Abstract: Characteristics of moving webs are measured using a radiation source shutter which is rotatably movable between an opened-shutter position and a closed-shutter position and structured to permit access to the radiation source in the closed-shutter position. The source is configured to produce a fan-shaped radiation beam which passes through the web to a detector. The sizing of the fan-shaped beam and the detector together with the spacing the source and the detector are such that the beam width is substantially less than the detector while its length is greater than the detector. This novel beam shaping, detector arrangement provides composition insensitivity, increases solid beam angle and superior streak detection by aligning the beam length dimension with the direction of web movement.

Abstract: A low-cost detector of hydrogen-containing compounds in gas or thin-film samples is disclosed. The device preferably includes an alpha particle source, an energy degrading medium, a charged particle detector (e.g. a solid state diode detector), and amplification, threshold, counting, logic, timing circuits, humidity correction apparatus, and alarm/display. The invention relies upon the use of the energy degrading foil to pass selectively certain particles. Energetic alpha particles from a radioactive source enter the sample and hydrogen nuclei, or protons, elastically scattered by alpha particles, are able to penetrate the energy degrading foil which is thick enough to stop the alpha particles. The protons are detected and a suitable output signal can be produced to provide an accurate measure of the quantity of hydrogen in the gas or thin-film sample. The hydrogen detector can be combined with a smoke detector to produce an apparatus capable of detecting both smoke and hydrogen.

Abstract: A method and means is provided for characterizing interfacial electron states in solid heterostructures using a variable energy positron beam to probe the solid heterostructure. The method includes the steps of directing a positron beam having a selected energy level at a point on the solid heterostructure so that the positron beam penetrates into the solid heterostructure and causes positrons to collide with the electrons at an interface of the solid heterostructure. The number and energy of gamma rays emitted from the solid heterostructure as a result of the annihilation of positrons with electrons at the interface are detected. The data is quantified as a function of the Doppler broadening of the photopeak about the 511 keV line created by the annihilation of the positrons and electrons at the interface, preferably, as an S-parameter function; and a normalized S-parameter function of the data is obtained.

Abstract: An X-ray volume analysis method of crystalline defects of a part (11), comprises the steps of positioning the part in the plane situated at equal distance from the focus of an X-ray source and a focusing plane (14); illuminating the part from a punctual X-ray source (10) by a beam of a large spectral width .DELTA..lambda. and of determined angular opening .DELTA..theta., the opening .DELTA..theta. of the beam being fixed by .DELTA..theta..ltoreq..DELTA..lambda./2d.cos.theta., d being the interreticular distance for the considered reticular planes; orienting the part (11) to obtain the diffraction on a chosen family of reticular planes (30); and collecting and analyzing the X-ray beam near the focusing plane or beyond.

Abstract: There is provided radioactive particles having a ceramic matrix and an element which can be bombarded with neutrons to produce a gamma ray-emitting isotope. The particles are manufactured by mixing the ceramic components and the element, forming particles, sintering the particles, and the particles are subsequently made radioactive by bombardment with neutrons. Particles injected into wells or flow apparatus are traced by adding the radioactive particles and detecting the radioactive particles with gamma ray-sensitive instruments. Particles containing different elements are detected by spectral analysis of gamma rays.

Abstract: A distance between a radiation source and a detector is first set to a first distance and the number of pulses of a .gamma.-ray is detected. Then, the distance between the radiation source and the detector is set to a second distance different from the first distance and the number of .gamma.-ray pulses is detected. A density .rho. of a sample is finally calculated on the basis of a ratio of the two detection pulse numbers which were detected. The radiation source is set on the surface of the sample or in the sample. The sample detector is set on the sample surface. Fundamentally, one radiation source and two detectors are used. In the case of using one radiation source and one detector, either one of them is moved and the number of pulses is detected twice.

Abstract: A positron microscope utilizes a time-of-flight adjustment and a beam gate to distinguish images produced by respective types of positronium events. If the time-of-flight of secondary electrons is approximately between 30 and 40 ns, then the electron image will represent prompt annihilations and parapositronium distributions in the target. For time-of-flight between 50 and 100 ns longer than the processing time of the electronic gating circuitry, the electron image will be a map of long-lived orthopositronium events.

Abstract: Observing and detecting the spatial distribution of beta emissions by placing the specimen on a converter window, which converts the energetic beta particles to low energy, secondary electrons, which emerge from the opposite side of the window. The secondary electrons are then microscopically imaged by an emission microscope, preferably onto a position sensitive detector. The technique is able to achieve microscopic resolution with quantitative and rapid data acquisition. It is particularly suited to detecting the spatial distribution of specimens tagged with tritium. Preferably, the specimen is supported in proximity to the converter window (e.g.

