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Promethium polonide synthesis and characterization
J. inorg, nucl. Chem., 1970, Vol. 32, pp. 2911 to 2918.
Pergamon Pres~.
Printed in Great Britain
PROMETHIUM POLONIDE SYNTHESIS AND CHARACTERIZATION C. J. KERSHNER and R. J. DESANDO Monsanto Research Corporation, Mound Laboratory*. Miamisburg, Ohio 45342 (Received 11 February 1970)
Abstract-Promethium pol0nide was prepared by reacting '4rpm metal with gaseous ~mpo. The compound formed was assigned the 1 : 1 stoichiometry on the basis of calorimetric and X-ray analyses. The compound melted at 1292_+25°C and possessed a BI sodium chloride type structure with an a0 = 6.360 _+0'012A and a calculated density of 9-61 g/cm3. The observed melting point and structural properties of PmPo agreed with the expected values based on the trends within the series of previously studied rare earth polonides. INTRODUCTION THE PREPARATION a n d c h a r a c t e r i z a t i o n of c o m p o u n d s f o r m e d b e t w e e n p o l o n i u m a n d rare earth m e t a l s h a v e b e e n e x p l o r e d for all the rare e a r t h series e x c e p t p r o m e t h i u m ( e l e m e n t 61)[1]. P r o m e t h i u m was o m i t t e d f r o m the initial rare earth p o i o n i d e w o r k d u e to the difficulties a s s o c i a t e d with o b t a i n i n g sufficient q u a n t i t i e s of this n o n - n a t u r a l - o c c u r r i n g e l e m e n t in a high purity metallic f o r m suitable for r e a c t i o n with p o l o n i u m . H o w e v e r , ion e x c h a n g e t e c h n i q u e s are n o w well develo p e d for isolating large q u a n t i t i e s of '47pm from fission p r o d u c t w a s t e s , a n d t47pm c a n be o b t a i n e d in high c h e m i c a l a n d isotopic p u r i t y [ 2 ] . A m e t h o d for p r e p a r i n g metallic p r o m e t h i u m in milligram q u a n t i t i e s has also b e e n d e v e l o p e d , thus p r o v i d i n g the n e c e s s a r y i n g r e d i e n t to e x t e n d the p o l o n i d e studies to i n c l u d e p r o m e t h i u m [3]. T h e w o r k to be d i s c u s s e d was c a r r i e d out with the i n t e n t of c o m p l e t i n g the initial i n v e s t i g a t i o n of the series of rare earth p o l o n i d e s - specifically their m e l t i n g points and their X - r a y diffraction c h a r a c t e r i s t i c s . EXPERIMENTAL The ~TPm was obtained from Oak Ridge National Laboratory, Oak Ridge, Tennessee, as the sesquioxide with a 657 Ci/g value on the shipping date. The '-'"~Pometal was obtained from inventory at Mound Laboratory and was greater than 95 per cent pure. with tellurium and oxygen as the major impurities. Reagent grade chemicals were used in the anhydrous halide and reduction steps. In preparation for the reaction with polonium, milligram quantities of promethium metal were prepared by lithium reduction of anhydrous promethium chloride. The technique and apparatus used for these chloride reductions were similar to those employed by Weigel in his promethium fluoride ~Mound Laboratory is operated by Monsanto Research Corporation for the U.S. Atomic Energy Commission under Contract No. AT-33-1-GEN-53. I. C. J. Kershner, R. J. DeSando, R. F. Heidelberg and R. H Steinmeyer, J. inorg, nucl. Chem. 28, 1581 (1966). 2. E. J. Wheelwright et al., Ion-Exchange Separation ~ff"Killocude Quantities ~ff"High P,rity Promethiam. BNWL-318 (December, 1966). 3. F. Weigel, Preparation and Properties o f Promethium and Some o f Its Compounds, Presented at the Fifth Rare Earth Conference. Iowa State University, Ames. Iowa (August 30-3 I, September I, 1965). 291 I
2912
C.J.
