Search

The isovector and isoscalar components of neutron-proton pairing are investigated in the N=Z unstable nuclei of the fp-shell through the two-nucleon transfer reaction (p,$^{3}$He) in inverse kinematics. The combination of particle and gamma-ray detection with radioactive beams of $^{56}$Ni and $^{52}$Fe, produced by fragmentation at the GANIL/LISE facility, made it possible to carry out this study for the first time in a closed and an open-shell nucleus in the fp-shell. The transfer cross-sections for ground-state to ground-state (J=0$^{+}$, T=1) and to the first (J=1$^{+}$, T=0) state were extracted for both cases together with the transfer cross-section ratios σ(0+,T=1)/σ(1+,T=0). They are compared with second-order distorted-wave born approximation (DWBA) calculations. The enhancement of the ground-state to ground-state pair transfer cross-section close to mid-shell, in $^{52}$Fe, points towards a superfluid phase in the isovector channel. For the “deuteron-like” transfer, very low cross-sections to the first (J=1$^{+}$, T=0) state were observed both for $^{56}$Ni(p,$^{3}$He) and $^{52}$Fe(p,$^{3}$He) and are related to a strong hindrance of this channel due to spin-orbit effect. No evidence for an isoscalar deuteron-like condensate is observed.

International audience; The last proton bound calcium isotope $^{35}$Ca has been studied for the first time, using the $^{37}$Ca($p, t$)$^{35}$Ca two neutron transfer reaction. The radioactive $^{37}$Ca nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce tritons $t$ that were detected in the MUST2 detector array, in coincidence with the heavy residues Ca or Ar. The atomic mass of $^{35}$Ca and the energy of its first 3/2$^+$ state are reported. A large $N=16$ gap of 4.61(11) MeV is deduced from the mass measurement, which together with other measured properties, makes $^{36}$Ca a doubly-magic nucleus. The $N = 16$ shell gaps in $^{36}$Ca and $^{24}$O are of similar amplitude, at both edges of the valley of stability. This feature is discussed in terms of nuclear forces involved, within state-of-the-art shell model calculations. Even though the global agreement with data is quite convincing, the calculations underestimate the size of the $N = 16$ gap in 36Ca by 840(110) keV.

International audience; The low-lying structure of $^{15}$C has been investigated via the neutron-removal $^{16}$C$(d,t)$ reaction. Along with bound neutron sd-shell hole states, unbound p-shell hole states have been firmly confirmed. The excitation energies and the deduced spectroscopic factors of the cross-shell states are an important measure of the $[(p)^{-1}(sd)^{2}]$ neutron configurations in $^{15}$C. Our results show a very good agreement with shell-model calculations using the SFO-tls interaction for $^{15}$C. However, a modification of the $p$-$sd$ and $sd$-$sd$ monopole terms was applied in order to reproduce the $N=9$ isotone $^{17}$O. In addition, the excitation energies and spectroscopic factors have been compared to the first calculations of $^{15}$C with the $ab~ initio$ self-consistent Green's function method employing the NNLO$_{sat}$ interaction. The results show the sensitivity to the size of the $N=8$ shell gap and highlight the need of going beyond the current truncation scheme in the theory.

Background: Significant uncertainties exist in the $^{22}$Ne($p,γ$)$^{23}$Na reaction rate due to the possible influence of an unobserved resonance state at $E_\mathrm{x} = 8862$ keV ($E_\mathrm{r,c.m.} = 68$ keV). Purpose: To study excited states in $^{23}$Na above the proton threshold to determine if this resonance state, and other unconfirmed resonance states in $^{23}$Na, exist. Methods: The non-selective proton inelastic scattering reaction at low energies was used to search for excited states in $^{23}$Na above the proton threshold. Protons scattered from various targets were momentum-analysed in the Q3D magnetic spectrograph at the Maier-Leibnitz Laboratorium, Munich, Germany. Results: The resonance states reported at $E_\mathrm{x} = 8862$, $8894$ and $9000$ keV were not observed in the present experiment at any angle. This result, combined with other non-observations of these resonance states in other reactions, results in a strong presumption against the existence of these resonance states. Conclusions: The previously reported resonance states at $E_\mathrm{x} = 8862$, $8894$ and $9000$ keV are unlikely to exist and should be omitted from future evaluations of the $^{22}$Ne($p,γ$)$^{23}$Na reaction rates. Indirect studies using low-energy proton inelastic scattering are a simple and yet exceptionally powerful tool in helping to constrain astrophysical reaction rates by providing non-selective information of the excited states of nuclei., 1 single-panel figure and 5 double-panel figures. 1 table of results. Paper to be submitted to Physical Review C

The 12C + 16O fusion reaction plays a role in the later stages of carbon burning, influencing the evolution of both massive stars and Type Ia Supernovae: when most of the carbon is depleted, by the main fusion reaction 12C + 12C, the abundance of 16O nuclei is significantly higher. Therefore 12C + 16O can indeed have a strong impact on the process. In this brief contribution, preliminary data analysis results of a new indirect measurement of the 12C + 16O, performed at astrophysical energies via the Trojan Horse Method, will be presented and discussed.

