US2987623A - Method and apparatus for radiometric analysis - Google Patents

Description

June 6, 1961 B. F. scoTT 2,987,623

METHOD AND APPARA US FOR RADIOMETRIC ANALYSIS Filed July 15, 1955 5 Sheets-Sheet 1 J m M J w b a 3 6 w 3 l J f M j l lf a 6 f 7 A v M 8 Z 7 j k y 5 MW c 4 w June 6, 1961 B. F. scoTT 2,987,623

METHOD AND APPARATUSx FOR RADIOMETRIC ANALYSIS Filed July 15, 1955 3 Sheets-Sheet 2 FH-j-2 FIEE June 6, 1961 B, E SCOTT 2,987,623

METHOD AND APPARATUS FOR RADIOMETRIC ANALYSIS Filed July l5 1955 3 sheets-sheet s FUE L i /72 F15-5 J70 l j /564 l /42 154 /fzo 5 138 /45 il j g I 5 l JZ@ /gal 124 5 l. fzz` l l" 150 x` /14/ f 776/ fog L J/o/ 'T l. -126 4/ l? -az 2,987,623 METHOD AND APPARATUS FOR RADIOMETRIC AYALYSIS l Benjamin F. Scott, Chicago, Ill., assgnor to Nuclear- Chicago Corporation, a corporation of Delaware Filed July 15, 1955, Ser. No. 522,329

17 Claims. (Cl. Z50-83.6)

This invention relates to a method and apparatus for radometric analysis, and more specifically to a radiometric method and apparatus for indicating the concentration of phosphate ion in boiler water which has been treated with phosphate to precipitate calcium therefrom, so that this concentration may be continuously controlled.

It is conventional in steam power plants, particularly in large power plants such as those used by utility companies for the production of electrical power, to eliminate the calcium content of the boiler water by adding thereto a highly soluble phosphate compound, such as tri-sodiumphosphate, the phosphate ion combining with the calcium ion to form the relatively insoluble precipitate calcium phosphate, which is removed from the system. It is found necessary in many installations to add phosphate at fairly frequent intervals in order to keep the calcium content of the boiler water at suitably low levels. This is occasioned by the fact that in many installations calcium in a secondary heat exchange loop containing, for example, raw river water, despite all reasonably economical precautions, leaks into the primary heat exchange loop, particularly in the condensers employed at the low-pressure side of the turbines. Thus, in order to prevent the appearance in the system of any substantial amounts of unprecipitated calcium, it is necessary to maintain a substantial excess of phosphate in the system at all times. However, it is obviously not desirable that the phosphate excess be permitted to reach extremely large values. Accordingly, it is now the custom to perform, on a routine basis, chemical analyses of the boiler Water at frequent intervals, for example once an hour, in order to determine the remaining excess phosphate ion concentration, adding phosphate when the concentration falls below a predetermined level.

Such chemical analyses by conventional methods and apparatus require the expenditure of a great deal of time on the part of skilled technicians and the cost of continually running such analyses is accordingly high. Furthermore, since the performance of the analysis is an extended operation, it is impractical with the methods and apparatus heretofore used to make the test for phosphate ion concentration at desirably brief intervals.

The proper excess phosphate ion concentration normally maintained lies in the range of ten to fifty parts per million. The present method of producing an indication of the ion concentration in this range is far simpler and less time-consuming than the conventional methods heretofore employed. The method and apparatus of the present invention render continual sampling of the boiler water and recording of successive indications of phosphate ion concentration an essentially automatic operation requiring little or no attention upon the part of an operator. Furthermore, as will hereinafter be seen, the method and apparatus of the invention may readily be adapted for completely automatic control of the phosphate ion concentration, provision being made for automatic introduction of added phosphate upon the falling of the level of the concentration thereof to a predetermined value in the range above recited.

As will be seen, parts of the apparatus and method of the invention, although particularly well adapted for indieating the phosphate concentration in boiler water, will also be found highly useful for analogous purposes in other applications.

For complete understanding of the method and apparatus of the invention, reference is made to the attached drawings in which:

FIGURE 1 is a schematic diagram of an electrical and mechanical system constituting an embodiment of the apparatus of the invention;

FIGURE 2 is a vertical sectional view of a device for metering and feeding measured samples of boiler water constituting a portion of the device of FIGURE l;'

FIGURE 3 is a vertical sectional view of a device for storing and feeding measured samples of radioactive calcium solution, constituting a portion of the device of FIG- URE l;

FIGURE 4 is a vertical sectional view of an assembly for counting the radioactivity of a supernatant in the presence of a precipitate, constituting a portion of the device of FIGURE l;

FIGURE 5 is a view partially in longitudinal section and partially in elevation of a radiation counter constituting a portion of the device of FIGURE 4;

FIGURE 6 is a sectional view taken along the line 6 6 of FIGURE 5; and

FIGURE 7 is a view in elevation of the shell or body portion of the counter of FIGURE 5.

