ASTM D3084-05(2012)
(Practice)Standard Practice for Alpha-Particle Spectrometry of Water
Standard Practice for Alpha-Particle Spectrometry of Water
SIGNIFICANCE AND USE
Alpha-particle spectrometry can either be used as a quantitative counting technique or as a qualitative method for informing the analyst of the purity of a given sample.
The method may be used for evaporated alpha-particle sources, but the quality of the spectra obtained will be limited by the absorbing material on the planchet and the surface finish of the planchet.
SCOPE
1.1 This practice covers the processes that are required to obtain well-resolved alpha-particle spectra from water samples and discusses associated problems. This practice is generally combined with specific chemical separations, mounting techniques, and counting instrumentation, as referenced.
1.2 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.
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Designation: D3084 − 05 (Reapproved 2012)
Standard Practice for
Alpha-Particle Spectrometry of Water
This standard is issued under the fixed designation D3084; 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 carried out by several methods involving magnetic
spectrometers, gas counters, scintillation spectrometers,
1.1 This practice covers the processes that are required to
nuclear emulsion plates, cloud chambers, absorption
obtain well-resolved alpha-particle spectra from water samples
techniques, and solid-state counters. Gas counters, operating
and discusses associated problems. This practice is generally
either as an ionization chamber or in the proportional region,
combined with specific chemical separations, mounting
have been widely used to identify and measure the relative
techniques, and counting instrumentation, as referenced.
amounts of differentα -emitters. However, more recently, the
1.2 This standard does not purport to address all of the
solid-state counter has become the predominant system be-
safety concerns, if any, associated with its use. It is the
cause of its excellent resolution and compactness. Knoll (3)
responsibility of the user of this standard to establish appro-
extensively discusses the characteristics of both detector types.
priate safety and health practices and determine the applica-
4.2 Of the two gas-counting techniques, the pulsed ioniza-
bility of regulatory limitations prior to use.
tion chamber is more widely used as it gives much better
2. Referenced Documents
resolution than does the other. This is because there is no
2 spread arising from multiplication or from imperfection of the
2.1 ASTM Standards:
wire such as occurs with the proportional counter.
C859 Terminology Relating to Nuclear Materials
C1163 Practice for MountingActinides forAlpha Spectrom-
4.3 The semiconductor detectors used for alpha-particle
etry Using Neodymium Fluoride
spectrometry are similar in principle to ionization chambers.
D1129 Terminology Relating to Water
The ionization of the gas by α-particles gives rise to electron-
D3648 Practices for the Measurement of Radioactivity
ion pairs, while in a semiconductor detector, electron-hole
D3865 Test Method for Plutonium in Water
pairs are produced. Subsequently, the liberated changes are
D3972 Test Method for Isotopic Uranium in Water by
collected by an electric field. In general, silicon detectors are
Radiochemistry
usedforalpha-particlespectrometry.Thesedetectorsaren-type
base material upon which gold is evaporated or ions such as
3. Terminology
boron are implanted, making an electrical contact. A reversed
3.1 For definitions of terms used in this practice, refer to bias is applied to the detector to reduce the leakage current and
Terminologies D1129 and C859. For terms not found in these to create a depletion layer of free-charge carriers. This layer is
thin and the leakage current is very low. Therefore, the slight
terminologies, reference may be made to other published
glossaries (1, 2). interactions of photons with the detector produce no signal.
Theeffectofanyinteractionsofbetaparticleswiththedetector
4. Summary of Practice
can be eliminated by appropriate electronic discrimination
(gating) of signals entering the multichannel analyzer. A
4.1 Alpha-particle spectrometry of radionuclides in water
semiconductor detector detects all alpha particles emitted by
(also called alpha-particle pulse-height analysis) has been
radionuclides (approximately 2 to 10 MeV) with essentially
equal efficiency, which simplifies its calibration.
This practice is under the jurisdiction ofASTM Committee D19 on Water and
4.4 Semiconductor detectors have better resolution than gas
is the direct responsibility of Subcommittee D19.04 on Methods of Radiochemical
Analysis.
detectors because the average energy required to produce an
Current edition approved June 1, 2012. Published August 2012. Originally
electron-hole pair in silicon is 3.5 6 0.1 eV (0.56 6 0.02 aJ)
approved in 1972. Last previous edition approved in 2005 as D3084 – 05. DOI:
compared with from 25 to 30 eV (4.0 to 4.8 aJ) to produce an
10.1520/D3084-05R12.
