JANUARY, 1968 THE ANALYST Vol. 93, No. I 102 A Sequential Scheme for the Determination of Several Fall-out Nuclides in Water BY F. M. BATHIE AND B. A. BURDEN (Ministry of Technology, Laboratovy of the Government Chemist, Covnwall House, Stamford Street, London, S.E.1) A method is described for the sequential separation and measurement of fall-out nuclides of ruthenium, molybdenum, tellurium, antimony and tin in water. The nuclides, together with added carriers, are separated from 10 litres of sample by precipitation and solvent-extraction methods, and are counted on a low background anti-coincidence p-counter. Chemical recoveries of added carriers range from 46 per cent. for antimony to 66 per cent. for molybdenum. The limits of detection range from 0.02 to 0.08 pico- curies per litre.THIS paper describes a sequential separation scheme for the fall-out nuclides of ruthenium, molybdenum, tellurium, tin and antimony in a single sample of water. Several sequential schemes1 9293,4 have been published that deal with various combinations of fall-out nuclides, but do not include nuclides of tellurium, tin and antimony. The method by Osmond, Owers, Healy and Mead5 and Osmond, Evett, Arden, Lovett and Sweeny6 that deals with strontium, caesium, barium and cerium nuclides has been extended in this laboratory to include nuclides of manganese, zirconium, yttrium and rare earths.' This latter scheme, and the one described in this paper, thus provide a means of examining water for all of the fall-out nuclides with a half-life greater than about 3 days, except iodine-131 and silver-111.Several methods exist8 for determining any one of the five elements discussed in this paper, but the present method was developed primarily for use with drinking waters, in which the activities are very low. Large volumes of water are therefore required, and it is more convenient to use a sequential separation scheme. The volume of water that can be used is limited both by the hardness of the water and the volatility of ruthenium. Thus, evaporation of water under acidic conditions may lead to loss of ruthenium, and under alkaline conditions large amounts of water solids are precipitated, particularly from hard waters. It was found convenient to precipitate ruthenium from a 10-litre sample, and subsequently concentrate the supernatant liquid by evaporation before determining the other elements in the sequential scheme.EXPERIMENTAL An outline of the separation scheme is given in Fig. 1, but decontamination steps for individual nuclides are not shown; the numbers in parentheses are those referred to in the text. The 10 litres of water containing carriers for the five elements are treated with sodium hypochlorite solution to oxidise the ruthenium and ensure exchange between carrier and fall-out activity. Ruthenium is oxidised to perruthenate ion, Ru0,-, and possibly some ruthenate ion, RuO,2-. It is reduced to ruthenium(1V) by addition of ethanol and, on boiling the slightly alkaline solution, the flocculent hydroxide precipitates and settles out fairly rapidly, thus enabling the clear supernatant liquid to be siphoned off.With hard waters, some water solids will also be deposited at this stage, and may carry down some of the tellurium, antimony and tin; the precipitate will also contain any insoluble matter originally present in the sample. Rain water, for example, often contains organic and siliceous solids in suspension. This insoluble material accompanying the ruthenium hydroxide precipitate is rendered soluble by fusion with alkali, separated from the ruthenium, and returned to the main solution before the separation of the remaining four elements. The fusion converts the ruthenium to sodium ruthenate, which, although water-soluble, is easily reduced to the 0 SAC; Crown Copyright Reserved. 12 BATHIE AND BURDEN: A SEQUENTIAL SCHEME FOR THE [Auta&St, VOl.93 insoluble hydroxide. Ruthenium, therefore, appears in both the aqueous and acidic extracts of the fused melt, and is precipitated from both, as the hydroxide, and the precipitates are combined. Reduction to ruthenium metal with magnesium and acid effectively separates this element from tin and antimony, but some tellurium may still be associated with it. This is, however, separated in the next stage when ruthenium tetroxide is extracted with carbon tetrachloride. The ruthenium is finally precipitated as the metal with magnesium and acid for chemical-yield determination and counting. In an attempt to obtain more durable counting sources for ruthenium, some experiments were carried out on electroplating of this element from solutions of ruthenium nitrosyl ~hloride.~ Adherent and lustrous deposits were only obtained, however, when the thickness of the deposit was less than 1 mg per cm2; thicker deposits tended to flake off the cathode.The low background anti-coincidence counters in use in this laboratory can only accept sources of l-inch diameter, which limits the amount of carrier that can be used during the separation. The electroplating was, therefore, abandoned, but it may offer some advantages where a low-background counting system is available that will accept large area sources. The remaining four elements are separated after evaporating the acidified sample to a few hundred millilitres. Molybdenum is first precipitated with benzoin a-oxime, and is centrifuged, together with some water solids deposited during the evaporation. The insoluble material, which may contain some tin and antimony deposited during the evaporation, is rendered soluble by fusion with alkali and, after separation of molybdenum, is added to the main tin and antimony fraction.Molybdenum is re-precipitated with benzoin a-oxime, re-dissolved, and decontaminated by iron(II1) hydroxide scavenges. It is finally precipitated with 8-hydroxyquinoline for counting and chemical-yield determination. Tellurium is precipitated next by reduction to the metal with hydrazine and sulphur dioxide. The technique used for the decontamination