Dose distribution in electron-irradiated PMMA: effect of dose and geometry

Depth-dose distributions for an electron beam are generally determined with either a stack irradiation geometry or a wedge (generally with an angle of about 50°–60°) made from an electrically-conducting material (such as, aluminium) or a non-conducting material (such as, PMMA). If the non-conducting wedge is thicker than the electron range, the stored charge in the material could influence the measured depth-dose distribution. This effect was investigated for 7-MeV electrons for PMMA with the wedge angle varying from 0° to 60°. The maximum-to-surface dose ratio was used as a characteristic parameter of the shape of the distribution. The depth-dose distribution measured by a dosimetry film placed inside the wedge-pair was similar to the standard shape when the wedge angle was larger than about 55° (dose ratio 1.5). However, as the angle was decreased, this ratio sharply increased almost linearly up to about 15°, and then leveled off at about 3. We also studied the effect of the surface dose on this dose ratio for the wedge angle of 0°, where we found that the ratio increased with the dose. Both of these effects can be explained by the presence of the electrostatic field around the dosimetry film due to stored charge in the non-conducting PMMA.     

Radical-based grafting of GMA on sutures of different nature

Irradiation of a number of different sutures largely employed in the clinical practice with either high energy electrons or with γ-rays followed by quenching with glycidyl methacrylate (GMA) conveniently led to derivatization through a radical-based process. The radicals involved were detected by means of ESR spectroscopy and were characterized on the basis of their ESR spectral parameters which were also found to be consistent with the hfs constants predicted by DFT calculations. Evidence of the GMA derivatization of the sutures was obtained via(13)C CP-MAS NMR spectroscopy, while its extent was evaluated gravimetrically.     

Antioxidant and antimicrobial properties of Casteanea sativa Miller chestnut honey produced on Mount Etna (Sicily)

The aim of this study was the evaluation of antibacterial and antioxidant properties of Monofloral Etna Castanea sativa Miller honeys. Escherichia coli ATCC 25,922, Pseudomonas aeruginosa ATCC 27,853, Enterococcus faecalis ATCC 29,211 and Staphylococcus aureus ATCC 29,213 were investigated for their susceptibilities to two different honeys. Antioxidant activity was evaluated by ORAC, NO scavenger assays, FRAP and DPPH. Antioxidant activity and antibacterial properties were compared with chestnut honeys from different geographical areas and with Manuka honey. UPLC-MS/MS was used for major components characteri sation.     

.OH radical reaction with CH2Cl2: Direct spectrophotometric observation of.CHCl2 radical formation

Hydrogen abstraction from methylene chloride by the^.OH radical in aqueous solution is monitored by direct observation of the^.CHCl₂ radical absorption build-up at 220 nm, yielding a bimolecular rate constant of /5.8±0.2/xlo⁷ M^–1s^–1 at room temperature. A spectral band extending from 220 nm to 330 nm is assigned to the dichloromethyl radical.     

A glycopeptide antibiotic chiral stationary phase for the enantiomer resolution of hydroxy acid derivatives by capillary electrochromatography

Separation of hydroxy acid enantiomers was achieved by using capillary electrochromatography (CEC) employing a chiral stationary phase (CSP) based on MDL 63,246 (Hepta-Tyr), a macrocyclic antibiotic of the teicoplanin family. The chiral selector was chemically bonded to 5 num diol-modified silica particles and the CSP mixed with amino silica (3:1 w/w) was packed into a 75 num ID fused-silica capillary. The CEC experiments were carried out by using an aqueous reversed-phase mode for the enantiomeric resolution of hydroxy acid compounds. Good enantioresolution was achieved for mandelic acid (MA), m-hydroxymandelic acid (m-OH-MA), p-OH-MA, and 3-hydroxy-4-methoxymandelic acid (3-OH-4-MeO-MA). The CEC system was less enantioselective towards 2-phenyllactic acid (2-PhL) and 3-PhL while mandelic acid methyl ester (MA-Et-Est) enantiomers were not resolved. Several experimental parameters, such as organic solvent type and concentration, buffer pH, capillary temperature, on enantioresolution factor, retention time, and retention factor were studied.     

