The cesium sputter ion source is a 40-sample MCSNICS normally biased at -43 kV.Typical output from a φ=1 mm sample pressed in Al cathodes for 12C- ions is 30 mA at 6 kV probe voltage and a total injection energy of 67 kV.

 

 

 

 

 

 

 

A spherical electrostatic analyzer (r = 30 cm, plates gap = 5 cm) cuts the sputter energy tail of the beam, with a bending angle of ± 45°. The ESA can be rotated in view of the installation of a second ion source

 

 

The 90° double focusing L.E. magnet (r = .457 m, gap = 38 mm, ME/Z2 = 15) allows high resolution mass analysis for all stable isotopes in the periodic table. The insulated stainless steel chamber can be biased up to -15 kV for beam sequencing.

 

 

 

 

Typical injection times for 14C AMS are 350 ms for mass 12, 850 ms for m=13, and 100 ms for m=14.12C and 13C currents in the LE side Faraday cup are integrated for .1 ms and 8 ms, respectively.

 

The NEC 9SDH-2 Pelletron accelerator is housed in a lead-shielded steel tank filled with SF6 at ~85 psig. Two Pelletron chains are used in the charging system; about 100 mA are delivered to the terminal for operation at 3 MV. For 14C AMS the accelerator is operated at 2.55 MV; typical ripple, as measured by a capacitive pick off, is .7 kV peak-to-peak. Stabilization is achieved by GVM feedback on the charging system PS; the long term stability, over about 24 hours needed for a batch of 40 samples, is better than 1 kV. In the stripper Ar is recirculated by two turbo-pumps; the working pressure is 10 m. During 6 months of operation no tank opening was needed.

 

 

The double focusing 90° HE bending magnet has r=1.27 m, ME/Z2=176 and M/DM = 725, so that, e.g., 236U5+ at 3 MV can be analyzed with a beam spot size of 3.5 mm. For 14C AMS, 12C and 13C charges are measured via two off-set Faraday cups and high-precision current integrators, typically for .25 and 8 ms per cycle. On the average, the precision of 13/12 ratios is ~0.15%, while precision and accuracy of δ13C measurements are ~0.25% and ~0.1%.

 

 

The two 45° electrostatic spherical analyzers (r= 2.54m and gap=3 cm) are operated at ± 40 kV; energy resolution is E/DE = 700. The isotopic contamination is suppressed so that virtually 0 counts are observed out of the 14C ROI.

 

The four-anode ionization chamber, filled with isobutane at p=50 Torr, as well as most of the set up and control of the entire system is handled by the AccelNet computer based system via CAMAC interfaces or Ethernet.

Power by G. Porzio 

   

  

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