Search

https://u.ganil-spiral2.eu/10.26143/GANIL-2016-E710.html

International audience

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.

The gyromagnetic factor of the low-lying E=251.96(9) keV isomeric state of the nucleus ^{99}Zr was measured using the time-dependent perturbed angular distribution technique. This level is assigned a spin and parity of J^{π}=7/2^{+}, with a half-life of T_{1/2}=336(5) ns. The isomer was produced and spin aligned via the abrasion-fission of a ^{238}U primary beam at RIKEN RIBF. A magnetic moment |μ|=2.31(14)μ_{N} was deduced showing that this isomer is not single particle in nature. A comparison of the experimental values with interacting boson-fermion model IBFM-1 results shows that this state is strongly mixed with a main νd_{5/2} composition. Furthermore, it was found that monopole single-particle evolution changes significantly with the appearance of collective modes, likely due to type-II shell evolution. ispartof: Physical Review Letters vol:124 issue:11 ispartof: location:United States status: Published online

International audience; The gyromagnetic factor of the low-lying E=251.96(9) keV isomeric state of the nucleus Zr99 was measured using the time-dependent perturbed angular distribution technique. This level is assigned a spin and parity of Jπ=7/2+, with a half-life of T1/2=336(5) ns. The isomer was produced and spin aligned via the abrasion-fission of a U238 primary beam at RIKEN RIBF. A magnetic moment |μ|=2.31(14)μN was deduced showing that this isomer is not single particle in nature. A comparison of the experimental values with interacting boson-fermion model IBFM-1 results shows that this state is strongly mixed with a main νd5/2 composition. Furthermore, it was found that monopole single-particle evolution changes significantly with the appearance of collective modes, likely due to type-II shell evolution.

The nuclear g factor and quadrupole moment (Qs) have been measured for the low-lying isomeric 1+ state of $^{34}$Al, using the β-detected nuclear magnetic resonance (β-NMR) and quadrupole resonance (β-NQR) methods. Spin-polarized $^{34}$Al isotopes were produced in a one-neutron pickup reaction induced by a $^{36}$S beam on a $^{9}$Be target at a kinetic energy of 77.5 MeV/nucleon, and were collected with the LISE fragment separator at GANIL. The measured g factor (|g| in a range of 1.757±0.014) and quadrupole moment (|Qs|=38(5) mb) are in good agreement with shell-model calculations using effective interactions. The similarity between the g factor of 34mAl and that of $^{32}$Al confirms a dominant neutron 2p1h configuration π(d5/2)−1⊗ν(d3/2)−1(f7/2)2 of 34mAl. In addition, the enhanced quadrupole moment of 34mAl relative to that of $^{32}$Al suggests that the neutron 1p1h excitation across the N=20 shell gap introduces extra nucleon–nucleon correlation and deformation.

The nuclear g factor and quadrupole moment (Qs) have been measured for the low-lying isomeric 1+ state of 34Al, using the β-detected nuclear magnetic resonance (β-NMR) and quadrupole resonance (β-NQR) methods. Spin-polarized 34Al isotopes were produced in a one-neutron pickup reaction induced by a 36S beam on a 9Be target at a kinetic energy of 77.5 MeV/nucleon, and were collected with the LISE fragment separator at GANIL. The measured g factor (|g| in a range of 1.757±0.014) and quadrupole moment (|Qs|=38(5) mb) are in good agreement with shell-model calculations using effective interactions. The similarity between the g factor of 34mAl and that of 32Al confirms a dominant neutron 2p1h configuration π(d5/2)−1⊗ν(d3/2)−1(f7/2)2 of 34mAl. In addition, the enhanced quadrupole moment of 34mAl relative to that of 32Al suggests that the neutron 1p1h excitation across the N=20 shell gap introduces extra nucleon–nucleon correlation and deformation. © 2018 The Author(s)

International audience; The spin-alignment of fragments produced in spontaneous and neutroninducedfission reactions is found to be up to 40%. This amount of spin-alignmentallows the measurement of gyromagnetic factors of s isomeric states using the wellknown TDPAD method. This observable is a very sensitive probe of the singleparticlestructure of nuclear states and frequently allows one to determine thevalence nucleon configuration. Isomers produced by spontaneous fission are difficultto measure due to their low production rates and the ones produced by neutroninducedfission and selected in a spectrometer could not be measured because oneneeds to have fully stripped isotopes to preserve the spin-alignment in the vacuum.The measurement performed at the RIKEN Nishina Center accelerator usingthe abrasion-fission reaction of a 238U80+ beam at 345 MeV/u energy on the N=5999mZr and 98mY will be presented. The obtained results show the opportunity toperform gyromagnetic factors measurement of neutron-rich s-isomers produced bythe abrasion-fission reaction.

