In order to demonstrate the possibility of identifying the material within ship’s underwater hull, sunken ships, or other objects on the sea fl oor, tests with a 14 MeV sealed tube neutron generator
incorporated inside a small submarine were performed in the test basin fi lled with sea water. The results obtained for inspection of diesel fuel and explosive presence behind single and double hull structures are presented

Dario Matika

Davorin Sudac

Vladivoj Valković

HRČAK - Portal of Croatian Scientific and Professional Journals

1361(2010)1, 13-17INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER... V. VALKOVIĆ, D. MATIKA, D. SUDACUDC UDC 629.5.022:621.039Vladivoj VALKOVIĆ1Dario MATIKA2 Davorin SUDAC3Inspecting the Inside of Sunken Ships and Ship’s Underwater HullOriginal scientifi c paperIn order to demonstrate the possibility of identifying the material within ship’s underwater hull, sunken ships, or other objects on the sea fl oor, tests with a 14 MeV sealed tube neutron generator incorporated inside a small submarine were performed in the test basin fi lled with sea water. The results obtained for inspection of diesel fuel and explosive presence behind single and double hull structures are presented.Keywords: neutron interrogation, explosive, diesel fuel, sunken ships, ship hullKontrola unutrašnjosti potopljenih brodova i podvodnih dijelova brodaIzvorni znanstveni radS ciljem demonstracije mogućnosti identifi kacije materijala unutar podvodnog dijela broda, unutar potopljenih brodova i ostalih predmeta na morskom dnu, izvršeni su eksperimenti sa cijevnim 14 MeV neutronskim generatorom smještenim unutar male podmornice u bazenu napun-jenom morskom vodom. Prikazani su rezultati dobiveni inspekcijom dizelskog goriva i eksploziva smještenih iza jednostruke i dvostruke konstrukcije trupa broda.Ključne riječi: neutronska inspekcija, eksploziv, dizelsko gorivo, potopljeni brodovi, trup brodaAuthors’ addresses (Adrese autora):1 A.C.T. d.o.o., Prilesje 4, 10000 Zagreb, Croatia2 Institute  for Research and Devel-opment of Defence Systems, Ilica 256b, 10000 Zagreb3 Rudjer Boskovic Institute, P.O. Box 180, 10002 Zagreb, CroatiaReceived (Primljeno): 2009-09-15Accepted (Prihvaćeno): 2010-02-2Open for discussion (Otvoreno za raspravu): 2011-03-311 IntroductionMany of the materials on the bottom of the seas are due to numerous shipwrecks. There is a global risk of marine pollution from over 7800 sunken World War II vessels worldwide. Nu-merous efforts are made to compile data on WWII shipwrecks. The recent efforts include so called South Pacifi c Regional En-vironment Programme (SPREP) and AMIO databases of WWII shipwrecks [1-3]. Although work on the Pacifi c SPREP database is relatively complete, work on shipwrecks in other oceans has only recently commenced. The Atlantic, Mediterranean and In-dian Ocean (AMIO) WWII shipwreck database of is in its initial stages. Currently, the AMIO database contains information on the location and ownership of over 3953 WWII vessels, over 1000 gross tons, equalling to over 20 million tons of shipping, lying at the bottom of world’s oceans. The distribution of WWII shipwrecks from both databases is shown in Table 1.Some areas in Europe are of special interest because of large amouts of dumped ammunitions. These inclide the Baltic Sea, the Atlatic Ocean and the North Sea, and the Mediterranean [4-8]. Inspection of the cargo area within the ship’s body below water surface for the presence of threat materials is also required in the fi ght against terrorist activities. In such a scenario a detec-tion system needs to approach the ship’s underwater hull and analyze the material present at the other side of the ship’s hull, i.e. in the ship’s cargo area. Even though boat and ship building dates back to ancient times, some production technologies have been slow to change, illustrated by an only recent shift in technology at major ship-yards. The building of large ships is one of the most obvious applications of heavy plate fabrication. Iron vessels were fi rst built on a regular basis in England in the 1830s, and the fi rst such naval fi ghting vessel was used in England’s First China War of 1841-43. Steel began to replace iron construction in the 1870s as steel became more affordable [9]. Modern commercial ship hulls continue to be built with 14- to 19-millimeter-thick (0.5- to 0.75-inch) plate. Carbon steel is low-cost and easy to repair. These materials normally are specifi ed American Bureau of Shipping grade A, although sometimes grades B and H are used.Early hulls were riveted, but this approach evolved to 100 percent welded seams by World War II. The submerged arc Table 1  AMIO & SPREP