kV Energy Research Articles

555 Practice changing landmark study- multi-institutional analysis of image guided superficial radiotherapy (IGSRT) for the treatment of non-melanoma skin cancer (NMSC)

Practice changing landmark study- multi-institutional analysis of image guided superficial radiotherapy (IGSRT) for the treatment of non-melanoma skin cancer (NMSC). NMSC is generally treated in dermatology offices using surgical techniques. This study presents the largest multi-institutional retrospective modern series of Image Guided Superficial Radiotherapy (IGSRT) for Non-Melanoma Skin Cancer (NMSC). Between July 2013 and December 2019, 2424 NMSC lesions treated with IGSRT at 3 clinics in Texas and 1 clinic in NY were analysed. All lesions received 50, 70 or 100 kiloVoltage(kV) energy IGSRT 2-4 times weekly. KV energy selection was determined by ultrasound depth measurements and/or tumor characteristics. Patients returned 3-6 weeks after completion of therapy for dermoscopy/clinical evaluation and ultrasound imaging to confirm complete tumor clearance. Patients were then followed every 2-12 months thereafter. Any lesions in the treatment site suspicious for residual or recurrent tumor were biopsied. Exclusion criteria included tumors greater than 4 cm in diameter or non-movable tumors adherent to deeper structures. Follow-up ranged from 0.1-62.8months. At a mean follow up of 15.8 months, 29 patients with 77 lesions expired, all without recurrence. Kaplan-Meier (KM)Tumor control rates at 1, 2 and 5 years were 99.5%, 99.4% and 99.4% respectively. One, 2 and 5 year KM Overall-Survival (OS) for the entire group was 97.6%, 95.8% and 85.8% and unaffected by disease status or treatment. This study represents the largest study of NMSC treated with non-invasive IGSRT. The 99% cure rate is comparable to the best cure rates of other invasive modalities such as Mohs micrographic surgery. This innovative non-surgical technology with its high cure rate in the treatment of NMSC has the potential to transform the practice of dermatology with regard to treatment of NMSC.

Transmission Electron Microscope Using a Linear Accelerator.

High-voltage transmission electron microscopes (HVTEMs), which can visualize internal structures of micron thick samples, intrinsically have large instrument sizes because of the static voltage isolation. In this Letter, we develop a compact HVTEM, employing a linear accelerator, a subpicosecond beam chopper, and a linear decelerator. 100kV electrons initially accelerated by a static field are accelerated at radio frequency (rf) up to 500kV, transmitting through the sample and finally rf decelerated down to 200kV to be imaged through a 200kV energy filter. 500kV imaging, as well as subnanometer resolution at 200kV, have been demonstrated.

Dose to water versus dose to medium from cavity theory applied to small animal irradiation with kilovolt x-rays

Dose reporting is a matter of concern in the preclinical field as the different dose descriptors dose-to-water-in-medium and dose-to-medium-in-medium coexist. For kV photons differences between both quantities are expected to be amplified due to photon energy absorption coefficients differences for different media, and could represent a limiting factor for accurate translation of pre-clinical research into clinical trials. The main goal of this study was to analyse the relationship between and for kV irradiation of small animals, using different flavours of the intermediate cavity theory (ICT).Irradiations of mathematical phantoms and a mouse CT scan, both with different voxel sizes and materials, were investigated. A modified version of the Monte Carlo code DOSXYZnrc was used to derive and convert to using ICT. Local photon spectra were generated in different regions of the mouse.Depending on energy and cavity size, which we equate to the voxel size, ranged from 0.68 to 4.37 times . Higher kV energy combined with very small cavity sizes yielded decreased in comparison to ; this behaviour was reversed for larger cavities combined with lower kV energies. Hence, the impact of the cavity dimensions on estimated is significant on pre-clinical kV beams. and in the ex vivo male mouse were found to differ by −29% to 286%. Caution is advised when using the ICT due to a lack of consensus on weighting factor (d-parameter) deriving methods; for the same irradiation conditions, different d-values affected up to 20%. Pre-clinically, such divergence between dose descriptors could enable biological damage.The abiding debate over which quantity to favour is foreseen to linger while it is unclear which quantity correlates better with the biological effects of ionizing irradiation: preclinical radiotherapy might represent an ideal platform for measurement-based studies to settle this fundamental question. Finally, dose distribution comparisons require caution and should use the same reporting quantity.

