A5068046939- Nuclear physics research studies
- Nuclear Physics and Applications
- Quantum Dots Synthesis And Properties
- Advanced Chemical Physics Studies
- Nuclear reactor physics and engineering
- Spectroscopy and Quantum Chemical Studies
- Astronomical and nuclear sciences
- Atomic and Molecular Physics
- Semiconductor Quantum Structures and Devices
- Perovskite Materials and Applications
- Chalcogenide Semiconductor Thin Films
- Photochemistry and Electron Transfer Studies
- Organic Electronics and Photovoltaics
- Radiation Therapy and Dosimetry
- Advanced NMR Techniques and Applications
- Atomic and Subatomic Physics Research
- Radiation Detection and Scintillator Technologies
- Nuclear Materials and Properties
- Analytical Chemistry and Sensors
- Photoreceptor and optogenetics research
- Spectroscopy and Laser Applications
- X-ray Spectroscopy and Fluorescence Analysis
- Quantum Chromodynamics and Particle Interactions
- Molecular Junctions and Nanostructures
- Atmospheric and Environmental Gas Dynamics
Optica
2020-2025
Instituto de Ciencia de Materiales de Sevilla
2025
University of Oregon
2018-2023
Lawrence Livermore National Laboratory
1979-2017
University of California, Berkeley
2005-2015
Jet Propulsion Laboratory
2005-2015
University of Toronto
2005-2012
McMaster University
2002-2004
California Institute of Technology
2002
University of Minnesota
1977
The neutron spectra from the V/sup 51/(p,n)Cr/sup 51/ reaction exhibit a peak at Cr/sup excitation energy of 6.5 Mev. properties this suggest that direct, chargeindependent, charge-exchange occurs in region to state is analogous initial state. Charge independence shown imply Qvalue for final equals Coulomb difference DELTA E/sub c/ between and nuclei. Q- -values are found agree closely (p,n) reactions on 51/, Fe/sup 56/, Co/sup 59/. (T.F.H.)
The agreement of Coulomb displacement energies derived from the nonmirror ($p,n$) isobaric reaction with those obtained mirror and ($T=1$) nuclei beta decay has been previously demonstrated. Using Livermore 90-in. cyclotron time-of-flight facility, we have measured additional in mass region $70\ensuremath{\le}A\ensuremath{\le}108$. These measurements indicate possible shell effects which were not observed because paucity data. With availability 20.5-MeV protons, energy extended to...
The 14.8-Mev protons from the Livermore variable-energy cyclotron have been used to study ($p, n$) spectra 13 selected target nuclei with mass numbers 48 93 for a laboratory angle of 23\ifmmode^\circ\else\textdegree\fi{}. Neutron energies were determined using standard time-of-flight techniques. All show one strong neutron group at an energy corresponding in excitation final nucleus isobaric counterpart (analog state) ground state, i.e., $Q$ value is usual Coulomb displacement. forward...
The relaxation of atomic polarization in buffer-gas-free, paraffin-coated cesium vapor cells is studied using a variation on Franzen's technique ``relaxation the dark'' [Franzen, Phys. Rev. 115 850 (1959)]. In present experiment, narrow-band, circularly polarized pump light, resonant with Cs D2 transition, orients atoms along longitudinal magnetic field, and time-dependent optical rotation linearly probe light measured to determine rates orientation particular hyperfine level. change during...
Quantum dots (QDs) have discrete quantum states isolated from the environment, making QDs well suited for information processing. In semiconductor QDs, electron spins can be coherently oriented by photoexcitation using circularly polarized light, creating optical orientation. The optically induced spin orientation could serve as a unit data storage and Carrier is also envisioned to key component in related, though parallel, field of spintronics. However, population rapidly loses its...
Theory and experiment are combined to investigate the nature of low‐energy excitons within ordered domains 6,13‐bis(triisopropylsilylethynyl)‐pentacene (TIPS‐PEN) polycrystalline thin films. First‐principles density functional theory many‐body perturbation calculations, along with polarization‐dependent optical absorption spectro‐microscopy on domains, show multiple peaks that composed excitonic states delocalized over several molecules. While first peak is a single transition retains...
