ASTM D6866-24
(Test Method)Standard Test Methods for Determining the Biobased Content of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis
Standard Test Methods for Determining the Biobased Content of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis
SIGNIFICANCE AND USE
4.1 This testing method provides accurate biobased/biogenic carbon content results to materials whose carbon source was directly in equilibrium with CO2 in the atmosphere at the time of cessation of respiration or metabolism, such as the harvesting of a crop or grass living its natural life in a field. Special considerations are needed to apply the testing method to materials originating from within artificial environments. Application of these testing methods to materials derived from CO2 uptake within artificial environments is beyond the present scope of this standard.
4.2 Method B utilizes AMS along with Isotope Ratio Mass Spectrometry (IRMS) techniques to quantify the biobased content of a given product. Instrumental error can be within 0.1-0.5 % (1 relative standard deviation (RSD)), but controlled studies identify an inter-laboratory total uncertainty up to ±3 % (absolute). This error is exclusive of indeterminate sources of error in the origin of the biobased content (see Section 22 on precision and bias).
4.3 Method C uses LSC techniques to quantify the biobased content of a product using sample carbon that has been converted to benzene. This test method determines the biobased content of a sample with a maximum total error of ±3 % (absolute), as does Method B.
4.4 The test methods described here directly discriminate between product carbon resulting from contemporary carbon input and that derived from fossil-based input. A measurement of a product’s 14C/12C or 14C/13C content is determined relative to a carbon based modern reference material accepted by the radiocarbon dating community such as NIST Standard Reference Material (SRM) 4990C, (referred to as OXII or HOxII). It is compositionally related directly to the original oxalic acid radiocarbon standard SRM 4990B (referred to as OXI or HOxI), and is denoted in terms of fM, that is, the sample’s fraction of modern carbon. (See Terminology, Section 3.)
4.5 Reference standards, available to all...
SCOPE
1.1 This standard is a test method that teaches how to experimentally measure biobased carbon content of solids, liquids, and gaseous samples using radiocarbon analysis. These test methods do not address environmental impact, product performance and functionality, determination of geographical origin, or assignment of required amounts of biobased carbon necessary for compliance with federal laws.
1.2 These test methods are applicable to any product containing carbon-based components that can be combusted in the presence of oxygen to produce carbon dioxide (CO2) gas. The overall analytical method is also applicable to gaseous samples, including flue gases from electrical utility boilers and waste incinerators.
1.3 These test methods make no attempt to teach the basic principles of the instrumentation used although minimum requirements for instrument selection are referenced in the References section. However, the preparation of samples for the above test methods is described. No details of instrument operation are included here. These are best obtained from the manufacturer of the specific instrument in use.
1.4 Limitation—This standard is applicable to laboratories working without exposure to artificial carbon-14 (14C). Artificial 14C is routinely used in biomedical studies by both liquid scintillation counter (LSC) and accelerator mass spectrometry (AMS) laboratories and can exist within the laboratory at levels 1,000 times or more than 100 % biobased materials and 100,000 times more than 1% biobased materials. Once in the laboratory, artificial 14C can become undetectably ubiquitous on door knobs, pens, desk tops, and other surfaces but which may randomly contaminate an unknown sample producing inaccurately high biobased results. Despite vigorous attempts to clean up contaminating artificial 14C from a laboratory, isolation has proven to be the only successful method of avoidance. Completely separate chemical ...
General Information
Relations
Standards Content (Sample)
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: D6866 − 24
Standard Test Methods for
Determining the Biobased Content of Solid, Liquid, and
Gaseous Samples Using Radiocarbon Analysis
This standard is issued under the fixed designation D6866; 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* may randomly contaminate an unknown sample producing
inaccurately high biobased results. Despite vigorous attempts
1.1 This standard is a test method that teaches how to
to clean up contaminating artificial C from a laboratory,
experimentally measure biobased carbon content of solids,
isolation has proven to be the only successful method of
liquids, and gaseous samples using radiocarbon analysis. These
avoidance. Completely separate chemical laboratories and
test methods do not address environmental impact, product
extreme measures for detection validation are required from
performance and functionality, determination of geographical
laboratories exposed to artificial C. Accepted requirements
origin, or assignment of required amounts of biobased carbon
are:
necessary for compliance with federal laws.
