An apparatus for the purification of radon

OF OF SCIJlmOE HONOURS

'!'HYSfCft\1l

SCIENCE! LI!)RAR.'(.

iHESII

AN .APPAHA'IifJS J!'OR

0 0 N '11 _{E N' rp}

s.

!ntrodxwt'L on & •

.

.

1 2

~rhe It-'J,dioac~ii vi ty

of

Jt'J,don _••

.

.

.

.

₃

11

I F~O]J.J,tion of the Hcl.don

.. .

.

12

-

21

f[lf)() ~l?u:c i:fieat :ton _Appn.:ratuB

.. .

.

'Y) L.L

41

Perfo:rnv:mce of the Appnrr:1.tus:

i'Aeclw,ni cal :Performance

112

_·43

Ylel(l

.. .

.

₁₁₄

-

_~57

Pur:Lt;{

_5B

64

IJ.1 i )!](') o:f O})(J:L'n.tton

..

₆₅

66

1.

of radium in lmitable pos:lt:i.ons on and a:connd the canc,n·ous groNth; d.osngo

boing eon.tro11ed. lW the l'ad.iu:m content of onch needle, and i.tr3 'dmo of nJ>pli-en!cion. Such operation.s n,re e:xtrmoel;y dn:ngerouG, in thltt the neel:1J.er4 ~1,re

of ra.dtn,tlon emitted by the need1ef4 rem:::dns alrnot~t connta.nt. su.nh neeillJ.~I'l also limits thfd.:r u.~:;r~.

The high cost of

HEt.don l11cts a hf1.lf 1 lf o per1.od of 3~ 8~~~5 dayf'!, compart0d vd. th thnt of racU.um, of 1~580 ye1~rs.

Connequ.c~ntl;~r i tn aet:t vi'cy is n.p})reeia.ble only over i tr:l f:i.rrrt fc\•1 dayr1, h.<:~v1.ng

:i.s thereby largely elln11ru1.ted, rdnco 1n~~t radon neoclles \•rouJ.cl lJe qulte ~~nfe,

even H' zt:Ul imdcle the ;pattentt after a month or so. Moreover, the dosage

ct-tn be arran{o;ed so thfJ,t the needle::! m·e left perma,nently tn the pn.t.tent, thB

d.o!HJ :inbep;rat:tng to the requ:i.recl t:lmotmt in i.nfini te t:lm0.

·the tumoUI' :ls rath<":Y.' :lnaccec;~dh1e, thil'! met;hod if"! very conv(cJn:lent. A further ad.van

Jtt-"my times more useful,

ointmfmt, nnr1.tttng a vmak nlpha rad:l.nt:ton. A Bolu't.ion o:f :cttdon :tn vat'leline

X rays.

Ji'or theso reason.t3, and ce:rt.a.in otho:rf? it h.as been d~~cid.erl to const ruet a ple.nt ln this Domin :ton, for the ~m:pply of radon from rad :I. urn. Such a plrmt ':.JIHJ l'let up in \ve11ington somB yen3'El ago, but met VJ:!.1;h an ucc1.clent, and. wa.l'l

A :portion of tho radi mn used. in thEJ above plnnt ha\s been

to eorw'Gru.ct 1:1:n a.]:)pt;u~atufi :for th(~ iFJOlFJ.t1.on and purification of l'rtdon :from

nri.;:mCl 1:1:tth rm unknmm amount of 1Jn,:d:mn ehlori.de, and other :trnpm•lt:ieg o:f' an unce:cta:tn nA.tu.re.

the :end.on :'J.!'il T'mticipa,ted.

(3) The radon rnu.st 'be obteJ.ned in rmf:f1.cirmt pur:lt.y fol.' tberapt:mt.:i.c lH!El

~l:i.thout goinf'~ into d.etails, H can 'be stated. thi:l.t

1:ri.th a mtn:tnmJn of o:x:posuro to the rrJclon, and :t ts pa.x·ent rad.hun. In the pre~1ent

(1)

v1ork, the toleranne dose han l)oGn taken as 1 r~. per \'rc~E)k , e.nd every effort

An estimate of the 11 r 11 unit is gatned from the fo11ow'lng

In thlr1 section some aceoun'li will lwl givrm of the rrtdiat:tons met with in the rac):i:mrl nerios of radio-·elem~mte., A r)r:tef nm.themG.t:tca1 treatment w:tll be nCJCGnB~:;.ry to exp1rdn thfj ealculation of ·y:l.El1Cl.f.1 of rnr'Lon from r.9.d:i.ur~, m1u

he.l.f lives o:f each w~rnber, e,nd. the~ naturf': of the radiation emit't;~~d :'Ln nach.

Hn.

C"

19.,

7

mbw.

~

_HaG'

3.

0~) m1. m~~

/315'

1 ~

~

_{- 8}

1,.

5

X ).0 S(~(H~.

Ra B

1_{Pbe sho:ct rang<:\:' of alpba 8.nd. lx~ta rayn render~! them ha.rll11esc; when}

Gamma racltat'lnn i.s of

dfl,n(!;t~r₁ but 1JPCause it; lr, this, e.lone, 'I?Jhich iu required for thern:pentic um~.

1 nto ro.don.

R"Hl:tum

:n,

formed b:y the d.Gcompord .. Hon of n.").

omttn

an a.ppl.'f:lClR.l)le

't

radi.rd;ion, o.ml 1b 01 th(:; next memhc'r

d.lflphwt~

nJl

:i.nt~mle

{ acti·vity. Ra G t'lecrJ.yr:: 11y

t~Jo

menhnniFmm, forming o.

04%

of Bn,

cu

to

99.96%

of Il.a 01 • The

i

activity of Rtl

en

is ner;1lg:l1)1e, i·rbile Ra 01

cmttr:~

on1ye( rncl:tn.tion. The lai;nrlnt:~mller~~ are govern~<Jcl l);y the long hn.lf life of RacUum JJ, 1c1.11d. racU::d; e o n1y very c·mnld y.

mother element.

d t

\·Jhi ch :int egx•at efl to

1

"-1

&&oaee·~teo(2)

•r

·- 1og₀ ?

Novt let Nr1 l)e tho rnunl)nl' of atomn of Rn ]n'esent aftt-)r t FH3Conds.,

<~ '

Th:i.!:1 l.'ftclon ·l.s oEling formed 'by 1;he decompos:l.tlon of H:.1, and :i.s deea;J,ring at a rate pro~po:r'tioni"l.l t.o N,.

r.

d

cl t

f.-

N

1 1 flolt&IJP&,IIi&$(4)

Th:ts i'Jill oe integrated in full, 9,S i t 18 required for fuxther reference.

+ -,..._

2 N2 i\.1 No 0

- A.lt. t

'")..2t

Multiplying 1\v the in.tegr:::d;ine; factor c ·· , cl N • .,

L.

d. t

A

gBneral 7--;:d; EJ N?

integrD.t :ton of t.h:lf~ may

f...JNo,

K

_,,,m=•'''•'CO

(~ - i\J)

n;ystcm 'ts f:Cf:le from roil.on (i.e. conshltr> only of rad.:i.~un), then o when t;

?-. 1N o (il

2 - i\.1)

may be w:ei t t; en arl the vEn·y good

N

2

0

(1

(\.t

- l

~rh:ts equation g:tvefJ the theoretical yield of r~,.don (N,,) :formed. Pt.fter

( .

amou.nts of i'adon :l.n (mries.

5

preficnt in a system in equ:lllbriu.m w:lth on('l grn.m o:f :rnil.i.um, isolated :from it£l

_;t'Jt

/:'!JJ 11

_t.

11 _{inc:cea!'los, in ~quat:i.on}

₍₈₎

_{above, the far:1;or e ' becorneg}

6.,

-~,t

ted, b.'bl<::m of the function (

:l -

o c ) are availa1)lf::J

:J..B a ,':';11irl~:~ to the :propel' safet;y- px'eeaut:i.olH:l to be nclopt;ecl in the opern.tion of.

Oonl:'.ld.or system starting with N __ atoms of Rn, ioolnt

.f..

radhun, n.ml f:com i tB decay prod1.wt~!

or t second

constant kJ:?. 1iJ1emon1;

No. of atoras pro:w:nt Dee~:ty constant

Rn

i\.R

Rt:t A

N

_A

i\A

fJ'om i tel

lle. 13 Th:J~

c

NB

No

ill3 ilc

~M1 llefor:o, tb.e follov.ring oqu1:1.tiomi will

o1)ta.in:--... (11)

0 . . . (11A)

d t $$Ge&••e•(J.2)

•• d. ·No ••••....• ( 14)

tE'ld integrat:ton and. subst i tu.tton evo1veE the followine eque,tion for N.D and

~A. t

0 ]

+

--~---(/\0- r-g)

()..A-~)

(>--:t-Ct.Il)

]

... (J.h)

While erwh memlJer of ther-w o:x~Ql'e~~sions in of f1:ign:i.flcaneo for nmall VDJ.'lWB o:J:' t , :l t 1 S fOUnd that D.:i' te t' BOillG

1m como neglit~i-ble :tn cornparLJon Hl t;b the

flv·e hmn'f;, _1\Ht tm:·m e J- ,

tbo terms

' J.

··~A'"

e ,

to the nro:-1.11 half liVOE> of the rwtlve <lepoHJts Hg A, B8, Jll, n.nd

no,

0 conrpa:r.E-Ju vdth tl1o;f; of r:.J,don :i.toelf. A:fteJ: sueh f:i.ve holtrFJ the:n, tho nm"\1Je:c of Fd;orns of Hrt 0 present will 'be glven 'by the equation,

••••••••• ( 1'()

.A Blmilo,:c :fo:cm o:l' t'j:XlJl'PfJS:io:o holcl.s fox• N.

