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Separation of nuclear reaction products in the gas phase—I
J. inorg, nucl. Chem., 1975, Vol. 37, pp. 15-19. Pergamon Press. Printed in Great Britain.
SEPARATION OF NUCLEAR REACTION PRODUCTS IN THE GAS PHASE--I SEPARATION
OF
Tc IN A FLOW
OF
OXYGEN
K. B,~CHMANN and V. MATSCHOB Fachbereich fi.ir Anorganische Chemie und Kernchemie der Technischen Hochschule, Darmstadt,
Germany
(First received l February 1974: in final form 29 March 1974)
Abstract--The separation of nuclear reaction products in the gas phase has been investigated using a 252Cf source. A detailed study of the behaviour of Tc-nuclides which form a volatile oxide with oxygen has been carried out. The yields of technetium are given as a function of the oxygen concentration, the temperature of the cooling trap and the temperature of the transfer tube. The total yield of Tc is t> 50 + 15 per cent.
1. I N T R O D U C T I O N THE INVESTIGATIONof nuclear reactions or decay properties of nuclei ask more and more for experimental methods which provide rapid and selective separations and enable the identification of only a few atoms. Therefore in the last decade the on-line technique has been developed with the aim to m a k e production, separation and identification a continuous process. One possibility to separate short-lived nuclides continuously is to form volatile c o m p o u n d s with the recoil products of a nuclear reaction, a n d to separate them in a gas stream according to their different volatilities and adsorption heats, respectively or other properties. In order to collect a given element at a detector position the experimental conditions have to be optimized by changing the gas flow velocity, the gas composition, the temperature of the transfer tube, the temperature of the collection zone and the wall material. An impressive example is given by Z v a r a et al.[1-3] who applied such techniques in their research for element 104 while speculating on the high volatility of its tetrachloride. We have used the spontaneous fission of 252Cf as a source for the production of recoil atoms a n d studied separations in inert gases a n d with chlorinating gases [4-7]. In this study the selective separation of technetium in a N 2 / O 2 gas stream has been investigated.
2.
/ "
/~
Paraffin I
T
~ 02
/
~~
detecto
/
Heat windings
~Cf-source II C/c'
Nz
,/
/
i~
Fig. 1. Experimental set-up.
fission process in a 252Cf source ( ~ 1 #g) which is protected by a Ni-foil ( ~ 1 mg/cm2). They are stopped in a flow of inert gas (N2) and transported to an 02 gas inlet ( ~ 2 cm behind the source). The volatile species are transported through a pyrex tube (6 mm and 150 cm length) which could be heated up to 400°C, to a trap in which the temperature was varied between - 4 0 ° C and 100°C. The radio nuclides were identified by gamma ray spectroscopy with a germaniumlithium detector and by checking the half-lives of the gamma ray transitions. The results are summarized in Table 1. If several transitions have been evaluated only the most suitable line (high intensity and no interferences) is listed. The errors are statistical errors. Some of the experiments were repeated and showed deviations larger ( ~ 15 per cent) than the statistical errors. Use was made of the short-lived Tc isotopes with mass 102-108. It was not possible to detect ' '°Tc, since the transition with the energy 240.2 keV[8] was overlapped by the 242.4 keV transition in l°aTc.
EXPERIMENTAL PROCEDURE
Figure 1 shows schematically the experimental set-up. Since this arrangement has been described in detail in a previous publication[5] only a short summary will be given here. The recoil atoms are produced by the spontaneous 15
16
K. BACHMANN and V. MATSCHOB
+~ +~ +1 +l -'l-I+1 +1 +1
+~ +1 +~ +~
+~ +1 +~ +1 +1 +1 +1 +t
+~ +1 +l +~
Q "O
8
"7-,
o
r~ "O
[-
"O
g, ,.-
t~
I +ll +J+~+l+l
+~+~+t+t
e.,
e-,
_=_= ,It.
