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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.

Treatment of food with ionising radiations in order to increase its shelf-life is largely employed in many countries. Because of restrictions issued by different governments on the use of this technique, in addition to the identification of irradiated foodstuffs, it may be important to determine the radiation dose administered to the foodstuffs. An EPR based protocol to reconstruct the administered dose from samples of irradiated meats (rabbit, pork and duck) within an uncertainty of ±25% is reported. © 2010 Elsevier Ltd.

An easy-to-use and robust energy monitoring device has been developed for reliable detection of day-to-day small variations in the electron beam energy, a critical parameter for quality control and quality assurance in industrial radiation processing. It has potential for using on-line, thus providing real-time information. Its working principle is based on the measurement of currents, or charges, collected by two aluminium absorbers of specific thicknesses (dependent on the beam energy), insulated from each other and positioned within a faraday cup-style aluminium cage connected to the ground. The device has been extensively tested in the energy range of 4–12 MeV under standard laboratory conditions at Institute of Isotopes and CNR-ISOF using different types of electron accelerators; namely, a TESLA LPR-4 LINAC (3–6 MeV) and a L-band Vickers LINAC (7–12 MeV), respectively. This device has been also tested in high power electron beam radiation processing facilities, one equipped with a 7-MeV LUE-8 linear accelerator used for crosslinking of cables and medical device sterilization, and the other equipped with a 10 MeV Rhodotron TT100 recirculating accelerator used for in-house sterilization of medical devices. In the present work, we have extended the application of this method to still lower energy region, i.e. from 1.5 to 2.4 MeV. Also, we show that such a device is capable of detecting deviation in the beam energy as small as 40 keV.

Gamma-irradiated NaCl samples of different origin were studied with the aim to find a reliable, easy-to-use, low-cost standard for the PSL technique, an increasingly used screening method for irradiated food identification. Five different natural salt types (rock and sea salts) purchased in the local markets were studied along with a laboratory-grade NaCl. High sensitivity and reproducibility of the PSL response are good properties of salt, but the pronounced fading of the signal may be a severe limitation of its use as a reference material. The high sensitivity along with the linear dose dependence of the PSL response opens up the interesting possibility of salt as suitable material for retrospective and environmental dosimetry, especially in the case of accidental irradiation or malevolent use of ionizing radiation. Again, the extreme sensitivity of the PSL signal to light and the pronounced fading must be considered limiting factors, and further basic research is required before practical applications of salt be feasible.

Reliability of the photo-stimulated luminescence (PSL) technique, as screening method for irradiated food identification, has been tested with three kinds of herbs and spices (oregano, red pepper and fennel), prepared in two different ways (granular: i.e. seeds and flakes, or powdered), over a long period of storage with different light exposures. The irradiated samples kept in the dark gave always a positive response (the sample is correctly classified as “irradiated”) for the overall examination period. The samples kept under ambient light conditions, in typical commercial glass containers, exhibited a reduction of the PSL signal, more or less pronounced depending on the type of food and packaging. The different PSL response of the irradiated samples is to be related to the quantity and quality of the mineral debris present in the individual food. It was also found that, for the same type of food, the light-induced fading was much stronger for the flaked and seed samples than for the corresponding powder samples, the penetrating capability of light being much more inhibited in powdered than in whole seeds or flaked form samples. The observed light bleaching of the PSL signal in irradiated herbs and spices is of practical relevance since it may lead to false negative classifications.

Plasma treatments are widely used in microelectronic industry, but they may leave some residual passivated damage in the gate oxides at the end of the processing. The plasma-induced damage can be amplified by metal interconnects (antenna) attached to the gate during the plasma treatments. Ionising radiation reactivates this latent damage, which produces enhanced oxide charge and Si/SiO2 interface state density. Two CMOS technologies have been investigated, with 5 and 7 nm gate oxides. Threshold voltage shifts, transconductance decrease, and interface traps build-up are always larger for plasma damaged devices than for reference devices.

Films of polymethylmethacrylate (PMMA) and polystyrene (PS) containing alpha-terthiophene (3T) undergo a radiochromic effect when exposed to electrons and gamma rays. The films turn either red-green or red, due to the formation of oligomeric radical cations. In both matrixes, absorbance at 465 nm grows linearly with dose when alpha-terthiophene concentration reaches 12%. Explored range goes up to ~ 2 x 10^6 Gy, with dose rates spanning over three orders of magnitude. Concerning their application as dosimeters, a higher sensitivity characterises the 3T-PMMA moiety, suggesting its suitability from the kGy range up to 1 MGy. Above this value films become fragile. 3T-Polystyrene films are less sensitive, but more radiation resistant. Therefore they better suit the medium-to-high dose dosimetry range. Dose rate influences the response sensitivity in a complex way, however above 80 and up to 3.6 x 10^4 Gy/min an approximate linearity exists between log(dose rate) and sensitivity, as in the analogous cellulose triacetate system.

