Angular Distributions Of Cross Section Research Articles

Study of the one-neutron transfer reaction in 18O + 76Se collision at 275 MeV in the context of the NUMEN project

Heavy-ion one-nucleon transfer reactions are promising tools to investigate single-particle configurations in nuclear states, with and without the excitation of the core degrees of freedom. An accurate determination of the spectroscopic amplitudes of these configurations is essential for the study of other direct reactions as well as beta-decays. In this context, the 76Se(18O,17O)77Se one-neutron transfer reaction gives a quantitative access to the relevant single particle orbitals and core polarization transitions built on 76Se. This is particularly relevant, since it provides data-driven information to constrain nuclear structure models for the 76Se nucleus.The excitation energy spectrum and the differential cross section angular distributions of this nucleon transfer reaction was measured at 275 MeV incident energy for the first time using the MAGNEX large acceptance magnetic spectrometer. The data are compared with calculations based on distorted wave Born approximation and coupled channel Born approximation adopting spectroscopic amplitudes for the projectile and target overlaps derived by large-scale shell model calculations and interacting boson-fermion model.These reactions are studied in the frame of the NUMEN project. The NUMEN (NUclear Matrix Elements for Neutrinoless double beta decay) project was conceived at the Istituto Nazionale di Fisica Nucleare–Laboratori Nazionali del Sud (INFN-LNS) in Catania, Italy, aiming at accessing information about the nuclear matrix elements (NME) of neutrinoless double beta decay (0νββ) through the study of the heavy-ion induced double charge exchange (DCE) reactions on various 0νββ decay candidate targets. Among these, the 76Se nucleus is under investigation since it is the daughter nucleus of 76Ge in the 0νββ decay process.

Analysis of the one-neutron transfer reaction in O18+Se76 collisions at 275 MeV

Purpose: We want to analyze transitions to low-lying excited states of the residual and ejectile nuclei in the 76Se(18O, 17O) 77Se one-neutron stripping reaction at 275-MeV incident energy and determine the role of single-particle and core excitation in the description of the measured cross sections. In addition, we explore the sensitivity of the calculated cross section to different nuclear structure models. Methods: The excitation energy spectrum and the differential cross-section angular distributions are measured using the MAGNEX large acceptance magnetic spectrometer for the detection of the ejectiles and the missing mass technique for the reconstruction of the reaction kinematics. The data are compared with calculations based on distorted-wave Born approximation, coupled-channels Born approximation, and coupled reaction channels adopting spectroscopic amplitudes for the projectile and target overlaps derived by large-scale shell-model calculations and interacting boson-fermion model. Results: Peaks in the energy spectra corresponding to groups of unresolved transitions to 77Se and 17O are identified. The experimental cross sections are extracted and compared to theoretical calculations. A remarkable agreement is found, without using any scaling factors, demonstrating that the adopted models for nuclear structure and reaction take into account the relevant aspects of the studied processes. The main transitions which contribute to the cross section of each peak are identified.

Multichannel experimental and theoretical constraints for the Cd116(Ne20,F20)In116 charge exchange reaction at 306 MeV

Charge exchange (CE) reactions offer a major opportunity to excite nuclear isovector modes, providing clues about the nuclear interaction in the medium. Moreover, double charge exchange (DCE) reactions are proving to be a tempting tool to access nuclear transition matrix elements (NME) related to double beta-decay processes. Through a multi-channel experimental analysis and a consistent theoretical approach of the $^{116}$Cd($^{20}$Ne,$^{20}$F)$^{116}$In single charge exchange (SCE) reaction at 306 MeV, we aim at disentangling from the experimental cross section the contribution of the competing mechanisms, associated with second or higher order sequential transfer and inelastic processes. We measured excitation energy spectra and absolute cross sections for elastic + inelastic, one-proton transfer and SCE channels, using the MAGNEX large acceptance magnetic spectrometer to detect the ejectiles. For the first two channels, we also extracted the experimental cross section angular distributions. The experimental data are compared with theoretical predictions obtained by performing two-step distorted wave Born approximation and coupled reaction channel calculations. We employ spectroscopic amplitudes for single-particle transitions derived within a large-scale shell model approach and different optical potentials for modeling the initial and the final state interactions. The present study significantly mitigates the possible model dependence existing in the description of these complex reaction mechanisms, thanks to the reproduction of several channels at once. In particular, our work demonstrates that the two-step transfer mechanisms produce a non negligible contribution to the total cross section of the $^{116}$Cd($^{20}$Ne,$^{20}$F)$^{116}$In reaction channel, although a relevant fraction is still missing, being ascribable to the direct SCE mechanism, which is not addressed here.

