Page 72 - Astounding Pulp V2

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TRANS~IUTATION, 19 39
72 ASTOL"'.\'DI'.\'G SCIE'.\'CE-FlC:T fO~
THUS no natural isotopes of lithium could only 1 e cxpe ·t<'cl in thl' lightt·,·
tions ,.. nu1~1be r of particle~ from the boron fol-
- · : ,ctually he: succceclcd in doing beyond those with weights 6 and 7 seem elemem ; in hoth ca:-es a ch:\1-~(.•d I an,
JU::,t that i 1 19 19 ; workin<r nn a \ ·c r·v l?\\ ed an cxpo11c11t1al cun·e. with a half ~o exist; nitrogen ( z = 7) has only the clc must :-trike a nucku:-. :ind tlw natu
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t small seal (• . 1c: did gc.:t pn,tons from ni- life ~f severa_l minutes-the half life i isotopes of mass 14 and 15. It can ral rcpubi n 0f the 1wn po--itin• part i-
/~gc n nuc.:lei bomba1·dcd with a lpha par- th e tlln e required fur acliYity to cl hardly be regarded that this narrow dis- cles ,·arics. of cour:::e. wit h thl' prPduct
. ~cl rcase
1~ C:,. Cnfonu nate ly he dic.tn·l rcc.:og- to one half its initial \·alue- s11111 ar to tribution of isotopic weights is mere co- of their charges. Thu::. in the l~!'-t' Pi
th
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111ze what he ,~as do incr. h is attention e case ot natural rad ioacti \·e ct· . the boron rca'tion dc:.-:<·ribecl. the repul
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·w as f h · • . g rations ; mte- incidence, but instead it may be inferred
. ocuscd on the protons which w et e that the narrow region thus defined by sion is proportional tn 5 x .2 = IO: in
cm,tt~d. and he d id not attempt any ( ~) '(i'he g rowth of the emi s • the known isotopes represent stable pos- the ca e of the c:i.rlX'tt rcact it>n.
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f 1
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If
e xaminatio11 o t 1e n1trocrcn 1tse . 'Lfc p_art1cles simila rly followed an e. ion of sibilities, and any other isotopes would 6 x 1 = 6. But the n:·pubion itff a
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r
might have found- but :ait. t 1al • - xponen- be unstable. And so Curie and J oliot transmutation of. say. plat in111n w ould lw
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curve. with the same tran f .
~t \Vas not until J 934 that the first t1011 constant . 01 ma- suggested that the N 10 which was -using alpha part i ·ks- 7~ x 2 = 1 ;,ll '.
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artificial t ra ns mutat1on was 1c e •fi d 7 1ow. there .-honld be 110 rcpul~i011 (\i
1 ntl e as
s uch and . t. . . . . ( ~) The i1;tensity of the emitted r f?rn1ed on the impact of the alpha par-
' . 1 is 111t1mately associated with d1at1on from the boron was d I a- ticle with the boron nucleus was un- neutral particles by the nude11s. and
the discover ~ f ·n . d. . . upon the intensity of the alpha ep1:ent~ elnt acting on this idea in 1°34. Fermi . th<'
Y o art, c1a l ra 10act1v1ty .
I 11 th at year C · · stable, and would decompose according
• d une a nd J oliot-the mar- used; but ' r 1c es brilliant Italian physici:.-:t. t riecl tht· ei-
n e ?aug h te ,· of Iviada m e C urie-were ( ) the half life of decay , . to the reaction fect of neutrons in producin~ an ilil·i:d
4
18
. p .
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,vo1·kmg in tl 1e C une labo1·atory in ans 1N = oC + 1e+, radioacti,·ity. .•\l 011cc the proce~s w as
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1nvest1gat111g ti 1e e 1111ss10 11 o positrons pendent _of the intensity of the ~~s linde- the 1N 13 thus being converted into the a success, and it was the p1·ocess we
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f
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mg particles.
