Sub kGy photon irradiation alterations in graphite

Present work concerns polymer pencil-lead graphite (PPLG) and the potential use of these in elucidating irradiation-driven structural alterations. The study provides detailed analysis of radiation-induced structural interaction changes and the associated luminescence that originates from the energy absorption. Thermally stimulated emission from the different occupied defect energy levels reflects the received radiation dose, different for the different diameter PPLGs. The PPLG samples have been exposed to photon irradiation, specifically x-ray doses ranging from 1 to 10 Gy, extended to 30–200 Gy through use of a60Co gamma-ray source. Trapping parameters such as order of kinetics, activation energy and frequency factor are estimated using Chen's peak-shape method for a fixed-dose of 30 Gy. X-ray diffractometry was used to characterize the crystal structure of the PPLG, the aim being to identify the degree of structural order, atomic spacing and lattice constants of the various irradiated PPLG samples. The mean atomic spacing and degree of structural order for the different diameter PPLG are found to be 0.3332 nm and 26.6° respectively. Photoluminescence spectra from PPLG arising from diode laser excitation at 532 nm consist of two adjacent peaks, 602 nm (absorption) and 1074 nm (emission), with mean energy band gap values within the range 1.113–1.133 eV

Tailored Ge-doped fibres for passive electron radiotherapy dosimetry

Study has been made of the thermoluminescence yield of various novel tailor-made silica fibres, 6 and 8 mol % Ge-doped, with four differing outer dimensions, comprised of flat and cylindrical shapes, subjected to electron irradiation. Main thermoluminescence dosimetric characteristics have been investigated, including the glow curve, dose response, energy dependence, minimum detectable dose, effective atomic number, linearity of index and sensitivity of the fibres. The studies have also established the uncertainties involved as well as the stability of response in terms of fading effect, reproducibility and annealing. In addition, dose-rate dependence was accounted for as this has the potential to be a significant factor in radiotherapy applications. The 6 and 8 mol % fibres have been found to provide highly linear dose response within the range 1 to 4 Gy, the smallest size flat fibre, 6 mol% Ge-doped, showing the greatest response by a factor of 1.1 with respect to the highly popular LiF phosphor-based medium TLD100. All of the fibres also showed excellent reproducibility with a standard deviation of < 2% and < 4% for 6 and 8 mol % Ge-doped fibres respectively. For fading evaluation, the smallest 6 mol% Ge-doped dimension flat fibre, i.e., 85 × 270 μm displayed the lowest signal loss within 120 days post-irradiation, at around 26.9% also showing a response superior to that of all of the other fibres. Moreover, all the fibres and TLD-100 chips showed independence with respect to electron irradiation energy and dose-rate. Compared with the 8 mol% Ge-doped optical fibres, the 6 mol% Ge-doped flat optical fibres have been demonstrated to possess more desirable performance features for passive dosimetry, serving as a suitable alternative to TLD-100 for medical irradiation treatment applications

The potential use of car windscreens for post-accident dose reconstruction in the periphery of nuclear installations

Cars of a variety of brands are usually parked at a fixed but increasing distance in the periphery of nuclear installations. Herein we focus on the potential use of car windscreens for post‐accident dose reconstruction from unplanned nuclear events and natural disasters, also in regard to unexpected events arising during large‐scale use of radioactive and nuclear materials. The situation requires identification of analytical techniques that could both readily and reliably be used to assess absorbed dose, sufficient to prompt remedial action where necessary. Samples from three widely used car brands—Honda, Toyota and Proton—are studied in respect of their thermoluminescence (TL) yield. Key TL dosimetric features in the gamma‐ray dose range of 1–100 Gy are examined. An ERESCO model 200 MF4‐RW X‐ray machine has also been used for energy response studies; a Harshaw 3500 TLD reader equipped with WinREMS software was used for the luminescence measurements. All brands exhibit linearity of TL yield versus dose, the samples from Honda showing the greatest response followed by that of the Toyota and Proton brands. The marked energy dependence reflects the effect of the strongly Z‐dependent photoelectric effect. Signal fading was investigated over a period of 28 days, the Toyota and Proton brand windshield glass showing a relatively low loss at 52.1% and 52.6% respectively compared to a 56.7% loss for that of the Honda samples. This work forms the first such demonstration of the potential of car windshield glass as a retrospective accident dosimeter