O18+Se76 elastic and inelastic scattering at 275 MeV

Background: An accurate description of the initial and final state interactions in the O18+Se76 collision is demanded by the NUMEN project. The study of single and double charge exchange nuclear reactions is the main purpose for NUMEN, since these can be used as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To date, the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for the NUMEN double charge exchange studies are poorly known. The O18+Se76 case, here under study, is particularly relevant due to its connection with the Ge76 neutrinoless double-β decay. Purpose: In this work the authors want to characterize the initial-state interaction for the O18+Se76 reactions at 275 MeV incident energy determining the optical potential and evaluating the effect of couplings with the inelastic scattering on the elastic channel. Methods: The angular distributions of differential cross section were measured in the angular region between 4∘ and 22∘ in the center-of-mass reference frame. The cross sections were compared with theoretical calculations, that adopt different optical potentials. Coupling effects on the elastic channel were determined into the coupled channels formalism. Results: The excitation energy spectrum of the colliding nuclei and the cross section angular distributions were measured with satisfactory energy resolution. The elastic scattering cross section is not well reproduced in the full angular range explored when the optical model approach is adopted. A good agreement is found using coupled channel calculations. The initial state interaction for the O18+Se76 nuclear reactions at 275 MeV is determined. Conclusions: Coupled channels effects are crucial to obtain a good description of the measured elastic and inelastic channels cross sections, even at large transferred momenta where the optical model approach fails in reproducing the experimental data. The role of channel coupling could be relevant also in the analysis of other open reaction channels in the same collision and should be accounted for in double charge exchange analyses as well.Received 19 December 2020Revised 6 October 2021Accepted 10 November 2021DOI:https://doi.org/10.1103/PhysRevC.104.054610©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsLow & intermediate energy heavy-ion reactionsNuclear reactionsNuclear structure & decaysNucleon-nucleon interactionsTransfer reactionsProperties59 ≤ A ≤ 896 ≤ A ≤ 19TechniquesCollective modelsNuclear data analysis & compilationNuclear reaction analysisOptical, coupled-channel & distorted wave modelsSpectrometers & spectroscopic techniquesNuclear Physics

One-proton transfer reaction for the O18+Ti48 system at 275 MeV

Single-nucleon transfer reactions are processes that selectively probe single-particle components of the populated many-body nuclear states. In this context, recent efforts have been made to build a unified description of the rich nuclear spectroscopy accessible in heavy-ion collisions. An example of this multichannel approach is the study of the competition between successive nucleon transfer and charge exchange reactions, the latter being of particular interest in the context of single and double beta decay studies. To this extent, the one-proton pickup reaction Ti48(O18,F19)Sc47 at 275 MeV was measured for the first time, under the NUMEN experimental campaign. Differential cross-section angular distribution measurements for the F19 ejectiles were performed at INFN-LNS in Catania by using the MAGNEX large acceptance magnetic spectrometer. The data were analyzed within the distorted-wave and coupled-channels Born approximation frameworks. The initial and final-state interactions were described adopting the São Paulo potential, whereas the spectroscopic amplitudes for the projectile and target overlaps were derived from shell-model calculations. The theoretical cross sections are found to be in very good agreement with the experimental data, suggesting the validity of the optical potentials and the shell-model description of the involved nuclear states within the adopted model space.1 MoreReceived 27 May 2021Accepted 8 September 2021DOI:https://doi.org/10.1103/PhysRevC.104.034617©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsDouble beta decayLow & intermediate energy heavy-ion reactionsNuclear reactionsTransfer reactionsTechniquesOptical, coupled-channel & distorted wave modelsSpectrometers & spectroscopic techniquesNuclear Physics

Cross Sections for Neutron-Production from 6- and 10-MeV Neutrons Incident on 10B and 11B

Using time-of-flight techniques, we have measured neutron emission spectra from 6- and 10-MeV incident neutron energies on 10B and 11B for laboratory angles between 20 and 145 deg using the unique neutron source reaction 1H(t,n). Double-differential cross sections and their integrated values have been extracted for elastic and inelastic processes, and their integrated values are summarized. In cases where discrete scattering peaks could be analyzed, differential cross-section angular distributions have been extracted and are compared to other results and to evaluated nuclear data.