When a non-conducting plastic block is irradiated with high-energy electrons, the thermalised electrons are trapped in the block if the range of the incident electrons is less than its thickness. These stored charges set up an electrostatic field in the block that can affect the trajectories of the incident electrons. The strength and the shape of the field depend on the intrinsic properties of the material as well as on the irradiation geometry. For this study, we selected various commercial electrical insulators such as polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene (PE), Teflon (PTFE), polyvinylchloride (PVC) and nylon. We measured the influence of the electrostatic field on depth-dose distribution in these materials using GafChromic® film dosimeters, and the subsequent leakage of the stored charge. This is an extension of our previous work on PMMA. The effect on the depth-dose distribution was most pronounced in PMMA, while in PTFE and PE it was minimal. On the other hand, PC showed an intermediate behaviour. Nylon and PVC electrically broke down at low doses. We have attempted an explanation of this behaviour of the various plastics based on radiation-induced conductivity, the measured leakage charge and also on their intrinsic electrical properties such as dielectric constant and dielectric strength.

The radiation-induced UV-vis spectrum of α -terthiophene radical cation in solid is reported. The radical cation initiates an oligomerization in the CTA matrix producing permanently coloured conjugated polarons. The specific net absorbance at 465 nm is linearly related with dose up to 2×10 6 Gy, for electrons and gamma irradiation. The decrease of the UV typical absorption (355 nm) and of four IR bands of α -terthiophene is linear with dose, as well. Although sensitivity is influenced by dose rate, it turned out that a linear relationship holds between sensitivity and log dose rate, in the range from 2 to 10 5 Gy/min. These findings suggest a potential application of the system for dosimetric purposes over a wide range of dose and dose rate.

Poly(vinyl alcohol) (PVA) films containing methyl viologen (MV2+) that colours blue upon exposure to ionizing radiation were investigated as possible dosimeters for use in radiation processing applications. In order to find the most suitable composition of the PVA-MV2+ film, different concentrations of the dye have been studied. The absorbance values at selected wavelengths, obtained from irradiation of the PVA film containing the most suitable MV2+ concentration, can be satisfactorily related to the absorbed dose over a wide range, from 50 Gy up to 40 kGy. The effects of dose, dose rate, humidity and temperature on the response of the PVA-MV2+ dosimeter film have been studied under laboratory conditions. We conclude that the PVA film containing MV2+ is a promising tool for the absorbed dose measurements in several industrial applications of ionizing radiations.

MOS capacitors with 8 nm thick oxides have been irradiated by an 8 MeV LINAC electron beam. C-V and I-V measurements have shown a positive trapped charge, higher for irradiation performed under negative gate bias, as a consequence of preferential charge recombination at the cathodic interface. No saturation of the positive trapped charge is measured up to 20 Mrad(Si). Neutral defects induced by irradiation have been studied, by performing positive and negative Fowler-Nordheim injection. The distribution of neutral defects is similar to that of trapped holes, indicating a correlation between trapped holes and neutral defects. Electrical stresses performed after irradiation have shown that the accumulation kinetics of oxide defects is similar in both unirradiated and irradiated devices.

Irradiated CaSO 4 :Dy, a well known thermoluminescent material widely employed for personal and environmental dosimetry, was studied by electron paramagnetic resonance spectroscopy in the 10 3 − 10 7 Gy dose range. A reliable dose assessment can be performed in that range by measuring the concentration of the radiation induced paramagnetic centers (SO 3 ) − and (VCa) 2− . (VCa) 2− center was very stable over time while (SO 3 ) − center showed a dose dependent fading. Dose dependent sensitization effects in the yield of both centers were also observed up to about 10 6 Gy.

