US2793295A

US2793295A - Mass spectrometer

Info

Publication number: US2793295A
Application number: US406746A
Authority: US
Inventors: William C Wiley
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1954-01-28
Filing date: 1954-01-28
Publication date: 1957-05-21
Anticipated expiration: 1974-05-21

Description

W. C. WILEY MASS SPECTROMETER May'zl, 1957 Filed Jan. zaza, 1954 3 'Sheets-Sheet l A IN1/Emmy` A L//a/A/Vc, L//LEV .'5 Sheets-Sheet 2 lFfiltad Jan. 28. 1954 INVENTOR.

L//LL/AM CLJ/5V www@ M2 May 21, 1957 Filed Jan. 28, 1954 W. C. WILEY MASS SPECTROMETER 3 Sheets-Sheet C5 INVENToR.

L//LL/AM 6. A//4EV MRM 14770)?/VEV irons.

Sie@ Parent MASS SPECTROMETER William C. Wiley, Detroit, Mich., assigner to Bendix Aviation Corporation, Detroit, Mich., acorporation of Delaware Application January 28, 1954, Serial No. 406,746

Claims. (Cl. Z50-41.9)

IThis application is a continuation/in part of copending VapplicationSerial No. 325,082 led December 10, I1952, 'byWilliam C. Wiley-and now abandoned.

-Thislli-nv'ention vrelates to mass spectrometers, and more particularly to fma'ssspectrometers for producing relatively strong and clear indications as to the masses of different ions.

Some mass-spectrometers utilize' pulses of ions to deter- In these spectrometers, ions The ions of relatively light mass .have `a-greater velocity imparted to them by theforce thanfthe ions of heavy mass, thereby travelling through -the predetermined distance before'the ions'of heav)l mass. l'By measuring the relative times 'atwhich the ions of`diiierent mass travel through'the predetermined distance, the masses of the ions can be determined.

Since the ions are rmoving in pulse form, the number of ions in each pulse is relatively limited. This Vcauses signals of relatively weak strength to be produced by the ions after their movement through the predetermined distance. :Because of the relative weaknessof the signals, amplifiers are 'employed to increase thestrength vof the signals so that clear indications of the ion fmassescan be obtained.

In some time-of-ight mass :'spectrometers now in use, electronic amplitiers'are'emplo'yed to increase the strength of the Voutput signals. These amplifiers `varefairly expen- -sive because they must have a large .gain and 'afsensitive response overa -widerange 'of frequencies. Other mass spectrometers now in use 'employ `-electron :multipliers Lto increase the strength of the output signals. :Such multipliers have not been entirely successful fsincethey require a large amount of space to produce a satisfactory gainlin signal strength. Because of their excessive 'size,.theielec tron multipliers now used in time-of-ight mass -spectrometers are also yheavy and costly.

This invention provides a mass spectrometer which ampliiies the output signals fromwthe spectrometer simply, efficiently and inexpensively. The rvamplification is :provided by an electron multiplier having a Aiirst pluralityfof plates for collecting dilerent lateral portions of each ion pulse. Each plate in the rst plurality produces a number of electrons proportional to the number of ions collected by the plate and directs these electrons towards successive plates in the plurality. The eleetron'multiplier also includes a second plurality of plates, a first' one of which receives electrons from the rst plurality of plates and produces a proportionately increased number of elec- Each of the other platesin the second plurality receives electrons from a preceding plate in the plurality and produces'a proportionately increased number of electrons. The output signals from the spectrometer areiobtained by collecting the electrons emitted by ythe last .plate inthe'second plurality.

2,7 93,295 'Patented May 2 1, 1957 vIce 2 An object of this invention is to provide a mass spectrometer forproducing a kpulse of ions and for lmposing aiforce on vthe ionsto' produce a separation of the ions on thefbasis of their mass during their travel through a predetermined distance.

:multiplier of relatively small size and weight to consid- Verably-am'plify the output signals produced by the ions.

Astill further object is' to provide a mass spectrometer `of the above vcharacter which includes an electron multiyplierso.constructedas to receive ion pulses of relatively large' widthand Sto amplify without any material distortion the signals'fproducedlby the ions ineach pulse.

