P h y s ic s u n de r H it le r

8. 225 / ST S . 042, P h y s i c s i n t h e 20t h C e n t u r y Pr of e s s or Da v id K a is e r , 1 9 O c tobe r 2 0 2 0

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1. de u ts c h e Ph y s i k Re v i s i t e d

2. N u c l e a r Fi s s i o n *

3. H e i s e n b e rg a n d t h e “U r a ni u m M a c hi ne”

* S e e Le c t u r e N o t e s on “ E ne r g y r e l e a s e d f r om n u c l e a r f i s s i on”

Jo h a n n e s S t a r k Ph i l i p p L e n a r d

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B e gi nni ng a s e a r l y a s s pr i ng 1 9 2 0 , pol i t i c a l oppor t u ni s t s t ook a d v a nt a g e of Al b e r t E i n s te i n ’ s ne w fa me t o s t a g e “a nt i - re l a t i vi t y ” r a l l i e s . T he pu bl i c fa c e s of t he mo v e me nt i nc l u d e d Ge r ma n ph y s i c i s t Nobe l l a u r e a t e s Jo h a n n e s S t a r k a nd Ph i li pp L e n ar d .

T he r he t or i c of t he de u t s c h e Ph y s i k mo v e me nt w a s t ha t of t he “ ta tm e n s c h ”: t he “ma n of a c t i on. ” Ne w t on, Ga l i l e o , a nd F a r a d a y ha d a l l be e n “ A r y a n, ” a c c or d i ng t o L e na r d ; he a r gu e d t ha t t he y pa r t ook of t he s a me l e a d e r s hi p s pi r i t a s H i t l e r .

T hou gh t he g r ou p be g a n on t he fr i ng e s , t he y q u i c k l y g a i ne d po w e r fu l a d he r e nt s , e s pe c i a l l y onc e t he Na z i s a c hi e v e d po w e r i n J a n u a r y 1 9 3 3 . T he n a d v oc a t e s of

de u t s c h e Ph y s i k t ook c ha r g e of t he Ge r ma n E d u c a t i on Mi ni s t r y , w i t h a u t hor i t y o v e r a l l pr ofe s s or i a l a ppoi nt me nt s i n t he u ni v e r s i t i e s .

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Le t t e r f r o m t h e E m e r g e n c y Co m m i t t e e i n A i d o f Di s p l a c e d Ge r ma n S c h o l a r s , J u l y 1 9 3 3

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B y s pr i ng 1 9 3 3 , t he Na z i s ha d be gu n t o i mpl e me nt ne w “c i v i l s e r v i c e ” l a w s , w hi c h ba r r e d non- A r y a ns fr om hol d i ng g o v e r nme nt pos i t i ons ( i nc l u d i ng u ni v e r s i t y fa c u l t y ) . T hi s t r i g g e r e d a l a r g e e x od u s of s c hol a r s ou t of Ge r ma n y .

A bou t 1 0 0 ph y s i c i s t s a nd ma t he ma t i c i a ns e mi g r a t e d t o t he UK a nd US : Al b e r t E i n s te i n t o t he I ns t i t u t e for A d v a nc e d S t u d y i n P r i nc e t on; E r w i n S c h r ö d i n ge r t o O x for d a nd t he n Du bl i n; Em m y N oe t h e r t o B r y n Ma w r ; Ma x B o r n t o Ca mbr i d g e a nd t he n E d i nbu r gh; Ha n s B e th e t o Cor ne l l ; Ja m e s F r a n c k t o Chi c a g o; Fe l i x B l o c h t o S t a nfor d ; Vi k i W ei ssk op f t o R oc he s t e r a nd t he n MI T , . . .

