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1.
The anisotropy of the yield and energy of neutrons generated in a small-size plasma focus chamber with a total neutron yield of about 4 × 109 DD neutrons per shot was investigated experimentally. The neutrons were recorded using scintillation detectors on a 3-m-long flight base. The measurements were performed at the angles 0° and 90° with respect to the chamber axis. The maximum neutron energy measured by the time-of-flight method at the angles 0° and 90° was found to be 2.8 and 2.5 MeV, respectively. The measured anisotropy of the neutron yield was in the range 1.15–1.88. The integral DD neutron yield of the source was measured using the activation method (by activating silver isotopes). It is found that the neutron yield and the yield anisotropy depend linearly on the discharge current jump ΔI at the instant of neutron generation. 相似文献
2.
B. V. Kuteev P. R. Goncharov V. Yu. Sergeev V. I. Khripunov 《Plasma Physics Reports》2010,36(4):281-317
The review describes physical principles underlying efficient production of free neutrons, up-to-date possibilities and prospects
of creating fission and fusion neutron sources with intensities of 1015–1021 neutrons/s, and schemes of production and application of neutrons in fusion-fission hybrid systems. The physical processes
and parameters of high-temperature plasmas are considered at which optimal conditions for producing the largest number of
fusion neutrons in systems with magnetic and inertial plasma confinement are achieved. The proposed plasma methods for neutron
production are compared with other methods based on fusion reactions in nonplasma media, fission reactions, spallation, and
muon catalysis. At present, intense neutron fluxes are mainly used in nanotechnology, biotechnology, material science, and
military and fundamental research. In the near future (10–20 years), it will be possible to apply high-power neutron sources
in fusion-fission hybrid systems for producing hydrogen, electric power, and technological heat, as well as for manufacturing
synthetic nuclear fuel and closing the nuclear fuel cycle. Neutron sources with intensities approaching 1020 neutrons/s may radically change the structure of power industry and considerably influence the fundamental and applied science
and innovation technologies. Along with utilizing the energy produced in fusion reactions, the achievement of such high neutron
intensities may stimulate wide application of subcritical fast nuclear reactors controlled by neutron sources. Superpower
neutron sources will allow one to solve many problems of neutron diagnostics, monitor nano-and biological objects, and carry
out radiation testing and modification of volumetric properties of materials at the industrial level. Such sources will considerably
(up to 100 times) improve the accuracy of neutron physics experiments and will provide a better understanding of the structure
of matter, including that of the neutron itself. 相似文献
3.
V. F. Tarasenko 《Plasma Physics Reports》2011,37(5):409-421
Conditions under which the number of runaway electrons in atmospheric-pressure air reaches ∼5 × 1010 are determined. Recommendations for creating runaway electron accelerators are given. Methods for measuring the parameters
of a supershort avalanche electron beam and X-ray pulses from gas-filled diodes, as well as the discharge current and gap
voltage, are described. A technique for determining the instant of runaway electron generation with respect to the voltage
pulse is proposed. It is shown that the reduction in the gap voltage and the decrease in the beam current coincide in time.
The mechanism of intense electron beam generation in gas-filled diodes is analyzed. It is confirmed experimentally that, in
optimal regimes, the number of electrons generated in atmospheric-pressure air with energies T > eU
m
, where U
m
is the maximum gap voltage, is relatively small. 相似文献
4.
A. A. Akunets S. S. Anan’ev Yu. L. Bakshaev P. I. Blinov V. A. Bryzgunov V. V. Vikhrev I. V. Volobuev S. A. Dan’ko A. A. Zelenin E. D. Kazakov V. D. Korolev B. R. Meshcherov S. L. Nedoseev V. G. Pimenov E. A. Smirnova G. I. Ustroev A. S. Chernenko V. A. Shchagin 《Plasma Physics Reports》2010,36(8):699-708
Results are presented from experimental studies of the plasma formation dynamics in a Z-pinch produced from a cylindrical microporous agar-agar load. The experiments were performed on the S-300 facility at a current of 2 MA and current rise time of 100 ns. To enhance the energy concentration, a deuterated polyethylene neck with a mass density of 50–75 μg/cm3 and diameter of 1–2 mm was made in the central part of the load. The spatiotemporal characteristics of the Z-pinch were studied using an optical streak camera and fast frame photography in the optical and soft X-ray spectral ranges. X-ray emission was detected using semiconductor and vacuum diodes, and neutron emission was studied by means of the time-of-flight method. It is found that, in the course of continuous plasma production, hot spots with a diameter of 100 μm form in the pinch plasma. The hot spots emit short soft X-ray pulses with a duration of 2–4 ns, as well as neutron pulses with an average neutron energy of about 2.45 MeV. The maximum neutron yield was found to be 4.5 × 109 neutrons per shot. The scenario of hot spot formation is adequately described by two-dimensional MHD simulations. 相似文献
5.
A. A. Samokhin 《Plasma Physics Reports》2010,36(8):682-698
Studies of physical phenomena in magnetically insulated transmission lines (MITLs) of high-power pulsed current generators,
analysis of operation of existing megavolt generators, and designing of new high-current generators with a power of up to
∼10 TW require creating an efficient numerical code for modeling the propagation of a high-power electromagnetic pulse in
an MITL. This paper presents basic theoretical concepts of MITL operation in the framework of telegraph equations with allowance
for electron leakage and variations in the electrode emissivity and analyzes propagation of an electromagnetic wave in the
MITLs of the ANGARA-5-1 eight-module facility toward a dynamic load installed in the central unit with a matrix inductance. 相似文献
6.
An LBO (Li2B4O7) walled ionization chamber was designed to monitor the epithermal neutron fluence in boron neutron capture therapy clinical irradiation. The thermal and epithermal neutron sensitivities of the device were evaluated using accelerator neutrons from the 9Be(d, n) reaction at a deuteron energy of 4 MeV (4 MeV d-Be neutrons). The response of the chamber in terms of the electric charge induced in the LBO chamber was compared with the thermal and epithermal neutron fluences measured using the gold-foil activation method. The thermal and epithermal neutron sensitivities obtained were expressed in units of pC cm2, i.e., from the chamber response divided by neutron fluence (cm?2). The measured LBO chamber sensitivities were 2.23 × 10?7 ± 0.34 × 10?7 (pC cm2) for thermal neutrons and 2.00 × 10?5 ± 0.12 × 10?5 (pC cm2) for epithermal neutrons. This shows that the LBO chamber is sufficiently sensitive to epithermal neutrons to be useful for epithermal neutron monitoring in BNCT irradiation. 相似文献
7.
In this study, Monte Carlo codes, Geant4 and MCNP6, were used to characterize the fast neutron therapeutic beam produced at iThemba LABS in South Africa. Experimental and simulation results were compared using the latest generation of Silicon on Insulator (SOI) microdosimeters from the Centre for Medical Radiation Physics (CMRP). Geant4 and MCNP6 were able to successfully model the neutron gantry and simulate the expected neutron energy spectrum produced from the reaction by protons bombarding a 9Be target. The neutron beam was simulated in a water phantom and its characteristics recorded by the silicon microdosimeters; bare and covered by a 10B enriched boron carbide converter, at different positions. The microdosimetric quantities calculated using Geant4 and MCNP6 are in agreement with experimental measurements. The thermal neutron sensitivity and production of 10B capture products in the p+ boron-implanted dopant regions of the Bridge microdosimeter is investigated. The obtained results are useful for the future development of dedicated SOI microdosimeters for Boron Neutron Capture Therapy (BNCT). This paper provides a benchmark comparison of Geant4 and MCNP6 capabilities in the context of further applications of these codes for neutron microdosimetry. 相似文献
8.
