Vol.32,

A simulation method for measurement of the cross-section of the ¹⁴N(n, α)¹¹B reaction with gas and solid samples using a gridded ionization chamber (GIC) has been established. Using the simulation, the experimental spectra of both ¹⁴N(n, α)¹¹B events and background from other reactions can be predicted, and the experimental scheme can be optimized. According to the simulation results, the optimal experimental parameters, including the pressure of the working gas and the compositions of the working gas and the sample, can be determined. In addition, the simulation results can be used to determine the valid event area and calculate the detection efficiency for valid events. A measurement of the cross-sections of the ¹⁴N(n, α)¹¹B reaction at E_n = 4.25, 4.50, 4.75, 5.00, 5.25, and 5.50 MeV, based on the 4.5-MV Van de Graff accelerator at Peking University (PKU) using a GIC as the detector for the outgoing α particles, has been performed. The good agreement of the spectra from the simulation and experiment demonstrated the universality of this simulation method, which can be used to accurately measure neutron-induced light-charged particle emission reactions.

363

In this paper, a new M3Y-type effective nucleon-nucleon interaction,derived based on the lowest order constrained variational approach (LOCV) and termed B3Y-Fetal, has been used in DDM3Y1, BDM3Y1, BDM3Y2, and BDM3Y3 density-dependent versions in a heavy ion (HI) optical potential based on four types of a real folded potential and a phenomenological Woods-Saxon imaginary potential to study the elastic scattering of the ¹⁶O+¹⁶O nuclear system within the framework of the optical model (OM) by computing the associated differential cross-sections at various incident energies. The results of the folding analyses have shown the DDB3Y1-Fetal and BDB3Y1-Fetal, out of the four folded potentials, give a reasonably better description of the elastic data of the nuclear system. These best-fit folded potentials are followed, in performance, by the BDB3Y2-Fetal, with the BDB3Y3-Fetal potential coming last. This performance trend was also demonstrated by the optical potentials based on the M3Y-Reid interaction. Furthermore, the best-fit folded potentials, renormalized by a factor N_R of approximately 0.9, have been shown to reproduce the energy dependence of the real optical potential for ¹⁶O scattering found in previous optical model analyses creditably well. In excellent agreement with previous works, they have also been identified in this work to belong to the family of deep refractive potentials because they have been able to reproduce and consistently describe the evolution of Airy-like structures, at large scattering angles, observed in the ¹⁶O scattering data at different energies. Finally, a comparison of the performances of B3Y-Fetal and M3Y-Reid effective interactions undertaken in this work has shown impressive agreement between them.

471

A newly developed digital data acquisition system, which is based on the Digital Pulse Processor Pixie-16 modules by XIA LLC, was tested with the γ-ray detector array of the China Institute of Atomic Energy using the γ-ray source and in-beam γ-rays. A comparison between this digital data acquisition system and the conventional analog data acquisition system was made. At a low count rate, both systems exhibit good and comparable energy resolutions. At a high count rate above 8.8 k/s, while the energy resolution obtained by the analog system deteriorates significantly, the energy resolution obtained by the digital system is nearly unchanged. Meanwhile, experimental data with higher statistics can be collected by the digital system. The advantage of this digital system over the conventional analog system can be ascribed to its excellent capability of handling pile-up pulses at higher count rates, and the fact that it has nearly no dead time in data transmission and conversion.

419

Tomographic perfusion imaging is a significant imaging modality for stroke diagnosis. However, the low rotational speed of the C-arm (6 to 8 s per circle) is a challenge for applying perfusion imaging in C-arm cone beam computed tomography (CBCT). Traditional reconstruction methods cannot remove the artifacts caused by the slow rotational speed or acquire enough sample points to restore the time density curve (TDC). This paper presents a dynamic rollback reconstruction method for CBCT. The proposed method can improve the temporal resolution by increasing the sample points used for calculating the TDC. Combined with existing techniques, the algorithm allows slow-rotating scanners to be used for perfusion imaging purposes. In the experiments, the proposed method was compared with other dynamic reconstruction algorithms based on standard reconstruction and the temporal interpolation approach. The presented algorithm could improve the temporal resolution without increasing the X-ray exposure time or contrast agent.