of this element is basically that reported by Meinke.10 Tin and antimony are precipitated together as sulphides, and are decontaminated by two tellurium metal and two lead sulphide scavenges.These elements are separated by extracting the antimony into 2-ethylhexan-1-01 and light petroleum from concentrated hydrochloric acid, as described by Orlandini, Wahlgren and Barclay.ll In this extraction the antimony, after oxidation to the quinquivalent state, is extracted to better than 99 per cent. and tin is extracted to about 9 per cent. The contamination of the antimony by tin is reduced by washing the solvent phase several times with hydrochloric acid; antimony is finally precipi- tated with 8-hydroxyquinoline for chemical-yield determination and counting. Tin is further purified by extraction into isobutyl methyl ketone, and is finally precipitated with cupferron and ignited to tin(1V) oxide, in which form it is weighed and counted.The time taken to complete the above separation and purification scheme averages 5 days, which includes 1 day for evaporating 10 litres to 600 ml on a 1200-watt boiling-ring. The average chemical recoveries of added carriers are given in Table I. TABLE I AVERAGE CHEMICAL RECOVERY OF ADDED CARRIERS Fraction .. . . Ruthenium Molybdenum Tellurium Antimony Tin Recovery, per cent. . . 60 66 63 46 49 Range . . .. .. 30 to 60 40 to 90 40 to 80 30 to 60 20 to 60 RECOVERY OF ADDED RADIONUCLIDES- As a check, recovery experiments were carried out by adding known amounts of radio- nuclides to simulated water samples. The samples were processed by the method, and the count-rates of the final sources were corrected for decay and chemical recovery. The radio- nuclides used were ruthenium-106 (half-life 1 year), molybdenum-99 (half-life 67 hours), tellurium-132 (half-life 78 hours), antimony-124 (half-life 60 days) and tin-113 (half-life 118 days).Chemical forms of these species were as follows: ruthenium-106, as ruthenium trichloride ; molybdenum-99, as ammonium molybdate ; tellurium-132, as sodium tellurite; antimony-124, as antimony trichloride; and tin-113, as tin(1V) chloride. The antimony and tin nuclides, although not fission products, were used for convenience. The latter nuclide decays by electron capture to indium-113m (half-life 104 minutes), which emits a 0-393-MeV y-photon. When the tin sources had been prepared, the daughter was allowed to grow to equilibrium before counting in a y-spectrometer. The other four nuclides were counted inJanuary, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER 3 a /3-counter, and for tellurium, the daughter, iodine-132 (half-life 2.3 hours), was allowed to come to equilibrium before counting.The results are listed in Table 11. As it is im- possible to match the chemical forms of the active species used in these experiments with those present in fall-out, the results of the recovery experiments given in Table I1 are not, in themselves, conclusive evidence of complete recovery of the fall-out nuclides in a sample. Sample 1 2 3 4 TABLE I1 RECOVERY OF ADDED RADIONUCLIDES FROM SIMULATED Ruthenium-106 Molybdenum-99 - - Added, Found, Added, Found, counts counts Re- counts counts Re- Per per covery, per per covery, minute minute per cent.mmute minute per cent. 3608 3456 95.8 9610 9154 95.3 3516 3560 101.3 39,960 38,390 96.1 3588 3420 95.3 9860 9345 94-9 3646 3460 95.0 40,250 38,880 96.6 TABLE I I-contilzwed Antimony-124 r Added, Found, counts counts Re- per per covery, Sample minute minute per cent. 1 7672 8108 105.7 2 7072 7257 94.6 3 7672 7313 95.3 4 7672 7740 100.9 WATER SAMPLES Tellurium-132 P Added, Found, counts counts Re- Per minute minute per cent. 4710 4337 92.1 3380 3435 101.6 4425 4224 95.6 11,125 11,660 104.7 per covery, Th-113 Added, counts mmute 3335 3330 3252 2978 per Found, counts Per minute 3160 3247 3035 333.4 Re- covery, per cent. 94.5 97.5 102.5 101.9 Samples 1, 2 and 3 were drinking waters containing 100, 40 and 20 mg of calcium per litre, respectively.Sample 4 was rain water. RADIOCHEMICAL PURITY OF COUNTING SOURCES- To ascertain the level of contamination of each of the final counting sources by other radionuclides, several decontamination experiments were carried out. Simulated water samples, with known amounts of possible contaminants present, were processed by the method. The final sources were counted and decontamination factors calculated in the normal way from the ratio of count-rate added to the count-rate found in the sources. Contaminants used included a mixture of fission products containing strontium-90 - yttrium-90, cerium-144 - praseodymium-144, promethium-147, caesium-137 and zirconium-95, and a solution of radium D.E.F. (lead-210, bismuth-210 and polonium-210). The extent of contamination of the ruthenium and tin sources by tellurium-132, antimony-124 and molybdenum-99, and of the ruthenium, molybdenum, tellurium and antimony sources by tin-113, was also deter- mined.The results are listed in Table 111. The decontamination factors are in excess of 2 x 103, except for the antimony source contaminated with tin-113, when a figure of 230 was obtained. This was considered adequate in this instance, as the fission yields of the two fission-product nuclides of tin, tin-123 and tin-125, are relatively low. TABLE I11 DECONTAMINATION FACTORS Decontamination factor from- telluriurn-133, antimony-124 and Fraction molybdenum-99 tin-113 Ruthenium . . 3 x 10s >8 x lP Molybdenum . . - >8 x 108 Tellurium . . - >8 x 108 Antimony .. - 2-3 x lo2 Tin . . .. 