Proton-rich Region Research Articles

A technique for studying (n,p) reactions of astrophysical interest using radioactive beams with SECAR

The formation of nuclei in slightly proton-rich regions of the neutrino-driven wind of core-collapse supernovae could be attributed to the neutrino-p process (νp-process). As it proceeds via a sequence of (p,γ) and (n,p) reactions, it may produce elements in the range of Ni and Sn, considering adequate conditions. Recent studies identify a number of decisive (n,p) reactions that control the efficiency of the νp-process. The study of one such (n,p) reaction via the measurement of the reverse (p,n) in inverse kinematics was performed with SECAR at NSCL/FRIB. Proton-induced reaction measurements, especially at the mass region of interest, are notably difficult since the recoils have nearly identical masses as the unreacted projectiles. Such measurements are feasible with the adequate separation level achieved with SECAR, and the in-coincidence neutron detection. Adjustments of the SECAR system for the first (p,n) reaction measurement included the development of new ion beam optics, and the installation of the neutron detection system. The aforementioned developments along with a discussion on the preliminary results of the p(58Fe,n)58Co reaction measurement are presented.

Possibilities of synthesizing new proton-rich nuclei with 40 ≤ Z ≤ 60 using multinucleon transfer reactions * *Supported by the ational Natural Science Foundation of China (12175064, U2167203). Hunan Provincial Education Department (Key project 20A290)

Multinucleon transfer reactions near the Coulomb barrier are investigated based on the improved dinuclear system (DNS) model, and the deexcitation process of primary fragments are described using the statistical model GEMINI++. The production cross sections of Ca+ Sn and Ni+ Te based on the DNS model+GEMINI++ are calculated and compared with experimental data. The calculated results reproduce experimental data. The cross sections of fusion-evaporation, fragmentation, and multinucleon transfer reactions in the region are also provided in this paper. The results show that in the region, fusion-evaporation and fragmentation reactions have good results in the relatively proton-rich region, but in the extreme proton-deficient region, the MNT reaction is still promising for synthesizing proton-rich nuclei.

Beyond the proton drip line: Bayesian analysis of proton-emitting nuclei

The limits of the nuclear landscape are determined by nuclear binding energies. Beyond the proton drip lines, where the separation energy becomes negative, there is not enough binding energy to prevent protons from escaping the nucleus. Predicting properties of unstable nuclear states in the vast territory of proton emitters poses an appreciable challenge for nuclear theory as it often involves far extrapolations. In addition, significant discrepancies between nuclear models in the proton-rich territory call for quantified predictions. With the help of Bayesian methodology, we mix a family of nuclear mass models corrected with statistical emulators trained on the experimental mass measurements, in the proton-rich region of the nuclear chart. Separation energies were computed within nuclear density functional theory using several Skyrme and Gogny energy density functionals. We also considered mass predictions based on two models used in astrophysical studies. Quantified predictions were obtained for each model using Bayesian Gaussian processes trained on separation-energy residuals and combined via Bayesian model averaging. We obtained a good agreement between averaged predictions of statistically corrected models and experiment. In particular, we quantified model results for one- and two-proton separation energies and derived probabilities of proton emission. This information enabled us to produce a quantified landscape of proton-rich nuclei. The most promising candidates for two-proton decay studies have been identified. The methodology used in this work has broad applications to model-based extrapolations of various nuclear observables. It also provides a reliable uncertainty quantification of theoretical predictions.

High spin states of Zr isotopes around A = 80 mass region — A study on cold and hot rotating nuclei

