hiệu chỉnh phổ gamma bằng phương pháp monte carlo

1
MỞ ĐẦU
1. Tính cấp thiết, ý nghĩa khoa học và thực tiễn







             







cao.



2. Mục tiêu, đối tƣợng và phƣơng pháp nghiên cứu



gamma.
Đối tƣợng nghiên cứu 


2
Phƣơng pháp nghiên cứu 

3. Bố cục của luận án
Lpnêu lên các
  
, danh 

CHƢƠNG 1
TỔNG QUAN
1.1. Tổng quan về các vấn đề nghiên cứu
hân tích 

.
Trong  
các  : phông,  
 trùng phùng .
1.1.3. Những vấn đề liên quan đến luận án



, 

            


và 

152
Eu và

134
Cs.

3







  





 

1.2. Hiệu chuẩn hệ phổ kế gamma
1.2.1. Hiệu suất đỉnh năng lƣợng toàn phần (FEPE)

P
ε
) 
gamma phát ra  
[18], [22].       
 

 

   
 
p
i
P
i
N E B E
EC
A.I E .t




  
(1.1)
t:

p
(E):
N
P
(E): 
B(E): hông.
γ
I
(E): 
A: 

4
T : 

i
i
C
: 

1.2.2. Hiệu suất tổng (TE)

T
ε
) 
    trong     [18],
[22].

241
Am,
109
Cd,
51
Cr,
203
Hg,
137
Cs,
54
Mn,
65
Zn . . .)
[6], [57]:

 

R
T
i ETZ
i ETZ
N E C AvgC .ETZ



(1.2)
 , N
T
(E) R 
, C
i
là h i, AvgC
ETZ
là 

 sau:

 
   
 
T
T
γ
N E - B E
ε E =
A.I E .t



(1.3)
t 
 
T
εE
   ,
 
T
NE
:  , B(E):  
phông, A: ,
γ
I
(E): , t là
 (s).

CHƢƠNG 2
NGHIÊN CỨU HÀM ĐÁP ỨNG CỦA HỆ PHỔ KẾ GAMMA
SỬ DỤNG ĐẦU DÕ HPGe BẰNG CHƢƠNG TRÌNH MCNP5
2.2. Giới thiệu chƣơng trình MCNP
MCNP [1], [2], [6], [60]       
Monte   

5

 ).
2.2.2. Cấu trúc của chƣơng trình MCNP







2.2.3. Đánh giá phân bố độ cao F8

 và


Tuy nhiên,



              
gamma (GEB).
2.3.1. Phổ đơn năng
  -LNHB
 
54
Mn,
109
.
 
54
Mn  , k  
toàn

            
109




6

Hình 2.9

54
Mn -LNHB

Hình 2.11

109
-LNHB
 th
109
     -50keV

     


7

109
Cd.
2.3.2. Phổ đa năng

88

          


-gamma và gamma -tia X.

Hình 2.15

88
Y trên -LNHB





152

          tia X và  
gamma), tia X (39,5keV.
        
152
E   



8

Hình 2.16
152
-LNHB eV
 


Hình 2.17 

152
-LNHB  400keV

9
2.3.3. Phổ nguồn đa đồng vị
Hình 2.18 và 2.19  



Hình 2.18 
-LNHB eV

Hình 2.19
-LNHB  400keV

10
2.4. Kết luận chƣơng 2
 
             

 

      

54
-

109
Cd. 



109
Cd.


57
Co,
60
Co,
88


57
Co có

gamma-
152
Eu




241
Am,
109
Cd,
57
Co,
139

Ce,
51
Cr,
113
Sn,
85
Sr,
137
Cs,
60
Co,
88

1836,06keV 


CHƢƠNG 3
TÍNH TOÁN HỆ SỐ TRÙNG PHÙNG TỔNG SỬ DỤNG PHƢƠNG
PHÁP MONTE CARLO ĐỂ XÁC ĐỊNH HIỆU SUẤT TỔNG
3.1. Nghiên cứu ảnh hƣởng của quá trình thứ cấp lên phổ gamma

11
3.1.1. Ảnh hƣởng tán xạ từ giá đo và buồng chì

.

Hình 3.1: 
G

 có  không

  


Hình 3.4, 3.5, 3.6 và 3.7   
60
Co
và
54




tán x


12

Hình 3.4
60
 eV

Hình 3.5 
60
Co 500keV 

Hình 3.6 
54
Mn  


13

Hình 3.7 
54
Mn  500keV 

 
54
Mn và
60


 không
-14%.
Bảng 3.1 


(1)

(2)

 
chì (3)

(2)/(1)

(3)/(1)
54
Mn
1125834

1110170
971153
0,99
0,86
60
Co
2211212
2207668
1942414
1,00
0,88


(1)

chì  có giá


chì  không


(4)/(1)

(5)/(1)
54
Mn
1125834
1074735
923348
0,95

0,82
60
Co
2211212
2113792
1852026
0,96
0,84

14
 
-
-
3.4. Hiệu chỉnh trùng phùng tổng
3.4.1. Xác định hệ số trùng phùng tổng cho nguồn dạng hình học
điểm
nh ETNA [34] 
trùng phùng  
LNHB.   