+--
Separation of nuclear reaction products vi
4,xIO 4
rO T
C
i x ~
3xIO 4
.(2 rO
, ,
~tLl '~ ~
2xlO 4
iO 4
17
T
- <22 I
I O0
[
200
Energy,
I
500
500
400
keY
Fig. 2. Gamma ray spectra taken with N 2 (lower curve) and with N2/O 2 (98/2 per cent) (upper curve); transfer tube at 200°C, cooling trap at 0°C. 3. DISCUSSION OF THE RESULTS In recent publications[4--6] it has been found that some of the 252Cf recoil products are transported in an inert gas stream. Under the conditions used in these experiments Xe, I, and Te were measured in the trap. Only a minor fraction of Tc (Fig. 5, dashed line) was transported with N 2. When 02 is added to the inert gas I, Te, Tc, Ru and Rh lines are measured in the cooling trap. In this study only the transportation of Tc will be discussed. No gamma lines of Mo isotopes could be found so that the precursor could be excluded and a true transportation of Tc was secured. Figure 2 shows in the lower part the spectrum with inert gas and in the upper part the spectrum after addition of 02. Figure 3 shows the Tc-transport as a function of the O2-concentration, which was varied between 2 and 50 per cent. (The temperature of the transfer tube was 200°C and the temperature of the cooling trap 0°C). No obvious dependence could be found in this range. Since this is valid for all To-nuclides studied, a further indication is given that a Mo-precursor is not involved in the transportation. Figure 4 shows the yield of Tc-nuclides as a function of the temperature of the cooling trap. The values at -40* are not really comparable since they were determined at a temperature of 400°C of the transfer tube and then corrected for a temperature of 200°C. The other values were determined at a temperature of 200°C in the transfer tube. The steep rise with decreasing temperature might be an indication that the technetium-species which has been formed is rather volatile.
~
bo~
Tc-104
m ~ ~ m
Tc-106
,%
5 x ' o'
o
~
O
~
o
/
~
T
c
-
Tc-108 Tc-I05
O
1
0
2
(xlO)
4 1 , . . . ~
ol
2
I
I
30 02 ,
T c -IO7 Tc-103
50
%
Fig. 3. Yield of Tc-nuclides as a function of the O2-concentration ; transfer tube at 200°C, cooling trap at 0°C. In Table 2 the melting points and boiling points of the known technetiumoxides are summarized. Tc20? is most volatile but an estimation of collision numbers shows that a formation of a species with two Tc-atoms is highly improbable. Sch/ifer[12] has found that in
18
K. B,%CHMANNand V. MATSCHOI3
2`5x'°°I
105 ~
%
/
X% I0
TC-1106
%,I
.c
`sx)o' o.,_
J/ / // / / ~ ' 1~ l T o~---~Z~. - f o 7 ''°5 ~Tc-103 --.L~'-°L-,
ii~//"
\ ~\
I
0
I00
200
300
Temp. of the ?ronsf. fube,
•%
Fig. 5. Yield of Tc-nuclides as a function of the temperature of the transfer tube (the dashed line represents the values for N2). ~,,Tc-107 ~
o
I -40
"o..