International audience; [Background] Abundance anomalies in some globular clusters, such as the enhancement of potassium and the depletion of magnesium, can be explained in terms of an earlier generation of stars polluting the presently observed ones. It was shown that the potential range of temperatures and densities of the polluting sites depends on the strength of a few number of critical reaction rates. The reaction has been identified as one of these important reactions. [Purpose] The key ingredient for evaluating the thermonuclear reaction rate is the strength of the resonances which, at low energy, are proportional to their proton width. Therefore the goal of this work is to determine the proton widths of unbound 31P states. [Method] States in 31P were studied at the Maier-Leibnitz-Laboratorium using the one-proton transfer reaction. Deuterons were detected with the Q3D magnetic spectrometer. Angular distribution and spectroscopic factors were extracted for 27 states, and proton widths and resonance strengths were calculated for the unbound states. [Results] Several unbound states have been observed for the first time in a one-proton transfer reaction. Above 20 MK, the reaction rate is now entirely estimated from the observed properties of states. The reaction rate uncertainty from all resonances other than the resonance has been reduced down to less than a factor of two above that temperature. The unknown spin and parity of the resonance dominates the uncertainty in the rate in the relevant temperature range. [Conclusion] The remaining source of uncertainty on the reaction rate comes from the unknown spin and parity of the resonance which can change the reaction rate by a factor of ten in the temperature range of interest.

Detailed spectroscopy of the neutron-deficient nucleus $^{36}$Ca was obtained up to 9 MeV using the $^{37}$Ca($p$,$d$)$^{36}$Ca and the $^{38}$Ca($p$,$t$)$^{36}$Ca transfer reactions. The radioactive nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid Hydrogen target CRYPTA, to produce light ejectiles (the deuteron $d$ or triton $t$) that were detected in the MUST2 detector array, in coincidence with the heavy residues %identified by a zero degree detection system. %States have been measured up to 9 MeV. Our main findings are: i) a similar shift in energy for the 1$^+_1$ and 2$^+_1$ states by about -250 keV, as compared to the mirror nucleus $^{36}$S, ii) the discovery of an intruder 0$^+_2$ state at 2.83(13) MeV, which appears below the first 2$^+$ state, in contradiction with the situation in $^{36}$S, and iii) a tentative 0$^+_3$ state at 4.83(17) MeV, proposed to exhibit a bubble structure with two neutron vacancies in the 2s$_{1/2}$ orbit. The inversion between the 0$^+_2$ and 2$^+_1$ states is due to the large mirror energy difference (MED) of -516(130) keV for the former. This feature is reproduced by Shell Model (SM) calculations, using the $sd$-$pf$ valence space, predicting an almost pure intruder nature for the 0$^+_2$ state, with two protons (neutrons) being excited across the $Z$=20 magic closure in $^{36}$Ca ($^{36}$S). This mirror system has the largest MEDs ever observed, if one excludes the few cases induced by the effect of the continuum., Paper of 5 pages, 3 figures. Contains also a supplementary material of 3 pages and 4 figures

The 26Al abundance holds a special role in present-day astrophysics, since it is a probe of active nucleosynthesis in the Galaxy and a valuable constraint of Galactic core-collapse supernovae rate. It is estimated through the detection of the 1809-keV γ-line of the daughter 26Mg and from the superabundance of 26Mg in comparison with the most abundant 24Mg isotope in meteorites. Accurate knowledge of the reaction rates involving 26Al, its stable counterpart 27Al and 24Mg is then mandatory. Moreover, these nuclei enter the MgAl cycle playing an important role in the production of Al and Mg isotopes. Recently, high-resolution stellar surveys have shown that the Mg-Al anti-correlation in red giants of globular clusters may hide the existence of multiple stellar populations, and that the relative abundances of Mg isotopes may not show correlation with Al.The common thread running through these astrophysical scenarios is the 27Al(p,α)24Mg reaction, which is the main 27Al destruction channel and directly correlates its abundance with the 24Mg one. Since available reaction rates show an order of magnitude uncertainty owing to the vanishingly small cross section at astrophysical energies, we have applied the Trojan Horse Method to deduce the reaction rate with no need of extrapolation. The indirect measurement made it possible to assess the contribution of the 84-keV resonance and to lower the upper limits on the strength of nearby resonances, with potential important impact for astrophysics. In particular, modifications in the 27Al and 24Mg abundances up to ∼30% are predicted for intermediate mass stars.

The structure of the unbound 15F nucleus is investigated using the inverse kinematics resonant scattering of a radioactive 14O beam impinging on a CH2 target. The analysis of 1H(14O,p)14O and 1H(14O,2p)13N reactions allowed the confirmation of the previously observed narrow 1/2− resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2− and 3/2− resonances. The newly observed levels decay by 1p emission to the ground of 14O, and by sequential 2p emission to the ground state of 13N via the 1− resonance of 14O. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2− and 3/2− resonances may be collectivized by the continuum coupling to nearby 2p- and 1p-decay channels. The observed excitation function 1H(14O,p)14O and resonance spectrum in 15F are well reproduced in the unified framework of the GSM.

