共查询到20条相似文献,搜索用时 93 毫秒
1.
H. A. Das 《Journal of Radioanalytical and Nuclear Chemistry》1999,242(3):587-593
The use of “small” research reactors with applicable thermal neutron fluxes of ≤1012.cm−2.s−1 in (instrumental) activation analysis based on γ-spectrometry, and in isotope production for radiotracer experiments is surveyed
on the absis of the experience at ECN, Petten, The Netherlands and elsewhere. The aim is to provide a practical guideline
for the application of “small” reactors in both fields. Reproducibility and knowledge of the physical parameters of irradiation
and counting are essential and thus the first task of the radioanalyst. Emphasis is laid on the use of short-lived radionuclides.
This implies the elimination of an additional source of bias in γ-spectrometry. Some suggestions are made on eventual projects
of current interest. 相似文献
2.
B. Långström U. Obenius S. Sjöberg G. Bergson 《Journal of Radioanalytical and Nuclear Chemistry》1981,61(1-2):273-280
“ACTIVA” is an activation analysis programme written for small computers (16 to 32 k-words) in FORTRAN-IV. Input-mode for
operating commands is interactive, guided with self-explenatory questions. This enables the evaluation of gamma-spectra which
could be registered under 4 different conditons (flux, geometry, etc.) with two different counting systems existing in Atominstitute.
In each case another data-library with different calibration factors will be chosen and used automaticly. Programme “ACTIVA”
is originally designed for gamma-spectra registered with “Loss-Free-Counting” (LFC) electronic with 2×2048 channels, but can
be modified for 1024 or 4096 channels easily. Two different multichannel analysers (MCA) can be chosen for data-input: ORTEC-6240
MCA, or NOVALFC (Loss-Free-Counting). The correct energy calibration constants will also be chosen automaticly. The programme
has a modular constraction and combined (linked) with overlay technique. 相似文献
3.
E. P. Mignonsin 《Journal of Radioanalytical and Nuclear Chemistry》1982,69(1-2):197-217
In non destructive activation analysis, either relative measurements or parametric counting techniques are used. However,
in so complex media as biological or geological samples, where a lot of radionuclides are produced, an accurate determination
of an element, must take into account, the “background shape and height effect” due to the other radionuclides. To achieve
accuracy in such determinations, a new method is developed. 相似文献
4.
The accuracy of the live-time circuit of a 400-channel analyzer was studied in detail, and was found to be unsatisfactory
even for long-lived radionuclides. It was found that automatic live-time correction with the multi-channel analyzer gave rise
to increasing positive errors with increasing count rate; this overall positive error was composed of a positive error due
to the slowness of the electronic circuitry, and a smaller negative error due to the finite pulse-width. Adequate correction
could be performed by feeding the information from the dead-time output of the multi-channel analyzer to an external live-time
circuit with variable oscillator frequency and pulse-width. Four methods for dead-time correction were compared experimentally
in the case of short-lived radionuclides (T as low as 7 sec): the method of Bartošek et al., the method of Schonfeld, the
use of a sufficiently short counting time as compared to the half-life, and the live-time mode of counting without additional
correction. These four methods were applied to the determination of oxygen and silicon in rocks by 14 MeV neutron activation
analysis. Results are given for USGS standard rock G-2.
Research associate of the I. I. K. W. 相似文献
5.
W. C. Burnett R. Wong S. B. Clark B. Crandall 《Journal of Radioanalytical and Nuclear Chemistry》1998,235(1-2):173-178
Although potentially very useful as a screening tool, currently-applied “gross” alpha/beta analyses are often considered unreliable
by the environmental monitoring community. We describe here an alternative approach based on direct counting of pressed soil
“wafers” to estimate total alpha/beta activities. The system was calibrated using a series of natural soils and sediment standards
with total α/β activities estimated by use of a combination of available certified values, equilibrium assumptions, and our
own measurements. A set of 10 such standards that span a wide range of activities were prepared by thoroughly mixing several
grams of selected NIST and IAEA natural matrix standards together with reagent grade cellulose in a 4∶1 sample-to-binder ratio
and pressing in a 40-mm stainles steel die. The resulting wafers, assumed to be at infinite thickness for expected radionuclides,
were counted in a gas flow proportional counter set for simultaneous α/β counting. Both the alpha and beta count rates increased
in a linear, systematic manner with increasing total estimated activities. This technique should prove to be an inexpensive,
simple, and waste-free approach for screening total radioactivity in soil samples. 相似文献
6.
