Short-range correlation (SRC) in nuclei refers to nucleons forming temporally correlated pairs in close proximity, giving rise to the high momentum of the nucleons beyond the Fermi surface. It has been reported that bremsstrahlung gamma production from the neutron-proton process in heavy-ion reactions provides a potential probe to the SRC abundance in nuclei. In this paper, we present in detail the precision measurement of bremsstrahlung gamma rays in 124Sn + 124Sn reactions at 25 MeV/nucleon using the Compact Spectrometer for Heavy IoN Experiment (CSHINE). A comprehensive experimental and analysis framework is established to ensure the reliability and robustness of the extracted results. Background contributions are evaluated and subtracted using independent methods, and the consistency of the analysis is systematically validated. By comparing the experimental gamma spectrum with isospin-dependent Boltzmann-Uehling-Uhlenbeck simulations, the high momentum tail (HMT) fraction of RHMT = (20 +/- 3)% is derived in 124Sn nuclei. This work provides a detailed and validated experimental framework for extracting SRC information from bremsstrahlung gamma-ray emission and demonstrates the feasibility of studying nucleon SRCs with high precision in low-energy heavy-ion collisions.

In this study, a compact 16-channel integrated charge- and current-sensitive preamplifier, called CCPA, was developed for a large-scale detector array used in nuclear physics experiments. The CCPA was designed to achieve pulse-shape discrimination for silicon detectors. CCPA has a fast response of typically less than 6 ns for the pulse rise time and a low equivalent noise of 1.5 keV at zero input capacitance. The energy dynamic range and pulse decay time can be easily adjusted for different applications by changing feedback capacitance C_f and resistance R_f . A good energy resolution of 26.87 keV was achieved for 5.486 MeV α particles from ^241Am . The pulse-shape discrimination method was applied for the first time in an experiment carried out on the Radioactive Ion Beam Line in Lanzhou (RIBLL1), and CCPA demonstrated high resolution and stability in beam experiments. The experiment identified low-energy α particles as low as 5 MeV by the pulse-shape discrimination method, as well as hundreds of MeV charged particles. This provides a new routine for the high-precision measurement of low-energy charged particles emitted by light nuclear reactions.

A liquid-nitrogen-cooled cryogenic gas target system has been developed and installed for radioactive ion beam (RIB) production at the Radioactive Ion Beam Line in Lanzhou (RIBLL). Light-element gases (H_2, D_2, and ^4He) filled in the target cell were cooled to cryogenic temperatures, with the gas-cell outlet temperature typically monitored at 82–86 K during beam irradiation and operating pressures up to 1000 mbar. The system was used to produce ^7Be, ^16N, and ^15O RIBs via the ^1H(^7Li, ^7Be)n, ^2H(^15N, ^16N)p, and ^1H(^15N, ^15O)n inverse kinematics reactions, yielding purities of 85%, 99%, and 95%, with intensities of 1.02×10^6, 2.7×10^5, and 1.0×10^5 pps, respectively. A ^93mMo isomer beam was also produced via the ^4He(^94Zr, 5n)^93mMo reaction, achieving an intensity of 5.38×10^3 pps and a purity of 20% (which can be further improved to ∼50% with offline time-of-flight gating). By delivering a broader range of high-intensity secondary RIBs, this setup establishes a robust platform at RIBLL for low- and medium-energy nuclear astrophysics and reaction studies.

Experimental and theoretical investigation of the fragmentation reaction in the Fermi-energy domain is currently of particular importance for not only nuclear physics but also some interdisciplinary fields.In the present study,neutron-rich 14C and 16C ion beams at 27.5 MeV/nucleon were used to bombard carbon and polyethylene(CD2)n targets.Energy and angular distributions of the produced fragments were measured.Background events ori-ginating from the carbon content in(CD2)n target were efficiently excluded using an extended E-P plot method.Ex-perimental results are systematically analyzed using the HIPSE-SIMON dynamic model.The comparison reveals that,for the carbon target,the HIPSE-SIMON calculation overestimates the yields of the beam-velocity component for fragments near the projectile and also the energy phase space for fragments far away from the projectile,suggest-ing that fine tuning of the overall interaction profile adopted in the model is required.In contrast,for reactions with the deuteron target,the model calculation can reasonably reproduce the experimental data.The implication of the fragmentation mechanism on the validity of the invariant mass method,as frequently used to reconstruct the cluster-ing resonant structures in light nuclei,is also discussed.

