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1.
Using as eluent a sequence of 3M HCl, 12M HCl, and 8M HNO 3, a mixture of 210Pb, 210Bi, and 210Po may be clearly separated on a column of Dowex 1×2−100 anion exchange resin. A Cherenkov count in H 2O and the variation in count rate with time confirm that the nuclides emerge in the order 210Pb→ 210Bi→ 210Po. If 12M HCl is replaced by 1.5M H 2SO 4/2.3 M Na 2SO 4, a clean separation also results, but recovery of 210Po becomes considerably more difficult. All three nuclides are readily detectable by liquid scintillation counting, with the
efficiency for 210Pb in the 60–70% range. The Cherenkov aqueous counting efficiency for 210Bi is ∼14–15%. 相似文献
2.
Liquid scintillation counting of radionuclides emitting beta radiation with E max>2 MeV has been investigated. Fluor volume effects were similar to those for low energy beta radiation, and pulse height spectra
broadened in a predictable manner with no pulse clipping up to 4.913 MeV. Large changes in sample channels ratio due to color
quenching resulted in progressively smaller losses of counting efficiency as beta energy increased. Counting efficiences were
estimated to be near 100 percent for 34Cl m, 36Cl, 32P and 38Cl. Cerenkov counting of 38Cl by liquid scintillation counter was volume dependent for both counting efficiency and pulse height spectrum. Counting efficiencies
for 34Cl m, 36Cl, 32P and 38Cl were estimated to be 57.0, 7.5, 42.7 and 66.3%, respectively. Pulse height spectra were shifted to greater pulse heights
as a function of beta E max, supporting the possibility of energy discrimination for beta emitters by Cerenkov pulse height spectrum analysis. The advantage
of singles Cerenkov counting over coincidence Cerenkov counting was greatest for 36Cl and least for 38Cl; this advantage was amplified more for samples of 36Cl which had been color quenched than for similarly quenched samples of 38Cl or 32P. 相似文献
3.
The Environmental Survey Laboratory is responsible for the monitoring of radioactivity due to natural and artificially produced radionuclides in a variety of samples available around the nuclear facilities at Tarapur. Standard methods of radiochemical separation and counting are followed to determine -emitters in various matrices. To make the measurement simple and detect lower levels of contamination in some of the matrices, a method was developed to measure the high energy gross -activity primarily due to 90Y in borehole water and urine samples of occupational workers by Cerenkov counting in a liquid scintillation analyser. Cerenkov counting results of borehole samples were compared with the total gross -activity measured by a low background beta-counter. The combined measurements were used to evaluate 90Sr and 137Cs levels without chemical separation or gamma-spectrometry. Cerenkov counting technique was also utilised to evaluate 40K in drinking water and intercomparison water samples. The paper presents the methodology and results of a few measurements using the technique. 相似文献
4.
A radiochemical technique for estimation of 90Sr concentration by direct extraction of 90Y with bis (2-ethylhexyl) phosphate (HDEHP) in toluene was developed and standardized. About 90% 90Sr retained in the aqueous phase at the optimized pH 4–4.5. Cerenkov counting with 0.04 g mL−1 sodium salicylate as a wavelength shifter resulted in 7.5 fold increase its Cerenkov counting efficiency. The method was validated by estimating 90Sr in certified reference materials like, IAEA TEL 2016-03 drinking water, Spruce needle and IAEA-156 Clover. The interference of naturally occurring Ra and its β progeny especially Pb was eliminated by means of Cerenkov counting. Conventional radiochemical separation was used to compare 90Sr activity in effluent samples. 相似文献
5.
Absorption method is shown to be suitable for direct determination of pure β-emitting, isotopes in samples containing more
than one β-emitter. This method consists of (1) measurement of the β-counting rate as a function of the thickness of the absorber
placed in between the sample and the β-detector and (2) decomposition of the complex absorption curve by computation in order
to obtain the contributions of the nuclides to the total counting rate one by one. The method is presented through two examples
of its practical application in the field of environmental radioanalysis: 90Sr and 147Pm isotopes were determined in aerosol samples contaminated by Chernobyl radioactivity and in hot particles of Chernobyl origin
using a simple end-window Geiger-Müller counter as a β-detector. 相似文献
6.
