Two proton transfer reactions between pairing rotational states with 104 MeV16O on142Nd,144Sm,148Sm and152Sm

(¹⁶O,¹⁴C) reactions on target nuclei with open proton shells, which are members of protonpairing rotational bands have been studied. For all target nuclei strong transitions to the ground states are observed. The reduced groundstate transition strength's (after removal ofQ-value dependence) are almost equal for all four target nuclei. Additional data on (¹⁶O,¹⁵N), (¹⁶O,¹³C) and (¹⁶O,¹²C) reactions are used to discuss the enhancement in the two proton transfer.     

Unexpected interference patterns observed in the 12C(14N, 13N)13C reaction at energies close to the Coulomb barrier

The reaction ¹²C(¹⁴N, ¹³N)¹³C has been measured at 28, 32, 34 and 36 MeV beam energies. The energy dependence of the measured interference pattern cannot be reproduced by DWBA calculations which take account of the interference between proton and neutron transfer. A rather strong asymmetry of the angular distributions about θ_c.m. = 90° has been observed.     

Elastische Elektronenstreuung an14N,15N,16O und18O bei kleiner Impulsübertragung

Elastic electron scattering cross sections of¹⁴N and¹⁶O have been measured relative to the proton and of¹⁵N and¹⁸O relative to the lighter isotope (¹⁴N,¹⁶O resp.) using gas targets. The momentum transfer ranged from 0.22 to 0.48 fm^?1. The data were analyzed by phase shift calculations assuming harmonic oscillator shell model charge distributions. The following rms charge radii have been deduced: R_m(¹⁴N)=2.540±0.020 fm R_m(¹⁵N)=2.580±0.026 fm R_m(¹⁶O)=2.718±0.021 fm R_m(¹⁸O)=2.789±0.027 fm. The errors include statistical and systematic uncertainties and an estimate of effects due to the choice of the model. The radius differences of the isotopes are smaller than the values predicted by anA ^1/3 relation     

Two proton transfer reactions between pairing rotational states with 104 MeV16O on142Nd,144Sm,148Sm and152Sm

(¹⁶O,¹⁴C) reactions on target nuclei with open proton shells, which are members of protonpairing rotational bands have been studied. For all target nuclei strong transitions to the ground states are observed. The reduced groundstate transition strength's (after removal ofQ-value dependence) are almost equal for all four target nuclei. Additional data on (¹⁶O,¹⁵N), (¹⁶O,¹³C) and (¹⁶O,¹²C) reactions are used to discuss the enhancement in the two proton transfer.     

Interfering transfer processes in heavy-ion reactions

Heavy-ion reactions in which two different transfer processes may interfere are analyzed. Angular distributions of the reactions ¹⁴C(¹⁶O, ¹⁷O)¹³C and ¹⁴C(¹⁶O, ¹⁸O)¹²C were measured at incident energies of 20, 25 and 30 MeV. The strong oscillations observed at the Coulomb barrier together with a backward rise at higher energies are taken as evidence for the superposition of two competing transfer reactions. DWBA calculations for the two single transfer processes were performed using the fixed-range approximation, and the two transition amplitudes were summed coherently. The experimental angular distributions are well reproduced. The DWBA also explains the disappearance of the interference structures for higher transferred angular momenta l. Data on the reaction ¹¹B(¹⁶O, ¹⁵N)¹²C measured earlier are included in the analysis in order to show the systematic dependence on l-values.     

Enhancement of two-proton transfer in N = 82 nuclei: A study of 1p, 2p and (2p+2n) transfer reactions induced by 16O on 140Ce, 142Nd and 144Sm near the Coulomb barrier

One-proton, two-proton, and α-particle transfer have been studied on nuclei with closed neutron shell N = 82 using ¹⁶O beams of 63 to 66.5 MeV incident energy. Transfer probabilities defined in a semiclassical model are derived for the different reaction channels. For this purpose the Q-value and angular dependence of the cross section are discussed. The two-proton transfer to the ground states shows an enhancement by a factor 20–25 compared to other nuclei, showing the effect of the proton pairing in these nuclei (they correspond to equivalent neutron configurations in ^{108, 110, 112}Sn). The total transfer probability follows a common trend for all three target nuclei as a function of energy above the Coulomb barrier for the proton and two-proton transfer, respectively, but not for the four-nucleon transfer.     

