arXiv subjects

D. Beaumel

Publications and source records attributed to D. Beaumel.

36 records · Page 2Linked to original sources

arXiv2021

Evaluation of the $^{35}$K($p$,$γ$)$^{36}$Ca reaction rate using the $^{37}$Ca($p$,$d$)$^{36}$Ca transfer reaction

A recent sensitivity study has shown that the $^{35}$K$(p,γ)^{36}$Ca reaction is one of the ten $(p,γ)$ 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$(p,γ)^{36}$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 $γ$-width, were used to calculate the $^{35}$K$(p,γ)^{36}$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$(p,γ)^{36}$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$(p,γ)^{36}$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.

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arXiv2021

The MUGAST-AGATA-VAMOS campaign : set-up and performance

The MUGAST-AGATA-VAMOS set-up at GANIL combines the MUGAST highly-segmented silicon array with the state-of-the-art AGATA array and the large acceptance VAMOS spectrometer. The mechanical and electronics integration copes with the constraints of maximum efficiency for each device, in particular γ-ray transparency for the silicon array. This complete set-up offers a unique opportunity to perform exclusive measurements of direct reactions with the radioactive beams from the SPIRAL1 facility. The performance of the set-up is described through its commissioning and two examples of transfer reactions measured during the campaign. High accuracy spectroscopy of the nuclei of interest, including cross-sections and angular distributions, is achieved through the triple-coincidence measurement. In addition, the correction from Doppler effect of the γ-ray energies is improved by the detection of the light particles and the use of two-body kinematics and a full rejection of the background contributions is obtained through the identification of heavy residues. Moreover, the system can handle high intensity beams (up to 108 pps). The particle identification based on the measurement of the time-of-flight between MUGAST and VAMOS and the reconstruction of the trajectories is investigated.

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arXiv2021

Probing nuclear forces beyond the nuclear drip line: The cases of $^{16}$F and $^{15}$F

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.

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arXiv2020

Evaluation of the $^{13}$N($α$,p)$^{16}$O thermonuclear reaction rate and its impact on the isotopic composition of supernova grains

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($α$,p)$^{16}$O the reaction plays an important role since it is in competition with $^{13}$N $β^+$-decay to $^{13}$C. The $^{13}$N($α$,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($α$,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($α$,p)$^{16}$O reaction rate with meaningful uncertainty using a Monte Carlo approach. The present $^{13}$N($α$,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($α$,p)$^{16}$O reaction rate currently comes from the uncertain alpha-width of relevant $^{17}$F states.

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arXiv2019

Study of multi-neutron systems with SAMURAI spectrometer

The tetraneutron has been drawing the attention of the nuclear physics community for decades, but a firm conclusion on its existence and properties is still far from being reached despite many experimental and theoretical efforts. New measurements have recently been performed at RIBF with the SAMURAI spectrometer by applying complementary reaction probes, which will help to pin down the properties of this four-neutron system.

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arXiv2018

How different is the core of $^{25}$F from $^{24}$O$_{g.s.}$?

The neutron-shell structure of $^{25}$F was studied using quasi-free (p,2p) knockout reaction at 270A MeV in inverse kinematics. The sum of spectroscopic factors of $π$0d$_{5/2}$ orbital is found to be $1.0 \pm 0.3$. However, the spectroscopic factor for the ground-state to ground-state transition ($^{25}$F, $^{24}$O$_{g.s.}$) is only $0.36\pm 0.13$, and $^{24}$O excited states are produced from the 0d$_{5/2}$ proton knockout. The result shows that the $^{24}$O core of $^{25}$F nucleus significantly differs from a free $^{24}$O nucleus, and the core consists of 35% $^{24}$O$_{g.s}$. and 65% excited $^{24}$O.

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arXiv2018

Charged-particle decays of highly excited states in $^{19}$F

Neutron-capture reactions on $^{18}$F in the helium-burning shell play an important role in the production of $^{15}$N during core-collapse supernovae. The competition between the $^{18}$F($n,p/α$)$^{18}$O/$^{15}$N reactions controls the amount of $^{15}$N produced. The strengths of these reactions depend on the decay branching ratios of states in $^{19}$F above the neutron threshold. We report on an experiment investigating the decay branching ratios of these states in order to better constrain the strengths of the reactions.