The neutron-neutron (nn) correlation function has been measured in 25  MeV/u ^{124}Sn+^{124}Sn reactions. Using the Lednický-Lyuboshitz approach, the nn scattering length and effective range (f_{0}^{nn}, d_{0}^{nn}), as well as the reduced space-time size R^{(0)} of the neutron emission source are simultaneously extracted as (18.9_{-1.2}^{+1.3}  fm, 1.9_{-1.0}^{+1.3}  fm) and 4.12±0.12  fm, respectively. The measured nn scattering length is consistent with the results obtained in the low-energy scattering ^{2}H(π^{-},γ)2n, indicating heavy-ion collisions can serve as an effective approach for measuring nn interactions and further investigating the charge symmetry breaking of nuclear force. The space-time size extracted from momentum-gated correlation functions exhibits clear dependence on the pair momentum, with R^{(0)}=2.8±0.1  fm and 4.9±0.2  fm being determined for the high and low momentum neutrons, respectively.

LACPU, a Large Acceptance Charged particle detector array has been developed at Peking University. This system is capable of simultaneously detecting several direct reaction channels in inverse kinematics, including (d, p), (d, t), (d, 3He), (d, 4He), (d, d), (d, d '), and (d, 6Li), among others, in a single experiment. This paper reports on the solid angles, energy resolution, and particle identification capabilities of LACPU during its commissioning experiment with radioactive ion beams. Additionally, the optical potential parameters of 15C + p and 15C + d, which are essential for analyzing more complex reaction channels, have been extracted from the angular distributions of elastic scattering measured in the first experiment of LACPU.

A state-of-the-art detector array with a digital data acquisition system has been developed for charged-particle decay studies, including β -delayed protons, α decay, and direct proton emissions from exotic proton-rich nuclei. The digital data acquisition system enables precise synchronization and processing of complex signals from various detectors, such as plastic scintillators, silicon detectors, and germanium γ detectors. The system’s performance was evaluated using the β decay of ^32 Ar and its neighboring nuclei, produced via projectile fragmentation at the first Radioactive Ion Beam Line in Lanzhou (RIBLL1). Key measurements, including the half-life, charged-particle spectrum, and γ -ray spectrum, were obtained and compared with previous results for validation. Using the implantation–decay method, the isotopes of interest were implanted into two double-sided silicon strip detectors, where their subsequent decays were measured and correlated with preceding implantations using both position and time information. This detection system has potential for further applications, including the study of β -delayed charged-particle decay and direct proton emissions from even more exotic proton-rich nuclei.

The emission of neutrons from heavy ion reactions is an important observable for studying the asymmetric nuclear equation of state and the reaction dynamics. A 20-unit neutron array has been developed and mounted on the compact spectrometer for heavy ion experiments (CSHINE) to measure the neutron spectra, neutron- neutron and neutron-proton correlation functions. Each unit consists of a 15 x 15 x 15 cm3 plastic scintillator coupled to a cent = 52 mm photomultiplier. The Geant4 simulation with optical process is performed to investigate the time resolution and the neutron detection efficiency. The inherent time resolution of 212 ps is obtained by cosmic ray coincidence test. The n-y discrimination and time-of-flight performance are given by 252 Cf radioactive source test and beam test. The neutron energy spectra have been obtained in the angular range 30 degrees <= B lab <= 51 degrees in the beam experiment of 124 Sn + 124 Sn at 25 MeV/u with CSHINE.

Invariant-mass spectroscopy has been performed to search for possible resonance states in the loosely bound neutron-rich 15 C nucleus.By detecting alpha and 11 Be in coincidence,we reconstruct the excitation energy spectrum for 15 C.To estimate the physical background from non-resonant prompt alpha particles,we employ a recently proposed weighted event-mixing method with phenomenological reduced weighting at around the alpha-decay threshold to account for the depletion in the prompt alpha's contribution owing likely to the Coulomb final-state interactions.A new weighted mixed-event method that focuses on a robust treatment of the Coulomb effect is also proposed.Through fitting the spectrum using the background estimated with these two methods,up to two resonance state candidates are proposed.Further experiments with improved statistics and theoretical calculations are called for to confirm the se resonance states.

