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
223Ra
11.1 D
Decay
Mode
Alpha
224Ra
3.6 D
Alpha
226Ra
1622 A
Alpha
228Ra
5.8 A
Beta
Series
Actinium
(235U)
Thorium
(232Th)
Uranium
(238U)
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 deemanation system
Scintillation cell
Vacuum gauge
Stopcock 5
Helium gas in
Stopcock 3




Bubbler
Scintillation Cell
Vacuum System &
gauge
Avoid using Hg
manometer if
possible
Stopcock 4
Stopcock 1
Stopcock 2
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
from 222Rn & its
progeny are
collected
Zn(Tl)S
Quartz Window
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
system &
scintillation cell
needs to be
calibrated
Calibration
samples should be
prepared in the
same manner as
the samples.



The entire deemanation system
effects the
calibration
measurement
Use NIST
traceable
standards
Perform yearly or
after repairs
Calculations
D
GB
1
1
 t



2.22  E  V  Y 1  exp(  t ) exp(  t ) 1  exp(  t )
3
1
UNC 
DL 
2
3
1.96  (G  B) / t3
1
1
  t3



2.22  E  V  Y
1  exp(  t1 ) exp(  t 2 ) 1  exp(  t3 )
4.66  B / t3
1
1
  t3



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
SUMMARY OF METHOD
REGULATORY DEVIATIONS
METHOD PERFORMANCE
SAFETY
SAMPLE HANDLING &
PRESERVATION
INTERFERENCES
DEFINITIONS
EQUIPMENT
REAGENTS








METHOD:
DETERMINATION OF 226RA
CALIBRATION OF
SCINTILLATION CELLS
CALCULATIONS
QUALITY CONTROL
WASTE DISPOSAL
POLLUTION PREVENTION
REFERENCES
FIGURES
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
system needs to
be calibrated
Calibration
samples should be
prepared in the
same manner as
the samples.



Use isotope with
beta energy
approximately
equal to 0.404 keV
Use NIST
traceable
standards
Perform yearly or
after repairs
Calculations
D
GB
 t
1
1



2.22  E  V  R 1  exp(   t ) 1  exp(   t ) exp(   t )
2
2
UNC 
3
1.96  (G  B) / t
 t
1
1



2.22  E  V  R 1  exp(   t ) 1  exp(   t ) exp(   t )
2
2
2
DL 
1
3
1
4.66  B / t
 t
1
1



2.22  E  V  R 1  exp(   t ) 1  exp(   t ) exp(   t )
2
2
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
SUMMARY OF METHOD
REGULATORY DEVIATIONS
METHOD PERFORMANCE
SAFETY
SAMPLE HANDLING &
PRESERVATION
INTERFERENCES
DEFINITIONS
EQUIPMENT
REAGENTS








METHOD:
DETERMINATION OF 228RA
CALIBRATION OF
INSTRUMENT
CALCULATIONS
QUALITY CONTROL
WASTE DISPOSAL
POLLUTION PREVENTION
REFERENCES
FIGURES
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-228
1.90 y
Th-232
1.4×1010 y
Atomic
number
(Z)
Ac-228
6.13 hours
Ra-228
5.75 y
Mass
number
(N)
Ra-224
3.64 days
alpha decay
Rn-220
54.5 s
beta decay
Po-216
158 ms
Po-212
300 ns
67%
Bi-212
60.6 m
Pb-212
10.6 hours
Pb-208
33% stable
Tl-208
3.1 m
Th- decay series
232
U-234
2.48×105 y
U-238
4.4×109 y
Pa-234
1.18 m
Th-234
24.1 d
Atomic
number
(Z)
Th-230
8.0×104 y
Mass
number
(N)
Ra-226
1622 y
alpha decay
U decay series
238
Rn-222
3.825 d
beta decay
Po-214
1.6×10-4 s
Po-218
3.05 m
Bi-210
5.0 d
Bi-214
19.7 m
Pb-214
26.8 m
Po-210
138.4 d
Pb-210
22 a
Pb-206
stable
U-235
7.3×108 y
Pa-231
3.48×104 y
Th-231
25.6 h
Atomic
number
(Z)
Th-227
18.17 d
Ac-227
22.0 y
Mass
number
(N)
Ra-223
11.7 d
U decay series
235
Fr-223
22 m
alpha decay
Rn-219
3.92 s
beta decay
At-219
0.9 m
At-215
10-4 s
Po-211
0.52 s
Po-215
1.83×10-3 s
Bi-215
8m
Bi-210
5.0 d
Bi-211
2.15 m
Pb-207
stable
Pb-211
36.1 m
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
system needs to
be calibrated
Calibration
samples should be
prepared using
226Ra


