Vol.32,

A radiofrequency (RF) phase modulation method is applied to the Hefei Light Source II (HLS-II) storage ring to deeply investigate its longitudinal beam characteristics and improve the beam lifetime. A theoretical analytical model and corresponding experimental measurements of single bunch length and island phenomena are examined. From a series of online machine experiments, we demonstrate that the suitable phase modulation amplitude is 0.02 rad, corresponding to an optimum modulation frequency ranging from 19.6 to 20.7 kHz of the RF system. Furthermore, the overall beam lifetime can be increased by a factor of 2.38 as a result of the beam dilution effect.

453

A 325 MHz aluminum prototype of a spatially periodic rf quadrupole focusing linac was developed at the Institute of Modern Physics, Chinese Academy of Sciences, as a promising candidate for the front end of a high-current linac. It consists of an alternating series of crossbar H-type drift tubes and rf quadrupole sections. Owing to its special geometry, cavity fabrication is a major hurdle for its engineering development and application. In this paper, we report the detailed mechanical design of this structure and describe its fabrication process, including machining, assembly, and inspection. The field distribution was measured by the bead-pull technique. The results show that the field errors of both the accelerating and focusing fields are within an acceptable range. A tuning scheme for this new structure is proposed and verified. The cold test process and results are presented in detail. The development of this prototype provides valuable guidance for the application of the spatially periodic rf quadrupole structure.

532

We study the production and angular correlation of charm hadrons in hot and dense matter produced in high-energy nuclear-nuclear collisions within a multiphase transport model (AMPT). By triggering additional charm-anticharm quark pair production in the AMPT, the model describes the D⁰ nuclear modification factor in the low and intermediate p_T regions in Au+Au collisions at sNN=200 GeV reasonably well. Further exploration of the D⁰ pair azimuthal angular correlation for different centralities shows clear evolution from low-multiplicity to high-multiplicity events, which is associated with the number of charm quark interactions with medium partons during AMPT transport.

487

The Compact Spectrometer for Heavy Ion Experiment (CSHINE) is under construction for the study of isospin chronology via the Hanbury Brown-Twiss (HBT) particle correlation function and the nuclear equation of state of asymmetrical nuclear matter. The CSHINE consists of silicon strip detector (SSD) telescopes and large-area parallel plate avalanche counters, which measure the light charged particles and fission fragments, respectively. In phase I, two SSD telescopes were used to observe 30 MeV/u ⁴⁰Ar +¹⁹⁷Au reactions. The results presented here demonstrate that hydrogen and helium were observed with high isotopic resolution, and the HBT correlation functions of light charged particles could be constructed from the obtained data.

526

Neutrino detection in the 100 PeV energy region is the ultimate means of studying the origin of ultra-high-energy cosmic rays, which the large radio detection array Giant Radio Array for Neutrino Detection (GRAND) Project aims to use to decipher this century-old problem. The GRANDProto35 compact array is a microform of 35 radio prototype detectors for the GRAND experiment, which verifies the reliability of GRAND performance through operation, and data analysis of the prototype detectors. As radio detectors are a novel development in recent years, and their indexes need to be verified by traditional detectors, the GRAND Cooperation Group designed and constructed the GRANDProto35 coincidence array composed of radio detectors and scintillation detectors. This study simulated the changes in detection efficiency, effective area, and event rate of cosmic rays with zenith angle based on this coincidence array. The study found that the 10¹⁷ eV energy region is sensitive to GRANDProto35 detection. When the energy exceeded 10¹⁷ eV, the array detection efficiency could reach more than 95 % and the effective area was up to ∼2×10⁶ m². A simulation study on cosmic ray events with large zenith angles showed that the event rate detected by the array decreased significantly with increasing zenith angle, and the event rate of cosmic rays was approximately 0.1 per day for a zenith angle of 75. This serves as the background pollution rate for neutrino observation caused by large-angle cosmic-ray events, providing an important reference for further experiments. The study results will be verified after the joint operation of the coincidence array.

441

We present a comprehensive study on the individual sources of an inclusive photon production during high-energy hadronic collisions. The cross-section and invariant yields of inclusive photons are obtained as a function of pT at mid-rapidity (|y|<0.5) in p + p and Au + Au collisions at sNN = 200 GeV, respectively. These results provide crucial inputs to separate measurements of open bottom and charm hadron yield suppression in heavy-ion collisions, which are used to test the mass hierarchy of the parton energy loss in the quark gluon plasma created during these collisions. The procedure developed in this study can also be applied to other measurements of electrons from an open heavy-flavor hadron decay, such as the collective flow in the RHIC beam energy scan program.

436

Low-pressure distillation has been proposed as a suitable technique for the recovery of carrier salt from molten salt reactor spent fuel. A closed-chamber distillation system, in which the pump is stopped and pressure-induced salt distillation is performed, was arranged for fluoride salt treatment. A stair-step optimization process was demonstrated to improve the recovery efficiency by up to 99%. The pressure change curve was feasible for estimating the distillation process, and a method for displaying the pressure value online in order to determine the end-point was also developed. The decontamination factor of Nd in the condensate salt was deduced to be greater than 100 with 1 wt% NdF₃-FLiNaK distillation. The optimal conditions developed in this study showed a high recovery ratio for the fluoride carrier salt and a high separation efficiency for rare earth products.