\\
rc0 T e m p . of t h e
,50 fronsf, tube,
I00 *C
Fig. 4. Yield of Tc-nuclides as a function of the temperature of the cooling trap. the transfer of Re or rheniumoxides the species ReO~ (OH) might play a part if traces of water are present. In most of our experiments H20 was not completely removed (the Nz contained 15 vpm H20), but in the experiments in which H 2 0 has been frozen out, the same yield of Tc was measured. Since even in these experiments enough water molecules might be present, the formation of TeO~ (OH) can not be excluded. It is possible that under the experimental conditions a rather unstable and volatile technetiumoxide is formed which is still unknown. Table 2. The melting points and boiling points of technetium oxides
Oxide
Melting point (°C)
Boiling point (°C)
Slightly volatile at 900°C TcO 3 The existence of TcO 3 is discussed. Tc20~ 119.5 310.6 slightly TcO3(OH ) volatile TcO 2
400 oC
Reference 9 11 9 10
When discussing the nature of the transported species it should always be kept in mind that the transportation is not a function of the volatility alone but also a function of the adsorption heat. The adsorption on 'clusters was excluded, since experiments with quartz wool lead to the same yields. In addition the higher temperature should destroy the clusters. Figure 5 shows the yield of Tc-nuclides as a function of the temperature of the transfer tube. The maximum yield at 200°C can be explained in the following way: The yield which is measured by the counter is the result of several factors governing the different steps in the process: 1. Reaction yield, 2. Transfer yield, 3. Condensation and adsorption yield in the cooling trap and 4. Detector yield (distance between the detector and the position of the nuclide in the cooling trap). Probably the transfer yield increases with increasing temperature in the tube because the adsorption decreases. On the other hand the species which are formed might be decomposed at higher temperatures thus leading to lower yields. A second explanation for the lower yields at higher temperatures might be a different temperature gradient in the cooling trap which results in a lower detector yield. A small change in the profile of the temperature may cause a large effect in the counting efficiency. Figures 4 and 5 show that f9 r a separation of Tcnuclides a temperature of 200°C in the transfer tube and low temperatures in the cooling trap are the optimum conditions as to the yield. When a high selectivity (high decontamination factor) is desired then a higher temperature in the cooling trap gives a better separation from iodine. The separation from Te is satisfactory with the transfer tube at 200°C, since Te is transferred
Separation of nuclear reaction products with maximum yield at higher temperatures. The separation from Ru and Rh will be discussed in a subsequent publication[13]. Zaitseva et al.[14] have investigated the separation of Re from Au-targets at about 1000°C. Therefore we shall extend our study to higher temperatures. A determination of the transfer yield of I°5Tc (using the 252-2 keV peak) showed that 50 per cent of the 1°5Tc, which is stopped in the gas flow, is transferred and then adsorbed in the cooling trap. The applied method is described by other authors[4]. It should be emphasized that a complete separation of a certain element is not always necessary when using the gas phase method since each gamma ray transition shows a characteristic "chemical and physical" behaviour (pattern) which can be used for its identification. The authors would like to thank the "Gesellschaft fiir Schwerionenforschung" for financial support. Acknowledgement
REFERENCES
1. 1. Zvara, Y. T. Chuburkov, T. S. Zvarova and R. Caletka, Jt Inst. nuel. Res. Dubna Report D6-3281 (1967).
19
2. Y. T. Chuburkov, I. Zvara and B. V. Shilov, Jt Inst. nucl. Res. Dubna Report P7-4021 (1968). 3. 1. Zvara, Y. T. Chuburkov, R. Caletka and M. R. Shalaevskii, Jt Inst. nucl. Res. Dubna Report P7-3763 (1968). 4. W. Bfgl, K. B~ichmann, K. Biittner and N. Moheit, lnorg, nucl. Chem. Lett. 9, 405 (1973). 5. W. BSgl, K. B~ichmann and K. BiJttner, Radiochim. Acta. To be published. 6. K. B/ichmann, W. B6gl and K. BiJttner, Z. analyt. Chem. 267, 274 (1973). 7. K. B/ichmann, W. B6gl, W. Bfittner, M. Gebhardt, G. Helas, P. Hoffmann, H. Klenk, H. Klonk, R. Lauer, K. H. Lieser, V. MatschoB, B. Neidhart, A. Rosenberg, H. P. Sahner, B. Stojanik and W. Trautmann, GSIReport 73-14, 98 (1973). 8. F. F. Hopkins, J. R. White, G. W. Phillips, C. F. Moore and P. Richard, Phys. Rev. C5, 1015 (1972). 9. S. Tribalat, Rhenium et Technetium, pp. 154-158. Gauthier-Villars, Paris (1957). 10. K. Schwochau, Angew. Chem. inter, ed. 76, 9 (1964). 11. R. D. Peacock, The Chemistry of Technetium and Rhenium, p. 27. Elsevier, Amsterdam, North Holland (1966). 12. H. Sch/ifer, Z. anorg, allg. Chem. 400, 253 (1973). 13. W. B6gl and K. B~chmann, To be published. 14. B. Bayar, I. Votsilka, N. G. Zaitseva and A. F. Novgorodov, JINR P12-7164, Dubna (1973).
