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Neutronska proba za ispitivanje naftnih bušotina razvijena je na Institutu Ruđer Bošković u okviru HRZZ projekta IP-2018-01-4060 ''Nove primjene 14 MeV neutrona''. U ovom istraživanju ispitane su daljnje mogućnosti redukcije šuma u mjerenju C/O omjera metodom pridružene alfa čestice. Mješavina kvarcnog pijeska i grafitnog praha korištena je kao materijal od interesa , dok su plastične bočice ispunjene dizel gorivom korištene kao šum (smetnja) i predstavljaju tekućinu unutar naftne bušotine (npr. nafta). Podjela alfa detektora na četiri jednaka segmenta, omogućila je podjelu volumena oko osi neutronske probe na četiri kvadranta. Materijal od interesa i dizel smješteni su u različite kvadrante i pokazano je da su C/O vrijednosti u slučajevima kad je smetnja prisutna unutar statističke greške u odnosu na slučaj kada smetnje nema., The neutron probe for testing oil wells was developed at the Ruđer Bošković Institute within the HRZZ project IP-2018-01-4060 "New applications of 14 MeV neutrons". In this study, further possibilities of noise reduction in C/O ratio measurement by the associated alpha particle method were investigated. A mixture of quartz sand and graphite powder was used as the material of interest, while plastic bottles filled with diesel fuel were used as noise (interference) and represent the liquid inside the oil well (e.g. oil). Dividing the alpha detector into four equal segments, allowed portioning the volume around the neutron probe axis into four quadrants. The material of interest and diesel were located in different quadrants and it is shown that the C/O values in cases where interference is present are within statistical errors compared to the case where there is no interference.

A recently developed concept of a neutron probe (NP) -for C/O oil logging, based on associated alpha particle technique, has been developed and demonstrated by using a specially constructed NP. The NP contains a high-temperature alpha particle detector as well as a gamma detector with high energy resolution, suitable for a high-temperature environment. The probe was tested on samples collected from Croatian oil fields and on samples prepared with known C/O ratios. This NP in comparison to conventional neutron activation probes significantly reduces the background signal coming from the borehole and measures the C/O ratio depending on the azimuth angle around the borehole longitudinal axis. The time (position) resolution was found to be 2 ns enabling inspection of the C/O ratio in rock formations’ layers down to 10 cm thickness. The NP was successfully tested for different environmental temperatures up to 175 °C. The pulse amplitude degradation coming from the gamma detector was noticed to be a function of the temperature.

The aim of the research reported here is the development of a methodology for the measurement of small scale variations in chemical elements concentrations, in particular of carbon – oxygen ratio. Knowledge of the C/O ratio is of importance to many problems in various fields. Here we single out the application in obtaining important information about the oilfields. The most fundamental reservoir parameters – oil, gas and water content – are critical factors in determining how each oilfield should be developed. It is well established that carbon to oxygen ratio log yields accurate and repeatable data that can be used to identify and monitor reserves depletion. Recent improvements in neutron generator and gamma detector technologies resulted in small devices which allowed through-tubing measurements. Although the ratio of carbon and oxygen yields is a measure of the amount of oil around the tool it should be realized that a carbon signal can originate from several sources including the borehole, the cement behind the casing, the formation rock and the formation fluid. In order to evaluate these contributions individually we are proposing the modification of the neutron generator by insertion of segmented associated alpha particle detector. From the measurement of time of flight spectra (alpha particle detector – start signal ; gamma ray detector – stop signal) it would be possible to determine the location of gamma ray producing voxel and in such a way to determine radial variations in several chemical elements concentrations, in particular of carbon to oxygen ratio.

FNAA, underwater inspection, explosives

The maintenance and repair of reinforced concrete structures, especially those submerged in the sea-water, requires effective inspection and monitoring techniques for assessing the state of corrosion in reinforcement material. An underwater inspection system was developed which is able to monitor the reinforcement corrosion. The system is remotely operating vehicle (ROV) equipped with the sealed tube neutron generator (NG). By rotating the NG and by using the associated alpha particle technique it is possible to measure the concrete cover depth together with the reinforcing bar diameter. The possibility to estimate the carbon and chloride content in the concrete was investigated. Iron plates of different thickness, covered by 6 cm thick concrete block, were successfully detected and the thickness of the concrete cover was estimated. In addition, reinforced bar of one and three centimeters in diameter was identified and measured.