K E R S H N E R and R. J. D E S A N D O
reduction studies [3]. During three reduction experiments with NdCI3 as a nonradioactive substitute, refinements were made in the technique and apparatus that resu}ted in the capability of preparing 100 mg batches of metal in greater than 90 per cent yield with lithium and chlorine contents of less than 100 ppm each. The apparatus and technique used in the anhydrous promethium chloride preparations was a modification to milligram quantities of that technique described by Taylor for anhydrous rare earth chlorides in general[4]. Product yields from this technique are generally low, due to entrainment and carry-over of the rare earth chlorides with the subliming ammonium chloride. Although the rare earth was not lost and could be readily recovered, it was desirable to minimize these losses when working with milligram quantities of a radioactive species. Thus, a vertical entrainment trap and gravity refluxer were employed and found to work quite well. The vacuum sublimation and reduction apparatuses are shown in Figs. 1 and 2, respectively. Approximately lg batches of anhydrous promethium chloride were prepared by dissolving the promethium sesquioxide with 1g NH4CI in concentrated hydrochloric acid and evaporating the mixture to dryness on a hot plate. The residue was transferred to the vacuum sublimation apparatus, the apparatus was connected to a vacuum system, and the sample was pumped on for 16 hr to remove the last traces of unbound water. The final dehydration of the promethium chloride and sublimation
To vacuum system ( < i0 -z tarr)
Vacuum stopcock
24/40 Joint
IO in.
trap
Pyrex vessel
Tube furnace
Sample
vial
Fig. 1. Sublimation apparatus for anhydrous PmCIa preparation. 4. M. D. Taylor, Chem. Rev. 62,503 (1962).
Promethium polonide synthesis
2913
To vacuum system (< IO-4 torr)
~
f~--- Vacuum stopcock
24/40 Joint
Quartz vessel
Thermocouple Tube furnace Loose-fitting lid Tantalum reduction tube (5/8 in o.d. x I/ in. high) Tantotum wire basket for PmCI3 Reductant (Li metal)
Fig, 2. Promethium reduction apparatus.
of the excess ammonium chloride was accomplished by heating the sample under 10 -2 torr pressure. A 3 hr period was allowed for heating up to 350°C with an additional 4 hr at 350°C to remove all of the ammonium chloride. The product was weighed in a dry argon atmosphere and the 14rpm content determined by calorimetry. Batches of 50-100 mg of promethium metal were prepared by loading the corresponding quantity of the anhydrous chloride into the reduction basket with approximately 75 mg of lithium metal placed at the bottom of the reduction tube as shown in Fig. 2. The quarlz reduction vessel was evacuated to < 1 0 -.4 torr pressure, and the reduction was initiated by allowing the furnace temperature to rise slowly at an approximate rate of 40°C/min. When the furnace temperature reached 1000°C, the reduction assembly was withdrawn and allowed to cool to room temperature before it was opened. The product was a silver-coloured deposit between the wires of the tantalum reduction basket. Yield and purity calculations were based on weight and calorimetric measurements on the products. The polonides were prepared by heating the wire basket containing the promethium metal with polonium metal in compartmented, sealed reaction tubes using the procedure and apparatus previously described for the other rare earth polonide synthesis[l]. The promethium polonide reactions were carried out by heating the reactants for 2 hr at 850°C. A 50 per cent excess of polonium for the 1 : 1 compound was used. The unreacted polonium was distilled from the reaction chamber prior to isolating and calorimetering the product. Polonium-to-promethium ratios in the product were deter mined from calorimetry values on the promethium metal before reaction and the product. All work with the highly fl-active '4rPm and a-active e")Po was carried out in sealed gloveboxes. In addition, the
2914
C.J.
