Luminescence properties of α-Al2O3 dosimetric crystals exposed to a high-current electron beam

The spectra of pulsed cathodoluminescence (PCL) and thermoluminescence (TL) in TLD-500 detectors, which were exposed to a strong beam from a pulsed electron accelerator, have been studied. Additional bands in the PCL spectrum and new peaks in the TL curves, which are due to impurity ions, have been revealed. Luminescence bands of F- and F⁺-centers cannot be used in the dosimetry of strong electron beams using TLD-500 detectors because of the saturation of dose dependence and the decrease in the TL yield. It is shown that high doses from these beams can be measured by recording TL in the luminescence band of impurity titanium ions.     

Advances in synthesis and characterization of LiMgBO3:Dy

The low Z polycrystalline LiMgBO₃:Dy³⁺ material has been successfully synthesized by novel solution combustion synthesis and studied for its luminescence characteristics. LiMgBO₃:Dy³⁺ material has shown promising TL sensitivity with a broad dosimetric glow peak at 154 °C. Near the tissue equivalent TL phosphor with Dy dopant has half of the TL sensitivity as compared to commercial TLD-100. The kinetic parameters i.e. trap depth or activation energy and frequency factor from the glow curve derived by using peak shape method. The main dosimetric characteristics such as dose response and fading effect are investigated. The state of dopant confirmed using photoluminescence spectra.     

Photon dosimetry methods outside the target volume in radiation therapy: Optically stimulated luminescence (OSL), thermoluminescence (TL) and radiophotoluminescence (RPL) dosimetry

Dosimetry methods outside the target volume are still not well established in radiotherapy. Luminescence detectors due to their small dimensions, very good sensitivity, well known dose and energy response are considered as an interesting approach in verification of doses outside the treated region. The physical processes of thermoluminescence (TL), radiophotoluminescence (RPL) and optically stimulated luminescence (OSL) are very similar and can be described in terms of the energy band model of electron-hole production following irradiation.This work is a review of the main dosimetric characteristics of luminescence detectors which were used in experiments performed by EURADOS Working Group 9 for in-phantom measurements of secondary radiation (scattered and leakage photons). TL LiF:Mg,Ti detectors type MTS-7 (IFJ PAN, Poland), types TLD-100 and TLD-700 (Harshaw), OSL Al₂O₃:C detectors type nanoDot™ (Landauer Inc.) and RPL rod glass elements type GD-352M (Asahi Techno Glass Coorporation) are described. The main characteristics are discussed, together with the readout and calibration procedures which lead to a determination of absorbed dose to water.All dosimeter types used show very good uniformity, batch reproducibility and homogeneity. For improved accuracy, individual sensitivity correction factors should be applied for TL and OSL dosimeters while for RPL dosimeters there is no need for individual sensitivity corrections.The dose response of all dosimeters is linear for a wide range of doses.The energy response of GD-352M type dosimeters (with Sn filter) used for out-of-field measurements is flat for medium and low energy X-rays.The energy dependence for TLDs is low across the range of photon energies used and the energy correction was neglected. A significant over response of Al₂O₃:C OSLDs irradiated in kilovoltage photon beams was taken into account. The energy correction factor f_en was calculated by using the 2006 PENELOPE Monte Carlo code.With suitable calibration, all dosimeter types are appropriate for out-of-field dose measurements as well as for the in-phantom measurements of radiotherapy MV X-rays beams.     

Thermoluminescence and photoluminescence characteristics of K2YF5: Tb3++PTFE irradiated with 90Sr/90Y beta particles

This article presents results of thermoluminescence (TL) and photoluminescence (PL) measurements performed on beta-irradiated K ₂YF ₅:Tb ³⁺+PTFE pellets. K ₂YF ₅ crystals doped with 0.1% of trivalent optically active Tb ³⁺ ions in pellets form were investigated. The TL glow curve of K ₂YF ₅:Tb ³⁺+PTFE has a simple structure with two well-defined peaks centered at 170 and 307 °C. The TL sensitivity of the K ₂YF ₅:Tb ³⁺+PTFE irradiated with beta radiation was found to be higher than that of commercial phosphor TLD-100 (LiF:Mg,Ti), at the same conditions of irradiation and readout. Moreover, PL measurements performed on the terbium doped material show the presence of Terbium as Tb ³⁺ in the material.     

