Cessation Of Irradiation Research Articles

Influence of gamma radiation on the composition and physicochemical characteristics of olefins: post-radiation effects

The effect of gamma radiation on olefins was studied under static conditions at an absorbed dose of 65 kGy and at a dose rate ofP= 0.076 Gy/s. The effect of radiation on the physicochemical characteristics and structural and group composition of the resulting olefins has been established. Post-irradiation effects were studied immediately after irradiation and during 1, 2, 4, and 7 months later. When fuels are irradiated, polymerization of unsaturated hydrocarbons occurs. After cessation of irradiation, the postpolymerization process occurs The chemical instability of olefins in fuels leads to the formation of carbon deposits in the engine system, tanks, and valves. IR spectra, iodine values, density, and kinematic viscosity of irradiated samples were measured.

Red Persistent Luminescence and Trap Properties of Mg2SiO4: Mn2+, M3+ (M3+ = B3+; Al3+; Ga3+; In3+) Material

Abstract Persistent luminescence (PersL), also called long-lasting phosphorescence or simply afterglow, is a luminescence characterised by the emission of radiation from a few seconds to several days after the excitation source has been switched off. Over the past two decades, research on PersL materials, both in fundamental and applied physics, has developed rapidly; however, the explanation for the physical processes that cause afterglow still needs to be clarified. Today, PersL materials are used mainly for luminescent paints, safety signs and decorations. At the same time, research into using such materials in medicine, information storage, anti-counterfeiting technology, etc., is underway. Currently, information on the long persistent luminescence materials with emission in the blue and green spectral range is widely available. In contrast, the number of publications on the afterglow in the red and near-infrared spectral range is considerably lower. Within the framework of this research, Mg2SiO4: Mn2+; M3+ (M3+ = B3+; Al3+; Ga3+; In3+) materials were synthesised using solid state reaction synthesis. When excited with X-rays, the materials exhibited a broad Mn2+ PersL band with two maxima at approximately 625 nm and 730 nm. After cessation of irradiation, an afterglow of at least 6 hours could be observed. The research focuses on the trap properties of the materials. It was concluded that at least three discrete trap levels with activation energies approximately between 0.4–1.6 eV were present in the samples. Additionally, co-doping with Al3+; Ga3+; In3+ ions improved PersL longevity of the Mg2SiO4: Mn2+ material.

Photopolymerization-induced phase separation kinetics explored by intermittent irradiation

In this work, we explore the kinetics of the photopolymerization-induced phase separation (photo-PIPS) process and the interplay of mechanisms controlling the development of the microstructure in a photosensitive resin comprised of pentaerythritol tetraacrylate (PETA) and 2-ethylhexyl methacrylate (2-EHMA) monomers with polypropylene glycol (PPG, Mn = 4000 g/mol) linear polymer additive and diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO) photoinitiator. We control the kinetics of photopolymerization by interrupting the irradiation at various stages of the process and varying the light intensity. Evolution of the microstructure is monitored by transmittance testing and scanning electron microscopy (SEM) inspection of fractured surfaces that are exposed to methanol for the purpose of removing the phase-separated PPG content. The evolution of the network is monitored by real-time Fourier-transform infrared (FTIR) spectroscopy during irradiation and intermittent probing after the cessation of irradiation. Three mechanisms controlling the evolution of the microstructure are identified: phase separation, photoinitiator consumption, and microstructural refinement. Phase separation begins immediately after the onset of network development and leads to a rapid reduction of transmittance due to the formation of PPG-rich subdomains. Microstructural refinement takes place at later stages leading to a reduction of these subdomains, a gradual increase of the PPG concentration within subdomains and an associated increase of transmittance. TPO consumption takes place during irradiation and accounts, to a smaller extent, for the recovery of the transmittance. Interrupting the irradiation allows generation of materials with various degrees of conversion and sizes of phase-separated subdomains, which provides a new way to control material properties.