3. 80 thnt 'botl1 of the!'Je fol:I.Oi•T

- J •

th~cJ }m.lf live(; o:f :cn.d.on.

P;f:\. }l El.nd. Itn. 0, so that thln rruant1.ty muGt also :t'ol1o\·T the hnlf llfe of radon

/

it~mlf' after five hours. It ts not :pous:I1}1e to 1~;:tve n.n n.1}soJ.ute vD.Jue to tJ1lEJ

lE; 10 mi.11:tcu.:cles at mlcl-d.ay· on tbe snnHl d.t:tte, although this is ve:cy·noa:c)y

Yon 'l:rJE3 num'bcn~ of atonw o:f itfl, C 1.1Jhich will lle in tro.ndent

oqu:Ulrxd.um. t·d.th an mnount of Rn. ~:rhich eonnintml initioJ.ly· of a.tolrlf50

of ·t senoncl

NO\•! cons:tclo:r~ the srune nxaount of rn/ton ln c-lquili br:l.uJt1 1·rtiJh rr:u1:lmt1 n.nd. :tts d.ecn.;y products., The nu.m1Jer of atoms, (P) of ra/:l.:tum, y1;eld.ine; tho .':l.l)CJ>Jc~ amount

J?

deca;<{ constant rad.i.um, ~Phls :ce;mlt it> o1)ta.inod from equo..t:i.on (9).

(N°C) o:f Rt.1, C i.n equn:'i.ln'tu.m \·Jith J.:> atoms of R'l

0 N C

-~,_t.

••••••••• ( 19)

:ton to thq.t

0

1if

c

N

X e

ComJ;;n.ring this vlith

(17),

lt is found tha'G the rnti.o N(j b J' (L]) . : ~·

1.00B9

0

JIT ₀ ir, g:i.ven

of H.n lno1!1tAd from l'Gs :rm.rent rrldium, in h:i.gb.e:c th::w. thnt t3mount of RD. G

ln secular enuU lbr:i.nm Nl th thEl same qunnt :t t;y of r::cuJ.on 1)3r t't fn.ct.or of 1u 0009;

onl;y· \vithlts d.ec:n,;y· pl>od.uctB lm.t B.lso -vdth rnd:i.mn. The nnmo ronult muflt hold. for thr'

'6

r·ny actlvit;y of radon, and. lends. to tho tnterec:t:tng conc1urd.on

n.cti.vlt;y thn.n <Joe!~ one milJ:igr,<J.TI1 of radium.

Thus ln tho cane DJ)OVO cd.ted, :lt :i.}'l ovid.cnt th.rJ.t; the aetu1~.1 eontcm:t o:f the rf:l.ll.o:n s.<tmpJ.e mensured. t·Jould l1e, not lO wlllicurles, 1m:t

HOI·/(Wcn·, tho :fn.etoJ' :i.r:J ver;-,r GllW.ll, when aceount ho.n 11een tn.kon of

I

20

'

0 ',

',

200

~-

~-300

eo:rtain value of

'ti,

n .. ml them falls off with a ru:tlf l:ife fl:i.mlla:-r t.o that of radon. The graphs in fie;ure (J.) 0.:co btH~etl on thet'Hl · eq:rlfJ,tions, and

(1) IJ:'he gro\d;h o:f l1L1, B from R:n, expressing tho a:mtmnt rn:·e:1em

t

at

an;y-( ',)) L, 1H10 gl'OI:-rth of Rn.

c

from

:r.ad.o).l, n i mi 1 l'Lrly

ex:prensed.

(3)

IJ'he growth

of

0

ray tJ.cti vl ty in a

radon

tube, a~:;a-in ex:p:reflsed l?tf:i

a percentage of the r!k'1,;d.rmlm.

an ionization chmnl)<~r errrp1oylng 1 em. of lead filt:ratlon.

Stnee the

'6

:cadJ.ntion is mr:dnly d.u.e to Ra C the third. curve elogely

s

1C (J3)

+

(1-K) (C)

J3 pr'Jrcentage of maximum of I-t,'1 J3 n.cmmmlrJ,ted. 0 porcentB.ge of ma:d.mmu of Ha

e

aOC'\JJnulated,.

of filt:ca'd.on employ(Kl :i.n meD.su.:cement. Ya.lues of K have been determined. 11;7

f:com Jif>. C, so t.hnt ·the relB.ti ve cont:d button of J1'J, Il falls /3,£1 t h.e dep·th of

If the t:tme B1

knovm., curve (3) 1J.l10Ve pm:mits the calculation of

itf~

maxirrmm

0

rn.y D.ctlvity

o:pera't:l.on. Thjs redue'c;lon ln time of opero,tion :f:eom

60

to

30

wi.nu'Ges lowers the

:t't~,diation

exposure to 1

/5

of its value for 60 minu·teB. In

11 ..

e;ene:cal, it is.r3.(tvnntage01.J.S to handle the radon, where necessax·y, when it

:tG ju~1t:. fre!'lhly iFw1o,tetl from its clec~~\Y protl:uctD, for it then. ha::.; a very

rphe c:manatilv~ power, or ease of removDJ. of radon fx•om

(J.)

of radhun

from :t'DA:l:lum comJ!cnn·td.n clnpend.r:: not on1y on tlle t;ernpcl'::t'Gnro to 't·.rhi.eh they n:r.·f~

ou1)joci;od, hlt n.lr'lo on tho tlme of hea.t:tng.

0

Some

3

or

4

}:lour~; at ...:tl)ou.t 1000 0 may lJe l'<·Jq:tdrorl for n good e1 Thin does not appear to 'be a very roR.ti ~Jf1".ctor:r me tho d.

(2.)

preparations h~N<'l lleen lnveEJtigatecl t·rhich dl:::1ple.;~r of 100'/b, (

7)

Thtlts l:f rncU:mn :l.ons a.:re adcorl/ecl on

:t'fJ-f:Wlution, the lJ:t'OJ:nrat:i.on, 1,rhen dr:tod., w:U.l gi.ve off nomtl

95%

of :tts theorf:t.:icoJ. ;)d.c~ld. of radon.

Pur:tfi c.D:\;1 on the J.'E:mllt::.tnt rn.d.on ls in thts eanc!, qul tc simple •.

(G)

i•lermn" ha.s

1 '?.

-)·

SLlfficienii eonGi>ntrat:ton for tbenl.:pGnttc tlno. ~1ch a method is used in

(9) a cl.Ewice J!lrtdrnted. 'by n, Ge):rnr\n wanufrwtu,ri np; OX'i:';i),niBrd:,ion.

In view of thi~rJ Bimpl ici t,'! o:i:' rmr:lf ieat :ton, n.nd the cowple'GH :;:~JH1enee

tTntortu.nn.tol:y, tho

cp.1n.nti ty aml llJ1Cortainty of the :i.rnpu:clt:i.es in trw ::vvn.i1 al1l e rad:i um dol)a:cg

rrhe p:ceparat:l.on of the startiJW r•JD/ce:c).~;,] Hou1cl a1mo ct eertrd.nly lJe npset by tho impu.r:i. t:i.Pn, n.nd :in :'m:l cnse the oxtenrdve hancll:tne; of th~;

r;o:lut.1onn of cnJl:l:t)JJ1

eo111pletcJ;v ln s·o1utlon, no nolutrc1 are prerwnt on \·.rhoi.ch the rad.on ean. ·be acl~

(lo)

(Jmall h:tt rn;'J,;y- lJF; u.pp)~eetal)le tn ttmo. As :r-n/Lon nceumulr:d;er, tn 8.queous

etel;y· :comovod lJy :flUillping.

but tl.ppen.rs to l~e the only one [l.pp1i.cn.b1e ln tld s e~wo.

solution o:f

ry~he word. 11_{impux·i.ti.eo}11 _{is rnthcr mis1ead:i.n1~C, fllnee the rn,tio of}

(n)

:l.nrpud.tt8n to :cad.on may ·\·I<'Jl1 'IJe of i;ho or0.er of 500,000 to 1~ .A dJ.cJ-cussion of tho ·\m.rious Lnl[JttriM.en, top;ether ~·rith por>sil/l.e methods of reJnovnl,

14 ..

more pronounCf<<l i..n th(') l:i.quld pha:':le of tb.e ::;ystem. The rate of :fo:r'ml'ttion

of those

ga~oJe!'l

then depcmds (l

3)

f:i!:'stly, on the fraction of thfJ

rf:l.di~J,t:i.on

adso:rbml by the tifa ter, and. hence on the c!.imens i.ons of thJ"J oon{;a.lnlng VB£!.tl el;

on the rate, and this appe:u.>s to 'be {;he only frJ.etor for t·1h:i ch fieurefi are cwa.ila'ble., 'I1_{hu'3 Ch··*i!·Jr a.nd. Jbmso.y}

(14)

_{f:d;nte i;}·l8"t the we<3kly yleld of}

olectro-ly't;le f;t1G from • 21 grrm. of ra.d:ium in solution was

25

oe,. :ott

s.