Abstract: A Compton x-ray backscatter gage apparatus directing x-rays from an isotopic radiation source to a region of interest in a composite structure to monitor structural integrity. The backscattered x-rays from the region of interest are directed by guides in the gage housing to radiation detectors.

Abstract: Apparatus for continuously determining the basis weight of paper simultaneously at multiple points across the full width of a substrate. The apparatus includes a radioactive source which extends across one side of the web of paper. A detector array, on the opposite side of the substrate, detects the emission from the source. The array includes scintillating fibers and multi- or single-anode photomultipliers which may be connected by a scintillating or non-scintillating fiber optic elements to the photomultiplier.

Abstract: An apparatus for measuring the thickness of a coating on an elongate strip of material which moves along a predetermined path from a first location to a second location. The apparatus includes a measuring device, at least a portion thereof being mounted on a shuttle for movement parallel with the elongate strip. The shuttle is mounted on a support frame for movement back and forth along the frame. The shuttle is further provided with a target-spotting device. A drive extends between the shuttle and the support frame for reciprocating the shuttle along the frame.

Abstract: A dual sensor scanner includes an optical sensor and a nuclear sensor such as a beta gauge for sensing the basis weight or other parameters of paper as it is being produced by a paper making machine. The nuclear sensor signal is filtered to pass a low frequency portion and the optical sensor is filtered to pass a high frequency portion. The two filtered signals are combined to provide a substantially full frequency signal indicative of the basis weight of the paper. The sensor signals may be manually calibrated or, preferably, the nuclear sensor signal may be used to provide continuous on-line calibration of the optical sensor signal.

Abstract: A device for measuring the gap between the radiation source and the radiation sensor of a basis weight gauge. A caliper sensor measures the thickness of a sheet of material as it passes through the gap, while the caliper contact shoe rides on the sheet and urges it against a first side of the gap. A linear variable differential transformer measures the distance between a reference point on the contact shoe and the opposed side of the gap. The gap dimension is the sum of the sheet thickness, the distance between the caliper reference point and the second side of the gap, and a readily measurable constant.

Abstract: An improved basis weight measurement system which utilizes two means for irradiating a material to determine the distance from the radiating device to the material being surveilled and its mass per unit area. A portable, self-contained device applying this principle contains first and second radioactive emission means with corresponding detectors for each. A weaker emission is reflected back from the surface of the material to a detector, and a backscattered portion of a stronger emission is received by a detector after having penetrated the material. By virtue of there being two separately detectable emissions, the device can be used proximate the material being measured in order to perform the measurement without the need for direct contact between the device and the material. The measured basis weight is read directly from a digital Liquid Crystal Display, with the distance between the device and the surveilled material being indicated by Light Emitting Didoes.

Abstract: A positron microscope system utilizing image enhancement to overcome problems associated with low positron source flux can be operated in transmission and reflection modes. In the practice of the invention, slow positrons which are emitted after moderation of a positron source are focused, as a source beam, on a specimen target. In some embodiments, the source beam is swept over the specimen target, to effect scanning thereof. Image enhancement is effected by a channel electron multiplier array (CEMA) which may have a plurality of plates. The cloud of electrons which is generated by the CEMA in response to each incident positron is accelerated toward a long persistence phosphor screen. Image acquisition is achieved by a low light video system which delivers its signal to a memory which stores the data. The data is subsequently subjected to an image analysis algorithm which facilitates accumulation and signal averaging.

Abstract: A scanning spectral-analysis micro-probe subsystem, for a surface imaging system, utilizes a micro-probe to detect the precise position of a point on a sample object surface having surface dimensions changing responsive to surface absorption of incident radiation from a modulated radiation source. The modulated incident radiation causes the sample region dimensions, in the vicinity of the micro-probe, to be modulated, so that the micro-probe detects this dimensional modulation, with a detected modulation strength directly proportional to the incident radiation absorption.

Abstract: An apparatus and method for measuring the density of a low density medium ch as air by measuring the absorption of radioactivity decay particles such as alpha particles in the air. The apparatus includes a source of alpha particles from which the alpha particles are directed to the air sample to be measured. An alpha particle detector is spaced from the source by a path distance which traverses the air sample. The detector is located at an operating point which corresponds to the path distance where one half of the emitted alpha particles are detected. A control system employs a double sideband, suppressed carrier waveform generator which supplies a double sideband, suppressed carrier as a reference signal and supplies a double sideband, suppressed carrier waveform that is modulated by the detection signal.

