Heavy-ion storage rings are advanced large-scale nuclear physics experimental facilities that enable long-term storage and precise manipulation of accelerated heavy-ion beams. They serve as unique platforms for nuclear structure and nuclear astrophysics research. At present, the internationally representative heavy-ion storage rings in the field of nuclear physics research are: the Experimental Storage Ring (ESR) at the GSI Helmholtz Centre for Heavy Ion Research (Germany), the Cooler Storage Ring experimental ring (CSRe) at the Institute of Modern Physics, Chinese Academy of Sciences (China), and the Rare-RI Ring (R3) at the RIKEN Nishina Center (Japan). Over the past decade, researchers have conducted high-precision measurements of mass, decay lifetime, and nuclear reaction cross sections based on the aforementioned experimental platforms. Highlight experimental studies are outlined in this review, such as mass measurements of nuclei near the A = 20-70 proton drip line at CSRe, mass measurements of Pd-123 at R3, and lifetime determination of bound-state beta decay of fully stripped Tl-205(81+) and two-photon decay of Ge-72m(32+). These experimental efforts have provided crucial data for exploring the limits of nuclear existence, elucidating the characteristics of exotic nuclei, and simulating nucleosynthesis processes in astrophysical environments. The construction of the next-generation heavy-ion storage ring facility will provide superior experimental conditions for the aforementioned research endeavors, thereby facilitating advancements in nuclear physics frontier research.

The heaviest stable nuclei in the universe owe their existence to quantum shell structure, the grouping of protons and neutrons into discrete energy levels separated by gaps. The largest known neutron shell gap in stable nuclei, at N=126, stabilizes doubly-magic ^208Pb and is responsible for the characteristic abundance peak of heavy elements near gold and platinum produced by the rapid neutron-capture process (r-process). Whether this shell gap persists as protons are removed from lead is a question central to both nuclear structure and the modeling of heavy-element synthesis, yet it has remained unanswered due to the extraordinary difficulty of producing the relevant neutron-rich nuclei. Direct experimental knowledge in this region was essentially absent. Here we report the first precision mass measurements of ^203,204Pt and ^204,205,206Au, performed at GSI using a novel combination of Schottky and isochronous mass spectrometry in a heavy-ion storage ring. The N=126 isotones ^204Pt and ^205Au are more strongly bound than the extrapolated trend of the previously known mass surface by 403 and 464 keV, respectively, revealing an unexpectedly enhanced N=126 shell strength below doubly-magic ^208Pb. Furthermore, the proton-neutron interaction strength exhibits a hitherto unobserved bifurcation at N=126 as protons are removed from ^208Pb. Our results redefine the nuclear mass surface in the neutron-rich heavy-element region and provide direct experimental benchmarks for theoretical models whose extrapolations toward more exotic nuclei are essential for r-process nucleosynthesis calculations.

The measurement of the bound-state decay of Tl-205 at the Experimental Storage Ring (ESR) at GSI, Darmstadt, has recently been reported, with substantial impact on the use of 205Pb as an early Solar System chronometer and on the low-energy measurement of the solar neutrino spectrum via the LOREX project. Owing to the technical challenges in producing a high-purity Tl-205(81+) secondary beam, a robust statistical method was developed to estimate the variation in the contaminant Pb-205(81+) produced in the fragmentation reaction, which was subsequently transmitted and stored in the ESR. Here, we show that Bayesian and Monte Carlo methods produce comparable estimates for the contaminant variation, each with unique advantages and challenges given the complex statistical problems for this experiment. We recommend the adoption of such methods in future experiments that exhibit unknown statistical fluctuations.

The measurement of mass, or equivalently the binding energy, of exotic nuclei has reached the limits of nuclear existence, which are characterized by tiny production cross-sections and short half-lives. The isochronous mode of the Spectrometer Ring at the High Intensity heavy-ion Accelerator Facility project in China (HIAF-SRing) offers the capacity for such measurements. However, many factors limit the revolution time resolution of the isochronous mode of the large acceptance HIAF-SRing. Nonlinear field errors as well as fringe fields of the wide aperture dipoles and quadrupoles strongly excite the higher-order aberrations, which negatively affect the revolution time resolution. Moreover, the transverse emittance of the beam is inversely proportional to the revolution time resolution. Their influence is investigated here, and a possible correction scheme with sextupoles and octupoles is shown. With higher-order corrections, a mass resolution of , R(FWHM)=1x10(6)corresponding to a relative revolution time of sigma(T)/T similar to 4.9x10(-7) , is with the isochronous setting gamma t=1.43 within the momentum acceptance of %.

