ASTM E181-98
(Test Method)Standard Test Methods for Detector Calibration and Analysis of Radionuclides
Standard Test Methods for Detector Calibration and Analysis of Radionuclides
SCOPE
1.1 These methods cover general procedures for the calibration of radiation detectors and the analysis of radionuclides. For each individual radionuclide, one or more of these methods may apply.
1.2 These methods are concerned only with specific radionuclide measurements. The chemical and physical properties of the radionuclides are not within the scope of this standard.
1.3 The measurement standards appear in the following order: Sections Spectroscopy Methods: Calibration and Usage of Germanium Detectors 3 to 12 Calibration and Usage of Scintillation Detector Systems: 13 to 20 Calibration and Usage of Scintillation Detectors for 16 Simple Spectra Calibration and Usage of Scintillation Detectors for 17 Complex Spectra Counting Methods: Beta Particle Counting 25 to 26 Aluminum Absorption Curve 27 to 31 Alpha Particle Counting 32 to 39 Liquid Scintillation Counting 40 to 48
1.4 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
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Designation: E 181 – 98
Standard Test Methods for
Detector Calibration and Analysis of Radionuclides
This standard is issued under the fixed designation E 181; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
Sections
Calibration and Usage of Scintillation
1.1 These methods cover general procedures for the cali-
Detectors for Simple Spectra 16
bration of radiation detectors and the analysis of radionuclides.
Calibration and Usage of Scintillation
Detectors for Complex Spectra 17
For each individual radionuclide, one or more of these methods
Counting Methods:
may apply.
Beta Particle Counting 25-26
1.2 These methods are concerned only with specific radio- Aluminum Absorption Curve 27-31
Alpha Particle Counting 32-39
nuclide measurements. The chemical and physical properties
Liquid Scintillation Counting 40-48
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
Spectroscopy Methods:
priate safety and health practices and determine the applica-
Calibration and Usage of Germa-
bility of regulatory limitations prior to use.
nium Detectors 3-12
Calibration and Usage of Scintillation
2. Referenced Document
Detector Systems: 13-20
2.1 ASTM Standards:
E 170 Terminology Relating to Radiation Measurements
and Dosimetry
These methods are under the jurisdiction of ASTM Committee E-10 on Nuclear
Technology and Applications .
Current edition approved June 10, 1998. Published January 1999. Originally
{1 2
published as E 181 – 61 T. Last previous edition E 181 – 93 . Annual Book of ASTM Standards, Vol 12.02.
SPECTROSCOPY METHODS
3. Terminology 3.1.5 resolution, gamma ray—the measured FWHM, after
background subtraction, of a gamma-ray peak distribution,
3.1 Definitions:
expressed in units of energy.
3.1.1 certified radioactivity standard source—a calibrated
3.2 Abbreviations:Abbreviations:
radioactive source, with stated accuracy, whose calibration is
3.2.1 MCA—Multichannel Analyzer.
certified by the source supplier as traceable to the National
3 3.2.2 SCA—Single Channel Analyzer.
Radioactivity Measurements System (1).
3.2.3 ROI—Region-Of-Interest.
3.1.2 check source—a radioactivity source, not necessarily
3.3 For other relevant terms, see Terminology E 170.
calibrated, that is used to confirm the continuing satisfactory
3.4 correlated photon summing—the simultaneous detec-
operation of an instrument.
tion of two or more photons originating from a single nuclear
3.1.3 FWHM—(full width at half maximum) the full width
disintegration.
of a gamma-ray peak distribution measured at half the maxi-
3.5 dead time—the time after a triggering pulse during
mum ordinate above the continuum.
which the system is unable to retrigger.
3.1.4 national radioactivity standard source—a calibrated
radioactive source prepared and distributed as a standard
NOTE 1—The terms “standard source” and “radioactivity standard” are
reference material by the U.S. National Institute of Standards general terms used to refer to the sources and standards of National
Radioactivity Standard Source and Certified Radioactivity Standard
and Technology.
Source.
The boldface numbers in parentheses refer to the list of references at the end of
these methods.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E181–98
CALIBRATION AND USAGE OF GERMANIUM system at a fixed gain by determining the channel numbers
DETECTORS corresponding to full energy peak centroids from gamma rays
emitted over the full energy range of interest from multipeaked
4. Scope
or multinuclide radioactivity sources, or both. Determine
nonlinearity correction factors as necessary (5).
4.1 This standard establishes methods for calibration, usage,
8.1.1 Using suitable gamma-ray compilations (6-14), plot or
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.
covers the energy and full-energy peak efficiency calibration as
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 1 1 3(d where d are the estimated maximum system-
i i i
/
(total count rate of region of interest minus the Compton
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
5. Apparatus
gamma-ray peak, or peaks, using a tested method that provides
consistent results (see 12.2, 12.3, and 12.4).
5.1 A typical 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-
detector bias supply, linear amplifier, multichannel analyzer, f
lows:
and data readout device, for example, a printer, plotter,
oscilloscope, or computer. Gamma rays interact with the
N
p
E 5 (1)
f
detector to produce pulses which are analyzed and counted by
N
g
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
ized basis for the calibration and usage of germanium detectors
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-
tors.