Abstract: A method and apparatus for determining the enrichment of uranium dioxide powder is disclosed. A uranium dioxide powder is contained within a closed receptacle having a top, side and bottom wall surfaces. The receptacle is turned upside down so that the uranium dioxide powder is shifted within the receptacle to obtain a more uniform bulk density of the powder contained therein. The natural gamma radiation emission count of the powder is detected while the receptacle is upside down to determine the enrichment thereof.

Abstract: A device for counting particles of ionizing radiation comprises a detector and a reference source on the input side of the detector delivering reference radiation the spectrum of which is situated outside the spectrum of the ionizing radiation to be detected. The device further comprises an arrangement for discriminating the amplitude and energy of the received ionizing radiation and means for adjusting the relative positions of the amplitude levels on a scale of amplitude and the amplitudes of the pulses generated by the reference radiation. The device may be applied to monitoring the flowrate of leakage between primary and secondary circuits of a nuclear power plant steam generator.

Abstract: Measuring the distance to a surface of an object using ultrasonic energy pulses, an ultrasonic energy pulse is directed toward the object and the time is measured for the reflection to return so as to determine the distance to the object. A reference ultrasonic pulse is directed through a fixed and known distance to provide a reference measurement. To enhance the accuracy of the measurement, the air in the region traversed by the ultrasonic pulses is mixed by directing a swirling flow of air in this region so that the temperature of the air in the path of the reference measurement is more nearly representative of the temperature of the air where the distance measurement is taken.

Abstract: A procedure for measuring the formation of paper, wherein through a paper sample is passed radiation and the radiation that has passed through the paper is observed with a .beta. radiation detector for establishing a spectrum characterizing the formation of the sample, for radiation source being used a liner .beta. radiation source, and the .beta. radiation that has passed through the sample being observed in one dimension with a position-sensitive wire chamber detector operating in limited streamer mode.

Abstract: A pass-line independent measuring device for producing thickness related measurements (e.g., thickness, basis weight, density, etc.) of a moving web. The thickness measurements themselves are based on a nuclear source and detector mounted on one or both sides of the web, the source emitting radiation and the detector detecting emitted radiation from the web as an uncorrected measure of web thickness. An ultrasonic distance measuring means is fixedly associated with either the source, the detector, or both and continuously directs ultrasonic pulses in a direct path to the web, measures reflections in substantially a similar direct path, and by means of the time delay between a pulse and its reflection determines the actual pass-line of the web between the source and detector. The pass-line is used with a correcting function to correct the nuclear readings and provide a substantially accurate measure of web thickness corrected for pass-line.

Abstract: An apparatus for measuring the thickness of a coating on a work piece includes a table for receiving and positioning the coated work piece and beta-ray backscatter measuring instrument for determining the thickness of the coating on the work piece. An air gauge measures accurately the position of the surface of the work piece and causes the measuring detector instrument to be positioned a predetermined distance above the surface of the work piece. The air gauge includes an orifice having a known positional relationship with respect to the beta-ray measuring instrument. The air gauge positions the orifice a known distance above a particular location on the surface of the work piece. The apparatus then positions the beta-ray measuring instrument over that particular location on the work piece, at the predetermined distance above the surface.

Abstract: A detection system is disclosed for detecting the presence of a marking material placed on a textile substrate prior to a series of dyeing and finishing steps. Following such steps, the substrate carrying the marking material is illuminated by light having a preferred wavelength of about 900 nanometers. The light is preferably absorbed by the marking material, thereby reducing the amount of light reflected from the substrate carrying the marking material and triggering an alarm. In a preferred embodiment, the marking material contains carbon particles.

Abstract: Method and apparatus for measurement and control of an industrial process by detecting the average transmittance of a radiation beam which passes through the process material. A radiation source (28) having an intensity I.sub.o is positioned on one side of the material to be measured and a suitable radiation detector (32) is positioned on the other side. The transmitted radiation intensity, I, is measured by the sensor. An index Z commensurate with the degree of nonuniformity of the variable in the material is determined, and a process signal is generated from a quantitative relationship among I, I.sub.o, and the index Z. In a first embodiment implementedd in a system for measurement and control of the basis weight of paper in a paper production process, the index Z is indicative of the nonuniformity of the material mass distribution in the sheet and is determined by measurements with a separate formation gauge operating on-line with, but independently of, the basis weight sensor.