Quantum electrodynamics has been tested to accuracies below the parts-per-trillion level in light-mass systems. However, tests in heavy-mass systems with a large nuclear charge have not yet reached similar accuracy. Here we report the hyperfine-structure splitting in the 1s ground state of radioactive hydrogen-like 208Bi82+. We produced the isotope in a nuclear reaction and injected the beam into a storage ring to perform laser spectroscopy on samples of 105 ions of Bi82+ that have only a single remaining electron, which experiences extreme magnetic-field strengths. Our result for the hyperfine splitting is in excellent agreement with the most accurate prediction based on a combination of quantum electrodynamics calculations with an empirical treatment of the hyperfine-structure anomaly ratio extracted from laser spectroscopy on neutral atoms of 209Bi and 208Bi. This achievement paves the way for the most stringent test of quantum electrodynamics in strong magnetic fields and demonstrates the feasibility of laser spectroscopy on other exotic ions with low production yields.

Schottky mass spectrometry utilizing heavy-ion storage rings is a powerful technique for the precise mass and decay half-life measurements of highly charged ions. Owing to the nondestructive ion detection features of Schottky noise detectors, the number of stored ions in the ring is determined by the peak area in the measured revolution frequency spectrum. Because of their intrinsic amplitude-frequency characteristic (AFC), Schottky detector systems exhibit varying sensitivities at different frequencies. Using low-energy electron-cooled stored ions, a new method is developed to calibrate the AFC curve of the Schottky detector system of the Experimental Cooler Storage Ring (CSRe) storage ring located in Lanzhou, China. Using the amplitude-calibrated frequency spectrum, a notable refinement was observed in the precision of both the peak position and peak area. As a result, the storage lifetimes of the electron-cooled fully ionized ^56 Fe ^26+ ions were determined with high precision at beam energies of 13.7 and 116.4 MeV/u, despite of frequency drifts during the experiment. When electron cooling was turned off, the effective vacuum condition experienced by the 116.4 MeV/u ^56 Fe ^26+ ions was determined using amplitude-calibrated spectra, revealing a value of 2× 10^-10 mbar, which is consistent with vacuum gauge readings along the CSRe ring. The method reported herein will be adapted for the next-generation storage ring of the HIAF facility under construction in Huizhou, China. It can also be adapted to other storage ring facilities worldwide to improve precision and enhance lifetime measurements using many ions in the ring.

Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth1,2. Among such nuclei whose decay signatures are found in the oldest meteorites, 205Pb is a powerful example, as it is produced exclusively by slow neutron captures (the s process), with most being synthesized in asymptotic giant branch (AGB) stars3-5. However, making accurate abundance predictions for 205Pb has so far been impossible because the weak decay rates of 205Pb and 205Tl are very uncertain at stellar temperatures6,7. To constrain these decay rates, we measured for the first time the bound-state β- decay of fully ionized 205Tl81+, an exotic decay mode that only occurs in highly charged ions. The measured half-life is 4.7 times longer than the previous theoretical estimate8 and our 10% experimental uncertainty has eliminated the main nuclear-physics limitation. With new, experimentally backed decay rates, we used AGB stellar models to calculate 205Pb yields. Propagating those yields with basic galactic chemical evolution (GCE) and comparing with the 205Pb/204Pb ratio from meteorites9-11, we determined the isolation time of solar material inside its parent molecular cloud. We find positive isolation times that are consistent with the other s-process short-lived radioactive nuclei found in the early Solar System. Our results reaffirm the site of the Sun's birth as a long-lived, giant molecular cloud and support the use of the 205Pb-205Tl decay system as a chronometer in the early Solar System.

