The role of soil in NBT applications to landmine detection
problem
Jasmina Obhođaš*, Davorin Sudac*, Karlo Nađ*, Vlado Valković*1, Giancarlo
Nebbia**, and Giuseppe Viesti**
*Department of Experimental Physics, Ruđer Bošković Institute, Bijenička c.54, 10000 Zagreb, Croatia.
**Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Via Marzolo 8, 35100 Padova, Italy
1
Corresponding author: Vladivoj Valkovic, Institute Ruder Boskovic, Bijenicka c.54. 10000 Zagreb, Croatia, Email: [email protected] Tel: +385-1-468-0101; Fax: +385-1-468-0239
Abstract. Long-term observations of soil water content as well as determination of physical and chemical properties of
different types of soils in Croatia were made in order to provide the necessary background information for landmine explosive
detection. Soil water content is the key attribute of soil as a background in neutron backscattering technique (NBT) landmine
detection application. If the critical value of the soil water content is reached, the detection of landmine explosives is not
possible. It is recommended that soil moisture content for NBT application does not exceed 0.1 kg.kg-1 [1].
Nineteen representative samples of different soil types from different parts of Croatia were collected in order to establish soil
bank with the necessary physical and chemical properties determined for each type of soil. In addition soil water content was
measured on daily and weekly basis on several locations in Croatia. This procedure also included daily soil moisture
measurements in the test field made of different types of soils from several locations in Croatia. This was done in order to
evaluate the behavior of different types of soils under the same weather conditions.
1. INTRODUCTION
2. MATERIALS AND METHODS
Nineteen soil samples were collected from different
parts of Croatia in order to make a soil bank available
for testing and evaluating NBT and other mine
detection methodologies (Fig.1). These samples
represent different soil types, vegetation, ground
configuration and climate zones in land mine
contaminated
areas
of Croatia. Preliminary
determination of some basic physical and chemical
properties (texture, silicate analysis, major and trace
element analysis) for all soils has been performed. Soil
water content in profiles of -10, -20, -30 and -40 cm
was monitored at six locations in Croatia (Fig.1).
Locations are Zagreb (Ruđer Bošković Institute),
Križevci, Karlovac and three locations in Zadar. The
test field with different soil types was formed in the
Ruđer Bošković Institute campus in order to evaluate
the behavior of different types of soils under the same
weather conditions.
2.1. Soil bank
The soil bank is located at the Ruđer Bošković
Institute. Soil samples are placed in the wooden boxes
dimensions of 70x50x70 cm. Soils collected for soil
bank were cleaned from stone debris and hand stirred
in order to unify the sample but not to disturb the
texture of the soil.
FIGURE 1. Locations of samples collected for soil bank and
locations of soil moisture measurements which are presented
with their GPS coordinates. Mine fields are marked as black
areas.
CP680, Application of Accelerators in Research and Industry: 17th Int'l. Conference, edited by J. L. Duggan and I. L. Morgan
© 2003 American Institute of Physics 0-7354-0149-7/03/$20.00
895
Preliminary determination of some basic physical
and chemical properties included determination of soil
texture, silicate analysis and major and trace elemental
analysis. Analysis of soil texture was done at the Ruđer
Bošković Institute. Soil was air dried and sieved
through 2 mm θ sieve and than disintegrated by
International B-method. Texture of the soils was than
determinated by sieving (sand particles, 2-0.06 mm)
and by gravity sedimentation method (silt 0.06-0.002
mm and clay < 0.002 mm). Silicate analysis of 10
major elements (SiO2, TiO2, Al2O3, Fe2O3, MnO,
MgO, CaO, Na2O, K2O and P2O5) was done at the
Geological Institute of Zagreb. Silicon was determined
gravimetrically [2]. Alkali metals were determinate by
flame photometric analysis in the acid dissolution after
digestion of the sample in the mixture of acids
(HF+HNO3+H2SO4). Concentrations of Titanium,
Manganese and Phosphorus were determinated in the
same acid dissolution by the spectrophotometric
method. Calcium, Magnesium, Iron and Aluminum
were determinated by complex-formation titrations
using appropriate indicators. Relative errors were: 0,15
% for SiO2 and Al2O3, 0,05 % for MgO and CaO, 03 %
for TiO2, Na2O, K2O and P2O5, 0,08 % for Fe2O3, and
0,01 % for MnO. Elemental analysis of major and trace
elements was made at the Ruđer Bošković Institute.
