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Anomalous scattering of neutrons by helium and the d-d neutron spectrum

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ANOMALOUS SCATTERING OP NEUTRONS BY HELIUM
Ain) THE
4 - 4 NEUTRON SPECTRUM
I
A t h e s i s p r e s e n te 4 b y
Em m ett H
S u 4 s p e th
to
th e F a c u lt y o f
The R ic e
In s titu te
i
i n p a r t i a l f u l f i l m e n t o f th e
r e q u ir e m e n ts f o r th e 4 e g re e o f
|
D o c to r o f P h ilo s o p h y
The R ic e I n s t i t u t e
Mhy 1940
(
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
UMI Number: 3079738
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TABLE OF CONTENTS
I.
II.
III.
IV .
7.
71.
711.
G e n e ra l I n t r o d u c t i o n to
C lo u d Chamber I n v e s t i g a t i o n s .
A nom alous S c a t t e r in g o f N e u tro n s b y H e liu m and th e
d - d N e u tr o n S p e c tru m ; Emmett H u d s p e th and H e n ry
D u n la p .
To a p p e a r as p r e s e n te d i n th e P h y s ic a l
R e v ie w f o r June 1 , 194Q.
E le c tr o s c o p e I n v e s t i g a t i o n o f th e A nom alous S c a t­
t e r i n g o f N e u tro n s b y H e liu m ; T . W. B on ne r a n d
Em m ett H u d s p e th .
R esonances i n th e D i s i n t e g r a t i o n o f C arbon b y
D e u te ro n s ; T . W, B o n n e r a n d Em m ett H u d s p e th .
O b s e r v a tio n o f H1 a n d H® Ranges fr o m th e D i s i n t e g r a ­
t i o n o f D e u te riu m b y D e u te ro n s ; Em m ett H u d s p e th
a n d T . W. B o n n e r.
Low E n e rg y N e u tro n s f r o m t h e D e u te ro n -D e u te ro n
R e a c tio n ; Em m ett H u d s p e th and H e n ry D u n la p .
A b s t r a c t s p r e s e n te d t o th e A m e ric a n P h y s ic a l S o o ie t y
a t a n n u a l W a s h in g to n m e e tin g s .
The l a s t t h r e e p a p e rs a re r e p r i n t s ; I I I a n d 17
w i l l be p u b lis h e d i n e x te n d e d fo r m i n th e n e a r
fu tu re .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
GENERAL INTRODUCTION TO CLOUD CHAMBER INVESTIGATIONS
The w o rk r e p o r t e d
in
th is
c lo u d cham ber i n v e s t i g a t i o n s
ID1 +
and
D*' — E 5 +
H1
p a p e r h a s c o n s is t e d o f
o f th e n u c le a r r e a o t io n s :
Q.,
(1 )
!)*■ + D *-*- He3 + n ’ +
The s e c o n d r e a c t i o n has a ls o
(S ).
been u s e d as a n e u tr o n
s o u rc e f o r a s tu d y o f th e b a c k w a rd s c a t t e r i n g c r o s s sec­
t i o n f o r n e u tr o n s
i n h e liu m a n d i n h y d ro g e n .
o f t h i s w o r k a p p r o x im a t e ly f i f t y
I n th e
c o u rse
th o u s a n d c lo u d cham ber
e x p a n s io n s u n d e r v a r i o u s c o n d it io n s have been s t e r e o s c o p i o a l l y p h o to g ra p h e d a n d a n a ly z e d .
A v o lt a g e
d o u b lin g c i r c u i t o f th e C o c k c r o ft- W a lto n
ty p e was u s e d to o b t a in d e u te ro n s o f e n e r g ie s up to
A d ia g ra m o f t h i s
+200
c ir c u it
is
200 k v .
shown i n F ig u r e 1 .
kv
tra n s fo rm e r.
F ig u r e 1
A 72 k v t r a n s f o r m e r s u p p lie d th e h ig h v o lt a g e , w h ic h
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
z
was r e c t i f i e d and d o u b le d b y tw o k e n e tr o n s .
a c c e le r a t e d b y t h i s
e le c tr ic
a t a r g e t c o n t a in in g d e u te r iu m
fie ld
D e u te ro n s
were use d to
bom bard
( i n p a r a f f i n o r p h o s p h o r ic
IO N SOURCE.
H .I0 H T
CLOUD CHAMBER.
F ig u r e
2
a c i d ) , and th e d i s i n t e g r a t i o n p r o d u c ts have been o b s e rv e d
in
a c lo u d cham ber p la c e d as shown i n F ig u r e
The f o l l o w i n g g e n e r a l c o n c lu s io n s were
2.
drawn fro m
t h i s w o rk :
(a ) E ach o f th e n u c le a r r e a c t io n s
j
(1 ) a n d
o n l y one Q, v a lu e ; hence t h e E ^and He3 as fo rm e d i n th e s e
r e a c t io n s
e x h i b i t no e x c it e d s t a t e s .
(b ) T h e re is
a p p a r e n t ly a s h o r t ra n g e g ro u p o f r e c o i l
n u c l e i p ro d u c e d b y th e n e u tr o n s o f r e a c t io n
n e u tr o n s fr o m t h i s
fille d
c lo u d c h a m b e r.
T h is g ro u p
h e liu m - fille d
i
s id e r a t io n s a re s a t i s f i e d
ra n g e r e c o i l s
(2 ) when th e
r e a c t i o n are o b s e rv e d w it h a h y d ro g e n -
!
i
(2 ) has
cham ber i s
-used.
is
n o t p r e s e n t when a
Momentum a n d e u e rg y c o n -
b y a s s u m in g t h a t t h e s h o r t
o b s e rv e d i n h y d ro g e n a re d e u te ro n s p ro d u c e d
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
3
b y p r o t o n c a p t u r e o f t h e n e u tro n s
b u t th e
t h is
t h e o r e t i c a l c a lc u la t io n s
p ro c e s s a r e n o t i n
e m itte d , i n
r e a c t io n
fb r th e p r o b a b i l i t y
a g re e m e n t w i t h
(2 ),
of
o bse rve d , i n t e n s i t i e s .
(o ) An a n o m a lo u s ly h ig h backw ard, s c a t t e r i n g c ro s s s e c­
t i o n e x i s t s f o r n e u tr o n s o f a b o u t one Mev e n e rg y i n h e liu m .
The re s o n a n c e has a h a l f - w i d t h o f a b o u t 0 .7 M ev, and o n ly
one maximum was o b s e rv e d .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
ANOMALOUS SCATTERING OP NEUTRONS BY HELIUM
AND THE d - d NEUTRON SPECTRUM
In
an i n v e s t i g a t i o n o f th e
o b ta in e d , when L i 7
S h e p h e rd a n d H axby^
d is tr ib u tio n
is
^ - p a r tic le
s p e c tru m
bom barded b y d e u te r o n s , W illia m s ,
fo u n d t h a t t h e c o n tin u o u s
had s u p e rp o s e d o n i t
e n e rg y
a homogeneous g r o u p .
The c o n tin u o u s e n e rg y s p e c tru m was s u p p o se d to a r i s e fr o m
th e r e a c t i o n
L i7 +
D -*■ 2 He* +- n f , w h ile
g ro u p was a s c r ib e d to t h e r e a c t io n
Prom th e ra n g e o f t h i s g r o u p ,
i n th e r e a c tio n
make i t
is
L i 7 +- I) 7'—* He^-t- He4.
th e mass o f
c a lc u la t e d to
th e homogeneous
th e He
fo rm e d
be 5 .0 1 3 7 , w h ic h w o u ld
u n s ta b le a g a in s t d i s i n t e g r a t i o n 2
in t o
an o c - p a r tic l
a n d a n e u t r o n b y 0 .8 4 M ev.
