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The New CLOCIT Irradiation Facility for 40 Ar/ 39 Ar Geochronology: Characterisation, Comparison with CLICIT and Implications for High‐Precision Geochronology
Author(s) -
Rutte Daniel,
Becker Tim A.,
Deino Alan L.,
Reese Steven R.,
Renne Paul R.,
Schickler Robert A.
Publication year - 2018
Publication title -
geostandards and geoanalytical research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.037
H-Index - 73
eISSN - 1751-908X
pISSN - 1639-4488
DOI - 10.1111/ggr.12217
Subject(s) - triga , neutron flux , irradiation , fluence , geochronology , analytical chemistry (journal) , flux (metallurgy) , argon , radiochemistry , neutron , materials science , chemistry , physics , research reactor , nuclear physics , atomic physics , geology , chromatography , paleontology , metallurgy
The Cadmium‐Lined Outer‐Core Irradiation Tube ( CLOCIT ) is a new irradiation facility for 40 Ar/ 39 Ar geochronology at the Oregon State University TRIGA ® reactor. We report fluence (i.e., time‐integrated flux) parameters from the first four CLOCIT irradiations and compare them with the existing Cadmium‐Lined Inner‐Core Irradiation Tube ( CLICIT ). CLOCIT provides an average neutron flux equivalent of 1.45–1.53 × 10 −4 J h −1 ; about 55% of CLICIT . Radial fluence gradients were on the order of 0.2–4.2% cm −1 . A planar fit of J ‐values results in residuals in the range of uncertainty in the J ‐value, but systematic deviations resolve a non‐planar component of the neutron flux field, which has also been observed in CLICIT . Axial neutron fluence gradients were 0.6–1% cm −1 , compared with 0.7–1.6% cm −1 for the CLICIT . Production rate ratios of interfering reactions were ( 40 Ar/ 39 Ar) K = (4 ± 6) × 10 −4 and ( 38 Ar/ 39 Ar) K = (1.208 ± 0.002) × 10 −2 , ( 36 Ar/ 37 Ar) Ca = (2.649 ± 0.014) × 10 −4 , ( 38 Ar/ 37 Ar) Ca = (3.33 ± 0.12) × 10 −5 and ( 39 Ar/ 37 Ar) Ca = (9.1 ± 0.28) × 10 −4 , similar to the CLICIT values.