Usability of tartaric acid in dose measurements: an ESR study

Unirradiated tartaric acid samples do not exhibit any ESR signal. However, the ESR spectra of irradiated samples contain many resonance signals. The dose–responce curves of the resonance signals, denoted as I ₁, I ₂, I ₃ and I ₄ in the present study, were found to increase linearly with the applied radiation dose in the range of 0.04–25 kGy. Adjusting the microvawe power and modulation amplitudes of 1.0 mW and 1.0 mT, respectively, was found to increase the sensitivity of tartaric acid. From the dose–response curves and room temperature decay data, it was concluded that the I ₃ resonance signal of tartaric acid can be used for dose measurements at intermediate (0.04–0.4 kGy) and high dose (0.5–25 kGy) levels.     

自旋密度光栅和本征GaAs量子阱中的电子自旋双极扩散

为研究空穴对自旋极化电子扩散的影响,提出用自旋密度光栅方法来观察电子自旋扩散过程。由飞秒激光在本征GaAs多量子阱中激发产生瞬态自旋光栅和瞬态自旋密度光栅,并用于研究电子自旋扩散和电子自旋双极扩散。实验测得自旋双极扩散系数Das ＝25.4 cm 2/s,低于自旋扩散系数Ds ＝113.0 cm 2/s,表明自旋密度光栅中电子自旋扩散受到空穴的显著影响。     

Site-selective electron nuclear double resonance in the exchange-narrowed regime of the ESR in conducting solids

Electron nuclear magnetic double resonance on conduction electrons reveals the hyperfine interaction hidden by the fast electron spin exchange. We used the Overhauser shift technique to investigate the electron spin density of the conduction band of gallium oxide, beta-Ga(2)O(3). Due to the monoclinic structure, the conduction band of beta-Ga(2)O(3) is anisotropic and it is dominated by contributions from the two nonequivalent Ga sites. The large quadrupole couplings of the two gallium isotopes (69)Ga and (71)Ga (both with I = 3/2) are completely resolved in our double-resonance experiments. This resolved quadrupole interaction allows the determination of the electric field gradients at both gallium sites with high precision and high sensitivity. The resolved quadrupole splitting is the key to the site-selected determination of the hyperfine interaction. The concepts behind these double-resonance techniques are rather general and should be applicable in similar semiconductor systems.     

ESR Induced in CR-39 Plastic as a means of Gamma Ray Dosimetry

The gamma-induced ESR in CR-39 plastic has been studied and the possibility of using it as a gamma-ray dosimeter was investigated. The induced ESR was found to vary linearly with the dose up to 700 krad. The fading of the induced ESR signal at room temperature has been also investigated. The results suggest the possible use of CR-39 plastic for gamma dosimetry in the range 0 … 700 krad.

Es wurde die γ-induzierte ESR-Technik am CR-39 Plast untersucht und ihre Eignung als Gammastrahlen-Dosimeter geprüft. Die induzierte ESR variierte linear bis zu einer Dosis von 700 krad. Das Fading des induzierten ESR-Signals bei Zimmertemperatur wurde ebenfalls untersucht. Die Ergebnisse zeigten, daβ cine Verwendung des CR-39 Plast als Dosimeter für Gammastrahlen im Bereich von 0 … 700 krad möglich ist.     

An electron spin resonance study of Eu doping effect in La4/3Srs/3Mn2O7 single crystal

The effect of Eu3＋ ion doping in the La sites of single-crystal La4/3Srs/3Mn2O7 was investigated. Electron spin resonance （ESR） was applied to La4/3Sr5/3Mn2O7 and （Lao.8Euo.2）4/3Sr5/3Mn2O7 single crystals. A phase separation and phase transitions were observed from the ESR spectra data. Between 350 K and 300 K, both paramagnetic resonance （PMR） and anisotropic ferromagnetic resonance （FMR） lines were observed in the ab plane and the c axis direction, suggesting a coexistence of the paramagnetic （PM） phase and the ferromagnetic （FM） phase. The magnetization measurement reveals a spin-glass-like behavior in single-crystal （Lao.8Euo.2）4/3 Sr5/3Mn2O7 below the temperature of spin freezing Tf （- 29.5 K）.     