T he s e w e r e not e a s y t r a ns i t i ons : t he US w a s d e e p i nt o t he Gr e a t De pr e s s i on, s o t he r e w e r e ma ny US s c hol a r s l ook i ng for u ni v e r s i t y pos i t i ons . P l u s , e nt r e nc he d a nt i - Sem i ti s m

w i t hi n US u ni v e r s i t i e s fu r t he r hi nd e r e d pl a c e me nt s ( e . g . , J. R o b e r t O p p e n h e i m e r at B e r k e l e y i n 1 9 2 9 ) . Da r t mou t h: a r e fu g e e fa c u l t y c a nd i d a t e “s hou l d n ’ t s e e m t oo J e w i s h. ”

W i t hi n Ge r ma n y , Na z i offi c i a l s c r i t i c i z e d non- J e w i s h ph y s i c i s t s w ho s e e me d t o d e mons t r a t e i ns u ffi c i e nt l o y a l t y t o t he r e gi me , e . g . , b y c ont i n u i ng t o t e a c h “J e w i s h ph y s i c s ” ( s u c h a s r e l a t i v i t y ) .

Ad o l f H i t l e r w i t h s e v e r a l o f o t h e r N a z i p a r t y le a d e r s , N ü r n b e r g 1 9 2 7 .

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I n 1 9 3 7 , t he y bl oc k e d We r n e r H e i s e n b e r g fr om be c omi ng t he s u c c e s s or t o Ar n o l d S o m m e r f e l d a s O r d i na r i u s pr ofe s s or i n Mu ni c h. T he y or g a ni z e d a pr e s s c a mpa i gn a g a i ns t H e i s e nbe r g, l a be l i ng hi m a “w hi t e J e w ” a nd a t t a c k i ng hi m i n t he Ge s t a po pr e s s . T he a t t a c k s onl y s u bs i d e d a ft e r H e i s e nbe r g ’ s mot he r i nt e r c e d e d d i r e c t l y w i t h a c l os e fa mi l y fr i e nd : t he mot he r of He i n r i c h Hi m m l e r , c hi e f of t he pa r a mi l i t a r y Sc h u t z s t a f f e l (SS).

T he po w e r of t he de u t s c h e Ph y s i k mo v e me nt d e c l i ne d s oon a ft e r t ha t .

P h y s i c s w a s no l ong e r a s s oc i a t e d for t he r e gi me onl y w i t h phi l os oph y or i d e ol og y . Ne w v a r i a bl e : po w e r . B y t he l a t e 1 9 3 0 s , t he Na z i s be g a n t o t hi nk t ha t ph y s i c i s t s c ou l d be us e f ul t o t he R e i c h. W ha t ha d c ha ng e d ?

Nu cl e a r p h ys i cs .

Q u e s tion s ?

Th e N e u t r o n T hr ou ghou t t he l a t e 1 9 2 0 s a nd e a r l y 1 9 3 0 s , s e v e r a l r e s e a r c h g r ou ps w or k i ng on r a d i oa c t i v i t y s u s pe c t e d t he r e mi ght e x i s t a sec on d k i nd of pa r t i c l e w i t hi n a t omi c n u c l e i : a n e l e c t r i c a l l y ne u t r a l pa r t i c l e w i t h ma s s c l os e t o t he ma s s of t he pr ot on. Ir è n e a nd Fr é d é r i c J o l i o t - Curi e i n P a r i s w e r e e s pe c i a l l y a c t i v e i n t hi s a r e a . ( T he y s ha r e d t he 1 9 3 5 Nobe l P r i z e i n c he mi s t r y for t he i r s t u d i e s of “a r t i fi c i a l ” or i nd u c e d r a d i oa c t i v i t y . )

I n J a n u a r y 1 9 3 2 , B r i t i s h ph y s i c i s t Ja m e s C h a d w i c k

Sc h e m a t i c o f J a m e s C h a d w i c k ’ s 1 9 3 2 e x p e r i m e n t a t t h e Ca v e n d i s h L ab o r at o r y ( Cam b r i d g e , U K )

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( for me r s t u d e nt of Er ne s t R ut h e r f or d ) fol l o w e d u p on one of t he i r s u g g e s t i ons a nd c ond u c t e d a ne w e x pe r i me nt :

