US3053388A

US3053388A - Radiological sorting apparatus

Info

Publication number: US3053388A
Application number: US584375A
Authority: US
Inventors: Charles W Tittle
Original assignee: Gulf Research and Development Co
Current assignee: Gulf Research and Development Co
Priority date: 1956-05-11
Filing date: 1956-05-11
Publication date: 1962-09-11
Anticipated expiration: 1979-09-11

Description

Sept. ll, 1962 c. w. TITTLE: 3,053,388

RADIOLOGICAL soRTrNG APPARATUS Filed May 1l, 1956 1N VEN TOR. czar/ef /1/ zf/f/e.

United States Patent Oflice 3,@538 Patented Sept. 11, 1962 3,053,338 RADIOLGGICAL SORTENG APPARATUS Chartes W. Tittle, Newton, Mass., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed May 11, 1956, Ser. No. 534,375 2 Claims. (Cl. Z119-111.5)

This invention relates to a radiological apparatus, and more particularly pertains to examining radiologically a stream of material with respect to the concentration of one or more selected types of atomic nuclei contained therein and treating the stream of material according to a mode having such concentration as a parameter.

The invention is predicated upon the fact that many types of atomic nuclei have a substantial cross section, say in excess of one barn for the capture of slow neutrons to produce neutron-capture gamma rays, the energy spectrum of which is characteristic of the type of atomic nuclei interacting with the slow neutrons to produce the neutroncapture gamma rays. The cross section for such reactions as well as the distinctiveness of the gamma-ray energy spectrum produced by such reactions varies among the different types of atomic nuclei.

Though the principles of this invention are, in theory at least, applicable to some extent with respect to any type of atomic nuclei that undergoes neutron-capture gamma-ray radiative capture reactions; in general, the best results are obtained with respect to types of atomic nuclei having substantial neutron-capture cross sections and which are productive of gamma rays having relatively greater energies, particularly those types of atomic nuclei productive of neutron-capture gamma rays having energies of more than about 3 to 4 mev. For the most part, of all the common elements, the ones having a substantial cross section for slow neutrons to produce neutron-capture gamma rays of more than about 3 to 4 mev. include most of the metals, chlorine and sulfur. It is, of course, immaterial whether such elements are in their elemental or chemically combined states.

The principles of the invention have a broad area of application wherein a stream of material, either of fluid or solid character, is to be subjected to a mode of treatment dependent in some manner upon the concentration of a class of atomic nuclei contained in the stream of material where such class of atomic nuclei has a substantial cross section for the capture of slow neutrons to produce neutron-capture gamma rays. The term treatment is used in a broad sense, and is meant to include any manner or mode of processing or handling, physically or chemically, a stream of material prescribed as a function of the concentration of the defined class of atomic nuclei. For example, the term treatment is meant to include such modes of processing or handling a stream of material as introducing a substance into the stream of material at a rate dependent upon the concentration of the defined class or" atomic nuclei, causing the stream of material to flow at a rate dependent upon the concentration of the defined class of atomic nuclei, heating the stream of material to a temperature dependent upon the concentration of the defined class of atomic nuclei, segregating portions of the stream of material according to varations in the concentration of the defined class of atomic nuclei, etc.

Broadly, this invention comprises apparatus for passing a stream of material containing the defined class of atomic nuclei through a zone wherein there is a flux of slow neutrons, effecting an electrical potential or an electrical current having a magnitude substantially dependent upon the rate at which gamma rays are produced in the Zone having energies equal to at least one selected energy level component of the slow neutron-capture, gamma-ray energy spectrum of the class of atomic nuclei. Such electrical potential or current can be referred to ias an electrical signal. The magnitude of the electrical signal which is a measure of the concentration of the defined class of atomic nuclei, is then applied to control the treatment of the stream of material according to the prescribed mode.