Other 'objects andA advantages will be apparent from a .detailed"description of the invention 'and from the appended drawings' and claims.

flnfthedrawin'gs fFiguref lis-a somewhat vschematic View, partly in 'block form andipartly" in perspective, illustrating the electrical and mechanical features constituting one embodiment lof the invention;

y VFigurel2 lis. an :enlargedperspective view illustrating in detail oneembodimentlof Ian-electron multiplier forming apart of the masslspec'trometer shown in Figure. 1, certain .members Y'being broken away to'indicate other members more clearly; and

Figure "3 issan enlarged, simplified plan view of the embodiment of the electron multiplier shown in Figure 2 and schematically.illustratesrtheroperation of the `multiplier.

InY one embodiment :ofv the invention, a wedge-shaped filament 10 made from a suitable material such as tungsten isprovided. An electrode 12 is disposed at a 'relatively close-'distance to the filament 10,'such as '2 millimeters, and is` provided with af'vertical slot 14, the inter- Vmediateposition of -which is at substantially the same ver ticallevel'as the filament 10. An electrode 16 having a slot 718 corresponding substantially in shape and position to the slot 14 is separated from the electrode 12 by a relatively-small distance, such as 2 millimeters, and is in substantially Aparallel relationship to the electrode. A collector 20 is positioned at a relatively great distance from the electrode 16'1and in substantially parallel relationship totheelectrode.

vA `backing plate 22 is disposed in substantially perpendicular relationship to the electrode 16 and the collector v20rat an intermediate position' between the electrode and the collector. The plate y22 is positioned slightly to the rear of an imaginary line extending from the Atip of the lament 10 through the slots 14 :and 18 to the collector 20. An electrode 24 is separated :from the backing plate 22 by a relatively small distance, :such as '2 millimeters, so as to be positioned slightly infront of the imaginary line disclosed above. The electrode is disposed in substantially parallel relationship with the backing plate 22 and is provided with a horizontalslot 26.

Top and bottom slats 128 extend from the 'backing plate 22 to the electrode 24 lto form a compartment with the electrode 161 and the 'collector 20. A horizontal slot 30 is provided fin the bottom "slot 28 at a position directly below the imaginary line disclosed above. A conduit 32 communicates at one end with the slot 30 and at the other end with a receptacle 34 adapted to hold the molecules of the different gases and vapors in an unknown mixture.

An electrode 36 having a slot 38 corresponding substantially in shape and position to the slot 26 is disposed at a relatively small distance, such as 2 millimeters, in front of the electrode 26. An electrode 40 is positioned at a relatively great distance, such as 40 centimeters` from the electrode 36 and in substantially parallel relationship to the electrode 36. The electrode 40 is provided with a slot 42 corresponding in position to the slot 3S but slightly larger in its dimensions than the slot 38. The slot 42 is covered by a suitable wire mesh. The electrode 40 is provided at its left extremity with an auxiliary portion 43 which is slightly to the rear of the main portion of the electrode and substantially in parallel with such main portion.

An electron multiplier 44 is disposed at a moderate distance, such as 2 centimeters, in front of the electrode 40 to receive the ions passing through the slot 42. Although the electron multiplier may be considered as including the electrode 40, the electrode is shown separately in Figure l for purposes of providing clarity in the disclosure of the operation of the mass spectrometer. As will be disclosed in detail hereinafter, the electron multiplier 44 has a plurality of plates to produce a considerable gain in the signals which are formed when the ions reach the electron multiplier. A time indicator, such as an oscilloscope 46, is connected to an output terminal of the electron multiplier to show the relative times at which the ions of different mass reach the electron multiplier. An input terminal of the oscilloscope 45 is also connected to an output terminal of a pulse forming circuit 47 such that the sweep of the oscilloscope beam is initiated by a pulse from the circuit 47.

The electrode 12 normally has a positive voltage applied to it through a resistance 48 from a suitable power supply 50. A positive voltage of relatively low magnitude is applied to the collector 20 through a resistance 52 so that the collector will attract electrons owing through the slot 18 and electrons secondarily emitted from it by the impingement of the electrons from the filament 10. The filament 10, the backing plate 22 and the electrode 24 are connected to grounded resistances 54, 56 and 58, respectively, so as to be substantially at ground in the steady state operation. The electrodes 16, 36, and 40 are directly grounded.

