Sorption of Americium in Tuff and Pure Minerals Using Synthetic and Natural Groundwaters

Abstract

The distribution of Am between selected solid and liquid phases hag been studied using initial 24'Am solutions with a molarity smaller than 1 x 10-11. The synthetic and natural groundwaters used have pH values in the 7-8 range and a total alkalinity of approximately 1 mN which is mainly due to bicarbonate. Mruw spectrometric isotope dilution was utilized to determine the amount of Am in the solution phru+einitially and after equilibrium W= attained. Using this sensitive technique, 7 x 10* atoms of 241Am were accllrately measured. Our results indicate that the percent of Am lost to the walls of the container in the absence of geologic material varies from 35 to 84, The Am sorption codiicient determined is on the order of 10s ml/g for clinoptilol;te, 104 ml/g for tuff consisting mainly of alkali feldspax and cristobaiite, and 103 ml/g for romanecbite.

Radioactivity: A Tool to Explore the Past

“…The curve in Fig. 6 represents data that are in agreement for the 238 U/ 206 Pb and the 235 U/ 207 Pb systems under the concordia for- The curve represents data that agree for the 238 U/ 206 Pb and the 2 "U/ 2 " 7 Pb systems, i.e., no losses or gains of lead and uranium occurred since the formation of the samples. The numbers on the concordia curve indicate the age of the samples in 10 9 years.…”

“…Similar equations apply for 235 U/ 207 Pb and 232 Th/ 208 Pb. Comparison of different dating methods can be used for the verification of the closed system condition (i.e., concordia, Wetherill [51]).…”

“…This age corresponds for most of the samples to the time since their formation (e.g., crystallization from a melt or solution, etc.). Important examples for this dating possibility are the decays of ^'K into stable 40 Ar, and that of 87 Rb into stable 87 Sr, and the decay chains of 238 U, 235 U and 232 Th leading to the stable lead isotopes 206 Pb, 207 Pb and 208 Pb, respectively.…”

“…The 231 Pa/ 23S U method is based on the decay of 235 U through 23 'Th (/? ", 25.5 h) into 23, Pa. Again, the half-life of 23, Th is short enough to be always in secular equilibrium with 235 U, and the age of a sample can be calculated: 231 Pa/ 23S U = 1 -e".…”

“…For an age determination it is necessary to measure the fission track density, and the uranium content. Usually, this is done in two steps: i) the tracks that were naturally produced in minerals and glasses by 238 U spontaneous fission are counted; ii) the uranium concentration is determined from the tracks formed by 235 U-fission during a reactor irradiation in a well known thermal neutron flux. The age of the sample is calculated from:…”