Design and evaluation of a TNA explosive-detection system to screen carry-on luggage

Thermal neutron analysis (TNA) technology has been used for the non-destructive detection of explosives. The system uses a relatively weak ²⁵²Cf neutron source (1.03·10⁷ n/s) and two 3"×3" NaI(Tl) detectors. The presence of explosives is confirmed via detection of the 10.83 MeV prompt gamma-ray associated with nitrogen decay. The MCNP4A code was used to simulate the neutron and gamma transport through the system. The thermal neutron flux in the activation position was measured using gold and indium foils. The measured thermal neutron flux was lower, by not more than 9.5%, than that of simulation. In this report the results of the preliminary tests on the system are described.     

LIBS for landmine detection and discrimination

The concept of utilizing laser-induced breakdown spectroscopy (LIBS) technology for landmine detection and discrimination has been evaluated using both laboratory LIBS and a prototype man-portable LIBS systems. LIBS spectra were collected for a suite of landmine casings, non-mine plastic materials, and ‘clutter-type’ objects likely to be present in the soil of a conflict area or a former conflict area. Landmine casings examined included a broad selection of anti-personnel and anti-tank mines from different countries of manufacture. Other materials analyzed included rocks and soil, metal objects, cellulose materials, and different types of plastics. Two ‘blind’ laboratory tests were conducted in which 100 broadband LIBS spectra were obtained for a mixed suite of landmine casings and clutter objects and compared with a previously-assembled spectral reference library. Using a linear correlation approach, ‘mine/no mine’ determinations were correctly made for more than 90% of the samples in both tests. A similar test using a prototype man-portable LIBS system yielded an analogous result, validating the concept of using LIBS for landmine detection and discrimination.     

Thermal and environmental effects on Oligothiophene low-energy singlet electronic excitations in dilute solution: a theoretical and experimental study

The absorption spectra in dilute dichloromethane solution at 300 K of four Oligotiophenes (OT), namely 2,2′:5′,2″-Terthiophene, 2,2′:5′,2″:5″,2″′-Quaterthiophene, 4,4″′-Didodecyl-2,2′:5′,2″:5″,2″′-quaterthiophene and 5,5′′′′′-Dihexyl-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′:5′′′′,2′′′′′-sexithiophene, have been studied both experimentally and theoretically by using a combination of molecular dynamics simulations, time-dependent density functional theory (TD-DFT) and perturbed matrix method calculations. A deep analysis of the theoretical results, affected by a systematic although not dramatic underestimation of the absorption maxima due to the well-documented TD-DFT limitations, clearly indicates that both the environmental (solvent) and thermal effects significantly alter the Oligotiophenes photophysical properties mainly because of the wide repertoire of the S₀–S₁ energy gaps and electronic densities experienced in solution by the different conformers actually populated. In particular, all the investigated OT display a very high flexibility resulting in a very high repertoire of sampled conformations. The comparison of the calculated and experimental lineshape of the S₀–S₁ electronic transition has clearly indicated that for a correct modeling of OT spectral features, the lack of an exhaustive sampling of semiclassical configurational space of the overall system, i.e., solute in interaction with the solvent, might result in an incomplete picture even in the presence of well-documented important aspects such as reliable definition of excited electronic states and the inclusion of quantum vibronic effects.     

High performance liquid chromatographic separation of cholesterol oxidation products

Summary A fast, sensitive, high performance liquid chromatographic method for the simultaneous determination of cholesterol hydroperoxides and other major oxysterols, using two different detection systems (ultraviolet at 210 nm and light scattering), is here described. The hydroperoxy derivatives were obtained by cholesterol photoxidation, isolated by thin layer chromatography and joined with a standard mixture of 10 oxysterols (epoxy, hydroxy and keto derivatives). Aliquots were directly injected onto a 5-μm particle size, 25×0.46 cm i.d. Spherisorb S5 CN normal phase column, usingn-hexane/anhydrous ethanol (97:3, v/v) as mobile phase and a flow rate of 0.8 mL min⁻¹. This method allowed, in a single isocratic analysis, the separation and quantification of the primary and secondary cholesterol oxidation products in 30 minutes. The light scattering detector was particularly useful for the determination of nonderivatized 5,6-epoxides and cholestane-3β,5α,6β-triol. The sensitivity of both detectors was very similar for most of the oxysterols, except for the 5,6-epoxides and the 7-ketocholesterol. The method suitability for the determination of cholesterol oxidation products in food matrices was successfully tested on a saponified lipid extract from egg yolk powder.     