K E R S H N E R and R, J. D E S A N D O
handling of the anhydrous PmC13, the promethium metal and the PmPo reaction product was carded out in an argon atmosphere maintained at < 100 ppm oxygen and water vapor content by a molecular sieve dryer and regenerative oxygen removal unit. During the work it became necessary to enrich the 147pm stock to maintain a comparable isotopic content in the reaction products. This was accomplished by employing the cation exchange technique developed by Wheelwright et al. [2]. The exchange columns were sized to accommodate approximately 500 mg of rare earth with an elution column equivalent to two band lengths. The exchange conditions are shown in Table 1. An approximate 80 per cent center cut of the promethium band effluent solution was collected. The promethium was precipitated and collected as the oxalate, converted to the oxide by pyrolysis and then converted to the anhydrous chloride as previously described. Table 1. 147pm/1475mcation exchange parameters Resin Eluting agent Barrier ion Degassing column Feed column Elution column Temp. Eluant flow rate
Dowex 50W-X4 (50-100 mesh) D T P A (0.050 M; pH 6) erbium I I 1 10 mm i.d.; 9.6 m-equiv. 10 mm i.d.; 13-2 m-equiv. 6 mm i.d.; 16-8 m-equiv. 50°C 1 ml per rain.
Melting point determinations were carded out on approximately 100-mg samples of PmPo by a thermal analysis technique developed by Matson [5]. The thermal analysis apparatus shown in Fig. 3 consisted of a quartz vacuum chamber with a kin. quartz window, a radiation pyrometer (Land Model RN6), a d.c. null detector (Leeds & Northrup Model 9834-2) an optical pyrometer (Pyro Micro-Optical) and an X - Y recorder (Moseley 135A). The sample container was a sealed 0.020 in. wall tantalum can, 0.600 in, high, and 0.250 in. in dia. The bottom end cap was 0-010 in. thick, and the top cap was 0-020 in thick. A Ther-Monic Model 300A, 3-kw radiofrequency generator was used to heat the sample. The radiation pyrometer and prism holder were mounted on a hinged assembly so that either could be alternately focused on the sample without disturbing the optical alignment of the other. Cooling curves were carried out by heating the sample to a designated point above the melting point and recording the temperature-time curves for an incremental lowering of the heater power. The recording pyrometer spans were calibrated with the optical pyrometer. Window and pyrometer corrections were obtained from curves prepared by calibrations with a National Bureau of Standards Certified ribbon filament strip lamp. Emissivity corrections were made by reference to a dummy sample can with a blackbody hole. In the 1000-1600°C temperature range and with the size of sample cell described, well-defined reproducible plateaus could be detected for melting transitions in samples as small as 50 rag. The precision between runs with the same sample was found to be better than _+ 10°C. Experiments with nonradioactive material such as gadolinium, dysprosium and yttrium metals revealed that a +_25°C accuracy could be obtained with this technique and apparatus. Samples of PmPo were ground in an agate mortar and loaded into degassed quartz capillaries with 0.3 mm inner diameters and 0.03 mm wall thicknesses. X-ray diffraction patterns were obtained with M o K a radiation using aluminum foil in front of the film to reduce the background from the high E-active 147pm. The X-ray powder diffraction data were reduced with a full matrix least-squares program [6]. DISCUSSION Three batches of promethium metal were prepared- two of which were used for polonide syntheses; the third was used for X-ray structural analysis of the 5. L. K. Matson, J. D. Hastings and C. J. Kershner, A Study of Some (Gd or Dy) (Pb or Sn)x (Te, Se, or Po)l-~ Alloys. Presented at the Seventh Rare Earth Research Conference, Coronado, California (October 28-30, 1968). 6. D. E. Williams, Lattice Constant Refinement Program-2. USAEC Rep. I. S.-1052 (1964).
2915
P r o m e t h i u m polonide synthesis
~
~
uartz chamber RF"
i
',
~
col,
To < IO-5 torr vacuum
; i ~"---'~ -,'- ---,' ~ -
O-ring seals Stainless steel base Quartz window Gloveba,
,~--~!
~-
I I
I i
i
i ~
.do,
Quartz window Radiation pyrometer
"----4'
I~IVI
1 [:c nu de,ec,o,
x y,eco,de, I
Fig. 3. Thermal analysis apparatus.
metal. The yields and calculated isotopic and chemical purities of these samples are shown in Table 2. Two batches of promethium polonide were synthesized and their melting points determined. The product data and melting points for these two synthesis batches are given in Table 3. The observed thermal arrests were ascribed to melting transitions on the basis that they were the only detectable transitions in the 1000-1600°C temperature range where from previous rare earth polonide melting data[l] one would expect the promethium compound to melt. Table 2. 147pm metal preparations Batch No.