The electrons emitted by the filament 10 are attracted towards the electrode 12 because of the positive voltage on the electrode 12 with respect to the voltage on the filament. ln the steady state operation, the electrons are decelerated in the region between the electrodes 12 and 16 since the electrode 16 is at a lower potential than the electrode 12. This prevents any electrons from travel ing into the region between the backing plate 22 and the electrode 24 to ionize molecules of gas or vapor introduced into the region.

At predetermined times, negative pulses of voltage are applied to the filament 10 and the electrode 12 through coupling capacitances 60 and 62, respectively, from the pulse forming circuit 47. Upon the imposition of the voltage pulses, the voltage on the electrode 12 becomes negative with respect to the voltage on the electrode 16. This causes the electrons passing through the slot 14 to be accelerated in the region between the electrodes 12 and 16 and to pass through the slot 18 into the region between the backing plate 22 and the electrode 24.

Because of the acceleration imparted to the electrons by the electrodes 12 and 16, the electrons have a considerable amount of energy as they pass through the region between the backing plate 22 and the electrode 24. This causes the electrons to strike with considerable force molecules of gas or vapor introduced into the region from the receptacle 34 and to ionize the molecules into electrons and positive ions, most of which have a single positive charge.

The ions produced from molecules of gas or vapor are retained in the electron stream because of the opposite charge of the ions relative to the charge of the electrons. Since the electron stream has a relatively large negative charge, a considerable number of ions can be retained in the stream before the stream becomes saturated. The ions are retained in a relatively confined region because of the collimating action which is provided by the slots 14 and 18 and which may be provided by a magnetic field (not shown).

When a considerable number of ions have been formed for retention in the electron stream, the electron stream is interrupted by cutting off the pulses of voltage on the filament 10 and the electrode 12. By interrupting the electron stream, the ions retained in the stream are made available for easy withdrawal from their place of retention. The withdrawal of the ions is effectuated by the imposition of pulses of voltage on the backing plate 22 and the electrode 24. These pulses of voltage are applied to the backing plate 22 and the electrode 24 through suitable coupling capacitances 64 and 66 from the pulse forming circuit 47. r[he pulses of voltage on the backing plate 22 and the electrode 24 may be approximately +200 and volts, respectively.

Since the voltage pulse applied to the backngplate 22 is greater than the voltage pulse applied to the electrode 24, the ions are repelled by the plate 22 towards the electrode 24. The force imposed on the ions in the region between the backing plate 22 and the electrode 24 causes ions of relatively light mass to have a greater acceleration imparted to them than ions of heavy mass. The ions are further accelerated in the region between the electrodes 24 and 36 because of the voltage pulse on the electrode 24 relative to the ground potential on the electrode 36. The ions then travel through the region between the electrodes 36 and 40 at substantially the same velocities as that attained by them during their movement through the slot 38.

During their travel through the region between the electrodes 36 and 40, the ions become clearly separated on the basis of their mass. After traveling through the slot 42 in the electrode 40, the ions 'are attracted to the elec tron multiplier 44 to produce signals indicative of the relative times at which the ions of different mass reach the multiplier. The signals produced by the electron multiplier are indicated by the oscilloscope 46.

The imposition of the particular voltage pulses on the backing plate 22 and the electrode 24 provides a compensation for the differences in the positioning and in the random motion of individual ions during the time that the ions are retained in the electron stream. The differences in positioning of individual ions result from the fact that the electron stream has a finite width. The differences in the random motion of the individual. ions are produced as a result of thermal and other energy in the ions. Because of the differences in random motion, some of the ions are traveling towards the backing plate 22 and other ions are traveling towards the electrode 24 at the instant that they are accelerated towards the electrode. By providing a compensation for the differences in positioning and random motion of individual ions, a relatively sharp delineation between ions of different masses is obtained. The compensation provided by the imposition of the particular voltage pulses on the plate 22 and the electrode 24 is fully disclosed in :zo-pending application Serial No. 249,318 filed October 2, 1951, by

'William C. Wiley, now Patent No. 2,685,035 issued July One embodiment of the electron multiplier 44 shown in Figure l is illustrated in detail in Figures 2 and '3. The electron multiplier includes a plurality of plates such as plates 80, 82, 84, 86, 88 and 90. The plates are disposed in lateral relationship to each other such that the right extremity of each plate as shown in Figures 2 and 3 is contiguous to the left extremity ofan adjacent plate.

averages The plate 80 is further away from the `electrode 40 than any of the other plates, and each of the successive plates is disposed at a progressively closer distance to the electrode 40. The plates .80,.82 and 84 are disposed in front of the slot 42 inthe electrode 40 to receive different lateral portions `ofeach ionpulse that travelsthrough the slot.

