Energy deposition model for I-125 photon radiation in water

In this study, an electron-tracking Monte Carlo algorithm developed by us is combined with established photon transport models in order to simulate all primary and secondary particle interactions in water for incident photon radiation. As input parameters for secondary electron interactions, electron scattering cross sections by water molecules and experimental energy loss spectra are used. With this simulation, the resulting energy deposition can be modelled at the molecular level, yielding detailed information about localization and type of single collision events. The experimental emission spectrum of I-125 seeds, as used for radiotherapy of different tumours, was used for studying the energy deposition in water when irradiating with this radionuclide.     

未被俘获电子对多光子非线性Compton散射能量转换效率的影响

 应用单粒子理论和电子与光子非弹性碰撞模型，研究了未被俘获电子对多光子非线性Compton散射能量转换效率的影响。结果表明，未被俘获电子使该散射的频谱展宽随入射电子速度和与电子同时作用的光子数的增大而增大，随电子与光子非弹性碰撞成分的增大而减小，从而使能量转换效率近乎与电子入射速度正比降低。用低能电子入射，能有效地减小这种损失。     

光子与相对论麦克斯韦分布电子散射的能谱角度谱研究

光子与相对论麦克斯韦分布电子散射的描述及能谱角度谱计算非常复杂且费时.本文提出了一种光子与相对论麦克斯韦速度分布电子散射的蒙特卡罗(MC)模拟方法,该方法能够细致模拟高温等离子体中任意能量光子与任意温度电子的Compton和逆Compton散射问题.对于散射后光子的能谱和角度谱参数,可以根据电子温度抽样若干不同状态的电子,分别模拟其与光子发生散射,可以得到各次散射后的光子能量和偏转角度,取统计平均后的结果即可获得该光子与该温度电子散射的能谱和角度谱分布.根据该方法编写了光子与相对论电子散射MC模拟程序,开展了高温全电离等离子体中光子与相对论电子散射的能谱角度谱计算和分析,分析结果显示:热运动电子将展宽出射光子能谱,且低能光子与高温电子散射后的蓝移现象明显;出射光子的角度谱很复杂,其决定于入射光子能量、出射光子能量及电子温度.基于该方法计算并以数表形式给出的光子-相对论电子散射能谱角度谱数据,可以供辐射输运数值模拟程序使用.     

Excitation of the Characteristic K Series Radiation,Coherent and Incoherent Scatter of Low Energy Gamma Rays

On the basis of a simplified mathematical model there is calculated the probability of a photon of characteristic K series radiation excited by a photon of low energy gamma radiation hitting the detector. There are also included the probabilities for coherently and incoherently scattered primary radiation considering electron binding energies.     

Effects of magnetic field on photon-induced quantum transport in a single dot-cavity system

In this study,we show how a static magnetic field can control photon-induced electron transport through a quantum dot system coupled to a photon cavity.The quantum dot system is connected to two electron reservoirs and exposed to an external perpendicular static magnetic field.The propagation of electrons through the system is thus influenced by the static magnetic and the dynamic photon fields.It is observed that the photon cavity forms photon replica states controlling electron transport in the system.If the photon field has more energy than the cyclotron energy,then the photon field is dominant in the electron transport.Consequently,the electron transport is enhanced due to activation of photon replica states.By contrast,the electron transport is suppressed in the system when the photon energy is smaller than the cyclotron energy.     

Dynamic plasma screening effects on low-energy bremsstrahlung emission in nonideal plasmas

The dynamic screening effects on the low-energy electron–ion bremsstrahlung process are investigated for both the soft and hard photon radiations in nonideal plasmas. The impact-parameter analysis is employed to obtain the bremsstrahlung radiation cross section as a function of the impact parameter, projectile energy, radiation photon energy, thermal energy, and Debye length. The results show that the dynamic screening effect on the bremsstrahlung radiation is found to be more significant for distant encounters. In addition, the dynamic screening effect is found to be more important for the soft photon radiation and decreases with increasing the radiation photon energy.     

