DOUBLE ION COLLECTOR FOR THE THERMAL IONISATION MASS SPECTROMETER SMIT-1

A. Pamula, Adriana Dehelean, M. Leuca, I. Dobocan

National Institute for Research and Development of Isotopic and Molecular Technologies, P.O.Box 700, 71 – 103 Donath Str., 400293 Cluj-Napoca, Romania

One of the most important error source, affecting isotopic analyses by mass spectrometry when only one ion detector is available, is the fluctuation of the ion current supplied by the ion source while recording the mass spectrum. A way to avoid this disadvantage is the simultaneous detection of the ion currents of interest. Thus, the fluctuations, which could occur in the ion source, would affect in the same proportion the recorded signals and the measured ratio should remain constant.
The aim of the present work was the realization of an ion collector capable to detect simultaneously the 235U+ and 238U+ ions respectively, for the thermal ionization mass spectrometer SMIT-1 (designed and built in the mass spectrometry laboratory of our institute)
A numerical modeling for the entire magnetic analyzer and separately for the collector region was performed (using SIMION3D VERSION 7.0)[1] in order to find out the spatial location of the collector slits. A double electrostatic deflector ensures the deflection of the two ion beams in opposite directions towards two secondary electron multipliers. The amplified signals are measured with a double channel electrometer connected to a computer via an acquisition board DAQ PC-LPM-16 (National Instruments). The necessary software for data acquisition and processing was developed. 

[1]  David A. Dahl SIMION 3D VERSION 7.0 User’s Manual INEEL-95/0403 Rev. 5. February 2000