Sensitivity of analyzing power to distorting potentials in the quasifree reaction Ca40(p,pα)Ar36 at 100 MeV incident energy: Comparison with Be9 and C12 targets

Background: The ($p,p\ensuremath{\alpha}$) knockout reaction is useful for the study of preformed $\ensuremath{\alpha}$ clusters in atomic nuclei. At quasifree kinematic conditions above an incident energy of about 100 MeV the cross section and analyzing-power angular distributions extracted from the ($p,p\ensuremath{\alpha}$) knockout reaction are anticipated to resemble its free two-body counterparts. Several ($p,p\ensuremath{\alpha}$) knockout studies in the incident-energy range of 100--150 MeV on targets up to $^{12}\mathrm{C}$ confirm the predicted equivalence. However, the only experiment on $^{40}\mathrm{Ca}(p,p\ensuremath{\alpha})^{36}\mathrm{Ar}$ appears to fail the expectation spectacularly.Purpose: The reason for the drastic discrepancy between the experimental analyzing-power angular distribution for $^{40}\mathrm{Ca}(p,p\ensuremath{\alpha})^{36}\mathrm{Ar}$ and the trend of free elastic scattering of protons from $^{4}\mathrm{He}$ is investigated.Method: Guidance in general from the distorted-wave impulse approximation (DWIA) theory is employed. Specific focused theoretical calculations are performed.Results: As expected, for the ($p,p\ensuremath{\alpha}$) reaction on several light target masses up to $^{12}\mathrm{C}$, comparable cross section and analyzing-power angular distributions resemble free $^{4}\mathrm{He}(p,p)^{4}\mathrm{He}$ elastic scattering to a remarkable extent. The DWIA treatment for the $^{40}\mathrm{Ca}(p,p\ensuremath{\alpha})^{36}\mathrm{Ar}$ reaction, however, needs a more careful selection of the distortion optical-model parameters in the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Ar}$ outgoing channel. Global optical-model potentials used in the published work reproduce neither analyzing-power distribution of the $^{40}\mathrm{Ca}(p,p\ensuremath{\alpha})^{36}\mathrm{Ar}$ reaction, nor $\ensuremath{\alpha}\text{\ensuremath{-}}^{36}\mathrm{Ar}$ elastic scattering cross-section angular distributions. Use of appropriate optical potentials resolves the problem.Conclusions: The use of appropriate optical-model potentials which describe elastic scattering of $\ensuremath{\alpha}$ particles from $^{36}\mathrm{Ar}$ correctly appears to be crucial. The problem reported previously in the literature is resolved to a remarkable extent. There is a need to explore the two-body aspects of the quasifree ($p,p\ensuremath{\alpha}$) reaction for heavier targets further.

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.

Ne20+Ge76 elastic and inelastic scattering at 306 MeV

Background: Double charge exchange (DCE) nuclear reactions have recently attracted much interest as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-beta decay. In this framework, a good description of the reaction mechanism and a complete knowledge of the initial and final-state interactions are mandatory. Presently, not enough is known about the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for future DCE studies. Among these, the 20Ne + 76Ge DCE reaction is particularly relevant due to its connection with 76Ge double-beta decay. Purpose: We intend to characterize the initial-state interaction for the 20Ne + 76Ge reactions at 306 MeV bombarding energy and determine the optical potential and the role of the couplings between elastic channel and inelastic transitions to the first low-lying excited states. Methods: We determine the experimental elastic and inelastic scattering cross-section angular distributions, compare the theoretical predictions by adopting different models of optical potentials with the experimental data, and evaluate the coupling effect through the comparison of the distorted-wave Born approximation calculations with the coupled channels ones. Results: Optical models fail to describe the elastic angular distribution above the grazing angle (9.4{\deg}). A correction in the geometry to effectively account for deformation of the involved nuclear systems improves the agreement up to about 14{\deg}. Coupled channels effects are crucial to obtain good agreement at large angles in the elastic scattering cross section.

