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Jet impingement quenching heat transfer of LN2 on rock surface was experimentally investigated. The test plate was circular in shape and was 16 cm in diameter and 2 cm in thickness. An aluminum alloy specimen with the same configuration as the rock plate was also used to highlight the characteristics of rock material in affecting the LN2 jet impingement boiling heat transfer. Comparing to the aluminum, rock has a low thermal conductivity and the rock surface was distributed with micro pores and cavities. This surface character enabled a 100 °C increase of the rewetting temperature. An attempt was made to quantitatively explain the rewetting temperature enhancement using the local cold spot theory. The stagnation point on rock surface was directly wetted by LN2 jet without film boiling, for which the high rewetting temperature and fast temperature drop were proposed as the reasons. The maximum heat flux and wetting front velocity were investigated for both quenching samples and the results were compared to correlations in the literature.

To address the high rock strength and low drilling rate issues in deep oil/gas and geothermal exploitation, we performed mechanical property tests on three kinds of rock samples (granite, shale and sandstone) subjected to liquid nitrogen (LN2) cooling and conducted rock-breaking experiments using LN2 jet. Rock-breaking characteristics and mechanisms of LN2 jet, heat transfer features between LN2 and rock and thermal stress evolution in rock were analyzed. A novel high-pressure LN2 jet assisted drilling method was proposed accordingly. The study results show that LN2 thermal shock can significantly reduce uniaxial compression strength and elastic modulus of rock. Rock damage and corresponding mechanical deterioration become more pronounced with increasing rock temperature. The LN2 jet has merits of high rock-breaking efficiency and low threshold rock-breaking pressure. Rock failure under LN2 jet impact is characterized by large volume breakage and the rock-breaking performance becomes more significant with increase of rock temperature. Under the impact of LN2 jet, the damage of granite is the most remarkable among the three rock samples. Thus, this method works better for high temperature granite formations. It has a good application prospect in speeding up drilling rate in deep hot dry rock geothermal reservoirs. Key words: liquid nitrogen jet, cold shock, jet impact, rock-breaking experiment, assisted drilling, drilling rate improvement

Multi-walled carbon nanotube (MWCNT) and carbon fiber and flaky graphite reinforced copper foam/furan resin composite for a novel sliding contact material was fabricated using an acid purify and ultrasonic dispersion technology, followed by a mold pressing process. The microstructure, electrical resistivity, impact strength and current-carrying friction performances of the composites were measured to investigate the effect of the different MWCNT contents. The results showed that the MWCNTs had a good dispersion state in the composite and the percolation threshold was approximate 0.074–0.185 vol%. As addition of the MWCNTs, the impact strength and wear resistance of the composites could be raised by 45% and 22%, respectively.

The PDC (Polycrystalline Diamond Compact) bits are the most widely used bits in oil drilling engineering, in order to further improve their longevity and ROP (Rate of Penetration), single PDC cutter research is very important. However, previous work focused mostly on experiment and numerical simulation while analytical modelling still lacks progress. In this paper, a new analytical model of rock cutting force and failure surface is proposed based on the stress state calculation of each micro-unit inside the rock. The cutting force predicted by this model is well verified by experiments under different parameters like depth of cut, back rack angle, rock type, cutter size and confining pressure. It is also found that the shape of failure surface is a curved line rather than straight, and long and thin cuttings will be formed. Finally, on the basis of this model, the influence mechanism of each parameter on cutting force and the shape of failure surface are analyzed. The method and result of this study are expected to provide a better understanding of cutting force and rock breaking mechanism by PDC bits.

To determine the effect of liquid nitrogen (LN2) cooling on the damage of heated rock, we conducted a series of physical and mechanical tests on Shandong granite samples. These granites were first slowly heated to the target temperatures (25~600 °C) and held for 10 h, followed by rapid cooling with a coolant. Three coolants were used and compared in our experiment: air, water and LN2. Physical properties and mechanical properties were tested after thermal treatments. Microstructural changes were also observed using scanning electron microscope and optical microscope. According to experimental results, permeability of the heated granites increases significantly after LN2-cooling, while density, P-wave velocity, strength and elastic modulus reduce. As heating temperature rises, changes in these properties become more pronounced. Compared to air-cooling and water-cooling, LN2-cooling induces greater changes in the physical and mechanical properties at any target temperature. This indicates that LN2-cooling can damage the heated rocks more remarkably than the other two cooling treatments. According to microscopic analysis, inter-granular cracking is the primary failure mode during thermal treatment, and most of the inter-granular cracks distribute at the boundaries of quartz. Our results in this paper are of great value for understanding the characteristics of thermal damage induced by rapid cooling.

Liquid nitrogen (LN2) fracturing is a technology that can dramatically enhance the stimulation performances of high-temperature reservoirs, such as hot dry rock geothermal and deep/ultra-deep hydrocarbon reservoirs. The aim of the present study was to investigate the damage characteristics of high-temperature rocks subjected to LN2 thermal shock, which is a critical concern in the engineering application of LN2 fracturing. In our work, the rocks (granite, shale and sandstone) were slowly heated to different temperatures (25 °C, 150 °C and 260 °C) and maintained at the target temperatures for 10 h, followed by LN2 quenching. After thermal treatments, we tested the physical and mechanical properties of the rocks to evaluate their damages. Additionally, sensitivities of the three rocks to thermal shock were also compared and analyzed. According to our experiments, LN2 thermal shock can enhance the permeability of the rocks and deteriorate their mechanical properties significantly. Increasing rock temperature helps strengthen the effect of LN2 thermal shock, leading to more severe damage. Inter-granular cracking is the primary contribution to the rock damage in the LN2 cooling process. Compared with granite and shale, sandstone is less sensitive to LN2 thermal shock. The lower sensitivity of sandstone to thermal shock is mainly attributed to its larger pore spaces and weaker heterogeneity of mineral thermal expansion. The present paper can provide some guidance for the engineering application of LN2 fracturing technology.

High-spin states of $^{110}\mathrm{Ag}$ have been studied by in-beam $\ensuremath{\gamma}$-ray spectroscopic techniques using the fusion-evaporation reaction $^{110}\mathrm{Pd}$($^{7}\mathrm{Li}, \ensuremath{\alpha}3\mathrm{n}$)$^{110}\mathrm{Ag}$ at a beam energy of 46 MeV. The previously known level scheme of $^{110}\mathrm{Ag}$ is significantly extended and modified with the addition of 50 new $\ensuremath{\gamma}$ transitions and 21 new levels. In total, four new rotational bands are observed, among which two negative-parity coupled bands are assigned to the four-quasiparticle $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}{({g}_{7/2}/{d}_{5/2})}^{2}$ configuration based on the quasiparticle alignment analysis and cranked shell model calculations. The properties of both bands show general agreement with the fingerprints of chiral rotation, and thus such two negative-parity bands are suggested to be candidates for near degenerate chiral doublet bands. A new decoupled $\mathrm{\ensuremath{\Delta}}I=2$ band decaying directly to the yrast band is established, and probably results from one-particle-one-hole (1p-1h) proton excitation from the ${g}_{9/2}$ orbital to the ${g}_{7/2}$ orbital across the large $Z=50$ shell gap, i.e., the 2p2h $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ configuration. In addition to, a weak positive-parity sequence consisting of magnetic dipole $(M1)$ and no $E2$ crossover transitions is also identified in the present work.

