The exchange of isotopically enriched oxygen with 238PuO2

886

Notes

washed twice with hot acetic acid-acetic anhydride mixtures. It was dried to constant weight in vacuo at room temperature over potassium hydroxide. At all stages of the preparation it was important to exclude light. The product is also hygroscopic and exposure to light or air should be as limited as possible. The synthesis can be scaled up and although a small amount of eerie acetate remains in solution close to quantitative yields are attainable. It can be recrystallized from acetic anhydride-acetic acid mixtures but in most cases it was unnecessary.

Analysis Elemental analysis. Calcd. for CeCsH1~08: C, 25-8; H, 3.22. Found: C, 24-87, 24.54; H, 3.18, 3" 19. Ceric(lV). Ceric acetate was dissolved in concentrated sulphuric acid, diluted with water and an aliquot of a standard solution of ferrous ammonium sulfate added. Phosphoric acid was added and the solution back-titrated with standard Ce(IV) solution to the ferrous phenanthroline end point. Acetic acid did not interfere. Acetate. Approximately 60 mg eerie acetate was dissolved in trifluoroacetic acid and 2 ml water. An aliquot of a standard aqueous solution of propionic acid was added, and the mixture analyzed by gas liquid chromatography (Varian Aerograph, Model 600 HiFy, hydrogen flame detector, 20 per cent F F A P on acid washed Chromosorb W 60/80), by the internal standard method with calibration curves for acetic acid-propionic acid mixtures. Over a broad range of concentrations, the amount of trifiuoroacetic acid used had no effect on the analysis. Magnetic moments were determined by the Guoy and Faraday methods using Co[Ha(SCN)4] as a standard[9, 10]. Reflectance spectra were recorded from 250-2500 ~ on a Beckman Ratio Recording Reflectance spectrophotometer.

Acknowledgement-We wish to thank the United States Air Force Office of Scientific Research for a generous grant which supported this work, and the American Potash and Chemical Co. for generous samples of cerous compounds.

Department of Chemistry Case Western Reserve University Cleveland, Ohio

N E L S O N E. H A Y J A Y K. K O C H I

9. B. Figgis and J. Lewis, Technique of Inorganic Chemistry (Edited by H. Jonassen and A. WeissbergerL Vol. IV, p. 137ff. Interscience, New York (1965); Modern Coordination Chemistry (Edited by J. Lewis and R. Wilkins), I nterscience, New York (1960). 10. We wish to thank Professor John Fackler for the use of this apparatus.

J. inorg,nucLChem., 1968,Vol.30. pp~886 to 890, PergamonPress Ltd. Printedin GreatBritain

The e x c h a n g e o f i s o t o p i c a l l y e n r i c h e d o x y g e n wiLh ~ u O ~ (First received 21 June 1967; in revised form 31 July 1967) THE NEUTRONS emitted from ~'~Pu metal which contains no light element impurities are produced by spontaneous fission at the approx rate of 2-5 x 10a n/see per g[1-3]. The neutron $enermion rate from ~aaPuO2 is much higher than the spontaneous fission value and is principally due to the (ix, n) reaction of ~ O and 1sO, with little or no yield from 1eO[4]. Normal ~sPuO~ contains 0.037% 170 and 0-204% 1sO 1. A. H. Jaffery and A. Hirsch, A.E,C. Research and Development Report, ANL-4286, Argonne National Laboratory, University of Chicago, Argonne, Illinois (May 12, 1949), 2. W. W. T. Crame, G. H. Higgins and H. R. Bowman, Phys. Rev. 101, 1804 (1956). 3. D . A . Hicks, J. Ise, Jr. and R. V. Pyle, Phys. Rev. 101, 1016 (1956), 4. V. Keshishian and K. M. Broom, Jr. A I - 6 5 - 1 9 0 , Vol 9, Atomics International, Canoga Park, Calif. (March 7, 1966).

Notes

887

and exhibits a neutron emission of approximately 1.9 × 10~ n/sec per g. These differences in the (a,n) reactions have been used to study the oxygen exchange between ~ P u O z and gaseous oxygen of various isotopic enrichments. EXPERIMENTAL A sample of 2ssPuO2 prepared by ignition of plutonium(Ill) oxalate in air for 1 hr at 700°C was used in the exchange studies. The sample contained the normal distribution of oxygen isotopes. Analytical data for the oxide are summarized in Table 1. Table 1. Composition of 238pu0~