Visible-Light Photoinitiation of (Meth)acrylate Polymerization with Autonomous Post-conversion.

Conversion plateaus rapidly in radical photopolymerizations (RPPs) following discontinuation of irradiation due to rapid termination of reactive radicals, which restricts the wider use of RPPs in applications that involve nonuniform light access including those with attenuated light transmission or irregular surfaces. Based on our recent report of a radical dark-curing photoinitiator (DCPI) that continues polymerization beyond the cessation of irradiation by enabling latent redox initiation with photo-released amine in the presence of a suitable oxidant, we developed a new DCPI with an absorption spectrum that extends well into the visible range. Our design process involved a series of computational investigations of candidate molecules, including a systematic study of substituents and their position-dependent effects on absorption characteristics, electronic transitions, and the photochemical mechanism and its associated energetics. Our quantum chemical computations identified the target compound 5,7-dimethoxy-6-bromo-3-aroylcoumarin-DMPT/BPh4 and predicted that it would facilitate the dark-curing mechanism by concurrent photo-radical generation and photo-induced release of an efficient redox reductant under visible irradiation. This reductant-tethered chromophore was then synthesized and optically characterized with UV-vis spectroscopy that revealed its strong visible-light absorption with a molar absorptivity of 5710 M-1 cm-1 at 405 nm and 50 M-1 cm-1 at 455 nm. We then demonstrated extensive dark-curing of >35% additional conversion over 25 min following brief activation of the shelf-stable one-part system by irradiation with a 455 nm LED that was ceased at 20% conversion. In contrast, shuttering irradiation of the control formulation at that same point resulted in immediate cessation of conversion, which plateaued at 20%. We determined a remarkable initiator efficiency of 2.82 that results from the additional redox-generated radicals with a 77% photo-reductant generation quantum yield. The combination of superior photo- and dark-curing efficiencies of this new visible DCPI is expected to open new application opportunities in RPP, especially those involving resins that are highly light attenuating, surfaces that possess irregular features that produce uneven irradiance, and production lines where continued dark-curing downstream of the light activation step enhances line efficiencies.

UV and X-ray excited red persistent luminescence in Mn2+ doped MgGeO3 material synthesized in air and reducing atmosphere

Materials with long persistent luminescence (PersL) have caused widespread interest among scientists and industry for decades. Currently, there is widely available information on the long persistent luminescence materials with emission in the blue and green spectral range, while the number of publications on the afterglow in the red and near-infrared spectral range is considerably lower. In the course of this work MgGeO3 material doped with 0.1 mol% Mn2+ was produced using solid-state reaction synthesis in ambient and reducing atmospheres. The material exhibits a broad luminescence band with a peak around 680 nm, excited by either X-rays or UV. After cessation of irradiation, the afterglow up to 6 h when excited by UV and 15 h in the case of excitation by X-rays can be observed. Decay kinetics of the samples indicate that persistent luminescence in this material is a complex process that includes several different traps. Different thermally stimulated luminescence (TSL) techniques, such as Tstop – Tmax and Hoogenstraaten's methods were employed to draw conclusions about the nature of the traps and properties of the material. It was concluded that multiple traps with activation energy between 0.60 and 1.55 eV are present in the samples, furthermore the synthesis in reducing atmosphere promotes creation of additional closely overlapping deep traps, which, based on electron paramagnetic resonance (EPR) measurements, most likely are related to oxygen vacancies.

Analysis of Phototherapy Effectiveness Using Thermography

A thermographic study of low-intensity phototherapeutic effects on the human body in situ was carried out. The feature of the work was the measurement of the dynamics of surface temperature changes in a bio-object for 40 min after the cessation of irradiation. The relaxation character of the temperature behavior with quasi-oscillating phenomena during the selected observation period has been established. An explanation of the observed phenomena with the involvement of literature data is proposed. It is shown that 15-min irradiation at a radiation intensity of 14mWcm−2 is optimal for phototherapy at a wavelength of 640 nm. A conclusion was made about the possibility of considering changes in the local temperature of a bio-object as a correlated parameter to determine the optimal dose of radiation during phototherapy.

