The use of the TL and OSL phenomena for determination of absorbed dose rates of 90Sr + 90Y sources by a postal method

International recommendations establish that ⁹⁰Sr + ⁹⁰Y clinical applicators have to be calibrated in order to determine the absorbed dose rates in the case of the sources that do not have original calibration certificates, or to update the absorbed dose rates presented in the source certificates. Following these recommendations, a postal dosimetric system was developed to calibrate clinical applicators using two luminescent techniques: thermoluminescence (TL) and optically stimulated luminescence (OSL). In this work, Al₂O₃:C commercial detectors were characterized and their TL and OSL responses were analyzed. The results showed the efficiency and the optimal behavior of this material in beta radiation beams. After characterization, the system was sent to the Federal University of Sergipe (UFS), Brazil, for calibration of five ⁹⁰Sr + ⁹⁰Y clinical applicators, where the detectors were irradiated and returned to IPEN, for their evaluation and determination of the absorbed dose rates. A comparison between these absorbed dose rates and those adopted by the UFS as original was made; the differences obtained were within those of other studies, and they demonstrated the usefulness of the system.     

Cross-calibration between beta and gamma sources using quartz OSL: Consequences of the use of the SAR protocol in optical dating

The radiation dose delivered by the ⁹⁰Sr beta source of a TL-OSL reader and the one delivered by a ¹³⁷Cs gamma source were compared using OSL dating techniques and tools. Three sets of quartz of different origins (rock, sediment and loess) were studied and measured by the SAR protocol (Single aliquot regenerative dose protocol) after irradiations carried out either by the ⁹⁰Sr source or by a ¹³⁷Cs source. Measurements show that the values obtained by the SAR protocol must be corrected in order to provide an acceptable cross-calibration of the beta and gamma source. Once applied, measurement sets become self-consistent and compatible with expected values. The consequences of the above mentioned observations on the methodology of OSL dating are discussed and suggest that a mixed protocol be used including both the SAR protocol and an added dose techniques close to the SARA protocol (Single aliquot regenerative and added dose protocol).     

Neutron capture gamma ray investigation of Sr88 level structure

The level structure of Sr⁸⁸has been investigated at the Karlsruhe research reactor FR2 using thermal neutron capture in Sr⁸⁷. A pure thermal neutron beam was obtained by Bragg reflection from a lead single crystal. The target was natural strontium which gives a cross section contribution of about 87% for the reaction Sr⁸⁷(n,γ) Sr⁸⁸. High resolution measurements of the capture gamma ray spectrum have been performed by means of a 4 cm² × 0.5 cm lithium-drifted germanium diode. 146 gamma lines have been observed. Cascade relationships were studied by a double and triple coincidence apparatus containing 4″Ø × 5″ NaI(Tl) crystals and XP-1040 photomultipliers. In several cases coincident background was subtracted utilizing the doublewindow technique. By application of the triple sum coincidence method capture gammas from isotopes other than the investigated Sr⁸⁸ nucleus could be eliminated. Several new levels were established. A transition scheme is proposed and discussed. The neutron binding energy of Sr⁸⁸ is determined to be 11111±4 keV.     

Effects of strontium and calcium simultaneous substitution on electrical and structural properties of Pb1?x?yCaxSryTiO3 thin films

Ferroelectric Pb_1−x−y Ca _x Sr _y TiO₃ thin films (denoted by PCST90, PCST70, and PCST30) were deposited on the Pt/Ti/SiO₂/Si substrates by a chemical solution deposition method. Their properties were investigated from the viewpoint of crystal structure, microstructure, dielectric, and ferroelectric properties. X-ray diffraction patterns revealed the formation of PCST90, PCST70, and PCST30 thin films without any secondary phases. Infrared and Raman spectroscopy results show that a gradual phase transition from tetragonal to pseudocubic or cubic perovskite structure may occur in PCST thin films with the simultaneous increase of Ca²⁺ and Sr²⁺ contents. Both substitution of isovalent Ca²⁺ and Sr²⁺ at Pb²⁺-site enhanced the dielectric constant and reduced the remnant polarization. In addition, ferroelectric test analyses show that the PCST thin films undergo a ferroelectric-to-paraelectric phase transformation with an amount of Pb²⁺, Ca²⁺, and Sr²⁺ at 30%, 35%, and 35% mol, respectively. Hence, the absence of ferroelectric property may be attributed to a decreasing of the octahedron distortion in the perovskite structure accompanied by a weakening of long-range ferroelectric order.     