High spin structure of Zr isotopes, in particular, around [Formula: see text] has been studied in yrast and nonyrast regions. Spin dependence of shapes for the yrast levels are investigated by employing Cranked Hartree–Fock–Bogoliubov (CHFB) theory using a [Formula: see text] model interaction and the calculations are in good accord with the experimental data. The nonyrast states are treated by incorporating temperature degree of freedom using the statistical theory (ST). Highly deformed prolate shapes dominate the nonrotating proton rich region at low temperatures (T) with coexisting oblate and prolate shapes in [Formula: see text]Zr. Hot rotating nuclei show highest deformation around [Formula: see text] among all the other Zr isotopes even at high temperatures. [Formula: see text]Zr exhibits interesting structural transitions, hence studied in detail in yrast and non yrast regions. Triaxiality predominates in both yrast and nearly yrast (low temperature) regions at low spins with transition to elongated shapes at mid spin values 30–38[Formula: see text] to highly deformed oblate shapes at higher spins. CHFB predicts a strong backbending effect at 32[Formula: see text] and 40[Formula: see text]. A shape coexistence between the rare shape phase of noncollective prolate and oblate is reported in [Formula: see text]Zr at low temperature and [Formula: see text]. Prolate shape phase disappears with increasing temperature and spin but the nucleus remains highly deformed (with [Formula: see text] at spin [Formula: see text]40[Formula: see text]) even at high temperatures of the order of 3–3.5[Formula: see text]MeV, hence a very promising candidate for GDR probes of nuclear shapes.

Identification of highly deformed even–even nuclei in the neutron- and proton-rich regions of the nuclear chart from the B(E2)↑ and E2 predictions in the generalized differential equation model

We identify here the possible occurrence of large deformations in the neutron- and proton-rich ([Formula: see text]-rich and [Formula: see text]-rich) regions of the nuclear chart from extensive predictions of the values of the reduced quadrupole transition probability [Formula: see text] for the transition from the ground state to the first [Formula: see text] state and the corresponding excitation energy [Formula: see text] of even–even nuclei in the recently developed generalized differential equation (GDE) model exclusively meant for these physical quantities. This is made possible from our analysis of the predicted values of these two physical quantities and the corresponding deformation parameters derived from them such as the quadrupole deformation [Formula: see text], the ratio of [Formula: see text] to the Weisskopf single-particle [Formula: see text] and the intrinsic electric quadrupole moment [Formula: see text], calculated for a large number of both known as well as hitherto unknown even–even isotopes of oxygen to fermium (0 to FM; [Formula: see text]–100). Our critical analysis of the resulting data convincingly support possible existence of large collectivity for the nuclides [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], whose values of [Formula: see text] are found to exceed 0.3 and even 0.4 in some cases. Our findings of large deformations in the exotic [Formula: see text]-rich regions support the existence of another “island of inversion” in the heavy-mass region possibly caused by breaking of the [Formula: see text] subshell closure.

The evaporation residue in the fission state of barium nuclei within relativistic mean-field theory

The evaporation residue of barium isotopes is investigated in a microscopic study using relativistic mean field theory. The investigation includes the isotopes of barium from the valley of stability to the exotic proton-rich region. The ground as well as neck configurations for these nuclei are generated from their total nucleonic density distributions of the corresponding state. We have estimated the constituents (number of nucleons) in the elongated neck region of the fission state. We found the α-particle as the constituent of the neck of Ba-isotopes, referred to as the evaporated residue in heavy-ion reaction studies. A strong correlation between the neutron and proton is observed throughout the isotopic chain.

Nonlocality in deuteron stripping reactions.

We propose a new method for the analysis of deuteron stripping reactions, A(d,p)B, in which the nonlocality of nucleon-nucleus interactions and three-body degrees of freedom are accounted for in a consistent way. The model deals with equivalent local nucleon potentials taken at an energy shifted by ∼40 MeV from the "E(d)/2" value frequently used in the analysis of experimental data, where E(d) is the incident deuteron energy. The "E(d)/2" rule lies at the heart of all three-body analyses of (d, p) reactions performed so far with the aim of obtaining nuclear structure properties such as spectroscopic factors and asymptotic normalization coefficients that are crucial for our understanding of nuclear shell evolution in neutron- and proton-rich regions of the nuclear periodic table and for predicting the cross sections of stellar reactions. The large predicted shift arises from the large relative kinetic energy of the neutron and proton in the incident deuteron in those components of the n+p+A wave function that dominate the (d, p) reaction amplitude. The large shift reduces the effective d-A potentials and leads to a change in predicted (d, p) cross sections, thus affecting the interpretation of these reactions in terms of nuclear structure.

