ASTM D3648-04(2011)
(Practice)Standard Practices for the Measurement of Radioactivity
Standard Practices for the Measurement of Radioactivity
SIGNIFICANCE AND USE
This practice was developed for the purpose of summarizing the various generic radiometric techniques, equipment, and practices that are used for the measurement of radioactivity.
SCOPE
1.1 These practices cover a review of the accepted counting practices currently used in radiochemical analyses..
General Information
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Standards Content (Sample)
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Designation: D3648 − 04(Reapproved 2011)
Standard Practices for the
Measurement of Radioactivity
This standard is issued under the fixed designation D3648; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope IEEE/ASTM SI 10American National Standard for Metric
Practice
1.1 Thesepracticescoverareviewoftheacceptedcounting
2.2 ANSI/ISO Standards:
practices currently used in radiochemical analyses. The prac-
tices are divided into four sections: ANSIN42.14CalibrationandUseofGermaniumSpectrom-
etersfortheMeasurementofGamma-RayEmissionRates
Section
General Information 6 to 11
of Radionuclides
Alpha Counting 12 to 22
ISO Guide to the Expression of Uncertainty in
Beta Counting 23 to 33
Measurement, 1993
Gamma Counting 34 to 41
1.2 The general information sections contain information
3. Terminology
applicabletoalltypesofradioactivemeasurements,whileeach
3.1 Definitions:
of the other sections is specific for a particular type of
3.1.1 For definitions of terms used in these practices, refer
radiation.
to Terminology D1129. For an explanation of the metric
1.3 This standard does not purport to address all of the
system, including units, symbols, and conversion factors, see
safety concerns, if any, associated with its use. It is the
Practice IEEE/ASTM SI 10.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Summary of Practices
bility of regulatory limitations prior to use.
4.1 The practices are a compilation of the various counting
2. Referenced Documents
techniques employed in the measurement of radioactivity. The
2 important variables that affect the accuracy or precision of
2.1 ASTM Standards:
counting data are presented. Because a wide variety of instru-
D1066Practice for Sampling Steam
ments and techniques are available for radiochemical
D1129Terminology Relating to Water
laboratories, the types of instruments and techniques to be
D1943Test Method for Alpha Particle Radioactivity of
selected will be determined by the information desired. In a
Water
simple tracer application using a single radioactive isotope
D2459Test Method for Gamma Spectrometry of Industrial
having favorable properties of high purity, energy, and ample
Water and Industrial Waste Water (Withdrawn 1986)
activity, a simple detector will probably be sufficient and
D3084Practice for Alpha-Particle Spectrometry of Water
techniques may offer no problems other than those related to
D3085Practice for Measurement of Low-Level Activity in
3 reproducibility. The other extreme would be a laboratory
Water (Withdrawn 1987)
requiring quantitative identification of a variety of
D3370Practices for Sampling Water from Closed Conduits
radionuclides, preparation of standards, or studies of the
D3649PracticeforHigh-ResolutionGamma-RaySpectrom-
characteristic radiation from radionuclides. For the latter, a
etry of Water
variety of specialized instruments are required. Most radio-
chemical laboratories require a level of information between
these two extremes.
These practices are under the jurisdiction ofASTM Committee D19 on Water
and are the direct responsibility of D19.04 on Methods of RadiochemicalAnalysis.
4.2 A basic requirement for accurate measurements is the
Current edition approved Jan. 1, 2011. Published January 2011. Originally
use of accurate standards for instrument calibration. With the
approved in 1978. Last previous edition approved in 2004 as D3648–04. DOI:
present availability of good standards, only the highly diverse
10.1520/D3648-04R11.
radiochemistry laboratories require instrumentation suitable
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.
3 4
The last approved version of this historical standard is referenced on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
www.astm.org. 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3648 − 04(Reapproved 2011)
for producing their own radioactive standards. However, it is
advisable to compare each new standard received against the
previous standard.
D3648 − 04 (2011)
4.3 Thus, the typical laboratory may be equipped with 7.1.3 Instrumentation should never be located in a chemical
proportional or Geiger-Mueller counters for beta counting, laboratory where corrosive vapors will cause rapid deteriora-
sodium iodide or germanium detectors, or both, in conjunction tion and failure.
with multichannel analyzers for gamma spectrometry, and
7.2 Instrument Electrical Power Supply—Detectorandelec-
scintillationcounterssuitableforalpha-orbeta-emittingradio-
tronic responses are a function of the applied voltage; there-
nuclides.
fore, it is essential that only a very stable, low-noise electrical
supply be used or that suitable stabilization be included in the
5. Significance and Use
system.