SURFACE PHASE DECOMPOSITION IN Bi2Sr2CaCu2O7-y SINGLE CRYSTALS UNDER NITROGEN IONS IRRADIATION

The influence of irradiation by 30 keV nitrogen ions with a fluence 1×10¹⁸N⁺·cm^-2 on the crystal structure of single crystal Bi₂Sr₂CaCu₂O_7-y was investigated by means of X-ray photoelectron spectroscopy and X-ray diffraction. The irradiation caused a transformation from Bi₂Sr₂CaCu₂O_7-y (2212 phase) to Bi₂Sr₂CuO_5-x (2201 phase). It was observed that. a small amount of metallic bismuth with an average thickness of about 6.3nm appeared after the irradiation. The possible reaction mechanism under nitrogen-ion irradiation was discussed.     

Messung der zirkularen Polarisation der inneren und äußeren Bremsstrahlung

The polarisation of the internal bremsstrahlung γ's was detected by the Compton-forward-scattering with polarised electrons for three differentβ-decays: 1. for the allowed transition (P³²), 2. for the unique forbidden transition (Sr⁹⁰+Y⁹⁰), and 3. for the forbidden transition with forbidden spectrum (Bi²¹⁰=RaE). The detected polarisation values of P³² and (Sr⁹⁰+Y⁹⁰) agree with the theoretical values for the allowed transitions. The detected polarisation values for Bi²¹⁰ are smaller than the theoretical values of the allowedβ-transition by a factor of 0.62±0.08. The polarisation of the external bremsstrahlung was measured as a function of the atomic number (Z) using thick absorbers. The polarisation of the external bremsstrahlung decreases slowly with the increase of the atomic number. The polarisation of bremsstrahlung, which was extrapolated to an absorber with atomic numberZ=0, is in well agreement with the theoretical values of the infinitively thin absorbers.     

An Effect of Irradiation with Trivalent Boron Ions on Pinning in Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>CaCu<Subscript>2</Subscript>O<Subscript>8</Subscript> Thin Films as Revealed by MWA and Hall-Probe Measurements

Bi₂Sr₂CaCu₂O₈ thin films 200 nm thick were irradiated with 120 keV trivalent boron ions with the dose ranging from 10¹¹ to 10¹⁴ ion/cm². The critical parameters of the samples prior and after irradiation were monitored by non-resonance modulated microwave absorption and Hall-probe techniques. For low doses of 10¹¹–10¹² ion/cm², a slight increase in the critical current density and expansion of the area of the non-dissipative transport current flow were revealed. Such results are explained by the formation of separate areas of displaced atoms, which serve as effective pinning centers. The positive effects of irradiation faded away with dose increase of up to 10¹³–10¹⁴ ion/cm². This is due to overlap of radiation-induced defects and weak pinning on them.     

Dose rate dependence of first stage coloration of nacl doped with divalent impurities

Abstract

The amount of first stage coloration in NaCl doped with Ca²⁺, Sr²⁺ Cd²⁺, or Eu²⁺ has been investigated as a function of the X-irradiation dose rate. It was ascertained that in all cases the amount of first stage coloration is proportional to the square root of X-irradiation dose rate in agreement with the models recently developed by Comins and Carragher and Aguilar et al for F-center produc tion in the alkali halides doped with divalent impurities.     

Assessment of health risk associated with natural gamma dose rate levels and isodose mapping of Jordan

ABSTRACT

As a pioneering study in Jordan, an extensive measurement for external gamma dose rate (GDR) was conducted. A portable gamma radiation detector was used to perform these measurements at 1?m above the soil surface. A geographical positioning system Garmin was used to record a total of 823 measured points. The GDRs’ measurement ranged from 35 to 470?nGy?h^?1 giving a mean value of 90?nGy?h^?1, which was found to be one and half times higher than the world average of 59?nGy?h^?1. The lowest mean GDR 72?nGy?h^?1 was found in the Albalqa governate, while the highest mean GDR 131?nGy?h^?1 was found to be for the Alkarak governate. The mean annual effective dose was found to be 0.551?mSv, which is higher than the world average value of 0.48?mSv. This is a pivotal study evaluating the risks associated with GDR levels in Jordan that were the relative excess lifetime cancer risk, the mean collective effective dose, the mean weighted GDR and the mean lifetime dose that are 2.24?×?10^?3, 5538manSv?y^?1, 0.531?mSv and 39?mSv, respectively. The cosmic rays mean GDR was determined to be 20?nGy?h^?1. This study focuses on constructing GDRs’ baseline data in Jordan, which will be used to determine the possible change in the natural radiation due to other human activities in the future. ArcGIS software was employed to generate an isodose map to characterise exposure rates caused by GDR in Jordan.     

