Charge Exchange Reactions Research Articles

Nuclear Matrix Elements for Heavy Ion Sequential Double Charge Exchange Reactions

The theoretical approach to a sequential heavy ion double charge exchange reaction is presented. A brief introduction into the formal theory of second-order nuclear reactions and their application to Double Single Charge Exchange (DSCE) reactions by distorted wave theory is given, thereby completing the theoretical background to our recent work. Formally, the DSCE reaction amplitudes are shown to be separable into superpositions of distortion factors, accounting for initial and final state ion–ion interactions, and nuclear matrix elements. A broad space is given to the construction of nuclear DSCE response functions on the basis of polarization propagator theory. The nuclear response tensors resemble the nuclear matrix elements of 2νββ decay in structure but contain in general a considerable more complex multipole and spin structure. The QRPA theory is used to derive explicit expressions for nuclear matrix elements (NMEs). The differences between the NME of the first and the second interaction vertexes in a DSCE reaction is elucidated. Reduction schemes for the transition form factors are discussed by investigating the closure approximation and the momentum structure of form factors. DSCE unit strength cross sections are derived.

New ^{59}Fe Stellar Decay Rate with Implications for the ^{60}Fe Radioactivity in Massive Stars.

The discrepancy between observations from γ-ray astronomy of the ^{60}Fe/^{26}Al γ-ray flux ratio and recent calculations is an unresolved puzzle in nuclear astrophysics. The stellar β-decay rate of ^{59}Fe is one of the major nuclear uncertainties impeding us from a precise prediction. The important Gamow-Teller strengths from the low-lying states in ^{59}Fe to the ^{59}Co ground state are measured for the first time using the exclusive measurement of the ^{59}Co(t,^{3}He+γ)^{59}Fe charge-exchange reaction. The new stellar decay rate of ^{59}Fe is a factor of 3.5±1.1 larger than the currently adopted rate at T=1.2 GK. Stellar evolution calculations show that the ^{60}Fe production yield of an 18 solar mass star is decreased significantly by 40% when using the new rate. Our result eliminates one of the major nuclear uncertainties in the predicted yield of ^{60}Fe and alleviates the existing discrepancy of the ^{60}Fe/^{26}Al ratio.

Experimental Approaches to Neutrino Nuclear Responses for ββ Decays and Astro-Neutrinos

Fundamental properties of neutrinos are investigated by studying double beta decays (ββ-decays), while atro-neutrino nucleo-syntheses and astro-neutrino productions are investigated by studying inverse beta decays (inverse β-decays) induced by astro-neutrinos. Neutrino nuclear responses for these ββ and β-decays are crucial for these neutrino studies in nuclei. This reports briefly perspectives on experimental studies of neutrino nuclear responses (square of nuclear matrix element) for ββ-decays and astro-neutrinos by using nuclear and leptonic (muon) charge-exchange reactions

Charge exchange $$\varvec{{dp \rightarrow (pp)n}}$$ reaction study at 1.75 A GeV/c by the STRELA spectrometer

The differential cross sections of the charge exchange reaction \(dp \rightarrow (pp)n\) has been measured at 1.75 GeV/c per nucleon for small transferred momenta using the one arm magnetic spectrometer STRELA at the Nuclotron accelerator in JINR Dubna. The ratio of the differential cross section of the charge exchange reaction \(dp \rightarrow (pp)n\) to that of the \(np \rightarrow pn\) elementary process is discussed in order to estimate the spin-dependent part of the \(np \rightarrow pn\) charge exchange amplitude. The \(np \rightarrow pn\) amplitude turned out to be predominantly spin-dependent.

Low energy proton induced reactions with weakly bound nuclei for application purposes

Proton induced charge exchange reactions have been proposed as the mean for producing neutron beams for low energy Compact Accelerator-driven Neutron Sources. In view of our new measurements on proton induced reactions at low energies, and a re-new interest for building such neutron sources, we revise here critically cross sections of all reaction products at 3 and 5 MeV on $$^7$$ Li and $$^9$$ Be targets. We find that the ENDF/B-VIII.0 library is the most appropriate to be used for neutron rate estimation via the (p, n) channel. Further on, we suggest the breakup mechanism on a $$^9$$ Be target as a substantial source of neutron production and the breakup mechanism on a $$^7$$ Li target as a source of triton production, the last to be taken into account for radioprotection purposes.