The interaction of celecoxib (Celox) with cyclodextrins (CDs) has been investigated by phase solubility techniques. In this study, the influences of CD type, pH, buffer type, buffer concentration and temperature on the tendency of Celox to form inclusion complexes with CDs were examined. The tendency of Celox to complex with CDs is in the order HP-β-CD > β-CD > γ-CD > α-CD, where the complex formation constants ( K
11) were 1377, 693, 126 and 60 M −1, respectively. Also ionization of the slightly acidic Celox (p K
a=9.7) was found to reduce its tendency to complex (i.e., The K
11 values of Celox/β-CD in 0.05 M phosphate buffer were 976 and 210 M −1 for neutral and ionized Celox, respectively). Increasing citrate and phosphate buffer concentration enhances the tendency of ionized Celox to complex with β-CD as a result of a corresponding decrease in the inherent solubility ( S
0) of the Celox anion. On the other hand, these two buffers interact differently with neutral Celox and β-CD, where increasing phosphate buffer concentration at low pH enhances the complexation of neutral Celox by lowering S
0, while increasing citrate buffer concentration at low pH reduces complex formation as citrate buffer species, mainly citric acid, act as a solublizer and a competitor for Celox and β-CD. The contribution of Celox hydrophobicity for complex stability constitutes about 77% of the driving force for complex stability. The complex formation of neutral Celox with β-CD (Δ G
0=−28.6 kJ/mol) is driven by both enthalpy (Δ H
0=−21.7 kJ/mol) and entropy (Δ S
0=23.3 J/mol K) changes. 相似文献
7.
Tin is determined at the low nanogram level in biological samples by neutron activation using the pure β −emitter 121Sn of half-life 27 hours. The method is based on the concept of extracting tin selectively into an organic phase, which, after
addition of a scintillant (PPO), can be directly counted by liquid scintillation counting with near 100% efficiency. Tin is
first selectively extracted as its iodide into toluene, stripped and then re-extracted selectively into a toluene solution
of N-benzoyl N-phenylhydroxylamine for scintillation counting. Results are given for various biological reference materials. 相似文献
8.
β-cyclodextrin (βCD) and two guests (hexanoic acid and the hydrated fluoride ion) are considered as a system in the NMR chemical
shift fast exchange regime. The measured chemical shift variations for the βCD H5 protons are expressed as functions of the
mole fractions for the free and complexed states, and their slopes,
, are evaluated. When the NaF concentration is varied ([NaF] 0/mM = {50,100, 150, 200, 250}) for a defined value of the hexanoic acid concentration ([Hex] 0/mM = {5, 7.5, 10, 12.5, 15}), the chemical shift variations of the βCD H5 protons for 2.5 mM βCD solutions in D 2O present a second order polynomial variation with a minimum, suggesting two opposing trends. The first trend corresponding
to the decrease of Δδ values (relative shielding) is traced to increasingly negative values of
. Corresponding to the increase of Δδ values (relative deshielding), the second trend is mainly associated with the increase
of the mole fraction for the inclusion complex βCD·F(H 2O) 6−, as the concentration of NaF increases. The kosmotropic, stabilizing features of the fluoride ion are consistent with the
results of HF/6–31G* single point energy calculations showing that βCD·F(H 2O) 6− is energetically favourable, in contrast with βCD·Cl(H 2O) 6− and βCD·Br(H 2O) 8−. Due to its smaller size, F(H 2O) 6− is not appreciably distorted inside the βCD cavity as compared with Cl(H 2O) 6− and Br(H 2O) 8−. 相似文献
9.