Feasibility of multi‐contrast imaging on dual‐source photon counting detector (PCD) CT: An initial phantom study

Photon-counting-detector-computed tomography (PCD-CT) allows separation of multiple, simultaneously imaged contrast agents, such as iodine (I), gadolinium (Gd), and bismuth (Bi). However, PCDs suffer from several technical limitations such as charge sharing, K-edge escape, and pulse pile-up, which compromise spectral separation of multi-energy data and degrade multi-contrast imaging performance. The purpose of this work was to determine the performance of a dual-source (DS) PCD-CT relative to a single-source (SS) PCD-CT for the separation of simultaneously imaged I,Gd, andBi contrast agents. Phantom experiments were performed using a research whole-body PCD-CT and head/abdomen-sized phantoms containing vials of different I, Gd, Bi concentrations. To emulate a DS-PCD-CT, the phantoms were scanned twice on the SS-PCD-CT using different tube potentials for each scan. A tube potential of 80kV (energy thresholds=25/50keV) was used for low-energy tube, while the high-energy tube used Sn140 kV (Sn indicates tin filter) and thresholds of 25/90keV. The same phantoms were scanned also on the SS-PCD-CT using the chess acquisition mode. In chess mode, the 4×4 subpixels within a macro detector pixel are split into two sets based on a chess-board pattern. With each subpixel set having two energy thresholds, chess mode allows four energy-bin data sets, which permits simultaneous multi-contrast imaging. Because of this design, only 50% area of each detector pixel is configured to receive photons of a pre-defined threshold, leading to 50% dose utilization efficiency. To compensate for this dose inefficiency, the radiation dose for this scan was doubled compared to DS-PCD-CT. A 140kV tube potential and thresholds=25/50/75/90keV were used. These settings were determined based on the K-edges of Gd, andBi, and were found to yield good differentiation of I/Gd/Bi based on phantom experiments and other literature. The energy-bin images obtained from each scan (scan pair) were used to generate I-, Gd-, Bi-specific image via material decomposition. Root-mean-square-error (RMSE) between the known and measured concentrations was calculated for each scenario. A 20-cm water cylinder phantom was scanned on both systems, which was used for evaluating the magnitude of noise, and noise power spectra (NPS) of I/Gd/Bi-specific images. Phantom results showed that DS-PCD-CT reduced noise in material-specific images for both head and body phantoms compared to SS-PCD-CT. The noise level of SS-PCD was reduced from 2.55 to 0.90mg/mL (I), 1.97 to 0.78mg/mL (Gd), and 0.85 to 0.74mg/mL (Bi) using DS-PCD. NPS analysis showed that the noise texture of images acquired on both systems is similar. For the body phantom, the RMSE for SS-PCD-CT was reduced relative to DS-PCD-CT from 10.52 to 2.76mg/mL (I), 7.90 to 2.01mg/mL (Gd), and 1.91 to 1.16mg/mL (Bi). A similar trend was observed for the head phantom: RMSE reduced from 2.59 (SS-PCD) to 0.72 (DS-PCD) mg/mL (I), 2.02 to 0.58mg/mL (Gd), and 0.85 to 0.57mg/mL (Bi). We demonstrate the feasibility of performing simultaneous imaging of I,Gd, andBi materials on DS-PCD-CT. Under the condition without cross scattering, DS-PCD reduced the RMSE for quantification of material concentration in relative to a SS-PCD-CT system using chess mode.

