Optimization studies of photo-neutron production in high-<Emphasis Type="Italic">Z</Emphasis> metallic targets using high energy electron beam for ADS and transmutation

Monte Carlo calculations have been performed using MCNP code to study the optimization of photo-neutron yield for different electron beam energies impinging on Pb, W and Ta cylindrical targets of varying thickness. It is noticed that photo-neutron yield can be increased for electron beam energies ≥100 MeV for appropriate thickness of the target. It is also noticed that it can be maximized by further increasing the thickness of the target. Further, at higher electron beam energy heat gradient in the target decreases, which facilitates easier heat removal from the target. This can help in developing a photoneutron source based on electron LINAC by choosing appropriate electron beam energy and target thickness to optimize the neutron flux for ADS, transmutation studies and as high energy neutron source etc. Photo-neutron yield for different targets, optimum target thickness and photo-neutron energy spectrum and heat deposition by electron beam for different incident energy is presented.      

Deformed even-even nuclei in a quark-meson coupling model with tensor coupling

Neutron total cross sections of ¹⁹⁷Au and ^natTa have been measured at the nELBE photoneutron source in the energy range 0.1–10MeV with a statistical uncertainty of up to 2% and a total systematic uncertainty of 1%. This facility is optimized for the fast neutron energy range and combines an excellent time structure of the neutron pulses (electron bunch width 5ps) with a short flight path of 7m. Because of the low instantaneous neutron flux transmission measurements of neutron total cross sections are possible, that exhibit very different beam and background conditions than found at other neutron sources.     

Generation and control of a powerful electron-beam current in an accelerator based on a secondary-emission source and its application

An electron accelerator in which magnetron guns with secondary-emission cathodes of two types are used as a particle source is described. The electron-beam parameters are investigated in an electron energy range of 20–150 keV at a pulse length of 10–50 μs. Results of target irradiation by an electron beam are represented. The target surface structure is studied by the metallographic method, and the microhardness and strength of zirconium materials are measured. The possibility of beam current control by factors of 2.5–3.5 with various methods is shown.     

Spectrochemical Determination of Microimpurities in Mercury

Abstract

Mercury together with the microimpurities in it had been turned into iodides in advance in a vacuum ampule in the presence of collector - spectrally pure carbon powder, containing 2 per cent Li (as Li₂CO₃). The obtained mercury (II) iodide was separated from the microimpurities by sublimation at 100°C and the collector with the microimpurities was subjected to spectral analysis. The method allows the determination of 20 elements in mercury within detection limits of 10^?5 to 10^?7% and relative standard deviation 0.08 to 0.25. The method can be applied for the analysis of mercury (II) iodide, too.     

Ultraviolet-Cathodoluminescent 330 nm light source from a 2-inch wide CNT electron-beam emission under DC electric field

We report a 2-inch wide-area AlGaN-based ultraviolet (UV) – cathodoluminescence (CL) light source emission using electron beam (EB) pumped source under DC electric field from an AlGaN/GaN multi-quantum-well grown on a sapphire substrate. The EB-pumping is achieved by wide-area carbon nanotubes (CNT) based field emitters and is arranged via a metal mesh, thereby acting as a gate to pump the electron flow. We have carried out UV–CL measurements with a turn-on field emission in the anode voltage ranging between 5 kV and 9 kV at anode current up to 1 mA. The best results are obtained at the low consumption energy of 7 W (anode current 1 mA; anode voltage 7 kV). The 330 nm UV–CL emission shows an output power of ~225 mW, with an as-calculated power efficiency of ~3.6%. The CL measurements show (5–8) % defect luminescence in the visible region.     

Analysis of parameters of an electron beam from a plasma-filled diode

We analyze the properties of a high-current electron beam formed in an electron source based on a plasma-filled diode and a linear pulsed transformer. The beam parameters are determined by measuring bremsstrahlung X-rays and the beam current, as well as the photographs of the diode gap in the optical range, of the anode in X-rays, and beam autographs. A beam with a current of ～100 kA and a mean electron energy exceeding 0.7 MeV for an accelerating voltage amplitude of ～1 MV is obtained. The diameter of the generated beam is ～1 cm. The electron beam from the plasma-filled diode makes it possible to attain a high anode power density (>10¹⁰ W/cm²) for exciting shock waves, for obtaining high pressures, and for generating powerful X-rays.     

