Gamma-ray Scanning Research Articles

Gamma-ray spectrometry and geological maps as tools for cadmium risk assessment in arable soils

Farmers in some parts of Sweden have problems achieving quality assurance certification for their products due to frequently excessive cadmium (Cd) concentrations in wheat grain. Such problems are most frequent in areas where soils are affected by sedimentary rock containing alum shale. In this study we used aerial and ground-based gamma radiometry to assess Cd risk in food production at regional and field scale in one such area. A regional risk map for Cd in arable soils in the south-eastern tip of Sweden was created using aerial gamma-ray spectrometry measurements (238U, 232Th, and 40K) combined with maps on bedrock geology and Quaternary soil deposits. The map had 5 hypothetical risk categories. Category 1 areas (highest risk) had >5ppm 238U, category 2 had 3–5ppm 238U, category 3 till on Cambrian sandstone, category 4 fluvial deposits downstream from risk categories 1–3, and category 5 other arable soils (low risk). The high uranium (U) levels were caused by inclusion of alum shale fragments, which may also contain high amounts of Cd. The Cambrian sandstone is a possible source of high soil Cd concentrations (but low in U) since it in this area contains sphalerite (ZnS), which is high in Cd. Directed sampling revealed very high Cd concentrations in both soil and winter wheat grain in the higher risk categories. The R2 value for the positive correlation between Cd and estimated 238U in topsoil was 0.59. The risk categories based on soil properties were also useful in predicting Cd concentration in wheat but there were no differences between categories 2, 3 and 4, so for wheat three risk classes appeared more relevant. The spatial variation in Cd in the study area is considerable according to the risk classification and many farms include both high and low Cd areas. Use of a ground-based gamma-ray sensor for detailed mapping of fields at two farms in high Cd risk areas gave a fairly strong correlation between 238U and soil Cd (R2=0.68). When 232Th/238U ratio was used instead the relationship was even stronger (R2=0.75). The Th/U ratio can remove some of the noise in gamma recordings and may be useful in depicting high U areas. Airborne gamma-ray scanning also outlined the Cd risk areas fairly well (R2=0.39) at the field level. The results show that geological maps and gamma radiation mapping, calibrated with a few analyses of Cd concentrations in soils and crops, can be used for risk classification of soils at the regional scale in this type of landscape. Using gamma-ray data, many areas that would have been overlooked when using geological maps alone were classified as high risk. Ground-based gamma-ray scanning could be useful for farmers to identify fields and parts of fields where special consideration is needed to reduce the risk of high Cd in crops.

A new approach in gamma-ray scanning of rotating drums containing radioactive waste

The paper presents a new approach in the integral gamma scanning of rotating waste drums based on solving a first-kind Fredholm integral equation using a small number of measurements. Both numerical experiments and experimental results show that the nuclide inventory of waste drums can be determined accurately using the new approach especially when the waste drums contain multi-gamma emitters.

A New Method for Flow Regime Identification in a Fluidized Bed Based on Gamma-Ray Densitometry and Information Entropy

The accurate identification of the boundaries of the main flow regimes in fluidized beds is very important since the degrees of mixing and mass and heat transfer depend on the prevailing flow regime. Both the minimum fluidization velocity Umf (0.103 m·s−1) and the transition velocity Utrans (0.12 m·s−1) to bubbling fluidization regime have been successfully identified based on a newly developed maximum information entropy (IEmax) algorithm applied to gamma photon time series. The latter are recorded by means of gamma-ray densitometry scans performed in an air–polyethylene fluidized bed (0.438 m in ID) operated at ambient conditions. A comparison with the Kolmogorov entropy (KE) algorithm has found that the new approach yielded more accurate transition velocities. The value of Umf is also validated by means of the profiles of both bed pressure drop and bed height, respectively. It has been found, however, that these parameters are not capable of identifying the second transition velocity Utrans. It is demonstrated that the Umf value identified on the basis of IEmax is theoretically predictable. In the bubbling fluidization regime, a simple correlation between both the KE and IEmax values is developed.

Estimation of plutonium present in 200 litre waste drums containing high amount of beta gamma activity

The segmented gamma ray scanning system developed for the assay of plutonium present in 200 L waste drums was modified for the estimation of gram amounts of plutonium in the presence of high beta gamma activity. A multi gamma ray source of 152Eu having ~1 mCi activity was used for the determination of attenuation correction factors for high count rate drums. Dead time corrections were applied to arrive at the corrected count rates for all the gamma rays. Present study has shown that the estimation of ~1 g of 239Pu in a waste drum can be carried out in the presence of 137Cs up to an activity level of 20 mCi.

