Nghiên cứu tỷ số suất lượng đồng phân của phản ứng hạt nhân 116Cd(y,n)115m,g Cd sau vùng năng lượng cộng hưởng khổng lồ

ĐẠI HỌC QUỐC GIA HÀ NỘI
TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN





LẠI VĂN THẮNG


NGHIÊN CỨU TỶ SỐ SUẤT LƯỢNG ĐỒNG PHÂN
CỦA PHẢN ỨNG
HẠT NHÂN
116
Cd(γ,n)
115m,g
Cd SAU VÙNG NĂNG
LƯỢNG CỘNG HƯỞNG KHỔNG LỒ






LUẬN VĂN THẠC SĨ KHOA HO
̣
C

HÀ NỘI - 2012
ĐẠI HỌC QUỐC GIA HÀ NỘI
TRƯỜNG ĐẠI HỌC KHOA HỌC TỰ NHIÊN





LẠI VĂN THẮNG


NGHIÊN CỨU TỶ SỐ SUẤT LƯỢNG ĐỒNG PHÂN
CỦA PHẢN ỨNG
HẠT NHÂN
116
Cd(γ,n)
115m,g
Cd SAU VÙNG NĂNG
LƯỢNG CỘNG HƯỞNG KHỔNG LỒ


Chuyên ngành: Vật lý nguyên tử, hạt nhân và năng lượng cao
Mã số: 60.44.05

LUẬN VĂN THẠC SĨ KHOA HO
̣
C

CÁN BỘ HƯỚNG DẪN KHOA HỌC: TS. PHẠM ĐỨC KHUÊ




HÀ NỘI - 2012
MC LC
MƠ
̉
ĐÂ
̀
U 1
CHƢƠNG 1. PHẢN ỨNG QUANG HẠT NHÂN VA
̀
HA
̣
T NHÂN ĐNG PHÂN . 3
1.1. Mô
̣
t sô
́
đă
̣
c trƣng cu

̉
a pha
̉
n ƣ
́
ng quang ha
̣
t nhân 3
1.1.1. 







 3
1.1.2. 











5

 gi  7
1.2. Ht nhân đng phân 8
1.3. T s đng phân 11
CHƢƠNG 2: PHƢƠNG PHÁP THỰC NGHIỆM 15
2.1. Ngun photon hãm từ máy gia tc Linac 16
2.1.1. Nguyên lý hot động cu
̉
a ma
́
y gia tô
́
c linac 16
2.1.2. Cơ chê
́
ta
̣
o photon ha
̃
m tƣ
̀
ma
́
y gia tô
́
c electron. 17
2.1.3. Máy gia tc linac 100 MeV Pohang, Hn quc. 23
2.2. Phƣơng pháp kích hot v đo phổ Gamma 25
2.2.1. Nguyên lý của phƣơng pháp kích hot pho
́
ng xa

̣
. 25
2.2.2. Ghi nhận va
̀
phân tích phổ gamma. 28
2.2.2.1. 





 28
 Gamma 32
2.2.3. Một s biện pháp nâng cao độ chính xác của phép đo 33
2.2.3.1. Hiu chnh can nhi. 33
2.2.3.2 Hiu ng hp th tia gamma trong mu. 34
2.2.3.3. Hiu ng cnh. 34
CHƢƠNG 3: XÁC ĐNH T S SUÂ
́
T LƢƠ
̣
NG ĐÔ
̀
NG PHÂN 37
3.1. Thí nghiệm xác định t s suất lƣợng đng phân 37
3.2. Nhận diện đng vị phóng x v phản ứng ht nhân. 39
3.3. Xác định t s suất lƣợng đng phân bằng thực nghiệm. 44
KÊ
́
T LUÂ

̣
N 50
TI LIỆU THAM KHẢO 51










1

MƠ
̉
ĐÂ
̀
U
Mt trong nh quan tr











 



 u v t s 
cp nh  ca phn ng
h  

, v s ph thuc c mc
hn cht c 
c            liu thc
nghim v t s t cn thit trong vic thit k 
 ca mu, tu kin thc nghing
dng thc t   liu v t s c s dng vi nhi
t, ch tng v, che ch, [9-13].
T s  









 t din ca phn ng h
t

 (metastable state) (


m
) n 
(ground state) (

g
). 
k , 



































 
high

low
.

















ng, t s 


 s sung phn ng,
lowhigh
YYIR 
[11-13].
Lu





thc hin  t
s su phn ng quang h
116

115m,g
Cd 
bc x  : 50, 60, 


 , 









 






 






.
  , 








ng 






 (>30 MeV), 



 




,  ca phn 









.  u
 t s sung ca phn ng quang h
116
Cd
115m,g
Cd  
cng khng l 


 mt s  thc hin [17-21]. Tuy 














  , 










2
 . y, kt qu c ca bn lu
 n b sung s li   ng . 




