Transcript Analytical capability of neutron sensor incorporated into

Analytical capability of neutron sensor
incorporated into UNCOSS ROV
Project meeting and workshop:
Dubrovnik 30th November and 01st December 2011
LaBr3(Ce) 3”x3”
Detector shielding
ING-27 Neutron generator
Electronic box
DC/AC converter
Overall tagged neutron
beam
(3 x 3 pixels)
Control unit ING27
Battery
Power supply unit
of ING27
UXO
Tagged neutron beam window
Seafloor
Side view of the neutron based explosive detector.
Schematic presentation of the use of tagged
neutrons: neutron sensor
Project meeting and workshop:
Dubrovnik 30th November and 01st December 2011
Iron cylinder filled with the real sediment, on the left, and shell filled with 6.1 kg of
TNT surrogate (Si3C7H3N3O6), on the right. For the performance assessment in water, the
plastic tank (on the right) was filled with water up to the top of the objects.
Gamma and time spectra corresponding to the shell filled with 6.1 kg of TNT
surrogate (Si3C7H3N3O6) in air, for a 30 min acquisition with an average neutron emission of
2.4 x 107n/s. The time and energy spectra have been obtained by selecting pixels 4 and 5.
Gamma and time spectra corresponding to the iron cylinder filled with sediments in
air, for a 30 min acquisition with an average neutron emission of 2.4 x 10 7 n/s. The time and
energy spectra have been obtained by selecting pixels 4 and 5.
Energy spectra in air of the iron cylinder filled with sand (in green) Vs. shell filled
with TNT surrogate (in red). Note that the energy spectra were adjusted to a same 2.24 MeV
titanium peak pulse height. Below a zoom on C and O peaks.
Level of
water
Way of
rotation
40
3'' x 3'' NaI(Tl)
Rotation axis
went out from
the picture

Al ring
shield
API120 19
5
Sediment #171
Fe shield
Tagged neutron cone
axis
Submarine
Al slab
TNT
Sediment #321
‘’Surveyor’’
Vertical
axis
Level of
water
400
Oxygen
Carbon
1000
o
30
400
260
Oxygen
260
Carbon
800
300
300
600
200
200
Oxygen
Carbon
400
100
100
200
0 0
2 0
0
13
2
4
3
45
5
6
6
77
Energy (MeV)
Energy (MeV)
The gamma ray spectra of a 155 mm shell filled
with the Si3C7H3N3O6 (gray) and the cylinder
filled with the sea sediment (black). 9 ns time
window.
8
8
0
1
2
3
4
5
6
7
Energy (MeV)
The gamma ray spectra of a real 155 mm shell
(black) and the cylinder filled with the sea
sediment (red). 9 ns time window
8
•
•
•
Spectrum was fitted with the assumption that it contains only carbon, oxygen and iron
contributions. Contribution of the other elements like chlorine or sodium was ignored.
The fitting procedure was done by using Eq. (1) where the sum was done over the
channel (ch) number.
 
2
ch  chmax
a  Carbon(ch)  b  Oxygen(ch)  c  Iron (ch)  T arg et (ch)2
ch  chmin
T arg et (ch)

(1)
Carbon, Oxygen and Iron are pure elemental spectra. Parameters ''a'', ''b'' and ''c'' are
fitting parameters called carbon content, oxygen content and iron content,
respectively.
Oxygen, Carbon and Iron content for two different targets in dependance on the rotation
angle
155 mm grenade
155 mm cylinder filled with sand
Angle of rotation
Oxygen
Carbon
Iron
Oxygen
Carbon
Iron
22°
0.90±0.01
0.086±0.008
0.007±0.01
-
-
-
24°
0.865±0.01
0.0825±0.007
0.043±0.01
-
-
-
26°
0.857±0.009
0.071±0.006
0.06±0.01
0.871±0.009
0.037±0.006
0.12±0.01
28°
0.804±0.008
0.080±0.006
0.11±0.01
0.862±0.008
0.0425±0.00
55
0.12±0.01
Normal distribution for carbon content in the background and in the explosive devices
Average background
Treshold
b
False positive
Average explosive device
b
Detection probability
e
False negative
Detection probability of the real 155 mm shell for the rotattion angle 260 and the false
positive 10 %!
Measurement
Time (s)
1385
692.5
462
346
277
231
198
173
Detection probability
(%)
100
99.7
96.5
90.3
91.4
82.3
83.8
77.4
False negative (%)
0
0.3
3.5
9.3
8.6
17.3
16.2
22.6
Detection probability of the real 155 mm shell for the rotattion angle 260 and the false
positive 5 %!
1385
692.5
462
346
277
231
198
173
Detection probability
(%)
100
99.3
92.6
83.2
84.1
72.1
73.8
65.5
False negative (%)
0
0.7
7.4
16.8
15.9
27.9
26.2
34.5
Measurement
Time (s)
Detection probability of the real 155 mm shell for the rotattion angle 260 and the false
positive 0.13 %!
1385
692.5
462
346
277
231
198
173
Detection probability
(%)
99.4
87
53.6
38.6
35.3
23
25.5
18
False negative (%)
5.6
13
46.4
61.4
64.7
77
74.5
82
Measurement
Time (s)
‘’Surveyor’’
• One alpha pixel
• It is possible to rotate the neutron generator
• In the fitting procedure it was assumed that the gamma ray spectra contained
the contribution from the iron, oxygen and carbon only
• Time resolution ~2 ns
‘’Uncoss Rov’’
• 3x3 alpha pixels
• It is not possible to rotate the neutron generator
• In the fitting procedure it was assumed that the gamma ray spectra contained
the contribution from the more than three chemical elements
• Time resolution ~5 ns
Summary
• In order to improve time resolution
electronics was send back to Saclay
• In order to produce a better TNT simulant
a new chemicals were ordered
• Avio bomb was considered to be used as
a secondary target