1、Designation: D3648 04 (Reapproved 2011)D3648 14Standard Practices for theMeasurement of Radioactivity1This standard is issued under the fixed designation D3648; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 These practices cover a review of the accepted counting practices currently used in radiochemical analyses. The practicesare div
3、ided into four sections:SectionGeneral Information 6 to 11General Information 6 11Alpha Counting 12 to 22Alpha Counting 12 22Beta Counting 23 to 33Beta Counting 23 33Gamma Counting 34 to 41Gamma Counting 34 411.2 The general information sections contain information applicable to all types of radioac
4、tive measurements, while each of theother sections is specific for a particular type of radiation.1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.4 This standard does not purport to address all of the safety concerns, if
5、 any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology
6、 Relating to WaterD1943 Test Method for Alpha Particle Radioactivity of WaterD2459 Test Method for Gamma Spectrometry of Industrial Water and Industrial Waste Water (Withdrawn 1986)3D3084 Practice for Alpha-Particle Spectrometry of WaterD3085 Practice for Measurement of Low-Level Activity in Water (
7、Withdrawn 1987)3D3370 Practices for Sampling Water from Closed ConduitsD3649 Practice for High-Resolution Gamma-Ray Spectrometry of WaterIEEE/ASTM SI 10 American National Standard for Metric Practice2.2 ANSI/ISO Standards:4ANSI N42.14 Calibration and Use of Germanium Spectrometers for the Measuremen
8、t of Gamma-Ray Emission Rates ofRadionuclidesISO Guide to the Expression of Uncertainty in Measurement, 1993 to the Expression of Uncertainty in Measurement, 19933. Terminology3.1 Definitions:1 These practices are under the jurisdiction of ASTM Committee D19 on Water and are the direct responsibilit
9、y of D19.04 on Methods of Radiochemical Analysis.Current edition approved Jan. 1, 2011Jan. 1, 2014. Published January 2011January 2014. Originally approved in 1978. Last previous edition approved in 20042011 asD3648 04.D3648 04 (2011). DOI: 10.1520/D3648-04R11. 10.1520/D3648-14.2 For referencedASTM
10、standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard is referenced on www.astm.
11、org.4 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036.10036, http:/www.ansi.org.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 v
12、ersion. Becauseit 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 versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM Internat
13、ional, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.1 For definitions of terms used in these practices, refer to Terminology D1129. For an explanation of the metric system,including units, symbols, and conversion factors, see Practice IEEE/ASTM SI 10.4. Sum
14、mary of Practices4.1 The practices are a compilation of the various counting techniques employed in the measurement of radioactivity. Theimportant variables that affect the accuracy or precision of counting data are presented. Because a wide variety of instruments andtechniques are available for rad
15、iochemical laboratories, the types of instruments and techniques to be selected will be determinedby the information desired. In a simple tracer application using a single radioactive isotope having favorable properties of highpurity, energy, and ample activity, a simple detector will probably be su
16、fficient and techniques may offer no problems other thanthose related to reproducibility. The other extreme would be a laboratory requiring quantitative identification of a variety ofradionuclides, preparation of standards, or studies of the characteristic radiation from radionuclides. For the latte
17、r, a variety ofspecialized instruments are required. Most radiochemical laboratories require a level of information between these two extremes.4.2 Abasic requirement for accurate measurements is the use of accurate standards for instrument calibration. With the presentavailability of good standards,
18、 only the highly diverse radiochemistry laboratories require instrumentation suitable for producingtheir own radioactive standards. However, it is advisable to compare each new standard received against the previous standard.4.3 Thus, the typical laboratory may be equipped with proportional or Geige
19、r-Mueller counters for beta counting, sodium iodideor germanium detectors, or both, in conjunction with multichannel analyzers for gamma spectrometry, and scintillation counterssuitable for alpha- or beta-emitting radionuclides.5. Significance and Use5.1 This practice was developed for the purpose o