For example, the electrical signal can be applied to maintain the concentration of the defined class of atomic nuclei identified with the magnitude of the electrical signal at a constant concentration with a prescribed accuracy. Similarly, where the magnitude of the electrical signal is substantially a function of the concentration of a particular ingredient in the stream of material, such electrical signal can be utilized to control the rate of introduction of such ingredient or another into the stream of material. Another application of the electrical signal to control a treatment of a stream of material entails diverting portions of a stream of material for either recycling or differing subsequent treatment whenever the electrical signal exzeeds or falls below, as the case may be, a predetermined va ue.

The invention will be better understood upon reference to the three embodiments of the invention shown in FIG- URES 1, 2, and 3, wherein:

FIGURE l is a schematic illustration of apparatus for adding sufficient chlorine-containing substance to a stream of material to produce a constant total chlorine content therein;

FIGURE 2 is a schematic illustration of apparatus for diverting such portions of a stream of material from its 'normal course wherein the sulfur content thereof exceeds a predetermined maximum; and

FIGURE 3 is a schematic illustration of apparatus for diverting from its normal course such portions of a stream of metalliferous ore in which the general state of mineralization or metallic element content thereof falls below a predetermined minimum.

Referring to FIGURE 1, there is shown apparatus for proportioning streams of water relatively rich and lean as to total chlorine content so as to produce an aqueous stream having a substantially relatively constant total chlorine concentration. The apparatus comprises an electrically controlled proportioning valve Miof conventional design, such valve 10 being supplied with Water containing little or no chlorine by a conduit 12, and with an aqueous, chlorine containing solution by a conduit 14. The valve 10 is a conventional type such that when the voltage supplied thereto exceeds a predetermined value, the valve 10 progressively closes conduit 14 while opening conduit 12 until such time as the voltage supplied thereto falls below such predetermined value. On the other hand, whenever the voltage supplied to the valve 10 falls below a still lower predetermined value, the valve 1t)` progressively opens the conduit 14 while progressively closing the conduit 12 until such time as the voltage supplied thereto exceeds said lower predetermined value.

Liquids passing through the valve 1t) are discharged into a conduit 16, which communicates with a rhousing 18, the latter being provided with an outlet conduit 20. Disposed centrally within the housing 13 is a conventional neutron source (radium and beryllium, polonium and beryllium, or the target of anion accelerator) 22 surrounded by a combined neutron moderator (such as parafn) and gammaray shield (such as lead) 24. The numeral 26 designates a conventional scintillation phosphor and photomultiplier tube combination for detecting gamma rays, the same being disposed to extend into the housing 18 so that the scintillation phosphor thereof can be in close proximity to the contents of the housing 18.

The electrical output of the photomultiplier tube and phosphor combination 26 is conducted to a conventional amplifier 28 by leads 30 and B2, with the output of the amplifier 28 being fed to a conventional pulse-height analyzer 34 by leads 36 and 3S. Inasmuch as it is desired for the particular purpose'at hand that the output of the pulse-height analyzer 34 be substantially solely a function of the concentration of chlorine within the housing 18, the pulse-height analyzer 34 is adjusted to pass such pulses as represent detected gamma rays having energies lying within the ranges of 6.0 to 6.7 meV., and from 7.3 to 7.9 mev., since neutron-capture gamma rays of such energies are characteristic of chlorine, as will be readily understood by those skilled in the art. The optimum energy range or ranges to use in a particular instance will depend on the type and concentration of nuclei producing interfering gamma rays. The output of the pulse-height analyzer 34 is fed to a counting-rate meter 40 of conventional construction by leads 42. and 44, such counting-rate meter preferably being of the type that produces a direct output current or potential proportional to the rate at which pulses are received thereby from the pulse-height `analyzer 34. Alternatively, the output -of the counting-rate meter 40' can be linear (not proportional) to the rate at which pulses lare received thereby from theV pulse-height analyzer 34.

The-direct output current or potential of the countingrate meter 40, which for the purpose of the claims can be called an electrical control signal, is fed to an ampliiier 46 by leads 48 `and 50, with the output of the amplifier 46 being fed to the previously described electrically controlled proportioning valve l@ by

leads

52 and 54.

A conventional recorder 56 is connected in parallel with the valve l by leads 58 Iand 60, the recorder 56 being of. the conventional type that records a direct current or potential versus time.

