Szintillationslichtausbeute und ihre Richtungsabhängigkeit als Funktion der Temperatur von Anthrazen-, trans-Stilben- und para-Terphenyl-Kristallen bei Beschuß mitα-Strahlen

The scintillation light yield of thin trans-stilbene, para-terphenyl and anthracene crystals and an organic plastic scintillator bombarded with α-particles of ThB has been measured as a function of temperature betweent=20° C and the melting point. The light yield of all the specimens investigated has been found to be reduced with increasing temperature. In all cases at the melting point the light yield will be zero. The scintillation anisotropy of the organic crystal scintillators also has been investigated over the range of temperature mentioned above, and there it is independent of temperature and retains the value measured at room temperature.     

Absorption measurements in neutron irradiated silicon

Silicon samples have been neutron irradiated at 76 °K with fluences sufficient to allow measurement of the 1.7 μ divacancy band at 76 °K. The growth of the divacancy concentration and the recovery of the edge absorption were studied as a function of annealing temperature between 76 °K and 550 °K. Immediately after irradiation the divacancy concentration is about 25 per cent of its maximum value which is attained at 330 °K, the temperature at which the divacancies begin to anneal out. Increases in the 1.7 μ band intensity and recovery of the edge absorption can also be achieved at 76 °K by illuminating the sample with intense sub-bandgap light or white light. The experimental results suggest a neutron-induced cluster model in which the cluster is a vacancy-rich region whose annealing characteristics are controlled by the liberation and motion of vacancies. The injection effects can be explained by analogy to the charge state dependent mobility of the Si vacancy.     

Die Szintillations-Anisotropie von Anthrazen bei tiefen Temperaturen

An anthracene crystal is cooled down to liquid hydrogen temperature and is bombarded with alpha particles in two directions parallel to theb andc′ crystal axes. The ratio of maximum to minimm light yield (for alpha particles parallel toc′ andb, respectively) is reduced to 1.23 at 20.4° K. This ratio is 1.46 for ThC′ and 1.53 for ThC alpha particles at room temperature and is measured as a function of temperature between 20.4 and about 90° K.     

Magnetic anisotropy of Tb-Co amorphous films

A systematic investigation of the magnetic properties of Tb-Co amorphous films prepared using radio-frequency ion sputtering in a uniform magnetic field has been carried out. The main regularities of the change in the magnetic anisotropy parameters as a function of the composition (8–43 at % Tb), measurement temperature (5–350 K), and annealing temperature (up to 200°C) have been established. It has been shown that their interpretation can be performed within the framework of the model that takes into account the fluctuating local magnetic anisotropy of the terbium ions, columnar microstructure, and anisotropy of elastic stresses.     

Multifrequency electron paramagnetic resonance of ultramarine blue

Electron paramagnetic resonance spectra of the S^3/? radical center in ultramarine blue over a factor of about 2500 in frequency (258 MHz to 670 GHz) reveal a substantially Lorentzian shape, without resolution of g anisotropy. Variable temperature measurements found that the line width is independent of temperature, within experimental uncertainty, up to about 90 K at 9.5 GHz and between ca. 5 K and room temperature at 95 and 217 GHz, as expected for an exchange-narrowed signal. Analysis of the increase in the low-temperature line width as a function of frequency above 9 GHz is consistent with an exchange interaction of about 2· 10^?2 K. The line width increases as frequency is decreased from 2.7 GHz to 258 MHz which is attributed to the contribution from nonsecular terms that has been denoted the “10/3” effect.     

Temperature variations as a source of uncertainty in medical fiber-coupled organic plastic scintillator dosimetry

Fiber-coupled organic plastic scintillators have potential applications in medical dosimetry related to, for example, brachytherapy and external beam radiotherapy with MV photons. As medical dosimetry generally strives for high accuracy, we designed a study to assess if the light yield from commonly used scintillating fibers would change with temperature in the clinical range (15–40 °C). The study showed that the light yield in the peak regions of the scintillators studied decreases linearly with increasing temperature. For the blue BCF-12 and the green BCF-60 from Saint-Gobain, France we found temperature coefficients of −0.15 ± 0.01%/K and −0.55 ± 0.04%/K, respectively. These values are sufficiently large to warrant careful consideration for clinical measurements.     