The relative differential cross sections of the $$^{1}\hbox {H}(n, \,el)$$ reaction have been measured at the China Spallation Neutron Source (CSNS) Back-n white neutron source. A low-density polyethylene sample and a graphite foil were prepared for the foreground and background measurements, respectively. The charged particles were detected using the $${\vartriangle }E-E$$ telescope array of the Light-charged Particle Detector Array (LPDA) system. With 10 $${\vartriangle }E-E$$ telescopes, the relative differential cross sections of the $$^{1}\hbox {H}(n, \,el)$$ reaction were obtained from 70 $$^{\circ }$$ to 160 $$^{\circ }$$ in the center-of-mass system in the neutron energy ( $$E_{\mathrm{n}}$$ ) range from 6.14 to 52.48 MeV (23 energy points). The present work was the first experiment using the $${\vartriangle }E-E$$ telescope array of the LPDA system at CSNS. The present results are in good agreement with previous measurements, evaluations and theoretical calculations. Furthermore, this work is the first measurement in the 6.52 MeV $$\le E_{\mathrm{n}} \le $$ 9.09 MeV, 10.57 MeV $$\le E_{\mathrm{n}} \le $$ 12.43 MeV, and 18.05 MeV $$\le $$ $$E_{\mathrm{n}} \le $$ 20.05 MeV regions.

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*10^7 n/cm^2/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., Comment: 11 pages, 9 figures

The internal temperature environment of a hydrogen maser (H maser) is one of the main factors, which limit the frequency stability of hydrogen atomic clocks (HACs). In the present study, the thermodynamic interactions between the atomic transition frequency and the cavity-bulb assembly affecting the H maser were investigated, and the cavity-pulling effect and the bulb wall frequency shift effect induced by the change in temperature were quantitatively analyzed and calculated. Moreover, the effect of the temperature gradient on the temperature sensitivity of the frequency stability (i.e., the frequency-temperature effect) was qualitatively analyzed. The precision temperature control system was optimized based on the HAC temperature stability requirement through the simulation of the temperature field for different heating pattern methods. The optimization effect was verified experimentally, and the results show that after optimizing the design, the temperature stability is improved from ±0.005 K to ±0.001 K, and the frequency deviation is decreased from 3 × 10-15 to 1 × 10-15. The research results may provide theoretical and practical references for improving the frequency stability and accuracy of HACs.

Excited states of $$^{109}\hbox {Ag}$$ have been investigated by in-beam $$\gamma $$ -ray spectroscopic techniques using the $$^{110}\hbox {Pd}$$ ( $$^{7}\hbox {Li}$$ , $$\alpha 4\hbox {n}$$ ) $$^{109}\hbox {Ag}$$ reaction at a beam energy of 46 MeV. The level scheme of $$^{109}\hbox {Ag}$$ is significantly extended with the addition of more than 20 new $$\gamma $$ transitions. For the positive-parity yrast band, it is extended to $$41/2^{+}$$ state and $$2\hbar $$ higher than the earlier work. A negative-parity band decaying to the yrast band by eleven new linking transitions is identified, and several E2 crossover transitions of this band are observed, thereby confirming the spin-parity assignment and the ordering of dipole transitions above the $$I^{\pi } = 17/2^{-}$$ level. Experimental total angular momenta, kinematical and dynamical moments of inertia, and B(M1)/B(E2) ratio for the negative-parity band are compared with the predictions of self-consistent titled axis cranking relativistic mean-field model. Based on the theoretical description and the observed characteristics, the negative-parity dipole band is suggested as a magnetic rotational band arising from shears mechanism.

The three-dimensional Dirac semimetal $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ has attracted intensive attention recently for its exotic properties. Understanding the hot carrier excitation and its subsequent relaxation is a prerequisite for $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$-based optoelectronics functional in the infrared (IR) and terahertz (THz) frequency range. In this work, the photoexcited hot carrier dynamics of a bulk single crystal $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ in the mid-IR has been explored by using the time-resolved pump-probe reflectance ($\mathrm{\ensuremath{\Delta}}R/R$) measurement at room temperature under a strong optical pumping. By combining the experimental $\mathrm{\ensuremath{\Delta}}R/R$ results and theoretical modeling, we analyzed the transient hot carrier redistribution upon a strong photoexcitation and the subsequent interband transitions. We show that the $\mathrm{\ensuremath{\Delta}}R/R$ response of $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ has a complex behavior, due to the interplay of transitions between Dirac bands and transitions involving both the Dirac and non-Dirac bands. Throughout the mid-IR region measured, we find that $\mathrm{\ensuremath{\Delta}}R/R$ is contributed primarily by changes in the refractive index, rather than by changes in the extinction coefficient. Our findings can help understanding the transient hot electron excitation and relaxation in $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ under an intense optical pumping, and provide a valuable reference for the $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$-based ultrafast optoelectronics application.

The high-spin structure of $$^{109}\hbox {In}$$ was investigated with the $$^{100}\hbox {Mo}(^{14}\hbox {N},\, 5\hbox {n})^{109}\hbox {In}$$ fusion-evaporation reaction at CIAE, Beijing. Eleven new $$\gamma $$-rays of $$^{109}\hbox {In}$$ were identified, by which the bandheads of the $$\varDelta \textit{I}$$ = 2 rotational bands were confirmed. The configurations were assigned with the help of the systematic discussion. Furthermore, the rotational bands are compared with the tilted-axis cranking calculations based on a relativistic mean-field approach. The rotational bands involving the 1p1h excitation to the $$\pi d_{5/2}$$ and $$\pi g_{7/2}$$ orbitals are suggested as candidates for antimagnetic rotation based on the theoretical results.

