Dating the Sea of Marmara sediments by a uniform mixing model

The sedimentation rates and Pb-210 fluxes on sediment surfaces were measured in the north, northwestern and southwestern parts of the Sea of Marmara. Each core had varying thickness of constant Pb-210 activity regions followed by a decreasing part with sediment depth. The sedimentation rates of the samples collected from the Bosporus and the Dardanelles could not be analysed due to the homogenization of activity in the strong currents of these straits. A uniform mixing model is proposed for the simultaneous analysis of sedimentation rates, Pb-210 fluxes and mixing depths from the experimental data. In this model, the parameters were obtained by minimizing the multi-dimensional parameter space using a grid search algorithm. The Pb-210 fluxes were found to be about 0.048 Bq cm(-2) year(-1) for all sampling sites. The mass sedimentation rates were 0.19 and 0.073 g cm(-2) year(-1) at the shelves of the Bosporus and the Dardanelles and 0.055 and 0.064 g cm(-2) year(-1) in the northwestern and middle northern basins, respectively, of the Sea of Marmara. Copyright (C) 1996 Elsevier Science Limite

FINE-STRUCTURE OF MASS AND CHARGE-DISTRIBUTION IN LOW-ENERGY FISSION

Studies of finer details in mass and charge distribution in fission leads to a better understanding of the fission process. Experimental determination of independent and cumulative yields using radiochemical techniques as well as mass spectrometers and fission product recoil separators form the basis of such studies. It has been established that closed shells as well as an even number of nucleons influence both mass and charge distributions. The magnitudes of these effects may be estimated from existing experimental yield data and various fission models. Using our measurements of several fission yields and those existing in the literature we have calculated even-odd proton and neutron effects for various low energy fissioning systems. Where enough data existed, direct calculations were made, whereas for other cases the Z(p)-model of WAHL has been used. It is found that the even-odd proton effect is well established and pronounced in thermal neutron fission of U-235 and U-233. Lesser effects were found for reactor neutron induced fission of Th-232, thermal neutron fission of Pu-239 and spontaneous fission of Cm-245 and Cf-249. No effect seems to exist in the thermal neutron fission of Pu-241 and the spontaneous fission of Cf-252. The even-odd neutron effect is found to be much lower than the corresponding proton effect in U-235 and U-233 fissions and is nonexistent in the rest of the fissioning systems