Synchrotron radiation FTIR imaging in minutes: a first step towards real-time cell imaging

FTIR microscopy with a focal plane array (FPA) of detectors enables routine chemical imaging on individual cells in only a few minutes. The brilliance of synchrotron radiation (SR) IR sources may enhance the signal obtained from such small biosamples containing small amounts of organic matter. We investigated individual cells obtained from a cell culture specifically developed for transmission FTIR imaging using either a Globar or an SR source coupled to the same instrumentation. SR-IR source focussing was optimized to control the energy distribution on the FPA of detectors. Here we show that accessing the IR absorption distribution from all the organic contents of cells at 1 × 1 μm pixel resolution was possible only with high circulating current (≥1.2 A) illuminating a limited number of the FPA’s detectors to increase the signal-to-noise ratio of IR images. Finally, a high-current SR ring is mandatory for collecting FTIR images of biosamples with a high contrast in minutes.     

Nitrogen distribution measurements by neutron induced autoradiography

A method utilizing plastic track detectors was developed to determine the nitrogen distribution and concentration in the presence of boron in metals. Experiments were performed at the UVAR (cadmium ratio ≈25) and the NIST Reactor (cadmium ratio ≈3000). The minimum detectable concentration of nitrogen at a given concentration of boron has been estimated using the detector’s response to¹⁰B(n,α)⁷ Li reaction products in terms of track size distribution. The capability of the technique to detect nitrogen in the presence of boron has been demonstrated using 316L stainless steel with a nitrogen concentration of ≈560 ppm and a boron concentration of ≈0.86 ppm.     

Stand-off Raman spectroscopy: a powerful technique for qualitative and quantitative analysis of inorganic and organic compounds including explosives

A pulsed stand-off Raman system has been built and optimised for the qualitative and quantitative analysis of inorganic and organic samples including explosives. The system consists of a frequency doubled Q-switched Nd:YAG laser (532 nm, 10 Hz, 4.4 ns pulse length), aligned coaxially with a 6″ Schmidt–Cassegrain telescope for the collection of Raman scattered light. The telescope was coupled via a fibre optic bundle to an Acton standard series SP-2750 spectrograph with a PI-MAX 1024RB intensified CCD camera equipped with a 500-ps gating option for detection. Gating proved to be essential for achieving high signal-to-noise ratios in the recorded stand-off Raman spectra. In some cases, gating also allowed suppression of disturbing fluorescence signals. For the first time, quantitative analysis of stand-off Raman spectra was performed using both univariate and multivariate methods of data analysis. To correct for possible variation in instrumental parameters, the nitrogen band of ambient air was used as an internal standard. For the univariate method, stand-off Raman spectra obtained at a distance of 9 m on sodium chloride pellets containing varying amounts of ammonium nitrate (0–100%) were used. For the multivariate quantification of ternary xylene mixtures (0–100%), stand-off spectra at a distance of 5 m were used. The univariate calibration of ammonium nitrate yielded R ² values of 0.992, and the multivariate quantitative analysis yielded root mean square errors of prediction of 2.26%, 1.97% and 1.07% for o-, m- and p-xylene, respectively. Stand-off Raman spectra obtained at a distance of 10 m yielded a detection limit of 174 μg for NaClO₃. Furthermore, to assess the applicability of stand-off Raman spectroscopy for explosives detection in “real-world” scenarios, their detection on different background materials (nylon, polyethylene and part of a car body) and in the presence of interferents (motor oil, fuel oil and soap) at a distance of 20 m was also investigated.     

Total efficiency of gamma-ray detection by germanium semiconductor detectors

The total efficiency of γ-ray detection by Ge(Li) semiconductors is calculated for the energy range 0.1 to 10 MeV, for cylindrical detectors with radii from 0.25 cm to 2.5 cm and thicknesses from 0.1 cm to 1 cm, at distances between the source and detector ranging from 2 cm to 20 cm.     