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arXiv2014

Experimental study of the two-body spin-orbit force

Energies and spectroscopic factors of the first $7/2^-$, $3/2^-$, $1/2^-$ and $5/2^-$ states in the $^{35}$Si$_{21}$ nucleus were determined by means of the (d,p) transfer reaction in inverse kinematics at GANIL using the MUST2 and EXOGAM detectors. By comparing the spectroscopic information on the $^{35}$Si and $^{37}$S isotones, a reduction of the $p_{3/2} - p_{1/2}$ spin-orbit splitting by about 25% is proposed, while the $f_{7/2} -f_{5/2}$ spin-orbit splitting seems to remain constant. These features, derived after having unfolded nuclear correlations using shell model calculations, have been attributed to the properties of the 2-body spin-orbit interaction, the amplitude of which is derived for the first time in an atomic nucleus. The present results, remarkably well reproduced by using several realistic nucleon-nucleon forces, provide a unique touchstone for the modeling of the spin-orbit interaction in atomic nuclei.

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arXiv2013

Search for new resonant states in 10C and 11C and their impact on the cosmological lithium problem

The observed primordial 7Li abundance in metal-poor halo stars is found to be lower than its Big-Bang nucleosynthesis (BBN) calculated value by a factor of approximately three. Some recent works suggested the possibility that this discrepancy originates from missing resonant reactions which would destroy the 7Be, parent of 7Li. The most promising candidate resonances which were found include a possibly missed 1- or 2- narrow state around 15 MeV in the compound nucleus 10C formed by 7Be+3He and a state close to 7.8 MeV in the compound nucleus 11C formed by 7Be+4He. In this work, we studied the high excitation energy region of 10C and the low excitation energy region in 11C via the reactions 10B(3He,t)10C and 11B(3He,t)11C, respectively, at the incident energy of 35 MeV. Our results for 10C do not support 7Be+3He as a possible solution for the 7Li problem. Concerning 11C results, the data show no new resonances in the excitation energy region of interest and this excludes 7Be+4He reaction channel as an explanation for the 7Li deficit.

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arXiv2013

Structure of unbound neutron-rich $^{9}$He studied using single-neutron transfer

The 8He(d,p) reaction was studied in inverse kinematics at 15.4A MeV using the MUST2 Si-CsI array in order to shed light on the level structure of 9He. The well known 16O(d,p)17O reaction, performed here in reverse kinematics, was used as a test to validate the experimental methods. The 9He missing mass spectrum was deduced from the kinetic energies and emission angles of the recoiling protons. Several structures were observed above the neutron-emission threshold and the angular distributions were used to deduce the multipolarity of the transitions. This work confirms that the ground state of 9He is located very close to the neutron threshold of 8He and supports the occurrence of parity inversion in 9He.

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arXiv2010

Emergence of the N=16 shell gap in 21O

The spectroscopy of 21O has been investigated using a radioactive 20O beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be Jpi=5/2+ and Jpi=1/2+ respectively. Two neutron unbound states were observed at excitation energies of 4.76 +- 0.10 and 6.16 +- 0.11. The spectroscopic factor deduced for the lower of these interpreted as a 3/2+ level, reveals a rather pure 0d3/2 single-particle configuration. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 magic number. For the higher lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 71% branching ratio to the first 2+ state in 20O has been observed. The results are compared with new shell model calculations.

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arXiv2010

Probing the pairing interaction through two-neutron transfer reactions

Cross sections for ($p,t$) two-neutron transfer reactions are calculated in the one-step zero-range distorted-wave Born approximation for the tin isotopes $^{124}$Sn and $^{136}$Sn and for incident proton energies from 15 to 35 MeV. Microscopic quasiparticle random-phase approximation form factors are provided for the reaction calculation and phenomenological optical potentials are used in both the entrance and the exit channels. Three different surface/volume mixings of a zero-range density-dependent pairing interaction are employed in the microscopic calculations and the sensitivity of the cross sections to the different mixings is analyzed. Since absolute cross sections cannot be obtained within our model, we compare the positions of the diffraction minima and the shapes of the angular distributions. No differences are found in the position of the diffraction minima for the reaction $^{124}$Sn($p,t$)$^{122}$Sn. On the other side, the angular distributions obtained for the reaction $^{136}$Sn($p,t$)$^{134}$Sn with surface and mixed interactions differ at large angles for some values of the incident proton energy. For this reaction, we compare the ratios of the cross sections associated to the ground state and the first excited state transitions. Differences among the three different theoretical predictions are found and they are more important at the incident proton energy of 15 MeV. As a conclusion, we indicate ($p,t$) two-neutron transfer reactions with very neutron-rich Sn isotopes and at proton energies around 15 MeV as good experimental cases where the surface/volume mixing of the pairing interaction may be probed.

