Gamma-ray Backscatter Research Articles

Determination of positions of reinforcing bars in reinforced concrete by backscattered gamma rays—II. Experimental and Monte Carlo results

This paper is the second of two parts. Part I comprised the method for determining positions of reinforcing bars in reinforced concrete by backscattered gamma rays using Ba-133 and Cs-137. From the backscattered counting rate obtained by scanning the surface of reinforced concrete, the spacing the size and the depth of the reinforcing bars can be determined. Part II discusses the results of new experiments and the Monte Carlo calculations.

Remnant roof coal thickness measurement with passive gamma ray instruments in coal mines

The need to leave coal on the roof of a mined-out area occurs on both continuous miner and longwall sections and is derived from considerations of ground control, quality control, machine guidance, or simply good operating practice. Efforts at measuring boundary coal thickness using the nucleonic method is described. Natural gamma devices are the instruments of choice, and the use of gamma-ray backscatter sensing is discussed. The calibration of natural gamma background (NGB) instruments is described, and it is concluded that they cannot be used in areas where NGB radiation is not present. This radiation is ordinarily present in the fine-grained sedimentary rocks that bound many coal seams. >

Locating the positions of reinforcing bars in reinforced concrete using backscattered gamma rays : Tuzi, S.; Sato, O. Applied Radiation and Isotopes, Vol. 41, No. 10/11, pp. 1013–1018 (1990)

Locating the positions of reinforcing bars in reinforced concrete using backscattered gamma rays : Tuzi, S.; Sato, O. Applied Radiation and Isotopes, Vol. 41, No. 10/11, pp. 1013–1018 (1990)

A generalized approach to designing specific-purpose Monte Carlo programs: a powerful simulation tool for radiation applications

Well-designed Monte Carlo simulation programs provide the most accurate means of predicting the response of radiation measurement systems. Such simulations can replace large sets of experiments for the purpose of design optimization, calibration and analysis of sensitivity to measurement interferences. The use of detector response functions can extend Monte Carlo simulation to systems involving spectral responses. Compared to the use of general-purpose Monte Carlo codes, our work on developing specific-purpose codes has shown various advantages: greater “user-friendlines”, use of an optimum set of variance reduction methods, superior code performance in most cases, and better understanding of the basic physics of the problem. The specific-purpose codes are relatively easy to develop using modules that we have developed for geometry, cross sections, detector response functions, standard as well as new and/or improved variance reduction schemes, etc. The measurement applications for which we have designed and used specific-purpose Monte Carlo simulation codes in recent years include on-line capture gamma-ray analysis of coal; X-ray fluorescence analyzers; nuclear tools for oil-well logging by neutron moderation, pulsed neutron lifetime analysis and by gamma-ray backscatter; and industrial tomographic scanners.

An axially symmetric gamma-ray backscatter system for DuMond spectrometry

An axially symmetric spectrometer is described which evolved from a program of measuring Compton profiles with unusually high geometric efficiency. When fitted with a large-volume Ge detector for combined X-ray and γ-ray spectrometry, such as the 51 mm diameter LO-AX detector from EG&G, it allows Compton profiles to be measured at counting rates in excess of 20000 cps. The axially symmetric configuration is also suited to high-efficiency analyses of thick targets by both XRF and Rayleigh/Compton R/C ratios. The same spectra permit a competitive binary-system analysis based on the shape of the Compton profile. Both this new analysis, which we call DuMond spectrometry, and R/C analysis are applied to studies of osteoporosis in the calcaneus with promising results. The combination of high intrinsic and geometric detection efficiency makes it practical to use very weak sources ( ∼ 100 MBq) and unusually low, localized doses ( ∼ 1 μGy) per reading.

Locating the positions of reinforcing bars in reinforced concrete using backscattered gamma rays

A method for locating the positions of reinforcing bars in reinforced concrete by backscattered γ rays was investigated using 57Co and 133Ba. From the backscattered counting rate obtained by scanning the surface of reinforced concrete, the spacing, the size and the depth of the reinforcing bars can be determined. The method, computer simulation and future problems for miniaturization are presented.

