Environmental Laboratory Accreditation Course for Radiochemistry

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					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
Instrumentation & Methods:
Alpha Scintillation Counter
Ra226, Ra228


           Lynn West

  Wisconsin State Lab of Hygiene
Method Review

   Radium 226 (EPA 903.1)
   Radium 228 (EPA 904.0)
   Alpha-Emitting Radium Isotopes
    (EPA 903.0)
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
Radiochemical Characteristics

Isotope T1/2     Decay   Series
                 Mode
223Ra   11.1 D   Alpha   Actinium
                         (235U)
224Ra   3.6 D    Alpha   Thorium
                         (232Th)
226Ra   1622 A   Alpha   Uranium
                         (238U)
228Ra   5.8 A    Beta    Thorium
                         (232Th)
Radium 226 (EPA 903.1)

   Prescribed Procedures for
    Measurement of Radioactivity in
    Drinking Water
   EPA 600 4- 80-032
   August 1980
Interferences

   No radioactive interferences
   The original method does not use a
    yield correction
238U   decay series
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
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
A typical radon de-                                                         Scintillation cell
                           Vacuum gauge
emanation system
                                                                        Stopcock 5

                                                                      Helium gas in


                                                         Stopcock 3

     Bubbler                     Stopcock 4


     Scintillation Cell                                                              Stopcock 1

     Vacuum System
      & gauge
     Avoid using Hg
      manometer if
                                                        Stopcock 2


      possible             Components
                                                           Solution
                                                            level

                                               Vacuum applied
                              Support



                                                         Bubbler
                            O-ring joint
                                                     Sintered disc


                             Stopcock
Scintillation Cell
 222Rn   from sample is
    collected in the cell
   Progeny establish
    secular equilibrium
    in about 4 hrs
   The alpha counts          Zn(Tl)S


    from 222Rn & its
    progeny are             Quartz Window

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

          GB                1               1                t3
D                                                 
     2.22  E  V  Y 1  exp(  t1 ) exp(  t2 ) 1  exp(  t3 )


        1.96  (G  B ) / t3          1                 1                 t3
UNC                                                           
          2.22  E  V  Y     1  exp(   t1 ) exp(   t 2 ) 1  exp(   t3 )



        4.66  B / t3          1                 1                 t3
DL                                                     
       2.22  E  V  Y 1  exp(   t1 ) exp(   t 2 ) 1  exp(   t3 )
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
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
Method Quality Control, cont.

   Instrument operating procedure
    should describe
       Daily control charts and acceptance
        limits
       Required action
       Preventative maintenance
    Method SOP main sections
   SCOPE AND APPLICATION      METHOD:
   SUMMARY OF METHOD           DETERMINATION OF 226RA
   REGULATORY DEVIATIONS      CALIBRATION OF
   METHOD PERFORMANCE          SCINTILLATION CELLS
   SAFETY                     CALCULATIONS
   SAMPLE HANDLING &          QUALITY CONTROL
    PRESERVATION               WASTE DISPOSAL
   INTERFERENCES              POLLUTION PREVENTION
   DEFINITIONS                REFERENCES
   EQUIPMENT                  FIGURES
   REAGENTS
Radium 228 (EPA 904.0)

   Prescribed Procedures for
    Measurement of Radioactivity in
    Drinking Water
   EPA 600 4- 80-032
   August 1980
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.
232Th-   decay series
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
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)
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
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
Gas flow proportional counter
      window assembly
Instrument Calibration
   Each instrument        Use isotope with
    system needs to         beta energy
    be calibrated           approximately
   Calibration             equal to 0.404 keV
    samples should be      Use NIST
    prepared in the         traceable
    same manner as          standards
    the samples.           Perform yearly or
                            after repairs
        Calculations


             GB                t              1             1
  D                                2
                                                         
        2.22  E  V  R 1  exp(  t ) 1  exp(  t ) exp(  t )
                                             2            3             1




        1.96  (G  B) / t        t              1             1
UNC                     2
                                        2
                                                           
          2.22  E  V  R 1  exp(  t ) 1  exp(  t ) exp(  t )
                                                 2            3             1




        4.66  B / t           t              1             1
DL                 2
                                2
                                                        
       2.22  E  V  R 1  exp(  t ) 1  exp(  t ) exp(  t )
                                         2            3             1
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
Method Quality Control, cont.

