Determination of boron in glass by the nuclear track technique

Summary Determination of Boron in Glass by the Nuclear Track Technique The nuclear track technique using the¹⁰B(n)⁷Li reaction, has been applied to determine boron in concentration ranges (1.59 to 7.75%) ordinarily considered high for nuclear determinations. Factors limiting the overall precision of the method and restricting the linear dependence of track density on boron concentration are examined. Boron alpha track densities are used to construct planar profiles of boron distribution within the surface region of bulk glass and CVD films. Calibration curves for quantitative lateral profiling of surfaces are constructed and show the selective corrosion of borosilicate glass surface resulting in boron depletion.     

Synthesis and characterisation of functionalized borosilicate nanoparticles for boron neutron capture therapy applications

Boron Neutron Capture Therapy (BNCT) is a promising therapy for the cure of diffuse tumors. The successful clinical application of BNCT requires finding new boron-based compounds suitable for an efficient ¹⁰B delivery to the cancerous tissues. The purpose of this work is to synthesize borosilicate nanoparticles by a sol?Cgel recipe, and to functionalize them with folic acid in order to promote their capture by the tumor cells. Whereas sol?Cgel is a promising technique for the synthesis of nanoparticles, in case of borosilicate systems this approach is affected by significant boron loss during preparation. Here we show that functionalization of borosilicate nanoparticles with folic acid can reduce the boron loss. Moreover, preliminary biocompatibility tests indicate that functionalization strongly changes the reactivity of NPs towards blood cells, so favouring the potential use of these materials for clinical applications.     

Choice of boron shield in epithermal neutron activation determinations

Boron trioxide, boron nitride, boron carbide and elemental boron giving different boron surface densities have been used as neutron shields in epithermal neutron activation determinations. Boron ratios and advantage factors for 29 nuclides have been determined. A new expression of the advantage factor has been derived from statistics of radioactive decay viewpoint. A real improvement, in comparison with classical neutron activation methods, can be obtained for the determination of As, Br, Cd, I, Mo. Sb, Sn, Th, W and U by use of boron shields.     

Comparison of sample preparation methods for determination of free carbon in boron carbide by X-ray powder diffraction

Several sample preparation methods were evaluated for determination of free carbon in boron carbide powders by quantitative X-ray diffraction method, including ultrasonication, wet ball milling and dry ball milling–wet mixing. Quantitation was based on measuring the integral peak area ratio of the diffraction lines of graphite (002) to boron carbide (012) in samples spiked with pure graphite. The dry milling–wet mixing method provided the best precision and accuracy in all the measurements as well as in determination of free carbon in a boron carbide reference material. There was a linear relationship between the integral peak area ratios and graphite added to boron carbide samples which were purified from their free carbon content. The method provided a low detection limit of 0.05 wt% free carbon.     

Application of dicesium metaborate ion for the determination of boron by thermal ionisation mass spectrometry

Application of dicesium metaborate ion /Cs₂BO ₂ ⁺ / in Thermal Ionisation Mass Spectrometry /TIMS/ for the determination of boron present at sub ppm level in heavy water moderator as well as for the isotopic composition of boron in boron carbide is reported. Contamination of samples with natural boron while determining trace levels of boron in heavy water was checked by analysing SRM-952 isotopic reference material. The atom ratios of boron in B₄C were determined by directly fusing the material on the tantalum filament with Cs₂CO₃ as well as with Na₂CO₃ and also by following the conventional fusion procedures and the results were compared.     

Determination of boron in borosilicate glasses by neutron capture prompt gamma-ray activation analysis

Major levels of boron in borosilicate glasses have been determined nondestructively by neutron activation analysis. In contrast to chemical methods for determining boron as a major component, the described nuclear method has few interferences and does not require chemical separation of boron prior to its quantitation. The effects of neutron self-shielding by boron (1 to 8% by weight) are examined, minimized by dilution of powdered samples with high purity graphite, and circumvented by comparative analyses. Results of the analysis of a series of glasses with increasing boron composition are 1.150±.005% and 7.766±.035% for the low and high members of the series. Accuracy of these results depends upon comparative analyses with the certified Standard Reference Material, SRM 93a (3.89±0.02% B). Once analyzed, the glasses are useful as secondary standards for alpha track counting, and also ion and electron microprobe analyses of glasses.     