The effects of electron irradiation on the defects associated electronic levels in Schottky diodes on 4H silicon carbide epilayers grown by chemical vapour deposition were investigated by Deep Level Transient Spectroscopy (DLTS) and Capacitance-Voltage (C-V) characteristics. These investigations were performed before and after irradiation with 8.6 MeV electrons at different doses. After irradiation four new traps with enthalpies equal to (Ec-0.23 eV), (Ec-0.39 eV), (Ec-0.63 eV) and (Ec-0.75 eV) were detected. Their thermal stability, a key point to determine their structure on the basis of recent theoretical and experimental results, was carefully investigated since it was earlier observed that during DLTS temperature runs up to 500 K a slight but significant recovery of a few irradiation-induced levels occurs. This effect was previously observed in literature for the level (Ec-0.70 eV) after thermal treatment at 500 °C [1], but the present results indicate that it involves more than a single level and is also effective at lower temperature. DLTS analyses were also performed from room temperature to liquid nitrogen temperature and vice versa up to 500 K.The annealing kinetics is reported and a few conclusions on the structure of the defects involved in the recovery are drawn. The correlation with the diode charge collection efficiency is also reported.

This paper reports on the influence that temperature during irradiation and dose-rate have on the radiation-induced free-radical yield and time stability in non de-proteinized bone. Bone from chicken legs was irradiated in the 253-293 K temperature range and with two different sources (60Co, 0.6 Gy/s and 12 MeV electrons, 6 x 10(6) Gy/s). Temperature influences type and number of radicals, while radical concentration seems to slightly decrease with dose rate.

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.

This report is a short review of the work done in Italy on the electron irradiation of power semiconductor devices. Electron irradiation for carrier lifetime control has been investigated using a 12 MeV linear accelerator. These studies includes: modeling of electrical semiconductor component parameters, specific adjustment of carrier lifetime, DLTS measurements to identify and characterize the radiation-induced defects. The optimum conditions for radiation processing of various types of power diodes and thyristors have been determined. Equipment and methods for series production have been developed and tested with pilot production quantities, then put into operation for mass production.

Summary Reliability of the photo-stimulated luminescence (PSL) technique, both as screening and identification methods, has been tested with several kinds of irradiated herbs and spices over a long period of storage. To check the influence of storage modality on the PSL response, the samples were divided into groups kept in environments with different light exposure. The results clearly indicate a marked light-induced bleaching of the PSL signal, which may lead to a false negative classification, in a significant percentage, for spices stored in typical market conditions. To limit the occurrence of wrong classifications, the suggestion reported in the European Committee of Normalization Standard 13751 to draw the necessary amount of product from a light-protected position becomes mandatory. Thermoluminescence measurements, performed for comparison purposes, gave correct results for all the samples tested.

The radiation impact on antenna devices can give new insights on basic mechanisms underlying the latent plasma damage nature and radiation hardness of commercial CMOS technologies for space applications. When MOS structures are exposed to ionizing radiation, electron-hole (e/sup -/-h/sup +/) pairs are created along the track of the incident particle. Some fraction of these e/sup -/-h/sup +/ pairs will recombine, and that fraction is a function of the oxide material, the kind of radiation, and the applied oxide electric field. In general, thinner oxides are less prone to radiation effects than thicker ones; applied bias permits to investigate (modulate) the trap creation in the bulk oxide and at the interface. In this study X-rays and e-beam sources have been considered. Although an e-beam LINAC with 8 MeV electrons is a standard source for radiation hardness characterization, its use is difficult for irradiating wafer with a large diameter. On the other side, fully automated protestations with X-ray tubes are commercially available. As a fair comparison, for a given dose and SiO/sub 2/ oxide technology, X-rays usually have a larger detrimental impact on MOSFET I-V characteristics with respect to the e-beam. Electrical stresses reactivate the latent plasma damage as well as ionizing radiation, but fewer studies have addressed the latter aspect and most of them date back to the older MOS technologies of the 70's and 80's. More recently, plasma damage reactivation in a 17.5- nm oxide due to ionizing, radiation has been addressed. The rapid evolution of plasma equipments and MOS technologies, such as the reduction of the gate oxide thickness well below 10 nm and the increase of the metal levels, suggests extending this investigation to more recent CMOS generations. This has been the purpose of this work, which is concentrated on the latent damage reactivation induced by ionizing radiation on a commercial 0.35 /spl mu/m (t/sub ox/=7 nm) CMOS technology.

An α-terthiophene/cellulose triacetate film system exposed to γ-rays and electron beam shows two new bands in the visible region of the spectrum. The absorbance at 490 nm is almost stable for a long time and responds linearly to the dose applied up to 400 kGy. A second band developed at 700 nm depends on dose rate and may indicate a chain-growth. The main species responsible for the color change and EPR signal is likely to be an enlarged oligomer radical cation stabilized by a semiquinoid structure.