 








 , 

























, t qu c
tin 

.
Bn lu , 

i dung 

: Phn ng quang hng : 
t 

a phn ng quang hn 

 t
 s .
 c: t
ng cc 

  to 



 c

i thiu v c Linac 100 MeV tc.
 gamma: 
 ct  ph gamma, 






















 . Mt
s biu chnh nh 

.
nh t s sut c nghim: 

m ca phn ng
quang h
116
Cd
115m,g
Cd, 












.
Bu 52 trang, 14  , 8 bng biu.
  c thc hin t       c.
Vi lin luc thc hin t
Vn V
















3
CHƢƠNG 1. PHẢN ỨNG QUANG HẠT NHÂN V HẠT NHÂN
ĐNG PHÂN
1.1. Mô
̣
t sô
́
đă
̣
c trƣng cu
̉
a pha
̉
n ƣ
́
ng quang ha
̣
t nhân
1.1.1. 









c x n t 
t chy ra nhiu va chn.
 yu ca bc x gamma vi vt chu ng hp th quang
n, hiu ng Compton, hiu ng to cn ng quang h
Tit din
airphot Com p
   
  
+

T

A
t
din do hiu n
5
7/2
phot
Z
E



, tit din do hiu  Compton


Com
Z
E



, tit din do hiu ng to cp
2
air
ln(2E )
p
Z



,

T

A
 t din
tng cng cn ng quang ht Hiu  ch
ya bc x gamma vi vt cht  ng thp
x Compton chi u ng to
cp 

 ng cao [4].
Phn ng quang h hp th photon dng
p ph 
 i hu ki nhng phn ng

y rng cng t  cn phi lt,
ng ca phn ng h

 E
th
). B
 





  ng v   ng t  


 ng thp c x gamma tng
ng ln, c x c ht.
 n ng quang h

 u hp th
photon. Mu phn ng quang h 

 phn ng quang ht
 
p theo ca h
n ng hng c
 n ng quang h   thuc m   ng c 











4
ng t gamma tng gamma ti, phn ng quang h
 i hng vi nhiu loi phn ng
   n   n: (,n), (,p); phn ng sinh nhi 
(ch h,f); phn ng photospallation: (,xnyp); phn ng
to meson (,xn), hinh (
 n ng quang h

: cng
cc khng l (gi        gi 
(quasideutron, QDM) (30 MeVE140 MeV)   pion (E>140 MeV).
u din m gia tit din phn ng quang h
ng ca photon [6].









 Tit din phn ng quang hng photon.

ng ca phn ng (
ch  i cng cong tit di
 dch chuyn gic ca h
ng v hin trong c
tinh t ca tit ding vi s chng chc ca h
hp phn. Tit din phn ng quang ht cgauss
c gng khng l
u ng phc tu ng 

I
II
III
IV
E

(MeV)
Tiết diện phản ứng

1
10
100











5
1.1.2. 












     i 30 MeV, s hp th photon d n
p ph 
nhi i h,xn), (,p), (,pn);
(,f). 





 










 (,n) (,p) 





















 1 mb khi E




15  25




  .
 