Polycrystalline Diamond Compact (PDC) bits account for most of the footage drilled in the oil field. Abundant information relating to cutter-rock interactions and rock breaking mechanism are provided by the cuttings and Mechanical Specific Energy (MSE) in single cutter tests, which are crucial for insuring the longevity and rate of penetration (ROP) enhancement of PDC bits. In this paper, a series of linear cutting tests was conducted at different depths of cut, back rake angles and cutting speeds on three kinds of rock. The formation of cuttings was recorded frame by frame with a high-speed camera. Then, the cuttings were collected and divided into five groups by sieving. Finally, the mass fraction change of cuttings in each group was compared with the MSE variation. The results show that a PDC cutter does not move at a constant speed: relatively slower when crushing and faster when chipping, and crushing dominates almost the entire cutting process. The mass fraction of chunklike cuttings generated in chipping is increased with decreasing back rake angle, while increasing depth of cut and cutting speed; and the mass fraction of powderlike cuttings generated in crushing shows an opposite trend. Furthermore, because of the crystalloblastic texture and well-developed cleavages in calcite, far more chunklike cuttings and totally different fracture surfaces are found when cutting marble, compared with sandstone and granite. Finally, a strong correlation between the mass fraction of cuttings and MSE is found. This indicates that the mass fraction of cuttings could be deemed as a simple method to evaluate the efficiency of rock breaking by PDC cutters. The results in this paper are expected to provide guidelines to the selection of drilling practices and PDC bit design.

Severe leakage of drilling fluid and reservoir damage due to water and solid invasion during well drilling are the key factors that restrict economic exploitation of coal bed methane (CBM) in China. To solve these issues, this paper presents a method of CBM well drilling with the assistance of cryogenic nitrogen jet, in which no aqueous phase and solid phase are contained. To determine the feasibility of coal breaking by cryogenic nitrogen jet and the effects of different parameters, such as nozzle diameter, dimensionless standoff distance, nozzle pressure difference and exposure time, we conducted corresponding rock breaking experiments on artificial and natural coals with the cryogenic nitrogen jet and the water jet. Rock breaking features and the energy consumption by the two jets were compared. The results indicate that the cryogenic nitrogen jet has better rock breaking performances and consumes less energy. Under the same conditions, the average rock erosion volume and the energy consumption with the cryogenic nitrogen jet were 18.34 times larger and 90.8% lower than those with water jet, respectively. Visible netted fractures could be created on the surface of coal samples blasted with the cryogenic nitrogen jet, and thus rock breaking could be facilitated effectively. The outstanding rock breaking performances of cryogenic nitrogen jet are attributed to three mechanisms: high-velocity jet impact, thermal shock and gasification cracking effect. In addition, under our experimental conditions, the erosion volume and depth were proportional to the pressure difference and inversely proportional to the dimensionless standoff distance. When the nozzle diameter changed from 1.5 mm to 3 mm, the increases of erosion volume were 3% at the pressure difference of 5 MPa and 41.7% at the pressure difference of 10 MPa respectively. This indicates that the effect of nozzle diameter is more significant at relatively higher pressure drops. With the increase of exposure time, both of the rock erosion depth and volume rose, while with a smoother trend. The results of this study are expected to promote the application of cryogenic nitrogen jet in CBM well drilling.

Cryogenic nitrogen fracturing can provide a new insight into the stimulation of deep shale gas reservoirs. In order to investigate the physical and mechanical behaviors of high-temperature shales (298–533 K) subjected to LN2 cooling, we tested the permeability, P-wave velocity and uniaxial compressive strength (UCS) of shale specimens. In the experiment, two cooling ways were used and compared: cooling by LN2 immersion and cooling in air naturally. The scanning electron microscope (SEM) was employed to observe the micro-structural changes after cooling. To determine the effect of cooling rate on the rock damage, we conducted a transient 3D thermo-mechanical simulation using ABAQUS. The experimental results indicate that LN2 cooling induces significant damage in shales. At any given shale temperature, the enhancement of permeability and reductions of UCS and P-wave velocity after LN2 cooling are greater than those after air cooling. Differences in the physical and mechanical properties between two cooling groups become more significant with shale temperature rising. LN2 cooling can create obvious cracks on the surface of shales, and size and number of these cracks increase as temperature rises. According to the SEM observation, most of the cooling induced cracks are inter-granular cracks which are mainly attributed to the mismatch of thermal properties between particles. The simulation results indicate that the cooling rate has a positive impact on the thermal stress. Faster cooling rate generates higher tensile stress in the exterior region of rocks, which helps intensify the deterioration of the rocks.

This paper presents a numerical analysis of heat transfer and thermal stress in bottomhole rocks during geothermal drilling with high-pressure liquid nitrogen jet. The simulation is conducted by a three-dimensional model in transient state. The conjugate heat transfer method is employed to compute heat transfer between solid and liquid. The thermo-physical properties of liquid nitrogen and rocks are considered in detail. The results indicate that high velocity and turbulence kinetic energy of liquid nitrogen jet at impingement surface enhance heat transfer efficiency between cryogenic fluid and hot rock. Huge tensile stress is generated adjacent to the solid-liquid interface, which is favorable for rock breaking on bottomhole. The primitive rock temperature has a significant impact on maximal stress value. A set of experiments is conducted to validate the effects of thermal stresses on rock breakage. The thermal stresses diminish significantly under laboratory conditions without effective constraint on rock boundaries. In our experiments, the coal rather than other types of rock, was selected as working specimen due to its well-developed natural cracks and small tensile strength. Our results would shed light on the geothermal drilling with high-pressure nitrogen jet.

Indentation of rocks by the Polycrystalline Diamond Compact (PDC) cutter has great impacts on the cutting depth. However, a vast majority of previous studies only focused on the rock cutting process. Further insight into the failure characteristics of rocks subjected to PDC cutter indentation is required to optimize the design of PDC bits. In this paper, a set of experiments were conducted to investigate the effects of back rake angles and mechanical properties of rocks on the PDC cutter indentation. Penetration forces and Acoustic Emission (AE) signals were captured to determine rock failure modes (brittle failure or plastic failure), and the three-dimensional profilometer was used to identify the morphology features of penetration pits. Besides, the penetration efficiency and brittle failure index were defined to evaluate the crushing characteristics of rocks during penetration. The results show that plastic failure dominates the indentation process as the back rake angle is smaller than 20°, which significantly limits the growth of penetration depth. Based on the penetration force and the number of AE hit counts, chipping occurs in the indentation process when using the PDC cutter with greater back rake angles (>20°). Such phenomenon can be further confirmed by topography features of penetration pits. Moreover, the position of brittle failure moves from the front to the back of the cutter as the back rake angle exceeds 40°. Compared with granite and sandstone, chipping occurs more easily in the marble, indicating a higher brittle failure index. In conclusion, back rake angle has great effects on the rock cutting process and the indentation of rocks. Our current study is expected to provide theoretical guidance for the cutter layout in PDC bits.