Anion analysis in uranium ore concentrates by ion chromatography

In the present exploratory study, the applicability of anionic impurities for attributing nuclear material to a certain chemical process or origin has been investigated. Anions (e.g., nitrate, sulphate, fluoride, chloride) originate from acids or salt solutions that are used for processing of solutions containing uranium or plutonium. The study focuses on uranium ore concentrates (“yellow cakes”) originating from different mines. Uranium is mined from different types of ore body and depending on the type of rock, different chemical processes for leaching, dissolving and precipitating the uranium need to be applied. Consequently, the anionic patterns observed in the products of these processes (the “ore concentrates”) are different. The concentrations of different anionic species were measured by ion chromatography using conductivity detection. The results show clear differences of anion concentrations and patterns between samples from different uranium mines. Besides this, differences between sampling campaigns in a same mine were also observed indicating that the uranium ore is not homogeneous in a mine. These within-mine variations, however, were smaller than the between-mine variations.     

Cyclodextrins with heterocyclic substitution as GC stationary phases

Summary Two new cyclodextrin (CD) derivatives, heptakis{2,6-di-O-pentyl-3-O-[3′-(2″-chloro-4″,5″-dioxylmethene)-phenyl-5′-iso-oxazolylmethyl]}-β-CD (CD I) and heptakis{2,6-di-O-methyl-3-O-[3′-(2″-chloro)-phenyl-5′-iso-oxazolylmethyl]}-β-CD (CD II) were synthesized and coated on fused-silica capillary columns. Their chromatographic characteristics, including column efficiency, polarity, selectivity and phase transition were studied and compared with similar β-CD stationary phases. It was found that the heterocycle group has a significant effect on the selectivity of the CD stationary phases. Both stationary phases can be successfully used to separate many di- and trisubstituted benzene positional isomers and show stronger separation ability in separating low-polarity benzene positional isomers than other β-CD stationary phases.     

On the imaging of land mines using e+−e− pair production

The problem of disposing of abandoned land mines is very serious in many countries. Anti-personnel land mines (APM's) contain as little as 50 gram or less of explosive, which is enough to take off an adult's foot, or to kill a child. Anti-tank mines (ATM's), designed to penetrate the armour on the bottom of a tank, are much larger. Current techniques of finding them are not adequate. All practical high explosives contain 20% or more of nitrogen, which has a thermal neutron cross section of 75 mbarn, producing γ's of up to 10.8 MeV. The idea of using this property to detect explosives has been tested by others, but because of backgrounds is unable to find anything less than several hundred grams of explosive. The refinement proposed here is to convert the γs, track the resulting e⁺−e⁻ pairs in MWPC's, and use the information to locate the γ source, i.e. the mine. The directional information provided should reduce the backgrounds considerably. Result of an experimental test are presented, and possibilities for the future discussed.     

Potassium ion-selective polyaniline solid-contact electrodes based on 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6-ether ionophore

New ion-selective electrodes for potassium were developed and tested employing 18-crown-6-ether, dibenzo-18-crown-6-ether, and 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6-ether ionophores in PVC membranes with a polyaniline solid contact between the membranes and the Pt substrate. We compared the response characteristics of the solid-contact electrodes (SCEs) based on these ionophores and various plasticizers. Among the three ionophores, 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6-ether-based SCE produced the best results exhibiting a high reproducibility with negligible drifts in the standard potential with a response slope (RS) of 58.2 mV/decade: the detection limit (DL) of the potassium ion was 10^−5.80 M with linearity over five decades. This is a significant improvement for the response slope and detection limit compared to SCEs with valinomycin, 2,3-naphtho-15-crown-ether, and dibenzo-15-crown-5-ether ionophore, which showed 53–56 mV/decade of RS and 10^−5.3 M of DL. The response slope, detection limit, and selectivity were compared with other K⁺ ISEs reported until present. Finally, the new SCE was applied to determine potassium ions in artificial human serum with satisfactory results. However, the detection limit for the artificial serum was slightly diminished yielding a value of 10^−5.19 M (6.5 × 10⁻³ mM) which is still good. Electrodes with polypyrrole in place of polyaniline exhibited comparable results. The text was submitted by the authors in English.     

