14 research outputs found
Meson-exchange enhancement in first-forbidden -transitions: the case of K and Ca
The - decay of K and Ca have been investigated with the main motive of determining more accurately the first-forbidden - branches, in particular the rank-zero, J = 0, -transitions. K and Ca have been produced by fragmentation of U and Ti targets respectively, with a 1 GeV proton beam and subsequent on-line mass separation. For K, -ray spectroscopy, as well as delayed neutron spectroscopy by time of flight, were carried out to obtain a detailed decay scheme to 20 (bound and unbound) levels in Ca. The level structur e of Ca can be compared to recent calculations which incorporate 1p1h excitations from the f shell. The first-forbidden transition K(0)Ca(0) g.s. has been evaluated for the first time by a direct measurement of - and - activities. Its importance (61.0 7.4) is interpreted as an effect of the meson-exchange current (MEC) l eading to an enhancement factor of 62(5) in comparison with the value predicted by shell-model calculations using the impulse approximation. For the CaK decay, chemical selec tive production was obtained through separation of the molecular ion CaF without contamination by isobars. In these conditions, the measurement of very weak -branches, at a level of 10 decays, could be made and a limit, at the 2-confidence level, has been obtained for the 0 0 branch to the level at E = 2993 keV (I < 0.0046). Imp lications of these results on the general trend of meson-exchange enhancements of first-forbidden transitions within the framework of the spherical shell model are discussed
U/Pb ages of magmatism in the Zgounder epithermal Ag-Hg deposit, Sirwa window, Anti-Atlas, Morocco
International audienc
Integrated multi scale archaeological analysis in Béni Mellal-Khenifra District (Morocco). The case of the fortress of Ighram Aousser
The fortress of Ighram Aousser is located in Morocco, 10 km W of M’rirt and 120 km S of Meknés, on the so-called mines route. The lack of an organic and complete documentation and a concrete need to acquire new data about unexplored areas have required a multi-methodological research including the analysis of historical sources, archaeological surveys, topographic investigations, laser scanner modelling and geophysical prospections. All data were stored in a Geographic Information System, which allowed spatial analyses and the creation of thematic maps. The integrated geoarchaeological approach has led to a new archaeological map providing an updated view of the rich archaeological heritage in that territory. The article also offers a complete account of the valorization processes, the international promotion of the site and its long-lasting mining tradition