G. Kennedy 《Journal of Radioanalytical and Nuclear Chemistry》1995,193(2):239-245
A method has been developed for the correction of counting losses in NAA for the case of a mixture of short-lived radionuclides. It is applicable to systems with Ge detectors and Wilkinson or successive approximation ADC's and will correct losses from pulse pileup and ADC dead time up to 90%. The losses are modeled as a constant plus time-dependent terms expressed as a fourth order polynomial function of the count rates of the short-lived radionuclides. The correction factors are calculated iteratively using the peak areas of the short-lived radionuclides in the spectrum and the average losses as given by the difference between the live time and true time clocks of the MCA. To calibrate the system a measurement is performed for each short-lived nuclide. In a test where the dead time varied from 70% at the start of the measurement to 13% at the end, the measured activities were corrected with an accuracy of 1%. 相似文献
7.
The adsorption and migration behavior of a radionuclide in geological media heavily depends on its chemical forms in a given
chemical environment. In order to predict the temporal and spatial distribution of radionuclides around a disposal site when
its canister is damaged, it is necessary to develop coupled chemical speciation-solute transport models and relevant software.
For that reason, we wrote a new chemical speciation program CHEMSPEC. In this paper, the principles and structure of CHEMSPEC
are briefly described, and the strategy and algorithms that were used in this code are interpreted in some detail, such as
the measures adopted to prevent divergence in iteratively solving the mass balance equations, the “predictor-corrector” algorithm
for calculation of the number and quantities of solid species formed, and the alternate use of “freezing” and “defreezing”
oxidation states in handling of co-existent redox and precipitation equilibria. Four examples are given to illustrate CHEMSPEC’s
features and capabilities. 相似文献
8.
A method for the fast separation of short-lived nuclides in the gas phase is described. The attribution of new γ-lines to
a certain element is possible by the variation of the chemical and physical separation parameters and the determination of
the “yield” of a line, compared with the “yields” of well known nuclides. 相似文献
9.
Ho Manh Dung Menno Blaauw Daniel Beasley Maria Do Carmo Freitas 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(2):485-492
The k
0-based cyclic neutron activation analysis (k
0-CNAA) technique has been studied to explore the applicability at the Portuguese research reactor (RPI). In particular, for
the determination of elements which form short-lived radionuclides, particularly fluorine (20F, 11.16 s half-life) and selenium (77mSe, 17.36 s half-life) in polymer, biological and environmental samples. The detection limits obtained for F and Se were about
50 and 0.01 mg kg−1, respectively, in the investigated materials. The timing parameters for the procedure were 10 to 20 s for irradiation, 5 s
decay, 10 to 20 s counting, 5 s waiting and performed with eight cycles. The k
0-IAEA program was modified to use millisecond time resolution for irradiation, decay and counting times as needed for interpreting
k
0-CNAA data in terms of concentration, accuracy and detection limit. The quality control of the procedure was performed by
preparing a standard solution containing fluorine with different contents as well as using the certified reference materials
containing selenium from which the bias between the results and the certified values were within 15% for most elements at
the investigated content ranges. The analytical results for several other elements producing short-lived or detectable radionuclides,
e.g., Al, Ca, Cl, Cu, Dy, I, Mg, Mn, Ti, and V were also obtained by the k
0-CNAA procedure with accuracy within 12%. 相似文献
10.
A program in “INSTRUMENT BASIC” language is proposed for analysis of gamma-ray spectra obtained with Ge(Li) detectors and
accumulated in multichannel analysers on-line with minicomputers. The program locates the peaks, evaluates the corresponding
energy values, the net peak areas and the standard deviations on the areas. 相似文献
11.