We have measured the gamma-ray line production cross sections in proton-induced nuclear reactions on various target nuclei abundant in astrophysical sites over the incident energy range of Ep = 30 - 200 MeV. We carried out experimental campaigns in joint collaboration at the K = 200 cyclotron of iThemba LABS using a high-energy resolution, high-efficiency detection array composed of 8 Compton-suppressed clover detectors comprising 32 HP-Ge crystals for recording the gamma-ray spectra. In the current paper, we focus on de-excitation lines produced in proton irradiations of natC and Mylar targets. In particular, on the prominent 4.439 and 6.129 MeV lines of $^{12}$C and $^{16}$O which are among the strongest lines emitted in solar flares and in interactions of low-energy cosmic rays with the gas and dust of the inner galaxy. We report new gamma-ray production experimental cross section data for ten nuclear lines that we compare to previous low-energy data sets from the literature, to the predictions of the TALYS code of modern nuclear reactions and to a semi-empirical compilation. In first approach, performing calculations with default input parameters of TALYS we observed substantial deviations between the predicted cross sections and experimental data. Then, using modified optical model potential and nuclear level deformation parameters as input data we generated theoretical excitation functions for the above two main lines fully consistent with experimental data. In contrast, the experimental data sets for the other eight analyzed lines from the two proton-irradiated targets exhibit significant deviations with the predicted cross section values. We also report line-shape experimental data for the line complex observed at $E_g$ = 4.44 MeV in irradiations of the two targets. Finally, we emphasize the astrophysical implications of our results., Comment: 44 pages, 7 tables, 13 figures

[Background] Abundance anomalies in some globular clusters, such as the enhancement of potassium and the depletion of magnesium, can be explained in terms of an earlier generation of stars polluting the presently observed ones. It was shown that the potential range of temperatures and densities of the polluting sites depends on the strength of a few number of critical reaction rates. The reaction has been identified as one of these important reactions. [Purpose] The key ingredient for evaluating the thermonuclear reaction rate is the strength of the resonances which, at low energy, are proportional to their proton width. Therefore the goal of this work is to determine the proton widths of unbound 31P states. [Method] States in 31P were studied at the Maier-Leibnitz-Laboratorium using the one-proton transfer reaction. Deuterons were detected with the Q3D magnetic spectrometer. Angular distribution and spectroscopic factors were extracted for 27 states, and proton widths and resonance strengths were calculated for the unbound states. [Results] Several unbound states have been observed for the first time in a one-proton transfer reaction. Above 20 MK, the reaction rate is now entirely estimated from the observed properties of states. The reaction rate uncertainty from all resonances other than the resonance has been reduced down to less than a factor of two above that temperature. The unknown spin and parity of the resonance dominates the uncertainty in the rate in the relevant temperature range. [Conclusion] The remaining source of uncertainty on the reaction rate comes from the unknown spin and parity of the resonance which can change the reaction rate by a factor of ten in the temperature range of interest.

Globular clusters contain multiple stellar populations, with some previous generation of stars polluting the current stars with heavier elements. Understanding the history of globular clusters is helpful in understanding how galaxies merged and evolved and therefore constraining the site or sites of this historic pollution is a priority. The acceptable temperature and density conditions of these polluting sites depend on critical reaction rates. In this paper, three experimental studies helping to constrain astrophysically important reaction rates are briefly discussed., Comment: Submission to conference proceedings of INPC2022 in Cape Town

International audience; Neutron transfer reaction measurements, relevant to the neutrinoless double β decay candidate Sn124 and its daughter Te124, have been performed. Precise measurements of both neutron addition [(d,p),(He4,He3)] and removal [(p,d),(He3,He4)] cross sections have been used to determine the occupation of valence orbitals pertinent to neutrinoless double β decay in these two nuclei. This information could be used to constrain calculations of the nuclear matrix element for the neutrinoless double β decay of Sn124. The change in the ground-state neutron vacancies in proceeding from Sn124 to Te124 is mainly found in the d3/2,5/2 and h11/2 orbitals. The occupancies of states near the Fermi level are in reasonable agreement with shell model calculations.

International audience; Detailed spectroscopy of the neutron-deficient nucleus Ca36 was obtained up to 9 MeV using the Ca37(p,d)Ca36 and the Ca38(p,t)Ca36 transfer reactions. The radioactive nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce light ejectiles (the deuteron d or triton t) that were detected in the MUST2 detector array, in coincidence with the heavy residues identified by a zero-degree detection system. Our main findings are (i) a similar shift in energy for the 11+ and 21+ states by about -250 keV, as compared with the mirror nucleus S36; (ii) the discovery of an intruder 02+ state at 2.83(13) MeV, which appears below the first 2+ state, in contradiction with the situation in S36; and (iii) a tentative 03+ state at 4.83(17) MeV, proposed to exhibit a bubble structure with two neutron vacancies in the 2s1/2 orbit. The inversion between the 02+ and 21+ states is due to the large mirror energy difference (MED) of -516(130) keV for the former. This feature is reproduced by shell model calculations, using the sd-pf valence space, predicting an almost pure intruder nature for the 02+ state, with two protons (neutrons) being excited across the Z=20 magic closure in Ca36 (S36). This mirror system has the largest MEDs ever observed, if one excludes the few cases induced by the effect of the continuum.

