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- Author or Editor: S. Niese x
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Abstract
For89Sr and90Sr determination in grass samples neutron activation analysis was employed as an advantageous method for yield measurements during the separation process. From the activity ratio found conclusions on the source of radioactivity are possible taking into consideration the dependence on reactor operating time.
Abstract
Primary coolant samples from a research have been analyzed for239,240Pu,238Pu,238U,237Np and239Np. The determination of237Np and238U was carried out with the help of isotope dilution neutron activation analysis with239Np or238Np as tracer. For determination of239,240Pu and238Pu alpha spectroscopic isotope dilution analysis with238Pu as tracer was used.239Np was determined with the help of isotope dilution analysis using238Np as tracer. Nuclides were isolated by chemical separation on anionite resin. Before measurement, Pu isotopes were electrolytically deposited on stainless steel plates. Activity ratios referred to238U were reported. They are helpful for identification of the sources of actinide activity in reactor effluents.
Abstract
A survey of problems connected with the activation analysis of extremely pure materials is given. The treatment of the surface of the samples influences the results. The detection limit of counting radiochemically pure nuclides are determined by efficiency, background and counting interval. The background, which usually is reduced by selected construction materials, large shields and anticoincidence techniques also may be reduced by the βγ-coincidence technique. It is possible to arrange several small β-ray detectors closely to one large γ-ray detector. Several samples are measured at the same time with a long counting interval without interferences. The method was applied to the analysis of semi-conductor silicon.
Abstract
The advantage of 
, 
-coincidence spectroscopy for the measurement of radiochemically separated nuclides of low radioactivity is demonstrated. The background is reduced by about three orders of magnitude, and its main component, the natural radioactivity of the laboratory walls, is reduced by about four orders of magnitude. The contribution of cosmic rays becomes important at higher energies and within large shields.
Abstract
With this article we remember the discovery of solid and liquid scintillators 50 years ago.H. Kallmann andL. Herforth found out that aromatic hydrocarbons are suitable to convert the absorbed energy of nuclear radiation especially from β-particles into light. They found the quenching of impurities, the reduced photon yield of α-emitters and the different fluorescent decay time of α- and β-particles.
Abstract
Impurity profiles of selected samples are determined by neutron activation analysis. After irradiation and cleaning with a mixture of hydrochloric and nitric acid a layer of 20 μm was etched with hydrofluoric and nitric acid. In the layer 0.5 ng/cm2 Cu and 3 ng/cm2 Fe were found. In cutted slides of zonefloated silicon we found a deep profile expressed by the equation c=co·exp-(x/a)2, co=2 ppm, a=190 μm.
Abstract
Neutrons contribute to the background of low radioactivity measurements, especially with detectors in large lead shields above ground, and to a lower extent in underground laboratories of medium depth. We measured the natural neutron flux in the energy region of fission by commercial 3He filled proportional counters at different places above ground and in an underground laboratory, which is covered by 47 m of rock, and demonstrated the drastic reduction of the neutron flux in the underground and the influence of the materials of the environment.
Abstract
Beta-gamma-coincidence spectroscopy is a sensitive measurement technique in reactor neutron activation analysis. A simple counting device with a 4″×3″ NaI(Tl) crystal and a 32 mm×2 mm plastic scintillator is described and the advantage of the β-γ-coincidence technique, which has been successfully applied to the determination of iron and other impurities in semiconductor silicon, is discussed.
Abstract
The determination of impurities in semiconductor silicon by nondestructive and destructive NAA is described. To improve the detection limit, a multiple beta—single gamma detector assembly is used. It is shown that24Na is also produced from silicon by a (n, αp) reaction with reactor neutrons. The cross-section with fission neutrons is 1.8·10−9 barn.
