The molecular algebraic model based on three and four alpha clusters is used to describe the inelastic scattering of alpha particles populating low-lying states in $^{12}$C and $^{16}$O. Optical potentials and inelastic formfactors are obtained by folding densities and transition densities obtained within the molecular model. One-step and multi-step processes can be included in the reaction mechanism calculation. In spite of the simplicity of the approach the molecular model with rotations and vibrations provides a reliable description of reactions where $α$-cluster degrees of freedom are involved and good results are obtained for the excitation of several low-lying states. Within the same model we briefly discuss the expected selection rules for the $α$-transfer reactions from $^{12}$C and $^{16}$O.
Angular distributions for elastic and inelastic scattering of $^3$He from $^{12}$C were measured at energies 50.5 and 60 MeV. The Airy minimum of the prerainbow scattering was clearly observed in the angular distributions for the 0$_2^+$ (7.65 MeV) state of $^{12}$C (Hoyle state). The experimental results were analyzed with a coupled channels method with double folding potentials derived from the microscopic wave functions for the ground 0$_1^+$, 2$^+$ (4.44 MeV), 3$^-$ (9.64 MeV) and 0$_2^+$ states. The analysis supports the view that the Hoyle state is a three alpha particle condensate with …
The robust (spin and isospin zero) $α$-particle remains one of the best projectiles to probe the nuclear isoscalar excitations. In the present work, a microscopic folding model analysis of the \ac inelastic scattering to the 2$^+$ (4.44 MeV), 0$^+$ (7.65 MeV), 3$^-$ (9.64 MeV), 0$^+$ (10.3 MeV) and 1$^-$ (10.84 MeV) states in $^{12}$C has been performed using the 3-$α$ resonating group method wave functions. The isoscalar transition strengths of these states were carefully studied based on the coupled-channel analysis using the microscopic folded form factors. A correlation between the weak bi…
The energetic beam of (spin and isospin zero) $α$-particles remains a very efficient probe for the nuclear isoscalar giant resonances. In the present work, a microscopic folding model study of the isoscalar giant resonances in $^{208}$Pb induced by inelastic \aPb scattering at $E_{\rm lab}=240$ and 386 MeV has been performed using the (complex) CDM3Y6 interaction and nuclear transition densities given by both the collective model and Random Phase Approximation (RPA) approach. The fractions of energy weighted sum rule around the main peaks of the isoscalar monopole, dipole and quadrupole giant …
The total reaction cross section is related to the elastic scattering angular distribution by a basic quantum-mechanical relation. We present new experimental data for alpha-induced reaction cross sections on 64Zn which allow for the first time the experimental verification of this simple relation at low energies by comparison of the new experimental reaction data to the result obtained from 64Zn(alpha,alpha)64Zn elastic scattering.
The elastic scattering cross section measured at energies $E\lesssim 10$ MeV/nucleon for some light heavy-ion systems having two identical cores like $^{16}$O+$^{12}$C exhibits an enhanced oscillatory pattern at the backward angles. Such a pattern is known to be due to the transfer of the valence nucleon or cluster between the two identical cores. In particular, the elastic $α$ transfer has been shown to originate directly from the core-exchange symmetry in the elastic $^{16}$O+$^{12}$C scattering. Given the strong transition strength of the $2^+_1$ state of $^{12}$C and its large overlap with…
In order to discuss the spatial extention of the second 0+ state of 12C (Hoyle state), we analyze the inelastic form factor of electron scattering to the Hoyle state, which our 3 alpha condensate wave function reproduces very well like previous 3 alpha RGM/GCM models. The analysis is made by varying the size of the Hoyle state artificially. As a result, we find that only the maximum value of the form factor sensitively depends on its size, while the positions of maximum and minimum are almost unchanged. This size dependence is found to come from a characteristic feature of the transition densi…
The reaction mechanism of deep-inelastic multinucleon transfer processes in the $^{16}$O+$^{27}$Al reaction at an incident $^{16}$O energy ($E_{\rm lab}=134$ MeV) substantially above the Coulomb barrier has been studied both experimentally and theoretically. Elastic-scattering angular distribution, total kinetic energy loss spectra and angular distributions for various transfer channels have been measured. The $Q$-value- and angle-integrated isotope production cross sections have been deduced. To obtain deeper insight into the underlying reaction mechanism, we have carried out a detailed analy…
An effective, non-relativistic field theory for low-energy d+t -> n+alpha reaction is presented. The theory assumes that the reaction is dominated by an intermediate 5He* unstable spin 3/2+ resonance. It involves two parameters in the coupling of the d+t and n+alpha particles to the unstable resonant state, and the resonance energy level -- only three real parameters in all. All Coulomb corrections to this process are computed. The resultant field theory is exactly solvable and provides an excellent description of the d+t fusion process.
