beta-delayed fission of Ac-228

The basic process of an exotic decay mode namely P-delayed fission is simply introduced. The progress status of the study in the world is essentialized. The observation of P-delayed fission of Ac-228 is reported. The radium was radiochemically separated from natural thorium. Thin Ra sources in which Ac-228 was got through Ra-228 ->(beta-) Ac-228 were prepared for observing fission fragments from beta-delayed fission Ac-228. They exposed to the mica fission track detectors, and measured by an HPGe gamma-ray detector. The beta-delayed fission events of Ac-228 were observed and its beta-delayed fission probability was found to be (5 +/- 2) x 10(-12).

Search for beta-delayed fission of Ac-228

Radium was radiochemically separated from natural thorium. Thin Ra-228 ->beta Ac-228 sources were prepared and exposed to mica fission track detectors, and measured by an HPGe gamma-ray detector. The beta-delayed fission events of Ac-228 were observed and its beta-delayed fission probability was found to be (5 +/- 2)x10(-12).

Temperature annealing of tracks induced by ion irradiation of graphite

Highly oriented pyrolytic graphite (HOPG) samples were irradiated by Xe ions of initial kinetic energy of 3 MeV/u. The irradiations were performed at temperatures of 500 and 800 K. Scanning tunneling microscopy (STM) images show that the tracks occasionally have elongated structures under high-temperature irradiation. The track creation yield at 800 K is by three orders of magnitude smaller compared to that obtained during room-temperature irradiation. STM and Raman spectra show that amorphization occurs in graphite samples irradiated at 500 K to higher fluences, but not at 800 K. The obtained experimental results clearly reveal that the irradiation under high temperature causes track annealing.

Unified fission model for proton emission

The unified fission model (UFM) combining with the phenomenological assault frequency has been carried out to investigate the proton-radioactivity half-lives of spherical proton emitters. The results are in good agreement with the experimental data and other theoretical values, and newly observed spherical proton emitters have been analyzed. Finally, the effect of angular momentum transfer on half-life of proton emission has been discussed in detail and a formula can be used to describe this relationship.

Improvement of a Fission-Like Model for Nuclear alpha Decay

The alpha decay constant is the product of the penetrability P and assault frequency nu(0) in the fission-like model. An effective assault frequency P-nu replacing the previous assault frequency nu(0) is introduced for improvement of a fission-like model named the generalized liquid drop model (GLDM) to describe the nuclear alpha decay process more accurately. Two analytical formulae are proposed for the effective assault frequency due to experimental data within the GLDM. The improved model can be used to give accurate calculations for alpha decay half-lives.

Fission dynamics for capture reactions in 58,64ni + 208pb systems: New results in terms of thermal energy and neutron multiplicity correlated distributions

The neutron multidetector DéMoN has been used to investigate the symmetric splitting dynamics in the reactions 58.64Ni + 208Pb with excitation energies ranging from 65 to 186 MeV for the composite system. An analysis based on the new backtracing technique has been applied on the neutron data to determine the two-dimensional correlations between the parent composite system initial thermal energy (EthCN) and the total neutron multiplicity (νtot), and between pre- and post-scission neutron multiplicities (νpre and νpost, respectively). The νpre distribution shape indicates the possible coexistence of fast-fission and fusion-fission for the system 58Ni + 208Pb (Ebeam = 8.86 A MeV). The analysis of the neutron multiplicities in the framework of the combined dynamical statistical model (CDSM) gives a reduced friction coefficient β = 23 ± 2512 × 1021 s-1, above the one-body dissipation limit. The corresponding fission time is τf = 40 ± 4620 × 10-21 s. © 1999 Elsevier Science B.V. All rights reserved.

Arp2p, a potential substrate for NatB acetyltransferase in fission yeast, is important in actin patch nucleation and motility in arp2-1 and arm1 ts mutants

The actin cytoskeleton is a dynamic and complex structure in fission yeast that plays a major function in many cell processes including cellular growth, septa formation, endocytosis and cellular division. Computational studies have shown that Arp2p, which forms part of the Arp2/3 complex, is a potential substrate of NatB acetyltransferase which has specificity for proteins possessing an N-terminal Met-Asp or Met-Glu sequence motif. In arm1- mutants the loss of function of Arm1p, an auxillary subunit required for NatB activity, results in a temperature sensitive phenotype characterized by multiple septa, failure of endocytosis, and the inability to form actin cables. A temperature sensitive mutant of Schizosaccharomyces pombe arp2 gene exhibits a similar phenotype as seen by the formation of improper septa, slow growth, and the delocalization of actin patches. Four expression vectors encoding the open reading frames of arp2 and cdc8 (tropomyosin) were constructed with a modification changing the second residue to a Histidine, believed to mimic the charge distribution of natural acetylation by NatB. Constructs tested in normal yeast strains remained viable and grew normally in the presence of Met-His Arp2p and tropomyosin. Analysis of their ability to suppress the mutant phenotypes of arp2-1 and arm1- mutants is an area of research to be explored in future studies.

Two-hybrid analysis of the interaction between the fission yeast proteins Sal3 and Cdc25

Cdc25 is a mitosis triggering phosphatase in Schizosaccharomyces pombe, and is transported in to the nucleus during G2 phase by the importin-β protein Sal3. Cdc25 triggers mitosis and cell division by dephosphorylating tyrosine 15 of Cdc2. In sal3 mutants, Cdc25 is not transported into the nucleus and the cells halt in G2. The purpose of this study is to use a two-hybrid system to determine the nature of the relationship between Sal3 and Cdc25. Previous research has failed to detect any interaction between the two proteins, but specific modifications were made to the two-hybrid system in this study including the separation of Sal3 into its two binding domains, the addition of fluorescent tags to the fusion protein, and the reversal of plasmids in the fusion proteins. Unique PCR primers were successfully designed, based on a multiple alignment of Sal3 and its homologues, to separate Sal3 into its two domains.

Analysis of Latent Tracks for MeV protons in CR-39

For protons of energy up to a few MeV, the temporal evolution of etched latent tracks in CR-39 nuclear track detector has been numerically modeled by assuming that the electronic energy loss of the protons governs the latent track formation. The technique is applied in order to obtain the energy spectrum of high intensity laser driven proton beams, with high accuracy. The precise measurement of the track length and areal track density have been achieved by scanning short etched, highly populated CR-39 employing atomic force microscope.