SEPARATION OF NUCLEAR REACTION PRODUCTS IN THE GAS PHASE--I SEPARATION
OF
Tc IN A FLOW
OF
OXYGEN
K. B,~CHMANN and V. MATSCHOB Fachbereich fi.ir Anorganische Chemie und Kernchemie der Technischen Hochschule, Darmstadt,
Germany
(First received l February 1974: in final form 29 March 1974)
Abstract--The separation of nuclear reaction products in the gas phase has been investigated using a 252Cf source. A detailed study of the behaviour of Tc-nuclides which form a volatile oxide with oxygen has been carried out. The yields of technetium are given as a function of the oxygen concentration, the temperature of the cooling trap and the temperature of the transfer tube. The total yield of Tc is t> 50 + 15 per cent.
1. I N T R O D U C T I O N THE INVESTIGATIONof nuclear reactions or decay properties of nuclei ask more and more for experimental methods which provide rapid and selective separations and enable the identification of only a few atoms. Therefore in the last decade the on-line technique has been developed with the aim to m a k e production, separation and identification a continuous process. One possibility to separate short-lived nuclides continuously is to form volatile c o m p o u n d s with the recoil products of a nuclear reaction, a n d to separate them in a gas stream according to their different volatilities and adsorption heats, respectively or other properties. In order to collect a given element at a detector position the experimental conditions have to be optimized by changing the gas flow velocity, the gas composition, the temperature of the transfer tube, the temperature of the collection zone and the wall material. An impressive example is given by Z v a r a et al.[1-3] who applied such techniques in their research for element 104 while speculating on the high volatility of its tetrachloride. We have used the spontaneous fission of 252Cf as a source for the production of recoil atoms a n d studied separations in inert gases a n d with chlorinating gases [4-7]. In this study the selective separation of technetium in a N 2 / O 2 gas stream has been investigated.
2.
/ "
/~
Paraffin I
T
~ 02
/
~~
detecto
/
Heat windings
~Cf-source II C/c'
Nz
,/
/
i~
Fig. 1. Experimental set-up.
fission process in a 252Cf source ( ~ 1 #g) which is protected by a Ni-foil ( ~ 1 mg/cm2). They are stopped in a flow of inert gas (N2) and transported to an 02 gas inlet ( ~ 2 cm behind the source). The volatile species are transported through a pyrex tube (6 mm and 150 cm length) which could be heated up to 400°C, to a trap in which the temperature was varied between - 4 0 ° C and 100°C. The radio nuclides were identified by gamma ray spectroscopy with a germaniumlithium detector and by checking the half-lives of the gamma ray transitions. The results are summarized in Table 1. If several transitions have been evaluated only the most suitable line (high intensity and no interferences) is listed. The errors are statistical errors. Some of the experiments were repeated and showed deviations larger ( ~ 15 per cent) than the statistical errors. Use was made of the short-lived Tc isotopes with mass 102-108. It was not possible to detect ' '°Tc, since the transition with the energy 240.2 keV[8] was overlapped by the 242.4 keV transition in l°aTc.
EXPERIMENTAL PROCEDURE
Figure 1 shows schematically the experimental set-up. Since this arrangement has been described in detail in a previous publication[5] only a short summary will be given here. The recoil atoms are produced by the spontaneous 15
16
K. BACHMANN and V. MATSCHOB
+~ +~ +1 +l -'l-I+1 +1 +1
+~ +1 +~ +~
+~ +1 +~ +1 +1 +1 +1 +t
+~ +1 +l +~
Q "O
8
"7-,
o
r~ "O
[-
"O
g, ,.-
t~
I +ll +J+~+l+l
+~+~+t+t
e.,
e-,
_=_= ,It.