Isochronous mass spectrometry (IMS) of heavyion storage rings is a powerful tool for the mass measurements of short-lived nuclei. In IMS experiments, masses are determined through precision measurements of the revolution times of the ions stored in the ring. However, the revolution times cannot be resolved for particles with nearly the same mass-to-charge (m/q) ratios. To overcome this limitation and to extract the accurate revolution times for such pairs of ion species with very close m/q ratios, in our early work on particle identification, we analyzed the amplitudes of the timing signals from the detector based on the emission of secondary electrons. Here, the previous data analysis method is further improved by considering the signal amplitudes, detection efficiencies, and number of stored ions in the ring. A sensitive Z-dependent parameter is introduced in the data analysis, leading to a better resolution of ^34Ar^18+ and ^51Co^27+ with A/Z=17/9. The mean revolution times of ^34Ar^18+ and ^51Co^27+ are deduced, although their time difference is merely 1.8 ps. The uncorrected, overlapped peak of these ions has a full width at half maximum of 7.7 ps. The mass excess of ^51Co was determined to be -27332(41) keV, which is in agreement with the previous value of -27342(48) keV.

根据几种常用放射性核素的寿命计算方法,通过模拟数据研究了直接拟合法、对数时间法、极大似然法、观测时间受限时的极大似然法等四种寿命计算方法的适用范围。当观测时间不受限时,研究了在不同计数下寿命计算方法的适用范围。当观测时间受限时,研究了在不同观测时间窗口下寿命计算方法的适用范围。模拟中选用全剥离离子 94m Ru 44+ 作为目标核素,得到了不同计数及不同观测时间窗口下的寿命及其误差,并给出了四种方法的适用范围。 94m Ru 44+ 寿命的模拟结果与在兰州等时性质量谱仪上获得的实验结果在一倍标准偏差范围内一致,从而进一步验证了寿命计算方法的适用范围及模拟数据的可靠性。该模拟结果可为寿命测量实验设计提供理论依据和参考。

综述了兰州冷却储存环CSRe上转变能洛伦兹因子的测量与校正的最新进展,详细阐述了基于等时性质谱仪实验数据测量储存环的转变能洛伦兹因子的方法,以及利用CSRe二极、四极、六极磁铁校正转变能洛伦兹因子曲线的结果。实验结果表明,二极磁铁和四极磁铁可以平移转变能洛伦兹因子曲线,六极磁铁可以旋转转变能洛伦兹因子曲线。通过校正CSRe的转变能洛伦兹因子曲线,将CSRe对目标离子的质量分辨能力R=m/△m=3.15（9）×10~4（FWHM）(回旋周期相对误差σT/T=7.3（2）×10 -6 )提高到1.72（4）×10~5（FWHM）(σT/T=1.34（3）×10 -6 )。

The Isochronous Mass Spectrometry (IMS) is a powerful tool for mass measurements of exotic nuclei with half-lives as short as several tens of micro-seconds in storage rings. In order to improve the mass resolving power while preserving the acceptance of the storage ring, the IMS with two Time-Of-Flight (TOF) detectors has been implemented at the storage ring CSRe in Lanzhou, China. Additional velocity information beside the revolution time in the ring can be obtained for each of the stored ions by using the double TOF detector system. In this paper, we introduced a new method of using a 658 nm laser range finder and a short-pulsed ultra-violet laser to directly measure the distance and time delay difference between the two TOF detectors which were installed inside the 10−11 mbar vacuum chambers. The results showed that the distance between the two ultra-thin carbon foils of the two TOF detectors was ranging from 18032.5 mm to 18035.0 mm over a measurable area of 20×20 mm2. Given the measured distance, the time delay difference which comes with signal cable length difference between the two TOF detectors was measured to be Δtdelay1−2=99(26) ps. The new method has enabled us to use the speed of light in vacuum to calibrate the velocity of stored ions in the ring. The velocity resolution of the current double TOF detector system at CSRe was deduced to be σ(v)∕v=4.4×10−4 for laser light, mainly limited by the time resolution of the TOF detectors.

