Micro-track structure analysis for 100 MeV Si ions in CR-39 by using atomic force microscopy

To analyze the micro-track structure of heavy ions in a polymer material,parameters including bulk etch rate,track etch rate,etch rate ratio,and track core size were measured.The pieces of CR-39 were exposed to 100 MeV Si ions with normal incidence and were etched in 6.25N NaOH solution at 70 C.Bulk etch rate was read out by a profilemeter after several hours of etching.The other parameters were obtained by using an atomic force microscope(AFM)after a short time of etching.We have measured the second etch pits and minute etch pits to obtain the track growth curve and three dimension track structures to track the core size and etch rate measurements.The local dose of the track core was calculated by theδ-ray theory.In our study,we figure out that the bulk etch rate Vb=(1.58±0.022)μm/h,the track etch rate Vt=(2.90±0.529)μm/h,the etch rate ratio V=1.84±0.031,and the track core radii r≈4.65 nm.In the meantime,we find that the micro-track development violates the traditional track-growth model.For this reason,a scenario is carried out to provide an explanation.