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

It was already shown in the previous work that the tagged neutron inspection system (TNIS), which uses the associated particle imaging (API) technique, was able to detect explosive in a sea-going cargo container filled with an iron matrix with density 0.2 g/cm3 [1]. It was also shown the possibility of TNIS to detect the explosive in the organic matrix with density ≤ 0.25 g/cm3 [2]. In this work the possibility of TNIS to identify materials hidden behind or in front of dense organic goods is investigated. A paper target, which is a good explosive simulant, is put close to the flour surroundings. A triangle diagram is made from the number of counts in the carbon peak, number of counts in the oxygen peak and the number of counts in the transmitted neutron peak. Identification of the paper target is possible if some appropriate knowledge about the surroundings is known.

The container scanning system based on the elemental analysis of suspect cargo by use of fast 14 MeV neutrons with detection of associated alpha particle has been recently developed under the EU-FP6 "EURITRACK" project. The system is currently set-up in port of Rijeka, Croatia, to be tested and upgraded under the EU-JLS ERITR@C project. Here we present results of analysis performed on 152 screened containers selected by the Croatian Custom and detail descriptive statistical analysis of their shipping manifests. Statistics such as distribution functions of container types, type of packages, type of cargos and average cargo densities were obtained in order to establish the properties of standard cargo traffic. The analyses by using multivariate statistical approach that included principal component analysis (PCA) and between group analysis (BGA) have shown that cargo matrices can be classified as metallic (Fe, Al, Cu, Zn, Ni...), ceramic-glass (Si, O) and organic (C, O, N). In this paper the organic matrices have been analysed in more detail since they are identified as most difficult because of their potential interference with main elements contained in threat materials such as explosives or drugs. Density as a discriminating factor has been included for better recognition of different types of goods.

The EURopean Illicit TRAfficking Countermeasures Kit (EURITRACK) inspection system uses 14 MeV neutrons produced by the D(T, n α) reaction to detect explosives in cargo containers. Reactions induced by fast neutrons inside the container produce gamma rays, which are detected in coincidence with the associated alpha particle, the detection of which allows the neutron direction to be determined. The neutron path length is obtained from a neutron time-of-flight measurement, thus allowing the origin of the gamma rays inside the container to be determined, while the chemical composition of the target material is correlated with their energy spectrum. Gamma-ray spectra have been collected with the inspection portal equipped with large volume NaI (Tl) detectors, in order to build a database of signatures for various elements (C, O, N, Fe, Pb, Al, Na, Si, Cl, Cu, Zn) with a low energy threshold of 0.6 MeV. The spectra are compared with previous ones, which were acquired with a 1.35 MeV threshold. The new library is currently being tested to unfold the energy spectra of transported goods into elemental contributions. Results are compared with data processed with the old 1.35 MeV threshold database, thus illustrating the improvement for material identification.

Several tests have been done with the neutron generator incorporated inside a small submarine equipped also with a few other sensors like video cameras and a magnetometer. Following the detection of an anomaly on the sea bottom a neutron sensor is requested to check for the presence of explosives. In the experiment, the TNT explosive was measured behind an iron shield. Comparison was made with similar measurements when the TNT explosive was replaced by stones. By measuring the C/O ratio the TNT explosive was successfully identified. All the measurements were done first in air and after that repeated in freshwater and in sea water.

The EURopean Illicit TRAfficking Countermeasures Kit (EURITRACK) inspection system has been developed within the 6th EU Framework Program to complement X-ray scanners in the detection of explosives and other illicit materials hidden in cargo containers. Gamma rays are produced inside the cargo materials by 14 MeV tagged neutron beams, which yields information about the chemical composition of the transported goods. In the beginning of year 2007, the EURITRACK system was implemented in the Seaport of Rijeka, Croatia, primarily to carry out a demonstration using real containers to conduct a series of detection tests. This article reports tests performed with real samples of illicit drugs hidden in a metallic cargo with an average density of 0.2 g/cm3. Heroin and cocaine have been distinguished from benign substances based on their chemical composition. Marijuana, which chemical composition is similar to benign materials, cannot be distinguished from common organic goods. However, the detection of an unexpected organic substance inside the metallic cargo indicates that a suspicious object has been hidden in the container.

