,worlds ,)9 ,worlds3                    
,! ,/ory ( ,nucle> ,en]gy               
,volume #b        ,mass & ,en]gy  ,!    
,neutron  ,! ,/ructure ( ! ,nucleus     
by ,isaac ,asimov                ,u4 ,s4
 ,en]gy ,rese>* & ,developm5t           
,adm9i/ration                           
,(fice ( ,public ,affairs               
,wa%+ton1 ,d4,c4 #bjede                 
,libr>y ( ,congress ,catalog ,c>d       
,numb]3 #ge-ahidgg                      
#aigb    ,no?+ 9 ! hi/ory ( mank9d has  
op5$ our eyes to !  possibilities (     
sci5ce z has ! developm5t ( atomic p[]4 
,9 !  la/ #bjj ye>s1 p h se5 ! com+ ( ! 
/eam eng9e1 !  /eamboat1 ! railroad     
locomotive1 ! automobile1 ! airplane1   
radio1  motion pictures1 television1 !  
ma*9e age 9 g5]al4 ,yet none ( x  seem$ 
q s fanta/ic1 q s unbelievable1 z :at   
man has done  s9ce #aici ) ! atom 444   
!re seem to be almo/ no limits to :at   
may lie ahead3 inexhau/ible en]gy1 new  
worlds1 ev]-wid5+ k  ( ! physical       
univ]se4                                

,isaac ,asimov                          
,illu/ration3 ,photograph ( night sky   
,! ,u4 ,s4 ,en]gy ,rese>* & ,developm5t 
,adm9i/ration publi%es a  s]ies (       
booklets = ! g5]al public4    ,please   
write to ! foll[+ address = a title li/ 
or =  in=mation on a specific subject3  
,,us]da--,te*nical ,in=mation ,c5t]     
,p4 ,o4 ,box #fb    ,oak ,ridge1        
,t5nessee #cghcj                        
,illu/ration3 ,isaac ,asimov            
,,isaac ,,asimov receiv$ 8 academic     
degrees f ,columbia ,univ]sity &  is    
,associate ,pr(essor ( ,bio*emi/ry at ! 
,bo/on ,univ]sity ,s*ool  ( ,m$ic9e4 ,he
 is a prolific au?or :o has writt5 ov]  
#aej books 9  ! pa/ #bj ye>s1 includ+   
ab\t #bj sci5ce fiction works1 & books  
= *ildr54 ,8 _m excell5t sci5ce books = 
! public cov]  subjects 9 ma!matics1    
physics1 a/ronomy1 *emi/ry1 & biology1  
su* z ,! ,g5etic ,code1 ,inside ! ,atom1
 ,build+ ,blocks ( !  ,univ]se1 ,und]/&+
 ,physics1 ,! ,new ,intellig5t ,man's   
,guide to  ,sci5ce1 & ,asimov's         

,biographical ,encyclop$ia ( ,sci5ce &  
,te*nology4    ,9 #aife ,dr4 ,asimov    
receiv$ ! ,james ,t4 ,grady ,aw>d ( !   
,am]ican  ,*emical ,society = 8 major   
contribution 9 report+ sci5ce  progress 
to ! public4                            
,illu/ration3 ,photograph ( night sky   
,,cont5ts                               
,,volume #a    ,introduction            
#e    ,atomic ,weights                  
#f    ,electricity                      
#aa        ,units ( ,electricity        
#aa        ,ca?ode ,rays                
#ac        ,radioactivity               
#ag        ,! ,/ructure ( ! ,atom       
#be        ,atomic ,numb]s              
#cj        ,isotopes                    
#ce    ,en]gy                           
#dg        ,! ,law ( ,cons]vation (     
,en]gy                                  
#dg        ,*emical ,en]gy              
#ej        ,electrons & ,en]gy          
#ed        ,! ,en]gy ( ! ,sun           
#ee        ,! ,en]gy ( ,radioactivity   
#eg                                     

,,volume #b    ,mass & ,en]gy           
#fi    ,! ,/ructure ( ! ,nucleus        
#ge        ,! ,proton                   
#ge        ,! ,proton-,electron ,!ory   
#gf        ,protons 9 ,nuclei           
#hj        ,nucle> ,bomb>dm5t           
#hb        ,p>ticle ,accel]ators        
#hf    ,! ,neutron                      
#ib        ,nucle> ,sp9                 
#ib        ,discov]y ( ! ,neutron       
#ie        ,! ,proton-,neutron ,!ory    
#ih        ,! ,nucle> ,int]action       
#aja        ,neutron ,bomb>dm5t         
#ajg                                    
,,volume #c    ,nucle> ,fission         
#aag        ,new ,elem5ts               
#aag        ,! ,discov]y ( ,fission     
#abb        ,! ,nucle> ,*a9 ,reaction   
#abg        ,! ,nucle> ,bomb            
#aca        ,nucle> ,reactors           
#ada    ,nucle> ,fusion                 
#adg        ,! ,en]gy ( ! ,sun          
#adg        ,!rmonucle> ,bombs          
#adi        ,controll$ ,fusion          
#aea    ,beyond ,fusion                 

#aei        ,antimatt]                  
#aei        ,! ,unkn[n                  
#afd    ,read+ ,li/                     
#aff    ,illu/ration3 ,a field-ion      
microscope view ( atoms 9 a cry/al4 ,ea*
  t9y :ite dot is a s+le atom1 & ea* r+ 
sy/em is a cry/al facet  or plane4 ,!   
picture is magnifi$ #a1ejj1jjj times4   
,,mass ,,& ,,en]gy      ,9 #aijj x began
 to dawn on physici/s t !re 0 a va/ /ore
 (  en]gy )9 ! atom2 a /ore no "o e>li] 
_h imag9$ exi/$4 ,!  %e] size ( ! en]gy 
/ore 9 ! atom--millions ( times t kn[n  
to exi/ 9 ! =m ( *emical en]gy--seem$   
unbelievable at fir/4  ,yet t size      
quickly came to make s5se z a result ( a
 l9e (  rese>* t seem$1 at ! beg9n+1 to 
h no?+ to d )  en]gy4    ,suppose a ball
 7 ?r[n =w>d at a velocity ( #bj        
kilomet]s p]  h\r by a man on top ( a   
flatc> t is mov+ =w>d at #bj  kilomet]s 
an h\r4 ,to someone wat*+ f ! roadside !
 ball w\ld  appe> to be travell+ at #dj 
kilomet]s an h\r4 ,! velocity ( !  ?r[] 
is add$ to ! velocity ( ! ball4    ,if !

 ball 7 ?r[n =w>d at #bj kilomet]s an   
h\r by a man on top  ( a flatc> t is    
mov+ backw>d at #bj kilomet]s an h\r1 !n
 !  ball 7to someone wat*+ f ! roadside7
 w\ld seem to be n mov+  at all aft] x  
left ! h& ( ! ?r[]4 ,x w\ld j drop to ! 
gr\nd4    ,!re seem$ no reason 9 ! #ai? 
c5tury to suppose t light didn't  behave
 9 ! same fa%ion4 ,x 0 kn[n to travel at
 ! enorm\s spe$  ( j a trifle "u        
#cjj1jjj kilomet]s p] second1 :ile e>?  
mov$  9 its orbit ab\t ! sun at a spe$ (
 ab\t #cj kilomet]s p] second4  ,surely 
if a beam ( light beg9n+ at "s e>?-b\nd 
s\rce %one 9  ! direction ( e>?'s       
travel1 x ought to move at a spe$ (     
#cjj1jcj  kilomet]s p] second4 ,if x    
%one 9 ! opposite direction1 aga9/      
e>?'s motion1 x ought to move at a spe$ 
( #bii1igj kilomet]s p]  second4        
,c\ld su* a small diff]5ce 9 an enorm\s 
spe$ be detect$8    ,illu/ration3 ,alb]t
 ,a4 ,mi*elson    ,! ,g]man-,am]ican    
physici/ ,alb]t ,abraham ,mi*elson      
7#aheb-aica7 _h  inv5t$ a delicate      

in/rum5t1 ! int]f]omet]1 t c\ld comp>e  
! velocities ( diff]5t beams ( light )  
great precision4 ,9 #ahhg  he & a       
co-work]1 ! ,am]ican *emi/ ,edw>d       
,williams ,morley  7#ahch-aibc71 tri$ to
 measure ! comp>ative spe$s ( light1 us+
  beams head$ 9 diff]5t directions4 ,"s 
( ?is "w 0 p]=m$ at  ! ,u4 ,s4 ,naval   
,academy & "s at ! ,case ,in/itute4     
,! results ( ! ,mi*elson-,morley        
exp]im5t 7 unexpect$4 ,x  %[$ no        
diff]5ce 9 ! measur$ spe$ ( light4 ,no  
matt] :at !  direction ( ! beam--:e!r x 
w5t 9 ! direction ( ! e>?'s  movem5t1 or
 aga9/ x1 or at any angle to x--! spe$ (
 light always  appe>$ to be exactly !   
same4    ,to expla9 ?is1 !              
,g]man-,swiss-,am]ican sci5ti/ ,alb]t   
,e9/e9  7#ahgi-aiee7 advanc$ 8 8special 
!ory ( relativity0 9 #aije4  ,accord+ to
 ,e9/e9's view1 spe$s c\ld n m]ely be   
add$4 ,a ball  ?r[n =w>d at #bj         
kilomet]s an h\r by a man mov+ at #bj   
kilomet]s  an h\r 9 ! same direction    
w\ld n seem to be go+ #dj kilomet]s  an 

h\r to an obs]v] at ! roadside4 ,x w\ld 
seem to be go+ v  slightly less ?an #dj 
kilomet]s an h\r2 s slightly less t !   
diff]5ce c\ldn't be measur$4    ,h[ev]1 
z spe$s grew high] & high]1 !           
discrepancy 9 !  addition grew great] & 
great] 7accord+ to a =mula ,e9/e9       
d]iv$7 until1 at velocities ( t5s (     
?\s&s ( kilomet]s p]  h\r1 t discrepancy
 c\ld be easily measur$4 ,at ! spe$ (   
light1  :i* ,e9/e9 %[$ 0 a limit+       
velocity t an obs]v] w\ld  nev] rea*1 ! 
discrepancy became s great t ! spe$ ( ! 
light  s\rce1 h[ev] great1 add$ or      
subtract$ z]o to or f ! spe$ (  light4  
,accompany+ ?is 7 all sorts ( o!r       
effects4 ,x c\ld be %[n by  ,e9/e9's    
reason+ t no object possess+ mass c\ld  
move fa/]  ?an ! spe$ ( light4 ,:at's m1
 z an object mov$ fa/] &  fa/]1 its l5g?
 9 ! direction ( motion 7z measur$ by a 
/ation>y obs]v]7 grew %ort] & %ort]1    
:ile its mass grew  great] & great]4 ,at
 #bfj1jjj kilomet]s p] second1 its l5g? 
9 !  direction ( movem5t 0 only half :at

