Abstract: An x-ray reflectometry system for measuring thin film samples. The system includes an adjustable x-ray source, such that characteristics of an x-ray probe beam output by the x-ray source can be adjusted to improve the resolution of the measurement system. The x-ray probe beam can also be modified to increase the speed of evaluating the thin film sample, for situations where some degree of resolution can be sacrificed. In addition, or alternatively, the system can also provide an adjustable detector position device which allows the position of the detector to be adjusted to increase the resolution of the system, or to reduce the time it takes to evaluate the thin film material.

Abstract: Method and system for analyzing local composition and structure of a compound having one or more non-zero gradients in concentration for one or more selected constituents in a selected direction. A beam of X rays having representative energy E is received by a mono-capillary or poly-capillary device and is directed at a selected small region of the compound. A portion of the X rays is diffracted at the selected region by one or more constituents of the compound, at each of two or more diffraction angles relative to a selected surface or lattice plane(s) of the compound; and the diffracted portion of X rays for each of these diffraction angles is received and analyzed at an X-ray detector. A portion of the X rays excites fluorescence radiation that is received by a fluorescence detector to estimate the relative concentrations in a compound having two or more constituents. Fluorescence X rays and diffraction X rays can be detected at each desired translational position and rotation for a target site.

Abstract: A device and method having a stationary radiation source for directing polychromatic radiation such that the radiation is incident on a sample to be inspected in parallel or diverging rays, and a position-sensitive, energy-sensitive detector for measuring components of the radiation reflected by the sample thereby providing for the efficient and effective inspection of the sample.

Abstract: A grating that includes a multilayer structure that has alternating layers of materials, a plurality of grooves formed between a plurality of lands, wherein at least one structural parameter of the plurality of grooves and plurality of lands is formed randomly in the multilayer structure.

Abstract: A method and arrangement for measuring the moisture content of a flow of wood chips, through which collimated gamma radiation is directed attenuation of which in the flow of wood chips is measured. The flow of wood chips is shaped by transporting it on a trough-shaped conveyor in such a way that the length of a ray can be determined. The moisture content can be calculated on the basis of the proportion of gamma radiation passing through the flow of wood chips and the flow's thickness, as well as on the basis of the previously determined air content of the flow of wood chips.

Abstract: An X-ray micro-diffraction measuring method for detecting X-rays diffracted at a minute portion of a specimen upon irradiating the minute portion with X-rays is disclosed. A cylindrical stimulation type fluorescent member is arranged around the specimen. A sample facet of the specimen is tilted by, for example, 45° with respect to the stimulation type fluorescent member such that the stimulation type fluorescent member can receive both diffracted X-rays passing along a direction tangential to the sample facet and diffracted X-rays passing along a direction perpendicular to the sample facet. Diffracted X-ray images can be obtained on the stimulation type fluorescent by merely rotating the specimen about only the &phgr; axis thereof so as to perform the in-plane rotation without a rotation about the &khgr; axis. By eliminating a rotation about one axis from rotations about two axes for the specimen, it may be possible to avoid a degradation of measurement preciseness due to a crossing error of the two axes.

Abstract: Energy dispersive x-ray diffraction spectra are obtained from numerous volume elements within an object. A feature set such as a set of cepstrum coefficients is extracted from each spectrum and classified by a trained classifier such as a neural network to provide an indication of whether or not contraband such as explosives is present in the volume element. Indications for adjacent volume elements are evaluated in conjunction with one another, as by an erosion process, to suppress isolated indications and thereby suppress false alarms.

Abstract: A method of determining the concentrations of the constituents in a mixture of substances by way of an X-ray diffractogram of the mixture. The fundamental difficulty that it is not possible to determine the entire power spectrum (PS) of the diffraction is avoided by making a suitable estimate of the PS on the basis of the diffractions that can be observed. Using an estimate of the dispersive power of the individual atoms in the unity cells of the constituents and the PS, the absolute intensities are determined from the relative intensities and on the basis thereof the concentrations of the constituents in the mixture are determined.

Abstract: X-rays are irradiated to a sample to be measured including at least one layer of film formed on a substrate; an interference oscillation curve of the X-rays incident on the sample to be measured is measured; and a concentration of an element adhered on a surface of the sample to be measured and/or segregated in an interface of the film is measured. The interference oscillation curve is fitted to an analysis formula expressing an X-ray reflectance to thereby determining a density of a region of the sample to be measured, where the element is adhered or is segregated, and a concentration of the element is computed based on the density.