For convenience and ease of understanding, the system will be described with reference to FIGURE l, in which the components are shown in highly diagrammatic form, and the details of actual physical construction of particular components of the system of FIGURE 1 which are not well known to those skilled in the art will be presented as the description of the system proceeds.

As shown in FIGURE l, a sampling tube or pipe 10-is connected to the boiler (not shown) to withdraw samples of the boiler Water. The sampling tube 10 terminates in a three-way solenoid valve 14. The valve 14 is also connected to a conduit or spout 16 and to a sample metering and feed device 18. The metering and feed device 18 consists of a chamber 29 provided with a vertical tube 22 on the interior thereof, and a drain 24 at a level below the top of the tube 22. This construction, shown'diagrammatically in FIGURE l, is illustrated in greater detail in FIGURE 2. As shown in FIGURE 2, the cham.- ber 20 is formed, in the present embodiment, from a pipe or nipple 26 threaded into one arm of a T 28, the upper end of the chamber being formed by a cap 30 andthe lower end by a plug 32, the tube 22 extending axially through the plug 32 and being soldered thereto at 34. The lower end of the tube 22, as shown in FIGURE 2, is threaded into the valve 14. As shown in the schematic drawing of FIGURE l, the valve 14 is normally in a position to connect the tube 22 to the spout 16, but upon actuating the coil 36 of the solenoid valve, the tube 22 is connected to the tube or pipe 10, so that the boiler water flows from the boiler up through the tube 22, overiiowing into the chamber 20 up to the level of the drain 24, which may be connected to a waste system or returned to the boiler (such connection not being shown inthe drawings). The spout 16 terminates over an open-top mixing chamber 38. It will thus be seen that when the solenoid valve 14 is actuated by the flow of current through the coil 36 thereof, the boiler water fills the tube 22 and overows until the current through the coil 36 is cut o, at which point the sampling tube 10 is sealed by the valve, and the fixed quantity sample of boiler water in the tube 22 is dumped into the mixing chamber 38.

A second spout 40, similar to the spout 16, is connected to a second three-way solenoid valve 42 similar to the valve 14. In this case the feed pipe or tube 44, which is connected to the valve 42 in a manner similar to that in which the sampling tube 10 is connected to the valve 14, is fed from a reservoir or tank 46 containing calcium having a content of Cat5 in suitable liquid 'agences form. such as an. aqueous solution. ofV a highly solublel salt.

` Connected to the valve 42 in a manner similar to that inwhich the-feed device 18-'is connected to the.;valve 14 is ametering and feed device48.v This latter consistsessentially of a tube 50 formed of a metallicconductor and an VelectrodeV v52 projecting into fthe; open upper end. of the tube 50. The-connections of the. valve, 42 are similar to those of the valve 14. In the unenergized position of the solenoidV valve (the: position illustrated in the drawing) the; tube 48 is connected to the spout 40. When the. coil 54 ofthe solenoid valve is energized (as indicated by the arrow in the schematic indication of the valve in FIG- URE- 1), the reservoir or tank 46 is connectedto the tube 50; By means later to be described, the coil 54`is automatically deenergized when the liquid in the tube 50 reaches a suciently high level to contact the electrode 52. Thus upon energizing of the coil 54, the tube 50 iS filledk tol the preset level with the solution of radioactive calcium ion, and the Xed quantity of radioactive. calcium is then dumped into the mixing chamberl 38 throughthe spout 40.

The construction of the. metering and feed device; 48 for the radioactive solution, which is shown in highly schematic form in FIGURE 1, is illustrated in .more detailv in FIGURE 3. As seen in FIGURE 3, the tube-50 is threaded at its lower end into the valve 42. The elec- Vtrode 52 is a wire which is supported by an insulator 56 forming the ,central portion of a cap 58 threaded ontothe upper end vof a pipe or nipple 60 joined to an arm of a tee 62 similar to theteeZS, thus forming, with a plug 64 soldered at 66 to the tube 50, a chamber surrounding the tube. 50. and having ai.r drain line 66. The chamber surrounding the tube 50 is not illustrated inthe diagrammaticV showing of FIGURE l, since this chamber, and the drain Aconnecting thereto, are not essential to the-basic operationof the system, because in normal operation the levelaof the liquid in the tube 50 can never riseicompletely to.the-top of. the tube because of reversal ofthe position of the valve 42 upon contacting of the elctrode 52 as previously setforth, by reason ofthe electrical'connectons laterfto be described. The chamber and the drain 66 are providedin this portion of the system solely as a safeguard in vthe event of improper operation. of theV auto, matic shut-off, so that the radioactive solution will be carriedlto a suitable drain or'reservoir rather than overflowing on other portions of the equipment and contaminating the.l surrounding area.