Mechanical cutting assisted by high-pressure jet is a common and efficient drilling method in the exploration of hot dry rock (HDR). The drilling efficiency can be further improved with an in-depth understanding in the rock-breaking mechanism, which is a complex process involving the coupling of thermal stress, jet impact pressure and cutting force. To address such a multi-physics coupling issue, a loosely coupling method was adopted in this work to accomplish the exchange of data, including temperature, heat flux, nodes deformation and impinging pressure of jet in every time increment. In the fluid subdomain, the liquid nitrogen (LN2) jet and water jet were modeled and compared to demonstrate the potential of the novel jet in improving the drilling rate. In the solid subdomain, cutting force monitored in the experiment was loaded, and the concrete damage plastic model was employed to evaluate damage behaviors of the rock. Relative experiments were conducted to validate the reliability of simulation results. Results indicate that a great temperature difference develops on the coupling surface under the impingement of LN2 jet due to its cryogenic feature and lower heat transfer efficiency. Thereby, irreversible damage of the rock can be induced even at room temperature (298 K). As for the water jet, tensile damage is not observed until the rock temperature increases to 473 K. The assistance of jet impact on rock breaking is mainly reflected in two aspects: (1) the occurrence of tensile damage on the coupling surface facilitates the subsequent rock cutting; (2) the enhancement of tensile damage around the cutter promotes the initiation of cracks. Higher rock temperatures significantly improve the heat transfer rate and enhance the advantage of jet assistance. The present study can provide a new sight for the exploration of HDR.

The effect of nanosized NbC precipitates on electrochemical corrosion behavior of high-strength low-alloy (HSLA) steels in 3.5%NaCl solution has been investigated by the means of precipitate modulation, microstructure observation, electrochemical and immersion tests. The results showed that NbC precipitates markedly enhance the corrosion resistance of the H-contained steel, and the mechanism is that the plentiful and highly dispersed nanosized NbC particles acting as massive and effective hydrogen traps play a decisive role in the resistance to hydrogen activated corrosion. Moreover, it is evident that the inhibiting effect is related with the amount, size and distribution of the precipitates, and the optimized microstructures and precipitated phases improve the mechanical properties and resistance to hydrogen activated corrosion of HSLA steel.

Differential and angle-integrated cross sections for the $^{10}$B($n, {\alpha}$)$^{7}$Li, $^{10}$B($n, {\alpha}$$_{0}$)$^{7}$Li and $^{10}$B($n, {\alpha}$$_{1}$)$^{7}$Li$^{*}$ reactions have been measured at CSNS Back-n white neutron source. Two enriched (90%) $^{10}$B samples 5.0 cm in diameter and ~85.0 ${\mu}$g/cm$^{2}$ in thickness each with an aluminum backing were prepared, and back-to-back mounted at the sample holder. The charged particles were detected using the silicon-detector array of the Light-charged Particle Detector Array (LPDA) system. The neutron energy E$_{n}$ was determined by TOF (time-of-flight) method, and the valid ${\alpha}$ events were extracted from the E$_{n}$-Amplitude two-dimensional spectrum. With 15 silicon detectors, the differential cross sections of ${\alpha}$-particles were measured from 19.2{\deg} to 160.8{\deg}. Fitted with the Legendre polynomial series, the ($n, {\alpha}$) cross sections were obtained through integration. The absolute cross sections were normalized using the standard cross sections of the $^{10}$B($n, {\alpha}$)$^{7}$Li reaction in the 0.3 - 0.5 MeV neutron energy region. The measurement neutron energy range for the $^{10}$B($n, {\alpha}$)$^{7}$Li reaction is 1.0 eV $\le$ En < 2.5 MeV (67 energy points), and for the $^{10}$B($n, {\alpha}$$_{0}$)$^{7}$Li and $^{10}$B($n, {\alpha}$$_{1}$)$^{7}$Li$^{*}$ reactions is 1.0 eV $\le$ En < 1.0 MeV (59 energy points). The present results have been analyzed by the resonance reaction mechanism and the level structure of the $^{11}$B compound system, and compared with existing measurements and evaluations., Comment: 19 pages, 34 figures, to be published in Chinese Physics C

To verify the performance of the neutron total cross-sectional spectrometer, the neutron total cross section of carbon is initially measured in the energy range of 1 eV to 20 MeV using the time-of-flight method. The measurement is performed at the Back-n white neutron source with a 76-m time-of-flight path using the China Spallation Neutron Source. A multilayer fast fission chamber with 235U and 238U is employed as the neutron detector. The diameter and thickness of the natural graphite sample are 70 mm and 40 mm, respectively. Signal waveforms are collected using a data acquisition system. Off-line data processing was used to obtain the neutron time-of-flight spectra and transmissions. The uncertainty of the counting statistics is generally approximately 3% for each bin in the energy range of 1–20 MeV. It is determined that the results for the neutron total cross section of carbon obtained using 235U cells are in good agreement with the results obtained using 238U cells within limits of statistical uncertainty. Moreover, the measured total cross sections show good agreement with the broadening evaluated data.

In the original article, there were some errors in the list of authors and affiliations. Their correct version is given in this erratum.

High-spin states of $^{113}\mathrm{In}$ have been populated using the $^{110}\mathrm{Pd}(^{7}\mathrm{Li},4n)^{113}\mathrm{In}$ reaction at beam energies of 38 and 50 MeV. More than 50 new $\ensuremath{\gamma}$ transitions are observed in $^{113}\mathrm{In}$. Three previously observed magnetic dipole bands are extended to higher spin states, and several new $E2$ crossover transitions within the bands are observed in two of the dipole bands. A new positive-parity $▵I=2$ band built on the $\ensuremath{\pi}{d}_{5/2}$ configuration is established. The known $▵I=2$ band is extended to $51/{2}^{+}$ state, and a gentle up-bend associated to the alignment of neutrons in the normal-parity $\ensuremath{\nu}{g}_{7/2}/{d}_{5/2}$ orbitals is found. The properties of this band are discussed based on the self-consistent tilted axis cranking relativistic mean-field model calculations. The predicted $B(E2)$, deformation parameters ${\ensuremath{\beta}}_{2}$ and $\ensuremath{\gamma}$, and ${J}^{(2)}/B(E2)$ ratios indicate that the $▵I=2$ band based on the $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{({h}_{11/2})}^{2}$ and $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{({h}_{11/2})}^{2}{({g}_{7/2}/{d}_{5/2})}^{2}$ configurations, has the characteristics of antimagnetic rotation. Furthermore, the two-shears-like mechanism for the possible antimagnetic rotational bands is examined by investigating the orientation of the angular momenta.