4 x 104 - * The mixed fission products contained strontium-90 - promethium-147, caesium-137 and zirconium-95. mixed fission products* 3 x 106 2 x 106 3 x 106 3 x 106 1 x 107 yttrium-90, cerium-144 - radium D.E.F.2.2 x 108 >2 x 106 1.7 x 104 1 x 104 2.3 x 108 praseodymium- 1444 APPARATUS- BATHIE AND BURDEN : A SEQUENTIAL SCHEME FOR THE METHOD [Analyst, Vol. 93 A low background (about 1 count per minute) anti-coincidence /3-counter was used. Perspex $her-stick, 16 mm i.d. In frared lamps. Centrifuges. REAGENTS- Molybdenzzlm, tellurium and antimony carrier solutions-Prepare solutions of analytical- reagent grade ammonium molybdate, telluric acid and antimony potassium tartrate in water containing 10 mg of molybdenum, tellurium and antimony, respectively, per ml of solution.Ruthenium carrier solution-Dissolve ruthenium trichloride in a few millilitres of hydro- chloric acid and dilute with water to prepare a solution containing about 10 mg of ruthenium per ml of solution. Standardise the solution by precipitating the metal with magnesium and acid, as described in the Method, and by using a sintered-glass crucible for filtration and weighing. Count a portion of the ruthenium metal in a /3-counter to determine the level of ruthenium-106 present in the carrier solution. (Most commercial sources of ruthenium contain this nuclide.) Tin carriw solution-Heat sodium stannate with a few millilitres of hydrochloric acid and dilute with water to prepare a solution containing about 10 mg of tin per ml of solution. Standardise the solution by precipitation with cupferron (ammonium salt of N-nitrosophenyl- hydroxylamine) and ignition to tin(1V) oxide, as described in the Method.Lead, zirconium and iron carrier solutions-Prepare solutions of lead nitrate, zirconyl chloride and iron(II1) chloride in water containing about 5 mg of lead, zirconium and iron, respectively, per ml of solution. The strength of these solutions need not be accurately known. 8-Hydroxyquinoline solution-Dissolve 4 g of 8-hydroxyquinoline in a few millilitres of glacial acetic acid and dilute with 100 ml of water. Add 6 N ammonia solution until the solution becomes turbid and then glacial acetic acid until clear. This solution is stable for about 2 months, if kept cool. Sodium polysulphide solution-Dissolve 100 g of sodium sulphide and 8 g of sodium hydroxide in the minimum amount of water.Dissolve 3 g of sulphur in the hot solution, dilute to 200ml and filter. Cupferron solution-Prepare a 10 per cent. w/v solution of the ammonium salt of N-nitrosophenylhydroxylamine in water immediately before use, and filter. Benzoin a-oxime solution, 2 9er cent. w/v in ethanol. Sodium hydrogen suZ9hite solution-Saturate 5 per cent. w/v sodium hydroxide solution with sulphur dioxide gas. Sodium hyjbochlorite solutiow-Use a solution containing 10 per cent. of available chlorine. Potassium iodate solution, 7 per cent., aqueous. Poly(viny1 acetate) (Gelva) solution, 5 9er cent. w/v in methalzol. 2-Ethylhexan-1-01, 5 per cent. v/v in light petroleum (boiling range 80" to lOO"C)-EqUili- brate by washing with concentrated hydrochloric acid. Isobutyl methyl Ketone-Equilibrate by washing with 6 N hydrochloric acid.PROCEDURES FOR PRELIMINARY SEPARATIONS RUTHENIUM SEPARATION- To 10 litres of sample in a 12-litre flask add the following carriers: 10 mg of molybdenum and antimony, and 20mg of ruthenium, tellurium and tin. Add 10ml of sodium hypo- chlorite solution, mix and allow to stand for 30 minutes. Add 100ml of ethanol, followed by 50 per cent. sodium hydroxide until the solution is slightly alkaline (about pH 9 to 10, with universal indicator paper). Boil to coagulate the ruthenium precipitate, cool and allow it to settle overnight. Siphon off the bulk of the supernatant liquid (1) into a second flask and complete the separation by centrifuging the last few hundred millilitres in a 250-ml centrifuge jar. Wash the ruthenium (and any precipitated water solids) with water into a nickel crucible, add 5 ml of hydrofluoric acid and evaporate to dryness under an infrared lamp.Cool and add a further 5ml of hydrofluoric acid, and again evaporate to dryness.January, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER Dlscard. 5 Insoluble Solubler Ru02(2) I Dissolve in HCI. Add to Ru fraction (3) Sample + Ru, Mo, Sb, Sn and Te carriers i Oxidise with NaOCI. Add CzHsOH I I 1 Te lnsol u ble RuO2 + water solids I Fuse with Na2CO3 - Na202. Leach with water I fraction Reducd acidity Tellurium-I25m Organic’iayer (4) Aqueous layer -+ Ru fraction I 1 I Ruthenium-103 Ruthenium- 106 Sb I ,Soluble ( I ) I fraction Sn fraction I Extract with isobutyl methyl ketone Organic layer Aqueous layer A I Evaporate to 500ml., Add benzoin a-oxime Soluble (5)- Hydrazi j e + SO; Insoluble (7) Soluble (8) with NH40H. Pass HzS 1 S b A + SnS. Soluble rejected I Dissolve in HCI and oxidfse with KMn04. Extract with 2- ethyl hexan- 1 - 0 1 I lnsolu ble Mo + water solids Fuse with NazCO3. Leach with water I A Any insoluble Soluble Treat with HCI 1 F, Benzoin +-Soluble Insoluble asxime Discard. -A t--- Soluble Insoluble Mo benzoin a-oximate (6) I Mo fi - Molyb< iction mum-99 Mix the residue with five times its volume of anhydrous sodium carbonate and fuse over a Meker burner. When the initial reaction has subsided, add 2 to 3 g of sodium peroxide in portions, and fuse for a further 5 minutes. Cool and extract the melt with hot water.Centrifuge the solution and transfer the supernatant liquid into a beaker, and precipitate ruthenium hydroxide (2) from this aqueous extract by adding a few millilitres of ethanol. Heat the precipitate to coagulate it, centrifuge and add the supernatant liquid to (1). Treat the insoluble matter from the aqueous extract of the melt with the minimum volume of concentrated hydrochloric acid and heat it in a water-bath. Centrifuge it and transfer the supernatant liquid into another tube. If any insoluble matter remains, add 2ml of concentrated hydrochloric acid and heat in a water-bath. Add 10ml of water, centrifuge the mixture, and combine the supernatant liquid with the previous acidic extract ; discard any further insoluble matter.To the acidic extract add a few millilitres of ethanol, followed by 50 per cent. sodium hydroxide until ruthenium (and nickel) hydroxide (3) is precipitated. Heat to coagulate the precipitate, centrifuge it and add the supernatant liquid to (1).6 BATHIE AND BURDEN: A SEQUENTIAL SCHEME FOR THE [Arta@d, VOl. 93 Dissolve each of the ruthenium