International audience; The half-life of Ne19 was measured using a real-time digital multiparametric acquisition system, providing an accurate time stamp and relevant information on the detector signals for each decay event. An exhaustive offline analysis of the data gave unique access to experimental effects potentially biasing the measurement. After establishing the influence factors impacting the measurement such as after-pulses, pile-up, gain, and baseline fluctuations, their effects were accurately estimated and the event selection optimized. The resulting half-life, 17.2569±0.0019(stat)±0.0009(syst) s, is the most precise up to now for Ne19. It is found to be in agreement with two recent precise measurements and not consistent with the most recent one [L. J. Broussard , Phys. Rev. Lett. 112, 212301 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.212301] by 3.0 standard deviations. The full potential of the technique for nuclei with half-lives of a few seconds is discussed.

International audience

International audience

A nova is a thermonuclear runaway occurring in binary system of stars. The observation of the gamma rays emitted after anova is a way to better understand this phenomenon. According to the models, the line at 511 keV, produced in the annihilationbetween positrons and electrons, would be the most intense line several hours after the explosion. One of the main positron emitterswould be the $^{18}$F radioactive isotope. In order to improve the predictive power of the models, it is crucial to better determine theamount of $^{18}$F produced in the nova. Yet, the $^{18}$F destruction rate $^{18}$F(p,$\alpha$)$^{15}$O is given with large uncertainties. Measuring thespectroscopic properties (energy, width, spin) of states in the compound nucleus 19Ne should allow us to constrain the reaction rate.In this context, an experiment based on a new inelastic scattering method ($^{19}$Ne(p,p’)$^{19}$Ne∗) was performed at GANIL with theVAMOS spectrometer. The detection system has been adapted to detect for the first time high energy protons (p’). A good energyresolution in inverse kinematic has been reached ($\sigma$=33 keV). The angular distribution measurement of decaying particles shouldprovide the spin assignment of the states in a model independent way. Unfortunately, an unforeseen contamination has preventedus to complete this measurement. New spectroscopic information have been extracted and contributed to reduce the uncertaintyof the $^{18}$F(p,$\alpha$)$^{15}$O reaction rate in a significant way. The data are compatible with a new broad state below the proton threshold(6.41 MeV). This state seems to be sufficiently broad to contribute to the destruction reaction rate of $^{18}$F and reduces the chancesfor satellite detection., Une des clefs de la compréhension des novæ, (explosions thermonucleéaires intervenant dans les systèmes binaires d’étoiles) estl’observation des rayonnements gamma émis après l’explosion. Selon les modèles, la raie $\gamma$ à 511 keV, produite par l’annihilationdes positrons et des électrons, serait la plus intense plusieurs heures après l’explosion. Un des émetteurs principaux de positronsserait l’isotope radioactif $\beta$+ de $^{18}$F. L’amélioration du pouvoir prédictif des modèles passe par une meilleure connaissance de laquantité de $^{18}$F produite dans la nova. Or, le taux de destruction du $^{18}$F par la réaction $^{18}$F(p,$\alpha$)$^{15}$O est entaché d’incertitudes. Il est possible de contraindre ce dernier via l’étude des propriétés spectroscopiques (énergie, largeurs, spin) des états du noyaucomposé : le $^{19}$Ne. Dans ce contexte une expérience basée sur une nouvelle méthode de diffusion inélastique ($^{19}$Ne(p,p’)$^{19}$Ne∗) aété entreprise à GANIL auprès du spectromètre VAMOS. Un travail de reconfiguration a du être réalisé pour assurer une détectioninédite des protons (p’) issus de la diffusion inélastique avec ce spectromètre. Une très bonne résolution en énergie d’excitationpour une expérience en cinématique inverse (jusqu’à $\sigma$=33 keV) est atteinte. La mesure des distributions angulaires des particulesde décroissance devait fournir d’une manière indépendante des modèles le spin des états. Une contamination non attendue empêchecette mesure. De nouvelles informations spectroscopiques ont été collectées et tendent à améliorer les incertitudes associées au tauxde la réaction $^{18}$F(p,$\alpha$)$^{15}$O. Les données sont compatibles avec la présence d’un nouvel état large en dessous du seuil d’émissionproton (6.41 MeV). Cet état semble avoir une largeur suffisante (230 keV) pour contribuer significativement au taux de réaction dedestruction du $^{18}$F, amoindrissant les perspectives de détection par les satellites.

International audience

International audience; Dans la perspective d'étudier le phénomène stellaire explosif appelé nova, une expérience inédite de diffusion inélastique utilisant un faisceau radioactif de 19Ne sur une cible de protons a été menée en novembre 2013 à GANIL auprès du spectromètre VAMOS. Elle avait pour but de mesurer les propriétés des états du 19Ne situés dans la zone d'intérêt astrophysique s'étalant de 6 MeV à 7.2MeV d'énergie d'excitation. Pour la première fois, VAMOS a été configuré en mode spectrographe pour détecter des protons de hautes énergies (jusqu'à 25 MeV).

