A review of the developments in nuclear track methodology as published in the proceedings of the International Conference on Nuclear Tracks in Solids from 1990 to 2008

International audienceThe aim of this paper is to provide an overview of the developments in nuclear track methodology as published in the proceedings of the last ten meetings of the International Conference on Nuclear Tracks in Solids (ICNTS) from the Marburg (Germany) conference in 1990 to the Bologna (Italy) conference of 2008. Nuclear Tracks Methodology (NTM) examines the effects of the interaction between charged particles and solid materials and presents several desirable characteristics: the detectors can easily be cut into a size appropriate for any application and can be used in locations for which other radiation detectors are not suitable; the etching and reading instrumentation is relatively simple; there is a quasiinsensibility to gamma radiation for reasonable dose exposures (typically <1 kGy); after chemical etching the information recorded on the detector material is essentially permanent; and, finally, the system involves relatively low costs. These characteristics have contributed to the importance of NTM for radiation detection in an immense number of applications across a wide range of scientific and technological fields. This paper reviews the new ideas, topics, materials and applications related to NTM that have been presented over the past ten ICNTS meetings from 1990 to 2008, and analyzes the evolution of various topics. One could argue that the conferences themselves have been an important source of new ideas and applications for the nuclear track research community. Two important observations arise from this review. The first is that the contributions of the past ten international conferences can be conveniently classified into 12 categories. The second is that the number of papers published varied widely from conference to conference. Several factors contributed: the variation in the number of conference participants, the interests of local participants (who account for a disproportionate number of conference participants), the location of the conference, and the appearance of new international conferences devoted to topics similar to those covered by the ICNTS

Condensation d'ADN plasmidique par des diamines sur un substrat de graphite HOPG

National audienceCe travail vise à améliorer notre connaissance des effets produits par les électrons de basse énergie (EBEs) sur l'ADN. Parmi les composants radiosensibles, les acides nucléiques demeurent en effet une cible critique des EBEs. Ce type d'étude requiert un bon étalement et un contrôle des dépôts d'ADN plasmidique sur des surfaces conductrices. Nous avons étudié en détails la formation de complexes entre des polyamines et l'ADN plasmidique. Une partie du travail a consisté à caractériser les dépôts réalisés sur des substrats de graphite pyrolytique hautement orienté (HOPG) en employant des diamines pour condenser l'ADN. Nous avons montré que dans les conditions opératoires de cette étude, il est possible de créer des dépôts avec des épaisseurs calibrées, présentant un taux dégâts constant et suffisamment bas pour permettre des études ultérieures en gel d'électrophorèse. Ces dépôts, dont l'épaisseur varie de deux à plusieurs dizaines de nanomètres, ont la propriété remarquable de pouvoir être re-dissous dans l'eau sans qu'ils ne subissent de dommages supplémentaires. Les dépôts réalisés avec le diaminopropane ont été exposés aux EBEs et une première exploitation par désorption stimulée (ESD) et par relaxation de plasmide a été effectuée. Ces premiers résultats ouvrent de larges perspectives pour l'utilisation ultérieure des dépôts créés durant ce travail

Dissociative electron attachment to DNA-diamine thin films: Impact of the DNA close environment on the OH(-) and O(-) decay channels.

International audience: We measure the desorption of anions stimulated by the impact of 0-20 eV electrons on highly uniform thin films of plasmid DNA-diaminopropane. The results are accurately correlated with film thickness and composition by AFM and XPS measurements, respectively. Resonant structures in the H(-), O(-), and OH(-) yield functions are attributed to the decay of transient anions into the dissociative electron attachment (DEA) channel. The diamine induces ammonium-phosphate bridges along the DNA backbone, which suppresses the DEA O(-) channel and in counter-part increases considerably the desorption of OH(-). The close environment of the phosphate groups may therefore play an important role in modulating the rate and type of DNA damages induced by low energy electrons

Beam characterization of a lab bench cold cathode ultra-soft X-ray generator

International audienceThe aim of this work is to characterize the Ultra Soft X-ray (USX, 1.5 keV, Al Kα) photon beam of a customized lab bench cold cathode generator. Within this generator, the electron beam is slowed down in a thin aluminium foil (16 μm) supported by an easily exchangeable anode. It is shown that the thickness of the foil and the anode configuration determine the spatial distribution and the fluence rate of the photon beam, whereas accelerating voltage determines both fluence rate and energy spectrum feature. It is shown also that under specific operation parameters (i.e. accelerating voltage), a Gaussian energy distribution of the beam can be generated which is centred on the energy of the Al Kα line (1.5 keV). Dosimetric films of GAFCHROMIC® HD-810 were used to estimate the photon fluence rate distribution of the beam. Its variation, when the generator acts as a monoenergetic source, was characterized with the two different configurations of the anode assembly. Finally, it is verified that the anode assembly consisting in a flat washer, on which the aluminium foil is set, acts as a simple point-source

Kinetics of propagation of bystander effects in human cells cultures exposed to low fluences of high LET radiations