Temperaturabhängigkeit der Szintillationslichtausbeuten von p-Terphenyl-, Anthrazen- und Naphthalinkristallen bei Anregung mit α- und Β-Teilchen

The temperature dependence of the integral scintillation light yield of p-terphenyl, anthracene, and naphthalene single crystals excited byα- andΒ-particles was investigated betweenT=10 ?K andT=293 ?K. The variation of the scintillation anisotropy of p-terphenyl with temperature was measured as well. With decreasing temperature the scintillation light of anthracene and naphthalene is found to be emitted faster. The integral light yield of p-terphenyl shows a pronounced maximum atT=34 ?K which is caused by the delayed component only. The maximum is explained by triplet exciton trapping.     

14N PNQR investigation of the phase transition in s-triazine

¹⁴N PNQR frequencies, linewidths and spin lattice relaxation times were measured in s-triazine between 77° and 280°K. A second order phase transition was observed at 198.5°K. The temperature dependence and anisotropy of the relaxation times indicate a reorientation of the molecule around its three-fold axis.     

Ferromagnetism in laser-deposited GaMnAs layers

The properties of the GaMnAs layers grown by laser deposition on semi-insulating GaAs(100) substrates at temperatures from 300 to 650°C have been investigated. A strong anisotropy of the hysteretic curve of the angle of rotation of the plane of polarization with a change in the magnetic field direction in the sample plane was found during investigation of the magneto-optical Kerr effect (300 K). The domain structure in GaMnAs layers has been observed for the first time at room temperature by magnetic-force microscopy.     

Relaxation of the state with induced transverse magnetic anisotropy in the soft magnetic nanocrystalline alloy Fe73.5Si13.5Nb3B9Cu1

The residual lattice strains of nanocrystals, which are responsible for the formation of states with transverse magnetic anisotropy in samples of the Fe-Si-Nb-B-Cu alloys (Finemets) subjected to annealing under tensile loading with the subsequent relaxation annealing at temperatures in the range from 500 to 600°C, have been measured using X-ray diffraction. The relative extension and compression of interplanar spacings have been compared with the induced magnetic anisotropy constants determined from the magnetic hysteresis loops. It has been shown that, during the relaxation annealing at the nanocrystallization temperature (500?C540°C), the observed decrease in the residual strains is accompanied by a decrease in the transverse magnetic anisotropy constant. A linear correlation between the relative extension and compression of the interplanar spacings for different crystallographic planes and magnetic anisotropy constant has been revealed. The deviation from linearity is observed after annealing at a temperature of 600°C, which is explained by a possible increase in sizes of nanocrystals, changes in their structure, and partial crystallization of the amorphous matrix.     

Temperature dependence of azimuthal X-ray Photoelectron Diffraction (XPD) from Cu2p32 core level of Cu(001): Experiment and single scattering cluster calculations

The temperature dependence of X-ray photoelectron diffraction (XPD) affects in azimuthal distributions of $\text{Cu}\text{2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ core level intensities from a clean copper (001) single crystal has been measured in the range from ambient to 1010 K and for polar angles of emission relative to the surface of θ = 7° (corresponding to very high surface sensitivity) and θ = 45°. The XPD anisotropy ΔI/I_max at θ = 7° shows a decrease of 42.5% between ambient temperature and 1010 K while that for θ = 45° shows a 22.7% decrease over the same temperature range. Single scattering cluster calculations including Debye-Waller factors very well predict the variation of anisotropy with temperature at θ = 7°, while at θ = 45° theory significantly underestimates the decrease in ΔI/I_max, probably due to multiple scattering effects. The effective surface Debye temperature of 202 K deduced from theory and experiment for θ = 7° agrees well with prior determinations. The 7° XPD data give no evidence for surface melting effects on Cu(001) at temperatures up to T/T_melting = 0.74.     

Light scattering by single magnons in FeF3

Scattering of laser light from single magnons has been observed in the canted antiferromagnet FeF₃ as a function of temperature (260 – 360°K) and wave-vector (2 × 10⁵ ? 3 × 10⁴cm^?1). Measured magnon energies ranging up to 3.3 cm^?1 (260°K) and line widths are in good agreement with data from microwave resonance work.     

Spin nuclear conversion and phase transitions in solid CH4

Precision X-ray studies of the temperature dependence for the CH₄ lattice parameter were carried out in the 14–23°K range. Samples of equilibrium spin-modification composition reveals a volume jump of about 0.12 percent at 18 ± 0.1°K. This phase transition has been found to be essentially affected by inter-modification conversion.     