)arcl-
f ra m bo ron · - stable, naturally occurring carbon isotope
. . • LISing a s11nple arrangement In their first paper Curie and J r used in our little kct un~ dem on:.-:t ra-
1 <e
1 1 this · p 0 • 1 B. The Po was some of mass 13, with the emission of the posi- tion. The capsule o f boron ancl ra In n
·
13
0 0 s~ggested, as was later proved too l(?t trons which they obsenred. The , N is simply a source of neut1·ons. prod11n:>d
polonium , w 11c 1 emitted alpha particles exactly the case. that this artific" I be
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"v h ich on t ·1 . , dioacti · t 1 a ra- is a radioactive element, with a half life by the first reaction o i C u rie and J oliot :
.b ' s n <i ng the boron target B . • vi Y was the result of the fo of some 10.S minutes, and -they also pre-
l 1 e 1·ated po ·t . 1,B10 + :?He4 = ,N1~1 + o 111 .
b . s t r a ns w hich were detected ~ion of a new nit1·ogen isotope, unk:t~- dicted that it would also be formed by and it is these neu tron s. st 1·iking the sil-
t Y a s uitable device D-such as an elec- m nature, by the reaction: " 11 the bombardment of carbon with deu-
roscope or G - One day ve1·, which bri ng about the reaction :
h , .
eiger countei-.
t C) 1 emoved tl 1 · :;BIO +. 2He◄ = 1N1:.i + ot~l tons. This latter prediction was ful- -nAg10, + n1 = , 17 :\gtos + h \ /
0
d le p o on mm, and left the a neutron bemg emitted in the filled in the same year, when Crane,
et_~tctor running-astonishingly enough No · I process Lauritson and Harper, working in the - the h\ / represents gamma radiation o f
w , it 1acl long been Noted that I .
Po s t ran s contmued to com e out of the naturally occurring isotopes of the v _t ~e high volta~e laboratory at the California the appropriate energy to sa t isfy c 11 -
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zortondplate ! A nd there were several ou~ elements do not have any randan- Institute of Technology did actually servation of energy, in the relativic:tic
t~~ns is~losed by furthe r experimenta- . wei~hts. ~Jut that instead they foll 0111 produce it with deutons that had been sense-but since the 108 isotope of s ih•er
which at once proved this phe- particular t . ow a accelerated with a potential of a million is unstable-it is n ot known in nat tll"e-
pa tern, especially notal)l .f
nt~t,~fi1e1:al was_ the actual production , of we plot th . e t volts. The reaction may be written it is decomposed by the reaction :
a 1 1c1a rad 10act1v1ty in the boron: 2 , e atomic number, a . . t,Ag1os =-i sCd 10s -1- -1.e-
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( 1) 1 he decay d" · . w, the atomic weight, as in the gfiatnSl -- . oc12 + 1H2 = 1N1a + on1
, or 1m1nut1on of below. · gure and it represents the first completely with the production of the stable cad-
-. . . . mium isotope 108 and an electrnn. and,
10 N e • . • . -· artificial transmutation. Curie and J oliot lo, we have transm u ted silver to cad-
F had certainly made carbon out of boron, mium! In our experiment, then , the
. • _but they had used a natural source of
0 . • • • e1~ergy, polonium alpha particles, neutrons from the boron-radon capsule
N .. • 4~ whereas the later production of carbon strike the silve1· nucleus. transmute it
' to an unstable silver isotope, \,·hich de-
C • • isotope 13 from the i_sotope 12 was composes-with a half life of twenty-
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Z s B - - . - o- .- brought about solely by artificial elec- three seconds-and becomes cadmium .
B • trical energy. vVe demonstrated this in t h e lecture
e
Li • • 1: II But considering the voltages required by simply putting the p iece of s ilve r in
for accelerating protons or deutons-
He • • about 3 m.e. v.-and the natural energy front of a Geiger counter, showing n o in-
0 • • of alpha particles available from natu- crease in the number of counts, p lacing
the silver in the pa raffin spher e with the
0 - 5 10 -- rally radioactive sources- about 8.8· capsule for twenty seconds, and remov-
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• ' . w .20 rn.e.v,-ti:ansmutations of these sorts