41 research outputs found
Quantum transport through STM-lifted single PTCDA molecules
Using a scanning tunneling microscope we have measured the quantum
conductance through a PTCDA molecule for different configurations of the
tip-molecule-surface junction. A peculiar conductance resonance arises at the
Fermi level for certain tip to surface distances. We have relaxed the molecular
junction coordinates and calculated transport by means of the Landauer/Keldysh
approach. The zero bias transmission calculated for fixed tip positions in
lateral dimensions but different tip substrate distances show a clear shift and
sharpening of the molecular chemisorption level on increasing the STM-surface
distance, in agreement with experiment.Comment: accepted for publication in Applied Physics
Role of crystalline precipitates on the mechanical properties of (Cu0.50Zr0.50)100−xAlx (x= 4, 5, 7) bulk metallic glasses
Effects of Effective Dendrite Size on Dynamic Tensile Properties of Ti-Based Amorphous Matrix Composites
Continuing outcomes relevant to Evista:Breast cancer incidence in postmenopausal osteoporotic women in a randomized trial of Raloxifene
Untersuchungen an Beauveria tenella (NRRL 2334, 2335, 2336; bisher Agaricus campestris)
Investigation of alpha-induced reactions on the p nucleus Yb-168
Cross sections for the Yb-168(alpha,beta)Hf171- reactions were measured by means of the activation method using alpha particles with energies between 12.9 MeV and 15.1 MeV. The spectroscopy of the gamma rays emitted by the reaction products was performed using three different HPGe detector types, namely clover-type high-purity germanium detectors, a low-energy photon spectrometer detector, and a coaxial high-purity germanium detector. The results were compared to Hauser-Feshbach statistical model calculations. Within certain assumptions, astrophysical conclusions could be drawn concerning the production of the p nucleus Yb-168. The data in this work can serve as alpha contribution to the current very fragmentary experimental data base for charged-particle induced reactions. In addition, the absolute intensity for nine gamma-ray transitions following the electron capture decay of Hf-171 could be derived. (C) 2013 Elsevier B.V. All rights reserved
Activation method combined with characteristic X-ray counting : A possibility to measure (alpha, gamma) cross sections on heavy p-nuclei
For an improved modeling of the astrophysical nucleosynthesis of p-nuclei, low energy cross section data of alpha-induced reactions on heavy isotopes are needed. Technical difficulties hamper the experimental determination of these cross sections, therefore the relevant experimental data are almost completely missing. Here we present a new method for the cross section measurements, the activation technique based on the detection of characteristic X-ray radiation. The feasibility of the method is illustrated through the measurement of the Tm-169(alpha, gamma)Lu-173 and Tm-169(alpha, n)Lu-172 reaction cross sections. Despite the relatively long half-life of the reaction products (T-1/2 = 500 and 6.7 days, respectively) it was possible to measure the cross section of the Tm-169(alpha, gamma)Lu-173 reaction between E-c.m. = 13.16 and 17.08 MeV. The Tm-169(alpha, n)Lu-172 reaction cross section was derived from close above the threshold up to E-c.m.. = 17.08 MeV. Details of the new method and the experimental results are presented. (C) 2011 Elsevier B.V. All rights reserved.Peer reviewe
Alpha-induced reaction cross section measurements on Eu-151 for the astrophysical gamma-process
In order to extend the experimental database relevant for the astrophysical gamma-process towards the unexplored heavier mass region, the cross sections of the Eu-151(alpha, gamma)Tb-155 and Eu-151 (alpha, n)Tb-154 reactions have been measured at low energies between 12 and 17 MeV using the activation technique. The results are compared with the predictions of statistical model calculations and it is found that the calculations overestimate the cross sections by about a factor of 2. A sensitivity analysis shows that this discrepancy is caused by the inadequate description of the alpha+nucleus channel. A factor of 2 reduction of the reaction rate of Eu-151(alpha, gamma)Tb-155 in gamma-process network calculations with respect to theoretical rates using the optical potential by McFadden and Satchler (1966 Nucl. Phys. 84 177) is recommended