US2676266A - Cloud chamber - Google Patents

Description

April 20, 1954 E. w. cowAN 2,676,266

CLOUD CHAMBER Fild March 10, 1 951 uuuumuum- (I BY 6, g

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- IN VEN TOR. 5/6 5: M C OWAN Patented Apr. 20, 1954 CLOUD CHAMBER Eugene W; Cowan',-'Pasadena, Calif a assignorato California.. Institute Research. Foundation; fzjsv Pasadena,iCalif.,-:ac l iat 9n-0f;.C i mia Application Marchflm, 1951, Serial No. 214,977 (Cl. 2504-47.) .L

Claims.

My invention relates to cloud chambers; that is, to apparatusforuse-in the -study of cosmic rays as well as rays emitted from various radioactive sources.

Included in the objects of my invention are:

First, to provide a cloud chamber which isgcontinuously sensitive; that is, the chamber is' con-v tinuously maintainedin such a condition that, a zone ofthe chamber displays the phenomena of droplet formations on ion showing tracks with the passage of. each radio-active ray orion.

Second; to provide a continuously sensitive diffusion cloud chamber which is particularly simple of construction and readily operated effectively even by an inexpert student thereby providing an apparatus for the study .of cosmic rays and related phenomena which is ideally suited for classroom use, for individual use,-or even as a scientific toy.

Third; to provide a cloud chamber of thi type which readily lends itself foruse in conjunction,

with photographic recording or visual observation of cosmic rays or the, rays emitted from various.

radioactive substances such as radium or uranium bearing ores or apparatus such, as synchrotrons, .bevatrons, or other high-energy .particle' With the above and other objectsasmay appear hereinafter, reference i directed to the ace companying drawings in which:

Figure 1 is a transversesectional view showing one form of ray-cloud chamber.

Figure '2 is another transverse, sectional view showing a simplified form of my cloud chamber.

Reference is firstdirected to Figure 1. In this construction there is provided a base I mounted.

on legs 2 which also slidably support a platform}. The platform 3 is urged upwardly toward the base i by springs chamber a bio of Dry" Ice iiis interposed between the platform '3 and the base i so as to be held in intimate heat transferring relation with the base.

Seated on the base i, preferably in a shallow groove to prevent displacement is a lowercylinder G ofglass or transparent plastic material. On

top of this is an upper cylinder .1 of similar diameter. Between the two cylinders there is interposed a gasket 8 which is preferably formed of current-conductmg rubber or similar material;

In the operation of the cloud 2 r. The upper cylinder I supports a cover 9 which may have a central aperture 1 l} covered by a glass v window adapted to support acamera. If a camera is not used, the aperture i0 is closed. The under side of-the;cover 9 is provided with a shallow recess H under which is placeda distributor plate I2 oi sheet metal having a plurality of small perforations.- Underthe distributor-plate [2 ,is an absorbent pad l 3 This maybe formed of'clcth. Velvet has been foundparticularly suitable,

A liquid reservoir l4 having a suitable valve I5" is mounted so that a liquid-may be admitted to the reces l I, Several heaters I6 may be inserted in the cover 9. flhese may, be in the form of small soldering'irons. In addition,--a heating coil l1 may be provided around the aperture l0. 1

The base Land cover iimay be formed of conductive vmaterial or at least their confronting surfaces are conductive and are joined bya lead Wire I8. A'second lead wire 19 is connectedto the gasket, 8. The lead wires I8 and L9 are con nected through a switch 2% to ya low amperage source of direct current preferably having a volt age of one hundred to six-hundred volts depending upon the, size of the chamber formed by the cylinders 6 and 7,,

Operation of my continuous cloud chamber as follows In order to improveyisibility of the phenomena,

the absorbent pad I3 is black as is also the upper;

surface of thev base i.

The reservoir i4 is filled with a volatile, liquid; Methylpalcohol has been found quite satisfactory although various mixtures of methyl, ethyl alcoendiwat m bail a W l s Other 5 1 01 stances which have comparable volatilities; The chamber is sealed and-while various pressures may beused, it has been found satisfactgry" to operate the ghamber at atmospheric pressures.

