Lanthanide Doped Alkaline-Earth Metal Nanocrystalline as Ionising Radiation Storage Phosphors

This work involved the preparation methods, structural and spectroscopic characterisations of lanthanide ions (Ln = Sm, Eu) doped nanocrystalline alkaline-earth metal fluorides MF2 (M = Ca, Sr) as ionising radiation storage phosphors for potential applications in the field of computed radiography, dosimetry, and optical data storage. The structural characterisation was conducted using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and SEM and TEM energy dispersive spectroscopy (EDS). The storage mechanism of the phosphors was studied by photoluminescence spectroscopy (PL) and spectral hole- burning. The X-ray storage phosphor properties i.e. X-irradiation induced reduction of Sm3+ to Sm2+ and reverse photoionisation of Sm2+ to Sm3+, in CaF2:Sm3+ nanocrystals prepared by co-precipitation method were investigated by monitoring the PL intensities of both Sm3+ and Sm2+ ions. Both processes can be modelled by first-order dispersive kinetics. Besides, the Sm3+ to Sm2+ conversion upon X-irradiation in SrF2:Sm3+ were compared with CaF2:Sm3+. In addition, the X-ray storage phosphor properties in mechanochemically ball milled nanocrystalline CaF2:Sm3+ were explored in detail. The photoionisation of Sm2+ ions was also demonstrated by spectral hole-burning experiments of the X-irradiated nanocrystalline CaF2:Sm3+. The hole-burning rate decreased with the X-irradiation dose, while an increase was observed with an increase of the Sm concentration, manifesting the significance of the Sm3+ electron trap in the photoionisation of Sm2+ in CaF2. Furthermore, the Zeeman effects in magnetic fields up to 9 Tesla on the Sm2+ luminescence were investigated, in particular the splitting of the 7F1 ground state level and the quadratic dependence of the intensity of a forbidden transition. The photoinduced electron transfer between Eu2+ and Sm3+ in CaF2 nanocrystals prepared by a facile co-precipitation method was explored. The doping of divalent Eu was realised by reducing Eu3+ to Eu2+ in solution under nitrogen employing granular zinc. The forward and backward photoinduced electron transfer in CaF2:Eu2+,Sm3+ was investigated by monitoring the Eu2+ and Sm2+ luminescence signals, under ultraviolet (UV) light exposure at 310 and 340 nm. Importantly, this is the first report on the X-ray storage properties, spectral hole-burning, and photoinduced electron transfer phenomena of nanocrystalline CaF2:Sm3+, SrF2:Sm3+, and CaF2:Eu2+,Sm3+ powders

Investigation of silica-based TL media for diagnostic x-ray dosimetry

We focus on the development of Ge-doped silica thermoluminescent dosimeters with sensitivity superior to that of the LiF (Mg,Ti) phosphors popularly used in x-ray diagnostic imaging dosimetry, typically in the form of the product TLD-100. Of interest are Ge-doped silica telecommunication fibres (SMF) and tailor-made doped photonic crystal fibres (PCFc), the latter Ge-doped or also co-doped with boron. The PCFs are formed of capillaries that at high temperatures and under vacuum are made to collapse inwards (PCFc), the internal walls fusing and generating strain-related defects. To-date, the fabricated PCFc-Ge-B, PCFc-Ge and (SMF) have been observed to provide TL yields which weight-for-weight are some 15, 10 and 2 × that of TLD-100. In present study we test the linearity of TL yield for x-ray doses from 0.1- to 10 mGy, use being made of an x-ray tube operated at 80 kVp, a value typically selected in chest radiography. For a dose of 10 mGy, a study of energy dependence has been conducted using x-ray tube potentials of 80 kVp 100 kVp, and 120 kVp, with inherent filtration 0.9 mm Al measured at 75 kVp, and total filtration of 2.8 mm Al at 80 kVp

Developments in production of silica-based thermoluminescence dosimeters

This work addresses purpose-made thermoluminescence dosimeters (TLD) based on doped silica fibres and sol–gel nanoparticles, produced via Modified Chemical Vapour Deposition (MCVD) and wet chemistry techniques respectively. These seek to improve upon the versatility offered by conventional phosphor-based TLD forms such as that of doped LiF. Fabrication and irradiation-dependent factors are seen to produce defects of differing origin, influencing the luminescence of the media. In coming to a close, we illustrate the utility of Ge-doped silica media for ionizing radiation dosimetry, first showing results from gamma-irradiated Ag-decorated nanoparticles, in the particular instance pointing to an extended dynamic range of dose. For the fibres, at radiotherapy dose levels, we show high spatial resolution (0.1 mm) depth-dose results for proton irradiations. For novel microstructured fibres (photonic crystal fibres, PCFs) we show first results from a study of undisturbed and technologically modified naturally occurring radioactivity environments, measuring doses of some 10 s of μGy over a period of several months

