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Evaluation of procedures for 226Ra determination in samples with high barium concentration by α-particle spectrometry
Author’s Accepted Manuscript Evaluation of procedures for 226Ra determination in samples with high barium concentration by αparticle spectrometry L. Benedik www.elsevier.com/locate/apradiso
PII: DOI: Reference:
S0969-8043(15)30320-1 http://dx.doi.org/10.1016/j.apradiso.2015.11.089 ARI7272
To appear in: Applied Radiation and Isotopes Received date: 10 April 2015 Accepted date: 25 November 2015 Cite this article as: L. Benedik, Evaluation of procedures for 226Ra determination in samples with high barium concentration by α-particle spectrometry, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2015.11.089 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Evaluation of procedures for 226Ra determination in samples with high barium concentration by α-particle spectrometry
L. Benedik* Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
Abstract The γ emitter 133Ba is the most often used tracer in determination of 226Ra by αparticle spectrometry. If the source for α-particle spectrometry is prepared by microcoprecipitation, a high Ba concentration causes a thicker source layer which results in reduced counting efficiency due to self-absorption on the α spectrometer and consequently lower result for 226Ra, while not effecting the measurement of 133Ba in γ-ray spectrometry. If the electrodeposition is used, recoveries of deposited Ra and Ba are not necessarily the same and impurities of other α emitters may interfere with the α spectrum.
Keywords: Ra-226, Ra-225, Ba-133 and Th-229; radiochemical separation; electrodeposition; microcoprecipitation; α-particle spectrometry; γ-ray spectrometry
*
Corresponding author. Tel.: + 386 1 5885 347; fax: + 386 1 5885 346. E-mail address: [email protected] (L. Benedik).
1. Introduction Alpha-particle spectrometry in combination with radiochemical separation allows determination of very low activity concentrations of 226Ra. Some simple and specific separation methods for radium have been reported, but the preparation of sources of sufficient spectrometric quality, which requires many chemical operations, is difficult. Each step in the chemical separation process can result in unavoidable losses of the analyte, therefore yield tracers must be used to evaluate the chemical yield. For the preparation of the thin sources for high resolution α-particle spectrometry electrodeposition and/or micro-coprecipitation with rare earths are the most often used methods. In the case of 226Ra, several tracers such as for example 133Ba, 225Ra, 224Ra and 223
Ra have been used. Radium-224, which occurs naturally as a descendant of the Th decay scheme, is an -emitter and has a half-life of only 3.66 days. Due to its
232
short half-life continuous production of the isotope is necessary through a milking process from old stock of 232U. Radium-225 with a half-life of 14.8 days, the first descendant of 229Th, is a - and -emitter and it does not occur naturally (Crespo, 2000; Blanco et al., 2002). Its γ line at 40.0 keV has a reasonably high emission probability (30.0%), which make it suitable for measurement with a low energy γ-ray detector. On the other hand, its immediate descendants (225Ac, 221Fr, 217At) are emitters and evaluation of the recovery is possible via indirect measurement via 217At at 7076 keV using ingrowth-decay equations (Smith and Mercer, 1970; Hancock and Martin, 1991; Crespo, 2000; Blanco et al., 2002; Benedik et al., 2010). Barium-133 is often used as a yield tracer for radium (Lozano et al, 1997). Although Ba and Ra are both alkaline earth elements, there are significant differences in their chemical properties. Sill (Sill, 1987) demonstrated that 226Ra and 133Ba suffer from differences
in quantitative chemistry, which could lead to an inaccurate calculation of the chemical yield. Evaluation of procedures for determination of 226Ra in water samples by α-particle spectrometry with emphasis on the recovery using different yield tracers 223
Ra, 225Ra and 133Ba was presented in our previous study (Benedik et al, 2010). The aim of this study was to evaluate the stages of separation Ra from Ba in
waste water samples by using ion exchange and extraction chromatography and thin sources preparation for α-particle spectrometry with microcoprecipitation and electrodeposition, and to consider the use of 225Ra for yield determination.
2. Experimental 2.1. Samples Samples were collected in the surrounding of the former uranium mine and mill. During the process of yellow cake production, the major tailings consisted of the sulphuric acid-leached crushed ore, neutralized with lime and deposited on the waste disposal site. The mill tailings consists up to 1000 Bq kg-1 and up to 4000 Bq kg-1 d.w of 238U and 226Ra, respectively. Groundwater seeps through the tailings, leaching its constituents, which contaminate the outflow. Water samples contain elevated activity concentrations of uranium and radium (approximately 200 mBq/L) and high concentrations of calcium, magnesium, barium, sulphate and chloride ions.