Means, not-shown, are of course provided in the conventional manner for energizing the above-described electrical components.

The operation of the above-described apparatus will be readily understood. The liquid content of the housing 18 is subjected to a flux of slow neutrons emanating from thel neutron source 22 and the moderator and shield 2.4.

Slow neutrons in the liquid within the housing 18 react mainly with the nuclei of the isotope chlorine having a mass number of 35 to produce neutron-capture gamma rays, the most characteristic of which have energies lying within the ranges of 6.0 to 6.7 mev., and from 7.3 to 7.9 mev. A certain proportion of such neutron-capture gamma rays, determined by the geometry of the system and the performance characteristics of the components employed, are detected by the scintillation phosphor and photomultiplier tube combination 26 to produce electrieal pulses having heights that are a function of the energies of the detected gamma rays.

, Such pulses are amplified by the amplifier 28 with the pulse-height analyzer 134 being adjusted as previously mentioned to pass such pulses having heights as are produced as a result of the detection of gamma rays having energies lying Within the previously defined energy ranges. The pulses passing through the pulse-height analyzer 34 are fed to the counting-rate meter 4t), which lin turn produces a direct current electrical potential proportional to the rate at which pulses are received thereby from the pulse-height analyzer 34. Such direct current potential or electrical signal .is in turn amplified by the amplifier 46.

From the foregoing, it will be apparent that the output potential of the amplifier 46 is a function of the concentration of total chlorine within the housing .18, as the isotope of chlorine having a mass number of 35 constitutes an essentially fixed percentage (75.4 percent) of naturally occurring chlorine. Accordingly, the recorder 56 in making a record of the output potential of the amplifier 46 versus time makes a record interpretable as a record of how the concentration of total chlorine within the housing 18 varies with time. Also, as the valve 10 operates progressively to relatively close conduit l2 and open conduit 14 Whenever the control potential fed thereto from the amplifier 46 exceeds a predetermined value, and vice versa whenever the control potential drops to less than a lower predetermined value, it will be evident that the valve lil will operate in such a manner that the total chlorine concentration Within the housing `18 is maintained essentially within the limits identifiable with the aforementioned predetermined potential values.

Under some circumstances, a judicious selection as to the neutron-capture gamma-ray energies to be utilized as a criterion of the chlorine concentration and appropriate adjustment of the pulse-height analyzer may be required. For example, such circumstances may arise where there is a possibility that the liquid entering the chamber 18 may contain a significant concentration of atomic nuclei productive of a neutron-capture gammaray energy spectrum that to a significant extent is coincident with a part of the neutron-capture gamma-ray energy spectrum of the isotope chlorine having a mass number of 35. In such a case, a judicious selection of the gamma-ray energy or energies to be used as a criterion of the concentration of chlorine will be' made such that the gamma-ray energies selected constitute a significant part of the neutron-capture gamma-ray energy spectrum of chlorine but not a significant part of the neutron-capture gamma-ray spectrum of the otherwise interfering atomic nuclei. Ordinarily, as will be understood by those skilled in the art, such a suitable selection will be possible in the practice of the invention.

The apparatus shown in FIGURE 2 is` for the purpose of segregating portions of a iiuid stream of material according to whether the concentration of a particular type of atomic nuclei therein exceeds or falls below a predetermined concentration, such as segregating portions of a liquid as to the sulfur content thereof.

A liquid hydrocarbon stream of material subject to possible variations in sulfur content is introduced into a housing 62 by means of a conduit 64. The housing 62 discharges by means of a conduit 66 to an electrically controlled two-position valve 68 which when energized Iselectively communicates the conduit 66 with a conduit 70, and which when de-energized selectively communicates the conduit 66 with a conduit 72.

Means is provided to energize the yvalve 68 whenever the total sulfur content of the liquid in the housing 62 exceeds a predetermined amount and to de-energize the valve 63` whenever the total sulfur content of the liquid within the housing is below a predetermined amount.