Observation of the Exotic Isotope ^{13}F Located Four Neutrons beyond the Proton Drip Line.

A ^{13}F resonance was observed following a charge-exchange reaction between a fast ^{13}O beam and a ^{9}Be target. The resonance was found in the invariant-mass distribution of 3p+^{10}C events and probably corresponds to a 5/2^{+} excited state. The ground state was also expected to be populated, but was not resolved from the background. The observed level decays via initial proton emissions to both the ground and first 2^{+} state of ^{12}O, which subsequently undergo 2p decay. In addition, there may also be a significant proton decay branch to the second 2^{+} level in ^{12}O. The wave function associated with the observed level may be collectivized due to coupling to the continuum as is it located just above the threshold for proton decay to the 2_{2}^{+} state of ^{12}O.

Ion-Molecule Charge Exchange Reactions between Ar+ and trans-/cis-Dichloroethylene.

We report an ion velocity imaging study of the charge exchange reactions between Ar+ ion and trans-/cis-dichloroethylene in the collision energy range of 2.1-9.5 eV, and we find that the energy-resonant charge transfer plays a dominant role in the large impact-parameter reaction. The parent yields C2H2Cl2+ in the high-lying excited states are directly produced in the charge exchange reactions, while they prefer spontaneous fragmentations in photoionization. This significant difference indicates that the present charge exchange reactions are much slower than the photoelectron detachment. The structural relaxations of the target molecule are allowed in multiple dimensions of freedom during the charge transfer, which should be frequently observed for the charge exchange reactions with large molecules.

Initial State Interaction for the 20Ne + 130Te and 18O + 116Sn Systems at 15.3 AMeV from Elastic and Inelastic Scattering Measurements

Double charge exchange (DCE) reactions could provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To achieve this goal, a detailed description of the reaction mechanism is mandatory. This requires the full characterization of the initial and final-state interactions, which are poorly known for many of the projectile-target systems involved in future DCE studies. Among these, we intend to study the 20Ne + 130Te and 18O + 116Sn systems at 15.3 AMeV, which are particularly relevant due to their connection with the 130Te→130Xe and 116Cd→116Sn double-β decays. We measure the elastic and inelastic scattering cross-section angular distributions and compare them with theoretical calculations performed in the optical model, one-step distorted wave Born approximation, and coupled-channel approaches using the São Paulo double-folding optical potential. A good description of the experimental data in the whole explored range of transferred momenta is obtained provided that couplings with the 21+ states of the projectile and target are explicitly included within the coupled-channel approach. These results are relevant also in the analysis of other quasi-elastic reaction channels in these systems, in which the same couplings should be included.

Carbon dust in the evolved born-again planetary nebulae A 30 and A 78

ABSTRACT We present an infrared (IR) characterization of the born-again planetary nebulae (PNe) A 30 and A 78 using IR images and spectra. We demonstrate that the carbon-rich dust in A 30 and A 78 is spatially coincident with the H-poor ejecta and coexists with hot X-ray-emitting gas up to distances of 50 arcsec from the central stars of PNe (CSPNe). Dust forms immediately after the born-again event and survives for 1000 yr in the harsh environment around the CSPN as it is destroyed and pushed away by radiation pressure and dragged by hydrodynamical effects. Spitzer IRS spectral maps showed that the broad spectral features at 6.4 and 8.0 μm, attributed to amorphous carbon formed in H-deficient environments, are associated with the disrupted disc around their CSPN, providing an optimal environment for charge exchange reactions with the stellar wind that produces the soft X-ray emission of these sources. Nebular and dust properties are modelled for A 30 with cloudy taking into account different carbonaceous dust species. Our models predict dust temperatures in the 40–230 K range, five times lower than predicted by previous works. Gas and dust masses for the born-again ejecta in A 30 are estimated to be $M_\mathrm{gas}=4.41^{+0.55}_{-0.14}\times 10^{-3}$ M⊙ and $M_\mathrm{dust}=3.20^{+3.21}_{-2.06}\times 10^{-3}$ M⊙, which can be used to estimate a total ejected mass and mass-loss rate for the born-again event of $7.61^{+3.76}_{-2.20}\times 10^{-3}$ M⊙ and $\dot{M}=(5{\!-\!}60)\times 10^{-5}$ M⊙ yr−1, respectively. Taking into account the carbon trapped into dust grains, we estimate that the C/O mass ratio of the H-poor ejecta of A 30 is larger than 1, which favours the very late thermal pulse model over the alternate hypothesis of a nova-like event.

