IEC 61452:2021

Nuclear instrumentation - Measurement of activity or emission rate of gamma-ray emitting radionuclides - Calibration and use of germanium-based spectrometers

IEC 61452:2021 establishes methods for the calibration and use of high purity germanium spectrometers for the measurement of photon energies and emission rates over the energy range from 45 keV to approximately 3 000 keV and the calculation of radionuclide activities from these measurements. Minimum requirements for automated peak finding are stated. This document establishes methods for measuring the full-energy peak efficiency with calibrated sources.
The object of this document is to provide a basis for the routine calibration and use of germanium (HPGe) semiconductor detectors for the measurement of gamma-ray emission rates and thereby the activities of the radionuclides in a sample. It is intended for use by persons who have an understanding of the principles of HPGe gamma-ray spectrometry and are responsible for the development of correct procedures for the calibration and use of such detectors. This document is primarily intended for routine analytical measurements. Related documents are IEC 60973 and ISO 20042.
This second edition cancels and replaces the first edition published in 1995. This edition includes the following significant technical changes with respect to the previous edition:
a. title modified;
b. additional information on digital electronics;
c. information on Monte Carlo simulations;
d. reference to detection limits calculations.

General Information

• Status: Published
• Publication Date: 03-Jun-2021
• ICS: 17.240 - Radiation measurements
• Technical Committee: TC 45 - Nuclear instrumentation
• Drafting Committee: WG 9 - TC 45/WG 9
• Current Stage: PPUB - Publication issued
• Start Date: 11-Jun-2021
• Completion Date: 04-Jun-2021

Overview

IEC 61452:2021 - Nuclear instrumentation - Measurement of activity or emission rate of gamma‑ray emitting radionuclides - Calibration and use of germanium‑based spectrometers - defines methods for the calibration and routine use of high‑purity germanium (HPGe) spectrometers. The standard covers measurement of photon energies and emission rates from about 45 keV to 3 000 keV, calculation of radionuclide activities, and minimum requirements for automated peak‑finding and full‑energy peak efficiency measurement using calibrated sources. This second edition replaces the 1995 version and adds guidance on digital electronics, Monte Carlo simulations, and detection limits.

Key topics and requirements

• Energy calibration and resolution procedures for HPGe detectors.
• Peak finding and peak‑area determination: minimum requirements for automated algorithms and methods for fitting or non‑fitting analysis.
• Full‑energy peak efficiency: measurement methods with calibrated sources and functions describing efficiency vs. energy.
• Corrections and effects: treatment of background subtraction, radioactive decay corrections, pulse pile‑up (random summing), true coincidence (cascade) summing, and efficiency transfer corrections.
• Performance tests: verification of MCA/digital signal processing clocks, DC offset/pole‑zero settings, resolution and efficiency stability, and software peak‑finding performance.
• Uncertainty analysis: propagation of measurement uncertainties and validation of Monte Carlo efficiency models.
• Modelling and Monte Carlo: constructing detector and sample geometries, validating models, and estimating uncertainties for mathematical efficiency calculations.
• Practical annexes: procedures for detector characterization, shield construction, sample preparation, and formulas for coincidence summing corrections.

Applications and users

IEC 61452:2021 is intended for practitioners performing routine analytical gamma‑ray spectrometry who have foundational knowledge of HPGe detectors. Typical applications include:

• Environmental radioactivity monitoring and surveillance
• Nuclear decommissioning and waste characterization
• Radiological emergency response and contamination assessment
• Laboratory accreditation and quality assurance in nuclear instrumentation
• Research labs using HPGe spectrometers for radionuclide assay

Users: laboratory managers, radiation protection specialists, health physics teams, spectrometry analysts, and instrument developers.

Related standards

• IEC 60973 (related nuclear instrumentation topics)
• ISO 20042 (gamma spectrometry guidance)

IEC 61452:2021 provides practical, standardized methods and checks for reliable HPGe gamma‑ray measurements, improving comparability, traceability and quality of radionuclide activity determinations.

