Paired Ion Research Articles

Photoelectron spectroscopy of trisubstituted benzenes: Dichloroiodobenzenes

The electronic structure of isomeric dichloroiodobenzenes (C 6H 3ICl 2) has been investigated by HeI/HeII photoelectron spectroscopy. The spectra were assigned by Green’s functions calculations and comparison with the spectra of related dichlorobenzenes (C 6H 4Cl 2). The careful analysis of π-orbital and halogen lone pair ionization energies, enabled us to analyze substituent effects in detail, describing them in terms of resonance, inductive and spin–orbit coupling interactions. The use of several descriptors simultaneously, rather than a single one, appears to be necessary to unravel the effects in polysubstituted benzenes. Our method of analysis is capable of describing substituent effect in detail even in polysubstituted benzenes where kinetic or equilibrium methods become impractical.

Epithermal Neutron Beams for Clinical Studies of Boron Neutron Capture Therapy: A Dosimetric Comparison of Seven Beams

A comparison of seven epithermal neutron beams used in clinical studies of boron neutron capture therapy (BNCT) in Sweden (Studsvik), Finland (Espoo), Czech Republic (ReZ), The Netherlands (Petten) and the U.S. (Brookhaven and Cambridge) was performed to facilitate sharing of preclinical and clinical results. The physical performance of each beam was measured using a common dosimetry method under conditions pertinent to brain irradiations. Neutron fluence and absorbed dose measurements were performed with activation foils and paired ionization chambers on the central axis both in air and in an ellipsoidal water phantom. The overall quality of each beam was assessed by figures of merit determined from the total weighted dose profiles that assumed the presence of boron in tissue. The in-air specific beam contamination from both fast neutrons and gamma rays ranged between 8 and 65 x 10(-11) cGy(w) cm2 for the different beams and the epithermal neutron flux intensities available at the patient position differed by more than a factor of 20 from 0.2-4.3 x 10(9) n cm(-2) s(-1). Percentage depth dose profiles measured in-phantom for the individual photon, thermal and fast-neutron dose components differed only subtly in shape between facilities. Assuming uptake characteristics consistent with the currently used boronated phenylalanine, all the epithermal beams exhibit a useful penetration of 8 cm or greater that is sufficient to irradiate a lesion seated at the brain midline. The performance of the existing facilities will benefit from the introduction of advanced compounds through improved beam penetrability. This could increase by as much as 2 cm for the purest of beams, although the beam intensities generally need to be increased to between 2-5 x 10(9) n cm(-2) s(-1) to maintain manageable irradiation times. These data provide the first consistent measurement of beam performance at the different centers and will enable a preliminary normalization of the calculated patient dosimetry.

Halogens in Competition: Electronic Structure of Mixed Dihalobenzenes

The electronic structure of all isomeric dihalobenzenes C6H4XY (X, Y = Cl, Br, I) has been investigated by HeI/HeII photoelectron spectroscopy, Green's functions calculations, and comparison with the spectra of related dihalobenzenes C6H4X2 (X = Cl, Br, I). The careful analysis of measured pi orbital and halogen lone pair ionization energies enabled us to describe substituent effects in terms of resonance, inductive, steric, and spin-orbit coupling interactions.

05/00109 Thermo-hydrodynamic design and safety parameter studies of the TRIGA MARK II research reactor: Huda, M. Q. and Rahman, M. Annals of Nuclear Energy, 2004, 31, (10), 1101–1118

A heavily filtered fast neutron irradiation system (FNIS) was developed for a variety of applications, including the study of long-term health effects of fast neutrons by evaluating the biological mechanisms of damage in cultured cells and living animals such as rats or mice. This irradiation system includes an exposure cave made with a lead–bismuth alloy, a cave positioning system, a gamma and neutron monitoring system, a sample transfer system, and interchangeable filters. This system was installed in the irradiation cell of the Texas A&M University Nuclear Science Center Reactor (NSCR). For a realistic modeling of the NSCR, the irradiation cell, and the FNIS, this study used the Monte Carlo N-Particle (MCNP) code and a set of high-temperature ENDF/B-VI continuous neutron cross-section data. Sensitivity analysis was performed to find the characteristics of the FNIS as a function of the thickness of the lead–bismuth alloy. A paired ion chamber system was constructed with a tissue-equivalent plastic (A-150) and propane gas for total dose monitoring and with graphite and argon for gamma dose monitoring. This study, in addition, tested the Monte Carlo modeling of the FNIS system, as well as the performance of the system by comparing the calculated results with experimental measurements using activation foils and paired ion chambers.

