Spectroscopic and dosimetric comparison of tooth enamel separation methods for EPR retrospective dosimetry.

Precise estimation of individual radiation dose utilizing biomaterials (fingernail, bone, and tooth) is very challenging due to their complex sample processing. Despite, tooth enamel, the most mineralized tissue of tooth is used for this purpose due to its high radiation sensitivity and ability to produce radiation induced long lived CO2- radicals. However, human teeth are not always available, and invasive nature of sample collection adds to the complexity making dose estimation difficult. In such cases, animal teeth (goat, cow, and moose) can be used as a substitute for human teeth due to comparable enamel sensitivity. Moreover, separation of enamel from dentine is a crucial step towards accurate dose estimation from irradiated teeth. In this work, Indian goat teeth were used as it was readily available to us and the comparison of goat enamel sensitivity to radiation was found to be within ∼7.4 % that of human. The enamel samples were separated following two chemical methods; (1) density separation using sodium polytungstate, (2) alkaline denaturation using NaOH and the quality was compared based on their purity and radiation sensitivity. Combined results of spectroscopic characterization using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman analysis authenticated the crystallinity and purity of the separated enamel samples. The radiation sensitivity of separated enamel samples was compared by electron paramagnetic resonance (EPR) analysis as a part of dosimetric characterization. The suitability of both the samples for retrospective dosimetry and epidemiological studies was checked by validating the dose estimated from separated enamel samples with standard alanine/EPR dosimeter.

Ceramic based electronic component as retrospective radiation dosimeter.

Surface mount electronic devices (like resistors, capacitors, and inductors) extracted from the portable electronic devices (mobile phones, USB drives, etc.) have been studied for dose reconstruction using luminescence techniques for radiological or nuclear emergencies. In this work, carbon coated ceramic resistors removed from the electronic instruments are analyzed using thermo luminescence (TL) technique for the retrospective dose reconstruction. TL measurements on beta irradiated ceramic resistors exhibited one major dosimetric peak at around 540 K in addition to three other low temperature peaks. A linear beta dose response has been observed from 1 Gy to 125 Gy with Minimum Detectable Dose (MDD) of 0.1 Gy. The dose response is found to be supralinear below 1 Gy. The fading studies have been carried out and investigated up to 30 days. The important kinetic parameters for the material like TL trap depth, frequency factor and order of kinetics are evaluated by deconvolution method.

Exposure of patients to low doses of X-radiation during neuro-interventional imaging and procedures: Dose estimation and analysis of γ-H2AX foci and gene expression in blood lymphocytes.

Radiation has widespread applications in medicine. However, despite the benefits of medical radiation exposures, adverse long-term health effects are cause for concern. Protein and gene biomarkers are early indicators of cellular response after low-dose exposure. We examined DNA damage by quantifying γ-H2AX foci and expression of twelve candidate genes in the blood lymphocytes of patients exposed to low doses of X-radiation during neuro-interventional procedures. Entrance surface dose (ESD; 10.92-1062.55 mGy) was measured by thermoluminescence dosimetry (TLD). Absorbed dose was estimated using γ-H2AX focus frequency and gene expression, with in vitro dose-response curves generated for the same biomarkers. γ-H2AX foci in post-exposure samples were significantly higher than in pre-exposure samples. Among the genes analysed, FDXR, ATM, BCL2, MDM2, TNFSF9, and PCNA showed increased expression; CDKN1A, DDB2, SESN1, BAX, and TNFRSF10B showed unchanged or decreased expression. Absorbed dose, estimated based on γ-H2AX focus frequency and gene expression changes, did not show any correlation with measured ESD. Patients undergoing interventional procedures receive considerable radiation doses, resulting in DNA damage and altered gene expression. Medical procedures should be carried out using the lowest radiation doses possible without compromising treatment.

Studies on pelletised lithium magnesium borate TL material for eye lens dosimetry.