Such means comprises a conventional neutron source 74 surrounded by a combined neutron moderator and `gamma-ray shield 76 disposed within the housing 62. A photomultiplier tube and scintillation phosphor combination '78 is arranged to detect neutron-capture gamma rays produced within the liquid in the housing 62. As in the case of the previously described embodiment of the invention, the output of the photomultiplier tube and scintillation phosphor combination 78 is fed to an amplifier 80, the output of which is in turn fed to a pulseheight analyzer 82.

The pulse-height analyzer 82 is of conventional character and is adjusted, as will be understood by those skilled in the art, to pass solely pulses having heights corresponding t'o detected gamma rays having energies lying withinr the range of 4.7 to 5.5 mev., such gammaray energies being characteristic of neutron-capture gamma rays produced by the isotope sulfur having a mass number of 32. 'Ihe pulses passed by the pulse-height analyzerZ are -fed to a coun-ting-rate meter 84 of the same nature as the previously described counting-rate meter 40j. The output of the counting-rate meter 84 is fed to an amplifier 86, with the output of the amplifier 86 being connected to a solenoid 88 of a relay that includes a normally open switch 90. The output of the amplifier 86 is also connected to a recorder 92 that is similar to the previously described recorder 56; the recorder 92 and the solenoid 88 being connected in parallel as shown.

The switch 90 is connected by means of leads 94 and 96 to a battery 98 and the electrically controlled valve 68 for energizing the latter lwhenever the switch 90 is closed. It will be understood that a predetermined electrical current through the solenoid 88 is required in order to actuate the switch 90 to its closed position, the switch 90 being open whenever the electrical current through the solenoid 88 is less than such predetermined current and closed whenever the current exceeds such predetermined amount of current. A variable resistor 100 is in series with the solenoid 88. The arrangement is such that the switch 90 will close whenever the direct potential output of the amplifier 86 exceeds a potential fixed by the adjustment of the variable resistor 100. A conventional time-delay mechanism, not shown, can be connected to the switch 90 as is conventional in relays to delay the opening and closing thereof in relation to the time required for liquid to pass from the housing 62 to the Valve 68.

The operation of this embodiment of the invention will be quickly appreciated. A liquid hydrocarbon stream entering the housing 62 is subjected to a slow neutron flux within the housing 62 by the neutron source 74, and the moderator and shield 76. Slow neutrons react principally with the isotope sulfur having a mass number of 32 contained in the liquid hydrocarbon to produce neutron-capture gamma rays having energies characteristic of sulfur. Such gamma rays are detected by the scintillation phosphor and photomultiplier tube combination 78 which produces electrical pulses whose heights depend upon the energies of the detected gamma rays. Such pulses are amplified by the amplifier 80 and passed to the counting-rate meter 84 through the pulse-height analyzer 82. It will be appreciated that the pulse-height analyzer 82 is so adjusted as to pass solely electrical pulses having heights attributable to gamma rays of one or more portions of the neutron-capture, gamma-ray energy spectrum of sulfur, such as previously specified. Also, the pulse-height analyzer 82 is adjusted so as to discriminate against pulse heights attributable to gamma rays, originating from other causes, as will be appreciated.

The counting-rate meter 84 produces an electrical signal proportional to the rate at which pulses are fed thereto from the pulse-height analyzer 82. The electrical signal produced by the counting-rate meter S4 is amplified by the amplifier 86, and a record of such amplified signal versus time is made by the recorder 92. The amplified signal is applied to the solenoid 88 through the variable resistor 100, so that sufficient current ows through the solenoid 88 to close the switch 90 solely whenever the amplified signal exceeds a value predetermined by the adjustment of the variable resistor 100.

Accordingly, the electrically controlled valve 68 is energized solely whenever the total sulfur content or the liquid hydrocarbon stream passing through the housing 62 exceeds a predetermined concentration. Such energization of the valve 68 diverts the liquid hydrocarbon stream from its normal outlet course through the conduit '72 to a course through the outlet conduit 70. The utility of this embodiment of the invention will be evident upon assuming that the same is to be employed in conjunction with equipment for reducing the sulfur content of liquid hydrocarbons and receives liquid hydrocarbons therefrom through the conduit 64. The liquid hydrocarbons which are found to still contain an undesirably high concentration of sulfur can be recycled to the desulfurizing equipment by the conduit 70.

