Monte-Carlo calculation of the primary yields of H[sub 2] O[sub 2] in the [sup 1] H[sup +] , [sup 2] H[sup +] , [sup 4] He[sup 2+] , [sup 7] Li[sup 3+] , and [sup 12] C[sup 6+] radiolysis of liquid water at 25 and 300�C

Jay-Gerin, Jean-Paul; Filali-Mouhim, Abdelali; Meesungnoen, Jintana; Mankhetkorn, Samlee
January 2002
Canadian Journal of Chemistry;Jan2002, Vol. 80 Issue 1, p68
Academic Journal
Monte-Carlo simulations are used to calculate the primary yield of hydrogen peroxide (G[sub H2O2] ) of the radiolysis of pure, deaerated liquid water as a function of linear energy transfer (LET) of the incident radiation over the range ~0.3�100 keV �m[sup �1] , at 25 and 300�C. The radiations include [sup 1] H[sup +] , [sup 2] H[sup +] , [sup 4] He[sup 2+] , [sup 7] Li[sup 3+] , and [sup 12] C[sup 6+] ions with energies from 0.17 MeV to 3.6 GeV. At 25�C, it is found that our G[sub H2O2] values, calculated with protons of different initial energies, show a monotonic increase as a function of LET, in agreement with the commonly assumed expectation of an increase in molecular yields with increasing LET. Our calculated H[sub 2] O[sub 2] yields at 300�C increase significantly faster with LET than do their corresponding 25�C values, showing that the temperature dependence of G[sub H2O2] at higher LET is less than for low-LET radiation. We also report our results on the temporal variations of the H[sub 2] O[sub 2] yields, in the interval ~1 � 10[sup �13] � 1 � 10[sup �6] s, at 25 and 300�C and for the different types of radiation considered. Finally, we find that for incident ions of equal LET > 10 keV �m[sup �1] , G[sub H2O2] decreases as the ion velocity increases, from protons (or deuterons) to carbon ions. These differences produced in G[sub H2O2] by changing the type of radiation are explained by the greater mean energy of secondary electrons from the higher velocity ions, which penetrate to a greater average distance from the actual particle track, with a corresponding decrease in molecular yields. Our calculated G[sub H2O2] values compare generally well with the experimental data available from the literature and are also in good accord with the predictions of deterministic diffusion-kinetic model calculations reported earlier.Key words: liquid water, radiolysis, primary yields, hydrogen peroxide (H[sub 2] O[sub 2] ), linear energy transfer (LET), accelerated protons and heavy ions, temperature, Monte-Carlo simulations.� l'aide des m�thodes de simulation Monte-Carlo, nous calculons le rendement primaire de peroxyde d'hydrog�ne (G[sub H2O2] ) produit lors de la radiolyse de l'eau pure d�sa�r�e en fonction du transfert d'�nergie lin�ique (TEL) du rayonnement incident, dans la gamme ~0,3�100 keV �m[sup �1] , � 25 et 300�C. Les rayonnements ici utilis�s sont les ions [sup 1] H[sup +] , [sup 2] H[sup +] , [sup 4] He[sup 2+] , [sup 7] Li[sup 3+] et [sup 12] C[sup 6+] acc�l�r�s � des �nergies allant de 0,17 MeV � 3,6 GeV. � 25�C, nous trouvons que les valeurs de G[sub H2O2] , calcul�es pour des protons incidents de diff�rentes �nergies initiales, croissent de fa�on monotone en fonction du TEL, en accord avec ce que l'on attend en g�n�ral, � savoir que les rendements des produits mol�culaires augmentent avec le TEL. Les rendements calcul�s en H[sub 2] O[sub 2] � 300�C augmentent notablement plus vite avec le TEL que leurs valeurs correspondantes � 25�C, montrant qu'� TEL plus �lev� la d�pendance en temp�rature de G[sub H2O2] est moindre que pour des rayonnements � faible TEL. Nous rapportons aussi les r�sultats concernant les variations temporelles des rendements de H[sub 2] O[sub 2] , dans l'intervalle ~1 � 10[sup �13] � 1 � 10[sup �6] s, � 25 et 300�C et pour les divers types de rayonnements �tudi�s. Nous trouvons enfin que, pour des ions incidents d'�gal TEL > 10 keV �m[sup �1] , G[sub H2O2] d�cro�t lorsque la vitesse de l'ion augmente, en passant des protons (ou deut�rons) aux ions carbone. Ces diff�rences produites dans G[sub H2O2] en changeant le type de rayonnement sont expliqu�es par la plus grande �nergie moyenne des �lectrons secondaires �ject�s par les ions de plus haute vitesse, qui p�n�trent ainsi, en moyenne, � une plus grande distance de la trajectoire de la particule incidente, entra�nant une diminution concomitante des rendements mol�culaires. Nos valeurs calcul�es de G[sub H2O2] se comparent en g�n�ral bien avec les donn�es exp�rimentales disponibles dans la litt�rature et sont �galement en bon accord avec les pr�dictions de calculs mod�les diffusionnels d�terministes pr�sent�s ant�rieurement.Mots cl�s : eau liquide, radiolyse, rendements primaires, peroxyde d'hydrog�ne (H[sub 2] O[sub 2] ), transfert d'�nergie lin�ique (TEL), protons et ions lourds acc�l�r�s, temp�rature, simulations Monte-Carlo.


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