An efficient numerical tool for dose deposition prediction applied to synchrotron medical imaging and radiation therapy

Medical imaging and radiation therapy are widely used synchrotron‐based techniques which have one thing in common: a significant dose delivery to typically biological samples. Among the ways to provide the experimenters with image guidance techniques indicating optimization strategies, Monte Carlo simulation has become the gold standard for accurately predicting radiation dose levels under specific irradiation conditions. A highly important hampering factor of this method is, however, its slow statistical convergence. A track length estimator (TLE) module has been coded and implemented for the first time in the open‐source Monte Carlo code GATE/Geant4. Results obtained with the module and the procedures used to validate them are presented. A database of energy‐absorption coefficients was also generated, which is used by the TLE calculations and is now also included in GATE/Geant4. The validation was carried out by comparing the TLE‐simulated doses with experimental data in a synchrotron radiation computed tomography experiment. The TLE technique shows good agreement versus both experimental measurements and the results of a classical Monte Carlo simulation. Compared with the latter, it is possible to reach a pre‐defined statistical uncertainty in about two to three orders of magnitude less time for complex geometries without loss of accuracy.     

互补金属氧化物半导体器件空间低剂量率辐射效应预估模型研究

给出了一种新的预估互补金属氧化物半导体器件(CMOS器件)空间低剂量率辐射效应模型,相对线性响应预估模型,该模型在预估CMOS器件低剂量率辐射效应方面更接近实际试验结果,且不同剂量率辐射试验结果证实了所建模型的正确性.最后利用新建模型对处于空间低剂量率环境下CMOS器件的敏感参数进行了预估.     

Analysis of telescope array receivers for deep-space inter-planetary optical communication link between Earth and Mars

Optical communication technology shows promising prospects to fulfill the large bandwidth communication requirements of future deep-space exploration missions that are launched by NASA and various other international space agencies. At Earth, a telescope with a large aperture diameter is required to capture very weak optical signals that are transmitted from distant planets and to support large bandwidth communication link. A single large telescope has the limitations of cost, single point failure in case of malfunction, difficulty in manufacturing high quality optics, maintenance, and trouble in providing communication operations when transmitting spacecraft is close to the Sun. An array of relatively smaller-sized telescopes electrically connected to form an aggregate aperture area equivalent to a single large telescope is a viable alternative to a monolithic gigantic aperture. In this paper, we present the design concept and analysis of telescope array receivers for an optical communication link between Earth and Mars. Pulse-position modulation (PPM) is used at the transmitter end and photon-counting detectors along with the direct-detection technique are employed at each telescope element in the array. We also present the optimization of various system parameters, such as detector size (i.e., receiver field of view), PPM slot width, and the PPM order M, to mitigate the atmospheric turbulence and background noise effects, and to maximize the communication system performance. The performance of different array architectures is evaluated through analytical techniques and Monte-Carlo simulations for a broad range of operational scenarios, such as, Earth-Mars conjunction, Earth-Mars opposition, and different background and turbulence conditions. It is shown that the performance of the telescope array-based receiver is equivalent to a single large telescope; and as compared to current RF technology, telescope array-based optical receivers can provide several orders of magnitude greater data rates for deep-space communication with Mars.     

Analysis of the relationship between neutron dose and Cerenkov photons under neutron irradiation through Monte Carlo method

To theoretically explore the feasibility of neutron dose characterized by Cerenkov photons, the relationship between Cerenkov photons and neutron dose in a water phantom was quantified using the Monte Carlo toolkit Geant4. Results showed that the ratio of the neutron dose deposited by secondary electrons above Cerenkov threshold energy to the total neutron dose is approximately a constant for monoenergetic neutrons from 0.01 eV to 100 eV. With the initial neutron beam energy from 0.01 eV to 100 eV, the number of Cerenkov photons has a good correlation with the total neutron dose along the central axis of the water phantom. The changes of neutron energy spectrum and mechanism analysis also explored at different depths. And the ratio of total neutron dose to the intensity of Cerenkov photons is independent of neutron energy for neutrons from 0.01 eV to 100 eV. These findings indicate that Cerenkov radiation also has potential in the application of neutron dose measurement in some specific fields.     

A survey of the signal stability and radiation dose response of sulfates in the context of adapting optical dating for Mars

The Martian landscape is currently dominated by eolian processes, and eolian dunes are a direct geomorphic expression of the dynamic interaction between the atmosphere and the lithosphere of planets. The timing, frequency, and spatial extent of dune mobility directly reflects changing climatic conditions, therefore, sedimentary depositional ages are important for understanding the paleoclimatic and geomorphologic history of features and processes present on the surface of the Earth or Mars. Optical dating is an established terrestrial dosimetric dating technique that is being developed for this task on Mars. Gypsum and anhydrite are two of the most stable and abundant sulfate species found on the Earth, and they have been discovered in Martian sediments along with various magnesium sulfates and jarosite. In this study, the optical dating properties of various Ca-, Mg-, and Fe-bearing sulfates were documented to help evaluate the influence they may have on in-situ optical dating in eolian environments on Mars. Single-aliquot regenerative-dose (SAR) experimental procedures have been adapted to characterize the radiation dose response and signal stability of the Martian sulfate analogs. Jarosite was dosimetrically inert in our experiments. The radiation dose response of the Ca- and Mg-sulfates was monotonically increasing in all cases with characteristic doses ranging from ∼100 to ∼1000 Gy. Short-term signal fading also varied considerably in the Ca- and Mg-sulfates ranging from ∼0% to ∼40% per decade for these materials. These results suggest that the OSL properties of Ca- and Mg-sulfates will need to be considered when developing protocols for in-situ optical dating on Mars, but more enticingly, our results foreshadow the potential for gypsum to be developed as a geochronometer for Mars or the Earth.     

