Public index · Physics
Argon-42
⁴²Ar
Measured
Cosmogenic ⁴²Ar in the atmosphere. First ATTA count, 2026. Mass number 42.
⁴²Ar is argon with mass number 42. In 2026 Wan, Liang, Jia et al. counted it in air. Abundance (6.1 ± 0.5) × 10⁻²¹. Distinct from molybdenum, which is Z = 42.
What it supports
A named A=42 nuclide, now counted. Half-life about 33 years. USTC/IMP used isotope pre-enrichment with atom-trap trace analysis on 10 L STP argon. 204 atoms in 43 days are run parameters, not extra 42s. The 10⁻²¹ figure is measured. Neighbor door: molybdenum, proton count, not mass number.
What it does not
Not a 42-year half-life. Not 42 days. Detector-background use is the next search, not a second object.
ExactnessExact
Form42
UnitA
Strengthhard
When2026-04-14