Classical novae occur in close binary star systems consisting of white dwarf accreting matter from its companion, main sequence or red giant star. The accreting material provides fuel and the conditions necessary to initiate a thermonuclear explosion on the White Dwarf surface, leading to the synthesis of some heavier types of nuclei and the ejection of material into space. Among else, novae produce radioactive isotopes, such as 18F, that could be detected by their gamma-ray emission (one of the scientific objective of the INTEGRAL satellite) . Why do we focus on 18F? Because the annihilation of positrons generated by its $\beta^ +$ decay is the dominant source of gamma rays during the first hours of a nova explosion. So, The knowledge of the abundance of the 18F in novae is essential because its gamma rays (=511 keV) are one of the observables, which give insight into nuclear processes of novae. Depending on the temperature, the $\beta^ +$ decay and two nuclear reactions are in competition for the destruction of 18F : 18F(p, $\alpha$)15O and 18F(p,$\gamma$ )19Ne. Unfortunately, present radioactive beams intensities are not sufficient for a direct measurement of those reactions. Nevertheless, these two reactions rates strongly depend on the structure of 19Ne. In particular, the energies, spins, and decay widths of important 19Ne resonances must be determined in order to reduce their uncertainty. Today, only a few intrinsic properties of states have been measured yet experimentally in the excitation energy range of astrophysical interest (commonly called the Gamow window). Based on the success of the experiment performed at Louvain-La-Neuve (Belgium) in the past, we will realize soon at GANIL a new and accurate spectroscopy of 19Ne inside the Gamow window via an improved p,p' inelastic scattering reaction. The experimental setup combines an annular silicon detector and the magnetic spectrometer VAMOS. The latter will be used for the first time to detect protons at zero degree, on the spectrograph mode, thus it will be required to configurate it. This poster will present the topic, the motivations and the present status of experiment preparation.

A C5a-receptor antagonist was selected from human C5a phage display libraries in which the C terminus of des-Arg74-hC5a was mutated. The selected molecule is a competitive C5a receptor antagonist in vitro and in vivo. Signal transduction is interrupted at the level of G-protein activation. In addition, the antagonist does not cause any C5a receptor phosphorylation. Proinflammatory properties such as chemotaxis or lysosomal enzyme release of differentiated U937 cells, as well as C5a-induced changes in intracellular Ca2+ concentration of murine peritoneal macrophages, are inhibited. The in vivo efficacy was evaluated in three different animal models of immune complex diseases in mice, i.e., the reverse passive Arthus reaction in the peritoneum, skin, and lung. The i.v. application of the C5a receptor antagonist abrogated polymorphonuclear neutrophil accumulation in peritoneum and markedly attenuated polymorphonuclear neutrophil migration into the skin and the lung. In a model of intestinal ischemia/reperfusion injury, i.v. administration of the C5a receptor antagonist decreased local and remote tissue injury: bowel wall edema and hemorrhage as well as pulmonary microvascular dysfunction. These data give evidence that C5a is an important mediator triggering the inflammatory sequelae seen in immune complex diseases and ischemia/reperfusion injury. The selected C5a receptor antagonist may prove useful to attenuate the inflammatory response in these disorders.

Promyelocytic human leukemia HL60 cells can be differentiated into neutrophil-like cells that exhibit an NADPH oxidase activity through direct stimulation of protein kinase C (PKC) with PMA or through formyl peptide receptor activation. We have isolated a variant HL60 clone that exhibited a conditional PMA-induced oxidative response depending on the agent used for the differentiation. While cells differentiated with DMSO responded to either PMA or N-formyl peptide (N-formyl-Met-Leu-Phe-Lys or fMLFK), cells differentiated with dibutyryl-cAMP (Bt2cAMP) responded to fMLFK but very poorly to PMA. However, in Bt2cAMP-differentiated cells, the expression of the different PKC isoforms was similar to that observed in DMSO-differentiated cells. Moreover, PMA was able to induce a normal phosphorylation of the cytosolic factor p47phox and to fully activate extracellular signal-regulated kinases (Erk1/2). Interestingly, Bt2cAMP-differentiated cells exhibited a strong and sustained O2− production when costimulated with PMA and suboptimal concentrations of fMLFK which were, per se, ineffective. This sustained response was only slightly reduced by the conjunction of the mitogen-activated protein (MAP) kinase kinase (MEK) inhibitor PD98059 and wortmannin, a phosphatidylinositol-3 kinase (PI3K) inhibitor. Variant HL60 cells that were stably transfected with a constitutively active form of Rac1 were able, when differentiated with Bt2cAMP, to secrete oxidant following PMA stimulation. Altogether, the results suggest that, in addition to the phosphorylation of p47phox, the activation of NADPH oxidase requires the activation of a Rac protein through a pathway that diverges at a point upstream of MEK and that is independent of the activation of wortmannin sensitive PI3K.