US3132249A - Detection, segregation and counting of radiations of different energies - Google Patents

Description

4 Sheets-Sheet 1 May 5, 1964 R. c. MAGGIO ETAL DETECTION, SEGREGATION AND COUNTING OF RADIATIONS OF DIFFERENT ENERGIES Filed Feb. 16 1961 May 5, 1964 Filed Feb. 16, 1961 C. MAGGIO ETAL DETECTION, SEGREGATION AND COUNTING OF RADIATIONS OF DIFFERENT ENERGIES 4 Sheets-Sheet 2 4 Trae/var May 5, 1964 R. c. MAGGIO ETAL 3,132,249

DETECTION, SEGREGATION AND COUNTING OF' RADIATIONS OF DIFFERENT ENERGIES 4 Sheets-Sheet 5 Filed Feb. 16, 1961 m Uf May 5, 1964 R. c. MAGGIO ETAL 3,132,249

DETECTION, SEGREGATION AND COUNTING OF RADIATIONS OF DIFFERENT ENERGIES Filed Feb. 1e, 1961 4 sheets-sheet 4 7/'0//5 owner A7' TOR/VE Y AUnited States Patent O 3,132,249 DETECTION, SEGREGATIN AND COUNTING F RADIATENS 0F DIFFERENT ENERGIES Ralph C. Maggio, 2175 Hudson Terrace, Fort Lee, NJ., and Charles Christiansen, 1192 Walton Ave., Bronx 52, NKY.

Filed Feb. 16, 1961, Ser. No. 89,889 4 Claims. (Cl. Z50-83.6) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to the detection and segregation of radiations of different energies from a radioactive specimen to be examined, and particularly to radiation counters of the type wherein ionization of a confined body of a counting gas in an electric field by radiations penetrating said body of counting gas, produces counting pulses in a utilization circuit.

The detection of the presence, in the ambient atmosphere, or in a fluid or in any specimen to be examined, of low energy or soft beta particles or radiations, such as in radioactive hydrogen and compounds of hydrogen, has heretofore been ditticult and unsatisfactory, especially in the presence of other radioactive materials and compounds. Prior methods commonly in use for this purpose employed ionization chamber and scintillation crystal techniques. These prior methods had a number, of disadvantages including the following:

(a) They were not satisfactory for the detection of radioactive hydrogen and compounds of hydrogen particularly in the presence of other radioactive contaminants;

(b) The equipment employed was large, bulky and required complex electronics;

(c) The ionization chamber was sensitive to variations in temperature, humidity, pressure and aersols (smoke);

(d) The scintillation techniques require specially designed photo-multiplier tubes; and

(e) The scintillation method was not specific for hydrogen, the material must be prepared in very thin layers to respond to the hydrogen gas, and the method and equipment used required a special design for use with radioactive hydrogen and its compounds, to be operated by highly skilled personnel.

In the detection of radioactivity where there is a mixture of diiferent radiations such as alpha, beta and gamma radiations, the segregation, classiiication, and counting of the different radiations according to their penetrating energy is often desirable, and even radiations of the same kind may vary in different penetrating power or energy.l For example, some beta radiations are of soft or low energy, and have low penetrating power, while other beta radiations have much greater energy or higher penetrating power. The beta radiations from radioactive hydrogen and hydrogen compounds, such as tritium oxide, are not only dangerous to humans, but their presence is difficult to detect and the quantity determined by prior detection procedures, especially when other alpha, beta and gamma radiations are also present.

An object of this invention is to provide an improved device for the detection of low energy beta radiations, which may be used singly for low sensitivity or in a stacked array for higher sensitivities, which will be relatively insensitive to ambient temperature, humidity and aerosols, which can be made insensitive to beta particles with energies greater than tritium, and which is relatively simple, practical, convenient and inexpensive.

Another object of the invention is to provide an improved method of and apparatus for detecting the presence Fice of and segregating radiations according to their penetrating power or energy, which will be relatively simple and practical, and capable of being easily manipulated by non-scientific personnel.

s Another object is to provide an improved detector for radiations, employing very thin windows made of electrically non-conducting material, and which eliminates any insensitive zones of substantial areas such as are chal'- acteristic of GM tubes having electrically non-conducting windows.

