Self-radiolysis of tritiated water. 1. A comparison of the effects of super(60)Co gamma -rays and tritium beta -particles on water and aqueous solutions at room temperature

• Published in: RSC advances 2013-10, Vol.3 (42), p.19282-19299
• Main Authors: Kohan, Leila Mirsaleh, Sanguanmith, Sunuchakan, Meesungnoen, Jintana, Causey, Patrick, Stuart, Craig R, Jay-Gerin, Jean-Paul
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Computer simulation; Dosimeters; Energy measurement; Radicals; Radiolysis; Sulfates; Tritium
• ISSN: 2046-2069
• DOI: 10.1039/c3ra42984a

Monte Carlo simulations were used to investigate the chemistry of pure water and aqueous solutions after irradiation with different kinds of radiation: tritium beta -rays and high-energy electrons or super(60)Co gamma -rays. The objective of this work was to elucidate the mechanisms involved in the self-radiolysis of tritiated water, and to examine the importance of the effects of higher "linear energy transfer" (LET) by comparing super(3)H beta -electrons (mean initial energy of similar to 5.7 keV) with super(60)Co gamma -rays ( similar to 1-MeV electrons). We considered several chemical systems for which experimental data were available. These included pure water, aqueous solutions of sulfuric acid, and aqueous ferrous sulfate solutions in aerated 0.4 M H sub(2)SO sub(4) (Fricke dosimeter). Simulations clearly showed quantitatively different yields of radical and molecular products produced by the radiolysis of water with tritium beta super(-) particles compared with corresponding yields from gamma or energetic electron radiolysis. As a rule, lower radical and higher molecular yields were observed for super(3)H beta -rays. These differences in yields are completely consistent with differences in the nonhomogeneous distribution of primary transient species (i.e., the structure of electron tracks) in the two cases. In the "short-track" (columnar) geometry of tritium beta -electron radiolysis, radicals were formed in much closer initial proximity than in the "spur" (spherical) geometry of gamma radiolysis. The "short-track" geometry favors radical-radical reactions in the diffusing tracks, which increases the proportion of molecular products at the expense of the radical products. The same trend in yields of radical and molecular products was also found under acidic conditions as well as in the aerated Fricke dosimeter. Unfortunately, comparison with experimental data was rather limited due to the paucity of experimental information for the radiolysis of water by super(3)H beta -particles. Despite this deficiency, our simulations reproduced very well the significant increase observed in the yield of H sub(2) at the microsecond time scale for super(3)H beta -electrons ( similar to 0.6 molecule/100 eV) compared to super(60)Co gamma -rays (0.45 molecule/100 eV). Furthermore, our predicted yield of Fe super(3+) ions for tritium beta -electron radiolysis of Fricke (acidic ferrous sulfate) solutions compared well with the literature values ( similar to 11.9-12.9