共查询到20条相似文献,搜索用时 31 毫秒
1.
K. R. Jackman R. E. Gritzo S. R. Biegalski 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(1):223-226
Traditional ways of determining the absolute full-energy peak efficiencies of high-purity germanium (HPGe) detectors are often
time consuming, cost prohibitive, or not feasible. A software package, KMESS (Kevin’s Mesh Efficiency Simulator Software),
was developed to assist in predicting these efficiencies. It uses a semi-empirical mesh-grid method and works for arbitrary
source shapes and counting geometries. The model assumes that any gamma-ray source shape can be treated as a large enough
collection of point sources. The code is readily adaptable, has a web-based graphical front-end, and could easily be coupled
to a 3D scanner. As will be shown, this software can estimate absolute full-energy peak efficiencies with good accuracy in
reasonable computation times. It has applications to the field of gamma-ray spectroscopy because it is a quick and accurate
way to assist in performing quantitative analyses using HPGe detectors. 相似文献
2.
A Gamma Spectroscopy Logging System (GSLS) has been developed to study sub-surface radionuclide contamination. The absolute
counting efficiencies of the GSLS detectors were determined using cylindrical reference sources. More complex borehole geometries
were modeled using commercially available shielding software and correction factors were developed based on relative gamma-ray
fluence rates. Examination of varying porosity and moisture content showed that as porisity increases, and as the formation
saturation ratio decreases, relative gamma-ray fluence rates increase linearly for all energies. Correction factors for iron
and water cylindrical shields were found to agree well with correction factors determined during previous studies allowing
for the development of correction factors for type-304 stainless steel and low-carbon steel casings. Regression analyses of
correction factor data produced equations for determining correction factors applicable to spectral gamma-ray well logs acquired
under non-standard borehole conditions. 相似文献
3.
When neutron activation analysis of voluminous samples is performed using the absolute method, the detector absolute efficiency for -ray emiting distributed sources must be known. In this study, a Monte-Carlo program was developed to include the calculation of the effective solid angle subtended by a collimated detector from irregularly shaped voluminous samples. The program cna cope with dififerent sample shapes and geometries provided that the sample covers the view of the detector. Data such as the source and detector dimensions, the source-detector distance, the detector view at a cartain distance, the thickness and the composition of any intervening materials, the -ray energies of interest and the corresponding attenuation coefficients for each material are required. The method adopted for calculating the detector absolute efficiency of the voluminous sample in a certain geometry takes into account the effect by -rays baing emited from different position within the sample and also considers their attenuation in the sample material as well as any intervening materials between the sample and the detector and is compared with a reference point source. The alculations are varified experimentally using a distributed source of 75 mm diameter and 100 mm thickness and two semiconductor detectors. The difference between the calculated and measured absolute efficiencies did not exceed 4%. 相似文献
4.
Ş. Turhan A. Zarars?z H. Yücel 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(1):141-145
Summary The bremsstrahlung radiation energy spectra were produced by hard beta-emitters the 90Sr-90Y contaminated tea sample sources placed in a copper cylinder (cylinder counting geometry) and encapsulated in two Cu discs
(sandwich counting geometry). These energy spectra were directly measured by using two separate gamma-ray spectrometers with
a coaxial 110% efficient HpGe detector and a 110 cm3 HpGe well-type detector. The minimum detectable activity and the absolute efficiency of beta-activity for the sandwich and
cylinder geometries were found to be 23 Bq . kg-1 and (1.67±0.04)% and 55 Bq . kg-1 and (2.61±0.05)%, respectively. These results indicate that the bremsstrahlung radiation counting method can be applied to
some environmental studies when high efficient HpGe detectors, especially well-type HpGe are used. 相似文献
5.
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
6.
A method for the determination of trace amounts of 1-naphthylacetic acid (NAA) has been developed, based on solid-phase spectrofluorimetry. The relative fluorescence intensity of NAA fixed on Sephadex QAE A-25 gel was measured directly after packing the gel beads in a 1-mm silica cell, using a solid-phase attachment. The wavelengths of excitation and emission were 280 and 336 nm, respectively. The applicable concentration range was from 0.3 to 18 ng/ ml, with a relative standard deviation of 1.4% (for a level of 9 ng/ml) and a detection limit of 0.09 ng/ml. The method was applied to the determination of NAA in commercial formulations and natural waters. The method is more sensitive and selective than other methods described in the literature. 相似文献
7.
Typically, germanium detectors designed to have good sensitivity to low-energy photons and good efficiency at high energies
are constructed from n-type crystals with a boron-implanted outer contact. These detectors usually exhibit inferior resolution
and peak shape compared to ones made from p-type crystals. To overcome the resolution and peak-shape deficiencies, a new method
of construction of a germanium detector element was developed. This has resulted in a gamma-ray detector with high sensitivity
to photon energies from 14 keV to 2 MeV, while maintaining good resolution and peak shape over this energy range. Efficiency
measurements, done according to the draft IEEE 325-2004 standard, show efficiencies typical of a GMX or n-type detector at
low energies. The detectors are of large diameter suitable for counting extended samples such as filter papers. The Gaussian
peak shape and good resolution typical of a GEM or p-type are maintained for the high count rates and peak separation needed
for activation analysis. 相似文献
8.