precipitates (2) and (3) in 2 ml of concentrated hydro- chloric acid and, while warming, combine them in a single tube by using the minimum amount of water. Then reduce the ruthenium to the metal by careful addition of magnesium turnings, until there is excess of magnesium present. Dissolve this excess of magnesium by dropwise addition of concentrated hydrochloric acid, centrifuge the mixture and add the supernatant liquid to (1).Wash the ruthenium metal with hot water, adding the washing to (1). Add 5 ml of sodium hypochlorite solution and a few drops of 50 per cent. sodium hydroxide solution to the metal, and heat it in a water-bath for a few minutes, with occasional stirring. Allow the solution to cool, add a further 5 ml of sodium hypochlorite solution, and wash it into a 100-ml separating funnel with 10ml of water. Add 20ml of carbon tetrachloride, followed by concentrated hydrochloric acid, until the colour of the aqueous phase changes to a pale yellow; shake the solution for a few minutes and allow the phases to separate. Transfer the organic layer to a second separating funnel and repeat the extraction of the aqueous phase with a further 10 ml of carbon tetrachloride.When the phases have separated, add the aqueous phase to (1). Wash the combined organic extracts with 20 ml of water, adding the washing to (1) , and repeat this step twice more. Retain the carbon tetrachloride layer (4) for ruthenium purification. MOLYBDENUM SEPARATION- To the main solution (1) add concentrated hydrochloric acid until it is acidic and then 10 ml in excess. Evaporate the solution to low volume on a boiling-ring, wash it into a 1-litre beaker with water to give a volume of about 500 ml, add 30 ml of concentrated hydrochloric acid and cool the solution in ice - water. Add 10 ml of bromine water, followed by 10 ml of benzoin a-oxime, while stirring, and allow to stand in the ice-bath for 20 minutes, with occasional stirring. Centrifuge the molybdenum benzoin a-oximate ( j h s any precipitated water solids) in a 250-ml centrifuge jar, and retain the supernatant liquid (5) for separation of tellurium, tin and antimony. Wash the solids into a nickel crucible with water and evaporate to dryness under an infrared lamp.Then add 10ml of 40 per cent. hydrofluoric acid and again evaporate to dryness. Mix the residue with five times its volume of sodium carbonate and fuse it over a Meker burner. Cool the melt and extract it with hot water; centrifuge the solution. Dissolve any insoluble material in concentrated hydrochloric acid and add it to the main solution (5). To the aqueous extract, add 1 mg of iron carrier, centrifuge the solution and discard the iron(II1) hydroxide, transferring the supernatant liquid into a beaker, acidifying it carefully with concentrated hydrochloric acid, and boiling to remove carbon dioxide.Add a few millilitres of bromine water, cool the solution in an ice-bath and add 5 ml of benzoin oc-oxime to precipitate the molybdenum; centrifuge it and add the supernatant liquid to the main solution (5). Wash the precipitate with water, centrifuge it and add the washing to (5) , retaining the molybdenum precipitate (6) for purification. TELLURIUM SEPARATION- Evaporate the main solution (5) to about 250 ml. Add about 5 g of hydrazinium dichloride and bring the solution to the boil; saturate it with sulphur dioxide gas for 15 minutes. Boil the solution to coagulate the tellurium metal, and filter it through filter-paper pulp; retain the precipitate (7) for tellurium purification, and wash the filtrate (8) into a 1-litre beaker.TIN AND ANTIMONY SEPARATION- Reduce the acidity of filtrate (8) to about 0.2 N by adding ammonia solution (with indicator paper), and heat the solution to boiling. Pass hydrogen sulphide gas through the solution for 15 minutes, and allow the precipitate to settle for at least 2 hours, but preferably overnight. Pass hydrogen sulphide gas through the solution again for 15 minutes, and then centrifuge it in a 250-ml centrifuge jar; discard the supernatant liquid. Wash the precipitate into a 40-ml centrifuge tube with hydrogen sulphide water, centrifuge it, and discard the supernatant liquid. Add 5ml of concentrated hydrochloric acid, boil off the hydrogen sulphide, centrifuge the mixture and transfer the supernatant liquid into another tube.Wash the insoluble matter with 15 ml of hot water, centrifuge it and add the supernatant liquid to the previous acidic extract ; discard the insoluble matter, which is mainly rutheniumJanuary, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER 7 sulphide. Add 10 mg of tellurium carrier and about 1 g of hydrazinium dichloride, heat the solution in a water-bath, and pass sulphur dioxide gas through it. Centrifuge it and transfer the supernatant liquid into another tube. Add a further 10mg of tellurium carrier, heat the solution in a water-bath, and again pass sulphur dioxide gas through it. Centrifuge it and filter the supernatant liquid into a beaker; boil off sulphur dioxide and wash the solution into a centrifuge tube.Reduce the acidity to about 0.2 N with ammonia solution, and pass hydrogen sulphide gas through the solution. Centrifuge it to collect the tin and antimony sulphides, and discard the supernatant liquid; wash the precipitate with hydrogen sulphide water and discard the washing. Treat the tin and antimony sulphides with a few millilitres of sodium polysulphide solution plus a few drops of 50 per cent. sodium hydroxide, and heat them in a water-bath; dilute to 20 ml with water. Centrifuge and discard any insoluble matter (ruthenium sulphide). Add 5 mg of lead carrier and centrifuge it, then add a further 5 mg of lead carrier, centrifuge it again, and filter the supernatant liquid into another tube; discard the lead sulphide. Add 2 ml of glacial acetic acid and heat the solution in a water-bath to coagulate the precipitate.Centrifuge it to collect the tin and antimony sulphides and sulphur, and discard the super- natant liquid. Add 2 ml of concentrated