Evidence for a spin-aligned neutron-proton paired phase from the level structure of 92^{92}Pd

The general phenomenon of shell structure in atomic nuclei has been understood since the pioneering work of Goeppert-Mayer, Haxel, Jensen and Suess.They realized that the experimental evidence for nuclear magic numbers could be explained by introducing a strong spin-orbit interaction in the nuclear shell model potential. However, our detailed knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers ($N = Z$), the unique nature of the atomic nucleus as an object composed of two distinct types of fermions can be expressed as enhanced correlations arising between neutrons and protons occupying orbitals with the same quantum numbers. Such correlations have been predicted to favor a new type of nuclear superfluidity; isoscalar neutron-proton pairing, in addition to normal isovector pairing (see Fig. 1). Despite many experimental efforts these predictions have not been confirmed. Here, we report on the first observation of excited states in $N = Z = 46$ nucleus $^{92}$Pd. Gamma rays emitted following the $^{58}$Ni($^{36}$Ar,2$n$)$^{92}$Pd fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution {\gamma}-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling) in the ground and low-lying excited states of the heaviest N = Z nuclei. The strong isoscalar neutron- proton correlations in these $N = Z$ nuclei are predicted to have a considerable impact on their level structures, and to influence the dynamics of the stellar rapid proton capture nucleosynthesis process.Comment: 13 pages, 3 figure

Estudo in silico de derivados do G-CSF humano como antibacterianos

Na tentativa de obter novas substâncias com atividade antibacteriana, o objetivo desse trabalho foi avaliar o potencial antibacteriano de quatro peptídeos sintetizados, dos quais dois possuem sequência derivada da fragmentação in silico do G-CSF humano, enquanto os outros dois foram planejados teoricamente, verificando, assim, seu interesse como novos agentes terapêuticos na saúde humana. A avaliação foi realizada em duas etapas: análise in silico, que consistiu em predições de propriedades e parâmetros associados à ação antibacteriana, por meio de ferramentas computacionais; e o experimento in vitro para a determinação da concentração inibitória mínima (MIC) dos peptídeos contra bactérias Gram positivas e negativas. A maioria das predições foi favorável para os quatro peptídeos, pois os resultados determinados para hidrofobicidade, anfipaticidade, tamanho, estrutura secundária, carga líquida, potencial de ligação em membrana, meia-vida e índice de Boman encontram-se dentro de valores desejados para o potencial antibacteriano. Na análise in silico, apenas a predição algorítmica da atividade antimicrobiana gerou resultados desfavoráveis para os peptídeos com sequências derivadas do G-CSF (peptídeos 1 e 2), porém essa mesma predição foi positiva para os outros dois. O ensaio in vitro demonstrou que até a concentração mais alta utilizada dos quatro peptídeos (500 μg/mL) foi insuficiente para a determinação de sua concentração inibitória mínima, porém, observou-se considerável diminuição no crescimento de E. coli (58,7%) pelo peptídeo 4 e de E. fecalis (86,1%) e E. coli (54,9%) pelo peptídeo 3, em comparação com o controle de viabilidade. Esses valores indicam a presença de ação antibacteriana por parte dos peptídeos planejados teoricamente (peptídeos 3 e 4), corroborando com as predições computacionais. Dessa forma, é possível concluir que a análise in silico foi de suma importância para a seleção dos peptídeos a serem sintetizados, os quais apresentaram nos ensaios in vitro resultados em concordância com a predição computacional de atividade antimicrobiana.In attempt to obtain new substances with antibacterial activity, the aim of this study was to evaluate the antibacterial potential of four synthesized peptides, where two of them have sequence derived from human G-CSF in silico fragmentation, while the other two were theoretically planned, allowing the verification of their interest as new therapeutic agents at human health. The evaluation was performed in two stages: in silico analysis, consisting of predictions of properties and parameters associated with antibacterial effect, through computational tools; and the in vitro experiment for determination of the minimum inhibitory concentration (MIC) of the peptides against Gram positive and negative bacteria. Most predictions was favorable for all four peptides, showed by determined results of hydrophobicity, amphipathicity, size, secondary structure, net charge, membrane binding potential, half-life and Boman Index, considered as desirable values for antibacterial potential. In the in silico analysis, only algorithmic prediction of antimicrobial activity revealed unfavorable results for peptides with sequences derived from G-CSF (peptides 1 and 2), nonetheless, the predictions were positive for the other two. The in vitro assay showed that up to the highest concentration used of the four peptides (500 μg/mL) was insufficient for determination of minimum inhibitory concentration, however it was possible to observe significant growing decrease of E. coli (58.7%) by peptide 4 and E. fecalis (86.1%) and E. coli (54.9%) by peptide 3, when compared with the viability control. These values indicate the presence of antibacterial activity in the theoretically planned peptides (peptides 3 and 4), confirming the computational predictions. Thus, it is possible to conclude that the in silico analysis was very important for the selection of the peptides to be synthesized, which showed results of in vitro assays in agreement with the computational prediction of antimicrobial activity.Essa dissertação teve o apoio financeiro do Edital Universal 14/2011 CNPq (nº processo: 483036/2011-0) e do Edital PROEX nº 04/2011

How sharp is the transition into the N=20 island of inversion for the Mg isotopes ?

International audienceThe N=20 island of inversion is an excellent playground for testing shell model calculations. The Mg chain is a region of shell evolution still far from being well understood. In this paper we present preliminary results of a single-neutron knockout experiment from 31Mg performed at GANIL to study the structure of 31Mg and of the core 30Mg. The level scheme and longitudinal momentum distributions were mesured and spectroscopic factors were deduced. Negative parity states arise at low energy and the spectroscopic factor for the isomeric in 30Mg was determined to be smaller than foreseen in the standard picture. The preliminary experimental results are compared to state-of the art shell model calculations revealing opposed interpretations

Selected aspects of the structure of exotic nuclei and new opportunities with gretina

In this contribution, we present recent results related to the quadrupole collectivity in neutron rich carbon isotopes. B(E2) transitions strengths derived from lifetime measurements are interpreted in a seniority scheme, indicating an increase role of proton excitations due to the reduction of the p3=2-p1=2 spin-orbit splitting. We also discuss the evolution of the N = 40 shell closure with isospin and report on preliminary results of Coulomb Excitation experiments on 66;68Fe and 64Cr. Finally, a short review of the gamma-ray tracking technique and a status report of GRETINA are presented. Some aspects of the exciting physics campaign being carried out at NSCL/MSU are discussed