Subbarrier alpha transfer reaction 13C(6Li,d)17O(6.356 MeV, 1/2+) at 3.6 MeV is analyzed with a alpha + d + 13C three-body model, and the asymptotic normalization coefficient (ANC) for alpha + 13C --> 17O(6.356 MeV, 1/2+), which essentially determines the reaction rate of 13C(alpha,n)16O, is extracted. Breakup effects of 6Li in the initial channel and those of 17O in the final channel are investigated with the continuum-discretized coupled-channels method (CDCC). The former is found to have a large back-coupling to the elastic channel, while the latter turns out significantly small. The transf…
An R-matrix analysis of experimental nuclear data on the reactions 4He(alpha,alpha), 4He(alpha,p), 4He(alpha,d), 7Li(p,alpha), 7Li(p,p), 7Li(p,n), 7Be(n,p), 6Li(d,alpha), 6Li(d,p), 6Li(d,n) and 6Li(d,d), leading to the 8Be intermediate state, has been completed in the last two years. About 4700 data points from 69 experimental references are included. The excitation energy above the 8Be ground state is 25-26 MeV for all reactions except 4He(alpha,alpha) and 7Be(n,p). The data for the reactions 4He(alpha,alpha) and 6Li(d,d) do not fit well, but the other reactions fit with a chi^2/(point) of le…
The polarized d d -> alpha X reaction at beam energies close to the eta threshold shows very strong structure in the missing mass corresponding to the ABC enhancement. The deuteron tensor analysing power A_yy, and the slope of the vector analysing power A_y with respect to angle, have been measured for this reaction around the forward direction. Both signals are small, and their variations with the alpha-particle momentum are in broad agreement with a theoretical model in which each pair of nucleons in the projectile and target deuterons undergoes pion production through the NN -> d pi reactio…
A semi-microscopic model for the low-energy photodisintegration of the 9Be nucleus is constructed, and the experimental data are analyzed with its help. The older radioactive isotope data are supported by this analysis. The theoretical photodisintegration cross section is derived. The astrophysical rates for the reaction alpha + alpha + n -> 9Be + gamma and the reverse photodisintegration of 9Be are calculated. The new reaction rate for alpha + alpha + n -> 9Be + gamma is compared with previous estimations.
The properties of the alpha+28Si and 16O+16O molecular states which are embedded in the excited states of 32S and can have an impact on the stellar reactions are investigated using the antisymmetrized molecular dynamics. From the analysis of the cluster spectroscopic factors, the candidates of alpha+28Si and 16O+16O molecular states are identified close to and above the cluster threshold energies. The calculated properties of the alpha+28Si molecular states are consistent with those reported by the alpha+28Siresonant scattering experiments. On the other hand, the 16O+16O molecular state, which…
In a recent work, the cross section measurement of the 64Zn(p,alpha)61Cu reaction was used to prove that the standard alpha-nucleus optical potentials used in astrophysical network calculation fail to reproduce the experimental data at energies relevant for heavy element nucleosynthesis. In the present paper the analysis of the obtained experimental data is continued by comparing the results with the predictions using different parameters. It is shown that the recently suggested modification of the standard optical potential leads to a better description of the data.
