Alpha decay potential barriers and half-lives and analytical formula predictions for superheavy nuclei

International audienceThe synthesis of superheavy elements has advanced strongly recently and their main observed decay mode is alpha emission. Predictions of alpha decay half-lives of other possible superheavy nuclei are needed. The alpha decay potential barrier is often described using a finite square well for the one-body shapes plus an hyperbola for the Coulomb repulsion between the alpha particle and its daughter. An arbitrary adjustment of the parameters allows to reproduce roughly the experimental data. Here the alpha decay potential barriers are determined in the cluster-like shape path within a generalized liquid drop model including the proximity effects between the alpha particle and the daughter nucleus and adjusted to reproduce the experimental Qalpha. The ? emission half-lives are deduced within the WKB penetration probability through these barriers

Assault frequency and preformation probability of the alpha emission process

A study of the assault frequency and preformation factor of the α-decay description is performed from the experimental α-decay constant and the penetration probabilities calculated from the generalized liquid-drop model (GLDM) potential barriers. To determine the assault frequency a quantum-mechanical method using a harmonic oscillator is introduced and leads to values of around 1021 s−1, similar to the ones calculated within the classical method. The preformation probability is around 10−1-10−2. The results for even-even Po isotopes are discussed for illustration. While the assault frequency presents only a shallow minimum in the vicinity of the magic neutron number 126, the preformation factor and mainly the penetrability probability diminish strongly around N=126

Two-phase quasi-equilibrium in β-type Ti-based bulk metallic glass composites

The microstructural evolution of cast Ti/Zr-based bulk metallic glass composites (BMGCs) containing β-Ti still remains ambiguous. This is why to date the strategies and alloys suitable for producing such BMGCs with precisely controllable volume fractions and crystallite sizes are still rather limited. In this work, a Ti-based BMGC containing β-Ti was developed in the Ti-Zr-Cu-Co-Be system. The glassy matrix of this BMGC possesses an exceptional glass-forming ability and as a consequence, the volume fractions as well as the composition of the β-Ti dendrites remain constant over a wide range of cooling rates. This finding can be explained in terms of a two-phase quasi-equilibrium between the supercooled liquid and β-Ti, which the system attains on cooling. The two-phase quasi-equilibrium allows predicting the crystalline and glassy volume fractions by means of the lever rule and we succeeded in reproducing these values by slight variations in the alloy composition at a fixed cooling rate. The two-phase quasi-equilibrium could be of critical importance for understanding and designing the microstructures of BMGCs containing the β-phase. Its implications on the nucleation and growth of the crystalline phase are elaborated

On the liquid drop model mass formulas and alpha decay of the heaviest nuclei

International audienceThe coefficients of different macro-microscopic Liquid Drop Model mass formulas have been determined by a least square fitting procedure to 2027 experimental atomic masses. A rms deviation of 0.54 MeV can be reached. The remaining differences come mainly from the determination of the shell and pairing energies. Extrapolations are compared to 161 new experimental masses and to 656 mass evaluations. The different fits lead to a surface energy coefficient of around 17-18 MeV. Finally, alpha decay potential barriers are revisited and predictions of alpha decay half-lives of still unknown superheavy elements are given from previously proposed analytical formulas and from extrapolated Qalpha values

Clinical and in vitro analysis of Osteopontin as a prognostic indicator and unveil its potential downstream targets in bladder cancer

YesOsteopontin (OPN) plays an important role in cancer progression, however its prognostic significance and its downstream factors are largely elusive. In this study, we have shown that expression of OPN was significantly higher in bladder cancer specimens with higher T-stage or tumor grades. In addition, a high level of OPN was significantly associated with poorer survival in two independent bladder cancer patient cohorts totaling 389 bladder cancer patients with available survival data. We further identified Matrix metallopeptidase 9 (MMP9) and S100 calcium-binding protein A8 (S100A8) were both downstream factors for OPN in bladder cancer specimens and bladder cancer cell lines. Expression of OPN was significantly positively associated with that of MMP9 and S100A8, while overexpression of OPN resulted in upregulation of MMP9 and S100A8, and knockdown of OPN showed consistent downregulation of MMP9 and S100A8 expression levels. Importantly, expression levels of both MMP9 and S100A8 were significantly associated with higher T-stage, higher tumor grade and a shorter survival time in the bladder cancer patients. Interestingly, OPN expression only predicted survival in MMP9-high, but not MMP9-low subgroups, and in S100A8-low but not S100A8-high subgroups. Our results suggest that OPN, MMP9 and S100A8 all play a significant role in bladder cancer progression and are potential prognostic markers and therapeutic targets in bladder cancer. The mechanistic link between these three genes and bladder cancer progression warrants further investigation.University of Macau Multi-Year Research Grant (MYRG2015-00065-FHS

Preformation of clusters in heavy nuclei and cluster radioactivity

Within the preformed cluster model approach, the values of the preformation factors have been deduced from the experimental cluster decay half-lives assuming that the decay constant of the heavy-ion emission is the product of the assault frequency, the preformation factor and the penetrability. The law according to which the preformation factors follow a simple dependence on the mass of the cluster was confirmed. Then predictions for some most possible cluster decays are provided

Analytic expressions for alpha particle preformation in heavy nuclei

The experimental alpha decay energies and half-lives are investigated systematically to extract the alpha particle preformation in heavy nuclei. Formulas for the preformation factors are proposed. They can be used to guide the microscopic studies on preformation factors and perform accurate calculations of the alpha decay half-lives. There is little evidence for the existence of an island of long stability of superheavy nuclei (SHN)

Influence of casting temperature on the thermal stability of Cu- and Zr-based metallic glasses: theoretical analysis and experiments

Influence of casting temperature on the thermal stability of Cu- and Zr-based metallic glasses (MGs) was analyzed based on the monomer-cluster structural model using the Johnson-Mehl-Avrami (JMA) equation. The result indicates that increasing the casting temperature can enhance the thermal stability of MGs. It is suggested that it be attributed to the decrease in the amount of the local ordering clusters induced by the elevating casting temperature. The prediction is confirmed by continuous heating transformation diagrams constructed for the Cu- and Zr-amorphous samples obtained under different casting temperatures