Study of compression modes in 56Ni using an active target

De Isoscalaire reuzenmonopool resonantie en Isoscalaire reuzendipool resonantie zijn van belang bij het bestuderen van de nucleaire onsamendrukbaarheid in eindige kernen. Dit laatste zal gebruikt worden om onsamendrukbaarheid van kernmaterie te bepalen. Onsamendrukbaarheid van kernmaterie is een belangrijke invoer voor de toestandsvergelijking van nucleaire materie, dat op zijn beurt nuttig is bij het begrijpen van bepaalde astrofysische verschijnselen, zoals de massa's van neutronensterren en supernovae-explosies. Omdat Nikkel-56 onstabiel is, hebben we het experiment via inverse kinematica uitgevoerd. Echter is het uitvoeren van experimenten met exotische stralen nog steeds een uitdaging, aangezien stralen van dit soort kernen relatief lage intensiteiten hebben. Vandaar dat, om een redelijke opbrengst te krijgen, een dikke trefplaat nodig is. Echter degradeert dit de energieresolutie, en zeer laag-energetische deeltjes kunnen niet uit de trefplaat komen. Een goed alternatief is om een actief trefplaat te gebruiken, zoals MAYA op GANIL, waarin de trefplaat zelf wordt gebruikt voor detectie en de dikte daarvan kan worden vergroot zonder ernstig verlies van de energieresolutie. Vanwege de lage detectiedrempel in MAYA is detectie van zeer laag-energetische deeltjes mogelijk. Inelastische verstrooiing van de secundaire Nikkel-56-bundel, met een energie van 50 MeV/u, met gasvormig helium treedt daarbij op in het detectorvolume. De sporen van de lage-energie-terugstoot alfadeeltjes worden gemeten, waaruit hun verstrooiingshoeken, bereik en energieën bepaald konden worden, die vervolgens leiden naar de excitatie energie van Nikkel-56. In dit proefschrift, worden de resultaten van deze analyse getoond

Etude des modes de compression dans le 56Ni, à l'aide d'une cible active

The Isoscalar Giant Monopole Resonance and the Isoscalar Giant Dipole Resonance are important in studying the nuclear incompressibility in finite nuclei. Nuclear incompressibility is a key input to the equation of state of nuclear matter which is in turn useful in understanding some astrophysical phenomena such as masses of neutron stars and supernovae explosions. Because Nickel-56 is unstable, we performed the experiment in inverse kinematics. However, performing experiments with exotic beams is still a challenge, as beams of exotic nuclei have relatively low intensities. Hence, to get a reasonable yield, a thick target is needed. This, however, degrades the energy resolution and very low-energy particles will not come out of the target. A good alternative is to use an active target, such as MAYA at GANIL, in which the target can itself be used for detection and its thickness can be increased without a severe loss of energy resolution. Due to low-detection threshold in MAYA, detection of very low-energy particles is also possible. Inelastic scattering of the secondary Nickel-56 beam at an energy of 50 MeV/u with helium gas occurs within the detector volume. The nucleus of helium atom (also known as alpha particle) has spin and isospin both equal to zero. Therefore, it is an ideal probe to excite isoscalar resonances. The tracks of the low-energy recoil alpha particles have been measured, yielding their scattering angles, ranges and energies which then lead to the excitation energy of Nickel-56. In this thesis, results obtained from this analysis are shown.Les résonances géantes isoscalaires monopolaires et dipolaires sont importantes pour l'étude de l'incompressibilité nucléaire dans les noyaux finis. L'incompressibilité nucléaire est un élément clé de l'équation d'état de la matière nucléaire, à son tour utile pour comprendre certains phénomènes astrophysiques tels que les masses des étoiles à neutrons et les explosions de supernovae. Parce le Nickel-56 est instable, nous avons effectué l'expérience en cinématique inverse. Toutefois, la réalisation d'expériences avec des faisceaux exotiques est toujours un défi, car les faisceaux de noyaux exotiques sont de faibles intensités. Par conséquent, pour obtenir un rendement raisonnable, une cible épaisse est nécessaire. Ceci, cependant, dégrade la résolution de l'énergie, et les particules de très faible énergie ne sortiraient pas de la cible.Une solution consiste à utiliser une cible active, comme MAYA au GANIL, dans lequel la cible elle-même peut être utilisée pour la détection et son épaisseur peut être ajustée sans une perte sévère de la résolution en énergie. En raison du faible seuil de détection de MAYA, la détection de particules de très faible énergie est également possible. La diffusion inélastique du faisceau secondaire du nickel-56 à une énergie de 50 MeV/n avec de l'hélium gazeux se produit dans le volume de détection. Le noyau d'atome d'hélium dont le spin et l'isospin sont tous deux égaux à zéro est une sonde idéale pour exciter des résonances isoscalaires. Les traces des particules alpha de recul, de basse énergie, ont été mesurées. A partir de leurs angles de diffusion, l'énergie d'excitation du Nickel-56 a pu être reconstruite. Dans cette thèse, les résultats obtenus à partir de cette analyse sont présentés

Predicting the Redox Potentials of Phenazine Derivatives using DFT Assisted Machine Learning

