Progress of filtered neutron beams development and applications at the horizontal channels No.2 and No.4 of Dalat nuclear research reactor

he utilizations 
of the Dalat research reactor for researches and 
applications based on the neutron capture 
PROGRESS OF FILTERED NEUTRON BEAMS DEVELOPMENT AND APPLICATIONS AT  
 64 
reactions, the well thermal neutron beam at the 
channel No. 2 has been developed and serviced 
since 2011 [4]. The neutron filters for this 
0.0253eV neutron beam line are single crystals 
of 80cm Si and 6cm Bi. The measured thermal 
neutron flux at outer position of the beam line 
is 1.6 106 n/cm2.s, and the value of Cadmium 
ratio Rcd(Au) is 420. 
The neutron beams of 54keV and 148keV: 
The neutron filter technique has been 
applied at the horizontal channels of Dalat 
nuclear research reactor from 1990s [2, 3]. 
Firstly, the two neutron beams with mono-
energies of 54keV and 184keV were created at 
the channel No.4, and provided a good 
experimental station for basis researches on 
reactions of neutron with material in keV 
energy region. The filter information and 
physical parameters of these neutron beam 
lines are introduced in Table I [3], and the 
corresponding neutron spectra are shown in 
Figs. 3-4. 
Table I. Physical parameters of the 54keV and 148keV neutron beams at the channel No.4 
Parameters 54keV 148keV 
Neutron flux (n/cm
2
.s) 6.7x10
5
 3.9x10
6
Energy resolution (keV) 1.5 14.8 
Peak relative intensity (%) 78.05 95.78 
Beam collimated diameter 3 cm 3 cm 
Filter compositions 
B 0.2g/cm
2
Si 98cm 
S 35g/cm
2
B 0.2g/cm
2
Si 98cm 
Ti 1cm 
Fig. 3. Energy spectrum of the 148keV neutron beam at 
the channel No.4 of DNRR 
Fig. 4. Measured energy spectrum of the 54keV neutron 
beam at the channel No. 4 of DNRR 
0 200 400 600 800 1000 1200
0
2000
4000
6000
8000
10000
12000
14000
 Exp. data
 Fitted line
 Intensity
Channel
C
o
u
n
ts
0
1000
2000
3000
4000
1
4
8
k
e
V
In
te
n
s
ity
 (a
.u
)
5
4
k
e
V
0
20
40
60
80
100
120
140
160
180
200
8.0E+04 1.2E+05 1.6E+05 2.0E+05
Neutron energy (eV)
R
el
at
iv
e 
in
te
ns
ity
Unfolding spectrum
Transport calculation
VUONG HUU TAN, PHAM NGOC SON, NGUYEN NHI DIEN, TRAN TUAN ANH, NGUYEN XUAN HAI 
65 
The neutron beams of 24keV, 59keV and 133keV: 
As progressive necessary of reactor 
based mono-energetic neutron beam lines for 
experimental researches on neutron 
interaction with mater, the new three filtered 
neutron beam of 24keV, 59keV and 133keV 
have been developed and applied from 2008 
[3] based on the neutron source from the 
channel No. 4 of DRR. The characteristics of 
these neutron beam lines are introduced in 
the references [6, 7], and summarized in 
Table II. The calculated and measured energy 
spectra of these neutron beam lines are 
shown in Figs. 5-7. 
Fig. 5. Measured neutron spectrum for 24keV beam by 
proton recoil proportional counter 
Fig. 6. Calculated neutron spectrum for the 59keV 
filtered neutron beam 
Table II. Characteristics of the 24keV, 59keV and 133keV neutron beams at the channel No.4 
Parameters 24keV 59keV 133keV 
Neutron flux (n/cm
2
.s) 6.1x10
5
 5.3x10
5
 3.2x10
5
Energy resolution (keV) 1.8 2.7 3.0 
Peak relative intensity (%) 96.72 92.28 92.89 
Beam collimated diameter (cm) 3 3 3 
Composition of Filters 
B 0.2g/cm
2
Fe 20cm 
Al 30cm 
S 35g/cm
2
B 0.2g/cm
2
Ni 10cm 
V 15cm 
Al 5cm 
S 35g/cm
2
B 0.2g/cm
2
Cr 50g/cm
2
Ni 10cm 
Si 60cm 
5.0x10
-2
1.0x10
-1
1.5x10
-1
2.0x10
-1
0.0
2.0x10
2
4.0x10
2
6.0x10
2
8.0x10
2
1.0x10
3
 CFNB
 MCNP
In
te
n
s
it
y
 (
a
.u
)
E
n
 (MeV) 
Fig. 7. Calculated neutron spectrum for the 133keV filtered neutron beam 
PROGRESS OF FILTERED NEUTRON BEAMS DEVELOPMENT AND APPLICATIONS AT  
66 
III. NUCLEAR DATA MESUREMENTS 
Neutron capture cross section measurements: 
The measurements of neutron capture 
cross sections for a number of nuclides have 
been performed on the filtered neutron beams 
with mono-energies of 24, 54, 59, 133 and 148 
keV, at the Dalat nuclear research reactor. The 
measured neutron capture cross sections data 
were obtained relative to the standard capture 
cross sections of the 
197
Au(n,)198Au reaction 
by the activation method. An abridged 
description of data analysis procedure is 
presented as follows: 
The average capture cross sections, 
x
, for nuclide x at average neutron 
spectrum can be determined relative to 
that of 
197
Au standard by the following 
relations: 
 ;
),(
),(
xxxAu
c
AuAu
Au
a
AuAuAux
c
xx
a
NIftfC
NIftfC





