RESUMEN
The development of a medical facility for boron neutron capture therapy at Budker Institute of Nuclear Physics is under way. The neutron source is based on a tandem accelerator with vacuum insulation and lithium target. The proposed accelerator is conceived to deliver a proton beam around 10â¯mA at 2.3â¯MeV proton beam. To deliver a therapeutic beam for treatment of deep-seated tumors a typical Beam Shaping Assembly (BSA) based on the source specifications has been explored. In this article, an optimized BSA based on the 7Li(p,n)7Be neutron production reaction is proposed. To evaluate the performance of the designed beam in a phantom, the parameters and the dose profiles in tissues due to the irradiation have been considered. In the simulations, we considered a proton energy of 2.3â¯MeV, a current of 10â¯mA, and boron concentrations in tumor, healthy tissues and skin of 52.5â¯ppm, 15â¯ppm and 22.5â¯ppm, respectively. It is found that, for a maximum punctual healthy tissue dose seated to 11 RBE-Gy, a mean dose of 56.5 RBE Gy with a minimum of 52.2 RBE Gy can be delivered to a tumor in 40â¯min, where the therapeutic ratio is estimated to 5.38. All of these calculations were carried out using the Monte Carlo MCNP code.
Asunto(s)
Terapia por Captura de Neutrón de Boro/instrumentación , Neoplasias Encefálicas/radioterapia , Berilio/efectos de la radiación , Terapia por Captura de Neutrón de Boro/métodos , Terapia por Captura de Neutrón de Boro/estadística & datos numéricos , Simulación por Computador , Diseño de Equipo , Glioblastoma/radioterapia , Humanos , Litio/efectos de la radiación , Fantasmas de Imagen , Radioisótopos , Dosificación Radioterapéutica , Planificación de la Radioterapia Asistida por ComputadorRESUMEN
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.
Asunto(s)
Boratos , Litio , Manganeso , Dosimetría Termoluminiscente/métodos , Boratos/química , Boratos/efectos de la radiación , Espectroscopía de Resonancia por Spin del Electrón , Rayos gamma , Humanos , Litio/química , Litio/efectos de la radiación , Mediciones Luminiscentes/métodos , Manganeso/química , Manganeso/efectos de la radiación , Espectrofotometría InfrarrojaRESUMEN
A target cooling system was developed for an intense neutron source of p-Li reaction. The system consists of target cooling devices and protection devices for lithium evaporation. A pin-structure cooling device was developed to enhance cooling power. Functional graded material was utilized for the evaporation of lithium. Test experiments were performed by using the neutron exposure accelerator system for biological effect experiments (NASBEE) at the National Institute of Radiological Sciences (NIRS) in Japan. The target system was confirmed to be applicable for accelerator-based boron neutron capture therapy.
Asunto(s)
Terapia por Captura de Neutrón de Boro/instrumentación , Litio/química , Litio/efectos de la radiación , Aceleradores de Partículas/instrumentación , Protección Radiológica/instrumentación , Radiometría/instrumentación , Manejo de Especímenes/instrumentación , Diseño de Equipo , Análisis de Falla de Equipo , Ensayo de Materiales , Neutrones , Dosificación RadioterapéuticaRESUMEN
The near threshold (7)Li(p,n)(7)Be neutrons generated by incident proton energy having Gaussian distribution with mean energies from 1.85 to 1.95MeV, were studied as a practical neutron source for BNCT wherein an RFQ accelerator and a thick Li-target are used. Gaussian energy distributions with the standard deviation of 0, 10, 20 and 40keV for mean proton energies from 1.85 to 1.95MeV were surveyed in 0.01MeV increments. A thick liquid Li-target whose dimensions were established in our previous experiments (i.e., 1mm-thick with 50mm width and 50mm length) was considered in this study. The suitable incident proton energy and physical dimensions of Pb layer which serves as a gamma absorber and a Polyethylene layer which is used as a BDE were surveyed by means of the concepts of TPD. Dose distribution were calculated by using MCNP5. A proton beam with mean energy of 1.92MeV and a Gaussian energy distribution with a standard deviation of 20keV at a current of 10mA was selected from the viewpoint of irradiation time and practically achievable proton current. The suitable thicknesses of Pb gamma absorber was estimated to be about 3cm. The estimated thickness of the polyethylene BDE was about 24mm for an ideal proton current of 13mA, and was 18mm for a practical proton current of 10mA.
