Radioactividad natural en materiales de construcción

Some materials usually employed in building edification have been analyzed for their radioactive contents. The specific activities of all the gamma rays emisors present in fourteen differents samples have been determined. In all the cases, only low activities (under 2 Bq/g) have been found for these samples collected from the surroundings of Barcelona.Los radioisótopos contenidos en los materiales habitualmente empleados en construcción son analizados con espectrometría gamma. Se calculan las actividades específicas de los diferentes radioisótopos en catorce materiales seleccionados, provenientes de las cercanías de Barcelona, obteniéndose niveles de radioactividad bajos (inferiores a 2 Bq/g)

Ms-Evolution in Cu-Zn-Al SMA. Predictable Temperature and Time Actions on Parent Phase

Recently an increased interest has been noticed for order effects in Cu-based SMA. For instance, on the transformation temperature Ms values and its evolution after heat treatments and quench type effects. Usually, the experimental Ms values after quench fluctuate around ± 2 K. The interest for continuous actuators needs a more reduced and, in any case, predictable fluctuation domain. In this work, by using high resolution in temperature, time and resistance measurements on a Cu-Zn-Al alloy (1.48 e/a), the results establish a distribution of the evolution in two main actions : a relatively short time and a long time tail effects. Two temperature dependent time constants have been determined from the experiments, with different activation energies (13630 K and 10330 K). The two actions might be associated to different ordering processes. Furthermore, the experimental results allow to describe a representative model that can be used to predict the Ms evolution with temperature and time. The differences between simulated and experimental results for the Ms is about ± 0.15 K for temperature-time evolutions near room temperature

Guaranteed behaviour of shape memory alloys : After quench and long time effects in CuZnAl SMA

The use of Shape Memory Alloys (SMA) in critical "high tech" applications such as robotics and in continuous actuators needs an increased reliability and a guaranteed behaviour lasting several years. High resolution measurements enabled to quantify the time effects of aging near room temperature on the properties of CuZnAl SMA and to modelize the macroscopic behaviour. Some structural measurements showed small changes on the material structure