The neutron richness of the light charged particles emitted out of the fission plane in heavy ion reactions has been experimentally investigated via the production of A=3 mirror nuclei in ^86 Kr + ^nat Pb reactions at 25 MeV/u. The energy spectra and angular distributions of triton (t) and ^3 He in coincidence with two fission fragments are measured with the Compact Spectrometer for Heavy IoN Experiment (CSHINE). The energy spectrum of ^3 He is observed harder than that of triton in the fission events, in accordance with the phenomena reported as “ ^3 He-puzzle” in inclusive measurements. With a data-driven energy spectrum peak cut scenario, it is observed that the yield ratio R(t/^3He) increases with the angle to the fission plane, showing an enhancement of neutron-rich particle emission from out-of-fission-plane. A qualitative comparison with the transport model calculations suggests that this observation may serve as a new probe for the nuclear symmetry energy.

Atomic nuclei and dense nucleonic matter in neutron stars exhibit short-range correlations (SRCs), where nucleons form temporally correlated pairs in close proximity beyond mean-field approximation. It is essential to make precision measurement of the fraction of SRC since it carries the signature of underlying quark dynamics in nuclear medium. In this article, we present the first high-precision measurement of neutron-proton bremsstrahlung γ -ray emission from the symmetric Sn 124 + Sn 124 reactions at 25 MeV/u. From the observed spectral hardening, the precise SRC fraction in the Sn 124 nucleus is extracted to be ( 20 ± 3 ) % . This result provides a statistically unambiguous evidence of SRCs and demonstrates that low-energy heavy-ion collisions offer an approach to studying nuclear structure in connection with quark-level dynamics.

22Na(p,γ)23Mg and 19Ne(α,p)22Na are two crucial reactions in the so-called NeNa-MgAl cycle and the rapid-pro-ton process,their astrophysical reaction rates are indispensable inputs in understanding the outburst mechanism and element synthesis of novae.Since many proton resonance levels in odd-A compound nucleus 23Mg may be involved at nova temperat-ure,existing measurements can only provide partial effective information on the 22Na(p,γ)23Mg reaction,large discrepancies still exist in the astrophysical reaction rates of the two reactions.In the present work,22Na+p resonance scattering via thick target inverse kinematics was studied at RIBLL1 radioactive beam line in the HIRFL national laboratory at Lanzhou.Excita-tion functions of 22Na(p,p)are obtained in the energy range of Ec.m.=1.5 to 4 MeV.Obvious resonance structure is observed in the 23Mg compound nucleus,resonance parameters are deduced for 22 proton resonance states in 23Mg via R-matrix analys-is,which will be used for the evaluation of the astrophysical reaction rates of 22Na(p,γ)23Mg and 19Ne(α,p)22Na.

The 10 B( p , alpha ) 7 Be is an important destructive reaction for the 10B abundance in different astrophysical scenarios. Meanwhile, it may have a unignorable impact on models of new reactors for clean energy generation, and could provide an independent test for temperature analysis in the new generation of laser-driven facilities. S factors were determined for the 10 B( p , alpha ) 7 Be reaction at Ep = 120-274 keV through an activation method. The 478 keV gamma rays arising from the decay of 7 Be were detected by a low-background gamma-ray spectrometer. The present data show a significant inconsistency with respect to previous results using the activation technique, but agree well with the data of direct alpha detection. A global R-matrix analysis has been implemented based on the present and previous data. Further, a revised reaction rate was extracted relying on the fitting parameters.

The elastic scattering angular distributions of C-13 at 340 MeV and C-14 at 294 MeV and 342 MeV on a Pb-208 target, which correspond to approximately five times the Coulomb barriers, were measured at the Radioactive Ion Beam Line in Lanzhou. The data were analyzed within the optical model and continuum-discretized coupled-channels (CDCC) framework, and the results of both calculations could effectively account for the experimental data. The differential cross sections of elastic scattering revealed no particular suppression at the Coulomb nuclear interference peak angles, suggesting that the breakup coupling effects on the elastic scattering angular distributions were negligibly small in this incident energy region. The contributions from the couplings with inelastic states to the elastic cross sections were of minor importance within the angular range covered by these experiments.

The high momentum tail (HMT) of nucleons, as a signature of the short-range correlations in nuclei, has been investigated by the high-energy bremsstrahlung γ rays produced in 86Kr+124Sn at 25 MeV/nucleon. The energetic photons are measured by a CsI(Tl) hodoscope mounted on the spectrometer CSHINE. The energy spectrum ≥35 MeV can be reproduced by the Isospin- and Momentum-Dependent Boltzmann-Uehling-Uhlenbeck model calculations incorporating the photon production channel from np process in which the HMTs of nucleons is considered. A non-zero HMT ratio of about 15% is favored by the data. The effect of the capture channel np→dγ is demonstrated.