   Instrument operating procedure
    should describe
       Daily control charts and acceptance
        limits
       Required action
       Preventative maintenance
    Method SOP main sections
   SCOPE AND APPLICATION      METHOD:
   SUMMARY OF METHOD           DETERMINATION OF 228RA
   REGULATORY DEVIATIONS      CALIBRATION OF
   METHOD PERFORMANCE          INSTRUMENT
   SAFETY                     CALCULATIONS
   SAMPLE HANDLING &          QUALITY CONTROL
    PRESERVATION               WASTE DISPOSAL
   INTERFERENCES              POLLUTION PREVENTION
   DEFINITIONS                REFERENCES
   EQUIPMENT                  FIGURES
   REAGENTS
Alpha-Emitting Radium Isotopes
(EPA 903.0)
   Prescribed Procedures for
    Measurement of Radioactivity in
    Drinking Water
   EPA 600 4- 80-032
   August 1980
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
Th-232                    Th-228
1.4×1010 y                1.90 y
                                                                  Atomic
                                                                  number
             Ac-228
             6.13 hours
                                                                  (Z)

Ra-228                    Ra-224                      Mass
5.75 y                    3.64 days
                                                      number
                                                      (N)

                                                               alpha decay
                          Rn-220
                          54.5 s


                                                               beta decay

                          Po-216                  Po-212
                          158 ms                  300 ns
                                            67%
                                       Bi-212
                                       60.6 m
                                                                       232
                                                                            Th- decay series
                          Pb-212                Pb-208
                          10.6 hours        33% stable

                                       Tl-208
                                       3.1 m
             U-238                U-234
             4.4×109 y            2.48×105 y


                         Pa-234
                         1.18 m
                                                                              Atomic
             Th-234               Th-230                                      number
             24.1 d               8.0×104 y                                   (Z)

                                                             Mass
                                                             number
                                  Ra-226                     (N)
                                  1622 y


                                                                 alpha decay
238
   U decay series
                                  Rn-222
                                  3.825 d
                                                                 beta decay



                                  Po-218                Po-214                 Po-210
                                  3.05 m                1.6×10-4 s             138.4 d


                                                                     Bi-210
                                               Bi-214
                                                                     5.0 d
                                               19.7 m

                                  Pb-214                Pb-210                 Pb-206
                                  26.8 m                22 a                   stable
             U-235
             7.3×108 y


                         Pa-231
                         3.48×104 y
                                                                                 Atomic
             Th-231                   Th-227                                     number
             25.6 h                   18.17 d                                    (Z)
                         Ac-227                                  Mass
                         22.0 y
                                                                 number
                                      Ra-223                     (N)
                                      11.7 d


                         Fr-223                                       alpha decay
                         22 m
235
   U decay series
                                      Rn-219
                                      3.92 s
                                                                      beta decay
                         At-219                     At-215
                         0.9 m                      10-4 s


                                      Po-215                 Po-211
                                      1.83×10-3 s            0.52 s


                         Bi-215                                         Bi-210
                                                    Bi-211
                         8m                                             5.0 d
                                                    2.15 m

                                      Pb-211                 Pb-207
                                      36.1 m                 stable


                                                    Tl-207
                                                    4.79 m
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
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
Instrumentation (EPA 903.0)

   Low background gas flow
    proportional counter
       P-10 counting gas (10% CH4 & 90%
        Ar)
   Alpha scintillation counter
Instrument Calibration (EPA 903.0)
   Each instrument        Use NIST
    system needs to         traceable
    be calibrated           standards
   Calibration            Perform yearly or
    samples should be       after repairs
    prepared using
    226Ra
Calculations (EPA 903.0)