Dark current–voltage characteristics of vacuum deposited multilayer amorphous selenium-alloy detectors and the effect of x-ray irradiation

Doped and stabilized amorphous selenium (a-Se) alloys in a multilayer form are currently used as a photoconductor in direct conversion flat panel x-ray imagers in mammography and tomosynthesis. While much progress has been made on the physics of such detectors, there are still unresolved questions on such issues as the principles of operation of the so-called p-i-n detector structure in extinguishing the dark current. The present paper examines dark current transients after the application of a voltage in seven types of a-Se alloy based devices: i-layer, i-n, n-i, i-p, p-i, p-i-n, and n-i-p structures. The substrate was ITO coated glass, the top (radiation receiving) electrode was chromium, and the films were fabricated by vacuum deposition. The nominal device thickness was 200 μm, similar to commercial mammographic detectors. It is shown that n-i, i-n, n-i-p, and p-i-n devices have dark currents less than 1 pA mm−2 at an applied field of 10 V/μm. The dark current in the p-i-n device is the lowest at approximately 0.01 pA mm−2 at an applied field of 10 V μm−1. Experiments have been carried out by subjecting the detector to a staircase voltage-time profile during the voltage application (turn-on) and a staircase voltage ramp-down during the turning-off of the bias voltage. Step-voltage ramp-up and step-voltage ramp-down current transient are typical of expected dark current transient behavior in a semiconductor with traps in which carriers are captured and released from various trap centers in the bandgap. The dark current transients are qualitatively similar to those expected from a capacitor in parallel with a large resistor and both in series with a much smaller resistor. Current transients during charging and discharging experiments were integrated to find how much of the injected charge is released during discharge experiments. It is shown that the majority of this trapped charge is stored in the n-type and p-type blocking layers, near the contacts. The trapped carriers in the i-layer represent a very small portion. The evolution of the dark current upon single and repeated x-ray exposure has also been examined in n-i and p-i-n devices. Right after the cessation of irradiation, there is an excess or residual dark current whose magnitude is roughly ∼20 times higher in p-i-n and about ∼2 times higher in the case of n-i under an exposure of 3.36 R and a mean photon energy of 34.2 keV. The absorbed dose is 1.53 Gy. The excess dark current has a fast decay component with a time constant ∼10 s and a slow component with a time constant ∼100 s. It is shown that the decay in the irradiation induced excess dark current is very similar to the initial dark current. There is no permanent change in the dark current, and within a few hundred seconds, the dark current reaches the same level as that in the unexposed detector. The experimental results in this work highlight the distinct advantages of p-i-n and n-i-type a-Se multilayer structures in x-ray detection applications.

Simulation of photodynamically-induced thrombosis of the femoral vein of rats

The purpose of the work is to determine the conditions that ensure the formation of a stable thrombus in the femoral vein of rats with photodynamic damage.Material and methods. The experiments were carried out on male Wistar rats weighing 250–270 g. A photosensitizer (FS) Bengal rose (ACROS ORGANICS, USA) (BR) was administered intravenously at a dose of 17 mg/kg and after 60 minutes a vascular clamp was applied to the femoral vein. Distal to clamping, a 30-minute laser irradiation of a vein was performed (DPSS diode laser, Republic of South Korea, 532 nm, 60 mW, irradiation area – 1 mm2 ). The clamp was removed after 90 min after cessation of irradiation. The blood flow was recorded by the method of high-frequency Doppler ultrasound (MinimaxDoppler-K Russia). Cessation of blood flow was considered as an indicator of occlusion of femoral vein.Results. Rats, after the clamp was removed, had no blood flow in the irradiated veins, and after 24 hours it was not restored. Histology revealed severe damage of all layers of the vascular wall and the formation of a blood clot filling the lumen of the vessel. After a 30-minute irradiation without clamping the vein, the blood flow was maintained, although damage to the vascular wall was detected. Introduction of BR and clipping of the vessel without irradiation caused minimal damage to the vascular wall and did not lead to thrombosis.