High-spin states in $^{92}\mathrm{Nb}$ have been investigated by using in-beam $\ensuremath{\gamma}$ ray spectroscopy with the $^{82}\mathrm{Se}(^{14}\mathrm{N},4\mathrm{n})^{92}\mathrm{Nb}$ reaction at a beam energy of 54 MeV. The positive-parity decay sequences above the previously known state ${13}^{+}$ have been extended to ${I}^{\ensuremath{\pi}}\ensuremath{\ge}({20}^{+})$ by adding nineteen new $\ensuremath{\gamma}$ rays. The level structures in $^{92}\mathrm{Nb}$ have been interpreted in terms of the shell model calculations performed in the configuration space $\ensuremath{\pi}(1{f}_{5/2},2{p}_{3/2},2{p}_{1/2},1{g}_{9/2})$ for the protons and $\ensuremath{\nu}(2{p}_{1/2},1{g}_{9/2},1{g}_{7/2},2{d}_{5/2})$ for the neutrons. The calculated results show that the inclusion of proton core excitation relative to the $Z=38$ subshell closure and neutron particle-hole excitation for the $N=50$ shell closure are essential to adequately describe the experimental high-spin states at $I\ensuremath{\approx}(18--20)\ensuremath{\hbar}$ with excitation energies above 8.5 MeV.

China Spallation Neutron Source (CSNS) has been built and commissioned successfully in 2018 which is implemented by impinging 1.6 GeV protons onto a tungsten target with 25 Hz repetition frequency. An associated white neutron beam line exploiting the back-streaming neutrons, named Back-n, with a flight path of 55 m in endstation 1 (#ES1) and 76 m in endstation 2 (#ES2) was built mainly for nuclear data measurements. The Back-n beam line started running since the beginning of 2018 and the neutron energy spectrum was measured at the very beginning since it is an essential information for feasibility study and analysis of any measurement. In this paper, the measurement of the neutron energy spectrum of Back-n #ES2 is reported. The first result of the neutron flux from 1 eV to 100 MeV measured by a fission chamber based on the 235U(n, f) reaction is presented. The total neutron flux normalized to the proton beam power of 100 kW is $ 7.03 \times 10^{6}$ neutrons/cm2/s. The results show a good agreement with that of the Monte Carlo simulation as well.

The Back-n white neutron source (known as Back-n) is based on back-streaming neutrons from the spallation target at the China Spallation Neutron Source (CSNS). With its excellent beam properties, e.g., a neutron flux of approximately 1.8×107 n/cm2/s at 55 m from the spallation target, energy range spanning from 0.5 eV to 200 MeV, and time-of-flight resolution of a few per thousand, along with the equipped physical spectrometers, Back-n is considered to be among the best facilities in the world for carrying out nuclear data measurements. Since its completion and commencement of operation in May 2018, five types of cross-section measurements concerning neutron capture cross-sections, fission cross-sections, total cross-sections, light charged particle emissions, in-beam gamma spectra, and more than forty nuclides have been measured. This article presents an overview of the experimental setup and result analysis on the neutron-induced cross-section measurements and gamma spectroscopy at Back-n in the initial years.

The angle-differential cross sections of neutron-induced deuteron production from carbon were measured at six neutron energies from 25 to 52 MeV relative to those of n-p elastic scattering at the China Spallation Neutron Source (CSNS) Back-n white neutron source. By employing the Δ E-E telescopes of the Light-charged Particle Detector Array (LPDA) system at 15.1° to 55.0° in the laboratory system, ratios of the angle-differential cross sections of the 12C(n, xd) reactions to those of the n-p scattering were measured, and then, the angle-differential cross sections of the 12C(n, xd) reactions were obtained using the angle-differential cross sections of the n-p elastic scattering from the JENDL-4.0/HE-2015 library as the standard. The obtained results are compared with data from previous measurements, all of which are based on mono-energic neutrons, the evaluated data from the JENDL-4.0/ HE-2015 library and the ENDF-B/VIII.0 library, and those from theoretical calculations based on INCA code and Talys-1.9 code. Being the first white-neutron-source-based systematic measurement of the angle-differential cross sections of neutron-induced deuteron production reactions on carbon in several tens of MeV, the present work can provide a reference to the data library considering the lack of experimental data.

From microwave atomic clocks to light clocks, atomic or ionic clocks often rely on atom or ion trapping or manipulation technology. Trapping hydrogen (H) atoms in atomic storage bulbs (ASBs) is one of the key technologies of H atomic clocks. H atoms remain in an ASB for some time during which they undergo several relaxation processes (including spin-exchange collision relaxation, atom–wall collision relaxation, and magnetic-field inhomogeneity relaxation) and interact with the electromagnetic field within the resonant cavity in the TE011 mode, giving rise to continuous atomic transitions and self-oscillations. In this study, an optimal atomic storage time Tb for a H maser was determined by optimizing various collisional relaxation times of the atomic ensemble and reducing the width of the atomic resonance line through the continuously adjustable length and radius of the opening of an ASB at various atomic beam intensities ξ (which is the number of atoms in the atomic beam), namely, 3 × 1012 atoms/s, 4 × 1012 atoms/s, and 5 × 1012 atoms/s, while keeping the structural properties and physical conditions of the H maser unchanged. For ξ = 5 × 1012 atoms/s and Tb ≈ 0.8 s, a frequency stability of 0.95 × 10−15 could be achieved at 1000 s.

The Back-n is a high luminosity white neutron beamline at the China Spallation Neutron Source (CSNS). It started running in 2018 for various nuclear data measurements. A Light charged Particle Detector Array (LPDA) is designed for (n, lcp) reaction experiments, which includes a group of detectors and supporting systems. The Δ E-E telescope, consisting of a Low-Pressure Multi-Wire Proportional Chamber (LPMWPC) and a Si-PIN detector, is the core detector of the LPDA. From the beginning of 2018, several measurements have been performed using the Δ E-E telescopes, and the light charged particles such as 1H, 3H, 4He, and 7Li, were identified successfully. At present, the LPMWPC can identify the protons with energy as low as 0.5 MeV. In the near future, combining with CsI(Tl) crystals, a system consisting of sixteen telescopes with an energy acceptance from 0.5 MeV to 100 MeV (proton) will be constructed for general purpose of (n, lcp) measurements.