After oven drying (80°C), sieving, grinding and
homogenizing, concentrations of 15 elements (K, Ca,
Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Rb, Sr, Zr and Pb)
were measured by energy dispersive X-ray
fluorescence method (EDXRF). For first seven samples
a Simens X-ray apparatus, model Kristalloflex
710/710H, with working parameters of 35 kV and 35
mA was used. Measurements were done with Mo
anode and Mo secondary target in orthogonal
geometry. The irradiation time was 3000 s. X-ray
spectra were collected with a Si(Li) detector
(FWHM=195 eV at 5,9 keV) and were analyzed by
using AXIL program package. The relative errors were
15,3% for Ti, 19,2% for V, 35,9% for Ni and 10% for
other elements. The rest of samples were analyzed with
X-ray apparatus with the Oxford instruments X-ray
tube as a source and Mo anode, using the working
parameters: 20 kV and 0,9 mA. The angle between the
sample and the source and the angle between the
sample and the detector was 900 and 450, respectively.
Distance between sample and detector was 5 cm. As
X-ray detector Si-PIN thermoelectrically cooled
photodiode with the following characteristics was
used: Detector size = 2,4×2,8 (7 mm2), Si thickness =
0,3 mm, Be window = 25 µm, FWHM for 5,9 KeV 55
Fe 186-220 eV. The irradiation time was 3000 s.
Qualitative and quantitative analysis was carried out
using the AXIL computer code. The relative errors for
Cr, Mn, Fe, Ni, Cu, Zn and Pb were 5.2%, 5.3%, 0.4%,
2.6%, 1.7%, 0.5%, and 10.8%, respectively, and for
others 10 %.
2.2. Field measurements
Field measurements included monitoring of the soil
water content on daily and weekly basis at six locations
in different parts of Croatia (Fig.1.). Locations are; (i)
Zagreb; northwest part of Croatia, continental climate.
Measurements presented are from March to
November1 2001, done on daily basis at the Ruđer
Bošković Institute campus. Soil is pseudogley, which
is typical for Zagreb and its surroundings. In addition
this is also the location of the test field with 6 different
types of soil (Fig.2). Measurements in the test field
started in August 2001 on daily basis. (ii) Križevci;
north part of Croatia, continental climate. Loess type of
soil, which is wide-spread in Northern Croatia.
Measurements started in September 2001, once a week.
(iii) Karlovac; west part of Croatia, continental
climate. Close to the river Kupa, which was the
separation line during the war in Croatia, and because
of this extremely contaminated with landmines.
Characteristic of soils near rivers is a great variability
in soils texture. Measurements started in April 2001
and were performed twice a week. (iv) Zadar: south
part of Croatia, Mediterranean climate. There were
three measuring points (a) Punta Mika, shallow red
soil, (b) Bokanjac, silted brown soil and (c) Sabunike,
sand. The soil moisture was monitored at four depths (10, -20, -30 and –40 cm). The method based on the
measurement of soil dielectric properties (which is
determined primarily by its water content) was found
to be the most suitable. Variations of soil moisture
content have been measured with the Profile Probe
(type PR1), constructed by Delta-T Devices Ltd. The
probe measures soil moisture at all four profiles in the
same time throughout an access tube. The probe has
been calibrated for mineral soils, and the expected
error was estimated < ±0.1 m3.m-3 (10 % Vol) [3,4,5].
The error increases with depth due to the problems
with insertion of the tube, especially in clay soils. This
is unfortunately unavoidable, but the accuracy can be
improved by calibrating the probe for the specific soil
(this was not applied in this investigation). Data
acquisition was performed manually at suitable time
intervals, once a day, twice or once a week, depending
of the accessibility of terrain. The results of
measurements obtained with the Profile Probe were
compared to gravimetric measurements as a part of
QA/QC procedures.
________________________________________________________
1
Data obtained for all sites are given for the period concluded with
November 2001, which was the ending point of the soil water
content investigation included in the Diamine Project. The
monitoring of the soil moisture was continuing to September 2002.
896
Since volumetric percentage (% Vol) is not always
suitable for calculations, all results are also given in
mass percentages (% Mass) involving density of the
soils; % Mass = %Vol / ρ, where % Vol is an output of
the instrument and ρ is a soil density. Since density of
soils increases with water content, simple algorithm,
which is not presented here, was used to recalculate
results to % Mass.
composition of soils strongly depend of their texture.