2.2. Reagents All chemical reagents were of analytical grade. The ion exchange resin Dowex 50W-X8, (100-200 mesh, Serva) and SR-resin (Eichrom) were used.
The tracer solutions 133Ba (SRS 82709A-482) and 229Th (SRS 76224-482) used in the study were prepared from calibrated solutions purchased from Analytics, Inc (Atlanta, GA, USA). The producer maintains traceability to the NIST. A Pt solution (980 g/mL Pt in 5% HCl) was purchased from Aldrich Chemical Company.
2.3. Instruments An α spectrometer (CANBERRA's Alpha Analyst™) with passivated implanted planar silicon (PIPS) semiconductor detectors with an active area of 450 mm2 and 28% efficiency for 25 mm diameter discs was used for α-particle spectrometry measurements. The calibration of the detectors was made with a standard radionuclide source, containing 238U, 234U, 239Pu and 241Am (code: 67978-121), obtained from Analytics, Inc. A low energy HP Ge detector (Canberra, model GL2020-7500) was used for measurement of the γ emitting nuclides presented in Table 1. To avoid bias in the measurements, sample and standard were prepared in the same matrix and the measuring geometries. For evaluation of γ spectra, the Hyperlab program (2005) was used. Table 1
2.4. Radiochemical purification of radium from barium The analytical scheme for determination of 226Ra was based on coprecipitation of Ba(Ra)(Th)SO4 (Sill and Willis, 1964; Kimura and Kobayashi, 1985; Burnett and Tai, 1992). The water sample of 0.5 L was transferred to a glass beaker and acidified with concentrated H2SO4. After addition of 133Ba and 229Th (225Ra) tracers, coprecipitation of radium was done with addition of 1 mL of Ba-carrier (30 mg mL-1). After settling,
the suspension was centrifuged and washed with distilled water. The precipitate containing radium, barium, as well as thorium sulphate was converted to more the soluble carbonate with addition of K2CO3 and heating over a low flame (Eichrom, 2005). Depending on the separation, the Ra(Ba)(Th)CO3 precipitate was dissolved in 1M HCl and 3M nitric acid, respectively.
2.4.1. Purification of radium by ion exchange chromatography Purification of Ra from Ba was done according to described procedures (Alvarado et al., 1995; Lawrie et al., 2000) Precipitate of Ra(Ba)(Th)CO3 was dissolved in 5 mL of 1M HCl and passed down a Dowex 50W-X8 (100-200 mesh) cation exchange column (Ø =1 cm, h=8 cm). The column was washed with 1.5M HCl to remove as much Ba as possible along with other potential interfering ions such as Mg, Ca, U and Th. Finally the Ra was eluted from the column with 6M HCl (Crespo and Jiménez, 1997). For preparation of thin sources for α-particle spectrometric measurements electrodeposition and microcoprecipitation were used.
2.4.2. Purification of radium by SR-resin Due to higher affinity for Ba compared to Ra, SR-resin (Eichrom Industries Inc.) was used for separation of Ra from Ba (Lawrie et al., 2000). Precipitate of Ba(Ra)(Th)CO3 was dissolved in 5 mL of 3M HNO3 and passed down a column filled with 2g of SR-resin (Ø =1cm, h=8cm) in 3M nitric acid medium. Ra was eluted in approximately two column volumes after the dead volume of the column. For preparation of thin sources for α-particle spectrometric measurements electrodeposition and microcoprecipitation were used.
2.5. Source preparation for α-particle spectrometry 2.5.1. Electrodeposition The solutions from both separation procedures were evaporated to dryness. After evaporation to dryness, the sample was treated with 2 mL of concentrated HCl with addition of 400 µg of platinum standard solution and again evaporated to dryness. Residue was dissolved in 0.17M ammonium oxalate solution and acidified with HCl to pH 2.6 (Alvarado et al., 1995). Radium radioisotopes were electroplated for 2 hours at 600 mA on stainless steel disc. The disc with electroplated radium were measured by γ-ray spectrometry for 225Ra yield determination and by α-particle spectrometry for determination of 226Ra.