                   GB
         D
            2.22  E  V  I  R

                1.96  (G  B) / t
        UNC 
                2.22  E  V  I  R


                 4.66  B / t
       DL 
              2.22  E  V  I  R
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
Method Quality Control, Cont. (903.0)

   Instrument operating procedure
    should describe
       Daily control charts and acceptance
        limits
       Required action
       Preventative maintenance
    Method SOP main sections (903.0)
   SCOPE AND APPLICATION      METHOD:
   SUMMARY OF METHOD           DETERMINATION OF 228RA
   REGULATORY DEVIATIONS      CALIBRATION OF
   METHOD PERFORMANCE          INSTRUMENT
   SAFETY                     CALCULATIONS
   SAMPLE HANDLING &          QUALITY CONTROL
    PRESERVATION               WASTE DISPOSAL
   INTERFERENCES              POLLUTION PREVENTION
   DEFINITIONS                REFERENCES
   EQUIPMENT                  FIGURES
   REAGENTS
Instrumentation & Methods:
Gamma Spectroscopy


          Lynn West

  Wisconsin State Lab of Hygiene
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
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           222
     88 Ra         86
                      Rn   + 4He + energy
                             2
Review of Radioactive Modes of
Decay, Cont.

   Properties of
    Alpha Decay
       Alpha particle and




                               Counts
        progeny (recoil
        nucleus) have well-
        defined energies
        spectroscopy based
                                   4.5                             5.5
                                        Energy (MeV)

        on alpha-particle      Alpha spectrum at the theoretical
        energies is possible   limit of energy resolution
Review of Radioactive Modes of
Decay, Cont.

   Properties of beta (negatron)
    decay
       No change in mass number of progeny.
       Progeny gains 1 nuclear charge
       Beta particle, antineutrino, and recoil
        nucleus have a continuous range of
        energies
       no spectroscopy of elements is possible
       Often followed by emission of gamma
Review of Radioactive Modes of
Decay, cont.

   Cl-36




               Ar-36    Counts      Energy (MeV)



               Beta Emission from Cl-36.

      From G. F. Knoll,
      Radiation Detection and Measurement, 3rd Ed., (2000).
Review of Radioactive Modes of
Decay, Cont.

   Properties of Positron decay
       No change in mass number of progeny
       Progeny loses 1 nuclear charge
       Positron, neutrino, and recoil nucleus
        have a continuous range of energies
       no spectroscopy of elements is possible
        Positron is an anti-particle of an
        electron
Review of Radioactive Modes of
Decay, Cont.

   Properties of Positron decay
       When the positron comes in contact
        with an electron, the particles are
        annihilated
       Two photons are created each with an
        energy of 511 keV (the rest mass of an
        electron)
       The annihilation peak is a typical
        feature of a spectrum
Review of Radioactive Modes of
Decay, Cont.

   Other modes of decay
       Electron Capture
          Neutron deficient isotopes
          Electron is captured by the nucleus from
           an outer electron shell
          Vacancy left from captured electron is
           filled in by electrons from higher energy
           shells
          X-rays are released in the process
Review of Radioactive Modes of
Decay, Cont.

   Other modes of decay
       Auger electrons
          Excitation of the atom resulting in the ejection
           of an outer electron
       Internal conversion electrons
          Excitation of the nucleus resulting in the
           ejection of an outer electron
       Bremsstrahlung
          “Braking” radiation

          Photon emitted by a charged particle as it
           slows down
          Adds to the continuum
Review of Radioactive Modes of
Decay, Cont.

   Gamma Emission
       No change in mass, protons, or
        neutrons
       Excess excitation energy is given off as
        electromagnetic radiation, usually
        following alpha or beta decay
       Gamma emissions are high-energy,
        short-wave-length
Source:
http://lasp.colorado.edu
Review of Radioactive Modes of
Decay, Cont.