 (2) 
)1()1(
),(
321 ttt eee
tf



 , (3) 
where the superscript „x‟ denotes sample 
nucleus, and „Au‟ denotes the reference 
nucleus 
197Au. „C‟ stands for net counts of 
the corresponding gamma peak. „t1‟, „t2‟ and 
„t3‟ are irradiating, cooling and measuring 
times, respectively. „λ‟ is decay constant of the 
product nucleus; „εγ‟ is the detection efficiency 
of detector; „Iγ‟ is the intensity of interesting γ-
ray, and „fc‟ is the correction factor for self-
shielding multiple scattering effects that can be 
exactly calculated by the Monte Carlo method. 
In recent years, we have conducted a 
series of cross section measurements for 
neutron capture (n, ) reactions in different 
nuclides, and reported in scientific papers such 
as: 
109
Ag, 
186
W, 
158
Gd [8]; 
139
La, 
152
Sm, 
191
Ir, 
193
Ir [9]; 
185
Re and 
187
Re [10, 11]. In addition, 
the horizontal thermal Column of DNRR, a 
well thermalized neutron channel, has been 
also used for measurement of thermal neutron 
capture cross section and resonance integral of 
69
Ga and 
71
Ga [12]. A typical result of our 
measurements in comparison with data from 
other laboratories is shown in Fig. 7 [10]. 
Fig. 7. Neutron capture cross section of 
185
Re [10] 
Measurements of neutron total cross sections: 
The total neutron cross section 
measurements are being carried out by the 
transmission method for natural elements of U, 
C, Fe and Al, at the filtered neutron energies of 
24keV, 54keV, 59keV, 133keV and 148keV. 
The experimental value of neutron total cross 
section, t, can be exactly determined from the 
following expression: 
 0
1 1 1
ln lnt
d T d

 
 