~ Yield
Quantity (mg)
Isotopic purity ~'
0it Chemical purityt
1 2 3
93 97 91
70 72 93
74 85 85
83 > 99 > 99
*On preparation date. ?Total rare earth is a s s u m e d to be ~47pmand its decay product t47Sm"
2916
C . J . K E R S H N E R and R. J, D E S A N D O Table 3. Promethium polonide synthesis data and melting points 147pm Synthesis No.
metal batch No.
21°Po/ '47R.E.*T
~l°Po/ 147Pmf
M.P. (-+ 25°C)
1 2
1 2
1.00 0-86
1,35 1.02
1293 1290
*On date of synthesis. TThe daughter product of 14rPm is 147Sm and will also yield polonide.
The PmPo samples were found to be monophase and possess the BI sodium chloride type structure. The lattice parameter ao and the calculated density were found to be 6.360 +__0.012,~ and 9.61 g/cm 3 respectively. As shown in Table 4, satisfactory agreement was obtained between observed and calculated intensities (excluding absorption and temperature factor corrections). Table 4. Diffraction datafor PmPo (MoK~) sinZ0ob~ sin20cal
h2+k2+l 2
3 4 8 11 12 16 20 24 27 36 40 44
0.0130 0,0247 0,0389 0.0511 0.0733 0.0837 0-1275 0-1407
0-0094 0.0125 0.0250 0.0343 0.0375 0.0499 0.0624 0.0749 0.0843 0.1124 0.1249 0.1373
Iobs
vs s M M M M M M
Ical 3 100 80 < 1 31 15 < 1 38 30 < 1 18 21
A radial distribution curve was computed using the relation [7]: rD(r) a ~ exp ( - BS~ z) sin 2Ir (r[d~) J
where B is the temperature factor coefficient, and exp(-BS~ 2) is a convergence factor introduced in order to decrease spurious detail in the computed radial distribution function which would result from the data existing only to some finite value [8] of S [in this work B was chosen such that exp(-- BS~max) = O" 1] : Sj = (4~" sin 0j)/X = 2~'d~
with dj being the interplanar spacing of the jth Bragg peak. The rD(r) vs, radial distance curve for PmPo is shown in Fig. 4. The salient features of this curve 7. A. F. Berndt, U S A E C Rep. ANL-FGF-360 (June 25, 1962). 8. J. Waser and V. Schomaker, Rev. mod. Phys. 25, 671 (1953).
Promethium polonide synthesis
2917
Po - Po 5OO 4OO
d
300 200 "C g3
~rn-Po
~Po
I00 0 I00
\J
2OO
~ Ix,
- -
V
/
P o - Po
r
V
300 4OO 5
6
Radial distance
,
Fig. 4. Radial distribution curve for PmPo.
I j
6. 8 0 0
• •
6,700
!
Rare earth polonides__ Rare earth tellurides
I
6.600
/ //
6-500 o<
E 6-400
8 _J
\
/
! ! I
6.300
i
,
\
\
% "%1
,:/I
6 200
\
6-IO0
6.000 I 58
Lo
Ce
60
Pr
Nd
62
Pm
Sm
64
Eu Rare
Gd
66
Tb
Dy
68
Ha
Er
TO
Tm
earth
Fig. 5. Lattice constants for B1 type rare earth compounds.
Yb
Lu
2918
C. J. KERSHNER and R. J. DESANDO
are the nearest P m - P o distances at 3-16A, the octahedral edge distance at approximately 4.28,~, the corner to center separation at 5.17,~ and the unit cell distance at 6.27A. T h e s e distances are in good a g r e e m e n t with those obtained f r o m the cell parameters. T h e lattice constant of P m P o is that e x p e c t e d on the basis of the variation of lattice constants with atomic n u m b e r (Fig. 5) for the rare earth polonides and the corresponding rare earth tellurides [9]. T h e lattice constant of P m P o lies on the extrapolated line for the 3 + type rare earths in Fig. 4 and thus p r o m e t h i u m can be considered to have little or no divalent tendency. 9. K.A. Gschneider, Jr., In Rare EarthAlloys p. 375. Van Nostrand, New York (1961).
