Construction of the Two Foot Cloud Chamber and Some Preliminary Results on Cosmic Ray Energy Distribution at Sea Level Citation Katz, Leon (1943) Construction of the Two Foot Cloud Chamber and Some Preliminary Results on Cosmic Ray Energy Distribution at Sea Level. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/fcnh-kx30. https://resolver.caltech.edu/CaltechTHESIS:10042024-155804986 Abstract No abstract. Item Type: Thesis (Dissertation (Ph.D.)) Subject Keywords: (Physics) Degree Grantor: California Institute of Technology Division: Physics, Mathematics and Astronomy Major Option: Physics Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 1 January 1943 Record Number: CaltechTHESIS:10042024-155804986 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:10042024-155804986 DOI: 10.7907/fcnh-kx30 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 16772 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 04 Oct 2024 22:10 Last Modified: 04 Oct 2024 22:11 Thesis Files PDF - Final Version See Usage Policy. 20MB Repository Staff Only: item control page

CONSTRUCTION OF THE TWO FOOT CLOUD OH.AMBER AND SOME PRELIMINARY RESULTS ON COSMIC RAY ENERGY DISTRIBUTION AT SEA LEVEL A Thesis Submitted in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy at The California Institute of Technology Pasadena, California. by LEON KATZ 1943 This thesis is in the nature of a progress report on the large two foot cloud chamber being built by Dr. Carl D. Anderson and Dr. Seth Nadermeyer. The t hesis will serve the double purpose of recording and making available the experience of the cosmic ray group in buildi ng the chamber as well as reporting the results of some prelim.. inary measurements. CONSTRUCTION The general l ayout of the chamber, magnetic poles, cameras and li ghts is s hown i n Fi g. 1. The op t ical s ystem is shown in gr eate r det a il in Fi g. 2. See also photo graph of Fig. 10. The mirror and c ameras are mount ed as a unit which may be easily remo ve d from t he cloud chamber a.11d us ed for r eproj ecting the tracks. The advantag e s o~ t his set-up are obvious, s ince, with the sole exc ep t ion of the plate glass formin g the fro nt of the c hamber the smne op t ical s ystem that is us ed in photographing is used in reproj ecting t he film. Thus distortions from t his s ource are automatically elimin ... ated. To ap proximate t he act ual optical s y s t em eve n mor e closely t he tracks are projected t hrough a s hee t of plate glass similar to tha t which forms the f ro nt of t he cloud chamber, placed at a pproximately t he same position in the optical p ath. A cro ss s ection of t he cloud chambe r pr oper is s hown in Fig. 3. The di aphragm, whose design was arrived at t hrough a proce ss of evolut ioh, seems to operate satisfacto r ily. A f ew of t he diff iculties me t wit h i n al t e r na.tive designs · are as follows\ a simple rub ber diaphr.agm coming to re s t against a perfora ted pl a te ac ting as a stop, s eems to generate a h i gh GENERALLA.SSEMBLY OF CLOUD CHAMBER' MAGNET, LIGHTS and CAMERAS~ Inlet Leads Oil Cooling System Lights Field Coils - ······- / __, - " __, --t ·. , Cameras . Lights: ' Front Pole Piece C-oncrete Base Fig.l ' .. ~·,•, . Jl:(:~· l::.. , I / 'jijiEAR POLE P ';}Y{J-:,·• :.. '·_':·,:{;Stf~:5:> ........:...- -~ --'----'-"'-'-' - ' - -- .;.:_..., MIRROR ( AMERA CAMERA Figure 2. ~ WATER CcYOLING ADJ. EXPANSI BRASS RING ' <' ' ' \·. ' . .. / ,/ /I/ . /·,.,/ ,, , . >J :'-"i , 1/; / // /1, / , ', / , '"" "" c ___ '"-..."'··. ' ' ,, / ./ ,' /~ / ,• '•.· / •/I , , • 1 1 I', "- "'~ ~ // / ' ' ' // ·' / , ,/ / I Figure 3. / <<> '<:·\\:;~ '-. CORE OF ELECTROMAGNET t-3 '/ ;// /,1·/l!//;//'/ · ''1/1/ ;, ,,_//'/ /, ~ z / :-Y·1 ~~ ~\., ~~--, 1 / ?;;;l/(11 / 0' f,,/i 1/ / , l/ 1 I,. ; ·///,,/. 