A method and apparatus for determining the existence of misorientation in a crystal, comprising irradiating the crystal with X-rays pre-orientating any crystallographic plane of the crystal with respect to the axis of the X-rays, imaging X-rays received from the crystal so as to cause a plurality of effectively angularly-separated images to be formed, the energy of the X-rays being such that while carrying out the method at least some of the X-rays forming the images have intersected the whole depth of the portion of the crystal being examined, and determining the existence of any misorientation from the images.

The disclosure is directed to an apparatus and method for analyzing gem specimens. In the disclosed embodiment, a small cabinet includes a source discharge lamp for radiating electromagnetic energy over a broad spectrum of wavelengths. A gem specimen is placed in a small drawer that, upon closure, becomes an optically sealed chamber in communication with the radiation source. Also upon closure, a mechanical shutter mechanism permits registration between the radiation source, gem specimen and a photocell detector that senses radiation emitted from the gem specimen as a result of its interaction with the spectrum of wavelengths from the radiation source. This interaction comprises the combined processes of transmission of and absorption by the gem specimen of the source radiation, internal reflection and internal excitation (e.g., fluorescence), the latter of which produces a frequency shift to a narrow spectrum of energy which the photocell detector is specifically designed to sense. The output of the photocell detector is an analog signal that is processed by electronic circuitry in one of two manners. First, the signal is digitized through an analog to digital converter and is displayed as a numerical digital readout. In the second manner, the analog signal is compared with one or more groups of reference values corresponding to different species of gems. If the analog signal falls within a first arbitrary range of values, it is determined to be "natural". In a second arbitrary range, it is determined to be "synthetic". A third range falls between the first and second ranges, and a value within this range is indicative of a gem of indeterminate origin or an operational malfunction. Another group of reference values is used to determine either of two abnormal conditions; viz., a blockage of radiated energy to the detector or the absence of a gem from the specimen holder. The apparatus readout comprises a liquid crystal display that selectively indicates the mode of operation, the natural, synthetic or indeterminate nature of the gem specimen, and a digital readout of a unitless, arbitrary number which may be used to determine gem quality.

A colorless, transparent low defect density, synthetic type IIa diamond single crystal, in which the etch pits due to needle-shaped defects are at most 3.times.10.sup.5 pieces/cm.sup.2, and which can be applied to uses needing high crystallinity of diamond, for example, monochromators, semiconductor substrates, spectroscopic crystals in X-ray range, electronic materials, etc., is provided by a process for the production of the colorless, transparent low defect density, synthetic diamond single crystal by growing new diamond crystal on a seed crystal of diamond by the temperature gradient method which comprises using a crystal defect-free diamond single crystal, as a seed crystal of diamond, and optionally subjecting to a heat treatment in a non-oxidizing atmosphere at a low pressure and a temperature of 1100 to 1600.degree. C.

In order to test whether a diamond 2 comprises synthetic diamond material, a plurality of different zones of the diamond 2 are irradiated with radiation substantially of wavelength substantially 230 nm to 320 nm, an image or reading of the radiation transmitted by each zone of the diamond 2 being produced.

A high purity synthetic diamond with less impurities, crystals defects, strains, etc. can be provided, in which the nitrogen content is at most 10 ppm, preferably at most 0.1 ppm and the boron content is at most 1 ppm, preferably at most 0.1 ppm or in which nitrogen atoms and boron atoms are contained in the crystal and the difference between the number of the nitrogen atoms and that of the boron atoms is at most 1.times.10.sup.17 atoms/cm.sup.3. The strain-free synthetic diamond can be produced by a process for the production of a strain-free synthetic diamond by the temperature gradient method, which comprises using a carbon source having a boron content of at most 10 ppm and a solvent metal having a boron content of at most 1 ppm and adding a nitrogen getter to the solvent metal, thereby synthesizing the diamond.