A. Vidal-Quadras

Low energy heavy cosmic ions charge discrimination with plastic detectors

Abstract A method for high resolution (average ΔZ≈0.3) charge discrimination of very heavy (20⩽Z⩽29) low energy (E∼100MeV/nucl.) ions in plastic detectors is presented. The discrimination is based on an empirical relation between etch rate (Vt) and ionization [J(Z, β, k)] of the form Vt = A[(B/J) + 1]−η valid for high ionization at low residual ranges, where the etch rat e shows saturation. The method is used to determine the relative abundances of the elements in the iron group.

Indoor radon concentration measurements in some Spanish houses and dwellings with plastic nuclear track detectors

Abstract A passive dosemeter, based on Makrofol ED track detectors covered with aluminized Mylar, enclosed in the Karlsruhe diffussion chamber, has been used for radon concentration studies. Detectors have been irradiated, using a 241Am source, at different energies and fluences in order to obtain the electrochemical etching conditions that allow the optimum registration of alpha particles having energies over 3 MeV. Thirty dosemeters have been sent to the NRPB Radon Environmental Chamber for calibration. The sensitivity of the dosemeter has been calculated. Several dosemeters have, also, been exposed in houses and dwellings in the Barcelona and Madrid areas for monitoring. Values for radon concentration in the areas under study are presented.

Temperature effect in stratospheric balloon flight exposure of CR-39 plastic detector

Abstract A CR-39 stack equipped with a passive temperature control shielding was exposed to primary cosmic radiation in a balloon flight from Trapani (Sicily) to Arenosillo (Spain) at an average altitude of 4 g cm -2 residual atmosphere for 20 h. High vertical geomagnetic cut-off ensured the relativistic nature of registered ions. Stack temperature was monitored by means of thermal probes and associated electronics and transmitted by telemetry to an earth-based station. Temperature excursions were less than 16°C, which is shown to correspond to a 0.11e shift in the charge scale for relativistic iron ions. Best etching conditions were established for the VH relativistic component as well as a discrimination method for relativistic ions. Charge uncertainty was found to be 0.44e. Relative abundances for the iron group extrapolated to the top of the atmosphere are compared to those reported by other authors.

Long term ageing effect for energetic ultraheavy ion tracks in polycarbonate solid state nuclear track detectors

Abstract The charge resolution that one can obtain from long duration exposures of polycarbonate solid state nuclear track detectors has been recently questioned because of the “ageing effect”, caused by time evolution of the latent tracks recorded. Several exposures of polycarbonate stacks to different energetic ultraheavy ions at the Berkeley Bevalac have been undertaken as part of a detector response study related to the Ultraheavy Cosmic Ray Experiment on board the LDEF spacecraft and to carry out latent track time evolution studies. The results indicate that there is no significant evolution of the signal recorded in polycarbonates during an ageing period of almost three years, starting 6 to 8 weeks after exposure, when the detectors are stored at temperatures ranging from − 70 to + 25 ° C. The implications of these results for the expected charge resolution from the Ultraheavy Cosmic Ray Experiment are discussed.

Latent track intensification due to ageing in solid state nuclear track detectors

Abstract The effect of latent track ageing on the charge resolution that can be achieved in polycarbonate Solid State Nuclear Track Detectors exposed for long periods in space is investigated. Several exposures of polycarbonate stacks to different ultra heavy relativistic ions have been undertaken at the Berkeley Bevalac in order to study this effect. Following an increase in signal strength in the first few weeks after exposure, our results do not indicate any further significant change during a period of nearly three years. The implications of these results for the expected charge resolution from the Ultra Heavy Cosmic Ray Experiment are discussed.

A study of etching conditions and resolution power of plastic detector CR-39

Two Pershore Stacks (32 h cure cycle and 1% DOP and 96 h cure cycle and no additive) have been exposed to the Berkeley Bevalac Argon beam at 285 MeV/nuc and 425 MeV/nuc, respectively. Optimum previous termetching conditionsnext term have been found to be 70°C temperature and 18 h previous termetchingnext term time in 6.25 N OHNa aquaeous solution, corresponding to a mean bulk etch rate VB = (1.37±0.09) μm/h. The charge and mass previous termresolutionnext term power of the detector has been evaluated as ΔZ ≈ 0.3 e and ΔA ≈ 2 a.m.u..

A comparative study of bulk etch rate measurement methods in polycarbonate detectors

Abstract The response of a plastic detector to an incoming charged particle is given by the ratio of track etch rate υ t to bulk etch rate υ g along its path. Although the accurate determination of υ t offers no difficulty as cone length can be comfortably measured, there seems to be a certain ambiguity as how to measure υ g . Several LEXAN and TUFFAK polycarbonate plates have been exposed to normally incident Californium-252 fission fragments, etched in a stirred aqueous NaOH solution saturated with etch products and with a 0.05% of Dowfax sufactant, for different etching times, concentrations and temperatures. We have used three methods to measure υ g and we obtain consistent results in agreement with those published in the literature. Surface quality and, consequently, ellipses neatness, are far superior in TUFFAK than in LEXAN.

Lexan polycarbonate response to relativistic gold ions

Abstract A knowledge of the charge resolution power of polycarbonate detectors for ultra-heavy ions (Z ≥ 30) is essential to establish the cosmic ray spectrum in the UH region and to obtain useful information on nucleosynthesis and propagation mechanisms. In this paper, a systematic study of LEXAN polycarbonate response to relativistic (⋍ 1 GeV/N) gold ions (Z = 79) is presented. The influence on the detector sensitivity of etching conditions, such as NaOH concentration and bath temperature, is explored and the conclusion is reached that detector response is rather independent of them all, in agreement with the well known results at lower ionizations.

Heavy ion isotope resolution with polymer detectors

The heavy ion mass resolution power of polymer detectors Lexan and cellulose nitrate is systematically studied both for accelerator and for cosmic ions. It is concluded that a satisfactory isotopic discrimination, better than 1 u, is hardly attainable with these detectors.

Measurement of the relative composition of the Cosmic-ray iron group with Lexan polycarbonate

Relative abundances for the VH group of Cosmic Radiation (20≤Z≤28) at energiesE≤600 MeV nucl−1 have been measured by means of plastic detector LEXAN. The stack was exposed to cosmic rays during a 82 hr balloon flight at Sioux Falls (South Dakota) at an average altitude equivalent to 4 g cm−2 of residual atmosphere. A total number of 1058 events have been analyzed, out of which 675 have been unambiguously identified. Two different discrimination methods have been applied in order to test their influence on final spectra.Extrapolation to the top of the atmosphere has been achieved in the frame of the regular model including an energy loss term that has led to corrections of the order of 60% in the extrapolated abundances.The relative abundances so obtained are in reasonable agreement with those reported by other authors using electronic detectors. Abnormal high abundances of manganese and cobalt can be attributed to wide temperature variations during the registration interval.In spite of the poor mass resolution, a high abundance of54Fe has been evidenced, indicating a non-stellar origin for cosmic iron.