We have investigated the degradation of MOS structure due to high energy electron irradiation as a function of radiation dose and gate bias applied during the irradiation. Devices have been characterized by current–voltage measurements, in order to study charge accumulation also at the gate interface. Three types of oxide charge have been observed: the unstable positive charge, due to trapped holes induced by the electron irradiation; the negative charge in the oxide bulk, deriving from capture of electrons injected during electrical measurements in radiation generated traps; and border traps, at both oxide interfaces.

Many applications of silicon p/sup +/-n junctions as detectors require high voltage operation. In particular the LHC experiments, because of the radiation damage level, need very high bias working voltage to fully collect the ionising generated charge multi-guard structures can be used in order to improve the breakdown voltage of microstrip detectors, limiting the occurrence of critical fields in the proximities of a reverse biased p/sup +/-n junction. In this work we present results for different designs of multi-guard structures, before and after irradiation with ionising and non-ionising radiation sources (p,n,/spl gamma/), and for different doses. Various experimental techniques have been used, like DC and AC electrical characterizations, and light emission microscopy. Moreover, a simulation work is presented. Its purpose is to improve the design on the basis of the experimental results.

The effect of carnosine on irradiation inactivation kinetics of Aeromonas hydrophila was studied. In phosphate buffer, carnosine had no effect on survival of the pathogen, whereas in turkey meat supplemented with carnosine the adverse effect of irradiation on A. hydrophila was reduced. Peroxy radicals were toxic to A. hydrophila, and this effect was counteracted by carnosine. Accordingly, in a kinetic test carnosine was capable of scavenging peroxy radicals. These results indicate that a free radical scavenger antioxidant such as carnosine can increase the radiation resistance of A. hydrophila in meat due to the inhibition of lipid peroxidation

High-voltage operation can be a solution to obtain full charge collection in strongly irradiated silicon detectors. The maximum bias voltage which can be applied is limited by the breakdown point of the junction. We show how multiguard structures can enhance the breakdown voltage in p+–n silicon devices designed for applications in the LHC environment.

MOS capacitors with a 4.4 nm thick gate oxide have been exposed to /spl gamma/ radiation from a Co/sup 60/ source. As a result, we have measured a stable leakage current at fields lower than those required for Fowler-Nordheim tunneling. This Radiation Induced Leakage Current (RILC) is similar to the usual Stress Induced Leakage Currents (SILC) observed after electrical stresses of MOS devices. We have verified that these two currents share the same dependence on the oxide field, and the RILC contribution can be normalized to an equivalent injected charge for Constant Current Stresses. We have also considered the dependence of the RILC from the cumulative radiation dose, and from the applied bias during irradiation, suggesting a correlation between RILC and the distribution of trapped holes and neutral levels in the oxide layer.

The radiation hardness of FOXFET biased ac-coupled microstrip detectors, foreseen for the upgraded version of the vertex detectors (SVX') of the CDF experiment, has been studied. The detectors have been irradiated with 60 Co γ rays with doses up to 1 Mrad. Two basic effects have been investigated: a variation of the switching voltage up to 100% due to oxide charge accumulation and Si/SiO 2 interface trap formation, and a 12-fold increase of the total leakage current, likely to come from surface damage. Moreover, a 10-fold decrease of the FOXFET dynamic resistance is observed at low gate bias. Post-irradiation annealing effects at room temperature of the electrical detector parameters are currently under investigation, in particular on a single shot 1 Mrad irradiated device. Recovery phenomena toward the pre-irradiation values are observed only for the switching voltage due to the annealing of trapped oxide charge.

Irradiation of silicon power rectifiers with electrons of 12 MeV energy has been carried out. Minority carrier lifetime τ, forward voltage V F , reverse recovered charge Q RR , reverse recovery time t RR for the diodes, circuit commutated turn-off time t q , and on-state voltage V T for the thyristors are measured as a function of dose. Power diodes and thyristors obtained from 〈111〉 neutron transutation or phosphorus doped float-zone silicon slices having 120Ωcm and 65Ωcm starting resistivity respectively and Ga-diffused are irradiated at room temperature. A linear relationship between carrier lifetime of irradiated diodes and electron dose is found and the calculated damage coefficients are k τ = 1.1x10 -8 cm 2 /s and 7.2x10 -9 cm 2 /s for the low-level and high-level lifetimes respectively at 25°C. For irradiated thyristors the linear relationship between turn-off time and dose yields k tq = 3x10 -9 cm 2 /s at 125°C. Electron irradiation also affects the resistivity of the starting n-type silicon, increasing it of ≈ 15Ωcm for radiation doses > 1×10 4 Gy. A dose rate effect on the electrical characteristics of the devices using pulses of different duration is analyzed. Annealing studies are carried out at 150 °C, 200°C and 360°C to assess the stability of the defects produced by the electron bombardment by monitoring the variation of the electrical characteristics of the irradiated devices in the temperature range of interest. DLTS measurements performed on electron irradiated power rectifiers have revealed a complex defect pattern. The E 1 defect level (E c -0.17 ev) is the principal recombination center that controls lifetime following room temperature irradiation. The energy levels and capture cross sections of these irradiation induced-defects are reported. This study confirms that lifetime control in silicon power devices is feasible by high energy electrons. The major advantages of this technique over metallic diffusion or 60 Co γ-irradiation methods are: better quality, lower processing cost and higher device yields. Annealing after irradiation is important to ensure long-term device stability.