In the model calculations of heavy element nucleosynthesis processes the nuclear reaction rates are taken from statistical model calculations which utilize various nuclear input parameters. It is found that in the case of reactions involving alpha particles the calculations bear a high uncertainty owing to the largely unknown low energy alpha-nucleus optical potential. Experiments are typically restricted to higher energies and therefore no direct astrophysical consequences can be drawn. In the present work a (p,alpha) reaction is used for the first time to study the alpha-nucleus optical pote…
Background: The triaxial and hexadecapole deformations of the K=0+ and K=2+ bands of 24Mg have been investigated by the inelastic scatterings of various probes, including electrons, protons, and alpha particles, for a prolonged time. However, it has been challenging to explain the unique properties of the scatterings observed for the $4^+_1$ state through reaction calculations. Purpose: To investigate the structure and transition properties of the K=0+ and K=2+ bands of 24Mg employing the microscopic structure and reaction calculations via inelastic proton and alpha-scattering. Particularly, t…
The p + 6Li --> eta + 7Be reaction has been investigated with an emphasis on the eta meson and 7Be interaction in the final state. Considering the 6Li and 7Be nuclei to be alpha-d and alpha-3He clusters respectively, the reaction is modelled to proceed via the p + d [alpha] --> 3He [α] + eta reaction with the alpha remaining a spectator. The eta meson interacts with 7Be via multiple scatterings on the 3He and alpha clusters inside 7Be. The individual eta-3He and eta-alpha scatterings are evaluated using few body equations for the eta-3N and eta-4N systems with a coupled channel eta-N interacti…
[Background:] The band structure of the negative-parity states of $^{24}$Mg has not yet been clarified. The $K^π=0^-$, $K^π=1^-$, and $K^π=3^-$ bands have been suggested, but the assignments have been inconsistent between experiments and theories. [Purpose:] Negative-parity states of $^{24}$Mg are investigated by microscopic structure and reaction calculations via proton and alpha inelastic scattering to clarify the band assignment for the observed negative-parity spectra. [Method:] The structure of $^{24}$Mg was calculated using the antisymmetrized molecular dynamics~(AMD). Proton and alpha i…
Captures of alpha particles on the proton-richest Barium isotope, 130Ba, have been studied in order to provide cross section data for the modeling of the astrophysical gamma process. The cross sections of the 130Ba(alpha,gamma)134Ce and 130Ba(alpha,n)133Ce reactions have been measured with the activation technique in the center-of mass energy range between 11.6 and 16 MeV, close above the astrophysically relevant energies. As a side result, the cross section of the 132Ba(alpha,n)135Ce reaction has also been measured. The results are compared with the prediction of statistical model calculation…
Nuclear reactions involving alpha particles play an important role in various astrophysical processes such as the gamma-process of heavy element nucleosynthesis. The poorly known low-energy alpha-nucleus optical (AOMP) potential is a key parameter to estimate the rates of these reactions. The AOMP can be tested by measuring the cross section of alpha-scattering as well as alpha-induced reactions. Low energy elastic alpha-scattering on 144Sm has recently been measured with high precision. The aim of the present work was to complement that work by measuring the (a,n) cross sections on 144Sm at l…
The inelastic scattering of neutrino off 4He is calculated microscopically at energies typical for core collapse supernova environment. The calculation is carried out with the Argonne V18 nucleon--nucleon potential and the Urbana IX three nucleon force. Full final state interaction is included via the Lorentz integral transform (LIT) method. The contribution of axial meson exchange currents to the cross sections is taken into account from effective field theory of nucleons and pions to order O(Q^3).
Due consideration of proton optical--model potential (OMP) anomalies at sub-Coulomb energies for medium--weight nuclei is shown to be critical for the analysis of the unprecedented measurement of $^{59}$Cu$(p,α)^{56}$Ni reaction cross section at an energy of $\sim$6 MeV [Phys. Rev. C {\bf 104}, L042801 (2021)]. The variation in predicted cross sections from standard statistical--model calculations and the cross--section range corresponding to the anomalous proton imaginary--potential depth, for target nuclei off the line of stability, are distinct and well separated. Consequently, the new meas…
Given the established 2 alpha structure of 8Be, a realistic model of 4 interacting alpha clusters must be used to obtain a 8Be+8Be interaction potential. Such a four-body problem poses a challenge for the determination of the 8Be+8Be optical potential (OP) that is still unknown due to the lack of the elastic 8Be+8Be scattering data. The main goal of the present study is to probe the complex 8Be+8Be optical potential in the coupled reaction channel (CRC) study of the alpha transfer 12C(alpha,8Be) reaction measured at 65 MeV, and to obtain the spectroscopic information on the alpha+8Be cluster c…
We show that using parameters consistent with the charge symmetry violating difference between the strong nn and pp scattering lengths provides significant constraints on the amplitude for the dd -> alpha pi0 reaction.