One may e x p e c t th e s c a t t e r i n g o f n e u tr o n s b y h e liu m
to be e x tr e m e ly h i g i when -the e n e rg y o f th e n e u tr o n
s u ffic ie n t
to
p ro d u c e a n in t e r m e d ia t e He"*" n u c le u s
in
is
th e
s t a t e fo rm e d i n th e L i 7 r e a c t i o n -; t h i s s h o u ld o c c u r f o r a
n e u t r o n e n e rg y o f a b o u t one M ev, o r f i v e - f o u r t h s
th e e n e rg y o f i n s t a b i l i t y
o f He^
S ta u b a n d S tephens® have made a
g a tio n o f t h is
a nd i n
It
is
c lo u d cham ber i n v e s t i ­
p o in t b y o b t a in in g r e c o i l t r a c k s
e th a n e , u s in g n e u tr o n s fr o m
B,0-h n ; .
known4
th a t of
th a t th is
i n h e liu m
th e r e a c t io n
r e a c tio n y ie ld s
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Be^-h
fo u r
D
n e u t r o n g r o u p s , o f maximum n e u t r o n e n e r g ie s 4 . 5 , 4 . 0 ,
a n d 1 . 4 Mev a t a b o m b a rd in g e n e rg y o f 0 .9 Mev.
d u c in g th e b o m b a rd in g e n e r g y to
2 .5 ,
By r e ­
0 .6 M ev, S ta u b a n d S te p h e n s
re d u c e d th e e n e rg y o f th e 1 .4 -M e v g ro u p to a b o u t 1 .1 Mev
a t th e p o in t o f maximum n e u t r o n i n t e n s i t y .
c lo s e to
th e n e u t r o n e n e r g y c a lc u la t e d to
T h is
y ie ld
in th e
f b r n a tio n o f
He'5", a n d hence the r a t i o
s itie s
o f h e liu m t o
p r o t o n r e c o i l s fo rm e d b y t h i s
m ig h t be e x p e c te d to
be l a r g e .
of
is v e r y
a re s o n a n c e
th e i n t e n ­
g ro u p
T h is was fo u n d to
be th e
c a s e , and th e r a t i o
o f th e b a c k w a rd s c a t t e r i n g
c r o s s s e c t io n o f h e liu m to
h y d ro g e n ro s e to a b o u t 9 .5 a t
th is
p o in t.
W ith th e b o m b a rd in g e n e rg y in c r e a s e d to 0 .8 8
M ev, th e mean n e u tr o n
a n d tb e r a t i o
o b s e rv e d t o
p o in t,
o f th e
e n e rg y o f th e g ro u p becomes 1 .3 M ev,
c r o s s s e c tio n s a t
be a b o u t 6 . 5 .
th e r a t i o
d ro p p e d to
th is
p o in t was
A t 2 .3 M ev, t h e i r n e x t m easured
its
" n o r m a l" v a lu e o f a b o u t
1 . 4 , and re m a in e d n e a r ly c o n s ta n t a t t h i s v a lu e
up to
about
6 M ev.
A n e u t r o n g ro u p o f 0 .5 Mev e n e rg y fr o m C‘ %- D *—►
N 'V
showed a v e r y s h a rp d e c lin e
n'
1 . 1 M ev, a r t , / crii
S te p h e n s
h a v in g d r o p p e d t o
p o in t o u t
u n c e r ta in on e it h e r
fr o m th e maximum a t
0 .4 .
S ta u b a n d
t h a t th e shape o f th e c u rv e
is
s id e o f
o f th e
th e maximum b ecause
s m a ll num ber o f m easured p o i n t s .
ra th e r
I t w as th e p u rp o s e o f
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
I
6
th e p r e s e n t w o r k t o
in v e s tig a te
o b t a in in g m ore p o i n t s
in
th e a n o m a ly f u r t h e r ,
th e i n t e r v a l s
to
2 .5 Mev.
Expe r im e n t
U s in g a p p a ra tu s p r e v i o u s ly d e s c r ib e d ,®
we have made
a c lo u d -c h a m b e r s t u d y o f r e c o i l p r o to n s and r e c o i l h e liu m
n u c l e i p ro d u c e d b y n e u tr o n s f r o m
th e d - d r e a c t io n .
A
g ro u p o f n e u tr o n s o f mean e n e rg y 2 .5 Mev r e s u l t s fr o m
t h is r e a c tio n ,
and in
o r d e r t h a t n e u t r o n s o f a l l e n e rg ie s
b e lo w th e maximum m ig h t be o b t a in e d ,
th e t a r g e t was s u r ­
ro u n d e d b y a b o u t 3 cm o f p a r a f f i n a r ra n g e d a s shown i n
F ig .
1.
T h is
is
o f s u f f i c i e n t t h ic k n e s s to
ION
s c a t t e r ra n d o m ly
BEAM
TARGET
F ig u r e 1
Top and s id e v ie w s o f th e n e u t r o n s o u r c e , s h o w in g
t h e d i s t r i b u t i o n o f p a r a f f i n a b o u t th e t a r g e t .
The c lo u d ch a m be r was p la c e d a b o u t 15 cm to th e
r ig h t.
a b o u t o n e - h a l f t h e n e u tr o n s le a v in g th e t a r g e t .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Uo
7
p a r a f f i n was p la c e d on tw o s id e s o f th e t a r g e t ,
is
s in c e
it
d e s i r a b l e t o have th e s o u rc e a s s m a ll as p o s s ib le .
The t a r g e t was h e a v y p a r a f f i n , w h ic h was bom barded
w ith
d e u te ro n s o f a b o u t 140 h e r e n e rg y .
to
change th e
to
th e io n beam , s in c e t h e p a r a f f i n
c a rb o n .
ta rg e ts
I t was n e c e s s a ry
a f t e r a b o u t a th o u s a n d e x p o s u re s
became c o a te d w i t h
T h re e
new t a r g e t s w ere p u t i n
th e a lu m in u m cup
a t one tim e so
t h a t each t a r g e t change
d id n o t r e q u ir e
le ttin g
a ir
in to
th e s y s te m .
The io n s o u rc e was f la s h e d
f o r a f r a c t i o n o f a second a t e x p a n s io n o f th e c lo u d
ch a m b e r, a n d in s ta n ta n e o u s u n r e s o lv e d d e u te r o n c u r r e n t s
up to a b o u t 400 m ic ro a m p e re s w e re o b ta in e d .
A p p r o x im a te ly
2 5 ,0 0 0 e x p a n s io n s w e re p h o to g ra p h e d in t h i s
t a b u la t e d
tr a c ic d a t a were
c o rre c te d f o r
the
have a s m a lle r p r o b a b i l i t y o f h a v in g t h e i r
th e cham ber
The
p r o b a b ility o f
o b s e r v a t io n i n th e c lo u d c h a m b e r, s in c e
in
w o rk .
t h a n th e s h o r t e r o n e s .
lo n g e r t r a c k s
e n d - p o in ts
The cham ber was
p la c e d a b o u t 14 cm fr o m th e n e u tr o n s o u rc e and a t 9 0 ° t o
th e
b o m b a rd in g beam.
