ASTM D3649-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D3649 − 23
Standard Practice for
High-Resolution Gamma-Ray Spectrometry of Water
This standard is issued under the fixed designation D3649; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This practice covers the measurement of gamma-ray
emitting radionuclides in water by means of gamma-ray
2. Referenced Documents
spectrometry. It is applicable to nuclides emitting gamma-rays
2.1 ASTM Standards:
with energies greater than 45 keV. For typical counting systems
D1066 Practice for Sampling Steam
and sample types, activity levels of about 40 Bq are easily
D1129 Terminology Relating to Water
measured and sensitivities as low as 0.4 Bq are found for many
D2777 Practice for Determination of Precision and Bias of
nuclides. Count rates in excess of 2000 counts per second
Applicable Test Methods of Committee D19 on Water
should be avoided because of electronic limitations. High
D3370 Practices for Sampling Water from Flowing Process
count rate samples can be accommodated by dilution, by
Streams
increasing the sample to detector distance, or by using digital
D3648 Practices for the Measurement of Radioactivity
signal processors.
D4448 Guide for Sampling Ground-Water Monitoring Wells
1.2 This practice can be used for either quantitative or
D7902 Terminology for Radiochemical Analyses
relative determinations. In relative counting work, the results
E181 Guide for Detector Calibration and Analysis of Radio-
may be expressed by comparison with an initial concentration
nuclides in Radiation Metrology for Reactor Dosimetry
of a given nuclide which is taken as 100 %. For quantitative
measurements, the results may be expressed in terms of known
3. Terminology
nuclidic standards for the radionuclides known to be present.
3.1 Definitions—For definitions of terms used in this
This practice can also be used just for the identification of
practice, refer to Terminology D1129 and Terminology D7902.
gamma-ray emitting radionuclides in a sample without quan-
For terms not defined in this practice or in Terminology D1129
tifying them. General information on radioactivity and the
2 or Terminology D7902, reference may be made to other
measurement of radiation has been published (1,2). Informa-
published glossaries.
tion on specific application of gamma spectrometry is also
available in the literature (3-5). See also the referenced ASTM
4. Summary of Practice
Standards in 2.1 and the related material section at the end of
4.1 Gamma ray spectra are measured with modular equip-
this standard.
ment consisting of a detector, high-voltage power supply,
1.3 This standard does not purport to address the safety
preamplifier, amplifier and analog-to-digital converter (or digi-
concerns, if any, associated with its use. It is the responsibility
tal signal processor), multichannel analyzer, as well as a
of the user of this standard to establish appropriate safety,
computer with display.
health, and environmental practices and determine the appli-
4.2 High-purity germanium (HPGe) detectors, p-type or
cability of regulatory limitation prior to use.
n-type, are used for the analysis of complex gamma-ray spectra
1.4 This international standard was developed in accor-
because of their excellent energy resolution. These germanium
dance with internationally recognized principles on standard-
systems, however, are characterized by high cost and require
ization established in the Decision on Principles for the
cooling. Liquid nitrogen or electromechanical cooling, or both,
Development of International Standards, Guides and Recom-
can be used.
4.3 In a germanium semiconductor detector, gamma-ray
This practice is under the jurisdiction of ASTM Committee D19 on Water and
photons produce electron-hole pairs. The charged pair is then
is the direct responsibility of Subcommittee D19.04 on Methods of Radiochemical
Analysis.
Current edition approved June 1, 2023. Published July 2023. Originally approved
in 1978. Last previous edition approved in 2014 as D3649 – 06 (2014) which was For referenced ASTM standards, visit the ASTM website, www.astm.org, or
withdrawn January 2023 and reinstated in June 2023. DOI: 10.1520/D3649-23. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3649 − 23
collected by an applied electric field. A very stable low noise both of the 511 keV annihilation quanta may escape from the
preamplifier is needed to amplify the pulses of electric charge detector without interaction. This condition will cause single or
resulting from gamma photon interactions. The output from the double escape peaks at energies of 0.511 MeV or 1.022 MeV
preamplifier is directly proportional to the energy deposited by less than the photopeak energy. In the plot of pulse height
the incident gamma-ray. These current pulses are fed into an versus count rate, the size and location of the photopeak on the
amplifier of sufficient gain to produce voltage output pulses in pulse height axis are proportional to the number and energy of
the amplitude range from 0 V to 10 V. the incident photons, respectively, and are the basis for the
quantitative and qualitative application of the spectrometer.