hydrochloric acid to dissolve the tin and antimony sulphides, and boil off hydrogen sulphide. Then add 10 ml of water, centrifuge it, and transfer the supernatant liquid into another tube. Treat the sulphur again with 2 ml of concentrated hydrochloric acid, boil, dilute with 10 ml of water, centrifuge it and discard the sulphur, transferring the supernatant liquid into the first acidic extract. Pass hydrogen sulphide gas through the solution to precipitate tin and antimony sulphides, centrifuge to collect the precipitate, and discard the supernatant liquid.Add 2ml of concentrated hydrochloric acid to the precipitate and boil off hydrogen sulphide. Then wash the solution into a 100-ml separating funnel with 10 ml of concentrated hydrochloric acid, add about 40 mg of potassium permanganate and 10 ml of 2-ethylhexan- 1-01 and light petroleum, and shake the funnel for 10 minutes; allow the phases to separate and transfer the aqueous layer into a second separating funnel. Extract the aqueous phase with a further 5ml of 2-ethylhexan-1-01 and light petroleum, and combine this with the first organic layer. Then extract the combined organic layers with 5 ml of concentrated hydrochloric acid (adding a further 40 mg of potassium permanganate), and combine this with the first aqueous layer. Retain the organic layer (9) for antimony purification and the aqueous layer (10) for tin purification. PURIFICATION AND ISOLATION OF ELEMENTS- Ruthehm-Extract the ruthenium from the carbon tetrachloride (4) into 10 ml of 3 M sodium hydroxide solution to which just sufficient sodium hydrogen sulphite solution has been added to decolorise the carbon tetrachloride layer.Wash the aqueous layer into a centrifuge tube with about 10ml of water. Heat the solution in a water-bath and add 1 ml of ethanol to precipitate ruthenium hydroxide; centrifuge to collect the precipitate, and discard the supernatant liquid. Dissolve the precipitate in 3ml of concentrated hydrochloric acid by warming, and reduce it to the metal, as before, by careful addition of magnesium turnings. Wash the precipitate first with hot water and then with ethanol, discarding the washings.Make a slurry of the precipitate with ethanol, and filter it on a filter-stick through two tared Whatman NO. 42 papers (21 mm in diameter). Dry the papers in an oven at 80" C, keeping the source paper flat with a metal ring. Cool and weigh, and calculate the chemical recovery, assuming that both papers gain or lose the same weight. Mount the source on a planchet with a few drops of Gelva solution and count, both normally and through a 200mg per cm2 aluminium absorber. Molybdenzcm-Transfer the molybdenum benzoin a-oximate precipitate (6) into a beaker with a few millilitres of fuming nitric acid, add 1 ml of 60 per cent. perchloric acid and heat the solution under an infrared lamp. When charring occurs, add a few millilitres of fuming nitric acid and continue heating.When the wet combustion is complete, evaporate to dryness, cool and dissolve the residue in concentrated ammonia solution. Wash the solution into a centrifuge tube with 10 ml of water, warm and add 1 mg of iron carrier; centrifuge it and discard the iron(II1) hydroxide, transferring the supernatant liquid into a beaker. Then8 [Analyst, Vol. 93 add 10 ml of water, neutralise with dilute sulphuric acid, adding a few drops in excess, heat to boiling and add 5 ml of 8-hydroxyquinoline solution. Filter on a filter-stick and wash with hot water. Dry the papers in an oven at 105" C, with the source paper kept flat, as described for ruthenium. Cool, weigh and calculate the chemical recovery (the precipitate contains 23.05 per cent.of molybdenum). Mount the source on a planchet with a few drops of Gelva solution and count. Re-count, at intervals, for several half-lives of molybdenum-99. TeZZztrizw+-Transfer the filter pulp, containing tellurium metal (7) into a beaker and wet combust it with fuming nitric and perchloric acids. Evaporate to dryness, dissolve the residue in 5 ml oE concentrated hydrochloric acid, and evaporate to dryness. Dissolve the residue in 5ml of concentrated hydrochloric acid, and wash the solution into a centrifuge tube with 15 ml of water. Add about 1 g of hydrazinium dichloride, heat the solution in a water-bath and pass sulphur dioxide gas through it ; centrifuge it and discard the supernatant liquid. Add a few drops of concentrated nitric acid and evaporate the solution nearly to dryness; cool and dissolve the residue in a few drops of concentrated hydrochloric acid.Dilute it to 15 ml with water and neutralise with 6 N ammonia solution, adding 1 ml in excess. Heat the solution in a water-bath and add 1 mg of iron carrier; centrifuge it and discard the iron(II1) hydroxide, transferring the supernatant liquid into another tube. Add 5 ml of concentrated hydrochloric acid, followed by about 1 g of hydrazinium dichloride. Heat the solution in a water-bath and pass sulphur dioxide gas through it to precipitate tellurium metal. Centrifuge it and discard the supernatant liquid; wash the precipitate with water and discard the washing. Add a few drops of concentrated nitric acid to the precipitate, heating to dissolve it, wash the solution into a beaker with concentrated hydrochloric acid and evaporate it to dryness.Dissolve the residue in 5ml of concentrated hydrochloric acid and again evaporate to dryness. Dissolve the residue in 5 ml of concentrated hydrochloric acid and wash it into a centrifuge tube with 15 ml of water. Add about 1 g of hydrazinium dichloride, heat the solution in a water-bath and pass sulphur dioxide gas through it to precipitate tellurium metal; centrifuge it and discard the supernatant liquid. Wash the precipitate with water and discard the washing . Make a slurry of the precipitate with water and filter it on a filter-stick, washing the precipitate successively with water and ethanol. Dry the papers in an oven at 80" C , as described for ruthenium.Cool, weigh and calculate the chemical recovery. Mount