20、f summarizing the various generic radiometric techniques, equipment, andpractices that are used for the measurement of radioactivity.GENERAL INFORMATIONGENERAL INFORMATION6. Experimental Design6.1 In order to properly design valid experimental procedures, careful consideration must be given to the f
21、ollowing;6.1.1 radionuclideRadionuclide to be determined,6.1.2 relativeRelative activity levels of interferences,6.1.3 typeType and energy of the radiation,6.1.4 originalOriginal sample matrix, and6.1.5 requiredRequired accuracy.6.2 Having considered 6.1.1 6.1.5, it is now possible to make the follo
22、wing decisions:6.2.1 chemicalChemical or physical form that the sample must be in for radioassay,6.2.2 chemicalChemical purification steps,6.2.3 typeType of detector required,6.2.4 energyEnergy spectrometry, if required,6.2.5 lengthLength of time the sample must be counted in order to obtain statist
23、ically valid data,6.2.6 isotopicIsotopic composition, if it must be determined, and6.2.7 sizeSize of sample required.6.3 For example, gamma-ray measurements can usually be performed with little or no sample preparation, whereas both alphaand beta counting will almost always require chemical processi
24、ng. If low levels of radiation are to be determined, very largesamples and complex counting equipment may be necessary.6.3.1 More detailed discussions of the problems and interferences are included in the sections for each particular type ofradiation to be measured.7. Apparatus7.1 Location Requireme
25、nts:7.1.1 The apparatus required for the measurement of radioactivity consists, in general, of the detector and associated electronicequipment. The latter usually includes a stable power supply, preamplifiers, a device to store or display the electrical pulsesgenerated by the detector, or both, and
26、one or more devices to record information.7.1.2 Some detectors and high-gain amplifiers are temperature sensitive; therefore, changes in pulse amplitude can occur asroom temperature varies. For this reason, it is necessary to provide temperature-controlled air conditioning in the counting room.7.1.3
27、 Instrumentation should never be located in a chemical laboratory where corrosive vapors will cause rapid deteriorationand failure.D3648 1427.2 Instrument Electrical Power SupplyDetector and electronic responses are a function of the applied voltage; therefore, itis essential that only a very stable
28、, low-noise electrical supply be used or that suitable stabilization be included in the system.7.3 Shielding:7.3.1 The purpose of shielding is to reduce the background count rate of a measurement system. Shielding reduces backgroundby absorbing some of the components of cosmic radiation and some of
29、the radiations emitted from material in the surroundings.Ideally, the material used for shielding should itself be free of any radioactive material that might contribute to the background.In practice, this is difficult to achieve as most construction materials contain at least some naturally radioac
30、tive isotopes (suchas 40K, members of the uranium and thorium series, and so forth). The thickness of the shielding material should be such that itwill absorb most of the soft components of cosmic radiation. This will reduce cosmic-ray background by approximately 25 %.Shielding of beta- or gamma-ray
31、 detectors with anticoincidence systems can further reduce the cosmic-ray or Compton scatteringbackground for very low-level counting.7.3.2 Detectors have a certain background counting rate from naturally occurring radionuclides and cosmic radiation from thesurroundings; and from the radioactivity i
32、n the detector itself. The background counting rate will depend on the amounts of thesetypes of radiation and on the sensitivity of the detector to the radiations.7.3.3 In alpha counting, low backgrounds are readily achieved since the short range of alpha particles in most materials makeseffective s
33、hielding easy. Furthermore, alpha detectors are quite insensitive to the electromagnetic components of cosmic and otherenvironmental radiation.7.4 Care of Instruments:7.4.1 The requirements for and advantages of operating all counting equipment under conditions as constant and reproducibleas possibl
34、e have been pointed out earlier in this section. The same philosophy suggests the desirability of leaving all countingequipment constantly powered. This implies leaving the line voltage on the electrical components at all times. The advantage tobe gained by this practice is the elimination of the st
35、art-up surge voltage, which causes rapid aging, and the instability that occursduring the time the instrument is coming up to normal temperature.7.4.2 A regularly scheduled and implemented program of maintenance is helpful in obtaining satisfactory results. Themaintenance program should include not