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The generation and control of microwave electron cyclotron resonance (ECR) plasma cathode electron beam is studied experimentally. A complete set of discharge, electron beam extraction, focusing and measuring system was set up. The characteristics and performance of microwave ECR plasmas as electron beam extraction source were studied by measuring the current of water cooling target and the beam spot size on the target. Experimental results indicated that both microwave input power and accelerating voltage are conducive to improving electron beam current. The influence of gas pressure on the electron beam current was complex. With the increase of gas pressure, the electron beam current is characterized by decreasing first and then increasing. The extracted electron current of microwave ECR plasma cathode can reach 75mA at gas pressure of 7×10⁻⁴Pa, and the energy of the electron beam can reach 9keV. The energy utilization can reach 0.6. By adjusting the current of the focusing coil, the diameter of electron beam spot is reduced from 20mm to 13mm and the electron beam current keeps the value unchanged.     

微波电子回旋共振等离子体阴极电子束的实验研究

介绍了实验室研制的微波电子回旋共振(ECR)等离子体阴极电子束系统及初步研究结果，该系统包括微波ECR 等离子体源、电子束引出极、聚焦线圈等。通过测量水冷靶电流和靶上的束斑尺寸，实验研究了微波ECR 等离子体阴极电子束的流强、聚束性能等随电子束系统工作条件的变化。结果表明：微波输入功率越高、引出电压越高，引出电子束流强越大；工作气压对电子束流强的影响较复杂，随气压增加呈现出先降低后升高的特点；在7×10⁻⁴Pa 的极低气压下电子束流强可达75mA，引出电压9kV；能量利用率可达0.6；调整聚焦线圈的驱动电流，电子束的束斑直径从20mm 减小到13mm，电子束流强未有明显变化。     

TMSR白光中子源本底屏蔽设计

为了满足钍基熔盐堆对核数据的需求,中国科学院上海应用物理研究所自行设计并建造了紧凑型的15 MeV电子加速器驱动的白光中子源。电子直线加速器、中子产生靶以及探测器系统处于同一个实验大厅,中子/伽马射线本底较高,原有屏蔽并不能满足在低能区进行热中子物理实验测量的低中子本底需求。为了降低热中子本底,提高在热区的测量能力,需要对中子源进行局部屏蔽。根据调试运行经验以及模拟计算结果,分析了中子伽马射线本底的来源,利用MCNP5模拟计算了混凝土、铅、含硼聚乙烯对中子/伽马射线的屏蔽效果,优化设计了局部屏蔽方案。模拟计算结果显示,该屏蔽方案可将热中子本底降低三个量级,伽马本底降低两个量级。屏蔽后的实验测量结果表明,探测器处的有效热中子与本底热中子的比值达到约100:1,屏蔽效果显著,为后续在热中子能区顺利开展中子物理测量实验奠定了基础。     

Femtosecond Fourier interferometry of a nonideal plasma

Experimental diagnostic methods based on the measurement of the reflectance of a plasma are considered. The application of Fourier interferometry for measuring the dynamics of variation of the amplitude and phase of the complex reflectance of the Au plasma for various delay times in intervals shorter than 1 ps relative to the pumping laser pulse with a femtosecond time resolution is described in detail in the intensity range ∼10¹³–10¹⁴ W/cm². The variation of the complex refractive index of the heated Au target for a pump pulse intensity of ∼10¹²–10¹³ W/cm² is analyzed on the basis of experimental data using the Fresnel formulas.     

