ASTM D3648-95
(Practice)Standard Practices for the Measurement of Radioactivity
Standard Practices for the Measurement of Radioactivity
SCOPE
1.1 These practices cover a review of the accepted counting practices currently used in radiochemical analyses. The practices are divided into four sections: Section General Information 5 to 10 Alpha Counting 11 to 21 Beta Counting 22 to 32 Gamma Counting 33 to 40
1.2 The general information sections contain information applicable to all types of radioactive measurements, while each of the other sections is specific for a particular type of radiation.
1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
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Designation: D 3648 – 95
Standard Practices for the
Measurement of Radioactivity
This standard is issued under the fixed designation D 3648; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 These practices cover a review of the accepted counting 3.1 Definitions:
practices currently used in radiochemical analyses. The prac- 3.1.1 For definitions of terms used in these practices, refer
tices are divided into four sections: to Terminology D 1129. For an explanation of the metric
system, including units, symbols, and conversion factors, see
Section
General Information 5 to 10
Practice E 380.
Alpha Counting 11 to 21
Beta Counting 22 to 32
4. Summary of Practices
Gamma Counting 33 to 40
4.1 The practices are a compilation of the various counting
1.2 The general information sections contain information
techniques employed in the measurement of radioactivity. The
applicable to all types of radioactive measurements, while each
important variables that affect the accuracy or precision of
of the other sections is specific for a particular type of
counting data are presented. Because a wide variety of instru-
radiation.
ments and techniques are available for radiochemical labora-
1.3 This standard does not purport to address all of the
tories, the types of instruments and techniques to be selected
safety concerns, if any, associated with its use. It is the
will be determined by the information desired. In a simple
responsibility of the user of this standard to establish appro-
tracer application using a single radioactive isotope having
priate safety and health practices and determine the applica-
favorable properties of high purity, energy, and ample activity,
bility of regulatory limitations prior to use.
a simple detector will probably be sufficient and techniques
may offer no problems other than those related to reproduc-
2. Referenced Documents
ibility. The other extreme would be a laboratory requiring
2.1 ASTM Standards:
quantitative identification of a variety of radionuclides, prepa-
D 1066 Practice for Sampling Steam
ration of standards, or studies of the characteristic radiation
D 1129 Terminology Relating to Water
from radionuclides. For the latter, a variety of specialized
D 1943 Test Method for Alpha Particle Radioactivity of
instruments are required. Most radiochemical laboratories
Water
require a level of information between these two extremes.
D 2459 Test Method for Gamma Spectrometry of Water
4.2 A basic requirement for accurate measurements is the
D 3084 Practice for Alpha Spectrometry of Water
use of accurate standards for instrument calibration. With the
D 3085 Practice for Measurement of Low-Level Activity in
present availability of good standards, only the highly diverse
Water
radiochemistry laboratories require instrumentation suitable
D 3370 Practices for Sampling Water from Closed Con-
for producing their own radioactive standards. However, it is
duits
advisable to compare each new standard received against the
D 3649 Test Method for High-Resolution Gamma-Ray
previous standard.
Spectrometry of Water
4.3 Thus, the typical laboratory may be equipped with
E 380 Practice for Use of the International System of Units
proportional or Geiger-Mueller counters for beta counting,
(SI) (the Modernized Metric System)
sodium iodide or germanium detectors, or both, in conjunction
with multichannel analyzers for gamma spectrometry, and
scintillation counters suitable for alpha- or beta-emitting radio-
Precision and Bias These practices are under the jurisdiction of ASTM
Committee D-19 on Water and are the direct responsibility of D19.04 on Methods
nuclides.
of Radiochemical Analysis.
Current edition approved April 15, 1995. Published June 1995. Originally
e 1
published as D 3648 – 78. Last previous edition D 3648 – 78 (1987) .
Annual Book of ASTM Standards, Vol 11.01.
Annual Book of ASTM Standards, Vol 11.02.
Discontinued—See 1987 Annual Book of ASTM Standards, Vol 12.01.
