Dose rate measurements with a ruby-based fiber optic radioluminescent probe

Fiber optic radioluminescence dosimetry allows real-time dose rate measurements in complex, narrow geometries and at places of high dose rates, without exposing the operator or the susceptible electronics. The keys are the spatial separation of radiation sensitive probe and electronic processing system and their optical connection by a flexible light guide. The small probes are capable of measuring fields of high dose rate gradients and the sealed probe-tip qualifies for applications in the fluid milieu and even for in-vivo-dosimetry. One problem of fiber optic dosimetry is the generation of Cherenkov radiation and fiber luminescence in the irradiated light guide, the so called stem effect. Ruby (Al₂O₃:Cr) has a narrow radioluminescent emission at 694 nm and is a potential luminophor for fiber optic radioluminescence dosimetry. In this work the influence of the stem effect on our ruby-based fiber optic dosimetry system is examined. The behavior of ruby probes under irradiation up to 0.5 kGy, as well as their luminescence decay characteristics and the applicability for measurements in radiotherapeutic fields are investigated.     

Radioluminescence (RL) behaviour of Al2O3:C-potential for dosimetric applications

The radioluminescence (RL) of carbon doped aluminium oxide (Al₂O₃:C) TL dosimeter material (TLD-500) was investigated using a ¹³⁷Cs conversion electron source (which also emits β and γ) for simultaneous irradiation and luminescence excitation. Furthermore, RL dosimetry characteristics of this material were studied. The main RL emission occurs at 420 nm. That matches the known main TL and OSL emissions for this material as well as an emission that was investigated in earlier RL studies, excited at higher energies (4 MeV electrons) and very high pulse delivered doses (≈800 kGy·s⁻¹). Furthermore, the saturation dose for the main peak is reached at the dose level of ≈80 Gy as known from TL and earlier RL investigations. Other peaks at 700 and 790 nm and broad emission bands at photon energies higher than 3.00 eV and others between 2.00 and 2.50 eV were observed. The 700 nm emission shows growth also at higher dose levels, and saturates at an estimated dose of ≈800 Gy. The 790 nm emission reaches its maximum intensity at ≈10 Gy absorbed dose. The reported results give an outlook to the usability and the potential of Al₂O₃:C combined with RL measurements for radiation dosimetry as well as for beta source calibration, using radioluminescence.     

α-and γ-irradiation of aqueous DNA solutions

A simple exposure system has been developed for α-irradiation of aqueous DNA solutions, utilizing α-particles from an ²⁴¹Am surface source emitting in vacuo. Care is taken for uniform irradiation of the liquid samples at a variety of dose-rates and reliable dosimetry. For α-dosimetry simple but accurate analytical LET-energy and range-energy relations for liquid water are proposed. For γ dosimetry energy transfer by electrons is considered.     

Gamma and enclosure dosimetry for TL/ESR dating with the new Al2O3: C TL dosemeter

Al₂O₃: C manufactured by LAIKS-CORUND, Ekaterinenburg, Russia, offers several advantages for the measurement of environmental radiation: stability, low self-dose, high sensitivity and energy deposition features under gamma and beta irradiation very similar to quartz and quartz-like TL minerals. In the present work those properties were tested for in situ gamma dosimetry, by comparison with other dosimetric techniques. It was confirmed that this phosphor is very well adapted to this purpose. On the other hand, the new alumina can be made insensitive to external alpha radiation by means of thermal treatments. This α-insensitized alumina is very interesting for enclosure dosimetry in the perspective of quartz inclusion dating. In this technique, the quartz grains to be dated are faithfully simulated by alumina: the phosphor allows us to measure directly the dose that would be experienced by quartz grains (HF etched, as usual). However, because the attenuation of beta radiation by coarse grains must be taken into account in inclusion dating, the role of this factor was theoretically and experimentally—with Al₂O₃—explored. The preliminary experiments indicated that enclosure dosimetry with this new alumina was a promising technique.     