shipwreck databases – Distribution of shipwrecks globallyTablica 1 AMIO & SPREP baze podataka brodskih olupina – glo-balna distribucijaOcean/seas Number of vesselsTotal tonnageNumber of tankersNorth Atlantic 3002 15108305 452 South Atlantic 198 1143374 20 Mediterranean 305 1578910 19 Indian 313 1813398 35 Arctic 124 729569 2 Pacifi c 3276 12158895 273 14 61(2010)1,13-17V. VALKOVIĆ, D. MATIKA, D. SUDAC INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER...welding (SAW) process makes up the majority of welding today, using ceramic backup strips where possible to maximize one-side welding. Double-hull construction is a fairly recent and major design change that affected fabrication and assembly. This was dictated by the Oil Pollution Act of 1990, with the goal of reduc-ing the risk of major environmental disasters caused by fuel and leaking oil and petroleum cargoes. Tanker hulls must be made with double construction, while other transport vessels, such as those for containers and bulk dry cargo, must have double-hull construction only in their fuel tank areas. While the outer hull is 14 to 19 mm thick, the inner hull may be 12 to 14 mm thick.Only the outer hull details are shaped to contour; inner hull details are designed to allow fabrication from fl at plate. Power roll-ing shapes the outer hull components that require simple curvature, with contour checked against CAD-generated templates. Parts that need compound curvature are formed by selective heating. The latter method requires the skill and experience of craftsmen who now can refer to a CAD-generated graphic matrix, which predicts specifi c locations and amounts of heat to be applied.For today’s large naval combat vessels, aluminium is used for lighter-weight topside structure, and composites that resist corro-sion are used for secondary items such as gratings and decking. However, steel continues to be the material of choice for hull structure. HSLA (high-strength, low-alloy) steel use has evolved over the last 20 to 30 years. Its advantages include increased strength and reduced thickness, which provides a weight saving that, in turn, reduces fuel consumption.2 ExperimentalIt is often required to inspect ship hulls, either to detect po-tential anomalies attached to the hull, or to determine the nature of materials within the hull, especially in the case of sunken ships. The material to be inspected is hidden behind the tanker walls having a thickness up to 25 mm in older ships, while in the modern ones the walls are only 14 to 16 mm thick. In addition, the new tankers are required to have double hull construction, outer hull 14-19 mm thick (shaped to contour), and inner hull 12-14 mm thick (fl at plate).In order to demonstrate the possibility of identifying the material within sunken ships and other objects on the sea fl oor, we have performed tests with the 14 MeV sealed tube neutron generator incorporated inside a small submarine submerged in the test basin fi lled with sea water [10]. The principle of the method used is demonstrated in Figure 1. Figure 1  The principle of the tagged neutron sensorSlika 1 Princip rada senzora koji koristi obilježene neutroneFigure 2  Geometrical arrangement of the neutron sensorSlika 2  Geometrijski prikaz neutronskog senzoraThe geometrical arrangement for the experiment is shown in Figure 2. The investigated targets were 10 litres of diesel fuel, 5 kg of explosive and different chemicals (expected components of chemical warfare agents) placed behind a 16-mm steel plate in the fi rst measurement and behind a sandwich of 18-mm steel plate – 10-cm air bag – 16-mm steel plate in the second measure-ment respectively. Using the window on the measured alpha-gamma time spectrum, the gamma rays originating from the investigated volume were separated from the background radiation. By the inspection of the measured gamma spectra we were able to identify all the investigated materials in both measurement geometries.  The inspection system, the experimental set-up and the pres-entation of the perfomed measurement are given in Figures 3 to 6. The measurement results are presented in Figures 7 to 13.Figure 3 Inspection system to be submerged into the water poolSlika 3  Sistem za inspekciju pripremljen za uron u bazen na-punjen vodom1561(2010)1, 13-17INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER... V. VALKOVIĆ, D. MATIKA, D. SUDACFigure 4  Schematic presentation of the experimental set-up for double hull construction, outer hull 14-19 mm thick, inner hull 12-14 mm thickSlika 4  Shematski prikaz eksperimentalnog postava za kon-strukciju dvostrukog trupa, vanjski trup debljine 14-19 mm, unutarnji trup debljine12-14 mmFigure 