ion pair in a gas ionization chamber. Detector resolution,
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
defined as peak full-width at half-maximum height (FWHM),
Standards volume information, refer to the standard’s Document Summary page on
is customarily expressed in kiloelectron-volts. The FWHM
the ASTM website.
increases with increasing detector area, but is typically be-
The boldface numbers in parentheses refer to the list of references at the end of
this document. tween 15 and 60 keV. The background is normally lower for a
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3084 − 05 (2012)
semiconductor detector than for ionization chamber. Silicon 6. Interferences
detectors have four other advantages compared to ionization
6.1 The resolution or ability to separate alpha-particle peaks
chambers: they are lower in cost, have superior stability, have
will depend on the quality of the detector, the pressure inside
higher permissible counting rates, and have better time reso-
the counting chamber, the source-to-detector distance, the
lution for coincidence measurements. However, the semicon-
instrumentation,andthequalityofthesource.Ifpeaksoverlap,
ductor detector requires sophisticated electronics because of
abetterspectrometeroradditionalchemicalseparationswillbe
thelowchargethatisgeneratedbytheincidentα-particleinthe
required.
detector. Low-noise and high-stability, charge-sensitive pream-
plifiers are used prior to the detection, analog-to-digital
7. Apparatus
conversion, and storage of the voltage pulse by a multichannel
7.1 Alpha Particle Detector, either a silicon semiconductor
analyzer.Thecountingisnearlyalwaysperformedinavacuum
or a Frisch-grid pulse-ionization chamber.
chamber so that the α-particles will not lose energy by
7.2 Counting Chamber, to house the detector, hold the
collisions with air molecules between the source and the
source, and allow the detector system to be evacuated.
detector.
7.3 Counting Gas, for ionization chamber, typically a 90 %
4.5 A gridded pulse-ionization chamber was developed by
argon–10 % methane mixture, and associated gas-handling
Frischforhigh-resolutionalphaspectrometry.Theunitconsists
equipment.
of a standard ionization chamber fitted with a collimator
7.4 Pulse Amplification System, possibly including a
between the source and the collector plate and a wire grid to
preamplifier, amplifier, postamplifier, pulse stretcher, and a
shield the collector from the effects of positive ions. The
high-voltage power supply, as directed by the quality and type
resolution of a gridded pulse ionization chamber is from 35 to
of detector employed.
100 keV for routine work. The detector parameters that affect
resolution are primarily the following: statistical variations in
7.5 Multichannel Pulse-Height Analyzer, including data
the number of ion pairs formed at a given alpha energy, the
readout equipment. This is now often computer based.
variation in rise time of pulses, and the effects of positive ions.
7.6 Vacuum Pump, with low vapor-pressure oil and prefer-
An advantage of gridded ionization chambers is their ability to
ably with a trap to protect the detector from oil vapors.
count large-area sources with good efficiency.
8. Source Preparation
4.6 There are two reasons for collimating a sample in a
gridded ionization chamber. When thick-sample sources are
8.1 Thetechniqueemployedforpreparingthesourceshould
encountered, the alpha-particles emitted at a large solid angle
produce a low-mass, uniformly distributed deposit that is on a
would show an energy degradation upon ionization of the gas.
very smooth surface. The three techniques that are generally
The effect leads to tailing of the alpha-particle spectrum. This
employed are electrodeposition, microcoprecipitation, and
problem is reduced significantly by use of the collimator.
evaporation. The first two usually are preferred. Fig. 1 com-
Secondly, when the nucleus following anα -particle emission
pares the alpha-particle spectrum of an electrodeposited source
does not decay to a ground state, the γ-rays that may be
with that of an evaporated source.
produced are usually highly converted, and the conversion
8.1.1 Electrodeposition of α-emitters can provide a sample
electrons ionize the gas. The special mesh-type collimators
with optimum resolution, but quantitative deposition is not
stop the conversion electrons and collimate the source simul-
necessarilyachieved.Basically,theα-emitterisdepositedfrom
taneously.
solution on a polished stainless steel or platinum disk, which is
the cathode. The anode is normally made from platinum gauze
4.7 A more recently developed measurement method is
oraspiralledplatinumwire,whichoftenisrotatedataconstant
photon-electron-rejecting alpha liquid-scintillation spectrom-
etry. The sample is counted in a special liquid-scintillation
spectrometer that discriminates electronically against non-
alpha-particle pulses. The resolution that can be achieved by
this method is 250 to 300-keV FWHM. This is superior to
conventional liquid-scintillation counting, but inferior to sili-
con detectors and gridded pulse-ionization chambers. An
application of this method is given in Ref 4.
