A fitting procedure for palaeodose from old sandstone using IRSL

In the dating studies of old samples using the Infrared Stimulated Luminescence (IRSL), the validity of the curve-fitting employed is of critical importance. So, in this study, a new fitting procedure was suggested for obtaining the age of the old geological sample. IRSL technique was applied using multiple-aliquot procedure to feldspar isolated from sample. The paleodose results obtained, using linear and polynomial fitting, were (67.98±2) Gy, (30.49±2) Gy and 322.03 Gy from the suggested fitting procedure. After application of this procedure the age was found to be 551.4 ka. This work was supported by Karaelmas University under the project numbered 98-101-009-01.     

Measurement of multi-exponential optical decay processes by?phase-shift cavity ring-down

Multi-exponential decay waveforms are common occurrences in cavity ring-down spectroscopy and the respective ring-down times are typically obtained by fitting the ring-down waveform to the sum of exponential decay functions. In phase-shift cavity ring-down (CRD) spectroscopy the measurement of a single phase angle will not provide sufficient information and needs to be complemented by either intensity measurements or phase angle measurements at different modulation frequencies. Here, a formalism analogous to that developed for fluorescence lifetime spectroscopy is adapted to the phase-shift CRD technique and is tested for two types of waveguide CRD systems: (1) a single-mode fiber cavity in which light is confined by two identical Fiber Bragg Gratings and (2) a multimode fiber loop. By measuring the phase angle at different modulation frequencies, lifetimes for up to three different decay processes were obtained.     

Relaxation dynamics of space-charge gratings excited by nanosecond light pulses in highly iron-doped LiNbO<Subscript>3</Subscript> crystals

Transmission gratings are recorded with nanosecond light pulses in highly Fe-doped (0.5 to 3 wt%) as-grown and oxidized lithium niobate crystals. In as-grown samples, the diffraction efficiency decays exponentially after recording, and an exponential increase of the decay rate with decreasing mean distance between the Fe centers takes place. Such a behavior is typical for tunneling of electrons between Fe centers. A different and highly peculiar dark evolution of the gratings, which includes a strong transient increase of the diffraction efficiency during about 100 s after illumination, is observed in strongly oxidized crystals. This behavior is explained within a simple relaxation model which accounts for the pyroelectric effect. The long-time decay of the diffraction efficiency again follows an exponential law. In strongly oxidized crystals, the decay rate shows, however, a surprising decrease with decreasing mean distance between the Fe centers. This peculiarity is shown to be consistent with the present notion of hopping charge transport in highly doped strongly compensated semiconductors.     

Near-damage threshold femtosecond laser irradiation of dielectric surfaces: desorbed ion kinetics and defect dynamics

We study the modification of fluoride single crystals after irradiation with femtosecond laser pulses for a range of incident intensities from well below to near damage threshold. The behavior of the desorbed positive ion yields, as analyzed by time-of-flight mass spectrometry, is corroborated with temporal characteristics of radiation induced defects in fluorides. The ion yield evolution upon repetitive irradiation (incubation) exhibits the typical reduction of the multi-shot damage threshold with increasing number of pulses. The experimental data point towards an exponential growth of the transient defect density as the origin of this effect. On the other hand, measurements of the time decay of transient defect fluorescence inside the transparent sample show that the defect lifetime may be even longer than tens of milliseconds. To account for the incubation and the increase of the radiation-target coupling efficiency, a model relating the defect lifetime to a pulse-by-pulse accumulation of transient defects is presented, based on a calculation of the free electron density.     

Both experimental and theoretical investigations of solid-state 17O NMR for L-valine and L-isoleucine

We have presented an experimental investigation of the carboxyl oxygen NMR parameters for four distinct sites in l-valine and l-isoleucine. The carboxyl (17)O quadrupolar coupling constant, C(Q), and isotropic chemical shift, delta(iso), for these compounds are obtained by analyzing two-dimensional (17)O multiple-quantum magic-angle spinning (MQMAS) and/or 1D MAS spectra. The values of C(Q) and delta(iso) found to be in the range of 7.00-7.85 MHz, and 264-314 ppm, respectively. Extensive quantum chemical calculations at the density functional levels have been performed for a full cluster of l-valine molecules and a few theoretical models. The calculated results indicated that there was a correlation between the (17)O NMR parameters and C-O bond lengths, which was helpful for the spectral assignment. They also demonstrated that the torsion angle of l-valine plays an important role in determining the magnitudes of (17)O NMR parameters.     