' Inthetmixing chamber 38 is an agitator or mixing paddle. 68 having a shaft 70 which is constantly rotated by a motor (not shown). At the bottom of the conically oored mixing chamber 38 is a drain opening 72 to a solenoiddrain valve 74 connectedto a tube 76 which extends downward into a centrifugal radiation counting assembly for counting the radioactivity of a liquid in the presence of a solid precipitate, this assembly being'generally designated by the numeral 78.

The construction of the counting assembly 78 and a counterv constituting a portion thereof is shown in FIG- `URES 4 through 7 of the drawing. Referring to FIG- URE 4, it will be seen that the assembly 78 has an elongated' tubular housing 80. Coxial with, and rotatable in, thefhousing 80 is a tube or sleeve 82. The rotatable sleeve 82 is rabbeted or shouldered at 84 and 86 at the ends thereof. Secured to the lower end ofthe housing 80 by bolts 88 is an annular lower end cap 90 to which is connected a drain pipe 92. The cap 90 is formed with an annular channel or trough 94 which is kdrained Yhythe pipe 92. Resting on aninternal rabbet 96 on the uper end of the cap 90 is an annular spacer 98 having inwardly protruding ange 100 extending to the sleeve 8,2, asmall clearance being left to permit free rotation of the Vsleeve 82. Resting on the peripheral portion of the spacer 98 is the outer or stationary race 102 ofan annular ball` bearing, generally designated I104, The inner: race 106 of the bearing.y 104 istted ontothereduced diameter portion of the tube 82, the rabbet or shoulder 86 resting thereon.

At the upper end of the rotatable tube 82, the inner race 108 of a ball bearing. 1.10 rests on the rabbet or shoulder 84, the outer race V112 being held in place by an annular cap 114 securedto` the upper end of the housing by bolts 116V. A top cap4 1718 is secured to the annular cap 114 by'boltsf120. The cap 118.has a central annular boss 122 on the under side, nested into the annular cap 114.

Secured in a central aperture in the cap 118 by set screws 124 is a. cylindrical radiation counter generally designated 126. The construction of this counter is illustrated in FIGURES 5. through 7,. Referring` to these gures, it will be seen that the body or shell of the counter, generally designated' by the numeral 128 and shown separately int FIGURE 7, is formed from a tube. The lower end reg-ion ofl the tube is machinedV away to produce two large half-cylindrical windows, all that is left ofthe lower end-*after the machining operation being a ringk connected by elongated ribs 1F32 to the main upper portion of the body or shell 128. Around the lower portion,vwhich thus has a practically continuous single cylindrical window, is'wrappedk (FIGURES S. and 6)` a thiny sheet of mica 134, cemented to the lower ring portion 130 and to the upper or body portion 128 and also slightly lapped as shown at 136 and cemented to the ribs 132 to form a substantially gas-tight enclosure. Sealing the ends of the tube 128 are upper and lower end caps 138 and 148. The end craps 138 and 140 are provided centrally with suitable hermetic insulator assemblies 142 and 144.

The central conductor'of'the lower insulator assembly 144 is sealed. However, the tubular central conductor 145 of the. upperhermetic insulator assembly 1142 is left open, as shown at 146, toprovide a gas inlet passage into the counter. The centerwire of the counter, designated 1.48, issoldered. at 150A to the central conductor of the upper insulator; assembly 142 in such a manner asV to not impede; free ow of gas therethrough.

Extending throughboththe upper end cap 138 and the lower end cap andtraversing the length of the counterv adjacent to. one of the ribs 132 is a tube 152 constituting an extension, by a suitable coupling (not shown), of; the; tube.` 761 shownin FIGURE 1 as being connected to the mixingV chamber 38 through the solenoid valve 74. At itslower end (FIGURE 4) the tube 152 is bent to direct liquid fallingY therethrough to the inner wallv of the rotatable tubef82.- Along the opposite rib 132 extends anV additional tube 154, entering through the upper end cap 138 and terminating at the lower end of the counter. The tube 154 has a gas exit aperture 156 in the side wall thereof at its lower end.