5  Double hull construction, the air bag is placed between two iron plates so that the whole set-up can be im-mersed in waterSlika 5     Dvostruki trup: zrakom ispunjen jastuk postavljen između dvije željezne ploče tako da čitav postav može uroniti u voduFigure 6   Schematic presentation of the performed measure-ments;  targets were TNT explosive (5 kg) and diesel fuel (10 l), the submarine was positioned about 2 cm above the upper iron plateSlika 6    Shematski prikaz izvršenih mjerenja; mete su bile TNT eksploziv (5 kg) i dizelsko gorivo (10 litara), podmornica je pozicionirana 2 cm iznad gornje pločeFigure 7 Gamma ray spectra from TNT (5 kg) target (top line), logarithmic scale; target out (bottom line); the total number of  the tagged neutrons 24 x 107; measurement time: ~6900 sSlika 7    Spektar gama zraka iz mete TNT (5 kg) – gornja krivulja, logaritamska skala; donja krivulja je bez mete; ukupni broj označenih neutrona 24x107; vrijeme mjerenja: ~ 6900 sFigure 8 Gamma ray spectra from TNT (5 kg) target (top line), linear scale; target out (bottom line); the total number of the tagged neutrons 24 x 107; measurement time: ~6900 s Slika 8 Spektar gama zraka iz mete TNT (5 kg) – gornja krivulja, linearna skala; donja krivulja je bez mete; ukupni broj označenih neutrona 24x107; vrijeme mjerenja:~6900 sFigure 9   Gamma ray spectra from diesel fuel (10 l), top line, behind the iron-air-iron sandwich in the sea water, logarithmic scale; target out: bottom line; total number of tagged neutrons 18 x 107; measurement time: ~5240 sSlika 9 Spektar gama zraka iz mete dizelskog goriva (10 l) iza željezo-zrak-željezo sendviča – gornja krivulja, logari-tamska skala, donja krivulja je bez mete; ukupni broj označenih neutrona 18x107; vrijeme mjerenja: ~ 5240 s16 61(2010)1,13-17V. VALKOVIĆ, D. MATIKA, D. SUDAC INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER...Figure 10 Gamma ray spectra from diesel fuel (10 l), top line, be-hind the iron-air-iron sandwich in the sea water, linear scale, target out: bottom line; total number of tagged neutrons 18 x 107; measurement time: ~5240 sSlika 10     Spektar gama zraka iz mete dizelskog goriva (10 l) iza željezo-zrak-željezo sendviča – gornja krivulja, linearna skala; donja krivulja je bez mete; ukupni broj označenih neutrona 18x107; vrijeme mjerenja: ~ 5240 sFigure 11  Schematic presentation of the experimental set-up (single hull); the whole set-up is immersed in water; targets were TNT explosive (5 kg) and diesel fuel (10 l); the submarine was positioned about 2 cm above the iron plateSlika 11  Shematski prikaz eksperimentalnog postava (jednos-truki trup); čitav je postav uronjen u vodu, mete su bile TNT eksploziv (5 kg) i dizelsko gorivo (10 l); podmornica je pozicionirana na 2 cm iznad željezne pločeFigure 12   Gamma spectrum from diesel fuel behind the iron plate 16 mm thick (12 x 107 tagged neutrons, measurement t = 3438 s)Slika 12 Spektar gama zraka iz dizelskog goriva smještenog iza željezne ploče debljine 16 mm (12x107 označenih neutrona, vrijeme mjerenja t = 3438 s) Figure 13 Gamma spectrum from 5 kg of  TNT behind the iron plate 16 mm thick (12 x 107 tagged neutrons, measure-ment time 3490 s); logarithmic scale – bottom; linear scale - topSlika 13     Spektar gama zraka iz 5 kg TNT smještenog iza željezne ploče debljine 16 mm (12x107 označenih neutrona, vrijeme mjerenja 3490 s); logaritamska skala – donja slika; linearna skala – gornja slikaThe thickness of the iron plate positioned between the sub-marine and the explosive (mass 5 kg) was varied. Submarine to explosive (mass 5 kg) distance was 11 cm. The graph in Figure 14 shows the number of counts in carbon 4.44 MeV peak (black) and oxygen 5.62 MeV peak – fi rst escape peak of oxygen 6.13 MeV line (red) as a function of iron plate thickness. Solid lines correspond to the exponential fi t (a e-b x). The total number of tagged neutrons in each measurement was 3.6 x 108, with neutron beam of ~107 n/s corresponding to the measurement time of ~176 min. The measurements were done for a long time period in order to obtain better statistics. Conclusions on the existence of peaks can be reached in much shorter time.Table 2 contains the parameters of the exponential fi t (a e-bx) shown in Figure 14.1761(2010)1, 13-17INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER... V. VALKOVIĆ, D. MATIKA, D. SUDACTable 2 Parameters of the exponential fi t (a e-b x) shown in Figure 14Tablica 2 Parametri eksponencijalnog fi ta (a e-b x) prikazanog na slici 14Element a b (1/mm)Carbon 6169 ± 318 0.043 ± 0.004Oxygen 2379 ± 411 0.05 ± 0.02Figure 14  The number of counts in carbon 4.44 MeV peak (up-per) and oxygen 5.62 MeV peak – fi rst