Natural dead sea salt and retrospective dosimetry

Accidents resulting in widespread dispersal of radioactive materials have given rise to a need for materials that are convenient in allowing individual dose assessment. The present study examines natural Dead Sea salt adopted as a model thermoluminescence dosimetry system. Samples were prepared in two different forms, loose-raw and loose-ground, subsequently exposed to 60Co gamma-rays, delivering doses in the range 2–10 Gy. Key thermoluminescence (TL) properties were examined, including glow curves, dose response, sensitivity, reproducibility and fading. Glow curves shapes were found to be independent of given dose, prominent TL peaks for the raw and ground samples appearing in the temperature ranges 361–385 ºC and 366–401 ºC, respectively. The deconvolution of glow curves has been undertaken using GlowFit, resulting in ten overlapping first-order kinetic glow peaks. For both sample forms, the integrated TL yield displays linearity of response with dose, the loose-raw salt showing some 2.5 × the sensitivity of the ground salt. The samples showed similar degrees of fading, with respective residual signals 28 days post-irradiation of 66% and 62% for the ground and raw forms respectively; conversely, confronted by light-induced fading the respective signal losses were 62% and 80%. The effective atomic number of the Dead Sea salt of 16.3 is comparable to that of TLD-200 (Zeff 16.3), suitable as an environmental radiation monitor in accident situations but requiring careful calibration in the reconstruction of soft tissue dose (soft tissue Zeff 7.2). Sample luminescence studies were carried out via Raman and Photoluminescence spectroscopy as well as X-ray diffraction, ionizing radiation dependent variation in lattice structure being found to influence TL response

Recent advances in silica glass optical fiber for dosimetry applications

In this paper, we review the highly promising silica glass, fabricated as doped and undoped optical fiber for intended use in radiation dosimetry. The dosimetry techniques reviewed here, underpinned by intrinsic and extrinsic defects in silica glass, focus on Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Radioluminescence (RL), with occasional references to the much more established Radiation Induced Attenuation (RIA). The other focus in this review is on the various materials that have been reported earlier as dopants and modifiers used in silica glass optical fiber radiation dosimeters. This article also elaborates on recently reported optical fiber structures, namely, cylindrical fibers, photonic crystal fibers and flat fibers, as well as dimensions and shapes used for optimization of dosimeter performance. The various types of optical fiber radiation dosimeters are subsequently reviewed for various applications ranging from medical dosimetry such as in external beam radiotherapy, brachytherapy and diagnostic imaging, as well as in industrial processing and space dosimetry covering a dynamic dose range from μGy to kGy. Investigated dosimetric characteristics include reproducibility, fading, dose response, reciprocity between luminescence yield to dose-rate and energy dependence. The review is completed by a brief discussion on limitations and future developments in optical fiber radiation dosimetry

Dosimetric utility of structural changes in gamma irradiated graphite-rich pencils

9B and H grade carbon-based pencil (carbon concentrations approaching 81 and 62 wt respectively %) have been investigated for radiotherapy dosimetry applications, offering low dependence on photon energy and near soft tissue effective atomic number. Comparison has been made with highly oriented pyrolytic graphite (HOPG), a pure and ordered synthetic form of graphite. The samples were exposed to 60Co gamma ray doses from 0 to 20 Gy (encompassing the range of doses utilized in fractionated radiotherapy), structural interaction alterations resulting from the radiation doses being observed via Raman and Photoluminescence (PL) spectroscopy and X-ray diffraction (XRD). Among the most prominent features to be observed in Raman spectra are the so-called G and D peaks, appearing at 1578 cm−1 and 1348 cm−1 respectively. The intensity ratio ID/IG was used for further characterization of the dose-dependent defects produced in the graphitic materials. From PL measurement, sample average energy band gap values are observed to be within the region 1.114–1.116 eV, being considered direct bandgap-like semiconductors. The characteristic XRD crystal plane Miller index (002) peak was observed in order to calculate the atomic spacing, lattice constant and the degree of structural order of the irradiated samples

The effect of acute gamma radiation onto growth media for mother culture of a Volvariella mushroom

Potato Dextrose Agar (PDA) is a semicrystalline polymer made from amylopectin, agarose, and amylose, used in laboratories for Agar plate culturing for a multitude of fungal strains. The existing pretreatment method for the elimination of pathogenic bacteria, namely steam sterilization, has shown several drawbacks, including high cost, uneven heating due to temperature differentials and an inability to treat specimens volumetrically. These drawbacks are mitigated by gamma irradiation, being carried out in order to improve hygienic quality and germination control, retarding sprouting, also enhancing physical attributes of the food product. Present study investigates the growth and survival of pretreated potato dextrose agar (PDA) substrate with gamma irradiations, for doses ranging from 0 kGy (unirradiated) up to 20 kGy, particularly for Volvariella mushroom cultivation. The relative elemental composition of PDA substrate has been obtained through use of Energy Dispersive X-ray Analysis (EDX), identifying carbohydrate (53.35%), oxygen (45.29%) and 1.36% of mineral trace elements. Gamma irradiation doses to the PDA substrate of 0.5 kGy, 1 kGy and 1.5 kGy have been found to be associated with respective growth rates of 0.93 ± 0.03, 0.94 ± 0.02 and 0.89 ± 0.02 cm/day, the PDA becoming more amorphous and acidic with reduced viscosity at higher doses. The findings of this study could pave the way for a low-cost yet highly effective system for irradiation in mushroom, as well as offering a viable alternative to current conventional sterilizations, well suited to applications in food security

