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CitmplimtHti of tht AutMtr 
 
 ON THE DECAY OF EXCITED RADIOACTIVITY FROM 
 NATURAL GASES 
 
 BV MiM L. 0. JOHNiON 
 
 [Reprinted from the Physical Review, Vol. XX., No. 3, March, 1905] 
 
 

 iid^Ws^'riWiti^.'^W!^-:mrr;^*m 
 
[Kcprinud fioiii ili<- I'liv^n \\ Ki\1k\v, \,.|. \\ , N... j, M.inh, |i>i5.J 
 
 On tiik DfccAV ok Iaiitek RAnicACTurn ikum Naui;ai ("ia>i>. 
 
 I!V Ml- I,. I!. I..MN-..\. 
 
 IN a rerent jiajjer by I'roftssor J. C. M< Itnnan '• On the Radioai tivily 
 of Mineral Oils anil Natural (iases" ' it was shown that the natural 
 gases of Ontario contain an emanation whiih is siniilir to tli il fuinul 
 by other investigators in the gases lontaineil in certain s|)ring waters and 
 in the air drawn from the surface layers of the earth, and whi< h, from 
 its rate of decay as well as that of the radioai tivity excited in bodies 
 exjiosed to it, bears a strong resemblamc to the; emanation from railium. 
 
 In a i>a]ier by Miss lirooks^ the rtsiihs are jiresented of a scries of 
 measurements on the radiation from rods rendere<i railioa< live by e\|)Osurc 
 to the emanation from thorium, radium and actinium. In this |.a|ier it 
 s shown that, in the case of rods exposed for short perioils to the ema- 
 
 ion from thorium the radiation at first increases, reaching a maximum 
 .1 -■'bout two hours after removal, and then deiays ai< ording to an ex- 
 ntial law. A similar result was obtained w ilh rods exposed to the 
 eniunation from actinium, the only difference being that the niaximiim 
 intensity with this substance is reached in about ten minutes alter 
 removal. Hut when the rods were exposed to the emanation from 
 radium, it was found for all exposures that there was a rapid initial de- 
 crease in the intensity of the radiation for the first ten minutes ; after 
 which it remained constant for a length of time which decreased with 
 the increase in the i)eriod of the exposure ; then it droi)pcd gradually 
 and approached a zero value. 
 
 From these results it is evident that ai tivities excited in rods by ex- 
 posure to radium, actinium or thorium have certain characteristic s by 
 which they may be definitely distinguished. 
 
 The experiments described in this paper were c arried out in order to 
 examine more closely the emanation found in the natural gases mentioned 
 above, and to throw further light on the ipiestion whether the radio- 
 activity was due to the presence of the emanation from radium or due to 
 the materials themselves possessing the intrinsic jiroperty of radioactivity. 
 The behavior of the emanation was studied and a series of curves obtained 
 showing the decay of the radiation due to the excited activity on rods 
 exposed for different periods in the gas. It was found for all exposures 
 that the activity dropped at first and reached a steady state which length- 
 ened as the peiiod of exposure was shortened. It then gradually died 
 down to and approached a zero value. These curves are ver similar to 
 
 ' -Mistract of a paper presented at the Philadelphia meeting of the Physical .'Society on 
 Deceitilier !o, 1904- 
 
 ' Paper esented at International Electrii.d Congress at Si. I ouis, Scpltniber, KJO^. 
 3 Philosttphical Magazine, .September, lycH- 
 
 ^"Wi . \.wmm':^irsrr.s'^irf^-ysr'mr"''^KP- *:sfiis,^'«ipw«5*6»':iff «•■ 
 
17« 
 
 Tin: AMiiRiCAX riivsic.ii. society. 
 
 [\,.i., xx. 
 
 those yivcn by Mis-* lirooks for roils exposed to the emanation from 
 radium and, therefore, support the theory that the emanation found in 
 the natural gases dealt with is due to the presimce of radium at their 
 source. Moreover, I'rofessor Rutherford in his work o • Radioactivity '" 
 gives results showing that the amount of acti\ ity excilcd on a rod expose<l 
 to the emanation from radium is always directly jjroportional to the 
 amount of emanation present. To see if this was true of the active 
 emanation in natural gases, exposures of the s.nne period were made in 
 the same gas on different days and it was found that, as the activity of 
 the emanat on decreased, there was always a proiiortionate decre.\^e in the 
 amount of activity uhich it exciteil. 
 