Reducing ghosting due to k-space discontinuities in fast spin echo (FSE) imaging by a new combination of k-space ordering and parallel imaging

In multi-echo imaging sequences like fast spin echo (FSE), the point spread function (PSF) in the phase encoding direction contains significant secondary peaks (sidebands). This is due to discontinuities in adjacent k-space data obtained at different echo times caused by T₂ decay, and leads to ghosting and hence reduced image quality. Recently, utilising multiple coils for signal reception has become the standard configuration for MR systems due to the additional flexibility that parallel imaging (PI) methods can provide. PI methods generally obtain more data than is required to reconstruct an image. Here, this redundancy in information is exploited to reduce discontinuity-related ghosting in FSE imaging. Adjacent phase encoded k-space lines are acquired at different echo times alternately in the regions of discontinuity (called ‘feathering’). This moves the resulting ghost artefacts to the edges of the field of view. This property of the ghost then makes them amenable to removal using PI methods. With ‘feathered’ array coil data it is possible to reconstruct data over the region of the discontinuity from both echo times. By combining this data, a significant reduction in ghosting can be achieved. We show this approach to be effective through simulated and acquired MRI data.     

An electron spin resonance study of Eu doping effect in La_(4/3)Sr_(5/3)Mn_2O_7 single crystal

The effect of Eu3+ion doping in the La sites of single-crystal La4/3Sr5/3Mn2O7was investigated. Electron spin resonance(ESR) was applied to La4/3Sr5/3Mn2O7and(La0.8Eu0.2)4/3Sr5/3Mn2O7single crystals. A phase separation and phase transitions were observed from the ESR spectra data. Between 350 K and 300 K, both paramagnetic resonance(PMR)and anisotropic ferromagnetic resonance(FMR) lines were observed in the ab plane and the c axis direction, suggesting a coexistence of the paramagnetic(PM) phase and the ferromagnetic(FM) phase. The magnetization measurement reveals a spin-glass-like behavior in single-crystal(La0.8Eu0.2)4/3Sr5/3Mn2O7below the temperature of spin freezing Tf(～ 29.5 K).     

Ferromagnetic spin fluctuations in antiferromagnetic Pr1−xCaxMnO3: An ESR study

Electron spin resonance (ESR) measurements have been performed on polycrystalline samples of Pr_1−xCa_xMnO₃ (x=0.4, 0.5) in the temperature range of 100-300 K. The temperature dependence of ESR intensity, g value and linewidth shows the existence of ferromagnetic spin correlations in the paramagnetic state. With decreasing temperature, the ferromagnetic spin correlations switch to antiferromagnetic spin correlations in the charge ordering state and vanish at the antiferromagnetic ordering temperature T_N.     

Inversion of the electron spin resonance signal from a P1 center in a synthetic diamond crystal

We have studied the electron spin resonance (ESR) of a 0.59 carat synthetic diamond single crystal at room temperature. The crystal was grown on a “split-sphere” apparatus in the Fe-Ni-C system by the temperature gradient method. After high-temperature/high-pressure treatment of the diamond, it was observed that as the microwave power supplied to the sample increased from 70 μW to 70 mW in an H₁₀₂ cavity, the ESR signal from the P1 center (a nitrogen atom substituting for carbon at a lattice point of the diamond crystal: C-form nitrogen) is inverted. In the original diamond (before high-temperature/high-pressure treatment), no inversion of the ESR signal was observed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 9–12, January–February, 2006.     

Determination of T1-spin-lattice relaxation time in a two-level system by continuous wave multiquantum electron paramagnetic resonance spectroscopy in a presence of tetrachromatic microwave irradiation

Applicability of continuous wave multiquantum EPR methods to study relaxation times at X-band is examined. Multiquantum transitions excited in a two-level system by tetrachromatic irradiation are used for these studies. The Bloch equation model is applied to simulate lineshapes of the three quantum transitions as a function of frequency difference between exciting fields. The dependence of multiquantum transition signals on relaxation times and microwave amplitude is shown. On this basis a method of deducing relaxation times from these signals is formulated. The case of a homogeneously and inhomogeneously broadened resonance line is considered. Two experimental methods are used to verify the proposed hypothesis: the X-band continuous wave multiquantum EPR with four frequencies microwave field and saturation recovery EPR. The values of T₁ obtained from CW MQ EPR and SR EPR are compared.     