自由电子激光的能量转换

根据Ｗｅｉｚｓａｃｋｅｒ－Ｗｉｌｌｉａｍｓ近似，把自由电子激光模拟成相对论性电子与赝光子的碰撞，而光子被散射．按照这个物理模型，研究了电子与光子的能量交换，得到了散射光子能量与碰撞前光子能量之间的关系：ε_p=4γ²ε_p⁽⁰⁾散射光子能量的放大是以电子消耗能量为代价的分析。计算了能量交换的规模，并得出自由电子激光中能量转换效率最大为５０％. 关键词：     

Calculation of current induced by photon momentum in gaseous argon

The current induced by photon momentum in gaseous argon has been calculated in the single-electron approximation as well as with atomic electron correlations taken into account. It has been found that both the magnitude of the current and its direction relative to the photon momentum are dependent on photon energy.     

Electron-Impact Induced Molecular Fluoresence Spectroscopy

Abstract

By the bombardment of gaseous molecules with monoenergetic electrons the molecules can be electronically excited and/or fragmented, depending upon the energy supplied by the electrons. Any fragments which may be produced also have the possibility of being produced in electronically (as well as vibrationally and rotationally) excited states. The electronically excited molecules and fragments both possess the possibility of radiative decay (fluorescence). The measurement of this fluorescence as a function of both electron energy and photon wavelength is termed “electron-impact induced fluorescence spectroscopy.” A plot of fluorescence intensity as a function of the electron energy at a given photon wavelength is generally referred to as an “excitation function,” which is exactly analogous to the excitation spectrum which can be obtained in conventional (optically excited) fluorescence spectrometry. A plot of the fluorescence intensity as a function of photon wavelength at a given electron energy is termed the “fluorescence spectrum.” A three dimensional plot of the fluorescence intensity as a function of both the photon wavelength and the electron energy may also be constructed, and is referred to as an “excitation contour plot.”     

多光子非线性Compton散射的能量转换

研究了多光子非线性Compton散射中电子与光子的能量转换及其转换效率.结果表明:散射光子频率随电子吸收光子数n的增大而增大,随碰撞非弹性成分ξ的增大而迅速减小.在超强激光场中,当极端相对论性电子与光子发生多光子非线性Compton散射且被光场俘获时,能量转换效率趋于无限大,即电子可以从超强激光场中获得巨大的加速能量.用高速电子束入射并与光子发生多光子非线性Compton散射,是提高非线性Compton散射能量转换效率的重要途径.     

Ultrafast dissociation and electron excitation in polyatomic organic molecules upon multiple IR photon capture

We suggest a model that allows analysis of the photoprocesses in polyatomic organic molecules upon multiple IR photon capture. The dissociation and electron excitation of these molecules is shown to depend resonantly on the photon energy and intensity. The (CH₂)_n substructures of these molecules serve for IR photons as antennas that accumulate energy to values at which dissociation or electron excitation can be triggered. The model is applied to diphenylalkan molecules as an example.     

Two‐color operation of a free‐electron laser with a tilted beam

With the successful operation of free‐electron lasers (FELs) as user facilities there has been a growing demand for experiments with two photon pulses with variable photon energy and time separation. A configuration of an undulator with variable‐gap control and a delaying chicane in the middle of the beamline is proposed. An injected electron beam with a transverse tilt will only yield FEL radiation for the parts which are close to the undulator axis. This allows, after re‐aligning and delaying the electron beam, a different part of the bunch to be used to produce a second FEL pulse. This method offers independent control in photon energy and delay. For the parameters of the soft X‐ray beamline Athos at the SwissFEL facility the photon energy tuning range is a factor of five with an adjustable delay between the two pulses from ?50 to 950 fs.     

Optical control of spin-dependent thermal transport in a quantum ring

We report on calculation of spin-dependent thermal transport through a quantum ring with the Rashba spin-orbit interaction. The quantum ring is connected to two electron reservoirs with different temperatures. Tuning the Rashba coupling constant, degenerate energy states are formed leading to a suppression of the heat and thermoelectric currents. In addition, the quantum ring is coupled to a photon cavity with a single photon mode and linearly polarized photon field. In a resonance regime, when the photon energy is approximately equal to the energy spacing between two lowest degenerate states of the ring, the polarized photon field can significantly control the heat and thermoelectric currents in the system. The roles of the number of photon initially in the cavity, and electron–photon coupling strength on spin-dependent heat and thermoelectric currents are presented.     

