Applicability of the polyimide films as an SSNTD material

Track registration properties in polyimide films, KAPTON, for heavy ions have been examined by means of FT-IR spectrometry and the chemical etching in sodium hypochlorite solution. The effective track core size for the loss of CO and C–N–C composing imide bonds, and diphenyl ethers of C–O–C have been evaluated under the irradiations by Ne, Fe and Xe ions at energies less than 6 MeV/n. On the other hand, the etching property of the polyimide films has been examined in the sodium hypochlorite solution at temperature of 55 °C. Before the etchings, the films were exposed to H, C, Ne, Fe and Xe ions, at incident energies below 6 MeV/n. The etch pits are found only on the films exposed to Fe and Xe ions, indicating significant difference on the etch pit size between them. This implies that the polyimide film has charge or energy resolution for these relatively heavy ions. The threshold level of the etchable track registration is inferred to be around 2500 keV/μm. The effective track core radius at this stopping power for the loss of diphenyl ether is 1.6 nm, which is equivalent to the length between the adjacent diphenyl ether bonds in the polyimide chains. Breakings at two adjacent diphenyl ethers in radial direction of latent tracks may produce etchable tracks in KAPTON.

► Threshold of etchable track formation in KAPTON is examined. ► Threshold in the stopping power is about 2500 keV/μm. ► Corresponding track core radius for loss of C–O–C is 1.6 nm. ► Two adjacent breakings is the critical phenomena.