T~ I\, In the

ga£~e~J ten•e not evolved ::tn thl'll:r sf;o.Lctdometric rat :i.o'; an excer5s of h.yd.rogen be:Lng _pro sent. Thi~ b;c;.~ lJc:;en attr:l.1Jtttf3d t.o the :format ion of hydrogen

(15)

und.m.' rad:l.ochemlcr:•J. lnfltlrmce, and. certainly f'iOme H,0.-₁ .3~ppeo,rs in the

so1-r~ c

(lf))

u.tlon. Ikvtne;ston ol)j8cts to l'.hts theory, however, E1:tnce the exoeElS of hy(lrogen ls und:i.min:tshed 3,fter yen.rs of use o:f nuch a !'loJution.,

tl:d~J m~:w lle ., the excess hydrogEln }Jrcsents a. ·problem, for the g::tseG CRnnot lJe

methods of removal of H.., r:tnd

o,

hD,ve been. 1J.r.erl, recomhi.nat:ton

L L

'beinr; common })ractic~~. Many ty))es of Dpp8,ratus

14, lb-22

em:p1oy a npa.rk :for recoml1lnn.tion purpose!:\; hot meta.ll

.

:~, c eo,J.et . UJtl

(

~)) , OJ' n

20, ,

24

hot :platinum

wire"

effect a less ex:plod.ve n~et1orJ. J:i)):Cenf:' hydrogen

..,,, <)4

t.~L IJ C

15,.

. . ' . ( 20) . .

23 '

2~

\·nth plat:un:u11~ l'l:tthf~l' platect. onto ~t

,

o:t' merely rcm:r·romKhng

lt.

A further method for romovlne.; excesk~ hydrogen utili &:c•fl t t~1 h:!.gh en;p~~.c:tty ( 20)

for n,rl~;orpt1.on in hot JlP.JJ.aclium .

cal mct.hod.s for th~J :r·emoval of hydrogen tmd oxy₁~Gn vdll 1Je

ear1Jon dioxi(te l

AI:ph.A- racliat !.on ha~ a ver:l marke(l pb.ot.oeher(d.cal a.ction on o:egA.nic

li t'r.le rB.ff:tcul

ty.

:&'it;tlrns do not appear to havA bcf!n publ:'l. ched regD.rd:tng

cocks to ra.clon.

n.J:'fJ of :tnrportn.nce :i.n the Tll'fJsent \·ro:ck~ Fdnce the amou.nt of :cadon concerned

In an

of t,.,o lHre.~r~. volume, th1.s \voulcl 1.mp1y r:t prt'~flsur<'l of only

5

:X: J.Q T>1lftH, of

moreury0

(18)

Rutherford

11o.G r.tudied the removal of CG:rbon d:l. oxide, and f:i.nih1

.B'raet:tono1 con(l.en!"r:tt.ion of the m:i.xture of radon n.nd 000 \-JR,c~ r:tlr,o

L

but the t\·JO gasen hrwe

very

nbt:l.lnl' vo1atilit:l.os, Alt hou,,~h 000 ha~J

L

Ruther·ford flna1ly t rlod ::riJ.bf~tt tut lng

This

1m~thod. is too mesr.y for rouUne 11\:.Je, ancl d.oes not pr;rrn:i.t of V'(l!ry good. v;::wna.,

( 26)

GO 1.n a glans vmlled. o~rwt;em to a :fraction of a 'bar; but thereafter the

':1

'-·

act:i.on ll'l r~lov1, d.ep(~n<ltng on the rate of remova,J_ of this frtrongly adnorbed

(11)

Later work h~l.f.'l shmvn th'1.t by

Some water vn:pour e.ccmnpn.n1en the gasos purrr,oed. off radium solution,

ThhJ Vfrl>t<'lr ·J.:; US1Jn11;'! rempved. with phosphor:i.c 9.nhyttr:ir1.(~, lllet11o(l hae

lJe~:m

lntrod:twed l)y Alle·n anct 1!'rank1:tn(2

'7)

who ln a m:i.xture o:f dry ice and acetone.

but a very r:onvenhmt

employe(l a t:r•ap eoolE~d

0

sc'l ol)tr:dnEHl., n.vpro:d.m'J,tely -70 C, no contlonsat:ton of rad.on vmB o1:H:J , and.

ver;,r e:f:feet l.ve romovnJ of v,,ater vapour ref3Ulted0

exceed some 20 mms. o:f mereury, l

t

1 s p:Cfl:'Hmee in the ftnal produ.ct is no fc!e:cio1.w :tnconvenience • Dlnce the radon n.ncl impu:ri ties r~·l;i1l remo.inlng will

be conrp:cnnned to nea:cly atmonphe:ritJ pr<HJsure. However, th1A vapour vd.1l be

d.econrposet'l j,nto H..., ancl 0;, lJy radon, and j f any condensed. d:copr~ of l·.ratE"n_• are

~:.:, {

\'J8:t'!~ ellm:tnoJ;or:l fl'Olil the final contai.n~~r, tho D.l)OVO e:ffoc1; \·Jonlcl 1Jf3

since Lh!:J :i.nerease :i.n 'prc~snure on dEwomposi M.on of water VflJloUr vrou1cl -lJe only

17.

(

)

J,t'v"! llf;Hton 1111.~1 nug{';Rr~t.ed. thn:b some chlor1.ne 1~1 :fol'med in th13 rn<limn t:i.on of Hd.n chlo

·,. n.nd mny (1l)

lm romcrve,J. l'y o:x:ldrtt ion >:rt :.>h hoi; COf?fJE:t' o:dd.e , or 1>;)1 cnndt?JH;atlon in

-tee (ll)

I!c1l'LunJ:

HeJ.lu.m 1v111 ll(~ fe'.trred to m1 Inn

Comd.

0hom:i.cn1 mcthodf~ ronui.l'e

.. 0

n lJo'tll.ne; J.!Olut of

-b4

C at atmosphor:i.c :presf'\ure, 1)u.t. :1.ts eondcmn;'l,i;:ton tf:JYI\j)ern.-·

tur<~ :fo:c 'the nit nut() IJfU:tioJ. proncurer~ c:x:t sM. n(-s in the )TtJ.r:i :ficnt :i.on n.pparatuk>

(29)

'ls much lov-1e:c. .Hutho1•forcl h:'tn men.fmi·c~d 'Ghj_s· hlr!ll)fH'atnre to bE: of the

- - 1

--1 , I ; I

I I

121

I I I

I I I I

I I I

J

I

---- -~---

-3

12

L

. 0

not ftvrdJo,1Jle, 1mt

tt

appearn tbnt oven n,t ~JJ33 0, ol)ta:i.n,g,1)]8 t·r:l tb. 11, 1lqu:id

tbtfj t~?.niperaturo in not low enou.g:h to cond.en.Re lw<lroc;en~ oxygon, o:c heJ.tum,

so thnt tlws01 gn..rc:t'~s JW'l.y lle punrped 01J.t of the f~yF:tero \vh:llo. radon :Cf:1nia.inn

condorHc:ocl. in n l:iqu:td. a:tr trap. This trap nhouJ.d be an nmall an pusnibJ.e,

u.:n<l JGimB of punrplnr; ke:pt to a minirnmn, tw as to rednee th~) lof~R of r1:1ilon due

Cll.r1X)l1 (llo:x.tde cannot bB· :removed 'by :t:lltyrd.enJ metlwcls, aH oxplr~inecl

fien~tion

t;neo·un.tor(-~d. in tb.c l'ltera.tu.re

'Lo d:tr:wusB nll the pu.r:tf:i.cot:i.on 1xppo,:ratus

10~12, 'in v:i.ovr of thd.r nnm'ber n.nd. vad.cJty

~1

he follO\•Iing roay

The l>u~:1.ne Apr)arn. tus

( ~)3)

A d.iae;roxn of the ossent:i.nl features of this npparn,tus is ehovm in fi{';urc;

(

~?), It employs a chemicn.J pl~r:t:f:i.r:D.t:ton system, consif:·.t1n

1

~; of 1:.1, eopper ox:i.de

( 11) , nnd. a KOH

t

uJxl ( 9) DJ'O n1 f~ o empl o ;yo d .•

A :F',)Or. tuJ)c:J '. :J

Ji,<J,d.on and. it fl l mpur:i. t 1: e \"1 D..(~-eumuli::tt~;:; :in the r:,l.dJ.um fla.Hk (1), and EJ,re pumped. tnto th:l.s JJU.rification unit

toepler f11lmp. i•Jhen the mel'G'\try J.eveJ. ln (t'j) is 1owere<l to lJelOi'.l the J.ev0l of

.,

A

c

D

E

TRAP

F

I

RUBBER

TUBING

I::

8

l]J.

As thfl mercury

WJ1Vet provnn.t.1.ng ba.ck di.ffUEJ:lon of the gt:I.C\G1i:f rn:unpe<:i nbove th:lc~ valv<>. Th.e proeess may be repeo,b:;cJ. at will. de};)EmdJ.ng on the eff:i.c:i.ency of

~nrt:caction requl:eed. After r:ruffi.elcnt ti.me l1:1.s l;een e.llOWEJd :for purif:i.cnr

switches in close proximity to t Tlcen.1.uw of th:l.r~,

ot

F.tftm' t'ePtoval of the .

Thn uso of tho "!Cllghty· a.nd 'L:i me::: conrnJ.m:i.ng pumps hru> boen

)

( 27)

rmd. Allen and F'rankl:ln 'Jlht~ lnttor employ·

n dry teo trn.p to fTon?,e otd; water vapour i.n n. slrJ.e n.rm of tho Ft1:d:ficn.U.on uni-t ..• \'.'hen connect::ton ln mn.dE1 lx~hmen thtr, unit and. th.e roilJ.wn flask, tho

from Lbe :puri:fi en.t:ton unit into fl .. 1ar₁<>;o fJ1:tnk. from 1·rhi.eh it h'l :forcocl into

A sinrpl:Lf:i.ed clen:tp1 hn.s becm J.nt.roduced by Honderaon

(3c')

and.