The counter 126 is thus of the type frequently known as amica-window atmospheric pressure flow Geiger counter, employing. gaseous fillings such as those described in U.S. Patent 2,519,864 of Paul B. Weisz.

Atop the top cap 118 is a connector housing 158` having a tubular side wall 168'and a disk cap 162. A coaxial electrical connector 164 is mounted in the side Wall 160 and connected by a wire 166 to the hollow central conductor of ther he'nnetic insulator 142. A gas fitting or nipple 168 extending through the disk cap 162 is connected to the central conductor for gas ow, but electrically insulated, by a short length of flexible plastic tubing 170, the outer end of the nipple 168 being connected to a suitable tube 172 leading to the source of gas employed' for the ow counter. Flexible tubing 174 is joined to the end of the gas outlet tube 154 andleads to a suitable gas bubbler or other flow indicator (not shown). The tube 152 similarly extends out through the cap 162'.

Force-fitting into the lower end of the rotatable tube 82 is a plug 176 having a conically concave top to. form a n concave bottom for the chamber defined by the rotatable tube 82, and apertures 178 extending downwardly and radially outward to matching apertures 180 in the wall of the tube 82, thus forming a downward and radial ow path from the central portion of the bottom of the cham' ber formed by the tube 82 to the annular chamber formed by the mutually inverted lower end cap 90 and spacer 98, the flange 100 on the latter protecting the bearing 104 from the splashing of liquid in this bottom chamber, which is drained by the pipe 92. The lower end of the plug 176 is in the form of a boss 182 extending down through the annular end cap 90 and terminating in a shaft portion 184 which is coupled by a bushing 186 to a motor 18S (the latter being shown only in FIGURE l).

At the top end of the rotatable tube 82, a flanged sleeve 190 is press-fitted therein to form an inwardly extending lip or shoulder of the chamber delineated by the rotatable tube 82.

The counting assembly shown in FIGURE 4 operates in the following manner: The counter gas constantly ows through the counter :126 in the manner now conventional with flow-type counters. When a liquid ows into the tube 152, it flows entirely through the counter 126 without affecting the operation of the counter (the wall thickness of the tube 152 absorbing the beta radiations) and is deposited on the wall of the tube 82. With the tube 82 being spun at high speed, the liquid is spread on the wall of the tube 82 in a thin layer, conned at the bottom by the bottom plug 176 and at the top by the sleeve 19t). The cylindrical counter window permits the counter to see a maximum of the liquid in the circular annulus, thus maximizing the efficiency of the apparatus in counting the radioactivity of the liquid. Where the liquid contains undissolved precipitates or other undissolved substances in suspension or similar form, the heavier materials are forced by centrifugal action to the wall of the tube 82. Since beta particles of usual energies, such as the beta particles emitted by calcium (Cat5), are totally absorbed by even the smallest thicknesses of materials such as water, the counting assembly easily discriminates between the beta activities of the two phases present in the feed, and, by making the liquid layer sufliciently thick to absorb all the beta activity of the solid, the pulse output of the counter is made responsive entirely to the beta activity of the liquid or lighter phase.

When rotation of the tube 82 is stopped, as by stopping of the motor, the liquid drains through the bottom plug 176 by means of the apertures 178 and 180 into the bottom chamber, whence it immediately drains through the drain pipe '92. Upon recommencement of spinning of the tube 82, a new sample may be fed into the assembly through the tube 152.

It will be noted that the rotary tube or chamber 82 is much longer than the counter 126, and a large space is left between the lower end of the counter 126 and the plug 176 which forms the bottom of the centrifuge chamber. Such a spacing is required in order to prevent spurious results from collection of sediment on the bottom of the chamber. The collection of a slight sediment or residue of solid material on the wall of the tube 82 presents no substantial problems, both for the reason that the swhling action of successive samples tends to keep the wall relatively clean, the sediment being Washed away as the rotational motion slows after shutting olf of the motor, and the further reason that the radioactivity of the sediment is in any event absorbed by the layer of liquid in each new sample. However, the accumulation of sediment at the bottom of the chamber constitutes a more serious problem, both because of relatively small washing action by the liquid and because during the spinning operation, any sediment that remains on the bottom from previous batches is completely unshelded by liquid, the latter being distributed solely on the walls. Although the counter is sensitive only to radiations radial of the chamber, longitudinal radiations entering the annulus produce secondary radiations which may be counted. Therefore, the distance between the lower end ofth counter window and the oor or bottom of the spinning chamber is made at least five times the thickness of the annulus between the counter window and the wall of the tube 82, which keeps the solid angle subtended by the annulus for radiations from the bottom of the chamber so low as to produce a negligible response to such radiations.