Recombination centers introduced by irradiation with 12 MeV electrons in large area silicon diodes with p-i-n structure are studied with the Deep Level Transient Spectroscopy technique (DLTS). The effects of these levels on the electrical characteristics of the devices are related to their position E t in the silicon forbidden gap, their concentration and their electron capture cross section. Changes of defect configuration during an annealing process at 360 °C have been observed and a detailed analysis of the DLTS spectra has shown a complex defect pattern. Four major recombination centers have been identified: E c −E t =0.17 eV, E c −E t =0.19 eV, E c −E t =0.31 eV, E c −E t =0.39 eV, where E c is the energy corresponding to the lower limit of the conduction band. The first energy level, known as A-center, is the dominant recombination level controlling the minority carrier lifetime after room temperature irradiation. As the annealing proceeds the center at E c −E t =0.31 eV becomes the dominant one. The complex structure of the centers has been studied and demonstrated with the aid of proper modelling implemented on a set of numerical simulation tools. In this way it has been possible to analyze more accurately the defect kinetics during annealing. The study of the defect behaviour during the annealing process has resulted in an improved application of electron irradiation as a standard production technique in the manufacturing process of high power devices.

In methanolic solution deaerated with argon or hydrogen, the pentacoordinated complex bromobis-(1,2-bisdiphenylphosphinoethane)cobalt(II)bromide, [Co(DPE)2Br]Br, where DPE = 1,2-bisdiphenylphosphinoethane, is reduced to Co(DPE)2Br by e-solv. For the reaction, Co(DPE)2Br+ + e-solv→Co(DPE)2Br, a value of k = (4.4±0.4) × 1010 mol-1 dm3 s-1 has been determined. Co(DPE)2Br rapidly loses Br-, with a rate constant of (8.0±0.4) × 105 s-1, to give the known compound Co(DPE)2+. Evidence has been obtained for reactions of Co(DPE)2Br+ with the radicals H, ·CH2OH and (CH3)2COH which lead, ultimately, to the same final product, namely Co(DPE)2+. Rate constants for the known reactions, Co(DPE)2++H2→CoH2(DPE)2+ and Co(DPE)2++CO→(CO)(DPE)2+ were found to be k=(3.0±0.2)×104 mol-1 dm3 s-1 and (1.4±0.1)×104 mol-1 dm3 s-1 respectively. Bis-(1,2-bisdiphenylphosphinoethane)rhodium(I)chloride, [Rh(DPE)2]Cl, bis-(1,2-bisdiphenylphosphinoethane)rhodium(I)perchlorate, [Rh(DPE)2]ClO4, and bis-(cis-1,2-bisdiphenylphosphinoethylene)rhodium(I)chloride, [Rh(VPP)2]Cl, where VPP=cis-1,2-bisdiphenylphosphinoethylene, react with e-solv in methanolic solution deaerated with Ar. For the reactions Rh(DPE)2+ + e-solv→Rh(DPE)2 and Rh(VPP)2++e-solv→Rh(VPP)2 values of k=(3.0±0.3)×1010 mol-1 dm3 s-1 and (2.8±0.2)×1010 mol-1 dm3 s-1 respectively, have been calculated. The products of both reactions show an absorption band in the visible region (λmax=600 nm, ϵ600= (4.0±0.2)×103 mol-1 dm3 cm-1) and decay to the original compounds; this decay is ascribed to reaction with the solvent, viz. Rh(diphosphine)2+CH3OH→Rh(diphosphine)2++Products, where the rate constant is k=(3.6±0.3)×102 s-1 when diphosphine=DPE and k=(1.3±0.2)×103s-1 when diphosphine=VPP.