Abstract: A specimen holder and specimen grid orientation arrangement facilitating in-situ and ex-situ repeated analysis of a specimen in a microscope. The arrangement includes a specimen grid, to which the specimen is affixed, having an alignment aid. The arrangement also includes a specimen holder having an opening. The opening repeatedly receives and supports the specimen grid. A reference aid, located in the opening of the specimen holder, engages the alignment aid on the specimen grid to orient the specimen grid in a single position within the opening of the specimen holder. In specific embodiments, the alignment aid of the specimen grid may be a notch or an aperture; the reference aid of the specimen holder may be a raised surface or a pin.

Abstract: An x-ray spectrometer is provided comprising an X-ray source, a curved crystal monochromator which focuses a monochromatic x-ray beam onto a sample surface, the curved crystal monochromator comprising a shape which is substantially identical to a logarithmic spiral, and a position-sensitive x-ray detector. A method of measuring diffraction intensities from oriented samples in real time including providing an x-ray spectrometer comprising an X-ray source, a curved crystal monochromator which focuses a monochromatic x-ray beam onto a sample surface, the curved monochromator comprising the shape of a logarithmic spiral, and a position-sensitive x-ray detector; and providing a crystallographically oriented sample, exposing the sample to the focused x-ray beam of the x-ray spectrometer; and measuring the diffraction intensity at the position-sensitive detector.

Abstract: The invention relates to an examination method whereby a respective spectrum with a number of spectral values is measured for a number of locations. Collective evaluation of the old spectra is enabled by the following steps:a) formation of a data matrix from the spectral vectors formed by the series of spectral values of a respective spectrum, the spectral vectors being arranged in the columns (or in the rows) of the data matrix in a location-dependent manner,b) singular value decomposition of the data matrix in order to obtain three matrices whose product corresponds to the data matrix, the first (third) matrix consisting of spectrally dependent vectors, whereas the second matrix is a diagonal matrix and the third (first) matrix consists of location-dependent vectors,c) evaluation of at least one of the three matrices.

Abstract: The following arrangement is adopted to achieve an X-ray spectroscope capable of simultaneously spectrally analyzing, with a single spectral scanning, X-rays emitted from a point-like X-ray source in a plurality of wavelength ranges such that X-rays in a wide wavelength range can spectrally be analyzed with a single spectral scanning.

Abstract: In the case of simultaneous diffraction and fluorescence measurements in an apparatus for X-ray analysis comprising only one X-ray tube, a problem is encountered in that due to the presence of the collimators required for the fluorescence measurements only a very low X-ray power reaches the detectors, so that very long measuring times and/or an unfavorable signal-to-noise ratio occur. As a result, the detection limit for given measurements (low concentration of an element and/or light elements to be detected) becomes too high or the use of a (large and expensive) high-power X-ray tube is required. The invention utilizes a line focus tube 10 in combination with a single-slit collimator 14 for irradiating the sample 2, the fluorescence section 40 being constructed so as to have a plane or cylindrical analysis crystal 42 in combination with a location-sensitive detector 44. The diffraction measurements are performed by means of a conventional diffraction arrangement 24.

Abstract: A method of determining the compositions and thicknesses of metamorphic layers at heterointerfaces of periodic laminated structures, such as multiple quantum well structures. An X-ray diffraction pattern of the actual structure is measured and a theoretical X-ray diffraction pattern is calculated using dynamic X-ray theory and giving special attention to X-ray diffraction fringes near a satellite peak in the pattern. The thicknesses and compositions of the metamorphic layers are adjusted in a recursive analysis until the calculated pattern agrees with the measured pattern, thereby providing an accurate analysis of laminated periodic structures.

Abstract: An intelligent automatic gain stabilization method and apparatus for a radiation detection instrument automatically locate the position of a predetermined characteristic within an energy spectrum, automatically determine whether the characteristic is properly located, and automatically provide gain adjustment to the output of the radiation detection instrument to maintain measurement accuracy of the system.

