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

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

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

The radiation shielding offered by the commercial glass installed in Bangladeshi dwellings

One sign of a vibrant Bangladeshi economy has been the move away from the use of more traditional housing materials towards a preference for modern constructional media. Glass, one such example, used both decoratively and in a structural context, offers various advantageous properties and facets including a protective feature against radiation that has not previously been considered. Current interest examines the dosimetric possibilities offered by the commercial glass as a secondary shield and also in retrospective ionising radiation exposure analysis. Four popular brands of window glass are investigated, all available within the local market (PHP-Bangladesh, Usmania-Bangladesh, Nasir-Bangladesh and Rider-China), all with the same thickness and colour, varying in terms of elemental weight fractions as evaluated by energy dispersive X-ray analysis. As potential attenuators of transmitted radiation thereby forming secondary barriers against radiation exposure from penetrating radiations, the four brands of glass have been studied using photon energies from 59 up to 1332 keV, a range of values representative of that potentially encountered in incidents. Use has been made of a well-shielded high-purity germanium γ-ray spectrometer and associated electronics, providing for evaluation of the characteristic barrier parameters of half-value layer, radiation protection efficiency and effective atomic number (Zeff). Of the four brands investigated, Rider provides superior secondary shielding performance. Concerning potential retrospective dosimetry the effective atomic number of the glass samples are comparable with that of the commercial thermoluminescence (TL) dosimeter TLD-200. At high doses, the TL yields are sufficient to provide for retrospective accident dosimetry