Cha d w i c k i nfe r r e d t he ma s s of t he ne w pa r t i c l e ( t he “ ne ut r o n ”) fr om t he re c o i l ve lo c i t y of pr ot ons s c a t t e r e d fr om ( h y d r og e n- r i c h) pa r a ffi n w a x . ( Cha d w i c k r e c e i v e d t he 1 9 3 5 Nobe l P r i z e i n P h y s i c s for t hi s w or k . )

An d th e s e ar e R o m e p o l i c e o f f i c e r s c h e c ki n g ou r p a pe r w or k w hi l e w e w e r e w or k i ng on a do c u m e n t a r y f i l m a b o u t F e r m i a n d t h e ne u t r i no t hi s pa s t J a n u a r y …

R i ght a w a y , Enr ic o F e r m i a nd hi s g r ou p i n R ome be g a n bomba r d i ng e a c h e l e me nt of t he pe r i od i c t a bl e w i t h ne ut r o ns , t o i nd u c e r a d i oa c t i v e r e a c t i ons . T he y g ot a l l t he w a y t o u r a ni u m — t he he a v i e s t na t u r a l l y oc c u r r i ng e l e me nt i n t he pe r i od i c t a bl e — a nd fou nd s i gni fi c a nt r e a c t i on r a t e s , esp ec i a l l y w he n F e r mi pl a c e d a bl oc k of pa r a ffi n be t w e e n t he ne u t r on s ou r c e a nd t he u r a ni u m t a r g e t .

T he y as s u m e d t he y w e r e me a s u r i ng “N e p t u n i u m ”: t h e f i r s t tr a n s u r a n i c el em en t , j u s t a s t h e pl a ne t N e pt u ne i s t he ne x t pl a ne t i n ou r S ol a r S y s t e m be y ond U r a n u s .

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From left to right: © Springer Nature, © Karl Sandels, ©

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R e v is it in g T ra n s u ra n ic s

Ha h n a n d S t ra ssm a n n ’ s e x p e ri m e n t a l a r ra n g e m e n t , 1 9 3 8 (r e c o n s tr u c te d in th e D e u ts c h e s M u s e u m , M u n ic h )

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Li s e M e i t ne r a nd O t t o H a hn i n B e r l i n, c a . 1 9 3 8

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O t he r g r ou ps a c t i v e l y w or k e d on n u c l e a r t r a ns for ma t i ons a s s oc i a t e d w i t h ne u t r on c a pt u r e , i nc l u d i ng a t e a m i n B e r l i n: n u c l e a r c he mi s t s Ot t o H a h n a nd Fr i t z S t r a s s m a n n t og e t he r w i t h n u c l e a r ph y s i c i s t Li s e M e i tn e r .

Me i t ne r , fr om a J e w i s h fa mi l y i n A u s t r i a , w a s onl y a l l o w e d t o a t t e nd for ma l s c hool u nt i l a g e 1 4 . A ft e r r e for ms , s he r u s he d t hr ou gh t he s t a nd a r d hi gh s c hool c u r r i c u l u m, v i a se lf - s t u d y , i n a fe w mont hs a nd pa s s e d t he e nt r a nc e e x a m t o s t u d y ph y s i c s a t t he Uni v e r s i t y of V i e nna . S he w a s a mong t he fi r s t w ome n t o e a r n a P hD i n ph y s i c s an y w h e r e . A ft e r he r d e g r e e ( 1 9 0 5 ) , s he be g a n t o c ol l a bor a t e w i t h

H a hn i n B e r l i n— i n t he bas e m e n t , s i nc e w ome n w e r e not y e t a l l o w e d i n t he ma i n I ns t i t u t e .

A ft e r t he An s c h l u s s i n Ma r c h 1 9 3 8 , w he n Na z i Ge r ma ny t ook o v e r A u s t r i a , Me i t ne r be c a me s u bj e c t t o t he Na z i e mpl o y me nt l a w s , a nd l os t he r j ob .

R e v is it in g T ra n s u ra n ic s

?