The e n e rg y d i s t r i b u t i o n o f h e liu m
fro m tw e lv e
F ig u r e
2.
r e c o ils
th o u s a n d s t e r e o s c o p ic p i c t u r e s
th e
i s shown i n
The chamber was o p e r a te d w i t h w a te r v a p o r a n d
h e liu m a t a b o u t one a tm o s p h e re p r e s s u r e .
to
o b ta in e d
o p e r a te t h e chamber a t a lo w p r e s s u r e
e n e rg y o f th e r e c o i l s
It
is n e c e s s a ry
in o rd e r th a t
p ro d u c e d m a y b e more a c c u r a t e ly
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
8
r e s o lv e d i n t o
s m a ll i n t e r v a l s .
gas was 0 . 3 2 ,
c a lc u la t e d f r o m
The s t o p p in g power o f th e
th e known ra n g e o f th e
n e u tr o n s fro m th e d - d r e a c t i o n and th e
e n e rg y - ra n g e r e ­
l a t i o n s o f H o llo w a y a n d L i v i n g s t o n . 6
The t r a o k s w e re
09
10
F ig ir e
2
Number o f h e liu m r e c o i l s o b s e rv e d as a f u n c t i o n
o f th e n e u t r o n e n e rg y p r o d u c in g th e r e c o i l s .
t a b u la t e d i n
p a r tic le
2-mm i n t e r v a l s , w h ic h c o rre s p o n d s to
e n e rg y i n t e r v a l s
e n e rg y i n t e r v a l s
in
th e
th e cham ber fr o m 8 t o
tr ib u tio n
o f a b o u t 0 .1 5 M ev, o r n e u tr o n
o f a b o u t 0 . 2 M ev.
fo r w a r d d i r e c t i o n
Cf-
T r a c k s m e asu re d were
( 0 - 1 5 ° ) a n d had a le n g t h i n
30 mm.
The ene rgy-nu m b e r d i s ­
shown i n F ig u r e 2 was o b t a in e d b y r e d u c in g th e
2-mm ra n g e i n t e r v a l s o f th e r e c o i l of - p a r t i c l e s
to th e
c o r r e s p o n d in g n e u t r o n e n e rg y i n t e r v a l s .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
9
The e x p e rim e n t d e s c r ib e d a b o ve was r e p e a t e d w i t h
no change i n
c o n d it io n s e x c e p t t h a t m etha ne a n d a lc o h o l
were u s e d i n th e
c lo u d ch a m b e r.
The s t o p p in g pow er o f
t h i s m a x tu re w as fo u n d to be 1 .0 3 .
7
A b o u t 3500 expan­
s io n s w e re p h o to g ra p h e d and 173 r e c o i l s
d i r e c t i o n were m e a s u re d .
d is tr ib u tio n
T h is s e r v e s to
v a tio n
to
th e fo r w a r d
d e te r m in e th e
o f n e u tr o n s q u i t e w e l l a t e n e r g ie s up to
a b o u t £ M ev, b u t b e yo n d t h i s
lo n g t h a t
in
th e
p o in t th e t r a o k s a re
so
c o r r e c t i o n f a c t o r f o r p r o b a b i l i t y o f o b s e r­
i n th e 1 3 .5 cm cham ber i s
q jiite
la r g e .
I n o rd e r
d e te rm in e m ore a c c u r a t e ly th e n e u tr o n d i s t r i b u t i o n
above £ M ev, p h o to g r a p h s w ere made when the
was f i l l e d
c lo u d cham ber
w i t h a b o u t 80 p e r c e n t e th a n e a n d £0 p e rc e n t
a rg o n t o a t o t a l expanded p r e s s u r e
was a dded i n o r d e r t o
o f a b o u t 80 om.
lo w e r t h e e x p a n s io n r a t i o .
A rg o n
The
s t o p p in g p ow er o f t h e m ix t u r e w as fo u n d to be 1 .6 6 , and
£73 r e c o i l s
w ere m e a su re d on 1800 p h o to g r a p h s .
The p r o t o n r e c o i l s
e th a n e were t a b u la t e d i n
to
o b ta in e d i n m ethane and in
e n e rg y i n t e r v a l s
c o r re s p o n d in g
t h e e n e rg y i n t e r v a l s o f t h e h e liu m r e c o i l s
p r e v i o u s ly .
The d i s t r i b u t i o n
a fe w p e r c e n t w i t h
w hen th e
o b s e rv e d
i n m e th a n e a g re e d w i t h i n
t h a t o b ta in e d In e th a n e above one Mev
c u rv e s w e re c o r r e c t e d to e q u a l e n e rg y i n t e r v a l s .
I n th e lo w e s t e n e r g y i n t e r v a l (a b o u t 0 . 6 M e v ), o n l y th e
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
10
m e th a n e d a ta w ere vised, s i m e
th is
the
r e c o ils
p o i n t were o n ly a b o u t 6 mm lo n g .
n e x t two i n t e r v a l s
I n e a c h o f th e
a b o u t tw io e a s many tr a c lc s were ob­
s e r v e d i n m ethane as i n e th a n e , b u t t h i s
w e ll a r is e
tra c k s
fo re
in
i n e th a n e a t
d is c r e p a n c y m ig h t
fr o m s t a t i s t i c a l e r r o r , s in c e th e num ber o f
t h is r e g io n
i s s m a ll.
added t o g e t h e r , a n d th e
The tw o c u rv e s w ere th e r e
r e s u l t s a re shown i n
F ig u r e 3
100
M
3
o
K 200
z
o
o ISO
Q
100
i
so
as
to
IS
2.0
3 ? ig ir e 3
XT-umber-energy d i s t r i b u t i o n o f r e c o i l p r o to n s
p ro d u c e d i n m ethane a n d i n e th a n e .
I n o r d e r to o b t a i n th e r a t i o
o f c r o s s s e c t io n s
f o r h e liu m a n d h y d ro g e n a t v a r io u s
o f r e c o ils
e n e r g ie s , th e num ber
shown i n a g iv e n i n t e r v a l o f F ig u r e 2 w ere
d i v i d e d b y th e num ber o f r e c o i l s
i n th e
c o r r e s p o n d in g
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
11
i n t e r v a l o f F ig u r e
3.
As a m easure o f th e a b s o lu te r a t i o ,
th e v a lu e 1 . 4 a t 2 .5 Mev h a d p r e v i o u s ly be e n d e te rm in e d
2
b y S ta u b a n d S te p h e n s
b y u s in g an i o n i z a t i o n cham ber and
a m p lifie r ,
in
and a ls o b y p h o to g r a p h in g r e c o i l s
a m ix t u r e
o f m ethane a n d h e liu m i n
p ro d u c e d
a c lo u d cham ber.
T h is v a lu e was u s e d i n o u r e x p e rim e n t a s th e c o r r e c t
r a tio
o f th e a b s o lu t e
s c a t t e r in g c r o s s s e c t io n s a t 2 .5
M ev, a n d th e r e s u l t s a t
th e o t h e r e n e rg y i n t e r v a l s
a re
shown i n F ig u r e 4 .
to
t
i
•
V
i
M
M
4
§
&t
fi
2
0
09
10
to
T'
F ig u r e 4
H a tio o f th e b a c k w a rd s c a t t e r i n g c ro s s s e c t io n
f o r n e u tr o n s fry h e liu m a n d b y h y d ro g e n as a f u n c t i o n
o f th e n e u t r o n e n e rg y .
C o n c lu s io n s
It
w i l l be o b s e rv e d f r o m F ig x r e d t h a t t h e maximum
a t one Mev i s
i n ag re em e nt w it h t h a t o b ta in e d b y S ta u b
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
rr
and S te p h e n s . °
T h e ir r e s u l t a t t h i s
p o in t,
h o w e v e r, i s
a c c u r a te to a s m a lle r p r o b a b le e r r o r beca use o f th e la r g e
num ber o f r e c o i l s
a n d D u n n in g
8
!
/
th e
to
in v e s tig a te
C a r r o ll
be 0 . 0 5 , b u t f o r
fro m z e ro t o 0 .5 Mev t h e fo r m o f
n o t e s t a b lis h e d .
d i f f i c u l t to
F o r th e r m a l n e u tr o n s ,
h a ve fo u n d ^ hc/ ^
n e u t r o n e n e r g ie s
c u rv e i s
o b s e rv e d .
th e
T h is r e g io n w o u ld be e x tr e m e ly
b y use o f a c lo u d cham ber, s in c e
re d u c e d cham ber p r e s s u r e n e c e s s a ry t o
o b t a in t r a c k s
i
I
o f s u f f i c i e n t l e n g t h to m easure a c c u r a t e ly w o u ld e n t a i l
|
a la r g e num ber o f p h o to g r a p h s .
