Monte Carlo Calculation of the Primary Radical and Molecular Yields of Liquid Water Radiolysis in the Linear Energy Transfer Range 0.3–6.5 keV/μm: Application to¹³⁷Cs Gamma Rays¹

Abstract

Monte Carlo simulations of the radiolysis of neutral liquid water and 0.4 M H(2)SO(4) aqueous solutions at ambient temperature are used to calculate the variations of the primary radical and molecular yields (at 10(-6)s) as a function of linear energy transfer (LET) in the range approximately 0.3 to 6.5 keV/micrometer. The early energy deposition is approximated by considering short (approximately 20-100 micrometer) high-energy (approximately 300-6.6 MeV) proton track segments, over which the LET remains essentially constant. The subsequent nonhomogeneous chemical evolution of the reactive species formed in these tracks is simulated by using the independent reaction times approximation, which has previously been used successfully to model the radiolysis of water under various conditions. The results obtained are in good general agreement with available experimental data over the whole LET range studied. After normalization of our computed yields relative to the standard radical and molecular yields for (60)Co gamma radiation (average LET approximately 0.3 keV/micrometer), we obtain empirical relationships of the primary radiolytic yields as a function of LET over the LET range studied. Such relationships are of practical interest since they allow us to predict a priori values of the radical and molecular yields for any radiation from the knowledge of the average LET of this radiation only. As an application, we determine the corresponding yields for the case of (137)Cs gamma radiation. For this purpose, we use the value of approximately 0.91 keV/micrometer for the average LET of (137)Cs gamma rays, chosen so that our calculated yield G(Fe(3+)) for ferrous-ion oxidation in air-saturated 0.4 M sulfuric acid reproduces the value of 15.3 molecules/100 eV for this radiation recommended by the International Commission on Radiation Units and Measurements. The uncertainty range on those primary radical and molecular yields are also determined knowing the experimental error (approximately 2%) for the measured G(Fe(3+)) value. The following values (expressed in molecules/100 eV) are obtained: (1) for neutral water: G(e(-)(aq)) = 2.50 +/- 0.16, G(H(.)) = 0.621 +/- 0.019, G(H(2)) = 0.474 +/- 0.025, G((.)OH) = 2.67 +/- 0.14, G(H(2)O(2)) = 0.713 +/- 0.031, and G(-H(2)O) = 4.08 +/- 0.22; and (2) for 0.4 M H(2)SO(4) aqueous solutions: G(H(.)) = 3.61 +/- 0.09, G(H(2)) = 0.420 +/- 0.019, G((.)OH) = 2.78 +/- 0.12, G(H(2)O(2)) = 0.839 +/- 0.037, and G(-H(2)O) = 4.46 +/- 0.16. These computed values are found to differ from the standard yields for (60)Co gamma rays by up to approximately 6%.

Induction of in situ DNA double-strand breaks and apoptosis by 200 MeV protons and 10 MV X-rays in human tumour cell lines

“…The dose average LET value of 137 Cs gamma rays is reported as 0.91 (Meesungnoen et al 2001). Also reported values of dose average LET of 60 Co gamma rays range from 0.2-0.49 (Ibań ez et al 2009, International Commission on Radiation Units and Measurements (ICRU) report 16, 197016, , Ziegler et al 1985.…”

Behavioral Resistance of Caenorhabditis elegans Against High-LET Radiation Exposure

“…Suzuki et al (2009) reported that hydrogen peroxide (H 2 O 2 ), which is one of the reactive oxygen species (ROS) produced by lowand high-LET radiation exposure, decreases locomotory rate. On one hand, for 60 Co γ radiation at a neutral pH and room temperature, the G value of H 2 O 2 was 0.68, indicating that irradiation with 500 Gy produces 0.035 mM H 2 O 2 (Meesungnoen et al, 2001). On the other, its G value for high-LET radiation (100 keV/µm) was about 0.95 (Meesungnoen et al, 2005), resulted in 0.049 mM H 2 O 2 .…”

Dynamic fluorescence imaging of the free radical products of X-ray absorption in live cells

“…In aqueous biological samples, x-ray absorption is predominantly by water molecules. The primary free radical products of the radiolysis of water and their yields (molecules/100 eV) are ÁOH (2.80), e aq -(2.65), H 2 O 2 (0.68), and ÁH (0.60) (Meesungnoen et al 2001;Sehested et al 1973). There are many commercially available fluorescent ROS sensors that may respond to one or more of the above products.…”