Commissioning and performance characteristics of a pre-clinical image-guided radiotherapy system

Characteristics of a small-animal radiotherapy device, the X-RAD SmART, are described following commissioning of the device for pre-clinical radiotherapy research. Performance characteristics were assessed using published standards and compared with previous results published for similar systems. Operational radiation safety was established. Device X-ray beam quality and output dose-rate were found to be consistent with those reported for similar devices. Output steadily declined over 18 months though remained within tolerance levels. There is considerable variation in output factor across the international installations for the smallest field size (varying by more than 30% for 2.5 mm diameter fields). Measured depth dose and profile data was mostly consistent with that published, with some differences in penumbrae and generally reduced flatness. Target localisation is achieved with an imaging panel and with automatic corrections for panel flex and device mechanical instability, targeting within 0.2 mm is achievable. The small-animal image-guided radiotherapy platform has been implemented and assessed and found to perform as specified. The combination of kV energy and high spatial precision make it suitable for replicating clinical dose distributions at the small-animal scale, though dosimetric uncertainties for the narrowest fields need to be acknowledged.

Improvement of dose delivery with loading of tumor with gold nanoparticles in orthovoltage radiotherapy

Introduction: To enhance the dose to tumor, the use of high atomic number elements has been proposed. Objective: The aim of this study is to investigate the effect of gold nanoparticle distribution on dose enhancement in tumor when the tumor is irradiated by typical monoenergetic X-ray beams by considering homogeneous and inhomogeneous distributions of gold nanoparticles (GNPs) in the tumor. Materials and Methods: Methods: MCNP-4C Monte Carlo code was utilized for the simulation of a source, a phantom containing tumor and gold nanoparticles with concentrations of 10, 30 and 70 mg Au/g tumor. A 15 cm ×15 cm ×15 cm cubic water phantom was irradiated with a small planar source with four monoenergetic X-ray beams of 35, 55, 75 and 95 kV energy. Furthermore, tumor depths of 2.5 cm, 4.5 cm and 6.5 cm with homogeneous and inhomogeneous distributions of GNPs were studied. Each concentration, photon energy, tumor depth and type of distribution was evaluated in a separate simulation. Results: Results have shown that dose enhancement factor (DEF) in tumor increases approximately linearly with the concentration of GNPs. While DEF has fluctuations with photon energy, 55 keV photons have the highest DEF values compared to other energies. While DEF has relatively the same values with tumor located at various depths, inhomogeneous distribution of GNPs has shown different results compared with the homogeneous model. Conclusion: Dose enhancement can be expected with tumors in radiotherapy with low energy X-rays. Inhomogeneous model is recommended for the purpose of dose enhancement study because it mimics the real distribution of GNPs in tumor.

Semiconductor opening switch generator with a primary thyristor switch triggered in impact-ionization wave mode.

The results of the investigation involving a thyristor switch triggered in the impact ionization wave mode are presented. This switch is intended for operation as a primary switch in a nanosecond pulse generator with a semiconductor opening switch (SOS). The thyristor switch is based on commercial low-frequency tablet thyristors stacked in a joint assembly of up to 6 pieces connected in series. At a charging voltage of 2-12 kV and switching energy of up to 16 J, the switch operates with a discharge current of up to 8 kA, a current rise rate in the range from 14 to 54 kA/μs, and a switching efficiency of ∼0.9. It is shown that an increase in a voltage rise rate on thyristors at the triggering stage reduces energy loss in the thyristor switch during the current flow. The SOS pumping circuit contains one magnetic element-a pulse transformer, which simplifies the generator and increases its efficiency. The SOS generator has an output voltage of up to 300 kV and a peak power of up to 250 MW with a pulse duration of ∼50 ns. The thyristor switch in the generator operates at a voltage of 12 kV and provides current flow with the amplitude of up to 7.5 kA with a duration of ∼500 ns and a current rise rate of ∼54 kA/μs. The pulse repetition frequency of the generator is 1 kHz in the burst mode of operation.

