O.A. Bernaola

Submicroscopic kinetics of track formation in SSNTD

Abstract A theoretical description for submicroscopic kinetics of track formation in SSNTD is proposed. Kinetics of chemical attack in the primary damage region of the track is included. A good correlation between theory and experimental data obtained with Mazzeis replica method is achieved.

Induction time in Makrofol E

Abstract Induction time in Makrofol E is evaluated applying the nuclear track replica method and electron microscopy with 10 A resolution. The induction time is observed in foils with and without pre-etching. The track diameter vs etching time curves do not follow a linear relation for small track diameters.

Detection threshold in polymers

Abstract The replica technique for the observation of tracks by TEM, allowed the study of tracks in Makrofol E in regions of energy virtually “forbidden” by the traditional registration models. One or both critical extremes of energy where analyzed for particles such as protons, helium, deuterons and lithium, trying to find a correlation with any of the commonly proposed parameters to test detection threshold. Based on data at submicroscopic level the concept of threshold origin is discussed.

The submicroscopic track kinetic theory and the variational principle

Abstract The variational principle was used to obtain the general equations for chemical etching track profiles inside and outside the physical damage region produced by energetic ions in Makrofol E. The track profiles developed at very short etching times were used to obtain the velocity profiles in order to perform computer determinations of track profiles for longer etching times. Track profiles obtained by means of the variational principle and the submicroscopic track kinetic theory are in good agreement, and compare favorably with experimental results.

Relative biological effectiveness measurements of low energy proton and lithium beams on tumor cells

Abstract External proton and 6,7 Li beams, of energies around 24 and 48 MeV respectively, were produced and characterized dosimetrically at the Tandem accelerator TANDAR in Buenos Aires and used for radiobiology studies on tumor and normal cell cultures. The beam monitoring instrumentation of a dedicated beam line is discussed. Relative biological effectiveness (RBE) values (at 10% survival) have been measured as functions of projectile energy (0–21 MeV) for protons and 6,7 Li ions for different tumor (PDV, PDVC57) and reference cell lines (V79). The RBE values for these cell lines have been determined here for the first time but are similar to those reported in the literature for other cell lines.

Submicroscopic nuclear track kinetic theory applied to initial chemical etching of makrofol E

Abstract Chemical etching track profiles in the bulk region, as well as in the physical damage region, were described in a track kinetic theory by Mazzei et al. applying submicroscopic evaluations. In the present work this theory proves useful also to analyze the profiles of “new born” tracks. The equation describing height variations along each track profile is similar to that describing track velocity variation along the axis perpendicular to the ion incidence direction. The theory proves that for “new born” tracks, the chemical etching wave fronts generated in any point of the track are not exceeded by that wave front generated along the heavy ion incidence axis.

Ion tracks in an organic material: Application of the liquid drop model

Abstract The liquid drop model (LDM) was developed to perform radiation damage studies in metals in an ionic energy range where molecular dynamics cannot be used because of computational restraints. In this work, the model is extended in an effort to explain the observation of tracks in organic insulators in an energy range where other theoretical models fail. The detector material was Makrofol E and the studied ions had specific energies between 1.4 and 100 keV/n. The tracks were observed via a replica method by transmission electron microscopy. The electronic, as well as the nuclear energy deposition by an individual ion were considered, then the thermal spike evolution is studied. The LDM predicts track diameters much larger than previous models. Most of these tracks now can be developed. Although the model still has free parameters and shows some discrepancies with experimental data, its agreement is better than that obtained through the consideration of other models.

Applications of the submicroscopic nuclear track kinetic theory

Abstract The submicroscopic track kinetic theory (STKT) is able to deal with a broad range of cases. We derive here its behaviour for very short etching times (new born tracks) and also for long etching times, where the classical track kinetic theory is a particular case of the STKT. Experimental data obtained previously by Bean et al. using the electroconductivity method are then analyzed by the STKT method. We show that good agreement is obtained between Bean and STKT theoretical results for the track diameter evolution.

Thermal spike analysis of low energy ion tracks

Abstract The theoretical track diameter of low energy ions in organic materials is usually estimated through the model of dose deposition by delta rays, with results remarkably lower than the experimental values obtained via a replica method and electron microscopy. The track detector used here is Makrofol-E and the ions studied have specific energies between 1.4 and 100 keV/n. To evaluate the problem from another point of view, thermal effects for track formation, a modified version of the “liquid drop model” for insulators was applied. The electronic as well as nuclear energy deposition by an individual ion are considered and the thermal spike evolution is studied. The model allows for the formation of ion tracks in a range of energies previously considered as “forbidden”. There still exists a discrepancy between the experimental data and the track diameters predicted by the model, and although this difference is smaller than the obtained with previous calculations, it suggests the necessity of further adjustments.

Compound nucleus cross section in Makrofol E irradiated with 55 MeV alpha particles

Abstract A 55 MeV alpha particle beam is used to generate nuclear tracks in Makrofol E detectors. These tracks were produced by reaction products generated by compound nucleus reactions, as was demonstrated by compound nucleus cross section formation and elastic scattering analysis. The number of tracks versus collected charge and versus removal surface thickness were experimentally evaluated in good agreement with the theoretical predictions. So, an accurate beam dosimetry was performed by track counting method which proved particularly useful for low LET light ions evaluation.