共查询到20条相似文献,搜索用时 15 毫秒
1.
A method for the continuous on-stream determination of trace concentrations of uranium and thorium in flowing streams is developed.
The 14 MeV neutron generator was used for irradiation and the delayed neutron counting technique was employed in counting
the induced neutron activity. The dependence of the minimum detectable concentration on the irradiation, decay and counting
times, liquid flow-rate and the background was studied. At optimal conditions, uranium and thorium concentrations were determined
down to 20 and 100 ppm, respectively. The interference of the neutron emitting nuclide17m
O was reduced to an insignificant level by optimizing the decay time. 相似文献
2.
S. Taczanowski 《Journal of Radioanalytical and Nuclear Chemistry》1972,12(1):535-542
Based on the criteria of the maximum induced activity, the problem of the optimum sample shape was analyzed for a given volume
of sample. Its shape was assumed to be cylindrical and the optimum values for the height-to-diameter ratio (presented in the
included tables) were calculated under various circumstances. Coaxial and perpendicular sample—target irradiation geometries
were considered. 相似文献
3.
Concentrations of uranium and thorium in some West Malaysian limestones have been determined using neutron activation and delayed neutron analyses. These limestones are mainly calcium carbonates and contain uranium and thorium in concentrations of about a few parts per million. 相似文献
4.
The conventional method of measurement in 14 MeV activation analysis is to employ gamma-ray spectrometry. The method has the
advantage of good selectivity but this is at the expense of sensitivity. In order to improve sensitivity the authors have
employed Cerenkov counting techniques and by the careful use of absorbers in a specially designed cell together with double
decay procedures have still retained a considerable degree of selectivity. The method has been applied to neutron flux measurement
and to the majority of the elements in the periodic table. 相似文献
5.
G. C. Meggitt 《Journal of Radioanalytical and Nuclear Chemistry》1979,48(1-2):105-116
Cyclic activation using pneumatic shuttling system and switch off and on the neutron source and detector are described in
order to eliminate some uncertainties by the provision of more accurate timing, the measurement of the effective activating
neutron flux and the correction for the detection system dead time. 相似文献
6.
S. Tagesen 《Journal of Radioanalytical and Nuclear Chemistry》1981,61(1-2):183-189
A solution for the automation of a fast pneumatic transport system and its application is given. 相似文献
7.
R. J. Rosenberg 《Journal of Radioanalytical and Nuclear Chemistry》1981,62(1-2):145-149
A simple method for the determination of uranium and thorium by delayed neutron counting is described. One portion of the
sample is irradiated in a reactor and the delayed neutrons are counted. Another portion of the sample is mixed with B4 C powder absorbing the thermal neutrons, and irradiated in the same position. From those data, both uranium and thorium can
be calculated when a quantitative calibration has been made beforehand. The detection limits for the pure elements are 0.07
ppm for uranium and 2 ppm for thorium with the minimum analyzing time being 2 min. The accuracy of the method is investigated
by comparing results obtained by the method described here with results obtained by epithermal activation analysis. 相似文献
8.
A. G. Elayi 《Journal of Radioanalytical and Nuclear Chemistry》1985,90(1):137-144
The errors of analysis due to the different parameters involved in 14 MeV neutron activation analysis method are studied. Formulae to calculate these erros have been developed when possible. Otherwise they have been evaluated for special experimental situations. Special cases where some parameters become critical, as far as precision is concerned, have been mentioned. 相似文献
9.
P. Schlechte 《Journal of Radioanalytical and Nuclear Chemistry》1981,61(1-2):55-61
A fast, sensitive and routine methode for quantitative analysis of uranium and thorium in natural samples is described. The
identification is done by counting the delayed neutrons of mainly the short living fission products after sample-irradiation
with and without cadmium shielding. The rabbit system used is installed at the Forschungsreaktor Neuherberg, type TRIGA Mark
III. The limits of detection (relative to 2 g of sample weight) were specified to be 20 ppb (U) and 3 ppm (Th) using puls
irradiations, 150 ppb (U) and 15 ppm (Th) using 1 MW steady state reactor power. A single determination is done within less
than 60 s. The methods were proved by about 3000 measurements also including comparison experiments. 相似文献
10.
J. W. Mitchell S. Yegnasubramanian L. Shepherd 《Journal of Radioanalytical and Nuclear Chemistry》1987,112(2):425-433
Bulk and surface nitrogen levels of compression-molded samples of polyacrylonitrile, poly (styrene-co-acrylonitrile), poly(methacrylonitrile), polycaprolactam, polyimide, and a cured epoxy resin (EPON 828 — JEFFAMINE T-403, 100:50) were determined, respectively, by 14 MeV NAA (14N(n,2n)13N) and by analysis of proton tracks registered in cellulose nitrate detectors (CN85) as a result of their exposure to protons from the termal neutron induced reaction,14N(n,p)14C. Except for a few polymers, agreement of results obtained for nitrogen levels in the bulk and surface regions is within expected limits. Intrinsic limitations of the method for practical determinations of nitrogen are covered. The spatial homogeneity of materials consisting of nitrogen and non-nitrogen containing segments is easily determined by image analysis of proton track densities. These data are then used to construct nitrogen distribution plots and topographical maps. The potential ability of the proton track image analysis technique for distinguishing phase separation or immiscibility of nitrogen containing polymers is discussed. 相似文献
11.