An e le c t r o s c o p e s tu d y o f
c a rb o n n e u tr o n s w o u ld p r o b a b ly be more s a t i s f a c t o r y .
B eyond 1 . 1 Mev th e c u rv e show s no i n d i c a t i o n
maximum, f a l l i n g
1 .4
Mev.
to h a l f th e 1 .0 Mev maximum a t a b o u t
The p o i n t s
i n th e r e g io n
are a c c u r a t e
e s tim a te d e r r o r o f a b o u t Z5 p e r c e n t , w h ile
is
of a
th e
to an
a c c u ra c y
somewhat b e t t e r a t h ig h e r e n e r g ie s w here m ore r e c o i l s
w ere o b s e rv e d .
The a b s o lu te c r o s s s e c tio n , f o r h y d ro g e n a t p o in ts
b e lo w 2 Mev i s
n o t e x p e r im e n t a lly w e l l know n, b u t may be
Q
c a l c u l a t e d fro m t h e W ig n e r f o r m u la .
A c c o r d in g to
t h is r e la tio n ,
th e c r o s s s e c t io n b e lo w 2 Mev in c r e a s e s
r a p i d l y w i t h d e c r e a s in g n e u tr o n e n e r g y , r e a c h in g o n e - h a lf
th e
th e r m a l n e u t r o n v a lu e a t a b o u t 10Q k e v .
t i o n m u st o f c o u rs e
T h is r e l a ­
be known i n o r d e r t o c a l c u l a t e
a b s o lu t e h e liu m c r o s s s e c t io n s fr o m F ig u r e 4 .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
th e
13
The d - d N e u tr o n S p e ctru m
!
1
Bonner
10
h as o b s e rv e d th e n e u tr o n s fro m t h e
r e a c t i o n b y u s in g a c lo u d cham ber f i l l e d
I n a d d itio n to
th e r e c o i l s
t h e 2 .5 Mev n e u tr o n s fro m
a r is in g
d -d
w i t h m e th a n e .
i n th e cham ber fr o m
th e r e a c t i o n , a s e c o n d g ro u p
o f lo w e n e rg y r e c o i l s , o f a b o u t l / l O
t h e 2 . 5 Mev g r o u p , was fo u n d .
It
th e
in te n s ity
of
was assum ed t h a t th e s e
w e re p ro d u c e d b y lo w
e n e rg y n e u tr o n s com ing fr o m th e d -d
a
r e a c t i o n and t h a t th e He
p ro d u c e d s im u lt a n e o u s ly was
le ft
in a n e x c ite d s ta te
fin d
th e
!
d ro p s t o
th e g ro u n d s t a t e were n o t s u c c e s s -
f u l . 11
B a ld in g e r , H u b e r a n d S ta u b 3-2
t i o n cha m b e r a n a ly s is
The i o n i z a t i o n
!
A tte m p ts t o
/ - r a y o f a n i n t e n s i t y w h ic h m ig h t be e x p e c te d
when th e He
S
o f a b o u t 1 .8 9 M ev.
h a ve made a n i o n i z a ­
o f th e n e u tr o n s fr o m t h i s
cham ber was f i l l e d
w i t h h e liu m ,
r e a o tio n .
and r e c o i l
^ - p a r t i c l e s w e re r e c o r d e d b y an o s c i l l o g r a p h o p e r a te d b y
a lin e a r a m p lifie r .
T h e y a ls o
fo u n d a g ro u p o f lo w e n e rg y
I
j
r e c o ils
a t a n e n e rg y o f 1 .1 Mev, i n agreem ent w i t h
e n e rg y o f t h e g ro u p o b s e rv e d b y B o n n e r.
It
th e
a p p e a re d t o
|
f!
h a v e a n i n t e n s i t y a b o u t e q u a l t o t h a t o f th e h ig h e n e r g r
i
g r o u p , b u t i n v ie w o f th e a n o m a lo u s ly h ig h s c a t t e r i n g
s e c t i o n f o r n e u tr o n s o f t h i s
e n e rg y i n
h e liu m ,
c ro s s
th e r a t i o
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
o f th e n u m b e r o f h e liu m
w it h re s p e c t
g ro u p i s
r e c o ils
i n th e
to th e num ber o f r e c o i l s
lo w e n e rg y g ro u p
i n th e h ig h e n e rg y
much l a r g e r t h a n th e t r u e r e l a t i v e
t e n s itie s .
When th e p r o p e r c o r r e c t io n s f o r r e l a t i v e
s c a t t e r i n g c r o s s s e c t io n w e re a p p lie d .,®
te n s ity
n e u tr o n i n ­
o f th e lo w
th e m u t r o n
e n e rg y g ro u p was found, to
c e n t o f th e m a in p e a k .
in ­
be 11 p e r ­
T h is r e s u l t appeared, to be in good.
a g re e m e n t w i t h t h e i n t e n s i t y o b se rve d , b y B o n n e r.^ ®
A f u r t h e r s t u d y o f th e a u t h o r s
g ro u p was made b y o b s e r v in g th e
cham ber f i l l e d , w i t h
w e ll- d e fin e d , f a l l i n g
a n d th e
in te n s ity
_
w o ric, B o n n e r
14
o f th is
lo w e n e rg y
r e c o i l s p ro d u c e d i n a
h y d r o g e l, w here
much lo n g e r t r a c k s .
1_3
th e r e c o i l s
p ro d u c e d
I t was fo u n d t h a t th e g ro u p was
to z e ro on e i t h e r s id e o f 1 .1 Mev,
a g re e d w i t h
p r e v io u s w o r k .
In fu rth e r
fo u n d t h a t tw o g ro u p s were o b s e rv e d in
b o th h y d ro g e n a n d h e liu m .
Because o f
a t th e
th e a n o m a lo u s c r o s s s e c t io n
e n e rg y o f th e lo w
i n t e n s i t y g r o u p , th e
a c o n tin u o u s b a c k g ro u n d o f i n e l a s t i c a l l y
in h e liu m
e ffe c t of
s c a tte re d neu­
t r o n s w o u ld be o b s e rv e d as a g ro u p a t t h i s
p o in t.
The
e x is t e n c e o f a lo w e n e rg y g ro u p o f n e u tr o n s fro m th e
r e a c tio n
le a d s t o
th e o r e tic a l d i f f i c u l t i e s
■1 e
e x c it e d He , as S hare
i
in
d -d
r e g a r d to
T g
and S c h if f
h ave e m p h a s iz e d .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
15
F u r th e r m o r e ,
if
s u o h a n e x c i t e d s t a t e e x is t s
i n He , one
m ig h t r e a s o n a b ly e x p e c t a c o r r e s p o n d in g l e v e l i n H5 , b u t
no e v id e n c e f o r t h i s
has b e e n fb u n d . ^
I n v ie w o f th e s e f a c t s , we have made f u r t h e r o b s e r ­
v a t io n s an th e n e u tr o n s f r o m th e
*
cham ber f i l l e d
w ith
The cham ber i s
phragm ty p e , has g la s s w a l l s
o f l i g h t c o n s tr u c tio n .
p h o to g r a p h s .
th e r u b b e r d i a ­
o n ly 1 /8 in o h t h i c k , an d i s
V e lv e t p la c e d on a p e r f o r a t e d
d ia p h ra g m s e r v e s as a b a c k g ro u n d f o r
W ith th e
cham ber p la c e d a t 90 ° to
d e u te ro n beam a n d 15 cm fro m th e t a r g e t ,
I
A c lo u d
h e liu m a n d w a t e r v a p o r was o p e r a te d
a t a tm o s p h e r ic p r e s s u r e .
p l a t e a b o v e th e
d -d r e a c t i o n .
th e 1 4 0 -k e v
3200 e x p a n s io n s
showed 74 < X -r e a o ils w L th ia l5 ° o f th e fo r w a r d d i r e c t i o n .
i
j
These w ere d i s t r i b u t e d a s shown in F ig u r e
5.
j
i
so
29
2 20
09
15
LO
or
■a
F ig u r e 5
The d - d n e u t r o n s p e c tru m as o b s e rv e d i n h e liu m
a t 9 0 ° to th e b o m b a rd in g beam .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
16
F o u r te e n r e c o i l s
w ere
b e lo w 1 .5 Mev e n e rg y , w hich , y i e l d s
a n e u tro n i n t e n s i t y
in t h is
o f th e m a in g r o u p .