The polycrystalline diamond compact (PDC) bits have gained increasing favor since 1976. In order to further improve the ROP, the single PDC cutter tests were widely used. During these experiments, the cutting force is an important index to identify the efficiency of rock breaking. However, only the average value of cutting force was calculated in the previous researches. The variation trend of cutting force was not emphasized, which could reflect the process of rock failure to a large extent. In this study, a novel method to calculate the cutting force was used. At first, all the peak and valley values in the cutting force were picked out. With these points, the cutting force curves were separated into two parts: 1) rock loading process and 2) rock failure process. Then, the cutting force difference (△F), variation time (△t) and changing rate of cutting force (Ra) under different conditions were analyzed. Besides, we also calculated the changing rate of Ra with △F (SlRa). The results show that the variation trend of cutting force has a close relationship with the rock failure mode. That is, the above values at different cutting depth show significantly different characteristics in the unloading process of cutting force, which corresponding to the compression or the brittle failure of the rock, respectively. And the loading of cutting force is a stable process all the time. The results of this study are expected to introduce a new research perspective for the investigation of rock failure mode and working pattern of PDC cutters.

The Back-n white neutron source at the China Spallation Neutron Source (CSNS) was put into operation in 2018, providing a good platform for the cross-section measurement of neutron induced light charged particle ( l c p ) emission ( n , l c p ) reactions. Currently, in order to detect and identify light charged particles produced in ( n , l c p ) reactions at Back-n, a silicon detector array has been developed as a part of Light-charged Particle Detector Array. Composed of 15 silicon detectors, the array can detect the emitted particles ranging from 19.2°to 160.8°. The energy resolution of each silicon detector unit is better than 1% for 5.499 MeV α particles. Adopting this silicon detector array, several experimental measurements have been completed. Differential cross sections and angle-integrated cross sections in the neutron energy region ranging from the eV to the MeV range are extracted. Compared with previous measurements and evaluations, new results are obtained in the present measurements. These experiments indicate the feasibility of the silicon detector array in ( n , l c p ) reaction cross-section measurements.

The Stinger PDC cutter has a better performance than the conventional PDC cutter drilling for hard, interbedded and highly abrasive rocks. Although researchers have investigated the cutter's characteristic, such as impact resistance, wear resistance and cutter's life, the cutting behaviors of the Stinger PDC cutter still remains unclear. In this study, the single cutter tests were carried out with a Stinger PDC cutter and a conventional PDC cutter as comparisons. The cutting force, cuttings size, surface topography along the cutting trajectory and microscopic morphology of the fracture surface were compared and analyzed. The results show that the average cutting force of a Stinger PDC cutter is 46.14% lower than that of a conventional PDC cutter. The proportion of large cuttings (r > 2.36 mm) generated in the Stinger PDC cutter test is higher than that in the conventional PDC cutter test. In addition, the energy consumption of breaking rocks by a Stinger PDC cutter is 34.09% lower than that by a conventional PDC cutter. The cutting trajectory in the Stinger PDC cutter test has a “V” shape and the surface is relatively rough (Sa = 617.08 μm), while the conventional PDC cutter produces a “U” shape cutting trajectory and the surface is relatively smooth (Sa = 462.18 μm). Furthermore, the SEM analysis shows that the Stinger PDC cutter breaks granite mainly by tensile stress, which is different with the conventional PDC cutter by shear stress. The key findings of this work will help to reveal the rock-breaking process and mechanism with the Stinger PDC cutters.

Based on the China Spallation Neutron Source (CSNS) – Back-streaming white neutron source (Back-n WNS), the measurement of the U-238/U-235 fission cross section ratio in 1–20 MeV neutron energy region has been carried out by a multi-cell fast fission ionization chamber using the time-of-flight method. The measured resonance peaks of the 235U(n, f) reaction are in good agreement with those of the ENDF/B-8.0 database. The measured six groups of the U-238/U-235 fission cross section ratios in 1–20 MeV neutron energy region agree with those of the ENDF/B-8.0 database in trend, and the average discrepancies between experiment and database are from 1.9% to 2.6%. The relative experimental uncertainties are 2.3%–3.6% (1.4–20 MeV), and the measured data agree with those of database within experimental uncertainties at most energy points. The measured U-238/U-235 fission cross section ratio could provide information and data support in relevant nuclear data evaluation.

Cryogenic nitrogen jetting is a promising drilling rate improvement method, in which heat transfer plays an important role in inducing thermal stresses and facilitating rock breakage. In the present study, we aim to study flow field and heat transfer of a cryogenic nitrogen jet in two potential phase states (i.e. liquid and supercritical) under downhole conditions and determine the effect of some critical engineering parameters, including inlet pressure, ambient pressure and standoff distance, which are of concern for field applications of this method. Three different detached eddy simulation (DES) approaches were compared and validated to assess their performances in jet flow issues. These comparisons indicate IDDES showed better performance in predicting the flow field and heat transfer of jet flow, and thus was adopted for the present simulations. According to the simulation results, vorticity, dominant frequency fd of vortex instability and pressure oscillations grow with increasing inlet pressure for both free and impinging jets. Compared to the liquid nitrogen (LN2) jet, the supercritical nitrogen (SC N2) jet has higher vorticity magnitude and fd of temperature fluctuations, causing its vortex rings to breakdown in advance. The dominant frequency of temperature oscillations at the stagnation point falls at the same level as that of vortex instability in the shear layer, revealing the prevailing role of large-scale vortices in heat transfer. Under the same jet pressure condition, the heat transfer rate for SC N2 jet is constantly higher than that of LN2 jet. Increasing inlet pressure helps increase fd of temperature fluctuations and heat transfer rate for both LN2 and SC N2 jets. Under the same pressure difference (between inlet and outlet), lower ambient pressure is more conducive for SC N2 jets to enhance the vortex scale and heat transfer rate. In contrast, the ambient pressure has no significant influence on the LN2 jet. In the range of h/d ≤ 6, higher standoff distance delays the transition of vortex structures in the wall jet zone and contributes to the enhancement of heat transfer efficiency.

In the past two decades cooperating with Frank Laboratory of Neutron Physics (FLNP), Joint Institute for Nuclear Research (JINR) measurements of (n, α) reaction cross sections for 6Li, 10B, 25Mg, 39K, 40Ca, 54,56,57 Fe, 58Ni, 63Cu, 64,67 Zn, 95Mo, 143Nd and 147,149 Sm nuclei were performed in the MeV neutron energy region based on the 4.5 MV Van de Graaff accelerator at Peking University. In recent years, our measurements were extended in three aspects. Firstly, measurements were expanded from two-body reactions to three-body reactions such as 10B (n, t2 α). Secondly, the neutron energy region was extended from below 8 MeV to 8 - 11 MeV by using the HI-13 tandem accelerator of China Institute of Atomic Energy (CIAE), with which cross sections of 54,56 Fe(n, α)53,51Cr reactions were measured. Thirdly, based on the newly-built China Spallation Neutron Source (CSNS) Back-n WNS (White Neutron Source), differential and angle-integrated cross sections for 6Li(n, t) and 10B(n, α) reactions were measured in the neutron energy region from 1 eV to 3 MeV.

