The chemical state of 82Br, 81mSe and 76As recoil atoms in KBrO3 crystals

J, inorg, nucL Chem. VoL 43, No, 12, pp. 3043-3046,1981 Printed in Great Britain.

0022-1902t81/123043-04503.0010 PergamonPress Ltd.

THE CHEMICAL STATE OF 82Br, SlmSe AND 76AsRECOIL ATOMS IN KBrO3 CRYSTALS M. T. A. TEELINGt and A. H. W. ATEN, Jr.,@ Subfaculty of Chemistry, University of Amsterdam,Amsterdam,The Netherlands J. BOERSMAand P. W. F. LOUWRIER* Institute for Nuclear Physics Research (IKO), P.O. Box 4395, 1009AJ Amsterdam,The Netherlands and D. J. APERS Laboratoire de Chimie Inorganiqueet Nuclraire, Universit6 de Louvain,B-1348 Louvain-la-Neuve,Belgium

(Received 2 January 1981; received[or publication 17 July 1981) Abstract--The retention of S2BrO3-in KBrO3 activated with fast neutrons is about 18% at ambient temperature. Annealing at 523 K gives an increase to 50%. Simultaneously produced 8~mSeappears in about 90% as SeO42-at room temperature, which percentage increases to near 100%after annealing. The 76Asrecoil atoms appear 100%as AsO]-. A description is proposed, based on processes with different spectra of energies of activation. A model is given for these processes, based on the hypothesisthat the recoil atom stabilizes in the host lattice in a form which is compatible with, and may be imposed by the crystal structure of the host lattice. INTRODUCTION circumstances at least some of the factors mentioned The retention of radiobromine formed by thermal neu- above are the same for all recoil species. tron capture in alkali metal bromates has been studied extensively[I-9]. The bromine activity could be recoEXPERIMENTAL vered as BrO3-, BrO2-, BrO- and Br- in LiBrO3 and The details of the experiments are described NaBrO3[2], little or no BrOC and BrO- could elsewhere [22, 23]. All chemicals were analar grade qualbe detected in KBrO3. Thermal annealing increases ity and were used without further purification. KBr03 the retention while the BrOC and BrO- activities disapcrystals were activated at ambient temperature with fast pear and the Br- activity decreases. Some retention neutrons produced in the former l KO-synchro cyclotron values reported in the literature are given in Table 1. (now shut down). The neutron dose was about 160Gy. Selenium has been activated in several compounds [10-- After activation and thermal annealing the samples were 16]. In K2SeO4 the retention is strongly enhanced by split into three parts for the determination of radiobromate, ionizing radiation, even at 77K[15]. Some literature selenate and arsenate. values are given in Table 1. (i) Br-/BrO3-. For radiobromine only the retention Retention studies in lithium, sodium and caesium was determined. Activated KBrO3 was dissolved in 0.1 arsenates show retentions at room temperature of 50- molar KHCO3, containing OsO4 and ASP2- to reduce 70%[17-20]. The retentions for sodium and lithium BrO2- and BrO- to Br-. BrO3- and Br- were separated arsenate depend strongly on the concomitant y-radiation on a Dowex-I anion exchange column in the bicarbonate dose. form with 1 molar KHCO3 and 1 molar KNO3 solutions Several factors, such as crystal free space, crystal as eluents [2]. defects, concomitant ionizing radiation and the presence (ii) SeO]-/SeO~-. KBrO3 was dissolved in a solution of oxygen are known to affect the retention in of SePt- and SeO42- carriers at pH = 7. In one aliquot crystals [1,5, 6, 21] and it can be expected that the chem- SePt- was oxidized with Br2 and BaSeO4 was preical properties of the lattice constituents are also im- cipitated. To ascertain that all 8~r"SeO42-was recovered a portant. second precipitate was made. A second aliquot was In this paper results are reported for the activation of treated directly with Ba(NO3)2 to determine the selenate KBrO3 crystals with fast neutrons. S2Br, glmSe and 76As fraction. This was also repeated. Subsequently the are produced by the reactions SJBr(n,y)S2mBrI-,XS2Br, selenite was oxidized and precipitated to check the 8tBr(n,p)S~Se and 79Br(n,a)76As. As the activation activity balance. Extractions with CS2 or C2C13H[24] occurs simultaneously, the experimental conditions such showed that the activity in the Se° fraction was less than as dose, dose rate and temperature are the same, which 1% for unannealed as well as for the annealed samples. allows intercomparison of the reactions of these three (iii) AsO]-/AsO]-. KBrO3 was dissolved in a solution different recoil particles in the same matrix. Under these containing AsO~ and ASPS- carriers in 0.2 molar NaOH. Arsenate was precipitated as Mg(NH4)AsO4125]. The remaining arsenate was oxidized with Br2 and precipitated. In another aliquot all radioarsenic was oxidized and precipitated to check the activity balance. The activities *Author to whom correspondence should be addressed. tPresent address: Harshaw Chemical B. V. de Meern, The were measured with a NaI(T1) well type crystal. Annealing was performed during periods up to 60 min Netherlands. Deceased January, 1979. at temperatures between 350 and 500 K. JINC Vol 43, No. 12--A

