US2778944A - Electron multiplier - Google Patents

Description

Jan. 22, 1957 HARRINGTON 2,778,944

ELECTRON MULTIPLIER 3 Sheets-Sheet l Filed Jan. 1 9, 1953 INVENTOR DAN/[L 8. flMI/MWON MKW ATTORNEY Jan. 22, 1957 Filed Jan. 19, 1953 D. B. HARRINGTON 2,778,944

ELECTRON MULTIPLIER 3 Sheets-Sheet 2 MR-m 3 Sheets-Sheet 3 Filed Jan. 19, 1953 ATTORNEY United States Patent O ELECTRON MULTIPLIER Daniel B. Harrington, Detroit, Mich., assignor to Bendix Aviation Corporation, Detroit, Mich., a corporation of Delaware Application January 19,1953, Serial No. 331,882

14 Claims. (Cl. 250-419) This invention relates to mass spectrometers and more particularly to mass spectrometers for producing relatively strong and clear output signals so as to provide a sharp delineation between ions of different mass.

In some types of mass spectrometers, pulses of ions are utilized to distinguish between ions of different mass in an unknown mixture and to determine the relative abundance of the difierent ions in the mixture. The ions are formed from molecules of the different gases and vapors in the unknown mixture and are accelerated by a force from their place of formation after a relatively large number have been produced. The ions of relatively light mass have a greater velocity imparted to them by the force than the ions of heavy mass. Because of the diiferences in velocity, the ions of light mass travel through a predetermined distance before the ions of heavy mass and produce output signals atthe detector before the ions of heavy mass. By measuring the times at which the different signals are produced, the masses of the ions can be determined.

Since only a finite number of ions can be retained for acceleration in each pulse, the signals produced by the ions are relatively weak. Because of their weakness, the signals produced by the ions must be amplified considerably to produce output signals which provide a clear delineation between ions of adjacent atomic mas-s.

In some time-of-flight mass spectrometers now in use, the ampification is obtained by a plurality of electronic amplifier stages. In order to produce accurate output signals, such amplifiers have had to operate satisfactorily over a wide range of frequencies. As a result, such amplifiers have been relatively expensive. In other timeof-fiight mass spectrometers now in use, electron multipliers have been employed. Such electron multipliers have been disadvantageous because they have had to be bulky in order to produce a sufficient amplification. The large size of the electron multipliers has also caused them to be expensive.

This invention provides a time-of-fiight mass spectrometer having an electron multiplier which produces a considerable gain in amplification and which is relatively compact and inexpensive. The electron multiplier, includes a first plurality of plates, at least one of which is disposed to receive ions in each pulse and to produce a number of electrons in proportion to the number of ions that it receives. Other plates in the first plurality are disposed to receive electrons emitted by a preceding plate and to produce a proportionately increased number of electrons.

The electron multiplier also includes a second plurality of plates disposed in baek-to-back relationship to the first plurality, such that the second plurality is displaced from the first plurality in the direction of ion flow. A first plate in the second plurality is positioned to receive the electrons emitted by the last plate in the first plurality and to produce a proportionate number of electrons. Other plates in the second plurality receive electrons from a preceding plate in the plurality and produce a "ice proportionately increased number of electrons. The output signals are obtained by collecting the electrons emitted from the last platein the second plurality.

An object of this invention is to provide a mass spectrometer for producing pulses of ions and for measuring the time required for the ions of each mass in the pulse to travel through a predetermined distance.

A further object is to provide a mass spectrometer of the above character which includes a relatively compact and inexpensive electron multiplier for measuring the times required for the ions of diflerent mass to travel through the predetermined distance.

A further object is to provide a mass spectrometer of the above character having an electron multiplier for producing a considerable gain in the signals produced by the ions in each pulse so as to obtain a relatively sharp delineation between ions of adjacent atomic mass units over a wide range of values.

Still another object is to provide a mass spectrometer of the above character having an electron multiplier formed from a first plurality of plates which are disposed to face the flow of ions and a second plurality of plates disposed in opposed relationship to the first plurality of plates.

A still further object to provide a mass spectrometer of the above character having an electron multiplier formed from two pluralities of plates disposed in backto-back relationship to increase-the gain in the output signals Without any material increase in the space occupied by the multiplier.

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

In the drawings:

Figure l is a somewhat schematic View, partly in block form and partly in perspective, illustrating one embodiment of the invention;

Figure 2 is an enlarged perspectiveview illustrating in detail the electron multiplier shown in block form in Figure 1; and

Figure 3 is a top plan view of the electron multiplier shown in Figure 2.

In one embodiment of the invention, a wedge-shaped filament ltlmade from a suitable material such as tungsten is provided. An electrode 12 is disposed at a relatively close distance, such as 2 millimeters, from the filament 10. The electrode 12 is provided witha vertical slot 14, the median position of which is at substantially the same. horizontal level as the filament.

