Search for 22Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes

Classical novae are thermonuclear explosions in stellar binary systems, and important sources of 26Al and 22Na. While ¿ rays from the decay of the former radioisotope have been observed throughout the Galaxy, 22Na remains untraceable. Its half-life (2.6 yr) would allow the observation of its 1.275 MeV ¿-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of its nucleosynthesis. The 22Na(p,¿¿)23Mg reaction remains the only source of large uncertainty about the amount of 22Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in 23Mg. Here, we propose a combined analysis of particle-particle correlations and velocity-difference profiles to measure femtosecond nuclear lifetimes. The application of this method to the study of the 23Mg states, places strong limits on the amount of 22Na produced in novae and constrains its detectability with future space-borne observatories.Postprint (published version

Preliminary results of lifetime measurements in neutron-rich 53Ti

To study the nuclear structure of neutron-rich titanium isotopes, a lifetime measurement was performed at the Grand Accélérateur National d'Ions Lourds (GANIL) facility in Caen, France. The nucleiwere produced in a multinucleon-transfer reaction by using a 6.76 MeV/u 238U beam. The Advanced Gamma Tracking Array (AGATA) was employed for the γ-ray detection and target-like recoils were identified event-by-event by the large-acceptance variable mode spectrometer (VAMOS++). Preliminary level lifetimes of the (5/2−) to 13/2− states of the yrast band in the neutron-rich nucleus 53Ti were measured for the first time employing the recoil distance Doppler-shift (RDDS) method and the compact plunger for deep inelastic reactions. The differential decay curve method (DDCM) was used to obtain the lifetimes from the RDDS data

Search for 22^{22}Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes

Classical novae are thermonuclear explosions in stellar binary systems, and important sources of $^{26}$Al and $^{22}$Na. While gamma rays from the decay of the former radioisotope have been observed throughout the Galaxy, $^{22}$Na remains untraceable. The half-life of $^{22}$Na (2.6 yr) would allow the observation of its 1.275 MeV gamma-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of the nuclear reactions involved in the production and destruction of this nucleus. The $^{22}$Na($p,\gamma$)$^{23}$Mg reaction remains the only source of large uncertainty about the amount of $^{22}$Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in $^{23}$Mg. In the present work, a combined analysis of particle-particle correlations and velocity-difference profiles is proposed to measure femtosecond nuclear lifetimes. The application of this novel method to the study of the $^{23}$Mg states, combining magnetic and highly-segmented tracking gamma-ray spectrometers, places strong limits on the amount of $^{22}$Na produced in novae, explains its non-observation to date in gamma rays (flux < 2.5x$10^{-4}$ ph/(cm$^2$s)), and constrains its detectability with future space-borne observatories.Comment: 18 pages, 3 figures, 1 tabl

Lifetime measurement of the 2₁⁺ state in ⁷⁴Rb and isospin properties of quadrupole transition strengths at N = Z

Self-conjugate nuclei in the A ≈ 70–80 region have attracted a great deal of attention due to phenomena such as shape coexistence and increasing collectivity along the N=Zline. We investigate the structure of nuclei in this region through lifetime measurements using the GRETINA array. The first implementation of the Differential Recoil Distance Doppler Shift technique with fast radioactive beams is demonstrated and verified through a measurement of the well-known B(E2; 2₁⁺→ 0₁⁺)transition strength in ⁷⁴Kr. The method is then applied to determine the B(E2; 2₁⁺→ 0₁⁺) transition strength in ⁷⁴Rb, the heaviest odd–odd N=Z nucleus for which this quantity has been determined. This result and extended systematics along N=Z suggest the dominance of the isoscalar part of the quadrupole transition strengths in self-conjugate nuclei, as well as the possible presence of shape coexistence in ⁷⁴Rb

Fusion et réactions directes autour de la barrière Coulombienne avec le noyau riche en neutrons ⁸He