Direct determination of boron in a cobalt-based alloy by graphite furnace-atomic absorption spectrometry

A matrix modifier composed of nickel and zirconium, and a graphite tube treated with zirconium solution were proposed for the determination of boron in cobalt-based alloys by graphite furnace-atomic absorption spectrometry. The effects of this matrix modifier and the treated graphite tube were studied, and the combination of 60 mug of nickel and 20 mug of zirconium as matrix modifier, and a graphite tube soaked with 10 g 1(-1) of zirconium solution were found to give the highest analytical sensitivity. The interference effects of major components (cobalt) and eight minor components (chromium, nickel, tungsten, iron, tantalum, molybdenum, titanium, aluminium and manganese) were studied. Boron in four cobalt-based alloys was determined by graphite furnace-atomic absorption spectrometry employing the proposed matrix modifier and the treated graphite tube, without the preseparation of matrix. The relative standard deviation was 3.3% for 0.048% of boron. A characteristic mass was 500 pg.     

A gas flow proportional detection system for the determination of boron in aerosol samples and other sample types

This work describes the design, fabrication, and testing of a lucite bodied proportional gas detection system for the analysis of boron in selected samples via detection of the charged particles produced in the 10B(n,)⁷Li reaction induced by thermal neutrons. The detector was designed for internal placement of samples; the sample types of major interest were airborne aerosols collected on filters or particulate impaction plates. Samples were irradiated with the detector in the thermal neutron field produced in the graphite thermal column of the University of Lowell's one megawatt research reactor. Determined sensitivities for boron varied from 6.2·10^–8 to 1.73·10^–6 cpm·ng^–1 (n·cm^–2J·s^–1)^–1 depending on the physical characteristics of the samples. For a nominal counting time of ten minutes the lower limit of mass detection of natural boron was determined to be 12.1 nanograms. The analytical method was applied to the estimation of boron in fourteen samples of natural aerosols collected on membrane filters. Analysis of prepared samples and natural aerosol samples by ICP emission showed good agreement with analysis via the (n,) reaction. Application of the method to other sample types was demonstrated by the determination of boron in samples of borosilicate glass and borated polyethylene.     

Some physical properties of compacted specimens of highly dispersed boron carbide and boron suboxide

Structure, shear modulus and internal friction (IF) of compacted specimens of boron carbide and boron suboxide have been investigated. Microtwins and stacking faults were observed along the {100} plane systems of polycrystalline specimens of boron carbide. Electrical conductivity of the specimens was that of p-type. Concentration of holes varied from 10¹⁷ to 10¹⁹ cm⁻³. The IF was measured in the temperature range 80-300 K. It was shown that the IF of boron carbide and that of boron suboxide were characterized with a set of similar relaxation processes. Mechanisms of the relaxation processes in boron carbide and boron suboxide are discussed in terms of the Hasiguti model of interaction between dislocations and point defects.     

Rapid mass-spectrometric determination of boron isotopic distribution in boron carbide

Boron isotopic ratios are measured in boron carbide by thermionic ionization mass spectrometry with no prior chemical separation. A powder blend of boron carbide and sodium hydroxide is prepared, a small portion is transferred to a tantalum filament, the filament is heated to produce sodium borate, and the filament is transferred to the mass spectrometer where the(11)B/(10)B ratio is measured, using the Na(2)BO(2)(+) ion. Variables investigated for their effect on preferential volatilization of (10)B include the sodium hydroxide-boron carbide ratio and the temperature and duration of filament heating. A series of boron carbide pellets containing natural boron, of the type proposed for the control rods of the Fast Flux Test Facility reactor, were analysed with an apparently unbiased result of 4.0560 for the (11)B/(10)B ratio (standard deviation 0.0087). The pellets contained over 3% metal impurities typically found in this material. Time of analysis is 45 min per sample, with one analyst.     