光子能量沉积计算的一种新方法

光子沉积能广泛地应用于放射医疗和辐射防护领域。 MCNP程序中*F8功能统计的是进出网格的光子与电子能量差。 *F8只能采用真实网格, 计算效率较低。 由于光子的能量沉积都是通过次级电子来完成的, 对光子能量沉积的计算可转换为次级电子能量沉积的计算。 文中据此给出了一种新的光子能量沉积统计方法, 该方法只统计次级电子能量沉积, 且可以采用虚拟网格计数。 新方法若采用真实网格, 计算精度与效率与*F8完全一样; 若采用虚拟网格, 新方法计算精度略低, 但几何建模简单, 计算效率较高。 Energy deposition distribution is very important to study radiotherapy or radioprotection. The *F8 method of MCNP program counts the energy loss of photon and electron together. Only real grid is allowed to *F8, so its computation efficiency is low. This paper gives a new calculation method for energy deposition of photon. Because the energy deposition of photon is accomplished by secondary electron, only electron is counted in the new method. The real collision of the electron is counted by the new method, whereas *F8 only counts the information of particle across the interface. Moreover, virtual grid is allowed in the new method. With real grid, the new method has the same precision and efficiency as *F8. If virtual grid is adopted by the new method, although the precision is slightly down, the efficiency is greatly increased.     

The Research of Scattering Cross-Section and Energy-Extraction in FEL

ＴｈｅＲｅｓｅａｒｃｈｏｆＳｃａｔｔｅｒｉｎｇＣｒｏｓｓ－ＳｅｃｔｉｏｎａｎｄＥｎｅｒｇｙ－ＥｘｔｒａｃｔｉｏｎｉｎＦＥＬＴｈｅＲｅｓｅａｒｃｈｏｆＳｃａｔｔｅｒｉｎｇＣｒｏｓｓ－ＳｅｃｔｉｏｎａｎｄＥｎｅｒｇｙ－ＥｘｔｒａｃｔｉｏｎｉｎＦＥＬ￥ＺＨ...     

超二代像增强器多碱阴极光电发射特性研究

通过测量超二代像增强器多碱阴极的光谱反射率和透射率,根据能量守恒定律计算得到了多碱阴极的光谱吸收率.结果表明,只有当光子的能量大于1.333 eV以后,多碱阴极的吸收率才开始快速增大.这说明多碱阴极的光谱吸收存在一个1.333 eV的长波吸收限,入射光的光子能量如果小于该吸收限,多碱阴极将不吸收.在多碱阴极的表面电子亲合势进一步降低的情况下,多碱阴极光电发射的长波理论阈值由长波吸收限所决定.多碱阴极在吸收光子之后的电子跃迁过程中,跃迁电子的能量增加小于所吸收入射光子的能量,即存在一个"能量损失".光子的能量越高,所激发的跃迁电子所处的能级越高,能量损失越大.同时光子的能量越高,跃迁电子所处的能级越高,电子跃迁的几率越低.多碱阴极的量子效率由吸收率、跃迁几率和跃迁能级、扩散过程中的能量损失等因素共同决定,因此多碱阴极的量子效率存在长波阈的同时也存在短波阈.多碱阴极的量子效率在2.11 eV达到最大值之后,随着光子能量的增加而单调减小,在3.6 eV时,量子效率减小到零.多碱阴极在3.6 eV时的吸收系数仍然很高,但由于电子跃迁的几率低,同时电子扩散过程中的能量损失大,导致尽管多碱阴极对短波具有较高的吸收系数,但量子效率仍然较低.因此对多碱阴极所吸收的光子能量中,转换成为光电导、晶格热振动等其他非光电发射形式能量的比例而言,短波较长波高,对光电发射的贡献率而言,短波较长波低.     