The plates .S2 and 84 havesubstantially equal lateral dimensions but theplatef80 has a lateral dimension somewhat greaterthan. that provided for the plates 82 and 84. The plate 80 is disposed so that its right lateral portion isout of alignment withftheslot 42 in the electrode 40.

'.In'this way, the plate 80 receives a lateralA portion of the 'from the first portion in a directionsubstantially,perpendicular to the first portion and at aposition to `the left of the plate 90.

.A negative voltage of relatively large ymagnitude is applied to the plate 80 through a resistance y94 from a suitable high voltage power supply 96. Negative voltages of progressively decreasing magnitudes are applied to successive .plates in the plurality in accordance with the distance between each plate and the electrode 40. In this way, an electric field of .substantially constant .magnitude is produced between ,the electrode 40 -and each of theplates 80,82, :84,86, 88 and-90. Thepl-ate .92 is maintained at substantially :ground potential in its steady state operation because of its connection .to Va grounded resistance 98.

As a typical example, each of thefplates 80,82, 84,86, 88 and 90 may bemade from Va suitable material such kas beryllium copper having approximately 2% by Weight of beryllium. The plate 80 may be approximately-0.7" long as measured from right to left in Figure 2, and 'each of the otherplatesmayhave -a -length of approximately f/s in this direction. The height of each of the plates 80, 82, 84, 86, 88 and 90 as seen .inFigure 2 may be approximately l.

The plate 82 may be approximately 0.006" closer to the electrode -40 than the plate 80, and the .plate 8.4 may be a corresponding distance closer ,to theelectrode 40 than the plate 82. In like manner, the plates 86, 88 and 90 may be respectively closer to the electrode 40 than the plates 84, 86 and 83 by distances of approximately 0.022".

A voltage of approximately 4800volts may be applied to the plate 80 fromthe power supply 96, and voltages of approximately 4750 and --4700 volts may be applied to the plates l82 and 84, respectively. Voltages of approximately 4525, 4350 and 4175 'volts may be respectively applied to theplates :86, 88 and 90. A1- though each of the plates 80, 82, 84, 86, 88 and 90 has a different voltage applied to it, a substantially constant electric field is produced between the electrode 40 and the plates because of the differences in distance between the electrode 40 and the plates.

In the above example, a magnetic lield of approximately 340 Gauss may be produced by field poles 180 in the region between the electrode 40 and the plates 80, 82, 84, 86, 88 and 90. The magnetic field vis produced in a vertical direction substantially parallel to the faces of the plates 80, 82, 84, 86, 88 and 90.

Different lateral portions of each ion pulse traveling through the slot 42 impinge on the plates 80, 82 and 84. For example, the right lateral portion of each ion pulse 6 :as seen .in Figure .2' impinges onthe'plate 80. Because of'the material from which the .plate 80 Ais made, electrons are emitted fromY the surface of' the plate when the ions impinge on lthe plate. rThe number of electrons emitted by the plate ispproportional to the number of ions l'reaching th'e plate.

The V`electrons emitted'from the plateS travel in a vcycloidal path towardsthe plate v82 because of the combined action of the electric tield between the' electrode '40 and the plates and the magnetic iield vbetween the field poles 100. The cycloidalpath in which the electrons travel after leaving'the"plate"82 is illustrated at v102 4in Y Figurev 3.

At substantially'tlreendof` the cycloidal movement, the electrons impinge ontheplate 82. The 'electrons impinge -on the plate 82 with'a'suicie'nt force to cause electrons electrons emitted lbythe plate-82 are in turn subjected to a 4cycloidal movement.

The lz'l ratio' between the number of electrons imping- AVing on the platee82'and the numbero'f electrons emitted by `the plate is produced because `of 'the voltage difference betweenvthe` plates 80 and 82. On the basis of empirical studies, for example, a l1:1 ratio is produced when the plates v80 V'and S'2`have a composition of 2% beryllium copper and 'a voltage diierence of approximately 50 volts.

