Charge resolution of CR-39 plastic nuclear track detectors for intermediate energy heavy ions

Journal article, 2011

The charge resolution (delta Z) for heavy ions (nuclear charge: Z < 40) of 0.1-1 GeV/n energy in CR-39 plastic nuclear track detector (PNTD) and its dependence on etching time, and on projectile Z and energy were investigated and optimized as part of an effort to make precise measurements of projectile charge-changing cross sections. Two types of CR-39 PNTD, HARZLAS TD-1 and BARYOTRAK, were exposed to heavy ion beams with seven values of Z behind thick targets to produce projectile fragments. Following chemical etching (7 N NaOH at 70 degrees C) for varying etch times, delta Z of the projectiles was determined for each detector type. A strong dependence of delta Z on the amount of bulk etch (B) was seen. It was also observed that delta Z can be remarkably improved with longer etching time as a function of B-1/2, in accordance with the trend seen in other types of track detector such as glass nuclear track detector. However, for B >= 60 mu m (30 h etching), saturation occurs and there is no further improvement in delta Z. Analysis of the correlations between projectile Z, energy, detector response, and fluctuation of the response make it possible to develop a model to predict the delta Z for projectiles of given Z and energy. The predicted and measured values of delta Z show good agreement within 10%. We conclude that 4 <= Z <= 30 at intermediate energy can be identified with good delta Z in these detectors. The predictive model will be used in designing future cross section measurement experiments.