T h is
r e g io n o f l e s s t h a n 4 p e rc e n t
i s h ig h e r th a n th e b a c k g ro u n d
w h ic h m ig h t be e x p e c te d w i t h
th is
a p p a r a tu s , b u t
fo u n d t h a t th e b o m b a rd in g beam was s t r i k i n g
tu b e n e a r th e t a r g e t .
The beam i n t e n s i t y
it
was
th e g la s s
is
s u ffic ie n t
t o m e lt th e p a r a f f i n t a r g e t a n d make t h i n d e p o s it io n s
th is
g la s s t u b e ,
tro n s ta b u la te d
and i t
in
is
b e lie v e d t h a t some o f
F ig u r e 5 came fr o m t h e r e .
c u l t y was o vercom e b y a d d in g
a d e fin in g
th e n e u ­
T h is
s l i t to
fille d
|
c lo u d ch a m b e r p la c e d a t 5 1 ° t o
a n d u s in g a b o m b a rd in g v o lt a g e
th e
o f 130 k v j
y i e l d e d th e d a ta s h o rn
r e o o ils
ch a m b e r.
in
F ig u r e
o b s e rv e d , o n l y f i v e
TO
tu b e .
was
a h e liu m
th e b o m b a rd in g beam
th is
c o n d it io n s u n d e r w h ic h th e y o b s e rv e d h e liu m
b y use o f an i o n i z a t i o n
5
p ro d u c e d i n
d iffi­
the
The e x p e rim e n t o f B a ld in g e r , H uber a n d o ta u b
th e n r e p e a te d b y o b s e r v in g r e c o i l s
on
d u p lic a t e s
r e c o ils
F o u r th o u s a n d e x p a n s io n s
6.
O f a t o t a l o f e ig h t y
h ave e n e rg y b e lo w 1 .5 Mev.
A f t e r c o r r e c t i o n f o r c ro s s - s e c t i o n a l v a r i a t i o n w i t h n e u tr o n
e n e rg y , i t
is
n e u tr o n s i n
in te n s ity
th is
r e g io n
t h is
of
r e p r e s e n t s an i n t e n s i t y
of
le s s t h a n 2 p e r c e n t o f th e
o f th e m a in g r o u p .
f o r a s due t o
It
fo u n d t h a t
T h is ca n e a s i l y be a c c o u n te d
s c a t t e r i n g o f th e h igh, e n e r g y n e u t r o n s .
t h e r e f o r e a p p e a rs t h a t th e
lo w e n e rg y g r o u p o f
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
17
i
i
30
!
I
■rf— 1 i I—Lr—
il
10
*.0
F ig u r e
tA
5.0
6
“She d - d n e u tr o n s p e c tru m as o b s e rv e d i n h e liu m
a t 5 1 ° , u n d e r c o n d it io n s i d e n t i c a l w it h p r e v io u s
w o r k b y B a ld in g e r , H u b e r and S ta u b .
r e c o i l s w h ic h have been p r e v i o u s l y o b s e rv e d i n h e liu m
m ust be a t t r i b u t e d
uo th e
e f f e c t o f the
anom alous c ro s s
s e c t i o n on a n e u t r o n b a c k g ro u n d p ro d u c e d b y i n e l a s t i c
s c a tte r in g .
t h e tw o
fille d
it
is
T h is a s s u m p tio n , h o w e v e r, w o u ld n o t e x p la in
g ro u p s w h ic h have b e a i o b s e rv e d i n
w i t h m e th a n e 1^ a n d h y d r o g e n .1®
i n t e r e s t i n g to n o te t h a t th e
c lo u d cham bers
In th is
c o n n e c tio n
lo w e n e rg y r e c o i l s
a re
o f th e ra n g e one w o u ld e x p e c t fro m a d e u te ro n p ro d u c e d
b y p r o t o n c a p tu r e o f a S .5 Mev n e u t r o n .
fo r
such a c a p tu r e a t t h i s
e n e rg y i s ,
The c r o s s s e c t io n
h o w e v e r, on p r e s e n t
t h e o r e t i c a l g ro u n d s , e x t r e m e ly s m a l l , b e in g o f th e o r d e r
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
o f 1 0 “ 29
in g .
cm**, o r a b o u t
10“ ^ th e c r o s s s e c t io n f o r
s c a tte r­
R e c o ils p ro d u c e d b y c a p t u r e w o u ld a lw a y s p ro c e e d
i n t h e f o r w a r d d i r e c t i o n w it h r e s p e c t t o th e
n e u t r o n , w h ile o n ly 1 /3 3 o f th e
in g a re
in
r e c o ils
th e f o r w a r d d i r e c t i o n
o f c a p t u r e to
s c a tte r in g
p ro d u c e d by s c a t t e r ­
(0 -1 0 °).
in te n s ity
have
been o b s e rv e d .
g iv e
r is e
to a
Hence th e r a t i o
i n t h e f o r w a r d d i r e c t i o n becomes
3 . 3 x lO " ^ , a t h e o r e t i c a l v a lu e s t i l l to o
f o r th e r e l a t i v e
im p in g in g
of
th e tw o
s m a ll to a c c o u n t
r e c o i l g ro u p s w h ic h
Buch. a c a p t u r e w o u ld o f c o u rs e a ls o
- r a y , w it h a n e n e rg y o f a p p r o x im a t e ly
3 .5 Mev.
It
i s now p la n n e d to s t u d y th e n e u tr o n r e c o i l s
th e d - d r e a c t i o n
b y use o f a c lo u d cham ber f i l l e d
d e u te r iu m and com pare the r e s u l t s
w ith
fro m
w it h
th o s e o b t a in e d
u n d e r i d e n t i c a l c o n d it io n s w it h a h y d ro g e n - f i l l e d
ch am be r.
Such r e s u l t s w o u ld show w h e th e r n e u tr o n c a p tu r e b y p r o to n s
is
an a p p r e c ia b le f a c t o r w it h
s c a tte r in g a t
r e s p e c t to n e u t r o n - p r o t o n
2 .5 M ev.
A c k n o w le dgme n t s
!
We w is h t o e x p re s s o u r s in c e r e
fe s s o r H.
a n d to
a
a p p r e c ia t io n t o P ro ­
. W ils o n f o r h i s h e lp a n d i n t e r e s t i n
th is
w o rk ,
D r. T . W. B o n n e r f o r h is v a lu e d a d v ic e a n d s u g g e s tio n s .
We w is h to t h a n k M r. F ra n z v a n d e r H e n s t and H r .
d e T r ie s f o r t h e i r
a s s is ta n c e as m a c h in is t s .
i
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
P ie r s o n
ELECTROSCOPE INVESTIGATION OP THE ANOMALOUS
SCATTERING OP NEUTRONS BY HELIUM
The n u c le a r r e a c t i o n
Q .-value o f - 0 * 2 8 M ev.
fro m t h i s
C/1B>
Hence i t
D*'-** N /3-f n ' has a
is
p o s s ib le
to
o b t a in
r e a c t i o n m o n o k in e t ic n e u tr o n s o f a n y d e s ir e d
e n e rg y b y a l t e r i n g
th e e n e rg y o f th e b o m b a rd in g d e u te r o n s ,
w h ic h f a l l o n a t h i n
c a rb o n t a r g e t .
