Tham khảo tài liệu 'material science_ vol 1 of 2 - us doe (1993) episode 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Properties of Metals DOE-HDBK-1017 1-93 APPENDIX A Substituents on aromatic groups that extend the delocalized bonding network are further stabilizers. Finally saturated aliphatics are more radiation resistant than those that are unsaturated isolated double bonds are readily excited to ions or radicals. Organic compounds in order of decreasing radiation resistance are aromatics aliphatics alcohols amines esters ketones and acids. Extension to beta radiation is probably reasonable. In tritium gas however substantial differences in irradiation or polymer surface as compared to bulk can occur. This results from the greater density of tritium and the much greater range of the beta in the tritium gas outside the polymer compared to inside the polymer bulk. Some direct experience of polymers with tritium has been obtained. Teflon Viton or Kel-F exposure in tritium produces the acid TF noted as SiF4 gas in a glass system. Because of this acid production tritium moisture Teflon in a stainless steel system at pressures of approximately 1300 atm caused catastrophic stress corrosion cracking of thick stainless steel tube walls in 16 hours. Substituting deuterium for tritium or removing Teflon or moisture caused no failure. Radiation damage to Teflon is more severe than to all other thermoplastics. Teflon is therefore not recommended in the presence of concentrated tritium streams. Surface and bulk effects have been noted in numerous polymer tritium studies. In one study hardening of neoprene occurred throughout the bulk while hardening of natural rubber primarily occurred at the surface crack propagation . Total incorporation of tritium into a polyethylene powder was found not to be a function of the amount of powder but of the exposed surface area. Radiation-induced fluorescence from the surface of high-density polyethylene exposed to tritium was shown to be orders of magnitude greater than that from the bulk. Polyimides good in the presence of gamma radiation appear