Asunto(s)
Berilio/química , Terapia por Captura de Neutrón de Boro/instrumentación , Litio/química , Modelos Estadísticos , Neutrones/uso terapéutico , Aceleradores de Partículas/instrumentación , Absorción de Radiación , Berilio/efectos de la radiación , Simulación por Computador , Diseño de Equipo , Análisis de Falla de Equipo , Litio/efectos de la radiación , Ensayo de Materiales , Distribución Normal , Protones , Radiometría , Dosificación Radioterapéutica , Dispersión de RadiaciónRESUMEN
A compact Liquid-Lithium Target (LiLiT) was built and tested with a high-power electron gun at Soreq Nuclear Research Center (SNRC). The target is intended to demonstrate liquid-lithium target capabilities to constitute an accelerator-based intense neutron source for Boron Neutron Capture Therapy (BNCT) in hospitals. The lithium target will produce neutrons through the (7)Li(p,n)(7)Be reaction and it will overcome the major problem of removing the thermal power >5kW generated by high-intensity proton beams, necessary for sufficient therapeutic neutron flux. In preliminary experiments liquid lithium was flown through the target loop and generated a stable jet on the concave supporting wall. Electron beam irradiation demonstrated that the liquid-lithium target can dissipate electron power densities of more than 4kW/cm(2) and volumetric power density around 2MW/cm(3) at a lithium flow of ~4m/s, while maintaining stable temperature and vacuum conditions. These power densities correspond to a narrow (σ=~2mm) 1.91MeV, 3mA proton beam. A high-intensity proton beam irradiation (1.91-2.5MeV, 2mA) is being commissioned at the SARAF (Soreq Applied Research Accelerator Facility) superconducting linear accelerator. In order to determine the conditions of LiLiT proton irradiation for BNCT and to tailor the neutron energy spectrum, a characterization of near threshold (~1.91MeV) (7)Li(p,n) neutrons is in progress based on Monte-Carlo (MCNP and Geant4) simulation and on low-intensity experiments with solid LiF targets. In-phantom dosimetry measurements are performed using special designed dosimeters based on CR-39 track detectors.
Asunto(s)
Terapia por Captura de Neutrón de Boro/instrumentación , Litio/efectos de la radiación , Modelos Estadísticos , Neutrones , Aceleradores de Partículas/instrumentación , Radioterapia de Alta Energía/instrumentación , Simulación por Computador , Diseño de Equipo , Análisis de Falla de Equipo , Isótopos/química , Isótopos/efectos de la radiación , Litio/química , Radiometría , Dosificación Radioterapéutica , Radioterapia de Alta Energía/métodos , Dispersión de Radiación , SolucionesRESUMEN
A feasibility study on liquid lithium target in the form of a flowing film was performed to evaluate its potential use as a neutron generation target of (7)Li(p,n)(7)Be reaction in BNCT. The target is a windowless-type flowing film on a concave wall. Its configuration was adapted for a proton beam which is 30mm in diameter and with energy and current of up to 3MeV and 20mA, respectively. The flowing film of liquid lithium was 0.6mm in thickness, 50mm in width and 50mm in length. The shapes of the nozzle and concave back wall, which create a stable flowing film jet, were decided based on water experiments. A lithium hydrodynamic experiment was performed to observe the stability of liquid lithium flow behavior. The flowing film of liquid lithium was found to be feasible at temperatures below the liquid lithium boiling saturation of 342°C at the surface pressure of 1×10(-3)Pa. Using a proto-type liquid lithium-circulating loop for BNCT, the stability of the film flow was confirmed for velocities up to 30m/s at 220°C and 250°C in vacuum at a pressure lower than 10(-3) Pa. It is expected that for practical use, a flowing liquid lithium target of a windowless type can solve the problem of radiation damage and target cooling.
Asunto(s)
Berilio/química , Terapia por Captura de Neutrón de Boro/instrumentación , Litio/química , Membranas Artificiales , Aceleradores de Partículas/instrumentación , Radiometría/instrumentación , Berilio/efectos de la radiación , Diseño de Equipo , Análisis de Falla de Equipo , Litio/efectos de la radiación , Ensayo de Materiales , Neutrones , Dosificación Radioterapéutica , SolucionesRESUMEN
In this work we review all the available experimental neutron data for the (7)Li(p,n) reaction near threshold which is necessary to obtain an accurate source model for Monte Carlo simulations in Boron Neutron Capture Therapy. Scattered published experimental results such as cross sections, differential neutron yields and total yields were collected and analyzed, exploring the sensitivity of the fitting parameters to the different possible variables and deriving a consistent working set of parameters to evaluate the neutron source near threshold.
