The MORA project Delahaye, P.; Liénard, E.; Moore, I. ...
Hyperfine interactions,
2019/12, Letnik:
240, Številka:
1
Journal Article
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The MORA (
M
atter’s
O
rigin from the
R
adio
A
ctivity of trapped and oriented ions) project aims at measuring with unprecedented precision the
D
correlation in the nuclear beta decay of trapped and ...oriented ions. The
D
correlation offers the possibility to search for new CP-violating interactions, complementary to searches done at the LHC and with electric dipole moments. Technically, MORA uses an innovative in-trap orientation method which combines the high trapping efficiency of a transparent Paul trap with laser orientation techniques. The trapping, detection, and laser setups are under development. The project will first focus on the proof-of-principle of the in-trap laser orientation technique, before the actual measurement of the
D
correlation in the decay of
23
Mg
+
ions is undertaken firstly at JYFL and then later, at GANIL, with full sensitivity to new physics.
Isotopic effects in the fragmentation of excited target residues following collisions of 12C on (112,124)Sn at incident energies of 300 and 600 MeV per nucleon were studied with the INDRA 4pi ...detector. The measured yield ratios for light particles and fragments with atomic number Z < or = 5 obey the exponential law of isotopic scaling. The deduced scaling parameters decrease strongly with increasing centrality to values smaller than 50% of those obtained for the peripheral event groups. Symmetry-term coefficients, deduced from these data within the statistical description of isotopic scaling, are near gamma = 25 MeV for peripheral and gamma < 15 MeV for central collisions.
Directed and elliptic flow for the Au + Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4 pi multi-detector. For semi-central collisions, the ...elliptic flow of Z <= 2 particles switches from in-plane to out-of-plane enhancement at around 100 MeV per nucleon, in good agreement with the result reported by the FOPI Collaboration. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. The conditions for the appearance and possible origins of negative flow are discussed.
Recently, it has been observed that events with the same total transverse energy of light charged particles (LCP) in the quasitarget region, E{sub perpendicular12}{sup QT}, show two quite distinct ...reaction scenarios in the projectile domain: multifragmentation and residue production. This phenomenon has been dubbed ''bimodality.'' Using quantum molecular dynamics calculations we demonstrate that this observation is very general. It appears in collisions of all symmetric systems larger than Ca and at beam energies between 50A MeV and 600A MeV and is due to large fluctuations of the impact parameter for a given E{sub perpendicular12}{sup QT}. Investigating in detail the E{sub perpendicular12}{sup QT} bin in which both scenarios are present, we find that neither the average fragment momenta nor the average transverse and longitudinal energies of fragments show the behavior expected from a system in statistical equilibrium, in experiment as well as in QMD simulations. On the contrary, the experimental as well as the theoretical results point toward a fast process. This observation questions the conjecture that the observed bimodality is due to the coexistence of two phases at a given temperature in finite systems.
Using the quantum molecular dynamics approach, we analyzed the results of the recent INDRA Collaboration Au+Au experiments at GSI in the energy range between 60A and 150A MeV. It turns out that in ...this energy region, the transition toward a participant-spectator scenario takes place. The large Au+Au system displays, in the simulations as in the experiment, simultaneously dynamical and statistical behavior, which we analyze in detail. The composition of fragments close to midrapidity follows statistical laws, and the system shows bimodality, i.e., a sudden transition between different fragmentation patterns, as a function of centrality, as expected for a phase transition. The fragment spectra at small and large rapidities, on the other hand, are determined by dynamics, and the system as a whole does not come to equilibrium--an observation that is confirmed by FOPI Collaboration experiments for the same system.
Medical implants used in oral and orthopaedic surgery are mainly produced from titanium. Their biological behaviour, e.g. osseointegration, essentially depends on both the chemical composition and ...the morphology of the surface. Modifications achieved by excimer laser irradiation of titanium samples were investigated in order to improve their surface characteristics so as to facilitate biointegration. To enlarge the effective interfacial area of bone–implant contact, holes were ablated by laser pulses of ns or sub-ps length. During ns ablation, crown-like projecting rims formed around the borders of the holes. Ultra-short (0.5
ps) KrF excimer laser pulses were successfully applied to avoid these undesirable formations. Since a smooth dental implant surface is necessary to maintain a healthy connection with the soft tissues, laser polishing of samples was investigated, too. Irradiation with a series of ns laser pulses resulted in effective smoothing, as measured with atomic force microscope. X-ray photoelectron spectroscopy analysis of the laser-polished titanium surface revealed that laser treatment led to a decrease of the surface contamination and in thickening of the oxide layer. X-ray diffraction measurements demonstrated that the original
α-titanium crystal structure was preserved.
We study the anisotropy effects measured with INDRA at GSI in central collisions of
129Xe+
natSn at 50
A
MeV and
197Au+
197Au at 60, 80, 100
A
MeV incident energy. The microcanonical ...multifragmentation model with non-spherical sources is used to simulate an incomplete shape relaxation of the multifragmenting system. This model is employed to interpret observed anisotropic distributions in the fragment size and mean kinetic energy. The data can be well reproduced if an expanding prolate source aligned along the beam direction is assumed. An either non-Hubblean or non-isotropic radial expansion is required to describe the fragment kinetic energies and their anisotropy. The qualitative similarity of the results for the studied reactions suggests that the concept of a longitudinally elongated freeze-out configuration is generally applicable for central collisions of heavy systems. The deformation decreases slightly with increasing beam energy.
Good news for the experimentalists using stable ion beams! A chart of beams is now available online (
http://u.ganil-spiral2.eu/chart-ecos/
) (
Figure 1
).
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