The Isotopic Constitution of Lanthanum and Cerium

Abstract

The isotopic abundances of lanthanum and cerium have been determined by means of a mass spectrometer. In addition to the known lanthanum isotope of mass 139, a new isotope of mass 138 and abundance 0.089 percent has been discovered. Since this isotope is isobaric with two neighboring stable isotopes it should be radioactive. No activity was observed. Upper limits for the non-existence of other lanthanum isotopes were determined. The abundances of cerium isotopes of masses 136, 138, 140, and 142 were shown to be 0.193, 0.250, 88.48, and 11.07 percent, respectively. Upper limits for the non-existence of other cerium isotopes were determined.

Atomic weights of the elements. Review 2000 (IUPAC Technical Report)

“…The "g" annotation arises from the presence of naturally occurring fission products found in fossil reactors at Gabon, southwest Africa. In its 1961 report [22], CAWIA recommended A r (Ce) = 140.12 based on the average value of the mass-spectrometric measurements by Inghram et al [424] and Hibbs [354], which were in good agreement with earlier chemical determinations. As a result, CAWIA in 1969 [4] assessed the uncertainty U[A r (Ce)] to be 0.01.…”

“…As a result, CAWIA in 1969 [4] assessed the uncertainty U[A r (Ce)] to be 0.01. Consideration was also given to a determination by Umemoto [421], which, with atomic masses [49], calculates to A r (Ce) = 140.1148, compared with 140.1048 for Inghram et al [424] and 140.124 5 for Hibbs [354]. Though the atomic weight of Ce of 140.11(2) might be a slightly better value, CAWIA has not seen sufficiently compelling reasons to make a change until new results became available.…”

“…In its 1961 report [22], CAWIA recommended a value A r (La) = 138.91, based on the recalculation of two chemical determinations and the average of two mass-spectrometric determinations by Inghram et al [424] and White et al [127], using the atomic mass data by Everling et al [23]. In 1969, CAWIA [4] recommended A r (La) = 138.9055(3) based upon the same determinations, taking into account that two additional digits were justified in view of the small influence any mass discrimination could have on the atomic weight of this nearly monoisotopic element.…”

Atomic weights of the elements 2005 (IUPAC Technical Report)

“…Zhao et al [14] included measurements of seven different samples from China, the United States, and Japan in their study and found no evidence for measurable variations. The previous value, A r (Nd) = 144.24(3), was based on the average of isotope amount measurements of Inghram et al [15] and Walker and Thode [16] arriving at a value of 144.24 that was adopted in 1961 [17] and an evaluated uncertainty was included in 1969 [18]. Historical values of A r (Nd) include [6]: 1894, 140.…”

“…The previous atomic weight value was A r (La) = 138.9055(2), which was based on the average of the isotope amount data of Inghram et al [15] and White [20]. Historical values of A r (La) include [6] …”