(1) disclosure to clients that the laboratory(s) working with
1.2 These test methods are applicable to any product con- 14
their products and materials also works with artificial C
taining carbon-based components that can be combusted in the
(2) chemical laboratories in separate buildings for the
presence of oxygen to produce carbon dioxide (CO ) gas. The 14
handling of artificial C and biobased samples
overall analytical method is also applicable to gaseous
(3) separate personnel who do not enter the buildings of the
samples, including flue gases from electrical utility boilers and
other
waste incinerators.
(4) no sharing of common areas such as lunch rooms and
1.3 These test methods make no attempt to teach the basic
offices
principles of the instrumentation used although minimum
(5) no sharing of supplies or chemicals between the two
requirements for instrument selection are referenced in the
(6) quasi-simultaneous quality assurance measurements
References section. However, the preparation of samples for
within the detector validating the absence of contamination
the above test methods is described. No details of instrument
within the detector itself. (1, 2, and 3)
operation are included here. These are best obtained from the
1.5 This standard does not purport to address all of the
manufacturer of the specific instrument in use.
safety concerns, if any, associated with its use. It is the
1.4 Limitation—This standard is applicable to laboratories
responsibility of the user of this standard to establish appro-
working without exposure to artificial carbon-14 ( C). Artifi-
priate safety, health, and environmental practices and deter-
cial C is routinely used in biomedical studies by both liquid
mine the applicability of regulatory limitations prior to use.
scintillation counter (LSC) and accelerator mass spectrometry
NOTE 1—ISO 16620-2 is equivalent to this standard.
(AMS) laboratories and can exist within the laboratory at levels
1,000 times or more than 100 % biobased materials and
1.6 This international standard was developed in accor-
100,000 times more than 1% biobased materials. Once in the dance with internationally recognized principles on standard-
laboratory, artificial C can become undetectably ubiquitous
ization established in the Decision on Principles for the
on door knobs, pens, desk tops, and other surfaces but which
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1 Barriers to Trade (TBT) Committee.
These test methods are under the jurisdiction of ASTM Committee D20 on
Plastics and are the direct responsibility of Subcommittee D20.96 on Environmen-
tally Degradable Plastics and Biobased Products.
Current edition approved Feb. 1, 2024. Published February 2024. Originally
approved in 2004. Last previous edition approved in 2022 as D6866 - 22. DOI: The boldface numbers in parentheses refer to a list of references at the end of
10.1520/D6866-24. this standard.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6866 − 24
2. Referenced Documents marine, or forestry materials living in a natural environment in
3 equilibrium with the atmosphere.
2.1 ASTM Standards:
D883 Terminology Relating to Plastics 3.3.6 biogenic—containing carbon (organic and inorganic)
of renewable origin like agricultural, plant, animal, fungi,
2.2 Other Standards:
microorganisms, macroorganisms, marine, or forestry materi-
CEN/TS 16640:2014 Biobased Products—Determination of
als.
the biobased carbon content of products using the radio-
carbon method
3.3.7 biobased carbon content—the amount of biobased
CEN/TS 16137:2011 Plastics—Determination of biobased
carbon in the material or product as a percent of the total
carbon content
organic carbon (TOC) in the product.
ISO 16620-2:2015 Plastics—Biobased content—Part 2: De-
3.3.8 biogenic carbon content—the amount of biogenic
termination of biobased carbon content
carbon in the material or product as a percent of the total
EN 15440:2011 Solid recovered fuels—Methods for the de-
carbon (TC) in the product.
termination of biomass content
3.3.9 biobased carbon content on mass basis—amount of
ISO 13833:2013 Stationary source emissions—
biobased carbon in the material or product as a percent of the
Determination of the ratio of biomass (biogenic) and
total mass of product.
fossil-derived carbon dioxide—Radiocarbon sampling
and determination
3.3.10 biogenic carbon content on mass basis—amount of
biogenic carbon in the material or product as a percent of the
3. Terminology
total mass of product.
3.1 The definitions of terms used in these test methods are
3.3.11 break seal tube—the sample tube within which the
referenced in order that the practitioner may require further
sample, copper oxide, and silver wire is placed.
information regarding the practice of the art of isotope analysis
3.3.12 coincidence circuit—a portion of the electronic
and to facilitate performance of these test methods.
analysis system of an LSC which acts to reject pulses which are
3.2 Terminology D883 should be referenced for terminol-
not received from the two Photomultiplier Tubes (that count
ogy relating to plastics. Although an attempt to list terms in a
the photons) within a given period of time and are necessary to
logical manner (alphabetically) will be made as some terms
rule out background interference and required for any LSC
require definition of other terms to make sense.
used in these test methods (9, 6, 12).