A representation for the energy-loss integral corresponding to Cerenkov radiation by a charged particle in a uniaxial gyrotropic crystal

A new representation is found for the energy-loss integral corresponding to Cerenkov radiation of a charged particle in a uniaxial gyrotropic crystal, for the case in which the particles is moving at some nonvanishing angle with respect to the optic axis. Particular cases are analyzed in which the integration over the variables in wave-number space can be carried out completely in analytic form.Translated from Izvestiya VUZ. Fizika, No. 1, pp. 47–54, January, 1970.The authors thank Professor A. A. Sokolov for interest in this study and discussion of results.     

The Hawking radiation of the charged particle via tunnelling from the axisymmetric Sen black hole

Extending Parikh's semi-classical quantum tunnelling model, this paper has studied the Hawking radiation of the charged particle via tunnelling from the horizon of the axisymmetric Sen black hole. Different from the uncharged massless particle, the geodesics of the charged massive particle tunnelling from the horizon is not light-like. The derived result supports Parikh's opinion and provides a correct modification to Hawking strictly thermal spectrum developed by the fixed background space-time and not considering the energy conservation and the self-gravitation interaction.     

Utilizing a shallow trench isolation parasitic transistor to characterize the total ionizing dose effect of partially-depleted silicon-on-insulator input/output n-MOSFETs

We investigate the effects of 60 Co γ-ray irradiation on the 130 nm partially-depleted silicon-on-isolator(PDSOI)input/output(I/O) n-MOSFETs. A shallow trench isolation(STI) parasitic transistor is responsible for the observed hump in the back-gate transfer characteristic curve. The STI parasitic transistor, in which the trench oxide acts as the gate oxide,is sensitive to the radiation, and it introduces a new way to characterize the total ionizing dose(TID) responses in the STI oxide. A radiation enhanced drain induced barrier lower(DIBL) effect is observed in the STI parasitic transistor. It is manifested as the drain bias dependence of the radiation-induced off-state leakage and the increase of the DIBL parameter in the STI parasitic transistor after irradiation. Increasing the doping concentration in the whole body region or just near the STI sidewall can increase the threshold voltage of the STI parasitic transistor, and further reduce the radiation-induced off-state leakage. Moreover, we find that the radiation-induced trapped charge in the buried oxide leads to an obvious front-gate threshold voltage shift through the coupling effect. The high doping concentration in the body can effectively suppress the radiation-induced coupling effect.     

Transition radiation of a charged particle crossing the waveguide filled with a dispersive dielectric medium perpendicularly to the waveguide axis

The theory of charged particle transition radiation is developed for the case when the particle crosses the waveguide, which is filled with a piecewise-homogeneous dielectric, perpendicularly to the waveguide axis. The cases where the charged particle is flying between two dispersive plates and between two thin impedance films are considered.     

同步辐射光源在地球深部矿物研究中的应用

来自地球深部的矿物可能记录了地球形成和早期演化的历史,探索地球深部物质组成和它们形成的物理化学环境是一个十分前沿的科学问题.同步辐射X射线能量色散法对于解决微细矿物及包裹体矿物的晶体结构具有巨大的优势和潜力.在美国纽约长岛布鲁克海文国家实验室,利用同步辐射光源（Beamline X17C）和能量色散X射线衍射方法,开展了西藏铬铁矿中地幔深部矿物及中国大陆科学钻探钻孔岩心样品中地幔异常矿物的晶体结构分析,发现了一批新矿物种属和特殊的晶体结构,来自大陆科学钻探岩心样品的铁磷矿和西藏金刚石是两个例证.     

Attenuation of solar radiation by a water mist from the ultraviolet to the infrared range

A model is developed for the hemispherical transmittance of direct and scattered solar radiation from a cloudless atmosphere by a mist layer of water droplets in order to investigate the potential of water misting systems to serve as a protection from solar irradiation with particular emphasis on harmful UV radiation. The proposed model is based on published spectral experimental data for solar irradiation, Mie theory for interaction of the radiation with single spherical droplets, and radiative transfer theory. Known limiting solutions are employed to simplify the Mie calculations. The modified two-flux approximation is used to account for both direct and diffuse irradiation in lieu of a numerical solution for the full radiative transfer equation in anisotropically scattering media. The role of the governing parameters of a disperse water curtain of water droplets, water content, and droplet size for sample conditions is studied in some detail, particularly in the near-ultraviolet part of the spectrum where radiation can result in human tissue damage.     