1 ' , 1 /1~ II / 1 //I/1// / ;:,/1;//11· • /;.-,, // ' '!' 1 /1,, / .· ·-••--,- I '1 • '', / ~ / % 7--r-;1~ - -, ,--;-;,y - i,\ ' ~~~--~ \----< !-\$! ;\•:· i\\' _J!;__,j '11,.!/1::1/,flf/&)4· //l/i lJJfl·/4 • ·,--, '-~-~---.;-:-'\.-c-::, --·- · - '..'..LL ~~~ ~ ~ ",,'• "-.., .," '·,~·, ~ ,..', ''-.." ' ' 1 :,\ / / \ ~ 2>< ~ \ i., _,, \ BRON~E PLATE / 1· 1 ~--, / __, ,N, N,, f \,1~ RUBBER DIAPHRAGM .· '·'-'• ,,,~ .::-~1.-;,;,-:-:---r~-~7=-~~;;~~r~, _: , • . , , I: •. ; iii ' ,Y\ ' ) ~ ~ ~S • - _, , .. -b ~ • :1 k ' - ~i :~ 1,:::~.:•.:;:•ij.t~si~~~;(Tt.. \ OPEN MESH WIRE SCREEN BAKELITE SHEET ALUMINUM FOIL 0.002 B H -=::: 8 z t:,;j 8 m C t:,;j >< ::r: !):I '"O 5 0 ti ~ ~m td !):I I+" !):I ~ C td electrost at ic potential when it pulls away rapidly as the c hambe r expands, and gives ri se to ions which contaminate the chamber; on the other hand if t he rubber has a bakeli te sh eet glued to it for stiffness and t he motion of t he system is limited by a number of pegs placed around the perifery, t hen even a slight excess of pressure behind the diaphragm will buckle it sufficie ntly to cause distortion of the tracks due to the uneven mass motion of the air on expansion. The construction of the diaphragm as finally used will now be described. The first step in the construction was to stretch a sheet of rubber 12 inch thick on a brass hoop, Fig. 3. Then a ~ 6 inch circular she et of bakelite 22¼ inches in diamet er , whose edges 1,vere t h inned down, was fastened to the rubber with bakelite cement (see below). The edges of the bakeli te sheet were then secured with a strip of rubber; half of the rubber strip on t he bake lite sheet was glued with bakeli te cement, the other half was fastened by rubber ceme nt to the rubber. Sheet of Aluminum 0.002 inches t h ick gro und ing wire R~er strip - BRASS HOOP ... 6 ... A sheet of aluminum foil 0.002 inches thick was then glued with bakelite cement to the rubber sheet on the opposite side of the bakelite disc. It was found convenient to iron the foil down with a warm pressing iron, which smoothed it out and fastened it more securely. Thin flexible grounding wires were then fastened to the aluminum on one end and grounded to the cloud chamber on the other. The end fastened to the foil was secured with a copper sheet clip as show~ Copper strip ~ ~Flexib~e ALUMINUM ------..._,r-----_..i:;:;;;4iiii_iiii~j;;ij;OC~;:~ -~~~~m ~ - - - - - -1 ~ ., -=7~ --~~~~--= · =·=:~~,-~ grounding wire Solder through hole in aluminum sheet As will be seen from Fig. 3. the diaphragm in the compressed position does not rest directly against the perfor~ ated bronze plate, but is held away from it by a number of small stops, these are for the purpose of avoiding local overexpansions. Care was taken to avoid any such tdead 1 spaces which might cause local over-expansions and thus cont ,sminate the chamber. When compressing the chamber, the air pressure behind the diaphragm is slowly raised until the diaphragm rests securely against these stops. Graph l shows the chamber pressure as a ···--- - - - · - • · - · ·· · · · ·· - · - -••.s - - · · - - ·- ·--- ! : . . .. ., ... 21.5 _. ______ ,,.,- ~t i l 0 ---------:-----<i>-- ----~ bO ::r:: . - ~ \ .. . -- - - .... , .. . r -· - Diaphram solidly against st~p s ~ 0 ~ :::> Cl) Cl) 21.0 0 ~ P-. er:: r:il P'.1 ~ ::r:: -· i - Diaphram fir•t , tombhes stops 0 ; 20. 5 0 - - - - -- - " ' 7 1 ! - - - " ' l ~ ' « - l ! l " . - . O : t t i ' I N ~ - " - < " - ' " " < ! , l , ;J 0.1 0.2 0.3 0.4 ~ 0.5 ' ! i 0.6 0.7 0.8 0.9 PR~SS.U~ DIFn;RENCE CM ) Hi . (pressure behind diaphram - chamber pressure ) Grapn 1 . ,_..™_,,~-,..,...,_~. . , , _ ~ ~ ~ •~ •-~ - •·• r::::=1 • ,r.,,:.t .... 1.0 ... 8 ... HOSE CONNECTIONS HOLDING HOSE FROM CHAMBER n 1i It j ! ,,....,....