2.5.2. Microcoprecipitation A slightly modified procedure of microprecipitation based on filtration of the Ba(Ra)SO4 precipitate as described by Lozano (Lozano et al., 1997) was used. Remain solutions after both separation procedures were acidified with concentrated H2SO4. Precipitation of radium was performed with addition of Pb2+ solution. The PbSO4 precipitate containing radium was dissolved in 4 mL 0.1M EDTA, prepared in 0.5M NaOH. With stirring, 1:1 acetic acid solution was added until pH 4-5 was reached, thus precipitating RaSO4, while Pb2+ ions remained in solution. Saturated Na2SO4 solution and 0.125 mg mL-1 BaSO4 suspension were added, acting as a seeding precipitate to obtain small particles. The suspension was allowed to settle for 30 min and filtered through a 25 mm 0.1 μm polypropylene filter. The filter with Ba(Ra)SO4 deposit was dried and mounted on an aluminium disc and measured by γ-ray spectrometry for 225Ra yield determination and by α-particle spectrometry for determination of 226Ra.
3. Results and discussion The addition of 133Ba tracer allowed checking the purification of Ra from Ba by measurements with γ-ray spectrometry. 133Ba has intensive γ lines between 30 – 36 keV which do not overlap the 225Ra line at 40.1 keV. Fig 1 shows a γ-ray spectrum of mixed 225Ra and 133Ba tracers measured by a low-level HP Ge detector. Fig. 1. When separation with ion exchange chromatography was performed, Ra and Ba cannot be quantitatively separated since the Ba fraction contains up to 20% of Ra, while the reminder of the Ra fraction can be eluted with increasing hydrochloric acid concentration. It was found that Th isotopes could be present in the Ra fraction, for that reason prior separation of Th by anion exchange or TEVA resin should be performed to prevent cross contamination. Since the separation of Th before separation of Ra by cation exchange chromatography is quite time consuming, we wished to find a way to separate Ba from Ra. As proposed Lawrie (Lawrie et al., 2000) we used SR spec resins. The experiment showed that even when such high amounts of Ba are present (30 mg of Ba2+), it is still well retained on the column. Ra being eluted in approximately two column volumes after the dead volume of the column. Fig. 2 shows elution of radium from barium from SR resins in 3M nitric acid. Fig. 2. As was already mentioned, electrodeposition for preparation of thin source for α particle-spectrometry was checked. A low electrodeposition efficiency was obtained (less than 40%). On the other side, if separation of Ra from Th is not complete, Th is also deposited on the disc. Fig. 3 shows an α-particle spectrum of isolated radium radioisotopes with impurities of 229Th, prepared by electrodeposition. When 229Th is
present as an impurity, determination of recovery via 217At is not correct. Activity of 217
At not depends only on its origin from separated 225Ra, but its activity permanently
increases also due to its ingrowth from impurities of 229Th.. Detailed evaluation of recovery via 217At is described elsewhere (Crespo, 2000: Benedik et al., 2010). Fig. 3. Fig. 4 shows an α-particle spectrum of isolated radium radioisotopes with their decay products prepared by Ba(Ra)SO4 microcoprecipitation after separation of Ra from Ba by using SR resins. Recoveries obtained when microcoprecipitation as technique for source preparation was applied were between 60 – 80% for all samples analysed. Fig. 4.
4. Conclusions Evaluation of the stages for separation of Ra from Ba by using cation exchange chromatography and Sr spec resins and their influence on the radiochemical purification and on the quality of thin sources preparation for α-particle spectrometry with microcoprecipitation and electrodeposition were studied. Gamma emitting tracers 225Ra and 133Ba were used for checking the efficiency of radiochemical purification. When for separation the cation exchange chromatography was applied in the electrodeposited source impurities of 229Th were observed. Presented study showed that SR Spec resin is the right choice for separation of Ra from Ba due to their higher affinity for Ba compared to Ra. Due to the low electrodeposition efficiency obtained, Ba(Ra)SO4 microcoprecipitation after chemical separation was therefore considered as a method of source preparation.
Acknowledgements This work was financially supported by Ministry of Education, Science and Sport of Slovenia (Project P1-0143).