 x 0 at re/1 & its mass  0 twice :at x  
04 ,z ! spe$ ( light 0 approa*$1 its    
l5g?  w\ld approa* z]o 9 ! direction (  
motion1 :ile its mass w\ld  approa* !   
inf9ite4    ,c\ld ?is really be s8      
,ord9>y objects nev] mov$ s fa/ z to    
make  _! l5g?s & masses %[ any          
measurable *ange4 ,:at ab\t  subatomic  
p>ticles1 h[ev]1 :i* mov$ at t5s ( ?\s&s
 (  kilomet]s p] second8 ,! ,g]man      
physici/ ,alfr$ ,he9ri* ,bu*]]          
7#ahfc-aibg7 report$ 9 #aijh t spe$+    
electrons did ga9 9 mass  j ! am\nt     
pr$ict$ by ,e9/e9's !ory4 ,! increas$   
mass )  en]gy has be5 confirm$ ) great  
precision 9 rec5t ye>s4  ,e9/e9's       
special !ory ( relativity has met _m    
exp]im5tal te/s  exactly ev] s9ce & x is
 g5]ally accept$ by physici/s today4    
,e9/e9's !ory gave rise to some?+ else z
 well4 ,e9/e9 d$uc$  t mass 0 a =m (    
en]gy4 ,he work$ out a relation%ip 7!   
8mass-en]gy equival5ce07 t is express$ z
 foll[s3                                
,e  mc    :]e ,e repres5ts en]gy1 m is  

mass1 & c is ! spe$ ( light4    ,if mass
 is measur$ 9 grams & ! spe$ ( light is 
measur$ 9  c5timet]s p] second1 !n !    
equation w yield ! en]gy 9 a  unit call$
 8ergs04 ,x turns out t #a gram ( mass  
is equal to                             
#ijj1jjj1jjj1jjj1jjj1jjj1jjj 7#ijj      
billion billion7 ergs ( en]gy4 ,!  erg  
is a v small unit ( en]gy1 b #ijj       
billion billion ( !m  m\nt up4    ,!    
en]gy equival5t ( #a gram ( mass 7&     
rememb] t a gram1 9  ord9>y units1 is   
only _/ ( an ounce7 w\ld keep a         
#ajj-watt light  bulb burn+ = #ce1jjj   
ye>s4     ,illu/ration3 ,,en]gy ,,creat$
 comp>$ to ,,matt] 7,,or ,,mass7        
,,de/roy$    ,x is ?is va/ diff]5ce     
betwe5 ! t9y quantity ( mass & !  huge  
am\nt ( en]gy to :i* x is equival5t t   
obscur$ !  relation%ip ov] ! ye>s4 ,:5 a
 *emical reaction lib]ates en]gy1  !    
mass ( ! mat]ials und]go+ ! reaction    
decreases slightly--b  v slightly4      
,suppose1 = in/ance1 a gallon ( gasol9e 
is burn$4 ,! gallon (  gasol9e has a    

mass ( #bhjj grams & comb9es ) ab\t     
#aj1jjj grams  ( oxyg5 to =m c>bon      
dioxide & wat]1 yield+ #a4ce million    
billion ergs4 ,t's a lot ( en]gy & x w  
drive an automobile =  "s #be to #cj    
kilomet]s4 ,b by ,e9/e9's equation all t
 en]gy is  equival5t to only a little   
ov] a million? ( a gram4 ,y />t )       
#ab1hjj grams ( react+ mat]ials & y end 
) #ab1hjj grams m9us a  million? ( a    
gram or s t 0 giv5 (f z en]gy4    ,no   
in/rum5t kn[n to ! *emi/s ( ! #ai?      
c5tury c\ld h  detect$ s t9y a loss (   
mass 9 su* a l>ge total4 ,no wond]1 !n1 
t f ,lavoisi] on1 sci5ti/s ?\ght t ! law
 ( cons]vation  ( mass held exactly4    
,radioactive *anges gave (f mu* m en]gy 
p] atom ?an *emical  *anges did1 & !    
p]c5tage loss 9 mass 0 correspond+ly    
great]4 ,! loss ( mass 9 radioactive    
*anges 0 f\nd to mat* !  production (   
en]gy 9 j ! way ,e9/e9 pr$ict$4    ,x 0 
no long] q accurate to talk ab\t !      
cons]vation ( mass  aft] #aije 7ev5 ?\gh
 mass 0 j ab\t cons]v$ 9 ord9>y  *emical

 reactions s t ! law c\ld cont9ue to be 
us$ by *emi/s  )\t tr\ble74 ,in/ead1 x  
is m prop] to speak ( !  cons]vation (  
en]gy1 & to rememb] t mass 0 "o =m (    
en]gy  & a v conc5trat$ =m4    ,!       
mass-en]gy equival5ce fully expla9$ :y !
 atom %\ld conta9  s great a /ore (     
en]gy4 ,inde$1 ! surprise 0 t           
radioactive  *anges gave (f z little    
en]gy z !y did4 ,:5 a uranium atom broke
  d[n ?r\gh a s]ies ( /eps to a lead    
atom1 x produc$ a million  times z mu*  
en]gy z t same atom w\ld release if x 7 
involv$  9 ev5 ! mo/ viol5t ( *emical   
*anges4 ,nev]!less1 t  enorm\s en]gy    
*ange 9 ! radioactive breakd[n repres5t$
 only  ab\t "o-half ( #a ( ! total en]gy
 to :i* ! mass ( !  uranium atom 0      
equival5t4    ,once ,ru!r=d work$ out ! 
nucle> !ory ( ! atom1 x became  cle> f !
 mass-en]gy equival5ce t ! s\rce ( !    
en]gy (  radioactivity 0 likely to be 9 
! atomic nucleus :]e almo/ all  ! mass (
 ! atom 0 to be f\nd4    ,! att5tion (  
physici/s !re=e turn$ to ! nucleus4     

,,! ,,/ructure ,,( ,,! ,,nucleus      ,!
 ,proton    ,z e>ly z #ahhf ,eug5       
,gold/e91 :o 0 work+ ) ca?ode rays1     
also /udi$ rays t mov$ 9 ! opposite     
direction4 ,s9ce !  ca?ode rays         
7electrons7 7 negatively *>g$1 rays mov+
 9 !  opposite direction w\ld h to be   
positively *>g$4 ,9 #aijg ,j4 ,j4       
,?omson call$ !m 8positive rays04       
,once ,ru!r=d work$ out ! nucle>        
/ructure ( ! atom1 x seem$  cle> t !    
positive rays 7 atomic nuclei f :i* a   
numb] (  electrons _h be5 knock$ away4  
,^! nuclei came 9 diff]5t sizes4    ,7 !
 nuclei s+le p>ticles--a diff]5t "o = e 
isotope (  e elem5t8 ,or 7 !y all built 
up out ( numb]s ( /ill small]  p>ticles 
( a v limit$ numb] ( v>ieties8 ,might x 
be t !  nuclei ow$ _! positive          
electrical *>ge to ! fact t !y  conta9$ 
p>ticles j l ! electron1 b ones t c>ri$ 
a  positive *>ge r ?an a negative "o8   
,all attempts to discov] ?is 8positive  
electron0 9 ! nuclei fail$1  h[ev]4 ,!  
smalle/ nucleus f\nd 0 t produc$ by     

knock+ !  s+le electron (f a hydrog5    
atom 9 "o way or ano!r4 ,?is hydrog5    
nucleus _h a s+le positive *>ge1 "o t 0 
exactly equal 9 size  to ! negative *>ge
 on ! electron4 ,! hydrog5 nucleus1     
h[ev]1  0 mu* m massive ?an an electron4
 ,! hydrog5 nucleus ) its  s+le positive
 *>ge 0 approximately #ahcg times z     
massive z !  electron ) its s+le        
negative *>ge4    ,0 x possible to knock
 ! positive *>ge loose f ! mass ( !     
hydrog5 nucleus8 ,no?+ physici/s did    
c\ld manage to d t4 ,9  #aiad ,ru!r=d   
decid$ ! attempt %\ld be giv5 up4 ,he   
sugge/$  t ! hydrog5 nucleus1 = all its 
high mass1 %\ld be consid]$  ! unit (   
positive electrical *>ge1 j z ! electron
 0 !  unit ( negative electrical *>ge4  
,he call$ ! hydrog5 nucleus a  8proton0 
f ! ,greek ^w = 8fir/0 because x 0 !    
nucleus (  ! fir/ elem5t4               
,illu/ration3 ,"o proton balances #ahcg 
electrons4    ,:y ! proton %\ld be s mu*
 m massive ?an ! electron is /ill  "o ( 
! unansw]$ my/]ies ( physics4      ,!   

,proton-,electron ,!ory    ,:at ab\t !  
nuclei ( elem5ts o!r ?an hydrog58       
,all ! o!r elem5ts _h nuclei m massive  
?an t ( hydrog5 &  ! natural fir/ guess 
0 t ^! 7 made up ( "s appropriate  numb]
 ( protons closely pack$ toge!r4 ,!     
helium nucleus1 :i* _h  a mass f\r times
 z great z t ( hydrog51 might be made up
 ( #d  protons2 ! oxyg5 nucleus ) a mass
 numb] ( #af might be made up (  #af    
protons & s on4    ,?is guess1 h[ev]1   
ran into imm$iate difficulties4 ,a      
helium nucleus  might h a mass numb] (  
#d b x _h an electric *>ge ( #b4 ,if x  
7 made up ( #d protons1 x ought to h an 
electric *>ge ( #d4 ,9  ! same way1 an  
oxyg5 nucleus made up ( #af protons     
ought to h a  *>ge ( #af1 b 9 actual    
fact x _h "o ( #h4    ,c\ld x be t      
some?+ 0 cancell+ "p ( ! positive       
electric  *>ge8 ,! only ?+ t c\ld d s   
w\ld be a negative electric  *>ge#a & ^!
 7 to be f\nd only on electrons z f> z  
anyone  knew 9 #aiad4 ,x seem$          
reasonable1 !n1 to suppose t a nucleus  

w\ld conta9 ab\t half z _m electrons 9  
addition to ! protons4  ,! electrons 7 s
 light1 !y w\ldn't affect ! mass mu*1 & 
!y w\ld succe$ 9 cancell+ "s ( !        
positive *>ge4    ,?us1 accord+ to ?is  
e>ly !ory1 n[ kn[n to be incorrect1 !   
helium nucleus conta9$ n only #d        
protons1 b #b electrons 9  addition4 ,! 
helium nucleus w\ld !n h a mass numb] ( 
#d & an  electric *>ge 7atomic numb]7 ( 
#d - #b1 or #b4 ,?is 0 9 accordance  )  
obs]vation4    ,?is 8proton-electron    
!ory0 ( nucle> /ructure acc\nt$ =       
isotopes v nicely4 ,:ile oxyg5-#af _h a 
nucleus made up ( #af  protons & #h     
electrons1 oxyg5-#ag _h "o ( #ag protons
 & #i  electrons1 & oxyg5-#ah _h "o (   
#ah protons & #aj electrons4 ,!  mass   
numb]s 7 #af1 #ag1 & #ah1 respectively1 
b ! atomic numb]  0 #af - #h1 #ag - #i1 
& #ah - #aj1 or #h 9 ea* case4    ,aga91
 uranium-#bch has a nucleus built up1   
accord+ to ?is !ory1 (  #bch protons &  
#adf electrons1 :ile uranium-#bce has "o
 built up ( #bce  protons & #adc        

electrons4 ,9 ^! cases ! atomic numb]   
is1  respectively1 #bch - #adf & #bce - 
#adc1 or #ib 9 ea* case4 ,! nucleus  ( !
 #b isotopes is1 h[ev]1 ( diff]5t       
/ructure & x is n  surpris+ !re=e t !   
radioactive prop]ties ( !               
two--prop]ties t involve ! nucleus--%\ld
 be diff]5t & t !  half-life (          
uranium-#bch %\ld be six times z long z 
t (  uranium-#bce4    ,! pres5ce (      
electrons 9 ! nucleus n only expla9$ !  
exi/5ce ( isotopes1 b seem$ ju/ifi$ by  
two fur!r  consid]ations4    ,fir/1 x is
 well kn[n t simil> *>ges repel ea* o!r 
& t  ! repulsion is /rong] ! clos]      
toge!r ! simil> *>ges are  =c$4 ,doz5s (
 positively *>g$ p>ticles squeez$ into !
 t9y  volume ( an atomic nucleus c\ldn't
 possibly rema9 toge!r = m  ?an a t9y   
fraction ( a second4 ,electrical        
repulsion w\ld s5d !m  fly+ ap>t at     
once4    ,on ! o!r h&1 opposite *>ges   
attract1 & a proton & an  electron w\ld 
attract ea* o!r z /rongly z #b protons  
7or #b  electrons7 w\ld repel ea* o!r4  

