Stck!' SECURITY INFORMATION 576?
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StCK!' SECURITY INFORMATION 576?: LOS ALAMOS SCIENTIFIC LABORATORY of the UNIVERSITY OF CALIFORNIA Report written: May 1953 1 his document consists of _23_ pages No. 2 ^ of 30 copies, Series A THE PREPARATION AND CRYSTAL STRUCTURE OF SOME INTERMBTALUC POLONIUM COMPOUNDS by ■ Willard G. Witte man Angelo L. Gtorgt t Dwayne T. Vlei_ CLASSIFICATION CANCELLED DATE----------- L-J tL r£J.- For I be Atomic Encigy Commission •14 & Chief, Declassification Branch0 ^ ^ _ 3 R E S T R I C DATA This document contains restricted data as the Atomic Energy Act of 1948. Its trans- mittal or the disclosure of Its contents In an to an unauthorised person Is prohibited. SECURITptFORMATION * ORMATION ABSTRACT A micro technique for the preparation of Inter metallic polonium compounds is described. Advantages of the technique are: 1. Polonium compounds can be prepared on a microgram scale and in a closed system. 2. Reaction temperatures can be se lected over a wide range. 3. The rate of reaction can be determined by gamma count ing. 4. The reaction product is formed in a quarts capillary of suitable dimensions for direct X-ray diffraction study. 5. The decomposition pressure of the compound can be determined as a function of temperature. 0. Stoichiometric ratios of the elements in the intermetallic compounds or solutions can be determined. Compounds of polonium with beryllium, calcium, magnesium, and nickel were p re pared by this technique ana their composition and crystal structure investigated by X-ray diffraction. The results obtained for the beryllium, calcium, and magnesium compounds are: o S Reaction Crystal Density, Compound Tem p., °C Form Type o «o<*> gm/cc BePo 600 cubic ZnS 5.838 a 0.006 7.31 CaPo 550 cubic NaCl 6.514 t 0.006 6.01 MgPo 450 hexagonal NIAs 4.345 t 0.010 7.077 i 0.020 6.72 Nickel and polonium apparently form compounds with a composition and a crystal struc ture which vary continuously between NlPo and NlPOg and between NIAs and Cd(OH)g structures, respectively. Attempts to correlate experimentally determined mole ratios and calculated lattice constants were unsuccessful. A sim ilar investigation of polonium with tantalum, wolfram, and molybdenum evidenced no reaction at 500°C. ^ ACKNOWLEDGMENT The authors are deeply grateful to W. H. Zacharlasen tor his assistance in determining the crystal structure of magnesium polonide. CONTENTS Abstract 3 Acknowledgment 3 1. Introduction 5 3. Experimental Procedure 6 3.1 Purification of Polonium 0 2.2 Preparation and Loading of Quarts Capillary 0 2.3 Heating the Quarts Capillary 8 2.4 Preparation of 8ample for Calorimetry and X-ray Analysis 12 3.5 Calorimetry 12 3.6 X-ray Diffraction Procedures 13 3. Preparation of Individual Samples 13 3.1 Beryllium Polonlde 13 3.3 Calcium Polonlde 13 3.3 Magnesium Polonlde 13 3.4 Magnesium Teliurlde 13 3.8 Nickel Polonlde 13 3.0 Wolfram, Molybdenum, and Tantalum 14 4. X-ray Diffraction Results 14 4.1 Beryllium Polonlde (BePo) 14 4.2 Calcium Polonlde (CaPo) 17 4.3 Magnesium Polonlde (MgPo) 18 4.4 Nickel Polonlde (NlPo) 21 5. Conclusion 22 0. References 23 $E(tf I. Introduction Little Is known concerning high temperature reactions oi polonium metal with other metals. The early literature on this phase of polonium chemistry contains only fragmentary information of doubtful significance. More recently, in an Investigation of the action of mol* tea polonium on gold, platinum, nickel, and tantalum surfaces, Witte man and Vler* found tvi dance of compound or alloy formation with the first three metals, but found no reaction with tantalum. In addition, Goode2 has reported the preparation and Identification of tine polonide (ZnPo), lead polonide (PbPo), sodium polontde (Na^Po), platinum polonldt (PtPoj), and nickel polonide (NlPo). The reaction of polonium with nickel, beryllium, tantalum, wolfram, molybdenum, mag nesium, and calcium Is described below. The reactions of polonium with nickel and beryllium were chosen since neutron sources manufactured by this laboratory are almost exclusively polonium-beryllium sources In all-nickel containers. Tantalum, wolfram, and molybdenum were selected for Investigation in a search for metals that could be used with polonium at high temperatures without reaction. The complete absence of reaction found with these metals indicates thetr usefulness at high temperatures and suggests that polonium deposits can be recovered most easily from them. The reactions with magnesium and calcium are among those which might be expected to lead to simple stable compounds with polonium. Savere limitations are imposed on experimental procedures that can be considered for 3 an investigation of high temperature reactions involving polonium metal. The high volatility