BSTJ 10: 4. October 1931: Contemporary Advances in Physics, XXII - Transmutation. (Darrow, Karl K.)

15.8 MB·English

Contemporary Advances in Physics, XXII
‘Transmutation

By KARL K, DARROW

In gyre at red ese ade a he Cen Labor

wee ‘he eat ecortwe eres

fre tg by sgn See oe inchis acl,
Ander “he costo ofthe taper weer Pie eapeinenter eye The
iii

Het tape bit

ei it ese etter
IP a aa atl oe St

ott iin the omnes eet eae hn
‘been the drcem af the human race for many’ centuries, ney even for
rlennia. In special and practical cases, chit fs probably true; 1
fippote that from the daw of history mose men postered of stures of
lead or silver have Lanalie delves ly reaming af tee bela
lange co yo. Bu ne general see I rate ae One eae
noc eapire to transform eles inl element oe does ot kao what
tleinente are; ad on ene bad sac knowlege cantries age. Sucely
any af the chemical reaetions whiel we onsiler commonplace,
any ofthe commpounas old al set which the len chemist maker
in his ouive, would have seemed to ancient or co edval no less
‘wonderful than any “wansmutation” which he could possibly imagine
Could the Florentine or the Gree have Eeon rue more amazed by
change of silver into copper, sham bythe aynteie of dye out of tot
fr cau, the growth of a diamond out of black carbon in a fssnaee?
Ve soem unlikely: for the very special wonderment and adit
which the fsstamell chge will evoke from 2 scisatit of tly
‘eso taehieved Tine hin, weld aes ut ofa wins deed ale
to Greele and Florentine. Oni the made aur Ina how saueh it
ould lifer, whe parca way Ge woul erannceal sll that haw
tme Delure,

Fer his power of apprecarion, this moder wuluolar would have
two sslonee tn thank "These are te chemistry of he nse ts
the ehtcent century, with ie uncounted and uneauctate alleys «
twanulyze and syathetive are convet and transfor, wii Belt the
‘eventual conclusion iat auverreath the encles and chanyeal'e var
isty of vie ie mutter shee re certain aubsta.ts wis am neither be
undetizal nor analyzed nor converted ou iat sneer; and the
Dhysice of he renter, wen penetrated deep ints ie atom of hese
tsTreable subetances. and thee disencerel te ecundte and all be
Uazsailale part, athe the chee: ofeach eement is oonecrved,
‘The former proved that all knows chemial elemgim are meds by
ceiling chese etoms or rearing them apart; the later showed that
what happens in every sch evert nity be nna asa rearangerset
Ef Macks of ecrwns, which form the outer pert of remy atom Kut
nest Trthes proves shat such a ehge sia af lve to copper
fr of mercury to gol, must oF scetaily iuvalve sething far nose
talicol—aometiing whies the payesce af alia sities ed
feveniplly ne reves i the ater thee i a inner wear the
fence c?attraelinn seitrly she leerontocs are el gels tis
Tete whieh muse te reached aud alta. one omen Seta be tra
foes’ Sata enoches

‘Theestatement, beng a iis a deeviption of the geageainy a che
sesmperhape T shold aay, a designing of is astm, for these
Ulimate portices of matter afc sa he evel va suler system enter
that the tar sequins to be proved by explocation, The explorer.

G2: ot for thse pimnee are alphacperiees corpuscles loth are
recounimable as auch, for if they strike sesinst a tuoeecent ae
ech makes Hts separace luminous ai’. Lee toi IM) © ofa cent
foster in diameter, taey aye suall tnongh to pecetote the elecerone
Mel of eae, whieh are epresd over epacea tens af thomas of
Eanes ass. The electron near wach they yess deviate cr

but fl, bene of fee ten on eevesctiwsamidh thre say Ene
lose with nergy which may be a8 geeat ae an elector oould sequire
fron a patentialrize of sith mow vals they are able ty approach
the pastiveporsons of te atti truce nn stv Chesed
thonoelvas. "They are, in fact, extremely well Head for the tank of
oa nnd, SYSTEM TECHNICAL TOURNAL

exploration which in 1911 Rutherford imposed upon them, and of which
they pete fo Bim hag the nin thers is a macive particle
Doettvelyrharged lie themschves less Hhasn 0-* centimeter in diam
ter, They could not perce the eletrose which surround 1h
‘nucteiy” beasing charges uf which the sum compen fs ow
Dut tue evince makes we srare ol tbe existence ofthis Nek, and
Gt the geneel theorems tht fhe atom of th enone of te peaic
te consists of lerons surrounding a leaf Us ny dicen
farsi having e charge + Neartd amass alma! the ste as fe entre