Referring now again to FIGURE l, it will be seen that a cable 192 connects the counter to a counting-rate meter and power supply 194, adapted to supply appropriate voltage for the counter and to indicate (and record, if desired) the counting rate. The cycle of operation of the device is controlled by a continuously operating motordriven cycling switch shown schematically at 196. In the highly diagrammatic indication of the drawing, the cycling switch 196 is shown as having a single movable contact and a plurality of commutator segments. It will be understood, however, that this representation is used solely for the purposes of simplification of the drawing, and that in actual practice the diagrammatic showing of the switch may represent any of a large variety of timecycling devices, including cam types, commutator types, and many other types of multi-circuit timers. In a particular embodiment of the device diagrammatically illustrated, the timer employed an entire cycle of ten minutes, constantly repetitive; however, it will be obvious that longer or shorter timing cycles may readily be employed.

Since the illustrated device is designed for continuous operation, and the time cycle is constantly repetitive, and further, as will hereinafter be seen, there is a substantial overlapping in time between operations performed on one sample and operations performed on a succeeding sample, the cycle of operation has no well-defined beginning or end; however, for convenience, it may be con-sidered that the beginning of the cycle of the cycling switch 196 is the position shown in the drawing, i.e., the condition in which no circuit is closed by the timer switch. For convenience of understanding, the contacts diagrammatically illustrated as commutator segments will herein be designated with alphabetical su'ixes corresponding to the order in which the circuits are closed.

The contact or segment 198a, whose circuit is first Y. closed by the rotor 260, activates and inactivates the coil 36 of the solenoid valve 14. The Contact or Segment 198b starts and stops the motor 188. The contact 198C controls the opening and closing of the drain valve 74 on the mixing chamber 38. The contact 19M activates and inactivates the counting rate meter and power supply 194 (it being understood, of course, that the latter electronic circuits receive independently power from sources not shown, the contact 198d merely controlling suitable switches or relays in the meter and power supply 1'94 to provide activation and inactivation without the necessity of completely turning this equipment on and oi with the resultant alternate heating and cooling of filaments and charging and discharging of condensers, etc.). The contact .198e controls the activation and inactivation of the coil 54 of the valve 42; however relay contacts 202, of a latching relay generally indicated at 204 and having a. rst winding 206 adapted to open the contacts 202, a latch 26S holding the contacts 202 open after the withdrawal of power from the winding 266, and an unlatching winding 2l@ adapted to release the latch, are in series with the contact 198e, which accordingly loses control when the contacts 262 are in the open position. The contact 1981, the last contact to be actuated in the cycle, controls the actuation of the unlatching winding 210.

Accordingly, when the switch is in the condition illustrated in the drawing, which has been arbitrarily designated as the starting position, both of the valves 14 and 42 are in the dump position wherein the tubes 22 and 50, constituting the boiler water sample feed and the radioactive calcium feed, are connected to the spouts A2' 16j andi 40, the metered4 amountsY of solutions previously introduced'V into the tubes '242;.and' 5.0 being agitated by the' constantly-running paddle wheel 68, a precipitatek of calcium phosphate forming Vin the mixing chamber 38, the yalve 74 being closed; the motor 188 'being stopped, and the counting rate meter and power supply 194v being inactivated.

When the rotor 200 reaches the segment 19801, the coil 36. is energized to bring the valve 14 to the till position wherein the pipe or tube 18, which is connected to the source of boiler water under test, is connected to the metering and feed device 18 andr immediately thereafter the segment 19821 is contacted to commence operation ofthemotor 188. With the motor in operation, the valve 74 isthen opened by the contact 198C and the mixture. of precipitate and supernatant in the mixing chamber 38 is dumped into the counter assembly 78, the liquid immediately being spread into a thin layer vwhose radioactivity may be counted, the radioactivity of the precipitate being shielded fro'm the counter by this layer. After a short intervah the valve 74 is again closed, and at about the same time the counting rate meter and power supply 194 i'sV activated by the Contact 198:1. The indication and recording continues during a substantial part of the cycle, to permit the counting rate meter to reach equilibrium and also to provide an indication o'ver a sutiicient period so that the indication given is not subject to gross inaccuracy by reason of statistical iiuctuations in the meter reading. Shortly thereafter, the Valve 14 is again returned` to its normal position, thus dumping the new sample o'f boiler water into the mixing chamber 38. At about the same time, the rotor 200 contacts the segment 198e, which actuates the valve 42 to connect the Ca15 source 46 to the feed tube 48, which lls until contact is made by the liquid with the electrode 52. The liquid has` sutiiciently high conductivity to conduct current for actuation of the relay 284 and thus produces opening of Y the. contacts 202, thus deenergizing the coil 54 and return.-