Stress evolution in Si during low-energy ion bombardment

Abstract

Ultrasonic cavitation of molten gallium: Formation of micro- and nano-spheres

Pure gallium has a low melting point (29.8°C) and can be melted in warm water or organic liquids, thus forming two immiscible liquid phases. Irradiation of this system with ultrasonic energy causes cavitation and dispersion of the molten gallium as microscopic spheres. The resultant spheres were found to have radii range of 0.2–5μm and they do not coalesce upon cessation of irradiation, although the ambient temperature is well above the m.p. of gallium. It was found that the spheres formed in water are covered with crystallites of GaO(OH), whereas those formed in organic liquids (hexane and n-dodecane) are smooth, lacking such crystallites. However, Raman spectroscopy revealed that the spheres formed in organic liquids are coated with a carbon film. The latter may be the factor preventing their coalescence at temperatures above the m.p. of gallium.

Effect of Cross-Link Density on Photoplasticity of Epoxide Networks Containing Allylic Dithioether Moieties

A new diepoxide monomer (ADTDE) containing an allylic dithioether moiety has been synthesized to extend the suite of monomers that form networks exhibiting radical-mediated photoplasticity. These cross-linked polymers show permanent shape change under load and stress relax only when under the stimulus of visible or UV radiation. The Lewis base-catalyzed reaction of the epoxide groups in ADTDE with tri- and tetrafunctional thiols was monitored by differential scanning calorimetry and infrared spectroscopy. These curing systems were found to be more efficient than anionic, cationic, or anhydride polymerizations. The dynamic mechanical thermal analysis of ADTDE with the tetrathiol showed that the network was rubbery at room temperature which is considered ideal for the demonstration of photoplasticity. The photoinduced creep behavior was shown to be controlled by the presence of active free radicals in the matrix—on cessation of irradiation, the creep was terminated. The stress relaxation of the stretched ne...

Ignition and extinction of homogeneous energetic materials by a light pulse

Numerical calculations using a model of unsteady combustion of melting energetic materials were performed to simulate the results of qualitative experiments on the ignition and quenching of energetic materials by a light pulse. The parameters of the model composition were chosen to correspond to combustion with the burning-rate control reaction in the gas phase to ensure the stability of self-sustained combustion after the cessation of irradiation. Regions of stable ignition in the coordinates “radiant flux amplitude-irradiation time” were obtained for compositions with different transparency for igniting pulses of three shapes: rectangular, linearly decreasing to zero, and exponentially decreasing. Extinction conditions of the steadily burning composition by a rectangular light pulse were calculated.

Heterogeneous thermoradiation processes for hydrogen production from steam

A experimental flow unit for investigation of the radiation-catalytic decomposition of gases and liquids over the temperature range of 50–500°C in a 60Co γ-radiation field was designed and fabricated. The process of radiation-catalytic decomposition of steam in the presence of solids with different chemical compositions and structures was studied. The effect of the dose rate and the contact time of the reaction mixture with the solid on the rate of hydrogen formation was revealed. It was shown that the hydrogen formation efficiency decreases after cessation of irradiation.