Diagnostics of a hollow relativistic electron beam from the transfer function of a converting target

Methods for measuring angular, geometrical, and energy characteristics of a hollow relativistic electron beam using the transfer function of a converting target are developed. A relationship between the anisotropy parameters of bremsstrahlung behind the target, angular characteristics of electrons, and geometrical parameters of the electron beam in the target plane is established. The energy balance equation that describes the interaction between the electron beam and converting target is studied. The transfer function of the target and its behavior versus electron energy are found. The time and integral characteristics of the electron beam are examined.     

Analyses of the factors for the demagnetization of permanent magnets caused by high‐energy electron irradiation

Demagnetization owing to high‐energy electron irradiation has been analyzed for permanent magnets used in insertion devices of synchrotron radiation sources, using the Monte Carlo code FLUKA. The experimental data of a thermally treated Nd₂Fe₁₄B permanent magnet with a copper or a tantalum block at electron energies ranging from 2 to 8 GeV were compared with the calculation data of the absorbed doses, photoneutron production distributions and star densities. The results indicate that low‐energy photoneutrons and bremsstrahlung photons are not involved in the demagnetization process, and suggest that the star density owing to the photoneutrons is strongly correlated with the demagnetization process.     

Electron temperature and concentration in the laser erosion plasma of lead and gallium

Time-averaged values of the electron temperature and concentration at distances of 1 and 7 mm from a target have been determined from the emission characteristics of the laser erosion plasma of lead and gallium. The plasma was produced in a vacuum (3–12 Pa) as the corresponding target was exposed to radiation of a neodymium laser (τ = 20 ns, λ = 1.06 μm, f = 12 Hz, W = 10⁸–10⁹ W/cm²). The energy distribution of excited atomic states has been analyzed. The time dependence of the electron temperature at a distance of 7 mm from the target is presented.     

Development of a Method for Measurement of Photonuclear-Reaction Cross Sections with the Aid of Simulated Quasimonoenergetic-Photon Spectra

A procedure for measuring photonuclear-reaction cross sections by employing the method of quasimonochromatization of the bremsstrahlung photon spectrum is developed. This procedure permits determining reaction cross sections via measuring the reaction yield at three fixed values of the electron energy. The procedure is equivalent to measuring the cross section in question for quasimonochromatic photons. Bremsstrahlung-photon spectra are obtained using state-of-the-art simulation means involving the GEANT4 code as applied to a specific experiment with allowance for its geometry, target thicknesses, electron-beam parameters, etc. The results obtained by simulating quasimonochromatic distributions of bremsstrahlung photons are presented for experiments at the LUE-8-5 linear electron accelerator of Institute for Nuclear Research (Moscow, Russian Academy of Sciences). These results are found to be in good agreement with the experimental energy distribution of the cross section for the reaction ¹¹¹Cd(γ, γ') in the energy range between 5 and 8 MeV.     

Photoneutron reactions in the range of giant dipole resonance

The well-known significant systematic disagreements between data on partial photoneutron reaction cross sections obtained in experiments using quasimonoenergetic annihilation photons and bremsstrahlung were investigated using objective physical criteria of data reliability. It was shown that many data are not reliable because of significant systematic uncertainties of the photoneutron multiplicity sorting methods used. The experimental–theoretical method for evaluation of reliable partial reaction cross sections was proposed and many new data were obtained.     

(Im-)possible ISOL beams

Refractory elements, i.e. elements with very high melting point and low vapor pressure, cannot be released in atomic form from an ISOL target. Therefore most of these elements are presently not available as ISOL beams. However, when reactive gases are introduced into the target, they may form volatile compounds with the refractory elements, allowing for an easier transport to the ion source. Particularly useful are high-temperature stable fluorides and oxides. By these chemical evaporation methods so far ISOL beams of the refractory elements C, Zr, Hf and Ta have been produced. We discuss how ISOL beams of B, Ti, Nb, Mo, Tc, Ru, W, Re, Os and Ir could be produced in a similar way.     

Generating and probing a two-photon fock state with a single atom in a cavity

A two-photon Fock state is prepared in a cavity sustaining a "source mode" and a "target mode," with a single circular Rydberg atom. In a third-order Raman process, the atom emits a photon in the target while scattering one photon from the source into the target. The final two-photon state is probed by measuring by Ramsey interferometry the cavity light shifts induced by the target field on the same atom. Extensions to other multiphoton processes and to a new type of micromaser are briefly discussed.     