Four-body distorted wave theory appropriate for nucleon-nucleus reactions leading to 3-body continuum excitations of two-neutron Borromean halo nuclei is developed. The peculiarities of the halo bound state and 3-body continuum are fully taken into account by using the method of hyperspherical harmonics. The procedure is applied for A=6 test-bench nuclei; thus we report detailed studies of inclusive cross sections for inelastic $^6$He(p,p')$^6$He$^*$ and charge-exchange $^6$Li(n,p)$^6$He$^*$ reactions at nucleon energy 50 MeV. The theoretical low-energy spectra exhibit two resonance-like struc…
The radiative capture cross sections for the 3He(alpha,gamma)7Be and 3H(alpha,gamma)7Li reactions are calculated in the fully microscopic fermionic molecular dynamics approach using a realistic effective interaction that reproduces the nucleon-nucleon scattering data. At large distances bound and scattering states are described by antisymmetrized products of 4He and 3He/3H ground states. At short distances the many-body Hilbert space is extended with additional many-body wave functions needed to represent polarized clusters and shell-model-like configurations. Properties of the bound states ar…
The outline of the presentation is as follows: I. Nucleon Distribution in the Deuteron from $e-D$ and $p-D$ Processes. II. Quark Distribution in Deuteron from its Fragmentation to Pions and Deep Inelastic $e-D$ scattering. III.Difference of These Two Distributions and Its Possible Understanding.
We investigate the triple-alpha reaction at low energies, by assuming a direct process. The Coulomb potential of three $α$ particles is examined carefully. The three-body continuum wave functions are generated by calculating an adiabatic potential barrier. We discuss the influence of the $αα$ potential, and compare our reaction rates with the literature. The reaction rate at $T=0.01$\,GK is about 10$^3$ times larger than that of NACRE.
We study nuclear effect in the $F^A_3(x)$ structure function in the deep inelastic neutrino reactions on iron by taking into account Fermi motion, binding, target mass correction, shadowing and anti-shadowing corrections. Calculations have been done in a local density approximation using relativistic nuclear spectral functions which include nucleon correlations for nuclear matter. Results for $F^A_3(x)$ have been compared with the results reported at NuTeV and also with some of the older experiments reported in the literature.
We present a Monte Carlo calculation of the astrophysical rate of the 15O(alpha,gamma)19Ne reaction based on an evaluation of published experimental data. By considering the likelihood distributions of individual resonance parameters derived from measurements, estimates of upper and lower limits on the reaction rate at the 99.73% confidence level are derived in addition to the recommended, median value. These three reaction rates are used as input for three separate calculations of Type I x-ray bursts using spherically symmetric, hydrodynamic simulations of an accreting neutron star. In this w…
The status of the theoretical effort to calculate charge-symmetry-breaking pion production reactions will be presented. The main emphasis will be on the d d -> alpha pi0 reaction, especially in relation to the recent IUCF experiment. Suggestions for future theoretical and experimental work will be made.
Using imaginary-time theory, it is shown that the triple-alpha reaction rate can be reliably calculated without the need to solve scattering problems involving three charged particles. The calculated reaction rate is found to agree well with the empirical NACRE rate, which is widely adopted in stellar evolution calculations. The reason for this is explained using $R$-matrix theory. Extremely slow convergence is found to occur when a coupled-channel expansion is introduced, which helps to explain the very different reaction rates obtained using different theoretical approaches.