Another indicated phase transformation in ytterbium

The electrical resistivity of polycrystalline samples of Yb showing the f.c.c.-h.c.p. transformation has been determined in the range 300–1088°K. Three anomalous features are observed: first, a hysteretic and reversible transformation is indicated at about 560°K. Second, a sharp discontinuity in the temperature dependence of the resistivity is observed at about 660°K and, third, a discontinuous transition is observed at about 970°K. The latter is tentatively attributed to the onset of the b.c.c. phase in material of this purity, but since no high temperature X-ray investigation has been possible, no certain interpretation of any of these features can presently be given.     

Optical absorption in layered MnGaInS<Subscript>4</Subscript> single crystals

Optical absorption in MnGaInS₄ single crystals has been studied. Direct and indirect optical transitions are found to occur in the range of photon energies of 2.37–2.74 eV and in the temperature range of 83–270 K. The temperature dependence of the band gap has been determined; its temperature coefficients E _gd and E _gi are −5.06 × 10⁻⁴ and −5.35 × 10⁻⁴ eV/K, respectively. MnGaInS4 single crystals exhibit anisotropy in polarized light at the absorption edge; the nature of this anisotropy is explained.     

Scattering mechanisms in p-type GaSb in the temperature range 30–300°K

In a former paper[1], we have shown that the magnetoresistance coefficient in p-type GaSb (1+ξ) remains close to 1 at 77°K and that the mobilities ratio remains equal to 6 in the temperature range 77–300°K.We show from these results that between 30 and 300°K, the predominant scattering is a mixed scattering by lattice vibrations and ionized impurities. Interband scattering is the predominant process for light holes, while heavy holes undergo intraband scattering. In this temperature range, this mechanism accounts for the mobility variation, a result which had not been found so far on p-type GaSb.     

Spin reorientation in the low temperature phase of KMnF3

The temperature dependence of anisotropy fields of the canted antiferromagnet KMnF₃ at the low temperature phase has been investigated by analysing the antiferromagnetic resonance. The results show that there exists a second-order magnetic transition associated with the spin reorientation at T₀ ～ 50°K in the absence of applied fields.     

Study of combined magnetic and electric hyperfine interactions for cadmium in Dysprosium by time differential perturbed angular correlations

The combined magnetic and electric hyperfine interaction at the site of a¹¹¹Cd impurity in magnetically ordered Dysprosium has been investigated as a function of temperature by time differential perturbed angular correlation measurements. Three different phases have been found in metallic Dy with transition temperatures of 85 and 179 °K in agreement with the results of bulk material measurements. In the paramagnetic phase above 179 °K a pure electric quadrupole interaction has been observed. The various contributions to the electric fieldgradient are analyzed and it is shown, that the dominant contribution comes from the conduction electrons. In the ferromagnetic phase which extends from 0 to 85 °K the magnetic hyperfine field at the site of¹¹¹Cd has the same temperature dependence as the spontaneous magnetization. The value of the hyperfine field at 4.2 °K is ¦H _eff¦=(221 ± 4) kG. At 85 °K a transition to the antiferromagnetic phase of Dy occurs, which shows a hysteresis of the transition temperature. In the antiferromagnetic phase the temperature dependence of the hyperfine field deviates considerably from the magnetization curve. It is suggested that this deviation might be due to a temperature dependence of thes-f exchange interaction.     

Channelingeffekte bei der Lichtausbeute von Anthrazen-, Naphthalin- undp-Terphenylkristallen bei Anregung mit α-Teilchen

The scintillation light yield of anthracene atT=300 °K andT=80 °K and of naphthalene andp-terphenyl atT=80 °K was investigated for impact directions in the (a, c)-plane. The light yield was measured for welldefined integration times. The relative depth of the channeling-minimum observed for impact directions parallel to thec-axis of anthracene is found to increase with increasing integration times. For the first time channeling-minima of the light yield were observed at impact directions parallel to thec- and the [102]-axis of naphthalene and thec- and [¯102]-axis ofp-terphenyl. The [¯102]-axis ofp-terphenyl shows a more pronounced effect than thec-axis.     

Optical absorption in MnIn2S4 single crystals

Optical absorption in MnIn₂S₄ single crystals has been studied. Direct and indirect optical transitions are found to occur at photon energies of 1.90?C2.16 eV in the temperature range of 80?C342 K. The temperature dependence of the band gap is determined; its temperature coefficients E _gd and E _gi are found to be ?4.84 × 10^?4 and ?6.33 × 10^?4 eV/K, respectively. The electron-phonon interaction is the main mechanism of the temperature shift of the intrinsic-absorption edge. MnIn₂S₄ single crystals exhibit anisotropy in polarized light at the absorption edge in the temperature range of 90?C190 K; the nature of this anisotropy is explained.