escape peak of oxygen 6.13 MeV line (lower) as a function of iron plate thicknessSlika 14 Broj događaja u ugljikovom vrhu 4,44 MeV (gornja kriv-ulja) i kisikovom sekundarnom vrhu 5,62 MeV, od 6,13 MeV linije (donja krivulja) u funkciji debljine željezne ploče The number of counts in 4.44 MeV carbon peak for different iron plate thicknesses is shown in Table 3, while Table 4 gives the number of counts in 5.62 MeV oxygen peak for different iron plate thicknesses under the identical experimental condi-tions (see above).Table 3 The number of counts in 4.44 MeV carbon peak for dif-ferent iron plate thicknessesTablica 3 Broj događaja u ugljikovom 4,44 MeV vrhu u funkciji debljine željezne pločeThickness (mm)Number of counts in 4.44 MeV peakError0.0 5985 5428.0 4797 58115.0 3053 44523.0 2405 38832.0 1101 33440.0 1303 489Table 4 The number of counts in 5.62 MeV oxygen peak for dif-ferent iron plate thicknessesTablica 4 Broj događaja u kisikovom 5,62 MeV vrhu u funkciji debljine željezne pločeThickness (mm)Number of counts in 5.62 MeV peakError0.0 2203 4138.0 2119 50615.0 857 27923.0 684 245 In comparison with benign materials, TNT explosive is char-acterized with a high C/O ratio. However, in the case of thicker iron plates conclusions can be drawn in some situations from the presence of carbon peak only.3 ConclusionsIt is often required to inspect ship hulls, either to detect potential anomalies attached to the hull, or to determine the nature of materi-als within the hull, especially in the case of sunken ships. Older tanker walls have a thickness up to 25 mm, while the modern ones are only 14 to 16 mm thick. In addition, the new tankers are required to have double hull construction, outer hull 14-19 mm thick (shaped to contour), inner hull 12-14 mm thick (fl at plate).In order to demonstrate the possibility of identifying the material within sunken ships and other objects on the sea fl oor we performed tests with the 14 MeV sealed tube neutron genera-tor incorporated inside a small submarine submerged in the test basin fi lled with sea water. Measurements were performed with the following targets: 10 litres of diesel fuel, 5 kg of explosive and different chemi-cals (expected components of chemical warfare agents) placed behind a 16-mm steel plate in the fi rst measurement and behind a sandwich of 18-mm steel plate – 10-cm air bag – 16-mm steel plate in the second measurement respectively. Using the window on the measured alpha-gamma time spec-trum, the gamma rays originating from the investigated volume were separated from the background radiation. By the inspection of the measured gamma spectra we were able to identify all the investigated materials in both measurement geometries.  References[1]  MONFILS, R.: “The Global Risk of Marine Pollution from WWII Shipwrecks: Examples from Seven Seas”, Submitted to International Oil Spill Conference, Miami, Florida, 2005.[2]  …: SPREP  “Regional Strategy to Address Marine Pollution from WWII Shipwrecks in the Pacifi c”. Phase 1-Report and Preliminary Risk Assessment. CD-ROM, 2003.[3]  …: OSPAR Commission “Overview of Past Dumping at Sea of Chemi-cal Weapons and Munitions in the OSPAR Maritime Area”, Revise, ISBN 1-904426-54-9, 2004.[4]  …: Advisory Committee on Protection of the Sea (ACOPS) “Coastal Survey of Packaged Chemical and other Hazardous Items 2002/2003”, Maritime and Coastguard Agency Research Project No. 488, London, October 2003. Australian Goverment, Department of Defense, Chemi-cal Warfare Agent Sea Dumping off Australia, Revised and updated edition 2003, Canberra ACT 2600.[5]  …: United Nations Environmental Programme “Dumping Sites of Ammunitions in  the Mediterranean Sea”, UNEP (DEPI)MED WG. 316/inf. 12 23, May 2007.[6]  FEDOROV, L.A.: “Pre-Convention Liquidation of Soviet Chemical Weapons’ in “Sea-Dumped Chemical Weapons: Aspects, Problems and Solutions”, Ed. AV Kaffka, Kluwer, Academic Publishers, Dordrecht, 1996, p 17 - 27.[7]  …: HELCOM “Report on Chemical Munitions Dumped in the Baltic Sea”, Report to the 16th Meeting of the Helsinki Commission 8-11 March 1994 from the Ad Hoc Working Group on Dumped Chemical Munitions, HELCOM CHEMU, January 1994.[8]  KAFFKA, A.V.: “Sea-Dumped Chemical Weapons: Aspects, Problems and Solutions”. Proceedings of the NATO Advanced Research Work-shop on “Sea-Dumped Chemical Munitions”, Kaliningrad, Russia, January 12-15, 1995. [9]  WALDROP, P.S.: “A parting of the (inclined) ways - US shipbuilding sails toward modern fabrication, assembly”,September 12, 2002, www.thefabricator.com[10] VALKOVIC, V., SUDAC, D., MATIKA, D., KOLLAR, R.:  “An un-derwater system for explosive detection”, SPIE Conference,Orlando, 2007, Proc. paper 6540-35.

