Diamond detectors exhibit significant potential for measuring 14 MeV neutrons generated by fusion plasmas in tokamak experiments, owing to their exceptional radiation hardness and thermal stability. Monte Carlo simulation serves as a vital tool for designing and optimizing the performance of diamond detectors; however, discrepancies among the nuclear data libraries can considerably affect simulation outcomes. To systematically assess these influences, this study conducts comparative simulations based on five major international nuclear data libraries, with a focus on the response of diamond detectors to D-T neutrons under different nuclear data conditions. The results indicate a high level of consistency across libraries in both the 12C(n, el)12C and 12C(n, alpha)9Be reactions, with all libraries yielding a similar detection efficiency of approximately 0.035% for the latter. The main discrepancies emerge from the 12C(n, n+3 alpha) reaction, where the CENDL library produces notably higher count rates in the corresponding energy region. Additionally, the response matrix of the diamond detector in the energy region of 1-20 MeV was simulated, offering essential input for forward simulations and spectrum unfolding. The sensitivity of the diamond detector to neutrons and gamma rays across different energies was also investigated. This study provides a valuable theoretical basis and data support for the accurate simulation, appropriate nuclear data library selection, and structural optimization of diamond detectors in fusion neutron diagnostic applications.

High-spin states of 67Ga have been studied via the 58Ni(12C, 3p) 67Ga fusion-evaporation reaction at a beam energy of 50.4 MeV. Three negative-parity bands and three positive-parity bands in 67Ga are established. The observation of one new E3 transition linking the positive-parity pi 1g9/2 band and negative-parity pi 2p3/2 band provides evidence of octupole correlations in 67Ga. The characteristics of octupole correlations in the 67Ga are discussed in terms of the reflection-asymmetric triaxial particle rotor model and microscopic relativistic mean field + Bardeen-Cooper-Schrieffer model.

We report here the first observation of the 0(2)(+) state of He-8, which has been predicted to feature the condensatelike alpha + (2)n + (2)n cluster structure. We show that this state is characterized by a spin parity of 0(+), a large isoscalar monopole transition strength, and the emission of a strongly correlated neutron pair, in line with theoretical predictions. Our finding is further supported by the state-of-the-art microscopic alpha + 4n model calculations. The present results may lead to new insights into clustering in neutron-rich nuclear systems and the pair correlation and condensation in quantum many-body systems under strong interactions.

Received 26 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.039903©2023 American Physical Society

We report here the first observation of the 0_{2}^{+} state of ^{8}He, which has been predicted to feature the condensatelike α+^{2}n+^{2}n cluster structure. We show that this state is characterized by a spin parity of 0^{+}, a large isoscalar monopole transition strength, and the emission of a strongly correlated neutron pair, in line with theoretical predictions. Our finding is further supported by the state-of-the-art microscopic α+4n model calculations. The present results may lead to new insights into clustering in neutron-rich nuclear systems and the pair correlation and condensation in quantum many-body systems under strong interactions.