Standards Content (Sample)

IEC 61452 ®
Edition 2.0 2021-06
INTERNATIONAL
STANDARD
colour
inside
Nuclear instrumentation – Measurement of activity or emission rate of gamma-
ray emitting radionuclides – Calibration and use of germanium-based
spectrometers
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IEC 61452 ®
Edition 2.0 2021-06
INTERNATIONAL
STANDARD
colour
inside
Nuclear instrumentation – Measurement of activity or emission rate of gamma-

ray emitting radionuclides – Calibration and use of germanium-based

spectrometers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.240 ISBN 978-2-8322-9813-8

– 2 – IEC 61452:2021 © IEC 2021
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references . 9
3 Terms, definitions and symbols. 10
3.1 Terms and definitions . 10
3.2 Symbols . 15
4 Installation of instrumentation . 16
5 Peak analysis and calibration procedures . 16
5.1 Energy calibration . 16
5.2 Energy resolution calibration . 17
5.3 Peak-finding algorithm . 17
5.4 Peak position and area measurement . 17
5.5 Efficiency calibration measurement . 18
5.5.1 General . 18
5.5.2 Standardization coefficient for specific radionuclides . 18
5.5.3 Detector efficiency as a function of energy . 18
5.5.4 Efficiency function . 19
6 Gamma-ray measurements with HPGe spectrometers . 21
6.1 Measurement of gamma-ray energies . 21
6.2 Measurement of gamma-ray emission rates and radionuclide activities . 21
6.2.1 General . 21
6.2.2 Subtraction of interference peaks in the background . 22
6.2.3 Radioactive decay . 23
6.2.4 Pulse pile-up (random summing) . 25
6.2.5 True coincidence (cascade) summing . 26
6.2.6 Efficiency transfer corrections . 26
7 Performance tests of the spectrometry system . 29
7.1 General . 29
7.2 Multichannel-analyser and digital signal processing clocks . 29
7.3 DC offset and pole-zero settings . 29
7.4 Energy calibration . 29
7.5 Spectrometer efficiency and energy resolution . 29
7.6 Pulse pile-up (random summing) . 30
8 Performance tests of the analysis software . 31
8.1 General . 31
8.2 Test of automatic peak-finding algorithm . 31
8.3 Test of independence of peak-area from the gross peak-height to continuum-
height ratio. 33
8.4 Test of the doublet-peak finding and fitting algorithms . 34
9 Verification of the entire analysis process . 37
9.1 Assessment of the magnitude of true coincidence summing . 37
9.2 Deviations in the relative full-energy-peak efficiency . 40
9.3 Accuracy of the full-energy-peak efficiency . 41
10 Radionuclide identification . 41
10.1 General . 41

10.2 Identification through multipeak analysis and correction for interference from
other radionuclides . 42
10.3 Detection limits . 42
11 Uncertainties and uncertainty propagation . 42
12 Mathematical efficiency and correction factors modelling . 45
12.1 General . 45
12.2 Mathematical full energy peak efficiency calculations . 46
12.2.1 General . 46
12.2.2 Construction of the detector model . 46
12.2.3 Creation of sample geometries . 47
12.2.4 Validation of the detector and sample container . 47
12.2.5 Estimation of uncertainties for Monte Carlo codes for full energy peak
efficiencies . 47
12.3 Estimation of uncertainties from geometry variations . 48
12.4 Efficiency transfer . 49
12.5 True coincidence summing corrections . 49
Annex A (informative) Procedures for characterization of a HPGe gamma-ray
spectrometer . 51
A.1 General . 51
A.2 Adjustment of the pole-zero cancellation and direct current level . 51
A.2.1 Rationale for systems using analog electronics . 51
A.2.2 Adjustment of the pole-zero cancellation . 51
A.2.3 Adjustment of the direct current (DC) level . 51
A.3 Adjustment of the lower-level discriminator (LLD), ADC zero and initial
energy scale . 53
A.3.1 Rationale . 53
A.3.2 Adjustment of the lower-level discriminator . 53
A.3.3 Adjustment of the ADC zero and initial energy scale . 53
A.4 Check of the multichannel analyser (MCA) real-time clock . 54
A.4.1 Rationale . 54
A.4.2 Instructions . 54
A.5 Digital electronics . 55
A.6 Measurement of energy resolution and peak-to-Compton ratio . 55
A.6.1 Rationale . 55
A.6.2 Measurement of the energy resolution at 122 keV and 1 332 keV . 56
A.6.3 Measurement of the peak-to-Compton ratio for Co . 57
A.7 Correction for losses due to counting rate . 57
A.7.1 Rationale . 57
A.7.2 Empirical or source method . 58
A.7.3 Live-time extension method (see [18]) . 60
A.7.4 Pulser method (see [10], [14] and [17] to [22]) . 61
A.7.5 Virtual pulser and add "N" counts method . 65
A.8 Measurement of the full-energy peak efficiency curve . 65
A.8.1 Rationale . 65
A.8.2 Measurement of standardization coefficients for specific radionuclides . 65
A.8.3 Measurement of the detector efficiency versus energy for large sample-
to-detector distances . 66
A.8.4 Measurement of the detector efficiency versus energy for small sample-
to-detector distances . 69
A.9 Preparation of reference sources from standard solutions . 70