Latest developments in silica-based thermoluminescence spectrometry and dosimetry

Using irradiated doped-silica preforms from which fibres for thermoluminescence dosimetry applications can be fabricated we have carried out a range of luminescence studies, the TL yield of the fibre systems offering many advantages over conventional passive dosimetry types. In this paper we investigate such media, showing emission spectra for irradiated preforms and the TL response of glass beads following irradiation to an Am-241-Be neutron source located in a tank of water, the glass fibres and beads offering the advantage of being able to be placed directly into liquid. The outcomes from these and other lines of research are intended to inform development of doped silica radiation dosimeters of versatile utility, extending from environmental evaluations through to clinical and industrial applications. (C) 2015 Elsevier Ltd. All rights reserve

Estimasi Value At Risk (VaR) Model Arima(p,d,q) Dengan Simulasi Monte Carlo Pada Data Saham PT. LIPPO KARAWACI TBK.

Return merupakan salah satu data deret waktu yang dapat dimodelkan dengan pemodelan ARIMA(p,d,q). Fluktuasi tingkat pengembalian (return) dapat mencerminkan besar kecilnya risiko yang akan diperoleh. Value at Risk (VaR) merupakan salah alat ukur yang dapat menghitung besarnya kerugian (risiko) terburuk yang terjadi pada portofolio maupun saham dengan tingkat kepercayaan tertentu dan dalam periode tertentu. Salah satu metode perhitungan VaR yang sering digunakan adalah metode simulasi Monte Carlo. Studi simulasi dilakukan karena memiliki salah satu kelebihan yaitu dapat menganalisa ketidakpastian dimana tujuannya adalah untuk menentukan bagaimana variasi eror mempengaruhi performa dari sistem yang dimodelkan. Monte Carlo dapat dihitung dengan dua pendekatan yaitu pendekatan statis (deterministik) dan pendekatan dinamis. Berdasarkan hasil simulasi, kedua pendekatan menghasilkan estimasi risiko yang fluktuatif. Pada pendekatan statis (deterministik) menghasilkan peramalan risiko yang meningkat seiring bertambahnya periode waktu peramalan. Sementara itu pada pendekatan dinamis menghasilkan nilai risiko yang lebih konvergen seiring bertambahnya periode waktu peramalan

Environmental radioactivity monitoring via newly developed optical fiber based thermoluminesence dosimeter / Siti Rozaila Zahariman

Thermoluminesence dosimeters (TLD) are increasingly being used in a variety of fields, including in support of medical irradiations, environmental radioactivity monitoring, food sterilization, the radiation processing industry and in other such involvements. The conventional phosphor based TLDs suffer in performance, due in part to their manifestly hygroscopic nature and poor resolution. In their use as TLDs, the optical fibers do not suffer from these drawbacks and in addition are seen to offer a number of other potential advantages, including sensitivity, stability and reliability. These factors help to introduce the fibers as a potential alternative to the phosphor-based TLDs. Recent studies have highlighted the use of optical fibers in radiation dosimetry applications for a wide range of electron and photon beam irradiations. Nevertheless, they have yet to be investigated at the very much lower environmental doses, with practically no very low doses studies. Realizing the importance of low dose environmental radioactivity monitoring, highly sensitive optical fiber based TLD materials in the form of collapsed Photonic Crystal Fiber (PCFc) has been developed here. In this study, the newly developed collapsed PCFs (with different dopant concentrations of Ge and B) together with phosphor based TLDs (TLD-200 and TLD-100) have been buried in eight selected areas within Gebeng, Pahang (off-site of the Lynas Advanced Materials Plant) to obtain exposure records for two, four, six, and eight months. The TLD readout doses (via a TLD reader) are compared with the bulk radioactivity in the associated soils obtained via HPGe gamma-ray spectrometry. Parameters concerning thermoluminesence (TL) for the samples induced by x-ray and gamma-ray irradiation have been investigated, including the linearity of dose response, energy response, fading, effective atomic number and glow curve. Present study indicates that the developed PCFs could be advantageously utilized in very low dose radiation dosimetry applications