16O, 24, 26Mg, 28Si, 32S, 40Ca(α, 12C) and multi-α-cluster transfer reactions

The (α, ¹²C) reaction has been studied on a variety of nuclei, A = 16 to 40, at E_α = 90.3 MeV. The data indicate a rapid fall-off of cross sections with increasing target mass, approximately as A_t^{?5 ± 1}. This and other systematics are used to estimate cross sections for multi-α-cluster transfer reactions in heavy nuclei and suggest σ_T < 10^?34 cm² consistent with present experimental limits. The data for ²⁴Mg(α, ¹²C)¹⁶O has been studied in more detail and indicates a selective population of final states including ¹⁶O g.s., with oscillatory angular distributions in some instances. Finite-range distorted-wave Born approximation calculations for direct ⁸Be pickup have been performed utilizing cluster overlap amplitudes obtained with zero-order SU(3) wave functions. The calculations are in qualitative, and often quantitative, agreement with shapes and absolute magnitudes of the measured angular distributions although the cross sections for certain α-cluster states (2⁺, E_x ≈ 7 MeV; 4⁺, E_x ≈ 10.3 MeV) are greatly overestimated with this model. Other more complicated mechanisms, such as successive α-transfer, cannot be excluded. The systematics of the calculated ⁸Be cluster overlaps and the calculated and measured (α, ¹²C) cross sections are investigated, and implications for multi-α-cluster transfer reactions are discussed.     

Halo or skin in the excited states of some light mirror nuclei

The properties of three pairs of mirror nuclei ¹³N- ¹³C, ¹⁵N- ¹⁵O and ²¹Na- ²¹Ne (these mirror nuclei are all made of a good inert core plus an unpaired valence nucleon) are investigated by using the nonlinear relativistic mean-field (RMF) theory. It is found that the calculated binding energies with two different parameter sets are very close to the experimental ones for both the ground states and the excited states except for the large deformed nuclei. The calculations show that the 2s_1/2 excited states of ¹⁵N and of ²¹Na are both weakly bound with a proton halo and a proton skin (or a pigmy proton skin), respectively. In addition, the 1d_5/2 excited state of ¹³C and the 2s_1/2 excited state of ¹⁵O are also weakly bound with a neutron skin, respectively. The ratio of the valence nucleon radius to matter radius is deduced and it can be regarded as an additional criterion for the existence of exotic structure. The unbound 2s_1/2 and 1d_5/2 excited states of ¹³N are also discussed.     

Kernradien von12C,13C,14N und16O aus Elektronenstreuung zwischen 30 und 60 MeV

Elastic electron scattering cross sections of¹²C,¹⁴N and¹⁶O relative to the proton, and of¹³C relative to¹²C have been measured. Using harmonic oscillator wave functions the followingrms charge radiiR _m were deduced by phaseshift calculations: 2.395 (28) fm for¹²C, 2.384 (47) fm for¹³C, 2.492 (33) fm for¹⁵N, 2.666 (33) fm for¹⁶O. The ratioR _m (¹³C)/R _m (¹²C) is 0.995±0.008. The errors given do not include uncertainties from the model dependence of the evaluation which may be of the same magnitude.     

Nuclear mass formula with a Yukawa-plus-exponential macroscopic model and a folded-Yukawa single-particle potential

We use a Yukawa-plus-exponential macroscopic model and a folded-Yukawa single-particle potential to systematically calculate the ground-state masses of 4023 nuclei ranging from ¹⁶O to {279}112. The method is also used to calculate the fission-barrier heights of 28 nuclei ranging from ¹⁰⁹Cd to ²⁵²Cf. We introduce several previously neglected physical effects, including a smaller nuclear radius constant, a proton form factor, an exact diffuseness correction, an A⁰ term, a chargeasymmetry term, and microscopic zero-point energies. The nuclear radius constant is determined from elastic electron scattering and microscopic calculations of nuclear density distributions, the range of the Yukawa-plus-exponential folding function is determined from heavy-ion elastic scattering, the surface-energy constant and surface-asymmetry constant are determined from the fission-barrier heights of the 28 nuclei that are considered, and the remaining constants are determined from the ground-state masses of 1323 nuclei ranging from ¹⁶O to ²⁵⁹No for which experimental values are known with experimental errors less than 1 MeV. For the final formula, the root-mean-square error in the ground-state masses is 0.835 MeV and the root-mean-square error in the fission-barrier heights is 1.331 MeV. Some of the remaining discrepancies in the groundstate masses can be understood in terms of instabilities with respect to ε₃ and ε₆ deformations.     