5.1 This practice was developed for the purpose of summa-
7.3 Shielding:
rizing the various generic radiometric techniques, equipment,
7.3.1 The purpose of shielding is to reduce the background
and practices that are used for the measurement of radioactiv-
count rate of a measurement system. Shielding reduces back-
ity.
ground by absorbing some of the components of cosmic
radiation and some of the radiations emitted from material in
GENERAL INFORMATION
the surroundings. Ideally, the material used for shielding
should itself be free of any radioactive material that might
6. Experimental Design
contribute to the background. In practice, this is difficult to
6.1 In order to properly design valid experimental proce-
achieve as most construction materials contain at least some
dures, careful consideration must be given to the following; 40
naturally radioactive isotopes (such as K, members of the
6.1.1 radionuclide to be determined,
uraniumandthoriumseries,andsoforth).Thethicknessofthe
6.1.2 relative activity levels of interferences,
shieldingmaterialshouldbesuchthatitwillabsorbmostofthe
6.1.3 type and energy of the radiation,
soft components of cosmic radiation.This will reduce cosmic-
6.1.4 original sample matrix, and
ray background by approximately 25%. Shielding of beta- or
6.1.5 required accuracy.
gamma-ray detectors with anticoincidence systems can further
reduce the cosmic-ray or Compton scattering background for
6.2 Having considered 6.1.1-6.1.5, it is now possible to
very low-level counting.
make the following decisions:
7.3.2 Detectors have a certain background counting rate
6.2.1 chemical or physical form that the sample must be in
for radioassay, from naturally occurring radionuclides and cosmic radiation
from the surroundings; and from the radioactivity in the
6.2.2 chemical purification steps,
detector itself. The background counting rate will depend on
6.2.3 type of detector required,
theamountsofthesetypesofradiationandonthesensitivityof
6.2.4 energy spectrometry, if required,
the detector to the radiations.
6.2.5 length of time the sample must be counted in order to
obtain statistically valid data, 7.3.3 In alpha counting, low backgrounds are readily
achieved since the short range of alpha particles in most
6.2.6 isotopic composition, if it must be determined, and
materials makes effective shielding easy. Furthermore, alpha
6.2.7 size of sample required.
detectors are quite insensitive to the electromagnetic compo-
6.3 For example, gamma-ray measurements can usually be
nents of cosmic and other environmental radiation.
performed with little or no sample preparation, whereas both
alpha and beta counting will almost always require chemical 7.4 Care of Instruments:
processing.Iflowlevelsofradiationaretobedetermined,very 7.4.1 The requirements for and advantages of operating all
large samples and complex counting equipment may be nec- counting equipment under conditions as constant and repro-
essary. ducibleaspossiblehavebeenpointedoutearlierinthissection.
6.3.1 More detailed discussions of the problems and inter- The same philosophy suggests the desirability of leaving all
ferencesareincludedinthesectionsforeachparticulartypeof counting equipment constantly powered. This implies leaving
radiation to be measured. the line voltage on the electrical components at all times. The
advantagetobegainedbythispracticeistheeliminationofthe
start-up surge voltage, which causes rapid aging, and the
7. Apparatus
instabilitythatoccursduringthetimetheinstrumentiscoming
7.1 Location Requirements:
up to normal temperature.
7.1.1 The apparatus required for the measurement of radio-
7.4.2 A regularly scheduled and implemented program of
activity consists, in general, of the detector and associated
maintenance is helpful in obtaining satisfactory results. The
electronic equipment. The latter usually includes a stable
maintenance program should include not only checking the
power supply, preamplifiers, a device to store or display the
necessary operating conditions and characteristics of the com-
electrical pulses generated by the detector, or both, and one or
ponents, but also regular cleaning of the equipment.
more devices to record information.