This is because larger particles are made of minerals
resistant to weathering, such as flint or other primary
silica minerals, while particles of clay dimensions are
mostly made of minerals which are not resistant to
weathering such as clay minerals and other secondary
alum silica minerals. That is why Si prevails in sand
soils (samples #10 and #13) while concentrations of Al
are diminished. Si and Al also indicate soils formed
from silicaclastic rocks, while Ca indicates soils
formed from precipitated rocks such as limestones and
dolomites. Sand from Sabunike (#17) with large
amount of Ca (Tab.1.) was found few hundred meters
from the sea. This sand was sedimented on the sea
bottom and lifted to the surface by tectonic processes.
Ca in soils #1, #2, #7, #11, #16 and #17 (Tab.1.)
indicates soils that lay on limestones, and Mg and Ca
in soils #4 and #9 (Tab.2.) indicate soils that lay on
dolomite-limestone sediments. Trace elements (Tab.2.)
show somewhat less diversity than major elements.
Gaps of Ca concentrations in Tab. 2. for the first seven
samples are consequence of measurements with the
instrument having sensitivity not good enough for this
element. In addition for samples from #8-#19 it was
possible to measure Ca, but it was not possible to
measure Sr and Zr. For other gaps in tables,
concentrations were below minimum detection limits.
Results show that after all, some trace element
variations do exist. In red soil samples (#2, #7, #9, #11
and #15), concentrations of Mn excel concentrations of
Mn in other soils. Also samples #10 and #19, which
are soils from vineyard, have greater amount of Cu.
2.2.1. Test field
The test field was formed in order to simulate
behavior of different soils under the same conditions.
This test field is situated in Zagreb at the campus of the
Ruđer Bošković Institute. It is made of six distinct
soils, in Fig. 2 marked with letters from “a” to “f”. Soil
with letter “g” is actually a terrain in which the test
field is made and also the location of measurements
started in March 2001. Soils have been separated from
the surrounding terrain by walls of impermeable folia
with an access tube centered in the middle of each soil.
They are about 60 cm in diameter and down to 70 cm
in depth. They are all designated as disturbed, bare
soils (with no vegetation cover). The test field is
located in a gentle slope so the good drainage is
ensured.
3.2. Results of soil moisture measurements
Maximum water capacity and water retention in soils
will mostly depend of their structure and texture.
Where the amount of clay particles is greater, the water
capacity and water retention will be higher. The critical
value of soil water content for NBT mine detection
technique is estimated to be 0.1 kg.kg-1 (10 % Mass).
Here are presented preliminary results of soil moisture
content in situ measurements for different types of
soils in Croatia in profiles of –10, -20, -30 and –40.
(i) Zagreb. The soil moisture content at the profile of
–10 cm decreased from the values around 40 % Vol in
March, that correspond to 20 % Mass, to below 10 %
in May. The months June and July were rainy so the
soil moisture content increased to around 30 % Vol (17
% Mass). Values in August were around 10 % Vol (7
% Mass), and till November increased to 40 % Vol
again. At the profile of –20 cm, the soil moisture
content decreased from values around 50 % Vol (25 %
Mass) in March to values below 20 % Vol (12 %
Mass) in May. In August, they were below 30 % Vol
FIGURE 2. Photo of the test field located at the Institute
Ruđer Bošković campus. Soil types: a. Red soil from
Rogoznica, b. Black soil from Baranja, c. Sand soil from
Đurđevac, d. Brown soil from Turanj, e. Brown soil from
Osijek, f. Pseudogley, original soil, disturbed, g. Pseudogley,
original soil, undisturbed.
3. RESULTS AND DISCUSSION
3.1. Physical and chemical properties of
soils
Physical and chemical properties of soils are mostly
determined by their structure and texture e.g. by
composition, size and arrangement of their particles,
among which particles of clay dimension (<0,002 mm)
have the largest influence because of their size, shape,
configuration and great specific surface. Elemental
897
(17 % Mass) and in November around 50 % Vol. At
the profile of –30 cm the values were around 60 % Vol
(26 % Mass) till May, when they decreased to 20% Vol
(11 % Mass). In June and July the soil moisture content
increased to less than 50 % Vol (23 % Mass). In
August it was below 30 % Vol (16 % Mass) and in
November increased again to 60 % Vol. At the profile
of -40 cm the values went up to 70 % Vol (30 %
Mass). These values were too high according to the
gravimetrical method, so the results are questionable.
