Understanding and simulating the material behavior during multi-particle irradiations.

A number of studies have suggested that the irradiation behavior and damage processes occurring during sequential and simultaneous particle irradiations can significantly differ. Currently, there is no definite answer as to why and when such differences are seen. Additionally, the conventional multi-particle irradiation facilities cannot correctly reproduce the complex irradiation scenarios experienced in a number of environments like space and nuclear reactors. Therefore, a better understanding of multi-particle irradiation problems and possible alternatives are needed. This study shows ionization induced thermal spike and defect recovery during sequential and simultaneous ion irradiation of amorphous silica. The simultaneous irradiation scenario is shown to be equivalent to multiple small sequential irradiation scenarios containing latent damage formation and recovery mechanisms. The results highlight the absence of any new damage mechanism and time-space correlation between various damage events during simultaneous irradiation of amorphous silica. This offers a new and convenient way to simulate and understand complex multi-particle irradiation problems.

Energy deposition by heavy ions: additivity of kinetic and potential energy contributions in hillock formation on CaF2.

Modification of surface and bulk properties of solids by irradiation with ion beams is a widely used technique with many applications in material science. In this study, we show that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of medium energy (3 and 5 MeV) highly charged ions (Xe(22+) to Xe(30+)) as well as swift (kinetic energies between 12 and 58 MeV) heavy xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be lowered substantially. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface.

Online in situ x-ray diffraction setup for structural modification studies during swift heavy ion irradiation.

The high energy density of electronic excitations due to the impact of swift heavy ions can induce structural modifications in materials. We present an x-ray diffractometer called ALIX ("Analyse en Ligne sur IRRSUD par diffraction de rayons X"), which has been set up at the low-energy beamline (IRRadiation SUD - IRRSUD) of the Grand Accélérateur National d'Ions Lourds facility, to allow the study of structural modification kinetics as a function of the ion fluence. The x-ray setup has been modified and optimized to enable irradiation by swift heavy ions simultaneously to x-ray pattern recording. We present the capability of ALIX to perform simultaneous irradiation-diffraction by using energy discrimination between x-rays from diffraction and from ion-target interaction. To illustrate its potential, results of sequential or simultaneous irradiation-diffraction are presented in this article to show radiation effects on the structural properties of ceramics. Phase transition kinetics have been studied during xenon ion irradiation of polycrystalline MgO and SrTiO(3). We have observed that MgO oxide is radiation-resistant to high electronic excitations, contrary to the high sensitivity of SrTiO(3), which exhibits transition from the crystalline to the amorphous state during irradiation. By interpreting the amorphization kinetics of SrTiO(3), defect overlapping models are discussed as well as latent track characteristics. Together with a transmission electron microscopy study, we conclude that a single impact model describes the phase transition mechanism.

Venlafaxine in the treatment of postpartum depression.

BACKGROUND: Although postpartum depression is a highly prevalent illness, antidepressant treatment studies of postpartum depression are sparse. Incomplete recognition and treatment of puerperal illness place women at risk for chronic depression and may have adverse effects on child development. METHOD: An 8-week, flexible-dose, open study of venlafaxine (immediate release; mean dose = 162.5 mg/day) was performed in a group of 15 women who met DSM-III-R criteria for major depressive disorder with onset within the first 3 months postpartum. Patients were assessed at baseline and every 2 weeks across the study. Measurements of outcome included the 17-item Hamilton Rating Scale for Depression (HAM-D), the Kellner Symptom Questionnaire, and the Clinical Global Impressions scale (CGI). RESULTS: Despite baseline scores of depression that were particularly high, response to treatment was robust. Twelve of 15 patients experienced remission of major depression (HAM-D score < or = 7 or CGI score < or = 2). Dramatic decrease in anxiety paralleled the decrease in depression across the sample. CONCLUSION: Venlafaxine is effective in the treatment of postpartum major depression. Early identification of women who suffer from postpartum mood disturbance is critical to minimize the morbidity associated with untreated mood disturbance and the effect of depression on children and families.

Defect-unbinding and the Bose-glass transition in layered superconductors.

