Gamma-ray Transmission Research Articles

デュアルエネルギーγ線透過法による鉱物の分析試験

For application of dual energy gamma-ray transmission techniques to practical mineral grade analysis, some problems including selection of gamma-ray energies, influence of sample thickness and main causes of errors in measurement have been examined.The relationships between the R-values (the ratio of mass attenuation coefficients for low and high energy gamma-rays) and the effective atomic numbers for various samples (e.g., iron ore, coal and coke, limestone, minerals and gem stones) were determined using different energy combina-tions of gamma-rays from 152Eu. On the basis of the experimental results, the optimum conditions for analysis of minerals were discussed.

Determinação da condutividade hidráulica do latossolo roxo distrófico por atenuação de raios gama e tensiometria.

Results for the hydraulic conductivity of a dark red latosol (Oxisol) under laboratory and field conditions are presented. The laboratory experiments simulated field conditions through the measurement of the soil water content profiles as a function of time in soil columns. The data were obtained by the 241 Am gamma-ray transmission method, using standard gamma ray spectrometry equipament. Tensiometers at the depths of 10 and 25 cm were used to obtain the soil water content profiles as a function of time in the field experiments. The hydraulic conductivity functions were determined through internal soil drainage. The results showed higher values of the hydraulic conductivity measured in the field, compared with the laboratory values. The hydraulic conductivity determination methods presented distinct values for the field experiments as well as for the laboratory ones.

Approximating Model for Multilayer Gamma-Ray Buildup Factors by Transmission Matrix Method: Application to Point Isotropic Source Geometry

An approximating formula recently proposed by the authors for gamma-ray buildup factors of multilayered shields is applied to point isotropic source problems.The formula, which is formulated in vector form with a four-group approximation, handles the gamma-ray energy spectrum directly and uses the transmission and albedo matrices to take gamma-ray transmission and back-scattering effects into consideration. The gamma-ray transmission and back-scattering probabilities through a 1-mean-free-path-(mfp-) thick shell depend on the shell curvature. This phenomenon plays an important role in simulating the gamma-ray buildup factor in point isotropic source geometry. In this model, the dependence is described by simplified expressions. The feasibility of the formula for systematically describing the point isotropic buildup factors was tested by using buildup factors calculated by the Monte Carlo method as reference data. The materials used in the tests were water, iron, and lead, and the source energies assumed were 0.5, 1, and 10MeV. Through the tests, the method was found to reproduce the reference data of double-layered shields of these materials very well. With the same parameters, the buildup factors of three-layered shields are also reproducible. Buildup factors computed with two different group structures were examined to test the adequacy of the energy group structure adopted. The group structure previously adopted was found to be adequate in the energy range of 0.5 to 10 MeV

Transmission of Neutrons and Secondary Gamma Rays Through Concrete Slabs

Ambient dose equivalent transmission factors for both neutrons and secondary gamma rays are reported for broad beams of monoenergetic neutrons obliquely incident on slabs of ordinary concrete. The transmission factors were calculated using the MCNP Monte Carlo code for 22 incident neutron energies from 0.025 eV to 14 MeV, slab thicknesses up to 100 cm, and eight angles of incidence. Also examined are effects of hydrogen content in the concrete and choice of the type of dose response.

Effect of soil compactness on the growth and quality of carrot

Effect of soil compactness on the growth and quality of carrot

デュアルエネルギーγ線透過法の実用化試験 金合金の品位鑑定への応用

For practical use of dual energy gamma-ray transmission techniques in various fields, necessary conditions have been examined experimentally.The study revealed the necessary conditions shown in the following : (1) the shape and size of the collimator aperture for a gamma-ray beam must be changed according to those of a sample to be measured, (2) a sufficiently intense gamma-ray source is required which provides counting rates of tens of thousands per minute, (3) the ratio of N/N0 must be in a range of 0.8-0.1, and (4) the value of R with a minimum error calculated should be adopted.

A New Approximating Model for Gamma-Ray Buildup Factors of Stratified Shields

A new approximate expression for gamma-ray buildup factors of multilayered shields is proposed. The expression is formulated based on the vector form and considers the gamma-ray energy spectrum directly. It treats the gamma-ray transmission by a transmission matrix and the backscattering by an albedo matrix. Its capability of reproducing the buildup factors for multilayered shields is demonstrate by using double-layered shields composed of two materials of water, iron, and lead at 1 and 10 MeV. The data of three-layered shields of these materials are also very well reproduced. The mechanism of the density effect arising, which appears in the buildup factor for a point isotropic source, is clearly interpreted by the current method to be a geometrical effect. A correction factor for incorporating the density effect into the current expression is derived. The modified expression is successfully applied to buildup factors for a 0.5-MeV point isotropic source for two-layered shields of water and iron.