Determination of Traces of Toxic Elements in Dimethylaminoborane upon Their Concentration for Atomic Emission Analysis

A technique of atomic emission determination of traces of toxic elements in dimethylaminoborane with detection limits of n·10^–5–10^–8 wt. % has been developed. To reduce the detection limits, a technique of separation of the basic component in the form of boron fluoride, with concentration of microimpurities on a graphite collector, was used.     

Study of microimpurities and charge states in homogeneous hydrocarbon films (Redeposited from a T-10 tokamak deuterium plasma discharge) using XRF analysis, IR spectroscopy, EPR, and I-V characteristics

Microimpurities and charge states of homogeneous deuterated hydrocarbon films redeposited from a T-10 tokamak deuterium plasma discharge are studied spectroscopically using x-ray fluorescence (XRF) analysis, electron paramagnetic resonance (EPR), infrared (IR) spectroscopy; current-voltage (I-V) charachteristics are also measured. Twelve microimpurities (mainly, those of transition metals Fe, Mo, Cr, Ni, Ti, etc., with relative concentrations of 50–7000 ppm) have been discovered. The resulting broad EPR (9.9 GHz, 6000 G) line with g-factors of g = 2.053–2.093 and g = 4.3 assigned to paramagnetic impurities confirms their presence. The presence of different charge states on two sides of the film (one facing the plasma and another facing the vacuum-chamber wall) and the difference in the IR spectra of these states are established. This can be explained by the process of film formation under the influence of the tokamak plasma.     

Clinical simulations of prostate radiotherapy using BOMAB-like phantoms: Results for neutrons

This paper presents in-phantom photoneutron equivalent doses induced by external radiotherapy, these are necessary to assess organ-averaged equivalent doses to derive the risk of secondary cancer development, associated with non-target organ exposures. The measurements were performed by Working Group 9 “Radiation Protection Dosimetry in Medicine” of the European Radiation Dosimetry Group (EURADOS) for simulations of clinical radiotherapy treatments of prostate cancer. The photoneutron dose measurements were carried out in a BOMAB-like water-filled phantom, by means of superheated emulsions (superheated drop detectors SDD and bubble damage BTI^® detectors) and Poly-Allyl-Diglicol-Carbonate (PADC) solid state nuclear track detectors. Dose data were acquired in a three-dimensional matrix of reproducible measurement points, which are spaced according to detectors size. Four clinical protocols for the treatment of the prostate tumor were considered and compared, by measuring the doses delivered to the planning target volume (PTV) and to peripheral radiosensitive regions (i.e. colon-rectum and bladder). The clinical irradiations were performed in two clinical radiotherapy facilities based on Varian Clinac 2300 CD accelerator: Santa Chiara University Hospital (Pisa, Italy) and Centre of Oncology M. Skłodowska-Curie Memorial Institute (Krakow, Poland). An additional tomotherapy prostate cancer treatment was also simulated in Campo di Marte Hospital (Lucca, Italy). Radiation qualities of 6, 12, 15, 18 and 20 MV were used; all of these are capable of producing photoneutrons. Data from this work span most of the X-ray beam energies and prostate treatment modalities used in the current clinical practice. These data permit the assessment of doses absorbed by a radiotherapy patient either at the treatment volume or at out-of-field organs. Comparison of different dosimeters, under the same irradiation conditions, showed that dosimeters generally agreed within their 20% 1 SD uncertainty. Comparison of different treatment modalities in the two contributing clinical centers (Pisa and Krakow) were also possible, as well as a comparison of dose profiles resulting from the different treatment techniques, delivered at the same primary photon energy. It was in particular found that photon acceleration energies as low as 6 MV are able to produce a non-negligible photoneutron component, which causes an undue dose to the patient of the order of tens microsievert per unit photon dose delivered at the target volume.