R. Van Grieken A. Speecke J. Hoste 《Journal of Radioanalytical and Nuclear Chemistry》1973,13(1):225-233
The effects of inaccurate sample sizes and sample positioning on 14 MeV neutron activation analysis results are estimated
for 30, 20 and 10 mm diameter targets. It appears that axial positioning is the most critical parameter and that using a larger
tritium target will yield an overall improvement of the reproducibility.
Aspirant of the N.F.W.O. 相似文献
12.
N. K. Mumba L. Vas Cs. M. Buczkó 《Journal of Radioanalytical and Nuclear Chemistry》1985,95(5):311-322
Applicability of a small neutron generator and a dual rectangular tube sample transfer system for analyses of U and Th using delayed fission neutron technique has been investigated. A way of optimizing the timing parameters is reported. At a fast neutron flux of 108 n.cm–2s–1, 0.02 w% U can be determined. For thorium determination this method is less sensitive. The Cd difference technique can be used for the simultaneous determination of U and Th but it has lower sensitivity.This work was supported in part by the IAEA. 相似文献
13.
M. T. Valentini Ganzerli L. Maggi V. Caramella Cresp 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(1):143-146
Uranium and thorium were analyzed in commercial bottled waters and in fresh waters, such as tap water, by neutron activation
analysis. The analysis was applied after a preconcentration step from a batch of 1–3 dm3 water under investigation. The adsorption was performed in the presence of a small amount (about 1 g) of an adsorber derived
from the salt of a-hydroxyquinoline and benzilic (diphenylglycolic) acid, adsorbed onto charcoal. The preconcentration method
has shown to be rapid and reliable. The overall method was set in order to have an alternative method of comparison with other
different methods of analysis. The proposed method may be applied to different fresh water samples.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Samples of nominal 18 carat and 21 carat gold jewelleries from the local market were non-destructively bulk analyzed using neutron activation analysis. Neutrons of 14 MeV energy were used with a fast pneumatic sample transfer system. The actual gold contents, as well as the composition of the base metals in these samples were determined. The fast neutron activation was found to be an efficient, quick and accurate method of characterizing the precious metal objects routinely in bulk, with a large sample throughput. The results demonstrate the commercial availability of the technique for non-destructive bulk analysis of precious metal objects. 相似文献
15.
Uranium in thorium matrixes or in minerals and ores containing thorium is determined by epithermal neutron activation analysis (ENAA). In some minerals and ores, such as monazite sands, the analysis can be carried out by purely instrumental means with no chemical separation of uranium or thorium from the irradiated matrix. For thorium compound matrixes with very low uranium contents, a rapid radiochemical separation method, based on the retention of uranyl ion on anion-exchange resins, is first carried out, before counting the gamma-ray peaks for239U in multichannel analysers coupled to NaI(Tl) scintillators or to Ge(Li) detectors. 相似文献
16.
A neutron activation method is described for the determination of thorium and uranium in rocks at the microgram and submicrogram levels. Radiochemical separations are carried out using the alpha-active nuclides protactinium-231 and neptunium-237 as tracers. The method is applied to the Standard granite XXX and the standard diabase XXX. 相似文献
17.
K. Ogiwara T. Oi T. Ossaka M. Mukaida T. Honda 《Journal of Radioanalytical and Nuclear Chemistry》1995,191(2):273-278
Uranium and thorium contents of solar salts were measured by neutron activation analysis. In advance of neutron irradiation, U and Th were concentrated and separated from some interfering elements by neutralization in which they were precipitated with aluminium hydroxide from solutions obtained by dissolving the salts in water or dilute nitric acid solution. The uranium and thorium concentrations determined were from several hundred ppt to 10 ppb. It was strongly indicated that uranium tends to remain in the solution (brine from seawater) phase in the process of solar salt production while thorium tends to transfer to the solid (solar salt) phase. 相似文献
18.
A. G. Elayi 《Journal of Radioanalytical and Nuclear Chemistry》1977,35(2):377-382
The screening effect produced by a sample upon a standard located behind it is calculated. Curves for the secreening effect
as a function of the sample material and of the sample depth are given. 相似文献
19.
Simultaneous determination of trace uranium and thorium by radiochemical neutron activation analysis
A method for the simultaneous, radiochemical neutron activation analysis of uranium and thorium at trace levels in biological materials is described, based on a technique known as LICSIR, in which a double neutron irradiation is employed. In the first, long irradiation233Pa (27.0 d) is induced by neutron capture on232Th and then the sample is cooled for several weeks. A second short irradiation to induce239U (23.5 m) is followed by a rapid sequential radiochemical separation by solvent extraction of239U with TBP and233Pa with TOPO. Chemical yields of239U and233Pa were measured for each sample aliquot using added235U and231Pa tracers from the -spectra of the separated fractions. The technique was validated by quality control analyses. 相似文献
20.
The possibility of the use of characteristic X-rays, emitted after IT of EC type of radioactive decay, for analytical purposes
in 14 MeV neutron activation analysis was investigated. Elements from Cr to U were theoretically considered and 24 of them
experimentally examined. The results showed usefulness of the technique for several elements in spite of the troublesome selfabsorption
effect. It is expected that the 0.1% determination limit can be achieved for the most suitable elements. 相似文献