Hybrid materials based on tetraethoxysilane (TEOS), tetrabutyl orthotitanate (TBOT), and hydroxyl terminated polydimethyl
siloxane (PDMS) have been prepared and characterized. The effects of HCl concentration and PDMS molecular weight (M W) have been analysed. The physical and chemical characteristics have been discussed based on the results obtained from the
characterization by Raman spectroscopy, nitrogen adsorption, mercury intrusion porosimetry and inverse gas chromatography
(IGC). Specific surface areas (SSA) and pore volumes increase with HCl concentration and are independent on the PDMS Mw. SSA
values as high as 300 m 2 g −1 have been obtained for hybrid materials prepared with HCl:(TEOS + TBOT) concentration of 0.3 and PDMS Mw of 550 g mol −1. These materials present the higher pore volumes and lower pore sizes. However, for HCl:(TEOS + TBOT) concentration of 0.5,
only macroporous materials are obtained with SSA values as low as 2–4 m 2 g −1, and pore sizes close to 10 μm. In general the presence of Ti on the SSA and porosities give a little decrease in such values.
Surface energies are consistent with those of organic–inorganic materials. Dispersive surface energies are higher for the
Si–Ti hybrid materials and, for all of them, they decrease with both HCl concentration and PDMS Mw. This result can be assigned
to the presence of a higher concentration of PDMS (or CH 3 groups) on the surface of the hybrid material as well as the presence of disordered anatase-like structures. On the other
hand, the acid and base properties are dependent on both HCl concentration and PDMS Mw. It has been observed that the acid
and base parameters of the Si–Ti hybrid materials are influenced by the disorder degree of the amorphous titanium oxide present
in them. As the disorder decrease both acid and base parameters increase. 相似文献
10.
The methodology for the rapid determination of 89,90Sr in wide range of activity concentration is given. Methodology is based on simultaneous separation of strontium and yttrium
from samples by mixed solvent anion exchange chromatography, mutual separation of 89,90Sr from 90Y by hydroxide precipitation and quantitative 89,90Sr determination by Cherenkov counting within 3 days. It is shown that Y and Sr can be efficiently separated from alkaline,
alkaline earth and transition elements as well as from lanthanides and actinides on the column filed by strong base anion
exchanger in nitrate form and 0.25 M HNO 3 in mixture of ethanol and methanol as eluent. Decontamination factor for Ba, La and other examined elements except calcium
is low and can not affect quantitative determination in predictable circumstances. Methodology for quantitative determination
by Cherenkov counting based on following the changes of sample activity over time is described and discussed. It has been
shown that 89,90Sr can be determined with acceptable accuracy when 89Sr/ 90Sr ratio is over 10:1 and that separation of Y enables reliable determination of 89Sr and 90Sr in wide range of 89Sr/ 90Sr ratios (60:1) and in some cases in presence of other yttrium and strontium isotopes. The methodology was tested by determination
of 89,90Sr in Analytics crosscheck samples (nuclear waste sample) and ERA proficiency testing samples (low level activity samples).
Obtained results shows that by using of low level liquid scintillation counter it can be possible to determine 89Sr and 90Sr in wide range of concentration activity (1–1,000 Bq/L/kg) with uncertainty below 10% within 2–3 days. Results also show
that accuracy of determination of 89Sr (and 90Sr) strongly depends on the determination of difference between separation and counting time when activity ratio of 89Sr/ 90Sr is high. Examination the influence of media and vial type on background radiation and counting efficiency has shown that
lowest limit of determination can be obtained by using of HNO 3 in plastic vials as counting media, because in this combination figure of merit is maximized. For the recovery of 50% and
100 min of counting time estimated MDA is 55 Bq and 90 Bq for 90Sr and 89Sr, respectively. Analysis of combined uncertainty shows that it mainly depends on uncertainty of efficiency and recovery
determination, uncertainty of activities determination for both isotopes and level of background radiation. 相似文献
11.