,x 0 ?\ght possible t !  pres5ce (      
electrons 9 a collection ( protons might
 someh[ limit !  repulsive =ce &        
/abilize ! nucleus4    ,second1 !re are 
radioactive decays 9 :i* beta p>ticles  
are s5t  fly+ out ( ! atom4 ,f ! en]gy  
involv$ !y c\ld come only  out ( !      
nucleus4 ,s9ce beta p>ticles are        
electrons & s9ce !y  come f ! nucleus1 x
 seem$ to foll[ t !re mu/ be electrons  
)9 ! nucleus to beg9 )4    ,!           
proton-electron !ory ( nucle> /ructure  
also seem$ to acc\nt  neatly = _m ( !   
facts ( radioactivity4    ,:y           
radioactivity at all1 = in/ance8 ,! m   
complex a nucleus is1  ! m protons mu/  
be squeez$ toge!r & ! h>d]1 x w\ld      
seem1 x mu/ be to keep !m toge!r4 ,m & m
 electrons seem$  to be requir$4        
,f9ally1 :5 ! total numb] ( protons 0   
#hd or  m1 no am\nt ( electrons seem$   
suffici5t to /abilize ! nucleus4    ,!  
mann] ( breakup fits ! !ory1 too4       
,suppose a nucleus gives (f  an alpha   
p>ticle4 ,! alpha p>ticle is a helium   

nucleus made up1 by  ?is !ory1 ( #d     
protons & #b electrons4 ,if a nucleus   
loses an alpha  p>ticle1 its mass numb] 
%\ld decl9e by #d & its atomic numb] by 
#d  - #b1 or #b4 ,&1 inde$1 :5          
uranium-#bch 7atomic numb] #ib7 gives (f
 an  alpha p>ticle1 x becomes           
?orium-#bcd 7atomic numb] #ij74         
,suppose a beta p>ticle is emitt$4 ,a   
beta p>ticle is an electron &  if a     
nucleus loses an electron1 its mass     
numb] is almo/ un*ang$4 7,an  electron  
is s light t 9 comp>ison ) ! nucleus1 we
 c ignore  its mass47 ,on ! o!r h&1 a   
unit negative *>ge is gone4 ,"o ( !     
protons 9 ! nucleus1 :i* _h previ\sly   
be5 mask$ by an electron1  is n[        
unmask$4 ,its positive *>ge is add$ to !
 re/ & ! atomic  numb] goes up by "o4   
,?us1 ?orium-#bcd 7atomic numb] #ij7    
gives up a  beta p>ticle & becomes      
protact9ium-#bcd 7atomic numb] #ia74    
,if a gamma ray is giv5 (f1 t gamma ray 
has no *>ge & !  equival5t ( v little   
mass4 ,t means t nei!r ! mass numb]  nor

 ! atomic numb] ( ! nucleus is *ang$1   
al?\gh its en]gy  cont5t is alt]$4      
,ev5 m elaborate *anges c be tak5 into  
acc\nt4 ,9 ! long run1  uranium-#bch1   
hav+ gone ?r\gh _m *anges1 becomes      
lead-#bjf4 ,^?  *anges include !        
emission ( #h alpha p>ticles & #f beta  
p>ticles4  ,! #h alpha p>ticles involve 
a loss ( #h  #d1 or #cb 9 mass numb]1   
:ile ! #f beta p>ticles contribute no?+ 
9 ?is respect4 ,&1  inde$1 ! mass numb] 
( uranium-#bch decl9es by #cb 9 rea*+   
lead-#bjf4 ,on ! o!r h& ! #h alpha      
p>ticles involve a decrease 9  atomic   
numb] ( #h  #b1 or #af1 :ile ! #f beta  
p>ticles involve an  increase 9 atomic  
numb] ( #f  #a1 or #f4 ,! total *ange is
 a decrease  ( #af - #f1 or #aj4 ,&     
inde$1 uranium 7atomic numb] #ib7 *anges
 to lead  7atomic numb] #hb74    ,x is  
useful to g into su* detail conc]n+ !   
proton-electron  !ory ( nucle> /ructure 
& to describe h[ attractive x seem$4  ,!
 !ory appe>$ solid & un%akable &1 inde$1
 physici/s us$ x  ) consid]able         

satisfaction = #ae ye>s4    --,& yet1 z 
we %all see1 x 0 wrong2 & t %\ld po9t a 
moral4  ,ev5 ! be/ seem+ ( !ories may be
 wrong 9 "s details &  require an       
ov]haul4      ,protons 9 ,nuclei    ,let
 u1 nev]!less1 g on to describe "s ( !  
progress made 9 !  #aibjs 9 t]ms ( !    
proton-electron !ory t 0 !n accept$4    
,s9ce a nucleus is made up ( a :ole     
numb] ( protons1 its mass ought  to be a
 :ole numb] if ! mass ( a s+le proton is
 consid]$ #a4  7,! pres5ce ( electrons  
w\ld add "s mass b 9 ord] to simplify   
matt]s1 let u ignore t47    ,:5 isotopes
 7 fir/ discov]$ ?is inde$ seem$ to be  
s4  ,h[ev]1 ,a/on & 8 mass spectromet]  
kept measur+ ! mass (  diff]5t nuclei m 
& m closely dur+ ! #aibjs & f\nd t  !y  
diff]$ v slightly f :ole numb]s4 ,yet a 
fix$ numb] (  protons turn$ out to h    
diff]5t masses if !y 7 fir/  consid]$   
sep>ately & !n z "p ( a nucleus4    ,us+
 mod]n /&>ds1 ! mass ( a proton is      
#a4jjghbe4 ,twelve  sep>ate protons w\ld
 h a total mass ( twelve times t1 or    

#ab4jici4 ,on ! o!r h&1 if ! #ab protons
 are pack$ toge!r into a  c>bon-#ab     
nucleus1 ! mass is #ab s t ! mass ( !   
individual  protons is #a4jjjjjj apiece4
 ,:at happ5s to ?is diff]5ce ( #j4jjghbe
  betwe5 ! proton 9 isolation & ! proton
 z "p ( a c>bon-#ab  nucleus8           
,accord+ to ,e9/e9's special !ory (     
relativity1 ! miss+ mass  w\ld h to     
appe> 9 ! =m ( en]gy4 ,if #ab hydrog5   
nuclei  7protons7 plus #f electrons are 
pack$ toge!r to =m a c>bon nucleus1  a  
consid]able quantity ( en]gy w\ld h to  
be giv5 (f4    ,9 g5]al1 ,a/on f\nd t z 
"o w5t on to m & m complicat$  nuclei1 a
 l>g] fraction ( ! mass w\ld h to appe> 
z en]gy  7?\gh n 9 a p]fectly regul>    
way7 until x rea*$ a maximum 9  !       
neighborhood ( iron4    ,iron-#ef1 ! mo/
 common ( ! iron isotopes1 has a mass   
numb] (  #ee4icdi4 ,ea* ( its #ef       
protons1 !re=e1 has a mass ( #j4iihh4   
,= nuclei m complicat$ ?an ^? ( iron1 ! 
protons 9 !  nucleus beg9 to gr[ m      
massive aga94 ,uranium-#bch nuclei1 =   

in/ance1 h a mass ( #bch4jejf1 s t ea* (
 ! #bch protons !y  conta9 has a mass ( 
#a4jjjb4    ,by #aibg ,a/on _h made x   
cle> t x is ! middle elem5ts 9 !        
neighborhood ( iron t are mo/ closely & 
economically pack$4 ,if a  v massive    
nucleus is brok5 up into some:at light] 
nuclei1 !  proton pack+ w\ld be tight] &
 "s mass w\ld be conv]t$ into  en]gy4   
,simil>ly1 if v light nuclei 7 jo9$     
toge!r into  some:at m massive nuclei1  
"s mass w\ld be conv]t$ into en]gy4     
,?is demon/ration t en]gy 0 releas$ 9   
any %ift away f  ei!r extreme ( ! li/ ( 
atoms accord+ to atomic numb] fits !    
case ( radioactivity1 :]e v massive     
nuclei break d[n to some:at  less       
massive ones4    ,consid] t uranium-#bch
 gives up #h alpha p>ticles & #f beta   
p>ticles to become lead-#bjf4 ,!        
uranium-#bch nucleus has a mass (       
#bch4jejf2 ea* alpha p>ticle has "o (   
#d4jjbf = a total ( #cb4jbjh2  ea* beta 
p>ticle has a mass ( #j4jjaed = a total 
( #j4jjibd2 & !  lead-#bjf nucleus has  

"o ( #bje4igde4    ,?is means t !       
uranium-#bch nucleus 7mass3 #bch4jejf7  
*anges into #h  alpha p>ticles1 #f beta 
p>ticles1 & a lead-#bjf nucleus 7total  
mass3  #bch4jjde74 ,! />t+ mass is      
#j4jdfa great] ?an ! f9al mass &  x is  
?is miss+ mass t has be5 conv]t$ into   
en]gy & is  responsible = ! gamma rays &
 = ! velocity ) :i* alpha  p>ticles &   
beta p>ticles are dis*>g$4      ,nucle> 
,bomb>dm5t    ,once sci5ti/s realiz$ t  
!re 0 en]gy :i* became available  :5 "o 
k9d ( nucleus 0 *ang$ into ano!r1 an    
important "q  arose z to :e!r su* a     
*ange c\ld be br\ght ab\t & regulat$  by
 man & :e!r ?is might n be made ! s\rce 
( useful p[] (  a k9d & am\nt undream$ (
 e>li]4    ,*emical en]gy 0 easy to     
initiate & control1 s9ce t involv$  !   
%ifts ( electrons on ! outskirts ( !    
atoms4 ,rais+ !  temp]ature ( a sy/em1 =
 in/ance1 caus$ atoms to move m quickly 
& sma% aga9/ ea* o!r h>d]1 & t 9 itself 
0 suffici5t  to =ce electrons to %ift & 
to initiate a *emical reaction t  w\ld n