A computer model of particle balance in ECR ion sources

The investigation of the widespread model of particle balance and energy transport [1–5] for calculating the ion charge state distribution (CSD) in an electron cyclotron resonance (ECR) ion source [6] is given. The modification of this model that makes it possible to describe the confinement and accumulation processes of highly charged ions in ECR plasma for the case of gas mixing is more precisely discussed. The discussion of the new technique for calculating the time confinement of ions and electrons, which is based on the Pastukhov theory [7, 8], is given: calculation of confinement times during two step minimization of special type functionals. The preliminary results obtained with this approach have been compared with available experimental data. The text was submitted by the authors in English.     

Tunable and reversible surface wettability transition of vertically aligned ZnO nanorod arrays

Vertically aligned zinc oxide (ZnO) nanorods (NRs) with different surface morphology were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrate. To study the effect of surface morphology on wettability, the contact angle (CA) of water was measured. It was demonstrated that the CA of the deposited ZnO NRs varied between 104° and 135° depending upon the surface morphology. The ZnO NRs became super-hydrophilic after ultraviolet (UV) illumination. However, the NR arrays were reconverted to their previous hydrophobic state after low temperature annealing (50 °C) in open atmosphere. Structural effect and preferential adsorption of water molecules on the defective sites of UV illuminated surface was used to explain the transition mechanism. Under the alternations of heat treatment and UV illumination, a reversible transition between hydrophobicity and super-hydrophilicity were observed.     

Isotopic dependence of electron screening in fusion reactions

The fusion reactions⁶Li(p, )³He,⁶Li(d, )⁴He, and⁷Li(p, )⁴He have been studied over the c.m. energy rangeE=10 to 1450 keV. Each reaction involved the use of hydrogen projectiles and LiF solid targets as well as Li projectiles and hydrogen molecular gas targets. In all cases the effects of electron screening on the low-energy fusion cross sections (exponential enhancement) have been observed; the effects are somewhat stronger in the case of atomicp ord projectiles compared to the case of molecularH ₂ orD ₂ gas targets. If isotopic effects on electron screening are negligible, all three reactions should exhibit the same enhancements for each set of experimental techniques. The measurements confirmed this expectation to a large extent.Supported in part by the Landesamt Nordrhein-Westfalen (IVA5-10600387), the Deutsche Forschungsgemeinschaft (Ro429/ 18-2 and Ro429/21-1), and the Comision Interministerial de Ciencia y Tecnologia (AEN90-0932)     

New mechanism for non-trivial intra-molecular vibrational dynamics

We investigate the time evolution process of one selected (initially prepared by optical pumping) vibrational molecular state S, coupled to all other intra-molecular vibrational states R of the same molecule, and also to its environment Q. Molecular states forming the first reservoir R are characterized by a discrete dense spectrum, whereas the environment reservoir Q states form a continuous spectrum. Assuming the equidistant reservoir R states we find the exact analytical solution of the quantum dynamic equations. S-Q and R-Q couplings yield to spontaneous decay of the S and R states, whereas S-R exchange leads to recurrence cycles and Loschmidt echo at frequencies of S-R transitions and double resonances at the interlevel reservoir R transitions. Due to these couplings the system S time evolution is not reduced to a simple exponential relaxation. We predict various regimes of the system S dynamics, ranging from exponential decay to irregular damped oscillations. Namely, we show that there are possible four dynamic regimes of the evolution: (i) independent of the environment Q exponential decay suppressing backward R - S transitions, (ii) Loschmidt echo regime, (iii) incoherent dynamics with multicomponent Loschmidt echo, when the system state is exchanged its energy with many states of the reservoir, (iv) cycle mixing regime, when long time system dynamics looks as a random-like. We suggest applications of our results for interpretation of femtosecond vibration spectra of large molecules and nano-systems.     

