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The New Mexico Geochronology Research Laboratory (NMGRL) in
Socorro is a state-of-the-art 40Ar/39Ar dating facility
administered by the New Mexico Bureau of Mines at the New Mexico
Institute of Mining and Technology. 40Ar/39Ar research at NMGRL
is directed by Bill McIntosh and Matt Heizler who have over 25
years combined experience in the field of argon geochronology
and thermochronology. The lab also employs two full-time
technicians, Lisa Peters and Richard Esser, who supervise
mineral separation, sample irradiation and analyses and data
reduction.
Since its christening in the winter of 1992, the NMGRL
laboratory has performed over 60,000 single sample
analyses. Necessary in this regard is the software developed by
Al Deino at the Institute of Human Origins in Berkeley,
California which allows for full automation of extraction line
and mass spectrometer functions . The software controls all
crucial valves which are operated via pneumatic air
drivers. Additional automation comes from laser and furnace
sample "packages" which can contain up to 221 and 17 individual
samples per load, respectively. Once under vacuum, sample
analyses do not require the physical presence of laboratory
personnel for extended periods of time.
Argon gas extraction at NMGRL is accomplished either by
resistance furnace or CO2 laser heating. The first method
consists of a double vacuum resistance furnace with molybdenum
crucible and crucible liner. Temperatures accuracy is ?10?C;
precision is ?1?C; maximum temperature is 1750?C. Argon blanks
for the entire furnace extraction line (dual stage) are on the
order of 5E-16 moles of 40Ar. The addition of a gate valve
between the crucible and sample holder in the near future will
likely decrease system blank as well as reduce turn around time
for sample changes.
The second argon extraction method employs a 10 watt CO2
laser. The CO2 laser provides many of the advantages of other
lasers used in argon extraction (e.g. Ar-ion and Nd-Yag) but
requires only a fraction of the cost to set up. The CO2 laser at
NMGRL is used mainly for the total-fusion of sanidine crystals
which include J-value determinations from Fish Canyon Tuff
(FC-1) sanidine monitors. System blanks for the laser (single
stage) are on the order of 2xE-16 moles of 40Ar.
Future innovations at NMGRL include the implementation of a
cold-finger to trap H2O from hydrous mineral phases. A new laser
system with smaller spot-size capabilities will be able to
examine within-grain variations in argon distribution. An
ion-counter on the mass spectrometer will allow smaller sample
sizes to be used without decreasing accuracy or precision. Also,
future integration of a Vacscan Quadrupole mass spectrometer
will allow pre-screening of potentially harmful gas before it is
equilibrated with the mass spectrometer.
Website: "http://www.ees.nmt.edu/Geol/labs/Argon_Lab/NMGRL_homepage.html"
[Summary provided by NMGRL]
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