3.3 Definitions:
3.3.13 coincidence threshold—the minimum decay energy
3.3.1 AMS facility—a facility performing Accelerator Mass
required for an LSC to detect a radioactive event. The ability to
Spectrometry.
set that threshold is a requirement of any LSC used in these test
methods (6, 12).
3.3.2 accelerator mass spectrometry (AMS)—an ultra-
sensitive technique that can be used for measuring naturally
3.3.14 contemporary carbon—a direct indication of the
occurring radio nuclides, in which sample atoms are ionized,
relative contributions of fossil carbon and “living” biospheric
accelerated to high energies, separated on basis of momentum,
carbon can be expressed as the fraction (or percentage) of
charge, and mass, and individually counted in Faraday collec-
contemporary carbon, symbol f . This is derived from “frac-
C
tors. This high energy separation is extremely effective in
tion of modern” (f ) through the use of the observed input
M
filtering out isobaric interferences, such that AMS may be used
function for atmospheric C over recent decades, representing
14 12
to measure accurately the C ⁄ C abundance to a level of 1 in
the combined effects of fossil dilution of C (minor) and
10 . At these levels, uncertainties are based on counting
nuclear testing enhancement (major). The relation between f
C
statistics through the Poisson distribution (4,5).
and f is necessarily a function of time. By 1985, when the
M
3.3.3 automated effıciency control (AEC)—a method used particulate sampling discussed in the cited reference was
performed, the f ratio had decreased to approximately 1.2 (4,
by scintillation counters to compensate for the effect of
M
quenching on the sample spectrum (6). 5).
3.3.4 background radiation—the radiation in the natural 3.3.15 chemical quenching—a reduction in the scintillation
environment; including cosmic radiation and radionuclides
intensity (a significant interference with these test methods)
present in the local environment, for example, materials of seen by the Photomultiplier Tubes (PMT, pmt) due to the
construction, metals, glass, concrete (7,8,9,4,6-14).
materials present in the scintillation solution that interfere with
the processes leading to the production of light. The result is
3.3.5 biobased—containing organic carbon of renewable
fewer photons counted and a lower efficiency (8, 9, 12).
origin like agricultural, plant, animal, fungi, microorganisms,
3.3.16 chi-square test—a statistical tool used in radioactive
counting in order to compare the observed variations in repeat
counts of a radioactive sample with the variation predicted by
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
statistical theory. This determines whether two different distri-
Standards volume information, refer to the standard’s Document Summary page on
butions of photon measurements originate from the same
the ASTM website.
photonic events. LSC instruments used in this measurement
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. should include this capability (6, 12, 15).
D6866 − 24
3.3.17 cocktail—the solution in which samples are placed 3.3.31 modern carbon—explicitly, 0.95 times the specific
for measurement in an LSC. Solvents and Scintillators— activity of SRM 4990B (the original oxalic acid radiocarbon
chemicals that absorb decay energy transferred from the standard), normalized to δ C = −19 % (Currie, et al., 1989).
solvent and emits light (photons) proportional in intensity to Functionally, the fraction of modern carbon equals 0.95 times
the deposited energy (8, 9, 6, 12). the concentration of C contemporaneous with 1950 wood
(that is, pre-atmospheric nuclear testing). To correct for the
3.3.18 decay (radioactive)—the spontaneous transformation
post 1950 bomb C injection into the atmosphere (5), the
of one nuclide into a different nuclide or into a different energy
fraction of modern carbon is multiplied by a correction factor
state of the same nuclide. The process results in a decrease,
representative of the excess C in the atmosphere at the time
with time, of the number of original radioactive atoms in a
of measurements.
sample, according to the half-life of the radionuclide (4, 6, 12).
3.3.32 noise pulse—a spurious signal arising from the elec-
3.3.19 discriminator—an electronic circuit which distin-
tronics and electrical supply of the instrument (6, 12, 23, 24).
guishes signal pulses according to their pulse height or energy;
3.3.33 phase contact—the degree of contact between two
used to exclude extraneous radiation, background radiation,
phases of heterogeneous samples. In liquid scintillation
and extraneous noise from the desired signal (6, 12, 13, 16).
counting, better phase contact usually means higher counting
3.3.20 dpm—disintegrations per minute. This is the quantity
efficiency (6, 12).
of radioactivity. The measure dpm is derived from cpm or
3.3.34 photomultiplier tube (PMT, pmt)—the device in the
counts per minute (dpm = cpm − bkgd / counting efficiency).