3043

M. T. A. TEELING et al.

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Table 1 Retention of bromine, selemum and arsenic in the~ neutron activated crystalline oxyauion salts Radionuclide

Retention

(%)

Temperature

(r)

Maximum retention after annealing(%)

Annealing temper~tur(

Iaef.

I

78Br,80Br,80mBr,82Bz

20-25

298-308

in KBrO 3

11-14

195

4,6,9

18

300

this

12

77

75Se in SeO~75Se

90

20

30% as SeO~-)

in SeO~-

623

2-4,7-9

673

75% as SeO~-)

86

pile:temperature

32

wo~

12

94-98

670

84

510

11,13,14

77

66

16

28

313 20O

1

95

300

98

473

17

50-70

300

90-100

473

17-20

/6As Ln AsO~/6As Ln AsO~-

RESULTS AND DISCUSSION

The retention of S2Brin KBr03 at ambient temperature is about 18%. This is in good agreement with the values found earlier for S2Br produced with thermal neutrons [7]. Figure 1 shows the isothermal annealing at various temperatures. Plateau values are reached after about 20 min at higher temperatures and after longer times at low temperatures. The annealing curves follow the classical pattern. The annealing curves of s'mSeO~- in KBrOa (Fig. 2) are similar to those of 75SEO2- in K2SeO4 activated with thermal neutrons. The value for the SeO 2fraction in unannealed samples is considerably higher than the value of 66% reported by de Jesus et a/.[16].

Figure 3 shows the plateaux values for the retention of KBrO3 as a function of the annealing temperature as reported in the literature. Figure 4 shows the distribution of S2Br, "roSe and 76As after isochronal annealing during 5 min. The conversion of radiobromine to bromate shows a rather abrupt change around 500 K, radioselenium as selenate shows a more continuous increase and radioarsenic remains constant at 100% arsenate. Thus radioselenate and radioar-

aZBrO3 --v--

4o 2C

/

o

2'o

~o-&53 K

go

t(:i.)

Fig. I. Isothermal annealing of S2BrOg in fast neutron activated KBrO3.

•

~ ~33 K •

379 K

9C

80

2'0

3'0

t (min)

Fig. 2. Isothermal annealing of slmSeO2- in fast neutron activated KBrOa.

10c ao

m+

n.*/. 6c

£o!

&86 K

Xo

"I~Q~T.'"

R'/.

o 523 K ~, Z,86K

O 523 K V 518 K

e ~ - - °". . . . . . . . . . . . . . . . 433K ..... ............................* ............ 379 K

'

.-~T:-~--~-~T---:~--~T~--

2c

6O R%

100

~o

~o

doK

TEMRDRATURE

Fig. 3. Plateau values for S2BrO3- after annealing of KBrO3 as a function of the annealing temperature for various experimental conditions. &, Aten and Joon[7], 4 hr annealing, thermal neutrons, dose < 10Gy. O, Anderson et al. [4], 3 hr annealing, 103G), neutron dose. II, Boyd and Larson[2], 1 hr annealing, 6.5 × l0s Gy dose. +, Apers et al.[3], 3 hr annealing,los Gy y-dose. Xl. This work, 1 hr annealing, 160Gy fast neutron dose.

The chemical state of 82Br, simse and 76Asrecoil atoms in KBrO3 crystals 8to; I

i

o !

40-

I I I

R%

R'/.