English

Inspecting the Inside of Sunken Ships and Ship’s Underwater Hull

Hrčak - Portal of scientific journals of Croatia

1361(2010)1, 13-17INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER... V. VALKOVIĆ, D. MATIKA, D. SUDACUDC UDC 629.5.022:621.039Vladivoj VALKOVIĆ1Dario MATIKA2 Davorin SUDAC3Inspecting the Inside of Sunken Ships and Ship’s Underwater HullOriginal scientiﬁ c paperIn order to demonstrate the possibility of identifying the material within ship’s underwater hull, sunken ships, or other objects on the sea ﬂ oor, tests with a 14 MeV sealed tube neutron generator incorporated inside a small submarine were performed in the test basin ﬁ lled with sea water. The results obtained for inspection of diesel fuel and explosive presence behind single and double hull structures are presented.Keywords: neutron interrogation, explosive, diesel fuel, sunken ships, ship hullKontrola unutrašnjosti potopljenih brodova i podvodnih dijelova brodaIzvorni znanstveni radS ciljem demonstracije mogućnosti identiﬁ kacije materijala unutar podvodnog dijela broda, unutar potopljenih brodova i ostalih predmeta na morskom dnu, izvršeni su eksperimenti sa cijevnim 14 MeV neutronskim generatorom smještenim unutar male podmornice u bazenu napun-jenom morskom vodom. Prikazani su rezultati dobiveni inspekcijom dizelskog goriva i eksploziva smještenih iza jednostruke i dvostruke konstrukcije trupa broda.Ključne riječi: neutronska inspekcija, eksploziv, dizelsko gorivo, potopljeni brodovi, trup brodaAuthors’ addresses (Adrese autora):1 A.C.T. d.o.o., Prilesje 4, 10000 Zagreb, Croatia2 Institute  for Research and Devel-opment of Defence Systems, Ilica 256b, 10000 Zagreb3 Rudjer Boskovic Institute, P.O. Box 180, 10002 Zagreb, CroatiaReceived (Primljeno): 2009-09-15Accepted (Prihvaćeno): 2010-02-2Open for discussion (Otvoreno za raspravu): 2011-03-311 IntroductionMany of the materials on the bottom of the seas are due to numerous shipwrecks. There is a global risk of marine pollution from over 7800 sunken World War II vessels worldwide. Nu-merous efforts are made to compile data on WWII shipwrecks. The recent efforts include so called South Pacifi c Regional En-vironment Programme (SPREP) and AMIO databases of WWII shipwrecks [1-3]. Although work on the Pacifi c SPREP database is relatively complete, work on shipwrecks in other oceans has only recently commenced. The Atlantic, Mediterranean and In-dian Ocean (AMIO) WWII shipwreck database of is in its initial stages. Currently, the AMIO database contains information on the location and ownership of over 3953 WWII vessels, over 1000 gross tons, equalling to over 20 million tons of shipping, lying at the bottom of world’s oceans. The distribution of WWII shipwrecks from both databases is shown in Table 1.Some areas in Europe are of special interest because of large amouts of dumped ammunitions. These inclide the Baltic Sea, the Atlatic Ocean and the North Sea, and the Mediterranean [4-8]. Inspection of the cargo area within the ship’s body below water surface for the presence of threat materials is also required in the fi ght against terrorist activities. In such a scenario a detec-tion system needs to approach the ship’s underwater hull and analyze the material present at the other side of the ship’s hull, i.e. in the ship’s cargo area. Even though boat and ship building dates back to ancient times, some production technologies have been slow to change, illustrated by an only recent shift in technology at major ship-yards. The building of large ships is one of the most obvious applications of heavy plate fabrication. Iron vessels were fi rst built on a regular basis in England in the 1830s, and the fi rst such naval fi ghting vessel was used in England’s First China War of 1841-43. Steel began to replace iron construction in the 1870s as steel became more affordable [9]. Modern commercial ship hulls continue to be built with 14- to 19-millimeter-thick (0.5- to 0.75-inch) plate. Carbon steel is low-cost and easy to repair. These materials normally are specifi ed American Bureau of Shipping grade A, although sometimes grades B and H are used.Early hulls were riveted, but this approach evolved to 100 percent welded seams by World War II. The submerged arc Table 1  AMIO & SPREP shipwreck databases – Distribution of shipwrecks globallyTablica 1 AMIO & SPREP baze podataka brodskih olupina – glo-balna distribucijaOcean/seas Number of vesselsTotal tonnageNumber of tankersNorth Atlantic 3002 15108305 452 South Atlantic 198 1143374 20 Mediterranean 305 1578910 19 Indian 313 1813398 35 Arctic 124 729569 2 Pacifi c 3276 