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arXiv2010

Probing pre-formed alpha particles in the ground state of nuclei

In this Letter, we report on alpha particle emission through the nuclear break-up in the reaction 40Ca on a 40Ca target at 50A MeV. It is observed that, similarly to nucleons, alpha particles can be emitted to the continuum with very specific angular distribution during the reaction. The alpha particle properties can be understood as resulting from an alpha cluster in the daughter nucleus that is perturbed by the short range nuclear attraction of the collision partner and emitted. A time-dependent theory that describe the alpha particle wave-function evolution is able to reproduce qualitatively the observed angular distribution. This mechanism offers new possibilities to study alpha particle properties in the nuclear medium.

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arXiv2007

Search for low lying dipole strength in the neutron rich nucleus $^{26}$Ne

Coulomb excitation of the exotic neutron-rich nucleus $^{26}$Ne on a $^{nat}$Pb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an $^{nat}$Al target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV $^{40}$Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the $^{25}$Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV. The reconstructed $^{26}$Ne angular distribution confirms its E1 nature. A reduced dipole transition probability of B(E1)=0.49$\pm$0.16 $e^2fm^2$ is deduced. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is obtained. The results are discussed in terms of a pygmy resonance centered around 9 MeV.

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arXiv2007

Indirect study of 19Ne states near the 18F+p threshold

The early E < 511 keV gamma-ray emission from novae depends critically on the 18F(p,a)15O reaction. Unfortunately the reaction rate of the 18F(p,a)15O reaction is still largely uncertain due to the unknown strengths of low-lying proton resonances near the 18F+p threshold which play an important role in the nova temperature regime. We report here our last results concerning the study of the d(18F,p)19F(alpha)15N transfer reaction. We show in particular that these two low-lying resonances cannot be neglected. These results are then used to perform a careful study of the remaining uncertainties associated to the 18F(p,a)15O and 18F(p,g)19Ne reaction rates.

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arXiv2003

D(18F,pa)15N reaction applied to nova gamma-ray emission

The 18F(p,alpha)15O reaction is recognized to be one of the most important reactions for nova gamma-ray astronomy as it governs the early E <= 511keV gamma emission. However in the nova temperature regime, its rate remains largely uncertain due to unknown low-energy resonance strengths. We report here the measurement of the D(18F,p)19F(alpha)15N one-nucleon transfer reaction, induced by a 14 MeV 18F radioactive beam impinging on a CD2 target; outgoing protons and 15N (or alpha-particles) were detected in coincidence in two silicon strip detectors. A DWBA analysis of the data resulted in new limits to the contribution of low-energy resonances to the rate of the 18F(p,alpha)15O reaction.

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arXiv2002

Study of the ^18F(p, alpha)^15O reaction for application to nova gamma-ray emission

The ^18F(p, alpha)^15O reaction is recognized as one of the most important reaction for nova gamma-ray astronomy as it governs the early =< 511 keV emission. However, its rate remains largely uncertain at nova temperatures due to unknown low-energy resonance strengths. In order to better constrain this reaction rate, we have studied the one-nucleon transfer reaction, D(^18F,p alpha)^15N, at the CRC-RIB facility at Louvain La Neuve.

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arXiv2002

A new experiment for the determination of the 18F(p,alpha) reaction rate at nova temperatures

The 18F(p,alpha) reaction was recognized as one of the most important for gamma ray astronomy in novae as it governs the early 511 keV emission. However, its rate remains largely uncertain at nova temperatures. A direct measurement of the cross section over the full range of nova energies is impossible because of its vanishing value at low energy and of the short 18F lifetime. Therefore, in order to better constrain this reaction rate, we have performed an indirect experiment taking advantage of the availability of a high purity and intense radioactive 18F beam at the Louvain La Neuve RIB facility. We present here the first results of the data analysis and discuss the consequences.

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