Optical properties of some fluoride compounds and their application to dosimetry

Effects of β, X and VUV irradiation on the optical properties have been studied in various simple and complex fluoride crystals by using optical absorption, X- and UV-excited luminescence (XL and PL), thermoluminescence (TL) and photo-transferred TL (PTTL) techniques. In most tested crystals, the main TL peaks with the same thermal activation energies appear after VUV as well as after X or β irradiation, thus indicating that the same traps are induced by the different types of radiation. The TL excitation spectra generally show absorption maxima on the long wavelengths tail of the fundamental absorption. Within this study, various dosimetric properties, as well as the possible application of the crystals as sensitive radiation detectors and dosimeters for the VUV have also been investigated. The TL sensitivities of the various studied materials have been compared to that of the classic dosimeter TLD-100 (LiF:Mg,Ti). For example, the sensitivity of SrF₂:Pr³⁺ has been found to be the highest among the examined crystals and at a dose of 90 Gy its response is higher by a factor of ～3 than that of TLD-100. The sensitivity of CsGd₂F₇:Pr³⁺ and KYF₄:Pr³⁺ are slightly higher than that of TLD-100, whereas that of nanostructured CaF₂:ZnO crystals is about twice that of TLD-100, but the sensitivity of LiF:Eu is much lower. The SrF₂:Pr³⁺ crystals also showed some important dosimetric properties.     

Detailed infrared spectroscopic study of thermal transitions in new hybrid [(CH3)2CHNH3]4Cd3Cl10 crystal

Phase transitions of tetra(isopropylammonium)decachlorotricadmate(II) [(CH₃)₂CHNH₃]₄Cd₃Cl₁₀ crystal have been studied by infrared, far infrared and Raman measurements in wide temperature range, between 11 K and 388 K. The temperature changes of wavenumber, center of gravity, width and intensity of the bands were analyzed to clarify cationic and anionic contributions to the phase transitions mechanism. The results of investigation showed earlier by differential scanning calorimetry (DSC), thermal expansion and dielectric measurements clearly confirmed the sequence of phase transitions at T₁=353 K, T₂=294 K and T₃=260 K. The current results derived from DSC and infrared measurements revealed additional phase transition at T₄=120 K.     

Pico-second photoelectric characteristic in manganite oxide La0.67Ca0.33MnO3 films

Ultrafast photoelectric characteristic has been observed in La_0.67Ca_0.33MnO₃ films on tilted SrTiO₃ substrates. A pico-second (ps) open-circuit photovoltage of the perovskite manganese oxide films has been obtained when the films were irradiated by a 1.064μm laser pulse of 25 ps duration. The rise time and full width at half-maximum of the photovoltage pulse are ～300 ps and ～700 ps, respectively. The photovoltaic sensitivity was as large as ～500 mV/mJ.     

Gas sensing properties of nanostructured MoO3 thin films prepared by spray pyrolysis

Thin films of molybdenum trioxide (MoO₃) were deposited on common glass using the chemical spray pyrolysis technique. A (NH₄)₆Mo₇O₂₄4H₂0 solution 0.1 M was used as the precursor one. The influence of substrate temperature on the crystallographic structure, surface morphology and electrical behavior of MoO₃ thin films was studied. MoO₃ can exist in two crystalline forms, the thermodynamically stable orthorhombic α-MoO₃ and the metastable monoclinic β-MoO₃ phase. XRD-spectra showed a growth of α-MoO₃ phase percentage as substrate temperature increases from 420 K up to 670 K. Films deposited in the 500–600 K range have a clearly porous surface structure of nanometer order as can be seen in SEM images. Changes up to six magnitude orders were observed in MoO₃ thin films electrical resistance when films temperature varied from 100 K up to 500 K. The sensing property of these MoO₃ films was also studied. The sensitivity was investigated in the temperature range 160 and 360 K for H₂O and CO gases, respectively. Both of them are of reducing nature. In all studied cases sensitivity decreases slowly as film temperature is raised. At room temperature the sensitivity changes from 12 up to 75% depending on substrate temperature. The sensitivity for CO gas was found to be lower than that of H₂O.     