Cyclic voltammetry was used in order to obtain carbon paste electrodes (CPEs) modified with α- and β-cyclodextrins (CPE α-CD, CPE β-CD) in HClO 4 media as electrolyte. The modified CPEs were obtained by applying 30 potential cycles, thus forming on the substrate a film
with electroactive characteristics; a rise in current for the anodic and cathodic peaks became apparent as the number of cycles
increased. Such behaviour confirmed the CPE modification by the species mentioned. The CPE α-CD and CPE β-CD exhibited significant stability before various electrolytes. In order to evaluate the sort of modification attained on the
CPEs, a study was conducted, varying the potential scan rate, that confirmed the CD's presence. The modified electrodes were
used to determine Pb(II) ions in solution within the range from 1×10 –5 M up to 1×10 –3 M. The CPE α-CD and CPE β-CD electrochemical response was studied by means of anodic stripping voltammetry of the Pb(II) ions, thereby giving a linear
relation between the current for the anodic peak as a function of Pb(II) concentration with r
2=0.996 for the CPE β-CD and 0.992 for the CPE α-CD.
Electronic Publication 相似文献
12.
Literature data on the stability constants of the fluoride complexes of the actinides in different oxidation states have been
compiled. In order to have a reasonable inter-comparison, the stability constant (β 1) values obtained in diverse ionic strength media are converted to so called thermodynamic stability constants, β
1
0
using the DAVIES equation (a modification of Debye-Huckel equation). A correlation of the β
1
0
values with the fundamental properties of the actinide ions using various models available in the literature has been attempted.
Using the values of inonic radii and best available values of the stability constants of a large number of metal ions from
recent compilations a comparative study of the various models or relations available in the literature has been tried. For
metal ions in general, the semi-empirical relation recently developed by BROWN, SYLVA and ELLIS (BSE equation)_gives the best
correlation. In an attempt to accommodate the unusual trend in the stability constants of the tetravalent actinides a modification
in a parameter of the BSE equation has been proposed. Good agreement between the theoretically calculated and experimentally
determined values for actinides in different oxidation states is obtained in most of the cases. Further improvements in theoretical
relation as well as experimental data are required for better correlation. 相似文献
13.
The determination of 90Sr through the Cerenkov radiation emitted by its descendant 90Y is a well-known method and firmly established in literature. Nevertheless, in order to obtain an accurate result based on a Cerenkov measurement, the experimental work must be extremely rigorous because the efficiency of Cerenkov counting is especially sensitive to the presence of colour. Any traces of colour in the sample produce a decrease in the number of photons detected in the photomultipliers and, therefore, this might cause a diminution in Cerenkov counting efficiency. It is essential not only to detect the effect of colour quenching in the sample but also to correct the decrease in counting efficiency. For this reason, colour quenching correction curves versus counting efficiency are usually done when measuring through Cerenkov counting. One of the most widely used techniques to evaluate colour quenching in these measurements is the channel ratio method, which consists of the measurement of the shift of the spectrum measuring the ratio of counts in two different windows. The selection of the windows for the application of the corrections might have an influence on the quality of the fitting parameters of the correction curves efficiency versus colour quenching degree and hence on the final 90Sr result. This work is focused on the calculation of the counting efficiency decrease using the channel ratio method and on obtaining the best fitting correction curve. For this purpose, empirical curves obtained through artificial quenchers have been studied and the results have been tested in real samples. Additionally, given that the Packard Tri-Carb 3170 TR/SL liquid scintillation counter is a novel detector for use in Cerenkov counting, the previous calibration of the Tri-Carb 3170 TR/SL detector, necessary for the measurement of 90Sr, is included. 相似文献
14.
The differential determination of 203Hg and 14C or 35S in double labelled biological samples is presented. The biological samples were mineralized with 70% HClO 4 and 30% H 2O 2 in minivals MILLI-6. The γ-activity of 203Hg was measured on a well scintillation counter. The total activity, due to 203Hg and 14C or 35S, was measured by the liquid scintillation technique after addition of Aquasol into the same vials. The method of external
standard channel ratio was used for standardization. Very good recoveries were obtained: 100±0.7% for 203Hg and 94.6–101.0% for 14C and 35S. This method could be used for other β, γ and β-active nuclides with similar β-spectra. 相似文献
15.
