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 angular distributions for the elastic scattering and breakup reactions of the mirror nuclei 12B and 12N on a 208Pb target, at incident energies of 255 MeV and 343 MeV, respectively, were measured at HIRFL-RIBLL. The elastic scattering and breakup angular distributions of the halolike nucleus 12N (Sp=0.601 MeV) have been measured simultaneously. Elastic scattering cross sections were accurately reproduced by continuum discretized coupled channel calculations, which did not exhibit any significant Coulomb rainbow suppression. We have analyzed the energy and angular distributions of inclusive 11B and 11C fragments, produced by direct reaction processes, taking into account the contributions from both elastic breakup (EBU) and nonelastic breakup (NEB). Since the breakup data is inclusive with respect to the final state of the core nucleus, the contribution of each of these core states was calculated separately and then the corresponding cross sections added together using as weights the spectroscopic factors for each configuration computed with the ab initio no-core shell model. The results were found to be mostly consistent with the experimental data and, furthermore, demonstrate that EBU is highly dependent on the binding energy, while the results of NEB show no clear effect.Received 25 July 2023Accepted 11 January 2024DOI:https://doi.org/10.1103/PhysRevC.109.014624©2024 American Physical SocietyPhysics Subject Headings (PhySH)Ab initio calculationsTechniquesTheoretical TechniquesMathematical physics methodsAb initio calculationsTechniquesTheoretical TechniquesAb initio calculationsResearch AreasBreakup reactionsDirect reactionsElastic scattering reactionsHeavy-ion reaction mechanismsUnstable nuclei induced nuclear reactionsProperties6 ≤ A ≤ 19TechniquesAb initio calculationsOptical, coupled-channel & distorted wave modelsRadioactive beamsShell modelNuclear Physics

Multinucleon transfer (MNT) reactions have received increasing interest in the synthesis of neutron-rich nuclei due to the distinct limitations of other reactions, particularly in the N = 126 region, which represents the last waiting point of astrophysical nucleosynthesis. However, it is still a challenging endeavor to describe the MNT process between heavy nuclei. In this study, we develop a theoretical framework that couples the Langevin dynamics iteratively with the master equation, which is based on the HICOL model (CLIM-H). The random transfer process is achieved by solving the master equation using the Monte Carlo method, where the parametric transfer probability with a Q window is employed. The isotope distributions for 58,64Ni+208Pb, as well as the angular and isotope distributions of the recently measured 206Pb + 118Sn, could be generally reproduced based on this method. Contrary to previous theoretical predictions which show a high production cross section of N = 126 nuclei, current calculations do not reveal appreciable cross sections. The distinguishing characteristic of this approach is its ability to generate not only the mass distribution but also the charge distribution self-consistently, which could provide references for many other studies using the multidimensional Langevin equation considering only the mass asymmetry degree of freedom.

The isomeric structure and properties in proton -rich nuclides are crucial for determining the path of the rapid proton capture process ( rp -process). For example, bound nuclei inside the dripline can have unbound isomeric states and change the rp -process pathway. The configuration interaction shell model is used to investigate nuclei around the Z = N line at the southwest region of 100 Sn. The excitation mechanism of 1 / 2 - 1 isomers is identified as dominated by exciting one nucleon in the 1 p 1 / 2 orbit to the 0 g 9 / 2 orbit. The study explores the decay properties of both the ground and isomeric states. Remarkably, competitive beta + decay and proton emission are predicted in the unbound 1 / 2 - 1 isomer of 97 Sn, suggesting potential influences on the rp -process pathway.

beta-delayed gamma-neutron spectroscopy has been performed on the decay of A=84 to 87 gallium isotopes at the RI-beam Factory at the RIKEN Nishina Center using a high-efficiency array of 3He neutron counters (BRIKEN). beta-2n-gamma events were measured in the decays of all of the four isotopes for the first time, which is direct evidence for populating the excited states of two-neutron daughter nuclei. Detailed decay schemes with the gamma branching ratios were obtained for these isotopes, and the neutron emission probabilities (P-xn) were updated from the previous study. Hauser-Feshbach statistical model calculations were performed to understand the experimental branching ratios. We found that the P-1n and P-2n values are sensitive to the nuclear level densities of 1n daughter nuclei and showed that the statistical model reproduced the P-2n/P-1n ratio better when experimental levels plus shell-model level densities fit by the Gilbert-Cameron formula were used as the level-density input. We also showed the neutron and gamma branching ratios are sensitive to the ground-state spin of the parent nucleus. Our statistical model analysis suggested J <= 3 for the unknown ground-state spin of the odd-odd nucleus Ga-86, from the I gamma(4(+)-> 2(+))/I-gamma(2(+)-> 0(+)) ratio of Ga-84 and the P-2n/P-1n ratio. These results show the necessity of detailed understanding of the decay scheme, including data from neutron spectroscopy, in addition to gamma measurements of the multineutron emitters.