7.1.2 Some detectors and high-gain amplifiers are tempera- 7.5 Sample and Detector Holders—In order to quantify
ture sensitive; therefore, changes in pulse amplitude can occur counting data, it is necessary that all samples be presented to
as room temperature varies. For this reason, it is necessary to the detector in the same “geometry.” This means that the
providetemperature-controlledairconditioninginthecounting samples and standards should be prepared for counting in the
room. same way so that the distance between the source and the
D3648 − 04 (2011)
particles emitted in the downward direction. Polyester film
with a thickness of about 0.9 mg/cm is readily available and
easily handled. However, it is too thick for accurate work with
thelowerenergybetaemitters.Forthispurpose,thinfilms(.5
to 10 µg/cm ) are prepared by spreading a solution of a
polymer in an organic solvent on water. VYNS (1), Formvar
(2), and Tygon (3) plastics have been used for this purpose.
7.6.1.3 The films must be made electrically conducting
(sincetheyareapartofthechambercathode)bycoveringthem
with a thin layer (2 to 5 µg/cm ) of gold or palladium by
vacuum evaporation. The absorption loss of beta particles in
the film must be known. Published values can be used, if
necessary, but for accurate work an absorption curve using
very thin absorbers should be taken (1). The“sandwich”
FIG. 1 The 4π-Counting Chamber
method, in which the film absorption is calculated from the
decrease in counting rate that occurs when the source surface
detector remains as constant as possible. In practice, this
is covered with a film of the same thickness as the backing
usually means that the detector and the sample are in a fixed
film, is suitable for the higher beta energies.
position. Another configuration often used is to have the
7.6.1.4 The source itself must be very thin and deposited
detector in a fixed position within the shield, and beneath it a
uniformly on the support to obtain negligible self-absorption.
shelf-like arrangement for the reproducible positioning of the
Various techniques have been used for spreading the source;
sample at several distances from the detector. 63
for example, the evaporation of Ni-dimethylglyoxime onto
7.6 Special Instrumentation—This section covers some ra- the support film (1), the addition of a TFE-fluorocarbon
diationdetectioninstrumentsandauxiliaryequipmentthatmay suspension (3), collodial silica, or insulin to the film as
be required for special application in the measurement of spreading agents, and hydrolysis (2) . Self-absorption in the
radioactivity in water. source or mount can be measured by 4-π beta-gamma coinci-
7.6.1 4-π Counter: dence counting (4, 5).The 4-π beta counter is placed next to a
7.6.1.1 The 4-π counter is a detector designed for the NaI(Tl) detector, or a portion of the chamber wall is replaced
measurementoftheabsolutedisintegrationrateofaradioactive by a NaI(Tl) detector, and the absolute disintegration rate is
source by counting the source under conditions that approach evaluated by coincidence counting (6, 7). By adding a suitable
a geometry of 4-π steradians. Its most prevalent use is for the beta-gamma tracer, the method has been used for pure beta as
absolute measurement of beta emitters (1, 2). For this well as beta-gamma emitters (8). Accurate standardization of
purpose, a gas-flow proportional counter similar to that in Fig. pure low-energy beta emitters (for example, Ni) is difficult,
1 is common. It consists of two hemispherical or cylindrical and the original literature should be consulted by those
chambers whose walls form the cathode, and a looped wire inexperienced with this technique.
anode in each chamber. The source is mounted on a thin
7.6.1.5 Photon (gamma and strong X-ray) scintillation
supporting film between the two halves, and the counts
counters with geometries approaching 4-π steradians can be
recorded in each half are summed. A 10% methane-90%
constructedfromNaI(Tl)crystalsineitheroftwoways.Awell
argon gas mixture can be used; however, pure methane gives
crystal (that is, a cylindrical crystal with a small axial hole
flatter and longer plateaus and is preferred for the most
covered with a second crystal) will provide nearly 4-π geom-
accurate work. The disadvantage is that considerably higher
etry for small sources, as will two solid crystals placed very
voltages, about 3000 V, rather than the 2000 V suitable for
close together with a small source between them. The counts
methane-argon, are necessary. As with all gas-filled propor-
from both crystals are summed as in the gas-flow counter.The
tional counters, very pure gas is necessary for very high
deviationfor4-πgeometrycanbecalculatedfromthephysical
detector efficiency. The absence of electronegative gases that
dimensions. For absolute gamma-ray counting, the efficiency
attach electrons is particularly important since the negative
of the crystal for the gamma energy being measured and the
pulse due to electrons is counted in this detector. Commercial
absorption in the crystal cover must be taken into account.
chemically pure (cp) gas
...
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