Isotope Geochemistry/Geochronology Research and Development - Multiuser New Capabilities
Calibration of MMhb-2, the Argon Standard
Task Objectives
The objective of this task is to calibrate the age of argon standard MMhb-2 hornblende,
to remeasure the isotopic composition of atmospheric argon, and to refine the
atomic weight of argon.
Statement of Work
Task no longer active.
Highlights & Key Findings
Several major tasks have already been accomplished for this project including:
- 3.3 kg of >99.9% MMhb-2 hornblende has been prepared and split into 10 g vials.
- The potassium concentration of both MMhb-1 and MMhb-2 has been measured by NIST and calibrated against the
nations primary potassium standard. Both batches of MMhb have the same potassium content within the limits of
analytical precision. The uncertainty of the K concentration is <0.25%
- Several spike systems have recently been calibrated by NIST. We have two spikes that will deliver molar quanties of
38Ar with about 0.1% precision and accuracy. NIST also calibrated three spike systems that will deliver mixtures of 40Ar
and 36Ar at about the same level of precision and accuracy.
- In 2003 the spike systems received necessary modifications to allow them to be used and moved.
- The starting gasses for the mixed 40Ar and 36Ar spikes were analyzed and shown to be virtually pure (chemically)
argon.
- Isotopic analyses of the starting gasses for the mixed 40Ar and 36Ar spikes should be completed by the end of the fiscal year.
- Lab work in Denver on the calibration of the MMhb-2, the composition of atmospheric
argon, and a refined atomic weight of argon were completed.
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U.S. Department of the Interior |
U.S. Geological Survey