## 4 Results and Discussion  
Figures 2a-e and 3a-e display the time evolutions of \(G\)(e\({}^{-}\)aq), \(G\)(H\({}^{\bullet}\)), \(G\)(H\({}_{2}\)), \(G\)(\({}^{\bullet}\)OH), and \(G\)(H\({}_{2}\)O\({}_{2}\)) as derived from our simulations of the radiolysis of pure, de-aerated water by 2 MeV neutrons. The results cover the period from -1 ps to 1 ms at temperatures of 300, 350, 400, 500, and 600 \({}^{\circ}\)C, respectively, all at 25 MPa. For comparison, Figure 3 also includes experimental data obtained from various authors [13; 30; 47; 48; 49]. Despite the relative scarcity of \(G\) values for fast neutron radiolysis, especially beyond the critical point in the SCW regime, there is generally good agreement between our computed yield values and the existing measurements. This agreement between experimental data and modeling a posteriori supports the validity of the assumptions used in our calculations, thereby affirming the reliability of our Monte Carlo code. Figure 1: The SRIM simulation of 1.264, 0.465, and 0.171 MeV recoil protons penetrating SCW at 400 \({}^{\circ}\)C and 25 MPa reveals total track lengths (or penetration depths) of \(\sim\)230, 50.5, and 14.1 \(\upmu\)m, respectively. These values were validated by our own Monte Carlo track structure simulations. A significant factor contributing to the observed straggling is the change in the charge state of the protons, due to electron capture and loss, as they move through the water. A total of 100 protons were simulated. Figure 2: Time evolution of yields for radiolytic species (e\({}^{-}\)\({}_{\text{aq}}\), H\({}^{\bullet}\), H\({}_{2}\), \({}^{\bullet}\)OH, and H\({}_{2}\)O\({}_{2}\)) formed during the radiolysis of pure, de-aerated water by 2 MeV neutrons at 300 \({}^{\circ}\)C (**a**), 350 \({}^{\circ}\)C (**b**), 400 \({}^{\circ}\)C (**c**), 500 \({}^{\circ}\)C (**d**), and 600 \({}^{\circ}\)C (**e**) at 25 MPa, calculated from our Monte Carlo track segment (recoil proton) yield simulations over the interval of 1 ps to 1 ms.  
Figure 3: Time evolution of \(G\)(e\({}^{-}_{\rm aq}\)) (**a**), \(G\)(\({}^{\bullet}\)OH) (**b**), \(G\)(H\({}^{\bullet}\)) (**c**), \(G\)(H\({}_{2}\)) (**d**), and \(G\)(H\({}_{2}\)O\({}_{2}\)) (**e**) during the radiolysis of pure, de-aerated water by 2 MeV neutrons at temperatures of 300 (green lines), 350 (orange lines), 400 (black lines), 500 (red lines), and 600 (blue lines) \({}^{\circ}\)C at 25 MPa. These calculations are derived from our Monte Carlo track segment (recoil proton) yield simulations over the interval of 1 ps to 1 ms. The symbols represent experimental data; they are color-coded for clarity to match the curves with which they are associated: (i, green) [PERSON] [30], (, green) [PERSON] et al. [47], (, green) [PERSON] [48] (recommended mean \(G\) values at \(\sim\)280-300 \({}^{\circ}\)C. According to the author, these values are likely accurate within \(\sim\)25%), and (B, orange) [PERSON] and [PERSON] [13]. The symbol (A, red) in Panel  
(a) represents [PERSON] \(G\)(e\({}^{-}\)aq) value of 0.59 molecule/100 eV at 400 \({}^{\circ}\)C and 24.8 MPa [49], positioned at an assumed measurement time of \(\sim\)3 \(\upmu\)s [50; 51]. Note that all the experimental data at 300 and 350 \({}^{\circ}\)C are positioned at the end of the spur/track expansion times, specifically within the range of \(\sim\)40 to 100 ns [52]. To our knowledge, no experimental yield values for fast neutrons at 500 and 600 \({}^{\circ}\)C have been reported to date. Currently, the only available measured value at very high temperatures and pressures for comparison with our results is that of [PERSON] [49] at 400 \({}^{\circ}\)C and 24.8 MPa (\(\rho\) = 0.163 g/cm\({}^{3}\)), which is \(G\)(e\({}^{-}\)aq) \(\sim\) 0.59 \(\pm\) 0.19 molecule/100 eV. Unfortunately, the exact timing of this measurement remains uncertain. According to prior studies [50; 51], it could have been conducted on a timescale of a few microseconds, which aligns well with our calculations (see Figure 3a).