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The calibration of a thick-walled ionization chamber by means of a sodium iodide scintillation spectrometer is described. The calibration was made for six bremsstrahlung energies in the range 6 to 19 Mev.

A survey of the literature on the calibration of light scattering instruments has been made, including an extensive bibliography. The values of the Rayleigh ratio R_90 and depolarisation P_u for benzene, toluene, carbon tetrachloride, and carbon disulfide and the excess turbidity of Cornell polystyrene and D.C./P.J.3 polystyrene (0.5% solutions in toluene) were tabulated for two wavelengths (4358 and 5461 Å). Examination of these results showed a larger variation in reported values than is generally assumed acceptable (only so-called "high" values have been considered). No correlation was found with the various standards used for the original calibration. Some aspects of the most usual methods of calibration are discussed and arguments are considered which would favor those values of R_90 (or excess turbidity) that are at the lower limits of the range reported (but still in the region of "high" values). The difficulty of using Einstein's equation in determining the exact values of R_90 is pointed out.

Fundamentals of the two-line method of emulsion calibration, in which the characteristic curve is derived from densities of two spectrum lines of constant relative intensity, photographed at different densitiy levels, are discussed. It has been found, that the principles of this method can be applied to the presentation of data obtained by any method of calibration, which is based on an intensity pattern following a geometrical series. The scope of the method is considerably widened by substitution of densities

A method is described which improves the precision of the energy calibration of a Ge(Li) spectrometer taking into account the relationship between cascade gamma rays.

A discussion is presented of certain calibration procedures employed in the region 30 to 1000 microns. Calculated positions for the pure rotational absorption lines of the CO, HCN, and N2O molecules are given, and a map of the pure rotational absorption lines of the H2O molecule as recorded with a Perkin-Elmer model 301 spectrophotometer is shown.

A Hall probe was used in measurements requiring the resolution of a few tenths of a gauss in a field of approximately 17 kgauss. The Hall probes exhibited a slow change of calibration with time. The calibration of one probe changed by nine parts in ten thousand over a period of 54 days. In the case of one generator, a step change in calibration was observed. The over-all system is briefly discussed. The changes in calibration are described, together with possible explanations for this behavior.

Four samples of Ludox colloidal silica were studied by the light transmission and angular scattering method and the size of particles determined. It was found essential for light scattering work to centrifuge the original Ludox solution in order to remove the aggregated material. After this treatment each Ludox sample regardless of age could be used successfully for calibration purposes. The apparent particle sizes in aqueous solutions of Ludox were smaller than those in 0.05 M NaCl solutions, the latter being in very good agreement with electron microscopic values, The refractive index increments of Ludox in water and 0.05 M NaCl were determined at three wavelengths. The influence of cell length and blackening of the cells in transmission measurements were also studied. Dissymmetries and depolarizations were small. All results indicated that particles of Ludox behave practically as Rayleigh seatterers. The usefulness of these results for the calibration of light scattering photometers is discussed.

With the development of ultra high vacuum technology the need is felt for improved methods for vaccum measurement. The conventional vacuum gages are either limited to relatively high pressures or those reaching very low pressures use physical phenomena which require an indirect calibration. In an attempt to improve this situation it is proposed to replace pressure measurements with «molecular counting» and, as one possible way to achieve it, the use of Rayleigh scattering of visible light is advanced. The advantages are manifold : the effect is calculable from first principles, the response is linear from atmospheric pressure down to ultra high vacuum, it requires no new technology, and, the act of measurement does not modify the medium to be measured. Data shall be presented to prove that a laboratory system can be created, giving good signal-to-noise ratios in the 10-8 to 10-9 torr range. The availability of «absolute» vacuum standards in a range covering about 10 orders of magnitudes is emphasized. Possible limitations of the method are discussed., Marton Ladisias. The use of light scattering for vacuum measurement. In: Bulletin de la Classe des sciences, tome 60, 1974. pp. 676-685.