“ A s c he mi s t s , w e m u s t a c t u a l l y s a y t he ne w pa r t i c l e s d o not be ha v e l i k e r a d i u m bu t , i n fa c t , l i k e ba r i u m; a s n u c l e a r ph y s i c i s t s , w e c a nnot ma k e t hi s c onc l u s i on, w hi c h i s i n c onf l i c t w i t h a l l e x pe r i e nc e i n n u c l e a r ph y s i c s . ”

Ha h n a n d S t ra ssm a n n , “ O n t h e sp l i t t i n g o f Ur a n i u m n u c l e i b y s l o w n e u t r o n s , ” De c . 1 9 3 8

Ha h n a n d S t ra ssm a n n ’ s e x p e ri m e n t a l a r ra n g e m e n t , 1 9 3 8 (r e c o n s tr u c te d in th e D e u ts c h e s M u s e u m , M u n ic h )

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W hi l e Me i t ne r f l e d Ge r ma ny a nd s ou ght s he l t e r i n S c a nd i na v i a , H a hn a nd S t r a s s ma nn c ont i n u e d t he i r ne u t r on - bomba r d me nt e x pe r i me nt s . T he y r e - d i d F e r mi ’ s fa mou s e x pe r i me nt m u l t i pl e t i me s — j u s t a s F e r mi w a s r e c e i v i ng hi s Nobe l P r i z e for t ha t w or k — a nd c onc l u d e d t ha t ne it h e r Fe r m i no r t he y ha d pr od u c e d t r a ns u r a ni c e l e me nt s . I ns t e a d :

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Li s e M e i t ne r

(1 8 7 8 – 1968) Ot t o R o b e r t F r i s c h

(1 9 0 4 – 1979)

I n De c e mbe r 1 9 3 8 , Me i t ne r r e c e i v e d a n u pd a t e fr om H a hn a bou t t he l a t e s t e x pe r i me nt s , i nd i c a t i ng t he pr e s e nc e of ba r i u m. W hi l e s k i i ng w i t h he r ne phe w , t he or e t i c a l ph y s i c i s t Ot t o R ob er t F r isc h , ne a r S t oc k hol m, t he y w or k e d ou t a ph y s i c al m o de l for n u c l e a r fi s s i on.

S l o w ne u t r ons w e r e k e y , be c a u s e of q u a nt u m t he or y . T he ne u t r on ’ s d e B r ogl i e w a v e l e ngt h be c ome s l a r ge for s l o w v e l oc i t i e s :

U 92

n wa v e l e n g t h : c o m p a r a b l e i n s i z e to th e e n tir e U n u c le u s . C a n s e t th e nu c l e u s wo b b l i n g lik e a liq u id d r o p

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A ft e r s pl i t t i ng, e a c h pi e c e c a r r i e s a bou t . T ha t l e a v e s

t o be r e l e a s e d a s “r a w ” e ne r g y , ev e r y t i m e a u r a ni u m n u c l e u s s pl i t s . A nd T ha t e s t i ma t e — ba s e d on s i mpl e Cou l omb r e pu l s i on be t w e e n t he t w o s ma l l e r n u c l e i

— ma t c he d a n i nd e pe nd e nt e s t i ma t e , ba s e d on b i n d i n g e n e r g y :

* S e e Le c t u r e N o t e s on “ E ne r g y r e l e a s e d f r om n u c l e a r f i s s i on”

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Fr i s c h r e t u r ne d t o Ni e l s B o h r ’ s I ns t i t u t e i n Cope nha g e n a nd t ol d B ohr a l l a bou t hi s a nd Me i t ne r ’ s i d e a s a bou t fi s s i on. H e s w or e B ohr t o s e c r e c y , s o he a nd Me i t ne r c ou l d c he c k t he i r w or k a nd pe r for m s ome fol l o w - u p t e s t s .