An electrode 16 having a slot 18 corresponding substantially in shape and position to the slot 14 is positioned at a relatively close distance, such as 2 millimeters, from the electrode 12 and in substantially parallel relationship to the electrode. A collector 20 is substantially parallel to the electrode 16 at a relatively great distance from the electrode.

A backing plate 22 is positioned between the electrode 16 and the collector 20 and in substantially perpendicular relationship to the electrode and the collector. The backing plate 22 is slightly to the rear of an imaginary line extending from the tip of the filament 10 through the slots 14 and 18 to the collector 20.

An electrode 24 having a substantially horizontal slot 26 is subsantially in parallel with the backing plate 22.

ment with the electrode 16 and the collector 26. A horizontal slot 3%) is provided in the bottom slat 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 difierent 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 short distance, such as 2 millimeters, in front of the electrode 24 and in substantially parallel relationship to the electrode. An electrode 49 is disposed at a relatively great distance, such as 40 centimeters, in front of the electrode 36 and in substantially parallel relationship to the electrode.

The electrode 40 is provided with a slot 42 covered by a suitable wire mesh. The slot 42 corresponds substantially in position to the slots 26 and 38 but is slightly larger in shape than the slots 26 and 38. The electrode 40 is also provided with an auxiliary portion 43 integral with the main portion of the electrode. The auxiliary portion 43 is substantially parallel to, and slightly to the rear of, the main portion of the electrode 4%.

An electron multiplier 44 is positioned at a moderate distance from the electrode 40 and in substantially parallel relationship to the electrode. Although the electron multiplier 44 may be considered as including the electrode 40, the electrode 40 is shown separately in Figure 1 for reasons which will be more clearly understood hereinafter. The electron multiplier 44 is connected to an input terminal of a time indicator, such as an oscilloscope 46, another input terminal of which is connected to an output terminal of a pulse forming circuit 47.

A positive voltage is normally applied to the electrode 12 through a resistance 48 from a suitable power supply St A slightly positive voltage is also applied from the power supply 50 through a suitable resistance 52 to the collector 20 so that the collector will attract back to it electrons secondarily emitted from it upon the impingement of electrons from the filament 10. The filament 10, the backing plate 22 and the electrode 24 are maintained substantially at ground potential in the steady state operation because of their connections to grounded resistances 54, 56 and 58, respectively. The electrodes 16, 36 and 40 are directly grounded.

Electrons emitted from the filament are attracted towards the electrode 12 because of the positive voltage on the electrode relative to the voltage on the filament. 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 deceleration prevents electrons from entering into the region between the backing plate 22 and the electrode 24 to ionize molecules of gas introduced into the region from the receptacle 34.

At predetermined times, negative pulses of voltage of substantially equal magnitudes are respectively applied from the pulse forming circuit 47 through suitable coupling capacitances 60 and 62 to the filament 10 and the electrode 12. Upon the imposition of a negative pulse of voltage on the electrode 12, the voltage on the electrode becomes negative with respect to the voltage on the electrode 16. This causes the electrons flowing through the slot 14 to be accelerated towards the elec trode 16 and to enter the region between the backing plate 22 and the electrode 24 with sufficient energy to ionize molecules of gas and vapor that they may strike. Upon the ionization of the molecules of gas and vapor, electrons and positive ions are formed, most of the ions having a single positive charge.

The ions produced from the molecules of gas and vapor are retained in the electron stream because of their opposite charge relative to the charge of the stream. Because of the relatively large charge on the electron stream, a considerable number of ions can be retained in the stream before the stream becomes saturated. The ions are retained in a relatively narrow space as a result .4 of the collimating action which is provided by the slots 14 and 18 and which may be provided by a suitable magnetic field (not shown).

When the number of ions in the electron stream approaches saturation, the electron stream is interrupted by cutting oil the voltage pulses on the filament 1t) and the electrode 12. Upon the interruption of the electron stream, the ions become available for easy withdrawal from their place of retention. The withdrawal is effectuated by the imposition of pulses of positive voltage on the backing plate 22 and the electrode 24. These voltage pulses are respectively applied to the backing plate 22 and the electrode 24 through suitable coupling capacitances 64 and 66 from the pulse forming circuit 47. The pulses applied to the backing plate 22 and the electrode 24 may be approximately +200 and +150 volts, respectively.

The voltage pulses applied to the backing plate 22 and the electrode 24 cause an electrical field of moderate intensity to be produced between the backing plate 22 and the electrode 24 and an electrical field of considerable intensity to be produced between the electrodes 24 and 36. Because of the electrical fields produced by the voltage pulses, the ions are moderately accelerated in the region between the backing plate 22 and the electrode 24 and considerably accelerated in the region between the electrodes 24 and 36. These accelerations cause the ions of relatively light mass to attain a greater velocity than the ions of heavy mass during their movement towards the electrode 36.