Pergamon Pres~.
Printed in Great Britain
PROMETHIUM POLONIDE SYNTHESIS AND CHARACTERIZATION C. J. KERSHNER and R. J. DESANDO Monsanto Research Corporation, Mound Laboratory*. Miamisburg, Ohio 45342 (Received 11 February 1970)
Abstract-Promethium pol0nide was prepared by reacting '4rpm metal with gaseous ~mpo. The compound formed was assigned the 1 : 1 stoichiometry on the basis of calorimetric and X-ray analyses. The compound melted at 1292_+25°C and possessed a BI sodium chloride type structure with an a0 = 6.360 _+0'012A and a calculated density of 9-61 g/cm3. The observed melting point and structural properties of PmPo agreed with the expected values based on the trends within the series of previously studied rare earth polonides. INTRODUCTION THE PREPARATION a n d c h a r a c t e r i z a t i o n of c o m p o u n d s f o r m e d b e t w e e n p o l o n i u m a n d rare earth m e t a l s h a v e b e e n e x p l o r e d for all the rare e a r t h series e x c e p t p r o m e t h i u m ( e l e m e n t 61)[1]. P r o m e t h i u m was o m i t t e d f r o m the initial rare earth p o i o n i d e w o r k d u e to the difficulties a s s o c i a t e d with o b t a i n i n g sufficient q u a n t i t i e s of this n o n - n a t u r a l - o c c u r r i n g e l e m e n t in a high purity metallic f o r m suitable for r e a c t i o n with p o l o n i u m . H o w e v e r , ion e x c h a n g e t e c h n i q u e s are n o w well develo p e d for isolating large q u a n t i t i e s of '47pm from fission p r o d u c t w a s t e s , a n d t47pm c a n be o b t a i n e d in high c h e m i c a l a n d isotopic p u r i t y [ 2 ] . A m e t h o d for p r e p a r i n g metallic p r o m e t h i u m in milligram q u a n t i t i e s has also b e e n d e v e l o p e d , thus p r o v i d i n g the n e c e s s a r y i n g r e d i e n t to e x t e n d the p o l o n i d e studies to i n c l u d e p r o m e t h i u m [3]. T h e w o r k to be d i s c u s s e d was c a r r i e d out with the i n t e n t of c o m p l e t i n g the initial i n v e s t i g a t i o n of the series of rare earth p o l o n i d e s - specifically their m e l t i n g points and their X - r a y diffraction c h a r a c t e r i s t i c s . EXPERIMENTAL The ~TPm was obtained from Oak Ridge National Laboratory, Oak Ridge, Tennessee, as the sesquioxide with a 657 Ci/g value on the shipping date. The '-'"~Pometal was obtained from inventory at Mound Laboratory and was greater than 95 per cent pure. with tellurium and oxygen as the major impurities. Reagent grade chemicals were used in the anhydrous halide and reduction steps. In preparation for the reaction with polonium, milligram quantities of promethium metal were prepared by lithium reduction of anhydrous promethium chloride. The technique and apparatus used for these chloride reductions were similar to those employed by Weigel in his promethium fluoride ~Mound Laboratory is operated by Monsanto Research Corporation for the U.S. Atomic Energy Commission under Contract No. AT-33-1-GEN-53. I. C. J. Kershner, R. J. DeSando, R. F. Heidelberg and R. H Steinmeyer, J. inorg, nucl. Chem. 28, 1581 (1966). 2. E. J. Wheelwright et al., Ion-Exchange Separation ~ff"Killocude Quantities ~ff"High P,rity Promethiam. BNWL-318 (December, 1966). 3. F. Weigel, Preparation and Properties o f Promethium and Some o f Its Compounds, Presented at the Fifth Rare Earth Conference. Iowa State University, Ames. Iowa (August 30-3 I, September I, 1965). 291 I
2912
C.J.