Radioactive ion beams like 8He, open new possibilities to investigate the influence of new and exotic structures on reaction mechanisms. This thesis presents the first investigations of reactions of the weakly bound, Borromean nucleus, 8He, at energies around the Coulomb barrier. The low intensity of radioactive ion beams ( ˜ 105pps ) necessitated the development of a new sensitive and selective technique for the precise and accurate measurement of fusion cross sections. In the 8He+197Au system, excitation functions for fusion and neutron(s) transfer were measured. In the 8He+65Cu system, differential and integral cross sections for various processes like elastic scattering, neutron transfer and fusion were measured using both, inclusive and exclusive measurements of characteristic γ -rays, charged particles and neutrons. These experimental results combined with coupled reaction channels calculations demonstrated the inter-connectivity among the various reaction processes. The internal structure of 8He influenced the tunneling process and neutron(s) transfer and interestingly, revealed an unexpected behavior within the Helium isotopic chain. Further, a systematic analysis of the known fusion excitation functions showed that the increase in sub-barrier fusion cross sections associated with the internal structure of nuclei, is in fact much larger for “normal” nuclei than for light, weakly-bound “exotic” nuclei.Les faisceaux d'ions radioactifs comme l'8He ouvrent de nouvelles perspectives pour étudier l'influence de nouveaux aspects structurels sur les mécanismes de réaction. Cette thèse présente les premières investigations sur les réactions induites par le noyau d'8He, faiblement lié et Borroméen, aux énergies autour de la barrière Coulombienne. La faible intensité des faisceaux d'ions radioactifs ( ˜ 105pps ) nécessite le développement de techniques sensibles et sélectives. Une méthode expérimentale a été développée pour mesurer précisément les sections efficaces de fusion. Dans le système 8He+197Au, les fonctions d'excitation de fusion et de transfert de neutron(s) ont été mesurées autour de la barrière. Les sections efficaces différentielles et intégrales pour la diffusion élastique, le transfert de neutron(s) et la fusion ont également été obtenues dans le système 8He+65Cu à partir de mesures inclusives et exclusives des rayons γ caractéristiques, des particules chargées et des neutrons. Ces résultats expérimentaux et les calculs en voies couplées illustrent l'interconnexion des différents processus. Cette étude permet de comprendre l'influence de la structure interne de l'8He sur l'effet tunnel et le transfert de neutron(s) et met en évidence un comportement inattendu au sein de la chaîne isotopique des Héliums. L'étude systématique des fonctions d'excitation de fusion montre que, contrairement aux attentes, l'augmentation de la probabilité de l'effet tunnel sous la barrière Coulombienne associée à la structure interne des noyaux est beaucoup plus importante pour les noyaux "normaux" que pour les noyaux légers "exotiques" faiblement liés

Fusion et réactions directes autour de la barrière Coulombienne avec le noyau riche en neutrons 8He

Les faisceaux d'ions radioactifs comme l'8He ouvrent de nouvelles perspectives pour étudier l'influence de nouveaux aspects structurels sur les mécanismes de réaction. Cette thèse présente les premières investigations sur les réactions induites par le noyau d'8He, faiblement lié et Borroméen, aux énergies autour de la barrière Coulombienne. La faible intensité des faisceaux d ions radioactifs (~10^5 pps) nécessite le développement de techniques sensibles et sélectives. Une méthode expérimentale été développée pour mesurer précisément les sections efficaces de fusion. Dans le système 8He+197Au, les fonctions d'excitation de fusion et de transfert de neutron(s) ont été mesurées autour de la barrière. Les sections efficaces différentielles et intégrales pour la diffusion élastique, le transfert de neutron(s) et la fusion ont également été obtenues dans le système 8He+65Cu à partir de mesures inclusives et exclusives des rayons gamma caractéristiques, des particules chargées et des neutrons. Ces résultats expérimentaux et les calculs en voies couplées illustrent l'interconnexion des différents processus. Cette étude permet de comprendre l'influence de la structure interne de l 8He sur l'effet tunnel et le transfert de neutron(s) et met en évidence un comportement inattendu au sein de la chaîne isotopique des Héliums. L'étude systématique des fonctions d'excitation de fusion montre que, contrairement aux attentes, l augmentation de la probabilité de l effet tunnel sous la barrière Coulombienne associée à la structure interne des noyaux est beaucoup plus importante pour les noyaux normaux que pour les noyaux légers exotiques faiblement liés.Radioactive ion beams like 8He, open new possibilities to investigate the influence of new and exotic structures on reaction mechanisms. This thesis presents the first investigations of reactions of the weakly bound, Borromean nucleus, 8He, at energies around the Coulomb barrier. The low intensity of radioactive ion beams (~10^5 pps) necessitated the development of a new sensitive and selective technique for the precise and accurate measurement of fusion cross sections. In the 8He+197Au system, excitation functions for fusion and neutron(s) transfer were measured. In the 8He+65Cu system, differential and integral cross sections for various processes like elastic scattering, neutron transfer and fusion were measured using both, inclusive and exclusive measurements of characteristic gamma-rays, charged particles and neutrons. These experimental results combined with coupled reaction channels calculations demonstrated the inter-connectivity among the various reaction processes. The internal structure of 8He influenced the tunneling process and neutron(s) transfer and interestingly, revealed an unexpected behavior within the Helium isotopic chain. Further, a systematic analysis of the known fusion excitation functions showed that the increase in sub-barrier fusion cross sections associated with the internal structure of nuclei, is in fact much larger for normal'' nuclei than for light, weakly-bound exotic'' nuclei.CAEN-BU Sciences et STAPS (141182103) / SudocSTRASBOURG-Bib.Central Recherche (674822133) / SudocSudocFranceF

