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. 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

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. Typical Alpha Spectrum
U232 Tracer

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

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 & SM7500-3H B)
Prescribed Procedures for Measurement of Radioactivity in Drinking Water
EPA
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 Background
Distilled
Recovery standard
Background
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
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

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

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

53. 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

54. 905.0 Method Summary Isolate Strontium Measure total strontium
Allow strontium to decay
Isolate strontium 90 daughter – yttrium 90
Measure yttrium 90

55. 905.0 Method Summary 1 L acidified sample Isolate Strontium
Add stable Sr carrier
Precipitate alkaline and rare earths as carbonate
Re-dissolve

56. 905.0 Method Summary Isolate Strontium(continued)
Precipitate as nitrate
Re-dissolve
Precipitate as carbonate
Determine chemical yield

57. 905.0 Method Summary Measure total strontium activity Determine 90Sr
Yttrium in growth – 2 weeks
Isolate yttrium
Determine 90Y

58. 905.0 Method Summary Determine 89Sr Calculated
Total strontium minus 90Sr

59. 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

60. 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

61. Calculations cont.
See handout

62. 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

63. 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

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

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

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

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