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Environmental Laboratory Accreditation Course for Radiochemistry: DAY TWO

Environmental Laboratory Accreditation Course for Radiochemistry: DAY TWO. Presented by Minnesota Department of Health Pennsylvania Department of Environmental Protection U.S. Environmental Protection Agency Wisconsin State Laboratory of Hygiene.

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Environmental Laboratory Accreditation Course for Radiochemistry: DAY TWO

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  1. Environmental Laboratory Accreditation Course for Radiochemistry: DAY TWO Presented by Minnesota Department of Health Pennsylvania Department of Environmental Protection U.S. Environmental Protection Agency Wisconsin State Laboratory of Hygiene

  2. Instrumentation & Methods: Alpha Scintillation CounterRa226, Ra228 Lynn West Wisconsin State Lab of Hygiene

  3. Method Review • Radium 226 (EPA 903.1) • Radium 228 (EPA 904.0) • Alpha-Emitting Radium Isotopes (EPA 903.0)

  4. Radium Chemistry • Chemically similar to Ca & Ba • +2 oxidation state in solution • Insoluble salts include: CO3, SO4, & CrO4 • Forms a complex with EDTA • Property used extensively in analytical procedures

  5. Radiochemical Characteristics

  6. Radium 226 (EPA 903.1) • Prescribed Procedures for Measurement of Radioactivity in Drinking Water • EPA 600 4- 80-032 • August 1980

  7. Interferences • No radioactive interferences • The original method does not use a yield correction

  8. 238U decay series

  9. 903.1 Method Summary • 1 L acidified sample • Ra co-precipitated with stable Ba as SO4 • Precipitate is separated from sample matrix & supernate is discarded

  10. Method summary cont. • (Ba-Ra)SO4 is dissolved in EDTA • Solution Transferred to a “bubbler” • After a period of ingrowth, 222Rn is purged for sample & collected in scintillation cell .

  11. A typical radon de-emanation system • Bubbler • Scintillation Cell • Vacuum System & gauge • Avoid using Hg manometer if possible

  12. Zn(Tl)S Quartz Window Scintillation Cell • 222Rn from sample is collected in the cell • Progeny establish secular equilibrium in about 4 hrs • The alpha counts from 222Rn & its progeny are collected

  13. Alpha Scintillation Cell Counter • Sample counted 4 hrs after de-emanantion • Alpha particles interact with Zn(Ag)S coating & emit light • Light flashes are counted on a scaler

  14. Radon Cell Counters

  15. Each instrument system & scintillation cell needs to be calibrated Calibration samples should be prepared in the same manner as the samples. The entire de-emanation system effects the calibration measurement Use NIST traceable standards Perform yearly or after repairs Instrument Calibration

  16. Calculations

  17. Calculations cont. • Computer programs should be hand verified • Decay constants and time intervals must be in the same units of time • Minimum background count time should be equal to the minimum sample count time

  18. Method Quality Control • Per each batch of 20 samples, analyze the following: • Method blank • Laboratory control sample • Precision sample • Matrix spike sample • Established action limits for each

  19. Method Quality Control, cont. • Instrument operating procedure should describe • Daily control charts and acceptance limits • Required action • Preventative maintenance

  20. Method SOP main sections • SCOPE AND APPLICATION • SUMMARY OF METHOD • REGULATORY DEVIATIONS • METHOD PERFORMANCE • SAFETY • SAMPLE HANDLING & PRESERVATION • INTERFERENCES • DEFINITIONS • EQUIPMENT • REAGENTS • METHOD: DETERMINATION OF 226RA • CALIBRATION OF SCINTILLATION CELLS • CALCULATIONS • QUALITY CONTROL • WASTE DISPOSAL • POLLUTION PREVENTION • REFERENCES • FIGURES

  21. Radium 228 (EPA 904.0) • Prescribed Procedures for Measurement of Radioactivity in Drinking Water • EPA 600 4- 80-032 • August 1980

  22. Interferences • The presence of 90Sr in the water samples gives a positive bias to the measured 228Ra activity. • Due to the short half-life of 228Ac, a b emitter of similar energy is substituted during instrument calibration. A high or low bias may result depending on which isotope is selected. • Natural Ba may result in falsely high chemical yield.

  23. 232Th- decay series

  24. 904.0 Method Summary • 228Ra in a drinking water sample is co-precipitated with Ba & Pb as SO4 • The (Ba-Ra)SO4 precipitate is dissolved in basic EDTA. The progeny, 228Ac, is chemically separated from its parent by repeatedly forming the (Ba-Ra)SO4 • Allow at least 36 hrs for the ingrowth of 228Ac & secular equilibrium

  25. 904.0 Method Summary, cont. • 228Ac is then separated from 228Ra by precipitation as a OH-. (Save supernate) • This is the end of ingrowth & the beginning of 228Ac decay • 228Ac is co-precipitated with Y as (Ac-Y2(C2O4)3)

  26. 904.0 Method Summary, cont. • Transferred to a planchet & b counted on a low-background a/b proportional counter • The Ba carrier yield is found by precipitating the Ba from the supernatant as BaSO4

  27. Instrumentation • Low background gas flow proportional counter • P-10 counting gas (10% CH4 & 90% Ar) • Due to short half-life of 228Ac, a multi-detector system is desirable • 6.13 hr • Processing time from start of decay to count is about 250 m

  28. Gas flow proportional counterwindow assembly

  29. Instrument Calibration • Use isotope with beta energy approximately equal to 0.404 keV • Use NIST traceable standards • Perform yearly or after repairs • Each instrument system needs to be calibrated • Calibration samples should be prepared in the same manner as the samples.

