Post-print, re-edited for inclusion in T. Tabata, edited with commentary, The Collected Works of Tatsuo Tabata Volume 10, IDEA-TR 14 (2018), of the paper published in Japanese Journal of Applied Physics, Vol. 25, Issue 10, October 1986, Pages L848–L849 (doi:10.1143/JJAP.25.L848) Copyright © 1986 by the Japan Society of Applied Physics Nondestructive Detection of Small Voids in Solids by Transmission Electron Spectrometry Shuichi Okuda, Tatsuo Tabata and Takeyoshi Seiyama Radiation Center of Osaka Prefecture, Shinke-cho, Sakai, Osaka 593 (Received August 14, 1986; accepted for publication September 20, 1986) A nondestructive method for detecting small voids in solids by means of trans- mission electron spectrometry has been investigated. With collimated probe-beams of 10-MeV electrons, transmission momentum-spectra have been measured for model samples of silicon carbide 5-mm thick in which a slit-type 200 or 600 μm by 200 μm cavity simulated a void. Between the spectra measured for regions with and with- out the cavity, small difference has been observable. The results have shown that, according to the change in the spectra, voids 200 μm or smaller can be detected by the present method. §1. Introduction Nondestructive evaluation with energetic electrons as probes 1) has been made by means of radiography in which electron dose distributions are mapped to detect defects or hetero- geneities in solids. The number and the energy of electrons, main factors determining the absorbed dose, can be separately measured with relatively high sensitivity and accuracy by using radiation detectors. These facts suggest that transmission electron spectrometry can be a possible means of detecting small defects in solids. Much work has been done recently on the evaluation of structural ceramics for small defects (usually voids). 2) Practically, defects as small as a few tens of micrometers in size must be detected. Conventional methods for nondestructive evaluation using ultrasonic waves, acoustic emissions or X-rays do not fulfill the practical requirements. The pur- pose of this work is to examine a nondestructive method for detecting small voids using transmission electron spectrometry. §2. Principle of the Method The energy or the momentum of transmitted electrons is distributed according to the statistical nature of the energy-loss process. In addition, the distribution of transmitted electrons reflects the structure of the medium traversed by the electrons. Voids on the paths, for example, cause a reduction of the energy loss making the transmitted energies 1