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1.
Time-resolved luminescence spectra from quartz can be separated into components with distinct principal and secondary lifetimes depending on certain combinations of annealing and measurement temperature. The influence of annealing on properties of the lifetimes related to irradiation dose and temperature of measurement has been investigated in sedimentary quartz annealed at various temperatures up to 900C. Time-resolved luminescence for use in the analysis was pulse stimulated from samples at 470 nm between 20 and 200C. Luminescence lifetimes decrease with measurement temperature due to increasing thermal effect on the associated luminescence with an activation energy of thermal quenching equal to 0.68±0.01eV for the secondary lifetime but only qualitatively so for the principal lifetime component. Concerning the influence of annealing temperature, luminescence lifetimes measured at 20C are constant at about 33μs for annealing temperatures up to 600C but decrease to about 29μs when the annealing temperature is increased to 900C. In addition, it was found that lifetime components in samples annealed at 800C are independent of radiation dose in the range 85–1340 Gy investigated. The dependence of lifetimes on both the annealing temperature and magnitude of radiation dose is described as being due to the increasing importance of a particular recombination centre in the luminescence emission process as a result of dynamic hole transfer between non-radiative and radiative luminescence centres.  相似文献   

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EPR (X- and Q-band) and electron spin relaxation measured by electron spin echo method (X-band) were studied for Ti2+(S=1) and Ti2+Ti2+ pairs in SrF2 crystal at room temperature and in the temperature range 4.2–115 K. EPR spectrum consists of a strong line from Ti2+ and quartets 2:3:3:2 from titanium pairs (S=2). Spin-Hamiltonian parameters of the pairs are g=1.883, g=1.975 and D=0.036cm-1. Temperature behavior of the dimer spectrum indicates ferromagnetic coupling between Ti2+. Spin–lattice relaxation of individuals Ti2+ is dominated by the ordinary two-phonon Raman process involving the whole phonon spectrum up to the Debye temperature ΘD=380K with spin–phonon coupling parameter equal to 215cm-1. Important contribution to the relaxation arises from local mode vibrations of energy 133cm-1. The pair relaxation is faster due to the exchange coupling modulation mechanism with the relaxation rate characteristic for ferromagnetic ground state of the pairs 1/T1[exp(2J/kT)-1]-1 which allowed to estimate the exchange coupling J=36cm-1. The theories of electron–lattice relaxation governed by exchange interaction are outlined for extended spin systems, for clusters and for individual dimers. Electron spin echo decay is strongly modulated by coupling with surrounding 19F nuclei. FT-spectrum of the modulations shows a dipolar splitting of the fluorine lines, which allows the evaluation of the off-center shift of Ti2+ in pair as 0.132 nm. The electron spin echo dephasing is dominated by an instantaneous diffusion at low temperatures and by the spin–lattice relaxation processes above 18 K.  相似文献   

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《Radiation measurements》2007,42(3):491-495
In this study the 222Rn concentration of mains water in 120 settlements in Hungary (Southern Hungary, the Balaton Highland region) was measured. The average 222Rn concentration was 5.56 (024.3)Bql-1. On the basis of the 222Rn concentration of mains water inspected in the Southern Great Plain region, it can be stated that the 222Rn concentration of mains water here is, as an average, half of the 222Rn concentration of fountains in the same region. This decrease in radon probably happens during the water management and storage of mains drinking water. The 222Rn concentration of spring-water examined in the region of the Balaton Highland exceeds the average 222Rn concentration of drinking water (average 27.1Bql-1).The radiation dose originating from the consumption of mains drinking water in case of adults does not reach the value of 0.1mSvyear-1, even as a conservative assessment (1lday-1 water consumption and 10-8SvBq-1 dose conversion factor).  相似文献   

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The current density–voltage (JV) behavior of polymer PDY 132 thin films has been investigated in hole-only device configuration, viz., ITO/poly(ethylene-dioxthiophene):polystyrenesulphonate (PEDOT:PSS)/PDY 132/Au, as a function of polymer (PDY) film thickness (150 nm and 200 nm) and temperature (290–90 K). Hole current density was found to follow two distinct modes of conduction, (i) low electric field region I: ohmic conduction where slope 1, and (ii) intermediate and high electric field region II: non ohmic conduction where slope 2. Region I has been attributed to the transport of intrinsic background charge carriers while region II has been found to be governed by space charge limited currents (SCLC) with hole mobility strongly dependent on electric field and temperature. The respective hole transport parameters determined from the SCLC regime, μp0 is 3.7×10?3m2/Vs, μp(0,T) is 3.7×10?8m2/Vs, and zero field activation energy (Δ0) of 0.48 eV is obtained.  相似文献   

