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
226
88 Ra
222
Rn
86
+ 42He + energy
Review of Radioactive Modes of
Decay, Cont.
Properties of
Alpha Decay


Alpha particle and
progeny (recoil
nucleus) have welldefined energies
spectroscopy based
on alpha-particle
energies is possible
Counts

4.5
5.5
Energy (MeV)
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
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
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,
Radon – 222Rn
Nickel – 63Ni
Carbon – 14C
131I
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


Distillation


Remove organic material
Collect middle fraction
Liquid Scintillation Counting
Calibration – Method

Raw water tritium standard



Background



Distilled
Recovery standard
Distilled
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


Reagent background


2 – 10 Xs detection limit
|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


4 laboratory fortified blanks (LFB)


< Detection limit (DL)
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
89Sr
50.55 days
Beta
MCL
pCi/L
80
90Sr
29.1 years
Beta
8
90Y
64.2 hours
Beta
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
Cause errors in recovery
Calcium


Precipitated as carbonate
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


Reagent background


2 – 10 Xs detection limit
|reagent background|< detection limit
Instrument drift
Quality Control, continued




Daily control charts
Acceptance limits
Corrective action
Preventative maintenance