– 4 – IEC 61452:2021 © IEC 2021
A.9.1 Rationale . 70
A.9.2 Preparation of standard sources . 70
A.9.3 Preparation of soil sources . 71
A.9.4 Preparation of filter sources . 72
Annex B (informative) Measurement of peak position, net area and their uncertainties . 73
B.1 General . 73
B.2 Non-fitting technique . 73
B.3 Fitting techniques . 74
Annex C (informative) Formulas for the true coincidence summing correction of
cascade gamma-rays . 76
C.1 Formulas for true coincidence summing correction factors . 76
C.1.1 General . 76
C.1.2 True coincidence summing correction factors for a simple decay
scheme . 77
C.1.3 Correction factor for the 591 keV gamma-ray emitted in the decay of
Eu . 79
C.1.4 General case . 84
C.1.5 Total efficiency calculation . 84
Annex D (informative) Construction of shields for HPGe spectrometers . 86
D.1 Construction materials . 86
D.2 Shield design . 86
D.2.1 General . 86
D.2.2 Shield design (for detectors counting a variety of low or high activity
level samples) . 86
D.2.3 Shield design for detectors counting only environmental samples of the
same size and shape . 87
D.2.4 Active shielding . 91
Bibliography . 94

Figure 1 – Full-energy-peak efficiency as a function of gamma-ray energy. 20
Figure 2 – 𝜺𝜺𝜺𝜺𝜺𝜺𝜺𝜺(𝐤𝐤𝐤𝐤𝐤𝐤)𝟎𝟎,𝟖𝟖𝟖𝟖𝟖𝟖 as a function of gamma-ray energy . 21
Figure 3 – Specification of times for decay corrections . 24
Figure 4 – Deviation in measured net peak area as a function of continuum height . 34
Figure 5 – Deviation in equally sized doublet peak areas for different separations . 36
Figure 6 – Deviation in unequally sized doublet peak areas for different pulse-height
ratios . 37
Figure 7 – Cascade-summing corrections for a Eu 591 keV gamma-ray . 39
Figure 8 – Partial HPGe gamma-ray spectrum of a long-lived mix . 40
Figure 9 – Results of Monte Carlo simulation to compute true coincidence summing
Cs in different geometrical conditions (point or volume)
correction factors: example of
(filter or water) source at different distances from the HP-Ge detector window . 50
Figure A.1 – Amplifier output pulses showing correct and incorrect pole-zero
cancellation . 52
Figure A.2 – Distribution of FWHM of spectral peaks as a function of energy . 56
Figure A.3 – Specification of times for pulse processing by an ADC . 58
Figure A.4 – Pulse pile-up correction as a function of integral counting rate . 60
Figure A.5 – Preamplifier and amplifier pulse shapes resulting from different pulser