~~c,I~ 1 1----~- ; I' R:RlES$URE RELEASE VALVE / TRIP MAGNET ?;::; :, .,,., ~ : / ~ .,.--~-· .../ ..., ~ EXPANSION V.ALVE Fig.4 - ~ -10 ... function of the pressure difference across the diaphragm. It will be seen that about 0.6 cm. of Hg pressure is sufficient to bring the diaphragm to its limit of motion in the forward· direction. The ratio of expa.~sion is limited by the distance which the diaphragm is allowed to travel in its backward motion. This distance is adjusted by moving the chamber closer or further from the back pole of the magnet by three screws. The rapid expulsion of t he air from behind the diaphragm is ac hieved by the use of e i ght two inch hose symmetrically con-nected with the cl12mber and linking it with the expansion valve, which is of a conventional desi gn as sketched in Fig. 4, and shown in photograph Fig. 4b. With this arrangement, ,the width of tracks due to the diffusion of ions indicates that about 0.02 seconds elapse between the instant the counters are tri pped and when expan~ sion is completed (ions weighted down with water drops.) The problem of illuminat ing a chamber wi t h sufficient light inte ns i ty to photo graph the minute droplets of water has always been a difficult one. In t his case it was resolved by the use of two argon filled stroboscopic lamps. These, when placed in an optical system to be described,and each fired by ... 11 ... a 48p-f conde nse r at 5000 volts, give sufficient li ght to re gist er the tracks on XX-super par1 film a t an f8 lens opening. It was necessary to construct the l amps from quarts tubing to withstand the high temperat ure developed in them when flas he d. See Fig. 5. They were filled to about 30 cm. of Hg. pres sure with argon ( of comme rcial purity 99. 6'%) after being thoroughly . outgassed. Tests indicate that the intensity of illumination fro m the flash is not sensitive to pressure changes of a few c ent imeters of Hg. of the gas with... in the lamps. Each lamp was enclosed in a wooden box, one side of which had three 4½ inch focal length plano-convex lenses (type used in conden se rs) as shown in Fig. 5. The beam of light obtained by the use of these lenses was limited to a fairly well defined she et about l½ inc he s wide and 30 i nches high. The lamps were flashed by a controlling circuit shown in Fig. 6. The circuit whic h expands the chamber (to be de- scribed l ate r) i mpre sse s a pulse on the input of the time delay circuit, where the signal i s delayed an appropriate time to allow the drops of moisture to grow on t he ions forming t he cosmic ray track (about ½a sec.). The delay / F AHNSTOCK CLIP TUNGSTEN ROD 3/32 in. DIAJ LENSES ! i I I ! ! ~ ! +: <tjl I I t I ! • I Jl·u I Incl QUART~ TUBE 5/16 in~ DIA. GRADED SEAL Fig .. 5 ... 13 .. circ_ui t in turn trips the thyratron wh ich allows the 4 f condenser to discharge through a high tension transformer causing a high frequency spark to traverse the lamps. spark This breaks down t he gas within t he lamps a~d allows the large condensers to discharge them. micro seconds. The flash lasts 25 .... 50 It has been found convenient to enclose the entire chamber in a dark room and to leave the camera shutter open. A few sample photographs are shown in Fig. 7. The construction of the high tension transformer is illustrated in Fig. 8. The chamber expansion is tripped by the simultaneous discharge of two Geiger counters. These are so arranged that a particle traversing them mu st also traverse the central illwninated portion of the chamber. The coincidence - circuit, which also acts as a pulse lengthene r, is of a conventional design and is shown in Fig.9 for record. The duration of the pulse at different points in the circuit is also indicated. A loud speaker in the plate circuit of the 884 tube indicates whether the counters are functionin g properly. The output pulse of t h is circuit s erves to trip the expa.