Nuclear collective rotation, which involves coherent contributions from many nucleons, has been well known for a long time. It is ascribed as a consequence of deformation and gives rise to regular rotational bands, which are characterized by strong electric quadrupole (E2) transitions. Studies of the rotational bands in nuclei have been in the forefront of nuclear structure physics and have led to many interesting phenomena including the backbending, superdeformed bands, and chiral doublet bands. In 1990s, a new type of rotational-like sequences, which have strong M1 transitions and weak or vanishing E2 transitions, have been discovered in weakly deformed or near-spherical nuclei and attracted a lot of interests. This new type of rotational structure cannot be understood in terms of conventional rotation of deformed nuclei but has been successfully interpreted in terms of the shears mechanism. In this interpretation, nuclear orientation is specified by the current distribution rather than the deformation. The magnetic dipole vector arises from proton particles (holes) and neutron holes (particles) in high-j orbitals, and rotates around the total angular momentum vector. In the subsequent experimental studies, the magnetic rotation phenomenon were found in the A similar to 60, A similar to 80, A similar to 110, A similar to 140, and A similar to 190 mass regions. Here, we report the studies of magnetic rotation in the A similar to 80 and A similar to 60 mass regions. The high-spin structures of 75As, 79Se and 62Cu were respectively populated via Zn-70(Be-9, 1p3n)As-75, Se-82(alpha, alpha 3n)Se-79 and Cr-54(C-12, 1p3n)Cu-62 heavy ion fusion-evaporation reactions. The dipole bands were established for the first time in these three nuclei. The properties of these dipole bands are investigated in terms of the self-consistent tilted axis cranking covariant density functional theory. In the calculation for As-75, Se-79 and Cu-62, the valence nucleon configurations of pi[(1g(9/2))1(1f(5/2))(-2)]circle times upsilon[(1g(9/2))(5)(fp)(-3)], pi[(1g(9/2))(1)(fp)(5)]circle times upsilon[(1g(9/2))(5)] and pi[(f(7/2))(-1)(p(3/2)f5(/2))(2)]circle times upsilon[(g(9/2))(1)(p(3/2)f(5/2))(4)] are used, respectively. The calculated energy spectra reasonably reproduce the experimental excitation energies of As-75, Se-79, and Cu-62. The evolutions of deformation parameters beta and gamma of these dipole bands driven by increasing rotational frequency are discussed. In contrast to the relatively large triaxial deformation of the dipole bands in As-75 and Cu-62, the dipole band of Se-79 has a relatively axially symmetric and small prolate deformation. With the increase of rotational frequency, the beta deformations for As-75, Se-79 and Cu-62 behave in a similar way, i.e., a smooth decrease in beta. Meanwhile, both. values of As-75 and Cu-62 show a smoothly increasing tendency. Based on the examination of the composition of the proton and neutron angular momentum vectors J(pi) and J(upsilon) as well as the total angular momentum J(tot)=J(pi)+J(upsilon) at both the bandhead and the maximum rotational frequency, the dipole bands in As-75 and Se-79 can be interpreted as novel stapler bands, where the valence nucleons in (1g(9/2)) orbital rather than the collective core are responsible for the closing of the stapler of angular momentum. Although not firmly confirmed in experiments, the dipole structure in Cu-62 may be a candidate of magnetic rotational bands. To unambiguously confirm this, further experimental investigations are strongly desirable.

Two nearly degenerate positive-parity bands with the πg9/22⊗νg9/2−1 configuration and three nearly degenerate negative-parity bands with the πg9/2(p3/2,f5/2)⊗νg9/2−1 configuration have been identified in 81Kr. They are interpreted as chiral doublet bands and pseudospin-chiral triplet bands, which is supported by the constrained covariant density functional theory and the multiparticle plus rotor model calculations. The present work reports two new chiral configurations πg9/22⊗νg9/2−1 and πg9/2(p3/2,f5/2)⊗νg9/2−1, and the first example of pseudospin-chiral triplet bands involving the π(p3/2,f5/2) pseudospin doublet.

The spectroscopy of 62Cu is studied via the 54Cr(12C, 1 p3n) 62Cu fusion-evaporation reaction. On the basis of the gamma -gamma coincidence analysis, angular distributions from oriented states, and linear polarization measurement, three positive-parity and three negative-parity level sequences in 62Cu are observed, including two new gamma -ray transitions and one new level. The collective structures are discussed in terms of the tilted axis cranking covariant density functional theory. Although not firmly confirmed in experiment, the properties of a magnetic rotational structure with the n(f7/2)-1(p3/2 f5/2)2 circle times v(g9/2)1(p3/2 f5/2)4 configuration have been discussed. Its angular momentum generation is probably due to the shears mechanism.

The spectroscopy of Ge-71 has been investigated via the fusion-evaporation reaction Ge-74(alpha, alpha 3n)Ge-71. Collective structures including a rotational band built on the 15/2(-) octupole state in Ge-71 have been established. The observation of strong E1 transitions and the well-behaved rotational sequence built on the 15/2(-) octupole state provide the first experimental evidence of an octupole rotational band in Ge isotopes, suggesting an enhanced octupole correlation around N = 40 in the A approximate to 70 region. A newly developed semimicroscopic cluster model provides a good description of the octupole characteristics of Ge-71.