the source on a planchet with a few drops of Gelva solution and count, both normally and through a 5 mg per cm2 aluminium absorber. When fresh fission products are present, re-count the source, at intervals, until the tellurium-132 - iodine-132 has decayed away. Antimony-To the 2-ethylhexan-1-01 - light petroleum phase (9), add 10 ml of concen- trated hydrochloric acid and 40 mg of potassium permanganate, and shake it for 10 minutes; allow the phases to separate and discard the aqueous layer. Repeat this step twice more. Extract the antimony from the organic layer by shaking it for 10 minutes with 20ml of water; allow the phases to separate and transfer the aqueous phase into a centrifuge tube.Pass hydrogen sulphide gas through the solution and centrifuge it to collect the antimony sulphide, discarding the supernatant liquid. Add 3 ml of concentrated hydrochloric acid and, after boiling off hydrogen sulphide, with stirring, add 15 ml of water, followed by 5 ml of 8-hydroxyquinoline solution and 2 ml of 25 per cent. ammonium acetate solution. Then add 6 N ammonia solution, dropwise, until antimony 8-hydroxyquinolinate is precipitated. Centrifuge it and discard the supernatant liquid; wash the precipitate with cold water until the washings are colourless. Make a slurry of the precipitate with water and filter it on a filter-stick. Dry the papers in an oven at 105" C, keeping the source paper flat, as described for ruthenium. Cool, weigh and calculate the chemical recovery (the precipitate contains 21.97 per cent.of antimony). Mount the source on a planchet with a few drops of Gelva solution and count, both normally and through a 12 mg per cm2 aluminium absorber. When fresh fission products are present, re-count the source, at intervals, until antimony-127 has decayed away. Tin-Dilute the aqueous phase (10) to twice its volume with water, add 20 ml of isobutyl methyl ketone and shake the mixture for 10 minutes; allow the phases to separate and transfer the aqueous layer into a second separating funnel. Extract the aqueous layer with a further 10 ml of isobutyl methyl ketone, and wash the combined organic layers with 10 ml BATHIE AND BURDEN: A SEQUENTIAL SCHEME FOR THEJanuary, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER 9 of 6 N hydrochloric acid and discard the washing.Extract the tin from the organic layer by shaking it for 10 minutes with 25 ml of water; allow the phases to separate and transfer the aqueous layer into a centrifuge tube. Pass hydrogen sulphide gas through the solution €or 15 minutes to precipitate the tin sulphide, centrifuge it, and discard the supernatant liquid. Add 3 ml of concentrated hydro- chloric acid, boil off hydrogen sulphide, with stirring, then add 20 ml of water and 5 ml of fresh cupferron solution, and allow the mixture to stand for 30 minutes, with occasional stirring. Filter it on a Whatman No. 30 paper and, after washing with water, transfer the paper to a silica crucible, dry and ignite the precipitate to tin(1V) oxide.Cool, make a shmy with ethanol, and filter it on a filter-stick. Wash the precipitate with ethanol and dry it in an oven at 80” C, with the source paper kept flat, as described for ruthenium. Cool, weigh and calculate the chemical recovery. Mount the source on a planchet with a few drops of Gelva solution and count, at intervals. CALCULATION- by the equation- The concentration, A,, of any nuclide in a water sample at the time of sampling is given 1 1 1 1 1 1 A , = C x x - x - x - x - x - picocuries per litre, x Y D v 2.22 where C = counting rate in counts per minute, corrected for lost counts and background, E = fractional counter efficiency for the nuclide counted, X = self-absorption correction factor, Y = fractional chemical recovery, D = decay factor for the time interval between sampling and counting for the V = volume of sample in litres.particular nuclide counted, and Where the nuclide is easily available as a standardised solution, a graph should be prepared relating counter efficiency with source weight. The terms E and X in the above equation are, therefore, combined in a single figure for these nuclides. At the present time this can be done for ruthenium-103, ruthenium-106 and molybdenum-99. For the other nuclides, efficiences were obtained from a general calibration graph relating counter efficiency for a 20-mg source with the maximum #3-energy of the particle. The counter efficiency for a 20-mg source of any nuclide is found by summing the individual efficiencies for each /3-particle, multiplied by the fraction each particle contributes to the total radiation. With the nuclides tellurium-125mJ tellurium-127m and tellurium-l29rn, which decay by isomeric transition, the emitted particle is a mono-energetic electron. For a normal #3-particle spectrum, the “average” energy is about one third of the maximum #3-particle energy.It was assumed, for the purpose of obtaining the counter efficiency, that the conversion electrons were equivalent to a normal /%particle of three times their energy. For nuclides, the efficiency of which is found in this way, the count-rates must be corrected for the self-absorption that occurs in the material of the source. Non-standardised solutions of the nuclides may be used for this purpose, as it is only necessary to plot a graph of relative counts against source weight and normalise the curve to give a self-absorption factor of unity at a source weight of 20 mg.This is possible for tellurium-132 - iodine-132, antimony-125 and tellurium-l25m (the last by separating the tellurium-l25m from an aged solution of antimony-125). For the other tellurium nuclides, a sample of tellurium metal was irradiated in a reactor. This gives many nuclides but, after allowing for decay, the predominant activities are those of tellurium-l27m, tellurium-127 and tellurium-l23m. A solution of these activities was used to prepare a self-absorption curve that could be used for the isomeric pairs tellurium-127m - tellurium-127 and