Here, four machine-learning models were employed to predict the redox potentials of phenazine derivatives in DME using DFT. A small dataset of 189 phenazine derivatives having only one type of functional group per molecule (20 unique groups) was used for the training. Models were validated on the external test-set containing new functional groups and diverse molecular structures and achieved reasonable accuracies (R2 > 0.57). Despite being trained on the molecules with a single type of functional group, models were able to predict the redox potentials of derivatives containing multiple and different types of functional groups with reasonable accuracy (R2 > 0.6). This type of performance for predicting redox potential from such a small and simple dataset of phenazine derivatives has never been reported before. Redox Flow Batteries (RFBs) are emerging as promising candidates for energy storage systems. However, new green and efficient materials are required for their widespread usage. We believe that the hybrid DFT-ML approach demonstrated in this report would help in accelerating the virtual screening of phenazine derivatives saving computational and experimental resources. This approach could potentially identify novel molecules for green energy storage systems such as RBF

Mass measurements of As, Se, and Br nuclei, and their implication on the proton-neutron interaction strength toward the N=Z line

Mass measurements of the nuclides As69,Se70,71, and Br71, produced via fragmentation of a Xe124 primary beam at the Fragment Separator (FRS) at GSI, have been performed with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher with an unprecedented mass resolving power of almost 1000000. Such high resolving power is the only way to achieve accurate results and resolve overlapping peaks of short-lived exotic nuclei, whose total number of accumulated events is always limited. For the nuclide As69, this is the first direct mass measurement. A mass uncertainty of 22 keV was achieved with only ten events. For the nuclide Se70, a mass uncertainty of 2.6 keV was obtained, corresponding to a relative accuracy of dm/m=4.0×10-8, with less than 500 events. The masses of the nuclides Se71 and Br71 have been measured with an uncertainty of 23 and 16 keV, respectively. Our results for the nuclides Se70,71 and Br71 are in good agreement with the 2016 Atomic Mass Evaluation, and our result for the nuclide As69 resolves the discrepancy between the previous indirect measurements. We measured also the mass of the molecule N14N15Ar40 (A=69) with a relative accuracy of dm/m=1.7×10-8, the highest yet achieved with an MR-TOF-MS. Our results show that the measured restrengthening of the proton-neutron interaction (dVpn) for odd-odd nuclei along the N=Z line above Z=29 (recently extended to Z=37) is hardly evident at the N-Z=2 line, and not evident at the N-Z=4 line. Nevertheless, detailed structure of dVpn along the N-Z=2 and N-Z=4 lines, confirmed by our mass measurements, may provide a hint regarding the ongoing ˜500 keV discrepancy in the mass value of the nuclide Br70, which prevents including it in the world average of Ft value for superallowed 0+?0+ ß decays. The reported work sets the stage for mass measurements with the FRS Ion Catcher of nuclei at and beyond the N=Z line in the same region of the nuclear chart, including the nuclide Br70

First Nuclear Reaction Experiment with Stored Radioactive 56Ni Beam and Internal Hydrogen and Helium Targets

The investigation of light-ion induced direct reactions using stored and cooled radioactive beams, interacting with internal targets of storage rings, can lead to substantial advantages over external target experiments, in particular for direct reaction experiments in inverse kinematics at very low momentum transfer, q. This new and challenging experimental technique enables high-resolution measurements down to very low q and provides a gain in luminosity from accumulation and recirculation of the stored beams. For performing first experiments of this kind a dedicated experimental setup housing several DSSD (Double-sided Silicon Strip Detector) and Si(Li) detectors for recoil particles, well suited for meeting the demanding UHV (Ultra High Vacuum) conditions of a storage ring, was recently designed, constructed and installed at the internal target of the ESR storage ring at GSI. From the interaction of a stored 56Ni beam with an internal H2 target, good quality differential cross section data for elastic proton scattering, measured with the aim to determine the radial shape of the nuclear matter distribution of 56Ni, were obtained. Preliminary results are presented. Being the first reaction experiment ever performed with a stored radioactive beam on a world-wide scale, this experiment can be considered as a breakthrough for nuclear structure and astrophysics studies, and, in addition, as a successful proof-of-principle of the new experimental concept. In addition, preliminary results from a feasibility study on inelastic α-scattering from 58Ni in inverse kinematics, where it was demonstrated that the Isoscalar Giant Monopole Resonance in 58Ni can be investigated by the present technique down to CM angles below 1 degree, are discussed. Such an experiment, performed in the future with the doubly magic 56Ni, would provide important information on the EOS of nuclear matter

A novel method for the measurement of half-lives and decay branching ratios of exotic nuclei

A novel method for simultaneous measurement of masses, Q-values, isomer excitation energies, half-lives and decay branching ratios of exotic nuclei has been demonstrated. The method includes first use of a stopping cell as an ion trap, combining storage of mother and daughter nuclides for variable durations in a cryogenic stopping cell (CSC), and afterwards the identification and counting of them by a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). We utilized our method to record the decay and growth of the 216Po and 212Pb isotopes (alpha decay) and of the 119m2Sb isomer ( t1/2=850±90 ms) and 119gSb isotope (isomer transition), obtaining half-lives consistent with literature values. The amount of non-nuclear-decay losses in the CSC up to ∼10 s is negligible, which exhibits its extraordinary cleanliness. For 119Sb isotopes, we present the first direct measurements of the mass of its ground state, and the excitation energy and decay branching ratios of its second isomeric state (119m2Sb). This resolves discrepancies in previous excitation energy data, and is the first direct evidence that the 119m2Sb isomer decays dominantly via γ emission. These results pave the way for the measurement of branching ratios of exotic nuclei.peerReviewe