The possibility of using a fast neutron beam with the associated alpha particle (AAP) technique in conjunction with a specially designed probe for carbon-to-oxygen (C/O) nuclear well logging was ...investigated. Measurements were performed to show the influence of borehole fluid, iron casing, and the cement around the casing in the C/O analysis. Tests were conducted by using fast neutron activation analysis (FNAA), as the conventional approach for C/O measurements in well logging and by using AAP. Analyzed samples were made from quartz sand and graphite powder mixed in different C/O ratios characteristic for the oil-containing formations. Diesel fuel was used as a simulant of the borehole fluid. Monte Carlo (MC) simulations were conducted and the results were compared with the experimental data. In both tests, the linear relation between the measured and real C/O ratios was obtained, but when the FNAA was used, the linear relation was significantly influenced mainly by the presence of the borehole fluid. Contrary to FNAA, the AAP technique resulted in a significant reduction of the background signal coming from the borehole fluid.
•A neutron probe for oil logging was developed with an outside diameter of 43 mm.•NP was equipped with a four-segmented alpha particle detector operable at high temperatures.•The possibility of ...measuring the C/O ratio as a function of the angle around the NP axis was shown.•Measurements were done on geological samples taken from Croatian oilfields.•Measurements on the high-temperatures show degradation of the signal coming from the gamma-ray detector.
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 14-MeV neutron-induced nuclear reactions which might contribute to better understanding of the so-called "cosmological lithium problem" have been discussed. The big bang nucleosynthesis theory ...predicted 7 Li overestimated value could be lowered by 2 n-induced reactions on Li isotopes and/or 7 Be destruction via resonance in the d + 7 Be → 9 B process. Proposals for 6 Li + 2 n and 7 Li + 2 n reactions' cross section evaluations and measurements are discussed in some details. In addition, we discuss also a preliminary measurements of n-n coincidences from the 10 B(n,2n) 9 B reaction with two neutron detectors placed outside the cone of 14-MeV tagged neutron beam. From the time-of-flight measurements and known geometry, we tried to deduce the neutron energies and calculate the 9 B missing mass spectrum. Improvements for better measurements are suggested.
A neutron-based sensor has been developed able to measure the water cut and the chlorine content in crude oil. The sensor is based upon the use of a pulsed fast neutron source. Two different cases ...were studied. Case ‘‘A’’: chlorine detection with no water present and case ‘‘B’’: water cut measurements with no chlorine present. The minimum detection limits for case A and case B were found to be (62 ± 6) mg/L and (2 ± 2) vol%, respectively.
•A neutron sensor for on-line determination of water-cut and chlorine impurities in crude oil was developed.•Measurements were done on geological samples taken from Croatian oilfields and on standard samples prepared in the laboratory.•Since both chlorine and oxygen have similar gamma-ray lines at 6.1 MeV, these two were separated by choosing a different pulsing frequency for the neutron beam.•A similar setup (neutron probe) could be easily made for monitoring individual wells.
The 14 MeV neutron induced nuclear reactions which might contribute to better understanding of so-called “cosmological lithium problem” have been discussed. The BBN theory predicted
7
Li ...overestimated value could be lowered by
2
n induced reactions on Li-isotopes and/or
7
Be destruction via resonance in d+
7
Be→
9
B process.
Proposals for
6
Li+
2
n and
7
Li+
2
n reactions cross section evaluations and measurements are discussed in some details.
We discuss also a preliminary measurements of n-n coincidences from the
10
B(n,2n)
9
B reaction with two neutron detectors placed outside the cone of 14 MeV tagged neutron beam. From the time-of-flight measurements and known geometry we deduce the neutron energies and calculate the
9
B missing mass spectrum.
It was demonstrated in the previous work that various threat materials could be detected inside the sea going cargo container by measuring the three variables, carbon and oxygen concentration and ...density of investigated material. Density was determined by measuring transmitted neutrons, which is not always practical in terms of setting up the instrument geometry. In order to enable more geometry flexibility, we have investigated the possibility of using the scattered neutrons in cargo material identification. For that purpose, the densities of different materials were measured depending on the position of neutron detectors and neutron generator with respect to the target position. One neutron detector was put above the target, one behind and one in front of the target, above the neutron generator. It was shown that all three positions of neutron detectors can be successfully used to measure the target density, but only if the detected neutrons are successfully discriminated from the gamma rays.