International audience; The structure of the unbound F15 nucleus is investigated using the inverse kinematics resonant scattering of a radioactive O14 beam impinging on a CH2 target. The analysis of H1(O14,p)O14 and H1(O14,2p)N13 reactions allowed the confirmation of the previously observed narrow 1/2− resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2− and 3/2− resonances. The newly observed levels decay by 1p emission to the ground of O14, and by sequential 2p emission to the ground state of N13 via the 1− resonance of O14. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2− and 3/2− resonances may be collectivized by the continuum coupling to nearby 2p- and 1p-decay channels. The observed excitation function H1(O14,p)O14 and resonance spectrum in F15 are well reproduced in the unified framework of the GSM.

The structure of the unbound $^{15}$F nucleus is investigated using the inverse kinematics resonant scattering of a radioactive $^{14}$O beam impinging on a CH$_2$ target. The analysis of $^{1}$H($^{14}$O,p)$^{14}$O and $^{1}$H($^{14}$O,2p)$^{13}$N reactions allowed the confirmation of the previously observed narrow $1/2^{-}$ resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2$^{-}$ and 3/2$^{-}$ resonances. The newly observed levels decay by 1p emission to the ground of $^{14}$O, and by sequential 2p emission to the ground state (g.s.) of $^{13}$N via the $1^-$ resonance of $^{14}$O. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2$^{-}$ and 3/2$^{-}$ resonances may be collectivized by the continuum coupling to nearby 2p- and 1p- decay channels. The observed excitation function $^{1}$H($^{14}$O,p)$^{14}$O and resonance spectrum in $^{15}$F are well reproduced in the unified framework of the GSM., Comment: 7 pages, 4 figures

A recent sensitivity study has shown that the $^{35}$K$(p,\gamma)^{36}$Ca reaction is one of the ten $(p,\gamma)$ reaction rates that could significantly impact the shape of the calculated X-ray burst light curve. In this work, we propose to reinvestigate the $^{35}$K$(p,\gamma)^{36}$Ca reaction rate, as well as related uncertainties, by determining the energies and decay branching ratios of $^{36}$Ca levels, within the Gamow window, in the 0.5 to 2 GK X-ray burst temperature range. These properties were studied using the one neutron pick-up transfer reaction $^{37}$Ca$(p,d)^{36}$Ca in inverse kinematics using a radioactive beam of $^{37}$Ca at 48 MeV nucleon$^{-1}$. The experiment performed at GANIL, used the liquid Hydrogen target CRYPTA, the MUST2 detector array for the detection of the light charged particles and a zero degree detection system for the outgoing heavy ions. The atomic mass of $^{36}$Ca is confirmed and new resonances have been proposed together with their proton decay branching ratios. This spectroscopic information, used in combination with recent theoretical predictions for the $\gamma$-width, were used to calculate the $^{35}$K$(p,\gamma)^{36}$Ca reaction rate. The recommended rate of the present work was obtain within a uncertainty factor of 2 at 1 sigma. This is consistent, with the previous estimate in the X-ray burst temperature range. A large increase of the reaction rate was found at higher temperatures due to two newly discovered resonances. The $^{35}$K$(p,\gamma)^{36}$Ca thermonuclear reaction rate is now well constrained by the present work in a broad range of temperatures. Our results show that the $^{35}$K$(p,\gamma)^{36}$Ca reaction does not affect the shape of the X-ray burst light curve, and that it can be removed from the list of the few influential proton radiative captures reactions having a strong impact on the light curve., Comment: Published 13 May 2021 in PRC

Stellar nucleosynthesis processes are of vital importance for nuclear physics: all the heavy elements are created by neutron capture reactions that take place in stars. To correctly study such reactions the neutron abundance available in the environment must be known, which means that also the so-called “neutron poisons” must be considered. The present work will focus on the reaction 17O(n,α)14C which removes neutrons from the stellar environment during the s-process. Even though the study of such reactions is of high interest, it still presents several technological problems regarding both the creation and characterization of the neutron beam and the radioprotection of the facility. Therefore, the Trojan Horse Method, an indirect method, has been chosen to study the 17O(n, α)14C reaction in the energy region of astrophysical interest, from 300 keV in the center-of-mass frame down to zero. In the present work, after briefly recalling the main features of the method and reporting on the state of the art for the reaction cross-section measurements, the latest THM experiment will be presented.

The unbound proton-rich nuclei $^{16}$F and $^{15}$F are investigated experimentally and theoretically. Several experiments using the resonant elastic scattering method were performed at GANIL with radioactive beams to determine the properties of the low lying states of these nuclei. Strong asymmetry between $^{16}$F-$^{16}$N and $^{15}$F-$^{15}$C mirror nuclei is observed. The strength of the $nucleon-nucleon$ effective interaction involving the loosely bound proton in the $s_{1/2}$ orbit is significantly modified with respect to their mirror nuclei $^{16}$N and $^{15}$C. The reduction of the effective interaction is estimated by calculating the interaction energies with a schematic zero-range force. It is found that, after correcting for the effects due to changes in the radial distribution of the single-particle wave functions, the mirror symmetry of the $n-p$ interaction is preserved between $^{16}$F and $^{16}$N, while a difference of 63\% is measured between the $p-p$ versus $n-n$ interactions in the second excited state of $^{15}$F and $^{15}$C nuclei. Several explanations are proposed.

