Radiation Chemistry


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19 Molecular and Radical Product Yields in Alpha-Radiolysis of 0.8N H S O 2

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M . V. V L A D I M I R O V A State Committee of Utilization of Atomic Energy, Moscow, USSR

The paper discusses the newest and most reliable results of investigations of α-radiolysis of 0.8N H S O as well as FeSO and Ce(SO ) solutions. Based on the results discussed the yields were calculated of radical products of radiolysis and the yield of water decomposition that proved equal to 3.35 molecule/100 e.v. in aerated solution. This G(—H O) value is lower than those determined before (3.5-3.7). The paper gives the values of the yields of intratrajectory reactions (H O + OH, H + OH, H O + H) calculated from the experimental data as well as the yield of track reaction (H + OH) calculated from the above relationship between the yields of radiolysis products and the LET value. The initial yields of water decomposition in α-radiolysis are cal­ culated; the yields of intratrajectory reactions (G= 4.35 molecule/100 e.v.) and the yield of H + OH reaction (G= 7.0 molecule/100 e.v.) taken into account. 2

4

4

4

2

2

2

2

2

2

2

H2O

H2O

his paper analyzes some experimental data obtained i n the radiolysis of 0.8N H S 0 effected by α-radiation of dissolved Po; the yields of some radiolysis products are estimated on their basis. 2

4

Two sufficiently complete reviews are available where experimental data are collected on a-radiolysis of aqueous solutions (7,14). It follows from these reviews that the yields are established with reasonable accu­ racy: G ( F e ) = 5.1 ion/100 e.v. (2, 8, 9, 12) in aerated and G ( F e ) = 3.53-3.57 ion/100 e.v. (8, 9, 12) in deaerated O.SN H S 0 solutions, hydrogen yields G ( H ) = 1.40 molecule/100 e.v. (9, 11), G ( H ) / F e = 1.60 molecule/100 e.v. (12), and G ( H 0 ) = 0.2 rad/100 e.v. (5). 3 +

3 +

0 2

2

4

2

2

2 +

2

The yields of other a-radiolysis products have been recently refined after the appearance of the above reviews. 280 Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

19.

Alpha-Radiolysis of

VLADiMiROVA

281

H SO 2

Jf

After careful determination of Ce -ion reduction yield in aerated 0.8IV H S 0 solution under the influence of dissolved Po the workers (2) offered the yield value G ( C e ) equal to 2.94 ± 0.06 ion/100 e.v. This value ranged formerly within 3.05-3.3 ion/100 e.v. {14). 4+

2

4

3 +

The G ( C e ) value found in ( I ) appears to be most reliable since it is equal to C e yields determined when other types of radiation are used whose L E T value ranges within 2-25 e.v./A. In the same work (2) the H 0 yield was found in 0.8N H S 0 which proved equal to 1.41 + 0.06 molecule/100 e.v. at the radiation doses of (4-10) Χ 10 e.v./ml. In previous work (4) G ( H 0 ) was found equal to 1.20 =b 0.1 molecule/ 100 e.v. W e cited the yield values that are not only newer but are also more reliable. Unfortunately, in some of the latest monographs on radia­ tion chemistry old data is given on a-radiolysis of 0.8N H S 0 , although new and more accurate results are already available. 3 +

3 +

2

2

2

4

17

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2

2

2

4

The question of determining water decomposition yield in a-radioly­ sis and difficulties in correlating the values of the yields of radiolysis radical products obtained in investigating various chemical systems have been repeatedly discussed in literature. To calculate H , O H , and H 0 following equations are used: 2

2

yields in deaerated solutions the

G(Fe ) = 2 G ( H 0 ) + G(OH) + 3G(H0 ) + G(H)

(1)

G(Ce ) = 2 G ( H 0 ) - G(OH) + G ( H 0 ) + G(H)

(2)

2G(H 0 ) + G(OH) + 3G(H0 ) = 2G(H ) + G(H)

(3)

3+

2

3+

2

2

2

2

2

2

2

2

2

In (2) the authors did not determine the C e yield in a deaerated solution, however, it can be estimated from the fact that the ratio of G ( C e ) 0 to G ( C e ) found for α-radiation (6) and other types of radiation equals ^ 1 . 0 5 . Substituting the known values into Equations 1-3 one finds the yields in a deaerated 0.8N H S 0 solution: 3 +

3 +

3 +

2

2

4

G ( H 0 ) == 1.20, G ( - - H 0 ) = 3.0 molecule/100 e.v. 2

2

2

G(OH) = 0.2, G ( H ) = 0.4 rad/100 e.v., The values obtained differ from those previously reported by us (12, 14). The yield of H radicals determined by calculation is shown to equal 0.4 rad/100 e.v. At the same time the discrepancy between the hydrogen yields, determined with and without F e ions being present in the solution and characterizing the H radical yield is equal to only 0.2. Thus, i n deaerated solutions there is a disagreement between G ( H ) , found by experiment and calculation. Added investigations are needed to clarify this disagreement. 2+

Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

282

RADIATION CHEMISTRY

1

To determine the yields i n aerated solutions the following equations are used: G(Fe )0 3 +