Large-area and low-temperature synthesis of few-layered WS2 films for photodetectors

WS2-based photodetectors were fabricated by sputtering and electron beam irradiation (EBI), and the effect of EBI on the crystallization of WS2 films was investigated. EBI at 1 kV energy for 1 min transformed the as-deposited amorphous structure of WS2 film into a two-dimensional (2D) layered crystalline structure with high uniformity over a 50.8 mm diameter wafer. Additionally, EBI enhanced the photoelectrical properties of WS2-based photodetectors. The as-deposited WS2 film yielded a responsivity of 0.10 mA · W−1 under 450 nm laser irradiation, but showed no response under 532 and 635 nm laser wavelengths. However, after 1 kV and 3 kV EBI of the WS2 films, the responsivities under laser irradiation at 450, 532, and 635 nm were 0.36, 1.37, and 0.19 mA · W−1, and 1.68, 2.45, and 1.09 mA · W−1, respectively. The substrate temperatures after 1 min of 1 kV and 3 kV EBI were 102 °C and 591 °C, respectively. The WS2-based photodetectors exhibited high responsivity in the visible light region despite their unique process conditions of low temperature and fast EBI treatment. Such desirable performance of the EBI-treated WS2 films shows significant potential for future large-area and low-temperature photoelectronic applications. Thus, we demonstrated that EBI is an attractive method for synthesizing 2D materials as it is fast, simple, controllable, and compatible with sputtering processes.

Kilovoltage transit and exit dosimetry for a small animal image-guided radiotherapy system using built-in EPID.

We investigated the potential use of the built-in electronic portal imaging device (EPID) in the small animal radiation research platform (SARRP) as a dosimeter in the kV energy range. To this end, we developed a method for converting portal images to a two-dimensional (2D) dose maps at the detector plane and object's exit surface and validated them against empirical dose measurements. We calibrated the SARRP's EPID to measure transit dose. The transit dose map was back-projected to calculate 2D dose distribution at the object's exit surface. The accuracy of transit and exit dose distributions was independently validated with a PinPoint ion chamber (IC) and Gafchromic EBT3 film measurements for a range of radiation dose rates (0.43-2.78 cGy/s), cone sizes (5-40 mm), in a homogeneous phantom of varying thickness (0-50 mm) and in an inhomogeneous phantom containing graphite, cork, air, and aluminum. In-air central axis (CAX) transit dose values measured with the EPID showed close agreement with film and IC measurements. The maximum differences in EPID in-air transit measurements with film or IC measurements were 1%. The EPID was capable of accurately measuring phantom transit dose independently of the attenuating phantom thickness, with average discrepancies of 0.5% and 2.9% with IC and film, respectively, where the maximum difference between the EPID and the IC was 1.8%. The results were slightly worse for film, with maximum differences in 4.9%. Output factor measurements using EPID were within 2.9% of both IC and film measurements. In addition, calculated exit doses agreed with film values within ≤3.1%, for attenuating phantom thicknesses ≥15 mm. The agreement became worse with decreasing phantom thickness; for thicknesses of 10 and 5 mm, agreements were ≤5.7% and ≤6.9%, respectively. Compared to film, transit and exit profiles measured with the EPID showed average differences <2% for both homogeneous and inhomogeneous materials. We developed and validated a novel 2D transit/exit dosimetry for a kV SA-IGRT system using an EPID. We verified the accuracy of our method to measure EPID transit and exit dose distributions for a range of dose rates, beam attenuation, and collimation. Our results indicate that the EPID can be used as a simple, convenient device for kV dose delivery verification in small animal radiotherapy.

Determination of dose enhancement caused by AuNPs with Xoft® Axxent® Electronic (eBx™) and conventional brachytherapy: in vitro study.

