Analytical capability of neutron sensor incorporated into UNCOSS ROV

Project meeting and workshop:Dubrovnik 30th November and 01st December 2011

Side view of the neutron based explosive detector.

Seafloor

ING-27 Neutron generatorDetector shielding

LaBr3(Ce) 3”x3”

Electronic box

Control unit ING27

Power supply unitof ING27

UXO

Overall tagged neutron beam

(3 x 3 pixels)

DC/AC converter

Battery

Tagged neutron beam window

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 ofTNT 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 TNTsurrogate (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 inair, for a 30 min acquisition with an average neutron emission of 2.4 x 107 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 filledwith 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.

‘’Surveyor’’

5

3'' x 3'' NaI(Tl)

API120

shieldAl ring

Tagged neutron coneaxis

Submarine

40

19

Al slabSediment #171

TNT

Sediment #321

Fe shield

Level ofwater

Level ofwater

Way of rotation

Rotation axiswent out from

the picture

Verticalaxis

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.

Energy (MeV)

0 1 2 3 4 5 6 7 8

0

200

400

600

800

1000

260

OxygenCarbon

Energy (MeV)

2 3 4 5 6 7 8

0

100

200

300

400

OxygenCarbon

30o

Energy (MeV)

0 1 2 3 4 5 6 7 8

0

100

200

300

400

260

CarbonOxygen

The gamma ray spectra of a real 155 mm shell (black) and the cylinder filled with the sea

sediment (red). 9 ns time window

• 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.

• (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.

max

min)(arg

)(arg)()()( 22

chch

chch chetT

chetTchIroncchOxygenbchCarbona

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±0.0055

0.12±0.01

Normal distribution for carbon content in the background and in the explosive devices

False positive

False negative

Detection probability

Treshold

Average background

Average explosive device

b

e

b

Detection probability of the real 155 mm shell for the rotattion angle 260 and the false positive 10 %!

MeasurementTime (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 %!

Measurement

Time (s)

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

Detection probability of the real 155 mm shell for the rotattion angle 260 and the false positive 0.13 %!

Measurement

Time (s)

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

‘’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