Since the plate T852; is'jpositionedlat an intermediate position with' respectto vthe lateral dimension of eachiorrpulse 'passing'through'theslot'42, it "receives the ions in the middle portionofJeah ion'pulse. Upon the impingenrent of these'ions, 'thev plate i8`2fproduce's Va' number of electrons proportionate 'to the number of vionsv impinging 'upon it. The proportion betweenrthe number of'electrons emitted "by the plate 82 andthenumber ofv ions impinging on 'the plateis substantially the'same as the proportion disclosed above for thev'plate 80.' 'The electrons 'emitted by -the lplate `321as -a result of the impingement of' ions upon the plate travel in substantially the same cycloi'dal 'path as the electrons which are 'emitted from the plate SZby the impingement 'of electrons from the plate 80.

In likemanner, the plate`84 produces electrons when the electrons lfrom theplate IS'Z'impin'ge on it. Theplate 84 also produces electrons when ions inthe :leftllateral portion of each'ion pulse travel 'through the slot 42in the electrode 40 and impinge on the plate. The electrons emitted bythe-plate 84 'travel in a cycloidal pathtowards the platev 86.

Because of the positioning of the plate 86, the plate does'not receive any of the ions in'each ion pulse. However, `the plate 86 does receive the electronstraveling towards it lfrom the plate84 and produces a proportionately increased number of electrons. A proportionately increased num'berof electrons is producedby the plate 86 because-of the dilierence in voltage between the plates 84 and 86. This diierence in voltage is determined empirically for each material that may be used. For example, a voltage difference of '175 volts between the plates 84 and 86 causes approximately twice as many electrons to be emitted by the plate 86 as by the plate 84 when the plates are made from 2% beryllium copper.

Similarly, the plate 88 emits a number vof electrons which is proportionately greater than the number of electrons traveling towards it in a cycloidal path from the plate 86, and :the plate 90 in turn produces a greater number of electrons 'than the number that is produced by the plate88. The electrons emitted by the plate 90 are collected by the plate 92, which produces output signals dependent upon 'the collection of electrons.

By providing a plurality of plates, each of which emits a greater number of electrons than its immediately preceding plate, a considerable gain in signal strength can be obtained over that produced by the ions in each ion pulse.

For example, it is possible to produce output signals having amplitudes substantially l million times as great as those produced by the ions in the ion pulse. The output signals are introduced to the oscilloscope 46 to provide a relatively sharp delineation between ions of diierent mass. Even though the ions in each pulse are received by a plurality of plates such as the plates 80, 82 and S4, output signals are produced which accurately indicate the relative abundance of te different ions in the pulse. Accurate signals are produced because the electrons emitted by the plate 80 travel to the plate 82 and cause substantially the same number of electrons to be emitted by the plate 82. A similar 1:1 ratio exists at the plate 84 between the number of electrons traveling towards the plate and the number of electrons emitted by the plate. In this way, the plate 84 produces a number of electrons corresponding to that which would have been produced if all of the ions in each pulse impinged on the plate.

By employing a plurality of plates to receive dilerent lateral portions of each ion pulse, the length of each of the plates 80, 82, and 84 as measured in a horizontal direction in Figures 2 and 3 can be maintained at a relatively moderate value. Since the lengths of the plates 86, 88 and 90 have to correspond substantially to the lengths of the plates which receive the ions, such as the plates 80, 82 and 84, the plates 86, 88 and 90 can also have moderate lengths. In this way, the overall length of the electron multiplier is maintained within reasonable limits without any material sacrifice in the gain produced by the electron multiplier. Because of the reduction in size, the weight of the electron multiplier is also relatively low, and its cost of manufacture is relatively inexpensive.

It should be appreciated that the time required for the electrons from each plate to travel to and impinge upon the successive plate in the plurality is in the order of 7 104 microseconds. For example, the electrons leaving the plate 80 require approximately only 7X10-4 microsecond to reach the plate 82. Since this period of time is considerably less than the 0.05 microsecond period required for the ions of a particular mass in each pulse to impinge on the electron multiplier, the use of a plurality of plates does not materially cloud the measurements that are obtained. Because of this, a relatively sharp deliniation is provided by the mass spectrometer between ions of adjacent mass units.