ingpthevalve 42 to its normal position wherein the contents of the tube 50 are dumped through the spout 40 intov the mixing chamber 38. The contacts 202 are held open by latch 288. Thereafter, the contact or segment 198 Vis reached by the rotor 200, and the Winding 210 unlatches` the contacts 282 to permit them to return to their normal closed position, in which the activation of the coil 54. is again controlled by the contact segment 198e-, Finally, at the end of the cycle, the counting rate meter. and power supply 194 is inactivated and the motor 188 is stopped. As the motor 188 stops, the liquid and the. precipitate on the wall of the centrifuge tube 82 drain out through the apertures 178. Thereupon, all o'f the, segments of the switch 196 are again disconnected from the rotor, and mixing of the boiler water and the calciumsolution previously deposited in the mixing chamber 38 during the counting of the previous sample continues in preparation for the next counting operation.

The amount of boiler `water employed in each operation and the amount of calcium solutio'n added thereto are of course not highly critical. However, the relation of the two must be selected to produce optimum accuracy of indication over the range of phosphate ion concentrations which it is desired to cover. The range of coverage is defined at the lower end of the range of phosphate ion concentrations by non-linearity due to the solubility product of calcium phosphate and at the upper end of the ranger ofj phosphate ion concentrations by the stoichiometrA-ic quantity of phosphate ion for the particular amount of calcium introduced. In addition, some non-linearity will be introduced at the upper end of the range, again because of the solubility product of the compound precipitated.

In one practice of the invention, wherein the content of phosphate ion in boiler water was monitored in the range of to 50 Vparts per million, 3.6 microcuriesof Cal5 were incorporated in sufficient calcium, in the form of aggancia? Y8 a: verysmall qnantityof aqueous solution of: calcium ily@ dii-oxide, to produce 36Y parts per million of calciumr in the 40 cc. samples ofboiler water whichtwere employed, the amount of calcium employed beingy sto'ichiometric with 5,6.7 parts per million of phosphate, and the radioactivity being of an intensity to produce about 10,000 counts per'minute at zero phosphate concentration (i.e., no' precipitation). A small amount of a phosphate-free surfactant (a surface-active agent such as Lux) was added to serve as a wetting agent to assureV that the precipitate would not form a surface crust preventing migration-ofalljof the precipitate to the walls of the centrifuge member `of the counting assembly. The counting rate registered or recorded on the counting rate meter was` a linear function ofthe original phosphate concentration in the boiler water over the range from 10 to 50 parts per million of phosphate io'n concentration, -within the limits of statistical error. The specific activity of the calcium introduced V(corresponding to the amount of the isotope Ca*5 present in the calcium employed) is selected to give ra countingv rate sufficient to produce a reasonably small statistical fluctuation and error over the perio'd of each measurement, while at the same time being sutticiently small to present no substantial hazard to personnel or equipment due to radioactivity, either in previous handling of the materials prior to' use, or in the course of the described process or subsequent disposal of the Waste therefrom.

Theuse of calcium as the radioactive precipitant for the phosphate greatly simplifies calibration of the'device and reproducibility of the results achieved thereby. Ca45 produces no daughter radioactive isotopes, decaying to stable scandium. Thehalf-life of Ca45 is 152 days, thus rendering the frequency of recalibration of the device relatively small. The4 pure beta activity of the C2145 essentially eliminates the necessity of any precautions by way of shielding or special care to' protect the operators, as is required where more highly penetrating radiationV is employed, -and also minimizes the response of the counter to radiations from the precipitate, since betas from the precipitate being centrifuged are absorbed by the liquid and betas from the botto'm of the chamber-are absorbed by the lower end of the counter.

Non-linearity of response due to solubility product limitations is essentially negligible in the region above 10 parts perl million of phosphate ion concentration, since in boilerwater having a pH of at least 9.0 calcium pho'sphate is so insoluble that the amount of compound remaining in solution will have no substantial effect on the amount of calcium precipitated, except where the original phosphate ion concentration is substantially above or below the range for which the system is designed.

