2021, Volume 38, Issue 1
The network calculation of 26Al nucleosynthesis in 3
In recent years, the cluster structure in nuclei has attracted a lot of attention. The goal of this work is to investigate the yield distribution of heavy ion collisions at Fermi energy and evaluate the
How to produce neutron-rich heavy nuclei is one of the hot topics in nuclear physics, multinucleon transfer reaction would be a possible route to synthesize these nuclei. The time-dependent Hartree-Fock (TDHF) theory is employed to study the multinucleon transfer reaction 136Xe+198Pt at Ec.m.=645 MeV. The nucleon transfer process, energy dissipation and orientation of the deformed reactants on the reaction are investigated. The state-of-art statistical model GEMINI++ is adopted to investigate the deexcitation process of the excited primary fragments. The secondary isotopic production cross sections of the projectile-like fragment are compared with the experimental data. The results indicate that the data of few transfer channels can be well reproduced by TDHF. Discrepancy is observed for large transfer channels and the possible reasons are discussed.
The D-meson production in high energy proton-proton(p-p) and proton-nucleus(p-A) collisions is an important approach to study the character of saturation gluon. By considering the strong coupling effects at leading order, the D meson production in high energy p-p and p-A collisions at LHC energies is studied in the framework of Color Glass Condensate(CGC). Using the dipole amplitude obtained from the KLR-AdS/CFT color dipole model through Fourier transform, and taking into account the cold nuclear matter effects, we investigate the D meson cross section in proton-lead (p-Pb) collisions at
To characterize the phase space distribution of the beam in C-ADS demo linac, beam parameters need to be measured with high accuracy at the exit of RFQ. Transverse information of the beam has been measured via the method of emittance reconstruction and the beam optics has been verified. A method has been adopted to measure beam longitudinal parameters by the SUM-signal of beam position monitors. The bunching voltage of the two bunchers and the SUM-signals in the downstream BPMs are recorded in the experiment. By combining the PSO(Particle Swarm Optimization) method with TraceWin simulation, the results are obtained with the consideration of space charge effect. The measured emittance is quite close to the simulated one in Toutatis.
The equidistant multi-gap acceleration structure is an asynchronous acceleration structure, when the velocity of the particle in the accelerated structure changes significantly, the phase of the particles at each gap is different. Current theories based on thin lens approximation do not take into account the variation in the velocity of the particles in the accelerated structure. This is reasonable in cases where the energy gain in a single cavity is small relative to the particle energy or where the acceleration gradient is small. This treatment is no longer sufficient when there is a significant change in the velocity of the particle in the structure. In this paper, the longitudinal motion dynamics of the beam in this equidistant multi-gap acceleration structure are modeled. By numerical simulations the phase space trajectories are obtained. The phase space trajectories are used to analyze the particles motion in the structure. The energy variations of particles with different initial energies are calculated when the electrical field gradients and gap numbers are different. Results show that compared with the properties of the beam motion predicted by the thin lens approximation theory, phase space trajectories are different, and its effects on energy gain as functions of acceleration gradient, the input energy, the cell numbers and so on are studied.
The power supply system of heavy ion accelerator requires high stability and ripple precision of excitation power supply. Because of the existence of magnet load, the ripple has an impact on the precise control of particle trajectory by magnetic field. To solve the above problems, a new combined algorithm based on SSOGI-RLSMC is proposed to reduce the output current ripple of excitation power supply under the influence of magnet load and improve the current stability. The new joint algorithm extracts the ripple component quickly and accurately by using the parallel Second-Order Generalized Integrator(SSOGI) as the ripple detector, and obtains the command current with high precision. The error signal is obtained by subtracting the command current and the compensation current of the DC active power filter, and the Reaching Law Sliding Mode Control(RLSMC) algorithm is used to track and compensate the error signal dynamically, so as to improve the direct current active power filter can suppress the ripple of the output current of the excitation power supply, so as to achieve the precise control of the particle trajectory. Finally, through MATLAB/Simulink simulation, it is proved that the new joint algorithm can effectively improve the accuracy and stability of the output current of the excitation power supply, and improve the ripple current suppression ability of the DC active power filter.
In order to provide a special method for rapid calculation of shielding thickness or validation of results of Monte Carlo code simulation for medical heavy ion accelerator, FLUKA is employed to perform the calculation of shielding parameters for 400 MeV/u 12C ions on iron and water targets. Firstly, the angle distribution and main compositions of the secondary radiation are studied, and then the attenuation curves of the dose equivalent are given, and the radiation source term(H0) and attenuation length(λ0) are obtained by fitting the data. Finally, the shielding design of a treatment room of medical heavy ion accelerator in Putian is taken as an example to introduce the application of the shielding parameters. The comparison with the simulation results shows that the shielding parameters given in this paper are reliable. These parameters can provide reliable reference data for shielding design of similar medical heavy ion accelerators.
In the measurement of ray intensity, the current signal from the integral ionization chamber is in the range of 10-10~10-15 A, which needs to be converted and amplified before it can be collected. A weak current signal amplification system is designed for the integral ionization chamber in this paper, using AC modulation technology to modulate the weak DC current signal to be measured into AC voltage signal, and then obtains the DC voltage signal after amplification, phase-sensitive detection, filtering and other circuit processing, and finally the data is collected. At the same time, the DC negative feedback is introduced into the system to shorten the response time of current measurement. The linear and response characteristics of the system were tested by the standard current source, and the β ray of tritium target was detected by an integral ionization chamber. The test results show that the system can effectively amplify the weak current signal in the range of 10-14~10-11 A with good linearity and response time characteristics, and the current measurement sensitivity is 10-14 A, the system has a good prospect of engineering application.
Silicon Photomultiplier (SiPM) is a new generation of semiconductor photon detector, which is widely used in high-energy physics, nuclear medical imaging and nuclear physics and other fields. As the bias voltage of different SiPM is different, a high voltage power supply with adjustable voltage and temperature adaptive function is designed to meet the working voltage demand of SiPM. High voltage power supply mainly uses DC/DC module to generate high voltage to supply power to SiPM.The voltage of the high-voltage power supply can reach up to 200 V. The DC/DC module outputs different voltage values by changing the resistance value of the potentiometer to carry out partial voltage. Finally, the stability of DC/DC module, temperature adaptive testing, the performance and working characteristics of the high-voltage power supply plate were completed. The results show that the integral nonlinearity of the DC/DC module is 0.14‰, and the module works steadily. At different temperatures, the maximum change rate of system gain is 1.12%, and the system gain remains relatively stable. The maximum fluctuation of the self-made high-voltage power supply is about 0.01 V, and the work is stable. The ripple coefficient is below 0.02%, with low ripple. Meanwhile, in the same test environment, the resolution of the all-purpose peak of the high-voltage power supply and the commercial power supply are 7.84% and 9.88% respectively, and the performance of the self-made high-voltage power supply is better than that of the commercial power supply.
In this paper, the algebraic reconstruction algorithm is applied to the newly developed High Energy Electron Radiography(HEER) technology to carry out three-dimensional imaging research, which realizes the accurate diagnosis of the internal structure information of the sample material. The Monte Carlo program and the particle tracking program are used to simulate the high-energy electron imaging process, including the interaction process between the electron beam and the target substance, and obtain the high-energy electron two-dimensional imaging results under the imaging angle of the sample. The ART(Algebraic Reconstruction Technique) algorithm and the Filtered Back Projection (Filtered Back Projection) algorithm were used to simulate experiment of Three-Dimensional High Energy Electron Radiography(TDHEER) respectively, and the three-dimensional images of the sample were reconstructed. These images have been quantitatively compared and analyzed through evaluation indexes. The results show that under the condition that the angle number of projection is 180, the reconstruction results of ART are closer to the original image of the sample, which have higher fidelity and fewer image artifacts. In order to further verify the simulation results, actual experiments were carried out, and the conclusions are the same as the simulation. The results of this study provide a basis for the optimization of the subsequent TDHEER.
Boron Neutron Capture Therapy (BNCT) is a new treatment of precision radiotherapy. Beam shaping assembly (BSA) is one of the key components in the facility of BNCT and of vital importance in producing neutron beams appropriate for BNCT treatment. BSA is used to moderate and fast neutrons to suitable energy range, reduce other unwanted ingredients, and meet the requirements for BNCT. In this work, based on a neutron source which produced by a 2.5 MeV/30 mA proton accelerator, the Monte Carlo simulation software MCNP was employed to design BSAs. A multi-terminal BSA scheme was designed to slow down the fast neutron beam generated by proton bombarded Li target to the thermal neutron energy range (<0.5 eV) and the epithermal neutron energy range (0.5 eV~10 keV). The proposed thermal neutron BSA scheme uses D2O as moderator, BeO as reflector, Bi as
We study the physical law of the influence of ion fluence on the electrical properties of magnetic tunnel junctions (MTJ). We find for the first time that high-energy ionization radiation damage caused the failure of MTJ electrical functions in our experiment. The main failure modes are high and low resistance state failures, of which 79.9% are high resistance state failures. Our results show that the damage caused by a single Ta ion with 10.9 MeV/u cannot cause the electrical function of MTJ to fail. Combining theoretical calculations and Monte Carlo simulation analysis, we derive that the damage to the tunnel insulating layer and the ferromagnetic film in the MTJ is the internal cause of high and low resistance state failure.
The transmission of 16-keV Cl– ions through Al2O3 nanocapillaries of 7 and 12 μm in thickness was studied both by experiment and simulation. It is found that the transmission of negative ions is different from that of positive ions through insulating nanocapillaries, where the deposited charges result in the so-called guiding effect. For the case of only the scattering, the transmitted angular distributions and charge state distributions from the simulations agreed well with the experimental results, i.e., the transmitted Cl– ions exits to the direction of the primary beam; the transmitted Cl0 and Cl– spread around the axis of the capillaries. The analysis of the simulated trajectories shows that the transmitted Cl+ ions spans from the axis of nanocapillaries to the primary beam direction; the transmitted Cl0 due to the single scattering is centered around the axes of the nanocapillaries while the transmitted Cl0 through multiple scattering shifts to the direction from the axes of the capillaries to the primary beam direction. From the simulations, it is found that the ratio of Cl+/Cl0 for the transmitted particles exited from the nanocapillaries of longer lengths is lower, in accord to the experiments. The increase of the length of the capillaries will lead to the drop of the portion of transmitted Cl0 by single scattering and the increase of the probability of the exiting of Cl0 through multiple scatterings. Therefore the probability of Cl+ ions changed to Cl0 is much larger than that Cl0 changed to Cl+ ions in the collision process, leading to the smaller ratio of Cl+/Cl0 for the transmitted particles exited from the nanocapillaries of longer lengths.
The positron trapping behavior of Ag precipitates at 823 K quenched and 20% deformation Al-4%Ag alloy at low temperature was studied respectively. It was characterized by positron annihilation lifetime spectroscopy (PALS) technology and coincident Doppler broadening spectroscopy (CDBS) in the temperature range of 10~293 K. The positions of the Ag precipitate peak in the Doppler broadening spectrum shows that there are Ag precipitates in both samples. The components of the lifetime spectrum analysis results show that the change of Ag precipitates with the measurement temperature has a strong temperature dependence at the range of 170~273 K. However, for two specimens with different types of defects, in the measurement data below 170 K, a difference in the positron trapping ability of the Ag precipitates in the sample was observed. With the decrease of the measurement temperature, both the positron lifetime and it’s intensity of the Ag precipitates in the quenched specimens begin to stabilize and lose their dependence on temperature. In the measurement below 170 K, the precipitating ability of the Ag precipitates in the deformed sample still has a strong temperature dependence, but the change amplitude is gradually weakening. In the end, when the measurement temperature increased to around room temperature (273~293 K), more and more positrons escaped from the Ag precipitate, gradually transitioned back to the free state or trapping by other deep traps, and lost the temperature dependence.
The EXchange FORmat (EXFOR) experimental nuclear reaction database and the retrieval system provide access to the wealth of low- and intermediate-energy nuclear reaction physics data, and become the most comprehensive compilation of experimental nuclear reaction data. Currently, there are 13 participants (nuclear data centers) of the International Network of Nuclear Reaction Data Centers(NRDC) which has been organized under the auspices of the International Atomic Energy Agency(IAEA) to coordinate the collection, compilation, and dissemination of nuclear data on an international scale. As the participant of NRDC, China Nuclear Data Center(CNDC) does its best for measurement of nuclear reaction quantities induced by neutron and charged-particle and research on the technique of database construction. The formation, development and current situation of EXFOR library, and its format, compilation and retrieval system were introduced. The work on compilation of experimental nuclear reaction data and study of the database construction technique in China was briefly summarized, such as scanning Chinese journals, compiling EXFOR entries, developing software, providing nuclear data service in China, collaborating with NRDC and so on.