UV photoelectron spectroscopic study of substituent effects in quinoline derivatives.

The molecular and electronic structure of eight substituted quinolines has been investigated by HeI/HeII photoelectron spectroscopy, Green's function calculations, and comparison with the spectra of related compounds. The correlation between nitrogen lone pair ionization energies and basicity in 18 substituted quinolines is discussed. The influence of different substituents has been quantified via the scheme that is based on experimental energy shifts. The relationships between nitrogen ionization energies, pK(a) values, and medicinal activity are also discussed.

Filtered fast neutron irradiation system using Texas A&M University Nuclear Science Center Reactor

A heavily filtered fast neutron irradiation system (FNIS) was developed for a variety of applications, including the study of long-term health effects of fast neutrons by evaluating the biological mechanisms of damage in cultured cells and living animals such as rats or mice. This irradiation system includes an exposure cave made with a lead–bismuth alloy, a cave positioning system, a gamma and neutron monitoring system, a sample transfer system, and interchangeable filters. This system was installed in the irradiation cell of the Texas A&M University Nuclear Science Center Reactor (NSCR). For a realistic modeling of the NSCR, the irradiation cell, and the FNIS, this study used the Monte Carlo N-Particle (MCNP) code and a set of high-temperature ENDF/B-VI continuous neutron cross-section data. Sensitivity analysis was performed to find the characteristics of the FNIS as a function of the thickness of the lead–bismuth alloy. A paired ion chamber system was constructed with a tissue-equivalent plastic (A-150) and propane gas for total dose monitoring and with graphite and argon for gamma dose monitoring. This study, in addition, tested the Monte Carlo modeling of the FNIS system, as well as the performance of the system by comparing the calculated results with experimental measurements using activation foils and paired ion chambers.

Concentration of heavy metal ions in water using thermoresponsive chelating polymer

Thermoresponsive polymers, poly( N-isopropylacrylamide) (PNIPAAm), having chelating functionalities were synthesized. PNIPAAm-imidazole (-Im) was precipitated and formed a gum-like aggregate in the neutral pH region at 50 °C, while PNIPAAm-carboxylic acid (COOH) and PNIPAAm-iminodiacetic acid (-IDA) remained soluble even at pH 7. An addition of a paired ion, dodecyltrimethylammonium ion, was effective for inducing the precipitation of those polymers. PNIPAAm-Im was useful for collecting copper(II), nickel(II), cobalt(II), and lead(II), but was ineffective for cadmium(II) recovery. In contrast, PNIPAAm-COOH collected cadmium(II), while insufficiently recovered cobalt(II) and nickel(II). PNIPAAm-IDA was the best choice for collecting all metal ions in neutral pH's. After 20-folds concentration, the metal ions in river and seawater were successfully determined by graphite furnace atomic absorption spectrometry (GFAAS).

Performance characteristics of the MIT fission converter based epithermal neutron beam

A pre-clinical characterization of the first fission converter based epithermal neutron beam (FCB) designed for boron neutron capture therapy (BNCT) has been performed. Calculated design parameters describing the physical performance of the aluminium and Teflon® filtered beam were confirmed from neutron fluence and absorbed dose rate measurements performed with activation foils and paired ionization chambers. The facility currently provides an epithermal neutron flux of 4.6 × 109 n cm−2 s−1 in-air at the patient position that makes it the most intense BNCT source in the world. This epithermal neutron flux is accompanied by very low specific photon and fast neutron absorbed doses of 3.5 ± 0.5 and 1.4 ± 0.2 × 10−13 Gy cm2, respectively. A therapeutic dose rate of 1.7 RBE Gy min−1 is achievable at the advantage depth of 97 mm when boronated phenylalanine (BPA) is used as the delivery agent, giving an average therapeutic ratio of 5.7. In clinical trials of normal tissue tolerance when using the FCB, the effective prescribed dose is due principally to neutron interactions with the nonselectively absorbed BPA present in brain. If an advanced compound is considered, the dose to brain would instead be predominately from the photon kerma induced by thermal neutron capture in hydrogen and advantage parameters of 0.88 Gy min−1, 121 mm and 10.8 would be realized for the therapeutic dose rate, advantage depth and therapeutic ratio, respectively. This study confirms the success of a new approach to producing a high intensity, high purity epithermal neutron source that attains near optimal physical performance and which is well suited to exploit the next generation of boron delivery agents.