.100

30-

20-

,p

90

I I

o

66o

gO

T(K) Fig. 4. Isochronal annealingduring 5 min of KBrO. senate are easily formed in a bromate matrix, although their structure is noticeably different from the bromate ion configuration. However, the S2Br recoil atoms which could stabilize as BrO3- in the KBrO3 lattice do so only with difficulty. Bromine has to overcome a threshold to form BrO3-. However, the retention increases from 20 to 90% [2, 7] upon annealing at 623 K. The bromihe recoil atom has the possibility to stabilize as Br- unless the energy available allows it to recombine to BrO3-. Such a process is observed in bromates doped with 82Br-2. The radiolysis of alkali metal bromates has been studied extensively, a review is given by Johnson[26]. Thermal annealing of the radiation induced damage is accompanied by an increase of the amount of Br- formed, whereas the oxidizing fragments disappear[4, 27]. However, the kinetics do not indicate that the annealing processes for the recoil particles and for the radiation damage are the same, although the same reacting species are assumed to participate [1, 26]. The experimental results for recoil bromine in KBrO3 can be understood by assuming three processes (I, II and III) with different spectra of energies of activation[28]. Process I operates mainly at temperatures below 300K[4] and leads to a retention of about 21% at ambient temperature. The experimental data for linear tempering[4] and the data in Fig. 4 indicate that between ambient temperature and 380 K no annealing occurs. Figures 3 and 4 indicate that two different processes occur above 380 K. Process II, which occurs between 380 and 460 K is insensitive to moderate doses of ionizing radiation (Figs. 3 and 4). Anderson et al.[4] report that annealing using linear tempering in the temperature interval between 373 and 623 K depends on the dimensions of the crystal. Aten and Joon[7] found that heating at 618 K prior to thermal neutron activation reduces the plateau value at 463 K linearly with the preheating time from 40 to 33% after 8 hr of heating. This indicates that diffusion plays an important role in this temperature interval. As a dose of 0.5MGy prior to neutron activation[4] has no influence on the linear tempering annealing, one can assume that process II is a reaction of the bromine recoil atom with either its original oxygen ligands or with debris created along its recoil track. Process III which

3045

occurs predominantly above 460 K is enhanced by ionizing radiation, although without radiation a retention of 85% is reached at high temperature[7]. Thus it seems that it is not so much the radiation induced debris which cause the retention to increase, but that it is more the energy stored in the crystal, which is released upon heating, which shifts the spectrum of energies of activation to lower energies. Thus process III is also a reaction between the recoil bromine and its original ligands or with debris produced along its recoil track. Process I is not influenced by ionizing radiation and does not depend on the pretreatment or the dimensions of the crystals. One can describe this process as oxygen transfer from the undamaged lattice to the bromine recoil atom. The processes in KBrO3 show some similarities with the phenomena observed in KMnO4129]. There, two processes could be distinguished, with different spectra of energies of activation. One of these processes is assumed to be the transfer of oxygen from the KMnO4 lattice to the recoil manganese. This occurs at low temperatures and is insensitive to radiation damage. The other process is the recombination of Mn recoils with their original oxygen ligands. This occurs at higher temperatures, and is suppressed by ionizing radiation. The retentions reported in this work are smaller than those reported by others in the temperature interval between 400 and 490 K; the values at 300 and at 520 K do not differ very much from published values. This difference can be attributed to differences in the pretreatment of the crystals [5, 7] and to a small extent, to the relatively short annealing time. The arsenic recoil species may comply with the crystal symmetry if it takes the form of AsO3-, although KAsO3 and KBrO3 have different crystal structures[30]. Yet, formation of non planar AsO3- might be favoured in comparison with AsO2- formation. This should account for the appearance of arsenate and the total absence of arsenite. The formation of this precursor of arsenate is complete at room temperature. As diffusion in KBrO3 becomes important at higher temperatures one can conclude that AsO3- is formed by oxygen transfer from the KBrO3 lattice to the arsenic recoil atom. Supposing the selenium recoil atom tends to form a structure compatible with the host lattice, it should form SeO3. This entity has a pyrimidal structure[14, 31] and is detected as a transient product in y irradiated K2SeO4[14]. However, there are strong indications that upon dissolution of irradiated K2SeO4 the SeO3- transforms into selenite ions. In the case of KBrO3 one has to assume that SeO3- is oxidized by BrO3- during dissolution of the crystals, while selenite remains unchanged. As this is not very probable, it may very well be that SeO~- or SeO3 are formed in the crystal. As most of the formation of the selenate precursor is complete at room temperature the formation at room temperature may be seen as a transfer of the oxygen ligand from the bromate lattice to the selenium recoil atom, whereas the additional formation above room temperature is the result of diffusive reactions with the original oxygen ligands or the debris created along the recoil track. The reaction model here proposed is based on the general idea that whatever radioisotope is formed in a host lattice, it will tend to stabilize in a form which is compatible with, and may be imposed by the matrix structure. This tendency is observed in a number of other systems. Thus it is found that in mixed crystals of KMnO4

3046

M. T. A. TEELING et al.

and KCiO4, and of KMnO4 and KReO4 the fraction of 56Mn as MnO4- increases with decreasing KMnO4 content, whereas in mixed crystals of KMnO4 and KBF4 the fraction of the activity found as MnO(- decreases [22, 29]. Also in mixed crystals of NaBrO3 and NaC103 the BrO3retention at 308 K increases with decreasing NaBrO3 content[2,32]. Also the formation of perbromate after B-decay of S3Se in K2SeO4133] and the formation of arsenate in K2SeO,t as a result of the decay of 73Se is not contrary to the idea of a recoil species which tries to reproduce the surrounding lattice structure [34].

