Showing papers in "Geophysics in 1972"
TL;DR: In this article, a simple transformation in the frequency domain yields an analytic function whose real part is the horizontal derivative of the field profile and whose imaginary part is vertical derivative of field profile.
Abstract: This paper presents a procedure to resoive magnetic anomalies due to two-dimensional structures. The method assumes that all causative bodies have uniform magnetization and a crosssection which can be represented by a polygon of either finite or infinite depth extent. The horizontal derivative of the field profile transforms the magnetization effect of these bodies of polygonal cross-section into the equivalent of thin magnetized sheets situated along the perimeter of the causative bodies A simple transformation in the frequency domain yields an analytic function whose real part is the horizontal derivative of the field profile and whose imaginary part is the vertical derivative of the field profile. The latter can also be recognized as the Hilbert transform of the former. The procedure yields a fast and accurate way of computing the vertical derivative from a given profile. For the case of a single sheet, the amplitude of the analytic function can be represented by a symmetrical function maximizing exactly over the top of the sheet. For the case of bodies with poiygonal cross-section, such symmetrical amplitude functions can be recognized over each corner of each polygon. Reduction to the pole, if desired, can be accomplished by a simple integration of the analytic function, without any cumbersome transformations. Narrow dikes and thin ilat sheets, of thickness less than depth, where the equivalent magnetic sheets are close together, are treated in the same fashion using the field intensity as input data, rather than the horizontal derivative. The method can be adapted straightforwardly for computer treatment. It is also shown that the analytic signal can be interpreted to represent a complex “field intensity,” derivable by differentiation from a complex “potential.” This function has simple poles at each polygon corner. Finally, the Fourier spectrum due to finite or infinite thin sheets and steps is given in the Appendix.
1,144 citations
TL;DR: In this article, the theory of magnetotelluric (MT) and some of the experimental, analytical, and interpretive techniques developed for its use in petroleum exploration in the past five years are described.
Abstract: The paper describes the theory of the magnetotelluric (MT) method, and some of the experimental, analytical, and interpretive techniques developed for its use in petroleum exploration in the past five years. Particular emphasis is placed on interpretation, since it is the area least amenable to routine treatment. Whereas present interpretation techniques are adequate, interpretation is the area of both the greatest progress and the greatest need for improvement. Field results are presented from traverses in South Texas bordering on the Gulf of Mexico, and the Anadarko Basin of southwestern Oklahoma. Wide station spacings were used, such as might typify basin evaluations. The South Texas results are compared directly with smoothed induction logs. No useable logs could be found for Oklahoma. Comparisons with known and inferred geology show that the surveys mapped resistivity successfully in the known parts of these basins as well as in portions inaccessible seismically. The capabilities and economics of the...
619 citations
TL;DR: In situ measurements of compressional (sound) velocity and attenuation were made in the sea floor off San Diego in water depths between 4 and 1100 m; frequencies were between 3.5 and 100 khz as mentioned in this paper.
Abstract: In‐situ measurements of compressional (sound) velocity and attenuation were made in the sea floor off San Diego in water depths between 4 and 1100 m; frequencies were between 3.5 and 100 khz. Sediment types ranged from coarse sand to clayey silt. These measurements, and others from the literature, allowed analyses of the relationships between attenuation and frequency and other physical properties. This permitted the study of appropriate viscoelastic models which can be applied to saturated sediments. Some conclusions are: (1) attenuation in db/unit length is approximately dependent on the first power of frequency, (2) velocity dispersion is negligible, or absent, in water‐saturated sediments, (3) intergrain friction appears to be, by far, the dominant cause of wave‐energy damping in marine sediments; viscous losses due to relative movement of pore water and mineral structure are probably negligible, (4) a particular viscoelastic model (and concomitant equations) is recommended; the model appears to apply...
487 citations
TL;DR: In this article, it was shown that there exists a simple, exact relationship between maximum entropy spectra and maximum likelihood spectra when the correlation function is known at uniform intervals of lag.
Abstract: In a long needed paper, R. T. Lacoss (1971) has presented many examples of spectra obtained by the maximum likelihood method and by the maximum entropy method and has shown that these newer techniques are in general superior to the more conventional spectral analysis methods. This short note shows that there exists a simple, exact relationship between maximum entropy spectra and maximum likelihood spectra when the correlation function is known at uniform intervals of lag. The data are of this form in almost all practical cases of time series analysis as well as in the special case of wavenumber spectral analysis of wave propagation as seen by a linear array of equally spaced sensors. The wavenumber case will be explicitly considered in this note since it requires the complex variable form of the theory.