天体演化过程中CNO核子辐射俘获反应

C和N核的质子辐射俘获反应对恒星平稳H燃烧阶段的能量产生和元素核合成起重要作用, C, N和O 核的中子辐射俘获是原初核合成和AGB星核合成的关键反应, 精确测定它们天体物理反应率有重要意义。 除13N(p, γ)14O和16N(n, γ)17N等不稳定核的核子辐射俘获反应外, 国际上已完成了其中若干反应的直接测量工作。 但12C(p, γ)13N, 13C(p, γ)14N和15N(p, γ)16O等CNO循环关键反应的实验测量还没有达到天体物理感兴趣的能区。 13C(n, γ)14C,15N(n, γ)16N和18O(n, γ)19O等中子辐射俘获反应测量的能量跨度较大, 截面仍存在较大的不确定性。 介绍了这些反应的研究进展, 并讨论了间接测量这些反应的方法和可行性。 The proton radiative capture reactions of C and N nuclei are important for the energy production and nucleosynthesis in the CNO cycle, and the neutron radiative capture reactions of C, N and O nuclei are key reactions for the inhomogeneous Big Bang nucleosynthesis as well as for the neutron induced CNO cycle in AGB stars. So far, most of these reactions have been measured except some reactions of the unstable nuclei, such as 13N(p, γ)14O and 16N(n, γ)17N. While the direct measured reactions, such as the  12C(p, γ)13N, 13C(p, γ)14N and 15N(p, γ)16O key reactions in CNO cycle, have not reached down to the stellar energies. In addition, the large uncertainties still exist in the measured neutron capture reactions such as 13C(n, γ)14C,15N(n, γ)16N and 18O(n, γ)19O. Thus it is significant to determine their astrophysical reaction rates via the indirect measurements. In this paper, the research status and feasibility of the indirect measurements for these reactions are discussed.     

Transfer and fragmentation reactions of14N at 60 MeV/u

Inclusive energy spectra and cross sections of reaction products close to the¹⁴N projectile (¹¹C,¹²C,¹³C,¹⁵N and¹⁵O) have been measured in the angular rangeθ _L =1.2°–4.2° at an incident energy of 60 MeV/u for five different target nuclei (¹²C,²⁷Al,⁵⁸Ni,⁹⁰Zr and²⁰⁸Pb). Two components are found to be systematically present in the energy spectra of the carbon isotopes, the first similar to that observed at relativistic energies and the second shifted down in energy characteristic for a very dissipative process. The dependence of the differential and integrated cross sections on the target mass indicates that the two-body final channels (¹⁴N,¹³C), (¹⁴N,¹⁵N) and (¹⁴N,¹⁵O) are strongly correlated to the fragmentation channels.     

Electric dipole transitions in neutron-rich nuclei

The structure of neutron-rich nuclei in several isotopes is investigated by shell model calculations. We study the electric dipole (E1) transitions in C isotopes focusing on the interplay between the low-energy Pigmy strength and the giant dipole resonance (GDR). Reasonable agreement is obtained with available experimental data for the photoreaction cross sections in ¹²C, ¹³C, and ¹⁴C with the inclusion of the quenching effects. A low-energy peak in the dipole strength in ¹⁵C is associated with a single-particle motion of the 1s_1/2 valence neutron relative to the ¹⁴C core. The calculated transition strength below the GDR in C isotopes heavier than ¹⁵C is found to exhaust about 50–80% of the cluster sum rule value and 12–16% of the classical Thomas-Reiche-Kuhn sum rule value. Next, we point out that the quadrupole and magnetic moments in the odd C isotopes strongly depend on configuration, which will be useful to determine the spin parities and the deformations of the ground states of these nuclei. The electric quadrupole (E2) transitions in even C isotopes are also studied. The isotopic dependence of the E2 transition strength is found to be reasonably well explained, although the calculated strength largely overestimates the unexpectedly small strength observed in ¹⁶C. The E1 strength in ¹⁸N and ¹⁹N as well as in Ne isotopes is also investigated.     

