Michel Fromm

Characterization of chemical and optical modifications induced by proton beams in CR-39 detectors

Abstract Chemical and optical modifications induced by 22.5 MeV protons slowed down into a 4.4 mm polyallyl diglycol carbonate (CR-39) stack, which was composed of 16 detectors of different thicknesses, are studied. Irradiation was performed perpendicular to the stack surface, in a vacuum chamber, with proton fluences ranging from 10 11 to 10 14 particles/cm 2 . These transformations are analyzed using fourier transform infrared (FTIR) absorption spectroscopy in the total attenuation reflection mode and UV–visible spectroscopy by following CO, CC and O–H bands evolution and by following the shift in the absorption edge towards the higher wavelengths. The chemical changes occurring in the CR-39 absorption spectra (both FTIR and UV) are analyzed versus the ion beam fluence, the beam penetration depth into the stack and the average deposited energy density. The results show that degradation of CR-39 presents a maximum in the depths ranging between 3500 and 4000 μm .

Damage induced to DNA by low-energy (0-30 eV) electrons under vacuum and atmospheric conditions.

In this study, we show that it is possible to obtain data on DNA damage induced by low-energy (0-30 eV) electrons under atmospheric conditions. Five monolayer films of plasmid DNA (3197 base pairs) deposited on glass and gold substrates are irradiated with 1.5 keV X-rays in ultrahigh vacuum and under atmospheric conditions. The total damage is analyzed by agarose gel electrophoresis. The damage produced on the glass substrate is attributed to energy absorption from X-rays, whereas that produced on the gold substrate arises from energy absorption from both the X-ray beam and secondary electrons emitted from the gold surface. By analysis of the energy of these secondary electrons, 96% are found to have energies below 30 eV with a distribution peaking at 1.4 eV. The differences in damage yields recorded with the gold and glass substrates is therefore essentially attributed to the interaction of low-energy electrons with DNA under vacuum and hydrated conditions. From these results, the G values for low-energy electrons are determined to be four and six strand breaks per 100 eV, respectively.

Propagation Distance of the α-Particle-Induced Bystander Effect: The Role of Nuclear Traversal and Gap Junction Communication

Abstract Gaillard, S., Pusset, D., de Toledo, S. M., Fromm, M. and Azzam, E. I. Propagation Distance of the α-Particle-Induced Bystander Effect: The Role of Nuclear Traversal and Gap Junction Communication. Radiat. Res. 171, 513–520 (2009). When cell populations are exposed to low-dose α-particle radiation, a significant fraction of the cells will not be traversed by a radiation track. However, stressful effects occur in both irradiated and bystander cells in the population. Characterizing these effects, and investigating their underlying mechanism(s), is critical to understanding human health risks associated with exposure to α particles. To this end, confluent normal human fibroblast cultures were grown on polyethylene terephthalate foil grafted to an ultrathin solid-state nuclear track detector and exposed under non-perturbing conditions to low-fluence α particles from a broadbeam irradiator. Irradiated and affected bystander cells were localized with micrometer precision. The stress-responsive protein p21Waf1 (also known as CDKN1A) was induced in bystander cells within a 100-μm radius from an irradiated cell. The mean propagation distance ranged from 20 to 40 μm around the intranuclear α-particle impact point, which corresponds to a set of ∼30 cells. Nuclear traversal, induced DNA damage, and gap junction communication were critical contributors to propagation of this stressful effect. The strategy described here may be ideal to investigate the size of radiation-affected target and the relative contribution of different cellular organelles to bystander effects induced by energetic particles, which is relevant to radioprotection and cancer radiotherapy.

Production and Validation of CR-39-Based Dishes for α-Particle Radiobiological Experiments

Abstract Gaillard, S., Armbruster, V., Hill, M. A., Gharbi, T. and Fromm, M. Production and Validation of CR-39-Based Dishes for α-Particle Radiobiological Experiments. Radiat. Res. 163, 343–350 (2005). The study of radiobiological effects induced in vitro by low fluences of α particles would be significantly enhanced if the precise localization of each particle track in the cell monolayer was known. From this perspective, we developed a new method based on tailor-made UV-radiation-cured CR-39, the production of which is described. Its validation both as a petri dish and as solid-state nuclear track detectors is demonstrated. With respect to the demands on solid-state nuclear track detectors in such experiments, these biologically compatible detectors have a controlled micrometric thickness that allows them to be crossed by the α particles. In this study, we present a method for obtaining 10-μm-thick CR-39, its chemical characterization, and its properties as a solid-state nuclear track detector under the environmental conditions of radiobiological experiments. The experimental studies performed with 3.5 MeV α particles show that their transmitted energy is sufficient enough to cross the entire cellular volume. Under optimal conditions, etched tracks are clearly defined 2 h after etching. Moreover, the UV-radiation-cured CR-39 represents an essentially zero background that is due to the short time between the production and use of the polymer. Under a confocal microscope, this thin solid-state nuclear track detector allows the precise localization of the impact parameter at the subcellular level.