The EAST plasmas heated with deuterium neutral beam injection and ion cyclotron resonance heating (ICRH) have been simulated by the TRANSP code. The analysis has been conducted using the full wave solver TORIC5, the radio frequency (RF)-kick operator, and NUBEAM to model the RF heating effects on fast ion velocity distribution. In this work, we present several simulated results compared with experiments for high power EAST scenarios, indicating that the interactions between ICRH and fast ions can significantly accelerate fast ions, which are confirmed by the increased neutron yield and broadened neutron emission spectrum measurements.

Given that the nuclei studied in the nuclear physics experiments are expanding away from the stable nuclear region, traditional analog electronics acquisition systems cannot satisfy the requirements of experiments that involve short-lived, low-yield nucleus productions under high background. In recent years, digital data acquisition systems have shown significant advantages over the analog electronics system and have been widely used in nuclear physics research such as studies of short-lived charged particle emitters which involve overlapping ion-particle or particle-particle signals, and studies of sub-microsecond isomers observed in fragmentation reactions. A general-purpose digital data acquisition system and a dedicated waveform analysis algorithm recently developed by the Group of Experimental Nuclear Physics, Peking University are introduced in this paper. This digital data acquisition system which is composed of 16-channel digital pulse processor Pixie-16 modules from XIA LLC is a versatile, flexible, and expandable data acquisition system designed for nuclear physics research. Although the triggerless mode, which records all live events without event selection, provides an attractive option for users because it has great flexibility for offline data analysis, it generates significant data streams in the experiments with high counting rates, which may then exceed the digital data acquisition system's I/O capability. Therefore, a flexible trigger system based on the field programmable gate array has been developed to accommodate different experimental needs. The trigger system is configured through the hardware description language (VDHL/verilog), which can set up and debug different experiment logics conveniently. Many offline analysis tools have been developed to help users quickly optimize parameters for various types of detectors without time-consuming tests and measurements. A comparison between this digital data acquisition system and the conventional analog data acquisition system has been made. At a low count rate, both systems exhibit good and comparable energy resolution. 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 data acquisition system remains nearly unchanged. Moreover, experimental data with higher statistics can be collected by the digital data acquisition system. The advantage of this digital data acquisition system over the conventional analog system is ascribed to its excellent capability of handling pile-up pulses at higher count rates, and nearly zero dead time in data transmission and conversion. An effective digital pulse processing method has been developed for the decomposition of pile-up pulses which result from the signals of mu s a decay. This method is able to decompose the multiple pile-up pulses with very close separation in time scale and large range of relative amplitude. The method was validated with the very short-lived a emitter Th-219 (T-1/2= 1.08 mu s) and the internal conversion electron decays of Ra-210,Ra-211 isomers (T-1/2=2.27, 4.0 mu s) produced by Ar-40+W-186. The results show that this method can resolve pile-up pulses with time separation as short as 80 ns. The energy resolution for signals with time separation down to 80 ns is 32 keV. The internal conversion electron decay with energy as low as 70 keV can be well identified. This digital data acquisition system has been successfully used in many experiments performed at China Institute of Atomic Energy, Institute of Modern Physics, Chinese Academy of Sciences, Dongguan Campus, Institute of High Energy Physics, Chinese Academy of Sciences, and South Africa iThemba LABS, and has demonstrated its versatility and high efficiency.