Electro-Motive Forces Generated in Concentration Cells of LiCl-Glycerol Solutions

Mean ionic activity coefficients of LiCl in Glycerol have been calculated in the concentration range 0.5-500mol.m-3, using the concentration cell technique. Up to the limit of the Debye-Huckel theory (C ≤ 1 mol·m-3), the experimental values lie below the limiting line, showing that the measured Electro-Motive-Force might have been false by using our previous cell design. An alternative method based on Fuoss Paired Ion Model has been used to deduce the theoretical data, and consequently, the values of the EMF'S. By comparing these data to those obtained experimentally with KCI and NaCl, we find that they are consistent with the results in aqueous solutions.

Measurement of Aryl and Alcohol Sulfotransferase Activity

Two methods are presented for determining the catalytic activity of aryl and alcohol sulfotransferases. The first assay is a simple and rapid procedure that is based on the extraction of a paired ion formed between the product organic sulfate and methylene blue. The second method employs HPLC analysis of the substrate-dependent formation of PAP, an assay that is particularly useful when the sulfuric acid ester product is chemically unstable.

Surfactants Usable for Electrospray Ionization Mass Spectrometry

Surfactants suppress the electrospray ionization (ESI) of various compounds. Here we demonstrate that fluorinated surfactants such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOSA) could be employed for ESI–MS without a significant decrease in sensitivity. Both PFOA and PFOSA could be applied to the analysis of ionic and nonionic compounds by micellar electrokinetic chromatography (MEKC)/ESI–MS, although the migration window was limited. Furthermore, in HPLC/ESI–MS, PFOA could function as a paired ion for enzymatically digested peptides as well as sulfonamides and significant effects of PFOA on the signal peak shape, retention times, and sensitivity of the analytes were observed compared to those of trifluoroacetic acid or sodium dodecyl sulfate (SDS). In addition, PFOA was applied to protein analysis by ESI–MS, and superior sensitivity was noted, compared to other surfactants such as octylglucoside, dodecylglucoside, and SDS. Although 21% of the original signal was observed in the presence of 1% PFOA, this surfactant could be easily removed by evaporation, which resulted in the recovery of 96% of the original signal. Because these fluorinated surfactants could also be used for solubilization, extraction, and disaggregation of proteins, they should greatly expand the applicability of the ESI–MS to the biological problems of proteins.

Phantom materials for boron neutron capture therapy

The aim of this work was to establish which reference phantom material is mostsuited for dosimetry under reference conditions of neutron beams for boronneutron capture therapy (BNCT). For this purpose, phantoms of dimensions15×15×15 cm3 and 30×30×30 cm3, composedof water, tissue-equivalent (TE) liquid, polyethylene (PE), polymethylmethacrylate (PMMA) and water containing 10 µg g-1 and30 µg g-1 10B were irradiated using the PettenBNCT beam. Activation foils and a diode detector were used for thedetermination of the thermal neutron fluence rate. The gamma-ray dose rate andthe fast neutron dose rate were determined using paired ionization chambers.In water, PMMA and TE liquid the absolute dose and fluence values agreedwithin 3% at a reference depth of 2 cm, with the exception of the gamma-raydose rate in PMMA, which was 12% lower than in water. Due to a higherhydrogen concentration in PE compared with water, the dose and fluence valuesin PE differed more than 30% from those in water. Only minor differences wereobserved between the percentage depth dose curves for the various dosecomponents in water, PMMA and TE liquid. The addition of 10 µg g-1 and 30 µg g-1 10B to water resultedin a decrease in the absolute thermal neutron fluence at 2 cm depth of about2% and 8%, respectively, and a decreased penetration of thermal neutrons atdepth for the 30 µg g-1 10B concentration.For reference dosimetry of an epithermal neutron beam for BNCT, both water andTE liquid are suitable phantom materials. For practical reasons, water istherefore proposed as reference phantom material. For measurements requiring asolid phantom, PMMA is proposed. The lower gamma-ray dose in PMMA compared towater, however, needs to be taken into account.

