Radiation effects in dry ice: models for a peak on the Arrhenius curve

• Published in: Applied radiation and isotopes 2000-05, Vol.52 (5), p.1259-1263
• Main Authors: Norizawa, K, Kanosue, K, Ikeya, M
• Format: Article
• Language: English
• ISSN: 0969-8043; 1872-9800
• DOI: 10.1016/S0969-8043(00)00081-6

Dry ice (solid CO 2) occurs in the polar caps of Mars, on the surface of Triton, and in places in the outer planets of our solar system. Radicals in γ-irradiated solid CO 2 have been studied by ESR for future applications of ESR dating on outer planets. The annealing curves for CO − 3 radical (ESR signal at g = 2.0126) can be described neither by the first-order nor the second-order decay kinetics. The peak observed in the Arrhenius plot can result from two parallel first-order kinetic processes. Radicals that provide overlapping signals are CO − 3 ( g 1 = 2.0057, g 2 = 2.0126, g 3 = 2.0161; activation energy E = 0.10 eV; frequency factor ν 0=4×10 1 s −1) and HO 2 ( g 1 = 2.0040, g 2 = 2.0055, g 3 = 2.0360), which have E = 0.28 eV and ν 0=7×10 5 s −1). Hence, HO 2 is more thermally stable, and use of HO 2 is promising for ESR dating.