PurposeThe purpose of this study was to determine dose enhancement (DE) and the possible clinical benefits associated with the inclusion of gold nanoparticles (AuNPs) in cancer cells irradiated by either an 192Ir brachytherapy source or a Xoft® Axxent® Electronic (eBx™) Brachytherapy.Patients and methodsBrachytherapy DE caused by AuNPs is investigated using two methods, namely 192Ir and eBx™ Brachytherapy. The second method, which was recently introduced clinically, operates at ~50 kV, which is also the optimal beam energy for DE. In this in vitro study, two cancer cell lines, lung (A549) and prostate (DU145), were used. Cells were incubated with 1 mM (2% w/w) concentration of AuNPs of ~15 nm in size. The control groups were exposed to a range of doses from 0 (control) to 6 Gy, with eBx™ and 192Ir sources separately. A clonogenic assay was conducted to determine cell survival curves.ResultsHigh dose enhancement factor (DEF) values were achieved in treated groups with low concentration of AuNPs with the 50 kV energy associated with the eBx™. The DE levels in eBx™ for Du145 and A549 cells were found to be 2.90 and 2.06, respectively. The results showed DEFs measured for the same cell lines using 192Ir brachytherapy to be 1.67 and 1.54 for Du145 and A549 cancer cells, respectively. This clearly indicates that much higher DE values are obtained in the case of eBx™ X-ray brachytherapy compared to 192Ir gamma brachytherapy.ConclusionThe higher DE values obtained with eBx™ compared to 192Ir brachytherapy can be attributed to the lower average energy of the former and being closer to the optimal energy for DE. This could potentially be utilized by medical practitioners and clinicians to achieve the same tumor control with a significantly lower dose from the eBx™ compared to the 192Ir brachytherapy treatment, thus bringing huge benefits to the brachytherapy-treated patients.

Investigation of a source model for a new electronic brachytherapy tandem by film measurement.

PurposeTo investigate the accuracy of a vendor‐supplied source model for a new Xoft Axxent 0‐degree titanium tandem by film measurement.MethodsWe measured the anisotropy factors at varying distances and angles from the tandem in water using radiochromic film (Gafchromic EBT3) and an Epson Perfection v750 desktop flatbed scanner (US Epson, Long Beach, CA). A 0‐degree tandem was placed vertically in a water phantom. Four pieces of film, each at varying depths, were positioned orthogonal to the longitudinal axis of the tandem for azimuthal anisotropy measurements. Polar anisotropy measurements were taken with the film aligned parallel to the tandem. An absolute dose calibration for the film was verified with a PTW 34013 Soft X‐Ray Chamber. The film measurements were analyzed using different color channels. The measured polar anisotropy for varying source positions was compared to the vendor's data. Azimuthal anisotropy was measured as a function of the radius and angle, and normalized to the mean value over all angles at the specified radius.ResultsThe azimuthal anisotropy of the tandem and source was found to be consistent for different positions along the tandem's longitudinal axis and at varying distances from the tandem. Absolute dose using a calibrated parallel plate chamber showed agreement to within 2% of expected TPS values. The custom tandem, which has a thicker tip than the wall, was attenuating the 50 kV photons more than expected, at the angles where the photons had more wall material to traverse. This discrepancy was verified at different distances from the tandem and with different measurement techniques. As distance increased, anisotropy values had better agreement.ConclusionsWe quantified the agreement between the measured and provided anisotropy factors for a new Xoft Axxent 0‐degree titanium tandem. Radiochromic film response at low kV energy was also investigated. Our results showed that vendor‐supplied TG‐43 values were appropriate for clinical use at majority of the angles. A rigorous quality assurance method for new electronic brachytherapy sources and applicators, along with complete knowledge of all dosimetric measuring tools, should be implemented for all parts of the verification and commissioning process.

