ASTM E181-98(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E181 – 98 (Reapproved 2003)
Standard Test Methods for
Detector Calibration and Analysis of Radionuclides
This standard is issued under the fixed designation E181; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
Sections
Detectors for Simple Spectra 16
1.1 These methods cover general procedures for the cali-
Calibration and Usage of Scintillation
brationofradiationdetectorsandtheanalysisofradionuclides.
Detectors for Complex Spectra 17
Counting Methods:
Foreachindividualradionuclide,oneormoreofthesemethods
Beta Particle Counting 25-26
may apply.
Aluminum Absorption Curve 27-31
1.2 These methods are concerned only with specific radio-
Alpha Particle Counting 32-39
Liquid Scintillation Counting 40-48
nuclide measurements. The chemical and physical properties
of the radionuclides are not within the scope of this standard.
1.4 This standard does not purport to address all of the
1.3 The measurement standards appear in the following
safety problems, if any, associated with its use. It is the
order:
responsibility of the user of this standard to establish appro-
Sections
priate safety and health practices and determine the applica-
Spectroscopy Methods:
bility of regulatory limitations prior to use.
Calibration and Usage of Germa-
nium Detectors 3-12
2. Referenced Document
Calibration and Usage of Scintillation
Detector Systems: 13-20
2.1 ASTM Standards:
Calibration and Usage of Scintillation
E170 TerminologyRelatingtoRadiationMeasurementsand
Dosimetry
These methods are under the jurisdiction ofASTM Committee E10 on Nuclear
Technology and Applications . For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 10, 1998. Published January 1999. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1961T. Last previous edition approved in 1998 as E181–98. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E0181-98R03. the ASTM website.
SPECTROSCOPY METHODS
3. Terminology 3.1.4 national radioactivity standard source—a calibrated
radioactive source prepared and distributed as a standard
3.1 Definitions:
reference material by the U.S. National Institute of Standards
3.1.1 certified radioactivity standard source—a calibrated
and Technology.
radioactive source, with stated accuracy, whose calibration is
3.1.5 resolution, gamma ray—the measured FWHM, after
certified by the source supplier as traceable to the National
background subtraction, of a gamma-ray peak distribution,
Radioactivity Measurements System (1).
expressed in units of energy.
3.1.2 check source—a radioactivity source, not necessarily
3.2 Abbreviations:Abbreviations:
calibrated, that is used to confirm the continuing satisfactory
3.2.1 MCA—Multichannel Analyzer.
operation of an instrument.
3.2.2 SCA—Single Channel Analyzer.
3.1.3 FWHM—(full width at half maximum) the full width
3.2.3 ROI—Region-Of-Interest.
of a gamma-ray peak distribution measured at half the maxi-
3.3 For other relevant terms, see Terminology E170.
mum ordinate above the continuum.
3.4 correlated photon summing—the simultaneous detec-
tion of two or more photons originating from a single nuclear
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
disintegration.
these methods.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E181 – 98 (2003)
3.5 dead time—the time after a triggering pulse during source should be used to check the stability of the system at
which the system is unable to retrigger. least before and after the calibration.
NOTE 1—The terms “standard source” and “radioactivity standard” are
8. Calibration Procedure
general terms used to refer to the sources and standards of National
Radioactivity Standard Source and Certified Radioactivity Standard
8.1 Energy Calibration—Determine the energy calibration
Source.
(channel number versus gamma-ray energy) of the detector
system at a fixed gain by determining the channel numbers
CALIBRATION AND USAGE OF GERMANIUM
corresponding to full energy peak centroids from gamma rays
DETECTORS
emittedoverthefullenergyrangeofinterestfrommultipeaked
or multinuclide radioactivity sources, or both. Determine
4. Scope
nonlinearity correction factors as necessary (5).
4.1 Thisstandardestablishesmethodsforcalibration,usage,
8.1.1 Usingsuitablegamma-raycompilations(6-14),plotor
and performance testing of germanium detectors for the
fit to an appropriate mathematical function the values for peak
measurement of gamma-ray emission rates of radionuclides. It
centroid (in channels) versus gamma energy.
coverstheenergyandfull-energypeakefficiencycalibrationas
8.2 Effıciency Calibration:
well as the determination of gamma-ray energies in the 0.06 to
8.2.1 Accumulate an energy spectrum using calibrated ra-
2-MeV energy region and is designed to yield gamma-ray
dioactivity standards at a desired and reproducible source-to-
emission rates with an uncertainty of 63% (see Note 2). This
detector distance. At least 20 000 net counts should be
method applies primarily to measurements that do not involve
accumulated in each full-energy gamma-ray peak of interest
overlapping peaks, and in which peak-to-continuum consider-
using National or Certified Radioactivity Standard Sources, or
ations are not important.
both (see 12.1, 12.5, and 12.6).