Annual Book of ASTM Standards, Vol 14.02 (Excerpts in Vol 11.02).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 3648 – 95
5. Significance and Use 7.3.1 The purpose of shielding is to reduce the background
count rate of a measurement system. Shielding reduces back-
5.1 This practice was developed for the purpose of summa-
ground by absorbing some of the components of cosmic
rizing the various generic radiometric techniques, equipment,
radiation and some of the radiations emitted from material in
and practices that are used for the measurement of radioactiv-
the surroundings. Ideally, the material used for shielding
ity.
should itself be free of any radioactive material that might
contribute to the background. In practice, this is difficult to
GENERAL INFORMATION
achieve as most construction materials contain at least some
naturally radioactive species (such as potassium-40, members
6. Experimental Design
of the uranium and thorium series, etc.). The thickness of the
6.1 In order to properly design valid experimental proce-
shielding material should be such that it will absorb most of the
dures, careful consideration must be given to the following;
soft components of cosmic radiation. This will reduce cosmic-
6.1.1 radionuclide to be determined,
ray background by approximately 25 %. Shielding of beta- or
6.1.2 relative activity levels of interferences,
gamma-ray detectors with anticoincidence systems can further
6.1.3 type and energy of the radiation,
reduce the cosmic-ray or Compton scattering background for
6.1.4 original sample matrix, and
very low-level counting.
6.1.5 required accuracy.
7.3.2 Detectors have a certain background counting rate
6.2 Having considered 6.1.1-6.1.5, it is now possible to
from naturally occurring radionuclides and cosmic radiation
make the following decisions:
from the surroundings; and from the radioactivity in the
6.2.1 chemical or physical form that the sample must be in
detector itself. The background counting rate will depend on
for radioassay,
the amounts of these types of radiation and on the sensitivity of
6.2.2 chemical purification steps,
the detector to the radiations.
6.2.3 type of detector required,
7.3.3 In alpha counting, low backgrounds are readily
6.2.4 energy spectrometry, if required,
achieved since the short range of alpha particles in most
6.2.5 length of time the sample must be counted in order to
materials makes effective shielding easy. Furthermore, alpha
obtain statistically valid data,
detectors are quite insensitive to the electromagnetic compo-
6.2.6 isotopic composition, if it must be determined, and
nents of cosmic and other environmental radiation.
6.2.7 size of sample required.
7.4 Care of Instruments:
6.3 For example, gamma-ray measurements can usually be
7.4.1 The requirements for and advantages of operating all
performed with little or no sample preparation, whereas both
counting equipment under conditions as constant and repro-
alpha and beta counting will always require chemical process-
ducible as possible have been pointed out earlier in this section.
ing. If low levels of radiation are to be determined, very large
The same philosophy suggests the desirability of leaving all
samples and complex counting equipment may be necessary.
counting equipment constantly powered. This implies leaving
6.3.1 More detailed discussions of the problems and inter-
the line voltage on the electrical components at all times. The
ferences are included in the sections for each particular type of
advantage to be gained by this practice is the elimination of the
radiation to be measured.
start-up surge voltage, which causes rapid aging, and the
instability that occurs during the time the instrument is coming
7. Apparatus
up to normal temperature.
7.1 Location Requirements:
7.4.2 A regularly scheduled and implemented program of
7.1.1 The apparatus required for the measurement of radio-
maintenance is helpful in obtaining satisfactory results. The
activity consists, in general, of the detector and associated
maintenance program should include not only checking the
electronic equipment. The latter usually includes a stable
necessary operating conditions and characteristics of the com-
power supply, preamplifiers, a device to store or display the
ponents, but also regular cleaning of the equipment.
electrical pulses generated by the detector, or both, and one or
7.5 Sample and Detector Holders—In order to quantify
more devices to record information.
counting data, it is necessary that all samples be presented to
7.1.2 Some detectors and high-gain amplifiers are tempera-
the detector in the same “geometry.” This means that the
ture sensitive; therefore, changes in pulse amplitude can occur
samples and standards should be prepared for counting in the
as room temperature varies. For this reason, it is necessary to
same way so that the distance between the source and the
provide temperature-controlled air conditioning in the counting
detector remains as constant as possible. In practice, this
room.
usually means that the detector and the sample are in a fixed
7.1.3 Instrumentation should never be located in a chemical
position. Another configuration often used is to have the
laboratory where corrosive vapors will cause rapid deteriora-
detector in a fixed position within the shield, and beneath it a
tion and failure.