Pulsed production of antihydrogen

Antihydrogen atoms with K or sub-K temperature are a powerful tool to precisely probe the validity of fundamental physics laws and the design of highly sensitive experiments needs antihydrogen with controllable and well defined conditions. We present here experimental results on the production of antihydrogen in a pulsed mode in which the time when 90% of the atoms are produced is known with an uncertainty of ~250 ns. The pulsed source is generated by the charge-exchange reaction between Rydberg positronium atoms—produced via the injection of a pulsed positron beam into a nanochanneled Si target, and excited by laser pulses—and antiprotons, trapped, cooled and manipulated in electromagnetic traps. The pulsed production enables the control of the antihydrogen temperature, the tunability of the Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. The production of pulsed antihydrogen is a major landmark in the AEbar{g}IS experiment to perform direct measurements of the validity of the Weak Equivalence Principle for antimatter.

Excitation of isobaric analog states from (p,n) and (He3,t) charge-exchange reactions within the G -matrix folding method

Differential cross sections of ($p,n$) and ($^3$He,$t$) charge-exchange reactions leading to the excitation of the isobaric analog state (IAS) of the target nucleus are calculated with the distorted wave Born approximation. The $G$-matrix double-folding method is employed to determine the nucleus-nucleus optical potential within the framework of the Lane model. $G$-matrices are obtained from a Brueckner-Hartree-Fock calculation using the Argonne Av18 nucleon-nucleon potential. Target densities have been taken from Skyrme-Hartree-Fock calculations which predict values for the neutron skin thickness of heavy nuclei compatible with current existing data. Calculations are compared with experimental data of the reactions ($p,n$)IAS on $^{14}$C at $E_{lab}=135$ MeV and $^{48}$Ca at $E_{lab}=134$ MeV and $E_{lab}=160$ MeV, and ($^3$He,$t$)IAS on $^{58}$Ni, $^{90}$Zr and $^{208}$Pb at $E_{lab}=420$ MeV. Experimental results are well described without the necessity of any rescaling of the strength of the optical potential. A clear improvement in the description of the differential cross sections for the ($^3$He,$t$)IAS reactions on $^{58}$Ni and $^{90}$Zr targets is found when the neutron excess density is used to determine the transition densities. Our results show that the density and isospin dependences of the $G$-matrices play a non-negligible role in the description of the experimental data.

Sub-threshold states in Ne19 relevant to F18(p,α)O15

Classical novae result from thermonuclear explosions producing several $\gamma$-ray emitters which are prime targets for satellites observing in the MeV range. The early 511 keV gamma-ray emission depends critically on the $^{18}$F(p,$\alpha$)$^{15}$O reaction rate which, despite many experimental and theoretical efforts, still remains uncertain. One of the main uncertainties in the $^{18}$F(p,$\alpha$)$^{15}$O reaction rate is the contribution in the Gamow window of interference between sub-threshold $^{19}$Ne states and known broad states at higher energies. Therefore the goal of this work is to clarify the existence and the nature of these sub-threshold states. States in the $^{19}$Ne compound nucleus were studied at the Tandem-ALTO facility using the $^{19}$F($^3$He,t)$^{19}$Ne charge exchange reaction. Tritons were detected with an Enge Split-pole spectrometer while decaying protons or $\alpha$-particles from unbound $^{19}$Ne states were collected, in coincidence, with a double-sided silicon strip detector array. Angular correlations were extracted and constraints on the spin and parity of decaying states established. The coincidence yield at $E_x$ = 6.29 MeV was observed to be high spin, supporting the conclusion that it is indeed a doublet consisting of high spin and low spin components. Evidence for a broad, low spin state was observed around 6 MeV. Branching ratios were extracted for several states above the proton threshold and were found to be consistent with the literature. R-matrix calculations show the relative contribution of sub-threshold states to the astrophysically important energy region above the proton threshold. The levels schemes of $^{19}$Ne and $^{19}$F are still not sufficiently well known and further studies of the analogue assignments are needed. The tentative broad state at 6 MeV may only play a role if the reduced proton width is large.

Stereodynamics Observed in the Reactive Collisions of Low-Energy Ar+ with Randomly Oriented O2.

Stereodynamics of the collisional reaction between mutually aligned or oriented reactants has been a striking topic of chemical dynamics for decades. However, the stereodynamic aspects are scarcely revealed for the low-energy collision with a randomly oriented target. Here in the dissociative charge-exchange reaction between randomly oriented O2 and low-energy Ar+, we, using the three-dimensional ion velocity map imaging technique, clearly observe a linear alignment and a nearly isotropic distribution of the O+ yields along the collision axis. These observations are rationalized with the Doppler kinetic models in which the O2 bond is assumed to be parallel or unparallel to the collision axis of the large impact parameter collision. The linearly aligned O+, as the predominant yield, is produced in the parallel collision, while a rotating O2+, as the intermediate in the unparallel collision, leads to the isotropic distribution of O+.

Recent experimental activity on heavy-ion induced reactions within the NUMEN project

The possibility to use a special class of heavy-ion induced direct reactions, such as double charge exchange reactions, is discussed in view of their application to extract information that may be helpful to determinate the nuclear matrix elements entering in the expression of neutrinoless double beta decay half-life. The strategies adopted in the experimental campaigns performed at INFN - Laboratori Nazionali del Sud are briefly described, emphasizing the advantages of the multi-channel approach to nuclear reaction data analysis.

A physico-chemical model to study the ion density distribution in the inner coma of comet C/2016 R2 (Pan-STARRS)

ABSTRACT The recent observations show that comet C/2016 R2 (Pan-Starrs) has a unique and peculiar composition when compared with several other comets observed at 2.8 au heliocentric distance. Assuming solar resonance fluorescence is the only excitation source, the observed ionic emission intensity ratios are used to constrain the corresponding neutral abundances in this comet. We developed a physico-chemical model to study the ion density distribution in the inner coma of this comet by accounting for photon and electron impact ionization of neutrals, charge exchange and proton transfer reactions between ions and neutrals, and electron–ion thermal recombination reactions. Our calculations show that CO2+ and CO+ are the major ions in the inner coma, and close to the surface of nucleus CH3OH+, CH3OH2+, and O2+ are also important ions. By considering various excitation sources, we also studied the emission mechanisms of different excited states of CO+, CO2+, N2+, and H2O+. We found that the photon and electron impact ionization and excitation of corresponding neutrals significantly contribute to the observed ionic emissions for radial distances smaller than 300 km and at larger distances, solar resonance fluorescence is the major excitation source. Our modelled ion emission intensity ratios are consistent with the ground-based observations. Based on the modelled emission processes, we suggest that the observed ion emission intensity ratios can be used to derive the neutral composition in the cometary coma only when the ion densities are significantly controlled by photon and photoelectron impact ionization of neutrals rather than by the ion–neutral chemistry.