Asunto(s)
Berilio/efectos de la radiación , Terapia por Captura de Neutrón de Boro/instrumentación , Litio/efectos de la radiación , Modelos Estadísticos , Aceleradores de Partículas/instrumentación , Berilio/química , Simulación por Computador , Diseño Asistido por Computadora , Diseño de Equipo , Análisis de Falla de Equipo , Isótopos/química , Isótopos/efectos de la radiación , Litio/química , Neutrones , Radiometría , Dosificación RadioterapéuticaRESUMEN
The characteristics of moderator assembly dimension was investigated for the usage of (7)Li(p,n) neutrons by 2.3-2.8MeV protons and W(p,n) neutrons by 50MeV protons. The indexes were the treatable protocol depth (TPD) and advantage depth (AD). Consequently, a configuration for W target with the Fe filter, Fluental moderator, Pb reflector showed the TPD of 5.8cm and AD of 9.3cm. Comparable indexes were found for the Li target in a geometry with the MgF2 moderator and Teflon reflector.
Asunto(s)
Terapia por Captura de Neutrón de Boro/instrumentación , Litio/efectos de la radiación , Modelos Estadísticos , Neutrones , Aceleradores de Partículas/instrumentación , Planificación de la Radioterapia Asistida por Computador/métodos , Tungsteno/efectos de la radiación , Simulación por Computador , Diseño de Equipo , Análisis de Falla de Equipo , Litio/química , Radiometría , Dosificación Radioterapéutica , Dispersión de Radiación , Tungsteno/químicaRESUMEN
Within the framework of accelerator-based BNCT, a project to develop a folded Tandem-ElectroStatic-Quadrupole accelerator is under way at the Atomic Energy Commission of Argentina. The proposed accelerator is conceived to deliver a proton beam of 30mA at about 2.5MeV. In this work we explore a Beam Shaping Assembly (BSA) design based on the (7)Li(p,n)(7)Be neutron production reaction to obtain neutron beams to treat deep seated tumors.
Asunto(s)
Berilio/efectos de la radiación , Terapia por Captura de Neutrón de Boro/instrumentación , Litio/efectos de la radiación , Modelos Estadísticos , Aceleradores de Partículas/instrumentación , Berilio/química , Simulación por Computador , Diseño Asistido por Computadora , Diseño de Equipo , Análisis de Falla de Equipo , Isótopos/química , Isótopos/efectos de la radiación , Litio/química , Radiometría , Dosificación RadioterapéuticaRESUMEN
A supramolecular lithium cation assemblies of crown ether, [Li 12-crown-4](+), has been used to replace conventional tetraalkylammonium counterion in thiolate/disulfide (ET(-)/BET) mediated dye-sensitized solar cells (DSCs), which exhibit high stability and efficiency of 6.61% under 100 mW·cm(-2) simulated sunlight illumination.
Asunto(s)
Colorantes/química , Éteres Corona/química , Disulfuros/química , Suministros de Energía Eléctrica , Litio/química , Energía Solar , Compuestos de Sulfhidrilo/química , Cationes , Colorantes/efectos de la radiación , Éteres Corona/efectos de la radiación , Disulfuros/efectos de la radiación , Transferencia de Energía , Diseño de Equipo , Análisis de Falla de Equipo , Litio/efectos de la radiación , Compuestos de Sulfhidrilo/efectos de la radiaciónRESUMEN
The LiMn2O4 and LiSn0.0125Mn1975O4 thin films were grown on Pt/Ti/SiO2/Si (100) substrate by RF magnetron sputtering. To obtain the structural stability and good cycle performance, deposition parameters, namely working pressure, sputtering gas ratio of Ar and O2, post-annealing temperature were established. The structure and surface morphology of thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electrochemical properties were estimated by two electrode half-cell test with WBCS 3000 (Wonatech, Korea) at constant current rate of 1 C-rate. The Sn substituted LiMn2O4 thin film deposited at 10 mtorr with mixture of argon and oxygen (Ar/O2 = 3/1) and then annealed at 500 degrees C in O2 atmosphere showed good cycle performance. The Sn substituted LiMn2O4 thin films showed larger capacity of -30 microAh/microm-cm2 and higher cyclability than LiMn2O4 thin films.