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Pulsed neutrons generated in a plasma focus device are used for the thermal neutron activation analysis (TNAA) of selected three elements having widely different half-lives varying from a few seconds to a few days [Dysprosium (Dy), Manganese (Mn) and Gold (Au)]. Neutron pulse having strength of (1.2±0.3)×109 neutrons/pulse with a pulse width of 46±5ns is produced by “MEPF-12” device operated at a filling gas (deuterium + 0.5% krypton) pressure of 3 mbar. The fast 2.45 MeV D–D neutrons are thermalized before irradiating the sample. The decay gammas from the radioisotopes 165mDy (T1/2=1.26min.), 56Mn (T1/2=2.58hrs.), and 198Au (T1/2=2.69days) produced via reactions, 164Dy(n,γ)165mDy, 55Mn(n,γ) 56Mn, and 197Au(n,γ) 198Au respectively are counted off-line in a lead shielded well type 76×76mm2 NaI(Tl) detector coupled to a calibrated 2048 channel analyzer. The values of half-lives evaluated from the measured decay gammas, 1.43±0.3min., 2.56±0.5hrs. and 2.84±0.6days respectively for the radioisotopes of Dy, Mn and Au, are seen to be close to the values reported in literature.  相似文献   

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Negative thermal expansion materials can experience significant stresses when they are used in composites. Under ambient conditions Zr2(WO4)(PO4)2 displays anisotropic negative thermal expansion (NTE) (αv=?14.0(10)×10?6K?1, αa=?7.9(5)×10?6K?1, αb=2.5(5)×10?6K?1, αc=?8.7(2)×10?6K?1 at 0 GPa). The effect of hydrostatic pressure on its thermal expansion characteristics was investigated by neutron diffraction between 300 and 60 K at pressures up to 0.3 GPa. No phase transitions were observed in the pressure and temperature range examined. The material was found to have a bulk modulus, B0, of 61.3(8) GPa at ambient temperature, and unlike some other NTE materials, pressure had no detectable effect on thermal expansion (αv=?14.2(8)×10?6K?1, αa=?7.9(3)×10?6K?1, αb=2.9(5)×10?6K?1, αc=?9.2(2)×10?6K?1 at 0.3 GPa).  相似文献   

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Samples of a typical tetrameric protein, the hemoglobin, at the concentration of 150 mg/ml in bidistilled water solution, were exposed to a uniform magnetic field at 200 mT at different temperatures of 15°C, 40°C and 65°C. Fourier Transform Infrared Spectroscopy was used to analyze the response of the secondary structure of the protein to both stress agents, heating and static magnetic field. The most relevant result which was observed was the significant increasing in intensity of the Amide I band after exposure to the uniform magnetic field at the room temperature of 15°C. This result can be explained assuming that protein's α-helices aligned along the direction of the applied magnetic field due to their large dipole moment, inducing the alignment of the entire protein. Increasing of temperature up to 40°C and 65°C induced a significant reduction of the increasing in intensity of the Amide I band. This effect may be easily explained assuming that Brownian motion of the protein in water solution caused by thermal molecular agitation increased with increasing of temperature, contrasting the effect of the torque of the magnetic field applied to the protein in water solution.  相似文献   

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The paper reports the results of numerical studies on the laser-driven acceleration of super-heavy ions by a multi-PW laser pulse of ultra-relativistic intensity attainable with the Extreme Light Infrastructure lasers currently being built in Europe. Using a multi-dimensional (2D3V) particle-in-cell code, it is shown that multi-GeV super-heavy (thorium) ion beams with an intensity of 10211022W/cm2, fluence 10171018cm?2 and time duration 20100fs can be produced from a sub-μm thorium target irradiated by a 150-J, 20-fs laser pulse with an intensity of 1023W/cm2. Such ion beams are impossible to obtain presently with the use of conventional RF-driven accelerators, so they can open the door to new areas of research in both nuclear and high energy-density physics.  相似文献   

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ZnO ceramics both with and without boric acid as a flux were sintered at TS=8001200°C and their luminescent characteristics were compared. In obtained samples UV as well as visible emission bands were observed. The addition of the flux was shown to cause the increase of grain size and the improvement of crystalline quality of the ceramics, which was ascribed to the creation of a liquid phase during the sintering process. It was found that the adding of 1 wt% of boric acid to ZnO powder allowed ceramics preparation without any pressing of the starting materials, in this case TS=950°C being enough to obtain firm and dense ceramics. This ceramics had higher intensity of UV emission and lower intensity of visible emission than ceramics sintered without the flux.  相似文献   

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We study the generation of cosmic magnetic fields during de Sitter inflation in a non-conformally-invariant effective model of massive electrodynamics containing a four-photon interaction term. We show that, if the photon self-coupling is strong enough, comoving magnetic fields correlated on scales of 10kpc and of intensities 10?22G?B0?10?19G are produced as excitation of the vacuum. If amplified by galactic dynamo, they naturally explain the existence of galactic magnetic fields.  相似文献   

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