Effect of a Prostaglandin – Given Rectally for Prevention of Radiation-Induced Acute Proctitis – on Late Rectal Toxicity

To assess the late effect of a prostaglandin, given rectally during irradiation, on late rectal toxicity. In the acute treatment setting no significant differences in reducing the incidence of acute proctitis symptoms in patients receiving misoprostol, however, significantly more rectal bleeding had been reported. A total of 100 patients who had undergone radiotherapy for prostate cancer had been entered into this phase III randomized, placebo-controlled, double-blind study with misoprostol or placebo suppositories. The toxicity was evaluated yearly after cessation of irradiation by the RTOG/LENT-SOMA scale. The median follow-up was 50 months. 20 patients suffered from grade 1, four patients from grade 2 as well, and three patients only from grade 2 toxicity. Frequency, bleeding and urgency were the most commonly reported symptoms. In keeping with other studies and clinical experience, the symptoms peaked within the first 2 years with a median for grade 1 of 13 months and for grade 2 of 15 months. The presence of acute toxicity grade 2 showed a correlation with the development of any late toxicity (p = 0.03). Any acute rectal bleeding was significant correlated with any late rectal bleeding (p = 0.017). Misoprostol given as once-daily suppository for prevention of acute radiation-induced proctitis does neither influence the incidence and severity of radiation-induced acute nor late rectal toxicity. Misoprostol has no negative impact on the incidence and severity of late rectal bleeding, in contrast to acute rectal bleeding. The routine clinical use of misoprostol suppositories cannot be recommended.

Photopolymerization of Vinyl Ether Networks Using an Iodonium Initiator: Effect of Radiation Intensity and Iodonium Concentration

Photo-differential scanning calorimetry (photo-DSC) was used to investigate the photocuring kinetics of visible light initiated cationic photopolymerization of triethylene glycol divinyl ether (TEGDVE) with a diphenyl iodonium salt initiator and the three photosensitizers: 1-chloro-4-propoxy-9H-thioxanthen-9-one (CPTXO), camphorquinone (CQ), and acridine orange (AO). The effects of water, a tertiary amine, and a radical scavenger were used to probe the photocuring mechanism. The rate of photopolymerization was approximately proportional to the incident light intensity, and in each system, the final conversions, as measured by photo-DSC, also increased with raised incident light intensity. The power-law dependence of the reaction rate on the concentration of iodonium salt with CPTXO and AO was ∼1.5, while the order is nearly unity with CQ as the photosensitizer, suggesting that these photosensitizers do not follow the same sensitization mechanism. For the three photosensitizers, the final conversions all increased with higher iodonium salt concentrations. After cessation of irradiation, a dark reaction was observed—although the rate of this process decreased rapidly with time (as shown by photo-DSC), the polymerization continued very slowly over a long period of time.

Simultaneous photocharging and luminescence intermittency in silicon nanocrystals

Contemporaneous measurements of the time dependence of photoluminescenceand concomitant electrical conduction in films of alkylated silicon nanocrystals(NCs) during and between periods of continuous-wave laser irradiation of arbitraryduration establish the role played by photoionization to a conducting state in theintermittent light emission from silicon nanocrystals. The luminescence and currentgenerated by electron photoejection both decay to non-zero, steady-state valuesduring irradiation with visible laser light at incident intensities in the range 0.25–0.30 ± 0.01 kW cm−2; on cessation of irradiation, the non-conducting photoluminescent state of the NCs issubstantially regained. These observations are consistent with a model in which the decay ofphotoluminescence is ascribed to autoionization of the silicon NCs with a most probable lifetime⟨Ta⟩, depending on particle size, and recovery of luminescence toelectron–hole recombination characterized by a most probable lifetime⟨Teh⟩. Valuesof ⟨Ta⟩ = 1.08 ± 0.03 s and ⟨Teh⟩ = 770 ± 300 s are extracted from nonlinear least-squares fitting to the time dependence of thephotoluminescence intensity. The temporal behavior of the transient photocurrent is foundto be quantitatively consistent with a one-dimensional model of diffusion of charge carriersbetween NCs. Integration of the time dependence of the photocurrent response coupledwith an estimate of the volume irradiated with the laser light suggests ionization of oneelectron per NC during photon irradiation.