Abstract: An X-ray analysis apparatus includes a scanning unit (1) with an X-ray source (3), a crystal holder (9) and an X-ray detection system (5) provided with an X-ray detector (7). The crystal holer (9) can be rectilinearly displaced in a fixed radiation pick-up direction (35) relative to the X-ray source (3). The crystal holder (9) and the X-ray detector (7) are mechanically coupled to one another via a plate (21) which can be driven by means of a motion mechanism. The X-ray source (3), the X-ray detector (7) and the crystal holder (9) remain positioned on a Rowland circle (11) during the displacement. The motion mechanism has a first guide (23) and a second guide (25). The drive direction of the first guide (23) encloses an acute angle .alpha. relative to the fixed pick-up direction (35).

Abstract: An accurate, real-time method for monitoring and analyzing crystalline specimens having polycrystalline platings. The method is capable of individual or simultaneous analysis of any combination of the following: 1) composition of the substrate and plating (even when the plating and substrate having common elements); 2) analysis of thickness of the plating(s); 3) analysis of the depth of the plating(s), e.g., the thickness of any overlay; 4) analysis of the crystalline phase depth simultaneous with phase composition; 5) the preferred crystalline orientation; 6) the strain in the substrate; and (7) crystallinity and grain size. The apparatus is similar to that of U.S. Pat. No. 5,148,458 issued to Ruud, with the apparatus of this invention having the several detectors placed on different arcs and/or radial distances from the specimen surface under investigation.

Abstract: An X-ray analysis apparatus including an artificial multi-layered grating for rendering X-ray beams to be monochromatic before they are incident on a specimen to be analyzed. This artificial multi-layered grating operates to diffract the X-ray beam, generated from an X-ray radiation source and subsequently impinging on a reflective surface of the artificial multi-layered grating, at a predetermined angle of diffraction to provide the monochromatic X-ray beams. The periodicity of the spacing of lattice planes of the artificial multi-layered grating is so chosen as to be of a value progressively varying along the reflective surface thereof with an increase in distance from the X-ray radiation source. The X-ray analysis apparatus herein disclosed is designed to avoid any possible reduction of the intensity of the X-ray beams which would occur when they are rendered to be monochromatic, and to increase the intensity of the X-ray beams to ensure an improved accuracy in spectroscopic analysis.

Abstract: A method for detecting and evaluating crystal defects existing in the extreme neighborhood of the surface of a crystal specimen through the use of X-ray analyzing micrography. Synchrotron radiation is used as the X-ray source. A monochromatic X-ray beam generated from the synchrotron radiation is directed into the crystal specimen at a glancing angle smaller than the critical angle of said crystal specimen relative to said monochromatic X-ray beam. The diffracted X-rays from the crystal specimen due to asymmetrical reflection are detected in order to observe the resulting diffracted image.

Abstract: This invention relates to a method and apparatus for analyzing a plurality of elements that are present on the surface of a material of interest or in its neighborhood, as well as a thin-film forming apparatus that is capable of measuring the composition of a sample during thin film formation in the process of semi-conductor fabrication. The apparatus are characterized in that a detector is isolated from the light and heat generated in a sample making mechanism by means of a shield which is not only heat-resistant but also transmissive of fluorescent X-ray containing soft X-rays of 1 Kev and below and that a mirror for total reflection of X-rays which is equipped with slits capable of adjusting the incident and exit angles of fluorescent X-rays from the sample excited with an excitation source as well as the ranges of those angles is provided either at the entrance or exit of said shield or at both.

Abstract: The invention relates to an apparatus and method for detecting the presence of an element of interest within an object. The object is positioned where a beam of gamma rays of the required energy are directed to be scattered by the element of interest. The gamma rays are provided by excited atoms of the element of interest. The excited atoms result from the reaction of hydrogen or heavier ions and a suitable target. The excited atoms deexcite, releasing gamma rays which are scattered by the element of interest within the object. The scattered gamma rays are detected, output signals are produced, processed and analyzed to determine the amount of the element of interest within the object. A preferred embodiment relates to the detection of nitrogen-based explosives in luggage.

Abstract: An X-ray spectroscopic analyzing apparatus which comprises a source of X-rays, a first analyzing crystal for diffracting the X-rays from the X-ray source, and a second analyzing crystal for diffracting the X-rays from the X-ray source and also for passing therethrough a diffracted X-ray component from the first analyzing crystal. The first and second analyzing crystals are so disposed and so positioned as to permit the diffracted X-ray components of different wavelengths to travel along a single path towards a sample to be analyzed. On an optical path extending between the X-ray source and the sample, a filtering means for cutting a portion of the X-rays which has a wavelength shorter than a predetermined wavelength.

Abstract: The invention is particularly useful for multi-element solutions wherein successive pairs of X-ray beams are generated and passed through the solution sample corresponding to each of the successive various elements the concentrations of which is to be measured, enabling the on-line concentration measurement of, for example, rare earth elements. Microprocessor control is provided of the presentation of successive X-ray emitting irradiated metal targets to the solution sample and with programming enabling on-line successive measurement of the concentration of each successive element, calibration and storage of such measurements and calculation to eliminate the contribution of other interfering elements from the successive elements to be measured, and display of the successive element concentrations. Applications of the invention may be found, also, in the fields of wet metallurgy for precious metals and less common metals, in the field of petrochemical industry and other chemical engineering applications.

Abstract: A light-weight hand-held contraband detection system (10) includes two different sources (74) of low energy gamma rays. Each gamma ray source selectively emits gamma rays at a different energy level, which gamma rays are directed to a specific volume (30) of an object, e.g. a vehicle, being searched. The hand-held detection system also includes a gamma ray detector (42) coupled to a visual indicator (14), which indicator visually indicates the relative number of back-scattered gamma rays reflected back from the object being searched. Back scattering of the emitted gamma rays occurs in differing degrees depending upon the density and contents of the particular volume of the object receiving the gamma rays. Certain changes in density reflect the possibility that contraband, such as drugs, may be concealed in the object being searched. In use, the system is gripped in a hand of the user and passed over the surface of the object being searched.

Abstract: An on-line slurry ash monitoring system for evaluating the composition of coal slurries in coal preparation plants. A coal slurry is introduced into a sample reservoir where it is removed and passed through a closed loop slurry transport system which causes the sample to be directed through a sensor and recirculated back to the reservoir. In order to enhance sensor accuracy, a sample is exposed to vacuum pressure conditions which removes gas bubbles and dissolved gases from the sample. The sensor is preferably a radiation absorption type in which characteristic absorptions of coal particles, ash and iron are evaluated by associated electronics to provide an output of slurry composition.

Abstract: A portable x-ray fluorescence spectrometer has a portable sensor unit containing a battery, a high voltage power supply, an x-ray tube which produces a beam x-ray radiation directed toward a target sample, and a detector for fluorescent x-rays produced by the sample. If a silicon-lithium detector is used, the sensor unit also contains either a thermoelectric or thermochemical cooler, or a small dewar flask containing liquid nitrogen to cool the detector. A pulse height analyzer ("PHA") generates a spectrum of data for each sample consisting of the number of fluorescent x-rays detected as a function of their energy level. The PHA can also store spectrum data for a number of samples in the field. A processing unit can be attached to the pulse height analyzer to upload and analyze the stored spectrum data for each sample.

Abstract: An X-ray analysis apparatus comprises an analysis crystal which is cylindrically curved in the saggital direction. As a result, a beam diffracted by the crystal is collimated in that direction, i.e. the plane of incidence of the X-ray beam, so that a substantial gain regarding radiation yield is obtained without loss of resolution.

Abstract: A method of positioning a sample for X-Ray spectroanalysis at a spectroscopic machine that includes the steps of determining the point of primary focus of an X-Ray beam upon a master grid and then placing the data upon a mating assembly grid that is positioned in an assembly well into which is positioned a grid support that carries the assembly grid with the primary focus point. Further steps include assembling a sample holder with one sheet of film in the assembly well. An interlocking member that locks the sample holder into interlocking relationship with both the grid support and the sample holder is then inserted into the well. The sample is then aligned upon the point of primary focus upon the film in the fixed sample holder. The sample holder is removed from engagement with the interlocking member and transferred to the sample holder support plate at the spectroscopic machine where the sample is aligned with the primary focus.

Abstract: A mineralogical record of whole core is produced by translating whole core relative to a X-ray diffraction source and detector and summing the resulting X-ray diffraction spectra from various surface portions of the core over an interval of the core.

Abstract: A method of analyzing a composition of an optical fiber base material to be measured by radioactive rays, which comprises the steps of irradiating radioactive rays from a radiation generator to the composition containing a plurality of elements or the substance, emitting the transmitted rays of the base material to a plurality of single crystals to produce several types of transmitted rays of specific energy, and measuring the transmitted rays by a radiation detector to analyze the compositions of the constituent elements in the base material. Thus, this method can accurately and economically analyze the composition in response to the constituent elements of the composition and the thickness of the composition.

Abstract: A multichannel X-ray spectrometer includes an X-ray tube with a transmission target and a holder for a specimen placed opposite the target, and spectrometric channels arranged around the specimen. These spectrometric channels include, successively arranged downstream fluorescent X-rays of the specimen, a common inlet annular slit with a radius R, focusing analyzer crystals, outlet slits, and detectors of X-rays. The common annular slit is spaced from the reference surface of the holder to a distance h equal to 0.5 R, where R is 0.5 dD/2L, where d is the diameter of the outlet port of the transmission target, D is the diameter of the fo-fusing ring of the focusing analyzer crystals, and L is the length of one of the focusing analyzer crystals.

Abstract: In an X-ray analysis apparatus provided with a detector comprising photodiode-detection elements, it is possible to eliminate the dark current and the background current from the measurement signals due to the fact that elements in the signal reading device can be combined. Due to the fact that also during the measurement at a stationary peak beside the signal amplitude also signal ratios can be obtained from combinations of detector elements, the correct position and amplitude of the peaks to be measured can be determined. The detector can also be provided with mutually separated detector elements which have such a surface area and configuration that the dark surrent can already be compensated thereby.

Abstract: A wavelength dispersive X-ray spectrometer is provided with a polycrystalline analyzer for analyzing characteristic spectra of a sample. The polycrystalline analyzer provides a multiple spectrum of characteristic lines which are separated by appropriate pulse height analysis. Each of these sets of characteristic lines of the elements of the sample are provided at different dispersion and wavelength ranges.

Abstract: An improved X-ray monochromatizing subassembly, method and system are provided by a plurality of X-ray dispersive structures which are spaced and aligned to intercept X-rays and reflect monochromatized X-rays from the intercepted X-rays. The system includes a source of X-rays and an X-ray detector for detecting the monochromatized reflected X-rays. The monochromatized X-rays can be designed to be diverging, parallel or converging and can be designed for a particular wavelength of interest.

Abstract: Different reflection patterns of monochromatic x-rays are used to determine quality defining parameters of fiber reinforced compounds.

Abstract: A gas injection type plasma X-ray source has a gas plenum for storing a discharging gas at a pressure in the range of 150 Torr and 1000 Torr, the stored gas being injected between a pair of electrodes through a gas valve. The electrodes are opposed to each other in a vacuum vessel, so that a gas jet for the production of a plasma is formed. A voltage is applied between the electrodes, so that a discharge plasma is produced between said electrodes. A linear plasma with a high temperature and a high density is produced by the pinch of the plasma due to its own magnetic field produced by the current flowing through the plasma, so that X-rays are emitted from the linear plasma. The X-ray source has a high conversion efficiency and a high discharge timing margin, and accordingly the stability and reproducibility of discharges are improved and the X-ray output is increased.

Abstract: An external standard intensity ratio method is used for quantitatively determining mineralogic compositions of samples by x-ray diffraction. The method uses ratios of x-ray intensity peaks from a single run. Constants are previously determined for each mineral which is to be quantitatively measured. Ratios of the highest intensity peak of each mineral to be quantified in the sample and the highest intensity peak of a reference mineral contained in the sample are used to calculate sample composition.

Abstract: A sequential x-ray spectrometer has a curved analyzer crystal and a position-sensitive detector. In order to obtain a high quantum yield or efficiency, an extensive suppression of scattered background radiation, and an increase of the measuring speed, the position-sensitive detector is arranged in a mobile fashion.

Abstract: Point source X-ray focusing device structures, materials and methods of forming them are provided which exhibit a greatly increased total reflected intensity for a desired X-ray wavelength of interest. The devices include one or more focusing elements which each have a focusing surface with a plurality of layer pairs formed thereon. The focusing surface and the layer pairs are designed to collect, reflect and concentrate the maximum X-ray flux from a point source to a focus point for a particular wavelength of interest.

Abstract: A two crystal detection system is provided for the measurement of X-ray spectra in which two half crystals are arranged at a fixed angular difference and each crystal is read out by a separate gas detector. In such a structure, both short "d" and long "d" spacings may be simultaneously measured. This construction of the present invention yields two integrated scanning channels in which both wavelength spectra can simultaneously be achieved.