+--
Separation of nuclear reaction products vi
4,xIO 4
rO T
C
i x ~
3xIO 4
.(2 rO
, ,
~tLl '~ ~
2xlO 4
iO 4
17
T
- <22 I
I O0
[
200
Energy,
I
500
500
400
keY
Fig. 2. Gamma ray spectra taken with N 2 (lower curve) and with N2/O 2 (98/2 per cent) (upper curve); transfer tube at 200°C, cooling trap at 0°C. 3. DISCUSSION OF THE RESULTS In recent publications[4--6] it has been found that some of the 252Cf recoil products are transported in an inert gas stream. Under the conditions used in these experiments Xe, I, and Te were measured in the trap. Only a minor fraction of Tc (Fig. 5, dashed line) was transported with N 2. When 02 is added to the inert gas I, Te, Tc, Ru and Rh lines are measured in the cooling trap. In this study only the transportation of Tc will be discussed. No gamma lines of Mo isotopes could be found so that the precursor could be excluded and a true transportation of Tc was secured. Figure 2 shows in the lower part the spectrum with inert gas and in the upper part the spectrum after addition of 02. Figure 3 shows the Tc-transport as a function of the O2-concentration, which was varied between 2 and 50 per cent. (The temperature of the transfer tube was 200°C and the temperature of the cooling trap 0°C). No obvious dependence could be found in this range. Since this is valid for all To-nuclides studied, a further indication is given that a Mo-precursor is not involved in the transportation. Figure 4 shows the yield of Tc-nuclides as a function of the temperature of the cooling trap. The values at -40* are not really comparable since they were determined at a temperature of 400°C of the transfer tube and then corrected for a temperature of 200°C. The other values were determined at a temperature of 200°C in the transfer tube. The steep rise with decreasing temperature might be an indication that the technetium-species which has been formed is rather volatile.
~
bo~
Tc-104
m ~ ~ m
Tc-106
,%
5 x ' o'
o
~
O
~
o
/
~
T
c
-
Tc-108 Tc-I05
O
1
0
2
(xlO)
4 1 , . . . ~
ol
2
I
I
30 02 ,
T c -IO7 Tc-103
50
%
Fig. 3. Yield of Tc-nuclides as a function of the O2-concentration ; transfer tube at 200°C, cooling trap at 0°C. In Table 2 the melting points and boiling points of the known technetiumoxides are summarized. Tc20? is most volatile but an estimation of collision numbers shows that a formation of a species with two Tc-atoms is highly improbable. Sch/ifer[12] has found that in
18
K. B,%CHMANNand V. MATSCHOI3
2`5x'°°I
105 ~
%
/
X% I0
TC-1106
%,I
.c
`sx)o' o.,_
J/ / // / / ~ ' 1~ l T o~---~Z~. - f o 7 ''°5 ~Tc-103 --.L~'-°L-,
ii~//"
\ ~\
I
0
I00
200
300
Temp. of the ?ronsf. fube,
•%
Fig. 5. Yield of Tc-nuclides as a function of the temperature of the transfer tube (the dashed line represents the values for N2). ~,,Tc-107 ~
o
I -40
"o..
