共查询到20条相似文献,搜索用时 62 毫秒
1.
H. Münzel F. Michel P. P. Coetzee V. Krivan 《Journal of Radioanalytical and Nuclear Chemistry》1977,37(1):267-273
The possible application of cyclotron-produced fast neutrons to activation analysis for oxygen based on the16O(n, p)16N reaction has been investigated. Neutrons were produced by bombarding a thick beryllium target with 22 to 45 MeV deuterons.
It was found that the sensitivity increases rapidly with the energy of the deuterons. Using 45 MeV deuterons and a 10 μA beam
current a sensitivity of about 20 counts per 1 μg oxigen could be achieved, enabling the determination of less than 1 μg oxigen.
In a direct comparison it was experimentally established that the sensitivity for cyclotron-produced neutrons assuming a deuteron
beam of about 10 μA, is up to two orders of magnitude higher than that achievable for 14 MeV neutrons with a flux of about
1010 n/s. The interference of fluorine is at about the same level for both the cyclotron-produced and 14 MeV neutrons. Using cyclotron-produced
fast neutrons in the investigated energy range, sodium and magnesium can also interfere, but only to a very much lower extent. 相似文献
2.
Characteristics of a source of thermal neutrons based on an evacuated NG-400 neutron generator with the maximum flux (Φf) 2 × 1011 neutron/s for 14 MeV neutrons and 2 × 109 neutrons/s for 3 meV neutrons have been investigated. The possibilities of its application for neutron activation analysis
have been estimated. The distribution, composition, and density (φT) values of the thermal neutron flux have been measured in the inner cavity of the moderator using activation detectors. φT was 2 × 108 and 2 × 106 neutrons/cm2 s for thermalized neutrons with energies of 14 and 3 MeV, respectively. The possibilities of the apparatus have been estimated
theoretically and experimentally for the cases of thermalized neutrons of 14 MeV and 3 MeV. 相似文献
3.
Ph. Albert J. Blouri Ch. Cleyrergue N. Deschamps J. Le Hericy 《Journal of Radioanalytical and Nuclear Chemistry》1968,1(5):389-396
The analytical procedure for the determination of sulfur in copper by activation with thermal neutrons is given. The purifications
necessary to obtain a radiochemically pure precipitate of baryum sulphate are described. The occurrence of some discrepant
values in the determinations led to the observation, for the first time, of abnormally high contents of35S* at a relatively important depth in the samples of irradiated copper (as deep as about 300 μ). Therefore it is necessary to
etch the samples to a depth of 300 μ at least on each surface, before doing the chemical separations. Owing to the great influence
of the reaction35Cl(n,p)35S*, the determination of sulfur by thermal neutrons is only possible at contents higher than 10−6, even if the chlorine concentration is very low (2·10−8 Cl introduces a correction in terms of sulfur of the order of 10−6). For sulfur contents lower than 10−6, the determination is made by irradiation in fast neutrons. The analytical procedure is described and the corrections in
the presence of phosphorus and chlorine are discussed. At contents of the order of 10−8, the corrections are very small and the determination of some 10−7 of sulfur is easy. Finally, the determination of phosphorus in copper by activation in thermal neutrons is given. The chemical
separations are the same as in the preceding case. Contents of the order of 10−8 phosphorus are determined without difficulty. The results of the determination of sulfur and phosphorus in many samples of
copper are indicated: OFHC copper, High Purity copper (99.999%) and different samples of zone refined copper prepared at the
Vitry’s Laboratory.
相似文献
4.
E. W. Haas R. Hofmann F. Richter 《Journal of Radioanalytical and Nuclear Chemistry》1982,69(1-2):219-233
The recoil energies of up to several MeV developed during nuclear reactions involving particle emission lead to the radionuclides
used in the analysis being redistributed between adjacent materials. In aluminum irradiated by reactor neutrons,24Na losses were observed up to a depth of 8·10−6 m; in the adjacent silicon, a24Na penetration depth was observed up to 4·10−6 m. Similar results were obtained from reaction products deriving from irradiation of Ti, Ni, N, S and Cl. This means that
the results of activation analysis investigations performed for the purpose of evaluating this type of reaction might contain
significant errors if thin layers, boundary zones of very small sample volumes are examined. In the analysis of surface layers
on silicon devices, completely erroneous results have been obtained in some cases due to the recoil phenomena described. 相似文献
5.