After the replacement of the access tube the values at –
40 cm decreased to around 40 % Vol (20 % Mass) and
remained mostly between 30- 45 % Vol (16-22 %
Mass).
TABLE 1. Concentrations of major elements in soil samples (%). Relative errors are: 0,15 % for SiO2 and Al2O3,
MgO and CaO, 03 % for TiO2, Na2O, K2O and P2O5, 0,08 % for Fe2O3, and 0,01 % for MnO.
Sample
SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 Ign.loss
Zemunik-1
55.67 0.46
7.04
3.35
0.09
0.60 12.28 0.03
1.19
0.01
18.88
Oklaj-2
44.22 0.47 10.05
3.99
0.07
1.35 23.72 0.15
1.65
0.02
14.03
Turanj-3
61.72 0.89 13.26
5.15
0.04
1.33
1.51
1.07
2.06
0.02
12.64
Cerovac-4
56.78 0.47
8.95
3.56
0.04
4.05
7.12
0.59
1.81 <0.01
16.38
Osijek-5
66.67 0.76 12.09
5.43
0.09
0.24
2.44
1.52
2.65
0.02
7.96
Baranja-6
58.86 0.70 12.95
4.97
0.06
2.25
3.08
1.68
2.20
0.02
12.91
Obrovac-7
49.63 0.72 14.02
6.14
0.14
1.73
7.51 <0.01 1.74
0.01
17.95
Đakovo-8
70.76 0.87 12.04
4.51
0.09
0.88
1.04
1.75
2.47
0.01
5.31
Dubrovn.-9
33.49 0.63 11.07
4.71
0.07
4.96 12.28 0.13
1.48
0.03
30.90
Kloš.Pod-10
80.09 0.50
7.62
3.87
0.09
1.22
0.81
1.32
1.26
0.02
2.83
Rogoznica-11 43.02 0.85 18.31
7.34
0.14
0.33
7.29
1.58
1.91
0.01
18.92
IRB-12
60.27 0.91 16.29
5.90
0.04
1.23
1.15
0.96
2.06 <0.01
10.98
Đurđevac-13 81.00 0.45
6.68
3.47
0.08
1.25
1.96
1.49
1.20 <0.01
2.13
DonjaJel.-14 59.86 0.94 17.80
6.06
0.10
1.45
0.95
1.23
3.03 <0.01
8.26
Hidrom-15
60.71 0.81 14.00
6.02
0.14
0.71
1.40
0.48
1.86
0.02
13.59
Bokanjac-16 60.85 0.70
5.97
2.83
0.05
0.70 12.37 0.70
1.17
0.01
14.38
Sabunike-17 33.18 0.18
2.91
1.92
0.04
2.26 31.01 <0.01 0.59
0.01
27.75
Križevci-18
63.34 0.85 14.46
6.94
0.09
0.83
2.13
1.84
2.65
0.02
6.69
0,05 % for
Total
99.60
99.72
99.69
99.75
99.87
99.68
99.59
99.73
99.75
99.63
99.70
99.79
99.71
99.68
99.74
99.73
99.85
99.84
TABLE 2. Concentrations of major and trace elements in soil samples as determined by XRF. For first seven samples the
relative errors are: 15,3% for Ti, 19,2% for V, 35,9% for Ni and 10% for other elements. For rest of the samples relative errors
for Cr, Mn, Fe, Co, Ni, Cu, Zn and Pb are 5.2%, 5.3%, 0.4%, 1.7%, 2.6%, 1.7%, 0.5%, and 10.8%, respectively and for others 10
%. Missing values are concentrations under the minimum detection limits.