NOTE 2—Uncertainty U is given at the 68% confidence level; that is,
8.2.2 For each standard source, obtain the net count rate
2 2
U 5 =(s 11 3(d where d are the estimated maximum system- (total count rate of region of interest minus the Compton
i / i i
atic uncertainties, and s are the random uncertainties at the 68%
i continuum count rate and, if applicable, the ambient back-
confidence level (2). Other methods of error analysis are in use (3, 4).
ground count rate within the same region) in the full-energy
gamma-raypeak,orpeaks,usingatestedmethodthatprovides
5. Apparatus
consistent results (see 12.2, 12.3, and 12.4).
5.1 Atypical gamma-ray spectrometry system consists of a
8.2.3 Correct the standard source emission rate for decay to
germanium detector (with its liquid nitrogen cryostat, pream-
the count time of 8.2.2.
plifier, and possibly a high-voltage filter) in conjunction with a
8.2.4 Calculate the full-energy peak efficiency, E, as fol-
f
detector bias supply, linear amplifier, multichannel analyzer,
lows:
and data readout device, for example, a printer, plotter,
N
p
oscilloscope, or computer. Gamma rays interact with the
E 5 (1)
f
N
g
detector to produce pulses which are analyzed and counted by
the supportive electronics system.
where:
E = full-energy peak efficiency (counts per gamma ray
f
6. Summary of Methods
emitted),
6.1 The purpose of these methods is to provide a standard-
N = net gamma-ray count in the full-energy peak (counts
p
izedbasisforthecalibrationandusageofgermaniumdetectors
per second live time) (Note 3) (see 8.2.2), and
for measurement of gamma-ray emission rates of radionu- N = gamma-ray emission rate (gamma rays per second).
g
clides. The method is intended for use by knowledgeable
NOTE 3—Any other unit of time is acceptable provided it is used
persons who are responsible for the development of correct
consistently throughout.
procedures for the calibration and usage of germanium detec-
8.2.5 There are many ways of calculating the net gamma-
tors.
ray count. The method presented here is a valid, common
6.2 A source emission rate for a gamma ray of a selected
method when there are no interferences from photopeaks
energy is determined from the counting rate in a full-energy
adjacenttothepeakofinterest,andwhenthecontinuumvaries
peak of a spectrum, together with the measured efficiency of
linearly from one side of the peak to the other.
the spectrometry system for that energy and source location. It
8.2.5.1 Other net peak area calculation methods can also be
is usually not possible to measure the efficiency directly with
used for single peaks, and must be used when there is
emission-rate standards at all desired energies. Therefore a
interference from adjacent peaks, or when the continuum does
curve or function is constructed to permit interpolation be-
not behave linearly. Other methods are acceptable, if they are
tween available calibration points.
used in a consistent manner and have been verified to provide
accurate results.
7. Preparation of Apparatus
8.2.5.2 Using a simple model, the net peak area for a single
7.1 Follow the manufacturer’s instructions for setting up
peak can be calculated as follows:
and preliminary testing of the equipment. Observe all of the
N 5 G 2 B 2 I (2)
manufacturer’s limitations and cautions. All tests described in
A s
Section 12 should be performed before starting the calibra-
where:
tions,andallcorrectionsshallbemadewhenrequired.Acheck
E181 – 98 (2003)
G = grosscountinthepeakregion-of-interest(ROI)inthe where:
s
T = live time of the sample spectrum,
sample spectrum,
s
T = live time of the background spectrum, and
B = continuum, and
b
I = number of counts in the background peak (if there is I = net background peak area in the background spec-
b
trum.
nobackgroundpeak,orifabackgroundsubtractionis
not performed, I = 0).
If a separate background measurement exists, the net back-
8.2.5.3 The net gamma-ray count, N is related to the net
p ground peak area is calculated from the following equation:
peak area as follows:
I 5 G 2 B (6)
b b b
N
A
N 5 (3)
p
where:
T
s
G = sum of gross counts in the background peak region
b
where T = spectrum live time.
s
(of the background spectrum), and
8.2.5.4 The continuum, B, is calculated from the sample
B = continuum counts in the background peak region (of
b
spectrum using the following equation (see Fig. 1):
the background spectrum).