Determination of boron and lithium in diverse biological matrices using neutron activation-mass spectrometry (NA-MS)

Summary Essential features of the neutron activation-mass Spectrometry (NA-MS) technique are described. Applicability of this technique for the simultaneous determination of boron and lithium is demonstrated for a diverse group of biomaterials. NA-MS is a nondestructive analytical technique, and dynamic in nature since its coverage extends to a broad range of concentration levels. Contamination after the irradiation step, extraneous by natural lithium or boron is inconsequential, since only the activation products are the analyted assayed. Coupling the nuclear activation phenomenon which generates ⁴He and ³He (from ¹⁰B and ⁶Li, respectively), with the high precision potential of mass spectrometry forms the bases of this technique. Under ideal conditions the detection limit is extendable to pg g^–1 concentration ranges and therefore, it is extremely well suited to investigate the natural concentration levels of boron and lithium in biomaterials. The potential of this method for the determination of lithium in biomedical trace element research is of special significance since determination of sub-ppb levels of lithium by other analytical techniques faces serious analytical difficulties mainly due to contamination control and in some cases to insufficiently low detection limits.     

Prompt gamma-ray neutron activation analysis methodology for determination of boron from trace to major contents

Prompt gamma ray neutron activation analysis methodologies were standardized using a reflected neutron beam and Compton suppressed γ-ray spectrometer to quantify boron from trace to major concentrations. Neutron self-shielding correction factors for higher boron contents (0.2–10 mg) in samples were obtained from the sensitivity of chlorine by irradiating KCl with and without boron. This method was validated by determining boron concentrations in six boron compounds and applied to three borosilicate glass samples with boron contents in the range of 1–10 mg. Low concentrations of boron (10–58 mg kg⁻¹) were also determined in two samples and five reference materials from NIST and IAEA.     

Determination of nitrogen in boron carbide by instrumental photon activation analysis

Boron carbide is widely used as industrial material, because of its extreme hardness, and as a neutron absorber. As part of a round-robin exercise leading to certification of a new reference material (ERM-ED102) which was demanded by the industry we analysed nitrogen in boron carbide by inert gas fusion analysis (GFA) and instrumental photon activation analysis (IPAA) using the ¹⁴N(γ,n)¹³N nuclear reaction. The latter approach is the only non-destructive method among all the methods applied. By using photons with energy below the threshold of the ¹²C(γ,n)¹¹C reaction, we hindered activation of matrix and other impurities. A recently installed beam with a very low lateral activating flux gradient enabled us to homogeneously activate sample masses of approximately 1 g. Taking extra precautions, i.e. self-absorption correction and deconvolution of the complex decay curves, we calculated a nitrogen concentration of 2260 ± 100 μg g⁻¹, which is in good agreement with our GFA value of 2303 ± 64 μg g⁻¹. The values are the second and third highest of a rather atypical (non-S-shape) distribution of data of 14 round-robin participants. It is of utmost importance for the certification process that our IPAA value is the only one not produced by inert gas fusion analysis and, therefore, the only one which is not affected by a possible incomplete release of nitrogen from high-melting boron carbide. Figure Twin-Detector system for analyzing spatially extended samples     

Neutron induced radiography in the determination of boron in drinking water

Neutron induced radiography has been applied to the determination of boron concentrations in drinking water, collected from natural springs of Reshian and Muzaffarabad areas of Azad Kashmir, Pakistan, using CR-39 etched track detectors. The technique is based upon the simultaneous irradiation with thermal neutrons of a sample of unknown concentration and a standard of known boron concentration, fixed on a track detector. The subsequent counting of alpha and ⁷Li tracks in the detector resulting from the ¹⁰B(n,)⁷Li nuclear reaction is done after chemical etching. Boron concentration in the sample is determined by comparing ⁷Li and alpha-particle track density with that of a standard of known boron concentration. Boron concentrations in drinking water samples from Muzaffarabad and Reshian area of Azad Kashmir have been found to vary from (0.054±0.001) mg/l to (0.250±0.004) mg/l with an average of (0.16±0.002) mg/l. The observed concentration of boron in drinking water has been found to be less than the provisional Maximum Acceptable Concentration level (0.4 mg//l) of WHO. The drinking water from the reported area has been found to be within safe limits as far as boron related health hazards are concerned.This revised version was published online in November 2005 with corrections to the Cover Date.     

