Radiation damage in 4H-SiC samples implanted by 70 keV oxygen ion beams was studied using photoluminescence and electron spin resonance techniques. ESR peak of g=2.0053 and two zero-phonon lines (ZPL) were observed with the implanted samples. Combined with theoretical calculations, we found that the main defect in the implanted 4H-SiC samples was oxygen-vacancy complex. The calculated defect formation energies showed that the oxygen-vacancy centers were stable in n-type 4H-SiC. Moreover, the VSiOC0 and VSiOC-1 centers were optically addressable. The results suggest promising spin coherence properties for quantum information science.

In designing a fixed bed adsorber, it is vital to understand dynamic adsorption properties of the unit. Temperature is an important effect on adsorbent performance, as the dynamic adsorption coefficients tend to increase with decreasing temperature. To minimize the volume of the fixed bed adsorber, the dynamic adsorption characteristics of Xe were studied at 77 K by employing a variety of adsorbents under different operational conditions. The carbon molecular sieve performed better than that of activated carbon. Both operational conditions and the presence of gaseous impurities were found to affect the adsorption properties.

There is considerable interest in potential aneutronic fusion reactors.One possible reaction is ¹¹B(p,α) 2α. However, the emitted alpha particles are energetic enough to generate neutrons by interacting with boron inside the reactor through the¹¹B(α,n)¹⁴N and ¹⁰B(α,n)¹³N reactions.To aid in evaluating neutron production within this potential aneutronic reactor, the total cross sections were measured for the ¹¹B(α,n)¹⁴N reaction between 2 and 6 MeV and for the ¹⁰B(α,n)¹³N reaction between 2 and 4.8 MeV. The results are presented and compared with previously reported results.

The Level-2 Probabilistic Safety Assessment (PSA) of pressurized water reactors studies the possibility of creep rupture for major reactor coolant system components during the course of high pressure severe accident sequences. The present paper covers this technical issue and tries to quantify its associated phenomenological uncertainties for the development of Level-2 PSA. A framework is proposed for the formal quantification of uncertainties in the Level-2 PSA model of a PWR type nuclear power plant using an integrated deterministic and probabilistic safety assessment approach. This is demonstrated for estimation of creep rupture failure probability in station blackout severe accident of a 2-loop PWR, which is the representative case for high pressure sequences. MELCOR 1.8.6 code is employed here as the deterministic tool for the assessment of physical phenomena in the course of accident. In addition, a MATLAB code is developed for quantification of the probabilistic part by treating the uncertainties through separation of aleatory and epistemic sources of uncertainty. Theprobability for steam generator tube creep rupture is estimated at 0.17.

It can be difficult to calculate someunder-sampled regions in global Monte Carlo radiation transport calculations. The global variance reduction (GVR) method is a useful solution to the problem of variancereduction everywhere in aphase space. In this research, a GVR procedure was developed and applied to the Chinese Fusion Engineering Testing Reactor (CFETR). A cylindricalCFETR modelwas utilized for comparingvarious implementations of the GVR methodto find the optimum.It was found that the flux-based GVR methodcouldensure more reliable statistical results, achievingan efficiency being7.43 times that of theanalog case. A mesh tally of the scalar neutron flux was chosen for the GVR method to simulate global neutron transport in the CFETR model. Particles distributed uniformly in the system were sampled adequatelythrough teniterations ofGVR weight window. All voxels were scored, and the average relative error was2.4% in the ultimate step of the GVR iteration.