U s in g th e n e u t r o n s fr o m t h i s
r e a c t i o n , we ha ve
made an i n v e s t i g a t i o n a t b a r io u s b o m b a rd in g e n e r g ie s o f
th e a c t i v i t y p ro d u c e d i n a W o lf f e le c tr o s c o p e
w i t h h y d ro g e n .
I
T h is a c t i v i t y has b e e n co m p a re d w i t h
t h a t p ro d u c e d u n d e r
scope was f i l l e d
It
fille d
th e
same c o n d it io n s
When th e e l e c t r o ­
w i t h h e liu m .
i s kn o w n t h a t s t r o n g gam m a-rays a r e o b ta in e d
when c a rb o n i s
bom barded w i t h d e u te r o n s , b u t t h i s
was s m a ll co m pa re d t o t h a t o b ta in e d fr o m n e u tr o n s
1
e ffe c t
in
h y d ro g e n o r h e liu m .
The g r a p h on th e f o l l o w i n g page shows th e r a t i o
o f th e a c t i v i t y
i n h e liu m t o t h e a c t i v i t y
as a f u n c t i o n o f t h e n e u tr o n
b o m b a rd in g v o lt a g e .
It
in
h y d ro g e n
e n e r g y , d e d u ce d f r o m th e
w i l l be o b s e rv e d t h a t th e c u rv e
I
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
20
8
-
M AXIM UM NOH.MAL.ireo TO 8.6
6
b"
-
-
2.
__________ I__________I_________ 1_________ 1__________ I_________ 1__________ I
0-4
0.T -
0 .8
O .t*
l.o
/. 4
1.2.
En m MEV
The r a t i o
f o r b a c k w a rd a o a t t e r in g o ro s s
s e c t io n s o f n e u tro n s as a f u n c t i o n o f n e u tr o n e n e rg y
i
shows th e same g e n e r a l shape a s t h a t p r e v i o u s ly o b ta in e d
b y th e c lo u d chamber i n v e s t i g a t i o n *
I t was n o t p o s s ib le t o
e x te n d th e d a ta to p o in t s
o f h ig h e r n e u tr o n e n e rg y , s in c e
th e p r e s e n t l i m i t o f
v o lt a g e
o f th e g e n e r a to r was r e a c h e d a t th e l a s t p l o t t e d
j
p o in t.
H o w e ve r, i f
|
j
|
b e y o n d th e p o i n t w here th e r a t i o
re s o n a n c e shows a h a l f - w i d t h o f a p p r o x im a te ly 0 .5 M ev;
|
t h i s v a lu e
|
c u rv e o f S ta u b a n d S te p h e n s , b u t
j
Mev h a l f - w i d t h o b ta in e d i n t h e c lo u d cham ber w o rk r e -
is
th e c u rv e i s
c o n tin u e d s y m m e t r ic a lly
re a c h e s a maximum, th e
l a r g e r th a n t h a t p r e v i o u s ly g iv e n b y th e
com pares w i t h t h e
I
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
0 .7
21
p o rte d in t h is
th e s is .
i
RESONANCES IN THE DISINTEGRATION OF CARBON BY DEUTERONS
In
th e c o u rs e o f t h e e le c t r o s c o p e
o f th e anom alous s c a t t e r i n g
in v e s tig a tio n
o f n e u tr o n s .by h e liu m ,
was fb u n d t h a t t h e y i e l d o f n e u tr o n s fr o m th e
it
r e a c t io n
C,x-+- D*--*- N n -v n ? showed re s o n a n c e s a t c e r t a i n bom bard­
in g e n e r g ie s .
The n e u tr o n s w e re d e t e c t e d b y use o f a
W o lf f e le o tr o s c o p e f i l l e d
w i t h h y d ro g e n , a n d th e g ra p h
on t h e f o l l o w i n g page shows th e n e u t r o n a c t i v i t y a s a
f u n c tio n o f
th e b o m b a rd in g e n e r g y o f t h e
d e u te r o n .
f
The e x is t e n c e
o f th e s e re s o n a n c e s was ch e cke d b y
o b s e r v in g t h e r a d i o a c t i v i t y o f N '3 , w h ic h decays w i t h
a te n m i n u t e - h a l f - l i f e
i
N/3-*- C/3 t- e * \
a c c o r d in g to
th e
The c a rb o n ( p a r a f f i n )
r e a c t io n
t a r g e t was
bom barded f o r f i f t e e n m in u te s b y d e u te ro n s o f a known
e n e rg y , th e a v e ra g e io n c u r r e n t w as m e a s u re d , and th e
d e c a y o f th e N/3 was f o llo w e d f o r tw e n t y o r t h i r t y
m in u te s a f t e r bom bardm ent b y use o f a G e ig e r c o u n te r .
T h is o b v io u s ly g iv e s a m easure o f th e n e u t r o n y i e l d ,
s in c e th e N
/5
is
fo rm e d s im u lt a n e o u s ly w i t h th e n e u t r o n s .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
22
From
H-
N
Ra o i o
r c t iv it y
K -Filleo E.lEerfcos
x_ -
20-
<
uJ
0 .6
0 .8
l.o
1.2.
OEUTER.ON ENER.CY
IN NEUTRON EMISSION
3o
A c t iv it y
electroscope.
0 .8
1.6
MEV.
in
( div )(s e c .)''
RESONANCES
IN
1.4.
l.o
1-4
DEUTER.ON ENERGY IN MEV.
RE.S0NhNC.E5 IN
Y-RflY EMISSION
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
23
The r e s u l t s
o b t a in e d f r o m
shown b y th e d o t t e d l i n e
c e d in g p a g e .
a g re e
in
The tw o
to
th e
o n th e f i r s t
,3
e x p e rim e n ts a re
g ra p h on th e p r e ­
c u rv e s w o u ld n o t be e x p e c te d t o
i n t e n s i t y b e c a u s e o f th e v a r i a t i o n w i t h e n e rg y
o f th e c r o s s s e c t i o n f o r
th is
th e N
o o l l i s i o n o f n e u tr o n s a n d h y d ro g e n ;
w o u ld te n d to make th e s o l i d
th e a b s o lu t e n e u t r o n y i e l d .
c u rv e to o h ig h com pared
On th e o th e r h a n d ,
if
a ll
io n s p ro d u c e d b y t h e r e c o i l p r o to n s a r e n o t o o lle o t e d ,
th e s o lid
c u rv e w o u ld bave s m a lle r o r d i n a t e s ;
th e e l e c t r o ­
sco p e y i e l d w o u ld in c r e a s e w i t h n e u tr o n e n e rg y , s in c e t h e
p r o t o n r e c o i l s p ro d u c e d w o u ld be lo n g e r .
h o w e v e r, e x h i b i t re s o n a n c e s w h ic h a re
m e n t.
B o th c u r v e s ,
i n a p p a re n t a g r e e ­
The re s o n a n c e s o c c u r a t 9 2 0 , 1 1 3 0 , a nd 1300 k v .
The / - r a y s p ro d u c e d i n
th e bom bardm ent o f c a rb o n
b y d e u te ro n s h a d been fo u n d p r e v i o u s ly b y B o n n e r and
3 e n n e tt t o
o b t a in e d i s
fir s t
show re s o n a n c e s , a n d th e c u rv e w h ic h th e y
shown i n th e lo w e r g ra p h on page 2 2 .
th r e e re s o n a n c e s f o r n e u tr o n s a n d f o r
The
J^-ra ys
o o c u r f o r n e a r l y t h e same e n e r g ie s o f bom bardm ent , th e
/-ra y s
e x h i b i t i n g re s o n a n c e s a t 9 2 0 , 1 1 6 0 , a n d 1280 k v ;
a f o u r t h s h a rp re s o n a n c e a t 1430 k v f o r th e
e m is s io n o f
I
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
24
/ - r a y s was n o t o b s e rv e d i n th e oase o f n e u tr o n s .
