US3136888A - Selecting mass spectrometer having substantially doubled resolving power - Google Patents

Description

June 9, 1964 ND A ETAL 3,136,888

SELECTING MASS SPECTROMETER HAVING SUBSTANTIALLY DOUBLED RESOLVING POWER Filed March 30, 1962 15 R MRwflM r OD O TNfiEZ 4 n 5. m? M mwm n K United States Patent I r 3,136,888 SELECTING MASS SPECTROMETER HAVING SUB- STANTIALLY DOUBLED RESOLVING POWER Karoly Andras and Andras Dallos, Budapest, Janos Erdlyi, Dunakeszi,.and Sandor Toth, Budapest, Hungary, assignors to Tavkozlesi Kutato Intezet, Budapest, Hungary Filed Mar. 30, 1962, Ser. No. 183,825

Claims priority, application Hungary Apr. 7, 1961 4 Claims. (Cl. 250-419) This invention relates to mass spectrometers and, more particularly, to a novel selecting mass spectrometer in which the principles of Aston and Busch are combined to obtain a substantial doubling of the resolving power and elimination of errors caused by energy spread of the ion source.

In spectrometers embodying the Aston principle, the ions moving perpendicularly to the magnetic field follow circular paths of different radii respectively proportional to the relative masses of the ions. On the other hand, in spectrometers operating on the Busch principle of measuring the specific charge, the particles are caused to follow helical paths, and the ratio between the charge and the mass is ascertained from the pitch of the helical path, this pitch being proportional to the angular velocity of the particles.

In accordance with the present invention, there is provided a selecting mass spectrometer operating on a novel combination of the Aston and Busch principles, and having novel construction and operational features. With the mass spectrometer. of the invention, the resolving power is doubled with respectto prior constructions, and the errors caused by the energy spread of the ion source are eliminated.

For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawings. In the drawings:

FIG. 1 is a perspective view, partly broken away, of a mass spectrometer embodying the invention; and FIG. 2 is a view taken on the line II--II of FIG. 1 and further illustrating certain relations of component elements of the spectrometer shown in FIG. 1.

Referring to the drawings, the mass spectrometer embodying the invention comprises an ion gun 1 operatively associated with a selecting diaphragm 2. The ions passing through the diaphragm 2 are directed between a pair of deflecting electrodes 3 which direct the ions through an arcuate gap 41 in the circular end 42 of a screening cylinder 4. The other circular end 43 of screening cylinder 4 is formed with one or more gaps or apertures 5, each of which has associated therewith a collector 6. All of the mentioned elements are mounted on the screening cylinder, and the entire arrangement is disposed within an evacuated envelope 7. Envelope 7 is positioned in a magnetic field whose direction is indicated by the arrow B of FIG. 1.

The ion gun I is disposed eccentrically of the axis of screening cylinder 4 and adjacent the outer surface of the circular upper end 42 thereof. The particles emerging from the ion gun are directed perpendicularly to the direction of the axially extending magnetic field B, and are thus constrained by the latter to follow a circular path as indicated at 8. The diaphragm 2 makes a particular selection of the ion beam and thus acts as a. filter with respect to the direction and energy spread of the ion stream from gun 1.

The ion beam or stream, the homogeneity of which is dependent upon the structure of the diaphragm 2, then passes between the deflecting electrodes 3 and through the arcuate gap 41. The beam follows a helical path Patented June 9, 1964 "ice due to force components acting parallel to the axis of V the screening cylinder 4, and thus the beam enters the screening cylinder. With a suitable correlation between the accelerating and deflecting voltages, and the magnetic induction, as set forth more fully hereinafter, the ion beam is caused to enter the gap 5 and to impinge upon the collector 6. Due to the filtering action provided by the diaphragm 2 with respect to the direction and energy spread of the beam from the ion gun 1, which amounts to a preselection of the ion beam, these characteristics of the ion beam cannot cause any errors in the measurement of the mass by measurement of the polar angle.

The polar angle of theillustrated helical path, as

measured in radians, is given by the following equation:

It will be noted that in the above equation, the factor m,

appearing in the denominator, is of the first power. Conversely, in the deflection formulae of mass spectroeters operating of the Aston principle, m is only of the half power. Thus it will be seen that the resolving power of the mass spectrometer illustrated in the drawing is twice that of mass spectrometers operating on the Aston principle.

The radius R of the helical path, as measured in meters, may be derived from the following formula:

In this formula, U is the accelerating voltage measured in volts.

As the resolving power of the described masss spectrometer increases toward that end of the spectrum having the smaller mass numbers, the spectrometer of the invention is particularly and preferably useful for analyzing gases at low pressure, utilizing a vacuum technique, since the mass numbers, in utilizing such technique, are generally below 50. a

By way of example, an experimental construction of the mass spectrometer embodying the invention may have the following parameters:

R=25 mm. D=3.5 mm. L=50 mm.

B, which is variable, may range fromg 0 to 0.2 webers per square meter.

U,, which is variable, may range from 0 to 50 volts.

U which is variable, may range from 0 to 30 volts.

With these parameters, the spectrometer according to the invention can be used to measure masses m from 1 to 50 kg.