Dynamics of Spin Temperatures in EPR on Rapid Switching of the Frequency Detuning of a Saturating Field

In the framework of the spin temperature in EPR in the absence of interaction with the lattice, the time-dependent change in the spin temperatures of the Zeeman subsystem and dipole-dipole reservoir has been investigated theoretically in the high-temperature approximation. It is shown that amplification in the system can be obtained by switching the detuning of the saturating field frequency. The approach to the solution of the problem is based on the fact that during the process of switching and establishment of both temperatures the total energy of the Zeeman subsystem and of the dipole-dipole reservoir is preserved. It has been established that the values of absorption or amplification in the system depend on the frequency detunings of the saturating field. In the presence of a probe field, the possibility of determining the value of the local magnetic field related to the time of transverse relaxation of the system is demonstrated.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 171–175, March–April, 2005.     

Effect of irradiation on ethyl 2‐amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐3‐carboxylate: an ESR study

Ethyl 2‐amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐3‐carboxylate [C₁₁H₁₅NO₂S] was synthesized by the Gewald method. Its single crystals were grown from an alcohol/ethyl acetate solution at 15 °C and characterized using IR and ¹H‐NMR. These single crystals were irradiated for 72 h at 298 K by a ⁶⁰Co gamma source with a dose speed of 0.864 kGy/h. After irradiation, electron spin resonance (ESR) measurements were carried out to study radiation‐induced radicals in the temperature range from 120 to 450 K. Additionally, for the single crystal, ESR angular dependencies were measured in the xy, xz and yz planes of the substance. This irradiated single crystal was analyzed based on the ESR spectra. Analysis of the spectra revealed that the radical was formed by a C–H bond fission at the carbon end of the substance. It was also observed that the color of the sample changed after irradiation. The hyperfine and g parameters were determined from the experimental spectra. It was inferred from these results that the hyperfine parameters and g value exhibited anisotropic behavior. The average values of these parameters were calculated as follows: g = 2.0088, A_H1=H2 = 20.70 G, A_H3=H4 = 10.80 G, A_Ha = 4.59 G, A_Hb = 3.24 G and, A_N = 6.10 G. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of local structure on electron paramagnetic resonance spectra for trigonal [Cr(H2O)6]3+coordination complex in the sulfate alums series: a ligand field theory study

A simple theoretical method is introduced for studying the interrelation between electronic and molecular structures.By diagonalizing the 120 × 120 complete energy matrices,the relationships between zero-field splitting(ZFS) parameter D and local distortion parameter △θ for Cr 3+ ions doped,separately,in α-and β-alums are investigated.Our results indicate that there exists an approximately linear relationship between D and △θ in a temperature range 4.2-297 K and the signs of D and △θ are opposite to each other.Moreover,in order to understand the contribution of spin-orbit coupling coefficient ζ to ZFS parameter D,the relation between D and ζ is also discussed.     

Structural phase transitions in Au thin films on Si (1 1 0): An in situ temperature dependent transmission electron microscopy study

We present a review on the formation of gold silicide nanostructures using in situ temperature dependent transmission electron microscopy (TEM) measurements. Thin Au films of two thicknesses (2.0 nm and 5.0 nm) were deposited on Si (1 1 0) substrate under ultra-high vacuum (UHV) conditions in a molecular beam epitaxy (MBE) system. Also a 2.0 nm thick Au film was deposited under high vacuum condition (with the native oxide at the interface of Au and Si) using thermal evaporation. In situ TEM measurements (for planar samples) were made at various temperatures (from room temperature, RT to 950 °C). We show that, in the presence of native oxide (UHV-MBE) at the interface, high aspect ratio (≈15.0) aligned gold silicide nanorods were observed. For the films that were grown with UHV conditions, a small aspect ratio (∼1.38) nanogold silicide was observed. For 5.0 nm thick gold thin film, thicker and lesser aspect ratio silicides were observed. Selected area diffraction pattern taken at RT after the sample for the case of 5.0 nm Au on Si (1 1 0)-MBE was annealed at 475 °C show the signature of gold silicide formation.