The unbound proton-rich nuclei 16F and 15F are investigated experimentally and theoretically. Several experiments using the resonant elastic scattering method were performed at GANIL with radioactive beams to determine the properties of the low lying states of these nuclei. Strong asymmetry between 16F–16N and 15F–15C mirror nuclei is observed. The strength of the nucleon- nucleon effective interaction involving the loosely bound proton in the s1 / 2 orbit is significantly modified with respect to their mirror nuclei 16N and 15C. The reduction of the effective interaction is estimated by calculating the interaction energies with a schematic zero-range force. It is found that, after correcting for the effects due to changes in the radial distribution of the single-particle wave functions, the mirror symmetry of the n- p interaction is preserved between 16F and 16N, while a difference of 63% is measured between the p- p versus n- n interactions in the second excited state of 15F and 15C nuclei. Several explanations are proposed. © 2021, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature. Part of a collection: Cluster Structure and Dynamics of Nuclei - A Tribute to Mahir Hussein. [] Preprint version available at: [https://arxiv.org/abs/2101.02132]

International audience; 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.

International audience; Background: A recent sensitivity study has shown that the K35(p,γ)Ca36 reaction is one of the ten (p,γ) reaction rates that could significantly impact the shape of the calculated x-ray burst light curve. Its reaction rate used up to now in type I x-ray burst calculations was estimated using an old measurement for the mass of Ca36 and theoretical predictions for the partial decay widths of the first 2+ resonance with arbitrary uncertainties. Purpose: In this work, we propose to reinvestigate the K35(p,γ)Ca36 reaction rate, as well as related uncertainties, by determining the energies and decay branching ratios of Ca36 levels, within the Gamow window of x-ray bursts, in the 0.5 to 2 GK temperature range. Method: These properties were studied by means of the one-neutron pickup transfer reaction Ca37(p,d)Ca36 in inverse kinematics using a radioactive beam of Ca37 at 48 MeV nucleon−1. The experiment was performed at the GANIL facility using the liquid hydrogen target CRYPTA, the MUST2 charged particle detector array for the detection of the light charged particles, and a zero degree detection system for the outgoing heavy recoil nuclei. Results: The atomic mass of Ca36 is confirmed and new resonances have been proposed together with their proton decay branching ratios. This spectroscopic information, used in combination with very recent theoretical predictions for the γ-decay width, were used to calculate the K35(p,γ)Ca36 reaction rate. The recommended rate of the present work was obtained within a uncertainty factor of 2 at 1σ. This is consistent with the previous estimate in the x-ray burst temperature range. A large increase of the reaction rate was found at higher temperatures due to two newly discovered resonances. Conclusions: The K35(p,γ)Ca36 thermonuclear reaction rate is now well constrained by the present work in a broad range of temperatures covering those relevant to type I x-ray bursts. Our results show that the K35(p,γ)Ca36 reaction does not affect the shape of the x-ray burst light curve, and that it can be removed from the list of the few influential proton radiative captures reactions having a strong impact on the light curve.

International audience; Nuclear deexcitation lines are regularly observed in the γ-ray emission spectra of strong solar flares. The most prominent lines are produced by interactions of protons and α particles, accelerated up to hundreds of MeV, with abundant nuclei of the solar atmosphere. Analysis and interpretation of these lines, which carry valuable information on the solar flare properties, need cross-section data for the γ-ray line emission in these interactions for a wide particle energy range. To this purpose, we measured the γ-ray emission in interactions of α-particle beams of Eα=50–90 MeV with target foils of C, Mg, Si, and Fe at the center for proton therapy of the Helmholtz-Zentrum Berlin. Setups of three high-purity Ge detectors and one LaBr3:Ce detector have been employed to detect the γ rays in two experiment campaigns. Relatively large distances of the detectors from the target and pulsed beams with sub-ns-wide pulses allowed the separation of beam-induced prompt γ-ray emission from the targets from other γ rays and neutron-induced background. γ-ray production cross sections for about 60 deexcitation lines from excited target nuclei or reaction products have been determined. For the strongest deexcitation lines from the major target isotopes, C12, Mg24, Si28, Fe56, there are now measured cross-section data from reaction threshold to Eα=90 MeV that can be directly used for astrophysical applications like solar flares. Comparison of the results with a cross-section compilation for strong γ-ray lines in solar flare emissions and the predictions of the talys nuclear reaction code were done. They underline the importance of cross-section determinations at accelerator laboratories for the establishment of an accurate cross-section data base in a wide projectile energy range.