Two-proton ($2p$) radioactivity provides fundamental knowledge on the three-body decay mechanism and the residual nuclear interaction. In this work, we propose decay width formulae in the extended R-matrix framework for different decay mechanisms, including sequential $2p$ decay, diproton decay, tri-body decay, and sequential two-diproton decay. The diproton and tri-body formulae, combined with information on the two-nucleon transfer amplitude and Wigner single-particle reduced width, can reproduce well experimental $2p$ radioactivity half-lives. For the case of $^{67}$Kr, theoretical predictions for direct $2p$ decay give much larger half-lives than the recent measurement from RIKEN. A combination of direct and sequential $2p$ emission is analyzed by considering a small negative one-proton separation energy and a possible enhanced contribution from the $p$-wave component. The present method predicts that $^{71}$Sr and $^{74}$Zr may be the most promising candidates for future study on $2p$ radioactivity. Our model gives an upper limit of 55(4) keV for the decay width of $4p$ emission in recently found four-proton resonant nuclide, $^{18}$Mg, which agrees with the observed width of 115(100) keV.

The cluster structure of the neutron-rich isotope 10Be has been probed via the (p, p alpha) reaction at 150 MeV/nucleon in inverse kinematics and in quasifree conditions. The populated states of 6He residues were investigated through missing mass spectroscopy. The triple differential cross section for the ground state transition was extracted for quasifree angle pairs (theta p,theta alpha) and compared to distorted-wave impulse approximation reaction calculations performed in a microscopic framework using successively the Tohsaki-Horiuchi-Schuck-Ropke product wave function and the wave function deduced from antisymme-trized molecular dynamics calculations. The remarkable agreement between calculated and measured cross sections in both shape and magnitude validates the molecular structure description of the 10Be ground-state, configured as an alpha-alpha core with two valence neutrons occupying pi-type molecular orbitals.

Accurate nuclear reaction rates for ^26 P( p , γ ) ^27 S are pivotal for a comprehensive understanding of the rp -process nucleosynthesis path in the region of proton-rich sulfur and phosphorus isotopes. However, large uncertainties still exist in the current rate of ^26 P( p , γ ) ^27 S because of the lack of nuclear mass and energy level structure information for ^27 S. We reevaluate this reaction rate using the experimentally constrained ^27 S mass, together with the shell model predicted level structure. It is found that the ^26 P( p , γ ) ^27 S reaction rate is dominated by a direct capture reaction mechanism despite the presence of three resonances at E = 1.104, 1.597, and 1.777 MeV above the proton threshold in ^27 S. The new rate is overall smaller than the other previous rates from the Hauser–Feshbach statistical model by at least 1 order of magnitude in the temperature range of X-ray burst interest. In addition, we consistently update the photodisintegration rate using the new ^27 S mass. The influence of new rates of forward and reverse reaction in the abundances of isotopes produced in the rp -process is explored by postprocessing nucleosynthesis calculations. The final abundance ratio of ^27 S/ ^26 P obtained using the new rates is only 10% of that from the old rate. The abundance flow calculations show that the reaction path ^26 P( p , γ ) ^27 S( β ^+ , ν ) ^27 P is not as important as previously thought for producing ^27 P. The adoption of the new reaction rates for ^26 P( p , γ ) ^27 S only reduces the final production of aluminum by 7.1% and has no discernible impact on the yield of other elements.