382 citations
TL;DR: In this article, a method for migration of seismic data based on numerical solutions of partial differential equations was developed for the geometry of a single source with a line of surface receivers, where the best receiver line for any reflector is just at (or above) the reflector.
Abstract: Earlier work developed a method of migration of seismic data based on numerical solutions of partial differential equations. The method was designed for the geometry of a single source with a line of surface receivers. Here the method is extended to the geometry of stacked sections, or what is nearly the same thing, to the geometry where a source and receiver move together along the surface as in marine profiling. The basic idea simply stated is that the best receiver line for any reflector is just at (or above) the reflector. Data received at a surface line of receivers may be extrapolated by computer to data at a hypothetical receiver line at any depth. By considering migration before stacking over offset, it is found that certain ambiguities in velocity analysis may be avoided.
184 citations
TL;DR: In this article, a general wave field is decomposed into transverse magnetic (TM) and transverse electric (TE) modes and the reflection coefficients are obtained in closed form.
Abstract: Solutions to the problem of radiation of dipole antennas in the presence of a stratified anisotropic media are facilitated by decomposing a general wave field into transverse magnetic (TM) and transverse electric (TE) modes. Employing the propagation matrices, wave amplitudes in any region are related to those in any other regions. The reflection coefficients, which embed all the information about the geometrical configuration and the physical constituents of the medium, are obtained in closed form. In view of the general formulation, various special cases are discussed.
162 citations
TL;DR: In this article, a well-to-well seismic propagation, shooting primacord charges into one well, and locking geophones into other wells several hundred meters away is described.
Abstract: Records have been obtained by well‐to‐well seismic propagation, shooting primacord charges into one well, and locking geophones into other wells several hundred meters away. Seismic arrivals containing a large amount of information have been recorded and analyzed by an iterative ray‐tracing technique. If the conditions are favorable, significant wave speed transition zones and small structures can be detected between wells.
106 citations
TL;DR: In this paper, the anomalous fields from a buried cylindrical inhomogeneity in an otherwise uniform half-space are analyzed, where the problem is rendered two-dimensional by assuming that the uniform line source of current is parallel to the subsurface cylinder.
Abstract: The anomalous fields from a buried cylindrical inhomogeneity in an otherwise uniform half-space are analyzed. The problem is rendered two-dimensional by assuming that the uniform line source of current is parallel to the subsurface cylinder. The multipole scattered field coefficients are obtained from the numerical solution to the associated singular Fredholm integral equation of the second kind. The horizontal magnetic field amplitude, the vertical magnetic field phase, and the amplitude and phase of the ratio of horizontal to vertical magnetic fields are shown to be diagnostic of the location of the inhomogeneity. The results have possible applications to electromagnetic location in mine rescue operations and to geophysical prospecting.
86 citations
TL;DR: A few methods in the processing and interpretation of magnetotelluric soundings over a stratified earth are investigated, with emphasis on the less commonly used time‐domain procedures.
Abstract: A few methods in the processing and interpretation of magnetotelluric soundings over a stratified earth are investigated, with emphasis on the less commonly used time‐domain procedures Analytical expressions of the theoretical transfer function between the magnetic‐ and electric‐field variations, both in frequency and time domain, are derived Their properties are studied, and recursive algorithms are given for their numerical computation On the other hand, a procedure is outlined which leads directly in the time domain to the experimental values of this transfer function It is similar to the methods used in seismic analysis for signal determination and makes use of the auto‐ and crosscorrelation functions of the measured field variations Finally, methods of interpretation, based either on a visual or on an automatic comparison of these theoretical and experimental transfer functions, are proposed For the case of automatic interpretation, complementary geologic data should be used where possible to t
76 citations
TL;DR: In this paper, a new method for continuing two-dimensional potential data upward from an uneven track is developed with special emphasis on solving a particular practical problem, that of magnetic data taken near the bottom of the ocean.
Abstract: A new method for continuing two‐dimensional potential data upward from an uneven track is developed with special emphasis on solving a particular practical problem, that of magnetic data taken near the bottom of the ocean. The method is based on the use of the Schwarz‐Christoffel transformation, which maps the original, irregular track into a horizontal straight line. It has been found to be very fast computationally and to suffer none of the restrictions found in some earlier two‐dimensional algorithms.