4.4 A multichannel pulse-height analyzer is used to deter-
The Compton continuum serves no useful purpose in photo-
mine the amplitude of each pulse originating in the detector,
peak analysis and must be subtracted when peaks are analyzed.
and accumulates in a memory the number of pulses in each
amplitude band (or channel) in a given counting time. Com- 4.6 If the analysis is being directed and monitored by an
puterized systems with stored programs and interface hardware online computer program, the analysis period may be termi-
can accomplish the same functions as hardwired multichannel nated by prerequisites incorporated in the program. If the
analysis is being performed with a modern multichannel
analyzers. The primary advantages of the computerized system
include the capability of programming the multi-channel ana- analyzer, analysis may be terminated when a preselected time
lyzer functions and the ability to immediately perform data or total counts in a region of interest or in a specified channel
reduction calculations using the spectral data stored in the is reached. Visual inspection of a display of accumulated data
computer memory or mass storage device. For a 0 MeV to can also be used as a criterion for manually terminating the
2 MeV spectrum, 4000 or more channels are typically needed analysis on either type of data acquisition systems.
in order to fully utilize a germanium detector’s excellent
4.7 Upon completion of the analysis, the spectral data are
energy resolution.
interpreted and reduced to radionuclide activities in becquerels
4.5 The distribution of the amplitudes (pulse heights) of the (Bq) or other units suited to the particular application. At this
pulses can be separated into two principal components. One of time the spectral data may be inspected to identify the
these components has a nearly Gaussian distribution and is the gamma-ray emitters present. This is accomplished by reading
result of total absorption of the gamma-ray energy in the the channel number from the x-axis and converting to gamma-
detector. This peak is normally referred to as the full-energy ray energy by multiplying by the appropriate keV/channel
peak or photopeak. The other component is a continuous one (system gain). In some systems the channel number or gamma-
lower in energy than that of the photopeak. This continuous ray energy in keV can be displayed for any selected channel.
curve is referred to as the Compton continuum and is due to Identification of nuclides may be aided by catalogs of gamma-
interactions wherein the gamma photons deposit only part of ray spectra and other nuclear data tabulations (3, 6 and 7).
their energy in the detector. These two portions of the curve are 4.7.1 Computer programs for data reduction have been used
shown in Fig. 1. Other peaks, such as escape peaks, backscat- extensively although calculations for some applications can be
tered gamma rays or X rays from shields, are often superim- performed effectively with the aid of a scientific calculator.
posed on the Compton continuum. Escape peaks will be Data reduction of spectra taken with germanium spectrometry
present when gamma-rays with energies greater than 1.02 MeV systems is usually accomplished by integration of the photo-
are emitted from the sample. The positron formed in pair peaks above a definable background (or baseline) and subse-
production is usually annihilated in the detector and one or quent activity calculations using a library which includes data
FIG. 1 Cesium-137 Spectrum
D3649 − 23
such as nuclide name, half-life, gamma-ray energies, and be held to less than 1 % by limiting the total counting rate to
–1
absolute gamma intensity. 2000 counts per second (s ). Refer to Test Methods E181 for
more information.
5. Significance and Use
6.4 The density of the sample is another factor that can
effect quantitative results. Errors from this source can be
5.1 Gamma-ray spectrometry is of use in identifying radio-
avoided by preparing the standards for calibration in solutions
nuclides and in making quantitative measurements. Use of a
or other matrices with a density comparable to the sample
semiconductor detector is necessary for high-resolution mea-
being analyzed.
surements.
5.2 Variation of the physical geometry of the sample and its
7. Apparatus
relationship with the detector will produce both qualitative and
7.1 Gamma Ray Spectrometer, consisting of the following
quantitative variations in the gamma-ray spectrum. To ad-
components:
equately account for these geometry effects, calibrations are
7.1.1 Detector Assembly:
designed to duplicate all conditions including source-to-
7.1.1.1 Germanium Detector—The detector may have a
detector distance, sample shape and size, and sample matrix
3 3
volume of about 50 cm to 150 cm , with a full width at
encountered when samples are measured.
one-half the peak maximum (FWHM) less than 2.2 keV at
5.3 Since some spectrometry systems are calibrated at many
1332 keV, certified by the manufacturer. A charge-sensitive
discrete distances from the detector, a wide range of activity preamplifier using low noise field effect transistors should be
levels can be measured on the same detector. For high-level
an integral part of the detector assembly. A convenient support
samples, extremely low-efficiency geometries may be used. should be provided for samples of the desired form.
Quantitative measurements can be made accurately and pre-
7.1.1.2 Shield—The detector assembly may be surrounded
cisely when high activity level samples are placed at distances by an external radiation shield made of a dense metal,
of 10 cm or more from the detector.
equivalent to 102 mm of lead in gamma-ray attenuation
capability. It is desirable that the inner walls of the shield be at
5.4 Electronic problems, such as erroneous deadtime
least 127 mm distant from the detector surfaces to reduce
correction, loss of resolution, and random summing, may be
backscatter. If the shield is made of lead or a lead liner, the
avoided by keeping the gross count rate below 2000 counts per
shield may have a graded inner shield of 1.6 mm of cadmium
–1
second (s ) and also keeping the deadtime of the analyzer
or tin lined with 0.4 mm of copper, to attenuate the 88 keV Pb
below 5 %. Total counting time is governed by the radioactiv-
X-rays. The shield should have a door or port for inserting and
ity of the sample, the detector to source distance and the
removing samples.
acceptable Poisson counting uncertainty.