Energy transfer from Tb3+ to Nd3+ in glycerol:D2O solution and frozen glass

The mechanism of energy transfer from Tb³⁺ to Nd³⁺ in glycerol:D₂O solution at 280 K, 300 K and in its frozen glass at 80 K, 120 K, 190 K and 250 K has been examined. Analysis of the intensity and lifetime measurements of ⁵D₄ level of Tb³⁺ shows that at 280 K and 300 K in solution the transfer rate varies as the square of the Nd³⁺ concentration. This suggests a dipole-dipole transfer in the glycerol:D₂O solution. However, at lower temperatures up to 190 K, where the solution freezes into a glass, the dependence observed is linear at lower Nd³⁺ concentrations and quadratic at higher concentrations. Moreover, the linear concentration dependence becomes more pronounced as the temperature of the glass is increased. This linear concentration dependence of the transfer rate and its temperature dependence have been ascribed to the migrational transfer accompanying the multipolar transfer. The coefficients of both the interactions at the above temperatures have been calculated.     

K0.3MoO3和Tl0.3MoO3派尔斯相变临界行为的比热研究

采用连续绝热加热法测量了K_0.3MoO₃和Tl_0.3MoO₃在100—220K温度范围内的比热。发现K_0.3MoO₃和Tl_0.3MoO₃分别在177.5K和172.3K发生派尔斯相变。对派尔斯相变附近比热临界行为的研究表明,K_0.3MoO₃和Tl_0.3MoO₃的临界区域宽度分别为6K和8K,临界行为属于三维XY模型普适类。 关键词：     

The response of thermally and optically stimulated luminescence from Al2O3:C to high-energy heavy charged particles

The thermoluminescence (TL) and optically stimulated luminescence (OSL) response of Al₂O₃ dosimeters to high-energy heavy charged particles (HCP) has been studied using the heavy ion medical accelarator at Chiba, Japan. The samples were Al₂O₃ single-crystal chips, of the type usually known as TLD-500, and Luxel^TM dosimeters (Al₂O₃:C powder in plastic) from Landauer Inc. The samples were exposed to ⁴He (150 MeV/u), ¹²C (400 MeV/u), ²⁸Si (490 MeV/u) and ⁵⁶Fe (500 MeV/u) ions, with linear energy transfer values covering the range from 2.26 to 189 keV/μm in water and doses from 1 to 100 mGy (to water). A ⁹⁰Sr/⁹⁰Y beta source, calibrated against a ⁶⁰Co secondary standard, was used for calibration purposes. For OSL, we used both continuous-wave OSL measurements (CW-OSL, using green light stimulation at 525 nm) and pulsed OSL measurements (POSL, using 532 nm stimulation from a Nd:YAG Q-switched laser). The efficiencies (η_HCP,γ) of the different HCPs at producing OSL or TL were observed to depend not only upon the linear energy transfer (LET) of the HCP, but also upon the sample type (single crystal chip or Luxel^TM) and the luminescence method used to define the signal—i.e. TL, CW-OSL initial intensity, CW-OSL total area, or POSL. Observed changes in shape of the decay curve lead to potential methods for extracting LET information of unknown radiation fields. A discussion of the results is given, including the potential use of OSL from Al₂O₃ in the areas of space radiation dosimetry and radiation oncology.     

Low temperature phase transition in the chain-like compounds NbSe3 and TaSe3

New transitions have been observed at low temperature by electrical measurements on the linear trichalcogenides NbSe₃ and TaSe₃. The resistivity of TaSe₃ drops near zero below 1.5 K which may indicate a superconducting transition. The resistivity of NbSe₃ drops below 2.2 K by 30 to 75% of its residual value at 4.2 K. However for TaSe₃ and NbSe₃ initial susceptibility measurements do not show any increase in diamagnetism indicating a flux expulsion. In addition the transitions below the critical temperatures are strongly non-linear with current density higher than 10^-3 A mm^-2.     

Cs3BiCl6 : Un compose ferroelastique presentant une polarisation remanente a temperature ambiante

X-ray diffraction, calorimetric, dielectric and thermocurrent measurements have been carried out on Cs₃BiCl₆ ceramic samples. Three phase transitions have been detected at T₁ = 395 K, T₂ = 684 K and T₃ = 727 K. The T₃ transition is of ferroelastic-paraelastic type. The low temperature phase is characterized by remanent polarization. The depolarization current results probably from charge traps in potential minima which disappear at rising temperature.     