and oxide-forming properties* of polonium metal require the reaction to be carried out In a closed system and either in an Inert atmosphere or in vacuum. The small quantities of polonium available, as well as the high specific alpha activity of polonium (32 curies of polonium weigh 7 mg and produce 1 watt of heat), exclude macro techniques. Finally, the radioactive decay of polonium to form lead at a rate of 1/2% per day^ requires both s purification of the polonium Immediately before use and a short period of Investigation with a particular sample. Because of these limitations, a method for studying these reactions was developed S te m SfCUKilY ItfOUWiON which take* advantage of the high vapor pressure of polonium metal. The method Is de scribed la some detail sloe# It offers a micro method for studying reactions with any element or compound which has a diffidently high vapor preasure. 3. Experimental Procedure The reaction chamber waa an evacuated and sealed quarts capillary with the metal to be investigated (referred to as "baa? metal" In subsequent discussion) In one end of the capillary and with a relatively large excess of freshly purified polonium metal In the other. The quarts capillary was positioned within a split furnace that maintained the base metal end of the cap illary at a temperature that was a selected number of degrees higher than the polonium end. Thus, the bane metal was exposed to polonium vapor at a pressure corresponding to the vapor pressure of polonium st the temperature of the colder end of the furnace and was fret of excels polonium. The reaction between the base metal and polonium was conveniently followed by count ing the gamma rays originating at the base metal end of the capillary. For this purpose, a Stllbene type scintillation gamma counter was used with a lead silt system (3/4" wide—6" long hole) which permitted the crystal to "see" only the base metal end of the capillary. Completion of the reaction was assumed when the gamma count reached a constant maximum value. Finally, the base metal end of the capillary was sealed off, and the sample obtained was cilorlmetered to determine the polonium content and was identified by X-ray diffraction photographs. 3.1 Purification of Polonium Polonium Is received by thie laboratory a t a metallic deposit on platinum gauxe. In this form, the polonium contains varying amounts of lead and, possibly, bismuth. The polo nium purification procedure consisted of the following steps:* a. The polonium was distilled from the platinum gauze onto a glass surface where it waa deposited as a polonium mirror. b. The polonium mirror waa dissolved In 15 ml of 7.8 N ftNO., and diluted to 78 ml 3 3 volume, and the polonium electroplated on a tantalum foil (0.010" thick). c. The polonium metal was distilled from the tantalum foil Into the quartz reaction chamber. 3.2 Preparation and Loading of Quarts Capillary The quarts capillary apparatus Is illustrated in the line drawing of Fig. 1. - 6 - StCREl The procedure for the preparation and loading of the capillary follows. a. Quarts tubing (3 to 4 mm I.D .) was cleaned, drawn Into a capillary (A), and scaled b. From 0.2 to 0.0 micromole of the base metal was weighed (or the weight obtained by using a known length of wire of known weight per unit length) and was placed at the ex treme end of the capillary at point (0 ). c. The tantalum foil (C) containing the polonium deposit was placed in the quarts tube. d. By use of Tygon tubing, the quarts tube was attached to a vacuum line and evacu ated to a pressure of less than 10'* mm of lig for a period of 1 hour. The quarts was then flame-sealed above the tantalum foil at point (D). e. The quartz clumber was wrapped in glass wool and placed in a horizontal chamber so that the capillary end extended approximately 1-1/4" beyond the edge of the furnace. The furnace was heated to 400°C for 18 hours. The temperature gradient caused the polonium to migrate and deposit as a narrow band ( F ) In the capillary. f. By means of a small flame, the capillary was separated from the tube at a point (G) between the polonium and the tantalum foil. 2.3 Heating the Quartz Capillary The capillary was positioned and heated within the capillary well of a "differential tem perature" furnace. The furnace asse '.bly was constructed In such a manner that a tempera ture differential at the extreme ends of the capillary could be maintained and controlled. Figure 2 Is a cross-sectional drawing showing the details of the furnace and its position relative to the scintillation counter. 2.3.1 Differential Temperature Furnace. A drawing giving the dimensions of the stain less steel furnace Is given in Fig. 3. A photograph Is also included (Fig. 4) which Illustrates the disassembled and assembled views of the fumace.