Optimisation on the two-layer stack gamma detectors of CsI(Tl) coupled with a pin photodiode for non-destructive testing

This paper proposed the two-layer stack scintillator-coupled photodiode detector to improve the measurement accuracy of the gamma-ray scanning. Both MCNPX and DETECT97 code were used to design the detector. The two manufactured two-layer stack gamma detectors were used to measure the density profile of the distillation column of the radiographic non-intrusive process diagnostic area. To compare the measurement accuracy of the density profile through the non-destructive transmission test, the relative error of the four fluids used for the process diagnostics was analysed. To summarise the measurement results with regard to the relative error of the NaI(Tl) detector and the manufactured detector by material as well as the total relative error, the total relative error of the NaI(Tl) detector was about 15.7 %, whereas that of the two-layer stack CsI(Tl) with photodiode detectors were about 5 %. This paper confirmed that the measurement accuracy of the detector proposed was improved by about three times as compared with the NaI(Tl) detector mostly used for non-destructive testing.

Evaluating the Reliability of an Accurate Performance in Tray Columns Using Gamma Ray Scanning Technique

The nondestructive techniques are applied to identify important data from the internal process of distillation towers, process towers, pressure vessels and etc. In recent, the gamma-ray scanning techniques as diagnostic tools for scanning of tray columns, packed columns, storage tanks, level measurement and density measurement of containing materials has been used widely. This paper has tried to model tray column failures. Also failures identification using real time analysis and scan profile interpretation has been investigated. This suggested model can be used before gamma ray scanning technique, calibration and adjustment of working conditions in industrial scale.

Simulators of tray distillation columns as tools for interpreting gamma–ray scan profile signals

Simulators of tray distillation columns were used to provide technical guidelines for interpreting signals from gamma ray scans used for analysing malfunctions in distillation columns. The transmitted radiation intensities at 0.05 m intervals were determined from top to the bottom of simulators of tray distillation columns exposed to 20 mCi of 137 Cs. Signals generated from the simulators were identical with the experimental signals obtained from the Stabilizer Column of the crude oil distillation unit at the Tema Oil Refinery Ghana Limited. Changes in the signal level were observed with changes in diameter, type of material (gasoline, air, debris, steel) and orient-ation of scan line. The analysis provided accurate interpretation of gamma scan profiles. Journal of Applied Science and Technology Vol. 13 (1 & 2) 2008: pp. 37-43

A comparison of alternating minimization and expectation maximization algorithms for single source gamma ray tomography

Lange and Carson (1984 J. Comput. Assist. Tomogr. 8 306–16) defined image reconstruction for transmission tomography as a maximum likelihood estimation problem and derived an expectation maximization (EM) algorithm to obtain the maximum likelihood image estimate. However, in the maximization step or M-step of the EM algorithm, an approximation is made in the solution which can affect the image quality, particularly in the case of domains with high attenuating material. O'Sullivan and Benac (2007 IEEE Trans. Med. Imaging 26 283–97) reformulated the maximum likelihood problem as a double minimization of an I-divergence to obtain a family of image reconstruction algorithms, called the alternating minimization (AM) algorithm. The AM algorithm increases the log-likelihood function while minimizing the I-divergence. In this work, we implement the AM algorithm for image reconstruction in gamma ray tomography for industrial applications. Experimental gamma ray transmission data obtained with a fan beam geometry gamma ray scanner, and simulated transmission data based on a synthetic phantom, with two phases (water and air) were considered in this study. Image reconstruction was carried out with these data using the AM and the EM algorithms to determine and quantitatively compare the holdup distribution images of the two phases in the phantoms. When compared to the EM algorithm, the AM algorithm shows qualitative and quantitative improvement in the holdup distribution images of the two phases for both the experimental and the simulated gamma ray transmission data.