Jye-Bin Lin Jui-Ping Lee Ding-Bang Lin Wen-Kang Chen Wen-Shan Liu Chien-Yi Chen 《Journal of Radioanalytical and Nuclear Chemistry》2009,280(3):481-487
Stray neutron distribution in a medical cyclotron vault room was evaluated by neutron activation analysis (NAA). Neutrons
were generated in the production of radioactive nuclides, such as 18F, 11C, 13N and 15O, for diagnostic usage. Indium foil was adopted to evaluate the stray fast and thermal neutron intensity based on 115In(nf, n′)115mIn and 115In(nth, γ)116m1In reactions, respectively. The indium foils were weighed, sealed and placed at 62 points around the 6.7×8.2 m2 cyclotron room. Additionally, each indium foil was exposed for over 80 minutes during cyclotron operation and γ-peaks were
analyzed using an HPGe detector to evaluate the number of stray fast (Φ
f) or thermal (Φ
th) neutrons. The minimum to maximum numbers of fast and thermal neutrons were (3.47±0.11)×103 to (1.06±0.21)×104 n·cm−2·s−1 and 9 to 965 n·cm−2·s−1, respectively. The minimum detectable limit for stray neutrons was included herein to demonstrate the reliability. Accordingly,
60 and two points, respectively, the confidence level associated with the reported intensities of fast and thermal neutrons
reached 95%. The low qualified ratio in the evaluation of stray thermal neutrons might have been caused by either the high
Compton scattering plateau or the low intensity of the gamma-ray peak in the relevant spectrum. 相似文献
6.
The silicon content in an aluminum-silicon alloy was measured by nondestructive fast neutron activation analysis with fission spectrum neutrons. A boron nitride irradiation container reduced the flux of thermal and epithermal neutrons at the sample position, enhancing the29Si (n, p)29Al reaction. A detection limit of 0.4% silicon in a 0.5 g alloy sample was obtained. 相似文献
7.
A. Lopez Molinero Alberto Morales Anselmo Villareal Juan R. Castillo 《Fresenius' Journal of Analytical Chemistry》1997,358(5):599-603
The generation of volatile species of silicon as a means to introduce silicon into an inductively coupled plasma has been
studied. It is based on the reaction between silicon and fluoride ions in sulfuric acid media and it was carried out using
different flow injection mountings. The first mounting works with an injection of 100 μL concentrated sulfuric acid and 150
μL silicon standard solution in a continuous 0.05 mol L–1 NaF solution flow. The method shows a linear response between the intensity of emission at 251.611 nm line and the silicon
concentration from 0.1 to 200 μg mL–1, with a reproducibility of 2% and a detection limit of 0.004 μg mL–1. The second mounting produces the volatile species by the reaction between two opposed aerosol flows in a home-made nebulization
chamber. This chamber has a Cross-Flow and a Meinhard nebulizer at either end. A linear response ranging from 0.1 to 1000
μg mL–1 of silicon solution is obtained and the reproducibility rises to 8%.The detection limit reached is 0.02 μg mL–1. The silicon content in real water samples was determined by applying both the above-mentioned methods and a third method
for reference.
Received: 6 November 1996 / Revised: 19 December 1996 / Accepted: 3 January 1997 相似文献
8.