   Gamma Emission Decay Schemes
                KEY
PE Photoelectric absorption
CS Compton scattering
                                                                                   γ
PP Pair production                                        Source
γ gamma-ray
e- Electron
                                             γ
e Positron

                                                                                                          e-



                                                     γ              γ
                                                                γ                                    e   511            γ


                                                                                        511      γ
                                       CS                                PE
                                  e-
                                                 γ                            e-
               Pb X Ray                                   e-
                                            CS

                                                           PP
Pb Shielding




                                                                    e-




                                                                                                          Pb Shielding
                                                     e-
                              γ                                                        511   γ
                                            CS                      e
                                   e-                     511   γ
   Gamma Spectrum Features




Source: Practical Gamma-Ray Spectrometry, Gilmore & Hemingway
Resolution
Basic Electronic Schematic – Gamma
Spectroscopy

                           Low Voltage
                           Supply




                                                     Multichannel
 Detector   Preamplifier                 Amplifier
                                                     Analyzer (MCA)




                       Detector Bias
                       Supply
Configurations of Ge Detectors
                                                                       Electrical contact



   True coaxial                          Closed-end coaxial


                                 n+ contact



                         Holes                                Holes




             Electrons
                                                        Electrons




                                                               +

p+ contact


   p-type coaxial,                                   n-type coaxial,
   ∏-type                                            v-type
Nature of Semi-conductors

   Good conductors are atoms with
    less than four valence electrons
   atoms with only 1 valance electron
    are the best conductors
   examples
       copper
       silver
       gold
Nature of Semi-conductors, Cont.

   Good insulators are atoms with
    more than four valence electrons
   atoms with 8 valance electron are
    the best insulators
   examples
       noble gases
Nature of Semi-conductors, Cont.

   Semiconductors are made of atoms
    with four valence electrons
   they are neither good conductors
    nor good insulators
   examples
       germanium
       silicon
Nature of Semi-conductors, Cont.

   Energy Band Diagram
      CONDUCTION
         BAND         CONDUCTION     CONDUCTION
                         BAND           BAND



       FORBIDDEN      FORBIDDEN
         BAND           BAND


                                    VALENCE BAND
                    VALENCE BAND
     VALENCE BAND


       Insulator    Semiconductor    Conductor
Nature of Semi-conductors, Cont.

   Covalent bonds are formed in
    semiconductors
       the atoms are arranged in definite
        crystalline structure
       the arrangement is repeated
        throughout the material
       each atom is covalently bonded to 4
        other atoms
Nature of Semi-conductors, cont.
Pure Semi-conductor

   Each atom has 8 shared electrons
   there are no free electrons
       or no electrons in the conduction band
   however, thermal energy can cause
    some valence electrons to gain
    enough energy to move in to the
    conduction band
       this leads to the formation of a “hole”
Nature of Semi-conductors, cont.
Pure Semi-conductor

   Both holes (+) & free electrons (-)
    are current carriers
   a pure semi conductor has few
    carriers of either type
   more carriers lead to more current
   doping is the process used to
    increase the number of carriers in a
    semiconductor
Nature of Semi-conductors, cont.
Pure Semi-conductor

   Impurities can be added during the
    production of the semiconductor,
    this is called doping
   The impurities are either trivalent or
    pentavalent
   trivalent examples
       indium, gallium, boron
   pentavalent examples
       arsenic, phosphorus, antimony
n-type Semiconductor
   An impurity with 5 valence electrons
    (group V) will form 4 covalent
    bonds with the atoms of the
    semiconductor
   One electron is left over & loosely
    held by the atom
   This type of impurity is known as
    donor impurities.
   There are more negative carriers
n-type Semiconductor



                    CONDUCTION
                       BAND

  Donor electron
  forbidden band                  Valence electron
                                  forbidden band

  Donor electron   VALENCE BAND
  Energy level
p-type semiconductors
   An impurity with 3 valence electrons
    (group III) will form 3 covalent
    bonds with the atoms of the
    semiconductor
   The absence of the fourth electron
    leaves a hole
   This type of impurity is known as
    acceptor impurities.
   There are more positive carriers
p-type Semiconductor, cont.