A Fast, Low-Dose Estimate of Bone Minerals in Vivo by Gamma-Ray Backscatter

A Fast, Low-Dose Estimate of Bone Minerals in Vivo by Gamma-Ray Backscatter

Effect on number albedo values for 662 keV photons from radiation shielding materials stratified with lead

Albedo measurements for backscattered gamma rays from semi-infinite scatterers have suitable applications in the design of gamma ray shields particularly in nuclear reactor and accelerator shields and in many other nuclear installations. The insertion of lead slabs into stratified combination with other shielding materials has been found to increase the shielding property appreciably. The stratified slabs of alternating heterogeneous layers have been found in this investigation to have a virtual homogeneous property with a definite effective atomic number. The purpose of the present investigation is to find out the extent to which the shielding property increases in binary configuration with lead and to investigate into the dependence of the saturation thickness of the shielding media on the effective atomic number of each configuration. The indigeneously designed Uniform Sensitivity Photon Counter used in this investigation has an edge over all previous methods of experimental measurements that it is independent of response correction. The number albedo values as well as angular distribution of backscattered photons for iron, aluminium and concrete stratified with lead slabs at 662 keV energy have been reported here.

Use of neutron and gamma radiation meters to estimate bulk density and correct for bias of sampling for water content in a swelling clay soil

Two radiation methods were used to estimate the bulk density of a three-dimensionally swelling grey clay soil used for furrow irrigation at Narrabri, N.S.W. Firstly, gamma ray scattering was calibrated with measurements of wet bulk density derived from undisturbed soil cores. Secondly, a high correlation between neutron counts and gravimetric water content in this soil provided a basis for predicting bulk density corrected for bias in sampling of shrinkage cracks by using a published theoretical model of three-dimensional soil shrinkage. Gamma ray backscattering was poorly correlated with wet bulk density (�w), possibly because dry bulk density and water content are negatively correlated in swelling soil, which restricted �w to a relatively narrow range of values. This technique is therefore not recommended for use in this soil. High correlation (0 82 < r < 0.98, all P < 0.001) between neutron counts and bulk density corrected for three-dimensional shrinkage was found at all soil depths between 0.1 and 1.5 m. A precision of k0.01 Mg m-3 required from three to six samples per mean, depending on soil depth. The mean relative difference between predictions of bulk density from neutron counts compared with independent estimates by the core method was <4.1% at depths below 0.3 m. The recommended procedure is therefore to predict bulk density from neutron counts in order to correct for sampling bias and bulk density effects associated with the neutron attenuation method. The method eliminates the need for additional sampling for bulk density in conjunction with the neutron moisture meter in soils that shrink and swell three-dimensionally. However, the method is not appropriate for detecting differences in bulk density between soils with different structure unless the constants used in the model and the shrinkage behaviour are known for each soil. The latter requirements would usually preclude the technique for this purpose. At low water contents near the permanent wilting point for cotton, neutron escape through shrinkage cracks did not cause problems at depths below 0.3 m. The neutron method should therefore be appropriate for use at depths below 0.3 m in dryland hydrological studies in this soil.

Quantitative estimates of the energy of pulsed x rays backscattered by air

Frequency, amplitude, and start-stop x ray measuring devices have been adequately studied and described [2, 3]. At the same time there is no adequate theoretical basis for stroboscopic measuring devices [4] based on the relation between the energy flux density of backscattered gamma rays recorded during a time interfal (gate) and a measurable parameter. In particular, the air background has a substantial effect on the results of measurements of the characteristics of an object under study in devices employing the backscattering of x rays.