Effects of ion beam irradiation on self-trapped defects in single-crystal Lu2SiO5

Ion irradiation effects on emission bands related to self-trapped defects in Czochralski-grown Lu₂SiO₅ (LSO) crystals has been investigated. Irradiation was carried out using 53 keV He⁺ and 40 keV H⁺ beams with doses of 1 and 2×10¹⁶ atoms/cm², respectively, at room temperature. Post-irradiation radioluminescence measurements were carried out in the 5-300 K temperature range using Mo-target X-ray excitation. Two emission bands were observed at 256 and 315 nm and assigned to self-trapped excitons (STE) and self-trapped holes (STH), respectively. The intensity of the bands was determined by the ballistic damage induced by irradiation, and no effects due to the chemical nature of implanted species were observed. Thermal-quenching activation energies of these defects as a function of irradiation conditions were extracted by applying the Mott-Seitz two-level model. Each band presents strikingly different behavior following irradiation; activation energy of the STH increases two-fold whereas the STE decreases three-fold. The results indicate a major role of surface effects on the radioluminescence of LSO. For comparative purposes, irradiated Lu₂O₃ was also investigated.     

Fiber-coupled Al2O3:C radioluminescence dosimetry for total body irradiations

In vivo dosimetry can be important and relevant in radiotherapy, especially when commissioning new treatment techniques at hospitals. This study investigates the potential use of fiber-coupled radioluminescence (RL) dosimetry based on Al₂O₃:C or organic plastic scintillators for this purpose in the context of Total Body Irradiations (TBIs) where patients are treated with large fields of 6 or 18 MV photons at an extended source-to-surface distance (SSD). The study shows that Al₂O₃:C dosimetry using the saturated-RL protocol may be suitable for real-time in vivo dosimetry during TBI treatments from the perspective of the good agreement with alanine dosimetry and other critical phantom tests, including the ability to cope with the large stem signal experienced during TBI treatments at extended SSD. In contrast, the chromatic stem removal technique often used for organic plastic scintillators did not work well in large fields with the tested calibration procedure and instrumentation. An apparent dose-rate effect discussed in a previous study of the RL properties of Al₂O₃:C (Andersen et al., 2011) was found to have resulted from an overlooked dead time problem in the counting system, and this potential caveat can therefore be removed from the list of potential problems associated with fiber-coupled Al₂O₃:C dosimetry using the saturated-RL protocol. This further has implications for TBI dosimetry using the RL Al₂O₃:C system due to large dose-rate differences between calibrations at the iso-center and in vivo measurements at extended source-to-surface distances.     

Thermoluminescence α-Al2O3:C detectors (TLD-500K): Some results of a long-term testing

Anion-defective α-Al₂O₃:C single crystals, commercially grown in Russia as TLD-500K detectors, have been increasingly used for environmental radiation measurements. These detectors have attracted great interest because of their high sensitivity and simple annealing procedure. The application of TLD for routine measurements in environmental monitoring, involving storage periods which may extend up to one year, imposes strict requirements on the fading, the change in sensitivity with long periods of time and other characteristics of the dosimeters. Many of these properties of TLD-500K have not yet been completely investigated and need to be further explored. This paper presents some results of long-term testing of the detectors. The variation in sensitivity within the detector group as well as changes of the sensitivity with time and number of read-outs were estimated. All tests were made by using low doses of irradiation, adequate for environmental dosimetry.     

Ion-beam irradiation effect on solid-phase growth of β-FeSi2

Effects of Ar⁺ ion-beam irradiation on solid-phase growth of β-FeSi₂ have been investigated. Fe (10 nm)/Si structures were irradiated with 25 keV Ar⁺ (5.0×10¹⁵ cm⁻²) at a temperature of 25°C (sample A) or 400°C (sample B), and subsequently annealed at 800°C. A reference was obtained after annealing without irradiation (sample C). X-ray diffraction results indicated that β-FeSi₂ was formed after annealing at 800°C for 5 h, and the formation rate was the fastest for sample A and the slowest for sample C, i.e., A>BC. However, Auger electron spectroscopy measurements showed that atomic mixing at Fe/Si interface before annealing was B>AC. These results suggested that amorphization of Si substrate, in addition to atomic mixing, enhanced the solid-phase growth of β-FeSi₂, which was confirmed experimentally. Moreover, a direct band gap of 0.89 eV was observed for the sample with pre-amorphization by the Fourier-transform infrared (FT-IR) spectroscopy measurements. These enhancement effects were attributed to that the phase transition to β-FeSi₂ was accelerated by atomic arrangement induced during annihilation of excess vacancies. These enhancement effects can be utilized for nano-fabrication of β-FeSi₂ by using focused ion-beam irradiation.     

