A new rapid neutron activation analysis system at Dalat nuclear research reactor
Nuclear Science and Technology, Vol. 4, No. 1 (2014), pp. 84-91
A new rapid neutron activation analysis system
at Dalat nuclear research reactor
H.V. Doanh*, C.D. Vu, T.Q. Thien, P.N. Son, N.T. Sy, N. Giang and N.N. Dien
Nuclear Research Institute, 01 Nguyen Tu Luc Street, Dalat, Vietnam
(Received 5 March 2014, accepted 12 March 2014)
Abstract: An auto-pneumatic transfer system has been installed at the Dalat research reactor for rapid
instrument neutron activation analysis based on very short-lived nuclides. This system can be used to
perform short irradiations in seconds either in the vertical channel 13-2 or in the horizontal thermal
column of the reactor. The transferring time of sample from irradiation to measurement position is
approximately 3.2 seconds. A loss-free counting system using HPGE detector has been also setup in
compacting with the pneumatic transfer system for measurement of sample’s activity, automatically
starting for data acquisition at irradiated sample’s arrival. This new facility was tested and shown to
have high potential for the determination of short-lived nuclides with half-lives from 10 100
seconds. This work presents the results of timing parameter measurements, characterization of
irradiation facilities, and application of this system to determining Selenium concentration in several
biological reference materials.
Keywords: Auto-pneumatic transfer system, neutron activation analysis, short-lived nuclides.
I. INTRODUCTION
In the recent years, through the IAEA
TC Project RER/4/028, a new automatic PTS
Instrumental neutron activation analysis
for rapid neutron activation analysis based on
(INAA) has been developed and applied at the
short-lived nuclides has been developed. This
500 kW Dalat research reactor (DNRR) since
facility consists of three main parts introduced
1984. Until now, it is capable of analyzing
in reference [1]. The first part, consisting of
more than 40 elements based on radionuclides
two aluminum irradiation tubes, which are
with short, medium and long-lived time. For
inserted into the vertical channel No.13-2 and
short-lived nuclides with half-lives from 2
the horizontal thermal column (TC) of the
minutes to 2.6 hours, samples are often
reactor. The second part is a digital signal
irradiated at the neutron channel No.7-1 of
processing spectrometer connected to a 40%
Dalat research reactor through a semi-auto
relative efficiency HPGe detector coupled with
pneumatic transfer system (PTS) with valid
a transistor reset preamplifier. The third part is
irradiation time from 45 seconds to 20
composed of pneumatic chambers, loading and
minutes. Measurements are often performed
using a gamma spectrometer coupled with a
HPGe (GMX-30190), but with manual
manipulation between loading and counting
procedures. Therefore, the shortest-lived
sliding devices in Cabin-1 which facilitates the
fully automatic irradiation-counting
procedures. It has also a sample automatic
loader for the sequential routing of the samples
in multi-samples operation mode: when the
measurement for one sample is finished, the
next sample is loaded and sent to the
irradiation and then counting positions. In this
nuclides that could be detected are 28Al (T1/2
=
2.24 min), 52V (T1/2 = 3.75 min), and 51Ti (T1/2
= 5.76 min).
©2014 Vietnam Atomic Energy Society and Vietnam Atomic Energy Institute
HO VAN DOANH et al.
system, there is also has optical sensors for
77mSe, 179mHf, 46mSc, and 110Ag can be used for
INAA at Dalat reactor, which the former
system can not detect.
controlling the transport of the capsule as a
sample carrier, and for accurately measuring
the capsule flight time from irradiation position
to detector. The installation diagram is shown
in Fig. 1.
The main purpose of this work is to test
the system for both mechanical and analytical
reliability. A systematic study has been carried
out including measurements for timing
parameters of the system and neutron flux at
irradiation positions, and the application of this
system to determining of Selenium in a number
of biological reference materials for validation
purpose.
This PTS system can be used to perform
short irradiations in seconds. The return time of
sample from irradiation position to counting
position is about 3.2 s. Timing information for
both irradiation and counting will be instantly
delivered to the activation analysis workstation
computer. The digital gamma spectrometer is
selected and tuned for accurate measurement at
high and varying counting rates, using loss-free
counting technology. Accordingly, shorter-
lived nuclides (half-life < 1 min) such as 20F,
Fig. 1. Diagram of the auto-pneumatic transfer system installed at DNRR.