Upon their movement through the slot 33 in the electrode 36, the ions travel at substantially the same velocities as that attained by them during their movement towards the slot 36, since the electrodes 36 and 40 are both at ground potential. During their movements in the field-free region between the electrodes 36 and 40, the ions become considerably separated on the basis of their mass. The ions then pass through the slot 42 and impinge on the electron multiplier 44 to produce output signals on the oscilloscope 46. The relative times at which signals are produced on the oscilloscope 46 provide an indication of the masses of the different ions in the unknown mixture.

Because of the particular voltage pulses on the backing plate 22 and the electrode 24, compensation is provided for ditferences in the positioning and random motion of individual ions during the time that the ions are retained in their place of formation. The difi'erences in positioning of individual ions result from the finite width of the electron stream. Diflerences in the random motion of individual ions are produced by the thermal and other energy in the ions. The random motion causes some ions to be traveling towards the backing plate 22 and other ions to be traveling towards the electrode 24 at the time that the ions are withdrawn in a pulse. The compensatory action provided by the application of the particular voltage pulses on the backing plate 22 and the electrode 24 is fully disclosed in co-pending application Serial No. 249,318 filed October 2, 1951, by William C. Wiley.

In Figures 2 and 3, an embodiment of the electron multiplier 44 is illustrated in detail. In addition to the electrode 40 also shown in Figure l, the electron multiplier includes a first plurality of plates 70, '72, 74, 76, 78, 8t) and 32 and a second plurality of plates 84, 86, 38, 90, 92, 94 and 6. The plates 70, 72, '74, 76, 78, and 82 in the first plurality are disposed to face the ions flowing through the slot 42 in the electrode 40. The plates 34, 86, 88, 9t 92, 94 and 96 in the second plurality are disposed in back-to-back relationship to the plates in the first plurality so as to face in a direction substantially opposite to that in which the plates in the first plurality are facing.

The plates 70, 72, 74, 76, 80 and 82 are disposed in laterally contiguous relationship to one another such that the left extremity of each plate lies adjacent the right extremity of a successive plate. The plates 72, 74, 76, 78, 80 and 82 have substantially equal widths, but the plate 70 has a greater width than any of the other plates in the first plurality. For example, the plates 72, 74, 76, 78, 80 and 82 may have a width of approximately and the plate 70 may have a width of approximately 0.7". Each of the plates may have a height of approximately 1".

The plate 70 is disposed to receive a lateral portion of each ion beam passing through the slot 40 equal to substantially one-third the width of the beam. With this disposition, the right extremity of the plate 70 is positioned to receive the ions traveling at the fringe of the beam in a non-linear path through the slot 42 in the electrode 40. The plate 72 is disposed to receive the intermediate portion of each ion beam passing through the slot 42, and the plate 74 is disposed to receive the left portion of each ion beam as seen in Figures 2 and 3.

The plates 76, 78, 80 and 82 are disposed to the left of the slot 42, as seen in Figures 2 and 3. A first portion of an electrode 98 is positioned directly behind the plate 82 in substantial alignment with the main portion of the electrode 40. The electrode 98 also has a second portion integral with the first portion and extending in a direction substantially perpendicular to the first portion at a position to the left of the plate 82. The electrode 98 is connected to a grounded resistance 99 so as to be maintained at substantially ground potential in the steady state operation.

A negative voltage of relatively large magnitude is applied to the plate 70 through a resistance 100 from a power supply 102. For example, a. voltage of approximately 6200 volts may be applied to the plate 70. When the plates in the first and second pluralities are made from a beryllium copper alloy having approximately 2% by weight of beryllium, approximately -6l50 and 6100 volts may be respectively applied to the plates 72 and 74. The differences between the voltages on the plates 70, 72 and 74 are chosen on an empirical basis .for the particular materials used. The particular voltage differences are imposed on the plates 70, 72 and 74 so that the plates 72 and 74 will emit substantially the same number of electrons as the number of electrons that strike the plates. In like manner, potentials of approximately -5900, -5700 and 5500 volts are respectively applied to the plates 76, 78 and 80 to cause the plates to emit approximately twice as many electrons as the number of electrons impinging on them. These voltages are also emperically chosen to obtain the 2:1 ratio disclosed above.