A relatively simple method has been developed for the determination of 210Pb via its -emitting daughter, 210Bi. Lead-210 was separated from interfering elements as lead sulphate. The precipitate was dissolved in an alkaline solution of EDTA and the Cerenkov signal produced by the build-up of 210Bi was counted 30 days after storage using tritium channel of a liquid scintillation counter. Cerenkov counting efficiency was found to be approximately 20%. A lower limit of detection of 5.1 mBq/1 (based on 3 of the background with 500 minute counting time) was achieved. Chemical recoveries in the range of 70–100% were determined gravimetrically. Interference associated with currently used methods is avoided. Data from from both spiked samples and natural samples are presented. 相似文献
16.
A new RNAA procedure was developed capable of low level determination of thallium in biological and environmental samples. After high fluence neutron irradiation in a nuclear reactor, wet ashing of samples and T1(I) separation by solvent extraction with sodium diethyldithiocarbamate at pH 13, several types of counting were employed to compare their detection limits and to utilize the self-validation principle of NAA. The following measurement modes were used: High efficiency counting of -rays of 202T1 and Hg X-rays produced on decay of 204T1 using a well-type HPGe detector, combined – ray and –-counting of 204T1 with the aid of a HPGe planar detector, and liquid scintillation counting and counting of Cerenkov radiation of –-particles of 204T1. The lowest detection limit of 0.034 ng of T1 was achieved on liquid scintillation counting of 204T1. The method was applied for the analysis of biological NIST SRMs 1515, 1573a, 1577b and environmental NIST SRM 1633a. Good agreement was found between the thallium certified value in SRM 1633a and values determined in this work by all counting modes. For SRM 1573a, results in agreement were obtained by two counting modes, while counting of Hg X-rays of 204T1 was only used for SRMs 1515 and 1577b. 相似文献
17.
80g
Br and 80m
Br (via its 80g
Br daughter) were measured with high efficiency in organic solutions by means of the Cerenkov radiation from the high energy
β-rays emitted in the 80g
Br decay. The efficiency for the contaminating 82Br activity was less than 1%. 相似文献
18.
Amongst various radionuclides of molybdenum, 90Mo and 99Mo have suitable β energy for clinical uses. In this paper we report separation of 99Mo from 99Mo- 99mTc equilibrium mixture. The liquid–liquid extraction technique has been employed using trioctylamine (TOA) diluted in cyclohexane
as organic phase and HCl as aqueous phase. At 10 −5 M HCl and 0.5 M TOA concentration 99mTc quantitatively transferred to the organic phase leaving 99Mo in the aqueous phase. The developed separation method is efficient and provides very high separation factor. 相似文献
19.
The component solubilities of the HCl-MgCl 2-H 2O system at −5°C were predicted by using the Pitzer ion interaction model and its extended Harvie and Weare model. The results
indicated that the model supplies a good prediction of the above-mentioned system. The values of parameters of β (0), β (1), and C
φ of HCl and MgCl 2 were obtained by using the same optimization methods as in the literature, while those of θ MgH and Ψ MgHCl were derived by extrapolating the published data of 5, 15, 25, 35, and 45°C, as well as coupling the activity coefficients
with the solubility data. The comparison between the calculated results and the experimental data indicated that the Pitzer
ion interaction model and its extended Harvie and Weare model are quite reliable in the solubility prediction.
The text was submitted by the authors in English 相似文献
20.
With reported values ranging from about 3 to 16, the aggregation number of aqueous sodium cholate micelles is not well established.
To provide new information on the aggregation of a bile salt, Taylor dispersion is used to measure the binary mutual diffusion
coefficient D of aqueous sodium cholate at concentrations from 0.001 to 0.100 mol-dm -3 at 25°C. The results are compared with calculated D values based on the association equilibrium nCholate - + βnNa + ⇋ (NaβCholate)
n
(β-1)n
where n is the aggregation number and β is the degree of sodium counterion binding. Fitting the association model to the diffusion
data gives n = 3.9±0.6 and β = 0.21 ±0.08. In contrast to the drop in D with increasing concentration of sodium cholate, the diffusion coefficients of sodium dodecylsulfate and other long-chain
ionic surfactants increase above the critical micelle region. The ent diffusion behavior of the surfactants is related to
changes in the driving forces and mobilities caused by ion association. 相似文献
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