shapes . 63

Figure A.6 – Gamma-ray spectrum of a mixed radionuclide standard . 69
Figure B.1 – Well-resolved peak with continuum . 74
Figure C.1 – A three-transition decay scheme . 79
Figure C.2 – Partial decay scheme of Eu . 80
Figure D.1 – Background spectra normalised to the Ge-crystal mass from two HPGe
detectors located in the same laboratory . 87
Figure D.2 – Expanded view of the background spectrum from the low-background
detector in Figure D.1 . 89
Figure D.3 – Background spectra from (top) a standard HPGe detector and shield,
(middle) a low-background HPGe detector and shield and (bottom) an ultra-low-
background and shield located underground at a depth of 500 m water equivalent . 89
Figure D.4 – The low energy part of a background spectrum from a HPGe detector with
a thin (0,4 µm) top dead layer and a 0,5 mm carbon-epoxy window . 91
Figure D.5 – Background gamma-ray spectrum recorded without sample and
successsive shielding steps to reduce the counting rates . 93

Table 1 – Net-peak areas as a function of continuum height . 34
Table 2 – Uncertainty propagation for simple functions . 44
Table 3 – Uncertainty contributions . 45
Table A.1 – Adjustment of energy channels to yield energy equation with zero intercept . 53
232 226
Table D.1 – List of typical background peaks from the Th and Ra decay chains in
a HPGe detector . 88

– 6 – IEC 61452:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR INSTRUMENTATION – MEASUREMENT OF ACTIVITY
OR EMISSION RATE OF GAMMA-RAY EMITTING RADIONUCLIDES –
CALIBRATION AND USE OF GERMANIUM-BASED SPECTROMETERS

FOREWORD
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IEC 61452 has been prepared by IEC technical committee 45: Nuclear instrumentation. It is
an International Standard.
This second edition cancels and replaces the first edition published in 1995. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Title modified;
b) Additional information on digital electronics;
c) Information on Monte Carlo simulations;
d) Reference to detection limits calculations.

The text of this International Standard is based on the following documents:
FDIS Report on voting
45/921/FDIS 45/925/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
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– 8 – IEC 61452:2021 © IEC 2021
INTRODUCTION
A typical gamma-ray spectrometer consists of a high purity germanium (HPGe) detector with
its liquid nitrogen or mechanically refrigerated cryostat and preamplifier, associated to either
analog or digital electronic modules including the detector biasing and signal processing
(amplification, multichannel conversion and storage) and data-readout devices. The
spectrometers include or are associated with computers and their acquisition software. A
radiation shield often surrounds the detector to reduce the counting rate from room
background radiation for shield construction guidelines). Primary interactions of the photons
(X- and gamma-rays) in the HPGe crystal (by photoelectric absorption, Compton scattering or
pair production) impart energy to electrons whose energy is finally released by creation of
electron-hole pairs. These electrons and holes are collected to produce a pulse whose
amplitude is proportional to the energy deposited in the active volume of the HPGe crystal.
These pulses are amplified, shaped and sorted according to pulse height to produce a
histogram showing, as a function of energy, the number of photons absorbed by the detector.
After the accumulation of a sufficient number of pulses the histogram will display a spectrum
with one or more peaks with an approximately normal (Gaussian) distribution corresponding
to photons that transferred their entire energy to the detector. These are superimposed on
continuum constituted by the events related to the partial deposition of energy.
The recorded peak area depends on the emission rate of the gamma-ray and on the detection
efficiency of the detector, which is energy dependent. The emission rate, R(E), for a gamma-
ray of energy E is determined by dividing the net area, N(E), in the full-energy peak by the
measurement live time, T , and full-energy-peak efficiency, ε(Ε), of the detector for the
L
counting geometry used. A curve or functional representation of the full-energy-peak
efficiency permits interpolation between available calibration points. Corrections may be
needed for:
a) decay of the source during sampling (e.g., with air filters) and counting and/or ingrowth;
b) decay of the source from a previous time to the counting period and/or ingrowth;
c) attenuation of photons within and/or external to the source that is not accounted for by the
full-energy-peak efficiency calibration;
d) solid angle correction that is not accounted for by the full-energy-peak efficiency
calibration;
e) true coincidence (cascade) summing;
f) loss of pulses due to pulse pile-up (at high counting rates).