Immunohistochemical survey of the distribution of epidermal melanoblasts and melanocytes during the development of UVB-induced pigmented spots

Repeated exposures to ultraviolet B radiation (UVB) induce pigmented spots on dorsal skin of (HR-1 x HR/De) F(1) hairless mouse. We showed previously that this mouse is suitable for studies of melanocyte function. To clarify the mechanism of development of pigmented spots induced by chronic UVB exposure. We used light and fluorescence microscopy to quantify changes in the numbers of differentiated melanocytes containing melanin pigments (MM) and melanoblasts/melanocytes immunohistochemically positive for tyrosinase-related protein (TRP)-1, TRP-2 (dopachrome tautomerase), and c-kit in epidermis during the development of pigmented spots in hairless mice chronically exposed to UVB (99 mJ/cm(2), 3 times/week, 8 weeks). The change in the number of TRP-1-positive cells during chronic UVB exposure was similar to that of MM: both increased dramatically during the stage of acute pigmentation, then decreased sharply after cessation of UVB, concomitantly with depigmentation; subsequently they increased gradually with the development of pigmented spots. In contrast, after two UVB exposures, no c-kit-positive cells were detected, then the number gradually increased during UVB irradiation, and continued to increase after cessation of irradiation; TRP-2-positive cells showed a rather similar pattern, except that they did not disappear initially. Our results indicate that chronic UVB irradiation induces differentiation and proliferation of melanoblasts, followed by an increase of differentiated melanocytes, leading to the development of pigmented spots. The sequence of expression of markers appeared to be c-kit, TRP-2, TRP-1, and finally melanin, as it is during normal melanocyte differentiation.

Effect of 14-MeV neutrons on strontium–aluminate-based long-lasting phosphor

Long-lasting phosphor (LLP) emits photons for a long period of time after the cessation of irradiation without external excitation. LLP exhibits not only a long-lasting emission but also strong fluorescence. The fluorescence and long-lasting emission properties of two types of strontium-aluminate-based LLPs – SrAl 2O 4:Eu 2+, Dy 3+ and Sr 4Al 14O 25:Eu 2+, Dy 3+ – are examined under 14-MeV neutron irradiation. The fluorescent spectra of the LLPs have characteristic peaks due to their dopants and the fluorescent intensity of Sr 4Al 14O 25:Eu 2+, Dy 3+ shows good radiation resistance for the neutrons, with a slight change after increasing the irradiation fluence up to 10 19 n/m 2. Long-lasting emissions are exhibited after neutron irradiation, and the emission spectra have one peak due to Eu 2+. A peak due to Dy 3+ ends immediately when the irradiation is stopped. Further, it is found that there is an optimum neutron fluence at which the longest decay time is obtained.

Two Stage Colour Modulation of Triarylmethine Dyes Derived from a Photochromic Naphthopyran

AbstractThe synthesis of the unsymmetrical triarylmethine dyes 4derived from a lithiated naphthopyran and diaryl ketones is reported. In toluene solution 4 display a typical reversible photochromic response becoming coloured upon irradiation with UV light and fading upon cessation of irradiation. At low pH an intensely coloured dye cation is generated and UV irradiation of this solution results in a further colour change as a consequence of photochromic cycling of the naphthopyran unit.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Granulosa cell tumor. The results of postoperative irradiation

Postoperative irradiation was done in 12 female patients with granulosa cell tumours between 1962 and 1981. The average follow-up period was 10 years and 10 females were alive without evidence of renewed tumour growth. A further patient died of cardiac infarction after 7 years. At the time of death she was free of recurrence or metastases. Only in one case multiple filiae developed in the lung, liver and skeleton 8 months after cessation of irradiation. The progression of these could not be arrested. Following the first therapeutic step, i.e. abdominal hysterectomy and bilateral adnectomy , radiotherapy represents an important additional therapeutic measure. Thus the unfavourable long-term prognosis of granulosa cell tumours can be beneficially influenced particularly in far-advanced cases or in recurrences.