References Alvarado, J. S., Orlandini, K. A., Erickson, M. D., 1995. Rapid determination of radium isotopes by alpha spectrometry. Journal of Radioanalytical and Nuclear Chemistry, Articles 194 (1),163-172. Benedik, L., Repinc, U., Štrok, M., 2010. Evaluation of procedures for determination of Ra-226 in water by α-particle spectrometry with emphasis on the recovery. Appl. Radiat. Isotopes 68, 1221-1225. Blanco, P., Lozano, J. C., Vera Tomé, F., 2002. On the use of 225Ra as yield tracer and Ba(Ra)SO4 microprecipitation in 226Ra determination by α-spectrometry. Appl. Radiat. Isotopes 57, 785-790. Burnett, W. C., Tai, W. C., 1992. Determination of Radium in Natural Waters by α Liquid Scintillation. Anal. Chem. 64, 1691-1697. Crespo, M. T., 2000. On the determination of 226Ra in environmental and geological samples by α-spectrometry using 225Ra as yield tracer. Appl. Radiat. Isotopes 53, 109-114. Crespo, M. T., Jiménez, A. S., 1997. On the determination of radium by alphaspectrometry. Journal of Radioanalytical and Nuclear Chemistry 221 (1-2), 149-152. Eichrom (2005) Analytical Procedures-Radium-228 in Water-RAW01. Rev 1.1. Analytical Procedures, Eichrom Technologies, Inc.
Hancock, G. J., Martin, P., 1991. Determination of Ra in Environmental Samples by α-particle Spectrometry. Appl. Radiat. Isotopes 42, 63-69. HyperLab (2005) System, Installation and Quick Start Guide, HyperLabs Software, Budapest, Hungary. Kimura, T., Kobayashi, Y., 1985. Coprecipitation of uranium and thorium with barium sulfate. Journal of radioanalytical and Nuclear Chemistry, Articles 91 (1), 59-65. Lawrie, W. C., Desmond, J. A., Spence, D., Anderson, S., Edmondson, C., 2000. Determination of radium-226 in environmental and personal monitoring samples. Appl. Radiat. Isotopes 53, 133-137. Lozano J.C., Fernandez F., Gomez J.M.G., 1997. Determination of radium isotopes by BaSO4 coprecipitation for the preparation of alpha-spectrometric sources. Journal of Radioanalytical and Nuclear Chemistry 223 (1-2), 133-137. NUCLEARDATA: (http://www.nucleardata.nuclear.lu.se/toi/). Sill, C. W., 1987. Determination of Ra-226 in ores, nuclear wastes and environmental samples by high resolution α-spectrometry. Nucl. Chem. Waste Manage, 7, 239-256. Sill, C. W., Willis, C. P., 1964. Precipitation of Submicrogram Quantities of Thorium by Barium Sulfate and Application to Fluorometric Determination of Thorium in Mineralogical And Biological Samples. Anal. Chem. 34 (3), 622-630. Smith, K. A., Mercer, E. R., 1970. The determination of radium-226 and radium-228 in Soils and Plants, using Radium-225 as a yield tracer. Journal of Radioanalytical Chemistry 5, 303-312.
Figure captions:
Fig. 1. Gamma-ray spectrum of mixed 225Ra and 133Ba tracers measured by a lowlevel HP Ge detector.
300 250
Ba-133
counts
200 150 100
Ba-133
Ra-225
50
0 20
30
40
50
Energy (keV)
Fig. 1.
Fig. 2. Elution of radium and barium from SR resins in 3M nitric acid.
35
Ra-225
30
Ba-133 % eluted
25 20 15 10 5 0 2
6
10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 70 74
Volume (mL)
60
Fig. 2.
Fig. 3. Alpha-particle spectrum of isolated radium radioisotopes with impurities of 229
Th, prepared by electrodeposition.
500
450 400
Counts
350 300 250
Ra-226
200 150
Th-229
100 50 0 4000
4500
5000
5500
6000
6500
7000
7500
Energy (keV)
Fig. 3.
Fig. 4. Alpha-particle spectrum of isolated radium radioisotopes, prepared by Ba(Ra)SO4 microcoprecipitation. 140
At-217
120
Ac-225
Counts
100 80
Fr-221
Ra-226
60 40
Rn-222
Po-218
20 0 4000
4500
5000
5500
6000
Energy (keV)
Fig. 4.
6500
7000
7500
Table 1: Radioactive characteristics of radionuclides used in this study (NUCLEARDATA).
Radionuclide
t1/2
Ba-133
10,52
Eα (Pα %)
Eγ (Pγ %)
(keV)
(keV) 30.625 (34.9) 30.973 (64.5) 34.920 (5.99) 34.987 (11.6) 35.818 (3.58) 356.017 (62.05)
7.340x103 y
Th-229
4814.6 (9.30) 4838 (5.0) 4845.3 (56.2) 4901.0 (10.2)
Ra-226
1600 y
4601 (5.55) 4784 (94.45)
Ra-225
14.9 d
40.09 (30.0)
Highlights:
Procedures for separation of radium from barium were tested
Sr spec resin allows quantitative separation of Ra from Ba.
