[en] A low background γ-ray detection system has been constructed for measuring the natural radioactivity in coal samples. It is based on a high-purity Ge detector mounted within a massive lead shield which reduces the normal background level by a factor of about 20. This makes it possible to measure the low intensity γ-rays from the natural radioactivity present in the samples. Using this equipment uranium and thorium concentrations in coal fly ash and bottom ash samples from a coal fired power plant located at Bathinda, India have been measured. The uranium activity found in the samples is within the range of concentrations observed in other countries while the thorium activity is found to be somewhat higher. (Author)

[en] A simulation study to compare neutron flux distributions and γ-ray count rates due to (n,γ) reactions originated by ²⁴¹Am-Be and ²⁵²Cf neutron sources has been carried out using the MCNP code in a range of bituminuous coals contained in a parallel-faced slab. The results show that the relationships between the γ-ray intensity as a function of hydrogen concentration and of any of the elements studied due to both sources, have some important differences. For the ²⁴¹Am-Be source, in a first approximation a single curve can be adjusted to the calculated α-ray count rate as a function of the hydrogen concentration, for bulk densities below 1.4 g · cm^-3, while for the ²⁵²Cf source for densities higher than 1.0 g centrdot cm^-3, different curves must be adjusted. In the range of concentrations studied, the γ-ray count rate of an arbitrary element per wt% increases continuously with the volume hydrogen content in the case of the ²⁴¹Am-Be source, while it shows saturation effects around 0.06-0.09 g · cm^-3 in the case of the ²⁵²Cf source. (author)

[en] Major and trace element chemistry has been used to investigate critical characteristics of 89 specimens of 15 minerals that are commonly found in sedimentary rocks. For kaolinites, Na⁺, Mg²⁺ and Ca²⁺ are exchangeable cations while other elements are essentially non-exchangeable. The compositional variability of most minerals is seen to be quite low (even for clay minerals) which bodes well for resolving the mineralogy of formations from down-hole elemental data. Nuclear parameters such as the photoelectric absorption cross sections, natural gamma-ray activity, thermal neutron absorption cross section and neutron porosities calculated from chemical analyses of minerals often exceed values calculated using simple chemical formulae. (author)

[en] Directional γ-ray profiles for petroleum reservoir heterogeneities such as vertical fractures, curved vertical fractures and horizontal fractures following injection of a radioactive tracer were determined by Monte Carlo simulation. The measured half-width of azimuthal angle profiles is roughly equal to the collimation angle of the detector. Energy sensitive detectors did not significantly improve the resolution of directional profiles relative to energy insensitive detectors. A change in fracture direction cannot be detected if the change occurs more than a few centimeters into the formation. (author)

[en] The aims of this work were twofold: to characterize, in an appropriate way, the depth of investigation of a dual-detector γ-γ density tool, and to predict, to a high level of accuracy, the response of the two detectors to radial density variations. This paper demonstrates, using the results of Monte Carlo calculations, that these objectives can be met using a radial response function which characterizes the sensitivity of the tool to radial density variations. The method is applied to predict the response of the tool to density perturbations produced by invasion effects. (author)

[en] The groundwater flow in the nearfield of a large diameter hole simulating a deposition hole for spent nuclear fuel has been examined by using a tracer technique. Radioactive bromine ⁸²Br and inactive sodium fluorescein were used as tracers. The observations indicate sparse and narrow flow channels with dispersion caused by diffusion across the velocity profile in the flow channel, or diffusion out of the flow channel. Drilling the large diameter hole has not changed the flow conditions. (author)

[en] Radon (²²²Rn) and its daughter products are present in an indoor atmosphere as attached and unattached fractions. The plateout of ²²²Rn daughters on surfaces and the rate of ventilation of the house decides the extent of the equilibrium between them. Since the daughter products are responsible for the inhalation dose, the equilibrium factor F, between ²²²Rn and its daughters must be known to assess the dose from measurements of ²²²Rn gas. Reported F values by several countries show a large variation from 0.03 to 0.95 depending on the type of house, the location, the height and the seasons. It is necessary to measure F for different types of construction to arrive at an average value. This paper presents methods of measurement, and the results. The assumption of a single value for F for calculating the dose would be erroneous. (author)

[en] Earthquake prediction is based on precursory phenomena and in recent years radon has emerged as a useful precursor. Radon emanation in soil-gas was continuously monitored from October 1988 to September 1989 at the Guru Nanak Dev University, Amritsar. Radon concentrations were measured using both instantaneous and time-integrated techniques. To eliminate the effect of spurious fluctuations, meteorological parameters, viz. air temperature, barometric pressure, wind velocity, relative humidity and rainfall were aloso monitored, continuously. A correlation matrix was computed for radon data and meteorological parameters to discriminate the signal from noise. Nine earthquake-related anomalies were recorded during this period. The anomalous increases in radon appear to be caused by strain changes, which precede the earthquake. (author)

[en] High grade uranium ore zones can yield erroneously low density log values, because of natural γ-radiation from the ²³⁸U radioactive decay series. Significant density log errors of this nature could have severe consequences on porosity, shale volume, and water saturation estimates, useful for hydrologic evaluations of roll-front uranium deposits. This problem can be overcome by recording a background radioactivity profile without the density log γ-ray source in the tool and using it to correct the density log values. (author)

[en] A simulation study of a PGNAA system for the analysis of coal with a ²⁵²Cf neutron source has been carried out using the MCNP code to investigate the effect on the system response of variable thickness, density and composition of the sample when the source is placed at the center of a moderating sphere of polyethylene. Results for different radii of the moderating sphere are reported. The results show that the geometry of the measuring arrangement can be chosen so that the γ count rate/wt% of an arbitrary element (including hydrogen) is independent both of the hydrogen content of the coal, ω_H, expressed as a mass fraction, and of the bulk density, d, or volume hydrogen content of the sample ν_H, at least in the range of ω_H-values commonly found in bituminous coals. The system response, defined as the magnitude of the output signal/wt% of an arbitrary element in the coal composition is then independent of composition and bulk density of the coal sample. (author)