Electrochemistry of coordination compounds: Part XIX. Electrochemical study of some cationic hydrido-complexes of iron(II)

The Electrochemical behaviour of a series of cationic hydrido-complexes of Fe(II) of general formula trans-[FeH(L)(DPE)₂] (BPh₄)(L=N₂, C₂H₅N, C₆H₅CN, CH₂CHCN, CH₃CN, P(OCH₃)₃, P(OC₂H₅)₃, CO; DPE=1,2- bis(diphenylphosphino)ethane) has been investigated in 1,2-dimethoxyethane at the platinum electrode. The reduction of these d⁶ complexes has been found to proceed by an ECE mechanism in which a one-electron transfer, generating a transient d⁷ species, is followed by the fast loss of one of the neutral ligands and a further one-electron reduction of the pentacoordinated intermediates to the final d⁸ anionic hydrides. The reduced species are stabilized considerably at low temperature. The ligands, L, are divided into two groups according to their bonding properties, with particular references to their ability to act as π- acceptors. Weak π-bonders (N₂, C₂H₅N, C₆H₅CN, CH₂CHCN, CH₃CN) are lost in the chemical step interposed between the two charge-transfer processes, whereas strong π-accepting ligands (CO and P(OR)₃) favour dissocia tion of one end of a diphosphine.     

Irradiated bivalve mollusks: Use of EPR spectroscopy for identification and dosimetry

High energy radiation treatment of foodstuff for microbial control and shelf-life extension is being used in many countries. However, for consumer protection and information, the European Union has adopted the Directives 1999/2/EC and 1999/3/EC to harmonize the rules concerning the treatment and trade of irradiated foods in EU countries. Among the validated methods to detect irradiated foods the EU directives also include Electron Paramagnetic Resonance (EPR/ESR) spectroscopy.We describe herein the use of EPR for identification of four species of bivalve mollusks, i.e. brown Venus shells (Callista chione), clams (Tapes semidecussatus), mussels (Mytilus galloprovincialis) and oysters (Ostrea edulis) irradiated with ⁶⁰Co γ-rays. EPR could definitely identify irradiated seashells due to the presence of long-lived free radicals, primarily CO₂⁻, CO₃³⁻, SO₂⁻ and SO₃⁻ radical anions. The presence of other organic free radicals, believed to originate from conchiolin, a scleroprotein present in the shells, was also ascertained. The use of one of these radicals as a marker for irradiation of brown Venus shells and clams can be envisaged. We also propose a dosimetric protocol for the reconstruction of the administered dose in irradiated oysters.     

Characterization of a power bipolar transistor as high-dose dosimeter for 1.9–2.2 MeV electron beams

Results of the characterization studies on a power bipolar transistor investigated as a possible radiation dosimeter under laboratory condition using electron beams of energies from 2.2 to 8.6 MeV and gamma rays from a ⁶⁰Co source and tested in industrial irradiation plants having high-activity ⁶⁰Co γ-source and high-energy, high-power electron beam have previously been reported. The present paper describes recent studies performed on this type of bipolar transistor irradiated with 1.9 and 2.2 MeV electron beams in the dose range 5–50 kGy. Dose response, post-irradiation heat treatment and stability, effects of temperature during irradiation in the range from –104 to +22 °C, dependence on temperature during reading in the range 20–50 °C, and the difference in response of the transistors irradiated from the plastic side and the copper side are reported. DLTS measurements performed on the irradiated devices to identify the recombination centres introduced by radiation and their dependence on dose and energy of the electron beam are also reported.     

Switching time control on bipolar power transistors by electron irradiation

High-frequency operation of electronic lamp ballasts is made possible by the controlled reduction of carrier lifetime in the base-collector junction of the two power transistors present in the circuit. The electron irradiation allows excellent control of the lifetime and, as a consequence, of the power transistors storage time on which the main operation parameters, working frequency and lamp power, depend. The recovery of the radiation induced defects, caused by the thermal processes that the irradiated devices undergo during packaging operations, has been investigated.     

Dose control in electron beam processing: Comparison of results from a graphite charge collector, routine dosimeters and the ISS alanine-based dosimeter

A 12 MeV linear accelerator is currently used for electron beam processing of power semiconductor devices for lifetime control and, on an experimental basis, for food irradiation, sludge treatment etc. In order to control the irradiation process a simple, quick and reliable method for a direct evaluation of dose and fluence in a broad electron beam has been developed. This paper presents the results obtained using a “charge collector” which measures the charge absorbed in a graphite target exposed in air. Calibration of the system with super-Fricke dosimeter and comparison of absorbed dose results obtained with plastic dosimeters and alanine pellets are discussed.