The volatile liquidevaporates from the pad anddescends in the chamber; By reason of the fact that the base of the chamber is chilled-bythe Dry Ice, there is a temperature gradient .from the top to-the bottom of the chamber, and a region is established'in which the air .containedin the.

cylinder is super-saturated with the vapor? In a cylinder about twelve inches of diameter and eight inchesin height,- the regionof super-saturation is aboutthree inches-high and occurs near the base. Within thi region of-super-saturation-,

traces are produced; whenever an -ion passesvisible "a. .ffiw seconds afterpassage oi the ion.

The trail gradually difiuses and sinks toward the 3 base. A rain-like phenomena may occur adjacent the base. In order to sweep or clear unwanted ion or minimize their effect a D. C. voltage is applied periodically by means or the switch 29. The effect of this is to sweep ions from the upper part of the chamber to the walls and pre vent their passing into the sensitive layer. Thus, the best time to observe ions is just after the sweep circuit has functioned, and the first ion tracks may be observed against a clear background. The liquid condenses on the base i and forms a layer or film. It is desirable to place an initial layer or of the volatile liquid on the base as this aids in sealing the joint between the lower cylinder and the base. Also liquid has sufficient conductivity to permit functioning of the sweep circuit even though the base be made of material other than metal. I

The size of the chamber is not critical nor are the temperatures highly critical. It is, of course, possible to use a refrigerant coil in place of the Dry Ice or use a mixture of Dry Ice or alcohol if it is desired to operate at other temperatures. Also asirnple expedient of thin layers of insu latin materials pla d. between the Dry ice and the base erve to va y the effective tempertaure of the base. 7

While the apparatus as shown in Figure 1 is relatively simple, this apparatus is intended primarily for research and scientific study. If desired, an extremely simple form of my cloud chamber may be made as shown in Fi ure 2. In this case a sub-base M of sheet material is provided to support a cake of Dry Ice The sub- (4L. base may be slightly dished to aid in centering the Dry Ice. Resting on the Dry Ice is a base which may be also formed of sheet metal or plastic. Its margin maybe slightly offset to form a lip on which is mounted a cylinder. 24. Over the cylinder 2 is placed a cover 25 of sheet material having a rim which serves to clamp the margins of an inner pad 26 stretched over the cylinder. One or more small apertures 2? may be provided for introduction of a volatile liquid such as methyl alcohol. If it isdesired to use a sweep voltage, leads 28 and '29 maybe connected to the cover 25 and base 2; The'leads 2S and 2E are connected to a D. C. source through a switch 3. The arrangement shown in Figure 2 operates in the manner of the first described structure except that ii the sweep voltage is used, the ions are swept downwardly rather than laterally. t should be observed that for demonstration purposes, it is not necessary to use a periodical sweep voltage if the normal background ionization which may occur is not sufficient to obscure observation of the ion tracks which may be of interest.

Having thus described certain embodiments and applications of my invention, I do not desire to be limited, but intend to claim all novelty in the appended claims.

I claim:

l. A cloud chamber, involvin a chamber sealed against the flow of gases into and out of said chamber, said chamber having a flat base and top and vertical side walls; means for chilling the base of said chamber substantially uniformly throughout its area; means for vaporizing substantially uniformly throughout the top of said chamber a volatile liquid, the contents of said chamber being maintained in a quiescent conchtion whereby within a region of said chamber substantially coextensive with the areas of said base and top there is established a super-saturated zone of said liquid in its vapor stage, susceptible to cloud trace formation on passage of free ions thcrethrough.

2. A cloud chamber, involving: a closed chamber sealed against the flow of gases into and out of said chamber and said chamber having a fiat substantially coextensive base and top and vertical side walls at least portions of said side walls being transparent; means for chilling the base of said chamber substantially uniformly throughout its area; means for distributing uniformly throughout substantially the entire upper side of said chamber a volatile liquid capable of vaporizing into said chamber, whereby on establishing a temperature gradient in the atmosphere in said chamber a zone containing the vapor of said liquid in a super-saturated state substantially co-extensive with'said bottom and top is formed, susceptible to cloud trace formation on passage of free ions therethrough.