(20)

D

l

K

N

)~=~=- To diffusion and oil pump

Mercury rcservoi r

A

20.

\'!Mle i t :i.n pomll.ble to fune j)Ota.r,cium hyclcocdtte onto the {.>;ln.f~S waUa of fieation tube, th1.

therefore not compJ.d,f3 in thiB

(ll)

A ph;ys1.en.1 method of puriflcntion l.'l!'W bcwn der~erlbed 1)y Od.(l:te NhMle

jn ( Lj).

Hith the

level Lo F x·nict~d nearJ;y- to tho llnr:le of the~ liquJ.d air tho

:c·emoved .•

l':,dnn into tho tullt:cJ K, whJch is coated N:tth :futHld KOII, a.nd theneo :l.nto the I,, by r~.ircli.ng the mercury through f1n.r;k

:a·.

Th:ts plrmt gj" vef\ a. very so.tisfactory perform:'tnce. Yields of the order m:t:nu.tes on.

~1_{ho ilnpuri tie~ l'emaining hrwc:1 1Jeen claimed. to he CO ( ) , but n,}

connicl.cn~·~·

2

with tho condenned radon sinco

t t ~ n J ·zof ' 1: t .

'

l , -1. • .1' ' }

eoncenTI1.'"J,OlH1 o,- ·)fl :cno.on n.re o• a.1nEJo. on a seeonr. com1.ensn,,:un1 0.1. 1<.10 ln

a.

1₁1_{hA method. i::;}

HlCH'fl eonvenlen.t th<C!.n oth<:n·::; cont-;idorecl, ln that the o,pparatuo

'I'hr3 KOH in

J?7

2C 3C 50

SCA1....£ -CM$.

RADON PURIFICATION APPARATUS

In Octdte's plant., the J;:md.:flcntion :l.n e:ffoctod :tn t'lro cl:l.ntinct r.topn, Ho-vHwAr tho c1.ry :lee

,,

their 'VII:1Y' to the liquid oxygen ~~ta.ge. uuch n prlnclple is ernp1o~red in tlH:l

On opanlne

thiG

cut off

from tho :rad>i.um r:Jolu.tton in flask (l) cll:f:f'u.se into tbcl d:r·y iee tro:p

(14);

1:1. qu:i.Ct oxygen sta.r~:n. The pWJ1piug act:ton :t~ only· }ytrtly d.ue to the tooplcr pump, hownve:c.

J:n tllo:t r

dif:ftWe oa.ck into the l':::t(liU.'ill flHr1k. Gince no such effect opor·:1.i;on here, the

clr;y :teo trap of

into 1.ts cond.en:3F),tion t1 , furthc-l::c cont 'bu{:; 1 ng ·l;o a good. ;ylelrl of this

J3y n, rat11er extemdve syf;teJrl of mercury seal:tng, all [?,'eased stopcocks llfwe been protected frow exposure to the rn.tlon; and :i.n fant th(!) radon en-countr-l:r.'S no grecMJe at all in the vrhole c;yBtem, except that VJhich the mereury

Evon th1.s :is largely trapped by thtc1 rq_Jlasbheail.s

35,3G,

rtml

37.

A dE~scr:tpt:ton of the routinG proeFH)UTe :for Ff"K'craction \vill mn.:ke the

Pofrit:ion D,:fter prevlou£1 e:xtrac1iion:

1_{.J:ihe cut off r.wstem of m<'J,t;rtc:Jtie vncm:mn vaJ:VtlS}

_(C)

_{nnd (10) u.i.llllave}

pu:d.f:i:eatlon s;ystem mft;y b<'l altel'ed w:Lthout affeetin12: the rnllon n..ccunm.ln,ting

contained ln trw r>toe1 renEH'Volr

(38),

and~ am::illn,r;y· nd,jn::;tn,lilc roBe:cvo:lr

(41),

\ri 11 lm r~.t th.e levels lnd:i.cated in tho cJ.:tagram.

left evacup,ted as o.n ttckUtionrtl procauMon, to J7elleve the pressux(~ on va1ve (10). Pre:rm.1:n.tion for extraction:

A gold caJ>ill8.r;y tube of suitnJ;Jo length mnnb l)e flttcd onto the KOH tube 2;'., and the 1rttter fi1lect with KOH.

tlto [J10VJ leak (40), and thence into the J:1Urif:i.cat:ton ~J;yrrcem nntil it reachen

Prep.<:JJ':i.n~~ the KOH tul1e eomd·~kl :i.n :i.ntro-d:ueing a :f:'evr Jle1lots of KOH :into the r,oction i.mrnecliately rYpposite the fit;ttre

in-mtfflcient tn :c(C;aeh the to:p of the ;joint, 1.trhlch iB tbcn noaletl e~x·terw;J ly

(39)

in now eloned, an<l the blt;h vacuum pump Givltched on,.

<> 1

J=:'

n

OJ . . l mnm. or

-/1

10 'rmn~~., \·lith

now oil in the pum~p. The dry lee traps (14) and (?9) ~U?e tJUl'roundecl t:Ji th

and tap (26) lo clo r~hif.l i;.<J~p it:1 }l(}ltf Sl'lalerl l·rl.·bb. mercury

hy

ll{~;

.-,;tcr()noel:;::

(3o),

unt:tl tho moreu:cy :ci Ci~) 8 to t:he

roqulred

1Bvel rtbove

(

)

.

'I:Jw next ·sent:ton, fo:c tho presnnt :i.t. ,,Jill suffice to rstr.\te th:0.t oxtrnction

(C)

and (10) are S\•!Hched off ..

f:l.1l:i.ng lt wlth rne:r.eury 1,-J:tth tho nid. of tap

(31).

tho mer(\UX'y f:com rif>ing too :f.nr u:p tho h1ft hand. tulYlng.

tht> only o:n.trn.ncc~ to U1e llquld ni r t.-.cn;_rJ ir, YW\•! th:con{;h tho toople:r pump.

to t1H~ toz:;p1er :pump :i tseJ.f. \'/hen tho mercury l0vol reacheG the po:lnt 11_{:X:11 ,}

ThL:; pump is of ve:t·y h:i.gh eapt:wH.y and. qu:!.ckly JoHtH'(1 the wercur·y

cont:lrn:t01J.H1y opEJrat lng. ~Jlhe e.xnct t:111te at which to Sl·riLeh on tho t:mmp .

"X" ancl 'begi.nr, to fa.11 again~

when 1. {:; 1 s :;1·: J.tchml off, In ·\.d.Eli'f of the vo llH;lo of mo:cm.t:cy 1·rhich must

)Jr'Cf1~.mro ln flrwk

(17)

:J.nd. the 1.'c:::;~er•.rolr; flO thnt JM:celll'Y conti.nuer.l to f'EJ.ll fOl' <:10mt:J sceoncls af1;cr Bivi.tehlng off the pump.

l10fore tho Hwrcur;y 1flVe1 :c:tsccJ

n.

Dt.td.ng t;};o lnto:cvnl, tho cut off

em lr1 o:ponn<l for a fu:cthcsr five Boconcls ( ) , so that a ln:cgo

tho mercu:cy in ca:pl11nry (113) ;~;l; the t.op of the oeeoml ntrokc of 1;hP ]JUli1J?.,

gcnr :cn.J.l~r adequate. /tel tb morcury reaches thcJ cr:~pilll'l.l'Jf fo:c tho nocond. t:i.me, 1t :'i. a.]JJ'vJc{J. to cont:lnu<1 f111:tng :lnto :fla~1k 19 until 1t :coachon thn

•.1.\.th HH1rcux·y.

L\tream of warm air. Th:lrs is pt'ov:i.(lod v.ri th ~" ,jet pun1p and heat eel

:c1

tho lrtclrc:m·;y mt~.y 1)(3 hol(l n.t n, lwvel ju.::t /:J.1Jove the ground joint for

vlhen.over po'>c:i.ble, ~~,11 bancl1ing of the p;old ca_p:i.lltlr;Jr 'LB carr:'i.od out at , rd. :nee the enc1 OfHJcl rn.don hv.r:1, nr1 :ynt 1 onl;•,r a lo1:r ~ cwt:Lvl ty. 1tl1wn

11et1Jrn to :tni

t:tal

poflit :i.on:

\•J:l:th tho vneuum pu.mp runnlnc;, nnd tDTJ (39) open, the mcreu:c,y· in run do\·Jn throngh tn.p

(33)

until a1Jo1J.t one th:trd of 1;he tcwpler :pmrtp is emptied..

for lt ~ At thlf3

1_{f'hr; outlet from the hle;h vacnmn punt]) 1eadn to the :tntoke of H. VElJ.'Y}

throur;hot;,'L. tb(; o:xtract:ton.

:i,

n o nco

mm~e ( "'(,) l' ' f_~ •• J n

and l>,y U:w une o:f tnps

(36)

::mel

(33)

the mercury :ir~ lowerecl below f1ont valvof; (:t,G) and (?4) to Hs 1n:ttlu1 potdtioll.

from

opo:n Gon.tlo wn.rroi.ng of the

Condensed water is

th~n

removed·from thi trap, tho

latter

cleAned

nnd

i.E: oncE3 rrlOl'O in ltr5 i.nitlal pofJ:!.t:i.on.

A fevJ remnrks on the genern1 ru.nni.n~ of ·the plnnt 1.vill beJ made~ at

r:tB tho hydrogon nnc1 oxygen arc }Jllmped off.