International audienceWe and others have previously shown, in confluent cell cultures exposed to low fluences of a particles, that the proportion of cells that upregulate stress-inducible proteins is much higher that the number of cells irradiated. This phenomenon, called bystander effect, is now well accepted and is thought to impact the health risks of exposure to ionizing radiation. Here, we investigate the kinetics of propagation of signaling events that lead to induction of DNA damage in bystander cells in confluent normal human AG1522 fibroblasts exposed to a mean dose of 0.2 cGy from 3.2 MeV a particles (LET ; 124 keV/lm) or 1 GeV/n iron ions (LET ; 151 keV/lm). We evaluated the formation of 53BP1 foci (p53 binding protein 1), which localizes at sites of DNA double strand breaks, as a function of time after irradiation. The fraction of cells whose nuclei were traversed by an irradiating particle was derived from Poisson statistics and estimates of cell geometry, particle fluence and energy loss. At a mean dose of 0.2 cGy, only 1.4% and 1.2% of the cells are traversed through the nucleus by a particle or iron ion tracks, respectively. The number of 53BP1 foci in control cells was ; 0.61 foci per cell. In a particle-irradiated cell cultures, the mean number of foci per cell was 0.73 (p,0.001) at 15 min; it reached 0.90 by 3h (p,0.001) after irradiation, following which a decrease was observed. The same trend was detected when the fraction of cells with foci was considered: it reached 61% at 3h which is higher than the expected 47.4% of the cells (46% in control + 1.4% traversed). The increase in foci formation over the expected value was eliminated when the cells were incubated with a specific inhibitor of ATM (Ataxia Telangiectasia Mutated protein). Analyses of bystander effects in iron ion-irradiated cell cultures and the effect of partial oxygen tension on the kinetic of 53BP1 foci formation in low fluences alpha particle-irradiated cell populations are in progress

Neutral Products Desorption from DNA Thin Films Induced by Low-Energy Electrons (0.5-20 eV)

International audienceLow-energy electrons (LEEs) are produced in great amount in the biological medium, when submitted to high-energy radiations. They have the ability to induce strand breaks in the DNA duplex, as proven by electrophoresis analysis of irradiated dry deposits. LEE interactions with target molecules induce the formation of different species such as anions, cations, radicals and neutrals. The desorption of anionic species from oligonucleotides and DNA under LEEs irradiation has been intensively explored. The involved mechanisms and sites were successfully identified, including the resonant formation of transient negative ions (TNI) below 15 eV. However, the desorption of neutral products was less explored [4], due to their difficult detection. Exploring this aspect will provide additional information and complete the picture of the dissociating pathways followed by TNIs

Non-targeted Stressful Effects in Normal Human Fibroblast Cultures Exposed to Low Fluences of High Charge, High-Energy (HZE) Particles: Kinetics of Biologic Responses and Significance of Secondary Radiations.

International audienceThe induction of nontargeted stressful effects in cell populations exposed to low fluences of high-charge (Z) and high-energy (E) particles is relevant to estimates of the health risks of space radiation. We investigated the up-regulation of stress markers in confluent normal human fibroblast cultures exposed to 1,000 MeV/u iron ions [linear energy transfer (LET) ∼151 keV/μm] or 600 MeV/u silicon ions (LET ∼50 keV/μm) at mean absorbed doses as low as 0.2 cGy, wherein 1-3% of the cells were targeted through the nucleus by a primary particle. Within 24 h postirradiation, significant increases in the levels of phospho-TP53 (serine 15), p21(Waf1) (CDKN1A), HDM2, phospho-ERK1/2, protein carbonylation and lipid peroxidation were detected, which suggested participation in the stress response of cells not targeted by primary particles. This was supported by in situ studies that indicated greater increases in 53BP1 foci formation, a marker of DNA damage. than expected from the number of primary particle traversals. The effect was expressed as early as 15 min after exposure, peaked at 1 h and decreased by 24 h. A similar tendency occurred after exposure of the cell cultures to 0.2 cGy of 3.7 MeV α particles (LET ∼109 keV/μm) that targets ∼1.6% of nuclei, but not after 0.2 cGy from 290 MeV/u carbon ions (LET ∼13 keV/μm) by which, on average, ∼13% of the nuclei were hit, which highlights the importance of radiation quality in the induced effect. Simulations with the FLUKA multi-particle transport code revealed that fragmentation products, other than electrons, in cell cultures exposed to HZE particles comprise <1% of the absorbed dose. Further, the radial spread of dose due to secondary heavy ion fragments is confined to approximately 10-20 μm. Thus, the latter are unlikely to significantly contribute to stressful effects in cells not targeted by primary HZE particles

Absolute cross section for loss of supercoiled topology induced by 10 eV electrons in highly uniform ∕DNA∕1,3-diaminopropane films deposited on highly ordered pyrolitic graphite.

International audience: It was recently shown that the affinity of doubly charged, 1-3 diaminopropane (Dap(2+)) for DNA permits the growth on highly ordered pyrolitic graphite (HOPG) substrates, of plasmid DNA films, of known uniform thickness [O. Boulanouar, A. Khatyr, G. Herlem, F. Palmino, L. Sanche, and M. Fromm, J. Phys. Chem. C 115, 21291-21298 (2011)]. Post-irradiation analysis by electrophoresis of such targets confirms that electron impact at 10 eV produces a maximum in the yield of single strand breaks that can be associated with the formation of a DNA(-) transient anion. Using a well-adapted deterministic survival model for the variation of electron damage with fluence and film thickness, we have determined an absolute cross section for strand-break damage by 10 eV electrons and inelastic scattering attenuation length in DNA-Dap complex films

Stereotactic radiotherapy in the treatment of brain metastases

This thematic review is part of a larger, comparative dosimetric analysis of the evaluation of treatment plans created by different modulated intensity irradiation, which is delivered by means a linear accelerator for the treatment of multiple metastases in the brain. There is currently no consensus as to which method is dosimetrically better. A further study will be aimed at determining the dosimetric advantages of each irradiation technique to introduce additional certainty into the planning process

Blazar spectral variability as explained by a twisted inhomogeneous jet

Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming1. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles2, with possible intervention of shock waves3,4 or turbulence5. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events6,7,8,9,10 and can also explain specific properties of blazar emission, such as intra-day variability11, quasi-periodicity12,13 and the delay of radio flux variations relative to optical changes14. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditions—such as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distribution—can explain snapshots of the spectral behaviour of blazars in many cases15,16. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities17 or rotation of the twisted jet6 cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016–2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory