Simulation of distribution of radiation energy density in water balls

The distribution of energy deposition density in radiate region and its surrounding areas from y-rays was simulated and analyzed for a water-ball model with Geant4 package （ Geant4.7.0,2005 ） developed by CERN （the Center of European Research of Nucleus）. The results show that the distribution depends strongly on the collimating condition of radiation beam. A well-collimated beam would reduce radiation effects on surrounding areas.     

Search for the Halo Effect in the ~1H(~6He,~6Li)n Reaction

The experiment is carried out using the secondary beam facility of the HI-13 tandem accelerator at China Institute of Atomic Energy, Beijing. The experimental setup is similar to the previously illustrated. A 7Li beam with energy of 44 MeV from the tandem impinged on a D2 gas cell at pressure of 1.5×105 Pa, in which 6He ions are produced via 2H(7Li, 6He)3He reaction. The front and rear     

Study of Mutagenic Effects of M_1 Generation of Maize Seeds Irradiated by Heavy Ions

In order to study M_1 biological effects induced by heavy ion irradiation on maize seeds, the embryosof dry maize seeds are irradiated with ~7Li and ~(12)C ions. The experiment is performed at the heavy ionscanning tube of the HI-13 tandem accelerator. The beam goes through a thickness of 25μm. Then themaize seeds are irradiated in the air uniformly. The linear energy transmission of ~7Li and ~(12)C are 120 and     

Numerical Simulation of Radial and Angular Distribution of γ-Ray＇s Energy Deposition in Scintillation Optical Fibre

Angular and radial distributions of the energy deposition of γ-ray radiation in scintillation optical fibres are simulated and analysed using the Geant4 system. The results show a linear relation between the energy deposition and the radius of the fibres. The deposition is roughly inversely proportional to sinθ with θ the incident angle relative to the fibre axis. The results could provide corrections to the measurements of the scintillation fibres used in monitoring the γ-ray radiation.     

Effects due to multiple scattering of fission fragments in layers of fissioning material

Computer simulation with the SRIM program is used to investigate the passage of fragments from ²³⁵U fission by thermal neutrons through 50–400 μg/cm² thick uranium layers. The calculations are performed in the two-fragment approximation: light ⁹⁷Mo and heavy ¹³⁹Ba. The energy spectra of the fission fragments emanating from the layer are calculated and the effects due to multiple scattering of the fragments in thin layers are estimated. __________ Translated from Atomnaya énergiya, Vol. 100, No. 1, pp. 57–63, January, 2005.     

Theoretical research on the transport and ionization rate coefficients in glow discharge dusty plasma

The electron kinetic model for investigating the transport and ionization rate coefficients of argon glow discharge dusty plasma is developed from the Boltzmann equation.Both of the electron-neutral and electron-dust collisions are considered as collision terms in the kinetic equation.The kinetic equation is simplified by employing the local approximation and nonlocal approach under the same discharge conditions,and the corresponding simplified kinetic equations are known as local and nonlocal kinetic equations respectively.Then the electron energy distribution function(EEDF)is obtained by numerically solving the local and nonlocal kinetic equations and the dust charging equations simultaneously.Based on the obtained EEDFs,the effective electron temperature,electron mobility,electron diffusion coefficient and ionization rate coefficient are calculated for different discharge conditions.It is shown that the EEDFs calculated from the local kinetic model clearly differ from the nonlocal EEDFs and both the local and nonlocal EEDFs are also clearly different with Maxwellian distributions.The appearance of dust particles results in an obvious decrease of high energy electrons and increase of low energy electrons when axial electric field is low.With the increase of axial electric field,the influence of dust particles on the EEDFs becomes smaller.The electron mobility and diffusion coefficients calculated on the basis of local and nonlocal EEDFs do not differ greatly to the dust-free ones.While,when dust density nd=10^6 cm^?3,the electron mobility increases obviously compared with the dust-free results at low axial electric field and decreases with the increasing axial electric field until they are close to the dust-free ones.Meanwhile,electron diffusion coefficients for dusty case become smaller and decrease with the increasing axial electric field.The ionization rate coefficients decrease when dust particles are introduced and they approach the dust-free results gradually with the increasing axial electric field.     

The plume diagnostics of 30 cm ion thruster with an advanced plasma diagnostics system

In order to achieve a better understanding of plume characteristics of LIPS-300 ion thruster, the beam current density, ion energy and electron number density of LIPS-300 ion thruster plume are studied with an Advanced Plasma Diagnostics System(APDS) which allows for simultaneous in situ measurements of various properties characterizing ion thruster, such as plasma density, plasma potential, plasma temperature and ion beam current densities, ion energy distribution and so on. The results show that the beam current density distribution has a double‘wing' shape. The high energy ions were found in small scan angle, while low energy ions were found in greater scan angle. Electron number density has a similar shape with the beam current density distribution.     

Analysis of the Anomalous Phenomenon in the Retarding Potential Analyzer Measurements

An anomalous phenomenon was observed in the retarding potential analyzer （RPA） measurements of the energy of the ion beam from an 8 cm argon ion source. The current-voltage （Ⅰ- Ⅴ） curve, which should theoretically descend, went up as the ion retarding potential was increased. Various explanations, such as the Townsend discharge theory and secondary electron emission etc. were proposed but denied by the theory application condition or the experiment results. An angle of about -10° was found between the axes of the ion beam and the RPA according to the contours of the ion beam density and direction. The particle simulation and experiment of the sum of the collector and wall current were conducted at different incident ion angles. The trends of the Ⅰ- Ⅴ curve in simulation results conformed with the experimental results in most cases. The ion trajectories were simulated at different retarding potentials with an incident angle of -10°. According ：to these results, the reason for the anomalous phenomenon is that when there is a specific angle between the axes of the ion beam and the RPA, more ions are repelled from the vicinity of the ion retarding grid to avoid striking on the grid as the ion retarding potential increases. These redundant ions reach the plate and thus lead to the formation of an ascending Ⅰ- Ⅴ curve.     

Beam optics study for energy selection system of SC200 superconducting proton cyclotron

To meet the demands on proton therapy in Russia and China, JINR and ASIPP have started to develop a proton therapy facility based on an isochronous superconducting proton accelerator. A 200 Me V/500 n A proton beam will be extracted from the SC200 superconducting proton cyclotron. Due to the energy of the cyclotron being fixed, an energy selection system(ESS) is employed to degrade such energy in order to match the particle energy to a shallower depth. In this article, calculation of beam optics, analysis of beam transmission, and correction of orbit distortion are presented. Studies show that the main factors influencing transmission efficiency of the SC200 ESS beamline are the degrader, collimator, slit, vacuum system, beam diagnostic system, and trajectory correction system. Through the beam optics study, the designed ESS beamline can provide 70–200 Me V proton beam to a treatment room, with a maximum emittance of24 p mm mrad. Also, the controllable momentum spread ranges from 0.1 to 1.0%, which is equivalent to an energy spread from 0.193 to 1.93%. The transmission efficiency about 0.204% can be obtained when the emittance is24 p mm mrad with an energy spread of ± 0.6%.     

Application of nuclear analytical techniques to trace elements in Cenozoic basalt and their mantle xenoliths from Aershan area in Inner Mongolia, China

Basaltic samples from different locations in Aershan area determined by instrumental neutron activation analysis (INAA) have the same distribution patterns of REE and trace elements. The similar REE contents of the same minerals without inclusions from different xenolith suggest that the mantle source region under different active volcanoes have the same composition. The REE content differences between the same minerals with and without melt inclusions selected from the same mantle xenolith indicate that the melt inclusions are rich in REE. The same patterns of trace elements of inclusions and host minerals from different xenolith analyzed by SRXRF suggest that the mantle fluid has no notable heterogeneity in Aershan area.     

ION RESONANCE AND SCATTERING TECHNIQUES FOR MEASURING SURFACE AND SUBSURFACE TOPOGRAPHY

Non- focused ion beams may be employed to investigate the surface profile and the shape of microscopic objects or periodic surfaces by using the known stopping powers of ions in solids. The energy spectra of the scattered or reaction ions are recorded as a function of the angles between the beam, the object and the detector, and of the energy of incident ions. The shape parameters may then be determined using computer codes. Presented also are the typical experimental results.     

Study on Fragments Emission in the 64Ni+64Ni Reaction at 40 AMeV

The multiplicity of fragments in Fermi energy heavy-ion collisions was experimen-tally extracted. Compared with the results of calculation using the antisymmetrized molecular dynamics (AMD) model which accounts for the primary fragments only, the results calculated using the AMD together with a statistical decay code GEMINI to account for the deexcitation of excited primary fragments are in better agreement with those extracted from the experiment. This observation indicates that the experimental multiplicity distribution may be significantly different from those of primary fragments.     

Production of dileptone with intermediate masses in an expanding quark-glunon matter

A strudy of dilepton spectra ,in intermediate mass region (IMR), from main background sources,quark phase,and secondary processes in hadronic phase on the basis of a relativistic hydrodynamic model has been carrid out .The comparison between these results indicates that in this mass region the contribution from the background sources dominates,and due to the effect of the phase boundary on the evolution of the system the contribution from the quark phase becomes more importhant than that from secondary processes.     

Preliminary Studies on Base Substitutions and Repair of DNA Mismatch Damage Stimulated by Low Energy N＋ Ion Beam Implantation in Escherichia coli

Ever since the low energy N+ ion beam has been accepted that the mutation effects of ionizing radiation are attributed mainly to direct or indirect damage to DNA. Evidences based on naked DNA irradiation in support of a mutation spectrum appears to be consistent, but direct proof of such results in vivo are limited. Using mutS, dam and/or dcm defective Eschericha coli imitator strains, an preliminary experimental system on induction of in vivo mutation spectra of low energy N+ ion beam has been established in this study. It was observed that the mutation rates of rifampicin resistance induced by N+ implantation were quite high, ranging from 9.2×10-8 to 4.9 ×10~5 at the dosage of 5.2 ×1014 ions/cm2. Strains all had more than 90-fold higher mutation rate than its spontaneous mutation rate determined by this method. It reveals that base substitutions involve in induction of mutation of low energy nitrogen ion beam implantation. The mutation rates of mutator strains were nearly 500-fold (GM2929), 400-fol     

A Mutant of Bacillus Subtilis with High-Producing Surfactin by Ion Beam Implantation

In order to generate a mutant of Bacillus subtilis with enhanced surface activity through low energy nitrogen ion beam implantation, the effects of energy and dose of ions implanted were studied. The morphological changes in the bacteria were observed by scanning electron microscope （SEM）. The optimum condition of ions implantation, 20 keV of energy and 2.6 × 10^15N^＋/cm^2 in dose, was determined. A mutant, B.s-E-8 was obtained, whose surface activity of 50-fold and 100-fold diluted cell-free Landy medium was as 5.6-fold and 17.4-fold as the wild strain. The microbial growth and biosurfactant production of both the mutant and the wild strain were compared. After purified by ultrafiltration and SOURCE 15PHE, the biosurfactant was determined to be a complex of surfactin family through analysis of electrospray ionization mass spectrum （ESI/MS） and there was an interesting finding that after the ion beam implantation the intensities of the components were different from the wild type strain.     

The Impact of Electrode Configuration on Characteristics of Vacuum Discharge Plasma

Generation characteristics of vacuum discharge plasma are very important for the applied research of metal plasma.The vacuum discharge electrode configuration and the cathode material affect the generation characteristics of the metal plasma which consists of metal ions coming from cathode and generated by vacuum discharge.In this research,the generation characteristics of the metal plasma generated by vacuum discharge are discussed for four patterns of electrode configurations,i.e.cone-mesh electrode setup,cone-cross line electrode setup,cone-line electrode setup and cone-ring electrode setup.Characteristics of the metal plasma,such as electron density,electron temperature,space potential,ion energy,are measured by the probe method for discussing the impacts of different electrode configurations on the density of generated metal plasma.Moreover,the diffusion velocities of the metal plasma are measured for cathode materials of Pb,Al,and Cu,respectively.The experimental results indicate that the plasma generated by the discharge of cone-ring electrode configuration possesses the maximum density and the metal plasma generated by the Al cathode possesses the fastest diffusion velocity and the highest kinetic energy.     

Nuclear Level Density and Spin Cut-off Parameters of Light Nuclei

Nuclear level densities, thermodynamic functions and spin cut-off factors have been deduced for nuclei in the mass region 24相似文献   

An improved thermometer for intermediate-mass fragments

An improved thermometer (TIB) is proposed for intermediate-mass fragments via the difference between isobaric yield ratios. The residual free energy of three isobars is replaced by that of the binding energy. The measured fragments in the 140A MeV 40, 48Ca+ 9Be (181Ta) and 58, 64Ni+ 9Be (181Ta) reactions are analyzed to obtain TIB ranging from 0.6 to 3.5 MeV. TIB is suggested to be a direct determination of temperature avoiding the fit-ting procedure.     

Research on Key Technique of Single Particle Effect Heavy Ion Microbeam Irradiation Experiment

正In 2001,the China Institute of Atomic Energy used pinhole collimation technology to build a heavy ion microbeam irradiation device.Since the commercial pinholes are mostly tapered and the inside finish is poor,the generated scattered ions cause ion energy distortion and the beam spot size     

Progress on Nuclear Reaction Mechanism and Its Application by Theory Group of CNDC

1 Nuclear Reaction Mechanism 1.1 The Channel Theory of Fission with Diffusive Dynamics The neutron Data obtained, by using the 800 MeV pulsed proton beam from LAMPF to produce neutron over a broad energy range(from 100 keV to nearly 800 MeV), show that the results of fission cross section calculated by traditional channel theory of fission calculation are significantly above the ex