The effect of energy peak drift on the calibration of a high resolution gamma-ray soil density gauge

High spatial resolution is obtained from a gamma-ray transmission density gauge by restricting the measured counts to a narrow band of the energy spectrum, close to the emission energy peak. The effect on measurement accuracy of any movement of this measurement window relative to the energy peak was investigated. The findings were related to anticipated energy peak movements in a proposed LED-based gain-stabilization system. Movements of the energy peaks during recording of unstabilized spectra prevented direct comparisons of spectra at different positions. A simulation procedure was, therefore, developed in which movements of the measurement window relative to sets of stable calibration spectra were examined. When analysing spectra, recorded using a gauge with a different gain-stabilization system, accuracy was found to be unaffected by simulated peak movements of up to 0.03 MeV in the direction of increasing energy. However, movements of stabilized spectra in the direction of decreasing energy, and of unstabilized spectra in either direction, increased measurement errors to twice the level of inherent measurement errors within 0.02 MeV, with errors in bulk density of up to 0.7 Mg m−3 for movements of 0.1 MeV. The spectra of the new LED-based stabilization system are expected to behave in a manner similar to the unstabilized system, therefore requiring regular monitoring of the peak position.

Non-destructive analysis of archaeological bronzes by nuclear techniques

This paper studies a method for overcoming the difficulty of corroded surfaces by means of nondestructive nuclear methods in the determination of the composition of archaeological bronzes. It consists of the combination of PIXE or XRF information with Gamma Ray Transmission (GRT) data. A wide range applicability of this combined method is established by comparison with profiles of concentrations along the bronzes' patina obtained by SEM-EDAX.

TRIALS OF A MULTIPHASE FLOW METER ON PRODUCTION PIPELINES FROM OIL WELLS

This paper describes trials of a new multiphase flow meter (MFM) on the Vicksburg offshore production platform and at the oil processing facilities on Thevenard Island. The flow meter is based on two specialised gamma-ray transmission gauges mounted on a pipe carrying the full flow of oil, water and gas.Two MFMs were used in both trials, one mounted on a vertical (up flow), and the other on a horizontal, section of a pipeline linking the test manifold to the test separator. Measurements were made on flows of oil/water/gas mixtures from each well, and on combined flows of different pairs of wells.The r.m.s. difference between the flow rates determined by the MFM and by the separator output meter was determined by least squares regression. For the Vicksburg trial, the ratio of r.m.s. difference and mean flow rate was 8.9 per cent for oil, 5.6 per cent for water, 5.2 per cent for liquids, and 8.2 per cent for gas for flows in the vertical pipeline and slightly larger for flows in the horizontal pipeline. For the Thevenard Island trial, the preliminary results for flows in the vertical pipeline show the ratio to be 6.8 per cent for oil, 6.0 per cent for water, 3.4 per cent for liquids, and 5.9 per cent for water cut.

Neutron activation analysis for sulphur in coal samples and moisture content by gamma-ray transmission

A neutron activation analysis method is described for the determination of sulphur in coal samples by analysing the beta spectrum emitted from 32P and 33P following the reactions 32S(n, p) 32P and 33S(n, p) 33P using 252Cf as a source of neutrons. The transmission of the combined gamma-rays emitted from three 137Cs and three 241Am sources is used to measure the water content of the coal samples.

Elemental analysis of biological matrices using tomographic techniques

Gamma-ray transmission tomography and neutron induced gamma-ray emission tomography (NIGET) where delayed gamma-rays from an activated sample are detected in a tomographic mode, were used to investigate the elemental composition and distribution of a salivary gland stone, nondestructively. Transmission tomography provided information about the distribution of the linear photon attenuation coefficient in the object and showed clearly the two regions of inorganic and organic material in a number of sections through it. In addition it was possible to derive from the data the concentration of Ca and the ratio of Ca to P in the stone. By using NIGET it was shown that the concentration of Ca and Na in the object can be mapped and quantitative measurements of these elements could be obtained in any particular location within the salivary gland stone. The spatial resolution which depends on detector collimation was 1 mm for transimission and 2 mm for emission measurements. Instrumental neutron activation analysis was also used to determine the concentration of five elements in the stone, as a whole.

New radiation hodoscope developments for arms control treaty verification

It is pointed out that new developments in hodoscope radiation detection technology offer a wide range of capabilities for arms control treaty verification (ACTV) applications. This concept uses an array of radiation detectors to image or detect objects inside opaque containments. Hodoscope systems can detect neutrons and/or gamma-rays. The systems can be based on transmission of radiation through the objects, can detect radiation stimulated in the objects, or can detect intrinsic object radiation. Laboratory measurements to demonstrate a range of potential applications have been performed. Gamma-ray transmission hodoscopes can be used to inspect canisters, rail cars, etc. to monitor objects such as rocket motors. The use of relatively weak isotopic radiation sources makes it unnecessary to employ expensive and high-intensity accelerators. The heavy metal of nuclear warheads is characterized by strong gamma-ray absorption, and these materials could be counted by low-resolution tomography. Absorbers located in line with objects will themselves be detected, and sources located in the object region will be subtracted out as background. Intrinsic gamma-ray radiation from warheads can also be detected in a passive-instrument mode. >