The Monte-Carlo technique was used to perform quantitative microdosimetric model calculations of cell survival after boron neutron capture irradiations in vitro. The high energy 7Li and alpha-particles resulting from the neutron capture reaction 10B (n,α)7Li are of short range and are highly damaging to cells. The biophysical model of the Monte-Carlo calculations is based on the track structure of these α-particles and 7Li-ions and the x-ray sensitivity of the irradiated cells. The biological effect of these particles can be determined if the lethal effect of local doses deposited in very small fractional volumes of the cell nucleus is known. This lethal effect can be deduced from experimental data of cell survival after x-ray irradiation assuming a Poisson distribution for lethal events. The input data used in a PC-based computer program are the radial dose distribution inside the track of the released particles, cell survival after x-ray irradiation, geometry of the tumor cells, subcellular 10B concentration, and thermal neutron fluence. The basic concept of this Monte-Carlo computer model is demonstrated. Validations of computer calculations are presented by comparing them with experimental data on cell survival. 相似文献
9.
AimThe feasibility of using 230 MeV proton cyclotrons in proton therapy centers as a spallation neutron source for Boron Neutron Capture Therapy (BNCT) was investigated.BackgroundBNCT is based on the neutron irradiation of a 10B-containing compound located selectively in tumor cells. Among various types of neutron generators, the spallation neutron source is a unique way to generate high-energy and high-flux neutrons.Materials and MethodsNeutron beam was generated by a proton accelerator via spallation reactions and then the produced neutron beam was shaped to be appropriate for BNCT. The proposed Beam Shaping Assembly (BSA) consists of different moderators, a reflector, a collimator, as well as thermal and gamma filters. In addition, the simulated Snyder head phantom was utilized to evaluate the dose distribution in tumor and normal tissue due to the irradiation by the designed beam. MCNPX2.6 Monte Carlo code was used to optimize BSA as well as evaluate dose evaluation.ResultsA BSA was designed. With the BSA configuration and a beam current of 104 nA, epithermal neutron flux of 3.94 × 106 [n/cm2] can be achieved, which is very low. Provided that we use the beam current of 5.75 μA, epithermal neutron flux of 2.18 × 108 [n/cm2] can be obtained and the maximum dose of 38.2 Gy-eq can be delivered to tumor tissue at 1.4 cm from the phantom surface.ConclusionsResults for 230 MeV protons show that with proposed BSA, proton beam current about 5.75 μA is required for this purpose. 相似文献
10.
《Molecular medicine today》1998,4(4):174-181
Boron neutron capture therapy (BNCT) is currently undergoing clinical trials in the USA, Japan and The Netherlands with patients afflicted with deadly brain cancer (glioblastoma multiforme) or melanoma. This therapy relies on a binary process in which the capture of a slow neutron by a 10B nucleus leads to an energetic nuclear fission reaction, with the formation of 7Li3+ and 4He2+ and accompanied by about 2.4 MeV of energy. The fleeting 7Li3+ and 4He2+ travel a distance of only about the diameter of one cell, and they are deadly to any cell in which they have been produced. Research in progress is concerned with the development of advanced boron agents and neutron sources, other than nuclear reactors, for the treatment of a variety of cancer types using novel 10B delivery methods. Non-malignant diseases such as rheumatoid arthritis offer additional opportunities for BNCT. The entire BNCT area awaits commercialization. 相似文献
11.
R.G. FAIRCHILD D.N. SLATKIN J.A. CODERRE P.L. MICCA B.H. LASTER S.B. KAHL P. SOM I. FAND F. WHEELER 《Pigment cell & melanoma research》1989,2(4):309-318
A number of groups in the United States have received funding that will permit evaluation of the clinical efficacy of the neutron capture therapy (NCT) procedure. Various reactors are being modified to allow the construction of an epithermal neutron beam. At the Brookhaven Medical Research Reactor (BMRR), the patient irradiation facility is being modified to produce an optimized epithermal neutron beam. An 80-cm-thick Al-D2O mixture (184 g/cm2, 25% D2O by volume) is being installed in the shutter assembly. One-dimensional calculations indicate that this configuration should provide an epithermal neutron flux density of ~1 × 109 n/cm2/sec at 3 MW and a concomitant fast neutron dose rate of ~2 × 10?11 rad per epithermal neutron (assuming a homogeneous Al-D2O mixture). The actual geometry will be an inhomogeneous array of D2O and Al layers producing parameters somewhat less favorable than those listed above; experimental verification is in progress. Significant gains have recently been made in selectively targeting B to melanoma with various melanaffinic compounds, including p-boronophenylalanine, and with boronated porphyrins that may be applicable to a variety of tumors. Neutron capture radiographs have been obtained with the above compounds, and efforts have been made to quantitate boron uptake in growing and quiescent or necrotic regions of tumor via double-labeling techniques obtained with tritiated thymidine. A correlation between therapeutic efficacy and the ability to deliver boron to viable areas of tumor has been observed. 相似文献
12.
Degradation of Carbazole by Microbial Cells Immobilized in Magnetic Gellan Gum Gel Beads 总被引:1,自引:1,他引:0
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Xia Wang Zhonghui Gai Bo Yu Jinhui Feng Changyong Xu Yong Yuan Zhixin Lin Ping Xu 《Applied microbiology》2007,73(20):6421-6428
Polycyclic aromatic heterocycles, such as carbazole, are environmental contaminants suspected of posing human health risks. In this study, we investigated the degradation of carbazole by immobilized Sphingomonas sp. strain XLDN2-5 cells. Four kinds of polymers were evaluated as immobilization supports for Sphingomonas sp. strain XLDN2-5. After comparison with agar, alginate, and κ-carrageenan, gellan gum was selected as the optimal immobilization support. Furthermore, Fe3O4 nanoparticles were prepared by a coprecipitation method, and the average particle size was about 20 nm with 49.65-electromagnetic-unit (emu) g−1 saturation magnetization. When the mixture of gellan gel and the Fe3O4 nanoparticles served as an immobilization support, the magnetically immobilized cells were prepared by an ionotropic method. The biodegradation experiments were carried out by employing free cells, nonmagnetically immobilized cells, and magnetically immobilized cells in aqueous phase. The results showed that the magnetically immobilized cells presented higher carbazole biodegradation activity than nonmagnetically immobilized cells and free cells. The highest biodegradation activity was obtained when the concentration of Fe3O4 nanoparticles was 9 mg ml−1 and the saturation magnetization of magnetically immobilized cells was 11.08 emu g−1. Additionally, the recycling experiments demonstrated that the degradation activity of magnetically immobilized cells increased gradually during the eight recycles. These results support developing efficient biocatalysts using magnetically immobilized cells and provide a promising technique for improving biocatalysts used in the biodegradation of not only carbazole, but also other hazardous organic compounds. 相似文献
13.
PurposeScanning proton therapy has dosimetric advantage over passive treatment, but has a large penumbra in low-energy region. This study investigates the penumbra reduction when multi-leaf collimators (MLCs) are used for line scanning proton beams and secondary neutron production from MLCs.MethodsScanning beam plans with and without MLC shaping were devised. Line scanning proton plan of 36 energy layers between 71.2 and 155.2 MeV was generated. The MLCs were shaped according to the cross-sectional target shape for each energy layer. The two-dimensional doses were measured through an ion-chamber array, depending on the presence of MLC field, and Monte Carlo (MC) simulations were performed. The plan, measurement, and MC data, with and without MLC, were compared at each depth. The secondary neutron dose was simulated with MC. Ambient neutron dose equivalents were computed for the line scanning with 10 × 10 × 5 cm3 volume and maximum proton energy of 150 MeV, with and without MLCs, at lateral distances of 25–200 cm from the isocenter. The neutron dose for a wobbling plan with 10 × 10 × 5 cm3 volume was also evaluated.ResultsThe lateral penumbra width using MLC was reduced by 23.2% on average, up to a maximum of 32.2%, over the four depths evaluated. The ambient neutron dose equivalent was 18.52% of that of the wobbling beam but was 353.1% larger than the scanning open field.ConclusionsMLC field shaping with line scanning reduced the lateral penumbra and should be effective in sparing normal tissue. However, it is important to investigate the increase in neutron dose. 相似文献
14.