                   CONDUCTION
                      BAND

 Acceptor hole
 forbidden band                  Valence electron
                                 forbidden band

 Acceptor hole    VALENCE BAND
 Energy level
     Depletion Zone
     p-type     n-type
     ++ +      -                   In the depletion zone
         ++           - -           the charge carriers
      ++        -   -
      + ++           -              have canceled each
          +    -    - -
                                    other out
      + ++
    - + +             -- -- +      voltage is developed
                       --
      ++ +
        +             --            across the depletion
       + ++           --            zone due to the charge
                                    separation
V
                       Vc

          Depletion zone
Calibration/Efficiency

   Ideally, calibration sources would be
    prepared such that a point
    calibration is performed for each
    nuclide reported
        this is totally impractical for analyzing
        routine unknown samples
   Sources should be prepared to have
    identical shape and density as the
    sample
Calibration/Efficiency

   Differences in density are less
    important than differences in
    geometry
       Newer software packages allow the
        user to create different efficiencies
        mathematically
   Source strength should not be so
    great as to cause pile-up
Calibration/Efficiency
   The calibration energies should cover the
    entire range of interest
   For close to the detector geometries,
    choose a multi-lined source made from a
    combination of nuclides which do not
    suffer from True Coincidence Summing
    (TCS). See Table 7.2 pg 153 Gilmore, G.
    and Hemingway, J. 1995. Practical
    Gamma-Ray Spectrometry. John Wiley &
    Sons, New York
Coincidence Summing
   True Coincidence Summing (TCS)
       The summing of gamma rays emitted
        almost simultaneously from the nucleus
        resulting in a negative bias from the
        true value
       Larger detectors suffer more from TCS
        than do smaller detectors
       TCS can be expected whenever
        samples contain nuclides with
        complicated decay schemes
Coincidence Summing

   True Coincidence Summing (TCS)
       TCS can be expected whenever
        samples contain nuclides with
        complicated decay schemes
       The degree of TCS is not dependent on
        count rate
       TCS is geometry dependent and is
        worse for close to the detector
        geometries
Coincidence Summing
   True Coincidence Summing (TCS)
       TCS is geometry dependent and is
        worse for close to the detector
        geometries
       Summed pulses will not be rejected by
        the pile-up rejection circuitry because
        the pulses will not be misshapen
       For detectors with thin windows X-rays
        that would normally be absorbed in the
        end cap may contribute to TCS
       Well detectors suffer the worst from
        TCS
Coincidence Summing

   True Coincidence Summing (TCS)
       Newer software packages have systems
        for reduces this problem
Coincidence Summing

   Random Coincidence Summing
       Also known as pile-up
       Two or more gamma rays being
        detected at nearly the same time
       Counts are lost from the full-energy
        peaks in the spectrum
       Affected by count rate
       Pile-up rejection circuitry reduces
        problem
Sample Preparation

   Acidify water samples
       Note: Iodine is volatile in acidic solutions
   Active material should be distributed
    evenly throughout the geometry
       Samples should be homogenous
   Calibration materials should simulate
    samples (actual or mathematical)
Daily Instrument Checks

   Short background count
   Linearity check
   Resolution check
   Additionally, a long background
    count is needed for background
    subtraction
Instrumentation & Methods:
Gamma Emitting
Radionuclides USEPA 901.1


          Jeff Brenner

  Minnesota Department of Health
EPA Method 901.1
Gamma Emitting Radionuclides

   Gamma Emitting Radionuclides




        g
EPA Method 901.1
What we’ll cover
   Scope of the method
   Summary of the method
   Calibration
       Determining energy calibration
       Determining efficiency calibration
       Determining system background
   Quality control
   Interferences
   Application
   Calculations
       Activity
EPA Method 901.1
Scope
   The method is applicable for
    analyzing water samples
   Measurement of gamma photons
    emitted from radionuclides without
    separating them from the sample
    matrix.
   Radionuclides emitting gamma
    photons with the following energy
    range of 60 to 2000 keV.
EPA Method 901.1
Gamma Emitting Radionuclides Summary