134
Cs và
152
Eu.
3.4.2. Xác định hệ số trùng phùng tổng cho nguồn dạng hình học trụ

 
152
Eu và
134

Cs 
t  
có  dày 1,12mm và plastic dày 1,5mm.
3.5. Kết luận chƣơng 3
 gamma 
             
500keV   ng góp chính vào
 .




152
Eu và
134



CHƢƠNG 4
PHÂN TÍCH HOẠT ĐỘ CỦA CÁC ĐỒNG VỊ PHÓNG XẠ
TRONG MẪU MÔI TRƢỜNG
4.1. Xác định hệ số suy giảm tuyến tính

15
P           
 
          .   
 
 
.

Hình 4.2: Pgamma  
133
Ba
 GC20- -447

Hình 4.3
-447

16







226
Ra.
4.2. Cải tiến buồng chì của hệ phổ kế GC20-VLHN
-
Hình 4.6 trình

GC20-



Hình 4.6



 

17

Hình 4.7

Hình 4.8

 


4.4.3. Xác định hoạt độ phóng xạ của mẫu

18
             
và hình
  [18], [22]:

   
   
p
i
i
P
N E B E
AC
E .I E .t





 

(4.2)
trong 
A (Bq).

p
(E)
N
P
(E)
,
 
γ
IE

t (s),
i
i
C
là .
4.4.4. Tiêu chuẩn đánh giá của IAEA
- 

22
ref lab ref lab
A A 2,58 u u   
(4.8)
t A

lab
là ho, A
ref

, u
lab
 u
ref

IAEA. H%.
- 

22
ref lab
ref lab
uu
P 100%
AA
   
  
   
   
(4.9)
 p  (A)

P LAP
(4.10)
LAP (g
nguyên IAEA.
 iá

i). Khi
RB<MAB, thì  (W)
là  (F)

19
[48].

riêng . 

-

4.4.5. Kết quả phân tích đối với mẫu IAEA-385

 .
Bảng 4.10-385 theo LAP và MAB
ng
v
Ho
(Bq/kg)
Sai s
(Bq/kg)
IAEA
[62]
(Bq/kg)
Sai s
(Bq/kg)

chính
xác
 tin

cy
(%)
Kt
lun
210
Pb
45,27
16,12
22,60
1,40
P
F
N
241
Am
8,46
0,83
4,10
0,31
F
P
W
234
Th
37,74
5,32
28,70
5,85
P
P

A
226
Ra
30,86
3,57
21,90
0,45
P
P
A
212
Pb
35,53
0,74
37,30
3,00
P
P
A
214
Pb
22,19
0,59
21,60
1,20
P
P
A
228
Ac

35,00
1,51
31,50
1,40
P
P
A
208
Tl
12,37
0,45
11,60
2,10
P
F
W
214
Bi
22,35
0,67
19,60
1,10
P
P
A
137
Cs
26,45
0,60
25,00

0,85
P
P
A
40
K
595,98
15,10
607,00
9,00
P
P
A


20

  2 


241


208
t qua

4.4.6. Kết quả phân tích của mẫu IAEA-434

 . 
 


Bảng 4.12-434 theo LAP và MAB
ng
v
Ho
(Bq/kg)
Sai s
(Bq/kg)
IAEA
[61]
(Bq/kg)
Sai s
(Bq/kg)

chính
xác
 tin
cy
(%)
Kt
lun
210
Pb
648,96
89,69
680,00
29,00
P
P
A

234
Th
129,62
17,74
120,00
6,00
P
P
A
226
Ra
715,21
18,04
780,00
31,00
P
P
A

4.4.7. Kết quả phân tích của mẫu IAEA-447
B.

.
-434
(phosphogysum) và IAEA-447 (moss-soil) và IAEA-
 so sánh 



21

Bảng 4.14-447 theo LAP và MAB
ng
v
Ho
(Bq/kg)
Sai s
(Bq/kg)
IAEA
[61]
(Bq/kg)
Sai s
(Bq/kg)

chính
xác
 tin
cy
(%)
Kt
lun
210
Pb
421,54
54,15
420,00
10,00
P
P
A
234

Th
24,43
2,08
25,50
1,50
P
P
A
226
Ra
24,96
1,64
25,10
1,00
P
P
A
212
Pb
33,49
0,91
37,00
0,25
P
P
A
214
Pb
21,18
0,19

26,00
5,00
P
P
A
228
Ac
36,54
2,94
37,00
1,00
P
P
A
208
Tl
11,88
0,34
13,00
1,00
P
P
A
214
Bi
16,29
0,18
24,80
1,00
P

P
A
137
Cs
430,99
9,78
425,00
10,00
P
P
A
40
K
536,98
13,84
550,00
0,75
P
P
A

KẾT LUẬN
  
 
 có   

1. Kết quả thu đƣợc
           





22
 






khác.
             -
y 
           
.