Effect of pressure relaxation during the laser heating and electron–ion relaxation stages

The multi-phase equation of state by Bushman et al. (Sov. Tech. Rev. 5:1–44, 2008) is modified to describe states with different electron and ion temperatures and it is applied to the non-equilibrium evolution of an aluminum sample heated by a subpicosecond laser pulse. The sample evolution is described by the two-temperature model for the electron and ion temperatures, while the pressure and density are described by a simplified relaxation equation. The pressure relaxation in the heating stage reduces the binding energy and facilitates the electron-driven ablation. The model is applied to estimate the ablation depth of an Al target irradiated by a subpicosecond laser pulse. It improves the agreement with the experimental data and provides a new explanation of the ablation process.     

The three-dimensional (2 + 1)-fluid model for relativistic nuclear collisions

A new multi-fluid model is constructed for describing high-energy heavy-ion collisions. It is assumed that two baryonic fluids formed by the projectile and target nucleons produce a third hadronic fluid via inelastic nucleon-nucleon collisions. The production and expansion dynamics of the hadronic fluid are investigated in detail. Two equations of state for this fluid are considered: one corresponding to an ideal gas of pions and resonances and another one corresponding to an interacting hadron gas described by the relativistic mean-field model. The effects of freeze-out and non-zero pion chemical potential are investigated. The rapidity and transverse momentum spectra of secondary pions are compared with the experimental data forS + S collisions at 200 GeV/nucleon.The authors thank J. Schaffner for his most valuable assistance in the application of the mean-field model. The authors are also grateful to H. Sorge and A. Jahns for fruitful discussions. This work was supported by the Gesellschaft für Schwerionenforschung (GSI) and the Bundesministerium für Forschung und Technologie (BMFT).     

Photoemission and coincidence studies on gas-phase molecules

This article describes Young’s double-slit experiment using high-energy core-level photoemission from N₂ molecules and experimental identification of interatomic Coulombic decay in Ar₂ dimers after Auger decay using k-resolved electron–ion–ion coincidence spectroscopy, aiming to illustrate the leading edge of gas-phase experiments using synchrotron radiation.     

Calculation of decay widths of ppμ* ν,J ion in non-adiabatic approach

We calculate decay widths of the metastable ppμ^* _ν,J molecular ion in non-adiabatic approach. The muonic molecular ion can be formed in collision of the excited pμ(2s) atoms with H₂. Then, decay of the ppμ^* _ν,J system opens a path for the muon from pμ(2s) to pμ(1s). We employ trial wave function which includes non-adiabatic terms to calculate some radiationless decay widths. The present results of the widths do not good agree with those given in our previous work, while are more close to recent data of other researchers.     

Ultrafast dynamic ellipsometry measurements of early time laser ablation of titanium thin films

The dynamics of laser ablated titanium thin films are investigated using a recently developed technique that measures time-resolved and one-dimensional spatially-resolved ablation dynamics in a single shot. Ultrafast dynamic ellipsometry, a technique based on space-shifted spectral interferometry, uses the time-dependent frequency of a chirped laser pulse to provide time encoding, allowing the picosecond probing of material dynamics in a single shot. With this technique, the sample is probed at two different incident angles with both s- and p-polarized light, which measures the motion of the material and any change in its complex refractive index. Ultrafast dynamic ellipsometry is applied to study the mechanism of initiation by laser-based optical detonators that employ the ablation of titanium thin films. The resulting data indicate that the titanium is ablated as a fragmented flyer and not as an expanding plasma.     

Systematics of half-lives for proton radioactivity

Half-life measurements for both ground-state and isomeric transitions in proton radioactivity are systematized by using a semiempirical, one-parameter model based on tunneling through a potential barrier, where the centrifugal and overlapping effects are taken into account within the spherical nucleus approximation. This approach, which has been successfully applied to alpha decay cases covering ∼ 30 orders of magnitude in half-life, has shown, in addition, very adequate at fitting all existing data on partial half-life, T _1/2p , of proton emission from nuclei. Nearly 70 measured half-life values have been analysed, and the data could be described by two straight lines relating the pure Coulomb contribution to half-life with the quantity (Z _d is the atomic number of the daughter nucleus, μ₀ is the reduced mass, and Q _p is the total nuclear energy available for decay). These straight lines are shown to correspond to different degrees of deformation, namely, very prolate ( δ ≳ 0.1 , and other shaped ( δ ≲ 0.1 parent nuclei. The goodness in reproducing the data attained in the present systematics allows for half-life predictions for a few possible cases of proton radioactivity not yet experimentally accessed.     