Other objects and advantages will be apparent from the following description of some embodiments and examples of the invention, and the novel features will be pointed out in connection with the appended claims,

In the accompanying drawings:

FIG..1 is 'a schematic perspective of half of a simple radiation detector, constructed in accordance with this invention,

FIG. 2 is a schematic plan of such a detector;

FIG. 3 is a diagram illustrating the manner of connecting a utilization circuit to such a detector;

FIG. 4 is a sectional elevation, on an enlarged scale, of a part of such a detector;

FIG. 5 is a schematic illustration of a stack of such detectors, and their individual utilization and counting circuits;

FIG. 6 is a sectional elevation of part of a stacked group of radiation detectors constructed in accordance with this invention, but having a common window between adjacent chambers of the stacked array;

FIG. 7 is a schematic elevation, with a conning ring in cross section, of a stacked varray of detection chambers, which may be employed in accordance with this invention in detecting the presence of low energy radiations in a uid to be examined;

FIG. 8 is a sectional elevation of a simple radiation detection device in which the cathode and anode' elements are dilerent in construction and arrangement than in the embodiment shown in FIGS. l and 2;

j FIG. 9 is a sectional elevation of another embodiment of single, radiation detection device, employing a modiiied anode and cathode arrangement and construction; and

' FIG. 10 is adiagram of an anti-coincidence circuit that may be employed in connection with the embodiment of FIG. 7.

In the embodiment of the invention illustrated in FIGS; l-4, the detector is of pancake shape, and cylindrical with a very short axial length. It has a peripheral, annular, metallic cathode 10, and a line wire, mesh screen 11 is disposed across and covers each end face of the annular cathode 10. Superposed on the outside face of each screen 11 and also covering each end face of the cathode ring is afilm 12 of an electrically non-conducting material that is impervious to the passage through it of iiuids, but is thin enough to pass through it any incident radiation from a radioactive material whose radiations it is desired to detect, classify, or segregate. The thickness of 'such a film should not exceed approximately 30 micrograms per square centimeter. Films or walls of the desired thinness so as to freely pass desired radiations usually are so weak mechanically for areas of desired size, that they are easily ruptured or broken. For this reason, the fine wire, mesh screen 11 serves to support the very thin iilm against rupture and enables one to use iilms of quite large face areas successfully. Mica is used quite extensively as a film-like wall and can be made extremely thin, but with this construction using the screen to support such a lm, it is now possible to use extremely thin films of various electrically non-conducting materials such as iilms of mica and synthetic plastics. An example of such plastics suitable for ilms is an air-dry lacquer enamel formed of netrocellulose containing varying amounts of hard gums and alkyds, which can be formed into films by sprays or dips, such as is sold under the trade mark Zapon. Another example of a film material which has been found to be particularly useful and practical for this purpose is a film of polyester material such as is sold under the trademark Mylar by DuPont Co. Such polyester films are commercially available in the market in thicknesses varying from 00025" to .0075" and their properties are described in detail in a bulletin published by Insulation Manufacturers Corporation having an othce at 565 West Washington Blvd., Chicago 6, Illinois, and copyrighted in 1953 by that corporation. Such films are also disclosed in a bulletin A-530 (September 1955) of E. I. DuPont de Nemours & Co. (Inc.) of Wilmington, Delaware. Films of luorocarbon polymer dispersions are also suitable for this purpose. One such polymer is tetrafluoroethylene resin. Any synthetic plastic material that can be made into very thin, fluid impervious films can be employed. The polyester films are particularly useful for this purpose because they are relatively strong against rupture even in very thin films. Films of nylon and cellulose acetate can be made very thin and can be used when supported by the Wire screens.

