Investigation of the X(5)-Structure in 176Os using Absolute Transition Probabilities

The investigation of the X(5) symmetry in a different mass region from the well established A = 150 region is a very actual topic in nuclear physics. The first example of an X(5) like nucleus, namely 178Os, outside the A = 150 mass region has been found by Moeller et al.[8,51]. From the energy spectrum, the neighbor nucleus 176}Os is considered as a good candidate for a nucleus where the critical point symmetry X(5) [2] can be observed. The aim of this work is to test the model predictions based on the X(5) critical point symmetry in the 176Os nucleus. Reliable and precise lifetimes of excited states in 176Os have been measured for the first time using the Recoil Distance Doppler Shift Method. Lifetime experiments were performed at the GASP array, INFN Legnaro and at the FN Tandem accelerator of the University of Cologne in combination with the Cologne plunger apparatus. In 176Os, the lifetime of eleven excited states were determined using the Differential Decay-Curve Method. In addition, the lifetime of excited states in 177Os were measured. These states were populated in a weaker reaction channel. In addition two dedicated experiments were performed to remeasure the lifetime of the first excited 2+ states in 176Os and178Os. The aim was to reduce the uncertainty of the B(E2; 2_1+ -> 0_1+) values, which are normally used to normalize transition strength within a nucleus for the comparison with theoretical models. The comparisons between the experimental transition quadrupole momenta Qt of 176Os derived from the experimental B(E2) strengths and the predictions of the X(5) model confirm the consistency of an X(5)-like description of this nucleus

Overview of recent TJ-II stellarator results

The main results obtained in the TJ-II stellarator in the last two years are reported. The most important topics investigated have been modelling and validation of impurity transport, validation of gyrokinetic simulations, turbulence characterisation, effect of magnetic configuration on transport, fuelling with pellet injection, fast particles and liquid metal plasma facing components. As regards impurity transport research, a number of working lines exploring several recently discovered effects have been developed: the effect of tangential drifts on stellarator neoclassical transport, the impurity flux driven by electric fields tangent to magnetic surfaces and attempts of experimental validation with Doppler reflectometry of the variation of the radial electric field on the flux surface. Concerning gyrokinetic simulations, two validation activities have been performed, the comparison with measurements of zonal flow relaxation in pellet-induced fast transients and the comparison with experimental poloidal variation of fluctuations amplitude. The impact of radial electric fields on turbulence spreading in the edge and scrape-off layer has been also experimentally characterized using a 2D Langmuir probe array. Another remarkable piece of work has been the investigation of the radial propagation of small temperature perturbations using transfer entropy. Research on the physics and modelling of plasma core fuelling with pellet and tracer-encapsulated solid-pellet injection has produced also relevant results. Neutral beam injection driven Alfvénic activity and its possible control by electron cyclotron current drive has been examined as well in TJ-II. Finally, recent results on alternative plasma facing components based on liquid metals are also presentedThis work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 under Grant Agreement No. 633053. It has been partially funded by the Ministerio de Ciencia, Inovación y Universidades of Spain under projects ENE2013-48109-P, ENE2015-70142-P and FIS2017-88892-P. It has also received funds from the Spanish Government via mobility grant PRX17/00425. The authors thankfully acknowledge the computer resources at MareNostrum and the technical support provided by the Barcelona S.C. It has been supported as well by The Science and Technology Center in Ukraine (STCU), Project P-507F

The mutable nature of particle-core excitations with spin in the one-valence-proton nucleus ¹³³Sb

The γ-ray decay of excited states of the one-valence-proton nucleus ¹³³Sb has been studied using cold-neutron induced fission of ²³⁵U and ²⁴¹Pu targets, during the EXILL campaign at the ILL reactor in Grenoble. By using a highly efficient HPGe array, coincidences between γ-rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 μs isomer. Lifetimes analysis, performed by fast-timing techniques with LaBr₃(Ce) scintillators, revealed a difference of almost two orders of magnitude in B(M1) strength for transitions between positive-parity medium-spin yrast states. The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations (both collective and non-collective) of the doubly magic nucleus ¹³²Sn and the valence proton, using the Skyrme effective interaction in a consistent way. The results point to a fast change in the nature of particle-core excitations with increasing spin