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

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

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

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

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

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

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 Energy (MeV) Counts 4.5 5.5 a spectroscopy of the elements based on alpha-particle energies is possible Alpha spectrum at the theoretical limit of energy resolution

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

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)

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

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

Alpha Spectrometer

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)

Typical Alpha Spectrum U232 Tracer

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

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 There are some other techiniques but probably not applicable to radiochemistry Organics must be completely removed to avoid damaging the detectors

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

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

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

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

Daily instrument checks One hour background Pulser check Stability check

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

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

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

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

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

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

Liquid Scintillation Counter Other considerations Dark adapt Static Quenching

Liquid Scintillation Counter Interferences Chemical Absorbed beta energy Optical Photon absorption

Liquid Scintillation Counter Instrument Normalization Photomultiplier response Unquenched 14C Standard

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

Liquid Scintillation Counter Method QC Background Reagent background Efficiency Method Quench correction

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Radiochemical Characteristics Isotope T1/2 Decay Mode MCL pCi/L 89Sr 50.55 days Beta 80 90Sr 29.1 years 8 90Y 64.2 hours N/A

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

Strontium Chemistry Chemically similar to Ca +2 oxidation state in solution Insoluble salts include: CO3 & NO3 “Real Chemistry”

Interferences Radioactive barium and radium Non-radioactive strontium Precipitated as carbonate Removed using chromate precipitation Non-radioactive strontium Cause errors in recovery Calcium Removed by repeated nitrate precipitations

905.0 Method Summary Isolate Strontium Measure total strontium Allow strontium to decay Isolate strontium 90 daughter – yttrium 90 Measure yttrium 90

905.0 Method Summary 1 L acidified sample Isolate Strontium Add stable Sr carrier Precipitate alkaline and rare earths as carbonate Re-dissolve

905.0 Method Summary Isolate Strontium(continued) Precipitate as nitrate Re-dissolve Precipitate as carbonate Determine chemical yield

905.0 Method Summary Measure total strontium activity Determine 90Sr Yttrium in growth – 2 weeks Isolate yttrium Determine 90Y

905.0 Method Summary Determine 89Sr Calculated Total strontium minus 90Sr

905.0 Method Summary Calculations include Recovery correction In-growth correction – yttrium Total strontium Strontium 90 Decay correction – yttrium Isolation of Y to end of count time

Calculation total strontium Total strontium activity (D) D = C / 2.22*E*V*R where: C = net count rate, cpm E = counter efficiency for 90Sr V = sample volume, liters R = fractional chemical yield 2.22 = conversion factor dpm/pCi

Calculations cont. See handout

Calculations cont. Verify computer programs 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

Instrumentation Low background gas flow proportional counter P-10 counting gas (10% CH4 & 90% Ar) Due to in growth and short half-life of 90Y, time is critical

Instrument Calibration Isotope specific calibration 89Sr 90Sr 90Y Use NIST traceable standards Perform yearly or after repairs

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

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

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