Page 1EIChroM Users’ Group Meeting Determination of 226 Ra in Environmental and Personal Monitoring Samples Billy Lawrie Geoffrey Schofield Laboratories

Page 2EIChroM Users’ Group Meeting Overview Introduction – Why measure 226 Ra? – Properties of Ra – Methods available – Difficulties Experimental Results and Discussion Conclusions

Page 3EIChroM Users’ Group Meeting Why Measure 226 Ra? There are 4 naturally occurring isotopes of Ra: 232 Th decay series 224 Ra(  emitter, t½ 3.66 days) 228 Ra(  - emitter, t½ 5.75 years) 235 U decay series 223 Ra(  emitter, t½ 11.4 days) 238 U decay series 226 Ra(  emitter, t½ 1600 years)

Page 4EIChroM Users’ Group Meeting Why Measure 226 Ra? (2) 226 Ra causes the most concern – long half life – radiological effects Toxic Widespread Concentrates in bones – increases internal radiation dose of individuals

Page 5EIChroM Users’ Group Meeting Properties of Radium Alkaline earth metal Only one oxidation state (+2) Not easily complexed – majority of compounds are simple ionic salts Ca, Sr, Ba & Ra form a series of closely related elements – problems in chemically isolating Ra Few complexes that pass into the organic phase – solvent extraction not suitable

Page 6EIChroM Users’ Group Meeting Methods of Determining Radium Detection following BaSO 4 co-precipitation Radon emanation Gamma ray spectrometry Thermal ionisation mass spectrometry (TIMS) Alpha spectrometry

Page 7EIChroM Users’ Group Meeting Barium Sulphate Co-precipitation Ba(Ra)SO 4 Tedious Slow Analyst dependent

Page 8EIChroM Users’ Group Meeting Radon Emanation Can only measure 226 Ra Indirect Time consuming Slow (20 days to achieve full equilibrium) 222 Rn is a gas – potential problems during sample handling Low levels of detection require large sample volumes

Page 9EIChroM Users’ Group Meeting Gamma Ray Spectrometry Limited to the analysis of 226 Ra Direct determination (186keV) – low  -emission probability – 235 U interference Determination via 214 Bi –time consuming equilibration between 226 Ra and 214 Bi Distribution of 214 Bi must be homogeneous throughout sample Standard must have the same configuration & density as sample – neither of these two options are easy to achieve.

Page 10EIChroM Users’ Group Meeting TIMS Shorter analytical time Improvement in analytical precision Reduction of the Ra sample size Requires Ra load to be extremely pure – in particular it has to be free from Ba

Page 11EIChroM Users’ Group Meeting Alpha Spectrometry Can determine all  -emitting Ra nuclides directly No consideration of equilibria loss High resolution surface barrier detectors – determination virtually specific – very few spectral interferences Can be performed in a timely manner – 2 days source prep. + counting time Electrodeposition gives robust source

Page 12EIChroM Users’ Group Meeting Difficulties Adsorption Dissolution Tracer Electrodeposition Interferences – chemical – spectral

Page 13EIChroM Users’ Group Meeting Adsorption Ra adsorbs onto suspended particles, colloids & container walls Precautions to avoid loss of radium – sampling – analysis Water samples acidified Collected in acid washed plastic containers Sample vigorously shaken before sub-sampling – re-suspend any adsorbed radium

Page 14EIChroM Users’ Group Meeting Dissolution Total dissolution required Must be free from suspended particles – eliminates loss of radium Microwave digestion Fusion

Page 15EIChroM Users’ Group Meeting Suitable Tracer Tracer v’s parallel standards 224 Ra – occurs naturally – short t½ (3.66 days) 225 Ra – not naturally occurring – also has a short t½ (14.8 days)

Page 16EIChroM Users’ Group Meeting Suitable Tracer (2) 133 Ba – acceptably long t½ (10.66 years) – non-isotopic – susceptible to error regardless of chemical similarity Ra parallel standard – parallel sample spiked with 226 Ra – best option for a batch laboratory 1. Sill, C.W. Nucl. Chem. Waste Manage. 1987, 7, 239