Pathological and immunohistochemical effects of electromagnetic fields on rat liver

The aim of this study was to investigate the possible effects of 50 Hz electromagnetic fields (EMFs) generated by high power lines on the morphology of rat liver and apoptosis. For this purpose, 28 adult male rats weighing 200-250 g were used. The treatment groups were kept in a shelter that were 7.5 m far from the high power lines carrying 170 kV (50 Hz) energy. The control animals (Group 1) were kept in an animal house where no electromagnetic fields were exposed. The animals of the groups 2, 3 and 4 were exposed to EMF (170 kV, 50 Hz) continously for 1, 2 and 3 months, respectively. At the end of the study periods, the animals were sacrificed and their livers were collected. Histopathological evaluation indicated that inflammatory cell infiltration localized in the portal areas was seen in the liver of experimental groups rats. Bax and Bcl-2 positive staining was observed in the liver of control and experimental groups, but both Bax and Bcl-2 staining was intense in Group 3. In conclusion, long- term exposure to EMFs may cause inflammatory changes and apoptosis in liver of rats.

Evaluation and clinical implementation of in vivo dosimetry for kV radiotherapy using radiochromic film and micro-silica bead thermoluminescent detectors

PurposekV radiotherapy treatment calculations are based on flat, homogenous, full-scatter reference conditions. However, clinical treatments often include surface irregularities and inhomogeneities, causing uncertainty. Therefore, confirmation of actual delivered doses in vivo is valuable. The current study evaluates, and implements, radiochromic film and micro silica bead TLD for in vivo kV dosimetry. MethodsThe kV energy and dose response of EBT3 film and silica bead TLD was established and uncertainty budgets determined. In vivo dosimetry measurements were made for a consecutive series of 30 patients using the two dosimetry systems. ResultsEnergy dependent calibration factors were required for both dosimetry systems. The standard uncertainty estimate for in vivo measurement with film was 1.7% and for beads was 1.5%. The mean measured dose was −2.1% for film and −2.6% for beads compared to prescription. Deviations up to −9% were found in cases of large surface irregularity, or with underlying air cavities or bone. Dose shielding by beads could be clinically relevant at low kV energies and superficial depths. ConclusionsBoth film and beads may be used to provide in vivo verification of delivered doses in kV radiotherapy, particularly for complex situations that are not well represented by standard reference condition calculations.

Dielectric charging research status and prospect

Dielectric charging phenomenon, caused by the interaction effect between space environment and spacecraft material, has a severe threat to the normal operation of spacecraft. Especially, the problem becomes more serious with the improvement of spacecraft operation voltage. An overview of dielectric charging research status, exsiting problems and prospect are reviewed. Firstly, dielectric charging phenomenon, hazards, research history and new challenges are introduced. There have five development stages: the initial attention, the focus of surface dielectric charging, the focus of deep dielectric charging, the rapid development of dielectric charging and new challenges and demands. The development demands of spacecraft dielectric in China are analysed. There have several insulation positions, which are easy to occur fault in practice. They include surface flashover on insulation material bewteen solar cells of solar array, surface flashover on insulation material between electrodes of solay array drive assembly, the insulation material in cables and pulse discharge of circuit board. Secondly, the specific research status and exsiting problems of surface dielectric charging and deep dielectric charging are summarized from the following aspects: dielectric charging mechanism, dielectric charging mitigation and numerical simulation. Next, the top issues about dielectric charging experiments and material characteristics are introduced. They include in-situ surface potential decay measurement and characteristics of dielectric radiated by electrons, in-situ space charge measurement and material characteristics under electron radiation, surface flashover characteristics of dielectric radiated by electrons in vacuum. Two kinds of space charge in-situ measurement, short-circuit PEA (Pulsed Electro-Acoustic) and open PEA are introduced. At present, there do not have the mature in-situ space charge measurement setup under electron radiation in China, the difficult points in design and debugging are analysed. It is interesting of the surface flashover of dielectric under electron radiation. The latest experimental results indicated that the flashover voltage shows a distinctly different variation tendency under the two cases (after electron radiation and during electron radiation). The first case of after electron radiation, flashover voltage becomes higher than that without electron radiation. Because of the effect of deposited electrons in dielectric surface layer and the changes of trap distribution inside material. The trap distributions of polyimide after electron radiation are calculated based on surface potential decay measurement and Simmons theory. The results show that the shallow trap level increases slightly with the increase of electron energy (3–11 keV), ranging from 0.81–0.85 eV, while the deep trap level remains unchanged about 0.94 eV; the second case of during electron radiation, flashover voltage exhibited a dramatic drop from 26.9 kV (energy: 5 keV) to 10.5 kV (energy: 30 keV), due to the combined effect of incident kinetic electrons flowing to dielectric surface and deposited electrons in dielectric surface layer. Finally, the key scientific issues in the filed of space dielectric charging are put forward and prospected based on the present research status.