Although different voltages are applied to the plates 70, 72, 74, 76, 78 and 80, the electrical field produced between the plates and the electrode 40 is substantially constant because of the differences in the longitudinal positioning of the plates. For example, the plate 70 may be positioned approximately 0.92 inch in front of theelectrode 40, and the plates 72 and 74 may be approximately 0.008 inch closer to the electrode 40 than the plates 70 and 72, respectively. Similarly, the plates 76, 78 and 80 may be approximately 0.030 inch closer to the electrode 40 than the plates 74, 76 and 78, respectively. For reasons which will be disclosed in detail hereinafter, the plate 82 is disposed further away from the electrode 40 than the plate 80 by a distance of approximately 0.010 inch. Because of this spacing, a potential of approximately 5565 volts is applied to the electrode 82 to maintain the substantially constant electrical field disclosed above.

An electrode 104 is disposed to the left of the plate 82 in substantially parallel relationship with the plate. The electrode 104 is disposed approximately 0.015 inch in back of the plate 82 and has a potential of approximately -5465 volts applied to it. The right side of the electrode 104 is formed from a plurality of tungsten wires 106, each of which is approximately 0.001 inch thick and is spaced approximately 0.010 inch from its adjacent wires.

The plate 84 is positioned in front of the plate 82 and is longitudinally separated from the electrode 104 by a distance of approximately 0.030 inch. The plates 86, 88, 90, 92, 94 and 96 are positioned approximately 0.030 inch in front of the plates 84, 86, 88, 90, 92 and 94, respectively. Each of the plates may have a width of approximately inch and .a height of approximately 1 inch.

An electrode 108 is positioned approximately 0.79 inch in front of the plate 84 and in substantially parallel relationship to the plate. The electrode 108 corresponds in construction to the electrode 40, except that it has no slot similar to the slot 42. The electrode 108 also performs certain functions similar to the electrode 40, as will be disclosed in detail hereinafter. In like manner, an electrode 110 corresponding in construction and function to the electrode 98-is associated with the plate 96. The electrode 110 is connected to a grounded resistance 112 so as to be maintained at substantially ground potential in the steady state operation.

Voltages of approximately 5265, -5065, 4865, 4665, 4465, -4265 and --4065 volts are respectively applied'to the plates 84, 86, 88, 90, 92, 94 and 96. The particular voltages are applied to the plates to produce a substantially constant electrical field between the plates and the electrode 108. The particular voltages are also applied to produce a 2:1 ratio between the number of electrons impinging on each plate and the number of electrons emitted by the plate.

In addition to the electrical fields produced between the first plurality of plates and the electrode 40 and between the second plurality of plates and the electrode 108, a magnetic field is also imposed on the electrons. As seen .in Figure 2, the magnetic field is imposed by a pair of field poles 114 such that the field extends in a vertical direction substantially parallel to the faces of the plates in the first and second pluralities. The field poles 114 are partially broken away in Figure 2 to show the other components in the electron multiplier 44 more clearly. In the particular example disclosed above, a magnetic field of approximately 314 Gauss may be applied between the field poles 114.

Difierent lateral portions of each ion pulse traveling through the slot 42 impinge on the plates 70, 72 and 74. For example, the right lateral portion of each ion pulse .as seen in Figures 2 and 3 impinges on the plate 70.

When the ions impinge on the plate 70, they cause a proportionate number of electrons to be emitted by the plate. The electrons emitted by the plate 70 are directed in a cycloidal path towards the plate 72 by the combined action of the electrical and magnetic fields in the region between the electrode 40 and the plates 70 and 72. This cycloidal path is illustrated at 116 in Figure 3.

When the electrons emitted by the plate 70 reach the plate 72, they cause a substantially equal number of electrons to be emitted by the plate 72. As previously disclosed, a 1:1 ratio is produced between the number of electrons impinging on the plate 72 and the number of electrons emitted by the plate because of the particular difference in the voltages applied to the plates 70 and 72.

The plate 72 also receives the ions in the intermediate lateral portion of each ion pulse and produces a number of electrons proportionate to the number of ions that it receives. This portion corresponds substantially to the proportion between the number of electrons emitted by the plate 70 and the number of ions impinging on the p ate.

The electrons emitted by the plate 72 travel in a cycloidal path 118 (Figure 3) towards the plate 74 and cause a substantially equal number of electrons to be emitted by the plate. The plate 74 alsoreceives the ions in the left lateral portion of each ion pulse and emits a by the electrical field produced '7 number of electrons proportionate to the number of ions that it receives. This proportion is substantially the same as the proportions disclosed above for the plates 70 and 72. The electrons emitted by the plate 74 travel in a cycloidal path 120 (Figure 3) towards the plate 76.

Because of the positioning of the plate 76, the plate does not receive any of the ions traveling in each pulse through the slot 42. The plate 76 does receive the electrons emitted by the plate 74 and emits a number of electrons proportionately greater than the number of electrons that it receives. With the particular voltage relationships disclosed above and with the plates made from a 2% beryllium copper material, the plate 76 emits ap proximately twice as many electrons as it receives.