12158895 273 14 61(2010)1,13-17V. VALKOVIĆ, D. MATIKA, D. SUDAC INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER...welding (SAW) process makes up the majority of welding today, using ceramic backup strips where possible to maximize one-side welding. Double-hull construction is a fairly recent and major design change that affected fabrication and assembly. This was dictated by the Oil Pollution Act of 1990, with the goal of reduc-ing the risk of major environmental disasters caused by fuel and leaking oil and petroleum cargoes. Tanker hulls must be made with double construction, while other transport vessels, such as those for containers and bulk dry cargo, must have double-hull construction only in their fuel tank areas. While the outer hull is 14 to 19 mm thick, the inner hull may be 12 to 14 mm thick.Only the outer hull details are shaped to contour; inner hull details are designed to allow fabrication from fl at plate. Power roll-ing shapes the outer hull components that require simple curvature, with contour checked against CAD-generated templates. Parts that need compound curvature are formed by selective heating. The latter method requires the skill and experience of craftsmen who now can refer to a CAD-generated graphic matrix, which predicts specifi c locations and amounts of heat to be applied.For today’s large naval combat vessels, aluminium is used for lighter-weight topside structure, and composites that resist corro-sion are used for secondary items such as gratings and decking. However, steel continues to be the material of choice for hull structure. HSLA (high-strength, low-alloy) steel use has evolved over the last 20 to 30 years. Its advantages include increased strength and reduced thickness, which provides a weight saving that, in turn, reduces fuel consumption.2 ExperimentalIt is often required to inspect ship hulls, either to detect po-tential anomalies attached to the hull, or to determine the nature of materials within the hull, especially in the case of sunken ships. The material to be inspected is hidden behind the tanker walls having a thickness up to 25 mm in older ships, while in the modern ones the walls are only 14 to 16 mm thick. In addition, the new tankers are required to have double hull construction, outer hull 14-19 mm thick (shaped to contour), and inner hull 12-14 mm thick (fl at plate).In order to demonstrate the possibility of identifying the material within sunken ships and other objects on the sea fl oor, we have performed tests with the 14 MeV sealed tube neutron generator incorporated inside a small submarine submerged in the test basin fi lled with sea water [10]. The principle of the method used is demonstrated in Figure 1. Figure 1  The principle of the tagged neutron sensorSlika 1 Princip rada senzora koji koristi obilježene neutroneFigure 2  Geometrical arrangement of the neutron sensorSlika 2  Geometrijski prikaz neutronskog senzoraThe geometrical arrangement for the experiment is shown in Figure 2. The investigated targets were 10 litres of diesel fuel, 5 kg of explosive and different chemicals (expected components of chemical warfare agents) placed behind a 16-mm steel plate in the fi rst measurement and behind a sandwich of 18-mm steel plate – 10-cm air bag – 16-mm steel plate in the second measure-ment respectively. Using the window on the measured alpha-gamma time spectrum, the gamma rays originating from the investigated volume were separated from the background radiation. By the inspection of the measured gamma spectra we were able to identify all the investigated materials in both measurement geometries.  The inspection system, the experimental set-up and the pres-entation of the perfomed measurement are given in Figures 3 to 6. The measurement results are presented in Figures 7 to 13.Figure 3 Inspection system to be submerged into the water poolSlika 3  Sistem za inspekciju pripremljen za uron u bazen na-punjen vodom1561(2010)1, 13-17INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER... V. VALKOVIĆ, D. MATIKA, D. SUDACFigure 4  Schematic presentation of the experimental set-up for double hull construction, outer hull 14-19 mm thick, inner hull 12-14 mm thickSlika 4  Shematski prikaz eksperimentalnog postava za kon-strukciju dvostrukog trupa, vanjski trup debljine 14-19 mm, unutarnji trup debljine12-14 mmFigure 5  Double hull construction, the air bag is placed between two iron plates so that the whole set-up can be im-mersed in waterSlika 5     Dvostruki trup: zrakom ispunjen jastuk postavljen između dvije željezne ploče tako da čitav postav može uroniti u voduFigure 6   