Thermal neutron activation analysis of some toxic and trace chemical element contents in Mentha pulegium L.

Our laboratory of neutron activation analysis is highly involved in nutrition applications in the framework of research activities using the Algerian research reactor. The medicinal and aromatic plants of Mentha pulegium L. have been largely used in traditional medicine for several centuries to contribute significantly to human health related to digestive ailments, it is also used to reduce nervousness and anxiety. The present study focuses on the analysis of leaves of M. pulegium L., for evaluation of essential and toxic elements using a sensitive nuclear analytical technique based on instrumental neutron activation analysis (INAA). Twenty-one elements were assessed (As, Ba, Br, Ca, Ce, Cr, Cs, Co, Eu, Fe, Hf, K, La, Na, Rb, Sb, Sc, Sm, Sr, Yb and Zn) and the accuracy of the method was evaluated by analyzing the Certified Reference Materials (CRMs) GBW 07605 (tea leaves) and NIST-SRM 1573a (tomato leaves). The daily intake of essential and toxic elements was determined and compared with the recommended values and was found to be well below the tolerance limits.

Production, isolation and characterization of radiochemically pure 163Ho samples for the ECHo-project

Several experiments on the study of the electron neutrino mass are based on high-statistics measurements of the energy spectrum following electron capture of the radionuclide 163Ho. They rely on the availability of large, radiochemically pure samples of 163Ho. Here, we describe the production, separation, characterization, and sample production within the Electron Capture in Holmium-163 (ECHo) project. 163Ho has been produced by thermal neutron activation of enriched, prepurified 162Er targets in the high flux reactor of the Institut Laue-Langevin, Grenoble, France, in irradiations lasting up to 54 days. Irradiated targets were chemically processed by means of extraction chromatography, which allowed separating the formed Ho from the 162Er target-material and from the main byproducts 170Tm and 171Tm, which are co-produced in GBq amounts. Decontamination factors of >500 for Er and of >105 for Tm and yields of 3.6·1016 and 1.2·1018 atoms of 163Ho were obtained, corresponding to a recovery yield of 95 % of Ho in the chemical separation. The Ho-fraction was characterized by means of γ-ray spectrometry, Inductively-Coupled-Plasma Mass Spectrometry (ICP-MS), Resonance Ionization Mass Spectrometry (RIMS) and Neutron Activation Analysis (NAA). In this process, the thermal neutron capture cross section of 163Ho was measured to σHo-163 to Ho-164m= (23±3) b and σHo-163 to Ho-164g= (156±9) b for the formation of the two isomers of 164Ho. Specific samples were produced for further purification by mass separation to isolate 163Ho from the Ho-isotope mixture, as needed for obtaining the energy spectrum within ECHo. The partial efficiency for this second separation step is (32±5) %.

DETECTOR RESPONSE FROM THERMAL NEUTRON ACTIVATION OF CONCEALED EXPLOSIVES

Explosives concealed in small quatitites (~100 g), buried in landmines or in baggage, can be detected by characteristic gamma rays produced by neutron activation. However, the detection response can be reduced by attenuation of the signal in the background medium. This paper carries out a Monte Carlo simulation, using MCNP-V, to estimate the gamma signal spectrum and intesity degradation at a sodium iodide (NaI) detector from a small sample of trinitrotoluene (TNT) explosive buried in limestone. It is found that the transmission across 25 cm of limestone is ~6% of the 2.2233 MeV hydrogen signal and ~20% of the nitrogen signal. An empirical formula, obtained from MCNP re-runs, is used to estimate the signal strength from TNT, buried at 5-25 cm in limestone, for a californium source (252Cf) emitting 2.31 x 107 n/s. It is found that for TNT mass in the range 0.1-3 kg, the signatures are in the range 20-2000 s-1 from nitrogen and 24-2400 s-1 from hydrogen. These estimates can be used to determine the scanning time for an explosives detection system.