Synthesis,structural investigations and biological studies on symmetrically substituted 3,3′,3",3"′-tetra-methoxyphenylimino phthalocyanine complexes

The present paper describes the synthesis and characterization of novel metal (II) 3,3′,3″,3‴-tetramethoxyphenylimino substituted phthalocyanines (M-MeOPhImPcs) of copper (II), cobalt (II), nickel (II) and zinc (II) by condensing the 3,3′,3″,3″′-tetra amino phthalocyanines with anisaldehyde. The dark bluish green colored tetraimino substituted phthalocyanine derivatives were characterized by various physico-chemical techniques like elemental analysis, magnetic susceptibility, electronic, IR, powder X-ray diffraction and thermo gravimetric analysis (TGA) to check the structural integrity and purity. The variations of magnetic moment as a function of field strength indicated the presence of inter molecular co-operative interactions. The complexes were also evaluated for their antifungal and antibacterial activities. This article was submitted by the authors in English.     

Mechanochemical synthesis of Na-β/β″-Al2O3

Na-β/β″-alumina powders were synthesized by a mechanochemical processing. The influences of mechanical activation in the phase composition and microstructure of the final powders were investigated. Fine Na-β/β″-alumina powders were obtained at a lower temperature than that of a conventional solid-state reaction processing. The mechanism of the mechanical activation was studied. It was found that mechanical activation greatly affected the calcining process and phase composition of the precursory powders.     

Formation of intermolecular hydrogen bonds in light-sensitive crystals of C-2′-(o-oxyphenyl)vinyl-N-p-methylphenyl nitrone,C-2′-(2″-oxy-5″-bromophenyl)vinyl-N-p-methylphenyl nitrone,C-2′-(2″-oxy-5″-bromophenyl)-vinyl-N-phenyl nitrone,and C-2′-(o-oxyphenyl)vinyl-n-methyl nitrone

This paper studies the crystal structure of new substituted light-sensitive azomethine N-oxides (nitrones): C-2′-(o-oxyphenyl)vinyl-N-p-methylphenyl nitrone (1), C-2′-(2″-oxy-5″-bromophenyl)vinyl-N-p-methylphenyl nitrone (2), C-2′-(2″-oxy-5″-bromophenyl)-vinyl-N-phenyl nitrone (3), and C-2′-(o-oxyphenyl)vinyl-N-methyl nitrone (4). In contrast to the compounds studied earlier [1, 2], C-2′-(β-oxy-α-naphthyl)vinyl-N-p-methylphenyl nitrone (5), C-2′-(β-oxy-α-naphthyl)vinyl-N-phenyl nitrone (6), C-2′-(o-oxyphenyl) vinyl-N-phenyl nitrone (7), and C-2′-(o-oxyphenyl)vinyl-N-p-bromophenyl nitrone (8), the nitrones studies in this work have anti-rather than syn-orientations of the nitrone and hydroxyl groups. Due to this spatial arrangement of the proton-donating hydroxyl and proton-accepting nitrone groups, molecules in crystals 1–4 are bonded by intermolecular hydrogen bonds (IHB) to form chains but not centrosymmetric dimeric associates (CDA). Two types of chain arrangements were revealed: “head-to-tail” and “head-to-tail, tail-to-head”. It is shown that the introduction of an alkyl substituent instead of an aryl one at the nitrogen atom of the nitrone group in 4 leads to a change in the geometry of the IHB in the H-associate. It is proven that the hydroxyl proton can undergo an intermolecular O→O transfer in the chain of hydrogen bonds in crystals 1–4, which can give rise to photochemical transformations in these crystals. Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 349–362, March–April, 1996. Translated by L. Smolina     

A DSC study of precipitation hardening in a WE43 Mg alloy

The phase transformations leading to hardening a Mg-Y-Nd-Zr (WE43) alloy submitted to thermal treatments are followed by calorimetric and microhardness measurements. A double-stage thermal treatment is adopted, the first at 210°C for 8 h and the second at 150°C, on samples quenched from a temperature higher than the conventional one. A secondary precipitation of the metastable phase β″ in the second stage makes the hardness increase with respect to the primary precipitation.     