Using pulsed-beam neutron time-of-flight spectrometry relative differential cross sections for $^{7}\mathrm{Li}(p,{n}_{0})^{7}\mathrm{Be}$(g.s.) and $^{7}\mathrm{Li}(p,{n}_{1})^{7}\mathrm{Be}^{*}$ (0.431 MeV) have been measured over the laboratory angular range 3.5\ifmmode^\circ\else\textdegree\fi{} to 159\ifmmode^\circ\else\textdegree\fi{} from an incident bombarding energy of 4.2 26 MeV. These integrated angle at 5 MeV resulting integral was normalized absolute measurement Macklin Gibbons...
Time-of-flight techniques have been used on the Livermore variable energy cyclotron to study ($p,n$) spectra from selected target nuclei. Previously reported neutron for 14.8-MeV protons all showed one strong group at an corresponding in excitation final nucleus isobaric counter-part (analog state) of ground state, i.e., $Q$ value is usual Coulomb displacement energy. With increase 18.5 MeV, measurements states extended include ${\mathrm{Rh}}^{103}$, Ag, ${\mathrm{In}}^{115}$, Sn, and...
The angular distributions of the neutrons from reactions ${\mathrm{Be}}^{9}(n, {n}^{\ensuremath{'}}){\mathrm{Be}}^{9*}$, $Q=\ensuremath{-}2.43$ Mev, and ${\mathrm{C}}^{12}(n, {n}^{\ensuremath{'}}){\mathrm{C}}^{12*}$, $Q=\ensuremath{-}4.43$ have been measured 25\ifmmode^\circ\else\textdegree\fi{} to 140\ifmmode^\circ\else\textdegree\fi{}, employing 14-Mev incident neutrons. Neither distribution is symmetric about 90\ifmmode^\circ\else\textdegree\fi{}; inelastically scattered are peaked in...
The spectroscopy of colloidal CdSe nanocrystals is investigated using two-dimensional photon echo (2DPE) with copolarized and cross-polarized pulse sequences. Clearly resolved excited state absorption features are observed to beat at the frequency longitudinal-optical phonon, phase this beating found be polarization-dependent. A simulation performed excitonic biexcitionic fine structure states predicted by theory, polarization-dependent allows each feature assigned a particular pathway....
Large-scale organic electronics manufacturing requires solution processing. For small-molecule semiconductors, processing results in crystalline domains with high charge mobility, but the interfaces between these impede transport, degrading device performance. Although understanding is essential to improve performance, their intermolecular and electronic structure unknown: they are smaller than diffraction limit, hidden from surface probe techniques, nanoscale heterogeneity not typically...
The ultrafast spectroscopy of single domains polycrystalline films TIPS-pentacene, a small-molecule organic semiconductor interest in electronic and photovoltaic applications, is investigated using transient absorption microscopy. Individual are distinguished by their different polarization-dependent linear nonlinear optical responses. As compared to bulk measurements, we show that the response within given domain can be tied more concretely specific physical processes transfer exciton...
From an essentially model-independent analysis of the ratio cross sections for reactions $^{7}\mathrm{Li}(p, {n}_{0})^{7}\mathrm{Be}_{\mathrm{g}.\mathrm{s}.}$, {n}_{1})^{7}\mathrm{Be}(0.43 \mathrm{MeV})$, and $^{6}\mathrm{Li}(p, {n}_{0})^{6}\mathrm{Be}_{\mathrm{g}.\mathrm{s}.}$, it is concluded that $\frac{{V}_{\ensuremath{\sigma}\ensuremath{\tau}}}{{V}_{\ensuremath{\tau}}}=0.66\ifmmode\pm\else\textpm\fi{}0.08$ independent bombarding energy from 10-20 MeV.
The angular distribution of the neutrons from ${\mathrm{C}}^{13}(p, n){\mathrm{N}}^{13}$ and ${\mathrm{N}}^{15}(p, n){\mathrm{O}}^{15}$ ground-state reactions has been measured in 10\ifmmode^\circ\else\textdegree\fi{} steps 0\ifmmode^\circ\else\textdegree\fi{} to 150\ifmmode^\circ\else\textdegree\fi{} for incident proton (laboratory) energies approximately 6.5, 6.9, 7.5, 8.1, 8.6, 8.9, 9.4, 10.6, 11.4, 12.2 Mev. Additional measurements were made ${\mathrm{C}}^{13}$ at 5.0, 10.2, 10.9, 13.3...