Acknowledgement--This work is part of the research program of the institute of Nuclear Physics Research (IKO), made possible by financial support from the Foundation for Fundamental Research on Matter (FOM) and the Netherlands Organisation for the Advancement of Pure Research (ZWO). REFERENCES I. C. W. Owens In Chemical EEects o/Nuclear Transformations in Inorganic Systems, (Edited by G. Harbottle and A. G. Maddock). North Holland, Amsterdam (1979). 2. G. E. Boyd and Q. V. Larson, J. Am. Chem. Soc. 90, 254 (1968). 3. D. J. Apers, F, G. Dejehet, B. S. van Outriyjve d'Ydenwalle, P. C. Capron, J. Jach and E. Moorhead, Radiochimica Acta 4, 193 (1963). 4. T. Andersen, H. E. Lundager Madsen and K. Oiesen, Trans Faraday. Soc. 62, 2409 (1966). 5. I. G. Campbell and C. H. W. Jones, Radiochimica Acta 9, 7 (1968). 6. J. J. Jach and G. Harbottle, Trans. Faraday Soc. $4, 520 (1958). 7. A. H. W. Aten Jr. and K. Joon, unpublished results. 8. G. Harbottle, J. Am. Chem. Soc. 82, 805 (1960). 9. S. R, Veljkovi~ and G. Harbottle, Z lnorg. Nucl. Chem. 24, 1517 (1962). 10. D. J. Apers In Chemical EHects of Nuclear Trans[ormations in Inorganic Systems, (Edited by G. Harbottle and A. G. Maddock). North Holland, Amsterdam (1979). 11. F. R. AI Siddique and A. G. Maddock J. Inorg. Nucl. Chem.34, 3007 (1972). 12. F. R. AI Siddique, A. G. Maddock and T. Palma, J. lnorg. Nucl. Chem. 34, 3015 (1972).

13. M. Cogneau, G. Dupl~tre and J. I. Vargas, J. Inorg. Nucl. Chem. 34, 3021 (1972). 14. G. Duplfitre and J. I. Vargas, J. Inorg. Nucl. Chem. 39, 1 (1977). 15. G. Duplfitre, J. Inorg. Nucl. ~hem. 40, 1839 (1978). 16. M. F. de Jesus F., R. M. Machado and G. Dupifitre, Radiochimica Acta 26, 41 (1979). 17. H. Kawahara and G. Harbottle, J. Inorg. Nucl. Chem. 9, 240 (1959). 18. V. G. Dedgaonkar and M. S. Barve, Radiochem. Radioanal. Lett. 27, 63 (t976). 19. V. G. Dedgaonkar and M. S. Barve, Radiochimica Acta 23, 9 (1976). 20. V.G. Dedgaonkar and M. S. Barve, Radiochimica Acta 24, i 17 (1977). 21. N. Saito, F. Ambe and H. Sano, Radiochimica Acta 7, 131 (1967). 22. M. T. A. Teeling, Thesis. University of Amsterdam (1980). 23. M. T. A. Teeling, J. Boersma and A. H. W. Aten Jr., J. lnorg. Nucl. Chem. 42, 1535 (1980). 24. D. J. Apers, C. Theyskens and P. C. Capron, J. Inorg. Nucl. Chem. 29, 858 (1967). 25. G. B. Bar6 and A. H. W. Aten, Jr., Symp. Chem. EHects of Nuclear Transformations, LA.E.A. Prague, Vol. 2. p. 233 (1961). 26. E. R. Johnson, the Radiation-Induced Decomposition of Inorganic Molecular Ions. Gordon & Breach, New York (1970). 27. M. Khare and S. M. Mohanty, J. Inorg. Nucl. Chem. 25, 1527 (1966). 28. A. G. Maddock, Physical Chemistry, Vol. 7, Reactions in the Condensed Phase, (Edited by H. Eyring). Academic Press, New York (1975). 29. M. T. A. Teeling and A. H. W. Aten, Jr., P. W. F. Louwrier, J. Boersma and D. J. Apers,.7..Inorg. Nucl. Chem.,accepted for publication. 30. R. W. G. Wyckof, Crystal Structures, Vol. 3. Wiley, New York (1965). 31. K. Aiki, J. Phys. Soc. Japan 29, 379 (1970). 32. C. W. Owens and G. E. Boyd, J. Inorg. Nucl. Chem. 35, 935 (1976). 33. D. Tenorio and S. Bulbulian, J. P. Adloff, Radiochem. RadioanaL Lat. 24, 61 (1976). 34. G. DuplAtre, J. Herment, Radiochem. Radioanal. Lett. 24, 137 (1972).