1 / 67

Environmental Laboratory Accreditation Course for Radiochemistry: DAY THREE

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

nalani
Télécharger la présentation

Environmental Laboratory Accreditation Course for Radiochemistry: DAY THREE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. Instrumentation & Methods: Laser Phosphorimetry, Uranium Richard Sheibley Pennsylvania Dept of Env Protection

  3. Laser Phosphorimeter • UV excitation by pulsed nitrogen laser 337nm • Green luminescence at 494, 516 and 540 • Excitation 3-4 X 10-9sec

  4. Laser Phosphorimeter • Measure luminescence when laser is off • Use method of standard addition

  5. Instrumentation & Methods: Alpha Spectroscopy, Uranium Lynn West Wisconsin State Lab of Hygiene

  6. 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

  7. Counts 4.5 5.5 Energy (MeV) Review of Radioactive Modes of Decay, Cont. • Properties of Alpha Decay • Alpha particle and progeny (recoil nucleus) have well-defined energies • spectroscopy based on alpha-particle energies is possible Alpha spectrum at the theoretical limit of energy resolution

  8. Instrumentation – Alpha Spectroscopy • Types of detectors • Resolution • Spectroscopy • Calibration/Efficiency • Sample Preparation • Daily Instrument Checks

  9. Types of detectors (Alpha Spectroscopy) • Older technology • Diffused junction detector (DJD) • Surface barrier silicon detectors (SSB) • Ion Implanted Layers • Fully depleted detectors • State-of-the-art technology • Passivated implanted planar silicon detector (PIPS)

  10. PIPS • Good alpha resolution due very thin uniform entrance window • Surface is more rugged and can be cleaned • Low leakage current • Low noise • Bakable at high temperatures

  11. Alpha Spectrometer Detector • An example of a passivated implanted planar silicon detector • 600 mm2 active area • Resolution of 24 keV (FWHM)

  12. Alpha Spectrometer

  13. Resolution • Broadening of peaks is due to various sources of leakage current – “Noise” • Low energy tails result from trapping of charge carriers which results from the incomplete collection of the total energy deposited • Good resolution increases sensitivity (background below peak is reduced) • Resolution of 10 keV is achievable with PIPS (controlled conditions)

  14. U-238 U234 U232 Tracer Typical Alpha Spectrum

  15. Calibration/Efficiency • Energy calibration • Efficiency can be determined mathematically using Monte-Carlo simulation • Efficiency can be determined using a NIST traceable standard in same geometry as samples • Efficiency determination not always needed with tracers

  16. Sample Preparation • Final sample must be very thin to insure high resolution and minimize tailing. Also should stable & rugged • The following mounting techniques are commonly used: • Electrodeposition • Micro precipitation • Evaporation from organic solutions • Organics must be completely removed

  17. Sample Preparation • Chemical and radiochemical interferences must be removed during preparation • Nuclides must be removed which have energies close to the energies of the nuclide of interest, ie 15 to 30 keV • Ion exchange • Precipitation/coprecipitation techniques • Chemical extractions • Chemicals which might damage detector must be elimanted

  18. Sample Preparation • A radioactive tracer is used to determine the recovery of the nuclide of interest • Since a tracer is added to every sample, a matrix spiked sample is not required

  19. Sample Counting • Mounts with a small negative voltage can be used to help attract the recoil nucleus away from the detector • Reduces detector contamination

  20. Sample Counting • Analyst can choose distance from detector • Trade off is between efficiency & resolution • Count performed slightly above atm. pressure to reduce contamination

  21. Daily instrument checks • One hour background • Pulser check • Stability check

  22. Instrumentation & Methods: Liquid Scintillation Counters & Tritium Richard Sheibley Pennsylvania Dept of Env Protection

  23. Liquid Scintillation Counter • Principle • Beta particle emission • Energy transferred to Solute • Energy released as UV Pulse • Intensity proportional to beta particle initial energy

  24. Liquid Scintillation Counter • Low energy beta emitters • Tritium – 3H • Iodine – 125I, 129I, 131I • Radon – 222Rn • Nickel – 63Ni • Carbon – 14C