A recent sensitivity study has shown that the $^{35}$K$(p,��)^{36}$Ca reaction is one of the ten $(p,��)$ reaction rates that could significantly impact the shape of the calculated X-ray burst light curve. In this work, we propose to reinvestigate the $^{35}$K$(p,��)^{36}$Ca reaction rate, as well as related uncertainties, by determining the energies and decay branching ratios of $^{36}$Ca levels, within the Gamow window, in the 0.5 to 2 GK X-ray burst temperature range. These properties were studied using the one neutron pick-up transfer reaction $^{37}$Ca$(p,d)^{36}$Ca in inverse kinematics using a radioactive beam of $^{37}$Ca at 48 MeV nucleon$^{-1}$. The experiment performed at GANIL, used the liquid Hydrogen target CRYPTA, the MUST2 detector array for the detection of the light charged particles and a zero degree detection system for the outgoing heavy ions. The atomic mass of $^{36}$Ca is confirmed and new resonances have been proposed together with their proton decay branching ratios. This spectroscopic information, used in combination with recent theoretical predictions for the $��$-width, were used to calculate the $^{35}$K$(p,��)^{36}$Ca reaction rate. The recommended rate of the present work was obtain within a uncertainty factor of 2 at 1 sigma. This is consistent, with the previous estimate in the X-ray burst temperature range. A large increase of the reaction rate was found at higher temperatures due to two newly discovered resonances. The $^{35}$K$(p,��)^{36}$Ca thermonuclear reaction rate is now well constrained by the present work in a broad range of temperatures. Our results show that the $^{35}$K$(p,��)^{36}$Ca reaction does not affect the shape of the X-ray burst light curve, and that it can be removed from the list of the few influential proton radiative captures reactions having a strong impact on the light curve., Published 13 May 2021 in PRC

The first investigation of the single-particle structure of the bound states of $^{17}$C, via the d(16C,p) transfer reaction, has been undertaken. The measured angular distributions confirm the spin-parity assignments of 1/2+ and 5/2+ for the excited states located at 217 and 335 keV, respectively. The spectroscopic factors deduced for these states exhibit a marked single-particle character, in agreement with shell model and particle-core model calculations, and combined with their near degeneracy in energy provide clear evidence for the absence of the N=14 sub-shell closure. The very small spectroscopic factor found for the 3/2+ ground state is consistent with theoretical predictions and indicates that the ν1d3/2 strength is carried by unbound states. With a dominant ℓ=0 valence neutron configuration and a very low separation energy, the 1/2+ excited state is a one-neutron halo candidate.

We present 12C+12C direct fusion measurements with STELLA UKFATIMA, that reach into the region of astrophysics interest relevant to massive stars (M⊙ ≈ 25) using self-supporting thin rotating carbon foils [1]. We demonstrate that detecting gammas and light charged particles in coincidence with nanosecond timing is key for effective background reduction achieving reliable measurements in the sub-nanobarn range. We give details about core developments of the detection apparatus as well as the coincidence-analysis procedure of low count statistics. The present data largely follows the phenomenological hindrance interpolation and shows indication for resonant behaviour at the lowest energy explored.

It has been suggested that hydrogen ingestion into the helium shell of massive stars could lead to high $^{13}$C and $^{15}$N excesses when the shock of a core-collapse supernova passes through its helium shell. This prediction questions the origin of extremely high $^{13}$C and $^{15}$N abundances observed in rare presolar SiC grains which is usually attributed to classical novae. In this context $^{13}$N($��$,p)$^{16}$O the reaction plays an important role since it is in competition with $^{13}$N $��^+$-decay to $^{13}$C. The $^{13}$N($��$,p)$^{16}$O reaction rate used in stellar evolution calculations comes from the CF88 compilation with very scarce information on the origin of this rate. The goal of this work is to provide a recommended $^{13}$N($��$,p)$^{16}$O reaction rate, based on available experimental data. Unbound nuclear states in the $^{17}$F compound nucleus were studied using the spectroscopic information of the analog states in $^{17}$O nucleus that were measured at the Alto facility using the $^{13}$C($^7$Li,t)$^{17}$O alpha-transfer reaction, and spectroscopic factors were derived using a DWBA analysis. This spectroscopic information was used to calculate a recommended $^{13}$N($��$,p)$^{16}$O reaction rate with meaningful uncertainty using a Monte Carlo approach. The present $^{13}$N($��$,p)$^{16}$O reaction rate is found to be within a factor of two of the previous evaluation, with a typical uncertainty of a factor 2-3. The source of this uncertainty comes from the three resonances at $E_r^{c.m.} = 221$, 741 and 959 keV. This new error estimation translates to an overall uncertainty in the $^{13}$C production of a factor of 50. The main source of uncertainty on the re-evaluated $^{13}$N($��$,p)$^{16}$O reaction rate currently comes from the uncertain alpha-width of relevant $^{17}$F states.

Gamma-ray production cross section excitation functions have been measured for $30$, $42$, $54$ and $66$ MeV proton beams accelerated onto targets of astrophysical interest, $^{nat}$C, C + O (Mylar), $^{nat}$Mg, $^{nat}$Si and $^{56}$Fe, at the Sector Separated Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with 8 Compton suppressed HPGe clover detectors was used to record $\gamma$-ray data. For known, intense $\gamma$-ray lines the previously reported experimental data measured up to $E_{p}\simeq$ $25$ MeV at the Washington and Orsay tandem accelerators were extended to higher proton energies. Our experimental data for the last 3 targets are reported here and discussed with respect to previous data and the Murphy \textit{et al.} compilation [ApJS 183, 142 (2009)], as well as to predictions of the nuclear reaction code TALYS. The overall agreement between theory and experiment obtained in first-approach calculations using default input parameters of TALYS has been appreciably improved by using modified optical model potential (OMP), deformation, and level density parameters. The OMP parameters have been extracted from theoretical fits to available experimental elastic/inelastic nucleon scattering angular distribution data by means of the coupled-channels reaction code OPTMAN. Experimental data for several new $\gamma$-ray lines are also reported and discussed. The astrophysical implications of our results are emphasised., Comment: 22 pages, 10 figures, five tables; regular article submitted to Phys Rev C

Classical novae result from thermonuclear explosions producing several $��$-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,$��$)$^{15}$O reaction rate which, despite many experimental and theoretical efforts, still remains uncertain. One of the main uncertainties in the $^{18}$F(p,$��$)$^{15}$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 $��$-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.