Schematic presentation of the performed measure-ments;  targets were TNT explosive (5 kg) and diesel fuel (10 l), the submarine was positioned about 2 cm above the upper iron plateSlika 6    Shematski prikaz izvršenih mjerenja; mete su bile TNT eksploziv (5 kg) i dizelsko gorivo (10 litara), podmornica je pozicionirana 2 cm iznad gornje pločeFigure 7 Gamma ray spectra from TNT (5 kg) target (top line), logarithmic scale; target out (bottom line); the total number of  the tagged neutrons 24 x 107; measurement time: ~6900 sSlika 7    Spektar gama zraka iz mete TNT (5 kg) – gornja krivulja, logaritamska skala; donja krivulja je bez mete; ukupni broj označenih neutrona 24x107; vrijeme mjerenja: ~ 6900 sFigure 8 Gamma ray spectra from TNT (5 kg) target (top line), linear scale; target out (bottom line); the total number of the tagged neutrons 24 x 107; measurement time: ~6900 s Slika 8 Spektar gama zraka iz mete TNT (5 kg) – gornja krivulja, linearna skala; donja krivulja je bez mete; ukupni broj označenih neutrona 24x107; vrijeme mjerenja:~6900 sFigure 9   Gamma ray spectra from diesel fuel (10 l), top line, behind the iron-air-iron sandwich in the sea water, logarithmic scale; target out: bottom line; total number of tagged neutrons 18 x 107; measurement time: ~5240 sSlika 9 Spektar gama zraka iz mete dizelskog goriva (10 l) iza željezo-zrak-željezo sendviča – gornja krivulja, logari-tamska skala, donja krivulja je bez mete; ukupni broj označenih neutrona 18x107; vrijeme mjerenja: ~ 5240 s16 61(2010)1,13-17V. VALKOVIĆ, D. MATIKA, D. SUDAC INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER...Figure 10 Gamma ray spectra from diesel fuel (10 l), top line, be-hind the iron-air-iron sandwich in the sea water, linear scale, target out: bottom line; total number of tagged neutrons 18 x 107; measurement time: ~5240 sSlika 10     Spektar gama zraka iz mete dizelskog goriva (10 l) iza željezo-zrak-željezo sendviča – gornja krivulja, linearna skala; donja krivulja je bez mete; ukupni broj označenih neutrona 18x107; vrijeme mjerenja: ~ 5240 sFigure 11  Schematic presentation of the experimental set-up (single hull); the whole set-up is immersed in water; targets were TNT explosive (5 kg) and diesel fuel (10 l); the submarine was positioned about 2 cm above the iron plateSlika 11  Shematski prikaz eksperimentalnog postava (jednos-truki trup); čitav je postav uronjen u vodu, mete su bile TNT eksploziv (5 kg) i dizelsko gorivo (10 l); podmornica je pozicionirana na 2 cm iznad željezne pločeFigure 12   Gamma spectrum from diesel fuel behind the iron plate 16 mm thick (12 x 107 tagged neutrons, measurement t = 3438 s)Slika 12 Spektar gama zraka iz dizelskog goriva smještenog iza željezne ploče debljine 16 mm (12x107 označenih neutrona, vrijeme mjerenja t = 3438 s) Figure 13 Gamma spectrum from 5 kg of  TNT behind the iron plate 16 mm thick (12 x 107 tagged neutrons, measure-ment time 3490 s); logarithmic scale – bottom; linear scale - topSlika 13     Spektar gama zraka iz 5 kg TNT smještenog iza željezne ploče debljine 16 mm (12x107 označenih neutrona, vrijeme mjerenja 3490 s); logaritamska skala – donja slika; linearna skala – gornja slikaThe thickness of the iron plate positioned between the sub-marine and the explosive (mass 5 kg) was varied. Submarine to explosive (mass 5 kg) distance was 11 cm. The graph in Figure 14 shows the number of counts in carbon 4.44 MeV peak (black) and oxygen 5.62 MeV peak – fi rst escape peak of oxygen 6.13 MeV line (red) as a function of iron plate thickness. Solid lines correspond to the exponential fi t (a e-b x). The total number of tagged neutrons in each measurement was 3.6 x 108, with neutron beam of ~107 n/s corresponding to the measurement time of ~176 min. The measurements were done for a long time period in order to obtain better statistics. Conclusions on the existence of peaks can be reached in much shorter time.Table 2 contains the parameters of the exponential fi t (a e-bx) shown in Figure 14.1761(2010)1, 13-17INSPECTING THE INSIDE OF SUNKEN SHIPS AND SHIP'S UNDERWATER... V. VALKOVIĆ, D. MATIKA, D. SUDACTable 2 Parameters of the exponential ﬁ t (a e-b x) shown in Figure 14Tablica 2 Parametri eksponencijalnog ﬁ ta (a e-b x) prikazanog na slici 14Element a b (1/mm)Carbon 6169 ± 318 0.043 ± 0.004Oxygen 2379 ± 411 0.05 ± 0.02Figure 14  The number of counts in carbon 4.44 MeV peak (up-per) and oxygen 5.62 MeV peak – ﬁ rst escape peak of oxygen 6.13 MeV line (lower) as a function of iron plate thicknessSlika 14 Broj događaja u ugljikovom vrhu 4,44 MeV (gornja kriv-ulja) i kisikovom sekundarnom vrhu 5,62 MeV, od 6,13 