S. Niese 《Journal of Radioanalytical and Nuclear Chemistry》1975,28(1-2):171-184
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. 相似文献
9.
Wolfgang Hennig Christopher E. Cox Stephen J. Asztalos Hui Tan Patrick J. Franz Peter M. Grudberg William K. Warburton Alan Huber 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(2):675-681
Measurement of radioactive xenon in the atmosphere is one of several techniques to detect nuclear weapons testing, typically using either scintillator based coincidence beta/gamma detectors or germanium based gamma only detectors. Silicon detectors have a number of potential advantages over these detectors (high resolution, low background, sensitive to photons and electrons) and are explored in this work as a possible alternative. Using energy resolutions from measurements and detection efficiencies from simulations of characteristic electron and photon energies, the minimum detectable concentration for Xe isotopes was estimated for several possible detector geometries. Test coincidence spectra were acquired with a prototype detector. 相似文献
10.
M. U. Rajput Mahmud Ahmad Waqar Ahmad 《Journal of Radioanalytical and Nuclear Chemistry》2002,251(3):457-462
The characteristic absolute efficiency response curves of a high purity germanium detector (HPGe) for different counting geometries have been established in the energy range 50–1500 keV by measuring the absolute efficiencies using both mono-energetic and multi-gamma emitting radionuclide point calibrated sources supplied by IAEA. Several fitting functions proposed in the literature were assessed for interpolation within the intermediate energy range of interest. The values of the function parameters have been determined by using the linear least square methods. The problems associated with the measurements of experimental efficiency data at small source–detector distances and the importance of the correlation matrix in the estimation of precise uncertainties have been shown. It was found that the inclusion of correlation matrices in the propagation of error formulae plays a significant role up to 450 keV gamma-ray energy and results in a drastic reduction of errors associated with the predicted efficiencies. The discrepancy at closer counting geometries in the absence of true gamma-gamma coincidence corrections is found to reach to about 30%. 相似文献
11.
J. H. Moon S. H. Kim Y. S. Chung J. M. Lim G. H. Ahn M. S. Koh 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(1):33-35
A delayed neutron counting system has been implemented at the HANARO research reactor in 2007. Thermal neutron flux measured
at the NAA #2 irradiation hole coupled to the delayed counting system, was higher than 3 × 1013 n cm−2 s−1. The delayed neutron counting system is composed of 18 3He detectors which are divided into three groups with six detectors and the collected signals of each group are processed
to a digital signal. The count numbers were measured with the uranium mass by using NIST SRMs under fixed analytical condition
and their correlation could be determined. Finally, delayed neutron activation analysis has been carried out for the determination
of uranium mass fraction in the collected environmental samples. 相似文献
12.
Monte Carlo simulations can be a powerful tool in calibrating high-resolution gamma-ray spectrometry based on high pure germanium (HPGe) detectors. The purpose of this work is to examine the applicability of Monte Carlo simulations for the computation of the efficiency transfer in various measurement geometries on the basis of the detected efficiency for point source geometry. For this, GEANT4 code was applied for the computation of the detection efficiency for incident gamma energy of radionuclide placed at different distances from HPGe detector from 50 to 2,000 keV in addition for volume sources of different compositions and densities. The experimental efficiency curves were compared with the prediction of the GEANT4 code. Efficiency is computed at discrete values of point and volume sources in different distances to derive new efficiencies values for other distances. 相似文献
13.
Characterization is a first step to site cleanup or decommissioning of a disused nuclear facility. Good knowledge of the inventory
of nuclides present, both type and location, is important in the design of an effective plan of remediation. Several systems
based on HPGe detectors have been developed, both commercially and at laboratories, and are already in use for this purpose.
Their use is somewhat complicated by the need for cryogenic cooling of the HPGe detector. Handling of liquid nitrogen in field
situations is always difficult. Recent developments in low-power electromechanical cooling for HPGe detectors have made possible
the construction of low weight, portable HPGe spectrometers with sufficient efficiency to perform the needed measurements
in reasonable count times, without the need for liquid nitrogen. A mobile system was modified to use a battery-powered, Sterling-engine
cooler on a nominal 40% relative efficiency detector. This system was characterized for efficiency and uniformity of response.
The baseline spectra were analyzed using the DOE EML 1-meter methods to obtain representative MDA values for several nuclides
of interest and typical counting times. 相似文献
14.