Azzam A. M. El-Atrash A. M. Ghattas N. K. 《Journal of Radioanalytical and Nuclear Chemistry》1974,22(1-2):63-74
The analysis of less than 10−9 g of the isotope204Pb in lunar samples was carried out by an (n, 2n) activation using high energy (>8. 8 MeV) neutrons. A procedure of using
the neutrons produced by bombardment of a specially designed Be sample holder with deuterons in a cyclotron was developed
and compared to irradiation carried out in the core of a nuclear reactor, Radiochemical separations and X ray-γ ray coincidence
counting techniques are necessary to achieve the required sensitivity. Although the flux of neutrons of sufficient energy
from the cyclotron procedure is somewhat lower can be obtained in the best reactor irradiations, the high radioactivity due
to other elements produced by the (n, γ) reactions in the reactor is eliminated. Radiochemical procedures for the analysis
of Bi, Tl, Zn in the same samples are also described. 相似文献
9.
A rapid, nondestructive method has been developed for determination of fluorine by activation with fast neutrons from a241Am-242Cm-Be source and counting the 6–7 MeV γ rays of the product nitrogen-16. The total neutron output of the source is 4.8·109 unmoderated neutrons per second and the flux is 1.4·108 fast n·cm−2· sec−1. The γ-ray detectors consist of two opposing, matched cylindrical NaI(Tl) crystals 10 cm long and 10 cm in diameter. The
sample is irradiated for 30 seconds, cooled for 4 seconds, and then counted for 30 seconds. The sensitivity is 4.8·104 counts nitrogen-16 per gram fluorine, and the limit of detection is 0.4 mg fluorine in a 10-gram sample. A reproducibility
of 0.24% is achieved. The relative standard deviation of the specific count rate of nitrogen-16 for 11 fluorine compounds
is 1.31%. 相似文献
10.
The Si-contents of flue-dust and sedimented dust from Czechoslovak mines were determined by instrumental activation analysis
with 14 MeV neutrons using a flux of 107 cm−2·s−1. The amounts determined range from 3 to 30 mg. 相似文献
11.
M. S. Abdelmonem A. A. Naqvi Hanan Al-Ghamdi Ghada Al-Misned 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(1):131-137
Performance of a 241Am-Be neutron source-based and 2.8 MeV neutrons-based moisture measurement setups have been compared using Monte Carlo simulation.
In the setup fast neutrons transmitted through the sample were detected by a fast neutron detector, which was placed behind
a massive long double truncated collimator. The setup geometry was optimized to detect maximum effect of 1–7 wt.% moisture
on the neutron intensity transmitted through the sample. The yield of neutrons transmitted through concrete, coal, wood and
soil samples containing 1–7 wt.% moisture was calculated for 2.8 MeV neutrons and neutrons from an 241Am-Be source. The slopes of the fast neutron intensities transmitted through the samples vs. their moisture contents are very
sensitive to the neutron energy and the sample composition. Higher slopes have been observed for the samples with larger bulk
density. The slopes of fast neutron yield show dependence on the incident neutron energy. Larger slopes have been observed
for neutrons with samller energy. Due to the overall large slopes of the transmitted intensity data of the samples for 2.8
MeV neutrons, it is expected to achieve better sensitivity in moisture measurements for a 2.8 MeV neutrons based moisture
setup. 相似文献
12.
The use of 2.8 MeV neutrons produced by the D(d, n)3He reaction should be taken into consideration in some applications of radioactivation analysis. The low number of elements
activable by these neutrons makes possible to minimize the matrix interference and the background below the characteristic
photopeaks. The very low dead-time of the spectrometric measurements permits the use of the maximum neutron flux available
now and in the future. The purpose of this paper is to define experimentally the sensitivity of determination for the 16 main
elements activable with a 400 keV Van de Graaff accelerator at a 2.8 MeV neutron flux of 2·106 n·cm−2·sec−1 on the sample. 相似文献
13.
M. Ördöch Á. Biróné G. Csath E. Szabó 《Journal of Radioanalytical and Nuclear Chemistry》1976,29(2):321-334
Rhodium, palladium, platinum and iridium have been determined in silver matrix by nondestructive activation analysis upon
activation with cadmium- and silver-filtered resonance neutrons. Experiments with different types of filter combinations are
reported. The sensitivity of the method is 5·10−3% for rhodium, 5·10−3% for palladium, 3·10−2% for platinum and 5·10−3% for iridium. 相似文献
14.