K E R S H N E R and R. J. D E S A N D O
reduction studies [3]. During three reduction experiments with NdCI3 as a nonradioactive substitute, refinements were made in the technique and apparatus that resu}ted in the capability of preparing 100 mg batches of metal in greater than 90 per cent yield with lithium and chlorine contents of less than 100 ppm each. The apparatus and technique used in the anhydrous promethium chloride preparations was a modification to milligram quantities of that technique described by Taylor for anhydrous rare earth chlorides in general[4]. Product yields from this technique are generally low, due to entrainment and carry-over of the rare earth chlorides with the subliming ammonium chloride. Although the rare earth was not lost and could be readily recovered, it was desirable to minimize these losses when working with milligram quantities of a radioactive species. Thus, a vertical entrainment trap and gravity refluxer were employed and found to work quite well. The vacuum sublimation and reduction apparatuses are shown in Figs. 1 and 2, respectively. Approximately lg batches of anhydrous promethium chloride were prepared by dissolving the promethium sesquioxide with 1g NH4CI in concentrated hydrochloric acid and evaporating the mixture to dryness on a hot plate. The residue was transferred to the vacuum sublimation apparatus, the apparatus was connected to a vacuum system, and the sample was pumped on for 16 hr to remove the last traces of unbound water. The final dehydration of the promethium chloride and sublimation
To vacuum system ( < i0 -z tarr)
Vacuum stopcock
24/40 Joint
IO in.
trap
Pyrex vessel
Tube furnace
Sample
vial
Fig. 1. Sublimation apparatus for anhydrous PmCIa preparation. 4. M. D. Taylor, Chem. Rev. 62,503 (1962).
Promethium polonide synthesis
2913
To vacuum system (< IO-4 torr)
~
f~--- Vacuum stopcock
24/40 Joint
Quartz vessel
Thermocouple Tube furnace Loose-fitting lid Tantalum reduction tube (5/8 in o.d. x I/ in. high) Tantotum wire basket for PmCI3 Reductant (Li metal)
Fig, 2. Promethium reduction apparatus.
of the excess ammonium chloride was accomplished by heating the sample under 10 -2 torr pressure. A 3 hr period was allowed for heating up to 350°C with an additional 4 hr at 350°C to remove all of the ammonium chloride. The product was weighed in a dry argon atmosphere and the 14rpm content determined by calorimetry. Batches of 50-100 mg of promethium metal were prepared by loading the corresponding quantity of the anhydrous chloride into the reduction basket with approximately 75 mg of lithium metal placed at the bottom of the reduction tube as shown in Fig. 2. The quarlz reduction vessel was evacuated to < 1 0 -.4 torr pressure, and the reduction was initiated by allowing the furnace temperature to rise slowly at an approximate rate of 40°C/min. When the furnace temperature reached 1000°C, the reduction assembly was withdrawn and allowed to cool to room temperature before it was opened. The product was a silver-coloured deposit between the wires of the tantalum reduction basket. Yield and purity calculations were based on weight and calorimetric measurements on the products. The polonides were prepared by heating the wire basket containing the promethium metal with polonium metal in compartmented, sealed reaction tubes using the procedure and apparatus previously described for the other rare earth polonide synthesis[l]. The promethium polonide reactions were carried out by heating the reactants for 2 hr at 850°C. A 50 per cent excess of polonium for the 1 : 1 compound was used. The unreacted polonium was distilled from the reaction chamber prior to isolating and calorimetering the product. Polonium-to-promethium ratios in the product were deter mined from calorimetry values on the promethium metal before reaction and the product. All work with the highly fl-active '4rPm and a-active e")Po was carried out in sealed gloveboxes. In addition, the
2914
C.J.
K E R S H N E R and R, J. D E S A N D O
handling of the anhydrous PmC13, the promethium metal and the PmPo reaction product was carded out in an argon atmosphere maintained at < 100 ppm oxygen and water vapor content by a molecular sieve dryer and regenerative oxygen removal unit. During the work it became necessary to enrich the 147pm stock to maintain a comparable isotopic content in the reaction products. This was accomplished by employing the cation exchange technique developed by Wheelwright et al. [2]. The exchange columns were sized to accommodate approximately 500 mg of rare earth with an elution column equivalent to two band lengths. The exchange conditions are shown in Table 1. An approximate 80 per cent center cut of the promethium band effluent solution was collected. The promethium was precipitated and collected as the oxalate, converted to the oxide by pyrolysis and then converted to the anhydrous chloride as previously described. Table 1. 147pm/1475mcation exchange parameters Resin Eluting agent Barrier ion Degassing column Feed column Elution column Temp. Eluant flow rate
Dowex 50W-X4 (50-100 mesh) D T P A (0.050 M; pH 6) erbium I I 1 10 mm i.d.; 9.6 m-equiv. 10 mm i.d.; 13-2 m-equiv. 6 mm i.d.; 16-8 m-equiv. 50°C 1 ml per rain.