---ision valve, the delay circuit of the flash lamps, the sweep field and the motor contr olli ng a rotary switch (aff ectionately called the 1 sewin g machine 1 ) which performs a number of switc hing oper~ - 14 - 48~d Each: made of 2 banks of 12 - 8~fd, 2000 volt condensers in parallel. llOa. c. J_ 866 . 10 ,000~ 5,000V STROB0S90PI LAMPS 5,000V /, COINCIDENCE liHRCUIT ~300... v. d., c. + TIME- DELAY CIRCUIT TRIGGER CIRCUIT FLASH LAMPS Fig. 6 T 4'j'fd ... 15 ... PRINTS OF ACTUAL TRACKS Fig. 7 -16- 20 TURNS PER PIE~ lOPIES OFT IRON STR ,~ _______ __,_ . ✓x FILLED WI TH PARAFFIN WOOD IMPREGNATEDIN PARAFFIN-BEES WAX MIXTURE HIGH TENSION COIL EACH PIE HAS 11 LAYERS OF ?O TURNS OF N0.28 ENAMEL-COTTON WIRE EACH LAYER WAS COATED WITH HOT PARAFFIN-BEES WAX MIXTURE AND WRAPPED WITH A LAYER OF VARNISH CLOTH~ FIG. 8 "" • I lO ' .... l I ! ~. 7xlO I I I I ... 5 sec . i . ~ Fig.9 ii I jj \ 6SJ7 \ \ \ \ 1. 2Xl0 -4se.c. l~~fffd. 01 ~~ 884 GEIGER COUNTER CIRCUIT ~(~ ~~ I __L.,,,,: ---+/. L _ _ _ _ _ _ ___ __1I I l~ :I -? 'i'Q.;j !!: > ..., I 0 l I I - - - - - - 7 6S l 'i. . I I GEIGER COUNTER: I ,- - - \ 5 xlO -5 sec. 2-50 VOLT 1~ ~? \ \ .... 4 8 x10 sec• --J I-' ... 18 ... at ions in sequence ( such as to move the films in the cameras after each exposure, etc.) The expansion valve is tripped by the firing of an FG17, a relay in series with the plate circuit, serves to interrupt the cur r ent allowing the tube to deionize. The in... ertia of t he relay is sufficiently great to allow the expansion valve trip to act. Considerabl e tr1uble was experienced with the sweep circuit. The conventional use of a strip of sh ee t foil, placed in the cemented joint betwe en th e glass ring f orming the chamber walls and the front pla te of the chamber, to act as one of the electrodes of the sweep field, leads to some difficulties, mainly because tli'e front plate of glass was so large that even when the swee p pote nt ial was cut off i mme diately after the counters were tripped ( 10 ... 3 sec.) t he charges accumula ted at the center of the pl a te leaked off slowly and caused seperation of the ions in the track. The difficulty was finally solved by placing an open mesh wire screen (about 2 inches between wires) near the inner front surface. of the chamber. Immediately aft er the chambe r ex~ pansion this screen was grounded (electronically). Any charges on the glass surface thus had their lines of force terminated on t his screen and the chamber was left field free. This mesh is shown in the drawing of Fig. 3 and can be seen as faint squares on the photographs of Fig. 7. It was found that subjecting the chamber to a -slow exM pansion after each regular expansion reduced the numter of background drops considerably, allowing the tracks to stand out more clearly. For this reason a slow expansion valve was incorporated in the chamber mec hanism and acted in the sequence of chamber op erations. Summarizing, the sequence of the chamber operations were as follows: a. Passage of particle through chamber resulted in a coincident discharge of both Geiger counters; the pulse from these passed through the coinci ... dence circuit arid was amplified sufficiently to operate the following mechanisms: ( i) chamber expansion valve (every effort was made to trip this valve as soon as possible after the passage of the cosmic ray through the chanber); (ii)trip~ ping of lamp flashing circuit; (iii) initiated circuit which dropped potential of sweep screen to zero; (iv) started motor of tsewing maahine 1 - 20 ... operations will be enumerated as they occurred in time sequence. o. After a~ appropriate delay (of the order