Use NIST
traceable
standards
Perform yearly or
after repairs
Calculations (EPA 903.0)
D
GB
2.22  E  V  I  R
UNC 
DL 
1.96  (G  B) / t
2.22  E  V  I  R
4.66  B / t
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
SUMMARY OF METHOD
REGULATORY DEVIATIONS
METHOD PERFORMANCE
SAFETY
SAMPLE HANDLING &
PRESERVATION
INTERFERENCES
DEFINITIONS
EQUIPMENT
REAGENTS








METHOD:
DETERMINATION OF 228RA
CALIBRATION OF
INSTRUMENT
CALCULATIONS
QUALITY CONTROL
WASTE DISPOSAL
POLLUTION PREVENTION
REFERENCES
FIGURES
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
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
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.
Counts
Cl-36
Ar-36
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
PP Pair production
γ gamma-ray
e- Electron
e Positron
γ
Source
γ
e-
γ
γ
γ
e
511
CS
e-
γ
Pb X Ray
e-
CS
PP
ee
CS
511
γ
511
γ
Pb Shielding
Pb Shielding
ee-
γ
PE
e-
γ
511
γ
Gamma Spectrum Features
Source: Practical Gamma-Ray Spectrometry, Gilmore & Hemingway
Resolution
Basic Electronic Schematic – Gamma
Spectroscopy
Low Voltage
Supply
Detector
Preamplifier
Detector Bias
Supply
Amplifier
Multichannel
Analyzer (MCA)
Configurations of Ge Detectors
Electrical contact
True coaxial
Closed-end coaxial
n+ contact
Holes
Electrons
Holes
Electrons
+
p+ contact
p-type coaxial,
∏-type
n-type coaxial,
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
FORBIDDEN
BAND
CONDUCTION
BAND
CONDUCTION
BAND
FORBIDDEN
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
Donor electron
Energy level
Valence electron
forbidden band
VALENCE BAND
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
Acceptor hole
Energy level
Valence electron
forbidden band
VALENCE BAND
Depletion Zone
p-type
++ +
++
++
+ + ++
+
+
- + ++
++++
+ ++
n-type
-
- - --- -- +
- ---
V
Vc
Depletion zone


In the depletion zone
the charge carriers
have canceled each
other out
voltage is developed
across the depletion
zone due to the charge
separation
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


Active material should be distributed
evenly throughout the geometry


Note: Iodine is volatile in acidic solutions
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
105.31
123.07
176.33
247.93
427.89
463.38
591.76
600.56
635.90
692.42
723.30
756.86
873.20
996.30
1004.76
1274.51
1596.45
Eu-155
Eu-155
Eu-154
Sb-125
Eu-154
Sb-125
Sb-125
Eu-154
Sb-125
Sb-125
Eu-154
Eu-154
Eu-154
Eu-154
Eu-154
Eu-154
Eu-154
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
105.31
176.33
427.89
463.38
600.56
996.30
1004.76
1274.51
Eu-155
Eu-155
Sb-125
Sb-125
Sb-125
Sb-125
Eu-154
Eu-154
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
105.31
123.07
176.33
247.93
427.89
463.38
591.76
600.56
635.90
692.42
723.30
756.86
873.20
996.30
1004.76
1274.51
1596.45
Eu-155
Eu-155
Eu-154
Sb-125
Eu-154
Sb-125
Sb-125
Eu-154
Sb-125
Sb-125
Eu-154
Eu-154
Eu-154
Eu-154
Eu-154
Eu-154
Eu-154
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




Low background check




Analyzed daily
Control chart
Establish action limits
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 manmade 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.