Determination of boron in glass by alpha-spectrometry

Alpha-spectrometric method has been used for the determination of boron in borosilicate glasses. For irradiation thermal neutrons with a flux of about 10⁵ n·cm^–2·s^–1, produced in a paraffin moderator surrounding a deuteron target of a small neutron generator, were used. Alpha-particles from the reaction¹⁰B(n, ) were detected by a Si solid state detector with a resolution of about 50 keV. The sensitivity of the method is 0.05 wt % boron in glass samples.This work was supported by the Hungarian Research Foundation (Contract No. 1734/91.).     

The effect of the sintering atmosphere on the densification of B4C ceramics

Densification of boron carbide during sintering may be improved by a two-stage process, namely heating to 2000°C under vacuum and sintering at 2190°C under argon. This sintering regime allows achieving a relative density of the ceramic bodies fabricated from a fine powder higher than 95%. The nitrogen treatment of the boron carbide phase at 1900°C leads to the formation of the BN phase and precipitation of graphite. Vacuum treatment of these samples at 2000°C leads to decomposition of the boron nitride phase. The liberated free boron may again react with graphite to form in situ boron carbide particles. The experimental investigations of the sintering behavior of the boron carbide phase under various atmospheres supported the thermodynamic predictions regarding the phase transformation. No evidence, however, was found for enhanced sintering under a nitrogen atmosphere.     

Establishing the difference between colloidal borosilicate and boron-modified colloidal silica via chelation of boron with catechol and dl-tartaric acid

Colloidal borosilicate and boron-modified colloidal silica sols were studied by ¹¹B NMR. Formation of B–O–Si chemical bonds is established in both materials. It is shown that boron present in colloidal borosilicate is stable towards the action of complexing agents catechol and tartaric acid. In contrast, the boron in boron-modified silica is readily complexed by these agents. The results presented herein demonstrate that B–O–Si bonds are homogeneously distributed throughout the colloidal borosilicate disperse phase, while in boron-modified colloidal silica they are concentrated at the surface of colloidal silica particles.     

Estimation of uncertainty in measurement of boron in Zr–Nb alloy samples by BF4 − ion selective electrode

Boron doped zirconium–niobium alloy is employed for neutron reactivity control in advanced nuclear reactors. An accurate knowledge of the boron content and uncertainty associated with the measurement result is essential for reactivity calculations. In view of the refractory nature of the alloy, boron determination in these matrices is a challenging task for analytical chemists. Also due to non-availability of matrix-matched reference materials, direct solid analysis cannot be resorted to. With this in view, a simple and sensitive method based on potentiometric determination of boron as tetrafluoroborate with tetrafluoroborate ion selective electrode has been developed. After dissolving the sample, boron was quantitatively converted to BF₄ ⁻ with the addition of HF. Potential response was measured with Orion 9305 BN BF₄ ⁻ ion selective electrode. The response of the ion selective electrode was Nernstian in the range of 0.1–100.0 μg/g of boron in the solution. The method has been validated by two independent methods namely spectrophotometry and inductively coupled plasma-atomic emission spectrometry (ICP-AES). All identifiable sources of uncertainties in the methodology have been individually assessed. The combined uncertainty is calculated employing uncertainty propagation law. The expanded relative uncertainty in the measurement (coverage factor 2) is 6.50%.     

The boron trifluoride nitromethane adduct

The separation of the boron isotopes using boron trifluoride·organic-donor, Lewis acid·base adducts is an essential first step in preparing ¹⁰B enriched and depleted crystalline solids so vital to nuclear studies and reactor applications such as enriched MgB₂, boron carbide, ZrB₂, HfB₂, aluminum boron alloys, and depleted silicon circuits for radiation hardening and neutron diffraction crystal structure studies. The appearance of this new adduct with such superior properties demands attention in the continuing search for more effective and efficient means of separation. An evaluation of the boron trifluoride nitromethane adduct, its thermodynamic and physical properties related to large-scale isotopic separation is presented. Its remarkably high separation factor was confirmed to be higher than the expected theoretical value. However, the reportedly high acid/donor ratio was proven to be an order of magnitude lower. On-going research is determining the crystal structure of deuterated and ¹¹B enriched ¹¹BF₃·CD₃NO₂ by X-ray and neutron diffraction.