, (E

)
res
, :
MeVAE
res
3.0
)(



(1.1)



















 , 
photon 10 20 
















 (giant
dipole resonance  GDR) . 

 i phn
ng quang hp trung  

(E < 30 MeV).
 ging 







 khng l 
ng hn t cng t 
thia ht lt, hn
ng do hp th o ra s ng ca hai loi cht l
Hing cng khng l ng vi tn s ci cng. Sau
   c ng khng l   t s chng chp
(superposition) do s a tt c . Mi mt nucleon
nhn mt phng t s hp th photon. Cng khng l ng
tt c ng nh  [4].
Hi         ng t gamma v 

ng E


-10
1,2x10hc
EE



(1.2)
  

i vng
E

ng t  >> R
nucl
 ch sau,
 










6

 th nht (Goldhaber- proton ca
hc thay th b  c trong ht
2ng ca li h bi
i lp. Tp hp cng cc trong hn s dao
c
K
M


, vi
ng ca h a lc thc hin bi
i hi t l vi di
mt ca h R
2

2
1/6
3
1KR
A
MR
R


   

c (E

)
res

= 35 A
-1/6
(MeV).
 th hai (Steinwedel-Jensen model), c ng
cc khng l     thay th xen k l t c
             2b).
ng hi t l vi kho R  A
1/3
n
s c
1/3
1K
A
MR


  

(E

)
res
= 60 A
-1/3
(MeV).
t qu vi thc nghim ch ra rng s ph thuc c
 kh  mt
h 
-1/3
+ 20,6 A

-1/6
(MeV).

2. S c h
c xp x  a cng cc khng
l i t i vt










7
 khi t 16 - biu di
-1/3
(MeV)
ng hi vi hng.
Tit din phn t xy ra phn t ht
   ng c  t ti bng 1 ht/cm
2
. a c ng
khng l c biu din gi vi ht
):

22
0

2
2
0
)()(
)(
EEE
E





(1.3)

0
ng cng;  rng cng; 
0
: g tit din
ci.
Bng s t din hp th quang hc
y s hp th ng c
ng khng l.
1.1.3. 
 gi  xui
vi s hp th ng cao (>i v
ng khng l  
dn t a photon v m ht  
photon v. Photon ti s i c-
i cp proton--
ng c hp th ng cn trong hiu ng quan

chi         
n momen ln gii
hai nucleon phi g ng h
t nhc t do. Tit din phn ng ca
gi  biu din bc sau [8]:
D
Z
.
A
Q D D
N
L
   

(1.4)
 s c g  L = 6.8
ng s  L = 10. c-
proton trong h, 





 
D
t din phn ng











8
 do. 
D
t t ci bng hai l
kt c
D
= 2.3 mb t ng photon E

= 4.452 MeV.
  
n c n
tn ti mt s ng nht gia kt qu thc nghi
thuy c cng c c nghi
-proton. S thng nht gia kt qu thc nghit
gi  ra r chi  
hp th photon bp nucleon.
1.2. Ht nhân đng phân



















 ,








 ,  , tr
chn l. 



 








 , 



















 (





 ) 













. Vi










. 



 , 






















xung quan






























.  , 

























 , 























.




 , 









 


 , 


















 , 


















.















 1921. 







1
, 








2
, 




 . 

















1
(

Th
234
90
) [4]:



UX
1

UZ
1

UX
2












9

Pa

234
91
, 





 : UZ
1





1.22 , 
2
6.7 

.















 1934 























 
ng s 










. H 
ng v
Br
80
35
ph



 (18  4.4


). 



 




























Br
80
35















 : 






().


, 

















. 

































 ,  

 (|l| > 4).
 , 






 : ( 1) 












 (2)  .












 ; 











 , 

. 













 
, 



, , 











-

, p,  .




 
 . 



 , 




 : 

















































.











   .
, 














10










 . 









 (n, p, ) 




























 ,



















.
 , 












, 

















 . 





 












 , 





.
 . 
 

























 









. 

,  

























   




 . , 










  











 ()  .  













Br
80
35






.
  . 




















 . 












   .
















 , 





  















. 







(





















 ) 
















 . 








 
: 










  























. 











 







Co
60
27

, 





















 ,
 
-







 0.24% 




99.76%.






 , 












. 











Sb
124
51
,










11
  60 , 20   




























 . 
242
Am, 



 , 





 














1/2
= 1.
-2
s, trong khi
T
1/2
~ 10
8

 . 

,
 









. 





  






 0.393 





 104 . 

, 







, 





 














.





 , 














 

















M, spin I, 



, 

 , th 








.
 . 


 

















. 
 ; 
trong  , 











  

.
 . T
, 












 






 . 

