The radioactivity of nickel, copper and zinc induced by neutrons of different energies is investigated. Some new reactions are reported.
The results obtained by various investigators when bombarding zinc with neutrons from different sources diverge greatly. F e r m i and his collaborators 1) used a (Rn + Be) source and observed two periods, one of 5 minutes and one of 10 hours, which must be ascribed to copper isotopes. McLennan, Grimmet and Read 2) also used the neutrons from a (Rn -r Be) source and irradiated zinc in water. They obtained periods of 6 minutes and 100 minutes. M a d s e n 3) found the same period of 100 minutes which, according to a chemical separation, must be attributed to a nickel isotope. The author 4) observed a period of 60 minutes in zinc bombarded with the slow neutrons from a (Be + 2H + P) source (P means that paraffine was used to slow down the neutrons). With the fast neutrons from a (Li + 2H) source he obtained the same period of 60 minutes and showed by chemical separation that this period is due to a zinc isotope. It was supposed that the same radioactive isotope Zn ~ was formed in the first case by capture and in the second case bythe (n, 2n) reaction. R o t b 1 a t 5) observed a period of 60 minutes with the neutrons from a (Rn + Be) source. A chemical separation showed, however, that this period must be ascribed to a nickel isotope ((n ,~) reaction). Bothe and Gentner6), irradiating zinc with gamma-rays, obtained a period of 38 minutes according to the reaction (,;, n). The same period was obtained by R i d e n o u r and H e n d e r s o n 7) in nickel bombarded with alpha-particles ((~, n) reaction). Pool, Cork and Thornton8), using the fast *) This half-value thickness depends largely upon the geometrical conditions and must therefore be considered a relative value.