 take place at l[] temp]atures4    ,to  
%ift ! protons )9 ! nucleus 78nucle>    
reactions07 & make  nucle> en]gy        
available 0 a h>d] problem by f>4 ,!    
p>ticles  involv$ 7 mu* m massive ?an   
electrons & correspond+ly  h>d] to move4
 ,:at's m1 !y 7 buri$ deep )9 ! atom4   
,no  temp]atures available to !         
physici/s ( ! #aibjs c\ld =ce atoms  to 
sma% toge!r h>d en\gh to rea* & %ake !  
nucleus4    ,9 fact1 ! only objects t 7 
kn[n to rea* ! nucleus 7  spe$+         
subatomic p>ticles4 ,z e>ly z #aijf1 =  
in/ance1 ,ru!r=d  _h us$ ! spe$+ alpha  
p>ticles giv5 (f by a radioactive       
sub/ance to bomb>d matt] & to %[ t      
sometimes ^! alpha  p>ticles 7 deflect$ 
by atomic nuclei4 ,x 01 9 fact1 by su*  
an  exp]im5t t he fir/ demon/rat$ !     
exi/5ce ( su* nuclei4    ,ru!r=d _h     
cont9u$ 8 exp]im5ts ) bomb>dm5t4 ,an    
alpha  p>ticle /rik+ a nucleus w\ld     
knock x free ( ! atom to :i* x  belong$ 
& s5d x %oot+ =w>d 7l "o billi>d ball   
hitt+  ano!r74 ,! nucleus t %ot ahead   

w\ld /rike a film ( *emical  t          
sc9tillat$ 7sp>kl$7 "u ! impact4 ,9 a   
r\gh way1 "o c\ld  tell ! k9d ( nucleus 
t /ruck f ! nature ( ! sp>kl+4    ,9    
#aiai ,ru!r=d bomb>d$ nitrog5 gas )     
alpha p>ticles & f\nd  t he obta9$ ! k9d
 ( sp>kl+ he associat$ ) !  bomb>dm5t ( 
hydrog5 gas4 ,:5 he bomb>d$ hydrog51 !  
alpha  p>ticles /ruck hydrog5 nuclei    
7protons7 & %ot !m =w>d4 ,to get        
hydrog5-sp>kl+ out ( ! bomb>dm5t (      
nitrog51 ,ru!r=d felt1  he mu/ h knock$ 
protons out ( ! nitrog5 nuclei4 ,inde$1 
z 0  lat] f\nd1 he _h conv]t$ nitrog5   
nuclei into oxyg5 nuclei4    ,?is 0 !   
fir/ "t 9 hi/ory t ! atomic nucleus 0   
alt]$  by delib]ate human act4          
,ru!r=d cont9u$ 8 exp]im5ts & by #aibd  
_h %[n t alpha  p>ticles c\ld be us$ to 
knock protons out ( ! nuclei ( almo/ all
  elem5ts up to potassium 7atomic numb] 
#ai74    ,!re 71 h[ev]1 limitations to !
 use ( natural alpha p>ticles  z !      
bomb>d+ ag5t4    ,fir/1 ! alpha p>ticles
 us$ 9 bomb>dm5t 7 positively *>g$  & s 

7 ! atomic nuclei4 ,?is meant t ! alpha 
p>ticles &  ! atomic nuclei repell$ ea* 
o!r & mu* ( ! en]gy ( !  alpha p>ticles 
0 us$ 9 ov]com+ ! repulsion4 ,= m & m   
massive nuclei1 ! positive *>ge grew    
high] & ! repulsion  /rong] until =     
elem5ts beyond potassium1 no collision  
c\ld be  =c$1 ev5 ) ! mo/ en]getic      
naturally occurr+ alpha  p>ticles4      
,illu/ration3 ,man-made transmutation4  
,nitrog5-#ad 7#g,n1#g,p7  ,helium-#d    
7#b,n1#b,p7 7,alpha p>ticle7            
,oxyg5-#ag 7#i,n1#h,p7  ,hydrog5-#a     
7#a,p7    ,neutron,n1 ,proton,p         
,second1 ! alpha p>ticles t are spray$  
t[>d ! t>get _c be  aim$ directly at !  
nuclei4 ,an alpha p>ticle /rikes a      
nucleus only  if1 by *ance1 !y come     
toge!r4 ,! nuclei t s]ve z _!  t>gets   
are s unimag9ably small t mo/ ( !       
bomb>d+ p>ticles  are sure to miss4 ,9  
,ru!r=d's fir/ bomb>dm5t ( nitrog51 x 0 
calculat$ t only #a alpha p>ticle out ( 
#cjj1jjj manag$ to /rike a  nitrog5     
nucleus4    ,! result ( ^! consid]ations

 is cle>4 ,!re is en]gy to be  ga9$ out 
( nucle> reactions1 b !re is also en]gy 
t mu/ be  exp5d$ to cause ^! nucle>     
reactions4 ,9 ! case ( nucle>  bomb>dm5t
 by subatomic p>ticles 7! only way1     
app>5tly1 9 :i*  nucle> reactions c be  
br\ght ab\t71 ! en]gy exp5d$ seems to be
  _m times ! en]gy to be extract$4 ,?is 
is because s _m subatomic  p>ticles use 
up _! en]gy 9 ioniz+ atoms1 knock+      
electrons  away1 & nev] initiate nucle> 
reactions at all4    ,x 0 z ?\gh ! only 
way y c\ld light a c&le w\ld be to      
/rike #cjj1jjj mat*es1 "o aft] ! o!r4   
,if t 7 s1 c&les  w\ld be impractical4  
,9 fact1 ! mo/ dramatic result ( alpha  
p>ticle bomb>dm5t _h  no?+ to d ) en]gy 
production1 b r ! rev]se4 ,new nuclei  7
 produc$ t _h m en]gy ?an ! />t+ nuclei1
 s t  en]gy 0 absorb$ by ! nucle>       
reaction r ?an giv5 (f4    ,?is came    
ab\t fir/ 9 #aicd1 :5 a ,fr5*           
husb&-&-wife team (  physici/s1 ,frdric 
,joliot-,curie 7#aijj-aieh7 & ,irne     
,joliot-,curie  7#ahig-aief7 7 bomb>d+  

alum9um-#bg 7atomic numb] #ac7 ) alpha  
p>ticles4 ,! result 0 to comb9e "p ( !  
alpha p>ticle ) !  alum9um-#bg nucleus  
to =m a new nucleus ) an atomic numb]   
two  units high]--#ae--;& a mass numb]  
?ree units high]--#cj4    ,! elem5t )   
atomic numb] #ae is phosphorus s t      
phosphorus-#cj  0 =m$4 ,! only isotope (
 phosphorus t occurs 9 nature1  h[ev]1  
is phosphorus-#ca4 ,phosphorus-#cj 0 !  
fir/ man-made  nucleus--! fir/ to be    
manufactur$ by nucle> reactions 9 !     
laboratory4    ,illu/ration3 ,frdric &  
,irne ,joliot-,curie    ,! reason       
phosphorus-#cj did n occur 9 nature 0 t 
its en]gy  cont5t 0 too high to all[ x  
to be /able4 ,its en]gy cont5t  dra9$   
away ?r\gh ! emission ( p>ticles t all[$
 ! nucleus  to *ange ov] into a /able   
"o1 silicon-#cj 7atomic numb] #ad74 ,?is
  0 an example ( 8artificial            
radioactivity04    ,s9ce #aicd1 ov] a   
?\s& k9ds ( nuclei t d n occur 9 nature 
h be5 =m$ 9 ! laboratory ?r\gh v>i\s    
k9ds (  bomb>dm5t-induc$ nucle>         

reactions4 ,e s+le "o ( !m prov$  to be 
radioactive4      ,p>ticle ,accel]ators 
,0 !re no?+ t c\ld be done to make      
nucle> bomb>dm5t m  effici5t & increase 
! *ance ( obta9+ useful en]gy out (     
nucle> reactions8    ,9 #aibh !         
,russian-,am]ican physici/ ,george ,gam[
 7#aijd-aifh7  sugge/$ t protons might  
be us$ z bomb>d+ ag5ts 9 place (  alpha 
p>ticles4 ,protons 7 only "o-f\r? z     
massive z alpha  p>ticles & ! collision 
might be correspond+ly less effective2  
on  ! o!r h&1 protons _h only half !    
positive *>ge ( alpha  p>ticles & w\ld n
 be z /rongly repell$ by ! nuclei4 ,!n1 
too1 protons 7 mu* m easily available   
?an alpha p>ticles4 ,to  get a supply ( 
protons "o only _h to ionize ! v common 
hydrog5  atoms1 i4e41 get rid ( ! s+le  
electron ( ! hydrog5 atom1 & a  s+le    
proton is left4    ,illu/ration3        
,artificial radioactivity4              
,alum9um-#bg 7#ad,n1#ac,p7  ,helium-#d  
7#b,n1#b,p7 7,alpha p>ticle7            
7#af,n1#ae,p7     ,n  ,phosphorus-#cj   

7,radioactive7 7#ae,n1#ae,p7            
,positron  ,silicon-#cj    ,neutron,n1  
,proton,p    ,( c\rse1 protons obta9$ by
 ! ionization ( hydrog5 atoms h  v      
little en]gy1 b c\ld en]gy be imp>t$ to 
!m8 ,protons c>ry  a positive *>ge & a  
=ce c !re=e be ex]t$ ^u !m by an        
electric or magnetic field4 ,9 a device 
t makes use ( su* fields1  protons c be 
accel]at$ 7made to g fa/] & fa/]71 & ?us
 ga9  m & m en]gy4 ,9 ! end1 if en\gh   
en]gy is ga9$1 ! proton  c\ld d m damage
 ?an ! alpha p>ticle1 despite ! =m]'s   
small] mass4 ,comb9e t ) ! small]       
repulsion involv$ & !  great] ease (    
obta9+ protons--& ! weight ( conv5i5ce &
  usefulness w\ld sw+ f> 9 ! direction (
 ! proton4    ,physici/s began to try to
 design 8p>ticle accel]ators0 & ! fir/  
practical device ( ?is sort 0 produc$ 9 
#aibi by ! two ,briti%  physici/s ,john 
,d\glas ,cockcr(t 7#ahig-aifg7 & ,erne/ 
,?omas ,s9ton  ,walton 7#aijc-    74 ,_!
 device1 call$ an 8electro/atic         
accel]ator01  produc$ protons t 7       

suffici5tly en]getic to initiate nucle> 
reactions4 ,9 #aica !y us$ _! accel]at$ 
protons to disrupt !  nucleus (         
li?ium-#g4 ,x 0 ! fir/ nucle> reaction  
to be br\ght  ab\t by man-made bomb>d+  
p>ticles4    ,o!r types ( p>ticle       
accel]ators 7 also be+ develop$ at ?is  
"t4 ,! mo/ fam\s 0 ! "o built 9 #aicj by
 ! ,am]ican  physici/ ,erne/ ,orl&o     
,lawr5ce 7#aija-aieh74 ,9 ?is device a  
magnet  0 us$ to make ! protons move 9  
gradually exp&+ circles1  ga9+ en]gy )  
ea* lap until !y f9ally mov$ out beyond 
!  influ5ce ( ! magnet & !n hurtl$ out (
 ! in/rum5t 9 a  /raight l9e at maximum 
en]gy4 ,?is in/rum5t 0 call$ a          
8cyclotron04    ,illu/ration3 ,inv5tors 
( "o ( ! fir/ accel]ators1 ,erne/ ,t4   
,s4  ,walton1 left1 & ,john ,d4         
,cockcr(t1 "r1 ) ,"l ,erne/ ,ru!r=d  at 
,cambridge ,univ]sity 9 ! e>ly #aicjs4  
,illu/ration3 ,! bomb>dm5t ( li?ium-#g )
 protons 0 ! fir/  nucle> reaction caus$
 by man-made p>ticles4      ,li?ium-#g  
7#d,n1#c,p7  ,hydrog5-#a 7,proton7      