A spectrofluorimetric method for the simultaneous determination of 1-naphthylacetic acid (NAA) and 1-naphthalenacetamide (NAD) was developed. The sample solution containing both analytes was equilibrated with Sephadex QAE A-25 gel by agitation and then only NAA was fixed on gel, while the remaining NAD stayed in the solution. The relative fluorescence intensity of NAA fixed on Sephadex QAE A-25 gel was measured directly after packing the gel beads in a 1-mm silica cell, using a solid-phase attachment. NAD was determined spectrofluorimetrically in the solution. The wavelengths of excitation and emission chosen for the determination of NAA were 280 and 336 nm, respectively, and for NAD determination 222 and 337 nm, respectively. The applicable concentration range was 12-60 ng ml(-1) for NAA and 6-120 ng ml(-1) for NAD. The detection limit was 3 ng ml(-1) for NAA and 2 ng ml(-1) for NAD. The method was applied satisfactorily to the determination of NAA and NAD in commercial formulations of phytohormones and soil samples. 相似文献
15.
At Ecole Polytechnique Montreal, the philosophy in performing neutron activation analysis (NAA) is long-term and application oriented. Thinking long-term implies a good understanding of the fundamentals of the method, of the samples, of the tools, reactor and detectors, and there must be constant innovation that is experimentally validated with extensive measurements. Application oriented means a NAA method developed to provide users with fast, sensitive, accurate and reliable analyses for various types of materials. This philosophy dictates the manner in which the developments in the areas of NAA software, peak-area calculation, dead-time correction, detection efficiency model, k 0 and Q 0 values, neutron moderation and neutron self-shielding are carried out. This paper presents a survey of the Laboratory’s methodology, reviewing a few of its unique features such as detector efficiency calibration and sample related perturbations of the neutron activation. These features are used as examples to provide the reader with an understanding of the philosophy and the evolution of the NAA method at Ecole Polytechnique. 相似文献
16.
Ş. Turhan 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(2):443-450
A 740 GBq 241Am-Be neutron source based prompt gamma-ray activation analysis (PGAA) setup in combination with a typical coaxial n-type
HPGe detector (REGe) system was used to analyze light elements like H, B, C, N, etc. The absolute full energy peak (FEP) efficiencies
of the shielded REGe detector for irradiation and counting geometries and for sources with different sizes (point, ampoule
and cylindrical) were measured in the 0.1–2.5 MeV energy range by utilizing calibrated sources (point, liquid and solid).
4th order polynomials were fitted to the experimental data. Efficiencies in far irradiation and counting geometries are compared. 相似文献
17.
C.M. Henderson Q.M. Jahan W.L. Dunn J.K. Shultis D.S. McGregor 《Radiation Physics and Chemistry》2010,79(2):144-150
Semiconductor detectors whose surfaces are coated with neutron-reactive material can be made to detect thermal neutrons, but with efficiencies only of a few percent. However, perforating the semiconductor material, filling the perforations with neutron-reactive material, and then coating the detector surface can lead to neutron detectors of much higher thermal neutron detection efficiencies, perhaps approaching or exceeding 50%. Several perforated semiconductor neutron detectors have been constructed, both for dosimetry and for position-sensitive neutron detection. The characterization of prototype devices based on these detectors is described. 相似文献
18.
Chhavi Agarwal Sanhita Chaudhury A. Goswami M. Gathibandhe 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(3):701-708
Monte Carlo simulation is important to get efficiencies for cases where the experimental efficiencies are difficult to get
such as for samples with nonstandard geometries and for large samples. In this paper, efficiency of the HPGe detector, routinely
used in our lab for a variety of samples, has been computed for point source geometry and its parameters has been optimized
to match MCNP and experimental efficiencies within 5% at different sample to detector distances. This optimized geometry was
then validated by efficiency transfer to other geometries. 相似文献
19.
Summary {\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}}
\viewkind4\uc1\pard\f0\fs24 The use of HPGe detectors in counting situations where the sample is not easily reproduced has increased the use of models to determine the counting efficiency for the specific geometry. The accuracy of these simulations of the germanium detector response relies on detailed knowledge of the performance of the detector. Several different types of detectors were measured at different energies using a pencil beam of gamma-rays. These measurements showed that the dead layer was not uniform from detector to detector. This and the construction details were used to calculate the efficiency for several detectors.
\par } 相似文献
20.
A combination of instrumental and preconcentration neutron activation analysis (NAA) methods has been developed for multielement determination in acid rain. Concentrations of 24 elements have been measured in the particulate matter of rainwater by the instrumental NAA method which involves 3 irradiation and 4 counting periods. Trace elements in the soluble fraction of rainwater have been preconcentrated using Chelex-100 resin. Various factors that could influence the retention of elements on to the resin have been examined, and reagent and other blanks investigated in detail. Concentrations of 15 elements have been measured by directly irradiating the resins. A graphite furnace atomic absorption spectrometry method has been used for determining Cd and Pb levels in the soluble fraction. Precision and accuracy of the methods have been evaluated, and limits of detection and determination calculated. The methods have been applied to rainwater samples collected from 36 locations across Canada. Enrichment factors, interelement and inter-ion concentration correlation coefficients are discussed 相似文献