"This lst the te enty which anyone i attack whe wiehes
te Lansonace che glo. Il takes ao part (ae T remarked abave) in
SOhenical poesomena, ia se engsion uf Rybs or of ays, in the

ecteal elects wie’ atons can achieve wien rey love charge and
fe becvrve ine. This for the wowulbe wanzaucer fsa fact of seus
impacts foe i the nucleus fm inlluence on tee, no mre ave they

fnything chemical at electric, Ty any cemipetature ot ay hse
tion whic: has ever beer aprlisl oa sel-tranemucing suletauce
"Ther eres he ator are wall sheeered rl highly essent; they
term asoblisious of ths would around them, #61 esi of she earth
is uconscions of the ie wpa its eurace,

Bite prepeti ofthe eloha-patile whic enable it to penetrate
to the neighborhunl nf the auslaue extreme int ess, bigs momen
thm, eormens sure of euctuated eneney—miy ey nat also que
ity in impinge drecly-oa the ator-ternel, a izvade the nucleus nd
Moruge gfe abate’ iithestaeeerableas all? Wemay be sure chat

Ihe aude of storey yvingen pecuaps excep, age comples, They
Ceimol Se tie altimata cad ieee le parila of ater for ration
edvity prives a siuie of them cluleprate of ehemeclves 10
falls od ite Hla while efor se reat Le facts tht the charge
Lal! ece multpla ofa common elarge ad tae maces of al ae ae
Inutipee of» enon mags mst surely talen a6 mein, That
Gf them are siarlures Bulle of decir aad protors. Te principle,
theeeiore, they stust be breveabln, i cay shey com he struck with
ustcen fave by haramers ofsftblesize. Now of al krswn vebles
ff neil lvee alpna-onniles ba combine the qualities of sale
resin grea: exe-Ey nul Hhesafore geem the wl alapte’ zo the task

"Such snus: kave her tle leas of Rusher i may’ be presumed
tint be wap meditating dean duving rhe wae, ance inthe fish year
therea‘ter he put sla a Ue est, ae wo became the ist co achieve
Iransnutsa Weyl the shadow of a loubt. There was of eure an
certaincy befocehand chat he would succeed, (Un the contrary there
‘Were apparently grave grounds for pessimism. We must take note of
Theses the peool tit they wove ot justified isnot. the leas important
part of Rutherford’ achievement

iret, evn the energy nt the alphapertiles right have been to
cama to injure a nucle. Teed, fer many Mids ofan ere ft
4400 smal to jdge from the wore of atherlord’s sco atthe Caven-
‘ls Lataacorys ant forthe vert thesa isnot uch woos to spate,
Trea the wee ots school appease that if the fastest alpha-par ticles
inoved with a speed ae great ae en-tenthe as ther actual epeed, ard
ho greater, che effer: would aever have been disesvered,

‘Seon sere ae rena tn ear hat the mice ace ton wml <0 be
struck exept hy the earest of chances, co rare achanee to e seviee
fil, The oleervatoas oa defcted phatase lat proved chat the
Teale of avon a fa te 10" en ons He impingg perce
no greater very’ tha missle ard a very tiny carget Had they besa
4 few orders of magnitude smaller than this masimum: lini, "square
hiss” would have boen too fom to notion, Ae a masse of fact, inthe
Fest of the stencil experiment, the proportion ofthese was nat
tone to every milion of alhacparticles traversing the layer f nitrogen
‘gas hich Rutherford was trving to tranemute.

“Vind, tae fragments of the broken nucle might not have been
abservable. Delicate ce are the methods of chemical analysis, chey
are not fine enous oo deseet alterations so infrequent aa these were
“expected tbe, ea were acy fount Asia ties ete
‘elves are detected in thvee way-—by the luminous splashes oF "sein-
lations eich they cause whi they impinge on Huresceat eevee,
by the trlls of watersroplets whieh they leave behind chem wher
they dosh through mesture-sotusaced air waist i suddealy cooled
Just before or just after their passage: and by the electieal discharge
(Gmallscte sparks) which they toch off when they pase trig
in the neigéborhond of a charged ard sharply ouinted tere. The
ton fast of ere arm due to ona which she parte forms hy detaching
loctrons from mlerules of he gas. ‘The slower the pastices, the
fewer the as: the low conspicuous ae these feta and the msore likey
tebe missed Se for the seintatone we know but Hitte of thelr
mechanism, but ve da know that he slower che particles, the fainter
the flashes, ‘Thus itis altogether reasoasble to suppose that when
nucle are broken inca Kagment, che fragments may be moving ta
slow’y co be noticed by any ef these three procedures! (One might
‘even suspect thee the pieces of a fractured nucleus may not have
a rns, svsriar rscusseat JOURNAL

the power of forgone or eenking aintlations, however fast chey
‘uve; bl Ilis woul be too pessimistic; thee i every reason 0 sup-
pose that they are ei ged corpuscles, therefore pga of Ihe ame
powers of aphaay2)