Luminescence and photoionization of X-ray generated Sm(2+) in coprecipitated CaF2 nanocrystals

We report photoluminescence and photoionization properties of Sm2+ ions generated by X-irradiation of nanocrystalline CaF2:Sm3+ prepared by coprecipitation. The nanocrystals were of 46 nm average crystallite size with a distribution of ±20 nm and they were characterised by XRD, TEM and SEM-EDS. At room temperature, the X-irradiated sample displayed broad electric dipole allowed Sm2+ 4f55d (A1u) → 4f6 7F1 (T1g) luminescence at 725 nm that narrowed to an intense peak at 708 nm on cooling to ∼30 K. The narrow f–f transitions of Sm3+ were also observed. The X-irradiation-induced reduction of Sm3+ + e− → Sm2+ as a function of X-ray dose was investigated over a very wide dynamic range from 0.01 mGy to 850 Gy by monitoring the photoluminescence intensities of both Sm2+ and Sm3+ ions. The reverse Sm2+ → Sm3+ + e− photoionization can be modelled by employing dispersive first-order kinetics and using a standard gamma distribution function, yielding an average separation of 13 Å between the Sm2+ ions and the hole traps (e.g. oxide ion impurities). The present results point towards potential applications of Sm doped CaF2 nanocrystals in the fields of dosimetry and X-ray imaging.Z. Siti Rozaila, Nicolas Riesen and Hans Riese

Measurement of the total activity concentrations of Libyan oil scale

Twenty-three oil scale samples obtained from the Libyan oil and gas industry production facilities onshore have been measured using high-resolution gamma-ray spectrometry with a shielded HPGe detector, the work being carried out within the Environmental Radioactivity Laboratory at the University of Surrey. The main objectives of this work were to determine the extent to which the predominant radionuclides associated with the uranium and thorium natural decay chains were in secular equilibrium with their decay progeny, also to compare differences between the total activity concentrations (TAC) in secular equilibrium and disequilibrium and to evaluate the measured activities for the predominant gamma-ray emitting decay radionuclides within the 232Th and 238U chains. The oil scale NORM samples did not exhibit radioactive equilibrium between the decay progeny and longer-lived parent radionuclides of the 238U and 232Th series

Measurement of the total activity concentrations of Libyan oil scale

Twenty-three oil scale samples obtained from the Libyan oil and gas industry production facilities onshore have been measured using high-resolution gamma-ray spectrometry with a shielded HPGe detector, the work being carried out within the Environmental Radioactivity Laboratory at the University of Surrey. The main objectives of this work were to determine the extent to which the predominant radionuclides associated with the uranium and thorium natural decay chains were in secular equilibrium with their decay progeny, also to compare differences between the total activity concentrations (TAC) in secular equilibrium and disequilibrium and to evaluate the measured activities for the predominant gamma-ray emitting decay radionuclides within the 232Th and 238U chains. The oil scale NORM samples did not exhibit radioactive equilibrium between the decay progeny and longer-lived parent radionuclides of the 238U and 232Th series

Thermoluminescence features of commercial glass and retrospective accident dosimetry

Five window glass brands popularly used in Bangladeshi dwellings have been analyzed for retrospective accident dosimetry, being inexpensive, highly effective as a barrier to moisture and naturally transparent at optical wavelengths. In examining their potential for dosimetry, study has been made of the annealing – irradiation - readout steps contributing to characterization of the various key thermoluminescence properties. These include the respective glow curves, relative sensitivity, dose response, energy response, reproducibility and fading. An ERESCO model 200 MF4-RW X-ray machine and a Gammacell-220 60Co source was used for sample irradiation, while a Harshaw 3500 TLD reader (USA) supported by WinREMS software was used for TL readouts. Within the γ-radiation dose range up to 50 Gy, the various TL parameters show Nasir glass (a locally produced glass brand) to offer the most promising performance for retrospective dosimetry. Fading studies indicate the reconstruction of absorbed dose to be possible for periods of up to four weeks post-exposure. Energy dispersive X-ray analysis shows the Zeff of the various glass to be in the range 12.5–15.1, closely according with that of TLD-200, a commercial dosimeter used for low-level environmental radiation dosimetry. Present work constitutes the first such study of low-cost commercial glass for doses in the range 10–50 Gy, previous literature relating to doses from 50 Gy up to 20 kGy. © 2019 Elsevier Lt