Ba-133 and Ra-225 as tracers were used
Electrodeposition and microcoprecipitation for source preparation were applied
PII: DOI: Reference:
S0969-8043(15)30320-1 http://dx.doi.org/10.1016/j.apradiso.2015.11.089 ARI7272
To appear in: Applied Radiation and Isotopes Received date: 10 April 2015 Accepted date: 25 November 2015 Cite this article as: L. Benedik, Evaluation of procedures for 226Ra determination in samples with high barium concentration by α-particle spectrometry, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2015.11.089 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Evaluation of procedures for 226Ra determination in samples with high barium concentration by α-particle spectrometry
L. Benedik* Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
Abstract The γ emitter 133Ba is the most often used tracer in determination of 226Ra by αparticle spectrometry. If the source for α-particle spectrometry is prepared by microcoprecipitation, a high Ba concentration causes a thicker source layer which results in reduced counting efficiency due to self-absorption on the α spectrometer and consequently lower result for 226Ra, while not effecting the measurement of 133Ba in γ-ray spectrometry. If the electrodeposition is used, recoveries of deposited Ra and Ba are not necessarily the same and impurities of other α emitters may interfere with the α spectrum.
Keywords: Ra-226, Ra-225, Ba-133 and Th-229; radiochemical separation; electrodeposition; microcoprecipitation; α-particle spectrometry; γ-ray spectrometry
*
Corresponding author. Tel.: + 386 1 5885 347; fax: + 386 1 5885 346. E-mail address: [email protected] (L. Benedik).
1. Introduction Alpha-particle spectrometry in combination with radiochemical separation allows determination of very low activity concentrations of 226Ra. Some simple and specific separation methods for radium have been reported, but the preparation of sources of sufficient spectrometric quality, which requires many chemical operations, is difficult. Each step in the chemical separation process can result in unavoidable losses of the analyte, therefore yield tracers must be used to evaluate the chemical yield. For the preparation of the thin sources for high resolution α-particle spectrometry electrodeposition and/or micro-coprecipitation with rare earths are the most often used methods. In the case of 226Ra, several tracers such as for example 133Ba, 225Ra, 224Ra and 223
Ra have been used. Radium-224, which occurs naturally as a descendant of the Th decay scheme, is an -emitter and has a half-life of only 3.66 days. Due to its
232
short half-life continuous production of the isotope is necessary through a milking process from old stock of 232U. Radium-225 with a half-life of 14.8 days, the first descendant of 229Th, is a - and -emitter and it does not occur naturally (Crespo, 2000; Blanco et al., 2002). Its γ line at 40.0 keV has a reasonably high emission probability (30.0%), which make it suitable for measurement with a low energy γ-ray detector. On the other hand, its immediate descendants (225Ac, 221Fr, 217At) are emitters and evaluation of the recovery is possible via indirect measurement via 217At at 7076 keV using ingrowth-decay equations (Smith and Mercer, 1970; Hancock and Martin, 1991; Crespo, 2000; Blanco et al., 2002; Benedik et al., 2010). Barium-133 is often used as a yield tracer for radium (Lozano et al, 1997). Although Ba and Ra are both alkaline earth elements, there are significant differences in their chemical properties. Sill (Sill, 1987) demonstrated that 226Ra and 133Ba suffer from differences
in quantitative chemistry, which could lead to an inaccurate calculation of the chemical yield. Evaluation of procedures for determination of 226Ra in water samples by α-particle spectrometry with emphasis on the recovery using different yield tracers 223
Ra, 225Ra and 133Ba was presented in our previous study (Benedik et al, 2010). The aim of this study was to evaluate the stages of separation Ra from Ba in
waste water samples by using ion exchange and extraction chromatography and thin sources preparation for α-particle spectrometry with microcoprecipitation and electrodeposition, and to consider the use of 225Ra for yield determination.
2. Experimental 2.1. Samples Samples were collected in the surrounding of the former uranium mine and mill. During the process of yellow cake production, the major tailings consisted of the sulphuric acid-leached crushed ore, neutralized with lime and deposited on the waste disposal site. The mill tailings consists up to 1000 Bq kg-1 and up to 4000 Bq kg-1 d.w of 238U and 226Ra, respectively. Groundwater seeps through the tailings, leaching its constituents, which contaminate the outflow. Water samples contain elevated activity concentrations of uranium and radium (approximately 200 mBq/L) and high concentrations of calcium, magnesium, barium, sulphate and chloride ions.