Tn all likeispod, many ator-kernels sve dituptod and their fate
oes unpervsived, Fevause the "products of iutegeation™ move too
Slowly: but sumelines these are fst enaugh to ba dacecred in uny of
the eee aforeccd way, ae we sal 68. There ie, however, yet a=
tar pil, Consicer the ulybarparcieles which pase close to nuclei
without dicupting them. They are deected, but the nuclei the
Teves sulfa resem which ses them ineo mocion. If hese belong
fo vemerts nf atomic weight grater “an 30, or let us say 40 to re
tn the safle side cir mare are 20 msc coger than thse othe alpha
onpuscle tha the speed they sexure i aeghgible. But if they belong
thine o aboties ofthe Pall-cis ightens semen, they snap eequire
u apeed so great that of themae'ves thy ri stake Zong ia a gas oF
Scnillations on # sceea, If an alpha particle, being iell a helium
tnuleus fics straight gaint ea kernel ofa helium atom but does not
fracaure it then sinioualy che etruck ices must Lake up the ence
peed of che vriking eorpuscle. Tic fa carbon or en exten nucleus
Which is thus sawicly struck, without being broken, ies tral see
faust be one hallo four tenths bal of Mealpha-parccte, Ard iit fe
2 hydrogen wucleusor proton which i Meveuim ofa equare sal eer
Fenpact it mnt goof with no les than sivee-tentx of the soe of the
Fimpinger. Ineidenciyy tle lauee ie slowee! dem to compensate for
‘he Kietic energy acctred by’ Le kere! which it trikes,

“The dangerous consequence is, thet in salam of mater of low
avemi weight whichis wnnfucled by alphacnays tere must be intact
Tin saply-moving kernels which may Be confuse, which indeed one
co haaly help confusing, with Uh expen plc of disincegration.
Moreover, ever in sivatunn ofan element of higher welght, 2 mesa
Fim oc a cube of sy there may be hydrogen enough to provideso many
Towrinac targets for the alparaym that the region ie ill with fast~
flying protine which are at eles diwuption, Fr every ease wtere
Corpuscles are sibserved waien are thought to he parta of fracurel
hace it must be peoved that they are pot ofthis kind, nor yet are
ratte lia patil

‘Non ss as index of the inital spend of an alpharpartcle people
generally tke fe “range” The tal of walerdvoplets which che
Particle leaves along its th though suddeny-sooled moist ai comes
toa suidea end (Piss 10, £53: the length of the tal, messuved to its
fend from the point srlnce the parce evtered the ai, sts ange in the
commeseponany ApvaNces ry PHYSICS oo

air and daponds in a known way (known by experiment) on Use speed
‘which the particle had at che moment of entry. Ur the range may be
desermined by moving backward a fnureszent screen placed apposite
the pint of entry of the corpuscles; he acini intone ave at first undat-
inished in number asthe screen recedes, but eventually they cease, and
‘ease quite suddenly; the distance tothe point of their eesaina i the
range. In ais at normal pressure end 15° temperature! Cue range of
‘the acest Lnown alpha-partcles (apart froma few very scanty easses)
fresh from ehe source is about $6 em, Ie has been determined for
sumer ates pases nel, and for any gas it varies inverasy ae the
ener.

TH folows then that if the Auorescent seen ie placed a€ a distance
Som the soiecr of alpina partis 29 greae Uh i les beyond their
ange i te nnn intervening, whaler aiillaions may ayer
upon stare rot doe co alta rays, Rut it urs mus yet flow that Be
ercen i neyond the rezch of protons speeded up in the way just do=
erie To find uae lwo this tis necessary to know the relation
Tietoren the spends of protons and their ranges. Now the cease of the
Eowingdown and stoping nf charged rovpizcs, protons and alph=
eile lik. in si ne they Mah Fey rato ate, ey ee
tlectsone Tone fom the trams wich They wesy ail spend. thelt
energy ia deing $0. The range of ether sort of corpace He substan
Hall the distance tough wl Lean My, before te major par of io
itil energy lise i his way, An aloha-particle has tice
the charge of a yraton, therefore extrvts electrons aftenes from the
tosis ae its curve, thereure ones eeney move quickly. UC ptiles
ofthe two Kade have equal range, the former mc initially Have ad
the giesier enryy- A thvoreiel smalysis frliewed by” Mohr sd
Darwin stows tba the ratio i that of the seamen of the charges
four to.one. Buc since the eatin of the masts is ievise four to ove,
the speeds are equal. Alpha-particles and. protons of equal itil
peed have ‘approximately} equal zarge. Now a I atatal chove,
lysdengen uel! stral ontrlly by sipha-partcies aequite a apeed 1.6
imei gret these, therefore 4 range equal to that of alpha part
tes smuvng 1.6 ms sft a shoe which made eh impact. It ea
face of experiance that the range of alas parsiclne varies ofa (not
exactly) as the cube oftheir speed. 1, reine, yee em
bared by rays of a stated sange X, lydeogen sich which aller
entra impacts wil be projected forward wth ranges amounting to