A time-of-flight neutron spectrometer based on the Time-Of-Flight Enhanced Diagnostic (TOFED) concept has been designed and is under development for the Large Helical Device (LHD). It will be the first advanced neutron spectrometer to measure the 2.45 MeV D-D neutrons (DDNs) from helical/stellarator plasmas. The main mission of the new TOFED is to study the supra-thermal deuterons generated from the auxiliary heating systems in helical plasmas by measuring the time-of-flight spectra of DDN. It will also measure the triton burnup neutrons (TBNs) from the d+t reactions, unlike the original TOFED in the EAST tokamak. Its capability of diagnosing the TBN ratios is evaluated in this work. This new TOFED is expected to be installed in the basement under the LHD hall and shares the collimator with one channel of the vertical neutron camera to define its line of sight. The distance from its primary scintillators to the equatorial plane of LHD plasmas is about 15.5 m. Based on Monte Carlo simulation by a GEANT4 model, the resolution of the DDN energy spectra is 6.6%. When projected onto the neutron rates that are typically obtained in LHD deuterium plasmas (an order of 1015 n/s with neutral beam injection), we expect to obtain the DDN and TBN counting rates of about 2.5 · 105 counts/s and 250 counts/s, respectively. This will allow us to analyze the DDN time-of-flight spectra on time scales of 0.1 s and diagnose the TBN emission rates in several seconds with one instrument, for the first time in helical/stellarator plasmas.

The disappearance of traditional magic numbers and the generation of new magic numbers in weakly-bound nuclei have always been the frontier of physics with radioactive beam. In recent years, the research based on large scientific devices around the world has got fruitful results. In the light neutron-rich region far away from the beta-stable line, it has been found that the traditional neutron magic numbers 8, 20, 28 disappear and the new neutron magic numbers 14, 16, 34 appear. In the medium and heavy neutron-rich regions, experimental and theoretical studies have shown that the traditional neutron magic numbers 50 and 82 tend to weaken or disappear with the increase of the neutron/proton ratio. For example, recent experimental studies have shown that the N=82 shell closure in Sn-132, Cd-130, and Pd-128 isotones is still robust, but a significant reduction of the N=82 gap was suggested to occur between Sn and Zr as a consequence of the absent Z=40 subshell gap. With the Z=47, the neutron-rich odd-A Ag isotopes are naturally of great interest. Their valence protons are assumed to fill the pi g(9/2) and pi p(1/2) orbitals, between which the Z=40 subshell gap is formed. The energy difference between the lowest lying 9/2(+) and 1/2(-) states in these neutron-rich odd-A Ag isotopes provides direct information on the Z=40 subshell gap. Therefore, to explore the N=82 shell evolution in Ag isotopes, the beta-delayed gamma-ray spectroscopy of neutronrich Ag-123,Ag-125 isotopes is investigated at the Radioactive Isotope Beam Factory of RIKEN in the framework of the Euroball RIken Cluster Array project. The long-predicted 1/2(-) beta-emitting isomers in Ag-123,Ag-125 are identified for the first time. Shellmodel calculations have been performed using the KSHELL code with the state-of-the-art monopole-based universal interaction V-MU plus a spin-orbit force from M3Y (V-MU+LS), and give an overall satisfactory description of experimental levels in Ag-123,Ag-125, particularly for the low-lying levels. The calculations indicate that, as approaching N=82, the wave functions from the pi g(9/2) and pi p(1/2) orbitals dominate low-lying states of Ag isotopes. With the newly observed 1/2(-) isomeric states in Ag-123,Ag-125, the systematic energy difference between the lowest 9/2(+) and 1/2(-) states along Ag isotopic chain indicates an increasing trend beyond 125Ag, which reveals that the Z=40 subshell gap starts to be restored toward N=82. Extrapolating the trend toward N=82, a considerable diminishment of the Z=40 subshell gap is expected. To get more insight into the microscopic origin of shell evolution in this region, the effective single-particle energies are calculated for the proton orbitals in the region of N=68-82 with the V-MU+LS interaction. It is found that, if only the central + spin-orbit parts are considered, the pi p(1/2) orbital lies below the pi g(9/2) orbital in the whole region of N=68-82. In contrast, with the inclusion of the tensor part (especially the pi g(9/2)-nu h(11/2) monopole), the pi g(9/2) orbital is affected much more than the pp1/ 2 orbital, and the spacing between pi g(9/2) and pi p(1/2) orbitals is notably reduced, consequently, resulting in the inversion of these two orbitals at N similar to 74, which is compatible with the experimental inversion position. The tensor force manifests its crucial role in the modification of the order of the proton orbitals and the size of the Z=40 subshell gap in Ag isotopes mainly through the pi g(9/2)-nu h(11/2) monopole. Vice versa, our calculations indicate that this tensor force will also influence the behavior of the nu h(11/2) orbital, which is important for the N=82 shell gap.

