Determining the spectroscopic quadrupole moment of the first 2+ state in 36Ar

Masters of ScienceA series of reorientation-effect Coulomb-excitation experiments were carried out at iThemba LABS from April to May 2016. Enriched ion beams of Ar, Ar and S were bombarded at safe energies, well below the Coulomb barrier, onto a heavyPt target with thickness 1mg/cm2. The three experiments were performed to determine the spectroscopic or static quadrupole moment , of the first excitation 2 in these nuclei in order to shed light on the zip-zap of nuclear shapes found at the end of the sd shell. This thesis will be dealing with the particular case of Ar, accelerated at a safe bombarding energy of 134.2 MeV. For this purpose, a particle-gamma coincidence experiment has been carried out using the AFRODITE array composed of 8 high-purity germanium clover detectors to detect the de-exciting gamma energies, coupled to a double-sided CD-type S3 silicon detector at backward angles composed of 32 sectors and 24 rings to detect the scattering particles. A new optimised sorting code has been developed which included fast computing processing, non-Doppler (194Pt) and Doppler correction (36Ar), add-back, and energysharing, particle and time tagging conditions. The peaks of interests in the spectra were analysed using the Coulombexcitation code GOSIA. Using the normalization method, a more precise determination of 2 0.093 eb has been accomplished

Introduction to Astronomy with Radioactivity

In the late nineteenth century, Antoine Henri Becquerel discovered radioactivity and thus the physics of weak interactions, well before atomic and quantum physics was known. The different types of radioactive decay, alpha, beta, and gamma decay, all are different types of interactions causing the same, spontaneous, and time-independent decay of an unstable nucleus into another and more stable nucleus. Nuclear reactions in cosmic sites re-arrange the basic constituents of atomic nuclei (neutrons and protons) among the different configurations which are allowed by Nature, thus producing radioactive isotopes as a by-product. Throughout cosmic history, such reactions occur in different sites, and lead to rearrangements of the relative abundances of cosmic nuclei, a process called cosmic chemical evolution, which can be studied through the observations of radioactivity. The special role of radioactivity in such studies is contributed by the intrinsic decay of such material after it has been produced in cosmic sites. This brings in a new aspect, the clock of the radioactive decay. Observational studies of cosmic radioactivities intrinsically obtain isotopic information which are at the heart of cosmic nucleosynthesis. They are best performed by precision mass spectroscopy in terrestrial laboratories, which has been combined with sophisticated radiochemistry to extract meteoritic components originating from outside the solar system, and by spectroscopy of characteristic gamma-ray lines emitted upon radioactive decay in cosmic environments and measured with space-based telescopes. This book describes where and how specific astronomical messages from cosmic radioactivity help to complement the studies of cosmic nucleosynthesis sites anad of cosmic chemical evolution.Comment: 20 pages, 9 figure

Positive pion scattering on 24Mg

The reaction (\u2724)Mg(pi(\u27+), piN) and the angular correlation between (\u2724)Mg first excited state deexcitation gamma rays and the nuclear recoil direction following pion inelastic scattering were studied at 200 MeV by means of coincidence measurements of outgoing charged particles and nuclear deexcitation gamma rays. The angular distribution of both pions and protons in coincidence with (\u2723)Na and (\u2723)Mg first excited state deexcitation gamma rays is consistent with those expected from quasi-free scattering. Comparison of results with final state nucleon charge exchange models suggests that final state nucleon charge exchange plays a minor role in single nucleon knockout reactions. The preliminary measurement of the angular correlation betwen (\u2724)Mg(\u272+) deexcitation gamma rays and the nuclear recoil direction is similar to the angular correlation W((theta)) = sin(\u272)(2(theta)) expected for non spin flip transitions

The lifetime of the 6.79 MeV state in 15O as a challenge for nuclear astrophysics and gamma-ray spectroscopy: a new DSAM measurement with the AGATA Demonstrator array

The determination of the thermonuclear reaction rates is a challenging task of nuclear astrophysics. In order to investigate this and other nuclear processes in the stellar medium, new techniques and new advanced setups for nuclear physics experiments are of vital importance. In this Thesis an advanced γ-ray spectroscopy system has been used in an experiment of astrophysical interest, that is a new Doppler shift attenuation measurement of the lifetime of the 6.79MeV state in 15O. An accurate measurement of this quantity is of paramount importance in the determination of the astrophysical S-factor and the derived cross section for the 14N(p, γ)15O reaction, the slowest one in the CNO cycle. The results of a new direct measurement of this nuclear level lifetime are discussed. The first excited states in 15O (and 15N) were populated via fusion-evaporation and Nucleon-transfer reactions of 14N on 2H (implanted at the surface of a ≈4 mg=cm2 Au layer) at 32MeV beam energy, provided by the XTU Tandem at the Legnaro National Laboratories. Gamma rays were detected with 4 triple clusters of the AGATA Demonstrator array, placed at backward angles, allowing to measure the angular distribution of the emitted γ rays in a continuous way. The energy resolution and position sensitivity of this state-of-the-art gamma spectrometer have been exploited to investigate lifetimes of nuclear levels in the ≈fs range via the Doppler Shift Attenuation Method. The deconvolution of the lifetime effects on the line-shapes of the gamma peaks from the ones due to the kinematics of the emitting nuclei has been performed by means of detailed Monte Carlo simulations of the gamma emission and detection. Coupled-channel calculations for the nucleon transfer process have been used for this purpose. Being one of the first experiments using this state-of-the-art γ ray spectroscopy tool, particular emphasis will be put in the description of the not trivial data replay and analysis, as well as the development of an ad hoc simulation tool. The comparison of experimental and simulated spectra of high-energy gamma-rays, de-exciting levels with lifetimes in the few fs range, will be shown for the 6.79MeV transition in 15O and for known cases in 15N, together with details of the chi-square analysis. Lifetime estimates for excited levels in 15N will be given and compared with previous results. The data analysis allows to give a new limit to the lifetime of the 6.79MeV state in 15O

Geologic history of Martian regolith breccia Northwest Africa 7034: Evidence for hydrothermal activity and lithologic diversity in the Martian crust

The timing and mode of deposition for Martian regolith breccia Northwest Africa (NWA) 7034 were determined by combining petrography, shape analysis, and thermochronology. NWA 7034 is composed of igneous, impact, and brecciated clasts within a thermally annealed submicron matrix of pulverized crustal rocks and devitrified impact/volcanic glass. The brecciated clasts are likely lithified portions of Martian regolith with some evidence of past hydrothermal activity. Represented lithologies are primarily ancient crustal materials with crystallization ages as old as 4.4 Ga. One ancient zircon was hosted by an alkali-rich basalt clast, confirming that alkalic volcanism occurred on Mars very early. NWA 7034 is composed of fragmented particles that do not exhibit evidence of having undergone bed load transport by wind or water. The clast size distribution is similar to terrestrial pyroclastic deposits. We infer that the clasts were deposited by atmospheric rainout subsequent to a pyroclastic eruption(s) and/or impact event(s), although the ancient ages of igneous components favor mobilization by impact(s). Despite ancient components, the breccia has undergone a single pervasive thermal event at 500–800°C, evident by groundmass texture and concordance of ~1.5 Ga dates for bulk rock K-Ar, U-Pb in apatite, and U-Pb in metamict zircons. The 1.5 Ga age is likely a thermal event that coincides with rainout/breccia lithification. We infer that the episodic process of regolith lithification dominated sedimentary processes during the Amazonian Epoch. The absence of pre-Amazonian high-temperature metamorphic events recorded in ancient zircons indicates source domains of static southern highland crust punctuated by episodic impact modification