Post on 15-Jan-2016
description
Neutron Capture Cross Sections from 1 MeV to 2 MeV by Activation Measurements
Korea Institutes of Geoscience and Mineral Resource
G.D.Kim, T.K.Yang, Y.S.Kim, H.J.Woo, H.W.Choi, and W. Hong
Korea Atomic Energy Research Institutes
J.H.Chang
Introduction
Activation method : Historically first means of measurement of NCCS in MeV range
relatively simple to carry out
completely selective for a given nuclide in a mixture of target isotopes
Energies : 1 MeV to 2 MeV fusion reactor material research
Material : 63Cu and 186W
Mono-energetic fast neutrons source : 3T(p,n)3He reaction.
In KIGAM NCCS are being measured by activation method
In KIGAM neutron facility
Proton energy stability of the used accelerator : within 1keV
Producible maximum neutron energy : 2.6 MeV
Target Analysis
RBS ERD
T : 4.6 x 1018 atoms/cm2 , Ti : 1.4 x 1019 atoms/cm2
TiT target
Neutron Energy Spread
Calculated neutron energy [keV]1950 2000 2050 2100 2150 2200 2250 2300 2350
Nor
mal
ized
yie
ld [C
ount
s/10
0uC
]
2.0e+4
4.0e+4
6.0e+4
8.0e+4
1.0e+5
1.2e+5
1.4e+5
1.6e+5
=12.2
En = 2077 keV
background
12C(n,tot)
fitting data
Calculated neutron energy [keV]1500 1550 1600 1650 1700 1750 1800
Nor
mal
ized
yie
ld [c
ount
s/10
0uC
]
40000
45000
50000
55000
60000
65000
70000
75000
80000
1669
=1416O(n,tot)
measured2 =resonance
2 + tithick2 , : NES 1.3 % at 2.1 MeV
NES 1.7 % at 1.67 MeV
Neutron Pulse Shape and Height Spectrum
KIGAM neutron facility
detector
sample beam
Cooling system
monitor
Target chamber
D =No act
(1-e e 1-e R d
-t1 -t3 )( )(
Dgamma counts per unit time, No : areal density of sample
: neutron flux, act : neutron captured cross section
: decay constant of activated sample
t1 : neutron irradiation time
t2 : elapsed time from irradiation to measurement
t3 : measured time of gamma ray, R : transition probability
d : absolute gamma ray efficiency
-t2 )
Neutron Captured Cross Section
f(t) ;time dependence factor, subscript“o” refers to standard reaction
Do = No o o Ro o fo/o …… (1)
D = N R f/…… (2)
(1)/(2) =
Do N R f o
D No o Ro o fo o
=0.693/t ½ , / = (pho/to)/(ph/t) , t :neutron irradiation time
= Do N (ph) to R f t1/2,0
D No (ph)o t Ro o fo t 1/2 o
Characteristics of Sample
Purity(%) Weight(g) diameter Thickness(cm)
Density(g/cm3)
Molecular weight(g)
ArealDensity(1022 ions/cm2)
Au-1 99.99 117.34 5.090 0.310 19.282 196.97 1.7633
Au-2 99.99 122.84 5.115 0.315 19.282 196.97 1.8280
Cu 99.99 111.85 5.050 0.604 8.92 63.546 5.3800
W 99.95 223.54 5.015 0.595 19.35 183.85 3.7299
Abundance : 63Cu = 69.2 %of Cu, 186W=28.6 % of W
Absolute Efficiency of HPGe detector
species Gamma energy[keV]
Thickness[mm]
Calculatedefficiency
Au 411 3.1 or 3.15
0.0285 or 0.0280
Cu 511 6.04 0.0290
W 686 5.95 0.0183
By MCNP code and standard mixed source
Transition Probability
Z
n
Z-1 Z+1
Z
A
A+1
A+1A+1
Z A+1*
Z+1* A+1
Z-1 A+1*
EC
transition Gamma energy[keV]
Transitionprobility
198Au-198Hg(-) 411 0.9503
64Cu-64Ni(+) 511 0.1750187W-187Re(-) 686 0.1499
By Table of Isotopes
Gamma Spectrum of 198Au
411 keV
Gamma Spectrum of 64Cu
511 keV
Gamma Spectrum of 187W and Background
686
479
Neutron energy(MeV) Irradiationtime(hr)
Elapsed timefrom
irradiationto
measurement(hr)
Neutron flux
Gamma
counts
(n,)cross section(mb)
Statis-tical
Error(%)
2.015 197Au 0.982 0.040 9,542,379
5,057 53.4
63Cu 0.792 0.144 9,578,893
1,811 5.44 2.91
1.813 197Au 0.584 0.071 9,793,896
5,315 59.6
63Cu 0.413 0.374 9,720,648
1,760 5.49 2.93
1.611 197Au 0.549 0.128 8,319,212
4,663 66.5
63Cu 0.625 0.050 8,460,925
1,814 7.21 2.91
1.409 197Au 0.682 0.243 6,444,751
4,479 69.4
63Cu 0.869 0.031 6,014,762
1,630 7.67 3.10
Measured Data Table
Neutron energy (MeV) 0 1 2 3 4R
adia
tive
capt
ured
cro
ss s
ectio
n [m
b]
0
4
8
12
16
20
63Cu(n,g)
P.White et. els
ENDF-6
OURS
V.A.TOLSTIKOV
Neutron Captured Cross Sections of 63Cu
Neutron energy [MeV]
0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8
Neu
tron
cap
ture
cro
ss s
ectio
n [m
b]
15
20
25
30
35
40
45
50
55
M.Lindner (J.NSE.59,381,197604)
P. White (J.NE. 19,325,1965)
ours
ENDF-6
Neutron Captured Cross Sections of 186W
t
ln IoI
( )
No
I : neutron counts in sample–in
Io : neutron counts in sample-out
No: areal density of sample
In scattering correction factor
Dt = (/4) (DL/L1L2)2 n(0o)
n(0o)= (kR +1)4/4k2 : diffraction theory based on a continuum model
R = 1.33 A1/3 10-13 cm, D is diameter of detector
L is distance from target to detector, L1 is distance from target to sample
L2 is distance from detector to sample
Total Cross Section
Neutron energy [MeV]0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Tot
al n
eutr
on c
ross
sec
tion
[bar
n]
0
1
2
3
4
5
6
Cu(n,tot)
Ours
Miller (52)
JEF-2.2
Total Cross Sections of Cu
Channel number
0 200 400 600 800 1000
Cou
nts
0
300
600
900
1200
1500
1800
Gamma Neutron
Sample in
Sample out
Total Cross Sections of W
Neutron energy [MeV]
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
Tot
al c
ross
sec
tion
[bar
n]
5.5
6.0
6.5
7.0
7.5
8.0
ours
P.W.Miller
ENDF-6
Results
Neutron capture cross sections of 63Cu and 186W
Total scattering cross section of Cu and W
Geometric Efficiency of HP Ge detector