Use of low-pressure tissue equivalent proportional counters for the dosimetry of neutron beams used in BNCT and BNCEFNT.

The absorbed dose in a phantom or patient in boron neutron capture therapy (BNCT) and boron neutron capture enhanced fast neutron therapy (BNCEFNT) is deposited by gamma rays, neutrons of a range of energies and the 10B reaction products. These dose components are commonly measured with paired (TE/Mg) ion chambers and foil activation technique. In the present work, we have investigated the use of paired tissue equivalent (TE) and TE+ l0B proportional counters as an alternate and complementary dosimetry technique for use in these neutron beams. We first describe various aspects of counter operation, uncertainties in dose measurement, and interpretation of the data. We then present measurements made in the following radiation fields: An epithermal beam at the University of Birmingham in the United Kingdom, a d(48.5) + Be fast neutron therapy beam at Harper Hospital in Detroit, and a 252Cf radiation field. In the epithermal beam, our measured gamma and neutron dose rates compare very well with the values calculated using Monte Carlo methods. The measured 10B dose rates show a systematic difference of approximately 35% when compared to the calculations. The measured neutron+gamma dose rates in the fast neutron beam are in good agreement with those measured using a calibrated A-150 TEP (tissue equivalent plastic) ion chamber. The measured 10B dose rates compare very well with those measured using other methods. In the 252Cf radiation field, the measured dose rates for all three components agree well with other Monte Carlo calculations and measurements. Based on these results, we conclude that the paired low-pressure proportional counters can be used to establish an independent technique of dose measurement in these radiation fields.

Neutron generator (HIRRAC) and dosimetry study.

Dosimetry studies have been made for neutrons from a neutron generator at Hiroshima University (HIRRAC) which is designed for radiobiological research. Neutrons in an energy range from 0.07 to 2.7 MeV are available for biological irradiations. The produced neutron energies were measured and evaluated by a 3He-gas proportional counter. Energy spread was made certain to be small enough for radiobiological studies. Dose evaluations were performed by two different methods, namely use of tissue equivalent paired ionization chambers and activation of method with indium foils. Moreover, energy deposition spectra in small targets of tissue equivalent materials, so-called lineal energy spectrum, were also measured and are discussed. Specifications for biological irradiation are presented in terms of monoenergetic beam conditions, dose rates and deposited energy spectra.

Mixed-field dosimetry measurement of a target assembly for an accelerator-based neutron source for boron neutron capture therapy

The objective of this work was to measure the neutron and gamma-ray absorbed dose components for a target assembly for an Accelerator-Based Neutron Source (ABNS) for Boron Neutron Capture Therapy (BNCT), and to compare these measurements with MCNP calculations in order to verify the calculations of the in-air neutron and gamma-ray absorbed dose components. The measurements were made using the paired ionization chamber technique. The measured neutron and gamma-ray specific absorbed dose components agreed with calculations within experimental errors, which were approximately 10%. The measured gamma-ray specific absorbed dose rate of 140 cGy s −1 A −1 ±12% is consistent with reported yields of 478 keV gamma rays due to the 7 Li (p, p′) 7Li * reaction. This specific gamma absorbed dose rate is significant and should not be neglected in moderator assembly design.

Study of the planarization of the tricordinate phosphorus in phospholes; photoelectron spectra and structure of partially planarized phospholes

The gradual flattening of the tricoordinate phosphorus in phosphole by the increasing steric bulk of the substituent group is shown on the HF/6-31G* optimized geometries of alkylarylphospholes. By the decreasing pyramidality, aromaticity indices show increase, as a result of the increased conjugation. The aromaticity of 1-(2,4,6-tri-tertiarybutyl)-phosphole is similar to that of furan according to the geometrical indices. In the photoelectron spectra of the alkylaryl substituted phospholes the phosphorus lone pair ionization energy also decreases along the decreasing pyramidality. 1-(2,4,6-tri-Tertiarybutyl-phenyl)-3-methylphosphole has the lowest ionization energy value ever reported for a phosphole.