Nuclear masses near the proton drip-line and their impact on nucleosynthesis in explosive stars

The interplay of the fundamental forces (here mainly the strong force and electromagnetic force) holds nucleons together to form atomic nuclei. However, in nature only less than ten percent of the total number of nuclei is stable. The majority of nuclei are unstable; that is, after having lived for a certain time, they change into the daughter nuclei by radioactive decay. The familiar decay types that can be found in most parts of the chart of nuclide are α-decay and β-decay. There are other important processes in which unstable nuclei can change into other ones. These occur, for example, in very neutronrich or proton-rich regions of the chart of nuclide. There are boundaries called drip-lines, which are the lines on the Z (proton)-N (neutron) plane where the nucleon separation energy is zero. The nuclear binding becomes weaker and weaker when moving from the stable region towards the drip-lines, and eventually no nucleus can exist beyond the drip-lines. Taking the proton-rich region as an example, near the proton drip-line, protons are only weakly bound and a proton radioactivity can occur. Also because of the small binding, nuclei near the proton drip-line may capture additional protons and become new, heavier nuclides if the capture conditions are present. Detailed knowledge on the nucleon-capture processes lies at the heart of the understanding of nucleosynthesis in the Universe——a very fundamental but unanswered question about how the heavy elements (i.e. those heavier than iron) are created. In order for nuclei to capture protons, a high temperature environment (usually above 1×10 9 K) is needed so that they can overcome the large coulomb barrier for charged particle reactions. A hydrogen rich

A systematic study on nuclear pairing energy under the relativistic mean-field model

Nuclear pairing energy of dozens of atomic nuclei in nuclear period chart are calculated along the stable line by extracting the swatch at a proton or neutron number interval of 4. Especially, we have studied the rule of pairing energy of the even-even nuclei of O isotopes changing with nucleon number under the relativistic mean-field model, and found, when energy gap Δ is fixed, the magnitude of nuclear pairing energy is related to nuclear shell structure. Thereof we propose a simple method to test closed shell, and further, we conclude that the neutron number N=6 is a new magic number not only in neutron-rich region, but also in proton-rich region of light nuclei.

Data needs for the astrophysical p-process

A status report is given on the experimental aspects of the astrophysical p-process that is responsible for the production of the heavy proton rich nuclei known as p-nuclei. The numerical modelling of the p-process scenario involves the knowledge of photodisintegration cross sections, mostly calculated through the Hauser-Feshbach statistical model approach. Recent experiments test the reliability of the model calculations in the proton rich region as well as providing indirect experimental information on the cross sections relevant to the p-process.

Systematic study of charge form factors of elastic electron-nucleus scattering with the relativistic eikonal approximation

We systematically investigate the elastic electron scattering on both stable and unstable nuclei with the relativistic eikonal approximation, where the charge density distributions of nuclei are from the self-consistent relativistic mean field model. Calculations show that the relativistic eikonal approximation can reproduce the experimental data of electron scattering on nuclei ranging from the light region, such as $^{12}\mathrm{C}$, to the heavy region, such as $^{208}\mathrm{Pb}$. This is the systematic test of the relativistic eikonal approximation for elastic electron scattering for both light and heavy nuclei. With this method, further studies are made of the variation of charge form factors along isotopic chains and the sensitivity of charge form factors to the changes of charge distribution. For isotopic chains with Z = 20 and 28, we find that the charge form factors vary significantly with neutron number. The charge form factors shift outward and downward when the target nucleus moves from the neutron-rich region to the proton-rich region along the isotopic chain. The significant shift shows that the charge form factor is very sensitive to a change of neutron number. If the isotopic shifts of the charge form factor are measured on the next-generation electron-nucleus collider (at RIKEN and GSI), the charge size and charge distribution can be determined for unstable nuclei. The calculations will provide a reference for future experiments.

Nuclear physics aspects of the astrophysical p-process

An overview is given on the experimental nuclear physics aspects of the astrophysical p-process that is responsible for the production of the heavy proton-rich nuclei known as p-nuclei. The nuclear physics input of the p-process scenario involves the knowledge of radiative capture cross sections, mostly calculated by the Hauser-Feshbach statistical model. Our experiments test the reliability of the model calculations in the proton-rich region as well as provide experimental information on the cross sections relevant to the p-process.