 The gas under investigation was confined in a cylinder about 60 cm. 
 long and 25 cm. in diameter. I'.rass rods were suspended in the gas by 
 insulating supi)orts, and conncled to ih- negative terminal of a I'oepler- 
 Holtz machine, which maintained a potential of 11,000 volts. Alter 
 exposure the rods were inserted in a seiond receiver of the same size 
 through which a gentle current of air was drawn in order to remove any 
 emanation adhering to them, Their activity was then determined by 
 means of measurements upon the comluctivity they imparted to the air 
 in the receiver. These measurements were made with a sensitive l)ol- 
 ezeleck electrometer, and as the rods were directly exposed to the air, 
 the conductivity imparted by them was due to all the types o'i rays which 
 they emitted. 
 
 In the paper referred to above by Professor Mi I.ennan it was shown 
 that when measurements were nnde upon the condm tivity of the gas as 
 it came from the well, it exhibited a steaily decrease, and fell to one half 
 
 T.Mii.i: I. 
 
 Ci'ii.lu li: ''v ,>f X.iliiril (/.; . 
 
 Time. 
 Hours. Minutes. 
 
 Current. 
 
 Arbitrary 
 Scale. 
 
 Time. 
 Hours. Minutes. 
 
 Arbitrary 
 Scale. 
 
 
 4 
 
 288 
 
 3 
 
 41 
 
 ',41 
 
 
 7 
 
 292 
 
 
 10 
 
 340 
 
 
 IS 
 
 296 
 
 5 
 
 55 
 
 327 
 
 
 21 
 
 301 
 
 12 
 
 45 
 
 310 
 
 
 27 
 
 307 
 
 23 
 
 20 
 
 283 
 
 
 44 
 
 313 
 
 47 
 
 25 
 
 215 
 
 1 
 
 
 320 
 
 71 
 
 15 
 
 172 
 
 1 
 
 31 
 
 331 
 
 95 
 
 15 
 
 135 
 
 1 
 
 40 
 
 335 
 
 119 
 
 
 104.5 
 
 2 
 
 46 
 
 340 
 
 145 
 
 
 78 
 
 ' Ruth<.rforJ. RiiliaacUviiy, page 274. 
 
 iiRSEH'IW 
 
 ^aki2^ r>.:^ja^'is^:^^- jgf^^?" .:^^'/ 
 
nil- AMi-.Kh.w rinsiiM. >i.{iin. 
 
 value in al)Oiit i.-S days. In the iirt-fnt in\c>iit:.ition the j;as was 
 • tiulieil unilrr slifjlitly dilTerent < iniiiustaiK l>. As sonn as it was rec eived 
 from the «ill a rod was exposKl in it at dinVreiit tunes and nnder nega- 
 tive electrification for ilitTerent periods. The rod in eac h e\|iosiire was 
 rendered active by the deposit of the subslar.ie caiisui); evi ited radioac- 
 tivity, and it was always found that the removal of the active rod was 
 followed by a rise in the conductivity of the gas to a n)a\iinum value, 
 after which it gradually fell ai cording to an experimental law in the same 
 manner as before. .\ typical set of observations on this \arialioi; in the 
 conductivity is given in Table I , and a curve representing them is shown 
 in Fig I. 
 
 In this case a negatively charged rod was exposed at i i,ooo volts in 
 the gas for ten hours, and it will 
 be seen from the values given al ive 
 that the conductivity steadily rose 
 and reached a maximum value m 
 about four hours after the removal 
 of the negatively charged rod. It 
 will also be seen that alter the 
 maximum value was reached the 
 conductivity fell to one half value 
 in about seventy hours. 
 
 In order to investigate how the 
 activity excited in a negatively 
 charged rod varied with the time 
 of ex|)osure, a series of exposures 
 for different p 'ods was made on 
 one day and tlic results of the^e 
 observations are given in Table II. 
 and curves illustrating them are 
 shown in Pig. 2. 
 