  30. Calculations

  31. Method Quality Control • Per each batch of 20 samples, analyze the following: • Method blank • Laboratory control sample • Precision sample • Matrix spike sample • Established action limits for each

  32. Method Quality Control, cont. • Instrument operating procedure should describe • Daily control charts and acceptance limits • Required action • Preventative maintenance

  33. Method SOP main sections Method SOP main sections • METHOD: DETERMINATION OF 228RA • CALIBRATION OF INSTRUMENT • CALCULATIONS • QUALITY CONTROL • WASTE DISPOSAL • POLLUTION PREVENTION • REFERENCES • FIGURES • SCOPE AND APPLICATION • SUMMARY OF METHOD • REGULATORY DEVIATIONS • METHOD PERFORMANCE • SAFETY • SAMPLE HANDLING & PRESERVATION • INTERFERENCES • DEFINITIONS • EQUIPMENT • REAGENTS

  34. Alpha-Emitting Radium Isotopes (EPA 903.0) • Prescribed Procedures for Measurement of Radioactivity in Drinking Water • EPA 600 4- 80-032 • August 1980

  35. Interferences (EPA 903.0) • Natural Ba may result in falsely high chemical yield • Ingrowth of progeny must be corrected for • Method only corrects for 226Ra progeny • Does not accurately measure 226Ra if other alpha emitting isotopes are present • Calibration based only on 226Ra

  36. Th-228 1.90 y Th-232 1.4×1010 y Atomic number (Z) Ac-228 6.13 hours Mass number (N) Ra-224 3.64 days Ra-228 5.75 y alpha decay Rn-220 54.5 s beta decay Po-216 158 ms Po-212 300 ns 67% 232Th- decay series Bi-212 60.6 m Pb-208 stable Pb-212 10.6 hours 33% Tl-208 3.1 m

  37. U-234 2.48×105 y U-238 4.4×109 y Pa-234 1.18 m Atomic number (Z) Th-234 24.1 d Th-230 8.0×104 y Mass number (N) Ra-226 1622 y alpha decay 238U decay series Rn-222 3.825 d beta decay Po-214 1.6×10-4 s Po-210 138.4 d Po-218 3.05 m Bi-210 5.0 d Bi-214 19.7 m Pb-210 22 a Pb-206 stable Pb-214 26.8 m

  38. U-235 7.3×108 y Pa-231 3.48×104 y Atomic number (Z) Th-231 25.6 h Th-227 18.17 d Ac-227 22.0 y Mass number (N) Ra-223 11.7 d Fr-223 22 m alpha decay 235U decay series Rn-219 3.92 s beta decay At-219 0.9 m At-215 10-4 s Po-211 0.52 s Po-215 1.83×10-3 s Bi-210 5.0 d Bi-215 8 m Bi-211 2.15 m Pb-207 stable Pb-211 36.1 m Tl-207 4.79 m

  39. 903.0 Method Summary • 1 L acidified sample • Ra co-precipitated with stable Ba & Pb as SO4 • 223Ra • 224Ra • 226Ra • Precipitate is separated from sample matrix & supernate is discarded

  40. 903.0 Method Summary, Cont. • Progeny ingrowth starts with the final (Ba-Ra)SO4 precipitation. • Since a correction factor is applied to correct for ingrowth, care needs to be taken to avoid disturbing the radon progeny ingrowth after this step • Transfer to tared planchet & dry under infra-red heat lamp

  41. Instrumentation (EPA 903.0) • Low background gas flow proportional counter • P-10 counting gas (10% CH4 & 90% Ar) • Alpha scintillation counter

  42. Instrument Calibration (EPA 903.0) • Use NIST traceable standards • Perform yearly or after repairs • Each instrument system needs to be calibrated • Calibration samples should be prepared using 226Ra

  43. Calculations (EPA 903.0)

  44. Method Quality Control (EPA 903.0) • Per each batch of 20 samples, analyze the following: • Method blank • Laboratory control sample • Precision sample • Matrix spike sample • Established action limits for each • Demonstration of capability

  45. Method Quality Control, Cont. (903.0) • Instrument operating procedure should describe • Daily control charts and acceptance limits • Required action • Preventative maintenance

  46. Method SOP main sections Method SOP main sections (903.0) • METHOD: DETERMINATION OF 228RA • CALIBRATION OF INSTRUMENT • CALCULATIONS • QUALITY CONTROL • WASTE DISPOSAL • POLLUTION PREVENTION • REFERENCES • FIGURES • SCOPE AND APPLICATION • SUMMARY OF METHOD • REGULATORY DEVIATIONS • METHOD PERFORMANCE • SAFETY • SAMPLE HANDLING & PRESERVATION • INTERFERENCES • DEFINITIONS • EQUIPMENT • REAGENTS

  47. Instrumentation & Methods: Gamma Spectroscopy Lynn West Wisconsin State Lab of Hygiene

  48. Instrumentation – Gamma Spectroscopy/Alpha Spectroscopy • Quick review of Radioactive Decay (as it relates to σ & g spectroscopy) • Interaction of Gamma Rays with matter • Basic electronics • Configurations • Semi-conductors • Resolution • Spectroscopy • Calibration/Efficiency • Coincidence summing • Sample Preparation • Daily instrument checks

  49. Review of Radioactive Modes of Decay • Properties of Alpha Decay • Progeny loses of 4 AMU. • Progeny loses 2 nuclear charges • Often followed by emission of gamma

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