Bulk analysis using nuclear techniques

A number of bulk analysis techniques developed particularly for the mining industry by the CSIRO Division of Mineral Physics are reviewed. With these techniques, analyses are obtained directly from 3–30 kg samples without further sample preparation, or from material located on conveyor belts. Because penetrating neutron and γ-radiation is used, measurements are obtained from a large volume of sample, which ensures that the analyses are representative of the bulk. γ-Ray techniques have been used to determine the grade of 25 kg samples of iron ore and to detect shale on conveyor belts. The bulk analyser for iron ore measures the backscattered gamma rays from a 60Co γ-ray source, and an accuracy of 0.35% Fe can be obtained. The on-stream shale detector distinguishes shale from high-grade iron ore by means of the greater natural γ-ray activity of the shale. A thermal-neutron irradiation technique (called SIROSA, for C SIRO On- Stream Analysis) that uses a 252Cf neutron source has been developed for the simultaneous determination of iron and aluminium (expressed as Al 2O 3) in iron ore on a conveyor belt. Although the speed of the conveyor has no direct effect on the iron measurements, it must not exceed about 3 m/min if good accuracy for alumina is required. Consequently, an auxiliary conveyor belt is required to avoid interference with normal ore processing. Dynamic trials have demonstrated that accuracies of 0.6% Fe and 0.1% Al 2O 3 can be obtained. Other applications of thermal-neutron activation analysis include the determination of alumina in 10–20 kg samples of bauxite and coal with accuracies of 0.5 and 0.2% Al 2O 3 respectively, and the determination of manganese and alumina in manganese ores. Fast-neutron activation analysis using 241Am-Be neutron sources has also been adapted to bulk analysis. Successful applications include the determination of silicon (expressed as SiO 2) in iron ores with an accuracy of 0.15% SiO 2, and the simultaneous determination of alumina and silica in bauxites with accuracies of 0.7% Al 2O 3 and 0.3% SiO 2. A combination of fast- and thermal-neutron activation has been applied to the determination of soil in shredded sugar cane with an accuracy of 0.1% soil.

A backscatter gamma-ray spectrometric method for the determination of ash in coal

The method described is based on gamma-ray backscattering and utilizes the energy dependence of the backscattered gamma-ray peak. In the present work, a pair of windows established on either side of the backscattered gamma-ray peak were used to determine the apparent position of the peak which was strongly correlated with ash content. This technique requires only a four-channel spectrometer system. Laboratory tests carried out on 30 coal samples, with a wide range of ash composition, showed that ash content could be determined with a standard deviation of 1.5% ash for ash contents between 7 and 58%.

The Fabrication of Mercuric Iodide Detectors for Use in Wavelength Dispersive X-Ray Analysers and Backscatter Photon Measurements

ABSTRACTThis paper describes the fabrication of mercuric iodide nuclear radiation detectors suitable for X and gamma ray spectrometry at room temperature. The active area of the detectors studied are between 0.2 and 1.5cm sq and they are up to 0.5mm thick. The method of producing a stable electrical contact to the crystal using sputtered germanium has been studied. The X-ray resolution of a 1.5cm sq. area detector at 32 keV is 2.3 keV FWHM when operated at room temperature in conjunction with a time variant filter amplifier. A factor which is important in the fabrication of the detector is the surface passivation necessary to achieve a useful detector life.This type of detector has been used on a wavelength dispersive X-ray spectrometer for energy measurements between 10 and 100 keV. The advantages over the scintillation counter, more commonly used, is the improved resolution of the HgI2 detector and its smaller size. The analyser is primarily used for the detection of low levels of heavy metals on particulate filters. The detectors have also been used on an experimental basis for gamma ray backscatter measurements in the medical field.

Backscattering of Neutrons and Secondary Gamma-Rays from Aluminum and Lead Slabs for 15-MeV Neutrons

To obtain neutron and secondary γ-ray albedos for 15-MeV neutrons, spectral measurements of backscattered neutrons and γ-rays from Al and Pb slabs were carried out for monodirectional beams of D-T neutrons using the associated particle method. In the experiment, an NE-213 scintillator was used for simultaneous measurement of the neutron and photon spectra with the aid of the pulse-shape discrimination technique. The obtained pulse height distributions were unfolded to energy spectra by the FERDO code. The accuracy of the measured spectra was examined using calculated results of the Monte Carlo code which was newly developed for the combined neutron and photon transport calculation. A fairly good agreement was obtained between the measured and calculated results, excluding some discrepancies which seemed to come from the inaccuracy in the cross section data used in the Monte Carlo calculation. The obtained neutron and photon data in this paper are very meaningful for the reference data of the neutron and s...