15.
Kathryn R. Williams 《Journal of Radioanalytical and Nuclear Chemistry》1996,212(5):361-371
A new method for the determination of aluminum and silicon has been developed for zeolite catalysts. In contrast to previous methods, thermal neutrons are used for the analysis of both elements, and cadmium absorbers are not needed. The silicon determination utilizes a one-hour irradiation to observe the31Si produced by the (n, ) reaction of30Si. A 15-second irradiation is used for the27Al(n, )28Al reaction. The28Al activity is corrected for the contribution from the28Si(n,p)28Al reaction by using the analyzed weight of silicon in the sample and the data for a silicon standard irradiated simultaneously with the zeolite and the aluminum standard. The quantitation limits are 0.012 g for silicon and 3.3×10–5 g for aluminum. Sodium presents a significant interference, but this element can be removed by taking advantage of the ion exchange properties of these materials. 相似文献
16.
A. Damkjaer 《Journal of Radioanalytical and Nuclear Chemistry》1981,67(2):413-419
A method for determination of the boron concentration in Fe−Ni−B metallic glasses has been developed. A solution of the alloy
is irradiated with neutrons from a 10 μg252Cf neutron source and the alpha-activity due to the reaction10B(n, α)7Li is recorded by a cellulose nitrate alpha-track detector immersed in the solution. After the exposure the alpha-tracks are
made visible in a microscope by etching the cellulose nitrate film in hot NaOH and the track density is determined. 相似文献
17.
W. W. Osterhage 《Journal of Radioanalytical and Nuclear Chemistry》1980,56(1-2):267-275
A compilation of the cross sections (n, p), (n, n′ p), (n, α) (n, n′ α) and (n,3He) for93Nb,92,95,96,97,98,100Mo by 14 MeV neutrons is presented in the form of a table containing the results of nearly 70 different measurements, mainly
obtained by activation analysis. Brief assessments of the experimental methods and the data status are given. 相似文献
18.
H. Yonezawa T. Shigematsu K. Kudo 《Journal of Radioanalytical and Nuclear Chemistry》1982,68(1-2):135-143
Oxygen in silicon was determined by the secondary nuclear reactions of6Li(n, α)T and16O(t, n)18F. Lithium fluoride was deposited in vacuum on fused quartz, covered with the sample and irradiated in a nuclear reactor.
The depth profiles of18F in fused quartz and in silicon were observed, and enough depth to eliminate surface oxygen was estimated. On the basis of
these results, oxygen was determined by the average cross-section method. Oxygen concentration in CZ silicon with various
growing condition was 5–26 ppm and was consistent with those determined by the infrared absorption method. The detection limit
of oxygen in silicon is 5 ppm. 相似文献
19.
The activation of18O and19F by the reactions18O(γ, p)17N and19F(γ, 2p)17N was determined as a function of the maximum energy of the bremsstrahlung beam. By the use of this method it is possible
to measure oxygen or fluorine by counting the delayed neutrons emitted by17N with a half-life of 4.2 sec.
相似文献
20.
A. Hirose H. Wada K. Kobayashi D. Ishii 《Journal of Radioanalytical and Nuclear Chemistry》1979,52(1):111-116
Thermal neutron activation analysis of hafnium in zircaloy was investigated with a Van de Graaff accelerator. Thermal neutrons
were obtained by moderating Be−D fast neutrons with paraffin blocks.179mHf isotope with a half-life of 18.6 s, produced by178Hf(n, γ)179mHf reaction, was utilized in the present analysis. This method made it possible to analyze hafnium rapidly and non-destructively
by using scandium as an internal standard material. Several tens to hundreds of ppm of hafnium in zircaloy samples were determined
within 2 minutes with a precision of about ±1%. 相似文献