LSC that counts the photons of light simultaneously at two
There are 2.2 × 10 dpm / μCi (6, 12).
separate detectors (24, 16).
3.3.21 dps—disintegrations per second (rather than minute
3.3.35 pulse—the electrical signal resulting when photons
as above) (6, 12).
are detected by the PMTs (6, 12, 13, 16).
3.3.22 effıciency—the ratio of measured observations or
3.3.36 pulse height analyzer (PHA)—an electronic circuit
counts compared to the number of decay events which oc-
which sorts and records pulses according to height or voltage
curred during the measurement time; expressed as a percentage
(6, 12, 13, 16).
(6, 12).
3.3.37 pulse index—the number of after-pulses following a
3.3.23 external standard—a radioactive source placed adja-
detected coincidence pulse (used in three dimensional or pulse
cent to the liquid sample to produce scintillations in the sample
height discrimination) to compensate for the background of an
for the purpose of monitoring the sample’s level of quenching
LSC performing (6, 13, 24, 16).
(6, 12).
3.3.38 quenching—any material that interferes with the
3.3.24 figure of merit—a term applied to a numerical value
accurate conversion of decay energy to photons captured by the
used to characterize the performance of a system. In liquid
PMT of the LSC (7, 8, 9, 6, 10, 12, 17).
scintillation counting, specific formulas have been derived for
quantitatively comparing certain aspects of instrument and
3.3.39 region—regions of interest, also called window
cocktail performance and the term is frequently used to
and/or channel in regard to LSC. Refers to an energy level or
compare efficiency and background measures (6, 12, 17).
subset specific to a particular isotope (8, 6, 13, 23, 24).
3.3.25 flexible tube cracker—the apparatus in which the
3.3.40 renewable—being readily replaced and of non-fossil
sample tube (Break Seal Tube) is placed (18, 19, 20, 21).
origin; specifically not of petroleum origin.
3.3.26 fluorescence—the emission of light resulting from
3.3.41 scintillation—the sum of all photons produced by a
the absorption of incident radiation and persisting only as long
radioactive decay event. Counters used to measure this as
as the stimulation radiation is continued (6, 12, 22).
described in these test methods are Liquid Scintillation Coun-
ters (LSC) (6, 12).
3.3.27 fossil carbon—carbon that contains essentially no
radiocarbon because its age is very much greater than the 5,73
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6866 − 22 D6866 − 24
Standard Test Methods for
Determining the Biobased Content of Solid, Liquid, and
Gaseous Samples Using Radiocarbon Analysis
This standard is issued under the fixed designation D6866; 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*
1.1 This standard is a test method that teaches how to experimentally measure biobased carbon content of solids, liquids, and
gaseous samples using radiocarbon analysis. These test methods do not address environmental impact, product performance and
functionality, determination of geographical origin, or assignment of required amounts of biobased carbon necessary for
compliance with federal laws.
1.2 These test methods are applicable to any product containing carbon-based components that can be combusted in the presence
of oxygen to produce carbon dioxide (CO ) gas. The overall analytical method is also applicable to gaseous samples, including
flue gases from electrical utility boilers and waste incinerators.
1.3 These test methods make no attempt to teach the basic principles of the instrumentation used although minimum requirements
for instrument selection are referenced in the References section. However, the preparation of samples for the above test methods
is described. No details of instrument operation are included here. These are best obtained from the manufacturer of the specific
instrument in use.
14 14
1.4 Limitation—This standard is applicable to laboratories working without exposure to artificial carbon-14 ( C). Artificial C
is routinely used in biomedical studies by both liquid scintillation counter (LSC) and accelerator mass spectrometry (AMS)
laboratories and can exist within the laboratory at levels 1,000 times or more than 100 % biobased materials and 100,000 times
more than 1% biobased materials. Once in the laboratory, artificial C can become undetectably ubiquitous on door knobs, pens,
desk tops, and other surfaces but which may randomly contaminate an unknown sample producing inaccurately high biobased
results. Despite vigorous attempts to clean up contaminating artificial C from a laboratory, isolation has proven to be the only
successful method of avoidance. Completely separate chemical laboratories and extreme measures for detection validation are
required from laboratories exposed to artificial C. Accepted requirements are:
(1) disclosure to clients that the laboratory(s) working with their products and materials also works with artificial C
(2) chemical laboratories in separate buildings for the handling of artificial C and biobased samples
(3) separate personnel who do not enter the buildings of the other
(4) no sharing of common areas such as lunch rooms and offices
(5) no sharing of supplies or chemicals between the two
(6) quasi-simultaneous quality assurance measurements within the detector validating the absence of contamination within the
detector itself. (1, 2, and 3)
These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcommittee D20.96 on Environmentally
Degradable Plastics and Biobased Products.