(Pike inate the, ster 13 294 Nats fa fa eens wlan
oe BELL SSR TacHNTCAL sonnsAT

(1.6), or about 4. times K— And (or instance} alr 2t normal te
perature ae! presse is bombard ly Use alpba-parils of eam
(Chwhich in thie gas ave a range eves centimeters, and scivlaions
trcobserre ena uoreecent seer beyond. che observer emusteerkin
‘bith the chunce that they may be de tothe nuclei of hydrogen mole
Cleo mised with the ar, ep long ts the dacance > the aren les than,
TE tines seven, or sey shirty, petimers

(On the griveple that the be way to eal with o posible sowree of
‘woable is tw evanine ie minute, Rutherford prepanel for his ttempt
at transmutation by a stidy af the nucle which ser struck anal which,

i=]

‘8g, 1. Reefs eppaaag fo cetecing yuna of gaze by the
vo Si Fens thn Faex Cha’
yi Stee A

"ooo a we sy when aia partis ave red ite hydrogen. His
‘pupil Masten had liga on sch 2 stacy 1914, snd ad observed
that scimlations appeared on ascren setup fr Bey the ukimate
each of thealpa-raye uno chan abner cestimetera, inasmuch as
Jin yeingen the range o either Find of elsyed eaxpuscle is abou: fove
times as pret as in ai. Resuming the research in 1910 (one never
needs to ask why Uniage begun in 1914 should have lain 20 long un
Continual) Rutherford counted the xinilladors and plotted their
ner for what, ia eet, were vim eintancen of the screen from.
Uhesousee. I ust pause to any thatin practice one docs nat drat the
sevens back go as to fnterptne cher ad thick: layers of gos between
and the point of entzy of the elpha-pectrtes: instead! one leaves it
lsed and varies the pressure ofthe gaa of ole inerpoate a sien of
‘hin o's of cumini or sume etzer metal o: ef mice, each of which
‘lows down the particles vo the same extent laa che eechicl language,
hae the stme “etopping-power") na.a lemon thickness of ie (Fo
instance, a thickness of ivicn of weight 143 mg. per equare em. is
‘equivalencin scopping-powe: to lem. ef sir at 13° C. and 760 mm. He.)
Treurves ofthe sorta hich me shall be interested, mumber-t-=cinti
lations ie ually plotted along the vertical axis, numberof-cent
reters-o-staleng the horizontal: but zeneral some other substance
dh dae foe the ai, nal it thickness ere ranaated inte enpvalent
ftekmen of this wend ge (at moma temperate ie pressure)
before the curve wits driven

Carver of thissort appear in Tig. 2. Allof thems were oitsined wih
‘etses bombarded hy alpniparticles of sevenaentimeter range. Noe

toa
nate Seat By" antec of “ihe Dic

“og, 2 Nunta af pt aig open re

tice first te curve marked: cavvesponds to ytrogen, mixed with
trl dios; snd i tetihes that te seinlationa didnot enze ni
the seosen wae shielded by she equivalent in mea) af thirty cent
meses of ai, the cmoune computed forthe urge ef hydrogen nucle
tuck censraly by abaha-corpoelen Fat as chese. (That many of
the mui! caning acitllations dl ot lave 20 gest a range ie eeelly
lcoouned for; itis det the fa. hat moat of the impacts are eeasibly
weet” the atrace parses dying ff obliquely wich Jess enersy
than they would have desived from a "squace Li.") But at thie
feniimeters of “aimequivaent." hey eeeae eal this sostains us
storing shat with any other gee ur any lid there are seatilations
‘when the sree foo me sbilded, they cant be due Lo adits
of hydeogen.