In like manner, the plates 78 and 80 emit approximately twice as many electrons as the number of electrons that impinge on them. The electrons emitted by the plate 89 are directed in a cycloidal path 122 (Figure 3) towards the plate 82. Since the plate 82 is positioned in front of the plate 80, the electrons complete their cycloidal movement before they strike the plate 82. The electrons then start to move in a cycloidal path 124 towards the electrode 104.

Since the electrode 104 is spaced in back of the electrode 82, the electrons moving in the cycloidal path 124 (Figure 3) reach the electrode 164 before they complete the cycloidal movement 124. As previously disclosed, the electrode 104 is formed at its right extremity from a plurality of spaced wires 106. Because of the spacing between the wires 1%, most of the electrons pass through the electrode 104.

The electrode 184 serves to electrically isolate the first plurality of plates '70, 72, 74, 76, 78, 8t and 82 from the second plurality of plates 84, 86, 88, 9t), 92, 94 and 96. Because of this electrical isolation, the electrical field produced between the electrode 168 and the second plurality of plates is substantially uninfiuenced by the electrical field produced between the electrode 44) and the first plurality of plates. This causes the electrons moving past the electrode 104 to become influenced almost entirely etween the second plurality of plates and the electrode 108. Since the electrons are also influenced by the magnetic field produced between the pole-pieces 114, they travel in a cycloidal path 126 towards the plate 84.

When the electrons strike the plate 84, they cause a proportionately increased number of electrons to be emitted by the plate. With a voltage ditference of approximately 280 volts between the electrode 104 and the plate 84, approximately twice as many electrons are emitted by the plate 84 as the number that impinge on it. In like manner, the plates 86, 88, 9t), 92, 94 and 96 emit a proportionately increased number of electrons relative to the number of electrons that impinge upon them. The electrons emitted by the plate 96 are collected by the electrode 110, and the resultant output signals are indicated on the oscilloscope 4-6.

The apparatus disclosed above has several important advantages. One advantage results from the use of a plurality of plates, such as the plates 7%, 72 and 74, to collect different lateral portions of each ion beam. Even though a plurality of plates are utilized to receive each ion pulse, output signals are produced which accurately indicate the mass and relative abundance of the difierent molecules of the gases and vapors in an unknown mixture.

The accurate measurements are obtained because the plate 72 is provided with electrical characteristics which cause it to emit substantially the same number of elec trons as the number of electrons impinging upon it. Similarly, the plate '74 emits substantially the same number of electrons as the number of electrons that is receives.

In this way, the plate 74- emits a number of electrons corresponding substantially to that which would have been produced if a plate having an extended width received all of the ions in each pulse.

ill

No material distortion in the output signals is produced by utilizing the plates 70, 72 and 74 to collect difierent lateral portions of each ion pulse. The reason for this is that the electrons produced by the plates 70 and 72 require approximately only 7X10- microseconds to reach the plates 72 and 74, respectively. This time is considerably less than the period of 15X 10- microseconds between the collection of the peak number of ions of an atomic mass unit and the collection of the peak number of ions of the next atomic mass unit.

By employing a plurality of plates to collect different lateral portions of each ion pulse, the width of each plate as seen in Figures 2 and 3 can be maintained at a relatively moderate value. Since the width of the plates 76, 78, Eli) and 82 are dependent upon the width of the plate or plates collecting the ions, the widths of the plates 76, 73, 8t and 82 can also be maintained within moderate limits. In this way, the total width of the electron multiplier can be minimized without any reduction in signal amplification.

Since each of the plates 76, 78, 89 and 82 in the first plurality and each of the plates in the second plurality amplifies signals produced by its preceding plate, a considerable gain in the output signals can be obtained over the strength of the signals produced by the ions themselves. By employing a sufficient number of plates, output signals can be produced having an amplitude approaching 1 million times the strength of the signals produced by the ions themselves.

The electron multiplier disclosed above operates to produce a considerable gain in signal strength without any material increase in the volume occupied by the multiplier since the plates 84, 86, 8S, 9!), 92, 94 and 96 lie in backto-back relationship to the plates 7h, 72, 74, 76, 78, 80 and 82. Because of this back-to-back relationship, the lateral dimensions of the electron multiplier are main tained within satisfactory limits and the length of the electron multiplier in the direction of ion flow is only slightly incraesed. Since volume is a factor in determining the cost of the multiplier, the cost of the multiplier disclosed above is also minimized by placing the second plurality of plates in opposed relationship to the first plurality of plates.

The disposition of the second plurality of plates in backto-back relationship to the first plurality of plates also does not produce any material distortion in the output signals. The output signals are not distorted since the electrode 104 effectively isolates the electrical field produced between the electrode 44 and the first plurality of plates from the electrical field produced between the electrode 108 and the second plurality of plates.