, (4) 
where „T‟ is transmission coefficient of 
the collimated neutron beam that transmitted 
through a purity sample with thickness d 
(cm); „ ‟ denotes density of the sample 
(Atom/cm
3). „0‟ and „‟ are measured 
neutron fluxes at before and after positions of 
the irradiating sample, respectively. A 
measurement of the transmission spectrum for 
0.1
1
10
1.E+04 6.E+04 1.E+05 2.E+05
Neutron energy (eV)
C
ro
s
s
 s
e
c
ti
o
n
 (
b
a
rn
)
ENDF/BVII
YU.N.TROFIMOV
M.LINDNER
S.J.FRIESENHAHN
A.K.CHAUBEY
R.P.ANAND
A.A.BERGMAN
This w ork
185Re(n,γ)186Re
VUONG HUU TAN, PHAM NGOC SON, NGUYEN NHI DIEN, TRAN TUAN ANH, NGUYEN XUAN HAI 
67 
54keV neutron beam at the channel No.4 of 
DNRR is shown in Fig.8. 
Fig. 8. Measured neutron spectrum of 54keV 
neutron beam transmitted through different 
thickness of C sample. 
IV. PGNAA APLICATIONS 
From 1998, the 148keV filtered neutron 
beam at the channel No.4 has been applied for 
possibility studies the method of in-vivo 
prompt gamma neutron activation analysis 
(IVPGNAA) that involves the exposure of the 
living human organs to a small dose of 
neutrons. At that time, IVPGNAA is a new 
technique for directly determination of toxic 
elements accommodated in a specific living 
human organ such as concentrations of Hg in 
kidney and Cd in liver. The research was 
carried out on a physical phantom installed at 
the channel No.4 [13]. The results given from 
this investigation introduced a high effective 
new experiment with 148keV neutron beam 
instead of thermal neutrons [13]. 
The low background and well thermal 
filtered neutron beam from the channel No.2 
[4] of Dalat nuclear research reactor is an 
advantage neutron source for prompt gamma-
ray neutron activation analysis (PGNAA). 
Accordingly, a modern Compton suppression 
PGNAA spectroscopy used a compact system 
of BGO-HPGe detectors was completely 
developed and installed at the experimental 
space of this beam port, from 2012. A 
preliminary study on calibration and analytical 
sensitivity for several domination elements has 
been conducted. A prompt gamma-ray 
spectrum of geometrical sample measured in 
single and Compton-suppression modes is 
shown in Fig.9. The results in this study allows 
us to estimate that the new PGNAA facility 
installed at the channel No.2 of DNRR is 
qualified to participate in analytical services at 
the Institute. A calibration curve for Boron 
analysis is presented in Fig.10, and the results 
of comparison analysis used standard soil 
sample (NIST-2711a) is given in Table III. 
Fig. 9. Prompt gamma-rays spectrum measured at 
the thermal neutron beam No.2 for soil sample, in 
single and Compton-suppression modes. 
10 20 30 40 50
0
5
10
15
20
25
c
p
s
g B
 Exp data
 Linear fitting
Model Line
Equation y = A + B*x
Reduced 
Chi-Sqr
0
Adj. R-Square 1
Value Standard Error
cps A -2.799 0.158620
cps B 0.520 0.00544162
Fig. 10. The calibration curve for Boron analysis by 
using the PGNAA facility at the channel No.2 
PROGRESS OF FILTERED NEUTRON BEAMS DEVELOPMENT AND APPLICATIONS AT  
68 
Table III. The results of comparison analysis used the standard soil sample (NIST-2711a), by using the 
PGNAA facility at the channel No.2 
Sample 
NIST-2711a 
(Standard sample: Montana soil) 
Elements Measured values Reference values 
B (g/g) 50.5 ± 2.9 50 
Gd (g/g) 7.59 ± 3.34 5 
Sm (g/g) 6.96 ± 1.07 5.93 ± 0.28 
Ca (%) 2.43 ± 0.59 2.42 ± 0.06 
Al (%) 7.1 ± 0.3 6.72 ± 0.06 
Si (%) 31.66 ± 3.93 31.4 ± 0.7 
K (%) 2.39 ± 0.28 2.53 ± 0.10 
Ti (%) 0.29 ± 0.06 0.32 ± 0.01 
Na (%) 2.02 ± 0.48 1.20 ± 0.01 
Fe (%) 3.01 ± 0.35 2.82 ± 0.04 
V. CONCLUSIONS 
The accomplishment of research 
activities on the topics of filtered neutron 
beams development and it‟s applications based 
on the neutron sources from the horizontal 
channel No.2 and No.4 of Dalat nuclear 
research reactor is reviewed in this report. The 
neutron filter technique has been effectively 
applied to provide mono-energetic neutron 
beam lines with qualified characteristics for 
related applications at the Nuclear Research 
Institute, VINATOM. The basis researches on 
experimental neutron induce nuclear reaction 
cross sections conducted by using these 
neutron beams have been performed with 
interesting results, and this research activity is 
proposed to be continued, in order to 
participate in providing of precise experimental 
nuclear reaction data and educational 
experiments. The new PGNAA facility 
installed coupling with the well thermal 
neutron beam at the channel No.2 plays as an 
important application of this channel for 
studies on neutron capture experiments and 
elemental analysis. This will be an important 
supplementation to the neutron activation 
analysis (NAA) method at the Dalat research 
reactor. 
The new development of neutron beam 
with possible mono-energy of 2keV, and 
extension of application studies such as Boron 
neutron capture therapy (BNCT) and neutron 
dosimeter calibration are proposed. 
ACKNOWLEDGEMENTS 
This research is partly funded by 
Vietnam National Foundation for Science 
and Technology Development 
(NAFOSTED) under grant number “103.04-
2012.59”. The authors are immensely 
grateful to Mr. Luong Ba Vien, Deputy 
Director of the Nuclear Research Institute, 
VINATOM, for his great encouragement 
and critical reading of the manuscript. 
VUONG HUU TAN, PHAM NGOC SON, NGUYEN NHI DIEN, TRAN TUAN ANH, NGUYEN XUAN HAI 
69 
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