2.2. Reagents All chemical reagents were of analytical grade. The ion exchange resin Dowex 50W-X8, (100-200 mesh, Serva) and SR-resin (Eichrom) were used.
The tracer solutions 133Ba (SRS 82709A-482) and 229Th (SRS 76224-482) used in the study were prepared from calibrated solutions purchased from Analytics, Inc (Atlanta, GA, USA). The producer maintains traceability to the NIST. A Pt solution (980 g/mL Pt in 5% HCl) was purchased from Aldrich Chemical Company.
2.3. Instruments An α spectrometer (CANBERRA's Alpha Analyst™) with passivated implanted planar silicon (PIPS) semiconductor detectors with an active area of 450 mm2 and 28% efficiency for 25 mm diameter discs was used for α-particle spectrometry measurements. The calibration of the detectors was made with a standard radionuclide source, containing 238U, 234U, 239Pu and 241Am (code: 67978-121), obtained from Analytics, Inc. A low energy HP Ge detector (Canberra, model GL2020-7500) was used for measurement of the γ emitting nuclides presented in Table 1. To avoid bias in the measurements, sample and standard were prepared in the same matrix and the measuring geometries. For evaluation of γ spectra, the Hyperlab program (2005) was used. Table 1
2.4. Radiochemical purification of radium from barium The analytical scheme for determination of 226Ra was based on coprecipitation of Ba(Ra)(Th)SO4 (Sill and Willis, 1964; Kimura and Kobayashi, 1985; Burnett and Tai, 1992). The water sample of 0.5 L was transferred to a glass beaker and acidified with concentrated H2SO4. After addition of 133Ba and 229Th (225Ra) tracers, coprecipitation of radium was done with addition of 1 mL of Ba-carrier (30 mg mL-1). After settling,
the suspension was centrifuged and washed with distilled water. The precipitate containing radium, barium, as well as thorium sulphate was converted to more the soluble carbonate with addition of K2CO3 and heating over a low flame (Eichrom, 2005). Depending on the separation, the Ra(Ba)(Th)CO3 precipitate was dissolved in 1M HCl and 3M nitric acid, respectively.
2.4.1. Purification of radium by ion exchange chromatography Purification of Ra from Ba was done according to described procedures (Alvarado et al., 1995; Lawrie et al., 2000) Precipitate of Ra(Ba)(Th)CO3 was dissolved in 5 mL of 1M HCl and passed down a Dowex 50W-X8 (100-200 mesh) cation exchange column (Ø =1 cm, h=8 cm). The column was washed with 1.5M HCl to remove as much Ba as possible along with other potential interfering ions such as Mg, Ca, U and Th. Finally the Ra was eluted from the column with 6M HCl (Crespo and Jiménez, 1997). For preparation of thin sources for α-particle spectrometric measurements electrodeposition and microcoprecipitation were used.
2.4.2. Purification of radium by SR-resin Due to higher affinity for Ba compared to Ra, SR-resin (Eichrom Industries Inc.) was used for separation of Ra from Ba (Lawrie et al., 2000). Precipitate of Ba(Ra)(Th)CO3 was dissolved in 5 mL of 3M HNO3 and passed down a column filled with 2g of SR-resin (Ø =1cm, h=8cm) in 3M nitric acid medium. Ra was eluted in approximately two column volumes after the dead volume of the column. For preparation of thin sources for α-particle spectrometric measurements electrodeposition and microcoprecipitation were used.
2.5. Source preparation for α-particle spectrometry 2.5.1. Electrodeposition The solutions from both separation procedures were evaporated to dryness. After evaporation to dryness, the sample was treated with 2 mL of concentrated HCl with addition of 400 µg of platinum standard solution and again evaporated to dryness. Residue was dissolved in 0.17M ammonium oxalate solution and acidified with HCl to pH 2.6 (Alvarado et al., 1995). Radium radioisotopes were electroplated for 2 hours at 600 mA on stainless steel disc. The disc with electroplated radium were measured by γ-ray spectrometry for 225Ra yield determination and by α-particle spectrometry for determination of 226Ra.