49 citations
TL;DR: In this paper, the authors applied the induced potentials method in groundwater and certain types of engineering geologic investigations and proved the dependence of induced potential on the particle-size distribution pattern, porosity, moisture content, interporous moisture, salinity degree, and temperature.
Abstract: The method of induced potentials is applied in groundwater and certain types of engineering‐geologic investigations. Because of the complex nature of induced polarization in ion‐conducting media, the subject still has not been sufficiently studied. This phenomenon is evidently associated with the diffusion processes occurring between narrow and wide capillaries and affected by membrane potentials in the presence of clay fractions. The laboratory experiments have proved the dependence of induced potentials of sandy‐clayey media on their particle‐size distribution pattern, porosity, moisture content, interporous moisture, salinity degree, and temperature. Modeling accomplished with horizontally layered sections and lenses of fresh and saline waters has given data for analyzing polarizability behavior in heterogeneous media. Field investigations have been carried out in Central Kazakhstan, the Crimea, Mordovia, Armenia, and the Moscow area. The data obtained testify to the applicability of this method for de...
TL;DR: In this article, an efficient procedure for the approximation of two-dimensional (2-D) fan filters is presented, where the Chebychev (or min-max) error criterion is used to measure the optimality of the approximation as opposed to previous designs which use the least square norm.
Abstract: An efficient procedure for the approximation of two‐dimensional (2‐D) fan filters is presented. The Chebychev (or min‐max) error criterion is used to measure the optimality of the approximation as opposed to previous designs which use the least‐squares norm. Since the direct solution of a 2‐D Chebychev approximation problem is difficult, a change of variables is introduced to convert the 2‐D approximation problem into an equivalent 1‐D low‐pass filter approximation problem. The response is opptimized in the 1‐D domain, and then the change of variables is applied to obtain the 2‐D filter. Thus the techniques of 1‐D Chebychev approximation are applied to yield a 2‐D fan filter.
TL;DR: In this article, a helicopter-towed multicoil electromagnetic system was developed using a 30-ft bird and a transmitted frequency of 918 hz. Its primary features of interest were low aerodynamic and geological noise, three-dimensional vector recording of anomalies, and quantity of geological information which is extracted by a computer-oriented interpretive procedure.
Abstract: A helicopter-towed multicoil electromagnetic system was developed using a 30-ft bird and a transmitted frequency of 918 hz. Its primary features of interest are (1) low aerodynamic and geological noise, (2) three-dimensional vector recording of anomalies, and (3) quantity of geological information which is extracted by a computer-oriented interpretive procedure. The multicoil system was developed to obtain more diagnostic geologic information about a conductor than was possible with other aerial electromagnetic equipment. This led to two approaches: (1) three-dimensional recording of anomalies was developed to provide information on the electrical current distribution within the conductor and, hence, on the geometry of the conductor and (2) high-resolution, low-frequency design was chosen to bias the response of the system toward high-conductivity targets to minimize interference from the usual geologic noise sources, thereby enhancing the response of discrete massive sulfide conductors. A consequence of these design criteria is a system yielding an advance in the state-of-the-art of aerial electromagnetic exploration.
TL;DR: In this article, the relation of in-situ compressional wave velocities to porosities, determined by seismic refraction for unsaturated near surface rocks from different areas in Arizona, New Mexico, and California, is grossly similar to relations determined by other investigators for water-saturated rock and unconsolidated sediments.
Abstract: The relation of in‐situ compressional‐wave velocities to porosities, determined by seismic refraction for unsaturated near‐surface rocks from different areas in Arizona, New Mexico, and California, is grossly similar to relations determined by other investigators for water‐saturated rock and unconsolidated sediments. The principal difference is that in the porosity range 0.0–0.2, compressional waves travel somewhat more slowly in unsaturated rocks than in water‐saturated rocks, and much more slowly, in the porosity range 0.2–0.8. The function, ϕ=−0.175 ln (α)+1.56, where ϕ is the fractional porosity and α is the compressional‐wave velocity, was obtained as a least squares fit to the experimental data. Bulk densities are reported for all samples; moisture contents are reported in some instances.
TL;DR: In this article, a 230 Mhz pulse-radar well-logging system for piercement-dome salt was used to estimate the position of the salt dome in Evangeline Parish, Louisiana.