325

Neutron and gamma-ray pulse signal discrimination technology is an essential part of many modern scientific fields, such as biology, geology, radiation imaging, and nuclear medicine. Neutrons are always accompanied by gamma rays due to their unique penetration characteristic; thus, the development of n-γ discrimination methods is especially crucial. In the present study, a novel n-γ discrimination method is proposed that implements a pulse-coupled neural network for n-γ discrimination. In addition, experiments were conducted on the pulse signals detected by an EJ299-33 plastic scintillator, which is especially suitable for n-γ discrimination. The proposed method was compared to three other discrimination methods, including the back-propagation neural network (BPNN), the fractal spectrum method, and the charge comparison method, with respect to two aspects: (i) the figure of merit (FoM) and (ii) discrimination time.The experimental results showed that the pulse-coupled neural network (PCNN) has a 26.49% improvement in FoM-value compared to the charge comparison method, a 72.80% improvement compared to the BPNN, a 66.24% improvement compared to the fractal spectrum method, and the second-fastest discrimination time of 2.22 s. In conclusion, the PCNN treats the input signal as a whole for analysis and processing, imparting it with an excellent anti-noise effect and the ability to process the dynamic information contained in a pulse signal.

550

A gas detector 140×140×140 mm³ in size, termed the compact active target time projection chamber (CAT-TPC), was developed in this study to measure resonant scattering associated with cluster structures in unstable nuclei. The CAT-TPC consists of an electronic field cage, double-thick gas-electron-multiplier foils, a general-purpose digital data acquisition system, and a newly developed two-dimensional strip-readout structure. The CAT-TPC was operated using a ⁴He (96%) + CO₂ (4%) gas mixture at 400 mbar. The working gas also serves as an active target for tracking charged particles. The overall performance of the CAT-TPC was evaluated using a collimated α-particle source. A time resolution of less than 20 ns and a position resolution of less than 0.2 mm were observed along the electron drift direction. Three-dimensional images of incident trajectories and scattering events can be clearly reconstructed under an angular resolution of approximately 0.45 degree.

346

In radiation measurement and digital nuclear spectrum systems, traditional nuclear signal processing circuits in nuclear electronics have been gradually replaced by digital algorithm modules with the application of high-performance programmable hardware logic devices (such as FPGA or DSP). Referring to the digital realization method of inverse RC integral circuit systems, the function of the pole-zero cancellation (PZC) circuit was analyzed, a new modified cascade equivalent model of PZC was established, and the time-domain digital PZC (DPZC) recursive algorithm was derived in detail in this study. Two parameters k_I and k_D are included in the new algorithm, where k_I should match the exponential decay time constant of the input signal to realize the pole-zero compensation, while the decay time constant of the output signal can be changed with the adjustable parameter k_D (which is larger than the decay time constant of the input signal). Based on the new DPZC algorithm module, two trapezoidal (triangular) shaping filters were designed and implemented. The amplitude–frequency characteristics of the output signal of the proposed trapezoidal shaping algorithm and the convolution trapezoidal shaping algorithm were compared, with fixed peaking time. The results show that the trapezoidal shaping algorithm based on DPZC can better suppress high-frequency noise. Finally, based on the NaI (Tl) scintillator (φ75 mm × 75 mm) detector and ¹³⁷Cs source, the effect of the k_D value on the energy resolution of the DPZC trapezoidal (triangular) shaping algorithm was studied. The experimental results show that, with an increase in k_D, the energy resolution of the system improved and reached the maximum when k_D was greater than 10, and the optimal energy resolution of the system was 7.72%.