P r e l i m in a r y w o rlc in d ic a t e s t h a t th e p r o to n s fo rm e d
a o c o r d in g to
th e r e a c t i o n
Q '% D **-£ C / 3 +- R 1
may e x h i b i t
re s o n a n c e s c o r r e s p o n d in g t o th o s e f o r n e u t r o n e m is s io n .
I f th is
be t r u e ,
it
is
l o g i c a l t o su pp ose t h a t a l l o f
th e re s o n a n c e s o c c u r i n th e f o r m a t io n
a te n u c le u s
th e
th e
in t e r m e d i­
i n th e bom bardm ent o f c a r b o n b y d e u te r o n s ;
th e n lo s e s i t s
1 0 .4 Mev e n e r g y o f e x c i t a t i o n
b y one o f th e f o l l o w i n g c o m p e tin g p r o c e s s e s ;
C/ V
n'
or
or
(IT ,3-> C ' V
e ")
—> C/ 3 + H 1
11 +~ f
The / - r a y s h a v e a n a v e ra g e e n e rg y o f a b o u t 3 .5 M ev,
as m e a su re d b y c o in c id e n c e G e ig e r c o u n te r s a t th e second
r e s o n a n c e , a n d hence t h e t r a n s i t i o n
be c o n s id e r e d a s p r o c e e d in g , a t l e a s t
11 ' * + /
m ust
i n m o st c a s e s ,
i n m ore t b a n one s t e p .
ii
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
REFEHEHCES
1
8
J • H. W illia m s , W, G. S h e p h e rd a n d R. 0 . H a xb y,
P h y s . R ev. 5 2 . 390 ( 1 9 3 7 ) .
C o n firm e d b y H. S ta u b
and W. E . S te p h e n s , P h y s . R ev. 5 4 . S36 (1 9 3 8 ) a n d
P h y s . R ev. 5 4 , 237 ( 1 9 3 8 ) .
A s t a b le s t a t e o f He® has bee n r e p o r t e d b y P . J o l i o t
a n d I . Z lo to w s lc i. Comptes re n d u s 2 0 6 . 1256 ( 1 9 3 8 ) . and
de P h y s . e t r a dT ' l g 3 g 3 " [ I 7 3 5
3
H . S ta u b and W. E .
S te p h e n s , P h y s . R ev. 5 5 . 131 (1 9 3 9 ).
4
T . W. B o n n e r a n d G. B r u b a ie r , P h y s . R ev. 50 . 308 (19S 6)
6
lil. G. H o llo w a y and M. S. L i v i n g s t o n , P h y s . R ev.
31 ( 1 9 3 8 ) .
7
The r a n g e - e n e rg y r e l a t i o n g iv e n b y M. S. L iv in g s t o n
a n d H. A . Be t h e , R e v. Mod. P h y s . 9 ^ 268 (1 9 3 8 ) w as u s e d .
8
H. C a r r o l l and J . R. D u n n in g , P h y s . R ev.
9
H. A . B ethe a n d R. P .
5 4 , 541
B a o h e r, R e v. Mod. P h y s . 8 ^
(1 9 3 8 ).
117
(1 9 3 6 ) .
10
T . W. B o n n e r, P h y s .
11
A . J . R u h lig , P h y s .
R e v. 5 4 , 308 ( 1 9 3 8 ) ; H. K a llm a n n a n d
E . K u h n , f f a t u r w is s . 2 6 . l3 o ( 1 9 3 8 ) ; S. K ilc u o h i a n d H. A o fc i,
P r o o . P h y s .-M a th .. S o ? ^ J a -p a n
20 ( 1 9 3 9 ) .
12
R e v. 5 2 ^ 685 (1 9 3 7 ) and
54.
5 3 ^ 711 (1 9 3 8 ) .
E . B a ld in g e r , P . H ub e r a n d H. S ta u b , H e lv . P h y s . A o ta 1 1 .
245 (1 9 3 8 ) .
13
E . H u d s p e th a n d H. D u n la p , P h y s . R ev. 5 5 , 587 ( 1 9 3 9 ).
14
T . W. B o n n e r, K a tu r e 1 4 3 ^ 681 ( 1 9 3 9 ) .
15
S . S h a re , P h y s . R e v . 5 3 ^
16
L. I.
17
P . E . M yers a n d L . M.
E . H u d s p e th and T . W.
S o h iff,
Phys.
875 (1 9 3 8 ).
R e v. 5 ^ 92 ( 1 9 3 8 ) .
L a n g e r, P h y s . R e v.
B o n n e r, P h y s . R ev.
54 . 90 ( 1 9 3 8 ) ;
T&T 308 ( 1 9 3 8 ) .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Reprinted fro m
T he
P hysical
V o L 54, N o . 4, 308-309, August 15, 1938
Printed in U. S. A.
R eview ,
Observation of H 1 and H 3 Ranges from, the Disintegration of Deuterium by Deutetons
Recent cloud cham ber experim ents1 on the energy
spectrum of recoil protons produced b y neutrons from the
reaction
H 3-|-H — >He3- r i i l
80
(O
uj
E^o
have shown the presence of a tow energy group o f neutrons,
and indicate the existence of an excitation level in H e 3 at
I.S 9 M e v . Ionization cham ber studies3 have led to this
same conclusion. In view of this excitatio n level in H e3
it seems reasonable to expect a sim ilar level in H 3. Conse­
q u e n tly we have looked for a short range group of protons
from the reaction
I F - F H 3— H 3+ H ‘.
W e used apparatus previously described.3 T h e protons
were observed in a cloud cham ber tilled w ith a ir and
alcohol vapor. T h e y were allowed to pass into the cham ber
through an alum inum foil which had a stopping power of
app ro xim ately 0.5 cm. A slit system defined the direction
MO
00
100
60
SO
RANGE OF PROTONS IN CM
F ig . I. Range distribution of protons from the disintegration of
deuterium by deuterons.
o f the disintegration particles to an angle of 9 9 .5 ° ± 2 ° to
the direction of the incident 100 kev deuterons, which
bom barded a D 3 P O 4 targ e t. T h e stopping power o f the
gas in the cham ber (1.18) was determ ined from the mean
range (14.7 cm ) o f the proton group o f m axim um energy.
Figure I gives the range d is trib u tio n of the protons
observed, and, con trary to w hat one m ig ht expect, there is
no indication of more than a single group. Prelim inary
experim ents w ith a D -O target frozen b y liquid a ir gave
sim ilar results, though a higher background was present.
F ro m this experim ent and th a t described below we con­
clude th a t H 3 is excited to a level between 0.4 and 2.9 M e v
in less than 2 percent o f the disintegrations, if a t a ll.
W h ile looking fo r low energy protons from the deuterium
reaction we observed the range o f the H 3 particles produced
in the same reaction. A n accurate d eterm ination of the
range o f these particles is useful in checking th e rangeenergy relation for H 3 particles, and hence the range-energy
curve fo r short range protons.
T h e H 3 particles were observed in a cloud cham ber
40
to
F ig. :
Ifl
2.6
14
4.Z
RANGE O F H5 RETICLES IN CM
Range distribution of the charged particles as observed in the
helium tilled cham ber.
filled w ith helium and w ater vapor. T h e y were allowed to
pass in to the cloud cham ber through the slit system and an
a lu m in u m foil w ith a stopping power o f 0.50 c m .1 Fig. 2
gives th e range d istrib ution of the particles. T h e stopping
power o f the gas was found to be 0 .3 0 ± 0 .0 1 cm for particles
w ith a range o f 3.S0 cm (polonium alpha-particles).
T h e most probable range is 1 .2 8 ± 0 .1 0 cm , which corre­
sponds t o a mean range of l . 3 t ± 0 . t 0 cm a t 99 .5°. Since the
stopping power o f the helium would probably be slightly
higher fo r t.3 cm particles than for polonium alphaparticles, this is a c tu a lly a lower lim it to the H 3 particle
range.