International audience; Background: It has been recently suggested that hydrogen ingestion into the helium shell of massive stars could lead to high C13 and N15 excesses when the shock of a core-collapse supernova passes through its helium shell. This prediction questions the origin of extremely high C13 and N15 abundances observed in rare presolar SiC grains which is usually attributed to classical novae. In this context the N13(α,p)O16 reaction plays an important role since it is in competition with N13β+ decay to C13. Purpose: The N13(α,p)O16 reaction rate used in stellar evolution calculations comes from the Caughlan and Fowler compilation with very scarce information on the origin of this rate and with no associated uncertainty. The goal of this work is to provide a recommended N13(α,p)O16 reaction rate, based on available experimental data, with a meaningful statistical uncertainty. Method: Unbound nuclear states in the F17 compound nucleus were studied using the spectroscopic information of the analog states in O17 nucleus that were measured at the Tandem-Alto facility using the C13(Li7,t)O17 α-particle-transfer reaction. The α-particle spectroscopic factors were derived using a finite-range distorted-wave Born approximation analysis. This spectroscopic information was used to calculate a recommended N13(α,p)O16 reaction rate with meaningful uncertainty using a Monte Carlo approach. Results: The N13(α,p)O16 reaction rate from the present work is found to be within a factor of two of the previous evaluation in the temperature range of interest, with a typical uncertainty of a factor ≈2–3. The source of this uncertainty has been identified to come from the three main contributing resonances at Erc.m.=221, 741, and 959 keV. This new error estimation translates to an overall uncertainty in the C13 production of a factor of 50 when using the lower and upper reaction rates in the conditions relevant for the N13(α,p)O16 activation. Conclusions: The main source of uncertainty on the re-evaluated N13(α,p)O16 reaction rate currently comes from the uncertain α-particle width of relevant F17 states.

Gamma-ray production cross section excitation functions have been measured for $30$, $42$, $54$ and $66$ MeV proton beams accelerated onto targets of astrophysical interest, $^{nat}$C, C + O (Mylar), $^{nat}$Mg, $^{nat}$Si and $^{56}$Fe, at the Sector Separated Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with 8 Compton suppressed HPGe clover detectors was used to record $��$-ray data. For known, intense $��$-ray lines the previously reported experimental data measured up to $E_{p}\simeq$ $25$ MeV at the Washington and Orsay tandem accelerators were extended to higher proton energies. Our experimental data for the last 3 targets are reported here and discussed with respect to previous data and the Murphy \textit{et al.} compilation [ApJS 183, 142 (2009)], as well as to predictions of the nuclear reaction code TALYS. The overall agreement between theory and experiment obtained in first-approach calculations using default input parameters of TALYS has been appreciably improved by using modified optical model potential (OMP), deformation, and level density parameters. The OMP parameters have been extracted from theoretical fits to available experimental elastic/inelastic nucleon scattering angular distribution data by means of the coupled-channels reaction code OPTMAN. Experimental data for several new $��$-ray lines are also reported and discussed. The astrophysical implications of our results are emphasised., 22 pages, 10 figures, five tables; regular article submitted to Phys Rev C

International audience; Neutrinoless double beta decay (NDBD) is expected to give the first direct measure of the effective neutrino mass.The uncertainty in the latter will be dominated by that in the relevant nuclear matrix element (NME) [1]. Of the various observables that could be used to constrain the NME, the occupancy and vacancy of ground state wavefunctions of the parent and daughter nuclei involved in NDBD, are important ingredients [1, 2]. Single-nucleon transfer reaction cross-sections can be used for this purpose, making use of the Macfarlane and French sum rules [3]

International audience; Stellar nucleosynthesis processes are of vital importance for nuclear physics: all the heavy elements are created by neutron capture reactions that take place in stars. To correctly study such reactions the neutron abundance available in the environment must be known, which means that also the so-called “neutron poisons” must be considered. The present work will focus on the reaction 17O(n, α) 14C which removes neutrons from the stellar environment during the s-process. Even though the study of such reactions is of high interest, it still presents several technological problems regarding both the creation and characterization of the neutron beam and the radioprotection of the facility. Therefore, the Trojan Horse Method, an indirect method, has been chosen to study the 17O(n, α) 14C reaction in the energy region of astrophysical interest, from 300 keV in the center-of-mass frame down to zero. In the present work, after briefly recalling the main features of the method and reporting on the state of the art for the reaction cross-section measurements, the latest THM experiment will be presented.