512

New generation synchrotron light sources are being designed and operated worldwide to provide brighter radiation by reducing the beam emittance to X-ray diffraction limits. Intra-beam scattering (IBS) and Touschek scattering in such facilities are significant and require attention because of their ultra-low emittance. Therefore, cure strategies need to be carefully studied to obtain high-quality photon beams. For the Shanghai Synchrotron Radiation Facility Upgrade (SSRF-U), a candidate lattice of the storage ring, reaching the soft X-ray diffraction limit, was designed and presented for the first time in this study. The emittance growth and beam lifetime in the SSRF-U storage ring were studied using particle simulations for a series of different machine configurations. The gains with RF frequencies of 100 MHz and 500 MHz were compared. Along with a better filling pattern, a more suitable RF frequency was adopted in the SSRF-U. The variations in the equilibrium beam emittance with beam coupling and bunch-lengthening were identified using simulations. Optimal beam coupling and required bunch-lengthening for the SSRF-U storage ring were thus determined. The fitness of the beam energy in the SSRF-U was subsequently assessed using the obtained parameters. Additionally, the Touschek scattering and beam lifetime were calculated, and an acceptable total beam lifetime was obtained.

358

The smuggling of special nuclear materials (SNMs) across national borders is becoming a serious threat to nuclear nonproliferation. This paper presents a feasibility study on the rapid interrogation of concealed SNMs by combining scattering and transmission nuclear resonance fluorescence (sNRF and tNRF) spectroscopy. In sNRF spectroscopy, SNMs such as ^{235, 238}U are excited by a wide-band photon beam of appropriate energy and exhibit unique NRF signatures. Monte Carlo simulations show that one-dimensional scans can realize isotopic identification of concealed ^{235, 238}U when the detector array used for interrogation has sufficiently high energy resolution. The simulated isotopic ratio ²³⁵U/²³⁸U is in good agreement with the theoretical value when the SNMs are enclosed in relatively thin iron. This interrogation is followed by tNRF spectroscopy using a narrow-band photon beam with the goal of obtaining tomographic images of the concealed SNMs. The reconstructed image clearly reveals the position of the isotope ²³⁵U inside an iron rod. It is shown that the interrogation time of sNRF and tNRF spectroscopy is one order of magnitude lower than that when only tNRF spectroscopy is used and results in a missed-detection rate of 10^-3. The proposed method can also be applied for isotopic imaging of other SNMs such as ^{239, 240}Pu and ²³⁷Np.

492

The algebraic collapsing acceleration (ACA) technique maximizes the use of geometric flexibility of the method of characteristics (MOC). The spatial grids for low-order ACA are the same as the high-order transport, which makes the numerical solution of ACA equations costly, especially for large-size problems. To speed up the MOC transport iterations effectively for general geometry, a coarse-mesh ACA method that involves selectively merging fine-mesh cells with identical materials, called material-mesh ACA (MMACA), is presented. The energy group batching (EGB) strategy in the tracing process is proposed to increase the parallel efficiency for microscopic cross-section problems. Microscopic and macroscopic cross-section benchmark problems are used to validate and analyze the accuracy and efficiency of the MMACA method. The maximum errors in the multiplication factor and pin power distributions are from the VERA-4B-2D case with silver-indium-cadmium (AIC) control rods inserted and are 104 pcm and 1.97%, respectively. Compared with the single-thread ACA solution, the maximum speed-up ratio reached 25 on 12 CPU cores for microscopic cross-section VERA-4-2D problem. For the C5G7-2D and LRA-2D benchmarks, the MMACA method can reduce the computation time by approximately one half. The present work proposes the MMACA method and demonstrates its ability to effectively accelerate MOC transport iterations.

639

In the case of a severe accident involving nuclear reactors, an important aspect that should be considered is the leakage of molten material from the inside of the reactor into the environment. These molten materials damage other reactor components, such as electrical tubes, grid plates, and core catchers. In this study, the moving particle semi-implicit (MPS) method is adopted and improved to analyze the two-dimensional downward relocation process of molten Wood’s metal as a representation of molten material in a nuclear reactor. The molten material impinges the Wood’s metal plate (WMP), which is mounted on a rigid dummy stainless steel in a cylindrical test vessel. The breaching process occurs because of heat transfer between the molten material and WMP. The formed breach areas were in good agreement with the experimental results, and they showed that the molten Wood’s metal spread above the WMP. The solid WMP fraction decreased with time until it reached the termination time of the simulation. The present results show that the MPS method can be applied to simulate and analyze the downward relocation process of molten material in the grid plate of a nuclear reactor.

510