Investigating the relation between heavy ion double charge exchange nuclear reactions and double beta decays

Heavy ion double charge exchange reactions (DCE) are discussed, within DWBA, in synergy with the main goal of the NUMEN project, i. e. to extract information on the 0νββ decay nuclear matrix element from DCE cross section measurements. The first step to reach this goal is to assess the analogy between the DCE nuclear matrix element and that describing 0νββ decay; then it is necessary to single out a term related to the desired double beta decay nuclear matrix element from the DCE cross-section expression (cross section factorization).Heavy ion DCE processes, are depicted in terms of sequence of two correlated or uncorrelated Single Charge Exchange (SCE) reactions, resembling in this way 0νββ and 2νββ decay, respectively. Here, the formalism for describing DCE reactions within the latter scenario is described.Once provided the formalism leading both to SCE and DCE cross section factorization, together with its limitations, a preliminary comparison with experimental DCE data is shown.

Eikonal method for charge-exchange reactions at intermediate energies

A novel description of charge-exchange reactions at intermediate energies is developed, based on both phenomenological or microscopic eikonal phase-shift functions. The results obtained within this eikonal approach are in good agreement with the distorted-wave Born approximation calculations within the energy region where both approximations should be valid. They also compare well with the experimental data, even at relatively low energy domain. At higher energies, relativistic kinematics have also been added and shown to be relevant. Owing to the microscopic feature of the formulation, our theory also has the advantage that it can be applied to high energies where the phenomenological optical potentials are rarely available.

Cross Section of Neutrino Absorption by the Gallium-71 Nucleus

The cross sections of neutrino absorption by the gallium-71 nucleus are obtained for neutrinos from artificial 37Ar, 51Cr, and 65Zn sources. The calculations rely on the new measurement of the energy threshold of this absorption reaction, and contributions of germanium-71 excited states to the total cross section are estimated by invoking the data on the 71Ga(3He,t)71Gе charge-exchange reaction. The results are important for searches for sterile neutrinos in calibration experiments.

Recent results on heavy-ion induced reactions of interest for neutrinoless double beta decay at INFN-LNS

The NUMEN project aims at accessing experimentally driven information on Nuclear Matrix Elements (NME) involved in the half-life of the neutrinoless double beta decay (0νββ). In this view measurements of Heavy Ion (HI) induced Double Charge Exchange (DCE) reaction cross sections are performed with high-accuracy. In particular, the (18O,18Ne) and (20Ne,20O) reactions are used as tools for β+β+ and β-β- decays, respectively. In the experiments, performed at INFN - Laboratory Nazionali del Sud (LNS) in Catania, the beams are accelerated by the Superconducting Cyclotron (CS) and the reaction ejectiles are detected the MAGNEX magnetic spectrometer. The measured cross sections are challengingly low (a few nb), being the total reaction cross section much larger (a few b), thus a high sensitivity and a large rejection capability are demanded to the experimental set-up. This limits the present exploration to few selected isotopes of interest in the context of typically low-yield experimental runs. A major upgrade of the LNS facility is under way in order to increase the experimental dataset of more than two orders of magnitude, still preserving the high sensitivity of the present set-up. When accomplished this effort will make the INFN-LNS as the state-of-the-art research infrastructure for the systematic study of all the cases of interest for 0νββ. In this view, frontiers technologies are going to be adopted for the accelerator and the detection systems. In parallel, advanced theoretical models are being developed in order to extract the nuclear structure information from the measured cross sections.

Halo-like structure in 7He nucleus

A study of the neutron structure of the ground state of 7He has been performed by means of registration and analysis of the decay channels of the residual nuclei following absorption of stopped pions. In particular, the reaction 9Be ()X have been investigated where X denotes any system with five neutrons and two protons – the constituencies of a 7He nucleus. It was shown that the structure of 7He is determined by correlations of two neutrons in the states 6He (0+), 6He (2+) and one neutron in the shell p3/2. The 4He+3n structure is not manifested in the ground state of 7He. The obtained results are consistent with the known data on considerable mixture of configurations “6He in its ground and first excited states plus a neutron” in the ground state of 7He. Comparison of the diffraction components of the differential cross-sections of the charge-exchange reactions (t, 3He) measured on 6Li and 7Li allowed extracting the radius of particle-unstable nucleus 7He. The latter occurred to be approximately equal to those of 6He and 8He. The obtained result indicates to existence of the halo-like structure in 7He.