of .05 sec.) the lamps were flashed and since the cameras had no shutters in them the track was recorded on the film. c. The tsewing machine• mechanism got ~nto operation and acted to move t he film in the cameras one frame. It also disconnect ... ed the trip ping mechanism from the Geiger counters so that no further expansions mi ght occurr, until the c hamber was again ready. After about fi f teen seconds, whic h was suffic i ent time to allow the chamber to become co mpressed, the slow ex "0ansion valve was op ene d for about a mi nu·~e. At t he end of this period of time the val ve was closed, the chamber allowed to sit inactive for about a minute, to co me to equilibrium, and the counters were again connected leavin g everyt :-iing in readiness for t he pa ssage of a new particle. MEASUREMENT OF TRACKS As previo usly me nt ion ed the curv a ture of t he tracks was measured by t he aid of t he same optical s ys tem wh ich had be en used to photograph them. The cameras and mirrors were built as a unit on a single frame which could be li fte d easily f rom betwee n the magnet and. chamber. photo graph of Fig. 10. This uni t is sh own in the The backs of t he c ameras were made removable so t hat projecting l amps c ould be attached, con-verting the cameras into projectors. In order to more clearly duplic ate the optical path ghrough which t he photographs were t aken a plate of glass, si milar to t hat forming t he f ront of the cloud ch::i.mber, was mo un ted in fro nt of the cameras and in approximately the same position. The whole unit was pl 2.ced on a table and a sheet of gr ound plate glass about three i nches wide by three f ee t lo ng , with a ground glass surface faci ng the c ameras, was placed in front of the unit at approximately the ~ame position whe2~ e the illumin ated portion of the chamber was situated. The track was t hen projected stereoscopically from t he two cameras on th is ground surface. It will be seen tha t if t he gr ound glass surface is not perfectly plane the n a gtraight line projected on it would appear curved when viewed at an angle to the line of projection. In order to elimin c= te t h is source of error and to give a straight line of reference, a fi ne silk thread was placed - 22 - Fig . 22 "'23 ... behind the ground gl ass in such a way that it t hrew a shadow on the glass. This shadow assumed the same lateral dis-- placement, due to-the variations i n the plane of the ground gm. ss, as those suffered by the projected track. Thus mea- surement of the increments between the track and the projected straight line at various points gave the curvature of the track. These measurements were made with a ca.thetomete r eyepiece mounted on a ruled steel support. The support was so mounted th a t it c ould be placed parallel to the cosmic ray track under observation. See photograph of Fig. 11. When so arranged the vernier scale in the eyepiece was at right angles to the trac k whose displacement from the straight lin~ could be measured directly. Readings on the ruled sc ale of the support loc ated the position of the measured lateral displacement along the track. MAGNETIC FIELD The magnetic field between the pole s was mapped with the aid of a searching coil. At the center of the ch amber , the field strength varied from 4500 gauss at the back of the illuminated portion to 4470 gauss at the front, with 540 amp- ... 