Differential cross-section data for the n-p and n-d elastic scattering (1H(n, el), 2H(n, el)) are collected and analyzed from EXFOR library. For En > 20 MeV, the experimental results for both reactions are scarce with large uncertainties and discrepancies in general. For En ≤ 20 MeV, the experimental results lack systematicness, most of which were measured around En = 14 MeV even though the differential cross sections of n-p scattering in 1 keV ≤ En ≤ 20 MeV region are recommended as standard. Taking these facts into account, more accurate and systematic measurements are planned. The experiments will be conducted using ΔE-E detectors of the Light-charged Particle Detector Array (LPDA) system at China Spallation Neutron Source (CSNS) Back-n White Neutron Source (WNS), and simulations are carried out. Using polyethylene and deuterated polyethylene as samples, both n-p and n-d scattering reactions are simulated along with the neutron-induced 12C background reactions, and the 2-D spectra and the counting rates of the ΔE-E detectors are obtained. According to the simulations, the applicable neutron energy range and positions of the detectors are recommended, and the beam time for the event and background measurements is suggested.

The high-spin structure of $^{109}\mathrm{In}$ has been investigated with the $^{100}\mathrm{Mo}(^{14}\mathrm{N}$, $5n)^{109}\mathrm{In}$ reaction at a beam energy of 78 MeV using the in-beam $\ensuremath{\gamma}$ spectroscopic method. The level scheme of $^{109}\mathrm{In}$ has been modified considerably and extended by 46 new $\ensuremath{\gamma}$ rays to the highest excited state at 8.980 MeV and ${J}^{\ensuremath{\pi}}=(45/{2}^{+})$. The new level scheme consists of eight bands, six of which are identified as dipole bands. The configurations have been tentatively assigned with the help of the systematics of neighboring odd-$A$ indium isotopes and the experimental aligned angular momenta. The dipole bands are then compared with the titled axis cranking calculation in the framework of covariant density function theory. The results of theoretical calculations based on the configurations, which involve one proton hole at the ${g}_{9/2}$ orbital and two or four unpaired neutrons at the ${g}_{7/2}$, ${d}_{5/2}$, and ${h}_{11/2}$ orbitals, show that the shape of $^{109}\mathrm{In}$ undergoes an evolution on both $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ deformations, and possible chirality is suggested in $^{109}\mathrm{In}$.

Back-n is a white neutron experimental facility at China Spallation Neutron Source (CSNS). The time structure of the primary proton beam make it fully applicable to use TOF (time-of-flight) method for neutron energy measuring. We implement the electronics of TOF measurement on the general-purpose readout electronics designed for all of the seven detectors in Back-n. The electronics is based on PXIe (Peripheral Component Interconnect Express eXtensions for Instrumentation) platform, which is composed of FDM (Field Digitizer Modules), TCM (Trigger and Clock Module), and SCM (Signal Conditioning Module). T0 signal synchronous to the CSNS accelerator represents the neutron emission from the target. It is the start of time stamp. The trigger and clock module (TCM) receives, synchronizes and distributes the T0 signal to each FDM based on the PXIe backplane bus. Meantime, detector signals after being conditioned are fed into FDMs for waveform digitizing. First sample point of the signal is the stop of time stamp. According to the start, stop time stamp and the time of signal over threshold, the total TOF can be obtained. FPGA-based (Field Programmable Gate Array) TDC is implemented on TCM to accurately acquire the time interval between the asynchronous T0 signal and the global synchronous clock phase. There is also an FPGA-based TDC on FDM to accurately acquire the time interval between T0 arriving at FDM and the first sample point of the detector signal, the over threshold time of signal is obtained offline. This method for TOF measurement is efficient and not needed for additional modules. Test result shows the accuracy of TOF is sub-nanosecond and can meet the requirement for Back-n at CSNS., 4 pages, 13 figures, 21st IEEE Real Time Conference

High spin states in 133Cs nucleus have been studied with the reaction 130Te (7Li, 4n) at a beam energy of 38 MeV. The level scheme has been expanded with spin up to 31/2 $\hbar$ . Compared with a recent paper, ground state band and other two collective band structures at lower spin states have been confirmed. Another collective band structure at higher spin states as well as some levels and transitions are updated. Compared with the experimental data, large-scale shell model and tilted axis cranking model calculations have been carried out. The results show that the band-head configuration of yrast band based on $7/2^{+}$ ground state and the side band built on the $5/2^{+}$ state are a pair of pseudospin partner states with $\pi \tilde{f}_{7/2,5/2}$ . The negative parity band based on 1071.5 keV level originates from $\pi h_{11/2}$ orbital. Another band built on 2642.9 keV level at high spin states has been proposed with oblate deformation. Other characteristics for these bands were also discussed.

High-spin states of $^{138}\mathrm{Pm}$ have been populated using the $^{124}\mathrm{Te}(^{19}\mathrm{F},\phantom{\rule{0.28em}{0ex}}5\mathrm{n})^{138}\mathrm{Pm}$ reaction at a beam energy of 105 MeV. A new positive-parity side band with the same $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ configuration as that of the yrast band is observed in $^{138}\mathrm{Pm}$. The properties of the two positive-parity bands show general agreement with the fingerprints of chiral rotation and thus these two bands are suggested to be candidates for near degenerate chiral doublet bands. Besides, odd-even spin staggering of the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ bands is studied systematically in odd-odd Cs, La, Pr, and Pm isotopes. As a result of this study we suggest that the spin value of lowest observed state of the yrast band be reassigned as 9 in $^{138}\mathrm{Pm}$. This new spin assignment is also supported by the argument of alignment additivity.

Four soybean storage protein subunit QTLs were mapped using bulked segregant analysis and an F2 population, which were validated with an F5 RIL population. The storage protein globulins β-conglycinin (7S subunit) and glycinin (11S subunits) can affect the quantity and quality of proteins found in soybean seeds and account for more than 70% of the total soybean protein. Manipulating the storage protein subunits to enhance soymeal nutrition and for desirable tofu manufacturing characteristics are two end-use quality goals in soybean breeding programs. To aid in developing soybean cultivars with desired seed composition, an F2 mapping population (n = 448) and an F5 RIL population (n = 180) were developed by crossing high protein cultivar ‘Harovinton’ with the breeding line SQ97-0263_3-1a, which lacks the 7S α′, 11S A1, 11S A2, 11S A3 and 11S A4 subunits. The storage protein composition of each individual in the F2 and F5 populations were profiled using SDS-PAGE. Based on the presence/absence of the subunits, genomic DNA bulks were formed among the F2 plants to identify genomic regions controlling the 7S α′ and 11S protein subunits. By utilizing polymorphic SNPs between the bulks characterized with Illumina SoySNP50K iSelect BeadChips at targeted genomic regions, KASP assays were designed and used to map QTLs causing the loss of the subunits. Soybean storage protein QTLs were identified on Chromosome 3 (11S A1), Chromosome 10 (7S α′ and 11S A4), and Chromosome 13 (11S A3), which were also validated in the F5 RIL population. The results of this research could allow for the deployment of marker-assisted selection for desired storage protein subunits by screening breeding populations using the SNPs linked with the subunits of interest.