445

The neutronic properties of molten salt reactors (MSRs) differ from those of traditional solid-fuel reactors owing to their nuclear fuel particularity. Based on the Monte-Carlo N particle transport code, the effects of the size and shape of the fuel salt channel on the neutron physics of an MSR cell is investigated systematically in this study. The results show that the infinite multiplication factor (k_∞) first increases and then decreases with the change in the graphite cell size under certain fuel volume fraction (FVF) conditions. For the same FVF and average chord length, when the average chord length is relatively small, the k_∞ values for different fuel salt channel shapes agree well. When the average chord length is relatively large, the k_∞ values for different fuel salt channel shapes differ significantly. In addition, some examples of practical applications of this study are presented, including cell selection for the core and thermal expansion displacement analysis of the cell.

455

Sinter is the main raw material in the blast furnace iron-making process, and basicity (CaO/SiO₂) is an important quality index of sinter. Prompt gamma-neutron activation analysis is a multi-elemental online detection technology that has been successfully applied in cement, coal, etc. Compared with cement as a raw material, sinter exhibits poor moderation ability and a large neutron absorption cross-section. Therefore, cement detection devices are not suitable for sinter mixture detection. In this study, a prompt gamma-neutron activation analysis equipment used for testing cement was re-optimized to render it suitable for measuring a sinter mixture. Using Monte-Carlo simulation, the comprehensive detection efficiency of the detection device improved by 71.52%. Because of the gamma ray self-shielding effect of the sinter mixture, the detection errors of CaO and SiO₂ are significant. By applying the gamma ray self-shielding correction algorithm, the detection accuracies improved, and their linear correlation coefficients R² exceeded 0.99. Furthermore, by applying an improved analyzer to a sintering plant, the first-grade product rate of the factory increased by 4.64%.

650

To study the effects of the gamma reflection of multi-element materials, gamma ray transport models of single-element materials, such as iron and lead, and multi-element materials, such as polyethylene and ordinary concrete, were established in this study. Relationships among the albedo factors of the gamma photons and energies and average energy of the reflected gamma rays by material type, material thickness, incident gamma energy, and incidence angle of gamma rays were obtained by Monte Carlo simulation. The results show that the albedo factors of single-element and multi-element materials increase rapidly with an increase in the material thickness. When the thickness of the material increases to a certain value, the albedo factors do not increase further but rather tend to the saturation value. The saturation values for the albedo factors of the gamma photons and energies and the reflection thickness are related not only to the type of material but also to the incident gamma energy and incidence angle of the gamma rays. At a given incident gamma energy, which is between 0.2 and 2.5 MeV, the smaller the effective atomic number of the multi-element material is, the higher the saturation values of the albedo factors are. The larger the incidence angle of the gamma ray is, the greater the saturation value of the gamma albedo factor, saturation reflection thickness, and average saturation energy of the reflected gamma photons are.

450

Jing-Yu Tang，Qi An，Jiang-Bo Bai，Jie Bao，Yu Bao，Ping Cao，Hao-Lei Chen，Qi-Ping Chen，Yong-Hao Chen，Zhen Chen，Zeng-Qi Cui，Rui-Rui Fan，Chang-Qing Feng，Ke-Qing Gao，Xiao-Long Gao，Min-Hao Gu，Chang-Cai Han，Zi-Jie Han，Guo-Zhu He，Yong-Cheng He，Yang Hong，Yi-Wei Hu，Han-Xiong Huang，Xi-Ru Huang，Hao-Yu Jiang，Wei Jiang，Zhi-Jie Jiang，Han-Tao Jing，Ling Kang，Bo Li，Chao Li，Jia-Wen Li，Qiang Li，Xiao Li，Yang Li，Jie Liu，Rong Liu，Shu-Bin Liu，Xing-Yan Liu，Ze Long，Guang-Yuan Luan，Chang-Jun Ning，Meng-Chen Niu，Bin-Bin Qi，Jie Ren，Zhi-Zhou Ren，Xi-Chao Ruan，Zhao-Hui Song，Kang Sun，Zhi-Jia Sun，Zhi-Xin Tan，Xin-Yi Tang，Bin-Bin Tian，Li-Jiao Wang，Peng-Cheng Wang，Zhao-Hui Wang，Zhong-Wei Wen，Xiao-Guang Wu，Xuan Wu，Li-Kun Xie，Xiao-Yun Yang，Yi-Wei Yang，Han Yi，Li Yu，Tao Yu，Yong-Ji Yu，Guo-Hui Zhang，Lin-Hao Zhang，Qi-Wei Zhang，Xian-Peng Zhang，Yu-Liang Zhang，Zhi-Yong Zhang，Lu-Ping Zhou，Zhi-Hao Zhou，Ke-Jun Zhu

Back-streaming neutrons from the spallation target of the China Spallation Neutron Source (CSNS) that emit through the incoming proton channel were exploited to build a white neutron beam facility (the so-called Back-n white neutron source), which was completed in March 2018. The Back-n neutron beam is very intense, at approximately 2×10⁷ n/cm²/s at 55 m from the target, and has a nominal proton beam with a power of 100 kW in the CSNS-I phase and a kinetic energy of 1.6 GeV and a thick tungsten target in multiple slices with modest moderation from the cooling water through the slices. In addition, the excellent energy spectrum spanning from 0.5 eV to 200 MeV, and a good time resolution related to the time-of-flight measurements make it a typical white neutron source for nuclear data measurements; its overall performance is among that of the best white neutron sources in the world. Equipped with advanced spectrometers, detectors, and application utilities, the Back-n facility can serve wide applications, with a focus on neutron-induced cross-section measurements. This article presents an overview of the neutron beam characteristics, the experimental setups, and the ongoing applications at Back-n.

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