高精度环形谱仪SRing(Spectrometer Ring)是强流重离子加速器装置(HIAF)的重要组成部分,其等时性模式为远离β稳定线的短寿命原子核质量和寿命的精确测量提供国际领先的科研条件.为了扩大短寿命原子核质量测量精度和范围,SRing等时性模式设计了两种光学:γt=1.43和1.67.质量分辨是衡量等时性储存环的最重要参数.二极磁铁的高阶场以及磁铁的边缘场能强烈地引起束流光学高阶畸变,对质量分辨产生影响,因此需要高极磁铁对其进行校正.介绍了SRing等时性模式的线性计算,对非线性磁场的影响进行了详细研究.应用六极磁铁和八极磁铁对非线性场和发射度的影响进行了校正后,离子的循环时间标准偏差σ(T)/T达到3.5×10?7,质量分辨?m/m达到1×106.

Isochronous mass spectrometry has been applied to 112Sn projectile fragments at the HIRFL-CSR facility in Lanzhou. To produce short-lived nuclei of interest, we used projectile fragmentation of 112Sn35+ primary beams in a ～10 mm thick 9Be production target. The fragments were selected and analyzed by RIBLL2 and injected into the experimental storage ring(CSRe) every 25 s. To measure revolution times of stored ions,we used a Time-Of-Flight detector installed in CSRe. A new particle identification method was developed to distinguish ions on the measured revolution time spectrum for each injection. Based on this method, the shifts of the revolution time due to instable dipole magnet fields can be corrected and the ground and isomeric states of 101In have been well-resolved. The measured excitation energy is consistent with the theoretical value in the error range of 112 keV. The lifetime of the isomeric states of 101In is more than 200 μs.

The decay of the fully stripped ion 94mRu44+ in the order of one hundred microseconds has been studied for the first time by using the Isochronous Mass Spectrometry (IMS) at the HIRFL-CSR facility in Lanzhou.94mRu44+ waS produced via projectile fragmentation of a 112Sn primary beam bombarding on a 9Be production target.After the in-flight separation with RIBLL2,the ions were injected into the experimental ring (CSRe) and then stored there.The revolution times of the stored ions were measured by a Time-of-Flight (TOF) detector.Due to the mass change of a 94mRu44+ ion caused by its de-excitation to the ground state,hence the revolution time change,the decay process of 94mRu44+ could be directly observed in the CSRe.The sensitive window for detection of the decay events and the measurement precision of the decay time have been determined in this work.At the same time,we measured the mass of short-lived 94mRu44+ with the half-life about one hundred microseconds,which is the shortest among nuclides that have been studied by using storage-ring mass-spectrometry.

Interaction cross sections (sigma(I)) and reaction cross sections(sigma(R)) are physical quantities which are strongly related to the nuclear size. In our previous study of sigma(I) for Ne isotopes, the deformation features of neutron-rich Ne isotopes in the so-called "island of inversion" region have been successfully observed, and also the formation of the deformed halo structure in Ne-31 has been indicated. In this study, sigma(I) for F19-27 up to the vicinity of the island of inversion have been measured at around 240A MeV using BigRIPS at RIBF, RIKEN. Our preliminary results are slightly larger than A(1/3) systematics and some of the data could be explained by nuclear deformation.

Recent results and progress of mass measurements of neutron-rich nuclei utilizing Isochronous Mass Spectrometry (IMS) based on the HIRFL-CSR complex at Lanzhou are reported. The nuclei of interest were produced through projectile fragmentation of primary 86Kr ions at a realistic energy of 460.65 MeV/u. After in-flight separation by the fragment separator RIBLL2, the fragments were injected and stored in the experimental storage ring CSRe, and their masses were determined from measurements of their revolution times. The re-determined masses were compared and evaluated with other mass measurements, and the impact of these evaluated masses on the shell evolution study is discussed.

The isochronous Mass Spectrometry(IMS) is a powerful experimental instrument for measuring masses of short-lived nuclides. In the IMS, the nuclides of interest are produced via the projectile fragmentation reaction, then injected into the storage ring after the in-flight separation with beam line. The yields of the nuclides of interest are usually very small accompanying a huge amount of contaminant nuclides, aggravating the load of time-of-flight(TOF) detector. In the IMS nuclear mass measurement experiment conducted at the HIRFL-CSR, we developed a method of purifying the secondary beam fragments to ease the burden of the TOF detector, which is based on the differences of the ions′ velocities in the beam line and realized by adjusting the injection time of secondary fragments using the Kicker system of the HIRFL-CSR. We tested and verified the method in an online experiment, and its performance is discussed in this paper.