US2544718A

US2544718A - Ion collector for mass spectrometers

Info

Publication number: US2544718A
Application number: US41493A
Authority: US
Inventors: Alfred O C Nier
Original assignee: University of Minnesota
Current assignee: University of Minnesota
Priority date: 1948-07-30
Filing date: 1948-07-30
Publication date: 1951-03-13
Anticipated expiration: 1968-03-13

Description

March 13, 1951 A. o. c. NIER ION COLLECTOR FOR MASS SPECTROMETERS 2 Sheets-Sheet 1 Filed July 5Q, 1948 INVENTOR. AL FRED 0. (ZN/5e ATTORNEYS March 13, 1951 A. o. c. NlER ION COLLECTOR FOR MASS SPECTROMETERS Filed July so, 1948 2 Sheets-Sheet 2 E E T M e 0 m w. n

W M, w

m m w T T A Patented Mar. 13, 1951 ION COLLECTOR FQR MASHS S ,us

* less ns 11s, 'Miffn.

ess y P! ,a r'pj Min 3 Glai lnsi (01. 250-414))" This invention relates to mass spectrometers and particularly to improvements in iofncollectors for mass spectrometers; 'Heretofcre, in the operation of mass spectrometers it has been u qmary to provide an evacuated vesselihaving ion generating and beaming electrodes therein for generating a stream or beam of ions. The beam of ions is carried through the magnetic field of a deflecting magnet which causes the beam to bedeflected, depending upon the massiof the ions The ionbea m passingout of the field then -rnoves along a straight course determined by the degree of deflectionandconsequent course of travel of the .heam of ions as they leave the field. flfheslightly varying'mass of ions causes h m fi fil fi fi a n degrees/and e are thns separated into slightly divergent paths after assing through themagneticfi'eld. It has heretofore lqeen the practice to collect said ions separately by causing theheamjoimping'e upon a gat ,c lleetin :ll 2. f l me l dneoelee rcd f hg elgct deh niir withenapert rss th 55 W a ,ee taiameun il .e. l

n m in e pslne ill e iqll il e ac d same said ap re I ha v ee igundt gcp t l xper e ced i QflP r fi Pn-Qffil te 111's onth iact l1a ;a te th perat d iQ 501 1 We. n theielectr des 1 ,1 9. parentlylbuil euh v caus s o h -len A1101??? i l al bemcrereadily v dispersed therefro th i ns icbwnce H fi th rhei sact aus lis. net we, thatthecalibration, o f a spectrometers dr fts dnring use.

It ts-a objec o thei re ii n LE rQ- a improved mass spectrometer ion 53tillefilijor in which .theiQns may. bec llt lid o .i fl 1 and for long periods of time without' di'ifi ul Itisalso an object, cf the-invention to pr pm i a spectre tercflllt q of cup. or chimneyshap d,\;$1l3 'a;ctei' wherem the ions are collected. It is lilgewise an op feict offthe ntip t pr Ylsl for. to

,ion collecting electrode having a plurality of separated cup or chimney shaped ion collecting portions positioned slightly out of alignment and with the, lower portion under a hole in the upper portion tor separately collecting ions which are defiected'to slightly di fferent amounts by. thelmagnetickfi'eld.

Other and further objects of the invention arethose inherent in the apparatus herein illustrated, descrilgedandjlainiedf Theinvention is illustrated withreference to the drawings in which Figurel isaside elevatipna view-95 291 3 section, ofra mass speqtrometer having i on col- 4 lection electrodes in accordance with the apparatus of the present invention;

z ceral este -t t sa {[{he /ion' collectors offth present invention may be usedi nlnyl e L "s t m f u e il ist atedh a {I n trorneter which is novel inother respects, and forms th sub ect atte .Q my ap l a i led riD iie zeni a iQe le q ll sfifi n for Ma Spectrometers] Serial no. new filed of e v en date herewith, now abandoned. The particular mass spectrometerillustra ed i ther f erely a .resprese'ntatiye environment in which the ion t sofithelpr senminv nt reil l t ted- "Referring to thfiQdITaWiIlgS the f rame-of the masstspectrometer isillustrated at H? and serves toxsupport .the heavy" magnet generally designated II I "whichmay he a permanent magnet vor an electromagnet halving magnet coils l2 and pole'faces, as shown by.;therdotted-line l3. From the frame of the electromagnet there is an upwardly e ;t'ending:bracket I 41which serves to support the' cross tube l5'of ithe'mass spectrometer evacuated vessel. The cross tube I5 is connected at its right end to the angle fitting [5 of the'ball jointfitting fT'towliich-the"upper end of the vacuum pump generally designated i8 is attached. From thetuEe-Ida' brace rod I9 extends dowfi be'twe'n tli'flole' magnetic circuit or the electromagnet I I and is attached to-a'nd helps 7 support the vacuum purse- 8 which therefore ensse edQ'c p ade;

the i11ustratediemhodim n ,p th Jim nt ce b curved portion 25 of the mass spectrometer tube.