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. it should also be appreciated that the electron multiplier disclosed above can be used with other charged particles than ions to amplify the signals produced by the particles. The electron multiplier can also be utilized to produce signals upon the introduction of uncharged particles. For example, an electron multiplier may be used in conjunction with nuclear equipment to detect and amplify neutrons, atoms and 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:

1. In combination, means for providing a plurality of ions, means for accelerating the ions in a lateral beam, a first plate disposed to receive at least a lateral portion of the ion beam and to produce a number of electrons substantially proper ionatc to the number of ions in the lateral portion, a second'plate disposed to receive the electrons produced by'thefirst plate andtoproduce .a substantiallylproportionately increased number of electrons, a third plate disposed in opposed relationship to the second plate to receive theelectrons produced by the second plate and to produce a substantially proportionate number of electrons, means disposedlto isolate the third plate from the second plate and to pass'to the third plate the electrons produced by the second plate, a fourth plate disposed to receive the electrons produced by the third plate and to produce a substantially proportionately increased number of electrons, and means for indicating the relative times at which electrons are produced by the fourth plate.

2. 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, first and second plates disposed in substantially lateral relationship to each other, third and fourth plates disposed in substantially lateral relationship to each other at a position removed from the first and second plates in the direction of ion flow, means for producing a first electrical field in the vicinity of the first and second plates, means for producing a second electrical field in the vicinity of the third and fourth plates, an electrode disposed to isolate the first'and second electrical fields and to pass electrons flowing from the second electrode towards the third electrode, the first plate being disposed to receive a plurality of ions in the-beam and to produce a substantially proportionate number of electrons, the second, third and fourth plates being disposed to receive the electrons from a preceding plate and to produce a substantially proportionately increased number of electrons, and means for indicating the relative times at which electrons are produced by the fourth plate.

3. 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 first plurality of plates substantially laterally aligned relative to one another, one of the plates being disposed to receive at least a lateral portion of the beam and to produce a proportionate number of electrons, other plates in the plurality being disposed to receive a plurality of electrons from preceding plates in the plurality and to emit a substantially proportionately increased number of electrons, a second plurality of plates displaced from the first plurality of plates in the direction of ion flow and reversely disposed relative to the firstplurality of plates, a first plate in the second plurality being disposed to receive the electrons from a last plate in the first plurality and to produce a plurality 'of electrons substantially proportionate to the number that it receives, means for electrically shielding the second plurality of plates from the first plurality and for passing the electrons flowing from a last plate in the first plurality tothe first plate in the second plurality, other plates in the-second plurality being disposed'to receive a plurality of electrons from preceding plates in the plurality and to emit a substantially proportionately increased number of electrons, and means for indicating the relative times at which electrons are emitted by the last plate in the second plurality.

4. A mass spectrometer, including, means for provid ing a plurality of ions, means for accelerating the ions in a lateral beam and in a longitudinal direction to produce a separation of the ions on the basis of their mass, a first plurality of plates substantially laterally aligned relative to one another, one of the plates being'dispos'ed to receive at least a lateral portion of the beam and to produce a proportionate number of electrons, other plates in the plurality being disposed to receive a plurality of electrons from preceding plates in the plurality and to emit a substantially proportionately increased number of electrons, a second plurality of plates displaced from the first plurality of plates in the direction of ion flow and reversely disposed relative to the first plurality .of plates,

a first-plate in the secondplurality being disposed to receive the electrons from a last plate in the first plurality and to produce a plurality of electrons substantially proportionate to the number that it receives, an electrode disposed laterally adjacent the last plate in the first plurality and the first plate-in the second plurality, the electrode being formed to pass the electrons flowing past the last plate in the first plurality to the first plate in the second plurality, means for imposing a voltage on the electrode to electrically shield the second plurality of plates from the first plurality of plates, other plates in the second plurality being disposed to receive a plurality of electrons from preceding plates in the plurality and to emit a substantially proportionately increased number of electrons, and means for indicating the relative times at which electrons are emitted by the last plate in the second plurality.