 Before commencing this set of exposures a rod connected to the nega- 
 tive terminal of the electrical machine was susjiended in the gas for about 
 two hours. It was then withdrawn and the t'lrst exposure was made. 
 During the intervals which elapsed l)ctween the different exposures, the 
 electric field was always ajiplied in the same manner to the gas, with the 
 object of making the exjwsures in the presenc e of a freshly produced 
 disintegration ])roduct. 
 
 The values given in Table II. and represented graphically in Tig. 2 
 show that for all periods of exposure the radiation decreased initially, 
 then reached a steady state which lengthened as the period of the 
 exposure decreased, after which it dropjied steadily and approached a 
 zero value. 
 
 Fig. 1. 
 
 ^^^:m^mmm^^mms^m;^s^\'', ::■■-. m'i' \ 'n,%rpj:istf 
 
 r--% " 
 
I So 
 
 nil AMI.KIiAX rin: 
 
 II .socii.iy. 
 
 I\..i \x. 
 
 T\r,i,i. II. 
 
 T wo-i 
 
 11 1 n M t c 
 
 Klvc-ii 
 
 ilr.ute 
 
 Tfn-m 
 
 inut« 
 
 Twenty 
 
 -minute 
 
 Kxp. 
 
 ^%UTt. 
 
 Enpo 
 
 »jrr. 
 
 Expoi 
 
 kurc. 
 
 E<)w 
 
 sure. 
 
 
 Cii'fcnt 
 
 
 mrrtrt 
 
 
 Current 
 
 Time in 
 Minute*. 
 
 Current 
 
 'line tn 
 linute^. 
 
 Arbitrary 
 
 Tim« in 
 
 Mirutf. 
 
 Arburary 
 
 ScaU-. 
 
 Tinre in 
 Miuutes. 
 
 Arbitrary 
 
 Stals. 
 
 Arbitrary 
 Scale. 
 
 I 
 
 25.0 
 
 1 
 
 4.H.9 
 
 1 
 
 61.0 
 
 1 
 
 79.5 
 
 2 
 
 18,0 
 
 6 
 
 28.0 
 
 T 
 
 55.0 
 
 -) 
 
 71.5 
 
 7 
 
 5 
 
 11 
 
 1').9 
 
 6 
 
 39.5 
 
 5 
 
 56.5 
 
 U.5 
 
 7.0 
 
 !6 
 
 19.3 
 
 U 
 
 32.5 
 
 6 
 
 51.5 
 
 16.5 
 
 4 5 
 
 21 
 
 17.2 
 
 15 
 
 29.0 
 
 11 
 
 49 5 
 
 21.5 
 
 4.0 
 
 31 
 
 16.2 
 
 25 
 
 31.0 
 
 16 
 
 51.0 
 
 26.5 
 
 -■■.il 
 
 36 
 
 14.9 
 
 31 
 
 30.0 
 
 21 
 
 50.5 
 
 31 
 
 4." 
 
 46 
 
 12.0 
 
 37 
 
 31.5 
 
 26 
 
 49.0 
 
 36 
 
 5,0 
 
 51 
 
 11.7 
 
 41 
 
 30.0 
 
 30 
 
 511.0 
 
 41 
 
 4.5 
 
 56 
 
 11.6 
 
 45 
 
 29.0 
 
 36 
 
 44.0 
 
 46 
 
 .? 5 
 
 61 
 
 9.7 
 
 51 
 
 24.0 
 
 40 
 
 44.5 
 
 51 
 
 J. 5 
 
 
 
 56 
 
 23.0 
 
 46 
 
 44.5 
 
 61 
 
 3.5 
 
 
 
 61 
 
 21.0 
 
 51 
 56 
 61 
 
 39.5 
 36.5 
 
 35 5 
 
 Korty 
 
 -miniitf 
 
 Oni-- 
 
 lOijr 
 
 Two- 
 
 ■ hour 
 
 I- our 
 
 • hour 
 
 Hxp 
 
 osur*' 
 
 tvpu 
 
 S-; re. 
 
 Expo 
 
 sure. 
 
 E.xposure. 
 
