Partial optimization of electrochemical-etching parameters for highly sensitive CR-39 fast neutron dosimeters.

Voltage gradient and frequency were studied for their influence on the electrochemical etching of CR-39 plastic irradiated with fission spectrum, fast neutrons. A power supply having outputs of up to 1.5 kV (rms) and 5 kHz was used. Differential voltage measurements under non-etching conditions indicated that the optimal values in electrochemical etching with this power supply would be 20 kV/cm and 1.3 kHz. That these parameters produced a maximum sensitivity was verified in subsequent electrochemical etching experiments for a standard 4 hr in 9N KOH with foils that were both unirradiated and irradiated. The introduction of a proton irradiator cover and a conventional etching step prior to the electrochemical etching, increased the sensitivity to neutrons (approximately 30-fold) and decreased the background track density to 4.4 +/- 0.6 tracks/cm2. The corresponding sensitivity was then 1.3 tracks/cm2/mrem with a minimum level of detectability (3 sigma) of 1.4 mrem.