P. Kubeš V. D. Korolev Yu. L. Bakshaev P. I. Blinov M. I. Ivanov E. D. Kazakov J. Kravárik D. Klír L. V. Korel’skiĭ E. V. Kravchenko K. Řezáč G. I. Ustroev A. S. Chernenko A. Yu. Shashkov 《Plasma Physics Reports》2008,34(1):52-59
Results are presented from Z-pinch experiments performed in the S-300 facility (Kurchatov Institute) at a maximum current of 2 MA and current rise time of 100 ns. The Z-pinch load was a 1-cm-long 1-cmdiameter cylindrical array made of 40 tungsten wires with a total mass of 160 μg, at the axis of which a 100-μm-diameter (CD2) n deuterated fiber was installed. Hard X-ray and neutron signals were recorded using five scintillation detectors oriented in one radial and two axial directions. The maximum neutron yield from the DD reaction reached 3 × 109 neutrons per shot. The average neutron energy was determined from time-of-flight measurements and Monte Carlo simulations under the assumption that the neutron emission time was independent of the neutron energy. The average neutron energy in different experiments was found to vary within the range 2.5–2.7 MeV. The fact that the average neutron energy was higher than 2.45 MeV (the energy corresponding to the DD reaction) is attributed to the beam-target collisional mechanism for the acceleration of deuterons to 100–500 keV. 相似文献
15.
Yu. L. Bakshaev P. I. Blinov V. V. Vikhrev S. A. Dan’ko V. D. Korolev B. R. Meshcherov S. L. Nedoseev E. A. Smirnova G. I. Ustroev A. S. Chernenko A. Yu. Shashkov 《Plasma Physics Reports》2006,32(7):531-538
Results are presented from measurements of neutron emission generated during discharges with current amplitudes of up to 3 MA and a current rise time of ~100 ns through profiled loads 10 mm in height and 4–5 mm in diameter. The experiments were performed with the S-300 eight-module high-power generator. To enhance the effect of energy accumulation, a≤1-mm-diameter neck was made in the central region of the load. An agar-agar foam of mass density 0.1 g/cm3 with an additive of deuterated polyethylene was used as a plasma-forming material. The formation of a hot plasma in the Z-pinch constriction was accompanied by the emission of soft X-ray (E = 1–10 keV), hard X-ray (E ≥ 30 keV), and neutron pulses with a minimum pulse duration of ≤10 ns. The neutron energy measured by the time-of-flight technique in three directions relative to the load axis (0°, 90°, and 180°) was found to be 2.5 ± 0.3 MeV, which corresponds to the dd reaction. The total neutral yield during the development of one constriction with a characteristic size of 100 μm attained 108 neutrons per pulse. 相似文献
16.
J. Uhlík 《Biologia Plantarum》1972,14(2):97-102
The first information concerning the cytogenetic efficiency of thermal neutrons in lentil are presented in this paper. The range of cytologically effective dosages of thermal neutrons in lentil was determined. This determination enables us to compare the efficiency with the mutagenic effect of thermal neutrons and with their effect on the growth and development of plants of M1 generation. These effects were already evaluated in previous communications. Thermal neutron irradiation significantly affected all the characters studied. A linear dependence of the effect on the dose of the neutron radiation was found for most of the analyzed characters. From a sample of scored cells, whose nuclei were in the anaphase or early telophase, 9.0 to 72.0% of them had chromosomal bridges and fragments after irradiation with dosages from 3.3×1011 n cm?2 to 4.5×1012 n cm?2. The highest number of rearrangements per one cell reached 2.16 after irradiation with 4.25×1012 n cm?2 while the lowest dosage used, 3.3×1011 n cm?2, induced 0.17 of chromosomal rearrangements per one cell. Irradiation with thermal neutrons is capable of inducing a large number of very complicated chromosome rearragements. 相似文献
17.
