US2686880A

US2686880A - Isotope separator

Info

Publication number: US2686880A
Application number: US252755A
Authority: US
Inventors: Jr William E Glenn
Original assignee: US Atomic Energy Commission (AEC)
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1951-10-23
Filing date: 1951-10-23
Publication date: 1954-08-17
Anticipated expiration: 1971-08-17

Description

Aug. 17, 1954 w. E. GLENN, JR

ISOTOPE SEPARATOR Filed OCT.. 23, 1951 Q5.. Y Q5 m6 vm Y V o o GT JNVENTOR. W/LL/AM E. GLS/VM JR Afro/wax Patented Aug. 17, `1954 William E. Glenn,

Jr., Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application October 23, 1951, Serial No. 252,755

6 Claims.`

lThis invention relates to an isotope separator` and more particularly to an apparatus for separating ions according to their respective masses.

The art of mass spectrometry has been greatly developed during recent years; however, the apparatus which has been designed heretofore, has

required the use of a magnetic field, complex control circuits, and intricate detecting equipment resulting in bulky and difcult-to-handle installations. These types of mass spectographs have been based on the theory that ions projected through a magnetic field are forced into curved paths according to their mass. Thus, with detecting equipment appropriately disposed along the ion paths, it is possible to determine the presence of ions of different masses in a test material. The present invention allows the determination of the mass of the ions present in a test material without the use of magnetic field and with a minimum of effort on the operators part. The present invention lends itself to mass production methods of manufacture and because of its simplicity can be made at a very reasonable cost.

It is therefore an object of this invention to provide a new and improved isotope separator.

Another object of the present invention is to provide a linear isotope separator wherein a magnetic structure is not necessary.

Still another object of this invention is to provide an apparatus of extreme sensitivity for determining the mass numbers of ions.

A still further object of this invention isto provide a method of separating and recovering a plurality of isotopes in small quantities.

Another object of the present invention is to` provide a compact and easily manufactured isotope separator characterized by its simplicity of operation.

Other objects and advantages will be apparent inthe following description and claims considered together with the accompanying drawing which shows a sectional view of the isotope separator and its associated electronic equipment.

Referring to the drawing in detail, there is shown an envelope II defining a vacuum charnber I2 therein. One end of the envelope il is open and formed with an outwardly extending flange I3. A centrally apertured cover plate I4, made of an insulating material such as hard rubber, has a plurality of holes I6 drilled to match a similar number of holes I'I drilled and tapped in the ilange i 3. Thus the cover plate I 4 can be secured to the flange I3 by bolts I8. To provide an airtight connection between the cover plate and flange, a rubber gasket I9 is fitted in a groove provided in the face of the flange I3. l As a means of evacuating the chamber IZ. the envelope II is provided with an exhaust outlet 22 communicating with a conventional vacuum pump23. i

i ing a photographic lin 5B .l ameter of the cylinder 5I Mounted centrally on the inner surface of the cover plate is a `rst copper tube section 2li having substantially the same diameter as the central aperture in the cover plate lli and having a flange Z5 bolted to the cover plate with bolts 21. A series of tube sections 28, similar to the iirst section 24 without the ii'ange 26, are mounted in 4axial alignment and in spaced-apart relation by means of two or more resistors 2S soldered between each successive pair of tube sections. The resistors 29 mounted in such a manner serve to support the series of tube sections 23 as a unit and also to distribute a voltage across the gaps formed, as will be explained more fully hereinafter. iThe series of tube sections 28 is terminated in a tube section 3l, which is similar to the rst tube section 2li, and having a flange 32. Attached to the flange 32 by nal board34 made of an insulating material such as that used for the cover plate ill. A ribbonlike filament 36 of a material such as tungsten or nickel-chromium alloy is mounted on pillars 3l which in turn are fastened to the terminal board 34 by bolts 33 in such a manner that the filament 3G is centrally located Within the tube section 3l Extending across the open end of the tube section Slis a screen-type grid structure 39. A similar grid structure is mounted across the opposing end of the adjacent tube section 28.

Acylindrical tube ft2 made of insulating material and having the same inner diameter as the central aperture of the cover pla-te I4, is formed on the cover plate on the side opposite the copper tube section 2li. Extending across the cylindrical tube 42 is a screen-type grid structure IM similar to the grid structure 33. An electrical connection 46 extends from the grid structure 4d to theexterior of the cylindrical tube 32. A slmilar grid structure di spaced apart along the longtudinal axis of the cylindrical tube l2 extends thereacross. An electrical connection iid extends from the grid structure il to the exterior of the cylindrical tube d2. A wide fiange dit having substantially twice the diameter of the cylindrical tube 42 extends outwardly from the second end of the cylindrical tube. A metallic cylinder 5i which, in the preferred embodiment, has an inside diameter substantially twice that of the inside diameter oi the cylindrical tube l2 and has one end thereof fastened by means of an outwardly extending flange 52 and bolts 53 to the Wide flange 59. The other end oi the metallic cylinder 5I has an outward iiange 54 which is fastened by means of bolts 56 to a cover plate 5l made of insulating material. Means for retainon the interior surface of the cylinder 5I comprising spring clips 5S is provided. Axially disposed within the cylinder 5I is a metallic rod iii which, in the preferred embodiment, has a diameter at least 0.1 the diand which is supported bolts 33 is a termiat one end by a machine screw 62 extending through the cover plate 51.