2.5.2. Microcoprecipitation A slightly modified procedure of microprecipitation based on filtration of the Ba(Ra)SO4 precipitate as described by Lozano (Lozano et al., 1997) was used. Remain solutions after both separation procedures were acidified with concentrated H2SO4. Precipitation of radium was performed with addition of Pb2+ solution. The PbSO4 precipitate containing radium was dissolved in 4 mL 0.1M EDTA, prepared in 0.5M NaOH. With stirring, 1:1 acetic acid solution was added until pH 4-5 was reached, thus precipitating RaSO4, while Pb2+ ions remained in solution. Saturated Na2SO4 solution and 0.125 mg mL-1 BaSO4 suspension were added, acting as a seeding precipitate to obtain small particles. The suspension was allowed to settle for 30 min and filtered through a 25 mm 0.1 μm polypropylene filter. The filter with Ba(Ra)SO4 deposit was dried and mounted on an aluminium disc and measured by γ-ray spectrometry for 225Ra yield determination and by α-particle spectrometry for determination of 226Ra.
3. Results and discussion The addition of 133Ba tracer allowed checking the purification of Ra from Ba by measurements with γ-ray spectrometry. 133Ba has intensive γ lines between 30 – 36 keV which do not overlap the 225Ra line at 40.1 keV. Fig 1 shows a γ-ray spectrum of mixed 225Ra and 133Ba tracers measured by a low-level HP Ge detector. Fig. 1. When separation with ion exchange chromatography was performed, Ra and Ba cannot be quantitatively separated since the Ba fraction contains up to 20% of Ra, while the reminder of the Ra fraction can be eluted with increasing hydrochloric acid concentration. It was found that Th isotopes could be present in the Ra fraction, for that reason prior separation of Th by anion exchange or TEVA resin should be performed to prevent cross contamination. Since the separation of Th before separation of Ra by cation exchange chromatography is quite time consuming, we wished to find a way to separate Ba from Ra. As proposed Lawrie (Lawrie et al., 2000) we used SR spec resins. The experiment showed that even when such high amounts of Ba are present (30 mg of Ba2+), it is still well retained on the column. Ra being eluted in approximately two column volumes after the dead volume of the column. Fig. 2 shows elution of radium from barium from SR resins in 3M nitric acid. Fig. 2. As was already mentioned, electrodeposition for preparation of thin source for α particle-spectrometry was checked. A low electrodeposition efficiency was obtained (less than 40%). On the other side, if separation of Ra from Th is not complete, Th is also deposited on the disc. Fig. 3 shows an α-particle spectrum of isolated radium radioisotopes with impurities of 229Th, prepared by electrodeposition. When 229Th is
present as an impurity, determination of recovery via 217At is not correct. Activity of 217
At not depends only on its origin from separated 225Ra, but its activity permanently
increases also due to its ingrowth from impurities of 229Th.. Detailed evaluation of recovery via 217At is described elsewhere (Crespo, 2000: Benedik et al., 2010). Fig. 3. Fig. 4 shows an α-particle spectrum of isolated radium radioisotopes with their decay products prepared by Ba(Ra)SO4 microcoprecipitation after separation of Ra from Ba by using SR resins. Recoveries obtained when microcoprecipitation as technique for source preparation was applied were between 60 – 80% for all samples analysed. Fig. 4.
4. Conclusions Evaluation of the stages for separation of Ra from Ba by using cation exchange chromatography and Sr spec resins and their influence on the radiochemical purification and on the quality of thin sources preparation for α-particle spectrometry with microcoprecipitation and electrodeposition were studied. Gamma emitting tracers 225Ra and 133Ba were used for checking the efficiency of radiochemical purification. When for separation the cation exchange chromatography was applied in the electrodeposited source impurities of 229Th were observed. Presented study showed that SR Spec resin is the right choice for separation of Ra from Ba due to their higher affinity for Ba compared to Ra. Due to the low electrodeposition efficiency obtained, Ba(Ra)SO4 microcoprecipitation after chemical separation was therefore considered as a method of source preparation.
Acknowledgements This work was financially supported by Ministry of Education, Science and Sport of Slovenia (Project P1-0143).
References Alvarado, J. S., Orlandini, K. A., Erickson, M. D., 1995. Rapid determination of radium isotopes by alpha spectrometry. Journal of Radioanalytical and Nuclear Chemistry, Articles 194 (1),163-172. Benedik, L., Repinc, U., Štrok, M., 2010. Evaluation of procedures for determination of Ra-226 in water by α-particle spectrometry with emphasis on the recovery. Appl. Radiat. Isotopes 68, 1221-1225. Blanco, P., Lozano, J. C., Vera Tomé, F., 2002. On the use of 225Ra as yield tracer and Ba(Ra)SO4 microprecipitation in 226Ra determination by α-spectrometry. Appl. Radiat. Isotopes 57, 785-790. Burnett, W. C., Tai, W. C., 1992. Determination of Radium in Natural Waters by α Liquid Scintillation. Anal. Chem. 64, 1691-1697. Crespo, M. T., 2000. On the determination of 226Ra in environmental and geological samples by α-spectrometry using 225Ra as yield tracer. Appl. Radiat. Isotopes 53, 109-114. Crespo, M. T., Jiménez, A. S., 1997. On the determination of radium by alphaspectrometry. Journal of Radioanalytical and Nuclear Chemistry 221 (1-2), 149-152. Eichrom (2005) Analytical Procedures-Radium-228 in Water-RAW01. Rev 1.1. Analytical Procedures, Eichrom Technologies, Inc.