Abstract: The present invention relates to a method, or process, for deriving compositional information from a multi-layer composition which includes the steps of obtaining multi-layer fractional composition information using a non-contact gauge such as an FTIR gauge; obtaining additional multi-layer composition information using a beta gauge; and, correcting for beta ray absorption differences among the layers of the multi-layer composition by combining the multi-layer fractional composition information with the additional multi-layer composition information obtained using the beta gauge.

Abstract: An improved beta activity counter is disclosed which provides for counting plural, preferably even numbers of, samples simultaneously, while allowing automated handling of sample vial racks which are different widths are multiples of the number of simultaneous testing cells. The number of indexing steps needed per rack are adjusted automatically according to the number of vials that each rack will hold. Quench counting of adjacent samples simultaneously via use of one external source is also provided.

Abstract: A system for determining the basis weight of cord reinforced tire fabric which involves the use of two radiation source, for example a collimated x-ray beam, and a beta ray source. One of the radiation sources and its corresponding sensor (e.g., the x-ray source) is used to determine the fractional area of the fabric not containing steel cords, while the other (e.g., the beta ray source) is used to measure the average attenuation of radiation passing through the fabric. Both sources and their corresponding sensors are movably mounted on a pair of beams which extend across the width of the fabric web. The source sensor assemblies continuously scan across the fabric width so that information from the entire fabric area is obtained.

Abstract: A method is shown for measuring naturally occurring pores in a specimen material. A positron is emitted from a radioactive source and enters a material to pick up an electron to form positronium. The positronium decays very rapidly into two gamma rays. The lifetime of the positronium depends on the size of the pore it is trapped within. The larger the pore, the longer the positronium will last. By measuring the decay rate of positrons over an extended time scale in the range from 30 to 500 nsec., a near relation can be developed between positronium lifetime and pore diameter.

Abstract: To produce an image of a component of part of an engineering structure such as an aero-engine using a positron emission tomography (PET) technique it is proposed to provide the component or part of the structure of interest with a surface coating containing a radioisotope labelling material. The radioisotope label may be provided by applying a film of lacquer, paint or the like containing the isotope, or the component etc. may be bombarded by suitably energetic ions in order to induce a reaction in which a selected isotope is produced.

Abstract: A positron microscope system utilizing image enhancement to overcome problems associated with low positron source flux can be operated in transmission and reflection modes. In the practice of the invention, slow positrons which are emitted after moderation of a positron source are focused, as a source beam, on a specimen target. In some embodiments, the source beam is swept over the specimen target, to effect scanning thereof. Image enchancement is effected by a channel electron multiplier array (CEMA) which may have a plurality of plates. The cloud of electrons which is generated by a CEMA in response to each incident positron is accelerated toward a long persistence phosphor screen. Image acquisition is achieved by a low light video system which delivers its signal to a memory which stores the data. The data is subsequently subjected to an image analysis algorithm which facilitates accumulation and signal averaging.

Abstract: The present invention relates to a process for the detection of superimposed sheets, the apparatus making it possible to perform this process and the application thereof to bank notes. The process for detecting superimposed sheets by evaluating their surface mass is characterized in that it comprises the stages of passing the sheets oriented in the direction of their width between a beta particle source and a Geiger-Muller counter, counting the number of particles received by the counter by measuring the frequency F.sub.g of the pulses from the Geiger counter to determine the surface mass and eliminating the notes having a high superimposition level by comparison with a limit value.

Abstract: A device to measure the extremely fast electrical waveform generated when atomic or subatomic particles of an identical type strike an electronic circuit or device. The device comprises a trigger element which signals the incidence of a particle on the electronic device and a picosecond sampler which receives the trigger signal and the waveform generated by the electronic device. The sampler obtains a measurement of a discrete point on the generated waveform each time a particle passes through the trigger element to the electronic device. The sampling point on the waveform can be moved by various techniques so that the entire waveform may be measured by the sampler.

Abstract: An apparatus and method for measuring the thickness of thin basal coatings on work pieces. The apparatus comprises a beta backscatter type measuring instrument including a work piece positioning system to permit the precise positioning of a coated work piece surface to radiation in a repeatable, non-destructive, non-contacting position with respect to the radiation source.