It will be appreciated that, by arranging outlet gaps 5, with their associated collector 6, in angularly spaced relation along a circular path concentric with the axis of the screening cylinder 4, ions having differing masses can be separated by varying the accelerating voltage U,

.3 without varying the deflecting voltage U which latter determines the helix ascent or descent angle.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A selecting mass spectrometer comprising, in combination, an evacuated envelope disposed in a magnetic field' extending unidirectionally of said envelope; an ion 1 gun in saidenvelope oriented to accelerate anion'stream perpendicularlyto the direction of the magnetic field to follow a circularpathunder the influence ofthe magnetic field; a diaphragm positioned in said envelope along said circular path in angularly spaced relation to said ion gun to selectively filter the ionstrearn with respect to direction and energy spread of the latter; a' pair of deflecting electrodes positioned in said envelope in-the path of ions passing through said diaphragm and oriented to provide an ion \velocity component axially of such circular path so that ions passing-between said electrodes will follow a helical path; and at least two ion collectors positioned in said envelope at selected points downstream of said electrodes so coordinated with the ion accelerating and deflecting voltages and with the strength of the magnetic field that ions following such helical path will enter said collectors; said ion collectors being arranged in angularly spaced relation along the circumference of a circle concentric with-said circular path and lying in a plane perpendicular to the axis of such circular path; whereby ions of different masses can be including a screening cylinder disposed within said envelope; said ion gun, said diaphragm and said pair of deflecting electrodes being positioned adjacent the outer surface of one end of said cylinder, and the axis of said cylinder being coaxial with said circular path; said deflecting electrodes directing the ions passing therebetween through an arcuate opening in one wall of said cylinder; said ion outlets being formed in the opposite end wall of said cylinder; said collectors extending outwardly from said gaps.

4. A selecting-mass spectrometer, as claimed in claim 1, including a screening cylinder disposed within said envelope coaxially with such circular path; said ion gun, said diaphragm and said pair of deflecting electrodes being positioned adjacent the outer surface of one; end wall'of said cylinder; said deflecting electrodes directing the ions passing therebetween to fiow through an arcuate gapin such one end wall; the other end wall of said cylinder being formed with at least two ion outlet gaps arranged in angularly spaced relation along the circumferenceof a circle coaxial with such circular path, whereby ions of different masses can be selectively directed to a selected one of said gaps by varying the accelerating voltagewhile maintaining the deflecting voltage constant; and a plurality of ion collectors equal in number to said gaps, each collector being operatively associated with a selectively directed to a selected one ofsaid collectors by varying the accelerating voltage while maintaining the deflecting voltage constant.

2. A selecting mass spectrometer, as claimed in claim 1, including means forming an ion outlet gap at each of such selected joints for passage of the ions into said collectors.

different respective one of said outlet gaps and extending outwardly therefrom.

ReferencesCited in the file of this patent UNITED STATES PATENTS 2,245,174 Banks June 10,1941 2,471,935 Coggeshall et al =May 3 1, 1949 2,698,905 Goudsrnit Jan. 4, .1955 2,709,750 Smith May 31, 1955 2,987,618 Long June 6, 1961

Claims (1)

1. A SELECTING MASS SPECTROMETER COMPRISING, IN COMBINATION, AN EVACUATED ENVELOPE DISPOSED IN A MAGNETIC FIELD EXTENDING UNIDIRECTIONALLY OF SAID ENVELOPE; AN ION GUN IN SAID ENVELOPE ORIENTED TO ACCELERATE AN ION STREAM PERPENDICULARLY TO THE DIRECTION OF THE MAGNETIC FIELD TO FOLLOW A CIRCULAR PATH UNDER THE INFLUENCE OF THE MEGNETIC FIELD; A DIAPHRAGM POSITIONED IN SAID ENVELOPE ALONG SAID CIRCULAR PATH IN ANGULARLY SPACED RELATION TO SAID ION GUN TO SELECTIVELY FILTER THE ION STREAM WITH RESPECT TO DIRECTION AND ENERGY SPREAD OF THE LATTER; A PAIR OF DEFLECTING ELECTRODES POSITIONED IN SAID ENVELOPE IN THE PATH OF IONS PASSING THROUGH SAID DIAPHRAGM AND ORIENTED TO PROVIDE AN ION VELOCITY COMPONENT AXIALLY OF SUCH CIRCULAR PATH SO THAT IONS PASSING BETWEEN SAID ELECTRODES WILL FOLLOW A HELICAL PATH; AND AT LEAST TWO ION COLLECTORS POSITIONED IN SAID ENVELOPE AT SELECTED POINTS DOWNSTREAM OF SAID ELECTRODES SO COORDINATED WITH THE ION ACCELERATING AND DEFLECTING VOLTAGES AND WITH THE STRENGTH OF THE MAGNETIC FIELD THAT IONS FOLLOWING SUCH HELICAL PATH WILL ENTER SAID COLLECTORS; SAID ION COLLECTORS BEING ARRANGED IN ANGULARLY SPACED RELATION ALONG THE CIRCUMFERENCE OF A CIRCLE CONCENTRIC WITH SAID CIRCULAR PATH AND LYING IN A PLANE PERPENDICULAR TO THE AXIS OF SUCH CIRCULAR PATH; WHEREBY IONS OF DIFFERENT MASSES CAN BE SELECTIVELY DIRECTED TO A SELECTED ONE OF SAID COLLECTORS BY VARYING THE ACCELERATING VOLTAGE WHILE MAINTAINING THE DEFLECTING VOLTAGE CONSTANT.

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