Evaluation of the radiation dose to a phantom for various X-ray exposure factors performed using the dose area product in digital radiography

The aim of this study is to measure the dose area product (DAP) in digital radiography by using a DAP meter to determine the X-ray exposure. Pediatric X-ray examinations can be obtained for any radiographic examinations using the selected radiographic examination parameters (kVp and mAs), the DAP information recorded. The best peak signal-to-noise ratio (PSNR) at a fixed tube voltage of 70 kVp was obtained at tube currents of 20 and 32 mA, whereas the best PSNR at a fixed tube current of 25 mA was obtained at a tube voltage of 73 kVp. The fixed tube voltage of 70 kVp and the fixed tube current of 25 mA could help to obtain the best image quality and depict the spatial resolution of an anthropomorphic torso phantom radiographic examination. The normalized data over the DAP were provided to determine the patient dose from radiography.     

Exact solution of the Landau-Lifshitz equations for a radiating charged particle in the Coulomb potential

We solve exactly the classical non-relativistic Landau-Lifshitz equations of motion for a charged particle moving in a Coulomb potential, including radiation damping. The general solution involves the Painlevè transcendent of type II. It confirms our physical intuition that a negatively charged classical particle will spiral into the nucleus, supporting the validity of the Landau-Lifshitz equation.     

Exact solution to the classical equation of motion for a charged particle in external electric and magnetic fields

An exact solution to the equation of classical motion of a charged particle in external uniform time-dependent electric and magnetic fields is obtained in two forms by two methods. An exact solution of a more general initial-value problem is found as well.     

A new concept of white light generation using a nano-waveguide for the solar radiation collection use

We propose a novel system of a nano-waveguide that can be used to generate the continuous optical spectrum, i.e. white light. A system consists of two micro-ring resonators and a nano-ring resonator that can be integrated into a single system. The large bandwidth signal is generated using a soliton pulse propagating within a Kerr-type nonlinear medium, whereas the continuous bandwidth or wavelength of light signal can be performed. Results obtained have shown the potential of using such a system for white light source generation and amplification, which is discussed. The amplified pulse can be stored within a nano-waveguide, which is allowed to form the continuous spectrum after amplification. Alternatively, the low-level solar radiation can be amplified, and the bandwidth signals can also be enlarged.     

Studies on the application of a low-voltage peak to the postsurgical follow-up CT scan in abdominal cancer patients in order to reduce the exposure of patients to radiation

This study examined the radiation dose, computed tomography (CT) number, contrast and image quality of patients requiring periodic follow-up abdominal CT examinations at various tube voltages. The subjects were divided into two groups. One group consisted of patients who underwent a clinical analysis and the other group was a phantom one. Somatom Sensation 16 (Siemens, Erlangen, Germany) was used. Twenty patients who underwent a periodic follow-up examination by CT were selected randomly. The tube current was fixed to 150 mA, and the tube voltage was adjusted according to the appropriate value of each examination. The computed tomography dose index (CTDI) values were measured. The CT number of each organ was measured by setting up a 1 cm diameter return on investment (ROI) in the abdominal organs at the same height of the first lumbar vertebra using images of the arterial phase. Two radiologists in consensus graded the quality of the abdominal images into three groups. An abdomen-shaped acrylic phantom was used in the phantom study. An ion chamber was inserted into the holes located at the center and periphery of the phantom, where the radiation dose was automatically displayed on the reader. Tube voltages of 80, 100, 120 and 140 kVp were applied to the phantom (diluted contrast medium with water at 1:10 ratio) and the phantom was scanned. The CT number was measured from a 1 cm diameter ROI at the center of the image. The CTDI value decreased by 36% at 100 kVp (7.50 mGy) compared with that at 120 kVp (11.70 mGy). According to the radiologists’ evaluation, there were 17 equivalent, 3 acceptable and 0 unacceptable levels in the group of 20 subjects. The radiation dose in the phantom study decreased with increasing tube voltages from 80 to 140 kVp. The peripheral and central doses decreased by 38% and 41%, respectively. The CT numbers at 80, 100, 120 and 140 kVp were 1365.9±4.4, 1046.1±3.7, 862.8±3.2 and 737.5±3.0 HU, respectively. In conclusion, in a follow-up observation for the detection of a recurrence or metastasis after surgery or patients with chronic abdominal diseases, the exposure doses can be reduced using a low-voltage peak CT examination without greatly changing the image quality.     

Energy filter composed of cylindrical and planar electrodes with the rectilinear trajectory of a charged particle beam at the entrance to and the exit from the system

In order to improve the resolution of an energy filter composed of cylindrical and planar electrodes with grounded diaphragms at the end faces, its operating mode in which a charged particle beam crosses the longitudinal axis of the filter twice is studied theoretically. The geometry and blending capacity of the filter that maximize its energy resolution are found. The parameters of the filter under study are compared with those of a similar energy filter in which the beam crosses the longitudinal axis once.