The study of (d,t) and (d, 3He) reactions in several 1p shell nuclei using vector-polarized beams

Cross-section and vector analyzing power angular distributions using 15 MeV deuterons were taken over an angular range of θ_1ab = 20–100° for the ¹⁰B(d, t)⁹B_{g.s.and 2.36 Mev state}, ¹⁰B(d, ³He)⁹Be_{g.s. and 2.43 Mev state}, ¹³C(d, t)¹²C_g.s., ¹⁴N(d, t)¹³N_g.s., and¹⁴N(d, ³He)¹³C_g.s. reactions, and vector analyzing power data alone were taken for the ¹⁶O(d, t)¹⁵O_g.s. and ¹⁶O(d, ³He)¹⁵N_g.s. reactions. Beams of vector-polarized deuterons were used for the vector analyzing power determinations. A comparison is made of the results for (d, t) and (d, ³He) reactions leading to mirror states when the self-conjugate targets ¹⁰B and ¹⁴N are used. The reactions provide evidence for a j-dependence of the vector analyzing power for l = 1 transfers in 1p shell nuclei. When the reactions involve a j-value admixture, the vector analyzing powers are used to attempt to determine percentage admixtures involved in the population of several final states.     

Resonance structure in 15N(p,n0)15O in the region Ep = 8.5–19.0 MeV

Excitation functions at seven angles, covering the energy range E_p = 8.5–19.0 MeV, have been measured for ¹⁵N(p, n_o)¹⁵O using time-of-flight methods. Angular distributions were also measured at five energies. Activation methods were used to determine the total cross section below the excited-state threshold. Ten resonances were observed, four of which have also been found in ¹⁵N(p, γ)¹⁶O data. The energies, widths and nucleon widths have been extracted and are used, together with proton capture data, to derive radiative widths for certain levels.     

β delayed emission of a proton by a one-neutron halo nucleus

Some one-neutron halo nuclei can emit a proton in a β decay of the halo neutron. The branching ratio towards this rare decay mode is calculated within a two-body potential model of the initial core + neutron bound state and final core + proton scattering states. The decay probability per second is evaluated for the ¹¹Be, ¹⁹C and ³¹Ne one-neutron halo nuclei. It is very sensitive to the neutron separation energy.     

Isotopic invariance of fission fragment charge distributions for actinide nuclei at excitation energies above 10 MeV

The fragment mass and energy distributions from the proton-induced fission of compound nuclei ²³³Pa, ^{234,236,237,239}Np, ^{239,240,241,243}Am, and ²⁴⁵Bk at proton energy E _p =10.3 and 22.0 MeV have been experimentally studied. It was revealed that the shapes of the asymmetric fission mass distributions are mainly defined by the proton numbers of compound nuclei and demonstrate only a weak dependence on the neutron ones. The detailed study of the fission fragment mass yields for compound nuclei Np and Am isotopic chains has shown that the asymmetric fission fragment charge distributions calculated within the unchanged charge density hypothesis for nuclei with equal Z _C practically coincide.     

Theoretical vibrational terms and rotational constants for the 15N substituted isotopologues of N2O calculated using normal hyperspherical coordinates

Variational calculations of the vibrational terms G_v and rotational constants B_v of the ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O and ¹⁵N¹⁵N¹⁶O isotopologues of nitrous oxide are carried out using normal hyperspherical coordinates. The Morse-cosine potential energy surface for N₂O previously determined by the authors by fitting to a set of experimental vibrational frequencies is employed. The G_v and B_v spectroscopic constants calculated for the ¹⁵N substituted isotopologues show an satisfactory agreement with those experimentally observed for a large number of vibrational bands of these isotopologues recently measured. Predicted calculated values of these spectroscopic constants for unobserved vibrational bands of the ¹⁵N substituted isotopologues are given in order to be of help in the identification and characterization of such bands, as a complement to the use of global effective Hamiltonians.     

The (3He,n) reaction on 16O and 18O

The (³He, n) reaction on ¹⁶O and ¹⁸O has been used to study low-spin states in ¹⁸Ne and ²⁰Ne up to E_x ≈ 8 and 20 MeV, respectively. The measured neutron angular distributions have been analysed using DWBA. By a comparison with shell-model calculations in the (s, d) shell it is found that most of the two-proton transfer strength can be explained within that shell. Important contributions, however, from the (f, p) shell in low-lying negative parity states are also present.