5. Significance and Use
5.1 Alpha-particle spectrometry can either be used as a
quantitative counting technique or as a qualitative method for
informing the analyst of the purity of a given sample.
5.2 The method may be used for evaporated alpha-particle
NOTE 1—Inner curve: nuclides separated on barium sulfate and then
sources, but the quality of the spectra obtained will be limited
electrodeposited.
bytheabsorbingmaterialontheplanchetandthesurfacefinish
NOTE 2—Outer curve: carrier-free tracer solution evaporated directly.
of the planchet. FIG. 1 Resolution Obtained on Six-Component Mixture
D3084 − 05 (2012)
rate. Variants of this technique may be found in Refs 5 and 6. ling the air pressure in the counting chamber so that 12 µg/cm
SeealsoTestMethodD3865.Poloniumcanbemadetodeposit of absorber is present between the source and the detector will
spontaneously from solution onto a copper or nickel disk (7). cause only a 1-keV resolution loss; however, the recoil
8.1.2 Micro-coprecipitation of actinide elements on a rare- contamination will be reduced by a factor greater than 500.
earthfluoride,oftenneodymiumfluoride,followedbyfiltration Recoiling atoms can also be reduced electrically (11). Rugge-
on a specially prepared membrane-type filter (see Test Method dized detectors can be cleaned to a limited degree.
C1163) also produces a good-quality source for alpha-particle
10.3 Qualitative identifications sometimes can be made
spectrometry. The microgram quantity of precipitant only
even on highly degraded spectra. By examining the highest
slightly degrades spectral resolution.
energy value, and using the energy calibration (keV/channel)
8.1.3 The evaporation technique involves depositing the
of the pulse-height analyzer, alpha-particle emitters may be
solution onto a stainless steel or platinum disk. The liquid is
identified. Fig. 2 shows a typical spectrum with very poor
applied in small droplets over the entire surface area so that
resolution.
they dry separately, or a wetting agent is applied, which causes
thesolutiontoevaporateuniformlyovertheentiresurface.The 11. Calculation
total mass should not exceed 10µ g/cm , otherwise self-
11.1 Analyze the data by first integrating the area under the
absorption losses will be significant. In addition, the alpha-
alpha peak to obtain a gross count for the alpha emitter. When
particle spectrum will be poorly resolved, as evidenced by a
the spectrum is complex and alpha peaks add to each other,
long lower-energy edge on the peak. This tailing effect can
corrections for overlapping peaks will be required. Some
contribute counts to lower energy alpha peaks and create large
instrument manufacturer’s computer software can perform
uncertainties in peak areas.Alpha sources that are prepared by
these and other data-analysis functions.
evaporation may not adhere tenaciously and, therefore, can
11.2 The preferred method for determination of chemical
flake causing contamination of equipment and sample losses.
recovery is the use of another isotope of the same element
9. Calibration
(examples: polonium-208 to trace polonium-210, plutonium-
236 to trace plutonium-239, and americium-243 to trace
9.1 Calibrate the counter by measuring α-emitting radionu-
americium-241). Add a known activity of the appropriate
clides that have been prepared by one of the techniques
isotope(s) to the sample at the beginning of the analysis,
described in Section 8.All standards should be traceable to the
perform the appropriate chemical separations, mount the
National Institute of Standards and Technology and in the case
sample, and measure it by alpha-particle spectrometry. The
of nonquantitative mounting, standardized on a 2π or 4π
chemicalyieldisdirectlyrelatedtothereductionintheactivity
alpha-particle counter. Precautions should be taken to ensure
of the added isotope.
that significant impurities are not present when standardizing
11.2.1 When the recovery factor is determined by the
the alpha-particle activity by non-spectrometric means. The
addition of a tracer, calculate the gross radioactivity
physical characteristics of the calibrating sources and their
concentration, C, of the analyte in becquerels per litre (Bq/L)
positioning relative to the detector must be the same as the
as follows:
samples to be counted. A mixed radionuclide standard can be
11.2.1.1 Radiotracer Net Counts:
counted to measure simultaneously the detector resolution and
efficiency,andthegainofthemultichannelanalyzer.Checkthe
N 5 G 2 B 2 I (1)
T T C
instrumentation frequently for consistent operation. Perform
2 1/2
t
S
background measurements regularly and evaluate the results at σ 5 G 1I1B 3 (2)
F S D G
NT T
t
B
the confidence level desired.
10. Procedure
10.1 The procedure of analysis is dependent upon the
radionuclide(s) of interest. A chemical procedure is usually
required to isolate and purify the radionuclides. See Test
Methods D3865 and D3972. Additional appropriate chemical
procedures may be found i
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