Isotope ~3SPu ~Pu 24°pu ~41pu ~4~Pu

Concentration in total Pu (wt. %) 79-12 16.34 3.46 0.91 0.17

Element

Concentration in Pu02

Np Th U AI B Be Mg

0.29wt.% <0.08 wt.% <0.01 wt. % 29 ppm <1 ppm < 0.5 ppm < 10 ppm

A sample of oxygen enriched in leO was prepared at this laboratory and was found to contain by mass spectrometry only a trace of 170 and 0.01% 180. Samples of oxygen enriched in 1so were obtained from Isomet Corp. (48.5% 1sO and 4.12% 170) and from Volk Radiochemicai Co. (91.6% 1sO and 1.2% 170). Neutrons were counted with a precision long counter which uses a polyethylene moderated boron trifluoride proportional counter. The kinetic data were obtained by neutron counting with a series 9140, Texas Nuclear Corp, counter located outside the alpha glovebox in which the experiment was performed. The z3sPuO2 was weighed into a small quartz container, then heated in a quartz reaction chamber to the exchange temperature and outgassed under vacuum for I hr. Isotopically enriched oxygen was then allowed to pass into the evacuated chamber containing the sample. Samples for mass spectrometric analysis were collected at the end of the reaction. RESULTS Since the exchange reactions were carried out in a quartz system, three competing reactions were possible. These are illustrated below: (gas) 02

(solid) PuO~ . . . . Ili

= Si02 (solid).

Reaction II does not occur at temperatures up to 1050°C[5,6]. Comparison of results obtained with a platinum sample container with those obtained for a quartz sample container indicated that reaction III did not occur. 5. D . A . Hutchison, J. chem. Phys. 22, 758 (1954). 6. B.Z. Shakhashiri and G. Gordon, J. inorg, nucl. Chem. 27, 2161 (1965).

888

Notes

Several samples of ~'~PuOa were heated in an oxygen environment enriched in 1sO. Measurement of the change in neutron emission rate was used to follow the rate of oxygen exchange. Figure 1 shows a plot of neutron emission vs. time at 1050°C for an exchange reaction. Table 2 lists the analytical results of these exchange experiments. These reactions proceeded to equilibrium in 15 to 20 rain over a temperature range of 850-1050°C. The mass spectrometric analysis of the 1sO concentration in the gaseous phase after 1 hr agreed well with the theoretical concentration of 1sO predicted for an equilibrium reaction. 5000

4000 A --

A - -

.

W

_J

3000

d =~ 2000

1000

0

I

I

I

1

I

4

8

12 Time, rain

16

20

24

Fig. 1. Neutron counts as a function of 1sO exchange reaction time. Table 2. Enriched oxygen- 18 exchange data

Reaction temp. for 1 hr (°C)

Specific emission (n/see per g)

Total gas pressure (oxygen) (mm Hg)

1050 850 850

2.1 (---1%) × los 4.3 (__-1%) × los 3.3 (-4-1%) × 106

57 85 41

Experimental 180 concentration in the gas phase (%) -66 50

Theoretical 1sO concentration in the gas phase (% 32 66 50

The reaction was first-order with respect to the concentration of 1sO as indicated by a plot (Fig. 2) of log (lsOt-lsO®) vs. time, where 1sOt is the percentage 1~O in the gas phase at time t and 1~O= is the 180 content theoretically predicted for the gaseous phase at the equilibrium condition. Samples of normal 2~PuO~ were also introduced to an oxygen environment enriched in 180. These experiments were performed to show the effect of isotopic oxygen concentration on the reduction of the neutron emission from 2~PuO2. Table 3 lists the weight of 2-~PuO~ reacted, the specific neutron emission from the oxide and the theoretical percentage of 180 at equilibrium. The generation of neutrons from the oxide heated at 105OSC decreased from 1.94 × los n/see per g to 4.8 x l0 s n/see per g. Over a temperature range of 850"-1050°C essentially complete exchange was observed in the enriched 180 studies. For the depleted 1~) studies, however, impurities present in PuO~ which also

Notes

889

1.3

O eD

0.!

! ,....-

0.7

B

o --I

0.5-

0.3

I

I

I

I

I

2

4

6 Time, min

8

I0

12

Fig. 2. First order kinetics plot for exchange reaction at 1050°C.

Table 3. Enriched oxygen-16 exchange data Reaction temp. for 1 hr (°C)

Specific emission (x 103) (n/sec per g)

Total oxygen in mPuo2 (x 10-3) (g atom)

Total oxygen in gas phase (x 10-1) (g atom)

Theoretical % lqZ) at equilibrium (x 10-2)

1050 950 850 750 650 550 450

4.8 (-2%) 5.0 (-+2%) 5.4 (-+2%) 5.8 (--.2%) 7.6 (+-2%) 9.6 (-+2%) 13.6 ( - 1%)