Multiple exciton generation in semiconductor nanocrystals: Toward efficient solar energy conversion

Within the range of photon energies illuminating the Earth's surface, absorption of a photon by a conventional photovoltaic semiconductor device results in the production of a single electron‐hole pair; energy of a photon in excess of the semiconductor's bandgap is efficiently converted to heat through interactions between the electron and hole with the crystal lattice. Recently, colloidal semiconductor nanocrystals and nanocrystal films have been shown to exhibit efficient multiple electron‐hole pair generation from a single photon with energy greater than twice the effective band gap. This multiple carrier pair process, referred to as multiple exciton generation (MEG), represents one route to reducing the thermal loss in semiconductor solar cells and may lead to the development of low cost, high efficiency solar energy devices. We review the current experimental and theoretical understanding of MEG, and provide views to the near‐term future for both fundamental research and the development of working devices which exploit MEG.     

Study on energy dependence of PAGAT polymer gel dosimeter evaluated using X-Ray CT

The normoxic polymer gel dosimeter evaluated with X-Ray computed tomography has emerged as a promising tool for measuring the dose delivered during radiotherapy in three dimensions. This study presents the dependence of PAGAT normoxic polymer gel sensitivity to different photon and electron energies. PAGAT polymer gel was prepared under normal atmospheric condition and irradiated with different photon energies of 1.25 MeV from Co-60 and 6 MV and 15 MV from linear accelerator and electron energies of 6, 9, 12, 15, 18 and 21 MeV from linear accelerator. Evaluation of dosimeter was performed with an X-Ray CT scanner. Images were acquired with optimum scanning protocols to reduce the signal-to-noise ratio. The averaged image was subtracted from the unirradiated polymer gel image for background. Central axis depth dose (PDD) curves obtained for each energy and polymer gel dosimeter measurements were in good agreement with diode and film measurements. Hounsfield (HU) – dose response curve for each photon and electron energy were derived from the PDD curve obtained from the gel dosimeter measurements. From the study it was clear that the HU-dose response curve was linear in the region 1–10 Gy. The dosimeter sensitivity was defined as a slope of these linear HU-dose response curves and found that the sensitivity of polymer gel decreases with increase in both photon and electron energies. This trend in dependence of PAGAT gel dosimeter sensitivity to different photon and electron energies was not dosimetrically significant. However, to evaluate the test phantom exposed with one energy using the calibration curve derived at another energy can produce clinically significant error.     

Electron and photon stimulated desorption of positive ions from alkali halide surfaces

We have observed desorption of positive ions from alkali halides stimulated by low energy electron and photon bombardment. Our experiments include the first measurements of electron stimulated desorption (ESD) of Na⁺ from NaCl and the first measurements of photon stimulated desorption (PSD) of positive ions from NaCl and LiF. The energy dependence data indicate that the initial onset for Na⁺ ejection by ESD occurs at the excitation threshold of the Cl(3s) core level. Similarly for the PSD of positive ions from NaCl and LiF we can relate incident photon beam energy dependent ion yields with the production of substrate core holes. The data provide insight into the mode of initial energy transfer to the solid which leads to desorption. ESD and PSD ion yields were measured to be on the order of 10^?7 ions per incident electron or photon.     

Quantum information and microscopic measuring instruments

The consideration of measuring instruments as macroscopic bodies leads to neglect of the microscopic processes that occur during measurements. This disregard is not justified in general cases. As an example of measurements using microscopic instruments, the scattering of a photon by an electron with electron interference at two slits(Compton effect) was used. The amount of information that can be obtained in such a process is inversely proportional to the wavelength of the incident photon. At large photon wavelengths(soft measurements), the pure state of the electron can be disrupted by an arbitrarily small extent; accordingly, the amount of information extracted in such an experiment is also arbitrarily small. It is shown that the energy price for a bit obtained in such a measurement tends toward a constant value for increasing the photon wavelength. Microscopic instruments can be used in situations where energy costs for measurements are important.