The sensitivity studies of a landmine explosive detection system based on neutron backscattering using Monte Carlo simulation

This paper carries out a Monte Carlo simulation of a landmine detection system, using the MCNP5 code, for the detection of concealed explosives such as trinitrotoluene and cyclonite. In portable field detectors, the signal strength of backscattered neutrons and gamma rays from thermal neutron activation is sensitive to a number of parameters such as the mass of explosive, depth of concealment, neutron moderation, background soil composition, soil porosity, soil moisture, multiple scattering in the background material, and configuration of the detection system. In this work, a detection system, with BF3 detectors for neutrons and sodium iodide scintillator for g-rays, is modeled to investigate the neutron signal-to-noise ratio and to obtain an empirical formula for the photon production rate Ri(n,?)= SfGfMf(d,m) from radiative capture reactions in constituent nuclides of trinitrotoluene. This formula can be used for the efficient landmine detection of explosives in quantities as small as ~200 g of trinitrotoluene concealed at depths down to about 15 cm. The empirical formula can be embedded in a field programmable gate array on a field-portable explosives' sensor for efficient online detection.

Optimization of Moderator Design for Explosive Detection by Thermal Neutron Activation Using a Genetic Algorithm

An optimal design analysis is carried out for an explosives’ detection system (EDS) based on thermal neutron activation (TNA) of a sample under investigation. The objective of this work is to use a genetic algorithm (GA) to obtain the optimized moderator design that would yield the “best” signal in a detection system. In a preliminary analysis, a full Monte Carlo (MC) simulation is carried out to estimate the effectiveness of various moderators, namely, water, graphite, and beryllium with respect to radiative capture (n,γ) reactions in a sample under investigation. Since MC simulation is computationally “expensive,” it is generally not used for random-search-based optimization analysis. Thus, more efficient methods are required for the design of optimal nuclear systems, where neutron transport is accurately modeled and iteratively solved for estimating the effect of independent design parameters. This paper proposes a computational scheme in which GA is coupled with the two-group neutron diffusion equation (DE) for carrying out an optimization analysis. The coupled GA-DE optimization scheme is demonstrated for obtaining the optimal moderator design. It is found that with considerably less computational effort than in an elaborate MC computation, the GA-DE approach can be used for the optimal design of detection systems.

Analiza tkiva okrog omajanih umetnih kolčnih debel iz poliacetala z uporabo nuklearnih metod

IntroductionThe influence of polyacetal wear particles on aseptic loosening of non-cemented isoelastic femoral stems with polyacetal coating remains unclear. The aim of our study was to use nuclear methods to prove the presence of polyacetal wear particles, to determine their morphology and to check their distribution in the tissues around loosend hip prosthetic components.MethodsTissue samples obtained during retrieval of 4 aseptic loosened primary hip prostheses with isoelastic stems made of polyacetal were subjected to nuclear analyses. Proton microbrobe method (mikro-PIXE) was used to prove the presence of polyacetal wear particles and to check for their morphology by detection of barium, which is molecularly in BaSO4 embedded in polyacetal. Thermal neutron activation was used to determine distribution pattern of polyacetal wear in the peri-prosthetic tissues.ResultsAgainst expectations, polyacetal wear particles were found rather rare, larger than 100 µm and present in pseudo-membrane samples around the loosened stem, but virtually absent in tissues away from their origin. Concentration of BaSO4 in polyacetal wear particles in pseudo-membrane samples was similar to the one in polyacetal coating (conc. Ba = 14217 µg/g and 14800 µg/g, respectively).ConclusionAccording to the results, the primary cause of the loosening of the isoelastic stems with polyacetal coating is most probably mechanical restlessness, which is responsible for local production of the large polyacetal wear particles responsible to accelerate the process of loosening. PIXE method and thermal neutron activation are sensitive quantitative nuclear methods suitable for direct or indirect detection of wear particles in the tissue around loosened prostheses and to determine morphology of wear particles and their distribution in the tissues.