85
A NEW RAPID NEUTRON ACTIVATION ANALYSIS SYSTEM AT …
II. EXPERIMENT
A. Timing measurements
recorded at the computer via a signal from the
fast solenoid providing the return gas (START
of return time) and from the optical sensor at
the detector station recording the arrival of
capsule (END of return time).
The accuracy of irradiation time of an
irradiation facility should be checked and
calibrated as a type of analytical qualify
control [2]. In this experiment, the absolute
irradiation time, the sample transferring time
from entrance to irradiation position of
aluminum tube (Tin) and the reverse movement
(Tout) were determined. The experiments were
done outside the reactor before installation of
irradiation facilities inside the reactor. The
arrangement of timing measurements is shown
in Fig. 2. The setup includes two NaI(Tl)
detectors placed at the top and bottom sides of
the irradiation tube. The detectors detect
gamma radiation pulses from a 131I source
inserted in a capsule while moving inside. The
counters are set for running in Multi-Channel
Scaler (MCS) mode; MCS mode records the
counting rate of events as a function of time.
B. Neutron spectrum parameters of irradiation
position
The neutron spectrum parameters
including thermal neutron flux th, fast neutron
flux f, the thermal flux to epithermal neutron
flux (epi) ratio were measured at sample
irradiation positions in channel No.13-2 and
thermal column using Au, Zr, and Ni monitors.
Monitors were inserted into a high purity
polyethylene vial and loaded into rabbit
(capsule) for irradiation. The activity
measurements were carried out by a calibrated
gamma-ray spectrometer combined with HPGe
detector (GMX-30190). The measured
spectrum were analyzed by using the k0-IAEA
program. The irradiation, decay and counting
times for each monitor are shown in Table I.
Typically monitors with masses of 4 mg for
Al-0.1%Au foil (IRMM-530R), 30 mg for pure
Ni (wire), 10 mg for Zr (foil) were irradiated
for 10 min at 13-2 channel (2 h at thermal
column), and the decay time is 1 day for 97Zr
and 3 days for 198Au, 95Zr and 58Co.
The return time from the irradiation to
the measurement positions was determined by
a series of irradiation (50 replicates) for a total
weight (capsule, vial and sample) of about 4.4
gram and air pressure of 3.1 bars over a
distance of 40 m for 13-2 channel and 36 m for
thermal column. The return times were
Fig 2. Arrangement for experiment of timing
86
HO VAN DOANH et al.
Table I. The irradiation, decay and counting times for the monitors.
Time/position
irradiation (monitor,
mass)
Decay
time
Counting time
(combination)
Measured
radionuclides
(T1/2, -rays in keV)
10 min/ 13-2 channel
2 hours/ thermal column
(Al-0.1% Au, ~ 4 mg)
(99.8% Zr, ~ 10 mg)
(99.98% Ni, ~ 30 mg)
~ 1 d
~ 3 d
97mNb (60 s, 743.4)*;
97Nb (16.7 h, 657.9)
198Au (2.7 d, 411.8);
95Zr (64 d, 765.8);
58Co (70.8 d, 810.8)
1 2 h
0.5 3 h (5 h)
* Nuclide 97mNb is decayed from nuclide 97Zr with half-life of 16.7h.
C. Determination of Selenium
were irradiated for 25 s, allowed 20 s delay
time to eliminate interference of 116mIn with a
half-life of 2.18 s [3, 4]) and counted for 25 s
at a distance of 10 cm from the detector
(GMX40-76-PL). The concentrations of
Selenium were determined by both k-zero and
relative methods.
A variety of reference materials (Tuna
Fish IAEA-436, Oyster tissue NIST 1566b,
Bovine Liver NIST 1577, Bovine Liver NIST
1577b) were selected to assess reliability of
this system on the short-time activation
application. All of the samples were irradiated
at a neutron flux of 4.21012 n.cm-2.s-1 in the
13-2 channel and counted on the calibrated
HPGe gamma-ray spectrometer (GMX40-76-
PL).
III. RESULTS AND DISSCUSION
A. Timing measurements
The results for average transferring time
of sample from the top to bottom of the
aluminum irradiation tube (Tin) is (0.628
0.021) s for the channel No.13-2 irradiation
tube (a length of 6 m) and Tout is (0.323
0.030) s (averaged for 90 runs over the three
days). For thermal column irradiation tube (a
length of 2.8 m), Tin is (0.248 0.019) s and
Tout is (0.146 0.004) s, as shown in Table II.
The result obtained for measuring the return
time from the irradiation position to the
measurement position was found to be (3.165 ±
0.002) s for channel No.13-2. That for thermal
column was (3.025 0.013) s. It should be
noted that this timing parameters are included
in the time required to start the detector after
receiving the start signal.