Abstract: A tank content gauging system including a plurality of radiation sources and a radiation detector mounted at a fuel tank, with the radiation detector positioned for receiving radiation from the sources and for producing an output which is an electrical analog of the detected radiation, a register for storing the detector output, a telemetry-on-demand switching unit for starting and stopping the detector operation from a point distant from the tank, a transceiver for sending "on" and "off" commands to the switching unit and receiving telemetry data from the register, a computer having the telemetry data and reference data as inputs for producing an output representing the quantity of fuel in the tank, and a display for indicating the quantity of fuel in the tank.

Abstract: The present invention provides an apparatus for detecting the depth position of the source rod of a portable nuclear measuring gauge having a housing with the elongate source rod extending vertically therethrough and mounted for vertical sliding movement to various depth positions. The apparatus comprises an elongate variable resistance element extending axially parallel to said source rod, means for slideably engaging the elongate variable resistance element as the source rod is moved to various depth positions so as to vary the resistance of said variable resistance element, and means electrically connected to said variable resistance element for sensing the changes in resistance thereof and converting such changes into an indication of the depth position of the source rod.

Abstract: A representation of oil flow in a gas turbine engine is obtained by injecting a compatible radioactive isotope label into the engine oil flow and detecting the radiation emitted from within the body with detectors mounted outside the body to produce signals representative of the quantity and direction of the radiation; the detector output signals are compensated for attenuation on passing through the engine in accordance with attenuation signals derived from a representation of the spatial distribution of the engine and of its materials, and signals from non-viable directions are discounted. The compensated detector output signals are used to generate a number of focal-plane tomograms from which an image in a desired plane may be re-constructed. The image may be formed on a background of the engine in the relevant plane generated from the representation thereof.

Abstract: A system for indicating cracks in a hollow aircraft blade, such as a helicopter blade. A system wherein a pressure differential is maintained within the blade with respect to the ambient atmosphere and including a pressure sensor for mounting on the blade in communication with the interior of the blade and having a member which moves in response to pressure changes within the blade, a beta radiation source mounted on the member and disposed for radiation transmission to a detector, a beta radiation detector for mounting on a nonrotating portion of the aircraft for receiving radiation from the source, and circuitry having the output of the detector as an input and providing an output which varies as a function of the position of the pressure sensor member for indicating the pressure condition within the blade. An improved beta radiation detector housing which substantially eliminates detector sensitivity to radar transmissions while maintaining sensitivity to nuclear radiation in the beta range.

Abstract: A device is described for the separation of airborne particles, such as particles of an aerosol, into grain size classes.

Abstract: A device of improved type for the separation of airborne particles by grain size is described.The principle characteristic of the present invention lies in the fact that it comprises: a first base body in which is formed a first cavity on the edge of which rests a plate on which is deposited a filter; two second bodies, one inside the other, in such a way as to define between them an annular channel in which is ducted filtered air and communicating with the said first cavity through a second cylindrical cavity defined by the lower surface of a base wall of the said inner second body and the upper surface of the said filter; and an annular nozzle located in the said channel and operable to eject into it a quantity of particle-bearing air in such a way that the particles of dust present in this are deposited on the said filter.

Abstract: A beta-attenuation densitometer is disclosed. The densitometer includes a source of beta radiation and a beta detector arranged to receive radiation from the source. The detector includes a scintillator that is caused to fluoresce by the radiation and a photomultiplier tube that detects the light emitted by the scintillator. The scintillator and photomultiplier are contained within a light-tight housing. Shock absorbing potting material protects the tube against damage.

Abstract: An apparatus for measuring the thickness of a coating on a continuously moving strip of material. The apparatus includes a frame (10), a shuttle (24) mounted on the frame for reciprocal movement thereon, an engaging pin (174) carried by the shuttle and capable of engaging the moving strip to cause the shuttle to be moved by the strip, a drive (120, 122, 118, 126, 116, 114, and 112) capable of moving the shuttle in a direction reverse to the movement of the strip, and measuring means, at least a portion of which is mounted on the shuttle. The apparatus further includes a support (172) mounted on the shuttle and capable of supporting the strip when the engaging pin is engaging the moving strip, and structure capable of adjusting the support (172) towards and away from the portion of the measuring means mounted on the shuttle to establish a predetermined spaced apart measuring distance.

