Studies of finer details in mass and charge distribution 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 Zp-model of WAHL has been used. It is found that the even-odd proton effect is well established and pronounced in thermal neutron fission of235U and233U. Lesser effects were found for reactor neutron induced fission of232Th, thermal neutron fission of239Pu and spontaneous fission of245Cm and249Cf. No effect seems to exist in the thermal neutron fission of241Pu and the spontaneous fission of252Cf. The even-odd neutron effect is found to be much lower than the corresponding proton effect in235U and233U fissions and is nonexistent in the rest of the fissioning systems.
We have collected sixteen total diet samples from two socioeconomic groups in Turkey by duplicate portion techniques. Samples
were homogenized with titanium-blade homogenizer, freeze dried and analyzed for their minor and trace elements mostly by neutron
activation analysis. Bread and flour samples were also collected from the same regions and analyzed similarly by instrumental
neutron activation analysis. We have determined concentrations of more than 25 elements in total diets, bread and flour, and
fiber and phytate in total diets. We have determined daily dietary intakes of these population groups, probable source of
elements through correlation coefficients, and enrichment factor calculations.
Concentrations of 30 elements in the atmospheric particulate material were determined by three defferent nuclear activation
techniques, namely; photon, thermal neutron and 14 MeV neutron activation analysis. Trace element concentrations observed
were interpreted in terms of Enrichment Factor, EF, of each element with respect to crustal abundance and coal in order to
find any possible correlation between the existance of highly enriched elements in the atmosphere and pollution source materials.
It was also found that enrichment factors of elements are inversly proportional with the size of particulate material.
One of the requirements of stable isotope tracer technique is detection of two isotopes of same element. It is preferable to use instrumental techniques in order not to contaminate the samples. Different instrumental nuclear techniques namely neutron activation analysis (NAA), photon activation analysis (IPAA), and prompt gamma ray activation analysis (PGAA) were tried on human blood samples. The techniques were found to be complementary to each other, NAA being the most sensitive of the three. Zinc is choosen for validation work among the three feasible elements (Zn, Cr, Se) for stable isotope tracer technique. As NAA was not sufficient to detect two isotopes of Zn, a radiochemical separation scheme was developed later.
The parameters of Isotonic Charge Distribution Model have been calculated for several isotones of three low energy fissioning systems. The global charge even-odd effects are determined as 0.27±0.04 for thermal neutron induced fission of233U(U233T), 0.27±0.05 for U235T and 0.13±0.05 for PU239T. The pre-scission kinetic energies for U235T and PU239T are estimated and found to be 16 MeV.
Atmospheric particulate material collected in Ankara was analyzed by instrumental neutron activation analysis. The results are interpreted with respect to trace element concentrations of the earth's crust. Volatile elements such as As, Sb, Zn, Br and Hg are highly enriched suggesting noncrustal origin. Enrichment factors increase with decreasing particle size.
Extensive experimental and evaluated yield data are now available for the fragments in low energy nuclear fission. Using these data we re-examined the influence of even nuclear numbers and closed shells on the mass and charge distribution in low energy fission. We used WAHL's Zp model and Ap model. We also examined the effects ofZ=50,N=82 and possiblyN=88 shells. A new method was developed based on two Gaussian curves for the even and odd products. TheEOZ andEON values calculated are based on these different methods and are seen to be consistent with each other in spite of the somewhat different definitions of the even-odd effect. The even-odd effect decreases with an increasing fissility parameter. TheEON values are substantially lower than the correspondingEOZ values, probably due to the effect of washing out the neutron pairing effect by prompt neutron emission. The magnitude of the even-odd effect varies with different mass regions. TheEOZ andEON values decrease as they go from asymmetric to symmetric regions in mass distributions.
The fate of dissolved Hg(II) in surface waters is an important component of the Hg cycle. A simple experimental methodology
was used to understand and measure the transport of Hg(II) from water to air and sediment. The use of radioactive dissolved
Hg tracer for the determination of evasion and deposition is found to be a very useful technique. The evasion of mercury was
investigated during a 140-hour period. It was observed that about a quarter of mercury chloride remained in the water phase,
the other quarter was emitted via the evasion process and half of it deposited in sediment.
Authors:S. Liu, C. Chung, J. Chuang, C. Wang, and N. Aras
Sixteen minor and trace element contents of diet samples from three different social population groups in Taiwan were determined. Samples were prepared using duplicate portion technique by collecting the 15 subjects ate and drank during a 3-day period. Samples were homogenized, freeze-dried, and elemental concentration of minor and trace elements were determined by instrumental neutron activation analysis. Elemental concentrations and daily dietary intake of the elements were compared with those in the other nations, and possible origins were discussed.
Authors:N. Aras, G. Yilmaz, S. Alkan, and F. Korkusuz
There is an evidence that some of the essential trace elements are crucial determinants of bone health. Excess or deficiency
of these elements has a role in the development of bone diseases, therefore research on trace elements in bone is very important.
Iliac crest bone biopsies were optioned from twelve persons undergoing orthopedic surgery due to any reason than osteoporosis.
Cortical and trabecular parts were separated, and blood and fats were removed. Up to 30 minor and trace elements were determined
in these samples by instrumental neutron activation analysis and other techniques and their relations were discussed.