In order to evaluate the limit of detection
of Se in biological samples, two 200mg
replicates of each material (IAEA 436 and
NIST 1566b) were weighed and packed in high
purity polyethylene bags. The samples were
irradiated for 5, 10, 15, 20, 25, 30, 35 and 40 s.
After a delay of 3.2 s (including both
transferring time of sample from irradiation
position to detector and the time required to
start the detector). Each sample were counted
for 20 s at a distance of 10 cm from detector.
To test accuracy for the analysis of the
Se concentration in biological reference
materials, four 200 mg replicates of each
material (IAEA 436, NIST 1566b, NIST 1577
and NIST 1577b) were weighed. The samples
87
A NEW RAPID NEUTRON ACTIVATION ANALYSIS SYSTEM AT …
Table II. The result of time measurements.
Irradiation
position
The transferring time throughout
aluminum irradiation tube (second)
The return time from irradiation
position to detector position (second)
Tin
Tout
This word
Manufacturer*
13-2 channel
3.165 ± 0.002
0.628 0.021
0.323 0.030
3.301 0.013
Thermal column
0.248 0.019
0.146 0.004
3.025 0.013
3.261 0.022
* Sample weight: 8 g for thermal column tube and 6 g for 13-2 channel tube,
operation air pressure: 3.1 bars, distance: 30 meters.
There are significant differences
between this work and that of the manufacturer
in capsule sample weight and distance from
irradiation position to measurement position.
Hence, there are differences ( 7%) in the
result of the return time from irradiation
position to detector position. However, it is not
a problem for analytical measurements.
channel No.13-2 and 4.91% for thermal
column. The relative error is less than 1% at
irradiation time of 5 s for channel No.13-2, and
10 s for thermal column. The large error for the
first second is due to delay of the system in
starting the irradiation timer and in ejecting the
capsule once the “end of irradiation” signal has
been received.
This timing delay problem can be
adjusted through the control unit and the
software package for managing optimal
operation and the analytical procedures.
However, it is not a problem for INAA because
the time parameters remain unchanged for all
samples, standards, and control material
Results for absolute irradiation time at
channel No.13-2 and thermal column were
determined by a series of irradiations ranging
from 1 to 30 s (3 replicates), as shown in Fig. 3
and Fig. 4. The relative error of irradiation time
in the first second is 16.02% for channel
No.13-2 and 26.43% for thermal column, and
those for irradiation time of 2 s is 1.5% for
18
16
14
12
10
8
28
24
20
16
12
8
6
4
4
2
0
0
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30
Irradiation time, second
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30
Irradiation time, second
Fig. 3. The relative error of irradiation time
for 13-2 channel.
Fig. 4. The relative error of irradiation time for
thermal column.
88
HO VAN DOANH et al.
B.Neutronspectrumparametersofirradiationpositions
energy [5], measured using the 58Ni(n,p)58Co
nuclear reaction. The thermal neutron flux at
the irradiation position in the thermal column
is 1.25E+11 n.cm2.s-1, associated with much
lower fast and epithermal neutron flux.
Hence, thermal column is a useful irradiation
channel for eliminating interference reactions
induced by fast neutron, in which sample is
irradiated in an extremely well thermalized
neutron field [6].
The results of the determination of
neutron spectra parameters are shown in Table
III. This table includes data obtained for the
thermal, fast neutron flux, the ratio of thermal
to epithermal neutron flux (th/epi). The
thermal neutron flux at the irradiation position
in the channel No. 13-2 is 4.2E+12 n.cm2.s-1,
and associated with 0.5 times of epithermal.
The integral fast neutron flux is 6.61E+12
n.cm-2.s-1 for all neutrons above 2.9MeV in
Table III. The results of neutron spectra parameters at irradiation positions in the channel No.13-2
and thermal column of DNRR.
th (n/cm2/s)
th /epi
F (n/cm2/s)
Irradiation position
(4.2 0.1) x 1012
(6.6 0.9) x 1012
10.7 2.4
13-2 channel
(1.24 0.03) x 1011
(8.4 0.5) x 108
195 4
Thermal column
C. Determination of Selenium
sensitivities for Se rapid determination in a
variety of biological matrices.
