Low-energy Coulomb excitation of 62^{62}Fe and 62^{62}Mn following in-beam decay of 62^{62}Mn

Sub-barrier Coulomb-excitation was performed on a mixed beam of $^{62}$Mn and $^{62}$Fe, following in-trap $\beta^{-}$ decay of $^{62}$Mn at REX-ISOLDE, CERN. The trapping and charge breeding times were varied in order to alter the composition of the beam, which was measured by means of an ionisation chamber at the zero-angle position of the Miniball array. A new transition was observed at 418~keV, which has been tentatively associated to a $(2^{+},3^{+})\rightarrow1^{+}_{g.s.}$ transition. This fixes the relative positions of the $\beta$-decaying $4^{+}$ and $1^{+}$ states in $^{62}$Mn for the first time. Population of the $2^{+}_{1}$ state was observed in $^{62}$Fe and the cross-section determined by normalisation to the $^{109}$Ag target excitation, confirming the $B(E2)$ value measured in recoil-distance lifetime experiments.Comment: 9 pages, 10 figure

Transition Rates between Mixed Symmetry States: First Measurement in 94Mo

The nucleus 94Mo was investigated using a powerful combination of gamma-singles photon scattering experiments and gamma-gamma-coincidence studies following the beta-decay of 94mTc. The data survey short-lived J^pi=1+,2+ states and include branching ratios, E2/M1 mixing ratios, lifetimes, and transition strengths. The mixed-symmetry (MS) 1+ scissors mode and the 2+ MS state are identified from M1 strengths. A gamma transition between MS states was observed and its rate was measured. Nine M1 and E2 strengths involving MS states agree with the O(6) limit of the interacting boson model-2 using the proton boson E2 charge as the only free parameter.Comment: 9 pages, 3 PostScript figures included, ReVTeX, accepted for publication in Physical Review Letters, tentatively scheduled for August 9, 199

Observation of isotonic symmetry for enhanced quadrupole collectivity in neutron-rich 62,64,66Fe isotopes at N=40

The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N=40. The results are interpreted by the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N=40 as governed by the number of valence protons with respect to Z~30. The deformation suggested by the experimental data is reproduced by state-of-the-art shell calculations with a new effective interaction developed for the fpgd valence space.Comment: 4 pages, 2 figure

Search for the electric dipole excitations to the 3s1/2⊗[21+⊗31−]3s_{1/2} \otimes [2^{+}_{1} \otimes 3^{-}_{1}] multiplet in 117^{117}Sn

The odd-mass $^{117}$Sn nucleus was investigated in nuclear resonance fluorescence experiments up to an endpoint energy of the incident photon spectrum of 4.1 MeV at the bremsstrahlung facility of the Stuttgart University. More than 50 mainly hitherto unknown levels were found. From the measurement of the scattering cross sections model independent absolute electric dipole excitation strengths were extracted. The measured angular distributions suggested the spins of 11 excited levels. Quasi-particle phonon model calculations including a complete configuration space were performed for the first time for a heavy odd-mass spherical nucleus. These calculations give a clear insight in the fragmentation and distribution of the $E1$, $M1$, and $E2$ excitation strength in the low energy region. It is proven that the $1^{-}$ component of the two-phonon $[2^{+}_{1} \otimes 3^{-}_{1}]$ quintuplet built on top of the $1/2^{+}$ ground state is strongly fragmented. The theoretical calculations are consistent with the experimental data.Comment: 10 pages, 5 figure

Single-conformation spectroscopy of hydrogen bonding networks: Solvation, synthetic foldamers, and neurodegenerative diseases

The hydrogen bond is one of the most important interactions in natural processes ranging from protein folding to chemical reactions. Two complementary methodologies are applied to understanding this important interaction: top-down and bottom-up. Top-down methods use large molecules, such as proteins, revealing secondary structure information. Bottom-up experiments are performed on small molecules, utilizing high-resolution spectroscopy to reveal underlying quantum mechanical effects. The complexity gap is formed between these two experimental regimes; between large and small molecules; between bulk and individual solvent molecules; between classical mechanics calculations and quantum chemical calculations. This dissertation will focus on the application of gas phase, single-conformation ultraviolet (UV) and infrared (IR) spectroscopies to the study of molecules and clusters in the size and solvation complexity gap, with the goal of bridging the gulf between the two experimental approaches. Single-conformation spectroscopy is perfectly suited to study solvation. Solvent molecules, in many instances water, can be frozen onto the solute in a stepwise manner. Here, we solvate a prototypical flexible bichromophore—1,2-diphenoxyethane (DPOE)—by stepwise addition of water molecules. Single-conformation spectroscopy reveals both the structural perturbations associated with water molecule addition and their effect on DPOE’s pair of closely spaced excited electronic states. These experimental studies provide excellent insight into solvent effects on vibronic and excitonic coupling, and can be used to further develop the models used to describe such processes. Similarly, single-conformation spectroscopy can reveal the effects of conformational flexibility on the innate conformational preferences and hydrogen bonding motifs in peptides. Results obtained from a study of a cyclically constrained γ peptide, γACHC, reveal that increased conformational flexibility can be controlled by synthetic chemists in order to direct folding into pre-programmed secondary structures and that these structures are stabilized with intramolecular rather than intermolecular hydrogen bonds. This theme of conformational flexibility is continued in studies of glutamine containing peptides. Glutamine—with its flexible, hydrogen bond forming sidechain—is intimately involved with neurodegenerative diseases such as Huntington’s disease. Single-conformation studies help reveal the delicate interplay between three different types of hydrogen bonds within the molecule: backbone-backbone, sidechain-backbone, and sidechain-sidechain hydrogen bonds. The importance of these competing hydrogen bonds on the conformational preferences will be discussed both locally and within the larger context of disease pathogenesis

Associations between lifestyle factors and an unhealthy diet.

: Unhealthy dietary patterns have been associated with other unhealthy lifestyle factors such as smoking and physical inactivity. Whether these associations are similar in high- and low-educated individuals is currently unknown

Strong fragmentation of low-energy electromagnetic excitation strength in 117^{117}Sn

Results of nuclear resonance fluorescence experiments on $^{117}$Sn are reported. More than 50 $\gamma$ transitions with $E_{\gamma} < 4$ MeV were detected indicating a strong fragmentation of the electromagnetic excitation strength. For the first time microscopic calculations making use of a complete configuration space for low-lying states are performed in heavy odd-mass spherical nuclei. The theoretical predictions are in good agreement with the data. It is concluded that although the E1 transitions are the strongest ones also M1 and E2 decays contribute substantially to the observed spectra. In contrast to the neighboring even $^{116-124}$Sn, in $^{117}$Sn the $1^-$ component of the two-phonon $[2^+_1 \otimes 3^-_1]$ quintuplet built on top of the 1/2$^+$ ground state is proved to be strongly fragmented.Comment: 4 pages, 3 figure