NUCLEAR INSTRUMENTATION – MEASUREMENT OF ACTIVITY
OR EMISSION RATE OF GAMMA-RAY EMITTING RADIONUCLIDES –
CALIBRATION AND USE OF GERMANIUM-BASED SPECTROMETERS

1 Scope
This document establishes methods for the calibration and use of high purity germanium
spectrometers for the measurement of photon energies and emission rates over the energy
range from 45 keV to approximately 3 000 keV and the calculation of radionuclide activities
from these measurements. Minimum requirements for automated peak finding are stated. This
document establishes methods for measuring the full-energy peak efficiency with calibrated
sources.
Performance tests are described that ascertain if the spectrometer is functioning within
acceptable limits. These tests evaluate the limitations of the algorithms used for locating and
fitting single and multiplet peaks. Methods for the measurement of and the correction for
pulse pile-up are suggested. A test to ascertain the approximate magnitude of true
coincidence summing is described. Techniques are recommended for the inspection of
spectral analysis results for large errors resulting from true coincidence summing of cascade
gamma-rays in the detector. Suggestions are provided for the establishment of data libraries
for radionuclide identification, decay corrections, the conversion of gamma-ray emission rates
to decay rates and Monte Carlo simulations.
The measurement of X-ray emission rates is not included because different functional fits are
required for X-ray peaks, which have intrinsically different peak shapes than gamma-ray
peaks. Further, X-ray peaks are complex multiplets (e.g., the K X-rays of Tl include 10
individual components that form four partially resolved peaks). This document does not
address the measurement of emission rates of annihilation radiation peaks or single- and
double-escape peaks resulting from partial energy deposition in the detector from pair
production. Escape peaks may require different fitting functions than comparable full-energy
peaks. Further, annihilation radiation and single-escape peaks have a different and larger
width than a gamma-ray peak of similar energy. Discussion of acceptable methods for
measuring the lower limits of detection as they relate to specific radionuclides is beyond the
scope of this document.
The object of this document is to provide a basis for the routine calibration and use of
germanium (HPGe) semiconductor detectors for the measurement of gamma-ray emission
rates and thereby the activities of the radionuclides in a sample. It is intended for use by
persons who have an understanding of the principles of HPGe gamma-ray spectrometry and
are responsible for the development of correct procedures for the calibration and use of such
detectors. This document is primarily intended for routine analytical measurements. Related
documents are IEC 60973 and ISO 20042.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60050-395:2014, International Electrotechnical Vocabulary (IEV) – Part 395: Nuclear
instrumentation – Physical phenomena, basic concepts, instruments, systems, equipment and
detectors
IEC 60050-395:2014/AMD1:2016
IEC 60050-395:2014/AMD2:2020
– 10 – IEC 61452:2021 © IEC 2021
IEC 60973, Test procedures for germanium gamma-ray detectors
ISO 11929 (all parts), Determination of the characteristic limits (decision threshold, detection
limit and limits of the confidence interval) for measurements of ionizing radiation –
Fundamentals and application
ISO 20042, Measurement of radioactivity – Gamma-ray emitting radionuclides – Generic test
method using gamma-ray spectrometry
JCGM 100:2008, Evaluation of measurement data – Guide to the expression of uncertainty in
measurement (GUM)
JCGM 200:2012, International vocabulary of metrology – Basic and general concepts and
rd
associated terms (VIM), 3 edition 2008 version with minor corrections
3 Terms, definitions and symbols
For the purposes of this document, the following terms and definitions apply, as well as those
given in IEC 60050-395 and JCGM 200.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia available at: http://www.electropedia.org/ and IEC Glossary available at:
http://std.iec.ch/glossary
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Terms and definitions
3.1.1
accuracy
closeness of agreement between a measured quantity value and a true quantity value of a
measurand
[SOURCE: JCGM 200:2012]
3.1.2
activity
A
number dN of spontaneous nuclear transitions or nuclear disintegrations for a radionuclide of
amount N produced during a short time interval dt, divided by this time interval
Note 1 to entry: The unit is becquerel (Bq).
[SOURCE: IEC 60050-395:2014, 395-01-05]
3.1.3
analog-to-digital converter
ADC
electronic device used to convert the amplitude of a voltage pulse from analog to digital
format
3.1.4
ADC conversion gain
number of channels over which the full amplitude span can be spread
Note 1 to entry: Usually 4 096 to 16 384 channels are used for HPGe gamma-ray spectrometry.