Defect characteristic of oxygen-deficient Ge-doped preform using photoluminescence spectroscopy

Study has been made of the Photoluminescence properties of Ge-doped silica preforms fabricated using the MCVD process and subsequently subjected to γ-ray irradiation. The photoluminescence emissions pointed to the presence of defects related to oxygen vacancies. Two types of preform were fabricated, obtained using a different flow rate and deposition temperature for each case. Results from the absorption spectra of the samples named as P1 and P2, show a signature absorption peak at 5.1 eV and 6.8 eV, indicative of oxygen-deficient and oxygen-rich defects respectively. Photoluminescence investigation have been carried out before and after the irradiation process with both samples reveal two main peaks at 1.5 eV. The highest intensity at 1.5 eV is known as an interaction between the Non- Bridging Oxygen Hole Centre (NBHOC) with the presence of impurity in the glass matrix. Upon irradiation, weak peak can be observed at 1.8 eV, sample P1 and P2, the PL intensity increases by a factor of 20 × and 50 × , respectively. This peak is associated with the oxygen deficient state in the sample. The peak referring to defect known as Germanium Lone Pair Centre (GLPC) are observed in both samples, peak shown at 3.1 eV, regardless of the Germanium Oxygen Deficient Centre (GODC) content. In regard to this, it can be concluded that this defect is generated independently in all germanium samples and are not correlated with the GODC band observed in the absorption band

Measurement of photoelectron generation in a gold coated glass slide

In thin low-Z media irradiated by photon energies of several tens of keV, the presence of a high-Z additive can result in manifest locally modified secondary electron dose. Present study analyses the photoelectron dose enhancement resulting from nanometre thickness gold (atomic number Z = 78) coated on commercial borosilicate (B2O3) glass microscope cover-slips. Two thicknesses of B2O3 cover-slip have been utilized, 0.13 ± 0.02 mm and 1.00 ± 0.01 mm, with single-sided Au coatings of 20, 40, 60, 80 and 100 nm. An additional uncoated glass slide has been kept as a comparator. The samples have been exposed to X-rays generated at kVp potentials, delivering a fixed dose of 2 Gy. Dose enhancement resulting from the 1.00 mm glass has been observed to be ~1.32 × that of the 0.13 mm thickness glass. The elemental composition of the samples has been obtained via Electron Dispersive X-ray (EDX), elemental content differences between the two thicknesses of glass leading to a difference in effective atomic number of less than 0.3%. The influence on photon yield of the gold coating and variations in elemental content has been modelled using Monte Carlo simulation, allowing comparison with the measured values of enhanced TL yield

Structural and defect changes in black carbon charcoal irradiated with gamma ray

This study investigates the use of black carbon charcoal as passive radiation dosimetry, offering low dependence on photon energy and near soft tissue effective atomic number with state-of-the-art techniques. Regression an�alyses have now been conducted using graphite manufactured commercially in the form of charcoal from three different types: mangrove, coconut, and green charcoal recycled from sawdust, working with photon-mediated interactions at radiotherapy dose levels. Explorations of changes in Raman spectroscopic characteristics, and photoluminescence dose dependence have been performed with a focus on the relationship between absorbed radiation energy and induced material changes, using a 60Co gamma-ray source doses ranging from 0 to 10 Gy. Raman spectroscopy has established to be an effective method for exploring defects in carbon-based materials due to its high sensitivity, most commonly focusing on the use of ID/IG parameter. While photoluminescence analysis will provide information on electronic properties and the band gap energy. The crystal structure of the black charcoal samples was characterised using X-ray diffractometry, with the goal of determining the degree of structural order, atomic spacing, and lattice constants of the various irradiated charcoal samples, supported by crystallite size assessments. The findings of this study could pave the way for a low-cost yet highly effective system for studying radiation-induced changes in carbon, as well as offering a viable alternative to current commercial dosimeters, well suited to applications in radiotherapy