N
The continuum counts in the background spectrum are
B 5 ~B 1 B ! (4)
1s 2s
2n
calculated from the following equation:
where:
N
N = number of channels in the peak ROI, B 5 ~B 1 B ! (7)
b 1b 2b
2n
n = number of continuum channels on each side,
B = sumofcountsinthelow-energycontinuumregionin
where:
1s
the sample spectrum, and
N = number of channels in the background peak ROI,
B = sum of counts in the high-energy continuum region n = number of continuum channels on each side (as-
2s
in the sample spectrum. sumed to be the same on both sides),
B = sumofcountsinthelow-energycontinuumregionin
1b
the background spectrum, and
B = sum of counts in the high-energy continuum region
2b
in the background spectrum.
8.2.5.5 If the standard source is calibrated in units of
Becquerels, the gamma-ray emission rate is given by
N 5 AP (8)
g g
where:
A = number of nuclear decays per second, and
P = probability per nuclear decay for the gamma ray
g
(7-14).
8.2.6 Plot, or fit to an appropriate mathematical function,
the values for full-energy peak efficiency (determined in 8.2.4)
versus gamma-ray energy (see 12.5) (15-23).
9. Measurement of Gamma-Ray Emission Rate of the
Sample
9.1 Place the sample to be measured at the source-to-
FIG. 1 Typical Spectral Peak With Parameters Used in the Peak
detector distance used for efficiency calibration (see 12.6).
Area Determination Indicated
9.1.1 Accumulate the gamma-ray spectrum, recording the
count duration.
NOTE 4—These equations assume that the channels that are used to
9.1.2 Determine the energy of the gamma rays present by
calculate the continuum do not overlap with the peak ROI, and are
adjacent to it, or have the same size gap between the two regions on both
use of the energy calibration obtained under, and at the same
sides.Adifferentequationmustbeused,ifthegapsareofadifferentsize.
gain as 8.1.
The peaked background, I, is calculated from a separate
9.1.3 Obtain the net count rate in each full-energy gamma-
background measurement using the following equation:
ray peak of interest as described in 8.2.2.
T
9.1.4 Determine the full-energy peak efficiency for each
s
I 5 I (5)
b
T
b energy of interest from the curve or function obtained in 8.2.5.
9.1.5 Calculate the number of gamma rays emitted per unit
live time for each full-energy peak as follows:
For simplicity of these calculations, n is assumed to be the same on both sides
N
of the peak. If the continuum is calculated using a different number of channels on p
N 5 (9)
g
the left of the peak than on the right of the peak, different equations must be used. E
f
E181 – 98 (2003)
When calculating a nuclear transmutation rate from a 10.1.4 Checktheefficiencycalibration(typicallymonthlyto
gamma-ray emission rate determined for a specific radionu- yearly)usingaNationalorCertifiedRadioactivityStandard(or
clide, a knowledge of the gamma-ray probability per decay is Standards) emitting gamma rays of widely differing energies.
required (7-14), that is, 10.2 Theresultsofallperformancechecksshallberecorded
in such a way that deviations from the norm will be readily
N
g
A 5 (10)
observable.Appropriate action, which could include confirma-
P
g
tion, repair, and recalibration as required, shall be taken when
9.1.6 Calculate the net peak area uncertainty as follows:
the measured values fall outside the predetermined limits.
2 2
N T
10.2.1 Inaddition,theaboveperformancechecks(see10.1)
s
S 5 G 1 ~B 1 B ! 1 ~S ! (11)
ΠS D S D
N s 1s 2s Ib
A
2n T
should be made after an event (such as power failures or
b
repairs) which might lead to potential changes in the system.
where:
N
11. Sources of Uncertainty
S 5 G 1 ~B 1 B ! (12)
ΠS D
Ib b 1b 2b
2n
11.1 Other than Poisson-distribution uncertainties, the prin-
and
cipal sources of uncertainty (and typical magnitudes) in this
S = net peak area uncertainty (at 1s confidence level),
method are:
NA
G = gross counts in the peak ROI of the sample spec-
s 11.1.1 The calibration of the standard source, including
trum,
uncertainties introduced in using a standard radioactivity
G = gross counts in the peak ROI of the background
b
solution, or aliquot thereof, to prepare another (working)
spectrum,
standard for counting (typically 63%).
N = number of channels in the peak ROI,
11.1.2 The reproducibility in the determination of net full-
n = number of continuum channels on each side (as-
energy peak counts (typically 62%).
sumed to be the same on both sides for these
11.1.3 The reproducibility of the positioning of the source
equations to be valid),
relative to the detector and the source geometry (typically
B = con
...