Chemical effects of neutron capture in thioantimony compounds

i. inorg,nucl.Chem..197I, Vol.33, pp. 4019-4023. PergamonPress. Printedin Great Britain

CHEMICAL

EFFECTS OF THIOANTIMONY

NEUTRON CAPTURE COMPOUNDS

IN

J. F. FACETTI and H. D. COLMfi~N Instituto de Ciencias, Universidad de Asunci6n, Paraguay, South America

(First received 18August 1969; in revised form 17 March 1971) Abstract--The distribution of the valence states of radioantimony was studied in a number of neutron irradiated thioantimony compounds. The high radiochemical yield of Sb v seemed to be related to the covalent character of the Sb-S bond, to the degree of hydration of the compounds, and to the radiation damage. INTRODUCTION

the activities formed after neutron irradiation of oxicompounds of antimony has been studied by various workers[l, 5]. Internal conversion of the neutron capture y-rays should result in oxidation[I], but no evidence of this was found, and electron transfer could have occurred in the solid state or in solution. The distribution of valence states in irradiated antimony oxides indicated a low yield of Sb v [2], in comparison with the values obtained with arsenic oxides [6, 7]. However, a linear relation was found in both Sb and As systems between the yield of the pentavalent fraction and the ratio of oxygen to the antimony or arsenic atoms in the molecule. The distribution found for KSb(OH)6 showed a high retention[3,4], although this depends on the pretreatment of the compound [4, 8]. The studies indicated that the majority of the radiactive atoms reached their final valence state immediately, or very shortly, after the nuclear reaction. The present work consists of a comparative study of distribution of activity of Sb m and Sb v formed on irradiating thioantimony compounds.

THE

DISTRIBUTION o f

EXPERIMENTAL Materials The irradiated compounds were the antimony sulfides and some antimony thiosalts. The sulfides used were analytical grade Sb~S3 and Sb2S5. The thiosalts, (NH4)3 SbS:~, Na~SbS:~. 9H~O and Na~SbS4. 9H20 were prepared and purified according to conventional methods[9-12]. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

A. Maddock and M. M. de Maine, Can. J. Chem. 34, 441 (1956). J. F. Facetti, J. inorg, nucl. Chem. 23, 759 (1962). T. Andersen and A. Knntsen, J. inorg, nucl. Chem. 23, 191 (1961). J. F. Facetti, E. Trabal and S. Torres, Trans. ,4 m. Nucl. Soc. 7, 441 (1964). J. F. Facetti, Radiochim. Acta 4, 164 (1965). H. Kawahara and G. Harbottle, J. inorg, nucl. Chem. 9,240 (1959). G. Bar6 and A. Aten, Prod. Symp. o f Chem. Eft. ofNucl. Transf IAEA, Vol. 2,233 (1961). T. Kambara, K. Kashihara and K. Hasegawa, Presented at Hot Atom Chem. Symp. Kyoto, 1967 (Unpublished). H. Moissan, Traite de Chimie Minerale Vol. III, p. 241. Masson et Cie (1904). N. Sidgwick, The Chemical Elements and Their Compounds Vol. 1. p. 791. Oxford University Press, Oxford (1950). B. Prunier, J. pharm. Chem. 3, 28 (1896). H. Moissan. Traite de Chimie Minerale Vol. IIl. p. 384. Masson et Cie (1904). 4019

4020

J.F.

F A C E T T I and H. D. C O L M A N

The last two salts form easily grown tetrahedral crystals, readily soluble in water. The NaaSbS3"9H20 was studied by X-ray diffraction. In preliminary experiments, the most intense lines for this compound were obtained at " d " values of 5.945.3.185 and 2-605 ,~. The composition of the compounds was checked by chemical analysis.