4.272 3.606 4.014 3.232 3.434 3.314 3-752

1.956 1-956 1.956 1.956 1.956 1.956 1.956

1.35 1.28 I '32 1.24 1.27 1.25 1.30

undergo an (~, n) reaction cause a discrepancy between the theoretical rate and the experimental emission rate. DISCUSSION Several oxygen exchange studies have been reported for nonradioactive metal oxides [7-9]. These reactions generally proceed by a first-order mechanism as does the oxygen exchange with mPuOz. At temperatures of 850°C and above complete exchange reactions were observed in 15-20 rain. The exchange studies with enriched leO and mPuO2 indicated that a reduction in neutron generation is feasible. 7. J. Novakova, K. Klier and P. Jim, 5th International Symposium on the Reactivity of Solids, p. 269. Munich, (1964). 8. E. R. S. Winters,J. chem. Soc. 1170(1950). 9. G. Houghton and E. R. S. Winters, Nature. Lond. 164, 1130 (1949).

890

Notes

Acknowledgement-The author wishes to thank M. Edward Anderson of this laboratory for his assistance in obtaining neutron emission data. Monsanto Research Corporation Mound Laboratory* Miamisburg, Ohio

D O N A L D L. P L Y M A L E

*Mound Laboratory is operated by Monsanto Research Corporation for the Atomic Energy Commission.

J. inorg,nucl.Chem.. 1968,Vol.30. pp. 890 to 89I- PergamonPress Ltd. Printedin Great Britain

Existence of a 1 hr 129Sn isomer not confirmed (Received 20 July 1967) STUDIES of isotopes of tin and antimony in the 126-130 mass region were in 1962 reported by Hageb¢ et al.[ 1] and independently by Dropesky and Orth [2]. There is a general agreement between the results reported by the two groups with the exception of 129Sn. Here Hageb¢ et al.[ 1] report two isomers with half-lives (8.0 ± 0.6) min and ( 1 . 0 - 0 . 1 ) hr respectively, with the longer lived species in much lower abundance in fission than the short-lived one. Dropesky and Orth, however, and later Uhler et al.[3] did not observe the long-lived isomer. During an attempt to clear up this ambiguity the present authors found that the antimony milking procedure used by Hageb¢ et al. failed to give consistent results when a more elaborate analysis could be performed as a result of using targets enriched in 2asU. Therefore a different procedure was developed based on selective extraction of tintetrachloride into benzene [4, 5] with subsequent isolation of the granddaughter tellurium. No long-lived 12gSnactivity was then found. Thus after a careful reinvestigation the present authors, about two years ago, came to the conclusion that the 1 hr 129Sn isomer reported in [1] was an artifact most likely caused by an unknown irreproducible behaviour of tin and antimony due to an instability of the ether thiocyanate system[6] used for separation of these two elements. This together with the time conditions used and low active samples seem to have indicated a too-slow decrease of the amounts of ~gSb formed in some of the experiments. As has been realized by Hageb¢ et aL[ 1], the 1 hr ]2gSn isomer did not fit the systematics proposed by Anderson [7] where the logarithm of the half-life is plotted vs. mass number for a series of related isomers belonging to the same element. This plot instead indicates a half-life of about 2 min for an isomer of ngSn. Having shown the 1 hr isomer not to exist, the present authors wanted to test the above assumption, but had to await the completion of the new reactor J E E P II at JENER, Kjeller, where facilities for fast target handling would be available. Due, however, to unexpectedly long delay in the construction no further work on this problem has so far been possible. Recently Chu and Marinsky [8] have independently proved the non-existence o f a 1 hr l~Sn isomer, and they also report the discovery of the expected 2 min species. In order, however, definitely to rule out the 1 hr species and as one of the present authors (A.C.P.) also collaborated in [1], a brief account of the experiments referred to above should be justified. Moreover since Chu and Marinsky [8] performed their studies by milking antimony from tin while the present authors used the tellurium granddaughters in their study following a suggestion by Dr. E. Hageb¢. 1. 2. 3. 4. 5. 6. 7. 8.

E. Hageb~b, A. Kjelberg and A. C. Pappas, J. inorg, nucL Chem. 24, 117 (1962). B.J. Dropesky and C. J. Orth, J. inorg, nucl. Chem. 24, 1301 (1962). J. Uhler, G. H. Neumann, O. Melin and T. Alv~ger, Ark. Fy$. 21, 35 (! 962). D. D. Gilbert and E. B. Sandell, Microchem. J. 4, 491 (1960). D. D. Gilbert and E. B. Sandell, J. inorg, nucl. Chem.24, 989 (1962). R. Bock, Z. analyt. Chem. 113, 110 (1951 ). G. Andersson, Nucl. Phys.24, 666 (1961). P. Chu and J. A. Marinsky, J. inorg, nucl. Chem.28, 1339 (1966).