The accompanying electr prises a iilament voltage supply 63, an accelerating voltage 64, a saw-tooth voltage supply 66. a unidirectional voltage supply |51, and a triggering circuit 53, all of which are conventional electronic components. The lament voltage supply has two terminals IIiI and |02. The terminal IBI is connected by a wire |03 to a terminal |24 on the external face of the cover plate I4. Internally the terminal |04 is connected by a lead |06 to a terminal |01 on the board 34 which is in turn connected by a wire |38 to one of the bolts 38 and thus to one side of the filament 35. The terminal |62 is connected by a lead I II to a terminal H2 on the cover plate I4 which is internally connected by a wire |i3 to a terminal I I4 on the board 34. The terminal I I4 is further connected by a lead H5 to the other bolt 33 which is electrically connected to the other side of the lament 36. Thus it is seen that the voltage of the iilarnent power supply t3 is connected across the lament 35.

The saw-tooth voltage supply 56 has two output terminals I4| and |42. The terminal I4I is connected by a lead |43 to the electrical connection 4G of the grid structure 44 in the cylindrical tube 42. The terminal |42 is connected by a lead |44 to the electrical connection I3 of the grid structure 41. Thus the saw-tooth voltage is applied across the two grids 44 and 41 in the cylindrical tubev 42.

The unidirectional voltage supply 61 has two output terminals I5| and |52. The terminal |5I is connected by a lead |53 62 in the center of the cover plate 51, which is electrically connected to the metallic rod 3 I The terminal |52 is connected through a lead |54 to one of the bolts 55 which is electrically connected to the metallic cylinder 5I. Thus it is seen that the voltage from the unidirectional voltage supply 31 is connected between the cylinder 5I and rod 5|.

Each of the

electronic components

63, 64, 56, 61, and 63 are supplied operating voltage from a commercial source of power ITI).

Now consider the operation of the above-described apparatus and circuits with a test material coated on the filament 35, the apparatus assembled, and the chamber I2 evacuated. Under these conditions the source of power I1II i"s energized and the lament voltage supply E3 furtc the machine screw'` onic equipment com- '4 nishes a heater voltage across the filament 3'3. With the heating of the filament, ions of the test material are formed in the region of the iilament age across the gaps between the tube sections.

Since the potential difference created along the tube sections 3|, 28, and 24 is positive in the region of the lament 33 and negative at the tube section 24, the positive ions of the test material formed by the heat of the filament 36 will be attracted away from the region of the filament 35. It is well known that a charged particle will be accelerated by an electric field and that the acceleration .is proportional to the product of the value of the electric eld and the mass unit of the charged particle. The mass unit of the charged particle is the ratio of the charge to mass of the particle. From this it is seen that ions having small mass will have short times of flight and that ions of heavier mass will have longer times of iiight.

To counteract the defocusing tendency of the electric eld at the gap adjacent to the lament 35 because of the proximity of the lament 36, the screen-type grids 39 and 4I are disposed across the adjacent openings of the two tube sections 3| and 23. Since the screen grid 39 covers the opening of the tube section 3|, a negative pulse of voltage from the triggering circuit 68 is applied between the screen grid 33 and the iilament 35 at a predetermined interval to withdraw the ions from the region of the filament 36 in a beam and to project them into the accelerating force of the electric eld present at the following gap. Thus the ions are accelerated through the tube sections 28 toward the grid structure 44 in the tube 42.

The triggering circuit 68 which applies a trigger pulse between the filament 36 and grid 39 and extracts ions from the filament also applies the same trigger pulse to the saw-tooth voltage supply 36. The trigger pulse is delayed for a predetermined time within the saw-tooth voltage supply 66 and initiates a saw-tooth pulse at a time when the lightest ions from the filament 36 are arriving at the grid 44. The saw-tooth pulse is applied between the grids 44 and 41, thus the light ions which arrive at the grid 44 when the saw-tooth voltage is near zero are accelerated very little. These light ions then enter the space between the cylinder 5I and rod 6I. The light ions, having a relatively low energy are deected sharply by the unidirectional voltage 61 applied between the cylinder 5| and rod 5|, The relatively light ions thus strike the film 58 in a circumferential band near the entrance end of the cylinder 5I and irradiates a band on the film. The heavier ions arrive at the grid 44 later than the light ions and therefore at a time when the saw-tooth voltage between the grids 44 and 41 is higher. The heavier ions thus have a higher energy imparted to them by the saw-tooth voltage than do the light ions. The heavier ions so energized enter the space between the cylinder 5| and rod 3| and are gradually deflected by the unidirectional voltage therebetween unt-il they strike the film 53 in a circumferential band near the closed end of the cylinder 5I. Thus it is seen that ions are separated according to their respective masses, and the relative amount of each io-n present is determined by the degree of exposure of the corresponding bands on the film.

