Mass Spectrometer:
The laboratory is built around an MAP 215-50 magnetic sector mass spectrometer with a Nier-type electron impact (EI) source. The magnet is an extended geometry electromagnet with Hall Probe feedback that keeps the peak position stable to better than 0.01 amu. Peak flats are approximately 0.08 amu wide with a Full Width at Half Maximum (FWHM) of approx. 0.14 amu and Full Width ( baseline to baseline) of approx. 0.18 amu. There are two detectors for the mass spectrometer: a faraday collector and an electron multiplier. The faraday cup is a narrow aperture, deep design with secondary electron suppression. Using a current to voltage converter with a 1 x 10¹¹ ohm feedback resistor the faraday cup can cover a beam intensity range of 1.2 x 10^-10 amps to approx. 1 x 10^-15 amps. With the source optimized for 40Ar, we have a sensitivity on the Faraday Cup of approx. 2.5 x 10¹¹ Volts/mole of ⁴⁰Ar. The electron multiplier (presently a Johnson focused mesh multiplier soon to be upgraded to a Balzers SEV 217 ) is situated behind an electrostatic filter to improve low signal noise and resolution. Nominally we run at a relative voltage gain (to the faraday) of about 100 but we vary this depending on the type of analysis. The Mass Spectrometer is kept at Ultra-High vacuum by a 30 lps ion pump and an active metal getter (SAES GP50). We are now upgrading various mass spectrometer components including a new electron multiplier, a reconditioning of the source and a new ion pump, which should be completed by the end of the summer of 2006.

Extraction Lines:
We presently have two extraction lines, one dedicated to the resistance furnace and another dedicated to the two lasers. Both have similar designs, consisting of a sample section, and a section of line containing active metal getters for cleaning the extracted gas. The sample section of the furnace line consists of the resistance furnace and sample tree. The resistance furnace is a double vacuum design with refractory metal crucible and liner. Temperature is measured by a type C thermocouple on the outside of the crucible. Temperatures inside and outside the crucible have been calibrated against another type C which itself has been externally calibrated. Temperatures within the liner reach set temperature within 1 to 5 minutes (depending on the temperature change and starting temperature) and are subsequently stable to +/- 1.0°K. Control is done by a Eurotherm temperature controller in a feedback loop with the resistance element power supply. The sample tree is made of Pyrex glass and hold up to 20 samples. The samples are introduced manually into the furnace. The sample chamber for the lasers consists of a 2-3/4Ó conflate flange with a machined well in which metal (copper or stainless steel) pans or planchettes can be placed. Up to one hundred small samples can be analyzed or smaller numbers of larger samples up to small rock sections (up to about 2 x 2 cm).. Both extraction lines contain active metal getters (SAES GP50, AP-10 and St172) for gas clean up. Getters are operated at various temperatures to crack hydrocarbons and clean up a wide range of gases. Both lines are pumped by turbo pump/rough pumps and ion pumps.

Lasers:
We have two lasers for gas extraction:

1. A Coherent diode laser providing up to 40 Watts CW output power at 811nm. Beam diameter can be adjusted from about 1mm to about 10mm, power is continuously adjustable. This laser is used for all small sample total fusions and incremental heating of small samples. This laser can fuse nearly all minerals. Some very clear minerals (such as some K-feldspars and glasses) do resist complete melting. To increase the laser beam coupling with these samples we include a small piece of degassed basaltic glass.
2. Our other laser is a Lambda-Physik ArF Excimer laser operating at 193nm with a maximum pulse energy of 200mJ (about 10 MW for a typical pulse). This laser is coupled to a New Wave Research optical system that allows beam size and power delivered to the sample to be adjusted. Holes sizes range from 10 to 150 microns. This laser is used for high resolution mapping of ages within grains (both free and in situ).

Almost all of the operation of the mass spectrometer, extraction lines and lasers is computer controlled. Both lines have sources of air Ar for inletting a controlled amount of Ar. This is measured on a regular basis to correct for mass spectrometer fractionation and monitor its performance.

Nearly all of our samples are irradiated at the McMaster University (Hamilton, Ontario, Canada) Research Reactor, although other reactors are occasionally used. Flux monitors are included with all samples. K and Ca salts or glasses are run on a regular basis to monitor production of secondary Ar isotopes. We use the Ar-Ar Calc software for reducing data.

All facilities for preparing samples for irradiation and for handling the radioactive samples are in site.