A charged particle array named MATE-PA,which serves as an auxiliary detector system for a Multi-purpose Active-target Time projection chamber used in nuclear astrophysical and exotic beam Experiments(MATE),was constructed.The array comprised of 20 single-sided strip-silicon detectors covering approximately 10％of the solid angle.The detectors facilitated the detection of reaction-induced charged particles that penetrate the active volume of the MATE.The performance of MATE-PA has been experimentally studied using an alpha source and a 36-MeV 14N beam injected into the MATE chamber on the radioactive ion beam line in Lanzhou(RIBLL).The chamber was filled with a gas mixture of 95％4He and 5％CO2 at a pressure of 500 mbar.The results indicated good separation of light-charged particles using the forward double-layer silicon detectors of MATE-PA.The energy resolution of the Si detectors was deduced to be approximately 1％(σ)for an energy loss of approximately 10 MeV caused by the α particles.The inclusion of MATE-PA improves particle identification and increases the dynamic range of the kinetic energy of charged particles,particularly that of the α particles,up to approximately 15 MeV.

The reaction kinetics of weakly bound nuclei in the nearbarrier energy region is currently one of the hotspots in nuclear physics research.The quasielastic scattering of the 7Be+120Sn system at 48.05 MeV was measured using a large solid angle covered silicon detector array,and its differential cross section was obtained in combination with Monte Carlo simula-tions.Based on the optical model,the angular distributions were fitted by the frequentist method and the Bayesian method,re-spectively.At the forward angles,the two methods give consistent results;at the backward angles,the results of the frequent-ist method show an obvious oscillatory structure,while the results of the Bayesian method are smooth,with an oscillatory up-ward trend near 180°.

In this study, we constructed two annular detector arrays comprising 24 wedge-shaped CsI(Tl) crystals, and tested them using an α source and radioactive beams of ^14-16 C on a CD _2 target. We compared the properties of a CsI(Tl) crystal encapsulated with various reflectors, revealing that using the 80- m-thick ESR film to pack the CsI(Tl) crystal yielded the largest light output with the smallest non-uniformity in light output ( Δ LO). For the 24 CsI(Tl) detectors with the 80- m-thick ESR films, the average energy resolution improved as the average light output increased; however, it deteriorated as the Δ LO value increased. To form two annular Si-CsI(Tl) telescopes for identifying the light-charged particles, the Δ LO value and energy resolution of each CsI(Tl) detector were maintained under 20 ^14-16 C + d. The results demonstrated that the Z = 1 and Z = 2 charged particles were adequately discriminated by the telescopes using the standard Δ E -E method.

Astrophysical reactions involving radioactive isotopes (RI) often play an important role in high-temperature stellar environments. The experimental studies on the reaction rates for those are still limited mainly due to the technical difficulties in producing high-quality RI beams. A direct measurement of those reactions would be still challenging in many cases, however, we can make a reliable evaluation of the reaction rates by an indirect method or by studying the resonance prorerties. Here we ntroduce recent examples of experimental studies on such RI-involving astrophysical reactions, performed at Center for Nuclear Study, the University of Tokyo, using the low-energy RI beam separator CRIB. One is for the neutron-induced destruction reactions of 7Be in the Big-Bang nucleosynthesis, and the other is the study on the 22Mg(α, p) reaction relevant in X-ray bursts, which was performed with the resonant scattering method from the inverse reaction channel.

The shape and internal structure of an atomic nucleus can change significantly with increasing excitation energy, angular momentum, or isospin asymmetry. As an example of this structural evolution, linear-chain configurations in carbon or heavier isotopes have been predicted for decades. Recent studies have found non-stability of this structure in 12 C while evidenced its appearance in 16 C. It is then necessary to investigate the linear-chain molecular structures in 14 C to clarify the exact location on the nuclear chart where this structure begins to emerge, and thus to benchmark theoretical models. Here we show a cluster-decay experiment for 14 C with all final particles coincidentally detected, allowing a high Q -value resolution, and thus a clear decay-path selection. Unambiguous spin-parity analyses are conducted, strongly evidencing the emergence of the π -bond linear-chain molecular rotational band in 14 C. The present results encourage further studies on even longer chain configurations in heavier neutron-rich nuclei.