3-D Confocal microscopy track analysis: a promising tool for determining CR-39 response function

Abstract A new method based on the use of the confocal microscope is described in order to evaluate the CR-39 response function for Li-7 ions with an incident energy of 10.77 MeV . This method uses the formulations developed by Fromm et al. and considers two etching velocities: V B represents the bulk etch rate and remains constant, and V T the track etch rate, which varies along the particles path. The confocal microscope seems to bring big improvements for track analysis. The first results of V T versus the particle range are presented and compared with the curves obtained by the sequential etching method. The obtained V T are plotted and compared to LET, REL 350 and the cumulative radial dose.

Track etch velocity study in a radon detector (LR 115, cellulose nitrate)

For radon dosimetry, complete knowledge of the detection area of the detector used for alpha particles emitted by radon and its two daughters (Po 218 and Po 214) is compulsory. Latent tracks in the detector induced by alpha particles are enlarged in a hot hydroxide sodium bath to make them observable by microscopy. This paper deals with the determination of the track etch velocity (VT). We compared two different approaches to calculate the VT: for the first one, the VT in considered as a function of the alpha particle energy. The VT is determined by using a track etch model based on the experimental study of the track diameters for normal incidence versus alpha particle energies. For the second approach, we assumed that the VT was directly correlated with the ionisation rate (I) created all along the alpha particle range in the detector. This ionisation rate, which depends directly on the alpha particle energy was calculated using the TRIm programme. The knowledge of the VT enabled us to determine the critical incidence angle for each energy under which the alpha particle did not induce an observable track. Results for each approach were compared with the experimental data obtained with a specific irradiator system. Finally, track detection efficiencies of LR 115 for radon and their standard deviations are proposed for a simple configuration.

Watching at the correlation between the specific track-etch rate and the primary physical parameters of the swift ion interaction with the CR-39

Abstract Analysis of etched nuclear tracks in CR-39 solid state nuclear track detectors has recently been made possible by the confocal microscope. This recent innovation has opened up some particularly interesting perspectives. The main originality of this microscopy technique is that it makes it possible to work on numerical, three-dimensional images of chemically etched nuclear tracks in the CR-39. We have studied the performances of this new approach for light ions (H, He, Li and C) with kinetic energies typically of the order of the MeV per nucleus. First, we determined the response functions of the CR-39 for these ions. We were then able to show that aside from decreasing the analysis time of traditional methods, the confocal microscope greatly increases the sensibility of the detection. The aim of this study was to find a correlation between the response functions and the primary physical parameters of the interaction between the ion and the material, such as the linear energy transfer (LET), the restricted energy transfer (RELω0), the integrated radial dose or the rate of ionization. Although these parameters presented a strong resemblance to the experimental response functions (they are all “Bragg” curves), none of them were correlated to the response function in an unambiguous way.

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.

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.

Inter-comparison of geometrical track parameters and depth dependent track etch rates measured for Li-7 ions in two types of CR-39

Abstract The depth dependent track etch rates of two types of CR-39, TASTRAK and BARYOTRAK, for Li-7 ions with incident energies of 4.82, 6.75 and 10.77 MeV have been evaluated from track length measurements. The pit lengths versus the etching time obtained by three different laboratories have the same trend, but did not agree completely. The differences can be attributed to an error margin of less than one decimal point in the etching temperature. Significant deviations were also present for the assessed track etch rates. Most of the deviation was attributed to the derivation step of the growth curves. A sufficient amount of data and reasonably smooth growth curves were required near the Bragg peak in order to make a precise estimation.

Ion track etching in isotropic polymers: etched track shape and detection efficiency

Abstract This paper describes the properties of isotropic polymeric nuclear track detector (polycarbonate) used in the field of particle detection. We will begin the paper by presenting an etching model whose etching kinetics we will assume to be controlled by two distinct velocities, namely VT (the etching rate along the latent track) and VB the etching rate of the bulk detector material. VT being variable and VB constant, we propose a model which enables the performance of numerical simulations as well as the understanding of detection characteristics. After the basic formalism has been exposed, the notion of critical angle registration will be explained along with delayed-action time. Detection efficiency can be calculated from these considerations. We cite some current applications, in particular uranium content determination, alpha dosimetry and neutron detection.