Abstract: Macroanalyzer system comprising in combination: a crystal for separating X-ray emitted from a sample, an X-ray detector for detecting X-ray which are separated by the crystal, and a solar slit member located between the crystal, sample and X-ray detector. An operation circuit receives the output of said X-ray detector to eliminate the effect of the X-ray passing through the solar slit.

Abstract: An apparatus for continuously measuring the elemental contents of a slurry ndependent of the slurry density and slurry composition, by utilizing X-ray fluorescence analysis. The apparatus includes a measuring chamber with a slurry flow channel and a first measuring window disposed on one side of the channel and a second measuring window disposed on the other side of the channel. A first source of primary radiation and a target are disposed behind the second measuring window. A detector is disposed behind the first measuring window. An annular source of primary radiation is provided around an open passage formed by a collimator between the detector and the first measuring window. The collimator collimates the primary radiation and the target radiation as well as the X-ray radiation excited by the first source and the annular source.

Abstract: A versatile focusing radiation analyzer for EXAFS, fluorescence EXAFS, Raman or modified Compton scattering, diffraction, Rayleigh scattering and other experiments is comprised of a concave focusing element (10) placed at the end of a central arm (11) pivoted at the center (24) of a circle (21). Side arms (12, 13) are also pivoted at the center (24). A platform (17) supports an X-ray source (50, 61, 66) or a sample (16) at the end of one side arm (12) while a platform (23) supports a detector (22, 63, 66), sample (51) and detector (52) or Mossbauer source (80). Constraining bars (14, 15) attached to the side arms and to a slide (29) in a slot (30) cause one side arm (13) to maintain an angle (.theta.) with the center arm equal to the angle of the other side arm (12) with the center arm as the center arm is driven relative to that side arm by suitable means (25-28).

Abstract: An X-ray fluorescence spectrometer comprising an X-ray source, a sample holder spaced from the X-ray source at a distance which ensures the illumination of the central portion of the sample not less than 0.3 ZU erg./s.cm.sup.2.w, where Z is the atomic weight of material of the X-ray anode and U is the voltage across the X-ray source, in kilovolts. The spectrometer further comprises a curved analyzing cristal for focusing the fluorescent radiation of the sample at an X-ray detector. The analyzing cristal and the detector are installed in an evacuated chamber. The X-ray source and the sample holder are positioned outside the evacuated chamber which has a window for passing X-ray radiation. The sample holder is positioned so that the average distance between the sample surface portion which produces radiation incident on the analyzing cristal and the window does not exceed the distance between said sample surface portion and the focus of the X-ray source.

Abstract: A method and apparatus for continuous measurement, by X-ray fluorescence lysis, of the elemental content of a slurry, independently of slurry density and slurry composition. The slurry, a source of primary radiation, a target, and a detector are arranged so that the slurry passes between the source and the detector, and a portion of the primary radiation excites the elements in the slurry to emit elemental X-ray radiation. The primary radiation also excites the target, to emit target radiation which passes through the slurry. The primary, target, and elemental radiations are absorbed by the detector, and the absorbed radiations are evaluated to determine the elemental content of the slurry.

Abstract: A method for continuously determining the water and fat content of a material such as butter which involves instantaneous measurements of the density of the substance, curd content, as well as either the dielectric constant or radiative backscatter intensity. Signals representing these nondestructive measurements are fed to a computer and compared with values of the same parameters which were previously measured by laboratory tests. The comparison permits a calculation of the composition of the substance, specifically fat and water content. In the case of a salted material, salt content can also be calculated.

Abstract: This invention relates to a novel method for both locating and evaluating subsurface uranium-bearing formations containing an apparent grade of up to approximately 5% of contained U.sub.3 O.sub.

Abstract: A method of measuring the content of a given element in a sample by means of X-ray radiation. The sample is first irradiated with primary radiation of a given wave length, to excite first composite fluorescent radiation from the sample whose content of said element is to be determined. Subsequent hereto the sample is then irradiated with primary radiation having a shorter wave length than the first mentioned radiation, to excite a second fluorescent radiation from said sample. The magnitude of the first fluorescent radiation is then subtracted from the magnitude of the second fluorescent radiation, whereat the difference therebetween constitutes the intensity of fluorescence radiation of the shortest wave length which can be excited by the primary radiation having the shorter wave length.