3.1.5
attenuation
net loss at the detector of primary photons of a given energy resulting from their interaction
with matter either due to the occurrence of scattering or absorption in the sample or in
material between the sample and the active volume of the detector
3.1.6
background
spectral data including peaks not caused by the source but rather resulting from radioactive
decay occurring in the surrounding environment or from cosmic ray interactions in or adjacent
to the detector (see 3.1.11)
3.1.7
calibration
determination of a value that converts a measured number into a desired physical quantity
(e.g., pulse-height into photon energy, or counts per second into emission rate)
3.1.8
cascade transitions
gamma-rays in the radioactive decay of a single radionuclide that are emitted sequentially and
within the resolving time of the spectrometer
3.1.9
true coincidence summing
simultaneous detection of two or more photons originating from a single radioactive decay
that results in only one observed (summed) pulse (also cascade summing)
3.1.10
combined standard uncertainty
standard uncertainty of the result of a measurement when that result is obtained from the
values of a number of other quantities, equal to the positive square root of a sum of terms, the
terms being the variances or covariances of these other quantities weighted according to how
the measurement result varies with changes in these quantities
Note 1 to entry: See JCGM 100:2008 GUM 1995 with minor corrections.
3.1.11
continuum
part of the pulse-height distribution lying underneath a peak including contributions
associated with the source, detector, and measuring conditions that affect the spectral shape
3.1.12
conventional true value
commonly accepted best estimate of the value of that quantity
Note 1 to entry: This and its associated uncertainty will normally be determined by a national or international
transfer standard, or by a reference instrument that has been calibrated against a national or international transfer
standard.
3.1.13
counting rate
number of pulses registered by the detector per unit of time being registered in a selected
-1
voltage or energy interval (expressed in s )
3.1.14
crossover gamma-ray
gamma-ray occurring between two non-adjacent nuclear levels

– 12 – IEC 61452:2021 © IEC 2021
3.1.15
dead time
time during which a counting system is unable to process an input pulse
3.1.16
direct current (DC) level
input or output voltage level on a DC-coupled instrument when there are no pulses present
3.1.17
direct current (DC) offset
difference between a current or voltage level and a reference level
3.1.18
emission intensity per decay
emission intensity and yield
P(E) or 𝑃𝑃 (𝐸𝐸)
𝛾𝛾
probability that a radioactive decay will be followed by the emission of the specified radiation
Note 1 to entry: Gamma-ray emission intensities are often expressed per 100 decays.
3.1.19
energy resolution, full width at half maximum
FWHM
width of a peak at half of the maximum peak height where the baseline is measured from the
continuum
3.1.20
energy resolution, full width at tenth maximum
FWTM
width of a peak at one tenth of the maximum peak height where the baseline is measured
from the continuum
Note 1 to entry: For a normal (Gaussian) distribution, FWTM is 1,823 times its FWHM.
3.1.21
error
measurement error
measured quantity value minus a reference quantity value
Note 1 to entry: The concept of ‘measurement error’ can be used both:
a) when there is a single reference quantity value to refer to, which occurs if a calibration is made by means of a
measurement standard with a measured quantity value having a negligible measurement uncertainty or if a
conventional quantity value is given, in which case the measurement error is known, and
b) if a measurand is supposed to be represented by a unique true quantity value or a set of true quantity values of
negligible range, in which case the measurement error is not known.
Note 2 to entry: Measurement error should not be confused with production error or mistake.
[SOURCE: JCGM 200:2012]
3.1.22
full-energy peak
photopeak
FEP
peak in the spectrum resulting from the complete (total) absorption of the energy of a photon
in the active volume of the germanium crystal and collection of all of the resulting charge