It should be appreciated that the electron multiplier disclosed above can be used in other apparatus than mass spectrometers to amplify the signals produced by an ion beam. Actulally, the electron multiplier can be used with any apparatus which produces a stream of discrete particles. Such particles may have no charge or may have a positive or negative charge. The positively charged particles may include ions and the negatively charged particles may include electrons. For example, the electron multiplier may be used in conjunction with nuclear equipment to detect and amplify the signals produced by atoms, neutrons or electrons.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved `are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

What is claimed is:

l. A mass spectrometer, including, means for providing a plurality of ions, means for accelerating the ions in a lateral beam to produce a separation of the ions on the basis of their mass, a lirst plurality of plates, each of the plates in the first plurality being disposed to collect a different lateral portion of the ion beam and to produce a plurality of electrons substantially the same proportion to the number of ions collected as produced by the other plates in the lirst plurality, means for moving the electrons produced by each of the plates in the rst plurality towards successive plates in the rst plurality to produce in each successive plate a number of electrons substantially the same as the number of electrons received by each plate, a second plurality of plates, each of the plates in the second plurality being adapted to receive the electrons produced by a preceding plate and to produce a proportionately increased number of electrons, the rst plate in the second plurality being adapted to receive the electrons traveling from the plates in the rst plurality, and means for indicating the relative times at which electrons are produced by the last plate in the second plurality.

2. A mass spectrometer, including, means for producing a plurality of ions, means for accelerating the ions in a lateral beam to produce a separation of the ions on the basis of their mass, rst and second series of plates disposed in lateral relationship to one another, each of the plates in the lirst series being disposed to collect a different portion of the ion beam and to produce a number of electrons in substantially the same proportion to the number of ions collected as are produced by the other plates in the first plurality, means operative on the plates in the iirst and second series to produce a cycloidal movement of the electrons emitted by each plate towards the next plate in the series, each of the plates in the first series being adapted to receive electrons from a preceding plate and to produce substantially the same number of electrons as are received by the plates, each of the plates in the second series being adapted to receive the electrons from ya preceding plate and to produce a proportionately increased number of electrons, a iirst plate in the second series being adapted to receive the electrons traveling from the plates in the first series, and an indicator for determining the relative times at which electrons are produced by the last plate in the second series.

3. A mass spectrometer, including, means for providing a plurality of ions, rneans for accelerating the ions longitudinally in a beam having a substantially tinite lateral dimension, a plurality of plates disposed in lateral relationship to one another and in a progressively longitudinal relationship, iirst plates in the plurality being disposed to receive different lateral portions of the ion beam -and to produce a number of electrons proportionate to the number of ions in the beam portion, each of the Erst plates being adapted to receive the electrons from a preceding one of the first plates and to produce substantially the same number of electrons that it receives, second plates in the plurality being adapted to receive electrons from a preceding plate in the plurality and to produce `a proportionately increased number of electrons, and an indicator for providing a determination of the relative times at which electrons are produced at the last of the plates in the second plurality.

4. A mass spectrometer, including, means for providing a plurality of ions, means for accelerating the ions in ya lateral beam to produce a separation of the ions on the basis of their mass, a first plurality of plates arranged in staggered relationship to one another to receive different lateral portions of the ion beam land to produce at each plate a plurality of electrons in the same proportion to the number of ions received as are produced at the other plates in the iirst plurality, each plate in the tirst plurality being disposed relative to an adjacent plate to receive the electrons produced by an adjacent plate and to produce substantially the same number of electrons as are received, a second plurality of plates arranged in staggered relationship t0 one another, the first plate in the second plurality being disposed relative to the last plate in the lirst plurality to receive the electrons produced by the last plate and to produce -a proportionately increased number of electrons, each of the other engages plates in lthe second plurality being disposed to receive the electrons produced by a preceding plate in the plurality and to produce a corresponding number of electrons, and means for indicating the relative times at which electrons are produced by the last plate in the second plurality.

5. A mass spectrometer, including, means for providing a plurality of ions, means for accelerating the ions in a lateral beam to produce a separation of the ions on the basis of their mass, a rst plate disposed to receive the ions traveling in a first lateral portion of the beam after Ithe travel of the ions through a relatively great distance and to produce a plurality of electrons in a first proportion to the number of ions received by the plate, -a second plate disposed to receive the ions in a second lateral portion of the beam and to produce a plurality of electrons in substantially the first proportion to the number of ions received by the plate, the second plate being disposed relative to lthe first plate to receive the electrons emitted by the first plate and to produce substantially the same number of electrons as are received, a third plate disposed relative to the second plate to receive the electrons from the second plate land to produce an increased number of electrons, and means for producing signals in accordance with the relative times at which electrons are received by the third plate to indicate the relative mass and abundance of the different ions in the plurality.