7.1.1.3 High Voltage Power/Bias Supply—The bias supply
required for germanium detectors usually provides a voltage up
6. Interferences
to 5000 V and up to 100 μA. The power supply should be
6.1 In complex mixtures of gamma-ray emitters, the degree regulated to 0.1 % with a ripple of not more than 0.01 %. Line
of interference of one nuclide in the determination of another noise caused by other equipment should be removed with rf
is governed by several factors. If the gamma-ray emission rates filters and additional regulators.
from different radionuclides are similar, interference will occur 7.1.1.4 Amplifier—An amplifier compatible with the pream-
when the photopeaks are not completely resolved and overlap. plifier and with the pulse-height analyzer shall be provided.
If the nuclides are present in the mixture in unequal portions 7.1.2 Data Acquisition and Storage Equipment:
radiometrically, and if nuclides of higher gamma-ray energies 7.1.2.1 Data Acquisitions—A multichannel pulse-height
are predominant, there are serious interferences with the
analyzer (MCA) or stand-alone analog-to-digital-converter
interpretation of minor, less energetic gamma-ray photopeaks. (ADC) under software control of a separate computer, per-
The complexity of the analysis method is due to the resolution
forms many functions required for gamma-ray spectrometry.
of these interferences and, thus, one of the main reasons for An MCA or computer collects the data, provides a visual
computerized systems.
display, and outputs final results or raw data for later analysis.
The four major components of an MCA are the ADC, the
6.2 Cascade summing may occur when nuclides that decay
memory, control, and input/output. More recently, digital
by a gamma-ray cascade are analyzed. Cobalt-60 is an ex-
signal processors (DSP) can directly amplify and digitize
ample; 1172 keV and 1333 keV gamma rays from the same
signals from the preamplifier, replacing individual amplifier
decay may enter the detector to produce a sum peak at 2505
and ADC components. The ADC digitizes the analog pulses
keV and cause the loss of counts from the other two peaks.
from the amplifier. These pulses represent energy. The digital
Cascade summing may be reduced by increasing the source to
result is used by the MCA to select a memory location (channel
detector distance. Summing is more significant if a well-type
number) which is used to store the number of events which
detector is used.
have occurred with that energy. Simple data analysis and
6.3 Random summing is a function of counting rate and control of the MCA is accomplished with microprocessors.
occurs in all measurements. The random summing rate is These processors control the input/output, channel summing
proportional to the total count squared and the resolving time over set regions of interest, and system energy calibration to
of the detector. For most systems random summing losses can name a few examples.
D3649 − 23
7.1.2.2 Data Storage—Because of the use of 10.2 Procedure:
microprocessors, modern MCAs provide a wide range of input 10.2.1 Preparation of Apparatus:
and output (I/O) capabilities. 10.2.1.1 Follow the manufacturer’s instructions, limitations,
and cautions for the setup and the preliminary testing for all of
8. Sampling
the spectrometry equipment to be used in the analysis. This
8.1 Collect the sample in accordance with Practice D1066,
equipment would include, as applicable, detector, power
Practices D3370, Guide D4448, or other documented proce-
supplies, preamplifiers, amplifiers, multichannel analyzers, and
dures.
computing systems.
10.2.1.2 Place an appropriate volume of a standard or a
8.2 Preserve the sample in a radioactively homogeneous
mixed standard of radionuclides in a sealed container and place
state. A sample can be made radioactively homogeneous by the
the container at a desirable and reproducible source-to-detector
addition of a reagent in which the radionuclides or compounds
distance. Section 6 provides information on cascade and
of the radionuclides present would be soluble in large concen-
random summing interferences that should be considered when
trations. Addition of acids, complexing agents, or stable,
establishing a source-to-detector distance. The solution should
chemically similar carriers may be used to obtain homogeneity.
–1
provide about 100 counts per second (s ) in the peaks of
Consideration of the chemical nature of the radionuclides and
interest and be made up of standard sources traceable to a
compounds present and the subsequent chemistry of the
nationally certified laboratory. In all radionuclide
method shall indicate the action to be taken.
measurements, the volumes, shape, physical and chemical
9. Test Specimens
characteristics of the samples, standards and their containers
9.1 Containment—Sample mounts and sample-counting must be as equivalent as practicable for the most accurate
containers must have a convenient and reproducible geometry. results. If precipitates or residues are to be analyzed, then the
Considerations include commercial availability, ease of use standards must be evaporated on the same type of mount as the
and disposal, and the containment of radioactivity for protec- sample.
tion of the working environment and personnel from contami-
10.3 Energy Calibration:
nation. The evaporation of liquid samples to dryness is not
10.3.1 The energy calibration (channel number of the mul-
necessary and liquid samples up to several litres may be used.
tichannel analyzer versus the gamma-ray energy) of the detec-
However, samples that have been evaporated to dryness for
tor system is accomplished at a fixed gain using standards
gross beta counting can also be gamma counted. Massive
containing known radionuclides. The standards should be in
samples may cause significant self-absorption of low-energy
sealed containers and should emit at least four different
gammas and degrade the higher-energy gammas. Therefore, it
gamma-ray en
...