 1 
 
 1:5.0 
 
 4 
 
 154.3 
 
 1 
 
 196.7 
 
 1 
 
 252.3 
 
 -> 
 
 122.0 
 
 7 
 
 141.3 
 
 5 
 
 174.7 
 
 4 
 
 218.3 
 
 6 
 
 102.5 
 
 ;i 
 
 130.8 
 
 ) 
 
 173.7 
 
 17 
 
 184.3 
 
 11 
 
 96.0 
 
 20 
 
 • '.i.a 
 
 il 
 
 163.2 
 
 35 
 
 152.3 
 
 16 
 
 91.5 
 
 25 
 
 126.3 
 
 16 
 
 154.2 
 
 42 
 
 137.3 
 
 21 
 
 93.0 
 
 30 
 
 120.3 
 
 26 
 
 148.2 
 
 52 
 
 1243 
 
 26 
 
 90.0 
 
 35 
 
 116.3 
 
 31 
 
 141.7 
 
 60 
 
 108.0 
 
 36 
 
 82.5 
 
 40 
 
 105. S 
 
 36 
 
 134.2 
 
 65 
 
 95.3 
 
 41 
 
 76.0 
 
 45 
 
 100.8 
 
 41 
 
 ; 'hi 
 
 69 
 
 89.5 
 
 46 
 
 73.5 
 
 50 
 
 90.8 
 
 46 
 
 113.2 
 
 
 
 52 
 
 66.5 
 
 55 
 
 83.3 
 
 51 
 
 108.7 
 
 
 
 56 
 
 61.0 
 
 60 
 
 7S.3 
 
 56 
 
 91.7 
 
 
 
 61 
 
 56.5 
 
 
 
 61 
 
 92.7 
 
 
 
 'I lu'st' curxf'- on a< i nuiit u\ iluii >imilaiity to those of Miss ISrook^ lor 
 CNposiire in the eniaiintifiii ol raihmn I'oriii another link in the i ham of 
 f\i(!cn(e whi' h leads to the conilusioi'. that the emanation Ibmul in 
 natural ;_'ases lias radiuni tor its sonrce. 
 
 .\s stated above the results )i\\t:\\ in Table I!, were obtained from 
 observations iii.ide in one day upon the same i,'as. Uurini; this jieriod as 
 I'ig. T shows, there was a gradual deeay of the emanation. To iletermine 
 the relation existing; between e>ccited rad oactivity and the strength of 
 the emanation iirodn( ing it a -eries of e\i)Osiires of five minute^ duration 
 was made on three sui eesive da\s in the same gas. 
 
 ifii^l'^JMMSPfS^^m^IJK^^i^' 
 
N". ,! 
 
 nil. .iMi i\'i j.y rins/it! mhii.j): 
 
 I Si 
 
 In m.iNint; tho- iiiei->ui ■iciil^ ihf < oiului tivitv i>\ tlio ":i-< ».!■> I'lr^t 
 
 made in ihc gas thii-^ tit-aUMl, 'I'lic -aim- |mi)( icl;iiv «a^ lollownl on fai li 
 (lay so as to maintain as far as |M>^>ililo tlu' viuio i ondition^. llii' rLsiilts 
 of tlu'sc obsorvations arc .L;ivt'n in ral)lc III. wliii l; i ontains a nc ord ot 
 the dctay of tlie activity L-M-itcd on each of the days. 
 
 T.vi;:.i. HI. 
 
 l-'.\-.il.;l l\,!./h<.i.ti: ilv (l-'r. -miniitr l^yf' ll'( i. 
 
 Column I. 
 
 1 First Day ■. 
 
 Ctjlumn H. 
 
 Time 
 1 Minutes. 
 
 Current 
 1 Arbitrary- 
 Scale . 
 
 Time 
 in Minutes. 
 
 1.52 
 
 no. 2 
 
 1.5 
 
 4 
 
 7l).2 
 
 9 
 
 S 
 
 o7 2 
 
 10 
 
 10 
 
 40.2 
 
 15 
 
 IS 
 
 J7.2 
 
 2'.) 
 
 20 
 
 3H.7 
 
 24 
 
 25 
 
 39.2 
 
 30 
 
 31 
 
 .3S.X 
 
 35 
 
 35 
 
 3S.8 
 
 4') 
 
 40 
 
 37.3 
 
 45 
 
 45 
 
 33.8 
 
 59 
 
 SO 
 
 31.3 
 
 hi 
 
 55 
 
 30.3 
 
 
 60 
 
 31.8 
 
 
 Current 
 Arbitiary 
 Seal . 
 