In the illustration the mass spectrometer tube is of the type having a branch portion 28 and a main portion 29, which forms the subject of my copending application entitled Difierential Collector Systems for Mass Spectrometers, heretofore referred to, but it is to be understood that the ion collection electrode of the present invention may be utilized in any mass spectrometer tube, regardless of whether it is the ordinary variety having only a main portion of the tube or of the type as illustrated herein having the main and branched portions of the tube.

After leaving the curved portion 25 of the tube the tube widens at 26 into the branched portion 23 and main portion 29 which separate from each other at the portion 21. Similar types of ion collecting electrodes are illustrated at 30 and 3] and are illustrated in detail in the enlarged views shown in Figure 2.

The main ion collecting tube is equipped with a duplex type ion collector shown opposite the bracket 3 i, which consists of a pair of ion collecting cups or

chimneys

33 and 34 which are supported by

posts

35 and 35, respectively, and connected through appropriate

glass squash seals

31 and 38 to lead wires passing through the terminal head 39. Above the cup or chimney 33 there is an electrode 40 which is supported by the post 4| from squash 42 and between the bottom of the cup 33 and the top of the cup 34 there is another electrode 41' which is supported by the post 34 from the squash 44. Above the electrode 40 is an apertured electrode 45 supported from the side walls of the tube 29. Each of the

electrodes

45 and 40 is apertured so that the beam of ions passing along the axis of the main branch 29 enters into the bore of cup or chimney 33, the open end of which is directed toward the oncoming stream of ions so as to collect the ions when they enter the cup or chimney 33. The cup 33 has a bottom which is apertured at 48 and through which ions of slightly different mass are adapted to pass. These ions fall through the aperture 49 of the plate 41 and thence fall into the cup or chimney 34 and are collected therein. It will be noted that cup or chimney 34 is entirely closed across the bottom.

Similarly, the ion collector 33 on the auxiliary or branch tube 28 is cup shaped, as illustrated at 50, and is supported by an appropriate post from the squash 52. Above the cup 53 is an apertured plate 53 which is supported by the post 54 from the squash 55. The plate 53 and cup 50 are connected through two lead wires 60 and BI through the connector terminal 56. Above the plate 53 is another plate 51 which is connected to the side wall of the tube 28, Both of the plates 51 and 53 are centrally apertured and the apertures are aligned so that ions falling down the axis of branch tube 28 will pass through the apertures in plates 51 and 53 and thence into the open end of cup 50 which is likewise directed so that its open end is toward the oncoming ions.

It has been found that the cups or

chimneys

33, 34 and 50 assist greatly in reducing the electric field in the position where the ions hit and hence prevent any reflected ions from being drawn upwardly and out of the cup. Moreover, the cup or chimney shape subtends a very small solid angle. Hence, only a small proportion of any ions reflected actually leave through the opening but are instead caught upon the side walls of the cup or chimney, however designated, and serve to place their charge upon that ele ment.

In this way difficulty previously experienced in operation of mass spectrometer tubes one to the drifting of the reading or due to the reluctance of ions to accumulate upon the collection electrodes has been completely overcome.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments herein.

What I claim is:

1. In an isotope mass spectrometer having an evacuatable vessel presenting an ion path, means in said vessel for projecting a beam of ions along said path and magnetic means for deflecting the ions in said beam, the improvement comprising a plurality of electrodes for collecting ions after they are deflected, said electrodes comprising a plurality of open ended cups arranged so that the open ends of the cups are directed oppositely to the path of movement of the deflected ions, said cups being arranged so that their axes are slightly displaced and one of them displaced farther along the path of movement of the ions than is the other the cup electrode most remote from the source of said ion beam being provided with a closed bottom and the cup electrodes intermediate said remote cup electrode and said ion beam source each having a bottom provided with an aperture, each of said apertures being aligned with the open end of the cup electrode immediately disposed to the rear thereof and separate circuits to each cup.

.2. In an isotope mass spectrometer having an evacuatable vessel presenting an ion path, means in said vessel for projecting a beam of ions along said path and magnetic means for deflecting the ions in said beam, the improvement comprising a plurality of plates positioned in overlying relation across the path of movement of the deflected ions, the plate most remote with respect to the oncoming stream of ions being continuous and the plates intermediate said remote plate and the oncoming stream of ions being provided with apertures for the passage of certain ions therethrough and a cylinder fastened to one of said intermediate plates around the aperture of said plate provided therein and forming with said plate a cup for trapping and collecting ions entering said cup, and circuit connections to said plates including that one forming the cup.

3. The apparatus of claim 2 further characterized in that at least two of said plates are provided with cylinders attached thereto and forming with said plates cups which have open ends directed toward the deflected ion stream, one of said cups being displaced axially in respect to the other and positioned beneath a hole in the bottom of the other cup.

ALFRED O. C. NIER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,354,122 Hipple July 18, 1944 2,427,484 West Sept. 16, 1947 OTHER REFERENCES Coggeshall et al.: Review ofScientific Instruments, May 1943, vol. 14, pages and 126.