Tagged neutron inspection system was used for the detection of explosive in water. Neutrons were produced in d+t nuclear reaction with API 120 sealed tube neutron generator. Five kilograms of the TNT explosive were measured in a pool filled with water. Measurements were done in target in, target out configuration. In addition, a sandwich made of 6 mm thick iron plates with explosive in between was placed between two layers of sea sediments and measured underwater. Sediments were collected in the Adriatic Sea. Measurements were repeated with TNT explosive replaced by rocks of similar size and shape. Neutron tube was rotated in order to find the position and dimension of explosive (rocks) in the sandwich. It was found that TNT can be detected in the water. Morover, TNT and, sea rocks have had distinguished ratio of carbon and oxygen while measured between 6 mm thick iron plates and placed between layers of sediments.

Matrix characterization in the threat material detection is of utmost importance, it generates the background against which the threat material signal has to be identified. Threat materials (explosive, chemical warfare, ...) are usually contained within small volume inside large volumes of variable matrices. We have studied the influence of matrix materials on the capability of neutron systems to identify hidden threat material. Three specific scenarios are considered in some details: case 1 - contraband material in the sea containers, case 2 - explosives in soil (landmines), case 3 - explosives and chemical warfare on the sea bottom. Effects of container cargo material on tagged neutron system are seen in the increase of gamma background and the decrease of neutron beam intensity. Detection of landmines is more complex because of variable soil properties. We have studied in detail space and time variations of soil elemental compositions and in particular hydrogen content (humidity). Of special interest are ammunitions and chemical warfare on the sea bottom, damping sites and leftovers from previous conflicts (WW-I, WW-II and local). In this case sea sediment is background source and its role is similar to the role of the soil in the landmine detection. In addition to geochemical cycling of chemical elements in semi-enclosed sea, like the Adriatic Sea, one has to consider also anthropogenic influence, especially when studying small scale variations in concentration levels. Some preliminary experimental results obtained with tagged neutron sensor inside an underwater vehicle are presented as well as data on sediment characterization by X-Ray Fluorescence.

It was already shown in the previous work that the tagged neutron inspection system (TNIS) was able to detect the explosive in the sea-going cargo container filled with the iron matrix with density 0.2 g/cm3 [1]. It was shown also the possibility of TNIS to detect the explosive in the organic matrix with density ¤0.25 g/cm3 [2]. In this work the possibility of TNIS to identify the materials hidden behind or in front of dense organic goods is investigated. Paper target, which is a good explosive simulant, is put close to the flour surroundings. Triangle diagram is made from the number of counts in the carbon peak, number of counts in the oxygen peak and the number of counts in the transmitted neutron peak. Identification of the paper target is possible if some appropriate knowledge about the surroundings is known.