Though the embodiment of FIGURE 2 has been described in connection with the sulfur content of a liquid hydrocarbon stream, it will be evident that this embodiment of the invention, as well as that shown in FIG- URE l, is applicable to the concentration of any element in the stream of material that produces a neutron-capture gamma-ray energy spectrum that is at least in part uniquely characteristic of such element as compared to other elements present in the stream of material. This is true whether the element is present in either its elemental state or is chemically combined, and it is immaterial as to how the element or its compounds are incorporated in the stream of material.

It should be noted that the character of the stream of material can in some cases ohviate or reduce the necessity for a neutron moderator, as where the stream is hydrogenous, and where fast neutrons cannot result in producing an excessive intensity of interfering gamma rays.

FIGURE 3 illustrates apparatus for removing such portions from la traveling bed of metalliferous ore wherein the metallic element content thereof falls below a predetermined minimum. The apparatus comprises a conveyor belt 102 supported by rollers 104 arranged to support a substantially uniformly distributed bed of ore 106 in the direction indicated by the arrow 108.

Disposed below the conveyor belt 102 in reasonably close proximity thereto is a neutron source 110 surrounded by a neutron moderator and gamma-ray shield 112. Situated directly above the neutron source 110 and above the bed of ore 102 is a combined scintillation phosphor and photomultiplier tube 114 that is similar to the combinations 26 and 78 of the previously described embodiments of the invention. The arrangement is such that slow neutrons pass outwardly from the neutron source 110 and the gamma-ray shield and neutron moderator 112 into the traveling bed of ore 106, with the combined scintillation phosphor and photomultiplier tube 114 being arranged to detect neutron-capture gamma rays produced within the ore 106.

The output pulses of the combined scintillation phosphor and photomultiplier tube 114 are fed to a pulseheight analyzer 116 after being amplified by an amplifier 118. The pulse-height analyzer 116 is arranged to pass such pulses having heights resulting from detected gamma rays having energies substantially uniquely characteristic of the metallic element (or elements) constituent of the ore material 106. The pulses passed by the pulse-height analyzer 116 are fed to a counting-rate meter 120 which produces a direct current or potential (signal) proportional to the rate at which pulses are received thereby from pulse-height analyzer 116. The signal of the countingrate meter 120 is amplified by `an amplifier 122 with the amplified signal of the amplifier 122 being fed to a solenoid 124 through a variable resistor 126. The output signal of the amplifier 122 is also fed to a recorder 128 of the type that produces a record of such signal versus time.

The solenoid 124 is arranged to close a normally open Aswitch solely whenever the current through the solenoid 124 exceeds' a predetermined amount. The solenoid-controlled or relay switch 130 is in Series with a battery 132 and a solenoid 134. fl'he solenoid 134 is operatively associated with an armature 136 that has a diverting blade 138 attached thereto.

The diverting blade 138 is angularly inclined to the path of travel of the ore material 106, say at 45, so that whenever the armature 136 and the blade 138 are lowered until the latter contacts the upper surface of the conveyor belt 102, the ore 106 immediately upstream of the blade 138 is caused to be diverted laterally from the conveyor belt 102. The arrangement is `such as to leave portions of the conveyor belt 102 that have traveled in contact with the blade 138 bare of ore material as indicated at 140. The armature 136 and the blade 138 are normally in the position Where the blade 138 engages the upper surface of the conveyor belt 102, the armature 136 and the blade 138 being raised to the positions shown thereof in ythe drawing where the blade 138 is above the traveling bed of ore 106 solely whenever the solenoid 134 is? energized by the closure of the relay switch 130. Conventional tirne-delay means, not shown, to delay the opening and closing of the relay switch 130 can be employed. The delay interval would be substantially the time required for the belt 102 -to travel from the combined photomultiplier tube and phosphor 114 to the blade 133.