Melting point determinations were carded out on approximately 100-mg samples of PmPo by a thermal analysis technique developed by Matson [5]. The thermal analysis apparatus shown in Fig. 3 consisted of a quartz vacuum chamber with a kin. quartz window, a radiation pyrometer (Land Model RN6), a d.c. null detector (Leeds & Northrup Model 9834-2) an optical pyrometer (Pyro Micro-Optical) and an X - Y recorder (Moseley 135A). The sample container was a sealed 0.020 in. wall tantalum can, 0.600 in, high, and 0.250 in. in dia. The bottom end cap was 0-010 in. thick, and the top cap was 0-020 in thick. A Ther-Monic Model 300A, 3-kw radiofrequency generator was used to heat the sample. The radiation pyrometer and prism holder were mounted on a hinged assembly so that either could be alternately focused on the sample without disturbing the optical alignment of the other. Cooling curves were carried out by heating the sample to a designated point above the melting point and recording the temperature-time curves for an incremental lowering of the heater power. The recording pyrometer spans were calibrated with the optical pyrometer. Window and pyrometer corrections were obtained from curves prepared by calibrations with a National Bureau of Standards Certified ribbon filament strip lamp. Emissivity corrections were made by reference to a dummy sample can with a blackbody hole. In the 1000-1600°C temperature range and with the size of sample cell described, well-defined reproducible plateaus could be detected for melting transitions in samples as small as 50 rag. The precision between runs with the same sample was found to be better than _+ 10°C. Experiments with nonradioactive material such as gadolinium, dysprosium and yttrium metals revealed that a +_25°C accuracy could be obtained with this technique and apparatus. Samples of PmPo were ground in an agate mortar and loaded into degassed quartz capillaries with 0.3 mm inner diameters and 0.03 mm wall thicknesses. X-ray diffraction patterns were obtained with M o K a radiation using aluminum foil in front of the film to reduce the background from the high E-active 147pm. The X-ray powder diffraction data were reduced with a full matrix least-squares program [6]. DISCUSSION Three batches of promethium metal were prepared- two of which were used for polonide syntheses; the third was used for X-ray structural analysis of the 5. L. K. Matson, J. D. Hastings and C. J. Kershner, A Study of Some (Gd or Dy) (Pb or Sn)x (Te, Se, or Po)l-~ Alloys. Presented at the Seventh Rare Earth Research Conference, Coronado, California (October 28-30, 1968). 6. D. E. Williams, Lattice Constant Refinement Program-2. USAEC Rep. I. S.-1052 (1964).
2915
P r o m e t h i u m polonide synthesis
~
~
uartz chamber RF"
i
',
~
col,
To < IO-5 torr vacuum
; i ~"---'~ -,'- ---,' ~ -
O-ring seals Stainless steel base Quartz window Gloveba,
,~--~!
~-
I I
I i
i
i ~
.do,
Quartz window Radiation pyrometer
"----4'
I~IVI
1 [:c nu de,ec,o,
x y,eco,de, I
Fig. 3. Thermal analysis apparatus.
metal. The yields and calculated isotopic and chemical purities of these samples are shown in Table 2. Two batches of promethium polonide were synthesized and their melting points determined. The product data and melting points for these two synthesis batches are given in Table 3. The observed thermal arrests were ascribed to melting transitions on the basis that they were the only detectable transitions in the 1000-1600°C temperature range where from previous rare earth polonide melting data[l] one would expect the promethium compound to melt. Table 2. 147pm metal preparations Batch No.