The margins of the screens 11 and films 12 are bent over upon the exterior peripheral surface of the cathode ring and secured thereto by encircling, adjustable conning clamp rings 13 or by suitable ceinents or adhesives. The cathode ring and the films 12 provide a closed chamber 14 in which, about midway between the film faces, is an anode element 15 of open skeleton shape such as a plurality of concentric metal rings 16 of diierent diameters, mechanically and electrically connected together and supported by a conductor bar 17 that extends through but is insulated from the cathode ring. This bar 17 is enclosed, after connection to the rings, in an electrically insulating coating of plastic material. The closed chamber 14 containing any suitable counting and quenching gas mixture, such as is commonly used in GM counters and other radiation detectors and counters. The screens 11 may be in contact with the annular cathode ring and, hence, also act as cathode elements. When radiation from a radioactive material penetrates either of the lms 12 and enters chamber 14, it will ionize the counting gas therein if there is an electric field in such chamber. Such a field is created when a substantial voltage differential is established between the anode and cathode elements; such as through connection to the anode and cathode elements of a utilization circuit (FIG. 3) employing wires 18 and 19 connected respectively to the elements 10 and 1S, and including therein means 20 for establishing such voltage differential across the anode and cathode elements and for counting the pulses created in the utilization circuit. This means 20 is commonly used in Geiger counters and other radiation detectors, and hence, is not here illustrated or described in detail. The chamber 14 is filled with the counting gas in any suitable manner, such as is employed to ll other counting chambers of GM tubes with such a gas. For example, the chamber may have spaced apart ports that can be opened and closed to enable the counting gas to be introduced into the chamber and flushout and replace the air previously therein.

In the embodiment illustrated in FIG. 5, a plurality of such detector units, E, F and G, such as are shown in FIGS. 1 4, may be assembled in close proximity to one another in face to face, stacked relation and conned in that face to face relation by any suitable means such as encircling straps H adjustable in encirclement length to confine the units against separation from one another. The anode and cathode of each unit are connected in series in an individual utilization and pulse counting circuit, such as was described in connection with FIG. 3. When radiation, such as alpha, beta and gamma rays, is

incident on the exposed face wall of and end cell or unit in the stack, the rays, if able to penetrate into the stack will be segregated and stopped progressively in the units according to their penetrating power. The pulses counted in the different successive, chambers or units will indicate how many radiations of any penetrating range have their energy absorbed and counted in each unit. The low energy beta particles or radiations, such as are emitted from radioactive hydrogen or its compounds, such as tritium oxide, for example, are largely absorbed and counted in the first chamber in the stack, whereas the gamma particles or radiations will pass on through more than one unit and be absorbed and counted in further chambers in the stack, but not counted in the first chamber penetrated.

In the embodiment illustrated in FIG. 6, chambers 14n, 14b and 14e are similar to the chamber 114 of FIGS. l-4, except `that they have a common film face wall between adjacent chambers. In this example, a plurality of annular metal cathode rings 10a, 10b and 10c are assembled edge to edge with a film of electrically non-conducting inaterial 12a and 12b between and separating the rings and insulating them electrically from one another. The exposed end faces of the end ones of the group of cathode rings are covered by fine metal wire screens 1-1 and superposed against Itheir outer faces are films 12 of electrically non-conducting material, like the films 12 of FIGS. 1 to 4. The margins of films 12a and 12b are bent over against the outer peripheries of the cathode rings, as shown, and the margins of screens 11 and films 12 are likewise bent over against the outside peripheries of the end cathode rings. A confining clamp band 21 that is adjustable in circumference surrounds the group of rings 10a, 10b and 10c and confines them in their as sembled relation as shown in FIG. 6. Elastic annular insulating gaskets 22 and 23 are preferably interposed be tween the inner periphery of ring 21 and the bent over margins of screens `11 and films 12, so that when tightened Vthey will clamp the cathode rings together and provide elastic pressure seating the films ito the cathode rings. The films 12 extend `at their margins further than the screens 11 so that such film margins are pressed firmly into contact with the cathode rings to close the chambers 14a, 14b and 14C. One exposed end wall for the cathode ring at one end of the stack, such as the outside face wall of chamber 14C, may, when desired, be made of impervious metal to stop and enable counting of gamma radiations in chamber 14C. In each chamber 14a, 14b and 14C are `anode elements 15 as in the chamber 14. The band 21 has apertures (not shown) through which access may be had to openable and closable passages through rings 10a, 10b and 16C for replacing air `in the chambers with a counting gas mixture, as done in prior detectors and counters. The cathode and anode for each chamber 14a, 14b and 14a are included in an individual utilization circuit (not shown), as explained for the individual detector units in FIG. 5.