   
 


.
-
434 (phosphogysum), IAEA-447 (moss-soil) và IAEA-385 (sediment) có

 
IAEA.
2. Những điểm mới của luận án
1. 

Đây đƣợc xem là nghiên cứu mới của luận án.

23
2.           

IAEA-385 (sediment). Đây đƣợc xem là nghiên cứu mới của luận án.
3. 
Đây đƣợc xem là nghiên cứu mới của luận án.

Kiến nghị về hƣớng nghiên cứu tiếp theo


1.  dò HPGe 
. 

2.    
GC20-VLHN  VLHN 


DANH MỤC CÁC CÔNG TRÌNH CỦA TÁC GIẢ
          
 Carlo

 Tạp chí khoa học và
phát triển công nghệ
33-40.
[2]. Truong Thi Hong Loan, Tran Thien Thanh, Dang Nguyen Phuong,
Tran Ai Khanh and Mai Van Nhon (2007), Monte  Carlo simulation
of HPGe detector response function with using MCNP code,
Communication in Physics, Vol 17, No 1, 59-64.
[3]. Truong Thi Hong Loan, Tran Thien Thanh, Dang Nguyen Phuong,

Tran Ai Khanh, Mai Van Nhon and Le Van Ngoc (2007), Gamma

24
spectrum simulation and coincidence summing factor calculation for
point sources with using MCNP code, Communication in Physics,
Vol 2, No 2, 110-116.

        

Monte  Carlo, Tạp chí khoa học và phát triển công nghệ
-66.
 

             
 Tạp chí khoa
học và phát triển công nghệ 
10, trang 66-76.
[6]. Tran Thien Thanh, Chau Van Tao, Marie Christine Lépy, Laurent
Ferreux (2010), The self  absorption corrections for marine sediment
sample in gamma      
Academic Conference on Natural Science for Master and PhD
Students from Cambodia - Laos  Vietnam, VNU-HCM publishing
house, 115-121.
[7]. Tran Thien Thanh, Hoang Duc Tam, Chau Van Tao, Truong Thi Hong
Loan (2010), Determination of activity of radionuclides in Moss-soil
sample with self-absorption correction, Proceeding of the topis
conference on Nuclear physics, High energy physics and
astrophysics (NPHEAP-2010), Science and technics publishing
house, 262-267.
[8]. M.C. Lépy, Chau Van Tao, Tran Thien Thanh et al (2010),

Intercomparison of Methods for Coincidence summing corrections in
gamma ray spectrometry, Applied Radiation and Isotopes 68, Issues

25
7-8, 1407-1412.
[9]. T.T. Thanh, L. Ferreux, M.C. Lépy, C.V. Tao (2010), Determination
activity of radionuclides in marine sediment by gamma spectrometer
with anti cosmic shielding, Journal of Environmental radioactivity
101, Issue 9, 780-783.
        
Tạp
chí Khoa học ĐHSP Tp.HCM-120.
[11]. Hoang Duc Tam, Tran Thien Thanh, Chau Van Tao, Le Thi Yen Oanh
(2012), Detemining attenuation coefficients of gamma rays in range
of energy from 81.0 keV to 1764.5 keV for some materials, Tạp chí
Khoa học ĐHSP Tp.HCM-67.


     , Tạp chí Khoa học ĐHSP
Tp.HCM-91.
[13]. M. C. Lépy, Chau Van Tao, Tran Thien Thanh et al, (2012),
Intercomparison of Methods for Coincidence summing corrections in
gamma ray spectrometry  Part II (Volume sources), Applied
Radiation and Isotopes 70, 2112-2118.
[14]. Tran Thien Thanh, Chau Van Tao, Hoang Duc Tam, Vo Thi Hong
Yen, (2012), Study the effect of natural background for gamma
spectrometer system, Journal of Science and Technology
Development, Vietnam National University  
16-23.
[15]. T. T. Thanh, C. V. Tao, T. T. H. Loan, M. V. Nhon, H. D. Chuong and

B. H. Au (2012), A detailed investigation of interactions within the
shielding to HPGedetector response using MCNP code, Kerntechnik
77/6, 458-461.