Irradiation The samples were irradiated in polyethylene tubes in the presence of air by doses of 6 x 10J4n/ cm 2 and 10~Sn/cm2 in two different reactors with fluxes of l0 TM and 10~3n/cm2/sec. A few samples of Sb2S3 were irradiated in evacuated ampoules. Analysis The activated compounds were dissolved in 1.3% sodium sulfide solutions. The various valence states were separated by paper electrophoresis[13] using Whatman 3MM paper. The voltage gradient was 30 V/cm and the electrolyte was 0.4% sodium sulfide solution. The position of the standard samples was determined by neutron activation of the paper strips. The samples were generally counted for 124Sb activity, after the 12zSb activity (Txn2'8 days) had decayed. The Na3SbS3.9H~O samples were counted for both mSb and ~24Sbactivity. RESULTS AND DISCUSSION

The activation of SbzS3 produced a radiochemical yield of 50-0 ___3.0 per cent of Sb m. The radiochemical yield of Sb v was 28.7 per cent at a flux of 10 lz n/cmZ/ see. and 36.3 per cent at a flux of 10~an/cm2/sec (see Table 1). This difference however was not observed in the other compounds. A third unidentified activity amounting to 18 per cent was also formed (see Fig. 1). No significant difference was found when the sample was irradiated in vacuo. Table 1. Distribution of Sb v in Sb2Sa at different fluxes qb--- 10TM 30.5 29.2 27.4 27.7 Mean 28.7__-0.6%

dp= 1013 34.2 36.4 38.5

36.3--_1%

The distribution of activity in the III and V valence states of antimony found for SbzS3, Sb2S5, Na3SbS4"9HzO and (NH4)3 SbS3 is shown in Table 2. The radiochemical yields of Sb v were higher in the thiocompounds than in the oxides and antimonates. Schlippe's salt (NaoSbS4) gave an Sb v yield comparable to that from KSb(OH)6 [2, 3]. In ammonium thioantimonate, however, the yield of Sb v was very low, and the retention (as Sb m) reached 83 per cent. An additional 8 per cent of the activity was found as background in the strips and could not be accounted for as either Sb In and Sb v. The activation of Na3SbS3"9HzO led to a high yield of Sb v, and an isotope effect was found (see Table 3). This was probably due to the isomeric states of 13. J. F. Facetti, H. D. Colmfin and E. Molinas, Rev. Soc. Cientf 9, 9 Asunci6n (1968).

Chemical effects of neutron capture

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Sb TM zxlo3

e U

Sb]~Z "

9_ I

I

5

I0

,I

I

15

20

distaaee (era)

Fig. 1. Typical electrophoresis histogram of the neutron irradiated Sb2Sa.

Table 2. Distribution of ~24Sb activity* 1248b yield % III

Compound 5b253 5b255 N~SbS4-9H20 (NH4)3SbS3

50.0±1.3 61.8±1-5 29.4±1.2 85.6±1.8

V

IV

28.7±0.6 37.3±1.6 69.8±0.9 5.0±1.9

18.0±1.4

* Flax of 10 TMn/cmZ/sec. Table 3. Distribution of 122Sband 124Sb activities

Yield % Compound

]~Sb III

V

Ill

Na3SbS3'9H20

44.1 --- 1.9

53-2 ± 2.2

35.6 ± 1.5

J24Sb V 62.1 - 1.7

J22Sb and 124Sb, which resulted in different activated forms of the thiocompounds. No isotope effect was observed previously in the oxycompounds of antimony. A linear relation was not observed between the sulphur content of the compound and the yield of Sb v. However, if sodium thioantimonate was completely dehydrated, the retention decreased to 50 per cent, and a linear relation now existed between the Sb v yield and the ratio of S/Sb in the sulfides and thioantimonate.