Stilbene crystal detectors are widely used as fast neutron measurement tools based on recoil proton detection, such as liquid scintillators. A compact stilbene crystal neutron spectrometer (CSCNS) has been installed at the Experimental Advanced Superconducting Tokamak (EAST) to obtain information on fuel ions produced in the plasma core because of its merits of good n/γ discrimination capability, high detection efficiency, and fast response. For the first time, CSCNS has been used for neutron emission spectroscopy measurements in EAST plasmas with neutral beam injection (NBI) heating. The CSCNS has the same horizontal line of sight as the time-of-flight enhanced diagnostics neutron spectrometer. Under NBI heating scenarios, the time trace of the neutron yield monitored by the CSCNS is similar to the one monitored by a standard 235U fission chamber. The experimental pulse height spectra are also similar to the simulated ones generated by folding the simulated neutron energy spectrum with the detector response functions. These results demonstrate the capability of the CSCNS for neutron diagnostics and the study of fast-ion physics in EAST.

Neutron emission spectroscopy (NES) measurements at Experimental Advanced Superconducting Tokamak (EAST) are described. Both measurements and simulations of the neutron energy spectrum were done for the NBI-heated plasma at EAST. The experimental results were measured by the time-of-flight (TOF) neutron spectrometer TOFED, which was moved outside the experimental hall and installed in the newly-built nuclear diagnostics laboratory. A fully digital data acquisition system based on the digitizers was designed and utilized for the TOFED, which satisfied all the primary scintillators and 16 secondary scintillators. The TOFED prototype firstly obtained the neutron time-of-flight spectra with optimized signal-to-noise ratio in the 2017 EAST experiment campaign, when the NBI heating systems were employed. The neutron time-of-flight spectra were distinctly broadened, compared to the simulation of neutron spectra from the thermal plasma with the code GENESIS. These experimental results demonstrate the capability of the time-of-flight neutron spectrometer TOFED to contribute to the studies on fast ion physics at EAST.

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 $$\gamma$$ -ray detector array of the China Institute of Atomic Energy using the $$\gamma$$ -ray source and in-beam $$\gamma$$ -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.

The time-of-flight enhanced diagnostics (TOFED) neutron spectrometer has been installed in TOFED house,which is a newly-built neutron diagnostic lab outside the EAST experimental hall.The line of sight (LOS) of TOFED is defined by the collimator going through the 150 cm biological shielding wall,which can reduce background neutrons very effectively for the neutron spectral measurements.The Monte Carlo code MCNP5 is used in the simulations to characterize collimation effects and the radiation safety of the new house.The collimator makes neutron flux almost fully perpendicular to S 1 detectors.In addition,the proportion of scattered neutrons in the LOS of the TOFED is obtained for the measured spectral data interpretation.The simulation results show that the TOFED house satisfies the requirement for the TOFED operations at EAST and gives a safe environment for personnel access during the EAST operation.

A general-purpose digital data acquisition system (GDDAQ) has been developed at Peking University. This GDDAQ, composed of 16-channel Digital Pulse Processor Pixie-16 modules from XIA LLC, is a versatile, flexible, and easily expandable data acquisition system for nuclear physics research in China. The software used by this GDDAQ is based on the CERN ROOT framework and developed and tested in CentOS 7 LINUX operating platform. A flexible trigger system has also been developed to accommodate different experimental settings. A user-friendly software GUI helps users monitor and debug the detection system in real timer or offline. Many offline analysis tools have been developed to help users quickly optimize parameters for various types of detectors without the need for time-consuming tests and measurements. This GDDAQ has been successfully implemented in several nuclear physics experiments and its versatility and high efficiency have been demonstrated.