The angular distributions of elastically scattered 14-Mev (nominal energy) neutrons have been measured for beryllium and carbon from 20\ifmmode^\circ\else\textdegree\fi{} to 140\ifmmode^\circ\else\textdegree\fi{}. Ring geometry, time-of-flight techniques, relatively low detector biases were used. A comparison with optical-model calculations by Bjorklund Fernbach indicates that the parameters fit medium heavy elements do not yield satisfactory fits carbon.
On the basis of quantum dot exciton states and selection rules for their excitation, a microscopic picture nonlinear optical spectroscopy that provides direct probe spin relaxation among is described. Equations motion which govern evolution third order population density are solved numerically to simulate measured signals. It shown how cross linearly-polarized pulse sequences in three-pulse transient grating experiments form polarization monitors history bright...
Neutron spectra produced by ($p,n$) reactions on $^{48}\mathrm{Ti}$, $^{49}\mathrm{Ti}$, $^{55}\mathrm{Mn}$, $^{58}\mathrm{Fe}$, and $^{63}\mathrm{Cu}$ ($\ensuremath{\alpha},n$) $^{45}\mathrm{Sc}$, $^{51}\mathrm{V}$, $^{52}\mathrm{Cr}$, $^{59}\mathrm{Co}$, $^{60}\mathrm{Ni}$ have been measured at four bombarding energies. The component of the corresponding to equilibrium (evaporation) processes was identified from angular energy dependence continuum cross sections. Level density parameters...
The electronic coupling values and approximate energy transfer rates between semiconductor single-wall carbon nanotubes are calculated using two different approximations, the point dipole approximation distributed transition monopole approximation, results compared. It is shown that fails dramatically at tube separations typically found in nanotube bundles ( approximately 12-16 A) disagreement persists large (>100 A, over ten diameters). When used Forster resonance theory, dipoles to...
Previously reported neutron spectra resulting from the ($p, n$) reaction all showed one strong group at an energy corresponding in excitation final nucleus to isobaric counterpart (analog state) of target ground state, i.e., $Q$ value for is usual Coulomb displacement energy. Using time-of-flight techniques and higher proton energies available 90-in. cyclotron after recent modifications, we have measured angular distributions neutrons 18.5-MeV protons on 19 targets between...
Thermal annealing is a widely used technique to enhance organic photovoltaic (OPV) efficiencies in bulk heterojunction devices. Combining studies and spectroscopic measurements with theoretical modeling provides more complete understanding of how aggregation influences energy transfer, an essential factor for performance. Here, we use situ absorbance single-shot transient absorption (SSTA) spectroscopy characterize the electronic structure excited-state dynamics squaraine molecules embedded...
Differential cross sections for the elastic scattering of 14.6 MeV neutrons from $^{9}\mathrm{Be}$, C, $^{27}\mathrm{Al}$, Fe, $^{59}\mathrm{Co}$, $^{89}\mathrm{Y}$, $^{93}\mathrm{Nb}$, In, $^{140}\mathrm{Ce}$, $^{181}\mathrm{Ta}$, $^{197}\mathrm{Au}$, $^{208}\mathrm{Pb}$, and $^{209}\mathrm{Bi}$ have been measured using a time-of-flight facility. The cover angular range 9.2\ifmmode^\circ\else\textdegree\fi{} to 159\ifmmode^\circ\else\textdegree\fi{}. Calculations carried out two local...
A spectroscopic study is reported of relaxation in the exciton fine structure CdSe nanorods measured using ultrafast cross-polarized heterodyned third-order transient grating (CPH-3TG) spectroscopy. The CPH-3TG spectroscopy probes dynamics population transfer between states accompanying spin flip (radiationless transitions associated with changes sign total angular momentum). Analysis data enabled elucidation pathways for (EFSR) involving all states. mechanism and origin EFSR are discussed...