Page 17EIChroM Users’ Group Meeting Chemical Interferences Major interferent is Ba A little makes a significant difference – 10  g can result in a 50% reduction in recovery of Ra 1 Can be minimised by: – limiting sample size to ~ 0.1g – washing column with 1.5M HCl 1 – adding (COONH 4 ) 2 to the ED solution 2 1. Alvarado et alJ. Radioanl. Nucl. Chem. 1995, 1, Orlandini et alRadiochim. Acta 1991, 55, 205

Page 18EIChroM Users’ Group Meeting Spectral Interferences 226 Ra produces a doublet – 4.602MeV (5.55%) & 4.785MeV (94.45%) 226 Ra daughters 222 Rn, 218 Po & 214 Po are present Main possible interferent is 234 U (4.773MeV) 234 U in equilibrium with it’s parent 238 U (4.194MeV) – if no 238 U then 234 U won’t be contributing to 226 Ra peak Shouldn’t pose a significant problem – U should be removed at the separation stage

Page 19EIChroM Users’ Group Meeting Electrodeposition One of the most awkward species to ED Partial deposition observed during deposition of 228 Th 1 Method for deposition at pH 8-9 developed by Roman 2 Orlandini et al showed advantage of using Pt and (COO NH 4 ) 2 Add  g amounts of Pt 3 – ‘Pt black’ film produced – Ra quantitatively plated – robust source (COO NH 4 ) 2 increases efficiency in presence of 5-10  g Ba 3 1. Sill, C.W. et al Anal. Chem. 1974, 46, Roman, D. Int. J. Appl. Radiat. Isot., 1984, 35, Orlandini, K.A. et al Radiochim Acta 1991, 55, 205

Page 20EIChroM Users’ Group Meeting Experimental - Overview Microwave digestion – double digestion procedure – HCl, HNO 3 & HF followed by EDTA & H 3 BO 3 Separation (BioRad AG-50W-X8 resin) 1 Ba elimination (EIChroM Sr.spec resin) 2 Electrodeposition [400  g Pt, 0.17M (COO NH 4 ) 2, 0.14M HCl] Counting (  -spectrometry) 1. Alvarado et alJ. Radioanal. Nucl. Chem., 1995, 1, Chabaux et alChem. Geol., 1994, 114, 191

Page 21EIChroM Users’ Group Meeting Experimental dissolveevaporatesample (1) 1M HCl (2) 1.5M HCl (3) 6M HCl waste evaporatesample (1) (1) & (2)(3) 3M HNO 3 waste (2)(1) evaporateelectrodeposit  -spec (2) 3M HNO 3 Pt ED sol. BioRad AG-50W-X8 EIChroM Sr.spec

Page 22EIChroM Users’ Group Meeting Intercomparison Results

Page 23EIChroM Users’ Group Meeting Recoveries from Marine Sediment Reference Sample IAEA-135

Page 24EIChroM Users’ Group Meeting Results from Environmental & Personal Monitoring Samples

Page 25EIChroM Users’ Group Meeting Results Summary Intercomparison results compare favourably with actual levels Marine sediment reference material IAEA-135 – mean result obtained from intercomparison exercise – 66 labs participated – 64 used  -ray spectrometry; 2 used Rn emanation – 11 outliers – recommended value 23.9Bqkg -1 – confidence interval Bqkg 95% confidence level – range of accepted results Bqkg -1 –from replicate parallel analysis obtained 23.6  3.6Bqkg -1 Good recoveries achievable on a variety of problematic matrices

Page 26EIChroM Users’ Group Meeting Conclusions Robust method Capable of analysing wide variety of matrices Good LOD’s achievable – 20mBqL -1 for water samples (100ml) – 20mBqg -1 for solid samples (0.1g) Future work will focus on 228 Ra –  -spectroscopy – electrodeposition disc used for 226 Ra

Page 27EIChroM Users’ Group Meeting Acknowledgements Thanks are expressed to: – Jim Desmond – Debbie Spence – Scott Anderson – Clare Edmondson