In methanolic solution deaerated with argon, the complexes of general formula t-FeH(L)(DPE)/sub 2/+, where DPE = 1,2-bis(diphenylphosphine)ethane and L = CH/sub 3/CN, CH/sub 3/CH/sub 2/CN, CH/sub 2/CHCN, C/sub 6/H/sub 5/CN, and p-CH/sub 3/C/sub 6/H/sub 4/CN, are reduced to FeH(L)(DPE)/sub 2/ by solvated electrons. For the reaction FeH(L)(DPE)/sub 2/+ + e/sub 8/-..-->.. FeH(L)(DPE)/sub 2/, k = (2.8 +- 0.3) x 10/sup 10/ M/sup -1/ s/sup -1/ for all of the compounds. With FeH(CH/sub 2/CHCN)(DPE)/sub 2/+ only, a reaction with the radical CH/sub 2/OH has also been observed. This reaction, which is supposed to proceed via addition of the radical to the coordinated CH/sub 2/CHCN, leads to the saturation of the double bond. When L = CH/sub 3/CN, CH/sub 3/CH/sub 2/CN, C/sub 6/H/sub 5/CN, and p-CH/sub 3/C/sub 6/H/sub 4/CN, FeH(L)(DPE)/sub 2/ rearranges, losing the ligand L to give the already known iron(I) complex, FeH(DPE)/sub 2/, which in methanol has a t/sub 1/2/ greater than or equal to 1 s. The rate constants for this process have been determined. The complex FeH(p-ClC/sub 6/H/sub 4/Cn)(DPE)/sub 2/+ on reacting with e/sub 8//sup -/ undergoes the detachment of Cl/sup -/ from the ligand, while the radical intermediate FeH(C/sub 6/H/sub 4/CN)(DPE)/sub 2/+ reacts rapidly with the solventmore » to give the complex FeH(C/sub 6/H/sub 5/N)(DPE)/sub 2/+ as final product.« less

An investigation into the reaction of solvated electron (e−s) with the two hydrido complexes trans-FeH{P(OCH3)3}(DPE)+2 and trans-FeH(CO)(DPE)+2, where DPE = 1,2-bis(diphenylphosphino)ethane, in methanolic solution deaerated with argon has been carried out using the technique of pulse radiolysis. The reaction of e−s with both complexes occurs with a rate constant k = (2.6 ± 0.3) X 1010 M−1 s−1 and yields a reduced intermediate of general formula FeH(L)(DPE)(DPE)sesqui, where (DPE)sesqui denotes a ring-opened DPE ligand. The conversion of one of the DPE from a bidentate to a monodentate form, upon reaction of the starting complex with e−s, is not distinguishable from the electron transfer; in fact only one process has been observed. The absorption spectra of the reduced species are stable over the 0.1 s/div. time scale of the instrument, and have been characterized over the range 300–650 nm. Their stability over a longer period of time has been checked using single pulse spectroscopy at high doses and continous γ radiolysis. Formulation of FeH(L)(DPE)(DPE)sesqui as a pentacoordinated species with a monodentate DPE ligand is supported by electrochemical and spectroscopic result. The behaviour of these two complexes is compared with that of the analogous complexes having the same general formula but with L = organonitrile ligands, and an interpretation of this behaviour is suggested.

Electron irradiation has been used to modify the electrical characteristics and to enhance the switching speed of high power GTO thyristors. The defects introduced by the impinging electrons have been annealed through several thermal steps, carried out at three different temperatures, after which the main electrical characteristics have been tested. The trade-off between static and dynamic characteristics, obtained with this method of lifetime control, has been compared with that obtained in standard gold doped devices. Special attention is paid to the control of power losses during the turn-off phase.

SummaryPulse radiolysis experiments were carried out on methanolic solutions of misonidazole and its azo and azoxy derivatives in order to obtain the spectra of their radical anions. The rate constants for the reaction of these compounds with e−s were 2·5 × 1010, 2·3 × 1010 and 1·9 × 1010 M−1s−1 respectively. The electro-chemical properties of the compounds were studied with the aim of producing their radical anions by electrolysis in aprotic medium (DMF, 0·1 M TEAP). The potentials at cathodic peaks were − 1·05, − 1·10 and − 1·18 V for misonidazole, azo and azoxy derivatives, respectively. The decay of the radical anion of misonidazole, which produces nitrite ions, was studied in particular, the corresponding rate constant being 2·8 × 10−4s−1. The possibility of using electrochemistry in the study of these transient species is discussed.