Evaluation of the applicability of MOSFET detectors in radiotherapy

MOSFET detectors of 1 mVcGy⁻¹ sensitivity were tested for the accuracy of absorbed dose measurements in radiation therapy with the use of photon and electron beams. Before a detector was used in the study, several calibration coefficients were determined to allow for different factors affecting its operation. Then, the detector exposure response was compared with the dose calculated in the anthropomorphic phantom by the Monaco and MasterPlan treatment planning systems. MOSFET detectors were placed inside the phantom during the irradiation. Three different plans for thorax and pelvis areas were studied. The paper presents the differences between planned and MOSFET measured doses delivered to the selected target areas using conventional and IMRT techniques.     

Semiconducting TlSr2RCu2O7 (R=rare earth) and its superconducting derivatives

Semiconducting TlSr₂RCu₂O₇ (R=Pr or Er) with a 1212-type structure has been synthesized in the single-phase form. Partial substitution of Sr²⁺ for R³⁺ converts this semiconductor to a 90 K superconductor TlSr₂(R_1–y Sr _y )Cu₂O₇. A combination substitution, Sr²⁺ for R³⁺ and Pb⁴⁺ for Tl³⁺, leads to the Ca-free 100 K superconductor (Tl, Pb)Sr₂(R, Sr)Cu₂O₇. The results are explained in the framework of the mixed Cu²⁺/Cu³⁺ valence.     

The status of strontium in biological apatites: an XANES/EXAFS investigation

Osteoporosis represents a major public health problem through its association with fragility fractures. The public health burden of osteoporotic fractures will rise in future generations, due in part to an increase in life expectancy. Strontium‐based drugs have been shown to increase bone mass in postmenopausal osteoporosis patients and to reduce fracture risk but the molecular mechanisms of the action of these Sr‐based drugs are not totally elucidated. The local environment of Sr²⁺ cations in biological apatites present in pathological and physiological calcifications in patients without such Sr‐based drugs has been assessed. In this investigation, X‐ray absorption spectra have been collected for 17 pathological and physiological calcifications. These experimental data have been combined with a set of numerical simulations using the ab initioFEFF9 X‐ray spectroscopy program which takes into account possible distortion and Ca/Sr substitution in the environment of the Sr²⁺ cations. For selected samples, Fourier transforms of the EXAFS modulations have been performed. The complete set of experimental data collected on 17 samples indicates that there is no relationship between the nature of the calcification (physiological and pathological) and the adsorption mode of Sr²⁺ cations (simple adsorption or insertion). Such structural considerations have medical implications. Pathological and physiological calcifications correspond to two very different preparation procedures but are associated with the same localization of Sr²⁺versus apatite crystals. Based on this study, it seems that for supplementation of Sr at low concentration, Sr²⁺ cations will be localized into the apatite network.     

Time-of-flight investigation of the intensity dependence of laser-desorbed positive ions from SrF2

The intensity dependence of the total and specific yields of positive ions desorbed from SrF₂ under 193 nm and 308 nm excimer-laser irradiation has been investigated by the time-of-flight method. The following positive ion species have been detected: F⁺, Sr⁺, Sr⁺⁺, SrF⁺⁺ and SrF ₂ ⁺ . The Sr⁺ and SrF⁺ emission yields are found to increase as E ⁿ, where E represents the laser energy per pulse. The exponent n is related to defect-initiated neutral particle emission and gas-phase ionization. The influence of surface damage on this power dependence is investigated. The F⁺ emission yield showed a quite different behaviour compared to that of the Sr⁺ and SrF⁺ emission. At both wavelengths the total positive ion emission yields saturate at a certain laser energy. In the saturation regime the SrF⁺ emission vanishes and alternative emission of F⁺ and Sr⁺ was observed at both wavelengths, but the total emission yield in the saturation regime (F⁺ + Sr⁺) remained constant. A Scanning Electron Microscope (SEM) was used to investigate the damage spots after laser irradiation for thermal effects.     