,helium-#d 7#b,n1#b,p7 7,alpha p>ticle7 
,helium-#d 7#b,n1#b,p7 7,alpha          
p>ticle7    ,neutron,n1 ,proton,p    ,! 
cyclotron 0 rapidly improv$1 us+ l>g]   
magnets &  increas+ly sophi/icat$       
design4 ,!re are n[1 at ?is "t (  writ+1
 8proton syn*rotrons0 7desc5dants ( t   
fir/ cyclotron7  t produce p>ticles )   
ov] a million times ! en]gy ( ^?        
produc$ by ,lawr5ce's fir/ cyclotron4 ,(
 c\rse1 ! fir/ cyclotron  0 only a qu>t]
 ( a met] wide1 :ile ! l>ge/ today has a
  diamet] ( "s #bjjj met]s4    ,z       
p>ticle accel]ators grew l>g]1 m        
effici5t1 & m p[]ful1  !y became ev] m  
useful 9 /udy+ ! /ructure ( ! nucleus  &
 ! nature ( ! subatomic p>ticles        
!mselves4 ,!y did n  s]ve1 h[ev]1 to br+
 ! dream ( useful nucle> en]gy any      
clos]4  ,?\gh !y br\ght ab\t ! lib]ation
 ( va/ly m nucle> en]gy  ?an ,ru!r=d's  
initial bomb>dm5ts c\ld1 !y also consum$
 a great  deal m en]gy 9 ! process4     
,x is n surpris+ t ,ru!r=d1 ! pione] 9  
nucle>  bomb>dm5t1 0 pessimi/ic4 ,to !  

end ( 8 days 7he di$ 9 #aicg7  he       
ma9ta9$ t x w\ld be =ev] impossible to  
tap ! en]gy (  ! nucleus = use by man4  
,hopes t 8nucle> p[]0 might "s day  run 
! _w's indu/ries 71 9 8 view1 an idle   
dream4    ,illu/ration3 ,erne/ ,o4      
,lawr5ce holds a model ( ! fir/         
cyclotron  9 #aicj1 a ye> aft] its      
conception4                             
,,! ,,neutron      ,nucle> ,sp9    ,:at 
,ru!r=d did n 7& c\ld n7 take into      
acc\nt 7 !  consequ5ces ( a completely  
new type ( nucle> bomb>dm5t involv+ a   
type ( p>ticle unkn[n 9 ! #aibjs 7?\gh  
,ru!r=d speculat$  ab\t ! possibility ( 
its exi/5ce74    ,! beg9n+s ( ! new pa? 
came ab\t ?r\gh ! reluctant  realization
 t !re 0 a flaw 9 ! app>5tly firmly     
gr\nd$  proton-electron picture ( nucle>
 /ructure4    ,! flaw involv$ ! 8nucle> 
sp904 ,9 #aibd ! ,au/rian physici/      
,wolfgang ,pauli 7#aijj-aieh7 work$ out 
a !ory t treat$ protons &  electrons z  
?\gh !y 7 sp9n+ on _! axes4 ,?is sp9    
c\ld be  9 ei!r direction 7or1 z we w\ld

 say 9 e>?ly t]ms1 f  we/-to-ea/1 or f  
ea/-to-we/74 ,quantum !ory has %[n t a  
natural unit exi/s = :at is call$ !     
angul> mom5tum ( ?is  sp94 ,measur$ 9   
t]ms ( ?is natural unit ( sp91 ! proton 
& !  electron h sp9 4 ,if ! p>ticle spun
 9 "o direction x 0 1  if 9 ! o!r x 0 -4
    ,:5 subatomic p>ticles came toge!r  
to =m an atomic nucleus1 ea*  kept its  
orig9al sp91 & ! nucle> sp9 0 !n equal  
to ! total  angul> mom5tum ( !          
individual p>ticles t made x up4    ,=  
in/ance1 suppose ! helium nucleus is    
made up ( #d protons & #b  electrons1 z 
0 ?\ght 9 ! #aibjs4 ,( ! #d protons1    
suppose t  two _h a sp9 (  & two ( -4   
,suppose also t ( ! #b  electrons1 "o _h
 a sp9 (  & "o ( -4 ,all ! sp9s w\ld    
cancel ea* o!r4 ,! total angul> mom5tum 
w\ld be z]o4    ,( c\rse1 x is also     
possible t all #f p>ticles 7 sp9n+ 9 !  
same direction2 all  or all -4 ,9 t case
 ! nucle> sp9 w\ld be  #c1 ei!r 9 "o    
direction or ! o!r4 ,if #e p>ticles 7   
sp9n+ 9  "o direction & #a 9 ! o!r1 !n !

 total sp9 w\ld be #b1 9 "o  direction  
or ! o!r4    ,illu/ration3 ,wolfgang    
,pauli lectur+ 9 ,cop5hag5 9 ,april     
#aibi4    ,9 %ort if y h an ev5 numb] ( 
p>ticles 9 a nucleus1 ea* )  a sp9 (  or
 -1 !n ! total sp9 is ei!r z]o or a :ole
  numb]1 no matt] :at comb9ation (      
positive & negative sp9s y  *oose4 7,!  
total sp9 is always writt5 z a positive 
numb]47    ,on ! o!r h&1 suppose y h    
li?ium-#g1 :i* 0 ?\ght to be  made up ( 
#g protons & #d electrons4 ,if ! #g     
protons 7 all  &  ! #d electrons 7 all -
 9 _! sp9s1 ! nucle> sp9 w\ld be  _/ -  
_/  _/4    ,if y h an odd numb] (       
p>ticles 9 ! nucleus1 y w f9d  t any    
comb9ation ( positive & negative sp9s w 
nev] give  y ei!r z]o or a :ole numb] z 
a sum4 ,! sum w always include  a       
fraction4    ,consequ5tly1 if "o        
measures ! sp9 ( a p>ticul> atomic      
nucleus  "o c tell at once :e!r t       
nucleus conta9s an ev5 numb] (  p>ticles
 or an odd numb]4    ,?is quickly rais$ 
a problem4 ,! nucle> sp9 ( ! common     

isotope1  nitrog5-#ad1 0 measur$        
accurately ov] & ov] aga9 & turn$ out   
to be #a4 ,!re seem$ no d\bt ab\t t & x 
c\ld !re=e be  conclud$ t !re 7 an ev5  
numb] ( p>ticles 9 ! nitrog5-#ad        
nucleus4    ,& yet1 by ! proton-electron
 !ory ( nucle> /ructure1 !  nitrog5-#ad 
nucleus1 ) a mass numb] ( #ad & an      
atomic numb] ( #g1  _h to be made up (  
#ad protons & #g electrons = a total (  
#ba  p>ticles altoge!r--an odd numb]4   
,! nucle> sp9 ( nitrog5-#ad indicat$    
8ev5 numb]0 & !  proton-electron !ory   
indicat$ 8odd numb]04 ,"o or ! o!r _h to
  be wrong1 b :i*8 ,! nucle> sp9 0 a    
matt] ( actual  measurem5t1 :i* c\ld be 
repeat$ ov] & ov] & on :i* all  agre$4  
,! proton-electron !ory 0 only a !ory4  
,x 0 !re=e  ! latt] t 0 que/ion$4       
,:at 0 to be done8    ,suppose x is     
wrong to c\nt protons & electrons inside
 ! nucleus z  sep>ate p>ticles4 ,0 x    
possible t an electron & a proton1  =c$ 
into ! close conf9em5t ( ! atomic       
nucleus might1 by !  =ce ( mutual       

attraction1 become s intimately connect$
 z to c\nt  z a s+le p>ticle4 ,"o ( !   
fir/ to sugge/ ?is1 z f> back z  #aibj1 
0 ,ru!r=d4    ,su* a proton-electron    
comb9ation w\ld be electrically neutral 
& 9  #aiba ! ,am]ican *emi/ ,william    
,drap] ,h>k9s 7#ahgc-aiea7 us$ !  t]m   
8neutron0 z a "n = x4    ,if we look at 
! nitrog5-#ad nucleus 9 ?is way !n x is 
made up1  n ( #ad protons & #g          
electrons1 b ( #g protons & #g          
proton-electron comb9ations4 ,in/ead ( a
 total ( #ba p>ticles1 !re  w\ld be a   
total ( #ad2 in/ead ( an odd numb]1 !re 
w\ld be an ev5  numb]4 ,! /ructure w\ld 
n[ acc\nt = ! nucle> sp94    ,b c\ld su*
 a revis$ !ory ( nucle> /ructure be made
 to seem  plausible8 ,! proton-electron 
!ory seem$ to make s5se because bo?     
protons & electrons 7 kn[n to exi/      
sep>ately & c\ld be  detect$4 ,if an    
intimate proton-electron comb9ation c\ld
 also exi/1  ought x n exi/ 7or be made 
to exi/7 outside ! nucleus & ought  x n 
be detect$ z an isolat$ p>ticle8        

,discov]y ( ! ,neutron    ,?r\gh\t !    
#aibjs sci5ti/s se>*$ = ! neutron b )\t 
success4    ,"o ( ! tr\bles 0 t !       
p>ticle 0 electrically neutral4         
,subatomic p>ticles c\ld be detect$ 9 a 
v>iety ( ways1 b e  s+le way 7"r d[n to 
! pres5t "t7 makes use ( _! electric    
*>ge4 ,! electric *>ge ( a spe$+        
subatomic p>ticle ei!r  repels electrons
 or attracts !m4 ,9 ei!r case1 electrons
 are knock$  (f atoms t are enc\nt]$ by 
! spe$+ subatomic p>ticle4    ,! atoms )
 electrons knock$ (f are n[ positively  
*>g$ ions4  ,droplets ( wat] vapor c =m 
ab\t ^! ions1 or a bubble ( gas  c =m1  
or a sp>k ( light c be se54 ,! droplets1
 ! bubbles1  & ! light c all be detect$ 
"o way or ano!r & ! pa? ( !  subatomic  
p>ticle c\ld be foll[$ by ! trail ( ions
 x left  beh9d4 ,gamma rays1 ?\gh !y    
c>ry no *>ge1 are a wave =m capable  (  
ioniz+ atoms4    ,all ! p>ticles & rays 
t c leave a detectable track ( ions     
beh9d are call$ 8ioniz+ radiation0 & ^! 
are easy to detect4    ,! hypo!tical    

proton-electron comb9ation1 h[ev]1 :i* 0
 nei!r  a wave =m nor a *>g$ p>ticle 0 n
 expect$ to be able to ionize  atoms4 ,x
 w\ld w&] among ! atoms )\t ei!r        
attract+ or  repell+ electrons & w\ld   
!re=e leave ! atomic /ructure  intact4  
,its pa?way c\ld n be foll[$4 ,9 %ort1  
!n1 ! neutron  01 s to speak1 invisible1
 & ! se>* = x seem$ a lo/ cause4  ,&    
until x 0 f\nd1 ! proton-electron !ory (
 nucle> /ructure1  :atev] its obvi\s    
defici5cies ) respect to nucle> sp91    
rema9$  ! only "o to "w )4    ,!n came  
#aicj4 ,! ,g]man physici/ ,wal!r        
,wilhelm ,georg ,bo!  7#ahia-aieg7 & a  
co-work]1 ,h4 ,beck]1 7 bomb>d+ ! light 
metal1  b]yllium1 ) alpha p>ticles4     
,ord9>ily1 !y might expect protons  to  
be knock$ out ( x1 b 9 ?is case no      
protons appe>$4 ,!y  detect$ "s sort (  
radiation because some?+ 0 creat+ c]ta9 
effects :ile ! alpha p>ticles 7 bomb>d+ 
! b]yllium b n  aft] ! bomb>dm5t ceas$4 
,illu/ration3 ,wal!r ,w4 ,g4 ,bo!    ,to
 try to det]m9e some?+ ab\t ! prop]ties 