Fluoride salt-cooled High-temperature Reactors (FHRs) includemany attractive features, such as high temperature, large heat capacity, low pressureand strong inherent safety. Transient characteristics of FHR areparticularly important for evaluating its operation performance.Thus, a specialized code OCFHR (Operation and Control analysis code of FHR)isused to studyan experimental FHR’s operation behaviors. The geometric modeling of OCFHR is based on one-dimensional lumped parameter method,and some simplifications are taken into consideration during simulation due to the existence of complex structures such as pebble bed, intermediate heat exchanger (IHX),air radiator (AR) and multiply channels. Apoint neutron kinetics modelis developed and neutronphysics calculation is neededto provide some key inputs including axial power density distribution, reactivity coefficients and parameters about delayed neutron precursors. For analyzing the operational performance, five disturbed transients are simulated, involvingreactivity step insertion, variations of coolant mass flow rate of primaryloop andintermediate loop, adjustment of air inlet temperature,and mass flow rate of air-cooling system. Simulation results indicate that inherent self-stabilityof FHRrestrains severe consequencesunderabove transients, and some dynamic featuresareobserved, such as large negative temperature feedbacks, remarkable thermal inertia, and high response delay.

Beam lifetime of a synchrotron is dominated by Touschek scattering. In the beamline Phase II project of Shanghai synchrotron radiation facility (SSRF), a passive third harmonic cavity is to be installed for bunch-lengthening and instability-suppressing. In this paper, the beam dynamics of the cavity is investigated. The parameters of passive operation are optimized to cancel the slope of RF voltage and lengthen the bunches. The Touschek lifetime increases are estimated for optimum and non-optimum voltage flattening. A tolerance of the operation is studied in case that there is a shift on detuning angle. The effect caused by reduction of harmonic voltage generated by lengthened bunch distribution is also estimated using iteration method. An increase of synchrotron frequency spread due to nonlinearity of the voltage giving to the bunch is found by using tracking simulation. This spread can help in damping coupled bunch instability through Landau damping.

The High Intensity Heavy Ion Accelerator Facility (HIAF) is under design at the Institute of Modern Physics (IMP) and will provide an intense ion beam for nuclear physics, atomic mass measurement research, and other applications. As the main ring of HIAF, the BRing accumulates beams to high intensity and accelerates them to high energy. To achieve high intensities up to 1e11 (²³⁸U³⁴⁺), the injection gain of the BRing must be as high as 88. However, multiple multiturn injection supported by the electron cooling system takes a long time, causing substantial beam loss under a strong space charge effect. Hence, a two-plane painting injection scheme is proposed for beam accumulation in the BRing. This scheme uses a tilted injection septum and horizontal and vertical bump magnets to paint the beam into horizontal and vertical phase space simultaneously. In this paper, the two-plane painting injection parameters are optimized, and the resulting injection process is simulated using the Objective Ring Beam Injection and Tracking (ORBIT) code. An injection gain of up to 110.3 with a loss rate of 2.3% is achieved, meeting the requirements of BRing.

A two stage echo-enabled harmonic generation (EEHG) scheme is proposed for a superconducting linac-driven FEL to produce coherent hard X-rays. Electron beams of quite different bunch lengths are separately used in each stage of EEHG and a monochromator is designed to purify the radiation from the first stage for seeding the second stage. Theoretical analysis and 3D simulations indicate that the proposed scheme can generate high repetition-rate coherent hard X-ray pulses directly from a conventional UV seed laser.

A novel surface muon capture system with a large acceptance was proposed based on the China Spallation Neutron Source (CSNS). This system was designed using a superconducting solenoid where a long graphite target was put inside it. Firstly, the spin polarization evolution was studied in a constant uniform magnetic field. As the magnetic field can interact with the spin of the surface muon, both the spin polarization and production rate of the surface muons collected by the new capture system were calculated by the G4beamline. Simulation results showed that the surface muons could still keep a high spin polarization (>90%) with different magnetic fields (0 to 10 T), and the large magnetic field is, the more surface muons can be captured. Finally, the proton phase space, Courant-Snyder parameters, and intensities of surface muons of different beam fractions were given with magnetic fields of 0 and 5 T. The solenoid capture system can focus proton and surface muon beams and collect π^± and μ^± particles. It can also provide an intense energetic positron source.