Lifetimes of metastable states in Sr II

The lifetimes of the 4d ²D _3/2,5/2 levels of Sr⁺ have been determined both experimentally and theoretically. The experiment was performed at an ion storage ring utilising collinear laser excitation. The calculation was performed by the Hartree-Fock method including relativistic effects and core polarisation. The obtained lifetimes (which are about 0.4 s) are discussed in detail and compared with earlier published results. In addition, calculated lifetimes of a large number of excited states in Sr⁺ are included. Received 15 February 2000 and Received in final form 20 March 2000     

Positron annihilation and magnetization studies of proton irradiated polycrystalline textured Bi2Sr2CaCu2O8+δ and Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10+δ superconductors

Proton irradiations on polycrystalline textured Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) and Bi_1.84Pb_0.34Sr_1.91Ca_2.03Cu_3.06O_10+δ (Bi-2223) samples have been carried out. The irradiation induced defect size increases with dose up to 5×10¹⁵ protons/cm² in Bi-2212, but remains effectively constant in Bi-2223 as revealed from positron lifetime measurements. Magnetization studies show that at moderate dose, there is no significant change in intergranular critical current density (J_c^int) in both systems. But intragranular critical current density (J_c) increases with dose in Bi-2212. A drastic fall in both J_c^int and J_c is observed at high dose in Bi-2223 as compared to Bi-2212.     

Roles of the band filling and the d orbitals hybridization on the conduction and magnetism of some Sr-based double perovskites: An LSDA+U study

We have systematically investigated the electronic structure and magnetic properties of the double perovskite oxides Sr₂CrZrO₆, Sr₂MnNbO₆, Sr₂FeMoO₆ and Sr₂NiRuO₆ in terms of band filling of different t_2g and e_g orbitals. Calculations of density of the states (DOS) were performed within the frame of the local spin density approximation and Hubbard potential (LSDA+U) employed in the Linear Muffin Tin Orbitals with Atomic Sphere Approximation (LMTO-ASA) method. The DOS of Sr₂FeMoO₆ was obtained and found to agree very well with published reports. Half-metallic character through the spin-down channel and the ferrimagnetic ordering was observed with notable hybridization among the 3d, p and 4d orbitals within Fermi level. A difference between the theoretically expected values and the calculated ones for the magnetic moment (Δm) of the 3d orbitals is determined and had been found to increase on going from Sr₂CrZrO₆ to Sr₂NiRuO₆. This increment in Δm indicates increment in the hybridization strength, which leads to long range ordering in Sr₂FeMoO₆ and Sr₂NiRuO₆ compounds. In comparison with reported experiments, the frustrated magnetism and weak ferrimagnetism states are the most possible ones in Sr₂CrZrO₆ in Sr₂MnNbO₆, respectively. The half-metallic character was also seen in Sr₂MnNbO₆ and Sr₂CrZrO₆ compounds while Sr₂NiRuO₆ shows normal metallic conduction and ferromagnetism in accordance with the superexchange interaction e_g²-o-e_g⁰ of Goodenough-Kanamori-Anderson (GKA).     

Effect of gamma irradiation on the dielectric response of a Sr0.75Ba0.25Nb2O6 relaxor single crystal

The effect of gamma irradiation from a ⁶⁰Co source at a dose D = 4.75 × 10⁴ R on the dielectric properties of a Sr_0.75Ba_0.25Nb₂O₆ (SBN-75) single crystal with a smeared phase transition is investigated in the low-and infralow-frequency ranges. The behavior of the dielectric response is compared with the behavior of the depolarization currents induced in unirradiated and irradiated samples of the Sr_0.75Ba_0.25Nb₂O₆ compound. The observed changes in the electrical properties of the Sr_0.75Ba_0.25Nb₂O₆ single crystal in the temperature range of the smeared phase transition are associated with the stabilization of the ferroelectric phase of the material in an internal bias field generated by radiation-induced defects.     

Density functional theory study on two-peak emission of Eu activators in Sr2SiO4

The supercells of pure and Eu-doped Sr₂SiO₄ were theoretically analyzed by density functional theory (DFT) calculations to investigate the typical two-peak emission of Sr₂SiO₄:Eu²⁺, which originates from two different Sr²⁺ (or Eu²⁺) sites in the Sr₂SiO₄ host structure. The Perdew-Wang generalized-gradient approximation (GGA) functional and the double numerical plus d-functions (DND) basis set with effective core potentials (ECP) were employed in the calculations of electronic properties. The electron transfer between Eu²⁺ ions placed at two different crystallographic Sr²⁺ sites was understood based on the accurate assignment of deconvoluted peaks of the two-peak emission to their corresponding crystallographic sites. This study ought to be instructive as a basic guideline to improve the color chromaticity of Sr₂SiO₄:Eu²⁺ for use in white light emitting diodes (WLEDs).     

Growth and comparison of physicochemical properties of pure,Ca and Sr doped NH4Sb3F10 single crystals for electro optic applications

Single crystals of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material.