 Time 
 in Minutes 
 
 90 
 
 1.5 
 
 4iJ 
 
 2.5 
 
 32 
 
 10 
 
 30 
 
 15 
 
 35 
 
 20 
 
 34 
 
 25 
 
 35.6 
 
 30 
 
 31.1 
 
 35 
 
 30.1 
 
 40 
 
 30.1 
 
 45 
 
 26.1 
 
 55 
 
 23.1 
 
 60 
 
 Column III, Third Day.. 
 
 Current 
 
 I Arbitrary 
 
 Scale . 
 
 64.5 
 
 55.5 
 
 24.5 
 
 27.5 
 
 2'i 
 
 28.5 
 
 28 5 
 
 27.5 
 
 25.5 
 
 25 
 
 19 
 
 20 
 
 wm 
 
l82 
 
 THE AMEKICAX Pf/yS/CAL .S0C/E1Y. 
 
 [Vol. XX. 
 
 The strength of the emanation jiresent in the gas on each day is given 
 in Table iV. 
 
 TAIiI.E IV. 
 
 Exposure. 
 
 First ilay 
 
 Second d.iy. 
 Third d.iy.... 
 
 Strength of EniKnKtion. 
 
 476 
 394 
 320 
 
 From an inspection of these values together with the results in Table 
 III. it will he seen, that a direct proportionality e.xists between the 
 strength of the emanation and the amount of activity excited. 
 
 Taiii.e V. 
 
 E.xtiltii A'lhfii'ihfi: ify {Ei:'e-iiifiititt' Jijc/^osiirt'). 
 
 Time in Minutes. 
 
 Column I, 
 First D«y) 
 Current. 
 
 Column II. 
 
 (Second Day) 
 
 Current. 
 
 Column III. 
 
 (Third Day) 
 
 Current. 
 
 1 
 
 110 
 
 108 
 
 94.8 
 
 10 
 
 40.2 
 
 38.4 
 
 36 
 
 20 
 
 38.7 
 
 42 
 
 41.1 
 
 35 
 
 38.8 
 
 37.3 
 
 40.4 
 
 40 
 
 37.3 
 
 36.1 
 
 37.4 
 
 45 
 
 33.8 
 
 36.1 
 
 36.7 
 
 Table V. contains a few of the results reduced on this basis. The 
 values of the activity obtsined in the first day are recorded in Column I. 
 and the intensity of the emanation is assumed to be unity. Columns 11. 
 and III. contain the readings obtained on the second and third days cor- 
 rected to an emanation of unit intensity. The general agreement of the 
 values recorded in the three columns justify the assumption of the law of 
 proportionality. 
 
 In the experiments tiescrilied in this jiaper the effects found were jiro- 
 duced by all the rays given off from the excited body. Experiments 
 are now in progress to investigate these effects still further and especially 
 to determine the decay curves on the basis of ,s and ;- radiations. 
 
THt PHYSICAL REVIEW 
 
 A JOVRNAL OF hXPERIMENTAL AND THEORETICAL PHYSICS 
 
 CONDUCTED 
 WITH THE CO-OPERATION OF THE 
 
 AMERICAN PHYSICAL SOCIETY 
 
 BY 
 
 EDWARD L. NICHOLS 
 CRKS8T UKRBITT, AlfD FRIDKBICK BSDKU 
 
 Two volumes of The Physical Review are published annually, 
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 Macmillan & Co., Ltd., London; or to Messrs. Mayer and Muel- 
 ler, Berlin. 
 
 The Physical Review beginning with Vol. XVI. ( January-June, 
 1903) is conducted with the co-operation of the American Phys- 
 ical Society. The separate publication of the Bulljitin of the 
 Society has been discontinued and its Proceedings .ire hereafter to 
 be published regularly in the Review. 
 
 Previous to Volume V. (July-December, 1897) The Physical 
 Review was published in annual volumes, each containing six bi- 
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 These may be obtained from the publishers at the former subscrip- 
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 Correspondence relating to contributions should be addressed 
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