No
K
Ca
Ti
V
Cr
Mn
Fe
Ni
Cu
Zn
As
Rb
Sr
Zr
Pb
%
%
ppm ppm ppm ppm % ppm ppm ppm ppm ppm ppm ppm ppm
1
0.8
3224
56
61
619
1.6
27
16
80
47
125
184
455
2
1.1
3540
86
140 1071 3.4
22
12
104
98
106
196
235
3
0.8
3694
65
105
933
3.7
19
16
108
126
118
484
35
4
0.8
2998
76
64
588
2.4
19
14
112
91
136
277
148
5
0.9
3872
83
87
920
3.2
27
16
80
114
107
424
399
6
1.2
4787
94
97
711
2.3
39
19
83
66
109
121
852
7
1.1
3832 111
198 1611 5.0
17
49
113
116
107
277
23
8
3.1
1.0 6197 363
86
864
4.3
59
34
108
88
50
9
1.6
4.9 3319 114
106 1032 3.6
58
43
132
62
31
10 1.4
0.4 2383
52
14
743
2.6
54
237
63
56
44
11 2.1
1.1 4552
45
41
1744 4.7
52
36
127
24
132
29
12 1.7
6.3 5780
73
31
905
4.5
47
50
109
11
59
13 1.4
4.2 3571 295
22
898
2.9
34
11
67
17
28
14 2.7
0.8 6842 116
148
665
4.2
45
49
171
17
22
15 1.9
0.5 5618
56
57
1184 4.9
75
51
137
20
27
16 1.4
8.4 2406 115
214
408
1.7
37
26
162
18
26
17 1.9 12.2 1354
48
117
504
1.6
57
34
190
19
25
18 2.7
0.8 7798 140
175
407
4.3
41
37
136
23
22
761 2.9
19 2.1 3.4 3842 124
46
31
125 190
13
13
disturbed and bare. They were cleaned from stone
debris and homogenized. That made them more
compact and values of soil moisture content in these
soils are greater compared to the same or similar soils
Six different types of soils were monitored in the test
field. These soils do not have original texture since
they were disturbed during the digging and
transportation to the test field. They are designated as
898
in-situ. Since different types of soil vary significantly
in soil water capacity and in soil water dynamics,
measuring of the different types in the same time under
the same conditions pointed out dependence of the soil
water content of the soil texture. Sand soils, for
example, have a very low water capacity and changes
in the moisture amount are fast and significant, while
clay soils keep a great amount of water and release it
very slowly. Results of the soil moisture measurements
are presented in the Fig. 3.
(10 % Mass). According to preliminary results of soil
moisture monitoring of different types of soils in
different parts of Croatia, with the aim to cover
versatile textures and structures of soils and versatile
hydrometeorological regimes, the values of soil
moisture often exceed the NBT soil moisture critical
value. Considering this, the results presented here
suggest that NBT is not suitable for landmine detection
in Croatia, but it could be recommended to the
countries with arid climate were arid soils with soil
moisture below 10 % Mass are quite common.
ACKNOWLEDGMENTS
The work presented in this report has been supported
in part by NATO collaborative linkage grant
SST.CLG.978317 and by EC project DIAMINE, IST2000-25237.
FIGURE 3. Graphical presentation of the results of the soil
moisture measurements from the test field at the Institute
Ruđer Bošković campus (% Mass). Results are presented for
the period from August to November 2001.
5. REFERENCES
1.
(ii) Križevci. The values were between 20-55 % Vol
(12-27 % Mass). (iii) Karlovac. The values measured
were between 7-55 % Vol (5-27 % Mass) at the profile
of –10 cm and –20 cm. Values at the profile of –30 cm
were between 20-60 % Vol (13-29 % Mass), and at the
profile of –40 cm, between 20-70 % Vol (13 - 31 %
Mass). (iv a) Punta Mika: Values at the profile of –10
cm were between 8-35 % Vol (7-25 % Mass). At the
profile of –20 cm were between 10-25 % Vol (9-19 %
Mass).(iv b) Bokanjac: The values of the soil moisture
content were between 10-45 % Vol (8-19 % Mass). (iv
c) Sabunike: Values were between 7-25 % Vol (5- 14
% Mass).
The results show that the soil moisture for different
types of soils in Croatia in 2001 often exceed the soil
moisture critical value recommended for NBT.
2.
3.
4. CONCLUSIONS
4.
Soil water content is the key attribute of soil as a
background in NBT landmine detection applications. If
the critical value of the soil water content is reached,
the detection of landmine explosives is not possible.
The critical value is reached when the density of the
hydrogen atoms in the landmine is equal to that in the
background soil. It is recommended that soil moisture
content for NBT application do not exceed 0.1 kg.kg-1
5.
899
Obhođaš, J., Sudac, D., Nađ, K., Valković, V.,
Nebbia, G. and Viesti, G., “The soil moisture
content: relevance to the landmine detection
by neutron backscattering technique”,
Presented at 5th International Topical Meeting
on Industrial and Radioisotope Measurements
Applications, IRRMA-5, Bologna, Italy 0912.09.2002, to be published in Nuclear
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(1992).
Whalley, W.R., “Considerations of the use of
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