Robust shell passivation of CdSe colloidal quantum dots to stabilize radioluminescence emission

Systematic characterization of semiconductor colloidal quantum dots (cQDs) response to ionizing radiation must be performed to use them in radiation detection. In this study, the robustness of multi-shell (MS) and core/shell (CS) cQDs was investigated under irradiation. Radioluminescence (RL) measurements with kV and MV photon beams revealed a better resistance of MS cQDs to ionizing radiation, with their spectra fluctuating by barely ∼ 1 nm. A systematic signal recovery between subsequent irradiations was noticed for MS cQDs only. A beam energy dependence of the RL stability was detected between kV and MV energies. At the same point of dose cumulated, the RL signal loss for the kV beams was observed to be ∼6-7% smaller than that of the MV beam, for both types of cQDs. These results demonstrate that MS cQDs are better candidates as ionizing radiation sensors than CS cQDs, especially in the kV energy range.

Effect of electron irradiation on DC surface flashover of polyimide in vacuum

The vacuum surface flashover voltage of dielectric material irradiated by electron-beam is very low, which is the key scientific issue for developing high-voltage and high-power spacecraft technology. This paper proposes a novel research way of considering the combined impact of incident kinetic electrons flowing to dielectric surface and deposited electrons in dielectric surface layer on dc surface flashover performance in vacuum. The experiments on dc surface flashover of polyimide in vacuum after electron irradiation and during electron irradiation were investigated. The experimental results indicated flashover voltage showed a distinctly different variation tendency under the two cases. The dc surface flashover voltage of polyimide after electron irradiation became higher than that without electron irradiation, because of the effect of deposited electrons in dielectric surface layer. During electron irradiation, the dc surface flashover voltage exhibited a dramatic drop from 26.9 kV (energy: 5 keV) to 10.5 kV (energy: 30 keV). Furthermore, the surface flashover characteristics exerts different changes for incident electrons of different energies levels. It has been experimentally indicated that the energy and incident trajectory of incident kinetic electrons flowing to polyimide surface are altered by the combined action of the reverse electric field created by deposited electrons and the applied electric field. As a result, the surface flashover characteristics were changed. This work provides a new insight into the vacuum surface flashover of dielectric material under electron irradiation, and can be used as the research basis of surface flashover mitigation methods in space environment.

Quantitative 3D Determination of Radiosensitization by Bismuth-Based Nanoparticles.

The nanoparticle-induced dose enhancement effect has been shown to improve the therapeutic efficacy of ionizing radiation in external beam radiotherapy. Whereas previous studies have focused on gold nanoparticles (AuNPs), no quantitative studies have been conducted to investigate the potential superiority of other high atomic number (Z) nanomaterials such as bismuth-based nanoparticles. The aims of this study were to experimentally validate and quantify the dose enhancement properties of commercially available bismuth-based nanoparticles (bismuth oxide (Bi2O3-NPs) and bismuth sulfide (Bi2S3-NPs)), and investigate their potential superiority over AuNPs in terms of radiation dose enhancement. Phantom cuvettes doped with and without nanoparticles where employed for measuring radiation dose enhancement produced from the interaction of radiation with metal nanoparticles. Novel 3D phantoms were employed to investigate the 3D spatial distribution of ionising radiation dose deposition. The phantoms were irradiated with kilovoltage and megavoltage X-ray beams and optical absorption changes were measured using a spectrophotometer and optical CT scanner. The radiation dose enhancement factors (DEFs) obtained for 50 nm diameter Bi2O3-NPs and AuNPs were 1.90 and 1.77, respectively, for 100 kV energy and a nanoparticle concentration of 0.5 mM. In addition, the DEFs of 5 nm diameter Bi2S3-NPs and AuNPs were determined to be 1.38 and 1.51, respectively, for 150 kV energy and a nanoparticle concentration of 0.25 mM. The results demonstrate that both bismuth-based nanoparticles can enhance the effects of radiation. For 6 MV energy the DEFs for all the investigated nanoparticles were lower (< 15%) than with kilovoltage energy.