The maintenance and repair of reinforced concrete structures, especially those submerged in the sea-water require effective inspection and monitoring techniques for assessing the state of corrosion ...in the reinforcement material. An underwater inspection system was developed which is able to monitor the corrosion of the reinforcement. The system is composed of a 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 thickness together with the reinforcing bar diameter. The possibility of estimating the carbon and chloride contents 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, reinforcing bar of one and 3 cm in diameter were identified and measured. All measurements could be performed without cleaning the concrete surface from fouling material.
•An underwater inspection system was developed which is able to monitor the state of reinforcement corrosion.•The system is composed of a remotely operating vehicle (ROV) equipped with the sealed tube neutron generator (NG).•All measurements could be performed without cleaning the concrete surface from fouling material.
In the frame of the FP7 UNCOSS project (Underwater Coastal Sea Surveyor), whose aim is to develop a neutron-based explosive detection system to identify unexploded ordnance (UXO) lying on the sea ...bottom, the choice of the gamma-ray detector is essential to reach the optimal performances. This paper presents comparative tests between the two candidates: NaI(Tl) and LaBr
3(Ce) detectors, in favour to the 3
in.×3
in. LaBr
3(Ce); thus, confirming the choice previously performed by numerical simulation because of its higher fast timing properties, spectral resolution, and efficiency per volume unit. The gamma-ray spectra produced by 14
MeV tagged neutron beams on the elements of interest (C, O, N, Al, Fe, Si, and Ca) have also been recorded with this detector in order to unfold the spectrum of the interrogated object into elementary contributions. A qualitative comparison with the gamma-ray spectra simulated with the MCNPX computer code and the ENDFB/VII.0 nuclear library has also been performed to validate the numerical model. An additional quantitative validation has been performed with an explosive-like material (ammonium acetate).
Relatively recently, in the last 20 years, it was discovered that methane hydrate (MH) deposits are globally distributed in the permafrost and oceans. Before 1965 when first deposits were discovered ...in nature, it was believed that MH can occur only in laboratory conditions or in vast parts of the Universe. Presently it is presumed that this solid crystalline compounds in which CH4 molecules occupies the water ice lattices (nominal chemical formula of MH is C4H62O23) can serve as an energy source favorably to the all of the world remaining conventional hydrocarbon sources. The worldwide estimates of MH deposits range from 2x1014 m3 to 3.053x1018 cubic meters. This uncertainty partly results from our limitations in geological understanding of the MH deposits, which is due to the relatively bad quality of data obtained by presently available seismic and electromagnetic techniques. Moreover, MH deposits can become vulnerable to climate changes, which were already occurring in geological past whit tremendous consequences for the global life on Earth. Thus, further development of advanced techniques is needed to enhance our abilities to better characterize, quantify and monitor the MH deposits. In the work presented 14 MeV neutrons and associated alpha particle imaging (API) where used to quantify the amount of MH in the sample. Samples were prepared from sea sediment, quartz sand and MH simulant. MH simulant with chemical formula C4H46O23 was made from sucrose (25 % by mass) and water. MH quantity was measured by measuring the carbon content in the sample 1-8.
A next generation system, as an upgrade of a robotic mobile system for anti-personnel landmine clearance, was considered. In contrast to the first generation system where the fast neutron activation ...method and the associated alpha particle imaging (API) was supposed to be used for finding the residual explosives and/or landmines, in the next generation system fast neutrons (FN) was considered to be used only for the confirmation of the explosive in the suspected object previously found by the ground penetrating radar (GPR), metal detector (MD) and infrared imaging (IR). Such system is expected to have the acceptable price and the optimal demining vehicle speed of 10 cm/s. In contrast to the previous system only one neutron generator (NG) is needed. In order to study the possibility of FN to confirm the presence of TNT explosive in the real environment the tests were made with the soil of different moisture contents. Comparative study was done by using the 7.62 cm × 7.62 cm BGO, 7.62 cm × 7.62 cm LaBr 3 : Ce and 7.62 cm × 7.62 cm NaI(Tl) gamma-ray detectors. Although nitrogen was easily detected in larger amount of TNT explosive, its signal was weak in detection of Anti-Personal (AP) mine like DLM2.4. The presences of soil additionally diminish the possibility of nitrogen detection even in the Anti-Tank mines (AT).
PDF