( ?is radiation1  ,bo! & ,beck] tri$    
putt+ objects 9 ! way ( ! radiation4 ,!y
  f\nd ! radiation to be rem>kably      
p5etrat+4 ,x ev5 pass$ ?r\gh  sev]al    
c5timet]s ( lead4 ,! only =m ( radiation
 t 0 kn[n  at t "t to come out ( bomb>d$
 matt] ) ! capacity (  p5etrat+ a ?ick  
lay] ( lead 0 gamma rays4 ,bo! & ,beck]1
  !re=e1 decid$ !y _h produc$ gamma rays
 & report$ ?is4    ,9 #aicb !           
,joliot-,curies repeat$ ! ,bo!-,beck] "w
 & got !  same results4 ,h[ev]1 among ! 
objects !y plac$ 9 ! pa? ( !  new       
radiation1 !y includ$ p>aff91 :i* is    
made up ( ! light  atoms ( c>bon &      
hydrog54 ,to _! surprise1 protons 7     
knock$  out ( ! p>aff94    ,gamma rays  
_h nev] be5 obs]v$ to d ?is1 b !        
,joliot-,curies  c\ld n ?9k :at else !  
radiation might be4 ,!y simply report$  
t !y _h discov]$ gamma rays to be       
capable ( a new k9d (  action4          
,illu/ration3 ,james ,*adwick    ,n s ! 
,engli% physici/ ,james ,*adwick 7#ahia-
    74 ,9 t same  ye> he ma9ta9$ t a    

gamma ray1 :i* possess$ no mass1 simply 
lack$ ! mom5tum to hurl a proton out (  
its place 9 ! atom4 ,ev5  an electron 0 
too light to d s4 7,x w\ld be l try+ to 
knock a  baseball (f ! gr\nd & into !   
air by hitt+ x ) a p+-pong  ball47      
,any radiation capable ( knock+ a proton
 out ( an atom _h to consi/  ( p>ticles 
t 7 !mselves pretty massive4 ,& if "o   
argu$ l  t1 !n x seem$ t ! radiation    
fir/ obs]v$ by ,bo! &  ,beck] _h to be !
 long-s\ght-= proton-electron           
comb9ation4  ,*adwick us$ ,h>k9s' t]m1  
neutron1 = x & made x (ficial4 ,he  gets
 ! cr$it = ! discov]y ( ! neutron4      
,*adwick manag$ to "w out ! mass ( !    
neutron f 8  exp]im5ts & by #aicd x 0 q 
cle> t ! neutron 0 m  massive ?an !     
proton4 ,! be/ mod]n data h ! mass ( !  
proton set at #a4jjghbe1 & t ( ! neutron
 j a trifle great] at  #a4jjhffe4    ,! 
fact t ! neutron 0 j ab\t z massive z ! 
proton 0 to  be expect$ if ! neutron 7 a
 proton-electron comb9ation4 ,x 0  also 
n surpris+ t ! isolat$ neutron ev5tually

 breaks up1  giv+ up an electron &      
becom+ a proton4 ,out ( any l>ge numb] (
  neutrons1 half h turn$ into protons 9 
ab\t #ab m9utes4    ,nev]!less1 al?\gh 9
 "s ways we c expla9 ! neutron by       
speak+ ( x z ?\gh x 7 a proton-electron 
comb9ation1 x  really is n4 ,a neutron  
has a sp9 (  :ile a proton-electron     
comb9ation w\ld h a sp9 ( ei!r #j or #a4
 ,! neutron1 !re=e1  mu/ be treat$ z a  
s+le un*>g$ p>ticle4      ,!            
,proton-,neutron ,!ory    ,z soon z !   
neutron 0 discov]$1 ! ,g]man physici/   
,w]n] ,k>l  ,heis5b]g 7#aija-    7      
reviv$ ! notion t ! nucleus mu/ be made 
up ( protons & neutrons1 r ?an protons &
 electrons4 ,x 0  v easy to swit* f !   
latt] !ory to ! =m]1 if "o simply       
rememb]$ to pair ! electrons ?\ght to be
 9 ! nucleus )  protons & give ! "n     
neutrons to ^! comb9ations4    ,?us1 !  
helium-#d nucleus1 r ?an be+ made up (  
#d protons & #b  electrons1 0 made up ( 
#b protons & #b proton-electron         
comb9ations2  or #b protons & #b        

neutrons4 ,9 ! same way ! oxyg5-#af     
nucleus  in/ead ( be+ made up ( #af     
protons & #h electrons1 w\ld be made up 
( #h protons & #h neutrons4    ,!       
proton-neutron !ory w\ld acc\nt = mass  
numb]s & atomic  numb]s p]fectly well4  
,if a nucleus 0 made up ( x protons & y 
neutrons1 !n ! atomic numb] 0 equal to x
 & ! mass numb] to  x  y4 7,x is n[     
possible to def9e ! mass numb] ( a      
nucleus 9  mod]n t]ms4 ,x is ! numb] (  
protons plus neutrons 9 ! nucleus47     
,illu/ration3 ,w]n] ,heis5b]g    ,!     
proton-neutron !ory ( nucle> /ructure   
c\ld acc\nt =  isotopes p]fectly well1  
too4 ,consid] ! #c oxyg5 isotopes1      
oxyg5-#af1  oxyg5-#ag1 & oxyg5-#ah4 ,!  
fir/ w\ld h a nucleus made up ( #h      
protons & #h neutrons2 ! second1 "o ( #h
 protons & #i neutrons2 &  ! ?ird1 "o ( 
#h protons & #aj neutrons4 ,9 ea* case !
 atomic  numb] is #h4 ,! mass numb]s    
h[ev] w\ld be #af1 #ag1 & #ah1          
respectively4    ,9 ! same way          
uranium-#bch w\ld h a nucleus built (   

#ib protons &  #adf neutrons1 :ile      
uranium-#bce w\ld h "o ( #ib protons &  
#adc  neutrons4    ,by ! new !ory1 c we 
suppose t x is neutrons r ?an  electrons
 t someh[ hold ! protons toge!r aga9/ _!
 mutual  repulsion1 & t m & m neutrons  
are requir$ to d ?is z  ! nucleus gr[s m
 massive8 ,at fir/ ! numb] ( neutrons   
requir$  is r\ghly equal to ! numb] (   
protons4 ,! helium-#d nucleus conta9s   
#b protons & #b neutrons1 ! c>bon-#ab   
nucleus conta9s #f protons & #f         
neutrons1 ! oxyg5-#af nucleus conta9s #h
 protons & #h neutrons1 &  s on4    ,= m
 complicat$ nuclei1 additional neutrons 
are ne$$4 ,9  vanadium-#ea1 ! nucleus   
conta9s #bc protons & #bh neutrons1 five
 m  ?an an equal am\nt4 ,9 bismu?-#bji1 
x is #hc protons & #abf neutrons1  #dc m
 ?an an equal am\nt4 ,= /ill m massive  
nuclei conta9+ a  l>g] numb] ( protons1 
no am\nt ( neutrons is suffici5t to keep
  ! assembly /able4 ,! m massive nuclei 
are all radioactive4    ,! mann] (      
radioactive breakd[n fits ! !ory1 too4  

,suppose a  nucleus gives (f an alpha   
p>ticle4 ,! alpha p>ticle is a helium   
nucleus made up ( #b protons & #b       
neutrons4 ,if a nucleus loses an alpha  
p>ticle1 its mass numb] %\ld decl9e by  
#d & its atomic numb] by  #b1 & t is :at
 happ5s4    ,suppose a nucleus gives (f 
a beta p>ticle4 ,= a mom5t1 t might     
seem puzzl+4 ,if ! nucleus conta9s only 
protons & neutrons & no  electrons1 :]e 
does ! beta p>ticle come f8 ,suppose we 
consid]  ! neutrons z proton-electron   
comb9ations4 ,)9 _m nuclei1 !  neutrons 
are q /able & d n break up z !y d 9     
isolation4  ,9 ! case ( c]ta9 nuclei1   
h[ev]1 !y d break up4    ,?us !         
?orium-#bcd nucleus is made up ( #ij    
protons & #add neutrons4  ,"o ( ^!      
neutrons might be view$ z break+ up to  
lib]ate an  electron & leav+ beh9d an   
unb\nd proton4 ,if a beta p>ticle leaves
  !n1 ! numb] ( neutrons decreases by "o
 & ! numb] ( protons  increases by "o4  
,! ?orium-#bcd nucleus 7#ij protons1    
#add neutrons7  becomes a               

protact9ium-#bcd nucleus 7#ia protons1  
#adc neutrons74    ,9 %ort1 !           
proton-neutron !ory ( nucle> /ructure   
c\ld expla9  all ! obs]v$ facts j z well
 z ! proton-electron !ory1 &  c\ld      
expla9 ! nucle> sp9s1 :i* !             
proton-electron !ory c\ld  n4 ,:at's m1 
! isolat$ neutron _h be5 discov]$4    ,!
 proton-neutron !ory 0 !re=e accept$ &  
rema9s accept$ to  ?is day4      ,!     
,nucle> ,int]action    ,9 "o place1 &   
only "o1 did ! proton-neutron !ory seem 
a little  weak] ?an ! proton-electron   
!ory4 ,! electrons 9 ! nucleus  7 ?\ght 
to act z a k9d ( glue hold+ toge!r !    
protons4    ,b ! electrons 7 gone4 ,!re 
7 no negative *>ges at all  inside !    
nucleus1 only ! positive *>ges ( !      
proton1 plus !  un*>g$ neutron4 ,z _m z 
#hc positive *>ges 7 to be f\nd 79  !   
bismu?-#bji nucleus7 squeez$ toge!r &   
yet n break+ ap>t4    ,9 ! abs5ce (     
electrons1 :at kept ! protons cl++      
toge!r8    ,0 x possible t ! electrical 
repulsion betwe5 #b protons is  replac$ 

by an attraction if ^? protons 7 pu%$   
toge!r closely  en\gh8 ,c !re be bo? an 
attraction & a repulsion1 ) !  =m] ! m  
important at v %ort range8 ,if ?is 7 s1 
t  hypo!tical attraction w\ld h to h two
 prop]ties4 ,fir/1 x  w\ld h to be      
extremely /rong--/rong en\gh to ov]come 
!  repulsion ( two positive *>ges at v  
close qu>t]s4 ,secondly1 x  w\ld h to be
 %ort-range1 = no attractive =ce betwe5 
protons (  any k9d 0 ev] detect$ outside
 ! nucleus4    ,9 addition1 ?is         
%ort-range attraction w\ld h to involve 
!  neutron4 ,! hydrog5-#a nucleus 0 made
 up ( a s+le proton1 b all  nuclei      
conta9+ m ?an #a proton _h to conta9    
neutrons also to be  /able1 & only c]ta9
 numb]s ( neutrons4    ,until ! discov]y
 ( ! neutron1 only two k9ds ( =ces1 or  
8int]actions01 7 kn[n 9 ! univ]se4 ,^! 7
 !  8gravitational int]action0 & !      
8electromagnetic int]action04 ,!        
electromagnetic int]action 0 mu* !      
/rong] ( ! two--trillions  & trillions &
 trillions ( times z /rong z !          

