Track Registration in Various Solid-State Nuclear Track Detectors

In a number of materials energetic, heavy nuclear particles leave trails of radiation-damaged material which can be selectively attacked by chemical reagents to produce tracks visible in the optical microscope. The track-registration characteristics of three such materials—muscovite mica, Lexan polycarbonate, and cellulose nitrate—were investigated using fission fragments and various heavy ions from argon down to helium, each over a wide range of energies. Curves of energy-loss rate $\frac{\mathrm{dE}}{\mathrm{dx}}$ versus particle energy were calculated for each solid, and the experimental results were displayed on the $\frac{\mathrm{dE}}{\mathrm{dx}}$ curves. It was found that for each detector there is a fairly narrow range of $\frac{\mathrm{dE}}{\mathrm{dx}}$ values over which the track-registration efficiency varies from unity to zero. This rapid drop in efficiency with $\frac{\mathrm{dE}}{\mathrm{dx}}$ makes it reasonable to define a critical energy-loss rate ${\left(\frac{\mathrm{dE}}{\mathrm{dx}}\right)}_{\mathrm{crit}}$ for each detector, which appears to be independent of energy and atomic number. Crude estimates of particle masses can be made using several detectors with different ${\left(\frac{\mathrm{dE}}{\mathrm{dx}}\right)}_{\mathrm{crit}}$. For example, for particles with energies less than ∼3 MeV/amu, the mass must exceed 3, 12, and 28 amu if tracks register in cellulose nitrate, Lexan polycarbonate, and muscovite, respectively. For particles such as fission fragments, with initial $\frac{\mathrm{dE}}{\mathrm{dx}}\gg {\left(\frac{\mathrm{dE}}{\mathrm{dx}}\right)}_{\mathrm{crit}}$, the track lengths are a fair approximation of the particle ranges. Particles incident at a very small angle to a detector surface are registered in mica but not in plastics or glasses. Solid-state track detectors presently offer unique advantages when heavy particles must be studied in the presence of a high background flux of light particles.