Analyzing powers and the role of multistep processes in the C12(Li7,t)O16 reaction

The analyzing powers $^{T}T_{10}\phantom{\rule{0.16em}{0ex}},^{T}T_{20}$, and $^{T}T_{30}$ for the $^{12}\mathrm{C}(^{7}\mathrm{Li},t$) reaction were measured and combined with new and previously determined angular distributions to probe the role of multistep processes through coupled channel Born approximation (CCBA) calculations employing new $\ensuremath{\alpha}$-particle spectroscopic amplitudes calculated with the phenomenological shell model in the unrestricted $psd$ space. Good descriptions of the cross-section angular distributions could be obtained except for the larger angles for the 6.05 MeV ${0}^{+}$ and 6.13 MeV ${3}^{\ensuremath{-}}$ states, while the analyzing powers were not generally described. The calculations presented demonstrate the sensitivity of the angular distributions of both the differential cross sections and the analyzing powers to various multistep routes. While the measured analyzing power $^{T}T_{30}$ is roughly zero for all states, the various CCBA calculations produced large and highly oscillatory values for this observable, showing that other multistep processes must be present beyond those taken into account in this work. Standard distorted wave Born approximation (DWBA) calculations were also carried out and these show considerable differences from the CCBA results but the description of the analyzing powers, while slightly improved, is still poor.

Simplistic distorted-wave Born approximation interpretation of the 11Li(p,t)9Li reaction

The reaction [Formula: see text]Li([Formula: see text])9Li(gs) at an incident energy of 4.3[Formula: see text]MeV is interpreted in terms of a simplistic distorted-wave Born approximation, which assumes simultaneous transfer of the halo neutrons. The halo neutrons involved in the reaction is treated as either a di-neutron cluster or individual entities. Either of these approaches appears to be a good approximation of the reaction mechanism, as would be expected from earlier studies. The dominant contribution to the yield of the reaction comes from the known (2[Formula: see text])2 neutron structure component of the ground state of [Formula: see text]Li. Furthermore, the cross-section angular distribution seems to be relatively insensitive to the fact that [Formula: see text]Li has an anomalously large radius due to its Borromean halo properties. Significantly this simple treatment of the reaction is in much better agreement with the experimental angular distribution than previous sophisticated calculations. The relevance and limitations of a more advanced theoretical treatment which includes coupled channel and sequential transfer are discussed in the context of the present results.

Nuclear structure studies performed using the (18O,16O) two-neutron transfer reactions

Excitation energy spectra and absolute cross section angular distributions were measured for the 13C(18O,16O)15C two-neutron transfer reaction at 84 MeV incident energy. This reaction selectively populates two-neutron configurations in the states of the residual nucleus. Exact finite-range coupled reaction channel calculations are used to analyse the data. Two approaches are discussed: the extreme cluster and the newly introduced microscopic cluster. The latter makes use of spectroscopic amplitudes in the centre of mass reference frame, derived from shell-model calculations using the Moshinsky transformation brackets. The results describe well the experimental cross section and highlight cluster configurations in the involved wave functions.

Photoproduction of Λ and Σ0 hyperons off protons with linearly polarized photons at Eγ=1.5–3.0 GeV

We report the measurement of the $\gamma p \rightarrow K^{+}\Lambda$ and $\gamma p \rightarrow K^{+}\Sigma^{0}$ reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward $K^{+}$ production angles using linearly polarized tagged-photon beams in the range of $E_{\gamma}=1.5$--3.0 GeV. With increasing photon energy, the cross sections for both $\gamma p \rightarrow K^{+}\Lambda$ and $\gamma p \rightarrow K^{+}\Sigma^{0}$ reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at $E_{\gamma}=1.5$--3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of $t$-channel exchange, is observed for the production of $\Lambda$ in the whole observed energy range. A lack of similar feature for $\Sigma^{0}$ production reflects a less dominant role of $t$-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of $K^{*}$ exchange in the $t$ channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the $t$ channel and the contributions of nucleon resonances indicates the major role of $t$-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime.

Two-neutron clustering aspects in the transitions induced by the 13C(18O,16O)15C reaction at 84 MeV incident energy

The 13C(18O,16O)15C reaction is studied at 84 MeV incident energy. The measured cross-section angular distributions are analysed by exact finite-range coupled reaction channel calculations. The two-particle wave functions are extracted using the extreme cluster and the independent coordinate scheme with shell-model derived coupling strengths.