25 - eres current t hro ugh the field coils. Curve A of Graph 2. Further curves are shown on Graph 2. It will be seen that the maximum variation throughout the illuminated portion of the chamber was from 4470 gauss to 5150 gauss, about 14'1o. From these measurements t he average field over the ce nt ral plane of the illumin2.ted region was calculated to be 4660 gauss at 540 amperes. Thus t he average field at 500 amperes was 4300 gauss, or possibily somewhat higher since the field does not drop off quite as fast as the current. RESULTS The results to be reported were taken more in the spirit of working wit h t he chamber and becoming acquainted with its idiosynchros~'.s in actual use rather t han to make any serious study of cosmic rays. It is felt, however, that the data obtained contains sufficient information to make it worth recording. The chamber was filled with air and saturated with aEsolute alcohol. As far as could be determined from press~ T - I ,~ ' ' J_ - -R=l H- ,-,l±±l: '-l;_:"R ' -w .~ ~•+fu .,1H'11:iJ:B±:1:t, , •..L• [a '' · ' ' ~+F· l_ _ --rj - __ - _ •• - FORM 1768E '- ' '' ' --j ➔ -~ ' ' .. T 7 ' ' n I I I ' ~ +H ,, - -H' ' ' :-,f ~ +~ t- I ., CURVE NQ, _ _ _ _ __ _ SJGNATURE._ _ _ _ _ _ _ _ _ _ DATi;:.__ _ _ __ - 27 - ure measuremen ts the expansion ratio was 1.155, ie. comp re ssed pres s ure in chamber was 96.2 cm. Hg. while the expanded pressure was 84.2 cm.Hg. at 25. 51o ( temp erat ure of wa.ter from rear water cool ed pole); the saturated vapor pres sure of ethyl alcohol at this te mperature is 6.2 cm.Hg. Thus 96.2 - 6.2 = 1.1 55 84.2 6.2 this seems to be rather low for a chamber filled wit h air. On the whole the measurement of trac k energies in t his prelimi na r y test was not too sati sfactory i n t he hi gher ene rgy range (over 6 M.E.V.). As far as c ould. be concluded f ro m the li mi ted. experie nce with the chprnber the mai nsource of error was due to disto r tio ns i n th e t racks the msel ve s and not in the accuracy of cur v ature mea,s urements . Lat eral dis place- ments of indiv idual trac k points fro m a strai ght line co uld be measure d an d repe ated towithin 0.01 cm. But the r esulting curve s were not very satisfactory a pprox i mati ons to parabolas in many cases. Particul arly discourag ing were some non-fi eld trac ks, wh ich showed as h i gh as l½ mm. first order curvature . It is felt t hat t he s e are not inheren t f aults of t he apparatus arid -.. 28 ... will be overco me with further work. The energy of a particle of el ect ron ic charge for energies ~ ~ C2 0 in t erms of the radius of c urvatures of its path in magne t ic f i eld is given by the well known equa ti on E = 300 Hf E = energy of particle in e.v. f = radius of curvature in cm. H = magnetic field strength in gauss The radius of curvature may be expres se d in terms of the track length and deflection from a strai ght line by the equation for h6 lt::... 1, Thus E = 300 H ~2 8 6 Now the average magnetic fi eld at 500 amperes as measured was 4300 gauss , therefore E in B.E.V. h and 6 in cm. ._ 29 - This is the equation used in the present work to calculate the track energies. If the error in measuring 8 is 68 then E = 1.61 X 10 ... 4 for It will also be found convenient to define a curvature er. 10 9 • 6210 er = E = ~ ( 80 ± 68) Assuming h ~ 50 cm and 66 ~ .02 cm. Ta0le I gives values of E, er and 6E for various values of .&0 .... 30 .... TABLE I Energy curvature and uncertainty in energy for various values of 80 with h = 50 cm. 88 = .02 cm. 6cr = t !!0 66 = ± .05 ± t.E AE/E 5 a 80 E 0.04 cm 0.1 0.2 0.4 10 BEV 4 2 1 5 BEV 0.8 0.2 0.05 0.5 0.2 0.1 0.05 .099 .248 .496 • 992 0.66 0.022 0.012 0.008 0.002 0.033 0.024 0.02 0.01 1.488 1.984 2.48 4.96 0.6 0.8 1 2 o. 50 0.40 0.20 A plot of these values is shown in Graph 3. Altogether 13 5 tracks were recorded. They are all listed in Table II, showing their energies and signs . To get an idea of the energy spectrum it is necessary to arrange these in groups of defin i t e energy intervals. Unfortunately resulting h istogram from such a small number of observ ations is a function of the size of the energy interval and of the place where its bounderies are chosen. The size of the interval finally chosen(½ B.E.V.) was suff iciently small not to mask any conto ur characteristics, yet suf f iciently large to constitute a fair statistical group. 