Delayed onset of odor detection in neonatal mice lacking tenascin-C.

International audienceThe olfactory bulb is one of the few regions in the adult mammalian forebrain in which neurons are constitutively replaced throughout life. New neurons generated in the subventricular zone migrate long distances along the rostral migratory stream to the olfactory bulb where they differentiate into interneurons. Neuronal precursor generation, migration and incorporation into the bulbar network occur in an environment rich in extracellular matrix molecules. We investigated the potential role of one of the constituents of the extracellular matrix, tenascin-C (TNC), in bulbar neurogenesis and olfactory performance using TNC-deficient mice. We found that TNC deficiency resulted in a delayed onset of olfactory responses in neonatal animals. This delay normalized at around postnatal day 10. Interestingly, this delay in early olfactory performance was not due to impaired bulbar neurogenesis as proliferation, migration, incorporation and fate determination of newborn bulbar interneurons were normal in TNC-deficient animals. Thus, we conclude that a constitutive lack of TNC does not affect bulbar neurogenesis, but instead leads to ontogenetically early impairments in olfactory detection

Encapsulated Sulfur targets for light ion beam experiments

A new method was developed to produce enriched Sulfur targets with minimum loss of material. This was made possible by inserting Sulfur in-between two 0.5 μm Mylar foils (C10H8O4). The initial aim was to ensure that the Sulfur targets reduce by no more than 50% of the initial thickness within 24 hours under the equivalent of 10 J/cm2 of integrated energy deposition by an energetic (Eb > 50 MeV) proton beam. There is no loss of enriched material while making the target, as all the material is deposited within the surface area to be exposed to the beam. During beam irradiation, the targets were frequently swivelled in order to expose each part of the target to the beam and achieve homogeneous irradiation. Targets of 0.4 mg/cm2 thickness were produced and characterised using ion beam analysis technique with a 3 MeV proton beam

Encapsulated Sulfur targets for light ion beam experiments

A new method was developed to produce enriched Sulfur targets with minimum loss of material. This was made possible by inserting Sulfur in-between two 0.5 μm Mylar foils (C10H8O4). The initial aim was to ensure that the Sulfur targets reduce by no more than 50% of the initial thickness within 24 hours under the equivalent of 10 J/cm2 of integrated energy deposition by an energetic (Eb > 50 MeV) proton beam. There is no loss of enriched material while making the target, as all the material is deposited within the surface area to be exposed to the beam. During beam irradiation, the targets were frequently swivelled in order to expose each part of the target to the beam and achieve homogeneous irradiation. Targets of 0.4 mg/cm2 thickness were produced and characterised using ion beam analysis technique with a 3 MeV proton beam