Abstract: Encouraging results of laboratory and field tests of radio‐frequency transmission in piercement‐dome salt led to the construction of a 230 Mhz pulse‐radar well‐logging system. Reflection data gathered during tests of the system in a well drilled into the Pine Prairie salt dome in Evangeline Parish, Louisiana, were reduced using techniques developed to pick out the best reflections from those recorded. An interpretive cross‐section and a contour map of the near flank of the dome were constructed from the reduced data. The upper flank position of the dome was confirmed by surface‐gravity data; the lower flank position was confirmed by slant drilling which intercepted the salt‐sediment interface at 8112 ft.
TL;DR: It is concluded from the literature that a very strong swing toward automatic processing and semi‐automatic methods of interpretation using computers has taken place in both methods during the time period under review.
Abstract: This paper reviews the literature in data processing and interpretation in gravity and magnetic methods for the period 1964–71. The topics that are covered include gravimetry, reduction of data, automatic contouring, map analysis and filtering, interpretation technique, and applications. It is concluded from the literature that a very strong swing toward automatic processing and semi‐automatic methods of interpretation using computers has taken place in both methods during the time period under review. The key to further development in this direction appears now to be with making more imaginative use of graphic display devices.
TL;DR: In this paper, a method is described for using a digital computer to construct contour maps automatically, where the region to be contoured is divided into quadrilaterals whose vertices include the data points.
Abstract: A method is described for using a digital computer to construct contour maps automatically. Contour lines produced by this method have correct relations to given discrete data points regardless of the spatial distribution of these points. The computer‐generated maps are comparable to those drawn manually. The region to be contoured is divided into quadrilaterals whose vertices include the data points. After supplying values at each of the remaining vertices by using a surface‐fitting technique, bicubic functions are constructed on each quadrilateral to form a smooth surface through the data points. Points on a contour line are obtained from these surfaces by solving the resulting cubic equations. The bicubic functions may be used for other calculations consistent with the contour maps, such as interpolation of equally spaced values, calculation of cross‐sections, and volume calculations.
TL;DR: In this paper, the authors presented a 3D seismic display of emerging wavefronts covering four sq mi of surface. But instead of showing the subsurface beneath a profile line, the 3D displays gave an, areal picture from the shallowest reflector to the deepest one that can be found seismically.
Abstract: The three‐dimensional seismic method is a different way of gathering and presenting seismic data. Instead of showing the subsurface beneath a profile line, 3-D displays give an, areal picture from the shallowest reflector to the deepest one that can be found seismically. Data are collected in the field with cross‐spreads that provide over 2000 evenly spaced depth points on each reflecting interface. Several variations of the cross‐spread technique give the same subsurface coverage while providing flexibility in data gathering. Because of the dense coverage, the method is best suited for problems requiring great detail, such as production problems. The usual presentation of 3-D data is a visual, moving display of emerging wavefronts covering four sq mi of surface. From this dynamic display, average velocity to each reflector and the dip direction and magnitude can be computed. The method has proved especially useful for the recognition of faults and determination of fault directions.
TL;DR: In this article, the authors show that for profile or flight line data for which the source can be assumed to be two-dimensional, all these operations amount to linear combination of the profile with its Hilbert transform.
Abstract: Three related operations commonly performed on total-field magnetic data are 1) conversion to vertical-field anomaly, 2) reduction to the pole, and 3) computation of pseudogravimetric anomalies. This note shows that for profile or flight line data for which the source can be assumed to be two-dimensional, all these operations amount to linear combination of the profile with its Hilbert transform.
TL;DR: In this paper, the authors used microearthquake equipment to measure noise levels, monitor natural earthquakes, and to make seismic refraction measurements along the Llano Uplift.
Abstract: Microearthquake equipment was used in the Texas Gulf Coast area to measure noise levels, monitor natural earthquakes, and to make seismic refraction measurements. There is a small correlation of the noise level with the distance from the Gulf of Mexico. Three horizons within the sedimentary section were successfully observed by seismic refraction measurements to the northeast along the strike. Beneath these is a 5.22 km/sec layer at a depth of 10 km, overlying a 6.45 km/sec layer at 16 km, which in turn overlies the mantle at 8.41 km/sec at a depth of 30 km. The observed velocities and depths correlated well with those of Cram (1961) about 40 km farther inshore. Refraction reception to the northwest was much poorer, with signal amplitudes about 15 times smaller than those to the northeast. A composite crustal structure southeast from the Llano Uplift, across the Gulf of Mexico is presented and discussed. More work is required to delineate the structure between our new profile and the Sigsbee Scarp, and th...