shelf-like arrangement for the reproducible positioning of the
7.2 Instrument Electrical Power Supply—Detector and
sample at several distances from the detector.
electronic responses are a function of the applied voltage;
therefore, it is essential that only a very stable, low-noise 7.6 Special Instrumentation—This section covers some ra-
electrical supply be used or that suitable stabilization be diation detection instruments and auxiliary equipment that may
included in the system. be required for special application in the measurement of
7.3 Shielding: radioactivity in water.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 3648 – 95
7.6.1 4-p Counter: vacuum evaporation. The absorption loss of beta particles in
7.6.1.1 The 4-p counter is a detector designed for the the film must be known. Published values can be used, if
measurement of the absolute disintegration rate of a radioactive
necessary, but for accurate work an absorption curve using
source by counting the source under conditions that approach very thin absorbers should be taken (1). The “sandwich”
a geometry of 4-p steradians. Its most prevalent use is for the
method, in which the film absorption is calculated from the
absolute measurement of beta emitters (1, 2). For this decrease in counting rate that occurs when the source surface
purpose, a gas-flow proportional counter similar to that in Fig.
is covered with a film of the same thickness as the backing
1 is common. It consists of two hemispherical or cylindrical film, is suitable for the higher beta energies.
chambers whose walls form the cathode, and a looped wire
7.6.1.4 The source itself must be very thin and deposited
anode in each chamber. The source is mounted on a thin
uniformly on the support to obtain negligible self-absorption.
supporting film between the two halves, and the counts
Various techniques have been used for spreading the source;
recorded in each half are summed. An argon (90 %)-methane
for example, the evaporation of Ni-dimethylglyoxime onto
(10 %) gas mixture can be used; however, pure methane gives
the support film (1), the addition of a TFE-fluorocarbon
flatter and longer plateaus and is preferred for the most
suspension (3), collodial silica, or insulin to the film as
accurate work. The disadvantage is that considerably higher
spreading agents, and hydrolysis (2). Self-absorption in the
voltages, about 3000 V, rather than the 2000 V suitable for
source or mount can be measured by 4-p beta-gamma coinci-
argon-methane, are necessary. As with all gas-filled propor-
dence counting (4, 5). The 4-p beta counter is placed next to a
tional counters, very pure gas is necessary for very high
sodium iodide scintillation crystal, or a portion of the chamber
detector efficiency. The absence of electronegative gases that
wall is replaced by a sodium iodide crystal, and the absolute
attach electrons is particularly important since the negative
disintegration rate is evaluated by coincidence counting (6, 7).
pulse due to electrons is counted in this detector. Commercial
By adding a suitable beta-gamma tracer, the method has been
chemically pure (cp) gases are ordinarily satisfactory, but they
used for pure beta as well as beta-gamma emitters (8). Accurate
should be dried for best results. A high-voltage power supply
standardization of pure low-energy beta emitters (for
for the detector, an amplifier, discriminator, and a scaler 63
example, Ni) is difficult, and the original literature should be
complete the system.
consulted by those inexperienced with this technique.
7.6.1.2 To convert counting rate to disintegration rate, the
7.6.1.5 Photon (gamma and strong X-ray) scintillation
principal corrections required are for self-absorption in the
counters with geometries approaching 4-p steradians can be
source and for absorption in the support film. The support film
constructed from NaI(Tl) crystals in either of two ways. A well
should be as thin as practicable to minimize absorption of beta
crystal (that is, a cylindrical crystal with a small axial hole
particles emitted in the downward direction. Polyester film
2 covered with a second crystal) will provide nearly 4-p geom-
with a thickness of about 0.9 mg/cm is readily available and
etry for small sources, as will two solid crystals placed very
easily handled. However, it is too thick for accurate work with
close together with a small source between them. The counts
the lower energy beta emitters. For this purpose, thin films (.5
2 from both crystals are summed as in the gas-flow counter. The
to 10 μg/cm ) are prepared by spreading a solution of a
deviation for 4-p geometry can be calculated from the physical
polymer in an organic solvent on water. VYNS (1), Formvar
dimensions. For absolute gamma-ray c
...
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