A new electronic system for the gamma-ray scanning technique

The gamma-ray scanning technique is widely used in the diagnosis and identification of faults in industrial installations in general and, in particular, in distillation columns considered as the most critical components in petrochemical plants. It provides essential data to optimise the performance of these columns and identify maintenance requirements. Due to the various difficulties that can arise when analysing a scanning profile and in order to benefit from the continuous advent of new technologies in the field of electronics and data processing, the team of the Division of Instrumentation and Industrial Applications of CNESTEN has conducted a project aimed at the elaboration of a new electronic system for acquisition, processing and interpretation of the scanning results. This system consists of two main modules: the first one is devoted to the preparation and control of the scanning operation conditions, while the second module has been developed to carry out easily and effectively the automatic (on-line) analysis and interpretation of the scan profiles.

An expert system for improving the gamma-ray scanning technique

The gamma-ray scanning technique is widely used in the diagnosis and identification of industrial installations, in general and, in particular, of distillation columns considered as the most critical components in petrochemical plants. It provides essential data to optimise the performance of columns and identify maintenance requirements. Due to the various difficulties that can arise while analysing a scanning profile and in order to benefit from the continuous advent of new technologies in the field of electronics and data processing, the team of the Division of Instrumentation and Industrial Applications of CNESTEN have conducted a project aiming the elaboration of an expert system for acquisition, processing and interpretation of the scanning results. This system consists of two main modules: the first one is devoted to the preparation and control of the scanning operation conditions, while the second module has been developed to carry out easily and effectively the automatic (on-line) analysis and interpretation of the scan profiles.

Personalized Body Segment Parameters From Biplanar Low-Dose Radiography

Body segment parameters are essential data in biomechanics. They are usually computed with population-specific predictive equations from literature. Recently, medical imaging and video-based methods were also reported for personalized computation. However, these methods present limitations: some of them provide only two-dimensional measurements or external measurements, others require a lot of tomographic images for a three-dimensional (3-D) reconstruction. Therefore, an original method is proposed to compute personalized body segment parameters from biplanar radiography. Simultaneous low-dose frontal and sagittal radiographs were obtained with EOS system. The upper leg segments of eight young males and eight young females were studied. The personalized parameters computed from the biplanar radiographic 3-D reconstructions were compared to literature. The biplanar radiographic method was consistent with predictive equations based on gamma-ray scan and dual energy X-ray absorptiometry.

Passive gamma-ray scanning for non-destructive characterisation of mixed oxide (MOX) fuel pins for BWRs

Uranium-plutonium mixed oxide (MOX) fuel is being fabricated at the Advanced Fuel Fabrication Facility, Bhabha Atomic Research Centre, Tarapur, as fuel for boiling water reactors (BWRs). The sintered fuel pellets are encapsulated in zircaloy-2 clad tubes using TIG welding of end plugs. Enrichment of plutonium dioxide is an important characteristic which needs to be assured by non-destructive means. The use of passive gamma-ray scanning for non-destructive monitoring of enrichment of plutonium dioxide in BWR MOX fuel rods is demonstrated. This paper describes the experiments on gamma-ray scanning of the welded MOX fuel rods carried out at AFFF, BARC and presents the results.

Scattered gamma-radiation utilized to measure remnant fresh absorbent in absorbent beds

High-energy gamma-ray (γ-ray) scans utilizing multiple forward scattered radiation are presented as a method of measuring the remnant bed life in sulfur absorbent beds. The patented measurement principle utilizes density changes resulting from the sulfur absorption process. Gamma spectra are recorded at various elevations with a detector positioned outside the vessel wall diametrically opposite to a 60Co source. A small energy interval in the low-energy region of the spectra is used to build up a profile for the absorbent bed showing the amount of remnant fresh absorbent. In this paper, the feasibility of the method is demonstrated for three hydrodesulfuriser vessels filled with sulfur absorbent. Experiments and simulation results verifying the validity of the technique are also presented.

A comparative study to investigate burnup in research reactor fuel using two independent experimental methods

Two independent experimental methods have been used for the comparative study of fuel burnup measurement in low enriched uranium, plate type research reactor. In the first method a gamma ray activity ratio method was employed. An experimental setup was established for gamma ray scanning using prior calibrated high purity germanium detector. The computer software KORIGEN gave the theoretical support. In the second method reactivity difference technique was used. At the same location in the same core configuration the fresh and burned fuel element's reactivity worth was estimated. For theoretical estimated curve, group cross-sections were generated using computer code WIMS-D/4, and three dimensional modeling was made by computer code CITATION. The measured burnup of different fuel elements using these methods were found to be in good agreement.