Hancock, G. J., Martin, P., 1991. Determination of Ra in Environmental Samples by α-particle Spectrometry. Appl. Radiat. Isotopes 42, 63-69. HyperLab (2005) System, Installation and Quick Start Guide, HyperLabs Software, Budapest, Hungary. Kimura, T., Kobayashi, Y., 1985. Coprecipitation of uranium and thorium with barium sulfate. Journal of radioanalytical and Nuclear Chemistry, Articles 91 (1), 59-65. Lawrie, W. C., Desmond, J. A., Spence, D., Anderson, S., Edmondson, C., 2000. Determination of radium-226 in environmental and personal monitoring samples. Appl. Radiat. Isotopes 53, 133-137. Lozano J.C., Fernandez F., Gomez J.M.G., 1997. Determination of radium isotopes by BaSO4 coprecipitation for the preparation of alpha-spectrometric sources. Journal of Radioanalytical and Nuclear Chemistry 223 (1-2), 133-137. NUCLEARDATA: (http://www.nucleardata.nuclear.lu.se/toi/). Sill, C. W., 1987. Determination of Ra-226 in ores, nuclear wastes and environmental samples by high resolution α-spectrometry. Nucl. Chem. Waste Manage, 7, 239-256. Sill, C. W., Willis, C. P., 1964. Precipitation of Submicrogram Quantities of Thorium by Barium Sulfate and Application to Fluorometric Determination of Thorium in Mineralogical And Biological Samples. Anal. Chem. 34 (3), 622-630. Smith, K. A., Mercer, E. R., 1970. The determination of radium-226 and radium-228 in Soils and Plants, using Radium-225 as a yield tracer. Journal of Radioanalytical Chemistry 5, 303-312.
Figure captions:
Fig. 1. Gamma-ray spectrum of mixed 225Ra and 133Ba tracers measured by a lowlevel HP Ge detector.
300 250
Ba-133
counts
200 150 100
Ba-133
Ra-225
50
0 20
30
40
50
Energy (keV)
Fig. 1.
Fig. 2. Elution of radium and barium from SR resins in 3M nitric acid.
35
Ra-225
30
Ba-133 % eluted
25 20 15 10 5 0 2
6
10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 70 74
Volume (mL)
60
Fig. 2.
Fig. 3. Alpha-particle spectrum of isolated radium radioisotopes with impurities of 229
Th, prepared by electrodeposition.
500
450 400
Counts
350 300 250
Ra-226
200 150
Th-229
100 50 0 4000
4500
5000
5500
6000
6500
7000
7500
Energy (keV)
Fig. 3.
Fig. 4. Alpha-particle spectrum of isolated radium radioisotopes, prepared by Ba(Ra)SO4 microcoprecipitation. 140
At-217
120
Ac-225
Counts
100 80
Fr-221
Ra-226
60 40
Rn-222
Po-218
20 0 4000
4500
5000
5500
6000
Energy (keV)
Fig. 4.
6500
7000
7500
Table 1: Radioactive characteristics of radionuclides used in this study (NUCLEARDATA).
Radionuclide
t1/2
Ba-133
10,52
Eα (Pα %)
Eγ (Pγ %)
(keV)
(keV) 30.625 (34.9) 30.973 (64.5) 34.920 (5.99) 34.987 (11.6) 35.818 (3.58) 356.017 (62.05)
7.340x103 y
Th-229
4814.6 (9.30) 4838 (5.0) 4845.3 (56.2) 4901.0 (10.2)
Ra-226
1600 y
4601 (5.55) 4784 (94.45)
Ra-225
14.9 d
40.09 (30.0)
Highlights:
Procedures for separation of radium from barium were tested
Sr spec resin allows quantitative separation of Ra from Ba.
Ba-133 and Ra-225 as tracers were used
Electrodeposition and microcoprecipitation for source preparation were applied