Abstract
This paper presents magnetic field measurements for the Superconducting Multipole Triplets (SMT) prototypes of the Super Separator Spectrometer (S
3
). These advanced magnets, based on ...innovative concept design, generate magnetic fields of quadrupole, sextupole, octupole, and dipole. Magnetic field measurements have been conducted with a prototype mapping system to align the magnets and assess their performance. Moreover, detailed information on the experimental setup will be presented along with magnetic field analysis on the SMT’s multipoles.
The atomic numbers and the masses of fragments formed in quasifission reactions are simultaneously measured at scission in ^{48}Ti+^{238}U reactions at a laboratory energy of 286 MeV. The atomic ...numbers are determined from measured characteristic fluorescence x rays, whereas the masses are obtained from the emission angles and times of flight of the two emerging fragments. For the first time, thanks to this full identification of the quasifission fragments on a broad angular range, the important role of the proton shell closure at Z=82 is evidenced by the associated maximum production yield, a maximum predicted by time-dependent Hartree-Fock calculations. This new experimental approach gives now access to precise studies of the time dependence of the N/Z (neutron over proton ratios of the fragments) evolution in quasifission reactions.
An atomic clock based on x-ray fluorescence yields has been used to estimate the mean characteristic time for fusion followed by fission in reactions 238U + 64Ni at 6.6 MeV/A. Inner shell vacancies ...are created during the collisions in the electronic structure of the possibly formed Z=120 compound nuclei. The filling of these vacancies accompanied by a x-ray emission with energies characteristic of Z=120 can take place only if the atomic transitions occur before nuclear fission. Therefore, the x-ray yield characteristic of the united atom with 120 protons is strongly related to the fission time and to the vacancy lifetimes. K x rays from the element with Z=120 have been unambiguously identified from a coupled analysis of the involved nuclear reaction mechanisms and of the measured photon spectra. A minimum mean fission time τ(f)=2.5×10(-18) s has been deduced for Z=120 from the measured x-ray multiplicity.
Decay spectroscopy of the odd-proton nuclei
249
Md and
251
Md has been performed. High-
K
isomeric states were identified for the first time in these two nuclei through the measurement of their ...electromagnetic decay. An isomeric state with a half-life of 2.8(5) ms and an excitation energy
≥
910
keV was found in
249
Md. In
251
Md, an isomeric state with a half-life of 1.4(3) s and an excitation energy
≥
844
keV was found. Similarly to the neighbouring
255
Lr, these two isomeric states are interpreted as 3 quasi-particle high-
K
states and compared to new theoretical calculations. Excited nuclear configurations were calculated within two scenarios: via blocking nuclear states located in proximity to the Fermi surface or/and using the quasiparticle Bardeen–Cooper–Schrieffer method. Relevant states were selected on the basis of the microscopic-macroscopic model with a deformed Woods–Saxon potential. The most probable candidates for the configurations of
K
-isomeric states in Md nuclei are proposed.
The low-lying spectroscopy of 6He was investigated via the 2-neutron transfer reaction p (He 8 , t) with the 8He beam delivered by the SPIRAL facility at 15.4 A MeV . The light charged particles ...produced by the direct reactions were measured using the MUST2 Si-strip telescope array. Above the known 2 + state, two new resonances were observed: at E a = 2.6 +/- 0.3 MeV (width Phi = 1.6 +/- 0.4 MeV) and at 5.3 +/- 0.3 MeV with Phi = 2 +/- 1 MeV . Through the analysis of the angular distributions, they correspond to a 2 + state and to an L = 1 state, respectively. These new states, challenging the nuclear theories, could be used as benchmarks for checking the microscopic inputs of the newly improved structure models, and should trigger development of models including the treatments of both core excitation and continuum coupling effects.
Reaction mechanism analyses performed with a 4pi detector for the systems 208Pb + Ge, 238U + Ni and 238U + Ge, combined with analyses of the associated reaction time distributions, provide us with ...evidence for nuclei with Z=120 and 124 living longer than 10(-18) s and arising from highly excited compound nuclei. By contrast, the neutron deficient nuclei with Z=114 possibly formed in 208Pb + Ge reactions have shorter lifetimes, close to or below the sensitivity limit of the experiment.
A simplified analytical model of an evolutionary nebula is used to generate temperature–density radial profiles following the procedure elaborated by Dubrulle (Icarus106, 59, 1993). Each nebula disk ...is characterized by its initial mass MD, its initial radius RD, and the coefficient of turbulent viscosity α. We show that these parameters may be constrained by comparing temperature–density profiles to properly chosen physical and chemical Solar System data. Relatively weak constraints come from theories of formation of giant planets. The deuterium over hydrogen ratios observed in fossil water in primitive objects of the Solar System are much more constraining. For each model of the nebula, the temporal and radial evolution of the deuterium enrichment factor in water with respect to the protosolar abundance (in H2) is calculated for the first time by integrating the equation of diffusion and is compared to observed deuterium enrichments in LL3 meteorites, giant planets, and comets. Observations cannot be fitted when we assume that H2O is uniquely produced in the hot inner part of the nebula. The agreement with observed data requires highly enriched deuterium ices initially infalling from the presolar cloud onto the whole nebula discoid. In order to fit measurements of D/H in LL3 meteorites, MD, RD, and α must be between 0.03 and 0.3 M⊙, 8 and 28 AU, and 0.003 and 1.0, respectively. The source of the turbulence consistent with these α values is discussed. High viscosity disks are characterized by MHD turbulence, while the low viscosity disks (α between 0.003 and 0.01) are characterized by hydrodynamical turbulence. Magnetic fields in the selected nebulae are also calculated. Their lifetime is found to be equal to 104 years for α=0.1 and 105 years for α=0.003. Scenarios providing us with an interpretation of the high D/H ratio observed in comets are discussed. The first scenario in which comets coming from the Oort cloud were formed very rapidly in the Uranus–Neptune region of the turbulent nebula and expelled toward the Oort cloud prior to the complete formation of these planets implies some reprocessing in the nebula of the cometary matter coming from the presolar cloud. It may not be easy however to expel comets toward the Oort cloud quite early in the history of the Solar System. It might be, according to the second scenario, that both comets coming from the Oort cloud and comets of the Jupiter family were formed farther than Neptune in a nonturbulent region of the nebula. In such a case, comets might have conserved to a large extent the chemical signature of the interstellar medium. Possible tests of the scenarios are considered.
PDF