The existing experimental value of the ratio ${B}_{4/2}\ensuremath{\equiv}B(E2;{4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})/B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ in $^{134}\mathrm{Ce}$ is less than unity, which is outside the range allowed by current collective models and is highly anomalous. In the present work, new lifetime measurements of excited states in $^{134}\mathrm{Ce}$ have been performed in order to clarify this discrepancy. Excited states of $^{134}\mathrm{Ce}$ were populated by the fusion-evaporation reaction $^{122}\mathrm{Sn}(^{16}\mathrm{O},4n)^{134}\mathrm{Ce}$. The recoil distance doppler shift method was employed, and reliable lifetimes for the ${2}_{1}^{+}, {4}_{1}^{+}, {10}_{2}^{+}$, and ${12}_{2}^{+}$ states were derived from the differential decay curve method. The resulting ${B}_{4/2}$ value is larger than unity, resolving the disagreement with traditional collective models. The new experimental data is in very good agreement with the calculation in the framework of the interacting boson model. The systematic evolution in collectivity of the Ce isotopes is discussed.

Carrier relaxation dynamics of InSe flakes is investigated by using time-resolved pump-probe reflectivity measurement. The photocarriers associated with the P xy orbital band-edge transition at 2.40 eV, which is coupled to the in-plane polarized light, is observed to possess a lifetime of ∼19 ps at room temperature and ∼99 ps at 10 K. The temperature and power dependent carrier lifetime suggests that Shockley-Read-Hall process is the dominant nonradiative recombination mechanism responsible for the carrier relaxation. In addition, the electron scattering with a 14.5 meV optical phonon plays an active role in the carrier relaxation with increasing temperatures. A broad absorption around 1.65-1.90 eV is observed. The photocarriers associated with this broad transition show a long lifetime of ∼200 ps that is nearly independent of temperature and photon energy. This is indicative of bound carriers by defects. Our experimental results provide essential information for the characteristics of carrier dynamics and defects in InSe flakes. The experimental findings are fundamentally important for further development of microelectronics and optoelectronics based on InSe.

A white neutron source for nuclear data measurement has been built and put into operation on China Spallation Neutron Source (CSNS). We developeda beam monitor for real-time online monitoring of neutron flux on the white neutron source. The beam monitor work simultaneously with other nuclear data measurement detectors to provide neutron flux for data analysis. To minimize beam disturbance and reduce the background generated by the monitor, a structure in which neutron conversion layer and Si detectors are separated is employed: A 6LiF film with a mass thickness of 360 μ g/cm 2 was deposited on a 10 μ m aluminum foil and placed inside the beam line. Eight Si-detectors with a size of 20 × 20 mm2 were placed around the film outside the beam to maximize the reception of secondary particles from the conversion layer and to avoid neutron beam irradiation. The simulation of the beam monitor (layout, counting rate, neutron disturbance, etc.), construction and online performance are described in the paper. Good online performance of the monitor was achieved during the CSNS white neutron source flux calibration experiment in March, 2018: The counting rate for the beam line operating at Ф30 mm and Ф60 mm beam pattern modes was normalized to 100 kW proton beam power, and the result is consistent with the simulation. The total uncertainty of the normalized counting rate is less than 1%. Moreover, the measurement of neutron flux in low energy region below 10 keV of the white neutron source by the monitor is discussed.

Due to the unique physical and chemical properties of liquid nitrogen (LN2), LN2 fracturing has been considered as a promising reservoir stimulation technique. In order to further investigate the feasibility of LN2 fracturing, a new device is designed to research the effect of LN2 fracturing under different conditions, such as different specimen sizes, temperatures, and confining pressures. The setup consists of three units: a high-pressure LN2 generating system, a true-triaxial loading and heating system, and a control and data acquisition system. Now, a series of experiments have been successfully carried out based on the setup. The results have proven the excellent fracturing effect of LN2 and the applications of this setup. The apparatus lays a foundation for the application of LN2 fracturing in both conventional and geothermal reservoirs.

The Chinese spallation neutron source was completed in May 2018 and then subsequently commissioned. The Back-streaming white neutron beam line can be used in neutron nuclear data measurement, neutron physics research, and nuclear technology. In these experiments, it is necessary to know the neutron energy spectrum, the neutron flux, and the neutron beam profile of the neutron beam. In this paper, we present the preliminary measurements of these parameters. The neutron energy spectrum and neutron flux are measured by the time-of-flight method with a fission chamber equipped with 235U and 238U samples and a 6Li-Si detector. The neutron beam profile is measured by a scintillator-CMOS detection system. The preliminary experimental measurements of the beam line are obtained. Among them, the energy spectrum measurement range of white neutrons is from eV to more than 100 MeV, which also gives an uncertainty analysis; the neutron fluence rate gives the full power value of the two experimental halls; the collimated white neutron beam spot is given under a diameter of 60 mm. The future plan is also given. The results of these experimental parameters can serve as the foundation for the future nuclear data measurement and detector calibration experiments of the beam line.

Passive walking model can make full use of the potential energy, which made it more efficient and more natural. So that it has become a hot spot in the current research. However, the condition of passive walking robot is heavily affected by its own structure and the external environment parameter, especially the slope angle which may result in a chaotic gait. In this paper, a control method capable of realizing stable passive walking on various slopes is introduced. In this way, we turned the chaotic gait into a limit cycle gait, then identified the slope angle of the chaotic gait. As a result, the suppression of chaotic gait is achieved. This method is suitable for slope of different angles. In the end of this paper, this method proved to be feasible and capable for slope of different angles.

The semimagic nucleus $^{89}\mathrm{Y}$ has been investigated using the $^{82}\mathrm{Se}(^{11}\mathrm{B},4n)$ reaction at beam energies of 48 and 52 MeV. More than 24 new transitions have been identified, leading to a considerable extension of the level structures of $^{89}\mathrm{Y}$. The experimental results are compared with the large-basis shell model calculations. They show that cross-shell neutron excitations play a pivotal role in high-spin level structures of $^{89}\mathrm{Y}$. The systematic features of neutron-core excitations in the $N=50$ isotones are also discussed.