לוח שנה משולב

Research of neutron-rich exotic isotopes can generate significant contributions to the understanding of the astrophysical rapid neutron capture process (r-process) of nucleosynthesis, and the extension of nuclear models to regions far from stability. In this talk I present an initiative to start a research program of neutron-rich exotic isotopes
in Israel.

In the short term, the plan is to study specific processes and characteristics in relevant facilities in the world. I will discuss medium- and high-energy neutron-induced fission rates and fission products distributions of several actinides, which serve as input to quantify fission recycling in the r-process; and the probabilities of beta-delayed multi-neutron emission (of applicable isotopes), which affect the beta decay chains during "freeze out", thus changing the resulting stable isotopes r-process abundances.

For the longer term, I explore the possibility of constructing a neutron-rich exotic isotopes facility at SARAF Phase II, mainly based on medium- and high-energy induced fission. Neutron induced fission has the advantage of generating isotopes with a higher neutron number, thus extending our reach to regions farther from stability. Preliminary estimations indicate that such a facility will be potent in a world competitive manner.

Ubiquitin and ubiquitin-like protein post-translational modifications (PTMs) are implicated in every aspect of cellular regulation. Yet, we still lack comprehensive understanding of their broad functions and the range of their cellular targets. We developed a PTM profiling platform, which establishes a broadly applicable and systematic approach to study regulation of PTMs in various biological processes and human diseases. In my talk, I will introduce this system and focus primarily on one example in which we gained mechanistic insight of PTM-based regulation of cyclin B1, which is required for proper mitotic progression.

Proper performance of voluntary movements requires the integration of both spatial and temporal information about the ensuing movements. The timing of actions is often considered to be dictated by cerebellar output that is relayed to the motor cortex via the motor thalamus. We investigated the mechanisms by which the cerebellar-thalamo-cortical (CTC) system controls temporal properties of motor cortical activity.
We found that in primates the CTC pathway efficiently recruits motor cortical neurons in primary motor and premotor areas. Cortical responses to CTC activation were dominated by prolonged inhibition mediated by a feedforward mechanism. We further found that cortical cells that integrated CTC input fired transiently and synchronously at movement onset, when the timing of action is dictated. Moreover, when preventing the flow of information in the pathway the phasic firing at movement onset was reduced, but the preferred direction of the cells remained unchanged. These changes in neural firing were correlated with altered motor behavior: the monkeys were able to perform the task but with increased reaction and movement times.
These results suggest that the CTC system affects cortical firing by changing the excitation-inhibition balance at movement onset in an extensive network of TC-activated motor cortical neurons. In this manner, the temporal pattern of neural firing is shaped, and firing across groups of neurons is synchronized to generate transiently enhanced firing.

Scientifically based attempts to synthesize new elements beyond uranium started in the middle of the 1930's, when the atomic model was established and the constituents of the atomic nucleus, protons and neutrons, were known. In this talk I will present a short history from early searches for ‘trans-uraniums’ up to the production and safe identification of shell-stabilized ‘Super-Heavy Nu-clei (SHN)’. The nuclear shell model reveals that these nuclei should be located in a region with closed shells for the protons at Z = 114, 120 or 126 and for the neutrons at N = 184. The outstanding aim of experimental investigations is the exploration of this region of spherical SHN. Experimental methods are described, which allowed for the identification of these nuclei. Systematic studies of heavy ion reactions for the synthesis of SHN revealed production cross-sections which reached values down to one picobarn and even below for the heaviest species. The systematics of measured cross-sections can be understood only on the basis of relatively high fission barriers as predicted for nuclei in and around the island of SHN. A key role in answering some of the open questions plays the synthesis of isotopes of element 120. Attempts aiming for synthesizing this element at the velocity filter SHIP will be reported. Finally, plans are presented for the further development of the experimental set-ups. Efforts performed at various laboratories will eventually reveal the change of shell strength as function of proton and neutron number, the location of the most stable nuclei and how long their lifetime will be, the optimum method of their production, and, possibly, the existence of nucleonic arrangements and shapes, which are presently still objects of speculation.