\\
rc0 T e m p . of t h e
,50 fronsf, tube,
I00 *C
Fig. 4. Yield of Tc-nuclides as a function of the temperature of the cooling trap. the transfer of Re or rheniumoxides the species ReO~ (OH) might play a part if traces of water are present. In most of our experiments H20 was not completely removed (the Nz contained 15 vpm H20), but in the experiments in which H 2 0 has been frozen out, the same yield of Tc was measured. Since even in these experiments enough water molecules might be present, the formation of TeO~ (OH) can not be excluded. It is possible that under the experimental conditions a rather unstable and volatile technetiumoxide is formed which is still unknown. Table 2. The melting points and boiling points of technetium oxides
Oxide
Melting point (°C)
Boiling point (°C)
Slightly volatile at 900°C TcO 3 The existence of TcO 3 is discussed. Tc20~ 119.5 310.6 slightly TcO3(OH ) volatile TcO 2
400 oC
Reference 9 11 9 10
When discussing the nature of the transported species it should always be kept in mind that the transportation is not a function of the volatility alone but also a function of the adsorption heat. The adsorption on 'clusters was excluded, since experiments with quartz wool lead to the same yields. In addition the higher temperature should destroy the clusters. Figure 5 shows the yield of Tc-nuclides as a function of the temperature of the transfer tube. The maximum yield at 200°C can be explained in the following way: The yield which is measured by the counter is the result of several factors governing the different steps in the process: 1. Reaction yield, 2. Transfer yield, 3. Condensation and adsorption yield in the cooling trap and 4. Detector yield (distance between the detector and the position of the nuclide in the cooling trap). Probably the transfer yield increases with increasing temperature in the tube because the adsorption decreases. On the other hand the species which are formed might be decomposed at higher temperatures thus leading to lower yields. A second explanation for the lower yields at higher temperatures might be a different temperature gradient in the cooling trap which results in a lower detector yield. A small change in the profile of the temperature may cause a large effect in the counting efficiency. Figures 4 and 5 show that f9 r a separation of Tcnuclides a temperature of 200°C in the transfer tube and low temperatures in the cooling trap are the optimum conditions as to the yield. When a high selectivity (high decontamination factor) is desired then a higher temperature in the cooling trap gives a better separation from iodine. The separation from Te is satisfactory with the transfer tube at 200°C, since Te is transferred
Separation of nuclear reaction products with maximum yield at higher temperatures. The separation from Ru and Rh will be discussed in a subsequent publication[13]. Zaitseva et al.[14] have investigated the separation of Re from Au-targets at about 1000°C. Therefore we shall extend our study to higher temperatures. A determination of the transfer yield of I°5Tc (using the 252-2 keV peak) showed that 50 per cent of the 1°5Tc, which is stopped in the gas flow, is transferred and then adsorbed in the cooling trap. The applied method is described by other authors[4]. It should be emphasized that a complete separation of a certain element is not always necessary when using the gas phase method since each gamma ray transition shows a characteristic "chemical and physical" behaviour (pattern) which can be used for its identification. The authors would like to thank the "Gesellschaft fiir Schwerionenforschung" for financial support. Acknowledgement
REFERENCES
1. 1. Zvara, Y. T. Chuburkov, T. S. Zvarova and R. Caletka, Jt Inst. nuel. Res. Dubna Report D6-3281 (1967).
19
2. Y. T. Chuburkov, I. Zvara and B. V. Shilov, Jt Inst. nucl. Res. Dubna Report P7-4021 (1968). 3. 1. Zvara, Y. T. Chuburkov, R. Caletka and M. R. Shalaevskii, Jt Inst. nucl. Res. Dubna Report P7-3763 (1968). 4. W. Bfgl, K. B~ichmann, K. Biittner and N. Moheit, lnorg, nucl. Chem. Lett. 9, 405 (1973). 5. W. BSgl, K. B~ichmann and K. BiJttner, Radiochim. Acta. To be published. 6. K. B/ichmann, W. B6gl and K. BiJttner, Z. analyt. Chem. 267, 274 (1973). 7. K. B/ichmann, W. B6gl, W. Bfittner, M. Gebhardt, G. Helas, P. Hoffmann, H. Klenk, H. Klonk, R. Lauer, K. H. Lieser, V. MatschoB, B. Neidhart, A. Rosenberg, H. P. Sahner, B. Stojanik and W. Trautmann, GSIReport 73-14, 98 (1973). 8. F. F. Hopkins, J. R. White, G. W. Phillips, C. F. Moore and P. Richard, Phys. Rev. C5, 1015 (1972). 9. S. Tribalat, Rhenium et Technetium, pp. 154-158. Gauthier-Villars, Paris (1957). 10. K. Schwochau, Angew. Chem. inter, ed. 76, 9 (1964). 11. R. D. Peacock, The Chemistry of Technetium and Rhenium, p. 27. Elsevier, Amsterdam, North Holland (1966). 12. H. Sch/ifer, Z. anorg, allg. Chem. 400, 253 (1973). 13. W. B6gl and K. B~chmann, To be published. 14. B. Bayar, I. Votsilka, N. G. Zaitseva and A. F. Novgorodov, JINR P12-7164, Dubna (1973).