Advantages and challenges of high-dose thermoluminescent detectors

The current status of high-dose luminescent detector investigations is discussed. The examples of successful applications of various materials for medium and high-dose luminescent detector creation are presented. High-dose irradiation effect on luminescence of TLD-500 (α-Al₂O₃:C) detectors has been described. The challenges of detector properties restoration after high-dose irradiation are considered.     

Neutron scattering study of the phase transitions in a doped polycrystalline Fe3O4: Zn0.005Fe2.995O4

Temperature dependent neutron elastic scattering and resistivity measurements have been made on a polycrystalline sample of Zn_0.005Fe_2.995O₄, which displayed a well-separated, bifurcated, heat-capacity anomaly. The lower-temperature anomaly (near 110 K) was found to be associated with a lattice distortion, but no change in neutron intensity was observed at the higher-temperature anomaly (near 119 K). The electrical resistivity of this sample also exhibited an abrupt change only at the lower-temperature anomaly. The downward shift of the lower-temperature, λ-type anomaly as a result of the very low Zn impurity is, however, confirmed by the neutron scattering results and demonstrates the extreme sensitivity of the structural transition to impurities.     

On the high temperature transition in V2O3

Magnetic susceptibility measurements on V₂O₃ powder sample using a vibrating sample magnetometer and microbalance with special attention to the region of 500–530K are reported. The high temperature transition in this compound is discussed in the framework of two interacting Hubbard bands obtaining a good qualitative agreement with thermal variations of the properties of V₂O₃.     

Superconducting effects in Hg3-δAsF6

Superconducting properties of Hg_3-δAsF₆ have been investigated by a.c. magnetic susceptibility measurements in the temperature range 1.25–4.2 K and magnetic field range 0–0.05 T and by resistivity measurements in the temperature range 1.25–4.2 K. The properties are attributed to mercury dispersed in isolated regions throughout the sample.     

Structure,electrical and magnetic properties of CaAs3, SrAs3, BaAs3 and EuAs3

The crystal structures and electrical properties of CaAs₃, SrAs₃, BaAs₃ and EuAs₃ have been studied by single crystal X-ray investigations, temperature dependent resistivity measurements and optical measurements. The structures of the triclinic CaAs₃ and monoclinic SrAs₃, BaAs₃ and EuAs₃ are closely related. The two-dimensional infinite polyanionic AS₃^2? nets are derivatives of the black phosphorus structure. CaAs₃ and BaAs₃ are semiconducting, while SrAs₃ and EuAs₃ show semimetallic behavior. The paramagnetic EuAs₃ undergoes a magnetic phase transition at 10.5 K.     

Electrical resistivity and magnetic susceptibility studies of the system Mn5Si3-Fe5Si3

Electrical resistivity measurements have been performed on the system Mn_5?x,Fe_xSi₃ for the compounds x = 0,1,2,3,4 and 5 from 4.2 K to above room temperature. From the shape of the ρ(T) curves it can be inferred that the transition from antiferromagnetic to ferromagnetic ordering occurs in the concentration range 3 ? x ? 4; for Fe₅Si₃ and MnFe₄Si₃ the ρ(T) curves are characterized by a break in their slope, whereas for x = 1,2 and 3 a large minimum appears. Mn₅Si₃ exhibits two successive minima at 74 and 105 K. Magnetic susceptibility measurements for x = 1, 2 and 3 give confirmation of the Néel temperature for x = 1 and 2, whereas for x = 3 the behaviour is more complex.     

Raman scattering and X-ray diffraction study of structural phase transitions in the perovskite-type layer compound (C3H7NH3)2CdCl4

The structural phase transitions of (C₃H₇NH₃)₂CdCl₄ (PACC) have been studied by means of Raman scattering. X-ray diffraction and DSC measurements It is shown that the order-disorder phase transition Abma ? Pbca occurs at 156 K and not at 183 K as previously proposed by Chapuis (Acta CrystB34, 1506 (1978)) Apparently, the transition at 183 K does not change the Abma space group; it is suggested that it could be related to the occurrence of an incommensurate phase Another structural transformation of PACC is detected at 114 K, but no conclusion can be given as far as the structure of the low-temperature phase is not determined.