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F A C E T T I and H. D. C O L M A N

Ammonium thioantimonate showed a very low yield of Sb v. Compared to the other thiosalts. A possible reductive effect of the ammonium after the neutron bombardement of different ammonium salts was mentioned previously [ 14-16], and the effect was attributed to the radiolysis products of the ammonium ion [15]. However, in the neutron irradiation of ammonium phosphate, the lower yield of the pentavalent fraction could not be due to irreversible reduction reactions with the ammonium[17]. Further, and as it was suggested[18], transfer of energy from fast neutron to hydrogen atoms can occur. In such a case, the energetic proton will provoke a larger damage in the material, which will reduce the yield of the Sb v recoil fraction. A third activity was encountered in the activation of SbzS3 in the electrophoresis, besides the Sb xHand Sb v activities. It has been shown[22] that, when the antimony trisulfide is dissolved in sodium sulfide solution, the Sb4S72- species is formed. The same behaviour can be expected for other trivalent antimony thiocompounds. But the nature of SbzS5 in sodium sulfide is unknown. Because the third activity was not observed in the irradiation of the other compounds, it is difficult to attribute it to some kind of solvent effect on the Sb HIor Sb v recoil species. It is tempting to look for an explanation of this third activity in the formation of metastable species of Sb w. Internal conversion of Sb Ill hot atoms could result in the formation of Sb v and Sb Iv. The Sb ~v valence state behaves [ 19] as a radical with a d 1° s J configuration, which dissociates into Sb nl and Sb v. The activation could probably form both the IV or V valence states. However, in the irradiated compounds, the Sb ~v disproportionates in the crystal into Sb IH and Sb v except in the case of Sb2Sa, where the Sb ~vspecies is trapped in the crystal defects. The higher yields of Sb v in the sulfides, as compared to the oxides, can be attributed to the type of lattice and to the marked covalent character of the Sb-S bond. Little is known about the structure of the thiocompounds except for Sb2Sa, but in respect of the type of bond, the Sb-S is 90 per cent covalent as compared with the 46 per cent partial ionic character of the Sb-O bond in the oxides [20]. This effect of the nature of the linkage on the antimony recoil atoms has been observed in previous work with lz2Sb and ~z4Sb formed under irradiation of antimony oxides[2,8], and n5Sb formed under irradiation of tin oxides[16]. Antimony oxides are semimolecular crystals [21] whereas tin oxides are simple ionic compounds. Yields of radioactive Sb v fraction were higher in the former than in the latter. The high yield of Sb v fraction in the hydrated compounds suggests that 14. G. Harbottle and N. Sutin, Advances in Inorganic and Nuclear Chemistry-I (Edited by H. J. Emeleus and A. G. Sharpe) p. 276. Academic Press, New York (1969). 15. N. Getoff, Proc. Syrup. on Chem. Eft. of Nucl. Transf. IAEA 2, 279 (1964). 16. J. F. Facetti, Radiochim. Acta 12, 82 (1969). 17. R. Claridge and A. Maddock, Chem. Eft. ofNucl. Transf. IAEA 1,475 (1961). 18. A . G . Kempe, D. Apers and P. Capr6n, Radiochim.Acta 12, 113 (1969). 19. R. S. Nyholm and M. L. Tobe, Advances in Inorganic Chemistry and Radiochemistry (Edited by H. J. Emeleus and A. G. Sharpe), Vol. 5. p. 1. Academic Press, New York (1963). 20. L. Pauling, The Nature of Chemical Bond pp. 97-104. Cornell University. Press (1960). 21. A. F. Wells, Structural Inorganic Chemistry p. 456. Clarendon Press, Oxford (1962). 22. R. Arntson, F. W. Dikson and G. Tunell, Science, 153, 1673 (1966).

Chemical effects of neutron capture

4023

degree of hydration plays a role. Complete dehydration of Na3SbS4 lowered the retention to 50 per cent. The same effect has been observed in KSb(OH)6 when it is partially dehydrated. Probably the reordering of O H radicals on the spikes could account for the oxidation of the initially formed species. If such is case, the oxidative function of the O H will be in competition with the reductive action of the " F " centers or hydrogen atoms formed or liberated under irradiation. The density of the " F " centers will depend on the structure of the compound, the type of lattice and the defects produced under irradiation. Acknowledgement-We thank E. Molinas for technical assistance and to the C N E A of Argentina, and the Instituto de Energia At6mica of Sao Paulo for the irradiations. The La Piedad Foundation and the Sociedad Cientifica del Paraguay provided financial assistance.