In the embodiment of FIG. 7, a plurality of four individual units 24, 25, 26 and 27, each like the unit of FIGS. 1-4, are assembled in face to face or stacked relation and confined in that relation by an encircling ring 28. There is a closed space 29 between the faces of the interior units 25 and 26, and the ring 28 has spaced apart inlet and outlet parts 30 and 31 leading to that space 29 through which a fluid having suspected radioactivity can be passed. Radiation from such suspected fluid, if it enters unit 25, will have its low energy particles absorbed and counted therein, and the higher energy particles will pass on through that unit into unit 24 and be stopped and counted in that chamber. Similarly, if radiations from the suspected fluid enter unit 26, the low energy particles thereof, such as the low energy beta rays, will be stopped and counted in that unit, and the higher energy particles or radiations that pass on into unit 27 will be stopped and counted there. Each unit will, of

course, have an individual counting and utilization circuit, and the circuits of units 24 and 25 will be embodied in an anti-coincidence circuit, so that if the radiation particles cause concurrent countings in b-oth branches of the anti-coincidence circuits, no count will be indicated, as they cancel one another out in the circuits. A similar arrangement is provided for units 26 Iand 27. With the four units, one obtains a counting for the radiations emitted at both sides of the suspected uid under examination in the space 29, and thus the counts are more accurate and complete than if only one pair such yas units 24 and 25, or 26 and 27 were employed. The ring 28 may be split in order to apply it to the units, and the edges along the split coupled and drawn together after assembly of the units in the face to face relation.

An anti-coincidence circuit such as may be employed in connection with the embodiment of FIG. 7 is illustrated schematically in FIG. 10.

In the embodiment of FIG. 8, an annular ring 32 of electrical insulating material has each of its end faces covered by a fine wire screen 33 that has been sprayed with or dipped in a liquid nlm-forming `agent of electrical insulatingr material so that the wires of the screen are coated with such iilm agent, and such agent forms thin bridging ilms across .the openings or meshes ofthe screen. Since the face area of each opening or mesh is quite small, a thinner iilm can be safely used to bridge it, because a thinner lm of smaller :area has the necessary mechanical strength. The thinner the bridging films, the more of the radiations that are able to pass through it, and the more sensitive the device is to radiations of low energy. The ring 32 may have small conduits 34 passing through it, by which a counting ygas may be passed through the chamber 35 between the screen 33 to flush out and replace the air in that chamber. These conduits 34 are scalable after the air inthe chamber 35 has been replaced by the counting gas. A conductor 36 is connected to one screen 33, and another conductor 37 is connected to the other screen, so that when these conductors 36 and 37 are included in a utilization circuit, one screen acts as a cathode and Athe other screen acts as an anode. This arrangement makes it p-ossible to make the thickness of the chamber 35 between screens 33 very small. A suitable sealing compound 32e may be lapplied over the margins of the screens and the exterior of the ring 32 to seal the screen to the ring 32.

`In the embodiment of FIG. 9, the construction is similar to that of FIG. 8, except that Itwo of such detection units are arranged in face to face relation as a stack, and one film-coated wire mesh screen is used as a common electrode and screen for two of the detection units. 'llhis com-mon screen is used as the anode element for the two adjacent chambers. To this end two annular rings 38 `and 39 are arranged in end to end relation, with an anode, iine wire mesh screen fait carrying the fluidimpervious thin lm clamped between Iadjacent ends cf the rings. The other screens 41 and 42, each also carrying a duid-impervious, thin iilm, -are secured across and close the exposed ends of the rings 38 and 39 to co-mplete the two closed chambers 43 and 44. A sealing compound 45 -is app-lied around the peripheries of the rings and over the margins of the screens to aid in confining the parts in this assembled relation. The chambers 43 and 44 have their air flushed out and replaced with a counting and quenching gas as usual in radiation detectors, and as described in connection with FIG. 8. Wires 46 are connected to the cathode screens `41 and 42 and a wire 47 is connected to -the anode screen common to the two adjacent chambers 43 and 44. The wires 46 and y47 are connected in the usual or any suitable utilization and counting circuit.