tellurium-129m - tellurium-129, as these have similar p-energies. A curve for tin-123 was prepared by using strontium-89 in the form of strontium oxide, as these two nuclides have similar maximum p-energies (tin-123 = 1.42 MeV and strontium-89 = 1.48 MeV), and strontium oxide and tin(1V) oxide (the counting form of the tin source) have similar average atomic numbers (strontium oxide = 23, and tin(1V) oxide = 22).POSSIBLE NUCLIDES PRESENT IN THE PURIFIED SOURCES- The purified ruthenium source will contain ruthenium-106 (half-life 1 year), with its daughter, rhodium-106 (half-life 30 seconds), in equilibrium. In fall-out less than a year old10 BATHIE AND BURDEN: A SEQUENTIAL SCHEME FOR THE [Analyst, Vol. 93 ruthenium-103 (half-life 40 days) will also be present. These are resolved by making use of the widely differing @energies of rhodium-106 and ruthenium-103 (ruthenium-106 has a maximum /3-energy of 0.039 MeV, which is too weak to count in an end-window Geiger counter).The transmissions of mthenium-106 - rhodium-106 and ruthenium-103 through a 200 mg per cm2 aluminium absorber are measured for these nuclides. Count-rates for each of these nuclides present in a sample source may then be found by simultaneous equations, and substituted separately in the above equation. The only active fission-product nuclide of molybdenum, of sufficient half-life to be found in fall-out, is molybdenum-99 (half-life 67 hours), and this would only be found in fall-out of recent origin. The tellurium source may contain a complex mixture of nuclides , including tellurium-125m (half-life 58 days) , the isomeric pairs tellurium-127m - tellurium-127 and tellurium-129m - tellurium-129 (half-lives 105 and 33 days, respectively), and, in fall-out of recent origin, tellurium-132 (half-life 78 hours).If the last is present, it is easily identified because its daughter, iodine-132 (half-life 2.3 hours), grows in after the final tellurium precipitation, so that the count-rate rises to a maximum after a few hours. The two nuclides in transient equilibrium then decay with a half-life of 78 hours, so that by following the count-rate for a few weeks the count from this pair may be separated from that from the remainder of the tellurium nuclides. Distinguishing between the two isomeric pairs tellurium-127m - tellurium-127 and tellurium-129% - tellurium-129 is difficult, as there is no large difference between half-life or /3-energy.In this laboratory no attempt has been made to distinguish between the two. In fall-out more than 2 years old, the only tellurium nuclide present would be tellurium-125m (half-life 58 days), the daughter of antimony-125 (half life 2-8 years). This nuclide may be distinguished from the two isomeric pairs by its considerably lower transmission through an aluminium absorber of 5 mg per cm2 (about 30 and 85 per cent., respectively). The antimony source will contain antimony-125 and, in recent fall-out, antimony-127 (half-life 94 hours) may be present. The latter decays to tellurium-127 (half-life 9-4 hours) in about 80 per cent. of its disintegrations, so that when this nuclide is present the count-rate rises at first, and then the two nuclides, in transient equilibrium, decay with the half-life of antimony-127.The remaining 20 per cent. of disintegrations decay to tellurium-127m (half-life 106 days), which appears, together with the supported amount of tellurium-127, in the “tail,” after the resolution of the decay curve. Also present in the “tail” (apart from counts from antimony-125 itself) are counts from tellurium-125% (half-life 58 days), produced in about 30 per cent. of the disintegrations of antimony-125. To obtain an accurate figure for antimony-125 it is, therefore, necessary to re-dissolve the antimony source when anti- mony-127 has decayed away, and to remove tellurium activities by scavenging with tellurium carrier. Two nuclides of tin may be found in fall-out, tin-123 (half-life 129 days) and tin-125 (half-life 9-63 days) , which are easily resolved by decay measurements.The purified antimony is then mounted and a count taken. RESULTS The sensitivity of detection of the various nuclides for a 10-litre sample, by using a counter with a background count-rate of 1 count per minute, is given below. Ru then- Ruthen- Molyb- Tellur- Tellur- Antim- ium-103 ium-106 denum-99 ium-129 ium-126m ony-I26 Tin-123 Limit of detection, picocuries per litre 0.08 0.02 0.06 0.02 0.06 0.06 0.02 These results were calculated from a count equivalent to three standard deviations of a background count of 3000 minutes’ duration. Chemical recoveries were as listed in Table I. A time interval of 5 days between sampling and counting was assumed. Several drinking waters12 have been examined radiochemically by using this procedure in conjunction with that developed by Wood and Richards.’ This work was carried out for the Ministry of Housing and Local Government, and the object was to account for all of the radioactivity present by comparing the total /%activity (directly determined, and ex- pressed as though all of the radiation was from strontium-90), with the sum of the individually measured nuclides, again calculated as strontium-90.The results are shown in Table IV. Samples of rain water collected on the roof of this laboratory have also been analysedJanuary, 19681 DETERMINATION OF SEVERAL FALL-OUT NUCLIDES IN WATER 11 TABLE IV COMPARISON OF THE SUM OF INDIVIDUALLY DETERMINED RADIONUCLIDES IN Figures expressed as strontium-90 in picocuries per litre DRINKING WATERS WITH THE TOTAL p-ACTIVITY DIRECTLY DETERMINED Sum of individual Sample nuclides Total /?-activity Manchester (October, 1962).. .. .. 20.3 21.4 Belfast (May, 1963) . . .. .. .. 104.1 99.6 Cardiff (May, 1963) ., .. * . .. 29.8 28.2 Belfast (August, 1964) . . .. .. 35.1 38.6 Cardiff (September, 1964) . . .. . . 13.1 11.6 Manchester (June, 1966) . . .. . . 11.1 10.7 Leeds (December, 1966) . . .. .. 8.9 8.9 London (May, 1966) .. .. .. 7.0 6-2 Pwllheli (July, 1966) .. .. .. 