Photochemical preparation of ZnO nanoparticles

Preparation of zinc oxide nanoparticles from aqueous solutions containing zinc nitrate or formate using UV irradiation was investigated. Analysis of solid phase formed during irradiation confirmed the presence of zinc oxide or zinc peroxide nanoparticles ranging in size from 1 to 70 nm, depending on initial precursors. Annealing at temperatures 650–1000 °C results in forming of rice-like zinc oxide particles, up to hundreds of nm in size. Photochemical method yields material with high chemical purity and uniform particle size distribution. In addition, photo-induced doping of zinc oxide with lanthanum was studied. Presence of lanthanum in zinc oxide crystal lattice and post-preparation treatment in reduction atmosphere significantly increase the UV excitonic luminescence at 395 nm in radioluminescence spectra.     

Real time dose rate measurements with fiber optic probes based on the RL and OSL of beryllium oxide

This work covers the examination of fiber optical probes based on the radioluminescence and real time optically stimulated luminescence of beryllium oxide. Experiments are carried out to determine the fundamental dosimetric and temporal properties of the system and evaluate its suitability for dose rate measurements in brachytherapy and other applications using non-pulsed radiation fields. For this purpose the responses of the radioluminescence and optically stimulated luminescence signal have been investigated in the dose rate range of 20 mGy/h to 3.6 Gy/h and for doses of 1 mGy up to 6 Gy. Furthermore, a new, efficient analysis procedure, the double phase reference summing, is introduced, leading to a real time optically stimulated luminescence signal. This method allows a complete compensation of the stem effect during the measurement. In contrast to previous works, the stimulation of the 1 mm cylindrical beryllium oxide detectors is performed with a symmetric function during irradiation. The investigated dose rates range from 0.3 to 3.6 Gy/h. The real time optically stimulated luminescence signal of beryllium oxide shows a dependency on both the dose rate and the applied dose. To overcome the problem of dose dependency, further experiments using higher stimulation intensities have to follow.     

α-and γ-irradiation of aqueous DNA solutions

A simple exposure system has been developed for -irradiation of aqueous DNA solutions, utilizing -particles from an ²⁴¹Am surface source emitting in vacuo. Care is taken for uniform irradiation of the liquid samples at a variety of dose-rates and reliable dosimetry. For -dosimetry simple but accurate analytical LET-energy and range-energy relations for liquid water are proposed. For γ dosimetry energy transfer by electrons is considered.     

Fiber-optic-coupled RbMgF3:Eu for remote radiation dosimetry

A portable fiber optic dosimeter has been developed that incorporates RbMgF₃:Eu²⁺ at the end of a multimode polymer fiber. It uses two stimulation sources and takes advantage of the range of stimulable traps in this compound. We observe radioluminescence (RL) during gamma ray irradiation and show that the low-dose RL increases linearly with increasing dose rate where the minimum detectible dose rate is ∼0.015 μSv/s. We show that pulsed infrared-stimulated (940 nm) optically stimulated luminescence (OSL) can be used for real time dose monitoring. The cumulative dose can be readout after irradiation where a linear OSL dose response was observed when stimulating at 505 nm and the minimum detectable dose is ∼50 μSv.     

Synthesis of ethyl α-cyanocinnamates under ultrasound irradiation

Knoevenagel condensation of ethyl cyanoacetate with aromatic aldehydes catalyzed by pyridine results ethyl α-cyanocinnamates in 80–96% yields under ultrasound irradiation.     

A TEM study of α-phase stability in Zr-2.5 Nb pressure tubes following neutron irradiation (A TEM study of α-phase stability)

The α-phase in Zr-2.5 Nb pressure tubes has been analysed after irradiation with neutrons for temperatures between 523 and 573 K. The α-phase contains Nb in supersaturated solid solution (about 0.5−1 wt% Nb) in the as-fabricated condition. Irradiation results in the formation of small discrete precipitates having diameters of about 5 nm. Energy Dispersive X-ray (EDX) analysis using a scanning transmission electron microscope (STEM) was complicated by the presence of a self-generated X-rays in the irradiated material and by the fact that the precipitates were small relative to the foil thickness (typically 100–200 nm). Techniques developed to measure segregation of impurities at interfaces were employed to show that the precipitates were Nb-rich, their formation being consistent with a decrease in Nb concentration in the matrix.     

Effect of γ-radiation on the birefringence of stretched polyethylene films

The spectral dependences of the birefringence and of the retardance of polyethylene films of thickness 67 μm exposed to γ-radiation doses up to 500 kGy are studied in the spectral range 400–700 nm. It is shown that the characteristics of polymeric polarization elements could be controlled by irradiation processes.     