Dosimetry and treatment planning for boron neutron capture therapy

Dosimetric techniques were developed for the determination of the various dose components in phantoms irradiated with an epithermal neutron beam for boron neutron capture therapy (BNCT). Using paired ionization chambers and activation foils, the accuracy (1 standard deviation, SD) in the determination of the absolute thermal neutron fluence, gamma‐ray dose and fast neutron dose amounted to 5%, 5%, and 18%, respectively. Methods were developed which assure an agreement between prescribed and actual obtained values of 1% (1 SD) for the absolute beam output and 5%–10% (1 SD) for the blood–boron concentration during irradiation. Clinical dosimetry studies were performed resulting in a set of reference beam data which are used for quality control, dosimetry intercomparisons and as input for a conventional semi‐empirical treatment planning system (TPS). Using these reference beam data and the electron and photon beam model of the TPS, the various dose components could be calculated fast and with a high accuracy in a homogeneous anthropomorphic head phantom. At the central axis, the agreement between measurements and calculations was within 2%–3% (1 SD). It is concluded that the accuracy in dosimetry, beam output monitoring, blood–boron monitoring and treatment planning is sufficient to start clinical studies of BNCT in Petten, The Netherlands.

Clinical dosimetry of an epithermal neutron beam for neutron capture therapy: Dose distributions under reference conditions

The aim of this study was to asses the dose distribution under reference conditions for the various dose components of the Petten clinical epithermal neutron beam for boron neutron capture therapy (BNCT). Activation foils and a silicon alpha-particle detector with a 6Li converter plate have been used for the determination of the thermal neutron fluence rate. The gamma-ray dose rate and the fast neutron dose rate have been determined using paired ionization chambers. Circular beam apertures of 8, 12 and 15 cm diameters have been investigated using a 15 x 15 x 15 cm3 solid polymethyl-methacrylate phantom, a water phantom of the same dimensions and a 30 x 30 x 30 cm3 water phantom at various phantom to beam-exit distances. The effect of phantom to beam-exit distance could be modeled using an inverse square law with a virtual source to beam-exit distance of 3.0 m. At a reference phantom to beam-exit distance of 30 cm, three-dimensional dose and fluence distributions of the various dose components have been determined in the phantoms. The absolute thermal neutron fluence rate at a reference depth of 2 cm in the 15 cm water phantom increased by 43% when the field size was increased from 8 to 15 cm. Simultaneously the gamma-ray dose rate increased by 46% while the fast neutron dose rate increased by only 5%. A reference treatment position at 30 cm from the beam exit allows convenient patient positioning with a relatively small increase in irradiation time compared to positions very close to the beam-exit. A more homogeneous distribution of thermal neutrons over a target volume, a higher absolute thermal neutron fluence rate and a lower contribution of the fast neutron dose to the total dose will result in improved treatment plans when using a 12 cm or 15 cm field compared to a 8 cm field. The dose distributions will be used as benchmark data for treatment planning systems for BNCT.

Heterocyclic pentaatomic molecules containing thio- and seleno-amido groups: linear relationship between nSe/nSe lone pair ionization energies and 1:1 adduct formation constants with diiodine

Heterocyclic pentaatomic molecules containing thio- and seleno-amido groups: linear relationship between nSe/nSe lone pair ionization energies and 1:1 adduct formation constants with diiodine

Spectroscopic investigations of dehydroepiandrosterone. Part II: Photoelectron spectrum and electronic structure

The gas phase electronic structure of dehydroepiandrosterone (3β-hydroxy-5α-androsten-17-one, DHEA) is elucidated from its Hel photoelectron spectrum, quantum chemical calculations, and correlation with spectra of the related molecules 5α-androsten-17-one (1) and epiandrosterone (3β-hydroxy-5α-androstan-17-one) (2). The lowest ionization energy event in DHEA is shown to correspond to a π-ionization energy of ∼8.5 eV, followed closely and overlapped in part by the carbonyl lone pair ionization at 8.7 eV.