Asunto(s)
Litio/química , Manganeso/química , Membranas Artificiales , Nanoestructuras/química , Nanoestructuras/ultraestructura , Óxidos/química , Estaño/química , Conductividad Eléctrica , Electroquímica/métodos , Calor , Litio/efectos de la radiación , Campos Magnéticos , Manganeso/efectos de la radiación , Ensayo de Materiales , Nanoestructuras/efectos de la radiación , Óxidos/efectos de la radiación , Ondas de Radio , Estaño/efectos de la radiaciónRESUMEN
We demonstrate the improved second-harmonic Talbot self-imaging through the quasi-phase-matching technique in a 2D periodically-poled LiTaO(3) crystal. The domain structure not only composes a nonlinear optical grating which is necessary to realize nonlinear Talbot self-imaging, but also provides reciprocal vectors to satisfy the phase-matching condition for second-harmonic generation. Our experimental results show that quasi-phase-matching can improve the intensity of the second-harmonic Talbot self-imaging by a factor of 21.
Asunto(s)
Litio/química , Litio/efectos de la radiación , Óxidos/química , Óxidos/efectos de la radiación , Refractometría/métodos , Tantalio/química , Tantalio/efectos de la radiación , Luz , Ensayo de Materiales , Dispersión de RadiaciónRESUMEN
Electrochemical processes associated with changes in structure, connectivity or composition typically proceed via new phase nucleation with subsequent growth of nuclei. Understanding and controlling reactions requires the elucidation and control of nucleation mechanisms. However, factors controlling nucleation kinetics, including the interplay between local mechanical conditions, microstructure and local ionic profile remain inaccessible. Furthermore, the tendency of current probing techniques to interfere with the original microstructure prevents a systematic evaluation of the correlation between the microstructure and local electrochemical reactivity. In this work, the spatial variability of irreversible nucleation processes of Li on a Li-ion conductive glass-ceramics surface is studied with ~30 nm resolution. An increased nucleation rate at the boundaries between the crystalline AlPO4 phase and amorphous matrix is observed and attributed to Li segregation. This study opens a pathway for probing mechanisms at the level of single structural defects and elucidation of electrochemical activities in nanoscale volumes.
Asunto(s)
Cristalización/métodos , Galvanoplastia/métodos , Litio/química , Litio/efectos de la radiación , Nanopartículas/química , Electroquímica/métodos , Electrólitos/química , Electrólitos/efectos de la radiación , Campos Electromagnéticos , Iones/química , Iones/efectos de la radiación , Ensayo de MaterialesRESUMEN
We present an all-solid-state laser source emitting up to 2.1 W of single-frequency light at 671 nm developed for laser cooling of lithium atoms. It is based on a diode-pumped, neodymium-doped orthovanadate (Nd:YVO(4)) ring laser operating at 1342 nm. Optimization of the thermal management in the gain medium results in a maximum multi-frequency output power of 2.5 W at the fundamental wavelength. We develop a simple theory for the efficient implementation of intracavity second harmonic generation, and its application to our system allows us to obtain nonlinear conversion efficiencies of up to 88%. Single-mode operation and tuning is established by adding an etalon to the resonator. The second-harmonic wavelength can be tuned over 0.5 nm, and mode-hop-free scanning over more than 6 GHz is demonstrated, corresponding to around ten times the laser cavity free spectral range. The output frequency can be locked with respect to the lithium D-line transitions for atomic physics applications. Furthermore, we observe parametric Kerr-lens mode-locking when detuning the phase-matching temperature sufficiently far from the optimum value.
Asunto(s)
Láseres de Estado Sólido , Litio/química , Litio/efectos de la radiación , Frío , Diseño de Equipo , Análisis de Falla de Equipo , Dosis de RadiaciónRESUMEN
The characterization of a liquid scintillator incorporating an aqueous solution of enriched lithium chloride to produce a scintillator with 0.40% (6)Li is presented, including the performance of the scintillator in terms of its optical properties and neutron response. The scintillator was incorporated into a fast neutron spectrometer, and the light output spectra from 2.5 MeV, 14.1 MeV, and (252)Cf neutrons were measured using capture-gated coincidence techniques. The spectrometer was operated without coincidence to perform thermal neutron measurements. Possible improvements in spectrometer performance are discussed.