The operation of the apparatus illustrated in FIG- URE 3 wil be readily appreciated. Slow neutrons enter the portion of ore material 106 immediately above the neutron source 110 and the ygamma-ray shield and neutron moderator 112. The slow neutrons react with the element to which the apparatus is arranged to be sensitive to produce neutron-capture gamma rays that are in turn detected by the combined photomultiplier tube and scintillation phosphor 114 which produces electrical pulses having heights dependent upon the energies of the gamma rays detected. As -mentioned previously, the amplied pulses produced by the `combined photomultiplier tube and scintillation phosphor 114 having heights uniquely characteristic of the element with respect to which the apparatus is arranged to be sensitive are passed by the pulseheight analyzer 116 to the substantial exclusion of pulses having other heights, as in the case of the previously mentioned embodiments of the invention. The rate at which -pulses are passed by the pulse-height `analyzer 116 is translated -into a direct current or potential proportional to such pulse rate by the counting-rate meter 120, the output of the counting-rate meter 120 being amplified by the amplifier 122. The recorder 128 connected to the output of the amplifier 122 produces a record of such output versus time, which for practical purposes amounts to a record with respect to time of the concentration of the `element in the ore material 106 to which the apparatus has been adjusted to be`sensitive.

The variable resistor 126 is adjusted so that just suiiicient current flows in the solenoid 124 to close the switch 130 whenever the output of the ampliiier 122 is of a predetermined value. With this arrangement, the blade 138 will be raised to the illustrated position thereof whenever the concentration in the ore material 106 of the element to which the apparatus is made sensitive exceeds a predetermined amount, and the blade 138 is lowered to its normal diverting position whenever `the concentration of such element falls below such predetermined amount.

The metallic element constituents of many types of ores produce neutron-capture gamma-ray energy spectra suitable for separating relatively lean and relatively rich portions of ore according to the disclosed principles of the invention. For example, the ore can be a common ore of nickel, such as nicolite, in which event the pulse-height analyzer can be adjusted to pass :only pulses having heights resulting from the detection of gamma rays having energies of from about 8.4 to 9.1 mev. Another example Would be a common ore of iron, such as siderite, in which event the pulse-height analyzer 116 can be adjusted to pass only pulses having heights corresponding to `detected gamma rays having energies of yfrom 7 .15 to 7.7

mev.

Alternatively, since a large number of the common metallic elements produce neutron-capture Igamma-ray energy spectra having signiiicant portions thereof above about 3 to 4 mev., the pulse-height analyzer 116 can be arranged to pass only pulses having heights resulting from the `detection Iof gamma rays having energies in excess of about 3 to 4 mev., depending on the principal constituents, so as to :achieve to some extent a separation of ore based upon the general extent of mineralization of the ore. The presence of sulfur or chlorine will notrinterfere too seriously with such separation, -as the highest concentrations of such elements will quite ordinarily occur in conjunction with higher degrees of mineralization. iln fact, as is well known, many ores are sultides or chlorides, in which case the separation may be made on the basis of the sulfur or chlorine content rather than the metal. 'For example,

S the principal ore of lead is galena (zPbS). Due to the small neutron-capture cross section of lead, it is advantageous :in the separation of galena to utilize the gamma rays of sulfur.

Among naturally occurring metallic elements or types `of atomic nuclei having a reasonably large cross section for capturing slow neutrons', and which produce especially characteristic slow neutron-capture gamma ray energy spectra particularly well suited to the practice of this invention, a number can Ibe mentioned. {These include iron, nickel, cobalt, manganese, aluminum, copper, chromium, titanium, mercury, cadmium, gold and silver. Outstanding important among naturally occurring nonmetallic elements or types -of atomic nuclei are chlorine and sulfur.

With respect to each of the illustrated embodiments of the invention, the conventional means for energizing the various components thereof have been omitted for the reason that such illustration could only serve to obscure novel features, since the necessity for energizing such components and the means for energizing such components will be clearly apparent to those skilled in the art.