Fast neutron activation analysis experiments were performed to investigate the analytical possibilities and prospective utilization of short-lived activation products. A rapid pneumatic transfer system for use with neutron generators has been installed and applied for detecting radionuclides with a half-life from 300 ms to 20 s. The transport time for samples of total mass of 1–4 g is between 130 and 160 ms for pressurized air of 0.1–0.4 MPa. The reproducibility of transport times is less than 2%. The employed method of correcting time-dependent counting losses is based on the virtual pulse generator principle. The measuring equipment consists of CAMAC modules and a special gating circuit. Typical time distributions of counting losses are presented. The same 14 elements were studied by the conventional activation method (single irradiation and single counting) by both a typical pneumatic transport system (run time 3 s) and the fast pneumatic transport facility. Furthermore, the influence of the cyclic activation technique on the elemental sensitivities was investigated. 相似文献
12.
Instrumental NAA based on short-lived radionuclides implies high initial total count rates which change appreciably over the counting period. This in turn necessitates corrections for three negative biases: losses due to differences in counting time between samples and standards; pile-up losses, and (residual) influence of dead-time. The procedure is demonstrated for the determination of Al, Ca, V and Mn in the IAEA Reference Material 395 Urban Dust. The obtained data are in good agreement with the reference values for this material. By limiting the total relative dead-time to 25%, statistical uncertainties are below 5%. 相似文献
13.
Kwo-Ping Chang Ching-Kuei Chen Lie-Hang Shen 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(1):153-157
Accurately determining the amount of a radionuclide actually administered to a patient is an important aspect of quality control
in nuclear medicine. In this study, in order to accurately assess the “apparent” radioactivities of radionuclides with impurities
by a dose calibrator, two methods, (1) curve fitting, and (2) relative sensitivities calculation, have been employed to determine
the parameter, M (relative response). From the comparisons between the measurement and re-calculated radioactivity using the M values, each method was found to have its own advantage and disadvantage, depending upon the fraction ratio of the impurity
as well as the energy level of the impurity’s photons. This study might be helpful for improving the assessment of radiopharmaceuticals’
“true” activity and its “apparent” activity measured by a dose calibrator. 相似文献
14.
15.
E. J. Baratta 《Journal of Radioanalytical and Nuclear Chemistry》1998,236(1-2):139-144
The U.S. Food and Drug Administration (FDA) is responsible for the wholesomeness of the nation's food supply. The FDA modified
its food monitoring program in January, 1973, to include radioactive isotopes. The methodology used to perform, analyses on
these food products are taken from the standerd setting societies such as the AOAC International, American Society for Testing
Materials and American Public Health Association Standard Methods. In addition, methods not tested by these societies are
taken from the literature or from Department of Energy manuals such as the Health and Safety Laboratory and also from Environmental
Protection Agency, Public Health Service, and Food and Agricultural Organization manuals. These include the methods for long-lived
radionuclides such as tritium, strontium-90, cesium-137 and plutonium. Also, the short-lived radionuclides such as iodine-131,
radiocesium, radiocerium and radioruthenium. In addition, they include the natural occurring radionuclides such as radium
and uranium isotopes. The activity concentrations of gamma-emitters such as radiocesium, iodine-131 and radioruthenium are
determined by gamma-ray spectrometry. This is done using intrinsic germanium detectors with the appropriate hardware and software.
The alpha and “pure” beta-emitters are determined by various radiochemical methods and techniques. The radiochemical methodology
and equipment used in analyzing these radionuclides are described and discussed. Also, the methodology and equipment for the
gamma-emitters are described in more detail in this paper. In addition, the limits of detection for the methods used will
be discussed. 相似文献
16.