Asunto(s)
Litio/química , Litio/efectos de la radiación , Neutrones , Compuestos Orgánicos/química , Conteo por Cintilación/instrumentación , Análisis Espectral/instrumentación , Diseño de Equipo , Análisis de Falla de Equipo , Isótopos/química , Isótopos/efectos de la radiación , Dosis de Radiación , SolucionesRESUMEN
The hierarchically structured mesoporous LiMn(2)O(4) (LMO) nanospheres were synthesized using a template-free self-assembly process that was coupled with ultrasound (U). The ultrasound technique suggested here is very powerful for controlling an ordered nanostructure and improving crystallinity with large single-crystalline domains. Owing to the hierarchical mesoporous structure and high crystallinity, U-LMO provides an excellent rate capability and cycle stability with a capacity retention of more than 98% up to 50 cycles at a 0.2C rate. Here, we demonstrate that mesoporous U-LMO nanospheres were fabricated to enhance the electrochemical performance and protect it from structurally significant collapsing because of high crystallinity.
Asunto(s)
Suministros de Energía Eléctrica , Litio/química , Litio/efectos de la radiación , Nanosferas/química , Nanosferas/efectos de la radiación , Óxidos/síntesis química , Sonicación/métodos , Electroquímica/instrumentación , Diseño de Equipo , Análisis de Falla de Equipo , Ondas de Choque de Alta Energía , Manganeso/química , Manganeso/efectos de la radiación , Nanosferas/ultraestructura , Óxidos/química , Óxidos/efectos de la radiación , Porosidad , Dosis de RadiaciónRESUMEN
We report on bulk and guided-wave second-harmonic generation via random Quasi-Phase-Matching in Lithium Tantalate. By acquiring the far-field profiles at several wavelengths, we extract statistical information on the distribution of the quadratic nonlinearity as well as its average period, both at the surface and in the bulk of the sample. By investigating the distribution in the two regions we demonstrate a non-invasive approach to the study of poling dynamics.
Asunto(s)
Diseño Asistido por Computadora , Litio/química , Litio/efectos de la radiación , Modelos Teóricos , Óxidos/química , Óxidos/efectos de la radiación , Refractometría/instrumentación , Tantalio/química , Tantalio/efectos de la radiación , Simulación por Computador , Campos Electromagnéticos , Diseño de Equipo , Análisis de Falla de Equipo , Luz , Refractometría/métodos , Dispersión de RadiaciónRESUMEN
We report on efficient cw high-power second harmonic generation in a periodically poled LiTaO3 crystal placed in a resonant enhancement cavity. We tested three configurations, differing in the coupling mirror reflectivity, and a maximum conversion efficiency of about 76%, corresponding to 6.1 W of green light with 8.0 W of fundamental power, was achieved. This is, to the best of our knowledge, the highest cw power ever reported using a periodically-poled crystal in an external cavity. We observed photo-thermal effect induced by photon absorption at the mirrors and in the crystal, which however does not affect stable operation of the cavity. A further effect arises for two out of the three configurations, at higher values of the input power, which degrades the performance of the locked cavity. We suggest this effect is due to the onset of competing nonlinearities in the same crystal.
Asunto(s)
Iluminación/instrumentación , Litio/química , Dispositivos Ópticos , Óxidos/química , Tantalio/química , Transferencia de Energía , Diseño de Equipo , Análisis de Falla de Equipo , Luz , Litio/efectos de la radiación , Óxido de Magnesio/química , Óxido de Magnesio/efectos de la radiación , Óxidos/efectos de la radiación , Tantalio/efectos de la radiaciónRESUMEN
We report on high energy optical parametric oscillation of 118 mJ output with ~70% slope efficiency in 10 ns duration of 30 Hz operation by using Mg-doped congruent composition LiTaO(3) (MgLT). The periodically poled MgLT device with ~30 microm period for quasi-phase matching (QPM) in 5-mm-thick crystal are prepared. MgLT crystal could become a candidate for high-energy and higher durability material of QPM device, compared to conventional Mg-doped congruent composition LiNbO(3).
Asunto(s)
Litio/química , Magnesio/química , Dispositivos Ópticos , Oscilometría/instrumentación , Óxidos/química , Tantalio/química , Diseño de Equipo , Análisis de Falla de Equipo , Luz , Litio/efectos de la radiación , Magnesio/efectos de la radiación , Ensayo de Materiales , Óxidos/efectos de la radiación , Dispersión de Radiación , Tantalio/efectos de la radiaciónRESUMEN
1W quasi-white-light source has been generated from a single lithium tantalate with cascaded domain modulation. The quasi-white-light is combined by proper proportion of the red, green and blue laser light. The red and the blue result from a compact self-sum frequency optical parametric oscillation when pumped by a single green laser. The efficiency of quasi-white-light from the green pump reaches 27%. This compact design can be employed not only as a stable and powerful RGB light source but also an effective blue laser generator.