A 10(9) neutrons/pulse transportable pulsed D-D neutron source based on flexible head plasma focus unit.

A 17 kJ transportable plasma focus (PF) device with flexible transmission lines is developed and is characterized. Six custom made capacitors are used for the capacitor bank (CB). The common high voltage plate of the CB is fixed to a centrally triggered spark gap switch. The output of the switch is coupled to the PF head through forty-eight 5 m long RG213 cables. The CB has a quarter time-period of 4 μs and an estimated current of 506 kA is delivered to the PF device at 17 kJ (60 μF, 24 kV) energy. The average neutron yield measured using silver activation detector in the radial direction is (7.1 ± 1.4) × 10(8) neutrons/shot over 4π sr at 5 mbar optimum D2 pressure. The average neutron yield is more in the axial direction with an anisotropy factor of 1.33 ± 0.18. The average neutron energies estimated in the axial as well as in the radial directions are (2.90 ± 0.20) MeV and (2.58 ± 0.20) MeV, respectively. The flexibility of the PF head makes it useful for many applications where the source orientation and the location are important factors. The influence of electromagnetic interferences from the CB as well as from the spark gap on applications area can be avoided by putting a suitable barrier between the bank and the PF head.

Evaluation of Energy Characteristics of High Voltage Equipment for Electro-Blasting Destruction of Rocks and Concrete

The splitting off concrete monolith via electro-blast technology is described. High- voltage investigations were performed using the electric-discharge blasting unit with charging voltage up to 15 kV and maximum energy of 126 kJ. Several series of experiments of multiborehole electro-blast with initiation of plasma channel by wire explosion have been carried out. The combined effect of pulse electric discharge and gas generating composition allows to increase the energy of electro-blasting. According to data obtained from experiments the average value of energy for concrete monolith splitting off of 1 m3 is about 1554 kJ. The energy of electrical discharge pulse is about 95 kJ and gas-generating composition has energy contribution of 3.8 kJ/g. For carrying out of one electric-discharge blasting experiment 6-8 minutes has been spent. Therefore, the efficiency of pulse power system is about (0.85-0.9) m3/h.

An alternative X-ray shielding material based on coated textiles

Lead-shielding products, such as lead aprons, are important materials for personal protection of physicians and patients from X-ray radiation during medical operations. However, lead has environmental disadvantages, with high toxicity. The aim of this study was to manufacture an environmentally friendly and flexible textile-based radiation shielding material. Tungsten, bismuth and barium sulfate powders were used as alternatives to lead with recognized shielding abilities against X-rays. The cotton fabrics were coated with silicone rubber that contains tungsten, bismuth or barium sulfate powders in equal weight fractions. X-ray attenuation ratios of the samples were measured at 80, 100 and 150 kV tube voltages in accordance with medical protection standards. Using the theoretical models, the thicknesses required for 90%, 95% and 99% attenuation ratios at the 100 kV energy level were also estimated for all the materials. The results showed that, at 60% weight ratio, 1.55 mm bismuth embedded coating can attenuate 90% of X-ray photons at the 100 kV level, while the required thickness of a tungsten embedded coating is 1.73 mm for the same protection level. At the same weight ratios the bismuth–silicone rubber blend reached better attenuation ratios per thickness in comparison with tungsten and barium sulfate powder–silicone rubber blends.