This construction of FIG. 9 has the advantages that the chambers 43 and 44 can be made rather shallow, since no space in the centers of the chambers is required for an anode, and the device is sensitive since it responds to radiations incident on either exposed face of the double chamber unit.

The thin films of electrically non-conducting material may be formed in any suitable manner or purchased in the open market. As a few examples, the material in uid but congealable form may be sprayed as a thin layer on a solid or liquid surface from which it may be stripped, or the screen may be dipped in the iilm material in fluid form and then lifted and held in air until it hardens, dries or sets. The film material in iiuid form also may be sprayed on the screen and then it forms lm bridges across the mesh openings and coats the wires of the screens. This coated screen is then dried or handled carefully until the iilm bridges set or harden. Other suitable ways of forming the films may also be employed. The iilm material may be any available iilm forming resin, such as a plasticized synthetic resin that can be made available in fluid form in order to form the iilm, and then caused to cure or harden. Solutions of such resins using a vaporizable solvent are useful, as are resins that may be made very fluid by heat. The resin or material, however, should be one which can be penetrated by radiations from radioactive materials.

The window iilms must be thin enough to pass or transmit therethrough beta particles or radiations with an average energy of 6 k.e.v. (kilo-electron volts) where E is the average for radioactive hydrogen and its compounds. It will appear from the foregoing that the detection, segregation, classiiication and counting of nuclear radiations in accordance with this invention is substantially insensitive to variations in the temperature, humidity, and aerosols of the ambient atmosphere, and is sensitive and useful for the detection, segregation and counting of low energy radiations thus making relatively simple, practical and inexpensive the detection of radioactive hydrogen and an indication of the relative amount of such hydrogen radiations. The wire mesh support also eliminates the insensitive zone which is characteristic of GM tubes having non-conductive windows.

A typical anti-coincidence circuit is illustrated in FIG. l0 which is operative to pass and count radiation pulses in one input circuit when no radiation pulse is concurrently applied to the other circuit, but which will not pass and count radiation pulses applied to the other or second input circuit alone or radiation pulses applied concurrently to both input circuits. The illustrated anti-coincidence circuit and others are well known, and a more complete disclosure of them is found in a book entitled Pulse and Digital Circuits, by Millman and T aub, chapter 13, page 404, FIGURES 1346, published in 1956 by Mc- Graw-Hill Book Company of New York, New York. One of these anti-coincidence circuits is connected to the utilization circuits of units 24 and 25', the utilization circuit of cell 25 (FIG. 7) being connected to input 1 of FIG. 10 and the utilization circuit of cell 24 (FIG. 10) being connected to input 2 of FIG. 10, so that if the radiation pulses penetrate unit 25 and not unit 24, they will be counted, but if they are strong enough to penetrate both units 24 and 25 they will cancel out one another and will not be counted. In this way only the gamma rays of low energy will be counted. Another similar anti-coincidence circuit is similarly connected to the units 26 and 27 so that the radiation pulses that penetrate only the unit 26 will be counted, and those that penetrate into both units 26 and 27 will cancel one another and not be counted.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

We claim:

1. A device for detecting the presence in a iluid to be examined of low energy beta radiations, which comprises an enclosure having a group of four relatively thin, closed chambers arranged in face to face relation in a stack and each chamber containing a counting gas, each of the adjacent face walls deiining said chambers being formed of a film impervious to the passage therethrough of fluids, but thin enough to pass therethrough low energy beta radiations, anode and cathode elements arranged in spaced apart relation in each chamber for creating, when a substantial voltage differential is established between the anode and cathode elements of each chamber, an electric field in each such chamber, said enclosure also having passage means for introducing a quantity of said uid between the adjacent faces of the center pair of said chambers, and anticoincidence circuits including the anode and cathode elements of each pair of said chambers at one side of said passage means, whereby when radiations from said uid in said passage means enters the first chamber at either side of said passage mean and its energy is absorbed there, a count pulse will occur in the circuit of that chamber, and if such radiation entering said irst chamber also passes through it into the second chamber of that pair, it will be counted in both chambers, but such double counting cancelled in the anticoincidence circuits for that pair of chambers.