The low-field Bose-glass transition temperature in heavy-ion irradiated Bi(2)Sr(2)CaCu(2)O(8+delta) increases progressively with increasing density n(d) of irradiation-induced columnar defects, but saturates for n(d) greater or = 1.5 x 10(9) cm(-2). The maximum Bose-glass temperature corresponds to that above which diffusion of two-dimensional pancake vortices between vortex lines becomes possible, and the "linelike" character of vortices is lost. We develop a description of the Bose-glass line that quantitatively describes experiments on crystals with widely different track densities and material parameters.

[Production of superoxide radicals with pulse radiolysis of water with high linear energy transfer]. / Production de radicaux superoxydes par radiolyse pulsée de l'eau à transfert d'énergie linéique (TEL) élevé.

The radiolysis of water with heavy ions of high linear energy transfer (LET) (-dE/dx) is characterized, in deaerated medium, by the production of superoxide anions, the radiolytic yields of which increase with the LET. Radiobiological interest in such radical species comes from the oxidative stress which may be generated by their dismutation in O2 and H2O2 in anoxic medium (radiotherapy with heavy ions). A brief review of the measurements of superoxide free radicals in aqueous solution by indirect or direct methods is presented. Moreover, some experimental results obtained by pulse radiolysis with Ar18+ ions (TEL = 290 keV x microm(-1)), are described. The interpretation of the kinetics takes into account the superoxide absorbance and that of hydrogen peroxide, which is present at the millisecond time scale.

Birth outcomes following prenatal exposure to fluoxetine.

BACKGROUND: Although pregnancy has frequently been described as a time of emotional well-being, some women experience significant antenatal depression that may require treatment with antidepressants. The purpose of this investigation was to examine the relative effects of early and late trimester exposure to fluoxetine and perinatal outcome. METHODS: Obstetric and neonatal records were reviewed for 64 mother-infant pairs where there was documented use of fluoxetine at some point during pregnancy. Differences in several measures of obstetrical outcome and neonatal well-being were examined in early trimester- and late trimester-exposed infants. RESULTS: No differences in birth weight and acute neonatal outcome were evident across the two groups, though there was a higher frequency of special care nursery admissions for infants with exposure to fluoxetine late in pregnancy. Special care nursery admissions could not be attributed to any specific factor. CONCLUSIONS: Given the growing numbers of women who are treated with antidepressants, including fluoxetine, during pregnancy, and the strong association between depression during pregnancy and risk for postpartum depression, patients may be best advised to continue treatment with antidepressants through labor and delivery versus making any change in intensity of treatment during the acute peripartum period.

Direct observation of HO2/O2- free radicals generated in water by a high-linear energy transfer pulsed heavy-ion beam.

The formation and decay of HO2/O2- radical from the radiolysis of water by heavy 36S16+ ions (2.7 GeV) have been observed by time-resolved absorption spectroscopy at 260 nm. The experiment was performed at the Grand Accélérateur National d'Ions Lourds (Caen, France). In deaerated water, for a linear energy transfer (LET) of 250 eV/nm, the yield of HO2/O2- is (6 +/- 2) x 10(-9) mol J-1. In aerated solution, an additional formation of O2- is observed due to the reaction of hydrogen atom and e(aq)- with oxygen. The experimental G values are compared to those obtained with light ions for the same LET. The importance of the initial velocity is discussed briefly.

Ionizing radiation dosimetry in the absorbed dose range 0.01-50 MGy based on resistance and ESR linewidth measurements of organic conducting crystals.

The materials studied in the present work as high-dose dosimeters are members of a large class of molecular crystals which are organic conductors of electricity. Very different from each other in the details of their molecular and crystal structures, they all behave in the same way when subjected to increasing high doses of radiation, at least from the point of view of their electronic transport properties, because of the quasi-one-dimensional character of the conduction process. Their resistivities increase exponentially with the absorbed dose while their electron spin resonance (ESR) linewidths decrease exponentially. Very small single crystals less than 10 micron thick can be used as dosimeters in the dose range 0.01-50 MGy for gamma rays as well as for electron irradiations, by applying four probe resistance measurements. Only a few compounds over a large number of candidates have been irradiated in the present work with gamma-rays, low energy x-rays and electrons. In some favourable cases the energy and temperature dependences of the dosimeters have been checked experimentally. Their mass energy absorption coefficients and electron stopping powers have been also calculated. It is hoped to extend this kind of dosimetry to lower and higher doses by trying new compounds from the large family of organic conductors or by improving the resistivity and ESR measurement techniques.