M. Bonardi

Excitation functions and production of arsenic radioisotopes for environmental toxicology and biomedical purposes.

Many arsenic radionuclides have come to be used as tracers in biology and in the study of environmental pollution of both water and soil. In nuclear medicine, radioactive 74 As has been employed as a positron emitter for the localization of brain tumors, cerebral occlusive vascular lesions, arterious-venous malformations, etc. The aim of the work described has been to study the excitation functions for the production of the arsenic radioisotopes from targets of natural germanium via nuclear reactions ( p, xn ).

Preparation of high specific activity radiotracers for radioanalytical studies

High specific activity radiotracers are very suitable for studies related to the toxicological impact of trace elements onto human health. In order to investigate the metabolic behaviour of Low Level Exposure (LLE) to trace elements, it is necessary to carry out in-vitro and in-vivo experiments with tracers whose concentration is of the same order of magnitude as the present environmental exposure values (ng-μg/kg day). Preparations, separations and purifications of some No Carrier Added (NCA) radiotracers (48V,95m,96Tc,195m,g,197m,gHg,199Au,202Tl) produced by either cyclotron or nuclear reactor irradiation, are presented and discussed. This work reviews the more recent advances in this field carried out by our groups.

Thin-target excitation functions and optimization of simultaneous production of NCA copper-64 and gallium-66,67 by deuteron induced nuclear reactions on a natural zinc target

Copper-64 is a radionuclide suitable for labeling of a wide range of radiopharmaceuticals for PET imaging, as well as systemic or local radioimmunotherapy of tumors. Among the possible methods for cyclotron production of No Carrier Added (NCA) 64Cu (61Cu), we investigated the deuteron irradiation on natural Zn target, via (d,axn) and (d,2pxn) nuclear reactions. This paper reports the preliminary results about the experimental determination and theoretical calculation of thin-target excitation functions in the energy range up to 19 MeV for 61Cu, 64Cu, 66Ga, 67Ga, 65Zn and 69mZn. A fast selective radiochemical separation of NCA 64Cu from Zn target and Ga radionuclides, with quality control tests is described too.

Photobleaching and photomineralization of azobenzene and substituted azobenzenes in aqueous solution by photocatalytic membranes immobilizing titanium dioxide

Abstract The kinetics of photobleaching (by spectrophotometric analysis) and integral photomineralization (by total organic carbon (TOC) analysis) of azobenzene ( I ) and substituted azobenzenes in aqueous solution were followed in laboratory-scale runs on photocatalytic membranes immobilizing 30±3 wt.% of semiconductor TiO 2 . Experiments were carried out by the technique described in preceding papers of this series, employing stoichiometric hydrogen peroxide as the oxygen donor. The following azobenzenes were examined: (4-diethylamino)-phenylazobenzene ( II ), 4′-(((4-diethylamino)phenyl)azo) benzoic acid ( III ), 4′-(((2-amino-5-diethylamino)phenyl)azo) benzoic acid ( IV ), 4′-(((2-acetamido-4-diethylamino)phenyl)azo) benzoic acid ( V ), 4′-(((4-dimethylamino)phenyl)azo) benzenesulphonic acid, sodium salt ( VI ) and 4′-(((2-acetamido-4-diethylamino)phenyl)azo) benzenesulphonic acid, sodium salt ( VII ). From the Langmuir-Hinshelwood treatment of the initial rate data as a function of the initial concentration ((0.10−1.0) × 10 −3 M), the kinetic parameter k and the pseudo-thermodynamic parameter K for photobleaching were obtained. With regard to photobleaching, I and II were certainly the most reactive, followed by IV . The remaining molecules showed a photo-oxidation rate of one-third to one-quarter of that of I chosen as reference structure. Consequently, the presence of an amino group in the 4-position ( II ) does not stabilize the azobenzene structure against photo-oxidation leading to bleaching, whereas the same group in the 2-position ( IV ) decreases the photobleaching rate by about 40% when a carboxylic group is also present in the I′-position. Acetylation of this amino group, such as in V , decreases the photobleaching rate more markedly. With regard to photomineralization, it was observed that, when photobleaching was virtually complete, a certain amount of TOC was already mineralized. The maximum amount of TOC remaining at the end of photobleaching ranged from about 90% to about 30%, varying with the dye structure and initial concentration as well as with the power and type of irradiation source. By examining the TOC concentration profiles as a function of the substituted azobenzene structure, the following hypotheses were proposed: 1. 1. during the photobleaching period, the ring containing the diethylamino group breaks down (more markedly if further amino or acetamido groups are present in the structure), and photomineralization of the other ring occurs more slowly: 2. 2. both rings break down, within certain limits, during photobleaching; however, the aliphatic fragments containing carboxyl or sulphonic groups are mineralized more slowly. The fact that a small initial plateau in the TOC profile is followed by another more evident plateau at the end of the photobleaching period, for both VI and VII , suggests that hypothesis (1) is more probable in these cases. When the second plateau is reduced to a sigmoidal curve or an inflection point, hypothesis (2) also needs to be considered.