Filamentation control in the temperature gradient argon gas

A novel technique of controlling the evolution of the filamentation was experimentally demonstrated in an argon gas-filled tube. The entrance of the filament was heated by a furnace and the other end was cooled with air, which resulted in the temperature gradient distribution along the tube. The experimental results show that multiple filaments are merged into a single filament and then no filament by only increasing the temperature at the entrance of the filament. Also, the filament can appear and disappear after increasing the local temperature and input pulse energy in turn. This technique offers another degree of freedom to control the filamentation and opens a new way for multi-mJ level monocycle pulse generation through filamentation in the noble gas.     

Photoluminescence decay and time-resolved spectroscopy of cubic yttria-stabilized zirconia

The time-resolved spectra and luminescence decays of cubic yttria-stabilized zirconia single crystals were investigated in the 100–300 K temperature range. At each temperature the time-resolved spectra are dominated by a yellow-orange broad band with a shoulder in the green region, and their shapes appear similar to those displayed in fluorescence. In addition, the shapes remain almost independent of the delay times over the range between 0.04 and 0.4 ms after excitation. The luminescence decays can be satisfactorily described by the superposition of two exponential functions, as well as by two expressions commonly given for decays related to disorder. In the three cases, the temperature dependences of the time constants and the other parameters derived from these expressions are analyzed. The time constants can be accounted for by assuming a radiative decay from two metastable levels with a typical separation of 0.057±0.005 eV. Some correlations between the parameters from the luminescence-decay formulae are given. The results are in good agreement with luminescence due to radiative recombinations at donor F-type levels in which complexes formed by oxygen vacancies in a disordered sublattice are involved.     

Phenomenological analysis of intermediate mass fragments emission in alpha induced reactions

Intermediate mass fragment emission in induced reactions on Al and Ti at 60 and 104 MeV, respectively has been analysed using phenomenological moving source model. Fragment emission at backward angles is found to be well explained by a single fusion-like source, whereas for forward angles an additional intermediate velocity source is required to explain the data. The relative contribution of the intermediate velocity source decreases sharply with angle for lower energies and it extends significantly to larger angles in the higher energy reaction. The fractional momentum transfer for the fusion-like source is in agreement with the corresponding Viola systematics value in the case of +Al reaction, whereas for +Ti reaction, it is larger than that obtained from the Viola systematics. The degree of incompleteness (in momentum transfer) is found to be fragment dependent; incompleteness being more for lighter fragments and vice-versa.     

Possible interpretation of the „anomalous“ behaviour of the proton spectrum at 0° from the deuteron fragmentation at 9 GeV/c

The momentum spectra of protons, produced at 0° as a result of fragmentation of relativistic deuterons on nuclei, are analyzed. Possible causes of the existing discrepancy of the data on the 0° proton spectrum from the¹ H(d,p)X reaction at 9.1 GeV/c with results of the impulse approximation calculations are considered. It is shown that taking into account the finite angular resolution of the experimental setup and the corresponding renormalization of the experimental data, on the one hand, and also the inclusion of the additional (to stripping) contribution of protons from the scattering of deuteron nucleons by target protons, on the other, make it possible to match these data with the results of calculations within the framework of the relativistic impulse approximation using the deuteron wave function for the Paris potential.     

Pre-equilibrium γ-ray emission in dissipative heavy-ion collisions

-rays are measured in coincidence with the dissipative complex fragments from the³⁵Cl +⁶⁴Ni reaction at 7.7 A MeV. Theoretical -ray coincidence spectra are determined through a fitting procedure using the contribution of the excited fragment statistical -decay calculated by means of the CASCADE code. Whereas the expected statistical spectra fit very well the data in the energy regionE =2 to 8 MeV, above this energy another emission mechanism in addition to the statistical decay has to be considered in order to reproduce the experimental spectra. Simulations based on the Vlasov equation suggest that this emission could come from the decay of dipole strength excited in the intermediate dinuclear system.The authors are greatly indebted with A. Boiano, A. Buccheri, M. Cipriano, F. Pagano and R. Rocco for their assistance during the set up of the experimental apparatus. Dr. J. Girard and the technical staff of the CEA/DAPNIA-DPhN are acknowledged for the valuable operation of the accelerator.