(137)Cs γ-ray sources, which have been proposed by the Public Health Service as a substitute for radium in the treatment of malignant diseases, require suitable calibration if consistency is to be achieved in radiation treatment. Several (137)Cs sources were calibrated using a graphite cavity ionization chamber in an open-air geometry. The contribution of scatter from the room surfaces was calculated and the source measurements corrected for this effect. A large-volume aluminum-walled ionization chamber was designed and fabricated for use in routine calibrations. This chamber will be used as a means for intercomparison of the source to be calibrated with one of the standards.

A single channel pulse-height analyzer with a dead time of about 0.15 μsec is described. The channel width is determined by the passive characteristics of a delay line and is a constant percentage of the discriminator setting. An important feature of the device is a paralysis circuit. Circuit diagrams and calibration curves are given.

This paper reports on quantitative measurements of the small angle scattering of various rayons and ramie fibers as functions of moisture content using a three slit vacuum camera and monochromatic radiation. The scattered intensity was normalized on sample thickness and primary intensity through determination of the absorbance of the sample and of the intensity of the transmitted beam measured in arbitrary units. From these data the scattering power as defined by Porod, being the mean square of the fluctuations of the electron density, was calculated. This quantity was then converted into electron units through calibration of the procedure with exposures of noble metal sols of known composition and thus of computable scattering power. The exprimental results were compared with the scattering power calculated for cellulose fibers when regarded as submicro tow-phase systems consisting of crystalline cellulose imbedded in a homogeneous mixture of noncrystalline cellulose and water. In the air-dry state a few of the rayon speciman examined exhibited a scattering power of magnitude consistent with theory. The majority yielded much higher values, up to six times larger (so does dry ramie). This is interpreted by the occurrence of submicro voids to a volume fracton of less than 0.75%, variable from fiber to fiber. This explanation is corroborated by the existenc of a distinct correlation between scattering power and gravimetric density of the fiber. In conclusion, microvoids are the principal scattering “particles” in dry fibers. The values of the scattering power of water swollen rayons and ramie can be interpretated on the basis of a three-pahse model, with the phases consisting of crystalline cellulose, a homogeneous mixture of amorphous cellulose with water, and water, respectively.

Although the speed of sound in air was measured with reasonable accuracy about the middle of the 17th century, intensity measurements did not properly begin until Rayleigh, in 1882, published his experiments with what came to be called the Rayleigh disc. The accuracy remained relatively low (about 10%) until about 1940. In the meantime the working standard for measurements in acoustics had come to be the condenser microphone which is a reciprocal transducer. By using the reciprocity method its calibration has improved by about two orders of magnitude, being now carried out to a precision of about 10-3. This is quite adequate for most purely physical measurements and more than adequate for many others such as sound absorption coefficients of surfaces or sound transmission loss of partitions. In most measurements of a psychoacoustical nature (threshold of hearing, loudness, etc.), or even where a human subject is involved in only a passive role, the errors of measurement are still very great being of the order of 10-1 or often greater.

Long-baseline interferometry achieves high resolution by using two or more widely separated radio telescopes and recording video signals on magnetic tapes, which are later brought together and cross-correlated. This paper contains discussions of the coherence and timing requirements and of calibration procedures. Applications to measuring brightness distributions and to spectroscopy are reviewed briefly. Some pertinent phenomena connected with radio-wave scattering in irregular media are discussed.

A spectroradiometer is described which is designed to make measurements of spectral radiance, irradiance, transmittance, and reflectance. In one minute the Hilger D300 monochromator is set to the next wavelength to be measured and a measurement is made of (a) the dark current of the photomultiplier, (b) the photocurrent produced by the reference source, (c) a voltage indicating the wavelength, and (d) the photocurrent produced by a test source. An integrating digital voltmeter with a 10-sec gate is used. The data are recorded on punched cards and analyzed by a digital computer. Experimental results are given to illustrate the performance. The applications described include calibration of standards of spectral radiance and irradiance from a blackbody at the freezing point of platinum and the developmet of a color temperature scale., The authors were affiliated with the National Research Council of Canada, Division of Applied Physics when they authored this article.