36、only checking the necessary operating conditions and characteristics of the components,but also regular cleaning of the equipment.7.5 Sample and Detector HoldersIn order to quantify counting data, it is necessary that all samples be presented to thedetector in the same “geometry.” This means that th
37、e samples and standards should be prepared for counting in the same way sothat the distance between the source and the detector remains as constant as possible. In practice, this usually means that thedetector and the sample are in a fixed position. Another configuration often used is to have the de
38、tector in a fixed position withinthe shield, and beneath it a shelf-like arrangement for the reproducible positioning of the sample at several distances from thedetector.7.6 Special InstrumentationThis section covers some radiation detection instruments and auxiliary equipment that may berequired fo
39、r special application in the measurement of radioactivity in water.7.6.1 4-pi Counter:7.6.1.1 The 4-pi counter is a detector designed for the measurement of the absolute disintegration rate of a radioactive sourceby counting the source under conditions that approach a geometry of 4-pi steradians. It
40、s most prevalent use is for the absolutemeasurement of beta emitters (1, 2).5 For this purpose, a gas-flow proportional counter similar to that in Fig. 1 is common. Itconsists of two hemispherical or cylindrical chambers whose walls form the cathode, and a looped wire anode in each chamber.5 The bol
41、dface numbers in parentheses refer to thea list of references appended to these practices.at the end of this standard.FIG. 1 The 4pi-Counting ChamberD3648 143The source is mounted on a thin supporting film between the two halves, and the counts recorded in each half are summed.A10 %methane-90 % argo
42、n gas mixture can be used; however, pure methane gives flatter and longer plateaus and is preferred for the mostaccurate work. The disadvantage is that considerably higher voltages, about 3000 V, rather than the 2000 V suitable formethane-argon, are necessary. As with all gas-filled proportional cou
43、nters, very pure gas is necessary for very high detectorefficiency. The absence of electronegative gases that attach electrons is particularly important since the negative pulse due toelectrons is counted in this detector. Commercial chemically pure (cp) gases are ordinarily satisfactory, but they s
44、hould be driedfor best results. A high-voltage power supply for the detector, an amplifier, discriminator, and a scaler complete the system.7.6.1.2 To convert counting rate to disintegration rate, the principal corrections required are for self-absorption in the source andfor absorption in the suppo
45、rt film. The support film should be as thin as practicable to minimize absorption of beta particles emittedin the downward direction. Polyester film with a thickness of about 0.9 mg/cm 2 is readily available and easily handled. However,it is too thick for accurate work with the lower energy beta emi
46、tters. For this purpose, thin films (.5 to 10 g/cm g/cm2) areprepared by spreading a solution of a polymer in an organic solvent on water. VYNS (1), Formvar (2), and Tygon (3) plastics havebeen used for this purpose.7.6.1.3 The films must be made electrically conducting (since they are a part of the
47、 chamber cathode) by covering them witha thin layer (2 to 5 g/cm g/cm2) of gold or palladium by vacuum evaporation. The absorption loss of beta particles in the filmmust be known. Published values can be used, if necessary, but for accurate work an absorption curve using very thin absorbersshould be
48、 taken (1). The “sandwich” method, in which the film absorption is calculated from the decrease in counting rate thatoccurs when the source surface is covered with a film of the same thickness as the backing film, is suitable for the higher betaenergies.7.6.1.4 The source itself must be very thin an
49、d deposited uniformly on the support to obtain negligible self-absorption. Varioustechniques have been used for spreading the source; for example, the evaporation of 63Ni-dimethylglyoxime onto the support film(1), the addition of a TFE-fluorocarbon suspension (3), collodial silica, or insulin to the film as spreading agents, and hydrolysis(2). . Self-absorption in the source or mount can be measured by 4-pi beta-gamma coincidence counting (4,5).The 4-pi beta counteris placed next to a NaI(Tl) detector, or a portion of the chamber wall is replaced by a NaI(Tl