6. A mass spectrometer, including, means for providing a plurality of ions, means for accelerating the ions in a lateral beam to produce a separation of the ions on the basis of their mass, a plurality of plates disposed in staggered relationship to one another, a first plate in the plurality being ladapted to receive a first lateral portion of the ion beam and to produce Ia proportionately increased number of electrons, a second plate in the plurality being adapted to receive a second lateral portion of the ion beam and to produce la number of electrons having substantially the same proportion to the number of ions as the proportion between the number of electrons produced by the first plate and the number of ions received by tne plate, the second plate being disposed relative to the first plate to receive the electrons produced by the first plate and to produce substantially the same number of electrons as are received, a third plate in the plurality being disposed relative to the second plate to receive the electrons produced by the second plate and to produce a proportionately increased number of eelotrons, and means for indicating the relative times iat which electrons are produced by the third plate.

7. A mass spectrometer, including, means for producing a plurality of ions, means for accelerating the ions in a lateral beam to produce a separation of the ions on the basis of their mass, a plurality of plates disposed in staggered relationship to one another, a first plate in the plurality being disposed to receive a first portion of the lateral beam and to produce a plurality of electrons bearing a first proportion compared to the number of ions received by the plate, a second plate in the plurality being disposed to receive a second portion of the lateral beam and to produce a plurality of electrons bearing substantially the first proportion compared to the number of ions received by the plate, the second plate being disposed relative to the rst plate to receive the electrons produced by the first plate and to produce substantially the same number of electrons as the number of electrons received by it, a third plate in the plurality being disposed relative to the second plate to receive the electrons produced by the 'second plate and to produce a proportionately increased number iof electrons, and means for indicating the relative times at which electrons are produced by the third late.

p 8. In combination, means for providing a plurality of particles and for directing the particles in a lateral beam, a first plate disposed to receive the particles in a first lateral portion of the beam after the travel of the particles through a particular distance and to produce a plurality of electrons in a first proportion to the number of particles that it receives, a second plate disposed to receive the particles in a second lateral portion of the beam and to produce a plurality of electrons in substantially the first proportion to the number of particles that it receives, the second plate being disposed relative to the first plate to receive the electrons emitted by the first plate and to produce substantially the same number of electrons as are received by it, a third plate disposed relative to the second plate to receive 4the electrons emitted by the second plate and to produce a proportionately increased number of electrons, and means for producing signals indicative of the electrons produced by the third plate.

9. In combination, means for providing a plurality of particles and for directing the particles in a lateral beam, a first plate disposed to receive the particles -in a first lateral portion of the beam after the travel of the particles through a particular distance and to produce a plurality of electrons in a first proportion to the number of particles it receives, a second plate disposed to receive the particles in a second lateral portion of the beam and to produce a plurality of electrons in substantially the first proportion to the number of particles it receives, means for providing an electrical field in a direction substantially perpendicular to the plates, means for providing a magnetic field in a direction substantially parallel to the plates to cooperate with the electrical field in producing a movement of the electrons emitted by each plate to a successive plate for the emission of electrons by the successive plate, the second plate disposed to receive the electrons emitted by the first plate and to produce substantially the same number of electrons as are received by it, a third plate disposed relative to the second plate to receive the electrons emitted by the second plate and to produce a proportionately increased number of electrons, and means for producing signals indicative of the electrons emitted by the third plate.

10. In combination, means for providing a plurality of particles and for directing the particles in a lateral beam, a first plate disposed to receive the particles in a first lateral portion of the beam after the travel of the particles through a particular distance and to produce a plurality of electrons in a first proportion to the number of particles it receives, a second plate disposed to receive the particles in a second lateral portion of the beam and to produce a plurality of electrons in substantially the first proportion to the number of particles it receives, the second plate being disposed relative to the first plate to receive the electrons emitted by the first plate and to produce substantially the same number of electrons as are received by it, a third plate disposed relative to the second plate Ito receive the electrons emitted by the second plate and to produce a proportionately increased number of electrons, means for providing electrical and magnetic fields in directions to produce a movement of electrons from the first plate to the second plate and from the second plate to the third plate, and means for producing silgnals indicative of the electrons produced by the third p ate.

References Cited in the le of this patent UNITED STATES PATENTS 2,664,515 Smith Dec. 29, 1953