9.7 10.6 London (March, 1964) . . * . .. 9.1 9.7 by the proposed method. A sample collected between November 4th, 1966, and November 7th, 1966, containing fall-out from the fourth Chinese nuclear test of October 27th, 1966, and a second sample collected between January 6th, 1967, and January 12th, 1967, contahing fall-out from the fifth Chinese nuclear test of December 28th, 1966, gave the results indicated in Table V.The nuclides determined in rain water after the fifth Chinese test include three pairs of the same elements, ruthenium-103 - ruthenium-106, tellurium-132 - tellurium-129m and antimony-127 - antimony-125. As the date of the explosion is known (December 28th, 1966), it is possible to compare the ratio of each pair of nuclides with the theoretical figure TABLE V ACTIVITY OF LONDON RAIN WATER Nuclide Ruthenium-103 . . Ruthenium-106 . . Molybdenum-99 . . Tellurium-132 . Tellurium-129m . . Antimony-127 . . Antimony-126 . . Tin-126 . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... Sample collected November 4th to November 7th, 1966, picocuries per litre 4.7 f 0.4 0.79 f 0.08 19.9 f 0.6 13.2 f 0.4 0.61 4 0-08 0.98 f 0.10 Sample collected January 6th to January 12th, 1967, picocuries per litre 1210 f 20 24.0 f 3.0 1660 f 50 3170 f 30 112 f 2 n.d. 173 f 6 7.7 f 0.3 a d . 29.1 f 0.4 The figures are calculated to 00.00 hours, November Bth, 1966, for the first sample and to 00.00 hours, January 7th, 1966, for the second. The limits are based on counting statistics only (90 per cent. confidence limits). n.d. = not detected. for several possible nuclear fuels. It is first necessary, however, to determine the contribution (for the longer-lived nuclides) of fall-out from previous tests. An approximate estimate was obtained from the antimony pair, as the ratio of activities of antimony-127 to antimony-125 is virtually independent of the nuclear fuel for fission neutrons.By using an average value for this ratio, the amount of “old” antimony-125 was calculated. The contribution of “old” rutheniurn-106, ruthenium-103 and tellurium-129m in the rain water was then calculated from the measured activities in the previous rainfall, the level being significant only for ruthenium-106. The corrected ratios of ruthenium-103 - ruthenium-106 and tellunum-132 - teIlurium-129wz are compared in Table VI with the theoretical ratios for fission of uranium-235, TABLE VI COMPARISON OF OBSERVED AND THEORETICAL RATIOS FOR FISSION BY FISSION NEUTRONS Observed ratio, December Theoretical ratio, calculated from r \ calculated to fission yields18 A Nuclide pair 28th.1966 Uranium-236 Uranium-238 Plutonium-239 Ruthenium-103 - ruthenium-106 . . 71.1 77.1 22.3 9.24 Tellurium- 132 - tellurium- 129m. . .. 253 237 236 150 Antimony-127 - antimony-126 . . .. - 552 626 62912 BATHIE AND BURDEN uranium-238 and plutonium-239 by fission neutrons, showing that agreement is good for uranium-236 fission. PILE-IRRADIATED URANIUM- A sample of uranium oxide was irradiated in the BEPO reactor at Harwell for 3 days at a thermal neutron flux of about 10l2 neutrons per cm2 per second. A weighed portion of the uranium was dissolved in acid in the presence of carriers, and the solution added to 10 litres of drinking water and passed through the experimental procedure described earlier. The object was to compare experimentally observed fission yields with figures quoted from the literature. The activity of strontium439 was measured and used as a monitor for determining the thermal neutron flux by using a fission yield of 4.79 per cent.The results are listed in Table VII. TABLE VII FISSION YIELDS FOR THERMAL-NEUTRON IRRADIATION OF URANIUM-235 Fission yield, per cent. Nuclide Ruthenium- 106 Ruthenium- 103 Molybdenum-99 Tellurium-132 . . Tellurium- 129m Antimony-127 . . Antimony-126 . . Tin-125 .. .. Sample 1 Sample 2 .. . . 0.38 0.40 .. .. 2*6* 2*8* .. . . 6.04 6.46 .. . . 4-36 - .. . . 0.16 I .. . . 0.11 0.13 .. . . 0.031 0.026 .. . . 0.011 0.012 * Figures obtained by y-counting. - 3 Literature 0~38’~ 3.014 6.0614 4.714 0.17’6 0.1 416 0.01 314 0.02114 We thank Dr. D. I. Coomber for his helpful advice, and the Government Chemist, Ministry of Technology, for permission to publish this paper. 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. 12. 13. 14. 16. REFERENCES Crouch, E. A. C., and Cook, G. B., J. Inorg. Nucl. Chem., 1956, 2, 223. Welford, G. A., Collins, W. R., Morse, R. S., and Sutton, D. C., Talanta, 1960, 5, 168. Buchtela, K., and Lesigang, M., Radiochimica Ada, 1963, 1, 208. Boni, A. L., Analyt. Chem., 1960, 32, 699. Osmond, R. G., Owers, M. J., Healy, C., and Mead, A. P., U.K. Atomic Energy Authority Report, A.E.R.E., R.2899, Hamell, 1969. Osmond, R. G. D., Evett, T. W., Arden, J. W., Lovett, M. B., and Sweeny, B., U.K. Atomic Energy Authority Report, A.E.R.E., AM.84, Harwell, 1961. Wood, R., and Richards, L. A., Analyst, 1966, 90, 606. U.S. Academy of Sciences, Nuclear Science Series, NAS-NS 3038 (1961), 3033 (1961) , 3023 (1960), 3029 (1961), 3009 (1960), U.S. Department of Commerce, Washington, D.C. Griess, J. C., J. Electrochem. Soc., 1953, 100, 429. Meinke, W. W., U.S. Atomic Energy Cornmission Report, AECD, 2738, Berkeley, California, 1949. Orlandini, K. A., Wahlgren, M. A., and Barclay, J., Analyt. Chem., 1965, 37, 1148. “Radioactivity in Drinking Water in the United Kingdom,” 1962, 1963, 1964 and 1966 results, Report by the Ministry of Housing and Local Government, Scottish Development Department, Ministry of Health and Social Services, Northern Ireland, Welsh Office, S.O. Code No. 75- 100-0-62 to 75-100-0-66, H.M. Stationery Office, London, 1963, 1964, 1966 and 1966, respec- tively. Rangarajan, C., Mishra, V. C., Lalit, B. Y., Gopalakrishnan, S., and Sadasivan, S., “Fission Products Data and its Application in Studying Fallout from Nuclear Weapon Tests,” AEET.209, Government of India Atomic Energy Commission, Bombay, India, 1965. KatkofT, S., Nucleonics, 1960, 18 (ll), 201. Hageboe, E., J. Inorg. Nucl. Chem., 1963, 25, 615. Received April 27th, 1967