Current edition approved March 15, 2022Feb. 1, 2024. Published March 2022February 2024. Originally approved in 2004. Last previous edition approved in 20212022
as D6866 - 21.D6866 - 22. DOI: 10.1520/D6866-22.10.1520/D6866-24.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6866 − 24
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
NOTE 1—ISO 16620-2 is equivalent to this standard.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
2.2 Other Standards:
CEN/TS 16640:2014 Biobased Products—Determination of the biobased carbon content of products using the radiocarbon
method
CEN/TS 16137:2011 Plastics—Determination of biobased carbon content
ISO 16620-2:2015 Plastics—Biobased content—Part 2: Determination of biobased carbon content
EN 15440:2011 Solid recovered fuels—Methods for the determination of biomass content
ISO 13833:2013 Stationary source emissions—Determination of the ratio of biomass (biogenic) and fossil-derived carbon
dioxide—Radiocarbon sampling and determination
3. Terminology
3.1 The definitions of terms used in these test methods are referenced in order that the practitioner may require further information
regarding the practice of the art of isotope analysis and to facilitate performance of these test methods.
3.2 Terminology D883 should be referenced for terminology relating to plastics. Although an attempt to list terms in a logical
manner (alphabetically) will be made as some terms require definition of other terms to make sense.
3.3 Definitions:
3.3.1 AMS facility—a facility performing Accelerator Mass Spectrometry.
3.3.2 accelerator mass spectrometry (AMS)—an ultra-sensitive technique that can be used for measuring naturally occurring radio
nuclides, in which sample atoms are ionized, accelerated to high energies, separated on basis of momentum, charge, and mass, and
individually counted in Faraday collectors. This high energy separation is extremely effective in filtering out isobaric interferences,
14 12 15
such that AMS may be used to measure accurately the C ⁄ C abundance to a level of 1 in 10 . At these levels, uncertainties
are based on counting statistics through the Poisson distribution (4,5).
3.3.3 automated effıciency control (AEC)—a method used by scintillation counters to compensate for the effect of quenching on
the sample spectrum (6).
3.3.4 background radiation—the radiation in the natural environment; including cosmic radiation and radionuclides present in the
local environment, for example, materials of construction, metals, glass, concrete (7,8,9,4,6-14).
3.3.5 biobased—containing organic carbon of renewable origin like agricultural, plant, animal, fungi, microorganisms, marine, or
forestry materials living in a natural environment in equilibrium with the atmosphere.
3.3.6 biogenic—containing carbon (organic and inorganic) of renewable origin like agricultural, plant, animal, fungi,
microorganisms, macroorganisms, marine, or forestry materials.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D6866 − 24
3.3.7 biobased carbon content—the amount of biobased carbon in the material or product as a percent of the total organic carbon
(TOC) in the product.
3.3.8 biogenic carbon content—the amount of biogenic carbon in the material or product as a percent of the total carbon (TC) in
the product.
3.3.9 biobased carbon content on mass basis—amount of biobased carbon in the material or product as a percent of the total mass
of product.
3.3.10 biogenic carbon content on mass basis—amount of biogenic carbon in the material or product as a percent of the total mass
of product.
3.3.11 break seal tube—the sample tube within which the sample, copper oxide, and silver wire is placed.
3.3.12 coincidence circuit—a portion of the electronic analysis system of an LSC which acts to reject pulses which are not received
from the two Photomultiplier Tubes (that count the photons) within a given period of time and are necessary to rule out background
interference and required for any LSC used in these test methods (9, 6, 12).
3.3.13 coincidence threshold—the minimum decay energy required for an LSC to detect a radioactive event. The ability to set that
threshold is a requirement of any LSC used in these test methods (6, 12).
3.3.14 contemporary carbon—a direct indication of the relative contributions of fossil carbon and “living” biospheric carbon can
be expressed as the fraction (or percentage) of contemporary carbon, symbol f . This is derived from “fraction of modern” (f )
C M
through the use of the observed input function for atmospheric C over recent decades, representing the combined effects of fossil
dilution of C (minor) and nuclear testing enhancement (major). The relation between f and f is necessarily a function of time.
C M
By 1985, when the particulate sampling discussed in the cited reference was performed, the f ratio had decreased to
M
approximately 1.2 (4, 5).
