Radioactivity standards

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

Radioactive standard, hght emission intensity cahbration, 1224... 

The digitized autoradiograms are analyzed with an appropriate software (e.g. AIDA, raytest), regions around the organs/tissues of interest can be drawn electronically. The radioactive standards, cut together with the whole-body sections are used as internal calibration. The information of the calibration curve provides the link between counts/area and radioactivity/area and... 

Inn KGW. 1987. The National Bureau of Standards fresh water lake sediment environmental-level radioactivity standard reference material. J Radioanal Nucl Chem 115 91-112. 

Hydrolyze an aliquot in O.IMHQ for 20 h at ST C and calibrate by strong cation exchange HPLC on a Whatman Partisil 10 SCX column or by column chromatography on Sephasorb, uang appropriate optical or radioactive standards. Detailed descriptions of these methods can be found elsewhere (6,7). 

Radioactivity Standards Reference, Sales Office, Bldg. 245, Rm Cl 14,... 

In addition, the LMRI elaborates and distributes radioactivity standards and references, and provides calibrations, measurements and testings in radioactivity and dosimetry, for measuring instruments and ionising radiation sources. These services are intended for research, industry and medicine. 

Among various techniques used for radioactivity standardization, the 4ti P-y coincidence counting method is undoubtedly the most important technique, and most radionuclides can be standardized by this technique or its extended techniques. Actually, most national standardizing laboratories in the world employ this method for the establishment of the national standards of various kinds of radionuclides. 

RNP complexes 0.2-1 x 104 cpm (generally 5 p.1 of a radioactive standard splicing reaction will suffice for autoradiography)... 

If methods are used in which the overall recovery is 70% or above, and if the possibility of accidental but undetected very large losses is reduced by using a minimum of steps and transfer operations, or by automation, it is questionable whether in practice the precision will be greatly increased by current techniques of using internal radioactive standards. In the case of many urinaiy steroids, conjugated internal standards would be required for full control of the procedure and are not yet generally available. Finally the technique itself is not error-free, even in the absence of isotope effects, and the usual techniques employed so far often involve very small volumes of volatile solvents in which transfer errors can be large unless very superior manual technique is used. 

Advantages and Limitations of IIDA. The main advantage of this method is that one can determine the quantity of a specific radioactive component of a sample without comparing it with a known radioactive standard. The method also avoids preparing standards with the same matrix as the sample in order to assure equivalent... 

Efficiency calibration requires a sample of defined shape and volume placed at a defined location relative to the detector. A sample frame may be needed for reproducible placement. Calibration can be performed with a radioactivity standard or by Monte Carlo simulation (see Sections 8.2 and 10.5). 

Although gamma rays are much less subject to attenuation than alpha and beta particles, a density correction is needed if the density of the sample deviates significantly from the density of the calibration standards. The effect of density on self-absorption for both the standard and the sample is estimated by Eq. (7.2) [x for this purpose is the photon attenuation coefficient in cm /g and x is the sample area density in g/cm. Values for ix in some common materials are listed in Table 2.2 and in its cited reference. If a large set of samples with consistent density is analyzed, it may be possible to prepare radioactivity standards at the same density to avoid the need for correction. Interpolating efficiency values as a function of density is feasible at energies above 0.1 MeV because the effect of minor density difference on counting efficiency is small. 

The facility should have a separate room for storing radioactive standard and stock solutions. This room usually is located near the sample receiving and processing area. Radioactive standards and solutions must be kept separate from other laboratory operations to prevent cross-contamination. The room should have cold storage capabilities and lockable cabinets. It should be designed to the same specifications as other sample preparation rooms, with a fume hood and computer access to permit dilution and other processing of radioactive standard reference materials and stock solutions. 

Appendix A2 Standard Methods, part 7000—Radioactivity (Standard Methods 2005)... 

Include radioactive standards during exposure if the results are to be quantified (see otQ 21)... 

The response of autoradiography film to radioactive decay is nonlinear At low levels film is relatively insensitive and at higher levels—once all of the silver ions have been converted to stable pairs of silver atoms—the latent image can develop no further. To take account of this, a senes of radioactive standards are... 

The identity of the eluted compounds is indicated at the top of the peciks. With the exception of the GR HX and XMP ATP pairs, other components in this profile were well separated. The peaks illustrated by the UV profile represented approximately 75 nmoles of each of the 16 standards. The peaks documented by the isotope counter represented 80-100 picomoles of radioactive standards. In this sample, radioactive X, XR and GMP were left out. Small amounts of radioactive impurities which were present in some of the standards, especially guanine, and eluted in an early peak. 

Fig. 2. Separation of artificial mixtures of nonradioactive and radioactive standards. Fro files of radioactive and nonradioactive standards recorded simultaneously by a two-pen chart recorder connected to the UV detector and liquid scintillation flow monitor. The analyzed sample contained 75 nmoles of each nonradioactive and 80-100 picomoles of radioactive standards.

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