Because of the non-linearity due to the solubility product of calcium phosphate, and 'because of the necessity of avoiding errors due to very small amounts of contamination, etc., it is desirable to calibrate the device in the region of at least li) parts per million phosphate ion co'ncentration (employing simulated boiler water prepared with known quantities of phosphate ion added), rather than employing as the calibration sample water having no phosphate ion concentration. By employing for calibrationV purposes simulated boiler water specimens having a phosphate ion concentration of 10 parts per million, only one calibration point is required for co'mplete calibration of the device. If the counting rate obtained at` lil-partsper million (with a simulated boiler water sample) is found, higher concentrations of bo'iler Water phosphate in successivesamples will produce percentages of the original (10 parts per million) counting rate diminishing linearly with a xed Yslope to the Value corresponding to 50 parts per million o'f phosphate.

As indicated in the drawing, the counting rate meter 194. is desirably-coupled to a suitable device 214 employed forfeedingphosphate to the boiler water to eiect automatic controlv of the phosphate concentration, in

aanmaaresponse -to the counting rate of -tlrc counter during the portion of each cycle in -which -it operates; "the .phosphate ion concentration may thus be maintained within -any desired limits. The feed device 214 'is not lfurther Shown, since a variety of forms thereof are readily lavailable. Optional provisions, such as us'hing and cleaning devices, calibration sample sources, and similar additions, will be obvious to persons skilled in the art.

From what has been said above, the monitoring of the phosphate ion concentration in ranges other than the l to 50 parts per million described above may readily be done by suitable variations of the quantities of boiler water and radioactiveadditi-ve, as willbe obvious to those skilled in the art. The particular embodiment of the method and apparatus of the invention described and illustrated is of course not limitative, 'many variants thereof being obvious from the description and the drawing of a single embodiment selected for purposes of illustration in accordance with the patent laws. Accordingly, 'the scopeA of the invention shall be deemed vto be limited only by the scope of the appended claims.

What is claimed is:

l. Radiation counting apparatus comprising a vertical tubular chamber having aperture in the upper end, a radiation detector on lthe axis of the chamber, an apertured end member at the lower end of the chamber, a ixedly mounted liquid conduit entering the chamber through one of said apertures, and selective means for spinning the chamber about its axis to centrifuge a liquid in -the chamber and for stopping the chamber to drain the liquid from the chamber through the end member, the conduit terminating within the chamber at a point substantially below the detector.

2. A method of producing an indication of the radioactivity of a ud containing a dispersed insoluble radioactive substance of greater specific gravity than the uid comprising the steps of introducing said uid containing said insoluble substance into a chamber and spinning the chamber to throw the insoluble substance against the wall thereof while producing an indication of the radioactivity existing at the axis of rotation, said uid being introduced in suicient quantity to form a layer absorbing substantially all of the radioactivity of the insoluble substance.

3. Radiation counting apparatus comprising Va vertical tubular chamber having an aperture in the upper end, a radiation detector on the axis of the chamber constructed and arranged to be sensitive only to radiations in the annulus between the wall of the chamber and the detector an apertured end member at the lower end of the chamber, a xedly mounted liquid conduit entering the chamber through one of said apertures and terminating at a point substantially below the detector, and selective means for spinning the chamber about its axis to centrifuge a liquid in the chamber and for stopping the chamber to drain the liquid from the chamber through the end member.

4. The apparatus of claim 3 wherein said end member is spaced from the detector by a distance equal to at least five times the thickness of the annulus, so that the detector is rendered insensitive to residual radioactive material remaining on the end member.

5. Apparatus for continually measuring the radioactivity of uids comprising a vertical cylindrical chamber having-an aperture in the upper end, a radiation detector mounted on the axis of the chamber, a concave conical lower end on -the chamber, an aperture in the apex of the conical end, a xedly mounted liquid conduit entering the chamber through one of said apertures and terminating at a point substantially below the detector, and means adapted to be activated and deactivated for rapidly spinning the chamber about its axis, whereby a fluid is spread upon the wall for measurement of its radioactivity during activation of the spinning means,

410 but may be drained from'the .chamber through the'ape.- ture on .deactivation -of .the 'spinning means.

6. Radiometric analysis apparatus comprising,'in combination, a mixing chamber, a centrifuge chamber below the mixing chamber, a valve in the bottom of lthe mix- Iing chamber, a radiation detector on the axis olf-:the centrifuge chamber forming an annulus with the wall thereof, la stationary uid ow connection between the valve and a portion of the centrifuge chamber below the detector, and a drain .aperture in the bottom of the chamber.