= 2G(H 0 )0

2

2

2

+ G ( O H ) 0 + 3G(H0 ) + 3G(H)0

2

2

G(Ce )0 = 2G(H 0 )0 3 +

2

2

2G(H 0 )0 2

2

2

2

2

+ G(H)0 + G(H0 ) - G(OH)0 2

2

(4) (5)

2

+ G ( O H ) 0 + 3 G ( H 0 ) = 2G(H>) + G(H)0> +

2

2

2

2[G(H 0 )0 2

2

2

-G(H 0 )] 2

(6)

2

The last term of Equation 6 expresses the yield of H radicals that took part i n the additional formation of H 0 i n aerated solutions. The H 0 formation may proceed i n tracks or in a track region by the following reactions: 2

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2

2

2

2

H + 0 -> H 0 , H 0 + H -> H 0 . 2

2

2

2

2

Since G ( H 0 ) 0 depends on the radiation dose and ranges within 1.4-1.2 molecule/100 e.v., this yield w i l l be considered a sought quantity, satisfying Equations 4, 5, and 6. 2

2

2

B y substituting the known quantities into these equations the yields are found i n aerated solutions: G ( O H ) 0 = 0.35, G ( H ) 0 = 0.55 rad/100 e.v. G ( H 0 ) 0 = 1.30, G ( - H 0 ) 0 = 3.35 molecule/100 e.v. W h e n calculating the yields i n aerated solutions the G ( H ) and G ( H 0 ) values were taken identical to those i n deaerated ones. The O H yield value turned out to be lower than the value that we gave before (12). The observed yield of water decomposition (3.35 molecule/ 100 e.v.) also proved lower than the values (3.5-3.6) that were widely used until recently. However, this yield G ( — H 0 ) 0 , equal to 3.35 molecule/100 e.v. agrees very well with what we found by using a different independent procedure. 2

2

2

2

2

2

2

2

2

2

2

Based on numerous experimental data on H and F e yields i n 0.8IV H S 0 for different types of radiation the G ( H ) , G ( F e ) 0 , G ( H ) 0 and G ( — H 0 ) 0 — L E T / e . v . / A . of radiation relationships were derived (10,13). 2

2

4

2

2

3+

3 +

2

2

2

In L E T region 3.0-25 e.v./A. these relationships take the form: G ( H ) = 1 . 1 + 0.02 ( L E T )

(7)

G ( H ) 0 = 1.50-0.25 Λ/(LET)

(8)

2

2

G(-H 0)0 2

2

= 3.65-0.195 y/jLKT)

+ 0.03(LET)

(9)

As calculated by Equation 9, the observed yield of water decompo­ sition is equal to 3.33 molecule/100 e.v. It should be noted that the radical product yields i n a-radiolysis are different in deaerated and aerated solutions.

Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

19.

VLADIMIROVA

Alpha-Radiolysis of

283

H SO 2

f/

The above yields of water decomposition were observed and ob­ tained when using scavengers of radical and molecular products—Fe and C e ions. W h e n using the same scavengers in γ-radiolysis the yield of water decomposition is known to equal 4.4 molecule/100 e.v. The observed yield of water decomposition and the yields of a-radiolysis products depend largely on the presence of various substances in solution that are capable of interacting with radicals. This was explained by Pucheault who considered it to be governed by intra-trajectory reactions taking place in a region of high local concentration of molecular and radical products. 2+

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4 +

H 0 2

H

+ O H —> H 0 + H 0

2

2

(a)

2

+ 0H-»H + H 0

2

(b)

2

H 0 2

+ H —> O H + H 0

2

(c)

2

One of the evidences for the occurrence of intra-trajectory reactions may be an increase of the yields of radiolysis molecular products in the pres­ ence of substances in solution that are scavengers of H or O H radicals and suppress Reactions a, b, or c. W e have shown that the H 0 yield in 0.8N H S 0 solution with glucose, methylene blue, and hydrogen present is increased substantially ( I I ) . This experimental data permitted the yield of Reaction a to be found; it is equal to 0.2. Our results agree well with the results of Hart (5). 2

2

2

4

Experiments on determination of H yield in presence of some scav­ engers of O H radicals permitted the yield of Reaction b to be found, that proved equal to 0.35-0.4 ( I I ) . 2

The question of the amount of the initial yield of water decomposi­ tion or of the initial yields of H and O H radicals is of interest. These yields include the yield of those radicals that take part in alpha-particle tracks in recombination reactions ( H -f- H , O H + O H ) , i n a track region in reactions of radiolysis molecular product decomposition ( H 0 + O H , H 0 + H , H + O H ) , and in a solution volume—in reactions with solutes. Only the recombination reaction H + O H was not taken into account. 2

2

2

2

2

The initial yield of water decomposition is G . o and is presented i n the following way: H 2

G

H 2

o = G = 2 G ( H ) + G ( H ) + G(b) + G(c) + G(a) - G(a) H

2

=

G ( - H 0 ) 4- G(a) + G(b) + G(c)

(10)