G. P. Westphal 《Journal of Radioanalytical and Nuclear Chemistry》1998,233(1-2):115-118
Two commercially available digital filters with selectable, fixed time constants and triangular pulse response are discussed
to outline their potential advantages over traditional analog filters with semi-Gaussian pulse shape. A solution for the “resolution
or throughput rate” dilemma is offered by the preloaded digital filter fulfilling the postulate for the ideal adaptive filter
with optimum resolution at any counting rate. Throughput rates of >100 kc/s are demonstrated for the preloded digital filter
at resolutions superior to those of fixed shaping time filters. 相似文献
17.
The vertical distribution of85Sr and137Cs in undisturbed single-contaminated agricultural soils have been studied during their irrigation with wet atmospheric precipitation
in dependence on time under laboratory conditions for about one year. The soil samples were collected from several localities
in the environment of nuclear power plants at Dukovany and Jaslovské Bohunice using a special auger. The samples were placed
into polyethylene columns of 9 cm in diameter and 20 cm in height. The activity of radionuclides in soil profiles after their
separation into single layers were counted by Ge(Li) semiconductor gamma-spectrometry. Based on the exponential depth distribution
of radionuclides, the values of their migration parameters as relaxation depth, migration rate and retardation factor were
calculated. The influence of the permanent grass cover and of the applied zeolite on the migration parameters of these radionuclides
was also investigated.
Presented at the Conference “Nukleonika '98”, Prague, Czech Republic, 9–10 September 1998, dedicated to late Professor František
Běhounek in honour of his 100th birthday. 相似文献
18.
Yu. K. Tovbin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(10):1647-1660
A historical information about the introduction of one of the main concepts in the theory of condensed phases, critical point,
is given. The initial term, “absolute boiling temperature,” introduced by D.I. Mendeleev was formulated on the basis of deeper
views on the nature of critical phenomena than later studies by T. Andrews, who suggested the term “critical temperature,”
which became well established with time. Most interesting estimation of the studies by Andrews was given by D.I. Mendeleev.
The concept of critical temperature and the investigations of D.I. Mendeleev were discussed. 相似文献
19.
Jevgenij Alion?ik Donatas Butkus 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(1):305-313
On the Stabatishke site near to Ignalina Nuclear Power Plant a near surface repository for low and intermediate-level short-lived
radioactive waste is being constructed to store the waste which was produced during the decommissioning of the Ignalina Nuclear
Power Plant. A possible spread of radionuclides from the near surface repository and the radiation level of expression are
one at the most important aspects while evaluating the safety of the repository. The article examines the specific activity
of artificial (137Cs, 90Sr) and natural (226Ra, 232Th, 40K) radionuclides in the soil of Stabatishke site of Ignalina NPP in pinewood; the spread of these radionuclides is determined
in the system “soil-tree”. The change of long term soil pollution with artificial radionuclides was estimated. This is a background
soil pollution which had been there before the exploitation of the near surface waste repository. The transfer factors of
natural (226Ra, 232Th, 40K) and artificial (137Cs, 90Sr) radionuclides from the 0-to-20-cm soil layer to different annual pinewood rings were measured. After estimation of the
position of pine roots in accordance to the soil vertical and the annual change of the plant biomass, the transfer factor
of 137Cs movement to different annual pinewood rings from the separate 0 to 20-cm soil layers was determined. 相似文献
20.
Yi Zhang Junkang Hao Changjie Zhou Kai Chang 《Journal of mathematical chemistry》2009,46(4):1203-1212
In this article, we propose a new method to measure DNA similarity based on a normalized Lempel-Ziv complexity scheme. The
new method can weaken the effect of sequence length on complexity measurement and save computation time. Firstly, a DNA sequence
is transformed into three (0,1)-sequences based on a scheme, which considers “A” and “non-A” , “G” and “non-G”, “C” and “non-C”
bases respectively. Then, the normalized Lempel-Ziv complexity of the three (0,1)-sequences constitute a 3D vector. Finally,
by the 3D vector, one may characterize DNA sequences and compute similarity matrix for them. The examination of similarities
of two sets of DNA sequences illustrates the utility of the method in local and global similarity analysis. 相似文献