TL;DR: In this article, electrical anisotropy measurements were made on selected dry metasediments and metavolcanics from the Precambrian complex of northern Michigan, and the results indicated that metamorphic rocks may be characterized by strongly anisotropic electrical properties.
Abstract: Laboratory electrical anisotropy measurements were made on selected dry metasediments and metavolcanics from the Precambrian complex of northern Michigan. Directional ac conductivity and dielectric‐constant values were obtained in six or more directions for each sample. These directional values were used to obtain a least‐square determination of the six independent coefficients needed to completely define the symmetric second‐rank, conductivity and dielectric constant tensors. Tensor principal values and directions were obtained from these coefficients. The results of this investigation indicate that metamorphic rocks may be characterized by strongly anisotropic electrical properties. The tensor representation surface symmetries reflect the symmetry of the rock fabric. Electrical anisotropy tends to increase, and the symmetry of the representation surfaces tends to decrease, at lower signal frequencies. The frequency spectra for all samples follow a relaxation‐type model, with critical frequencies occurri...
TL;DR: In this article, a cross-section showing the crustal structure from the east end of Kodiak Island across the continental terrace and slope to the Aleutian Trench is presented.
Abstract: Seismic refraction profiles near Kodiak, Alaska have provided data for construction of a cross‐section showing the crustal structure from the east end of Kodiak Island across the continental terrace and slope to the Aleutian Trench (Figures 1 and 2). Five reversed refraction stations and one unreversed station were available (Table 1); interpretation was aided by access to reflection profiles which cross the refraction lines (Shor, 1972).
TL;DR: For a given response of a one-dimensional filter, the weighting coefficients are calculated by solving a set of simultaneous equations with a simple matrix inversion procedure in this paper, where the problem of choosing a suitable decay in the high frequency response is discussed in detail.
Abstract: Methods for the design of spatial filters are discussed in this paper For a given response of a one‐dimensional filter, the weighting coefficients are calculated by solving a set of simultaneous equations with a simple matrix inversion procedure In the case of a two‐dimensional filter, the method for obtaining the coefficients of a double Fourier series representing a set of given values is used to design the spatial operator The problems connected with the length of the operator and the choice of a suitable decay in the high‐frequency response are discussed in detail In order to show the usefulness of these methods, the paper presents several examples of operators designed for computing the vertical gradient, the second vertical derivative, and downward continuation of potential field data A two‐dimensional vertical gradient filter is applied to the total field data obtained during a high‐resolution aeromagnetic survey over an area in the Precambrian Shield of Northeastern Ontario The calculated gr
TL;DR: Theoretical solutions for the electromagnetic response of a dipping interface in the field of normally incident plane waves are given in the form of inverse Lebedev-Kontorovich transforms as discussed by the authors.
Abstract: Theoretical solutions for the electromagnetic response of a dipping interface in the field of normally incident plane waves are given in the form of inverse Lebedev‐Kontorovich transforms. When the lateral resistivity contrast becomes very large, the resulting integral solutions simplify considerably and allow ready numerical evaluation. The amplitude response of the vertical magnetic field seems most diagnostic of the structural attitude of sloping interfaces, even though the vertical magnetic field phase appears relatively insensitive to dip changes compared to horizontal electric field phase. The disturbance in the homogeneity of the field caused by the presence of an inclined contact is postulated to be due to cylindrically diffused waves generated by the dipping interface and propagating along the earth’s surface. It would then seem that formulation of plane‐wave impedances from orthogonal components of the surface electric and magnetic fields would only be applicable at distances from the interface ...
TL;DR: In this article, an integral formulation for the fields of a loop current source over a horizontally stratified half-space and having a vertical axis was given for the case of source and observer on the interface but separated by a large numerical distance.
Abstract: An integral formulation is given for the fields of a loop current source which is located over a horizontally stratified half‐space and has a vertical axis. The electrical properties of the half‐space vary exponentially with the depth into the earth. An asymptotic solution is developed for the case of source and observer on the interface but separated by a large numerical distance. The approximate solution is then used to determine the mutual impedance between two small loops and between the loop and a horizontal electric dipole, when the antennas are on the interface. It is found that the effect of stratification on the mutual impedance is represented approximately by a single multiplicative factor.
TL;DR: In this paper, an electromagnetic depth sounding experiment with a horizontal loop carrying an oscillating current was carried out in Santa Clara Valley, California, where the field data were interpreted in terms of the polarization parameters of the magnetic polarization ellipse.