~ Yield
Quantity (mg)
Isotopic purity ~'
0it Chemical purityt
1 2 3
93 97 91
70 72 93
74 85 85
83 > 99 > 99
*On preparation date. ?Total rare earth is a s s u m e d to be ~47pmand its decay product t47Sm"
2916
C . J . K E R S H N E R and R. J, D E S A N D O Table 3. Promethium polonide synthesis data and melting points 147pm Synthesis No.
metal batch No.
21°Po/ '47R.E.*T
~l°Po/ 147Pmf
M.P. (-+ 25°C)
1 2
1 2
1.00 0-86
1,35 1.02
1293 1290
*On date of synthesis. TThe daughter product of 14rPm is 147Sm and will also yield polonide.
The PmPo samples were found to be monophase and possess the BI sodium chloride type structure. The lattice parameter ao and the calculated density were found to be 6.360 +__0.012,~ and 9.61 g/cm 3 respectively. As shown in Table 4, satisfactory agreement was obtained between observed and calculated intensities (excluding absorption and temperature factor corrections). Table 4. Diffraction datafor PmPo (MoK~) sinZ0ob~ sin20cal
h2+k2+l 2
3 4 8 11 12 16 20 24 27 36 40 44
0.0130 0,0247 0,0389 0.0511 0.0733 0.0837 0-1275 0-1407
0-0094 0.0125 0.0250 0.0343 0.0375 0.0499 0.0624 0.0749 0.0843 0.1124 0.1249 0.1373
Iobs
vs s M M M M M M
Ical 3 100 80 < 1 31 15 < 1 38 30 < 1 18 21
A radial distribution curve was computed using the relation [7]: rD(r) a ~ exp ( - BS~ z) sin 2Ir (r[d~) J
where B is the temperature factor coefficient, and exp(-BS~ 2) is a convergence factor introduced in order to decrease spurious detail in the computed radial distribution function which would result from the data existing only to some finite value [8] of S [in this work B was chosen such that exp(-- BS~max) = O" 1] : Sj = (4~" sin 0j)/X = 2~'d~
with dj being the interplanar spacing of the jth Bragg peak. The rD(r) vs, radial distance curve for PmPo is shown in Fig. 4. The salient features of this curve 7. A. F. Berndt, U S A E C Rep. ANL-FGF-360 (June 25, 1962). 8. J. Waser and V. Schomaker, Rev. mod. Phys. 25, 671 (1953).
Promethium polonide synthesis
2917
Po - Po 5OO 4OO
d
300 200 "C g3
~rn-Po
~Po
I00 0 I00
\J
2OO
~ Ix,
- -
V
/
P o - Po
r
V
300 4OO 5
6
Radial distance
,
Fig. 4. Radial distribution curve for PmPo.
I j
6. 8 0 0
• •
6,700
!
Rare earth polonides__ Rare earth tellurides
I
6.600
/ //
6-500 o<
E 6-400
8 _J
\
/
! ! I
6.300
i
,
\
\
% "%1
,:/I
6 200
\
6-IO0
6.000 I 58
Lo
Ce
60
Pr
Nd
62
Pm
Sm
64
Eu Rare
Gd
66
Tb
Dy
68
Ha
Er
TO
Tm
earth
Fig. 5. Lattice constants for B1 type rare earth compounds.
Yb
Lu
2918
C. J. KERSHNER and R. J. DESANDO
are the nearest P m - P o distances at 3-16A, the octahedral edge distance at approximately 4.28,~, the corner to center separation at 5.17,~ and the unit cell distance at 6.27A. T h e s e distances are in good a g r e e m e n t with those obtained f r o m the cell parameters. T h e lattice constant of P m P o is that e x p e c t e d on the basis of the variation of lattice constants with atomic n u m b e r (Fig. 5) for the rare earth polonides and the corresponding rare earth tellurides [9]. T h e lattice constant of P m P o lies on the extrapolated line for the 3 + type rare earths in Fig. 4 and thus p r o m e t h i u m can be considered to have little or no divalent tendency. 9. K.A. Gschneider, Jr., In Rare EarthAlloys p. 375. Van Nostrand, New York (1961).