T h e energy o f the H 3 particles e m itte d a t 99.5° was cal­
culated from the Q value o f 3.98 M e v .3 T h e energy of the
H 3 particles is 0.89 M e v a t this angle. T h e range o f a H 3
p article o f this energy theoretically is three times th e range
o f a proton w ith an energy o f 0.89 3 M e v . I f we use the
new range-energy curve of Livingston and Bet he for
protons, the mean range o f the H 3 particles should be
0.95 cm . T h is is beyond the lim its o f experim ental error
a nd we conclude th a t th e ir range-energy curve for protons
in this region is in e rro r. T h e experim ental range of 1.3 1 cm
is in much b etter agreem ent w ith the old curve of Livings­
ton and Bethe* w hich predicts an H 3 range o f 1.38 cm.
T h is suggested change in the range-energy relation for
protons is im p o rta n t since it would necessitate raising the
mass o f th e neutron, and lowering th e mass of H e 3 a n d C u .
E m m ett H c d speth
T . W . Bonner
T he Rice Institute.
H ouston. Texas.
Ju n e 21. t938.
1T . W . Bonner. Phys. Rev. 52. 685 (1937); 53. 7 11 (1938).
* Baldinger. H uber, an d S taub. Helv. P hys. Acta I I . 245 (.1938).
* T . W . Bonner. Phys. Rev. 52. 685 (1937).
*T h e stopping power or the toil was calculated b y assum ing 1.41
mg/cm* = 1 cm air.
»O liphant. ICerapton, an d Rutherford. Proc. Roy. Soc. A149. 406
(1935).
4 Livingston and Bethe. Rev. M od. P hys. 9. 245 (1937).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Reprinted from T h e P h y s i c a l R e v ie w , Vol. 55, No. 6. 587-588, March 15, 1939
Low Energy Neutrons from the Deuteron-Deuteron Reaction
In an expansion chamber study of the reaction
s
D + D —He»+n
Bonner1 discovered that the neutrons were not of a single
energy. Besides the previously established group of energy
2.50 M ev, a second group of about 1/10 the intensity of
the first group and of 1.08 M ev energy was found. Baldingcr and his associates,* by using an ionization chamber,
obtained results in agreement with Bonner’s work.
The existence of this low energy group of neutrons sug­
gests that the He* nucleus formed simultaneously in the
above reaction may be left excited to a level of 1.89 Mev,
and a gamma-ray of this energy would be expected when
the He* falls to its normal state. A search for such a gammaray was made by Ruhlig,* who found no evidence for it and
concluded that not more than one gamma-ray was emitted
for every 200 neutrons; this lim iting value is in agreement
with the work of Kallmann and Kuhn,4 who studied the
deuteron-deuteron reaction by using coincidence counters.
An excited state in He* suggests a similar excited level in
H*, but a study of the H * and H l recoils produced in the
above reaction gives no evidence for such a state.'* * The
existence of an excited state in either He* or H * is not in
agreement with present nuclear theory, as Share* and
SchifT* have emphasized.
The fact that neutrons also suffer inelastic collisions with
heavy nuclei would give rise to neutrons of low intensity
spread over a relatively wide range of low energies.'
In view of these facts we have made a closer study of the
neutrons from the d-d reaction, obtaining 100-kv deuterons
with apparatus previously described.1' The cloud chamber
was filled with hydrogen and alcohol vapor and placed
about 13 cm from D|PO« target in an aluminum cup, which
was substituted for the brass previously used. The low
stopping power o f the gas in the cloud chamber made it
possible to determine whether the low energy neutron
spectrum fell to a minimum on the low energy side. Neu­
trons of energy greater than about two M ev produced
recoil protons which passed completely across the chamber.
A ll proton recoils within 25° of the forward direction
which originated in the light beam and within four cm of
the chamber wall were tabulated, and 172 such tracks
were observed. O f this number, those that remained within
the chamber were measured for length and recoil angle.
The energies of the low energy neutrons were calculated,
and the results are shown in Fig. 1.
The stopping power (0.40-0.43) of the gas varies rather
rapidly with temperature and with range a t low energies;
this variation and sohie uncertainty in determination of
s
4
2
0
0
.4
12
1.8
ENERGY Or NEUTRONS IN MV
Rig . 1. Low energy neutron •pectrum In the deuteron-deuteron reaction.
recoil angles serve to widen the neutron spectrum found.
The intensity of the low energy group of recoil protons is
about J that of the high energy group. However, the colli­
sion cross section for neutrons of the low energy group,
according to the Wigner formula,11 is approximately twice
as great, so th a t the ratio of the intensities of the two
neutron groups is about -fa. This neutron group is well
defined and of such intensity that it can hardly be ascribed
to a group arising from inelastic collisions. The observed
energy of 1.1 M ev is in good agreement with Bonner’s
earlier value.
In order to make certain that the low energy neutrons do
not come from some other reaction, photographs were made
when deuterons bombarded a target of H ‘jPO«. No recoils
of any kind were observed.
It would therefore appear that the expected gamma-ray
has been overlooked or that other considerations are
necessary to explain the low energy neutrons.
We are grateful to Professor H . A . Wilson for his interest
and advice and to D r. T . W . Bonner for many suggestions.
E m m ett H u d speth
H en r y D unlap
T he Rice In stitu te.
Houston. Texas.
F ebruary 20. 1939.
• T . W . Bonner. P hys. Rev. 53, 711 (1938).
1 Baldinger. H u b er and Staub. Melv. Phys. A cta 11.245 (1938).
>A . J . Ruhlig. P hys. R ev. 54.308 {1938).
• H . Kallmann a n d E . K uhn. Naturwiss. 20. 106 (1938).
‘ E . Hudspeth an d T . W - Bonner. Phys. Rev. 54. 308 (1938).
' F . E . M yers an d L . M . Langer. Phys. R ev. 54. 90 (1938).
*•S . Share. Phys- R ev. 53. 875 (1938).
• L . I. Schiff. P hys. Rev. 54. 92 (1938).
1 M .S .L iv in g s to n a c d H . A . Bethe. Rev. M od. P h y s.9. 153 (1937).
*• T . W . Bonner. Phys. Rev. 52.685 (1937).
11H . A . B ethe a n d R . F . Bacber. Rev. Mod. Phys. 8. 117 (1936).
with permission of the copyright owner. Further reproduction prohibited without permission.
Reprinted from T
he
P h y s i c a l R e v i e w , V o l. S3, No. 11, 938, June 1, 1938
P r e s e n te d a t th e W a s h in g to n , D. C ., M e e tin g
A m e ric a n P h y s ic a l S o c ie t y , A p r i l , 1 9 3 8 .
o f th e
The Passage of Fast Neutrons Through Lead
i
i
I
j
!
.
T h e energy distribution of the neutrons
from the reaction H 2+ H 2—*-He3-f-«1 has been determined
after they passed through 3 cm of lead. The neutron
energies were found from the energies of the recoil protons
observed in a cloud chamber. T h e maximum neutron energy
(2.50 M ev) is unaffected by the lead within the experi­
mental error of 0.1 M ev. T h e energy distribution curve of
the protons in the forward direction (0—10°) is only slightly
affected by the 3 cm of lead. T h e effect of the lead is to
increase the relative number of protons with energies in the
interval 1.2 to 2.0 M ev. T h e results indicate th at 10-15
percent of the 2.5 M e v neutrons make inelastic collisions in
the lead with energy losses of from 0.5 to 1.3 M ev.
E m m ett H
u d speth
T. W. Bonner
Rice Institute, Houston, Texas.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
P r e s e n te d a t
th e W a s h in g to n , D. C .,M e e tin g o f
th e A m e ric a n P h y s i c a l S o c ie t y , A p r i l , 1 9 4 0 .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
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