X-ray dynamical diffraction induced only by the imaginary part of the scattering factor was measured using a Ge perfect crystal. The 844 integrated reflecting intensities near the K-absorption edge were measured in both the Bragg and the Laue cases. The intensities show the characteristic variations for the scattering factor having no real part, which agree well with theoretical predictions. There remains a slight difference between the theoretical [Fukamachi & Kawamura (1993). Acta Cryst. A49, 384-388] and the experimental energy position at which this occurs, which is related to the fine structure of the anomalous scattering factor above the absorption edge.

No abstract

The impurity-induced infrared absorption bands are measured a t low temperatures for AgBr : Li, AgBr : Na, and AgCl: Li. The absorption bands consist of those due to the localized mode, including the fundamental band, the higher frequency sidebands and the third harmonic bands, and those due to the band modes. The force constant change at the impurity site is discussed using a diatomic three dimensional model. The sideband spectra of the lithium and sodium localized mode in silver bromide are described by the theory based on two-phonon absorption processes. There are apparent differences in the phonon coupling mechanisms to the host lattice between the lithium localized mode and the sodium one in silver bromide. It is found that for AgBr:Li, the phonon coupling mechanism due to the cubic anharmonicity is dominant and the impurity is vupled to its surrounding ions more softly. On the contrary, for AgBr:Na, the contribution due to the second-order electricdipole moment mechanism is nearly equal to that due to the anharmonicity in high frequency limit of the sideband. Some absorption bands due to the impurity-induced band mode are observed a t 30,48, and 61 cm-1 in AgBr :'Li and AgBr : Na a t 2 K.Die defekt-induzierten infraroten Absorptionsbanden von AgBr : Li, AgBr : Na und AgCl : Li wurden bei tiefen Temperaturen gemessen. Die Absorptionsbanden bestehen aus denen der lokalisierten Moden, einschliel3lich der fundamentalen Bande, der hochfrequenten Seitenbanden und der dritten harmonischen Bande, und aus denen der Band-Moden. Die Federkonstantenanderung an der Defekt-Stelle wurde mittels eines zweiatomigen dreidimensionalen Modells diskutiert. Die Spektren der Seitenbanden der durch die Li-und Na-Defekte hervorgerufenen lokalisierten Moden in AgBr wurden mit der auf Zweiphononabsorptions-Prozessen begrundeten Theorie beschrieben. Es gibt einen deutlichen Unterschied im Phonon-Kopplungsmechanismus zum Wirtsgitter zwischen den lokalisierten Moden von Li und denen von Na. Es wird gefunden, dal3 fur AgBr : Li der Phonon-Kopplungsmechanismus infolge der kubischen Anharnionizitat uberwiegt und die Storstelk an die umgebenden Ionen schwacher gekoppelt ist. Im Gegensatz dazu ist fur AgBr:Na der Beitrag vom Dipolmoment zweiter Ordnung fast gleich dem der Anharmonizitat im hochfrequenten Grenzbereich der Seitenbanden. Einige Absorptionsbanden der defekt-induzierten Band-Moden wurden bei 30,48 und 61 cm-1 fur AgBr :'Li und AgBr : Na bei 2 K beobachtet.

A simple method of evaluating the measurement capability of a practical Fizeau-type flatness measurement machine is proposed. In this method, by measuring only the peak-to-valley (PV) value of a calibrated test flat, the measurement capability of the flatness measurement machine for the PV value is evaluated while maintaining the traceability of the measurement. A simple approximate equation for estimating the measurement capability of the flatness measurement machine is presented.

No abstract