Abstract: An electromagnetic depth sounding experiment with a horizontal loop carrying an oscillating current was carried out in Santa Clara Valley, California. The field data are interpreted in terms of the polarization parameters of the magnetic polarization ellipse. The chosen parameters are tilt‐angle, ellipticity, and the modulus of wavetilt. The electrical discontinuities deduced are in general agreement with well data and with a geologic section based on resistivity soundings. The results clearly reveal an intermediate, highly resistive layer, which is a permeable stratum for groundwater recharge. It is concluded that a portable electromagnetic sounding system, measuring only tilt‐angle and ellipticity, should easily locate highly resistive gravel deposits bounded by conductive clay beds. It is theoretically obvious that the system is useful in those regions where it is extremely difficult to inject current into the ground.
TL;DR: In this article, it is shown that it is possible to interpret some useful stratigraphic characteristics from seismic reflections, the interpretation being based upon the concept of sedimentation models, where the control of lithologic distribution by dominant depositional process is summarized.
Abstract: Seismic techniques have been used mainly for structural interpretation, but mounting interest in stratigraphic applications is evident. Estimation of sand‐shale ratios from seismically derived average velocities is a recent example of a stratigraphic application. Except in the case of tall pinnacle reefs, today direct location of stratigraphic traps by reflection methods is restricted, at best, to areas of very high quality data and abundant well control. However, it may be possible to interpret some useful stratigraphic characteristics from seismic reflections, the interpretation being based upon the concept of sedimentation models. Most stratigraphic sequences are not random stacks of various lithologies. Commonly, they are well organized and have units with characteristic contacts, thicknesses, lateral extents, lateral facies changes, and vertical sequence. These orderly characteristics are summarized in sedimentation models, where the control of lithologic distribution by dominant depositional process...
TL;DR: In this article, the telluric and magnetotelluric surveys utilizing natural 8-hz electromagnetic fields have been used to detect resistivity variations associated with some proven sulfide deposits.
Abstract: Telluric and magnetotelluric surveys utilizing natural 8‐hz electromagnetic fields have detected resistivity variations associated with some proven sulfide deposits. From an operational point of view the telluric method is preferred to magnetotellurics. Either method, however, can detect a conducting dike, providing that its width is greater than its depth of burial. For surveys where the telluric field is measured in a direction perpendicular to the strike of the conductor, theoretical profiles derived from two‐dimensional conductivity structures agree well with the field results. For this polarization, it is thus possible to use a general model as an aid to the interpretation of survey data.
TL;DR: In this article, a theoretical model has been developed in which small, random pressure variations in a convecting geothermal reservoir are suggested to suggest that high surface noise levels are associated with the presence of underground geothermal reservoirs.
Abstract: In recent years there has been increasing interest in the role of geothermal steam as a source of energy. Only recently has geophysical exploration begun to play a major role in the exploration for geothermal resources; heat flow, gravity, and resistivity measurements have been the techniques most used. One recent development is the discovery that high surface‐noise levels are associated with the presence of geothermal reservoirs below the surface. Field surveys using short‐period seismographs have been conducted in the Imperial Valley of California in areas where heatflow measurements or drilling have indicated the presence of a geothermal deposit. In all three surveys abnormally high noise levels were found above the reservoir in the frequency range of 0.5 to 5.0 hz. The ground‐noise anomalies show a more complex pattern than the associated heat flow and gravity measurements. A theoretical model has been developed in which small, random pressure variations in a convecting geothermal reservoir are sugges...
TL;DR: The physical principles of a new method for uranium detection based on use of a pulsed source of neutrons are presented in this paper, which employs measurement of the neutron time distributions in rock media following a burst of fast neutrons.
Abstract: The physical principles of a new method for uranium detection based on use of a pulsed source of neutrons are presented. The method employs measurement of the neutron time distributions in rock media following a burst of fast neutrons. A time‐ and energy‐dependent (but space‐independent) theory is developed for the four principal time distributions that follow production of fission neutrons by each of the two possible reactions: 1. Prompt thermal fission of 235U: a. Epithermal neutron time distribution, b. Thermal neutron time distribution. 2. Delayed fission of uranium: a. Neutron time distribution due to delayed fission in 235U, b. Neutron time distribution due to delayed fast fission in 238U. Theoretical analysis of these phenomena leads to the conclusion that the detection of uranium in rocks is possible using either the epithermal neutron time distribution from the prompt fission of 235U by thermal neutrons or the delayed neutron distribution from fast neutron fission of 238U or thermal neutron fissi...