Chemical etching studies of a Brazilian polycarbonate to fast neutron detection

Abstract

The Dosimetric Materials Laboratory (LMD) of the Radiation Metrology Center (CMR) is developing a personal dosimeter for fast neutrons using the technique of solid state nuclear track detectors (SSNTD). This technique is based on the recorded damage (tracks) in dielectric materials due to the impact of charged particles. The tracks are revealed and amplified for visualization in optic microscope through a technique known as chemical etching. The LMD is investigating a Brazilian commercial polycarbonate as a new passive fast neutron’s detector in substitution to the traditional materials, as the cellulose nitrate LR-115 and the polycarbonates Makrofol and CR-39. The variation of the etching parameters (chemical solution, time and temperature) alters the response of the material; the best revelation conditions provide the best relationship among the amount of revealed tracks, their clearness and the time spent for this. The polycarbonate studied is a resin of same chemical monomer of Makrofol (C16H14O3). Samples of 3 x 1 cm 2 of the polycarbonate were irradiated with 5 mSv of fast neutrons ( 241Am-Be) and revealed with the chemical solution PEW-40 (15% KOH, 45% H2O, 40% C2H5OH), commonly used for Makrofol. The studied etching parameters were time and temperature. Groups of four samples were revealed at temperatures of 50, 65, 75, 90 and 100oC with etching times varying from one to six hours. The used track’s counting procedure was that referred in the literature. The best response to fast neutrons was obtained at 75oC; in spite of their similar answers, smaller temperatures join larger uncertainties in the track’s counting and poorer clearness. At this temperature, the number of revealed tracks increases with the etching time approximately until a plateau at three hours. For etching times higher than four hours the polycarbonate presents overlap of tracks. If the temperature is adjusted to 75oC, the etching time should be in the plateau to avoid that small time errors alter significantly the counting of tracks. On the other hand, besides the tracks overlapping that implies in tracks counting errors, sensitivity curve plateau is reached for a higher elapsed time compared to the working day of a dosimetry laboratory.