In physical vapor deposition (PVD) on a magnetron cathode, temperature of sensitive components must be kept under threshold limit, so as to ensure the cathode reliability, the process reproducibility, and the best quality of thin films. This can be achieved by an adequate design to enhance the dissipation of heat generated at the cathode. In this paper, temperature distribution and streamlines velocity of the cathode coolant inside a cathode magnetron are analyzed by using CFD solver ANSYS FLUENT in the single phase method in combination with k-ε standards turbulent model. The results show that the design is appropriate under the calculation parameters, and for high heat densities some improvements are necessary to enhance heat dissipation and keep temperature under the threshold limit.

Improving imaging quality of cone-beam CT under large cone angle scan has been an important area of CT imaging research. Considering the idea of conjugate rays and making up missing data, we propose a three-dimensional (3D) weighting reconstruction algorithm for cone-beam CT. The 3D weighting function is added in the back-projection process to reduce the axial density drop and improve the accuracy of FDK algorithm. Having a simple structure, the algorithm can be implemented easily without rebinning the native cone-beam data into cone- parallel beam data. Performance of the algorithm is evaluated using two computer simulations and a real industrial component, and the results show that the algorithm achieves better performance in reduction of axial intensity drop artifacts and has a wide range of application.

The production mechanism of heavy neutron-rich nuclei is investigated by using the multinucleon transfer reactions of ^136,148Xe+²⁰⁸Pb and ²³⁸U+²⁰⁸Pb in the framework of a dinuclear system model. The evaporation residual cross sections of target-like fragments are studied with the reaction system ¹⁴⁸Xe+²⁰⁸Pb at near barrier energies. The results show that the final isotopic production cross sections in the neutron-deficient side are very sensitive to incident energy while it is not sensitive in the neutron-rich side. Comparing the isotopic production cross sections for the reactions of ²⁰⁸Pb bombarded with stable and radioactive projectiles, we find that neutron-rich radioactive beams can significantly increase the production cross sections of heavy neutron-rich nuclei.

Fluctuations of conserved quantities, such as baryon, electric charge, and strangeness number, are sensitive observables in relativistic heavy-ion collisions to probe the QCD phase transition and search for the QCD critical point. In this paper, we review the experimental measurements of the cumulants (up to fourth order) of event-by-event net-proton (proxy for net-baryon), net-charge and net-kaon (proxy for net-strangeness) multiplicity distributions in Au+Au collisions at sNN=7.7,11.5,14.5,19.6,27,39,62.4,200 GeV from the first phase of beam energy scan program at the Relativistic Heavy-Ion Collider (RHIC). We also summarize the data analysis methods of suppressing the volume fluctuations, auto-correlations, and the unified description of efficiency correction and error estimation. Based on theoretical and model calculations, we will discuss the characteristic signatures of critical point as well as backgrounds for the fluctuation observables in heavy-ion collisions. The physics implications and the future second phase of the beam energy scan (2019-2020) at RHIC will also be discussed.

The theoretical cross section calculations for the astrophysical p process are needed because most of the related reactions are technically very difficult to be measured in the laboratory. Even if the reaction was measured, most of the measured reactions have been carried out at the higher energy range from the astrophysical energies. Therefore, almost all cross sections needed for p process simulation have to be theoretically calculated or extrapolated to the astrophysical energies. The ¹¹²Sn(α,γ)¹¹⁶Te is an important reaction for the p process nucleosynthesis. The theoretical cross section of the ¹¹²Sn(α,γ)¹¹⁶Te reaction was investigated for different global optical model potentials, level density and strength function models at the astrophysically interested energies. Astrophysical S factors were calculated and compared with experimental data available in the EXFOR database. The calculation with the optical model potential of the dispersive model by Demetriou et al., and the Back-shifted Fermi gas level density model and Brink-Axel Lorentzian strength function model best served to reproduce experimental results at an astrophysically relevant energy region. The reaction rates were calculated with these model parameters at the p process temperature and compared with the current version of the reaction rate library Reaclib and Starlib.