3.3.15 chemical quenching—a reduction in the scintillation intensity (a significant interference with these test methods) seen by
the Photomultiplier Tubes (PMT, pmt) due to the materials present in the scintillation solution that interfere with the processes
leading to the production of light. The result is fewer photons counted and a lower efficiency (8, 9, 12).
3.3.16 chi-square test—a statistical tool used in radioactive counting in order to compare the observed variations in repeat counts
of a radioactive sample with the variation predicted by statistical theory. This determines whether two different distributions of
photon measurements originate from the same photonic events. LSC instruments used in this measurement should include this
capability (6, 12, 15).
3.3.17 cocktail—the solution in which samples are placed for measurement in an LSC. Solvents and Scintillators—chemicals that
absorb decay energy transferred from the solvent and emits light (photons) proportional in intensity to the deposited energy (8, 9,
6, 12).
3.3.18 decay (radioactive)—the spontaneous transformation of one nuclide into a different nuclide or into a different energy state
of the same nuclide. The process results in a decrease, with time, of the number of original radioactive atoms in a sample, according
to the half-life of the radionuclide (4, 6, 12).
3.3.19 discriminator—an electronic circuit which distinguishes signal pulses according to their pulse height or energy; used to
exclude extraneous radiation, background radiation, and extraneous noise from the desired signal (6, 12, 13, 16).
3.3.20 dpm—disintegrations per minute. This is the quantity of radioactivity. The measure dpm is derived from cpm or counts per
minute (dpm = cpm − bkgd / counting efficiency). There are 2.2 × 10 dpm / μCi (6, 12).
3.3.21 dps—disintegrations per second (rather than minute as above) (6, 12).
D6866 − 24
3.3.22 effıciency—the ratio of measured observations or counts compared to the number of decay events which occurred during
the measurement time; expressed as a percentage (6, 12).
3.3.23 external standard—a radioactive source placed adjacent to the liquid sample to produce scintillations in the sample for the
purpose of monitoring the sample’s level of quenching (6, 12).
3.3.24 figure of merit—a term applied to a numerical value used to characterize the performance of a system. In liquid scintillation
counting, specific formulas have been derived for quantitatively comparing certain aspects of instrument and cocktail performance
and the term is frequently used to compare efficiency and background measures (6, 12, 17).
3.3.25 flexible tube cracker—the apparatus in which the sample tube (Break Seal Tube) is placed (18, 19, 20, 21).
3.3.26 fluorescence—the emission of light resulting from the absorption of incident radiation and persisting only as long as the
stimulation radiation is continued (6, 12, 22).
3.3.27 fossil carbon—carbon that contains essentially no radiocarbon because its age is very much greater than the 5,730 year
half-life of C (4, 5).
3.3.28 half-life—the time in which one half the atoms of a particular radioactive substance disintegrate to another nuclear form.
The half-life of C is 5,730 years (4, 6, 22).
3.3.29 intensity—the amount of energy, the number of photons, or the numbers of particles of any radiation incident upon a unit
area per unit time (6, 12).
3.3.30 internal standard—a known amount of radioactivity which is added to a sample in order to determine the counting
efficiency of that sample. The radionuclide used must be the same as that in the sample to be measured, the cocktail should be the
same as the sample, and the Internal Standard must be of certified activity (6, 12).
3.3.31 modern carbon—explicitly, 0.95 times the specific activity of SRM 4990B (the original oxalic acid radiocarbon standard),
normalized to δ C = −19 % (Currie, et al., 1989). Functionally, the fraction of modern carbon equals 0.95 times the concentration
14 14
of C contemporaneous with 1950 wood (that is, pre-atmospheric nuclear testing). To correct for the post 1950 bomb C injection
into the atmosphere (5), the fraction of modern carbon is multiplied by a correction factor representative of the excess C in the
atmosphere at the time of measurements.
3.3.32 noise pulse—a spurious signal arising from the electronics and electrical supply of the instrument (6, 12, 23, 24).
3.3.33 phase contact—the degree of contact between two phases of heterogeneous samples. In liquid scintillation counting, better
phase contact usually means higher counting efficiency (6, 12).
3.3.34 photomultiplier tube (PMT, pmt)—the device in the LSC that counts the photons of light simultaneously at two separate
detectors (24, 16).
3.3.35 pulse—the electrical signal resulting when photons are detected by the PMTs (6, 12, 13, 16).
3.3.36 pulse height analyzer (PHA)—an electronic circuit which sorts
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