Recent epidemiological studies in various cohorts confirm that radiation induced cataract may occur at a threshold dose as low as 0.5 Gy. ICRP has recognised the higher radiosensitivity of eye lens and recommended to reduce annual eye lens dose limit from 150 to 20 mSv. Present dosimetry for eye lens is largely based on LiF based dosimeters. The present work is an attempt towards using near tissue equivalent lithium borate material namely lithium magnesium borate doped with terbium (LMB:Tb) in eye lens dosimetry. The material in powder form was synthesised using solid state sintering method and pelletised using poly tetra fluoro ethylene (PTFE) as binding agent. It was observed that 130 mg of 1 mm thick LMB:Tb pellet bound with PTFE showed stable glow curve structure and attractive dosimetric features in terms of sensitivity, fading, linearity, reusability etc. A proposal of 1.5 mm Teflon encapsulation corresponding to tissue equivalent thickness of 3 mm was put forward for an ideal dosimeter for the measurement in terms of Hp(3). Energy and angular dependence studies based on FLUKA simulations suggest a flat response for the prototype design. In addition to PTFE, various tissue equivalent encapsulations such as polyimide, polyamide 6 and PMMA were also evaluated using FLUKA code.

Radiation-induced defects in manganese-doped lithium tetraborate phosphor.

Lithium tetraborate doped with manganese synthesised by solid-state sintering technique exhibits a dosimetric peak at 280°C. The high-temperature glow curve results in no fading for three months. The sensitivity of Li2B4O7:Mn is determined to be 0.9 times that of TLD-100. The infrared spectrum of this phosphor indicates the presence of bond vibrations corresponding to BO4 tetrahedral and BO3 triangles. The mechanism for thermoluminescence in this phosphor was proposed based on the thermoluminescence (TL) emission spectra, kinetic analysis of TL glow curves and electron paramagnetic resonance (EPR) measurements on non-irradiated and gamma-irradiated phosphors. It was identified that oxygen vacancies and Boron oxygen hole centre (BOHC) are the electron and hole trap centres for TL in this phosphor. When the phosphor is heated, the electrons are released from the electron trap and recombine with the trapped holes. The excitation energy during the recombination is transferred to the nearby Mn(2+) ions, which emit light at 580 nm.

Synthesis and characterisation of BaSo4:Eu thermoluminescence phosphor.

Polycrystalline powder samples of BaSO(4) doped with Eu(2+) were prepared by solid-state reaction in different reducing atmospheres. Photoluminescence (PL), thermoluminescence (TL), TL kinetic and dosimetric studies have been carried out in this phosphor. The TL glow curve of BaSO(4):Eu(2+) showed only a single peak at 513 K unlike other phosphors and the TL intensity is about three to four times higher than that of CaSO(4):Dy, which is currently used as the radiation dosemeter for personnel monitoring in India. The TL dose response of the phosphor was found to be linear up to the dose range of 10(3) Gy beyond which saturation sets in. PL and TL spectra showed the characteristic emission of Eu(2+) ion. The TL parameters such as trap depth (E) or the energy required to release the electron or hole from the trap, frequency factor (s) and the order of kinetics (b) are determined by different methods such as isothermal decay, initial rise and variable heating rate.

High-sensitive CaSO4:Dy thermoluminescent phosphor synthesis by co-precipitation technique.

This paper describes the successful development of the co-precipitation technique for the preparation of a high-sensitive dysprosium-doped calcium sulphate (CaSO(4):Dy) thermoluminescent dosimetry (TLD) phosphor with dosimetric glow peak at approximately 230 degrees C which is a desired development in the field of radiation protection dosimetry. The main advantages of this co-precipitation technique over the conventional recrystallisation technique of phosphor preparation are: (i) preparation time is very less; (ii) quantity of sulphuric acid evaporated is insignificant; (iii) higher TL sensitivity -20% more than the present material; (iv) better glow curve structure; (v) lesser glow peak shift and better linearity to gamma and (vi) uniform crystal morphology and lower grain size-all grains are mostly cuboidal in shape, quite uniform and small (average size about 25 microm), suitable for manufacturing teflon discs in as-prepared form. Optimum values of various parameters in the method of preparation for a batch of 20 g CaSO(4):Dy phosphors to obtain maximum TL sensitivity, with favourable glow curves are studied.