TJilmplng, t)ut n qu:tck m0thorl of tef:d;:t ng th:i. s i.B n.1mo~t ermcmtia1 at; this i3tnge. 1_{Phe lnntrumont hn.fl l)c~nn cnJ:I. 'b:ce\tccl :-J.{::",cd.nEJt a N:1.0l80d}

1co;D:lJ.gtJ,

Rout:l.n€3

tho It 1. s only a

:Het\el'Vo:i.r

t\Jld. a J.:tttle l11E'!l'C'Ur,y :ru.n ln thl'01.."lj'!:h tar)

(3!i),

flllln{~ the comle<Jting tuJJin{~:m fJ'ho eonnflnting tubing on the other encl of the reBe:cvolr lr1 simi.J.arly flllnd, usi.nt: tn,pr;

(30), (Jl),

n.m1.

(3:?).

thfl vrhol.8 f:l.JTR tern is no1<T f'i lled. w:i.th mercury, thus cnB1J:r:ing that th('J eorrect

:unount in run :i.n, nml tho nmreury 'lti then f:i lJ eel lnto :ceservcdr

(38)

nne of the D.pprnpd.:J,t e

eo:>'li11ntEH1 the pror~erc1r:1~

Noreur,y liL'\'l l)e ompt:i.nd f·J'Oill th0 r:wr;tem ll,Y r1J.rmin,'r \. t n.J.l :into :cene:r'voir (

38)

₁

Opere>tton of 1;nEl,plor f)1llll}.l.

'Jlrw

HlOCit U.mo conRumlnt: p1:1.:rt of tho f:JY:tract1on lr4 tllo operat.:ton of ·blw

th0 proco~R nutom~tic. IIor .. rovor, the nxrv~t po:i.nt fl,t vrhlch tho vrwutJ.m pul!ip

eonrotruetlon:1.l n~JJcetf', po:i.nte.d. out ·~·1ho:te llfJC.ni'lsa.ry. vo 11lme of nn.eh :H'Jct :i. o:n \·d l.J. nJ. ;~o ll(~ el-l. r•.ctl:c; n cd.

Ff'h<'J

volnwn

roqnire<l for ·thls fL-tsk <1.C3}JOl1.d<1 on

on

~jt~''lE~ra,J. fs"et()rs, the most

i. mpor t;"'n

t.

l!eing the volume o:f \vtl. l cr n fHJ f~ f'i !'! n. roy t() oonrplet el ;\" di.nno1vo the rn.cl tum ties.

optn'r\t01' of tho :plant uncer·tn.:L ne

OllHly run :i.n \•/r~JJlngton, but th1s, agr-dn, b. vory

Otlx~r ft1ctor::l l)oa:c:i.ng on tht·1 volu.mo o:f tho flaflk .'3.ro at~ fq1J.ows:~~

lt,y

(1) Since certain a.mmmt. o{ tb.o wr:1.t0r solvent is removml at r;ach extr::wtion

30.

( 2) r:Po t'ln~mre (1 good yield of l~oiton, the vollJJTJe of gr:w in f3q11.lU brhun vr.l. th

.

(r)

the nolutlon mlwt 'bo sufi'le:l.ont1y Kof1e:c J hA,s nho•,-m tlm.t tho

solu-b:t 11 ty of rn.don o be;yT\ Iknr;>r I s lnw, · and 11/HJ

uhcro V g

1~:1 amount of radon 'Ln tho r:wlut:i.on

VEl vo lUJr\o of solutton

o( noluMU ty eo1Jffletent.

nJ.:3o ₁ 1·r:tth the totn1 cmJ. t eoneeni;:cn.t :lon :i.n tho oolut -Jon~ l1oi ng J.o,;rC:l'<~{L ~H~ rnoro

' 0

• 2G,

corrosxHmrlint~ to ?0 C lw.s 'beAn adopt.<:H1.

1:1lth ~~- g.•M; to sol1J.t:i.on ro;bio of ;J.:J, onJy

13%

of tho radon rmnaim1 diE~nolvod.

An tho gaG a1Jovt:; t.be so1ution ln romo\,red. (luring ex.t:cactlon o:f' tho I't:tdon,

nome rr.Hlon w:1l1 come out of rwlut l.on ·in order to maint:·J.1.n th0 oqu.tl i lrclum

J .~,

(33)

;;:

CJ

~"l:

....__

""

""'

"l:

lj__

C)

<:

C)

~

"--""

ltj

\..)

....__

ltj

~

0)

Lw

lf)

CJ

lf)

....__

C)

V)

cc

\..)

---of

(4)

All thEj nJ)0'\18 po:i.nt~1 favour a ln.rge volume fen· the r;:~.di'I)Jrl 1mt

tho limH eff en!;

:l.n Lhc :cacl:itml flank.

'out tl11G in time conmtm:ing, while voJ·umen of moren:c,y· :ln oxct':JDS of one or ti·Jo

f:i.gu1'e~1, lr; 420 1n n. 1()i1n

of o of tlw :t'D.rlon due to t;o1u'bll:lty.

In point of fn.ct, tt waf> found. por:d.1J1e to dtnool·vo th1;; :w::.1.:Un.ille :t'~:vllnm

in ;'00 cc. of w.1.tcr, with the n.d!Utio:n of alJout one t.euth of a. eo. of

c:cmcon-tr~ted h~lrochlorlc acid. fJ.1bl \,':W pnUJ'Cd into the above ('l~;Gk ttD

tq) to ?L]D ec.

beakor u:r;:11 _{to rotn:i.n th(< solu.t1 on :i.n} .A lootmly f:Htint; tln 1:Ut, not shovn1 in l.ho

la'ui.on of v.rater· into tho rHdium ~Jolu.tion from wore ac:co~~r:Ltble por:tit:tond. Ample prot.E=;ction i.:J provldecl by P.. 1oncl cylinder 110", two :i.nche&l in thiekno:;;.s, anr1 the vJhole iH <3o.closecl in n. fLee 1}roof g.~.fe, 11_Frr.

to the radJ:nm flask 1 G n.vrd Jnl)lo l;;v rPmovi ng h·TO 1Jl ockr.~ cui; out of th,, c;)711.r!de'l'.

1_flr1e

1 l<l 11D11 of the

with no 1.o0s

ln

protection,

·j ~. !'1 - ·f'·J . • ' ' ,<'>''lP''·' ~, ..• t \..> ('7)

oppo

33.

t;hat a pa.rti .. "J,l purHtcation 'b~/ !'::parking would be possible prior to extrRction. Moreover, the water formed would lJe return Ad to the T'1'l.dium r.olution. S1.n.cEl

~)40 cc. of !'lolu.tion were required. in the above flask, the totnl prerHmre

will not bui.ld up to s.parking ra.nge ln less tban nrJout

9

d::tys, on 1;he bi'H1h

( 14)

Thif'l i 1'1 much 1ef:lS than tho ;::werage interval

The l'lj;Jlash-head

(3),

preventR Fuiy 'bu'bbles of solution comlng over t•r:l.th the gas m~ it is pumped off. The col1Y!.ncting tuMne: has been extend.ed upward. to the point 11_D11 _{to fFtcilHate the f':t1linr, operat:'ton.}

'brEH'l.king off the t:i.p of the tub:i.ng At 11"011 _{nnd pourhlf~ liln the solut:ion, or} vm,ter, with th8 r~J.<l of a lonr; fnnm'll extendin{:r, 1H~low the Bide arm leVfll.

rrhe tube 11_:ID11

1 sealed :tnt;o the ground cone

(4),

is a sa.fety device for thA removal of aceumnJ:~J.i ng gn.s if tho cut off syl'!tem rmffA!'Pl ::tn accident and the tubing to the ril?:ht of it ha~ to be soa.led. off.

In

this

event, a

tube 8.nd tD~p may b(:'l fitted on at thfl grouncl ,joint, ::1nd. gaM!'\. pumped out

throu₁~ the tap. The Up of tube 11_E11 _{1:1ill lJA broken off prior to thts.}

At the point 11_{A11 , the c~mnecting tubing (liverges into}

_two

_channels,

lead~ing to either of two duplicate un:l.ts. The remainder of the app."lratun

pur:i.ficat:i.on. unit will 1Je able to J:1.'l,nd1e the :r.~:uion. One ['Jid e, o n1;y 1 of thA dupJicr:tte system Wi Jl be Consid.orecl, for e:_J.Ch i.('! imlepeniJ.ent of the

The trap (5) is i.ntencled to prevent any mercury rerwhing the SA,fe, :l.f

a. b:rEH:l.kJ9.ge in the cut off f!Yfitem should send it flying tn th:'lt clhection. The capacity of this tra,p is t'\Uffici.ent to hold all the mercury ttsed. in the cut off system, ~mel the tube ending at

"1!'

11 can easily 11e broken l'l,t i.t' !'1 ttp,

I

;==::;

(

~

{

X

~

MAGNETIC

L

f'T§/!1/11

ASBESTOS

~IRON

~

M£RCURV

======::;s~:M-

E

1 1 1 - - - t - k " - - -

k

The cut off l'lystem:

Tht<:< ei'H~entials of ~ cut off system 1.n this cafle rlre thA,t 1.t Elh~1,ll

bA greaseler,s, since it i~ in con~tant conta,ct with radon; anil ah"Jll 'be c~,,pa~i)le of 'being opened against pressure differences \'.fhich may arise in either direction.

The only simple solution C(mSif1ttl of a mercury tmA.l, of the type

uso<l to elose the by pasFJ (25) in figure

(5).