Analysis of straight edges by means of gammametry / Analyse gradliniger Ränder mittels Gammamesstechnik

In the present research work the influence of the detector collimation on the resolution of radiometric measurements is discussed for rectangular objects of constant thickness with dimensions larger than the radius of the collimator. To measure the width of an object a mathematical model is introduced. In addition, as alternative, the derivative function of the experimental data is used for the calculation of dimensions, which permits to reduce the time of calculation. The experimental verification was carried out by using an arrangement of a gamma-ray scanner consisting of a 137 Cs source (1.1 MBq) and a Nal(Tl) scintillator, a lead brick and two collimators with different radii.

Adjustments to Zatsiorsky-Seluyanov's segment inertia parameters

Zatsiorsky et al. (in Contemporary Problems of Biomechanics, pp. 272–291, CRC Press, Massachusetts, 1990a) obtained, by means of a gamma-ray scanning technique, the relative body segment masses, center of mass (CM) positions, and radii of gyration for samples of college-aged Caucasian males and females. Although these data are the only available and comprehensive set of inertial parameters regarding young adult Caucasians, they have been rarely utilized for biomechanical analyses of subjects belonging to the same or a similar population. The main reason is probably that Zatsiorsky et al. used bony landmarks as reference points for locating segment CMs and defining segment lengths. Some of these landmarks were markedly distant from the joint centers currently used by most researchers as reference points. The purpose of this study was to adjust the mean relative CM positions and radii of gyration reported by Zatsiorsky et al., in order to reference them to the joint centers or other commonly used landmarks, rather than the original landmarks. The adjustments were based on a number of carefully selected sources of anthropometric data.

Temperature sensitivity of surface channel effects on high-purity germanium detectors

The temperature sensitivity of surface channel effects on planar high-purity germanium detectors was measured using 60-keV gamma-ray scanning techniques, as part of a radiation damage study. When measured in this manner, the surface effects on most detectors showed extreme temperature sensitivity in the 72–95 K region. The effect of the surface channel increased with increasing temperature to such an extent that the efficiency, as measured by the count rate in the 1332-keV peak from a 60Co source, decreased by a factor of over two in some cases. Since the peak efficiency for the 1332-keV gamma ray decreased as the temperature increased throughout the operating range (72–120 K) the effect of the surface channel must continue to increase beyond the temperature (95 K) at which the 60-keV scan loses its sensitivity because of the strong attenuation of these much lower energy gamma rays. Radiation damage had no measurable effect on the surface characteristics. No correlation between the surface effects and the resolution changes of the 1332-keV peak was observed.

Isometric representation of data obtained using a Compton gamma-ray scanner : 39485 Bridge, B.; Harirchian, F.; Imrie, D.C.; Mehrabi, Y.; Meragi, A.R. Nondestructive Testing Communications, Vol. 4, No. 1, pp. 1–10 (1988)

Isometric representation of data obtained using a Compton gamma-ray scanner : 39485 Bridge, B.; Harirchian, F.; Imrie, D.C.; Mehrabi, Y.; Meragi, A.R. Nondestructive Testing Communications, Vol. 4, No. 1, pp. 1–10 (1988)

Standardization of a 50 GBq 152,154Eu extended volume source

The standardization of a 50 GBq 152,154Eu extended volume source is described, as used to determine the linear power dissipation of irradiated fuel pins in materials testing reactors. This source consists of a foil of irradiated europium rolled into a close cylindrical geometry within an aluminium housing. A solution of 152Eu was standardized and a quantitative 50 MBq strip source was prepared (of the same dimensions and in an identical housing to that of the 152,154Eu extended volume source). The sources were compared by measuring their spectra with the IRMM gamma-ray scanning system at a source-to-detector distance of approximately 4 m and a collimator diameter of 4 mm.

The application of gammametry to the study of reinforced concrete

The use of a gamma-ray scanner for the examination of reinforcement in concrete structures is discussed. The scanner consists of a 60Co source and a NaI(Tl) scintillator fixed to the source. A mathematical model is introduced to derive the principal features of the technique and to study the influence of the source-detector distance and the detector collimation on the resolution, sensitivity and tomographic properties of this device. An 18 cm thick mock up of a reinforced concrete column was built and scanned. Radii, positions, inclinations of rebars and the density of the sample were determined by fitting model parameters to the data. The results compare quite well with the known specifications of the mock up, showing that even a single one-dimensional scan may yield accurate information about rebars and conditions of a concrete slab.