We present the failure of the standard coupled-channels method in explaining the inelastic scattering together with other observables such as elastic scattering, excitation function and fusion data. We use both microscopic double-folding and phenomenological deep potentials with shallow imaginary components. We argue that the solution of the problems for the inelastic scattering data is not related to the central nuclear potential, but to the coupling potential between excited states. We present that these problems can be addressed in a systematic way by using a different shape for the couplin…
A recoil coincidence technique has been applied to measure the alpha-decay branching ratios of near-threshold states in 19Ne. Populating these states using the (p,t) reaction in inverse kinematics, we detected the recoils and their decay products with 100% geometric efficiency using a magnetic spectrometer. Combining our branching ratio measurements with independent determinations of the radiative widths of these states, we calculate the astrophysical rate of 15O(alpha,gamma)19Ne. Using this reaction rate, we perform hydrodynamic calculations of nova outbursts and conclude that no significant …
The dd -> alpha X reaction is studied in a model where each pair of nucleons in the projectile and target deuterons undergoes pion production through the NN -> d pi reaction. The condition that the two deuterons fuse to form an alpha-particle then leads to peaks at small missing masses, the well-known ABC enhancement, but also a broad structure around the maximum missing mass. With a simplified input amplitude the model gives a quantitative description of both the alpha-particle momentum and angular distributions for a deuteron beam energy of 1250 MeV.
A model for the d d -> alpha pi pi reaction, based on two parallel N N -> d pi reactions, is extended to incorporate a complete set of input amplitudes. While low-energy cross sections are underestimated, the rich structure observed in the alpha-particle momentum distributions for 0.8 < T_d < 1.9 GeV (the ABC effect) is extraordinarily well reproduced. In addition, a recent measurement of deuteron analyzing powers agrees quite well with our predictions, both in frequency and magnitude of the oscillations.
We explore the possibility to measure the elastic and inelastic $ωN$ cross section in $p{+}d{\to}d{+}ω{+}p_{sp}$ and $p{+}A$ reactions. Our studies indicate that the elastic scattering cross sections can be determined for $ω$ momenta above 1 GeV/c in $p{+}d$ reactions by gating on high proton spectator momenta whereas the $ωN$ absorption cross section down to low relative $ω$ momenta is most effectively studied in $p{+}A$ reactions at beam energies 2.0--2.7 GeV
The effects of initial-state Coulomb interactions in the charge-symmetry-breaking reaction dd -> alpha pi^0 are investigated within a previously published formalism. This is a leading order effect in which the Coulomb interaction between the two initial state protons leads to the breakup of the two deuterons into a continuum state that is well connected to the final alpha pi^0 state by the strong emission of a pion. As a first step, we use a simplified set of d and alpha wave functions and a plane-wave approximation for the initial dd state. This Coulomb mechanism, by itself, yields cross sect…
In this paper, we present the results of a study made for the effect of nuclear medium in the charged current induced quasielastic lepton production(CCQE) and the incoherent and coherent one pion production (CC1$π^+$)processes from $^{12}C$ in the $ν_μ$ energy region of 0.4-3GeV. The theoretical results are compared with the recent experimental results for the ratio of charged current $ν_μ$ induced one pion production cross section to the quasielastic lepton production cross section reported by K2K collaboration. We also present the results for the angular and momentum distributions of leptons…
Estimates are made of the d d -> alpha gamma gamma production cross sections in a model where each neutron-proton pair in the beam and target initiates an n p -> d gamma reaction. This approach, which successfully reproduces observables in two-pion production at intermediate energies, suggests that direct two-photon production could provide a very significant background to the measurement of the charge-symmetry-breaking (CSB) reaction d d -> alpha pi0. A non-vanishing CSB cross section has been reported which might be confused with such two-photon production under the given experimental condit…