International audience; The decay rate of neutrinoless double beta process is expected to give the first direct measure of the neutrino mass, if the corresponding nuclear matrix element can be reliably calculated [1]. A major complication in extracting the neutrino mass from the half-life of this decay is the uncertainty in the nuclear matrix element. There are certain experimental observable that may be placed to constrain the calculations of the matrix element [2]. One of the main ingredients in calculating the nuclear matrix element is the wave functions of the initial and final states, which are usually calculated based on different nuclear models [1, 2]. Single-nucleon transfer reactions can be used to probe the occupancy and vacancy of valence orbitals which can help to characterize the ground-state wave functions. The precise measurement of both neutron addition and removal cross-sections can be used to determine the occupation of valence orbits relevant to 0ν2β-decay, following the Macfarlane and French sum rules [3]. The method consists of requiring a normalization such that for a given orbit characterized by total angular momentum j, the sum of the measured occupancy and vacancy on the same target add up to the degeneracy of the orbit 2j+1. It has been shown that such measurements allowed for a detailed description of the energy and vacancy of the valence orbitals of 76Ge and 76Se, where 76Ge is a candidate for 0ν2βdecay. The results indicated that the Fermi surface is much more diffuse than in theoretical calculations [4]. Similar measurements have been recently performed on 130Te and 130Xe [5]. Both 76Ge and 130Te are subject of research for 0ν2β-decay programs known as GERDA, Majorana (for 76Ge) and CUORE (for 130Te). The present work is aimed to study neutron pickup and stripping transfer cross-sections on one of the 0ν2β-decay candidate 124Sn and its daughter 124Te. This nucleus is the focus of neutrino-less double beta decay study, at the upcoming underground India based Neutrino Observatory (INO). This information will be useful for constraining calculations of the nuclear matrix element for the 0ν2β-decay of 124Sn.

The $^{22}$Ne($\alpha,n$)$^{25}$Mg reaction is an important source of neutrons for the s-process. Due to the difficulty in directly measuring the cross section of this reaction and the competing $^{22}$Ne($\alpha,\gamma$)$^{26}$Mg reaction, indirect methods are frequently used to try to instead calculate the relevant reaction rates. Uncertainty, however, persists in the number and properties of the pertinent excited states of $^{26}$Mg. In this paper, the results of proton and deuteron scattering from $^{26}$Mg are presented, giving a list of levels in $^{26}$Mg. In addition, level assignments in $^{26}$Mg are discussed, including some possible changes to the previously accepted assignments in $^{26}$Mg., Comment: 12 pages, 3 figures, 2 tables. Fixed missing reference and some index labelling in figures, fixed page break problem under table

The direct component of the 60Fe(n,γ)61Fe cross section was investigated by populating the bound states of the 61Fe nucleus through the (d,pγ) transfer reaction in inverse kinematics using a radioactive beam of 60Fe at 27A MeV. The experiment was performed at GANIL using the MUST2 array and an annular double-sided silicon strip detector for the detection of the light charged particle in coincidence with the photons measured in the EXOGAM γ-ray detectors. For the first time, the spectroscopic factors of the first 3/2−, 5/2−, 1/2−, and 9/2+ states of 61Fe were deduced experimentally from an adiabatic distorted wave approximation analysis of the data. The obtained results show a very good agreement with the shell-model predictions. The calculated direct component of the (n,γ) cross section was found negligible and of about 2% of the total, indicating a dominant resonant component. ispartof: Physical Review C vol:95 issue:3 status: published

International audience; The direct component of the 60Fe(n,γ)61Fe cross section was investigated by populating the bound states of the 61Fe nucleus through the (d,pγ) transfer reaction in inverse kinematics using a radioactive beam of 60Fe at 27A MeV. The experiment was performed at GANIL using the MUST2 array and an annular double-sided silicon strip detector for the detection of the light charged particle in coincidence with the photons measured in the EXOGAM γ-ray detectors. For the first time, the spectroscopic factors of the first 3/2−, 5/2−, 1/2−, and 9/2+ states of 61Fe were deduced experimentally from an adiabatic distorted wave approximation analysis of the data. The obtained results show a very good agreement with the shell-model predictions. The calculated direct component of the (n,γ) cross section was found negligible and of about 2% of the total, indicating a dominant resonant component.

The C-12+C-12 fusion reaction is one of the most important for nuclear astrophysics since it determines the carbon ignition in stellar environments. Two experiments which make use of the gamma-particle coincidence technique to measure the C-12+C-12 S-factors at deep sub barrier energies are discussed. Results are presented showing a decrease of the S-factor below E-c.m. = 3 MeV.

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The proton-capture reaction Si26(p,γ)P27 was studied via Coulomb dissociation (CD) of P27 at an incident energy of about 500 MeV/u. The three lowest-lying resonances in P27 have been populated and their resonance strengths have been measured. In addition, a nonresonant direct-capture component was clearly identified and its astrophysical S factor measured. The experimental results are compared to Monte Carlo simulations of the CD process using a semiclassical model. Our thermonuclear reaction rates show good agreement with the rates from a recent compilation. With respect to the nuclear structure of P27 we have found evidence for a negative-parity intruder state at 2.88-MeV excitation energy.

International audience; A candidate resonant tetraneutron state is found in the missing-mass spectrum obtained in the double-charge-exchange reaction He4(He8,Be8) at 186 MeV/u. The energy of the state is 0.83±0.65(stat)±1.25(syst) MeV above the threshold of four-neutron decay with a significance level of 4.9σ. Utilizing the large positive Q value of the (He8,Be8) reaction, an almost recoilless condition of the four-neutron system was achieved so as to obtain a weakly interacting four-neutron system efficiently.