Comparison of beta-ray and gamma-ray transmission methods for measurement of frost density distribution

The application of beta-ray and gamma-ray transmission methods for the measurement of the frost density distribution on a vertical pipe is reported. The beta-ray source used is strontium-90; gamma rays are produced by the decay of americium-241. The frost is formed by free convection of moist air. The average density computed from radiation attenuation data is compared with measurements using a coring tool. The attenuation versus mass thickness curve for gamma rays is linear on a semilog plot, while for beta rays there is some scatter in the data. The low attenuation of the gamma rays by the annular frost layer causes large uncertainties of about 20–50% in the computed average density. For beta rays the uncertainty is less than about 20%, mainly because of the high attenuation. The uncertainty in the computed local density distribution for the beta-ray method varies from a few percent at the frost surface to about 30% near the tube wall.

Examination of concrete cylinders by gamma-ray transmission tomography : Huddleston, J.; Hutchinson, I.G. United Kingdom Atomic Energy Authority, Harwell, AERE-M-3493 (rev.) 8 pp. (Nov. 1987)

Examination of concrete cylinders by gamma-ray transmission tomography : Huddleston, J.; Hutchinson, I.G. United Kingdom Atomic Energy Authority, Harwell, AERE-M-3493 (rev.) 8 pp. (Nov. 1987)

デュアルエネルギーγ線透過法による金合金の品位鑑定

An application of the dual energy gamma-ray transmission techniques to gold alloy identification is presented. The measurement by dual energy gamma-ray transmission is independent of thickness and density of a sample. Due to this advantage, golden accessories such as necklaces, earrings and rings can be assayed inspite of their various thicknesses and irregular sectional shapes. Choice of a gamma-ray energy pair suitable for the object is important. The authors chose 511 keV and 1275 keV gamma-rays from 22Na. With this energy pair, R value (a ratio of mass attenuation coefficients for low and high energy gamma-rays) is predominantly related to the weight fraction of gold of the sample. Using a 370 kBq 22Na small source and a 50 mm dia.× 50 mm thick NaI (Tl) scintillator for 1200 seconds, a resolution of 2 % for the R value was obtained. This corresponds to approximately 5 % of the weight fraction of gold. A better resolution can be obtained by increasing the source activity or measurement time.

Combining PIXE and XRF with gamma-ray transmission to get accurate analysis of archaeological bronzes

A method that combines PIXE and XRF measurements with gamma-ray transmission has been developed. This method allows the measurement of the bulk composition of corroded bronze samples, which cannot be done with PIXE or XRF alone because these are near-surface techniques. The method is applied to several archaeological bronzes of the Final Bronze Age and First Iron Age of the region around Sevilla, Spain.

Examination of concrete cylinders by gamma-ray transmission tomography: 38819 Huddleston, J.; Hutchinson, I.G. United Kingdom Atomic Energy Authority, Harwell, AERE-M-3493 (rev.) 8 pp. (Nov. 1987)

Examination of concrete cylinders by gamma-ray transmission tomography: 38819 Huddleston, J.; Hutchinson, I.G. United Kingdom Atomic Energy Authority, Harwell, AERE-M-3493 (rev.) 8 pp. (Nov. 1987)

A DPA technique for simultaneously measuring bone, soft tissue, and fat content.

Although conventional dual photon absorptiometry (DPA) techniques can be used to estimate fat and soft tissue content, such estimates are not possible where bone is present. We propose a method that can make these estimates in the presence of bone in the extremities of the body. The combination of this method with the conventional method should yield fat and soft tissue composition from most points within the body. The proposed technique simultaneously measures thicknesses of bone, soft tissue, and fat. These thicknesses are determined of bone, soft tissue, and fat. These thicknesses are determined from a combination of gamma-ray transmission data at two energies and a measurement of total tissue thickness. To test the technique, a feasibility study was performed with known thicknesses of aluminum (simulating bone), lucite (simulating tissue), and polyethylene (simulating fat). A variety of thicknesses of each material were employed (Al: 0-1.3 cm, lucite: 0-5 cm, polyethylene: 0-5 cm). The accuracies (standard errors of the estimates) of the calculated versus true thicknesses of aluminum, lucite, and polyethylene were 0.6%, 2.6%, and 2.5%, respectively. The estimates of "bone" thickness were insensitive to the presence of varying thicknesses of "fat." (In contrast, application of the conventional DPA method to the same gamma-ray transmission data yielded underestimates in "bone" thickness due to "fat" by as much as 11%.) For a 60 minute (whole body) scan time, the reproducibility of the measurements of the thicknesses of aluminum, lucite, and polyethylene were 0.4%, 1.0%, and 1.3%, respectively. All of these values are in a clinically useful range.(ABSTRACT TRUNCATED AT 250 WORDS)

デュアル・エネルギーγ線透過法を用いる放射線応用計測の基本特性と応用

デュアル・エネルギーγ線透過法を用いる放射線応用計測の基本特性と応用