Anomalous intensity variation of backscattered gamma ray peaks

The intensity and spectral distribution of the backscattered photon distribution in the gamma ray spectra of 137Cs(662 keV), 54Mn(840 keV), 65Zn(1114 keV) and 60Co(1170 keV, 1330 keV) have been measured using a NaI(Tl) scintillation spectrometer with a heavy lead shield and without it. Contrary to expectation the intensity of the backscattered peaks is found to show a decreasing tendency when the detector is within the lead shield. This change, however, is found to become smaller with increasing energy of the incident gamma rays.

Backscattering of neutrons and secondary gamma-rays from aluminum and lead slabs for 15-MeV neutrons.

To obtain neutron and secondary γ-ray albedos for 15-MeV neutrons, spectral measurements of backscattered neutrons and γ-rays from Al and Pb slabs were carried out for monodirectional beams of D-T neutrons using the associated particle method. In the experiment, an NE-213 scintillator was used for simultaneous measurement of the neutron and photon spectra with the aid of the pulse-shape discrimination technique. The obtained pulse height distributions were unfolded to energy spectra by the FERDO code. The accuracy of the measured spectra was examined using calculated results of the Monte Carlo code which was newly developed for the combined neutron and photon transport calculation. A fairly good agreement was obtained between the measured and calculated results, excluding some discrepancies which seemed to come from the inaccuracy in the cross section data used in the Monte Carlo calculation. The obtained neutron and photon data in this paper are very meaningful for the reference data of the neutron and secondary γ-ray albedo calculation. The experimental technique in this work is shown to be useful in measuring the backscattered neutrons and γ-rays simultaneously for the incidence of D-T neutrons.

Gamma-ray backscatter applied to the on-line location of termite-damaged railway sleepers

A radioisotope system has been developed to locate groups of termite-damaged sleepers during continuous scans of a railway track. It depends on measuring the intensities of collimated beams of caesium-137 γ-rays backscattered from within the sleeper. The detected intensity varies with the amount of termite damage (i.e. voidage). Variations in intensity caused by changes in the density of sound sleepers are minimised by the geometrical arrangement of source, shields and detector. The Atomic Voidage Detector (AVD) has been tested in field trials on the Newman to Port Hedland railway, Western Australia. Four separate groups of termite-damaged sleepers were located and examined. The lower limit of detectable voidage depends mainly on the scanning speed and distribution of voids within the sleeper, and is very approximately 8% voidage at 10.7 km/h and 5% at 2.7 km/h.

The single backscattering of gamma rays

The paper presents the results of the single backscattering investigations of gamma rays in various materials. A simplified mathematical model is given for determining the probability that a photon scattered back by a single Compton scattering is incident on the detector. The probability is calculated as a function of the primary photon energy and the atomic number Z of the scatterer.

Possibilities of eliminating composition errors in gamma ray backscatter density measurement

The method of determining soil and building material densities by gamma ray backscatter gauges has been developed successfully in recent years. However, with regard to the accuracy of measurement, this method is subject to various sources of interference which are being eliminated more or less successfully in the course of its practical application. One of the major factors affecting accuracy unfavourably is the variation in chemical composition of samples tested. In this paper the possibility of eliminating errors due to variation in chemical composition by using the air-gap technique or the dual-gauge principle is discussed. Results of experimental measurements using these two methods are compared with results achieved by the single-gauge technique using one detector seated close to the surface of the sample tested. The values obtained are analyzed by a Hewlett-Packard 9820 computer program. The results of various measurements are given and compared. All measurements were accomplished by means of an NaJ(T1) scintillation detector and for 137Cs and 60Co sources.

A note on the equation of the gamma ray backscatter surface density gauge

Several equations proposed for a gamma ray backscatter surface density gauge have been obtained by fitting functions to experimental curves. Recently, a single general equation has been derived which gives the distribution of backscattered radiation, with distance from the source, for many source energies and materials. In this paper that equation is used to derive the equation relating count rate and density for a backscatter gauge.