gravitational  attraction4    ,!        
electromagnetic attraction1 h[ev]1      
includes bo? attraction  7betwe5        
opposite electric *>ges or betwe5       
opposite magnetic poles7  & repulsion   
7betwe5 l electric *>ges or magnetic    
poles74 ,9  ord9>y bodies1 ! attractions
 & repulsions usually cancel ea*  o!r   
entirely or ne>ly entirely1 leav+ v     
little ( "o or !  o!r to be detect$ z   
surplus4 ,! gravitational int]action1   
h[ev]1  includes only attraction & ?is  
increases ) mass4 ,by ! "t y  h gigantic
 masses su* z ! e>? or ! sun1 !         
gravitational  int]action betwe5 !m &   
o!r bodies is also gigantic4    ,bo? !  
gravitational & electromagnetic         
int]actions are long-range4  ,! int5sity
 ( ea* int]action decl9es ) di/ance b   
only z !  squ>e ( ! di/ance4 ,if !      
di/ance betwe5 e>? & sun 7  d\bl$1 !    
gravitational int]action w\ld /ill be   
"o-f\r? :at x  is n[4 ,if ! di/ance 7   
increas$ t5 times1 ! int]action w\ld    
/ill be #a_/7aj  #aj7 or #a_/ajj :at x  

is n[4 ,x is = ?is reason t             
gravitational & electromagnetic         
int]actions c make !mselves felt  ov]   
millions ( miles ( space4    ,b n[1 ) ! 
acceptance ( ! proton-neutron !ory (    
nucle>  /ructure1 physici/s began to    
suspect ! exi/5ce ( a ?ird              
int]action--a 8nucle> int]action0--mu*  
/rong] ?an !  electromagnetic           
int]action1 p]haps #acj times z /rong4  
,fur!rmore1  ! nucle> int]action _h to  
decl9e v rapidly ) di/ance mu*  m       
rapidly ?an ! electromagnetic int]action
 did4    ,9 t case1 protons 9 virtual   
contact1 z )9 ! nucleus1 w\ld  attract  
ea* o!r1 b if ! di/ance betwe5 !m 0     
increas$  suffici5tly to place "o       
outside ! nucleus1 ! nucle> int]action  
w\ld decrease 9 int5sity to less ?an !  
electromagnetic repulsion4  ,! proton   
w\ld n[ be repell$ by ! positive *>ge ( 
! nucleus  & w\ld g fly+ away4 ,t is :y 
atomic nuclei h to be s small2  x is    
only :5 !y are s t9y t ! nucle>         
int]action c hold  !m toge!r4    ,9     

#aicb ,heis5b]g tri$ to "w out h[ ^!    
int]actions might come  into be+4 ,he   
sugge/$ t attractions & repulsions 7 !  
result  ( p>ticles be+ con/antly &      
rapidly ex*ang$ by ! bodies  exp]i5c+ ! 
attractions & repulsions4 ,"u "s        
conditions1  ^! 8ex*ange p>ticles0 mov+ 
back & =? v rapidly betwe5 #b  bodies   
might =ce ^? bodies ap>t2 "u o!r        
conditions !y might  pull ^? bodies     
toge!r4    ,9 ! case ( ! electromagnetic
 int]action1 ! ex*ange p>ticles  seem$  
to be 8photons01 wave packets t made up 
gamma rays1 ,x rays1 or  ev5 ord9>y     
light 7all ( :i* are examples (         
8electromagnetic  radiation074 ,!       
gravitational int]action w\ld be !      
result (  ex*ange p>ticles call$        
8gravitons04 7,9 #aifi1 !re 7 reports t 
gravitons _h actually be5 detect$47     
,bo? ! photon & ! graviton h z]o mass & 
!re is a  connection betwe5 t & ! fact t
 electromagnetic int]action  &          
gravitational int]action decl9e only    
sl[ly ) di/ance4 ,= a  nucle>           

int]action1 :i* decl9es v rapidly )     
di/ance1 !  ex*ange p>ticle 7if any7    
w\ld h to h mass4    ,9 #aice !         
,japanese physici/ ,hideki ,yukawa      
7#aijg-    7 work$ out 9  consid]able   
detail ! !ory ( su* ex*ange p>ticles 9  
ord] to  decide :at k9d ( prop]ties ! "o
 involv$ 9 ! nucle>  int]action w\ld h4 
,he decid$ x ought to h a mass ab\t #bej
  times t ( an electron1 :i* w\ld make x
 ab\t _/ z massive z a  proton4 ,s9ce   
?is mass is int]m$iate betwe5 t ( an    
electron &  proton1 su* p>ticles        
ev5tually came to be call$ 8mesons0 f a 
,greek ^w mean+ 8int]m$iate04    ,once  
,yukawa publi%$ 8 !ory1 ! se>* 0 on = ! 
hypo!tical  mesons4 ,ideally1 if !y     
exi/$ )9 ! nucleus1 %oot+ back &  =?    
betwe5 protons & neutrons1 !re ought to 
be "s way (  knock+ !m out ( ! nucleus &
 /udy+ !m 9 isolation4  ,un=tunately1 ! 
bomb>d+ p>ticles at ! disposal (        
physici/s 9  ! #aicjs possess$ f> too   
little en]gy to knock mesons out (      
nuclei1  assum+ !y 7 !re 9 ! fir/ place4

    ,!re 0 "o way out4 ,9 #aiaa !       
,au/rian physici/ ,victor ,francis      
,hess 7#ahhc-aifd7 _h discov]$ t e>? 0  
bomb>d$ f e side  by 8cosmic rays04 ,^! 
consi/$ ( spe$+ atomic nuclei 78cosmic  
p>ticles07 ( enorm\s en]gies--9 "s      
cases1 billions ( times z  int5se z any 
en]gies available ?r\gh p>ticles produc$
 by mank9d4  ,if a cosmic p>ticle (     
suffici5t en]gy /ruck an atomic nucleus 
9  ! atmosph]e1 x might knock mesons out
 ( x4    ,9 #aicf ! ,am]ican physici/s  
,c>l ,david ,&]son 7#aije-    7 & ,se?  
,h5ry ,n$d]mey] 7#aijg-    71 /udy+ !   
results ( cosmic-p>ticle  bomb>dm5t (   
matt]1 detect$ ! exi/5ce ( p>ticles (   
int]m$iate mass4 ,?is p>ticle turn$ out 
to be light] ?an ,yukawa  _h pr$ict$2 x 
0 only ab\t #bjg times z massive z an   
electron4  ,mu* worse1 x lack$ o!r      
prop]ties t ,yukawa _h pr$ict$4 ,x did  
n int]act ) ! nucleus 9 ! mann] expect$4
    ,illu/ration3 ,hideki ,yukawa       
,illu/ration3 ,victor ,f4 ,hess         
,illu/ration3 ,c4 ,d4 ,&]son    ,9      

#aidg1 h[ev]1 ! ,engli% physici/ ,cecil 
,frank ,p[ell 7#aijc-aifi7  & 8         
co-work]s1 also /udy+ cosmic-p>ticle    
bomb>dm5t1 locat$  ano!r int]m$iate-siz$
 body1 :i* _h ! "r mass & all !  o!r    
appropriate prop]ties to fit ,yukawa's  
!ories4    ,&]son's p>ticle 0 call$ a   
8mu-meson01 soon abbreviat$ to 8muon04  
,p[ell's p>ticle 0 call$ a 8pi-meson01  
soon abbreviat$ to 8pion04  ,) !        
discov]y ( ! pion1 ,yukawa's !ory 0     
nail$ d[n & any  l+]+ d\bt z to !       
validity ( ! proton-neutron !ory        
vani%$4    ,illu/ration3 ,c4 ,f4 ,p[ell 
7,actually1 x turns out t !re are two   
=ces4 ,! "o ) ! pion  z ex*ange p>ticle 
is ! 8/rong nucle> int]action04 ,ano!r1 
involv$ 9 beta p>ticle emission1 =      
in/ance1 is a 8weak  int]action01 mu*   
weak] ?an ! electromagnetic b /rong] ?an
 !  gravitational47    ,! work+ out ( ! 
details ( ! /rong nucle> int]action     
expla9s fur!r ! va/ en]gies to be f\nd  
result+ f nucle>  reactions4 ,ord9>y    
*emical reactions1 ) ! electron %ifts t 

accompany !m1 involve ! electromagnetic 
int]action only4 ,nucle>  en]gy1 ) !    
%ifts ( ! p>ticles inside ! nucleus1    
involves  ! mu* /rong] nucle>           
int]action4      ,neutron ,bomb>dm5t    
,z soon z neutrons 7 discov]$1 x seem$  
to physici/s t !y  _h ano!r possible    
bomb>d+ p>ticle ( extraord9>y prop]ties4
  ,s9ce ! neutron lack$ any electric    
*>ge1 x c\ld n be repell$  by ei!r      
electrons on ! outside ( ! atoms or by !
 nuclei at !  c5t]4 ,! neutron 0        
completely indiff]5t to !               
electromagnetic  attraction & x j mov$  
along 9 a /raight l9e4 ,if x happ5$ to  
be head$ t[>d a nucleus x w\ld /rike x  
no matt] h[ heavy a  *>ge t nucleus     
might h & v (t5 x w\ld1 z a result1     
induce a nucle> reaction :]e a proton   
w\ld n h be5 able to4    ,illu/ration3  
,j4 ,rob]t ,opp5heim]    ,to be sure1 x 
seem$ j at fir/ t !re 0 a disadvantage  
to !  neutron's lack ( *>ge4 ,x c\ld n  
be accel]at$ directly by any  device    
s9ce t always dep5d$ on electromagnetic 

int]action to  :i* ! neutron 0 imp]vi\s4
    ,!re 0 "o way ( gett+ ar\nd ?is &   
?is 0 expla9$ 9 #aice  by ! ,am]ican    
physici/ ,j4 ,rob]t ,opp5heim]          
7#aijd-aifg7 & by 8  /ud5t ,melba       
,phillips4    ,use is made "h ( !       
nucleus ( ! hydrog5-#b 7deut]ium7       
nucleus4  ,t nucleus1 (t5 call$ a       
8deut]on01 is made up ( #a proton plus  
#a  neutron & has a mass numb] ( #b & an
 atomic numb] ( #a4 ,s9ce x  has a unit 
positive *>ge1 x c be accel]at$ j z an  
isolat$  proton c be4    ,suppose1 !n1 t
 a deut]on is accel]at$ to a high en]gy 
& is  aim$ "r at a positively *>g$      
nucleus4 ,t nucleus repels !  deut]on1 &
 x p>ticul>ly repels ! proton "p4 ,!    
nucle>  int]action t holds toge!r a s+le
 proton & a s+le neutron is             
comp>atively weak z nucle> int]actions  
g1 & ! repulsion ( !  nucleus t !       
deut]on is approa*+ may =ce ! proton out
 ( !  deut]on altoge!r4 ,! proton ve]s  
(f1 b ! neutron1 unaffect$1  keeps "r on
 go+ &1 ) all ! en]gy x _h ga9$ z "p (  