'ell ,, If 11 I<,, It t'f 13 1a >. iit cd II z ~ lo (J) a:: I.LI z ~ UJ i , ' S' 4 3 1 ~ IN CM. FORM 1768E CURVE NO, _ _ _ _ __ _ SJGNATURE _ __.o'---_ _ _ _ _ _ _ D A T E - - - - - - ... 32 ... TABLE E .0 8 BEV .10 .12 .1 5 .21 • 22 • 24 .25 .28 • 30 • 35 . 37 • 38 . 39 . 40 . 43 • 45 • 48 • 40 • 52 . 53 • 54 • 56 • 58 . 62 • 65 . 66 . 67 . 69 • 70 .71 • 73 . 82 . 83 • 84 • 85 . 87 • 88 Ne g. Pos. 1 l l l 4 1 l 1 1 1 2 1 1 1 l 2 1 1 2 1 1 1 1 1 1 l 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 2 1 1 E III Neg. Pos. . 89 BEV • 90 . 91 . 93 . 95 • 96 1.00 1 l l 1.0 7 1. 10 1. 14 1.19 1.20 1. 29 1 1 1 1. 30 1. 32 1. 33 1. 40 1. 49 1.52 2 1 l 2 l 1 l 1 1 1 1 1 2 1 1 1 1 1 1 2 1 1. 69 1. 74 1.76 1. 78 1.79 1. 81 1. 82 1. 83 1. 89 1. 97 2 . 00 2 .07 1 1 2 1 2 . 20 2 . 24 2.2 5 2 . 33 2. 44 2 . 49 2. 50 1 1 1 1 1 1 1 1 1 2 2 1 E 2. 60 BEV 2 . 62 2. 67 2. 69 2.8 5 3 .00 3 .10 3 . 30 3.50 3. 64 4. 57 4.60 5.10 5.18 5. 80 6 .10 7. 44 8. 80 9. 50 10 Ne g. Pos. 1 1 1 3 l 1 1 1 1 1 1 l 1 1 1 1 l 2 1 1 3 5 (1 doub tful) ... 33 ... To bring out fmy change ia t he distributi on due to where the i nterval boundries were chose n the analysis was carried out two ways with the intervals between * O - 0. 45 ; 0.46 - 0.95; 0. 96 - 1.45 etc. and O - 0.20; 0.21 - 0.70; 0.71 - 1.20 etc. These two t ypes of grouping are shown in Tabl es III and IV. TABLE III Energy I nterval .45 .95 0.96 - 1. 45 1. 46 - 1. 95 1. 96 ... 2.45 2.46 .... 2. 95 2. 96 - 3.45 3.36 - 3.95 -x 3.96 .. 4.95 -1( 4.96 ... 6.95 ¥ 6. 96 ... 9.45 9. 45 -1( 0 - o. 46 - No. Tracks Pos.+ Neg . Neg!.. Pos. 28 35 13 17 11 18 7 6 6 8 3 17 17 6 11 2 4 0 1 8 12 3 2 1.25 . 60 o. 50 o. 30 1 1 0.75 0.30 9 3 6 1 0 -x Table giv es number per 1/2 B.E.V.. interval * The first interval in each case was corrected by an appropriate weighing factor 50 ie: 0 - 0. 45 , number of tracks was multiplied by .• 45 0 ... 0.20, 50 number of tracks was multiplied by •.20 .... 34"' TABLE IV No. Tracks Energy Interval -¥ 0 ... .20 .21 ... • 70 . 71 ... 1.20 1.21 .... 1.70 1.71 ... 2.20 2.21 ... 2. 70 2. 71 ... 3.20 3.21'"' 3. 70 * Pos.+ Neg. Neg. Pos. 10 37 27 5 5 17 14 20 13 9 4 5 17 15 3 3 7 10 3 2 10 5 0 1 Corrected to 1/2 B.E.B·. int erval In ~able IV the group i ng is only carried out to 3.70 B.E.V. which covers the interesting part of the spectrum. These two sets of da ta were sup'peri:nposed on each other in the form of histograms in graphs 4 (pos. and neg .) 5 ( po s • ) an.d 6 ( neg . ) Using t hese curves it was then possible to obtain a set of represent ative points for drawing distributi on curves by taking the mean values of the two sets of data from these graphs . Such average values were ta~en at 1/4 B.E.V. inter- vals , as shown by dots on Graph 4 , and are plotted in graph No. 7. "'· uJ. tl'.) .z: 7 ~ FORM 1768£ 2 -; )\:}\f('.U.. :iO ·ON CURVE NO. _ _ ___ _ _ _ SJGNATURE _ _ _ _ _ _ _ _ _ _ DAT ....__ _ _ __ ..:. 0 FORM 1768E ':> '>''>~~.J.. ;i~ <;;>N CURVE N0, _ _ _ _ __ _ SIGNATUR~---------- □ATc;;.__ _ _ __ FORM 17 68£ CURVE NO. _ _ _ _ __ _ SIGNATURE _ _ _ _ _ _ _ _ _ _ QAT,___ _ _ __ The curve shows two maxima, one at 1.8 B.E.V. and the other at 2.6 B.E. V. It is seen that one of those maxima is due to the positively charged particles and the othe r is due to the negatively charged particles. Careful examination of the energy distribution curve in a paper by .Anderson and Neddermyer 1 shows similar secondary maxima. To bring these out more clearly the data given in that paper was analysed by the method of overlapping histograms (of 1/2 BEV intervals) and the resulting curve is shown in Graph 8. This graph also displays two maxima, though at somewhat higher energies. A similar analysis was carried out on data published by Blackett2 and the distribution obtained is shown in Graph 'd. Bla.ckett 1 s data shows one max ima, however Blackett points out that Fig. 7 of his paper shows two minima, one at E at E ~ 1. 