5. In combination, means for providing a plurality of ions, means for accelerating the ions in a lateral beam, a first plurality of plates facing the ion beam, at least one of the plates in the plurality being disposed to receive the ions in the beam and to produce a number of electrons substantially proportionate to the number of ions, other plates in the plurality being disposed to receive electrons from a preceding plate in the plurality and to produce a proportionately increased number of electrons, a second plurality of plates disposed in opposed relationship to the first plurality of plates, a first plate in the second plurality being electrically isolated from a last plate in the first plurality and being disposed to receive the electrons emitted from the last plate in the first plurality to produce a substantially proportionate number of electrons, means for isolating the last plate in the first plurality from the first plate in the second plurality and for passing to the first plate in the second plurality the electrons emitted by the last plate in the first plurality, other plates in the second plurality being disposed to receive the electrons emitted from a previous plate in the first plurality and to produce a substantially proportionately increased number of electrons, and means for indicating the relative times at which different electrons are emitted by the last plate in the second 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 first plurality of plates facing the ion beam, at least one of the plates being disposed to receive ions in the beam and to produce a substantially proportionate number of electrons, other plates in the plurality being disposed to receive electrons from preceding plates in the plurality and to produce a substantially proportionately increased number of electrons, a second plurality of plates disposed in back-to-back relationship to the first plurality of plates, means disposed adjacent to a last plate in the first plurality and a'first plate in the second plurality to electrically shield the first plurality of plates from the second purality of plates the first plate in the second plurality being disposed to receive the electrons produced by the last plate in the first plurality to produce a substantially proportionate number of electrons, a gate disposed to isolate the last plate in the first plurality from the first plate in the second plurality and to pass to the first plate in the second plurality the electrons emitted by the last plate in the first plurality, other plate in the second plurality being disposed to receive the electrons from preceding plates in the plurality and to produce a substantially proportionately increased number of electrons, and means for indicating the relative times at which electrons are produced by the last plate in the second plurality.

7. In combination, means for providing a plurality of ions, means for accelerating the ions in a lateral beam, a first plurality of plate facing the ion beam and arranged in staggered relationship with respect to one another, means for imposing a substantially constant electrical field on the plates in the direction of ion flow, means for iniposing a magnetic field on the plates in a direction substantially perpendicular to the direction of the electrical field, at least one plate in the plurality being disposed to receive .a plurality of the ions in the beam and to emit a substantially proportionate number of electrons, other plates in the plurality being disposed to receive the electrons emitted by a preceding plate and to emit a substantially proportionately increased number of electrons, a second plurality of plates displaced relative to the first plurality of plates in the direction of ion travel, an electrode disposed to electrically isolate the second plurmity of plates from the electrical field imposed upon the first plurality of plates and to pass the electrons emitted by the last plate in the first plurality, means for imposing a substantially constant electrical field on the plates in the second plurality in a direction substantially perpendicular to the plates, a first plate in the second plurality being (imposed to receive the electrons passed by the electrode and to produce a substantially proportionate number of electrons, other plates in the second plurality being disposed to receive the electrons emitted by a preceding plate in the plurality and to produce a substantially proportionately increased number of electrons, and means for indicating the relative .times at which electrons are emitted by the last plate in the second plurality.

8. A mass spectrometer, including, means for providmg 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 first plurality of plates facing the ion beam, each of the plates in the first plurality being laterally contiguous to its adjacent plates in the plurality and being slightly longitudinally displaced With respect to its adjacent plates, means for applying voltages on the plates to produce a substantially constant electrical field, means for imposing a magentie field in a direction substantially perpendicular to the electrical field, at least one of the plates in the first plurality being disposed to re ceive a plurality of ions in the ion beam and to produce a substantially proportionate number of electrons for movement in a cycloidal path towards a successive electrode in the first plurality, other plate in the plurality being disposed to receive a plurality of electrons from a preceding plate in the plurality and to produce a substantially propontionately increased number of electrons, a second plurality of plates removed from the first plurality of plates in the direction of ion flow, a first plate in the second plurality disposed to receive the electrons produced by a last plate in the first plurality and to produce a substantially proportionate number of electrons, other plates in the second plurality being disposed to receive a plurality of electrons from a preceding plate in the plurality and to produce a substantially proportionately increased number of electrons, and means for indicating the relative times at which electrons are emitted by the last plate in the second plurality.

9. In combination, a first plate disposed to receive discrete particles and to produce a number of electrons substantially proportionate to the number of particles, means for introducing a plurality of particles to the plate, a second plate disposed to receive the electrons produced by the first plate and to produce a substantially proportionately increased number of electrons, a third plate disposed in opposed relationship to the second plate to receive the electrons produced by the second plate and to produce a substantially proportionate number of electrons, an electrode disposed to isolate the third plate from the second plate and to pass to the third plate the electrons produced by the second plate, a fourth plate disposed to receive the electrons produced by the third plate and to produce a substantially proportionately increased number of electrons, and means for indicating the production of electrons by the fourth plate.