! deut]on accel]ation1 sma%es into !    
nucleus4    ,)9 a few mon?s ( _!        
discov]y1 en]getic neutrons 7 be+  us$  
to br+ ab\t nucle> reactions4           
,actually1 ?\gh1 physici/s didn't h to  
worry ab\t mak+ neutrons  en]getic4 ,?is
 0 a hangov] f _! "w ) positively *>g$  
p>ticles su* z protons & alpha p>ticles4
 ,^! *>g$ p>ticles  _h to be en]getic to
 ov]come ! repulsion ( ! nucleus & to   
sma% into x ) en\gh =ce to break x up4  
,neutrons1 h[ev]1 didn't h to ov]come   
any repulsion4 ,no matt] h[  little     
en]gy !y _h1 if !y 7 correctly aim$ 7&  
"s always  71 ?r\gh %e] *ance7 !y w\ld  
approa* & /rike ! nucleus4    ,9 fact1 !
 m sl[ly !y travell$1 ! long] !y w\ld   
/ay 9  ! vic9ity ( a nucleus & ! m      
likely !y 7 to be captur$  by "s ne>by  
nucleus ?r\gh ! attraction ( ! nucle>   
int]action4 ,! influ5ce ( ! nucleus 9   
captur+ ! neutron 0  great] ! sl[] !    
neutron1 s t x 0 almo/ z ?\gh !  nucleus
 7 l>g] & easi] to hit = a sl[ neutron  
?an a fa/  "o4 ,ev5tually1 physici/s    

began to speak ( 8nucle> cross sections0
  & to say t p>ticul> nuclei _h a cross 
section ( su* & su* a  size = ?is       
bomb>d+ p>ticle or t4    ,! effectiv5ess
 ( sl[ neutrons 0 discov]$ 9 #aicd by ! 
,italian-,am]ican physici/ ,enrico ,f]mi
 7#aija-aied74    ,( c\rse1 !re 0 !     
difficulty t neutrons c\ldn't be sl[$   
d[n once !y 7 =m$1 & z =m$ !y g5]ally _h
 too mu*  en]gy 7accord+ to ! new way ( 
look+ at ?+s74 ,at lea/ !y  c\ldn't be  
sl[$ d[n by electromagnetic me?ods--b   
!re 7 o!r  ways4    ,a neutron didn't   
always ent] a nucleus t x enc\nt]$4     
,sometimes1  if x /ruck ! nucleus a h>d1
 glanc+ bl[1 x b\nc$ (f4 ,if !  nucleus 
/ruck by ! neutron is _m times z massive
 z ! neutron1  ! neutron b\nc$ (f ) all 
its spe$ practically intact4 ,on !  o!r 
h&1 if ! neutron hits a nucleus n v mu* 
m massive  ?an itself1 ! nucleus reb\nds
 & absorbs "s ( ! en]gy1 s  t ! neutron 
b\nces away ) less en]gy ?an x _h4 ,if !
  neutron reb\nds f a numb] (           
comp>atively light nuclei1 x  ev5tually 

loses virtually all its en]gy & f9ally  
moves ab\t q  sl[ly1 possess+ no m en]gy
 ?an ! atoms t surr\nd x4    7,y c      
enc\nt] ?is situation 9 ord9>y life 9 ! 
case (  billi>d balls4 ,a billi>d ball1 
collid+ ) a cannon ball1 w j  b\nce1    
mov+ j z rapidly aft]w>d z be=e1 ?\gh 9 
a  diff]5t direction4 ,if a billi>d ball
 /rikes ano!r billi>d ball1  x w set !  
t>get ball mov+ & b\nce (f itself ) less
  spe$47    ,! en]gy ( ! molecules 9 !  
atmosph]e dep5ds on temp]ature4         
,neutrons t mat* t en]gy & h ! ord9>y   
quantity to be  expect$ at room         
temp]ature are call$ 8!rmal0 7f a ,greek
 ^w  mean+ 8heat07 neutrons4 ,!         
comp>atively light nuclei aga9/ :i*  !  
neutrons b\nce & sl[ d[n are 8mod]ators0
 because !y mod]ate  ! neutron's en]gy4 
,f]mi & 8 co-work]s 7 ! fir/ to mod]ate 
neutrons1 produce  !rmal neutrons1 & use
 !m1 9 #aice1 to bomb>d nuclei4 ,he     
quickly  not$ h[ l>ge nucle> cross      
sections became :5 !rmal neutrons 7  !  
bomb>d+ p>ticles4    ,x might seem t    

hope c\ld n[ rise 9 connection ) !      
practical  use ( en]gy d]iv$ f nucle>   
reactions4 ,neutrons c\ld br+ ab\t      
nucle> reactions1 ev5 :5 !y !mselves    
possess$ v little  en]gy1 s output might
 conceivably be m ?an input = ea*       
neutron  t /ruck4 ,fur!rmore because ( !
 l>ge cross sections involv$1  !rmal    
neutrons miss$ f> less frequ5tly ?an    
high-en]gy *>g$  p>ticles did4    ,b !re
 0 a cat*4 ,be=e neutrons c\ld be us$1  
h[ev] l[-en]gy  & h[ev] sure to hit1 !y 
_h to be produc$2 & 9 ord] to  produce  
neutrons !y _h to be knock$ out ( nuclei
 by bomb>dm5t  ) high-en]gy protons or  
"s o!r su* me?od4 ,! en]gy =m$ by  !    
neutrons 0 at fir/ nev] m ?an ! t9ie/   
fraction ( !  en]gies t w5t into =m+ !  
neutrons 9 ! fir/ place4    ,x 0 z ?\gh 
y c\ld inde$ light a c&le ) a s+le mat*1
  b y /ill _h to look ?r\gh #cjj1jjj    
useless pieces ( wood be=e  y f\nd a    
mat*4 ,! c&le w\ld /ill be impractical4 
,ev5 ) ! exi/5ce ( neutron bomb>dm5t1   
involv+ l[ en]gy &  high cross section1 

,ru!r=d c\ld1 ) ju/ice1 feel "r d[n to  
! "t ( 8 dea? t nucle> en]gy w\ld nev]  
be made available  = practical use4     
,& yet1 among ! exp]im5ts t ,f]mi 0 try+
 9 #aicd 0 t (  s5d+ 8 neutrons cra%+   
into uranium atoms4 ,ru!r=d _h no way  (
 tell+ 7& nei!r _h ,f]mi7 t ?is1 f9ally1
 0 ! r\te to  ! unimag9able4            
,,footnotes      #a,! attempt to "w out 
! /ructure ( ! nucleus result$ 9 a      
false1 b useful1 !ory t p]si/$ ?r\gh\t !
 #aibjs4 ,!      great advances 9 nucle>
 sci5ce 9 ?is decade 7 made 9 !         
light ( ?is false !ory &1 = ! sake (    
hi/orical accuracy1      !y are s       
pres5t$ "h4 ,! !ory n[ believ$ correct w
 be      pres5t$ %ortly1 & y w see h[   
matt]s c be *ang$ f      ! e>li] concept
 to ! lat] "o4      ,quotation ,cr$it   
,inside front cov]    ,copyright  by    
,abel>d-,%uman1 ,ltd41 ,new ,york4      
,repr9t$ by p]mission f ,inside ! ,atom1
                          ,isaac        
,asimov1 #aiff4      ,photo ,cr$its     
,cov]                 ,?orne ,films     

,page fac+ inside    ,! 8,horsehead0    
,nebula 9 ,orion1 ,hale    front cov]   
,obs]vatories4    ,au?or's ,photo       
,jay ,k4 ,kle9    ,cont5ts pages        
,lick ,obs]vatory    #fh                
,dr4 ,erw9 ,w4 ,muell]1 ,! ,p5nsylvania 
,/ate                                   
,univ]sity    #gj                       
,y]kes ,obs]vatory    #hf               
,f ,discov]y ( ! ,elem5ts1 ,m>y ,e4     
,weeks1                                 
,*emical ,education ,publi%+ ,company1  
#aifh4    #hi                    ,!     
,c5tral ,press ,photos1 ,ltd41 & ,sir   
,john                          ,cockcr(t
    #ia                    ,erne/ ,orl&o
 ,lawr5ce ,liv]more ,laboratory    #ic  
,samuel ,a4 ,g\dsmit    #if  #ig        
,nobel ,in/itute    #ii                 
,copyright  #aife by ,b>b>a ,lovett     
,cl9e1                          repr9t$ 
f h] volume ,! ,que/ion]s3              
,physici/s & ! ,quantum ,!ory by        
p]mission                          (    
,?omas ,y4 ,cr[ell1 ,inc41 ,new ,york4  

#aje  #ajf             ,nobel ,in/itute 
#ajg                   ,alan ,w4 ,ri*>ds
                          ,u4,s4        
,,gov]nm5t ,,pr9t+ ,,(fice3             
#aige----fdj--bhe_/ad                   
,a ^w ab\t ,,erda4444      ,! mission ( 
! ,u4 ,s4 ,en]gy ,rese>*  ,developm5t   
,adm9i/ration  7,,erda7 is to develop   
all en]gy s\rces1 to make ! ,nation     
basically  self-suffici5t 9 en]gy1 & to 
protect public heal? & welf>e &  !      
environm5t4 ,,erda programs are divid$  
into six major categories3              
,,cons]vation ,,( ,,en]gy--,m effici5t  
use ( exi/+ en]gy s\rces1  developm5t ( 
alt]nate fuels & eng9es = automobiles to
 r$uce  dep5d5ce on petroleum1 &        
elim9ation ( wa/eful habits ( en]gy     
consumption4     ,,fossil               
,,en]gy--,expansion ( coal production & 
! developm5t (  te*nologies = conv]t+   
coal to syn!tic gas & liquid fuels1     
improvem5t ( oil drill+ me?ods & (      
te*niques = conv]t+  %ale deposits to   
usable oil4     ,,sol>1 ,,geo!rmal1 ,,& 

,,advanc$ ,,en]gy ,,sy/ems--,rese>* on  
sol>  en]gy to heat1 cool1 & ev5tually  
electrify build+s1 on conv]sion  (      
und]gr\nd heat s\rces to gas &          
electricity1 & on fusion  reactors = !  
g5]ation ( electricity4     ,,environm5t
 ,,& ,,safety--,inve/igation ( heal?1   
safety1 &  environm5tal effects ( !     
developm5t ( en]gy te*nologies1 &       
rese>* on managem5t ( wa/es f en]gy     
production4     ,,nucle> ,,en]gy--,exp&+
 m$ical1 indu/rial & rese>* applications
  & upgrad+ reactor te*nologies = !     
g5]ation ( electricity1  p>ticul>ly us+ 
! bre$] concept4     ,,national         
,,security--,production & adm9i/ration (
 nucle> mat]ials  s]v+ bo? civilian &   
milit>y ne$s4    ,,erda programs are    
c>ri$ out by contract & coop]ation )    
indu/ry1  univ]sity communities1 & o!r  
gov]nm5t ag5cies4 ,= m  in=mation1 write
 to ,,us]da--,te*nical ,in=mation ,c5t]1
 ,p4 ,o4 ,box #fb1  ,oak ,ridge1        
,t5nessee #cghcj4        ,illu/ration3  
,,en]gy ,,rese>*  ,,developm5t          

,,adm9i/ration ,,usa                    
,unit$ ,/ates               ,en]gy      
,rese>* & ,developm5t ,adm9i/ration     
,(fice ( ,public ,affairs               
,wa%+ton1 ,d4,c4 #bjede                 
,transcrib]'s ,notes      --,reta9$     
publication in=mation f ! pr9t$ edition3
 ?is e,book    is public-doma9 9 !      
c\ntry ( publication4    --,9 ! text    
v]sion only1 und]l9$ or italiciz$ text  
is delimit$    by und]scores4    --,:]e 
possible1 ,,utf sup]script & subscript  
numb]s are us$2 "s    e-read] fonts may 
n support ^! *>act]s4    --,9 ! text    
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o!r subscript$ text is prec$$ by        
und]score & delimit$ by brackets4