Occurrence of the (4n + 1) Series in Nature

Abstract

"A small quantity of a Np-237, the long-lived ancestor of the 4n + 1 series, has been isolated from a natural source. The Th-229 content of the Th-230 obtained from Belgian Congo pitchblende concentrate and of Th-232 obtained from Brazilian monazite has been determined indirectly through isolation of the Ac-225 daughter. The mass ratio of Np-237 to U-238 in the Belgian Congo pitchblende concentrate has been determined as (1.8 +/- 0.4) x 10-(-12). The mass ratio of U-233 to U-238 in the same ore deposit is found to be (1.3 +/- 0.2) x 10-(-13). The ratio of the respective neutron-capture cross sections of U-238 in the ore body for the (n, 2n) and (n, gamma) reactions is calculated to be (1.3 +/- 0.6) x 10-(-3) on the basis of the relative Np-237 and Pu-239 contents."