10. In combination, a plurality of plates arranged in staggered relationship with respect to one another, each plate being disposed to receive the electrons from a proceeding plate in the plurality and to produce a correspondingly increased number of electrons, means for introducing a plurality of particles to a first plate in the plurality to produce an emission of electrons from the plate corresponding to the number of particles, a second plurality of plates displaced from the first plurality of plates in the direction of ion flow and inversely disposed relative to the first plurality of plates, a first plate in the second plurality being disposed to receive the electrons from a last plate in the first plurality and to produce a plurality of electrons substantially proportionate to the number that it rec ives, an electrode disposed to electrically shield the second plurality of plates from the first plurality and to pass to the first plate in the second plurality the electrons flowing from a last plate in the first plurality, other plates 1 in the second plurality being disposed to receive pluralities of electrons from the preceding plates in the plurality and to emit substantially proportionately increased numbers of electrons, and means for indicating the electrons emitted by the last plate in the second plurality.

11. In combination, means for providing a plurality of particles and for producing a flow of the particles, a first plurality of plates facing the flow of particles, at least one of the plates in the plurality being disposed to receive the particles and to produce a substantially proportionate number of electrons, other plates in the plurality being disposed to receive the electrons from preceding plates in the plurality and to produce substantially proportionately increased numbers of electrons, means for electrically shielding the second plurality of plates from the first plurality of plates and for passing the electrons from a last plate in the first plurality to the first plate in the second plurality, other plates in the second plurality being disposed to receive the electrons from preceding plates in the plurality and to produce substantially proportionately increased numbers of electrons, and means for indicating the electrons emitted from the last plate in the second plurality.

12. In combination, means for providing a plurality of particles and for producing a flow of the particles, a first plurality of plates facing the flow of particles, each of the plates in the first plurality being laterally contiguous to its adjacent plates in the plurality and being slightly longitudinally displaced with respect to its adjacent plates, means for applying voltages on the plates to produce a substantially constant electric field, means for disposing a magnetic field in a direction substantially perpendicular to the electrical field, at least one of the plates in the first plurality being disposed to receive a plurality of particles and to produce a substantially proportionate number of electrons for movement in a cycloidal path towards a successive plate in the first plurality, other plates in the plurality being disposed to receive a plurality of electrons from a preceding plate in the plurality and to produce a substantially proportionately increased number of electrons, at second plurality of plates removed from the first plurality of plates in the direction of particle fiow, means disposed to isolate the plates in the second plurality from the electrical field imposed on the plates in the first plurality and to pass electrons emitted by a last plate in the first plurality, a first plate in the second plurality disposed to receive the electrons passed by the last mentioned means and to produce a substantially proportionate number of electrons, other plates in the second plurality being disposed to receive a plurality of electrons from a preceding plate in the plurality and to produce a substantially proportionately increased number of electrons, and means for indicating the relative times at which electrons are emitted by a last plate in the second plurality.

13. In combination, a plurality of plates arranged in staggered relationship with respect to one another, each plate being disposed to receive the electrons from a preceding plate in the plurality and to produce a correspond ingly increased number of electrons, means for introducing a plurality of particles to a first plate in the plurality to produce an emission of electrons from the plate corresponding to the number of particles, a second plurality of plates displaced from the first plurality of plates in the direction of particle flow and arranged in staggered relationship with respect to one another, a screen electrode disposed to electrically isolate the second plurality of plates from the first plurality of plates and to recive and pass electrons emitted by a last plate in the first plurality, a first plate in the second plurality being disposed to receive the electrons passed by the electrode to produce a plurality of electrons substantially proportionate to the number that it receives, other plates in the second plurality being disposed to receive pluralities of electrons from preceding plates in the plurality and to emit substantially proportionately increased numbers of electrons, and means for indicating the electrons emitted by the last plate in the second plurality.

14. In combination, means for providing a plurality of particles and for producing a flow of the particles, at first plurality of plates arranged in cascade relationship with respect to one another and facing the flow of particles, means for applying voltages on the plates to produce a substantially constant electrical field, means for imposing a magnetic field in a direction substantially perpendicular to the electrical field, at least one of the plates in the first plurality being disposed to receive a plurality of particles 14 and to produce a substantially proportionate number of electrons for movement towards a successive plate in the first plurality, other plates in the plurality being disposed to receive electrons from a preceding plate in the plurality and to produce a proportionately increased number of electrons, a second plurality of plates arranged in cascade relationship with respect to one another and removed from the first plurality of plates in the direction of particle flow, a screen electrode disposed between a last plate in the first plurality and a first plate in the second plurality to electrically isolate the plates and to receive and pass electrons emitted by the last plate in the first plurality, the first plate in the second plurality being disposed to receive the electrons passed by the screen electrode to produce a substantially proportionate number of electrons, other plates in the second plurality being disposed to receive a plurality of electrons from a preceding plate in the plurality and to produce a substantially proportionately increased number of electrons, and means for indicating the electrons emitted by a last plate in the second plurality.

References Cited in the file of this patent UNITED STATES PATENTS 2,141,322 Thompson Dec. 27, 1938 2,642,535 Schroeder June 16, 1953 2.664.515 Smith Dec. 29, 1953

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