, 






 ,  n (









). 
138



1/2
= 2.
-10






236



1/2

1.3. T s đng phân

(
m
) (
g

):

m
g
IR



(1.5)










12
 , 
 
[11-13]:
high
low
IR



(1.6)





 c x t c, 
nh bng t s s

n 





:
high
low
Y
IR
Y

(1.7)

 



 , 


 , 








 u




, 







.  
[9].



























c
 spin J
c
. 



















, 



c
(E
c
, J
c
) 




c

c
.













 nucleon. 





, 




























. 































 .   , 






. 
i




i


f

f



.
 





 , 
 ,  . 























 qua










 . 
















13
 






( ). 
(E1). 









 . 











 
[9]:
hs
ls
P (E)
IR
P (E)

(1.13)


,  : (1) 


 

 , (2) 



















 ; 













 , (3)









 , (4) 












 ,  (5) spin
.


























,  . 




















:

n 1/2
2
J(J 1)
(J,E) (J) (E) E exp| 2(aE) | (2J 1)exp
2



      



(1.14)
= 0.5/4.2.   off (SCOP)  li




 :

2
2
t


(1.15)


 
.
  


:
(a) 



 
0








 1 


















*



c
= J
0
, J
0











14

1. 
0
= 0 
c
= 1 





 .

c
:

cc
P(J ) 2J 1
(1.16)
(b) 



 (,n), 









*







 





 . 











i

f










:

f
i
i
f
1
J
2
|S J |
f f i l n
l |S J |
1
SJ
2
P(J ) (J )P(J ) T (E )







(1.17)
, T
l
(E
n
) 





 l 
E
n
. 


n








 
:
(1.18)







:
U = at
2
 t (1.19)


, 




















.
(c) 















 








































 1 







sau:

1
2
2
U5
E4
aa





(1.20)













 (



 ). 







f






:

i
f i f
J
P(J ) P(J ) [J ]

(1.21)
(d) 



















  

, 



n.











15
(e) 
 : 







 (COS) 

 , 
















)J(J
2
1
COS
lowhigh

. 










 , 



















[9].






  






 



































 0 (
 ) 












 




 . 





















































 .  , 
 , 
























. 









  , 


. 

, 

































 . 















 



























 . 





 , 


























 .














  Vandenbosch

.
Phn l



 










 nh cho
 , 











 14
MeV. , 
 










 , , alpha.
















 


ch yu  ng cng khng l.


CHƢƠNG 2: PHƢƠNG PHÁP THỰC NGHIỆM











16
2.1. Ngun photon hãm từ máy gia tc Linac
2.1.1. Nguyên lý hot động cu
̉
a ma
́
y gia tô
́
c linac
Ngay t nhu th k 
mut ngun bc x  u c
ca hu thc t t 
ra thit b  t   ng l phc v cho vic
u c Ct ca vt chn d
s t, 



i vt ch u c
cng t c t t nucleon
ra khi hng ct bi lng





(7- 8 MeV). Trong thc t muu c
n ng ht bng t c t
    u c       n cn t 
n nhing
y s ng ch cng thp hoc
a c t cao [3].
Ni Th xu ng s dng ng
bii theo thi gian   gia tc c t
ng lt ca h thng. Ni
Nauy thit k c thng (linac) ba ta
Ising s dng tn s (RF- radio frequency) tn kali
ng 50 keV.
ng
gia tn cc gia tc bng xoay chin s
t tm gin cc. Ht chuyng theo mng thng.
n cc gia tc
bng xoay chin s t tm gin c
ht chuyng theo mng thng.
 c s dng v proton, ion
n i v   l   a ng s rt ln.
i ta khc ph  d  n. Tuy
v gp phi khi s d m











17
cao t khc phc hi ng gia tc
n t  i dng t i
m tn s cng ca h p vi tn s ng gia tc. Pha
cu  mi tru ch c
nhng t t ti v nh c
m cui ca nhng ng dc gia tc.
Vic hi t c thc hin bi t trc to ra t 
ng dng theo mng
thng.
c linac hong vi t ng bii dng sin
c gng gia tc to trong mt th gii
hi hc gia tc (cavity).  m
i vt nh hoc t i vi lo
sut ln. RF linac hong trong gii tn s t 
p cho vic gia tt nh i t
ht ni tn MHz). Ngun h 
loi ngun, ngu
i ngu
2.1.2. Cơ chê
́
ta
̣
o photon ha
̃
m tƣ
̀

ma
́
y gia tô
́
c electron.
ng vt cht s b
mng ch yc x
 mng do va cht qu ca s  i ca
electron vi electron c. Do khng ct nh 
 mng nc gia t
v o c i do l
ca h n ti s bc x n t 
gc x  c nh 
i nhng cc x
 ng gii hn s mc x 
th c lc
x ng l 7].
T mn ca electron trong vt ch
 yu sau [5]:










18

T mn ct cht
 yu sau:

colradtot
dx
dE
dX
dE
dx
dE



























(2.1)
 mng ca 
 mng cc sau:
])11(
8
1
12ln)12(
)1(2
.[ln
4
2222
1
22
2
2
4
2
















I
Evm
vm
en
dx
dE
e
e
e
col
(2.2)
 i ca electron:

2
2
2
1
cm
cm
E
e
e





(2.3)
ng hi  c (2.2) tr 

I
vm
vm
en
dx
dE
e
e
e
col
2
ln
4
2
2
4










(2.4)
ng hi E >> mc
2


]
8
1
12
[ln
2
22
2
2
4












I

E
vm
en
dx
dE
e
e
col
(2.5)
t ni vi electron c hai gii hu
quan tr
e
c
2
= 0,5 MeV, t i ngay c ng
 c 
Khi ht electron chuy  n gn h     
          i dng bc x n
ng gc x ng ca bc x i t c
i bng va electron. S mng h
gng do bc x bc x ng
bc x i vi hc
dt
vd
a



ng h
ng t ng:











19
W =
3
22
c
ze
2
3
2
a

(2.6)

Thay
a

=
m
F


ta thy s mng t l nghch vi
ng ht. Do vy, s mng ch  vi electron ch 
trng vt n mng ca electron ch
yi h 
o.
 mng do bc x  bc sau:
- ng hi, t
e
c
2
:

rad
dx
dE







=
3
16
nE
137
rZ
2
e

2
(2.7)
(g/cm
3
)
A
N
A
(2.8)
  cng, N
A
= 6,02.10
23

kh  ca hng.
r
e
=
2
e
2
cm
e
= 2,82.10
-13
 n ca electron (2.9)
- ng hi vi m
e
c
2

<< E << 137 m
e
c
2
Z
-1/3
:

rad
dx
dE







= nE
137
rZ
2
e
2
(4ln
2
e
cm
E2
-

3
4
) (2.10)
hoi vng hp E >> 137 m
e
c
2
Z
-1/3
:

rad
dx
dE







= nE
137
rZ
2
e
2
(4ln
3/1
Z

183
+
9
2
) (2.11)
T y:

rad
dx
dE







 Z
2
nE (2.12)
t li di v m












20
col







dx
dE
 n
e
 nZ (2.13)
c:
col
(dE/dx)
(dE/dx)
rad
 EZ (2.14)
N  t s gi mc
x  mng:
col
(dE/dx)
(dE/dx)
rad

800

EZ
(2.15)
c (2.15) cho th mc x c
(Z  8) v b mi
vy ra  ng E   
 mc x  b m
c gng ti hn. Trong min ng
ti h   m  ng do bc x   y  
ng electron gi t cht:
E = E
0
rad
x/
e

(2.16)

rad
g c x.
.1 minh ha t mng ca electron b
c x [5].
 , 
 . 














 . Tuy
, 

 ,  : 








,  ; 








; 










; 





 ,  . 

, 
  . , 








 5 30 MeV, 







1mm.










21

. T mng do va chc x ca e trong bia Cu.






 








 , 












 , 





 m
bt s ng c



. 
  
















 . 










, 









. 











 30% 










electron 10 MeV. 2.2 




.

t
o c i do la h i,
c x c x  
  c a electron t biu
din ph bc x a bia W khi bng 50, 60
70 MeV.










22


2.2. 

















, 

.









2.3. 

bc x o b 50, 60 70 MeV t bia


0.1 mm.

0 10 20 30 40 50 60 70
10
2
10
3

10
4
10
5
50MeV
60MeV
70MeV

Thong luong photon ham (/s/cm2)
Nang luong photon ham (MeV)