Isospin characters of nuclear excitations in $^{26}$Mg and $^{10}$Be are investigated via proton($p$) and alpha($α$) inelastic scattering. A structure model of antisymmetrized molecular dynamics (AMD) is applied to calculate the ground and excited states of $^{26}$Mg and $^{10}$Be. The calculation describes the isoscalar feature of the ground-band $2^+_1$($K^π=0^+_1$) excitation and predicts the neutron dominance of the side-band $2^+_2$($K^π=2^+$) excitation in $^{26}$Mg and $^{10}$Be. The $p$ and $α$ inelastic scattering off $^{26}$Mg and $^{10}$Be is calculated by microscopic coupled-channe…
$0^+$, $1^-$, $2^+$, and $3^-$ excitations of $^{28}\textrm{Si}$ are investigated via proton and $α$ inelastic scattering off $^{28}\textrm{Si}$. The structure calculation of $^{28}\textrm{Si}$ is performed with the energy variation after total angular momentum and parity projections in the framework of antisymmetrized molecular dynamics (AMD). As a result of the AMD calculation, the oblate ground and prolate bands, $0^+$ and $3^-$ excitations, and the $1^-$ and $3^-$ states of the $K^π=0^-$ band are obtained. Using the matter and transition densities of $^{28}\textrm{Si}$ obtained by AMD, mic…
Energy dissipative processes play a key role in how quantum many-body systems dynamically evolve towards equilibrium. In closed quantum systems, such processes are attributed to the transfer of energy from collective motion to single-particle degrees of freedom; however, the quantum many-body dynamics of this evolutionary process are poorly understood. To explore energy dissipative phenomena and equilibration dynamics in one such system, an experimental investigation of deep-inelastic and fusion-fission outcomes in the $^{58}$Ni+$^{60}$Ni reaction has been carried out. Experimental outcomes ha…
The classical trajectory model with stochastic breakup for nuclear collision dynamics of weakly-bound nuclei is further developed. It allows a quantitative study of the importance of incomplete fusion dynamics in the angular distribution of direct alpha-production. Model calculations indicate that the incomplete fusion contribution diminishes with decreasing energy towards the Coulomb barrier, notably separating in angles from the contribution of no-capture breakup events. This should facilitate the experimental disentanglement of these competing reaction processes.
The alpha-rich freezeout from equilibrium occurs during the core-collapse explosion of a massive star when the supernova shock wave passes through the Si-rich shell of the star. The nuclei are heated to high temperature and broken down into nucleons and alpha particles. These subsequently reassemble as the material expands and cools, thereby producing new heavy nuclei, including a number of important supernova observables. In this paper we introduce two web-based applications. The first displays the results of a reaction-rate sensitivity study of alpha-rich freezeout yields. The second allows …
The 146Sm/144Sm ratio in the early solar system has been constrained by Nd/Sm isotope ratios in meteoritic material. Predictions of 146Sm and 144Sm production in the gamma-process in massive stars are at odds with these constraints and this is partly due to deficiences in the prediction of the reaction rates involved. The production ratio depends almost exclusively on the (gamma,n)/(gamma,alpha) branching at 148Gd. A measurement of 144Sm(alpha,gamma)148Gd at low energy had discovered considerable discrepancies between cross section predictions and the data. Although this reaction cross section…
The $K^π=0^+_1$, $K^π=2^-$, and $K^π=0^-_1$ bands of $^{20}$Ne are investigated with microscopic structure and reaction calculations via proton and $α$ inelastic scattering off $^{20}$Ne. Structures of $^{20}$Ne are calculated with variation after parity and total angular momentum projections in the antisymmetrized molecular dynamics(AMD). The $K^π=0^+_1$ and $K^π=0^-_1$ bands have $^{16}\textrm{O}+α$ cluster structures, whereas the $K^π=2^-$ band shows a $^{12}\textrm{C}+2α$-like structure. Microscopic coupled-channel calculations of proton and $α$ scattering off $^{20}$Ne are performed by us…
Effective energy windows (Gamow windows) of astrophysical reaction rates for (p,gamma), (p,n), (p,alpha), (alpha,gamma), (alpha,n), (alpha,p), (n,gamma), (n,p), and (n,alpha) on targets with 10<=Z<=83 from proton- to neutron-dripline are calculated using theoretical cross sections. It is shown that widely used approximation formulas for the relevant energy ranges are not valid for a large number of reactions relevant to hydrostatic and explosive nucleosynthesis. The influence of the energy dependence of the averaged widths on the location of the Gamow windows is discussed and the results prese…
The $^{120}$Sn($p$,$pα$)$^{116}$Cd reaction at 392 MeV is investigated with the distorted wave impulse approximation (DWIA) framework. We show that this reaction is very peripheral mainly because of the strong absorption of $α$ by the reaction residue $^{116}$Cd, and the $α$-clustering on the nuclear surface can be probed clearly. We investigate also the validity of the so-called factorization approximation that has frequently been used so far. It is shown that the kinematics of $α$ in the nuclear interior region is significantly affected by the distortion of $^{116}$Cd, but it has no effect o…
A model for the $p(e,e'π^+)n$ reaction which combines an improved treatment of gauge invariant meson--exchange currents and hard deep--inelastic scattering (DIS) of virtual photons off nucleons is proposed. It is shown that DIS dominates and explains the transverse response at moderate and high photon virtualities $Q^2$ whereas the longitudinal response is dominated by hadronic degrees of freedom and the pion electromagnetic form factor. This leads to a combined description of the longitudinal and transverse components of the cross section in a wide range of photon virtuality $Q^2$ and momentu…
The 15O(alpha,gamma)19Ne reaction is one of two known routes for breakout from the hot CNO cycles into the rp process. Its astrophysical rate depends on the decay properties of excited states in 19Ne lying just above the 15O + alpha threshold. We have measured the alpha-decay branching ratios for these states using the p(21Ne,t)19Ne reaction at 43 MeV/u. Combining our branching ratio measurements with previous determinations of the radiative widths of these states, we calculate the astrophysical rate of 15O(alpha,gamma)19Ne. Using this reaction rate, we perform hydrodynamic calculations of nov…
We introduce a new framework for studying clustering and for calculating alpha partial widths using ab initio wave functions. We demonstrate the formalism for $^{20}$Ne, by calculating the overlap between the $^{16}$O$+α$ cluster configuration and states in $^{20}$Ne computed in the ab initio symmetry-adapted no-core shell model. We present spectroscopic amplitudes and spectroscopic factors, and compare those to no-core symplectic shell-model results in larger model spaces, to gain insight into the underlying physics that drives alpha-clustering. Specifically, we report on the alpha partial wi…
A simple model, based on two parallel and independent N N -> d pi processes, has recently been proposed for two-pion production in the d d -> alpha X reaction. It reproduces all observed features, including the sharp peak structure in momentum distributions (the ABC effect) and the strong oscillations in the deuteron vector and tensor analyzing powers. This model is now extended to describe also four-pion production with the same basic mechanism, but with two n p -> d pi pi processes as input. The calculations of the high missing mass spectra are within about 30% of the experimental data for b…
Background: The triple-alpha reaction is the key to our understanding about the nucleosynthesis and the observed abundance of $^{12}$C in stars. The theory of this process is well established at high temperatures but rather ambiguous in the low temperature regime where measurements are impossible. Purpose: Develop a new three-body method, which tackles properly the scattering boundary condition for three charged particles and takes into account both the resonant and the non-resonant reaction mechanisms on the same footing, to compute the triple-alpha reaction rate at low temperatures. Methods:…
The extremely small probability of quantum tunneling through an almost classical potential barrier may become not small under the action of the specially adapted nonstationary field. The tunneling rate has a sharp peak as a function of the particle energy when it is close to the certain resonant value defined by the nonstationary field (Euclidean resonance). Alpha decay of nuclei has a small probability since the alpha particle should tunnel through a very nontransparent Coulomb barrier. The incident proton, due to the Coulomb interaction with the tunneling alpha particle, plays the role of a …
The value of the alpha spectroscopic factor (S_alpha) of the 6.356 MeV 1/2+ state of 17O is believed to have significant astrophysical implications due to the importance of the 13C(alpha,n)16O reaction as a possible source of neutron production for the s process. To further study this effect, an accurate measurement of the 13C(6Li,d)17O reaction at E_lab = 60 MeV has been performed recently by Kubono et al., who found a new value for the spectroscopic factor of the 6.356 MeV 1/2+ state of 17O based on a distorted wave Born approximation (DWBA) analysis of these data. This new value, S_alpha ap…
