[en] In the production technology of fluorescent lamp they should define the partial pressure of Ar and Kr, neutron activation analysis is a suitable methods for this purpose. Gase and liquid samples are irradiated in the core of Dalat Nuclear Reactor after there treatments in 300s with neutron flux ∼4.10¹².n.cm^-2.s^-1 and measured on Hp Ge detecter. Data is collected by Canberra Series 35. This is simple methods, give fine gamma spectrum and high accuracy

[en] Short communications only

[en] Nuclear analytical techniques were used to determine the elemental compositions of suspended and bottom sediments collected at different sites in the Haiphong harbour area (northern Viet Nam). The study was aimed at: (1) understanding the origin of the sediment filling up the access channel and causing the expenditure of large sums of money for dredging operations; (2) determining the background concentrations of trace elements in the sediment. This would permit detection in the future of any pollution caused by the discharge of industrial wastes into the water because of the growing industrialization of the area. (3) Identifying the elements which can serve as activable tracers in sediment transport studies. The results obtained for the concentrations of nearly thirty elements show rather similar elemental compositions, reflecting a common origin of the sediments taken from different locations in the harbour area. The results did not allow identification of the pathway of the sediment transported to and deposited on the bottom of the access channel. On the other hand, a large difference was found in the elemental compositions of the sediment and the soil taken near to the channel island bank. This would definitely exclude any hypothesis on the interrelationship between the sediment at the bottom of the channel with the soil 'abraded' from the island. Among the trace elements with concentrations in the sediment at the ppm level, indium and selenium have been selected as being the most suitable activable tracers. Experiments on tracer preparation are in progress and some preliminary results have been obtained. The analysis also provides the background levels of the elements-pollutants, on the basis of which future industrial pollution can be revealed. (author). 4 refs, 1 fig., 1 tab

[en] Short communication

No abstract available

[en] Estimation of the mobile layer thickness in sediment transport study is always considered to be important for quantitative derivations of transport, whether for bed load transport rates or for percentage return and settling percentage rates in suspension transport. In view of application of the tracer technique, the mobile layer thickness is defined as the depth at which the tracer particles can intrude - the mixing depth. In this paper, the authors present a new approach to determine the mixing depth based on the principle that the scattering to peak ratio in gamma spectrum from the radioactive tracer-native sediment mixture is a function of the mixing depth because of scattering and absorption interactions of the radiation with the media. It is shown both from theoretical considerations and experiments that there is a rather clear relation between ratio and mixing depth. In this method. the mixing depth is derived from comparison of the ratio of counts in the spectrum obtained in the field with the calibration curve built in the laboratory by reproducing the geometrical conditions existing in the field. A case study of the mixing depth using Sc-46 tracer material in the experiments at Haiphong Navigation Channel is also presented. The mixing depth determined by the sampling and this method shows a rather good agreement.The practical capability of the method and the ability of application for common tracer isotopes such as Ir-192, Sc-46 are estimated. These isotopes are suitable to the range of mixing depth up to 30 cm

[en] As a consequence of intensive erosion processes typical of the humid tropical one, as well as of human activities destroying tropical forests, grasslands and protective mangrove swamps, etc, most navigable estuaries in Vietnam suffer seriously from sedimentation. In order to maintain the necessary depth for the 7.000 ton vessels entering and leaving ports, a large amount of money is spent annually on dredging operation. A lot of hydraulic and sedimentary surveys were carried out in the past by different groups of researchers. However, owing to the complexity of sediment processes in estuarine areas under the hydrometeorological conditions typical of the southwest Pacific, the use of just any modelling approach is not suitable. In many cases, the conclusions inferred from mathematical models have been the controversial matter. The tracer techniques, which have been employed in the country since 1991, have provided a very efficient tool to obtain a dynamic idea of sediment transport. Many investigations of bedload transport using Sc-46 labelled glass and Ir-192 glass as radioactive tracers were carried out from 1992 to 1996 at Haiphong harbour area. Bedload transport rates under effect of northeast monsoon and southeast monsoon at 5 zones located on both sides of the navigation channel were estimated. In bedload transport studies, apart from conventional methods for assessment of transport thickness, a new method using the ratio of photoelectric peak to Compton region of spectra acquired directly on the sea bed was put forward and applied. The influence of dredging materials at two dumping sites under different tidal phases on in fill rate in the access channel was assessed by radioactive tracers. The qualitative and quantitative information on sediment transport at some experimental sites given by tracers was used by modelling specialists who have undertaken hydraulic and sedimentary surveys in this region