The broad area of applicability of the principles of the invention will be manifest in the light of the preceding disclosure. The practice of the invention is generally applicable to any prescribed program of treating a stream ofdmaterial dependent upon the concentration of a class of latomic nuclei in the stream of material, where the treating step can be controlled according to the prescribed program by the magnitude of an electrical signal, provided that in its stream environment the class of atomic nuclei produces a reasonably intense slow neutron-capture gamma-ray energy spectrum having at least one portion substantially unique thereto.

lt will be appreciated that the results obtained through the practice of the invention are substantially free from disturbance by extraneous gamma rays or gamma rays produced by other processes, because of the discrimination afforded by the pulse-height analyzer. It will also be appreciated that any interferences that might possibly result from the production of gamma-active isotopes as a consequence of the neutron iiux are minimized by the movement of the stream of material without any accumulation of such isotopes in the vicinity of the gammaray detector, as well as the usually low energies of the gamma rays from such sources.

As will be evident, the illustrated embodiments of the invention are subject to numerous modifications and arrangements within the scope of the invention. Illustrative of such modilications is the fact that there can be substituted for the illustrated and described scintillation method of detecting gamma rays and producing electrical pulses having heights dependent upon the energies of the detected gamma rays other methods known to the art for such purpose, such as the pair spectrometer method, the magnetic spectrometer method, the crystal diffraction spectrometer method, the crystal conduction spectrometer method, and either the photoproton or photoneutron spectrometer methods. Though the illustrated and described scintillation method is preferred for reason of sensitivity, the manner in which such other methods could be used in lieu of the preferred method will be evident to those skilled in the art.

Accordingly, the actual scope of the invention should be ascertained by referring to the appended claims, rather than implying a more limited scope from the detailed description of the embodiments of the invention given for the purpose of conveying a full and complete understanding of the invention.

I claim:

l. In apparatus for treating a stream of material so as to segregate portions thereof having greater and lesser concentration of a class of atomic nuclei therein; the improvement comprising means for maintaining a slow neutron flux in a zone, means for passing the stream of material through said Zone, means for effecting an electrical signal having a magnitude that is substantially solely dependent upon the rate at which gamma rays are produced in said zone having energies equal to at least one selected energy level component of the slow neutron-capture gamma-ray energy spectrum of the class of atomic nuclei, and means for segregating portions of the stream of material with respect to which said signal has a magnitude above a predetermined value from those portions with respect to which said signal has a magnitude below said predetermined value.

2. Radiological apparatus comprising means for maintaining a slow neutron iluX in a Zone, means for passing a stream of material through said zone, gamma-ray detecting means including a `scintillation phosphor and a photomultipiier tube for detecting gamma rays produced in said zone and also for producing electrical pulses having heights dependent upon the energies of detected gamma rays, means for eiecting an electrical signal including a counting rate meter electrically coupled to the detecting means for producing an electrical signal having a magnitude dependent upon the rate at which pulses are received thereby from the detecting means, a pulse height analyzer electrically interposed between the detecting means and the signal effecting means for preventing pulses having heights within at least one predetermined range of heights from reaching the signal effecting means, and electromechanical control means electrically connected to said counting rate meter and mechanically connected to said means for passing the stream of material through said zone Varying the composition of said stream in response to said electrical signal.

References Cited in the iile of this patent UNITED STATES PATENTS Glacy Aug. 18, Fearon Dec. 4, Morton Aug. 1, Herzog Dec. 19, La Pointe Nov. 11, Rockett .Tune 2, Pringle et al. Aug. 10, Gaudin May 3, Ruble Oct. 25, Scherbatskoy Mar. 27, Juterbock et al May 1, McKay lune 26, Scherbatskoy Apr. 8, Putman Jan. 26,

FOREIGN PATENTS Canada Nov. 6,

OTHER REFERENCES Nuclear Physics Primer, U.S. Atomic Energy Comm. Pub. MDDC-1497.

Energy Levels of Light Nuclei, by Endt and Kluyver. Reviews of Modern Physics, vol. 26, pgs. 95-166,