the experimental results on these complex, flexible molecules with coarse-grained simulations providing a consistent understanding by colloid theories. Both experiments and simulations show that tracers in polydisperse solutions close to the effective particle radius Reff = ⟨ Ri3⟩1/3 diffuse approximately as if the suspension was monodisperse. The simulations further show that macromolecules of sizes R > Reff ( R < Reff) are slowed more (less) effectively even at nanosecond time scales, which is highly relevant for a quantitative understanding of cellular processes

Selecting cold 2n transfer in 162^{\bf 162} Dy(116^{\bf 116}Sn,118^{\bf 118}Sn)160^{\bf 160}Dy

Cold 2n transfer has been studied using the reaction $^{162}$Dy($^{116}$Sn,$^{118}$Sn)$^{160}$Dy at energies in the vicinity of the Coulomb barrier. The experiment was performed at the Heidelberg-Darmstadt Crystal Ball spectrometer which was extended by 6 Compton suppressed Ge-detectors. It is demonstrated, that the direct population of intrinsically cold states in the deformed $^{160}$Dy transfer product can be selected by identifying and suppressing excitations to states above the yrast line using the Crystal Ball. The probability for populating yrast states in the deformed $^{160}$Dy nuclei in a 2n transfer reaction increases from 7 % at grazing collisions up to $\approx$ 50 % at large impact parameters, while the probability for populating the ground state in the spherical 2n transfer product $^{118}$Sn stays about constant at $\approx$ 45 % for all measured impact parameters

Collective excitations built on the 2γ+{\bf 2^+_\gamma} state in 168^{168}Er

To examine the collectivity of the previously proposed $K^\pi = 4^+$ $\gamma\gamma$-two-phonon state in $^{168}$Er at an excitation energy of 2056 keV and of the first excited $K^\pi=0^+$ band at 1217 keV (b-band), a Coulomb excitation experiment has been carried out at the Heidelberg-Darmstadt Crystal Ball spectrometer. The B(E2) value connecting the $4^+_{\gamma\gamma}$ state to the $\gamma$-band was remeasured to be {\rm B(E}2,4^{+}_{\gamma\gamma}\!\to2^+_\gamma)= (600\pm 130)\;\mbox{e$^{2}$fm$^{4}$}, which almost exhausts the harmonic expectation. In addition, the B(E2) values connecting the band head of the lowest lying excited $0^+_{\rm b}$ band to the $2^+_{\rm g}$ and $2^+_\gamma$ states were measured to be B(E2, $2^{+}_{\rm g}\!\to0^+_{\rm b})=(4.4\pm 0.6$) e$^{2}$fm$^{4}$ and B(E2, $2^{+}_{\gamma}\!\to0^+_{\rm b})=(30.4\pm 4.6$) e$^{2}$fm$^{4}$; the latter is almost a factor of 10 smaller than the B(E2, $2^{+}_{\gamma}\!\to0^+_{\rm g})$ value, which shows that the $0^+_{\rm b}$ band head has no significant contribution of the $K^\pi = 0^+$ $\gamma\gamma$-two-phonon state in its wave function