Abstract: The present invention provides a nuclear radiation backscatter gauge which is capable of directly measuring the density of a thin top layer of material from a composite material comprised of the relatively thin top layer of material applied over an underlying base material. The gauge includes a nuclear radiation source and two radiation detector means so positioned with respect to the source as to form two geometrically differing source-to-detector relationships. A signal processing circuit responds to detected radiation from the two detector means to generate respective signals D.sub.G1 and D.sub.G2 representative of the components densities of the top and base layers as measured by the detector means. The density D.sub.T of the thin top layer is then determined by a signal processing means from the relationship ##EQU1## wherein k.sub.1 and k.sub.2 are empirically derived instrument constants.

Abstract: A device for the measurement of the amounts of components of loose mixtures comprises a beta radiation source, a backscattering detector, a casing integral with a tribranched hollow chamber, divided at its branching point by a beta radiation-permeable membrane, to form a top branch to contain the sample mixture, and bottom branches leading to the detector inlet and source, respectively, and a lid to close the top branch. The lid is linked to the source to place it in an "on" position on closure. The detector feeds via a comparator, an anticoincidence circuit, whose second input is connected to a tuned generator and whose output feeds a reversible counter via a double frequency divider. Instead a frequency divider may follow the comparator. This may be adjustable with a second frequency divider preceding the second input of the anticoincidence circuit.

Abstract: A beta radiation sensor and an X-ray radiation sensor are used to monitor the specific weights of both components of a two-component web, in particular, a web of magnetic recording material, by using the beta radiation sensor to measure the combined specific weight of the material. The measurement by the X-ray sensor permits such combined specific weight to be apportioned between the two components of the web. Cross talk between the two sensors arising from bremstrahlung produced by the beta radiation sensor is suppressed by softening the beta radiation beam with films of polyester, by shielding the housing in which the detectors of the two sensors are disposed with a sheet of phenolic, and by stopping down the aperture through the sheet of phenolic through which X-ray radiation enters the detector housing.

Abstract: An apparatus and method for measuring the amount of papermaking stock on a moving fabric in a fourdrinier papermaking machine, including a backscattering mass sensing device and a hydrofoil blade adapted to scrape water from the underside of the fabric and to support the mass sensing device in close proximity to the papermaking belt.

Abstract: Apparatus for measuring the bulk density and mass flow rate of pulverized coal entrained in air along a duct 6 comprises beta radiation source means 7, radiation detection means 8 and a shield 9 to intercept direct radiation falling on the detector means which thereby measures the diffuse radiation scattered by the coal particles. That measurement plus a signal indicating linear coal particle speed is fed to a data processor which calculates the bulk density and mass flow rate.

Abstract: An aperture device for measuring thin films has an aperture ring, of a material and thickness that is impenetrable by the radiation from radionuclides. The ring has a passage for emitted and reflected radiation extending approximately perpendicular to said ring, and a radiation device consisting of at least one collimating radiation source holder comprising a tube of a predetermined diameter that is permeable to radiation in the forward direction and has sides and a back that are impermeable to radiation and houses a radionuclide. The forward end surface of the tube lies behind the forward end surface of the passage. The cross-section of the passage is large compared to the cross-section of the radionuclide. A partition divides the passage into at least two chambers that are open at their rearward and forward ends. The partition has partition walls that are impermeable to radiation.

Abstract: A shielding arrangement for a coating thickness device utilizing the radiation backscatter technique. An isotope housing is provided having an aperture through which radiation can pass. A removable cover shield is attached to the housing to cover the aperture when the device is not in use. Means are provided to remotely remove the cover shield from the housing and expose the aperture. A secondary shield carried by the device is provided to swing into and out of covering relationship to the aperture to block radiation passage through the aperture between measurements. The secondary shield is operatively connected with the operating handle of the device to coordinate movement of the secondary shield with the position of the isotope housing. A tertiary shield, which can be of transparent plastic material, is provided between the measuring zone of the device and the operator to provide additional shielding during the times the secondary shield is not in covering relationship with the aperture.

Abstract: An apparatus for irradiating a continuously flowing stream of fluid is diosed. The apparatus consists of a housing having a spherical cavity and a spherical moderator containing a radiation source positioned within the spherical cavity. The spherical moderator is of lesser diameter than the spherical cavity so as to define a spherical annular volume around the moderator. The housing includes fluid intake and output conduits which open onto the spherical cavity at diametrically opposite positions. Fluid flows through the cavity around the spherical moderator and is uniformly irradiated due to the 4.pi. radiation geometry. The irradiation source, for example a .sup.252 CF neutron source, is removable from the spherical moderator through a radial bore which extends outwardly to an opening on the outside of the housing. The radiation source may be routinely removed without interrupting the flow of fluid or breaching the containment of the fluid.