Investigation of a fibre-coupled beryllium oxide (BeO) ceramic luminescence dosimetry system

The purpose of this study is to investigate the potential use of a beryllium oxide (BeO) ceramic as a radioluminescence (RL) and optically stimulated luminescence (OSL) probe material for fibre-coupled luminescence dosimetry. A portable dosimetry system, named RL/OSL BeO FOD was developed, consisting of a 1 mm diameter, 1 mm long BeO ceramic cylinder coupled to a silica/silica optical fibre. The reader measures the RL signal and also uses a 450 nm laser diode to stimulate the BeO ceramic. A second background optical fibre is used to remove the stem effect. The RL/OSL BeO FOD was characterised in a solid water phantom, using a 6 MV x-ray beam. The RL was found to be reproducible and have a linear response to doses ranging from 30 cGy–15 Gy and dose rates from 100 cGy/min – 600 cGy/min. The OSL response was linear to doses of 10 Gy, becoming supralinear at higher doses. Measured percentage depth curves using the RL/OSL BeO FOD agreed with those measured using an IC15 ion chamber to within 5%, beyond the build up region. It was also found that the RL from BeO ceramic is unaffected by the delivered dose to the probe and hence, it remains constant for a given dose-rate. The insensitivity of the RL to accumulated dose makes BeO ceramic potentially capable of accurate dose-rate measurements without any corrections for the accumulated dose. This study demonstrates the feasibility of BeO ceramic as a versatile fibre-coupled luminescence dosimeter probe.     

Radiofrequency-Driven and Slow-Magic-Angle-Sample-Spinning Polarization-Transfer Techniques: A Comparative Study

The rate constant of radiofrequency-driven (RF-driven) polarization transfer and that of polarization transfer under slow-magic-angle sample spinning (S-MAS) are compared using a model system, polycrystalline α-α′-¹³C₂-phthalic acid. While the rate constant under RF irradiation in static samples strongly depends on the orientation of the internuclear vector, the rate constant under S-MAS is hardly sensitive to that orientation and, thus, depends almost exclusively on the internuclear distance. Consequently, polarization-transfer rate constants obtained under S-MAS can be interpreted more simply when used to study local order in polycrystalline or amorphous solids.     

Radioluminescence of LiF:Mg,Ti induced by 4 MeV electrons

This paper reports on the radioluminescence characteristics of LiF:Mg,Ti induced by 4 MeV linear accelerator electrons. The main emission peak of the luminescence is found at 410 nm, but weaker emission occurs around 320, 360, 460, 520 and 560 nm as well. The relative intensities of the emission bands show a strong dependence on the Mg concentration of the sample. The radioluminescence signal reaches its maximum typically 1.5 ms after the irradiation pulse, and decays with a half-life of 4–6 ms. Both the build-up time and the half-life decreases with increasing Mg concentration. The luminescence yield shows a strong dependence on the irradiation dose.     

Determination of microquantities of Be in samples using α-sensitive track etch detectors

A new technique of determining Be content in samples using 4.66 MeV γ-rays is proposed. This energy range is sufficient to knock out the neutron from the ⁹Be nucleaus and to excite the first 2.9 MeV level of the ⁸Be nuclei. 1.5 MeV alpha particles are registered by means of CR-39 or cellulose nitrate detectors. Alpha particles produced in the reaction of γ-rays with Li nuclei which are contained in samples may cause the background. The latter is excluded by heating of samples before irradiation for Li molecules to be evaporated. ¹¹B nuclei do not produce alpha particles at the energy range of γ-rays presented above.The results obtained in the experiments of determining Be content in natural beryl crystal samples are in good agreement with their known chemical composition. Microparticles containing Beryllium were found in soil samples from the Ust-Kamenogorsk are deposit region, which contains 10⁻³ − 10⁻⁴ g/g of Be. The sensitivity of the method is 10⁻⁶ g/g of Be in solids.     

Ultrasound-promoted a green protocol for the synthesis of 2,4-diarylthiazoles under ambient temperature in [bmim]BF4

A mild, efficient, facile and eco-friendly procedure for the synthesis of 2,4-diarylthiazoles from arylthioamides and α-bromoacetophenones in 1-n-butyl-3-methylimidazolium tetrafluoroborate as a “green” media under ultrasound irradiation at room temperature is described. It is interesting to mention that only one product was obtained when two different α-bromoacetophenones were reacted with 1,3-phenyl dithioamide as the substrate. Work-up is very simple and there is no need to purify the product. A recycling study confirmed that the ionic liquid can be reused multiple times without a significant loss in its activity.