2

G_ o = G H2

0 H

= 2 G ( H 0 ) + G ( O H ) + 3G(a) + G(b) + G(c) 2

2

G ( - H O ) + G(a) + G(b) + G(c) a

Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

= (11)

284

RADIATION

CHEMISTRY

1

To find the initial yield of water decomposition in α-radiolysis one should know the yields of intra-trajectory reactions and the observed yield of water decomposition. B y substituting the values of G ( - H 0 ) = 3.35, G ( a ) = 0.2, G ( b ) == 0.4 and G ( c ) = 0.35 ( G ( c ) — a c c o r d i n g to Pucheault) into equation for G _ H O one obtains G . o = 4.3 molecule/100 e.v. Thus, the initial yield of water decomposition in α-radiolysis is almost the same as in γ-radiolysis. However, in γ-radiolysis all radicals and molecular products are readily used up in reactions with dissolved substances, and in a radiolysis they partially take up one another. W h e n investigating a-radi­ olysis of various systems we may have the value of the water decompo­ sition yield in the range >—' 3.2-4.3 molecule/100 e.v. 2

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2

H 2

Now the problem is to find the experimental evidence for the value G _ H o = 4.3 molecule/100 e.v. when investigating α-radiolysis of solutions containing energetic scavengers of H or O H radicals. W e have recently obtained such evidence when investigating α-radiolysis of acid N H C N S solutions. Using the mechanism of radiation-chemical reactions in these solutions, proposed by Duflo (3), we found the H radical yield in de­ aerated N H C N S solution concentrated to 0.1M to equal 1.65 rad/100 e.v., whereas the yield of water decomposition, calculated as the sum of 2 G ( H ) + G ( H ) equals 4.2 molecule/100 e.v. 2

4

4

2

For the sake of comparison it may be said that the yield of water decomposition in γ-radiolysis of similar solutions proved equal to 4.35 molecule/100 e.v. Developing the idea of the initial yield of water decomposition in α-radiolysis one may say that taking into account H -f- O H reaction that was not discussed above, it should be even more than the yield of water decomposition in γ-radiolysis. Based on the H and G ( — H 0 ) y i e l d L E T relationship (13) derived by us, we have performed a preliminary calculation, assuming conventionally the value of G . o γ = 6.0 molecule/ 100 e.v.; it showed that in going from γ- to α-radiation the G ( H -f- O H ) yield is increased from 1.5 to 2.7 and the yield of water decomposition from 6.0 to 7.0 molecule/100 e.v. Such an increase of the yield of water decomposition in α-radiolysis is in accordance with the idea suggested by Allen ( 1 ) about the origin of some new way of water decomposition in case of dense tracks. 2

2

H 2

Summing up the material discussed, it may be said that the experi­ mental data obtained supports the early assumptions of the proximity of the initial yield of water decomposition in α-radiolysis to the yields of water decomposition in γ-radiolysis. The use of the recent experimental data on α-radiolysis of 0.8IV H0SO4 containing F e S 0 and C e ( S 0 ) permitted the refinement of the 4

4

2

Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

19.

VLADiMiROVA

Alpha-Radiolysis of

285

H SO 2

value of the observed water decomposition yield and the radical product yields. The application of the calculation method based on derived relation­ ships between the yields of some radiolysis products and the amounts of linear energy transfer ( L E T ) made it possible to determine the value of the observed yield of water decomposition i n aerated solutions. The value obtained is i n agreement with the quantity G ( — H 0)C>2, found by the equation of material balance. 2

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Literature Cited (1) Allen, Augustine O., "The Radiation Chemistry of Water and Aqueous Solutions," D. Van Nostrand Company, Inc., Princeton, N . J., 1961. (2) Anta, M . C., Mariano, M . H., Santos, M . Z., J. Chim. Phys. 61 (4), 577 (1964). (3) Duflo, M . , Ann. Chim. 10, 551 (1965). (4) Ershova, Ζ. V., Valdimirova, M . V., At. Energ. (USSR) 5, 546 (1958). (5) Hart, E., Radiation Res. 2, 33 (1955). (6) Lefort, M . , Tarrago, X., J. Phys. Chem. 63, 833 (1959). (7) Pucheault, J., Actions Chim. Biol. Radiations 5, 31 (1961). (8) Steyn, J., J. S. African Chem. Inst. 14, 93 (1961). (9) Trumbore, C., Hart, E., J. Phys. Chem. 63, 867 (1959). (10) Valdimirova, M . V., At. Energ. (USSR) 17 (3), 222 (1964). (11) Vladimirova, M . V., Ershova, Ζ. V., "Transactions of 2nd All-Union Con­ ference on Radiation Chemistry," p. 162, Pub. Acad. Sci., Moscow, USSR, 1962. (12) Vladimirova, M. V., Kulikov, I. Α., Shulyatikova, L . G., Radiokhimya 8 (2), 226 (1966). (13) Vladimirova, M . V., Radiokhimiya 9 (3), 386 (1967). (14) Vladimirova,M.V., Usp. Khim. 4, 462 (1964). RECEIVED February 7,

1968.

Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

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286 RADIATION CHEMISTRY

Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

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