  25. Liquid Scintillation Counter • Energy Spectrum • Isotope specific • Beta particle • Neutrino • Total energy constant

  26. Liquid Scintillation Counter • Components • Vial with Sample + Scintillator • Photomultipliers • Multichannel Analyzer • Timer • Data collection & Output

  27. Liquid Scintillation Counter • Variables • Temperature • Counting room • Vial type glass vs. plastic • Cocktail • Energy window

  28. Liquid Scintillation Counter • Other considerations • Dark adapt • Static • Quenching

  29. Liquid Scintillation Counter • Interferences • Chemical • Absorbed beta energy • Optical • Photon absorption

  30. Liquid Scintillation Counter • Instrument Normalization • Photomultiplier response • Unquenched 14C Standard

  31. Liquid Scintillation Counter • Performance assessment • Carbon-14 Efficiency • Tritium Efficiency • Chi-square • Instrument Background

  32. Liquid Scintillation Counter • Method QC • Background • Reagent background • Efficiency • Method • Quench correction

  33. Tritium 3H (EPA 906.0 & SM7500-3H B) • Prescribed Procedures for Measurement of Radioactivity in Drinking Water • EPA 600 4-80-032 • August 1980 • Standard Methods 17th, 18th, 19th & 20th

  34. Interferences • Non-volatile radioactive material • Quenching materials • Double distill – eliminate radium • Static • Fluorescent lighting

  35. Tritium 3H Method Summary • Alkaline Permanganate Digestion • Remove organic material • Distillation • Collect middle fraction • Liquid Scintillation Counting

  36. Calibration – Method • Raw water tritium standard • Distilled • Recovery standard • Background • Distilled • Deep well water • Distilled water tritium standard • Distilled water to which 3H added • Not distilled

  37. Instrument Calibration • Calibrate each day of use • Instrument Normalization • Performance assessment • Carbon-14 Efficiency • Tritium Efficiency • Instrument Background • NIST traceable standards

  38. Calculations 3H(pCi/L) = (C-B)*1000 / 2.22*E*V*F Where: C = sample count rate, cpm B = background count rate, cpm E = counting efficiency F = recovery factor 2.22 = conversion factor, dpm/cpm

  39. Calculations Efficiency: E = (D-B)/G Where: D = distilled water standard count rate, cpm B = background count rate, cpm G = activity distilled water standard, dpm

  40. Calculations Recovery correction factor F = (L-B) / (E*M) Where: L = raw water standard count rate, cpm B = background count rate, cpm E = counting efficiency M = activity raw water standard (before distillation), dpm

  41. Quality Control • Batch Precision: • Sample duplicate OR • Matrix spike duplicate • Calculate relative percent difference • Calculate control limits • Should be < 20% • Frequency 1 per 20

  42. Quality Control, continued • Accuracy • Laboratory fortified blank • Matrix spike sample • 2 – 10 Xs detection limit • Reagent background • |reagent background|< detection limit • Instrument drift

  43. Quality Control, continued • Daily control charts • Acceptance limits • Corrective action • Preventative maintenance

  44. Standard Operating Procedure • Written • Reflect actual practice • Standard format – EMMC or NELAC

  45. Demonstration of Proficiency • Initial Method detection limit – MDL • 40 CFR 136, Appendix B • Alternate procedure • 4 reagent blanks • < Detection limit (DL) • 4 laboratory fortified blanks (LFB) • DL < LFB < MCL • Evaluate Recovery and Standard Deviation against method criteria

  46. Demonstration of Proficiency • Ongoing • Repeat initial demonstration of proficiency • Alternate procedure • 4 Reagent blanks and laboratory fortified blanks • Different batches • Non-consecutive days • Blank < Detection limit (DL) • LFB met method precision and accuracy criteria

  47. Instrumentation & Methods: Strontium 89, 90 Lynn West Wisconsin State Lab of Hygiene

  48. Method Review • Strontium 89, 90 • EPA 905.0, SM 7500-Sr B

  49. Radiochemical Characteristics

  50. Strontium (EPA 905.0, SM 7500-Sr B) • Prescribed Procedures for Measurement of Radioactivity in Drinking Water • EPA 600 4-80-032 • August 1980 • Standard Methods 17th, 18th, 19th & 20th

More Related