8.2.5 There are many ways of calculating the net gamma-
6.2 A source emission rate for a gamma ray of a selected
ray count. The method presented here is a valid, common
energy is determined from the counting rate in a full-energy
method when there are no interferences from photopeaks
peak of a spectrum, together with the measured efficiency of
adjacent to the peak of interest, and when the continuum varies
the spectrometry system for that energy and source location. It
linearly from one side of the peak to the other.
is usually not possible to measure the efficiency directly with
8.2.5.1 Other net peak area calculation methods can also be
emission-rate standards at all desired energies. Therefore a
used for single peaks, and must be used when there is
curve or function is constructed to permit interpolation be-
interference from adjacent peaks, or when the continuum does
tween available calibration points.
not behave linearly. Other methods are acceptable, if they are
used in a consistent manner and have been verified to provide
7. Preparation of Apparatus
accurate results.
7.1 Follow the manufacturer’s instructions for setting up
8.2.5.2 Using a simple model, the net peak area for a single
and preliminary testing of the equipment. Observe all of the peak can be calculated as follows:
manufacturer’s limitations and cautions. All tests described in
N 5 G 2 B 2 I (2)
A s
Section 12 should be performed before starting the calibra-
tions, and all corrections shall be made when required. A check where:
G = gross count in the peak region-of-interest (ROI) in the
source should be used to check the stability of the system at
s
sample spectrum,
least before and after the calibration.
B = continuum, and
I = number of counts in the background peak (if there is
8. Calibration Procedure
no background peak, or if a background subtraction is
8.1 Energy Calibration—Determine the energy calibration
not performed, I = 0).
(channel number versus gamma-ray energy) of the detector
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E181–98
I 5 G 2 B (6)
8.2.5.3 The net gamma-ray count, N is related to the net
b b b
p
peak area as follows:
where:
N
A
G = sum of gross counts in the background peak region
b
N 5 (3)
p
T
s
(of the background spectrum), and
B = continuum counts in the background peak region (of
where T = spectrum live time.
s b
the background spectrum).
8.2.5.4 The continuum, B, is calculated from the sample
spectrum using the following equation (see Fig. 1): The continuum counts in the background spectrum are
calculated from the following equation:
N
B 5 ~B 1 B ! (4)
1s 2s
2n
N
B 5 ~B 1 B ! (7)
b 1b 2b
2n
where:
N = number of channels in the peak ROI,
where:
n = number of continuum channels on each side, N = number of channels in the background peak ROI,
B = sum of counts in the low-energy continuum region in
n = number of continuum channels on each side (as-
1s
the sample spectrum, and sumed to be the same on both sides),
B = sum of counts in the high-energy continuum region B = sum of counts in the low-energy continuum region in
2s 1b
in the sample spectrum.
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-
detector distance used for efficiency calibration (see 12.6).
9.1.1 Accumulate the gamma-ray spectrum, recording the
FIG. 1 Typical Spectral Peak With Parameters Used in the Peak
count duration.
Area Determination Indicated
9.1.2 Determine the energy of the gamma rays present by
use of the energy calibration obtained under, and at the same
NOTE 4—These equations assume that the channels that are used to
gain as 8.1.
calculate the continuum do not overlap with the peak ROI, and are
9.1.3 Obtain the net count rate in each full-energy gamma-
adjacent to it, or have the same size gap between the two regions on both
ray peak of interest as described in 8.2.2.
sides. A different equation must be used, if the gaps are of a different size.
9.1.4 Determine the full-energy peak efficiency for each
The peaked background, I, is calculated from a separate
energy of interest from the curve or function obtained in 8.2.5.
background measurement using the following equation:
9.1.5 Calculate the number of gamma rays emitted per unit
T
s
live time for each full-energy peak as follows:
I 5 I (5)
b
T
b
N
p
N 5 (9)
g
where: E
f
T = live time of the sample spectrum,
s
When calculating a nuclear transmutation rate from a
T = live time of the background spectrum, and
b
gamma-ray emission rate determined for a specific radionu-
I = net background peak area in the background spec-
b
clide, a knowledge of the gamma-ray probability per decay is
trum.
required (7-14), that is,
If a separate background measurement exists, the net back-
N
g
ground peak area is calculated from the following equation:
A 5 (10)
P
g
9.1.6 Calculate the net peak area uncertainty as follows:
For simplicity of these calculations, n is assumed to be the same on both sides
2 2
N T
of the peak. If the continuum is calculated using a different number of channels on s
S 5 G 1 ~B 1 B ! 1 ~S ! (11)
˛ S D S D
N s 1s 2s Ib
A
the left of the peak than on the right of the peak, different equations must be used. 2n T
b
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E181–98
where: 11. Sources of Uncertainty
11.1 Other than Poisson-distribution uncertainties, the prin-
N
S 5 G 1 ~B 1 B ! (12)
˛ S D
Ib b 1b 2b
cipal sources of uncertainty (and typical magnitudes) in this
2n
method are:
and
11.1.1 The calibration of the standard source, including
S = net peak area uncertainty (at 1s confidence level),
NA
uncertainties introduced in using a standard radioactivity
G = gross counts in the peak ROI of the sample spec-
s
solution, or aliquot thereof, to prepare another (working)
trum,
standard for counting (typically 63 %).
G = gross counts in the peak ROI of the background
b
11.1.2 The reproducibility in the determination of net full-
spectrum,
energy peak counts (typically 62 %).
N = number of channels in the peak ROI,
11.1.3 The reproducibility of the positioning of the source
n = number of continuum channels on each side (as-
relative to the detector and the source geometry (typically
sumed to be the same on both sides for these
63 %).
equations to be valid),
11.1.4 The accuracy with which the full-energy peak effi-
B = continuum counts left of the peak ROI in the sample
1s
ciency at a given energy can be determined from the calibration
spectrum,
curve or function (typically 63 %).
B = continuum coun
...
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