Microscopic cluster model for the description of new experimental results on the C13(O18,O16)C15 two-neutron transfer at 84 MeV incident energy

The $^{13}\mathrm{C}(^{18}\mathrm{O},^{16}\mathrm{O})^{15}\mathrm{C}$ reaction is studied at 84 MeV incident energy. Excitation energy spectra and absolute cross-section angular distributions for the strongest transitions are measured with good energy and angular resolutions. Strong selectivity for two-neutron configurations in the states of the residual nucleus is found. The measured cross-section angular distributions are analyzed by exact finite-range coupled reaction channel calculations. The two-particle wave functions are extracted using the extreme cluster and the independent coordinate scheme with shell-model derived coupling strengths. A new approach also is introduced, the microscopic cluster, in which the spectroscopic amplitudes in the center-of-mass reference frame are derived from shell-model calculations using the Moshinsky transformation brackets. This new model is able to describe well the experimental cross section and to highlight cluster configurations in the involved wave functions.

Distorted-wave Born approximation study of the 11Li(p,t)9Li reaction

The reaction 11Li(p,t)9Li(gs) at an incident energy of 4 MeV is treated in terms of a simplistic distorted-wave Born approximation transfer. The halo neutrons involved in the reaction are treated as a di-neutron cluster transferred in a simultaneous process. This appears to be a good approximation of the mechanism. The dominant contribution to the reaction comes from the known (1s1/2)2 structure component of the ground state of 11Li, and the cross section angular distribution seems to be relatively insensitive to the fact that 11 Li has an anomalously large radius due to its Borromean halo properties. Significantly this simple treatment of the reaction is in much better agreement with the experimental angular distribution than a more sophisticated calculation.

Extracting the cross section angular distributions for15C high-energy resonance excited via the (18O,16O) two-neutron transfer reaction

The 13 C( 18 O, 16 O) 15 C reaction has been studied at 84 MeV incident energy. The ejectiles have been momentum analized by the MAGNEX spectrometer and 15 C excitation energy spectra have been obtained up to about 20 MeV. In the region above the two-neutron separation energy, a bump has been observed at 13.7 MeV. The extracted cross section angular distribution for this structure, obtained by using different models for background, displays a clear oscillating pattern, typical of resonant state of the residual nucleus.

Signals of the Giant Pairing Vibration in 14C and 15C nuclei populated by (18O,16O) two-neutron transfer reactions

The 12C(18O,16O)14C and 13C(18O,16O)15C reactions have been explored at 84MeV incident energy and the ejectiles have been detected at forward angles by the MAGNEX spectrometer. Thanks to the peculiarities of MAGNEX and to the ray-reconstruction technique, high-resolution spectra up to 22MeV excitation energy and high-quality cross-section angular distributions have been obtained. In the region above the two-neutron emission threshold, unknown wide structures have been observed in both the 14C and 15C residual nuclei. A detailed analysis of such resonances identifies them as the long-searched Giant Pairing Vibration. These data represent the first experimental signature of it.

Erratum: Incident-energy dependence of angular distributions of cross section and analyzing power for theNi58(p⃗,He3)Co56reaction between 80 and 120 MeV [Phys. Rev. C91, 024614 (2015)

Erratum: Incident-energy dependence of angular distributions of cross section and analyzing power for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mrow><mml:mmultiscripts><mml:mi>Ni</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>58</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mover accent="true"><mml:mi>p</mml:mi><mml:mo>⃗</mml:mo></mml:mover><mml:mo>,</mml:mo><mml:mrow><mml:mmultiscripts><mml:mi>He</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mspace width="0.16em" /><mml:mrow><mml:mmultiscripts><mml:mi>Co</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>56</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:mrow></mml:math>reaction between 80 and 120 MeV [Phys. Rev. C<b>91</b>, 024614 (2015)

Incident-energy dependence of angular distributions of cross section and analyzing power for theNi58(p⃗,He3)Co56reaction between 80 and 120 MeV

Incident-energy dependence of angular distributions of cross section and analyzing power for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">Ni</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>58</mml:mn></mml:mrow></mml:mmultiscripts><mml:mo>(</mml:mo><mml:mrow><mml:mover accent="true"><mml:mi>p</mml:mi><mml:mo>⃗</mml:mo></mml:mover><mml:mo>,</mml:mo><mml:mmultiscripts><mml:mi mathvariant="normal">He</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:mmultiscripts><mml:mo>)</mml:mo><mml:mmultiscripts><mml:mi mathvariant="normal">Co</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>56</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math>reaction between 80 and 120 MeV