This is not very convenient

whc~n opened against ].(l,:rge preRsure differences ho\•rever, and a sudden incret:~.fle

of pr8r-;r:~ure on one :~ide could. send thE) mercury flying •

.An al term~.t ive <;olut·ion is provided. N:i. th the Uf4e of two mat:",netically open'\.tcd vacuum vnlveA, ont"! of t·1hich ir:~ shoim in detRil in figure

(8).

This 11ft~ been dravm to rmtural si!".c. The valve conrd.r1

t

n of o. ground

,1

oint "A11 , the £Jocket pol'tion of 1trhleh is ~~8A.1ed onto a plunger 11_~1311_{, M that the}

A

Goft iron core "CII i.s

seB.led iru:dd.e the plunger, tightly pA,eked wHh an1JAstos 11_{D11 , to ensure}

the electi•omagnet "K11 _{is S1!Jitched on.}

ed beyond the normal ra.npe of the plunger to preclude any pol'lsi biJ i ty of breekH.ge Lf the plunger shouJcl 11_{overshoot11 • Vlhen the valve i~ closed and} not 1.n ur.e, the ,joint i~<~ f:H'lnled. \•Ji th mercury 11_F11 _{as shovrn, to render}

_t

_t vacuum He;ht. The mercury· syBtem is !:lhov.rn in full in figure

(r5),

consist-ing of a reservoir

(8),

which may 'be opened to t:J.tmo!>:pheric preesure, or to low vacuum leads, through the two way tap (9). Stopcock (7) controls the

exn.ct heie;ht to which the mercury is ndsed_ or loi•rered. Normally the

valve rema,1.ns closed ;:mel f-lealed. vri th mercury, but :tmrnedi~:1.te1;)' prior to extraction of radon, the mercury 1.s loweredt a. \•m.ter ,jet pump affordint<>: ample vaccum for the purpose.

f~-~·~---1 ~---~-1---8

A

0.05

35 ..

resist a, pressu:t~e diff~rE:mce higher on t.he sicle 11_{X11 • If a, grea,tt'lr presf'lure}

1milds tlp in the tube uyn, it 1,vill force the :plunger up, e.nowing r;as to hu.llllle through thf1 mercury. For this reason, t\~O such valves n,re used,

(6)

ancl (10) in fig.

(5).

These r{~l:'list pressures from eHher direction J?rovided thrc~.t the section bett·n~en them rf)mains eva,cua ted,. S:!.nce the \'/'hole

system is ah·Tr:tys roughly evacuated when the wtlves a.re closed, th:l.s condit:l.on is fulfilled in normttl use.

I f i t is desired to keep the valve opened for long periods, e, second plunger 11_{H" may be f>,licl under the plunger} 11_::B11 _{while it i.s rnised.}

tron eore 11JII is :l.nserted for thts ptlrpose. easily affC'Jct.s the requirf3d movement.

A small permanent magnet,

There is neceasarily .!), large g.9.p l1eohreen the iron core and electro-fJ1ht~ consid.er-n,bly reducEH5 the effi.ciency of the r(t~'l.gnet, ::mel a solenoid. a,ffo:ttling the

ma.ximum pull on the plunger has bflen designed especially for thls purpoBe 1Jy fvlr. Neale of the Engineer:l.ng Depa.rtment at Ca,nterhttry College. The ::1oleno:l.d. \vill carry

4

amps for a fE'lW seconcl!i, exerting a. tension on the plunger more th'),n sufficlt:mt to raise :l.t B,ga:l.nnt atmospheric preH!SUrEl0 It

is iron clnd_, as shown :l.n figure (~(), and. mnploys 2400 turns of number 24

s. \v.

(+.

enr1,melled copper vdre. The posit ion of ma.xlmum pull on the plunger

ba!'i l)een found experimenta..11y to be about 1 em. above this plunger, as shown. A switching circu:l. t for the m.g,p;net has been developed exper:imen.tally, and is shot:m in figure

(9).

The po~tJer source 1.s 230 volts D.C. from the mains: alternating current, as normally supplied, leads to overshoot:l.ng of the :plunger, as the period of one fHtieth of a second is of the !'lame order as the time requi.rf:d for the ra:l.sing of the plunger. The current p~ssing

through the me,gnet 11_W1 _{is controlled by a ma.ster switch "S", and a rotary}

A ran~e of resistances lk'l.s 'been chosen M that 1:1hen the arm 11:1?11 of the

!H'li tch is at :liE extreme position IlLII,

4. 4

amp!'! are pl't~s:i.ng.. This is the malli:imum current permlssa11le for a. fe~tJ seconds, and. is intended to raise

the plunger ag~1inst excessive prenoure or frictional res:l.l'ltance. After

raiz:i.ng the plunger,

.65

amps suffi.ce to hold it "Vre11 e,1)ove its socket,

and this current is ootai.necl at 1Jos1.tion 11_{:ID11 • This plunger is lo"Vrered} untn nee.rly touching its socket 'by std tching onto posit ion 11_{1)11 , and the}

rema,ining positions af:lorcl slightl~v lower cdrrentB, 1ov11Hing the plunger

gently onto it1_{s Rocket. All ,jax·rinf.: of the plunger is thereby avo:tdect.} Norma11y, the p1unger cnn bfl raisecl with •

65

amJ)S, so that the hi.e;her

cur-rents are not ref!Uired except uncier exceptional condlthms.

~1_{here proved. to be com~id.erable ~parking as the selecting arm moved}

from one terminal to the ne:xt, attributable ma.i.nly to the inductive affect

of the.magnet. This ha,s been reduced to a perrn:t ssa'ble d e~:ree ~tri th conden-sers, as incli. ct~.tod. in the figure.

A 11i1ot He;ht 11_N11 _{hHs 1Jeen included ~trhich glows 'l'rhen any current}

paMes through the ma.gnet. This is a

t

1PJatt neon lHmp, drawing only a

minute current, Fmd operating at varying voltagP-s, The voltA.ge a.cross the

points11_XII''Y'1_{varies from nearly 230 volts ,.,hen the e.rm is at} 11_:B11 _{to 110 volts} \•rhen the arm is nt fiLII. A series resistance of 100,000 ohms, 'brings th:l.s

within the range of the lamp.

Thefle vnlves h..·:we 'been developed from a type UMd by Allen Fmd

( 27)

Frankl:i.n .A d:i.agram of their valve h inset in figure

(8),

and. is. nn

accurate copy of the only available data on the r:nibject. ~1

h'ls valve rem~dns

continually senJ.ed \'11.th mercury, s:md is therel)y much more eas:Uy operated.

of the vn,lve~

ra1.f:led jufl·t I::J,l;ove the ,joint, 1m;t i'Iith l t 1 _{s be.se E:till d.:i.ppin}

1o; in mercury.

Moreover, PE~llet~::~ of mercury tend to udhere to the ground joint, preventing

it f s c1ordng pro:per1:Jr 'lr!hen the plunger is lowGred ar:>;ain.

J3efm'e proceeding to the remainder of the apparatus, some mention

should be made o:f the ty~pe of glass employed .. All sectiom; of the &l,pparatutJ 1.n \vhich racl.on is permi:mently accumulating, l.e. the radium flask etc., }Jave been made of soft socla glasr., wtth a wan thickne:::~A of one m:i.llimetre.

(11)

It :ts stated t.h(~;t, pyre:x gh1,oB clevHrifios more rea<l.:tly tht-Ul r10d[l, under the excesr3iVe r.,lyJha ray bomhq.rdJIWnt to v.rhich the~1e sec·blonfl n.re rmlJ,jeet.

Mt.,,ec1onaJ.d. and.

Mar/.~olefl<'J(

)d.:i.scur;s thP ·question of glass very fuJJ.y,

t.bc purification system !'lince it vli11 receive only occrviional al:phn ra<lia.t:ton.

strain set up lW :cadi.il,tlon :ts of no sm,:1:11 tlceount, and. vr:i.ll eaAdly ca,uGe cra,cJ:~G tn thtclc walled join·ts tl19.:t~ ht:tve not 1Jeen J?erfectlJr annea.lled .•

In view of the liquici Adr trap, pyrex har~ l)een used for the remainder of the £iywtem, 1)oing also more enr;;y to work vii th. '.IIhe ch"1.nge over from ~od.a

to pyrex is Ifh<1,de t)etween the valves (6) tmd (10). Graded. seals l1,<we not been avn:i.1able, so that a groun<.'l cone of soda g1a,ss fl

tt

lng in'Go a e;round socket of pyrex has been used .• The ,jotnt h::w been sea,iecl. externaJ.ly with

p:icetn wax, which 1ma,voida'bJ.y eY:-por:Jefl a mlnute are:::t of org.<.J,n:lc matter to the raclon.

The purification cwstem:

This s;1rstem begins with the water vapour trap, (

14).