3.1.23
full-energy-peak efficiency
𝜀𝜀(𝐸𝐸)
ratio between the number of counts in the net area of the full-energy peak to the number of
photons of that energy emitted by a source with specified characteristics for a specified
measurement geometry (i.e., source-to-detector distance, source type)
3.1.24
gamma-ray branching ratio
f(E)
for a given excited nuclear state, ratio of the emission rate of a particular gamma-ray to the
total transition rate from that state
3.1.25
gamma-ray emission rate
R(E)
rate at which a gamma-ray of a given energy from the decay of a particular radionuclide is
emitted from a given source
Note 1 to entry: The gamma-ray emission rate is the activity times the gamma-ray emission intensity.
3.1.26
live time
T
L
time interval of a count during which a counting system is capable of processing input pulses
3.1.27
multichannel pulse-height analyser
MCA
electronic device that records and stores pulses according to their amplitude. It consists of
three function segments:
– an ADC to provide a means of measuring pulse amplitude;
– memory registers (one for each channel of the spectrum) to tally the number of pulses
having an amplitude within a given voltage increment; and
– an input/output section that permits transfer of the spectral information to other devices
such as a computer, or other display or permanent storage media.
3.1.28
peak-to-Compton ratio for the 1 332 keV Co peak
ratio of the full-energy-peak height, for Co measured at 1 332 keV, to the average height of
the corresponding Compton plateau between 1 040 keV and 1 096 keV
3.1.29
pole-zero cancellation
pole-zero adjustment on the shaping amplifier adjusts the zero location of the pole-zero
network to exactly cancel the preamplifier output pole and thus provide single-pole (i.e., no
under or overshoot) response of the signal pulse at the amplifier output
Note 1 to entry: This operation converts the long-tailed preamplifier pulse to a short-tailed pulse suitable for
signal optimization and subsequent pulse-height analysis.
3.1.30
pulse baseline
average of the level from which a pulse departs and to which it returns in the absence of a
following overlapping pulse
– 14 – IEC 61452:2021 © IEC 2021
3.1.31
pulse pile-up
random summing
occurrence of two successive pulses closely associated in time but from separate decays
such that they contribute to each other's pulse height and shape
Note 1 to entry: Usually, the system processes the two inputs as a composite single pulse which is stored in a
spectral channel different from that at which either of the component pulses would have been stored.
Note 2 to entry: Pulse pile-up is a function of the square of the counting rate and of the amplifier pulse width.
3.1.32
real time counting period
T
r
counting time uncompensated for periods in which an instrument might be unable to respond
Note 1 to entry: Real time of a count equals live time plus dead time.
3.1.33
relative full-energy-peak efficiency
𝜀𝜀
r
ratio of full-energy-peak efficiency for a point source of Co (1 332 keV photons) to that of a
Nal(TI) crystal of 7,6 cm diameter × 7,6 cm high for a source-to-detector distance of 25 cm
-3
(that is 1,2 × 10 ).
n(1332)
ε = 0,833 × 10 × (1)
r
R(1332)
where
n(1332) is the measured full-energy peak counting rate;
R(1332) is the 1 332 keV gamma-ray emission rate from the Co source;
0,833 × 10 is the reciprocal of the full-energy-peak efficiency of the Nal(TI) detector at that
energy and distance.
3.1.34
sample
radioactive material measured using the HPGe detector to determine the activity and/or
emission rate
3.1.35
shaping-time constant
index
indicator of shaped pulse width (width of a shaped pulse at 50 % of its peak height). Unless
otherwise specified, that width is f
1/2
3.1.36
source
calibrated radioactive material used to determine the HPGe detector response
3.1.37
standardization coefficient
S (i,E)
c
factor used for the direct conversion of the counts contained under a net full energy peak of a
given energy, E, and from a specific radionuclide, i, to the activity of the radionuclide

3.1.38
total efficiency
𝜀𝜀 (𝐸𝐸)
t
ratio of the number of pulses recorded in the entire energy spectrum and the number of
photons emitted by the source of a given energy, E, for a specified source-to-detector
distance
3.1.39
uncertain
...