25 BEV. = 2.2 BEV, the other The one at 2. 2 BEV is taken to be exper:i:mentally esta.blished and t he other at 1.25 BEV to be 1 prob ably real 1 • The two minima in our graphs are surprisingly close to these values~ The reason why the minima at 1. 25 BEV does not appear on Graph 9 of t his paper se ems to be because of its extreme narrowness, being of the order of 0.2 BEV. 1 2 Fundame ntal Processes in the Absorption of Cosmic Ray Electrons a.nd Photons - C. D. Anderson and S.H. Neddermeyer - Papers and Discuss~ ions of the International Conference on Ph:irsics, London, 1934, Nuclear Physics. Further Measurements of the Cosmic Ray Energy Snectrum P.M.S. Blackett, Proc. Roy. Soc. Lon. 159, 1' (1937) F ORM l 7 68E CURVE NO._ _ _ _ __ _ SJGNATURE _ _ _ _ _ _ _ _ _ _ DAT E_ _ _ _ __ FORM 1768E CURVE NQ ., _ _ _ _ _ __ S!GNATURE _ _ _ _ _ _ _ _ _ _ OAT E _ _ _ _ __ w 42 ... The vertical lines drawn through the experimental points of ea.ch graph give the probable error according to 6N = ±.68 N, 8.nd the horizontal double headed arrows give llE at the various energies; those in Graph 7 are according to Table l, wh ereas those in Graph 9 were' taken from Blec kett I s paper. Since in the energy distribution graphs tiE varies as E2 it would be more instructive to examine the N - o curves in which t:,a is a constant inde pendent of o., The energies of Table II were expressed in terms of a and the resulting distribution was then divided in two manners into groups of a= 0.2 wide. These groups had boundries at 0 = .2, .2 - .3, .4 .... 6, etc. and 0 -.1, .1 -.3, .3- . 5. As before the overlapping hestograms were drawn and average values were taken from these distributions shown in Graph 10 were obtained. The distrib ut ion curve of the N N tra.cks shows two maxima, the p+ one a.t a = l. 2 corresponds to the first large maxima at E .8 BEV, the other at a= .45 correspo nds to the two secondary maxima, here the two peaks are crowded so closely togethe r ( a = .15 apart) t hat they are not resolv ed. Blackett has sug gested that t he secondary maxima may be due to selective absorption of the rays as they pass through H+.- L/c.+ H - r t + rt , I -i- r~ I tt± _L':T i+ l r++ 1 i-H -tr,· 1+; ru f rt +" '-+ _I f-H- - rr - rt ' L ' 7 I, ::i'.t..)::- i-PT ''L- .:. 4' 1-H!-J--t-t-f-H-ii+I-H--t--t-"' I-+ ..:... I - - --f,- -'· ' I l !I -, --rt=1:-'ffl'' ,1 -f :;:. -, -.. I 1-:=W- I -l-f - +1, 1--f-/- -- H-H+H+ H 'm-:-++ , ,_ H-+ :t -1-· - I -++ ++-!. L. ±l±t!-+_ •+1J-'j'ij'j" ++-'JJ-til:-i';'..~.e1...l..,--'"'1 - JI+' L!''-Ll,..J-.l.+.J.+l--H-l+R=F ' ,- -,TT '- I- : ~+I+ CL ' ~-+ 7 =t-' ' - -f- ,-i-t t-+-+ .f ' r+J j I::' T r r T r, ::j::;j-<~ -1 'T' '+ ' T +:j:7t ' ' ' ' -I -1- -+ h~~i -~·=,~ I- ' CT -,' -:- -~ - T ' ' J::1- -, + -;- ' I-!·_, c•=~t·· + . ++ II '' FORM 1768E CURVE NQ, _ _ _ __ _ _ S/GNATUR.____ _ _ _ _ _ _ _ _ QAT.____ _ _ __ the atmosphere . As an alternative cause, it is interesting to speculate t hat t he observed energy soectrum is due to a structure in the primar i es . One might even venture to tie it up with t he banded structure propos ed by Milli kan and Neher. 3 3 Energy Distribution of Incoming Cosmic Ray Particles ... R. A. Millikan and H. V. Neher, Proc. Am. Acd. Sci. 83 , 40 9 , ( 1940) A Hypothesis as to the Ori gin of Cosmic Rays and the Experime nt al Testing i n India and Elsewhere - Millikan, Neher and Pickering, Phys. Rev. 61, 397, (1 942 )