Preferential leaching and natural annealing of alpha-recoil tracks in metamict betafite and samarskite

Journal Article · Tue Mar 01 00:00:00 EST 1988 · J. Mat. Res.; (United States)

OSTI ID:5276120

Lumpkin, G R; Ewing, R C; Eyal, Y

Leaching experiments on naturally occurring, metamict betafite and samarskite minerals in a bicarbonate--carbonate solution show strongly enhanced release to the solution of short-lived /sup 228/Th relative to its parent isotope /sup 232/Th (by a factor of 3 to 6), but only slightly enhanced dissolution (by a factor of 1.2 to 2) of long-lived /sup 234/U and /sup 230/Th relative to /sup 238/U and /sup 232/Th, respectively. The betafite (a complex Ca--U--Ti--Nb oxide of the pyrochlore group, A/sub 2-//sub m/B/sub 2/X/sub 6/Y/sub 0-1/xH/sub 2/O) and samarskite (a complex Y--Fe--U--Nb oxide with varying stoichiometry between ABO/sub 4/ and AB/sub 2/O/sub 6/) are x-ray and electron diffraction amorphous having experienced doses of 2.2--2.8 x 10/sup 17/ alpha-decay events/mg (24--31 dpa) and 3.8--4.4 x 10/sup 17/ alpha-decay events/mg (39--45 dpa), respectively. The isotopic fractionation is attributed to the radiation damage created by the alpha-decay events. Individual alpha-recoil tracks are preserved for some time as disordered regions of higher chemical reactivity in already fully damaged, aperiodic areas that result from the alpha-decay events. The annealing time of the alpha-recoil track within the aperiodic atomic array of the metamict state is calculated to be 29,300 +- 8100 years for samarskite and 42,700 +- 13,700 years for the betafite. These data plus data on an earlier studied betafite sample (annealing time = 2000 +- 1300 years) give an average annealing time of 25,000 +- 21,000 years.

• Research Organization: Department of Geology, University of New Mexico, Albuquerque, New Mexico 87131
• OSTI ID: 5276120
• Journal Information: J. Mat. Res.; (United States), Vol. 3:2
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
OXIDE MINERALS
LEACHING
METAMICT STATE
ALPHA PARTICLES
ANNEALING
CALCIUM OXIDES
IRON OXIDES
NIOBIUM OXIDES
PARTICLE TRACKS
RADIOCHEMICAL ANALYSIS
RECOILS
TITANIUM OXIDES
URANIUM OXIDES
VANADIUM OXIDES
YTTRIUM OXIDES
ACTINIDE COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL ANALYSIS
DISSOLUTION
HEAT TREATMENTS
IRON COMPOUNDS
MINERALS
NIOBIUM COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
QUANTITATIVE CHEMICAL ANALYSIS
REFRACTORY METAL COMPOUNDS
SEPARATION PROCESSES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
URANIUM COMPOUNDS
VANADIUM COMPOUNDS
YTTRIUM COMPOUNDS
580400* - Geochemistry- (-1989)