Degradation of some chloro-aliphatic water contaminants by photocatalytic membranes immobilizing titanium dioxide☆

Abstract The TiO 2 -mediated photodegradation of chloroethanoic acid, trichloroethene and tetrachloroethene, chosen as model molecules of aliphatic chloro-organics was studied at 303±2 K by employing polymeric membranes photografted on cellulose to immobilize the TiO 2 (3.0–5.6 mg cm −2 ). The radiant flux in the absorption range and the volume-surface ratio in the photoreactor cell were kept constant at 2.5±0.2 mW cm −2 and 1.1±0.1 mL cm −2 respectively. The initial rate of photodegradation was studied as a function of the initial concentration of reactants by the linearized form of the Langmuir—Hinshelwood equation, by which rate constants k and equilibrium adsorption constants K were evaluated. Values of k (5.7±0.5 μmol h −1 ) are independent of the chemical nature of the three reactants investigated, in agreement with other literature findings. Values of K are compared with those measured in aqueous suspensions of TiO 2 with the same chloro-organics and with the values predicted by a mechanism involving hydroxyl radicals as the primary oxidant adsorbed on the photocatalyst surface. Satisfactory performance and potential technological advantages of photocatalytic membranes are discussed.

Kr(p, xn) excitation functions and 81Rb−81mKr generator studies

Excitation functions for (p, xn) reactions on natural thin krypton gas targets in the 10–45 MeV proton energy range were measured. Different thick target designs for 81Rb−81mKr production purposes were studied. Removability of 81mKr in water solution or in the gaseous phase for a cation exchange generator type was determined.

Cyclotron production, radiochemical separation and quality control of platinum radiotracers for toxicological studies

The increasing concentration of Pt, Pd and Rh in the environment is mainly due to the release of these elements from the catalytic converters of the motorvehicles. This situation makes it necessary to carry out metallotoxicological experiments on both cell cultures and laboratory animals, in order to assess their impact on living organisms after a Long Term and Low Level Exposure (LLE). Both nuclear reactionsnatIr(p,xn) andnatOs(α,xn) were investigated in the energy range up to 45 MeV for protons and 38 MeV for alpha-particles, in order to optimize the irradiation parameters for the production of188,189,191Pt. Several sets of thin- and thick-target excitation functions were determined experimentally by cyclotron irradiation at both Milano and Ispra cyclotrons. This paper reports the irradiation parameters studied and adopted and two radiochemical procedures for the separation of radio-Pt from an Os target, as well as from ruthenium, iridium and gold impurities. These procedures were used to obtain very high specific activity Pt radionuclides in No Carrier Added (NCA) form. Radionuclidic, radiochemical and chemical purity measurements were carred out by the use of several techniques like ψ-spectrometry, ion-exchange radio-chromatography, atomic absorption spectrometry and neutron activation analysis.

Mathematical modelling of pilot-plant photomineralization of chlorophenols in aqueous solution, by photocatalytic membranes immobilizing titanium dioxide

Abstract Photomineralization of 4-chlorophenol, 2,4-dichlorophenol, and pentachlorophenol, in 9.9×10−4−3.8×10−5 M aqueous solutions, in the presence of stoichiometric hydrogen peroxide, was studied using PHOTOPERM® CPP/313 membranes containing immobilized 30±3 wt.% TiO2, by following analytically both disappearance of absorbable chloro-organics (AOX), and mineralization of total organic carbon (TOC) content. Experiments were carried out in a PHOTOPERM®WP pilot plant, using monochromatic irradiation (254 nm) in the absorption range of semiconductor, with an absorbed power of 22±1 W. The initial rate of photodegradation, both regarding AOX and TOC analysis, was studied as a function of the initial concentration of substrate using the linearized form of the Langmuir-Hinshelwood equation, from which the rate constants κ and apparent adsorption contants ϰ were evaluated. These parameters, which are unable to fit the whole photomineralization kinetic curves, because they account only for initial rates, were employed, as starting values, to optimize, by numerical integration, a kinetic model which considers appearance and disappearance of all intermediates, as if they were represented by a hypothetical single molecule, mediating all of them. In this way, two couples of parameters, κ1 and ϰ1, κ2 and ϰ2 were obtained, relative to the two successive steps of the model (substrate disappearance and mineralization), able to reproduce the whole kinetics satisfactorily. Mean quantum yields of organic carbon mineralization, calculated by κ2 parameters, reach 75, 71, and 31 % for the chlorinated phenols in the order reported above, with respect to their maximum allowable quantum yields. These values are from 3 to 5 times greater than those measured in laboratory-scale experiments thus showing the excellent performance of the pilot-plant employed.

Optimization of irradiation parameters for67Ga production fromnatZn (p, xn) nuclear reactions

Excitation functions fornatZn (p, xn) and (p, pxn) nuclear reactions in the 5–45 MeV proton energy range were measured. Evaluations were made both of target thickness and proton energy in order to optimize the67Ga production rate, at the same time minimizing contamination by the66Ga. Optimal irradiation conditions, depending both on the beam current available and on the power dissipated into the target were determined.

Biochemical studies of current environmental levels of trace elements: Cyclotron production of radiothallium and its use for metabolic investigations on laboratory animals

Carrier-free201+202Tl have been produced in the cyclotron by (p, xn) reactions on mercury targets and used as a trcer for thallium in metallobiochemistry of heavy metal pollution. The separation of201+202Tl radioisotopes from Hg involved a solvent extraction method leading to labelled univalent Tl(I) ions. This radioactive solution was used to prepare different201+202Tl labelled compounds such as inorganic Tl(III) ions and organic dimethylthallium. Quality controls have been applied directly on the different radioactive solutions immediately before their administrations to rats in order to ensure that thallium had the chemical form expected. A summary of the main results concerning different aspects of the metabolic investigations on rats such as absorption, retention, excretion, transplacental transport and influence of the different chemical forms of thallium on its metabolism is also reported.