2. A device for detecting the presence in a specimen to be examined of low energy beta radiations, which comprises an enclosure having two relatively thin, closed chambers arranged in close proximity to one another in a face to face, stacked relation, and each chamber contan'mg a counting gas, the face walls defining said chambers being thin films impervious to the passage therethrough of fluid but thin enough to pass therethrough low energy beta radiations, each of said chambers having anode and cathode elements arranged therein in spaced apart relation to one another for creating, when a substantial voltage differential is established between such h te:

D Cl) anode and cathode elements in each chamber, an electric eld in that chamber, and means including an anticoincidence counting circuit for each chamber including therein the anode and cathode elements of that chamber, said circuits being coupled together to cancel counting pulses created in both circuits concurrently by radiation entering one of said chambers from any such specimen that may be adjacent an outside face wall of the pair of chambers and passing into and creating counting pulses in both of said chambers.

3. The device according to claim 2, wherein said thin lms are electrically non-conducting lilms each mechanically reinforced against pressure against its outer face by an abutting line wire mesh sheet.

4. The device according to claim 2, wherein said thin lms are of polyester material and have a thickness not exceeding about 30 micrograms per square centimeter.

References Cited in the tile of this patent UNITED STATES PATENTS 2,465,821 Smoluchowski Mar. 29, 1949 2,715,684 Schwarz Aug. 16, 1955 2,716,523 Driver Aug. 30, 1955 2,755,391 Keyes July 17, 1956 2,881,328 Hendee Apr. 7, 1959 2,899,582 lermsen Aug. 11, 1959 2,925,509 Hayes Feb. 16, 1960 2,976,421 Bayfield Mar. 21, 1961 3,619,363 Wiechering Ian. 30, 1962 OTHER REFERENCES A Thin, Wire-Aperture Proportional Counter, by Eisberg et al., The Review of Scientific Instruments, vol. 25, No. l1, November 1952, page 1129.

Claims (1)

1. 2. A DEVICE FOR DETECTING THE PRESENCE IN A SPECIMEN TO BE EXAMINED OF LOW ENERGY BETA RADIATIONS, WHICH COMPRISES AN ENCLOSURE HAVING TWO RELATIVELY THIN, CLOSED CHAMBERS ARRANGED IN CLOSE PROXIMITY TO ONE ANOTHER IN A FACE TO FACE, STACKED RELATION, AND EACH CHAMBER CONTAINING A COUNTING GAS, THE FACE WALLS DEFINING SAID CHAMBERS BEING THIN FILMS IMPERVIOUS TO THE PASSAGE THERETHROUGH OF FLUID BUT THIN ENOUGH TO PASS THERETHROUGH LOW ENERGY BETA RADIATIONS, EACH OF SAID CHAMBERS HAVING ANODE AND CATHODE ELEMENTS ARRANGED THEREIN IN SPACED APART RELATION TO ONE ANOTHER FOR CREATING, WHEN A SUBSTANTIAL VOLTAGE DIFFERENTIAL IS ESTABLISHED BETWEEN SUCH ANODE AND CATHODE ELEMENTS IN EACH CHAMBER, AN ELECTRIC FIELD IN THAT CHAMBER, AND MEANS INCLUDING AN ANTICOINCIDENCE COUNTING CIRCUIT FOR EACH CHAMBER INCLUDING THEREIN THE ANODE AND CATHODE ELEMENTS OF THAT CHAMBER, SAID CIRCUITS BEING COUPLED TOGETHER TO CANCEL COUNTING PULSES CREATED IN BOTH CIRCUITS CONCURRENTLY BY RADIATION ENTERING ONE OF SAID CHAMBERS FROM ANY SUCH SPECIMEN THAT MAY BE ADJACENT AN OUTSIDE FACE WALL OF THE PAIR OF CHAMBERS AND PASSING INTO AND CREATING COUNTING PULSES IN BOTH OF SAID CHAMBERS.

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