B ohr s a i l e d t o t he US i n J a n u a r y 1 9 3 9 t o s pe nd a s e me s t e r a t P r i nc e t on. H e w a s me t a t t he d oc k s i n Ne w Y or k Ci t y b y Enr ic o Fe r m i a nd Sa mu e l G o u d s mi t , a nd t ol d t he m im m e d ia t e l y a l l a bou t

Me i t ne r ’ s a nd F r i s c h ’ s w or k — t he n he t ol d E u ge n e W i gn e r , Al b e r t E i n s te i n , a nd Jo h n W h e e l e r ( B ohr ’ s for me r pos t d oc ) i n P r i nc e t on. W i t hi n d a y s , s e v e r a l l a bor a t or i e s u p a nd d o w n t he E a s t Coa s t ha d v e r i fi e d fi s s i on. ( E a s y t o d o onc e one k no w s t o c ond u c t t e s t s for ba r i u m a mong t he r e a c t i on pr od u c t s . )

T og e t he r w i t h W he e l e r , B ohr w or k e d ou t a mor e d e t a i l e d , q u a nt i t a t i v e a na l y s i s of n u c l e a r fi s s i on, d r a w i ng on Me i t ne r ’ s w or k t o i d e nt i fy t he mos t fi s s i ona bl e u r a ni u m i s ot ope t o be U 235 . T he i r a r t i c l e w a s pu bl i s he d th e s a m e d a y t ha t Na z i t r oops i n v a d e d P ol a nd , t r i g g e r i ng t he s t a r t of t he S e c ond W or l d W a r .

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Ev e r y one i n ph y s i c s k ne w i mme d i a t e l y t ha t n u c l e a r fi s s i on c ou l d l e a d t o bo m bs . An d t he y k ne w t ha t t he Ge r m a n s m u s t k no w t hi s , t oo!

F i s s i on ha d be e n i d e nt i fi e d i n a B e r l i n l a bor a t or y . A l t hou gh ma ny r e s e a r c he r s ha d f l e d Na z i Ge r ma n y , i t r e ma i ne d t he w or l d ’ s c e nt e r for n u c l e a r ph y s i c s a t t he t i me : We r n e r H e i s e n b e r g , Ot t o Ha h n , Ha n s Ge i ge r , Wa l t h e r B o t h e , Ma x P l a n c k , Ma x v o n L a u e , Ca rl Fr i e d r i c h v o n W e i z s ä c k e r , a nd mor e .

At e x a c tl y th e s a m e ti m e , t he S e c ond W or l d W a r e r u pt e d :

Ma r c h 1 2 , 1 9 3 8 : N a z i An sch l u ss of A u s t r i a .

De c e mb e r 1 9 3 8 : H a h n a n d S t r a s s ma n n i d e n t i f y b a r i u m a mo n g rea ct i o n p ro d u ct s ; M ei t n er a n d F ri s c h w o rk o u t n u cl ea r f i s s i o n

Ja n u a r y 1 9 3 9 : B o h r a r r i v e s i n N Y C , t e l l s o t h e r s a b o u t f i s s i o n Ma r c h 1 5 , 1 9 3 9 : N a z i s o c c u p y C z e c h o sl o v a k i a .

Se p t e m b e r 1 , 1 9 3 9 : N a z i s i n v a de P o l a n d.

Se p t e m b e r 3 - 10, 1939: U K , F r an c e , A us t r al i a, N e w Z e al an d , an d Ca n a d a d e c l a r e w a r a g a i n s t G e r m a n y .

Se p t e m b e r 1 7 , 1 9 3 9 : So v i e t s i n v a de P o l a n d.

Ge r ma n t a n k s c r o s s i n g i n t o P o l a n d ,

Se p t em b er 1 9 3 9

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information, see https://ocw.mit.edu/help/faq-fair- use/

Ei n s t e i n w i t h L e o S zi l a r d

(1 8 9 8 – 1964)

N u c le a r F is s io n

A p r i l 1939 : G e r m a n R e i c h M i n i s t r y o f Edu c at i o n h o l ds s e c r e t m e e t i n g o n m i l i t a r y a p p l i c a t i o n s o f n u c l e a r f i s s i o n , ba ns u r a ni u m e x por t s .