Carve € as obtained with oxygen: wt thee fit is ascribed to
commingled hydrogen; in any cave, it dogs wot extend beyond the
(Hcl point at whieh, were there sy Cashes stil to be ten, hey could
Elly be attributed to omething eae

Curve Ae moce ceneational: very Ufinitely it extends beyond the
itcal length: very definitely there ate corpuscles able to make their
Ipay thigh deeper strata of mation than cither the primary alpha
porivles or auch paces uf siray ydagen ators (0 hoch theory and
Experiment aceue us) se heer ight nd to svke,Thix reve wa
hinived with ait" Siore with pare oxygen there wos mo sign of tel
‘xtourslinacy corpuscles, ic Lo Be pres that they were due eo the
ther of te mais ows of Cae alt—an inference which the study of
pure uitogen made wre

"The mest astonishing wf: the curves’ D. Te steetches far beyond
the eeisical pont; fishes appeared om te meen wen even ag muh as
the equvelen: of ninety centaeser of ar lay beoenn iLand che ub
Slanee nics eh aplacaye were aeeing hich was aluminium inthe
form of thin Seal, "Tue, when fil of aminiuns [3 subject 0 the
impacts of thee nays ie eheows wt ronvinlen Unce times as geet
tiveas the very lama whih= crite might possibly diate by asc
Ingo verde hyrogen,

‘Ace theve then, feagments of diwupto nucs of cluminium oF n-
trogen? and are Uy protons?

Tn price the second esi x aaswerable by itself ie sie
to deflect the eccpuscles Sy wleriie snd magnetic fields, and measure
ther detections the value oftheir chergetoervs ratio (which if they
re protons i about HK ofthe value for nm weteua) could then be
‘computed, and incidestlly cher epeed alan, which itself would be
teal worth determining fn a way more dirt han by inference from
The range. Lue chougl such meacurements hve many times been
tmade on ocher kinds nf pasteles, and the technique is very well de
eloped, che apolration to those of this expecal kind is dificult bee
Cause they are ws few. Say that the apparatis isso buile that they
fall on only a part of the sreen; if « magnetic field is applied in the
‘roger sense to the region which they traverse, the spate whic Uity
fall auoves revises but the tastes aceon afeequest et the skit
rot obvious, and only by lengthy eountings can one be sure chat mace
‘of them appear in one place and less ia anotler when the Feld on
‘than when it is off, Rutherford howeves managed to wake crusting
‘evi €o prove that the shift is of che order of magica to be ex
pected. if th particles are pzotons having the sped inferred from cher
ange; anc incidentally thae they ae poscively carpe, meting
‘which hee been taken for granted but which requiees proof It was
‘wit the long-range corpuscles expelled from alumina, crom phowe
DBhorus ané from thorn that he ehieved those teal

The problem was then taken up by Steter in Vinay he tied he
scheme developed :o s0 high pitch by Aston in his famous serie of
fexperiments on isotopee—a echeme of which {shall vay ely that al
Tong it involves uth eleetsie and magnetic Held, they are 20 a
roriged that corpueles hangs comman value of charge-to-inasa catia
fare brought toa common focus itrespective of their sped (sa ‘ang at
These are not disper over ton wie en interval) therefore, By fata
"he fue ene ma recognize the Kind ef eorpuscle, 1a Fig. 3 appeass
a yort of Hi apparatiae: the sonroe of alphe-parles at @, che see of
wale subst a Sava each isthe ote of fons
arene pale nels whieh Steter ammged su cha ony a bears
ef corpuscles fllawing alziowe perfect'y garallel patas should enter
the cltlect'ng ls belo

‘Sli, ‘tom place wo place the mesure with which he examined
thexersn leerl the deficring held, nd counting the sinillations,
Sietter ful three foci which in the curve of Fig. 4 appear as uhvee
yeas (Uke ornate Using the mumber of dashes ia unie time over a
fiver area, che abscssatheqlntne of he midint ofthis rea from &
point taken as 210). From the penis af thee foc on the seen
Ffolloeed thatthe one on the right ws due w coryasee having the
[Coargetosman ratio of procons; te one in the idle, to alpha patt
few tiene om te Tet of which omly a part appears, to cocpuscles
1avig& charge tomas “tia haf a gone as tet of ga sbarpartce,
‘Two thea sxe proof vf alphiveays deleted Ey the metal a S, sone of
whic Tal lise ote of their positive charge though picking up a.
electron somewhere in taeinenrters; the thi is evidence of protons
fand sting evidence, for Stevver eximates she uncertainey of his
rearuremene ofcha:ge-to-miasy ratio ws is pester than five pee cent
‘Th enrve ai Wig. wae got wich aluminium a8 the metal which the
alplucraye bumbrded, Curves wese obtaied in the seme way with