MeV linije (donja krivulja) u funkciji debljine željezne ploče The number of counts in 4.44 MeV carbon peak for different iron plate thicknesses is shown in Table 3, while Table 4 gives the number of counts in 5.62 MeV oxygen peak for different iron plate thicknesses under the identical experimental condi-tions (see above).Table 3 The number of counts in 4.44 MeV carbon peak for dif-ferent iron plate thicknessesTablica 3 Broj događaja u ugljikovom 4,44 MeV vrhu u funkciji debljine željezne pločeThickness (mm)Number of counts in 4.44 MeV peakError0.0 5985 5428.0 4797 58115.0 3053 44523.0 2405 38832.0 1101 33440.0 1303 489Table 4 The number of counts in 5.62 MeV oxygen peak for dif-ferent iron plate thicknessesTablica 4 Broj događaja u kisikovom 5,62 MeV vrhu u funkciji debljine željezne pločeThickness (mm)Number of counts in 5.62 MeV peakError0.0 2203 4138.0 2119 50615.0 857 27923.0 684 245 In comparison with benign materials, TNT explosive is char-acterized with a high C/O ratio. However, in the case of thicker iron plates conclusions can be drawn in some situations from the presence of carbon peak only.3 ConclusionsIt is often required to inspect ship hulls, either to detect potential anomalies attached to the hull, or to determine the nature of materi-als within the hull, especially in the case of sunken ships. Older tanker walls have a thickness up to 25 mm, while the modern ones are only 14 to 16 mm thick. In addition, the new tankers are required to have double hull construction, outer hull 14-19 mm thick (shaped to contour), inner hull 12-14 mm thick (fl at plate).In order to demonstrate the possibility of identifying the material within sunken ships and other objects on the sea fl oor we performed tests with the 14 MeV sealed tube neutron genera-tor incorporated inside a small submarine submerged in the test basin fi lled with sea water. Measurements were performed with the following targets: 10 litres of diesel fuel, 5 kg of explosive and different chemi-cals (expected components of chemical warfare agents) placed behind a 16-mm steel plate in the fi rst measurement and behind a sandwich of 18-mm steel plate – 10-cm air bag – 16-mm steel plate in the second measurement respectively. Using the window on the measured alpha-gamma time spec-trum, the gamma rays originating from the investigated volume were separated from the background radiation. By the inspection of the measured gamma spectra we were able to identify all the investigated materials in both measurement geometries.  References[1]  MONFILS, R.: “The Global Risk of Marine Pollution from WWII Shipwrecks: Examples from Seven Seas”, Submitted to International Oil Spill Conference, Miami, Florida, 2005.[2]  …: SPREP  “Regional Strategy to Address Marine Pollution from WWII Shipwrecks in the Pacifi c”. Phase 1-Report and Preliminary Risk Assessment. CD-ROM, 2003.[3]  …: OSPAR Commission “Overview of Past Dumping at Sea of Chemi-cal Weapons and Munitions in the OSPAR Maritime Area”, Revise, ISBN 1-904426-54-9, 2004.[4]  …: Advisory Committee on Protection of the Sea (ACOPS) “Coastal Survey of Packaged Chemical and other Hazardous Items 2002/2003”, Maritime and Coastguard Agency Research Project No. 488, London, October 2003. Australian Goverment, Department of Defense, Chemi-cal Warfare Agent Sea Dumping off Australia, Revised and updated edition 2003, Canberra ACT 2600.[5]  …: United Nations Environmental Programme “Dumping Sites of Ammunitions in  the Mediterranean Sea”, UNEP (DEPI)MED WG. 316/inf. 12 23, May 2007.[6]  FEDOROV, L.A.: “Pre-Convention Liquidation of Soviet Chemical Weapons’ in “Sea-Dumped Chemical Weapons: Aspects, Problems and Solutions”, Ed. AV Kaffka, Kluwer, Academic Publishers, Dordrecht, 1996, p 17 - 27.[7]  …: HELCOM “Report on Chemical Munitions Dumped in the Baltic Sea”, Report to the 16th Meeting of the Helsinki Commission 8-11 March 1994 from the Ad Hoc Working Group on Dumped Chemical Munitions, HELCOM CHEMU, January 1994.[8]  KAFFKA, A.V.: “Sea-Dumped Chemical Weapons: Aspects, Problems and Solutions”. Proceedings of the NATO Advanced Research Work-shop on “Sea-Dumped Chemical Munitions”, Kaliningrad, Russia, January 12-15, 1995. [9]  WALDROP, P.S.: “A parting of the (inclined) ways - US shipbuilding sails toward modern fabrication, assembly”,September 12, 2002, www.thefabricator.com[10] VALKOVIC, V., SUDAC, D., MATIKA, D., KOLLAR, R.:  “An un-derwater system for explosive detection”, SPIE Conference,Orlando, 2007, Proc. paper 6540-35.

Inspecting the Inside of Sunken Ships and Ship’s Underwater Hull

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