ThlG reaches

2

c

£

mr:ty po£~si bly i.rrl])l'ove the efftciencyt but also le,"?,Ci to blochage of the trap vri th the ice formed. Such blocl:J'l.ges a:ce occasionally met \•ri th in Ocld.ie' s

(33)

apparatus. ·

:Jnoat ve-lve

(15)

wa,s set up 1)efore the lov1er vnlves

(16)

and

(24)

ha.d been included. At thiG stage it was e~ment:ial, and

it

br'lA'l been reta.inerl as an addi tionnl safety devlce to prevent any mercury reaching the safe. The conceouences of' rmch t\IOUld l)e r,o CJj.se.strous t,hn.t the posfli.bili ty of the lower v"'.1ves I not functioning has been })rovided for. The valve ht.'l.S been

desie;ned to afford a wide passage for gases ,,,hen o~pen, n.nd to

,,Ji

thst2.ncl a sudden uprush of mercury t·ri thou.t l1reaking. J!'1.gure (10) preBents a. natural sized db.gram of tb.e vnlvo. r:l'ho plunger KIA" w1.1l ju.r:~t float, when mercury lv.'w filled the wider flar~k to the point 11_IJ11_{• I:f" ~:md when sufficient mercury}

ha's entered the valve to fill i t to this height, further fi11ine; of the v<=•Jvc

the mercury has a t-ri.de flaAk to fil1 at th1.8 stage. The mercury enterg the valve rnainly through 11_{D11 , in such n direct:ton as to twoid a sudden}

up-MC1.rd. impact on the p1Un{->;er, and. 1.t rlk:<ty 1)e drained out through the crrpill9,ry tube 11_{E11 • ~Phe cror:ls sectional vie\I[S show the method of maint.aining a 1dde} passage when the valve is open.

The toeplnr pump (

17)

has been lll.:'1.de of one lH re capacity as explained

a1)ove. The by pa,es

(42)

is a standard. device, enabllnf; gases to enter the :pump v:ta this tube, rather than bubl.Jle th:cough a large volume of mercury

from the b~v:1e of the pump. The flask hae l)een supported in a metal cup,

packed w'i th ar:!"bestoe, and rigidly supported, as som<e

40

l11s. of mercury are involved.

39.

the cl:tstance X - Y, nmrtt 1)El greater than the optinmm pref~('lure of gaa that

is

to

be retained in

flask (19).

If too hip;h, however, the ffi(cll'cury ,je,rs the gle.ss as it falls, and 20 ems. vra.s fonnd to l)e permissn;ble from this

poj.nt of viet•r. Accord.ingly, flask (19) hg,s 1)oon made of sufficient volume

to accomodate tho mfl.Ximum anticipated. yield of gaa at a. pressuro of less (14)

than 20 ems. Referring ag::tin to G:r<ey and RttmAa.y' s figures, it ~1,ppears the .. t FJ. volume of 250 cc. should accornmocljl,te appro:xilllc3.tely a fortnight 1 s

yleld at a pressure of 19 ems., and this hEw been the volume chosen. A larger vo1ume lli<t~l advantages, but involves e.n unnecessn,ry vroight of mereury.

Severa1 de!:ligns have been considered for the Uqutd air tr~w; the

one chosen1

(20)

in figure

(5)

h•M r~everal nclv::mtages. It ie of a "straight through" cles:tgn, r;o that rm:"Jrcury can be r::dsed through :i. t after removal of the Hquld. The latter orJert'l.t:i.on is eas:i.ly effected. in

4

mi.nttt.e~ \·Ji th a

Horeover, i t hA..s the inestimable A.dvantage of a. flme.ll vollune, so that no very hi.gh vacuum :i.s requi:recl for removal of permanent

This means· tl:mt the time of evacuation may 'be kept down t-ri thout seriously effecti.ng the r<'Jsulta.nt concentration of radon.

The KOH tube has been macle of the form shown in (A), fic;·;ure (11). The KOH ean 'be retained in the blm·m out section, lovJer:J.ng the possibility of its getting below the ground joint if Hn.rmed too much. The method of wa:xing on the gold capHlary is also iJ1ustit':lted •.

( 0) in fie:ure (11) is a. form of collecting tube used for f:'.ealing

the ra.don into c;rna,ll glass seeds .. These latter have proved the most sn.tisfactory oontainerfl for· nulon intended for radon ointrnr-mt.,

l)e eaei ly broken under vaseline.

]'or determinat:!.ons of concentrt~,tion of :radon, eo11ecting vessels of type

(:B)

have been used.

6

'Vlith respect to mercury reservoir.

(38)

This permi. t~ all o:pe:ra:tions, except the final compression of the gas into H 1 _{s capi11ary, to 'be}

ef:feC'I:;-ed. from this reAervoir, insteH.cl of hEwing to adjust reservoir

(41)

at

The high vacu:ll!n leads:

All tubing leading from tap

(26)

to the high vacuum pump is

of'14

mrns.

internal diR,meter, or more, to facilli tate quick evacuation. In no ph,,ce

has this \'!ide :passage been rElduced, even in float valve (28). Stopcock

(26) is only of

5

mms. bore, but \•!O.s t,he only r-~ize avai1able. The le.rge volume trH,p

(2•1),

and float valve (

28), .

both situated a1)ove 1Jarometric height, l'lre intendecl to l)revent any mercnry reaching the pump.

Trap (29) protl!'lcts the pump a.g::tim~t condensable Vf:l,pours, and maintaLns The lower section of th1.n trap is removnlJle at the ground ,joint, so that it may be readily· clea.ned. and. clric'ld.

At

cert::d.n r4tEtg;eA, g::tses enter ·the :pump through

slow

leak

(40).

This h a meteJ. needle valve, and. is backed. l)y n. caldum chloride tube, not shown 1.n the fif',"'.lre.

General:

In general• the a.ppara.tus has 1Jeen Illr'lde ar4 compact af'! is consistent v1i th reasomctiJle ease of access. To ensure rigidity of conAtruct.ion :i.t

has been mount~)d on r:t piping framework, so th"J..t the w·eight of mercury and lead r:Jcreenine is eas1.ly taken. The radium sa.fe is separntAly mounted on a Bol:Ld 'block,and is bolted to the rc-HI1.'1inder of the syHtem. A tray is mounted. belovr the main system to catch any mercury that may break loose.

The accompanying photographs, :figures (12) and.

(13)

\1lll clarify the

above points. Unfortunately it has not oeen possible to secure a tdnr;l e

Certain sections o:f the dH}1licate lmH are vistble. 'I'hese do

not coincide exactly in all ca!H'ls since oth13r cleAigns have been tried, and in fact, as yet only one system has been completecl to the above descr:tption.

The more prominent sections are labelled. as in figure

(5).

Hot a.ir to lmb1>le off liquid air is heated in the copper Gpiral (S), ano. :filtered through,(rr).When required., the gla.ss tube

(V)

is clipped :l.nto the liqu:l.d air trap,a short length of rubber tubing ena.l)J.ing thi.s oper-. ation.

The IJerforu1ancc of ·blw: plant rrk'3,y 1)e cl:l.l::'\CUfiSed. conveniently under the follo'l.lri:ng

headings:--(1) HechanicaJ. perfo:r·mn.nce of the system

( ?) Yield of :t"'8 .. ctcm obtained.

(3)

:J?tlrity of resu1t1:1.nt rl'ldon

(LI) Ttme of oper·atlon, and rad.:tat::lon received during extract:i.on of the

radon.

on the w:wuum pnm:p at the top of the r~troke is cri.t:tcn.l and hard. 'Go jnd{•;o. If 1ef·t too long, f:l, large voll1me of morcury :rum; over :tnt() the ee:plJlary vaJvn,

on the noxt rd;roko of the punrp.

nwrc:ury l.1::vvo of ten hit the J i nu:i.d l.?.:t r t

To ohvL1i;e t.his cl:l:f.'ficult.y, the dE:n~ign of thl.B section of tb.o aprx·traturl

has been eJ:tered to tht.i.t shown be1o\•n

--A

43.

montHs OI)eration of the t:>yc;tem no far reeorded .• ~fi th the exception of one very- cold morning, 1:1hen A, cttr'rent of 1 amp. Vil:H:l reo~u.irocl to 11ft the vaJ:v<)

p1ungflr instead. of the UflU.:~,l

"65

amp., no sign of this plungers sticking has been olJl'>erved.

44 ..

Method of mea~urement of ·the

1_l1_{he r<:;don hr1.f:l been measured lJy virtue of the ionization l t prod.uces} in o.n j.onization ehi:-lm'ber d.e~dgned for the measurement of gamma rad.iat ion.

It lr; no-t~, J?X'OJ)Osed to d:i.sc·ns~J in detail tb.is ioni?m:t:ton chamber, nor ·the method of ampl:i.f:l.cation and measurement of the :ton:l?.:ation

mnrent

se1; up therein. H.f~acUngs and calculations J:>;:wc been carried. out hy the '"rHer, but the clenign and. methocl of operation of the mea.rm:rtng E\ystem are d:ue to

(34)

Mr. G. E. noth • In 11rief, the mr,thod. cmudstr1 in measur:i.ng thc~ i0n:iz!3.tion current cnnr:1e<l by o. known qtw .. nti ty of rv.clium :pl::teed 1n the chamber, fo1lo1:Jed. b;)r a simllt'l.r determlntJ;tion w:i.th thEl radon sample und.er 1i.ke conditions. Al1 due _precau.tions lnve been taken to 0nsu:r·e that the current ~o toearmred :l.s strictly proport :i.om.'l.l to the :intensi t~r of gBJama ro.din.Uon set up in the

(1) The voltag8 r:wrosn the ionhat:i.on ch'lmlH?r hs,s 'been su:fficientlJr hie;h (generally 1700 volts) to enrmre tlv:-J.t a satur1J,tion current is measured, i.e. tl1fl.t all the ions formocl ,:rh:i.ch rwe capable of hc.dng co11ected. on the collecting electrode, are so collected.

(2)

'ro

avold Brrors due to fluctua,tions in tb.e respontie of the f:1,!TI!)1i-f:i.cation system, the current prod.uced. by t;he radium standard hr:J.S l)een measured

a.t frequent intervals during each series of cleterm:lno,tions.

( 3)

Z8ro errors due to varying lJa,ckground e:f:fed, s nnd. other cau!'les have been cor:eect(;cl by sui table ad,jnl:itment 1Jefore each mea~m.rement.

