A novel of Russian author. Presumably, published in 1980s. An expedition to a remote galaxy on its way back to the Earth encounters a strange phenomena. During the passage through a "cloud" of some kind, the entire spaceship, with all passengers, is converted to anti-matter.
The characters realize this and the conclusion is appalling - they can't get back home. Author describes behavior of people then - some continue discovering ways to reach the Earth, some get embittered, one of the characters starts drinking.