Context.Accurate42Ti(p,γ)43V reaction rates are crucial for understanding the nucleosynthesis path of the rapid capture process (rpprocess) that occurs in X-ray bursts.Aims.We aim to improve the thermonuclear rates of42Ti(p,γ)43V based on more complete resonance information and a more accurate direct component, together with the recently released nuclear masses data. We also explore the impact of the newly obtained rates on therpprocess.Methods.We reevaluated the reaction rate of42Ti(p,γ)43V by the sum of the isolated resonance contribution instead of the Hauser-Feshbach statistical model. We used a Monte Carlo method to derive the associated uncertainties of new rates. The nucleosynthesis simulations were performed via the NuGrid post-processing code ppn.Results.The new rates differ from previous estimations due to the use of a series of updated resonance parameters and a direct S factor. Compared with the previous results from the Hauser-Feshbach statistical model, which assumes compound nucleus43V with a sufficiently high-level density in the energy region of astrophysical interest, large differences exist over the entire temperature region ofrp-process interest, up to two orders of magnitude. We consistently calculated the photodisintegration rate using our new nuclear masses via the detailed balance principle, and found the discrepancies among the different reverse rates are much larger than those for the forward rate, up to ten orders of magnitude at the temperature of 108K. Using a trajectory with a peak temperature of 1.95×109K, we performed therp-process nucleosynthesis simulations to investigate the impact of the new rates. Our calculations show that the adoption of the new forward and reverse rates result in abundance variations for Sc and Ca of 128% and 49%, respectively, compared to the variations for the statistical model rates. On the other hand, the overall abundance pattern is not significantly affected. The results of using new rates also confirm that therp-process path does not bypass the isotope43V.Conclusions.Our study found that the Hauser-Feshbach statistical model is inappropriate to the reaction rate evaluation for42Ti(p,γ)43V. The adoption of the new rates confirms that the reaction path of42Ti(p,γ)43V(p,γ)44Cr(β+)44V is a key branch of therpprocess in X-ray bursts.

Within the framework of the dinuclear system model, the reaction mechanisms for synthesizing target-like isotopes from Bk to compound nuclei Lv are thoroughly investigated in complete and incomplete fusion reactions of 48Ca +248Cm near Coulomb barrier energies. The production cross section of 292,293Lv as a function of excitation energy in fusion-evaporation reactions and target-like isotopic yields in multinucleon transfer reactions are evaluated, and a statistical approach is used to describe the decay process of excited nuclei. The available experimental data can be reproduced reasonably well with the model. The products of all possible formed isotopes in the dynamical preequilibrium process for collision partners at incident energy Elab = 5.5 MeV/nucleon are exported, systematically. It was found that the quasifission fragments are dominant in the yields. The optimal pathway from the target to compound nuclei shows up along the valley of potential surface energy. The effective impact parameter of two colliding partners leading to compound nuclei is selected from head-on collision to semicentral collision with L = 52 h over bar . The timescale boundary between complete fusion and multinucleon transfer reactions is about 5.7 x 10-21 s with effective impact parameters. The synthesis cross sections of unknown neutron-rich actinides from Bk to Rf have been predicted to be around several nanobarns.

β decay of proton-rich nuclei plays an important role in exploring isospin mixing. The β decay of ^{26}P at the proton drip line is studied using double-sided silicon strip detectors operating in conjunction with high-purity germanium detectors. The T=2 isobaric analog state (IAS) at 13 055 keV and two new high-lying states at 13 380 and 11 912 keV in ^{26}Si are unambiguously identified through β-delayed two-proton emission (β2p). Angular correlations of two protons emitted from ^{26}Si excited states populated by ^{26}P β decay are measured, which suggests that the two protons are emitted mainly sequentially. We report the first observation of a strongly isospin-mixed doublet that deexcites mainly via two-proton decay. The isospin mixing matrix element between the ^{26}Si IAS and the nearby 13 380-keV state is determined to be 130(21) keV, and this result represents the strongest mixing, highest excitation energy, and largest level spacing of a doublet ever observed in β-decay experiments.

The study of the origin of asymmetries in mirror β decay is extremely important to understand the fundamental nuclear force and the nuclear structure. The experiment was performed at the National Laboratory of Heavy Ion Research Facility in Lanzhou (HIRFL) to measure the β-delayed γ rays of 26P by silicon array and Clover-type high-purity Germanium (HPGe) detectors. Combining with results from the β decay of 26P and its mirror nucleus 26Na, the mirror asymmetry parameter δ ( ≡ft+/ft−− 1) was determined to be 46(13)% for the transition feeding the first excited state in the daughter nucleus. Our independent results support the conclusion that the large mirror asymmetry is close to the proton halo structure in 26P.