Security is no longer only exclusive part of the military and political spheres, but a complex phenomenon that demands a comprehensive approach, which includes socio-economic and environmental issues. One critical aspect of this integral approach concerns seas and coasts, on which local population relies for sustenance and livelihood options, and which underpins vital economic sectors such as trade, tourism, energy and defence. The protection of the coastal sea waters and harbours is of paramount importance for littoral nations. This has been a task with the increasing difficulty for its implementation due to the increase in sea traffic volume, both cargo and passengers, increase in other activities from tourism to resource exploitation. Lately, a new item has been added to this task, namely, protection from the eventual terrorist activities. The coastal sea floor is littered with many of man made objects and materials including a variety of ammunition. In addition, sediments in ports, harbors and marinas have increased concentrations of chemicals used as biocides in antifouling paints. Therefore, one has to develop capabilities of measuring concentrations of chemical elements in the sediments, determining the content of different containers, establishing the presence of threat materials, identifying the material within sunken ships. All littoral nations are investing lots of effort into the remediation of their coastal areas. In this report our efforts in evaluation of environmental security of specific locations in the eastern Adriatic Sea are being discussed. The length of Croatian Adriatic coast is on the continent 1, 880 km and on islands 4, 398 km, the total being 6, 278 km. Croatia has 1, 242 islands, large and small, populated with some 130, 000 inhabitants. Coastal region of Croatia is divided into seven administrative units, counties, called “ županija” . In this report the locations in Adriatic Sea and whole Mediterranean for which there are evidences that are contaminated by different ammunition are presented, as well as the maps showing the mine fields in the Adriatic Sea after the World War II. It is well established that today’ s reports on the findings of ship mines correspond to the edges of mine fields from the WW II. The available data and information on explosive devices found in Adriatic Sea are collected ; the tabular presentation on types and locations of explosive devices has been given. The locations of explosive devices, listed by counties, are known from the information collection campaign. It is estimated that on locations along Croatian Adriatic coast there are about 250 000 tons of explosives. The characteristics of explosive devices which could be found on the bottom of the sea are presented. Since the official Standard Operational Procedures (SOP) do not exist we have listed in this report the operational procedures which must be respected when the explosive device is found and when the location for its temporary removal is determined. In addition, we have so far collected some 500 sediment samples corresponding to approximately one sediment sample per 12.5 km of the coastal line. The collected sediment samples have been analyzed for 18 chemical elements by using EDXRF as an analytical tool. Contour maps of antifouling biocide elements (Cu, Zn, As and Pb) have been generated for the entire eastern coast of Adriatic Sea indicating the locations of “ hot spots” in the distribution of chemical elements used as biocides (Cu, Zn, As, Pb). In order to be able to establish if an object on the sea floor contains some sort of threat material (explosives, chemical warfare) a system using neutron sensor installed within an unmanned underwater vessel has been developed and tested. When positioned above the object such a system can inspect the object for the presence of the threat material by using alpha particle tagged neutrons from the sealed tube d+t neutron generator. It is often required to inspect ship hulls, either to detect potential anomalies attached to the hull, or to determine the nature of materials within hull, especially of sunken ships. We have performed tests with our system submerged in the test basin filled with sea water with targets being: 10 litters of diesel fuel, 5 kg of explosive and different chemicals (expected components of chemical warfare agents) placed behind 16 mm steel plate in the first measurement and behind sandwich 18 mm steel plate – 10 cm air bag – 16 mm steel plate in the second measurement, respectively.

The coastal sea floor is littered with many of man made objects and materials including a variety of ammunition. In addition, sediments in ports, harbors (civilian and military) and marinas have increased concentrations of chemicals used as biocides in antifouling paints. Therefore, one has to develop capabilities of measuring concentrations of chemical elements in the sediments, determining the content of different containers, establishing the presence of threat materials (explosives, chemical warfare), identifying the material within sunken ships. In this report the activities related to the development of capabilities for the evaluation of environmental security of the coastal sea floor are summarized: 1. Several hundred coastal sea sediment samples have been collected and analyzed for 18 chemical elements by using EDXRF as an analytical tool. Contour maps of antifouling biocide elements (Cu, Zn, As and Pb) have been generated for the entire eastern coast of Adriatic Sea indicating the locations of “ hot spots” in the distribution of chemical elements used as biocides (Cu, Zn, As, Pb). 2. In order to be able to establish if an object on the sea floor contains some sort of threat material (explosives, chemical warfare) a system using neutron sensor installed within an unmanned underwater vessel has been developed and tested. When positioned above the object such a system can inspect the object for the presence of the threat material by using alpha particle tagged neutrons from the sealed tube d+t neutron generator. 3. While the commonly used military explosives are characterized by the presence of only four chemical elements (C, H, N, O) chemical warfare agents usually have in addition one or more chemical element (P, S, Cl, F, As or Br). The results from the laboratory tests for the detection of the presence of these chemical elements are presented. 4. It is often required to inspect ship hulls, either to detect potential anomalies attached to the hull, or to determine the nature of materials within hull, especially of sunken ships. We have performed tests with our system submerged in the test basin filled with sea water with targets being: 10 litters of diesel fuel, 5 kg of explosive and different chemicals (expected components of chemical warfare agents) placed behind 16 mm steel plate in the first measurement and behind sandwich 18 mm steel plate – 10 cm air bag – 16 mm steel plate in the second measurement, respectively. The results of these measurements are presented.