7. Continua'l sample radiometric analysis apparatus comprising, in combination, the apparatus of claim 6, means for introducing into the mixing chamber measured quantities-of a liquid under analysis and .of a radioactive reagent forming a relatively insoluble compound with a component of the liquid, means for thereafter* opening the valve-to admit the liquid 'into the annulus, means for thereupon closing the valve and actuating the detector to indicate the radoactivity of the liquid, and means for then -again actuating said introducing `mea-us to .prepare a new sample for exposure to the detector during the exposure ofthe previous sample.

v8. A method of producing an indication of phosphate ion concentration in boiler water comprising the steps of withdrawing a sample of boiler Water, adding to the sample a quantity of `radioactive calcium, inserting the sample into a rotating chamber in sufficient quantity to spread the supernatant on the wall of the chamber :in suicient thickness to absorb substantially all of the radioactivity of the precipitate, and producing an indication of the radioactivity incident on the central portion of the chamber.

9. Radiation counting apparatus comprising -a vertical tubular chamber having a radially inwardly extending portion forming an axial aperture -at the upper end, a cylindrical `detector extending into the chamber through said aperture, and a liquid conduit extending longitudinally through the radiation counter and having the inner end thereof directed to the Wall of the chamber at a point substantially below the detector.

ll0. The apparatus of claim l wherein the radiation detector comprises a counter body permeable to bet-a particles and having therein electrodes adapted for the counting of beta particles, the conduit extending longitudinally through the counter body and being impermeable to beta particles.

l1. A method of producing an indication of the concentra-tion of a constituent of a liquid comprising the steps of adding to the liquid a radioactive reagent form- -ing an insoluble precipitate with the constituent, inserting the two-phase composition thus formed into the peripheral portion of a cylindrical chamber, spinning the chamber to form la liquid film of a thickness to shield the axial portion of the chamber from emanations from the precipitate, and producing an indication of the radioactivity incident upon the axial portion of the chamber.

l2. Apparatus for repetitively producing an indication of the concentration of a constituent of a liquid comprising means for adding to successive batches of the liquid equal quantities of a radioactive reagent forming -an insoluble precipitate with the constituent, a vertical cylindrical chamber having an aperture at the bottom, means for cylindrically spinning and stopping the chamber, means for introducing each batch into the chamber while the chamber is spinning, and means for indicating the radioactivity incident upon the axial portion of the chamber, whereby the indications of the indicating means constitute indications of the concentration of the constituent in each batch.

13. Apparatus for measurement of radioactivity comprising a housing, a vertical cylindrical chamber having apertures in the top and bottom thereof within the housing, bearing means supporting the chamber within the housing for rotation therein, a radiation detector on the axis of the chamber, a ixedly mounted inlet conduit aesmese 1I Y extending through one of said apertures and terminating within the chamber at a point below the detector, and motive means coupled to the chamber and adapted to selectively spin and stop the chamber.

V14. Radiation counting apparatus comprising a vertical tubular chamber having yan aperture in the lower end, a radiation detector on the axis of the chamber, a xedly mounted liquid conduit terminating within the chamber at a point substantially below the detector, and selective means for spinning the chamber labout its axis to centrifuge a liquid within the chamber and for stopping the chamber to drain the liquid from the chamber through said aperture.

15. The apparatus of claim 14 wherein the detector has a beta-ray transparent window facing the verticalV wall of the chamber.

16. Radiation counting `apparatus comprising a vertical tubular chamber having a radially inwardly extending portion forming an `axial aperture :at the upper end, a radiation detector having a beta-transparent Window, means extending through the aperture to mount the detector within the chamber with the window facing the vertical wall of the chamber, and a liquid conduit impermeable to beta-rays extending through the radiation counter and having the inner end thereof directed to the wall of the chamber at a point substantially below the detector.

-17-.-A method ofv producing 'an indication of the radio activity of a liquid containing a suspended radioactive substance of greater specic gravity than the liquid comprising the steps of introducing the liquid containing said substance into a chamber and spinning the chamber to throw 'the' suspended substance against the wall thereofvv while producing an indication of the radioactivity existing at the axis vof rotation, said liquid being introduced in suiicientquantity to form a liquid layer absorbing substantially all of the radioactivity of the suspended substance thus thrown against the wall.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Radioisotopes in Industry, edited by John R. Bradford, 1953, pp. 102-115.

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