在兰州重离子研究装置上，依托兰州放射性束流线，产生、分离和鉴别了同位旋第三分量 \begin{document}$ T_{Z}=-2 $\end{document} 的近质子滴线核28S，并通过使用包括双面硅条探测器和高纯锗探测器在内的探测阵列，开展了28S的 \begin{document}$\beta$\end{document} 延迟 \begin{document}$\gamma$\end{document} 衰变测量。实验准确测量了28S衰变中的5条 \begin{document}$\beta$\end{document} 延迟 \begin{document}$\gamma$\end{document} 射线，得到了子核28P相应能级的能量。首次提取出了 \begin{document}$\beta$\end{document} 衰变布居到28P低激发态的衰变分支比，并构筑了28S的全新部分衰变纲图。本工作为将来进一步比较28S和28Mg间的镜像不对称性提供了精确的实验数据。

A detailed beta-decay spectroscopic study of Al-22 was performed at the Radioactive Ion Beam Line in Lanzhou. With the beta-gamma-particle coincidence measurement by a high-resolution DSSD particle detection array and a high efficiency gamma-ray detection array, total eight excited states in Mg-22 fed by Gamow-Teller transitions was newly identified. The one-proton, two-proton, and a decays of the IAS at 14046(5) keV in Mg-22, which were partly observed in different experiments before, were identified simultaneously in the present work, providing accurate spectroscopic information about its decay. A more complete beta-decay scheme of Al-22 was constructed and compared to the shell-model calculations with the USD-type Hamiltonians, USDC and USDB.

在兰州重离子研究装置上,依托兰州放射性束流线,产生、分离和鉴别了同位旋第三分量TZ=?2的近质子滴线核28 S,并通过使用包括双面硅条探测器和高纯锗探测器在内的探测阵列,开展了28 S的β延迟γ衰变测量.实验准确测量了28 S衰变中的5条β延迟γ射线,得到了子核28 P相应能级的能量.首次提取出了β衰变布居到28P低激发态的衰变分支比,并构筑了28S的全新部分衰变纲图.本工作为将来进一步比较28S和28Mg间的镜像不对称性提供了精确的实验数据.

库仑势垒在低能重离子核反应中扮演了重要的角色,但它不能被直接测量,需通过不同类型的重离子核反应间接提取.目前对库仑势垒的系统研究大都比较依赖于所采用的相互作用势模型和反应理论模型.本工作采用实验熔合截面与能量的乘积相对于能量的一阶微分作为穿透系数,并将穿透系数最大值一半的位置定义为熔合反应的经验势垒高度.该定义不依赖于理论模型,具有优秀的稳定性和可靠性.依据该定义,采用耦合道模型CCFULL及Wong公式拟合12组具有代表性的实验熔合激发函数,进而提取库仑势垒高度.通过比较本工作中从实验值抽取的势垒高度和不同理论势模型预测的势垒高度,以及其随同位旋不对称度的变化,发现Bass80和WKJ公式与本工作的结果最吻合.

The mechanism of reactions with weakly-bound proton-rich nuclei at energies near the Coulomb barrier is a long-standing open question owing to the paucity of experimental data. In this study, a complete kinematics measurement was performed for the proton drip-line nucleus 17F interacting with 58Ni at four energies near the Coulomb barrier. Thanks to the powerful performance of the detector array, exhaustive information on the reaction channels, such as the differential cross sections for quasielastic scattering, exclusive and inclusive breakup, as well as for fusion-evaporation protons and alphas, was derived for the first time. The angular distributions of quasielastic scattering and exclusive breakup can be described reasonably well by the continuum-discretized coupled-channels calculations. The inclusive breakup was investigated using the three-body model proposed by Ichimura, Austern, and Vincent, and results indicate the non-elastic breakup is the dominant component. The total fusion cross sections were determined by the fusion-evaporation protons and alphas. Based on the measured exclusive breakup data, the analysis of the classical dynamical simulation code PLATYPUS demonstrates that the incomplete fusion plays a minor role. Moreover, compared with 16O+58Ni, both the reaction and total fusion cross sections of 17F+58Ni exhibit an enhancement in the sub-barrier energy region, which mainly arises from couplings to the continuum states. This work indicates that the information of full reaction channels is crucially important to comprehensively understand the reaction mechanisms of weakly bound nuclear systems.

The decay of 218Pa was investigated by means of α and γ spectroscopy. The nucleus was produced in the fusion reaction 40Ar+182W and separated in flight by the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). The known α decays of 218Pa were measured with improved precision and newly assigned to be originating from the ground state, which clarified the ambiguities in their previous assignments. In addition, a new isomeric state in 218Pa decaying with α-particle energies of 9691(15) keV, 9595(21) keV and a half-life of 135−32+62 μs was identified. The spins and parities of the involved states were tentatively assigned on the basis of the systematic α-decay properties of the odd-proton N=127 isotones and shell model calculations.