ALPHA PARTICLES, also called a-rays, the positively charged particles that are ejected by certain radioactive sub stances. (See RADIOACTIVITY.) They are helium atoms (see ATOM) which have lost one or two electrons (see ELECTRON) and are identical with the ionized helium which is produced by an electric discharge through this gas. (See POSITIVE RAYS ; and ELECTRICITY, CONDUCTION OF : in Gases.) 'AL-PHASI, ISAAC (1013-1103), Jewish rabbi and codifier, known as Riph, was born near Fez, and died at Lucena. He settled in Spain. His fame rests on his Talmudical Digest, which omitted all homiletical passages and also passages relating to religious duties practicable only in Palestine. He occupies an im portant place in the development of the Spanish method of study ing the Talmud. As opposed to the French rabbis, the Spanish sought to simplify the Talmud, and to free it from casuistical detail. His Digest was the forerunner of the great Codes of Maimonides and of Joseph Oaro.