Finally, measurements of detection
limits of Se in IAEA 436 and NIST 1566b
samples were performed. The results for these
measurements are presented in Fig 4. The
obtained results confirm that in irradiation
from 15 s to 25 s at irradiation position of the
channel No.13-2 coupled with counting for
roughly 20 s at 10 cm distance from detector,
the detection limits for Se is within the range
0.5 0.7 ppm, depending on the sample
composition. It provides adequate analytical
The accuracy for determination of
Selenium using the short-lived nuclide 77mSe
was evaluated by analyzing a number of
certified reference materials with different
levels of Se (IAEA 436, NIST 1566b, NIST
1577 and NIST 1577b). The agreement
between measured and certified values was
generally very good with u-score < 1.64, as
shown in Table IV.
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
NIST 1566b
IAEA 436
0
5
10
15
20
25
30
35
40
45
Irradiation time, second
Fig. 4. The detection limits of Se in IEAE 436 and 1566b.
89
A NEW RAPID NEUTRON ACTIVATION ANALYSIS SYSTEM AT
For the determination of the Selenium
lived nuclide, not only completion times are a
distinct advantage but analytical sensitivities
are also improved. The data for procedures are
listed in Table V.
by the instrumental neutron activation analysis,
the long-lived nuclide 75Se or the short-lived
nuclide 77mSe can be used [7]. With the short-
Table IV. The results of concentration analysis for Se in biological reference materials.
Certificated
value
(in ppm)
k-zero method
The relative method
This work
Reference
material
This work
(in ppm)
u-score
0.12
u-score
(in ppm)
IAEA 463
NIST 1566b
NIST 1577
NIST 1577b
0.66
0.27
0.29
0.39
4.63 0.48
2.06 0.15
1.10 0.10
0.73 0.06
4.55 0.50
4.19 0.46
0.71
2.48 0.57
1.24 0.31
0.70 0.11
2.18 0.42
1.17 0.22
0.80 0.17
0.43
0.24
Table V. Parameters were used for INAA analysis of Selenium in biological sample by
using 77mSe and 75Se isotopes.
Radionuclide
Half-life
75Se
77mSe
120 d
17.4 s
Activation
20 h at 3.5 x
1012 (n/cm2/s)
1525 s at 4.2
x 1012
(n/cm2/s)
Decay time
Counting time
Detection limit
20 d
23 h
20 s
25 s
1.4 ppm
0.6 ppm
Sample: IAEA
436
4.63 ± 0.48
ppm
4.63 ± 0.48
ppm
The results
4.35 ± 1.1 ppm
4.19 ± 0.46
ppm
column and channel No.13-2 were also
determined in order to establish analytical
procedures using the k0-NAA method. The
system was applied to determine the
concentration of Se in the biological sample by
using the short-lived nuclide 77mSe. The results
obtained through this research have opened a
new possibility on using INAA technique for
measurement of extremely short-lived nuclides
at Nuclear Research Institute.
IV. CONCLUSION
A fast pneumatic sample transfer system
for analyzing of extremely short-lived nuclides
by neutron activation analysis has been
installed and operated at Dalat nuclear research
reactor. In this study, time parameters of the
system were calibrated, thereby reducing
irradiation time to seconds with precision.
Neutron spectra parameters of the thermal
90
HO VAN DOANH et al.
[4] L.S. McDowell, et al., Determination of
ACKNOWLEDGEMENTS
Selenium in individual food items using the
short-lived nuclide 77mSe, Journal of
Radioanalytical and Nuclear Chemistry, Vol.
110, No. 2, p. 519 (1987).
This project was carried out under the
nuclear research and development program of
the Ministry of Science and Technology,
Vietnam.
[5] A. D. Becker, Characterization and use of the
new NIST rapid pneumatic tube irradiation
facility, Journal of Radioanalytical Chemistry,
Vol. 233, No. 1-2, p. 155 (1998).
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[1] S.S. Ismail, A new automated sample transfer
system for instrumental neutron activation
analysis, journal of Automated Methods and
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[6] R. Gwozdz, F. Grass, J. Dorner, Fluorine
analysis of standard materials by short-time
activation analysis using 20F, Journal of
Radioanalytical and Nuclear Chemistry, Vol.
169, No.1, p. 57 (1993).
[2] Yong-Sam Chung, et al., Characteristics of a
new pneumatic transfer system for a neutron
activation analysis at the HANARO research
reactor, Nuclear Engineering and Technology,
Vol. 41, No. 6, p. 813 (2009)
[7] D. Behni, et al., Combination of Neutron
Activation Analysis, Tracer Techniques, and
Biochemical Methods in the Investigation of
Selenium
Metabolism,
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[3] U.M. El-Ghawi, et al., Determination of
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