(5)

rpo avoid errorf1 in readlng the mill iam!')ter employed in measurement,

varying the reslst::J,nce ln series vJith the meter. Correction for such resist-anee h:"l,fl been rnnde in caJ.ett]r-d;i:ng the mean reading. ·

One further I>Oi n t s houlcl

oe

noted:

--rphe :i.oniz::J;\·,:i.on chaml)el' ls in the form of cylin<J.er t vrith the rn.di.rtting SO'\.J.!'C8

plnced lnsicle 1.n a nr11<11ler concentric cylind.er of lead. to elimlnrde

o<

nntt~ racliB,t ion. S:l.nce tba.t ra.cliation proceeding from the end.f:l of n. long f~ource

muFJt JXtsB thl'ough th:ts lencl cy·llnd.or at an antr;le, :tn orcler to reach certain

seetions of the ion:i?.atlon ehaml)er, the avera1<l;e filtration due to the al1ove

leo.d e;y·linder ir1 g:ceo.tel' fo:c a long som'ee tbn.n for 1'1, r;hort one.

Thns the OOB(H'Ved rl.ctiv:i.'ty of 1\ sourcE) of 10 ems. aet:ive length Hl

r4mnller tbnn tlvJ.t due to the. name 8lllOU>"'lt of rn.don enelofwd :i.n 8, eouree of

'1 c + .. l "'e. ] , .. l " .• J. J·J

3

Clll q

c • · c V ~ . GJ ?..:.., tJ , . ~. Q

to make G,ppro:x:i.mate coneet:to:n for this <Jmn.11 effed., tihich V.''l.ries Hith th(J :wtiye length n·r +.he nonree.,

01Jf.lel'V:tng the a.bovo precautions ancl corre,c1;ions, liUCh (tetArmin'3.t:tone a:fforcl a me9A3Ure of the ¥ray n.c·l;tvity of a

r~1.don

CRJi1p1e at the tiTI•e of meaou:ce-nmnt. I!' or ca1eu1attons of yie1cl hov1ever, the radon cont~'lnt at the time of

removoJ from thH pud.f1.c:J.t:i.on appara.tu.s :is r{3qui:ced.

il1ustrate the ealculations i.nvolved .• Ar; exp1ained. previonsl~r, the r~l.d.on may

oe

1neasu.red. l)efore or after it reacheEl transient equll:i.l)r:i.um vrith it' 1> decay :p:rocluctn •

.A certEd.n radon sample was ll1(~Dou:,'ecl at

5

P.Jv!. on the day of itn extraction,

by compl:';l .. t'ison ~·lith a rndium :prepara)c:ton of content

9. 96

mgfl. Thi.s stH.ndar<l rn.dium p:ce:pn.rt',tion \·18.f4 enclosed in a orass contR.iner, rednclng its act lvi ty by

h·?

Li.6,

and. j. tf'. Hcti ve length 11D.\'\ 'bE, en tal-cen ns approxirmOJ,toly

7

mms.

The rad.on r:lample wn.s enclosed in a gold c;l.pillary tulJe of •

3

mms. waJJ thicknerJfl, eqnivn1en1; to a.

3%

recluctton in

If

aetivity (a:'~ previou1'lly dete:rm:tned) and

8. 5

cm:'l. 1onr;. \'fi tr1 the use of trm active 1one;th con;oetion

eurve~ it is rwen thf:!.t Lf this radon were encJ OHecl ln a son:ree

7

mms. long,

ancl wi.tuat<·Jd in the same posit:l.on :l.n thE'l 'chaml)er a~3 tlw to:tonda:ccl,

it

~·JOu1d

d:l.flpla.y

rz%

greater 8.cti vHy,

The rn.t:l.o of the :i.onizatlcm current EH3t up "by the radon sam~o1e to that rrak:i.ng the ~~.l)OV8 C011T'ent:lons into acom.mt, tho content of the sanrph~ at thEl time of measuremex:d'

wa.s:-102

JOO 100

The m).mp1o was 0xtra.etecl

n.t

rn:ldda,y on the c;n.me dny, r:10 that.

5

hours hrwe eln.JHled :i.n VJh:i.eh :1 t han decayed. The roiJ.on content of the snmple nt

~)quat:ton (ll

A):-- 'A

t

N. e 2

X

or, expref:1sinr, th.e rad.on tn

mill1.euriflfl!-Nt

N

-:>..2t

0 e ···

vrhere

26.

2 mcs.

t

5

b.rs.

N0 - mill 1curie content of the sam:ple at midday.

A.r.>t

Evalu}J,ting the factor (e- c ) , t•re have N₀

=

~~7.2 mcr1.

AFl ~1, proof tha.t the ol)servEHl a.ctivity of rmch racton f'!amplef'. cl.oes

47.

r:Po ln'ing out the e:x.po:aent:i.nJ nature o:f thr,, dEJC:~ny, logar:tthmic gm,ph Jl8,pe:r hl'ls been mnployed, r1.ncl the

:lnd:i.cate. li'urthPr, the f:llope of th1.s l:tne if', :O>Ueh that tho rn.d_oh hrw cleoa;v-1:rhich iri ln agreElment with the rweepted half life period. of r1:1.clon, of

rr.hts degree of nt:,reement is probab1y fm:tuHom1 r.dnce the e:x:porimental

E·.·;•.ror· 4a .J..:iJ n·pn~oviJnn~ely c::t •. ~.l:!- .L<- • • O ... lJ L 0d f_/Ot lmt 1 t does afford fo:rmn.l proof that the gag

and (lG), :,wxl their rosultlng e;raphr:1 in fjl";uro (1). Such equ::J:t, lon::; hD,ve been

derived on the 1'l.ssunrption that :in:i.tloJly, the r~;y·stem condsts only· of rad.on,

1·d th none; of itn deca;y procluctB. Th:l.s i.e> not stricJr;J~r true tn pr[wt:l.ee,

the ·lmlk of the y-ield is eornprc·H1~_\nc1 into it. 'l.'hls f:'lmall amount Hill form acU.ve deposit on the container lJefore i t ir4 noalecl off, so that at the precise monwni; at \orh:l.ch the mcrcu:cy in rairwd to tho sNtl off point, the eontain1.ng verJf:!el already contnins some active de:ponit, and invn.llclates

Hovrever, the volume of the container j,s generally

culn.tion of ~l'adon content of BUCh a cont~~.iner wtth a time error of alJout 10 rJeconds, elating from the molilent at. which the nw:ccnry reD .. ched. tlle se9.l off point.

In c1:H1es where the mercur;y· is lowered again before sealing off the

ro.don, this method tfJ not appJ.i m:t'ble, <"m<l mcafmremen t s trnlf~t awai. t equil1.-brium. Thi.s former method involver! :::1, delay of nome five hours, :md. alrlO ler-lcl!'l to gree.ter radiation e::cposrtl'E-), HO th'lt it :ts not so convoni.ent as

the one ,ju~rt discussed. An exa"~:n:rle of such a. mearmreme:b.t is ~;iven

bel01!T:-03

A certaLn rR.don containAr W'l.S meatmre.d at li:-' hrs. on the dD.y of Hs extraction, and G.:fter mald.ng; FJ.l1 clue con'.eetions, its gamm~. tC\ctivity was

Thh m;xnple \'ms r.ealect off from the extrndion plant

'bnt t lK~ rr~/lor1 t n. :t t b.l~d 1Jeen co mpre rJs etl to t l1o poi11t of 8ea.J.i n.e; off t-J/G

.. 51

1 • •

JO nrs., :1.. e.

72

m:umtes 'befor0 th8 ac1ovo me[wurement. Applying graph

(3)

in fi.,<:>;LJ.re (1) it is r~een that in 72 minutE!S a rA.don sample h~H1 reHched_

62.6%

of its rr.::J.:x.tmum a.ct:tvity, when mea.su:ced 1:rith .<m ioniz['l.t,ion cbnrn1)e:C

employing 1 em. of lead filtration, as in the prAr~ent case. ]'urther, th:i.C'!

decayed. ·t;o 96.8

%

of its ini U.al value, as d_ecluced from equation (11 A).

ThLUl the radon content of the sample :'l.t the tim~; of removal from th~1

100

x

-6?.6

100 X

96:"8

l+t

1

tt +

!-!- "":! t:t- + f:ri

oc

gi

'Fi ff:t f = _{1' +} f

t

u

f·H ;

~ it:; ,;:r t:-r ;,;

I

J

X ~

-;..

I

"

1

ttt

~ ~~~nE

~~

. t+' 1.4

i!t:

j++ 1-i 1---! I

4: ;f_

_i

1 >< ~

~ ~

tttf-

~

1_-'+!

1+4" I P:: .J

hl

·d f+

'+i- ;!

lj:fi

'=

R=+

+;:

rttl ;) T !+!

!:t ,,, _rtf

If

f

!++ += it

-b

~

₁

t H It

1+-

.

. tt+

0

,

....

t

8

t ~ _:+t

..je.

.. j:i:j: 1'1

f;'-t'

~IB

1'

f

fFi =tt

!ttt t7 I t1

1'-I+ _~

t.

:t

I

$~

4

I

i++

J +

:t

!--'-'

ij 11 1:!:! It

tt

i± j:j:' _{I !::I}

I+! ++

,1:1

20 :; Iii

t

FI GURE

11_D

l! I ~ ~l

=. + 't _I

j

~

I

m

~~~

~ ~ Eh IF l+t fro

=

ttJl!b...

I

:Kt fl ...

j~oo