3. A cloud chamber, comprising: a closed chamber sealed against the flow of gases into and out of said chamber, said chamber including a base member, a top member and side walls; means for establishing a preselected temperature differential between said top and base members wherein said base is the coldest and a corresponding temperature gradient in the atmosphere between said membe 's; and means for including a moistrue-distributor pad underlying said top member distributing a volatile liquid under and adjacent said top member for vapor diiiusion vertically through said chamber whereby a supersaturated zone is established, and. resulting in formation of cloud traces on passage of free ions a volatile liquid, the contents of said. chamber being maintained in a quiescent condition whereby within a region of said chamber there is established a super-saturated zone of said liquid in its vapor stage, susceptible to cloud trace formation on passage of free ions therethrough; and means for applying periodically an electric potential between portions of said chamber to sweep free ions therefrom.

5. A cloud chamber, involving: a closed chamber having at least portions of its walls transparent; means for chilling the base of said chamber; means for distributing throughout substantially the entire upper side of said chamber a volatile liquid capable of vaporizing into said chamber, whereby on establishing a temperature gradient in the atmosphere in said chamber a zone containing the vapor or said liquid in a supersaturated state, susceptible to cloud trace formation on passage of free ions therethrough; and means for applying periodically an electric potential between portions of said chamber to sweep free ions therefrom.

6. A cloud chamber, comprising: a closed chamber including a base member, a top member and side walls; means for establishing a preelected temperature differential between said top and base members wherein said base is the coldest and a corresponding temperature gradierr the atmosphere between said members; and means for distributing a volatile liquid under and adjacent top member for vapor diilusion through said chain-b er whereby a super-saturated zone is established, and resulting in formation of cloud traces on passage of free ions through said atmosphere; and means for applying periodically an electric potential between portions of said chamber to sweep free ions therefrom 7. A continuously sensitive difiusion cloud chamber, involving: means for vaporizing a volatile liquid substantially uniformly throughout one side of a closed chamber sealed against the flow of gases into and out of said chamber; means for chilling an opposite side of said chamber substantially uniformly throughout its area to produce a temperature gradient in the atmosphere of said chamber between said sides, whereby said vapor reaches a point of super-saturation in a region between said sides sufficient to exhibit cloud trails on passage of ions through said chamber.

8. A continuously sensitive diffusion cloud chamber, involving: a bottom plate; a top plate; means defining walls transparent at least in part between said plates to form therewith a closed chamber sealed against the flow of gases into and out of said chamber; means for chilling said bottom plate substantially uniformly throughout its area; means for distributing a volatile liquid substantially uniformly throughout the under side of said top plate for difiusion throughout said chamber; said chilling means tending to maintain a temperature gradient in the atmosphere of said chamber diminishing toward said bottom plate to establish a super-saturated region within said chamber.

9. A continuously sensitive diffusion cloud chamber, involving: a bottom plate; a top plate, means defining walls transparent at least in part between said plates to form therewith a closed chamber; means for chilling said bottom plate; a simple means for distributing a volatile liquid under said top plate for diffusion throughout said chamber; said chilling means tending to maintain a temperature gradient in the atmosphere of said chamber diminishing toward said bottom plate to establish a super-saturated region within said chamber; a conductor ring in said Walls between said plates; and means for applying a momentary voltage impulse across said conductor ring and said plates to sweep ions laterally from said chamber to said walls.

10. A continuously sensitive difi'usion cloud chamber, involving: a bottom plate; a top plate, means defining walls transparent at least in part between said plates to form therewith a closed chamber; means for chilling said bottom plate; means for distributing a volatile liquid under said top plate for diffusion throughout said chamber; said chilling means tending to maintain a temperature gradient in the atmosphere of said chamber diminishing toward said bottom plate to establish a super-saturated region within said chamber; and means for applying a momentary potential between said plates to sweep ions from said chamber.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,883,116 Tomlinson Oct. 18, 1932 2,418,523 Neddermeyer et a1. Apr. 8, 1947 2,566,307 Boyle Sept. 4, 1951 OTHER REFERENCES Cosmic Rays, J anossy, published by the Oxford Univ. Press, London, England, 1948, pgs. 56-66.

Introduction to Modern Physics, published by McGraw-Hill Book 00., Inc., New York, N. Y., 1947, pg. 572.

Cosmic Rays, Hewlett, General Electric Review, May 1948, page 23.

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