Speciation of four selenium compounds using high performance liquid chromatography with on-line detection by inductively coupled plasma mass spectrometry or flame atomic absorption spectrometry

An analytical method for the speciation of selenomethionine, selenocystine, selenite and selenate by high performance liquid chromatography (HPLC) with atomic spectrometric detection is presented. An organic polymeric strong anion exchange column was used as the stationary phase in combination with an aqueous solution of 6 mmol L^–1 of salicylate ion at pH 8.5 as the mobile phase which allowed the isocratic separation of the four selenium analytes within 8 minutes. The separated selenium species were detected on-line by flame atomic absorption spectrometry (FAAS) or inductively coupled plasma mass spectrometry (ICP-MS). The signal-to-noise ratio of the FAAS detector was optimized using a hydrogen-argon entrained-air flame and a slotted-tube atom trap (STAT) in the flame. The limit of detection (3 σ) achieved by the HPLC-FAAS system was 1 mg L^–1 of selenium (100 μL injections) for each of the four selenium species. More powerful selenium detection was achieved using an ELAN 5000 ICP-MS instrument. Selenium was measured at m/z = 82. The ICP-MS signal intensity was enhanced by a factor of 3–4 after addition of 3% methanol to the chromatographic mobile phase and by using an increased plasma power input of 1300 W. The limit of detection achieved under these conditions was 1 μg L^–1 (100 μL injections). The HPLC-ICP-MS system was used for selenium speciation of selenite and selenate in aqueous solutions during a BCR certification exercise and for selenium speciation in the certified reference material, BCR No. 402 White Clover. Extraction experiments revealed that the selenium species in the biological material were extractable only in the presence of water in the extraction medium. The results indicated that selenate and a compound of unknown identity U were present in the plant sample. Received: 4 September 1996 / Accepted: 12 December 1996     

Synthesis and curing behavior of a novel liquid crystalline epoxy resin

This article described the synthesis and mesomorphic behavior transition of a novel liquid crystalline (LC) epoxy resin 4-(2,3-epoxypropoxy)biphenyl,4″-(2,3-epoxypropoxy)phenyl-4′carboxylate (EBEPC), which combined a hydroxyl benzoic aromatic ester and biphenol rigid-rod group. EBEPC showed a clear nematic schlieren texture under curtain conditions. The reaction kinetics of EBEPC cured by 4,4′-diaminodiphenyl-methane (DDM) was studied by using an isoconversional method under isothermal conditions with differential scanning calorimetry (DSC). The isothermal DSC data can be fitted reasonably by an autocatalytic curing model. Smectic phases had been observed in the EBEPC/DDM curing system. The results of DSC showed that the formation of the LC phase had pronounced influence on the curing reaction.     

New steroidal glycosides from the stem bark of <Emphasis Type="Italic">Mimusops elengi</Emphasis>

Two new steroidal glycosides (1 and 2) have been isolated from the ethanolic extract of the stem bark of Mimusops elengi L. and characterized as stigmasta-5,22-dien-3β-ol-3β-D-glucuropyranosyl-(6′β→1″)-D-glucopyranoside (1) and β-sitosterol-3β-(3″′,6″′,7″′-trihydroxynaphthyl-2″′-carboxyl)-4″-glucopyranosyl-(1″→4′)-glucopyranoside (2) along with the known compounds stigmasta-5-en-3β-ol, lup-20(29)-en-3β-ol, and stigmasta-5-en-3β-D-glucopyranoside. Their structures have been elucidated on the basis of spectral data analysis and chemical reactions.     

COHN analysis: Body composition measurements based on the associated particle imaging and prompt-gamma neutron activation analysis techniques

The measurement of the body’s carbon (C), oxygen (O), hydrogen (H), and nitrogen (N) content can be used to calculate the relative amounts of fat, protein, and water. A system based on prompt-gamma neutron activation analysis (PGNAA), coupled with the associated particle imaging (API) technique, is being developed for this purpose. A compact D, T neutron generator (∼10⁷ n/s output) with an internal alpha-particle detector is used. The counting system consists of 6 shielded bismuth germanate (BGO) detectors (10.2 cm × 10.2 cm × 10.2 cm) operated with fast-timing electronics to detect only gamma-rays within a 100 ns time window following a trigger pulse generated by the alpha detector. The body can be scanned from the shoulders to the knees within about 30 min, with the equivalent whole-body dose <0.4 mSv. The cumulative gamma-ray spectra in the 2 MeV to 8 MeV region is collected and analyzed for multiple peaks attributed to body C,O,H, and N. Measurement precision for each element, based on tissue-equivalent phantoms, are in the 2–5% range, which are sufficient for population studies in adults. Further improvements are needed to extend the measurements to pediatric clinical research studies.