In the presently described embodiment of the invention the cylinder has a diameter substantially twice that of the rod 6| has a diameter substantially 0.1 the diameter of the cylinder 5| and the length of the cylinder is substantially twice its diameter. With these dimensions it has been a simple matter to separate as many as ten ions of Successive mass numbers for a given set of operating voltages and conditions. It is readily apparent that many of the parameters involved may be adjusted to shift the range of masses of ions detectable or to extend the range thereof.

If it is desirable to collect ions as well as to separate ions of different masses it is possible to utilize a cylinder 5i having circumferential slits therein instead of a hlm. 'Ion collecting chambers would then be disposed outside of the cylinder 5l communicating with the slits.

As well as being useful for micro-chemistry work, the present invention is useful in the petroleum industry and in the control of some chemical and manufacturing processes.

It is to be noted that the filament 36 may be replaced with numerous types of ion generators which readily adapt themselves to ionizing continuously-changing test materials. Nor is it desired to limit the type of material which may be tested to solids which can be coated on the iilament, for it is apparent that the filament 35 can be replaced with apparatus for ionizing a vapor or gas.

While the salient features of this invention have been described in detail with respect to one embodiment, it will, of course, be apparent that numerous modiiications may be made within the spirit and scope of the present invention and it is therefore not desired to limit the invention to the exact details shown except insofar as they may be defined in the following claims.

What is claimed is:

1. An isotope separator for determining the mass units of a test material comprising an evacuated chamber, means for ionizing said test material, electric field means for linearly accelerating said ions through said chamber in accordance' with their mass units, a pair of accelerating grids disposed in the path of said ions, means connected between said grids for impressing linearly varying voltage, an electrostatic deflecting chamber disposed in the path of said ions beyond said accelerating grids, and means for collecting said ions within said defiection chamber.

2. An isotope separator for determining the mass units of a test material comprising an evacuated chamber, a plurality of linearly disposed tube sections within said chamber, means for ionizing said test material disposed at one end of said tube sections, electrical means for establishing accelerating electric fields between said tube sections whereby said ions are accelerated and linearly separated in accordance with their mass units, a pair of accelerating grids disposed transversely in the path of said ions in spaced-apart relation, accelerating voltage means applied between said accelerating grids, an electrostatic ion deflector disposed adjacent said grids and parallel to the path of said ions for the lateral deflection of said ions, and means for determining the disposition of said ions in said electrostatic ion defiector.

3. An isotope separator for determining the cylindrical tube 52; the

mass units of a test material comprising an evacuated chamber, a plurality of linearly disposed tube sections within said chamber, means for ionizing said test material at one end of said tube sections, resistance means connected between said tube sections, electrical means connected across said linearly disposed tube sections for establishing accelerating electric fields between said tube sections, ion accelerating grids disposed at the other end of said tube sections, an electrostatic deflection chamber disposed in the ion path beyond said accelerating grids whereby said ions are deflected radially outward from their normal paths, and ion collecting means disposed in the path of the deflected ions.

4. An isotope separator for separating a test material according to its mass units comprising an evacuated chamber, means for ionizing said test material, electric field means for linearly accelerating said ions through said chamber for linearly separating said ions according to their mass units, accelerating grids disposed in the path of said ions, a saw-tooth accelerating voltage applied between said accelerating grids whereby ions are accelerated according to the voltage existing between said accelerating grids at their time of arrival thereat, an axial electrode disposed in the path of said ions beyond said accelerating grids, a closed cylindrical electrode disposed coaxially about said axial electrode, a unidirectional voltage applied between said axial electrode and said cylindrical electrode, and a photographic film axed to the interior surface of said cylindrical electrode.

5. A isotope separator for separating ions according to their mass units comprising a time-offiight mass spectrograph for linearly bunching.

ions according to their mass units, accelerating means disposed in the path of said ions, whereby said ions are forwardly accelerated according to their time of arrival at said accelerating means, electrostatic means for radially deflecting said ions from the ion path, and ion collection means disposed in the path of the defiected ions.

'6. An isotope separator for separating ions according to their mass units comprising a time-ofight mass spectrograph for linearly bunching ions according to their mass units, accelerating grids disposed in the path of said ions, a sawtooth accelerating voltage applied between said accelerating grids whereby ions are accelerated according to the voltage existing between said accelerating grids at their time of arrival thereat, an axial electrode disposed in the path of said ions beyond said accelerating grids, a cylindrical electrode enclosing said axial electrode and coaxial therewith, a unidirectional voltage applied between said axial electrode and said cylindrical electrode, and ion detecting means afiixed to the interior surface of said cylindrical electrode.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,582,216 Koppius Jan. 15, 1952 2,642,535 Schroeder June 16, 1953 OTHER REFERENCES