   Water sample is
    preserved in the
    field or lab with
    nitric acid

   Homogeneous
    aliquot of the
    preserved sample
    is measured in a
    calibrated
    geometry.
EPA Method 901.1
Gamma Emitting Radionuclides Summary
   Sample aliquots are counted long
    enough to meet the required sensitivity.
EPA Method 901.1
Gamma Emitting Radionuclides Summary
EPA Method 901.1
Gamma Emitting Radionuclides Summary
EPA Method 901.1 Calibrations
Gamma Emitting Radionuclides

    Library of radionuclide gamma energy
     spectra is prepared
    Use known radionuclide concentrations in
     standard sample geometries to establish
     energy calibration.
    Single solution containing a mixture of
     fission products emitting
        Low energy
        Medium energy
        High energy
        Example (Sb-125, Eu154, and Eu-155)
EPA Method 901.1
Gamma Emitting Radionuclides Summary

                              86.54   Eu-155
                             105.31   Eu-155
                             123.07   Eu-154
                             176.33   Sb-125
                             247.93   Eu-154
                             427.89   Sb-125
                             463.38   Sb-125
                             591.76   Eu-154
                             600.56   Sb-125
                             635.90   Sb-125
                             692.42   Eu-154
                             723.30   Eu-154
                             756.86   Eu-154
                             873.20   Eu-154
                             996.30   Eu-154
                            1004.76   Eu-154
                            1274.51   Eu-154
                            1596.45   Eu-154
EPA Method 901.1
Gamma Emitting Radionuclides

   Counting efficiencies for the various
    gamma energies are determined
    from the activity counts of those
    known standard values.
   A counting efficiency vs. gamma
    energy curve is determined for each
    container geometry and for each
    detector.
EPA Method 901.1
Gamma Emitting Radionuclides Summary

                               86.54   Eu-155
                              105.31   Eu-155
                              176.33   Sb-125
                              427.89   Sb-125
                              463.38   Sb-125
                              600.56   Sb-125
                              996.30   Eu-154
                             1004.76   Eu-154
                             1274.51   Eu-154
EPA Method 901.1 Calibrations
Gamma Emitting Radionuclides

   FWHM used to monitor peak shape
       Smaller tolerance for low energy
       Greater tolerance for high energy
   Document a few FWHM to
    determine instrument drift
EPA Method 901.1
Gamma Emitting Radionuclides Summary

                               86.54   Eu-155
                              105.31   Eu-155
                              123.07   Eu-154
                              176.33   Sb-125
                              247.93   Eu-154
                              427.89   Sb-125
                              463.38   Sb-125
                              591.76   Eu-154
                              600.56   Sb-125
                              635.90   Sb-125
                              692.42   Eu-154
                              723.30   Eu-154
                              756.86   Eu-154
                              873.20   Eu-154
                              996.30   Eu-154
                             1004.76   Eu-154
                             1274.51   Eu-154
                             1596.45   Eu-154
EPA Method 901.1
Gamma Emitting Radionuclides Summary
EPA Method 901.1
(Determine System Background)

   Contribution of the background
    must be measured
   Measure under the same conditions,
    counting mode, as the samples
   Background determination is
    performed every time the liquid
    nitrogen is filled
EPA Method 901.1
(Batch Quality Control)
   Instrument efficiency check
       Analyzed daily
       Control chart
       Establish action limits
   Low background check
       Analyzed weekly
       Control chart
       Establish action limits
   Analytical Batch
       Sample Duplicates at a 10% frequency
       Sample Spikes at a 5% frequency
       Control chart
       Establish action limits
EPA Method 901.1
Interferences
   Significant interference occurs when
    counting a sample with a NaI(Tl)
    detector.
       Sample radionuclides emit gamma
        photons of nearly identical energies.
   Sample homogeneity is important to
    gamma count reproducibility and
    counting efficiency.
       Add HNO3 to water sample container to
        lessen the problem of radionuclides
        adsorbing to the container
    EPA Method 901.1
    Application
   The limits set forth in PL 93-523, 40 CFR
    34324 recommend that in the case of man-
    made radionuclides, the limiting
    concentration is that which will produce an
    annual dose equivalent to 4 mrem/year.

   If several radionuclides are present, the
    sum of their annual dose equivalent must
    not exceed 4 mrem/year.

				
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