The research was provided on the small plasma focus device with the Mather-type electrodes in configuration with an auxiliary
electrode placed in front of the anode. It works at the current maximum of 200 kA. The total neutron yield from D-D reaction
reaches 105–107 per one shot. The hard X-rays and neutrons were detected with scintillation detectors and the soft X-rays with a PIN detector
and four MCP frames. We present preliminary results obtained from different configurations of the anode (inner electrode)
and auxiliary electrode and we compare these results with that obtained in configuration without auxiliary electrode. The
auxiliary electrode decreased both the neutron yield and the time of hard X-ray and neutron production. Different electrode
faces has influence on the energy distribution of generated neutrons. 相似文献
18.
G. N. Dudkin B. A. Nechaev V. N. Padalko V. M. Bystritsky V. V. Gerasimov R. V. Kublikov S. S. Parzhitsky V. L. Stolupin J. Vozniak V. I. Veretel’nik É. G. Furman 《Plasma Physics Reports》2005,31(12):1039-1047
Results are presented from experimental studies of the neutron emission generated in the collision of deuterium plasma flows produced in discharges in crossed E × H fields and propagating in opposite directions in a neutral gas across an external magnetic field. It is shown that the interaction of oppositely propagating deuterium plasma flows gives rise to the generation of soft X-ray emission and neutron emission from the dd reaction (dd → 3He + n) and is accompanied by an almost complete depolarization of the flows and rapid variations in the magnetic field (at a rate of ~1011 G/s). The measurements were performed at energies and velocities of the flows of up to 600 J and 3.5 × 107 cm/s, respectively. The plasma density in each flow was ~1015 cm?3. The upper estimates for the astrophysical S factor and the effective cross sections of the dd reaction obtained from our measurements are compared to theoretical calculations and to the results of experiments performed in the MIG high-current accelerator (Institute of High-Current Electronics, Russian Academy of Sciences, Tomsk). 相似文献
19.
ATSUKO KOMURA TAKESHI TOKUHISA TOSHIO NAKAGAWA AKIHIRO SASASE MASAMITSU ICHIHASHI SOLDANO FERRONE YUTAKA MISHIMA 《Pigment cell & melanoma research》1989,2(4):259-263
We previously established methods which have enabled us to target a sufficient number of 10B atoms on human melanoma cells to destroy them by thermal neutron irradiation. Monoclonal antibodies were here used as vector of 10B atoms on the target cell. Thermal neutrons require at least 10910B atoms to destroy the cell. In order to accumulate an adequate number of 10B atoms on target cells, our first approach was to make an effective compound that contains 12 atoms of 10B in a molecule. The second step was to conjugate the compound with an avidin molecule (10B12-avidin). One molecule of the 10B12-avidin carries about 30 atoms of 10B. This 10B12-avidin can be specifically targeted on human melanoma cells by biotinated monoclonal antibodies specific for the cells. Furthermore, the number of 10B atoms on target cells can be augmented by a hapten-antihapten monoclonal antibody system. The cultured human melanoma cells treated with these methods were damaged by thermal neutron irradiation. This is the first study that indicates thermal neutrons do injure target cells boronated by monoclonal antibodies. 相似文献
20.
Measurement of boron concentration in biological tissues is a fundamental aspect of boron neutron capture therapy, because the outcome of the therapy depends on the distribution of boron at a cellular level, besides on its overall concentration. This work describes a measurement technique based on the spectroscopy of the charged particles emitted in the reaction 10B(n,α)7Li induced by thermal neutrons, allowing for a quantitative determination of the boron concentration in the different components that may be simultaneously present in a tissue sample, such as healthy cells, tumor cells and necrotic cells. Thin sections of tissue containing 10B are cut at low temperatures and irradiated under vacuum in a thermal neutron field. The charged particles arising from the sample during the irradiation are collected by a thin silicon detector, and their spectrum is used to determine boron concentration through relatively easy calculations. The advantages and disadvantages of this technique are here described, and validation of the method using tissue standards with known boron concentrations is presented. 相似文献